1.     Aromatic Hydroxylation by Cytochrome P450 Enzymes: Model Calculations of Mechanism and Substituent Effects

Christine Bathelt*, Adrian J. Mulholland and Jeremy N. Harvey
School of Chemistry, University of Bristol, Cantock's Close, BS8 1TS, UK


The cytochrome P450 enzymes play a central role in drug metabolism by catalysing the biotransformation of a wide variety of xenobiotics [1]. Understanding the mechanism of these processes is vital for predicting reactivity of chemicals and reducing toxic side effects of drugs. We have studied the mechanism and selectivity of cytochrome P450 mediated hydroxylation for a number of aromatic compounds using B3LYP density functional theory computations. Our calculations show that addition of the active species Compound I to an aromatic carbon atom proceeds via a transition state with partial radical and cationic character. Ring substituents with both electron-donating and electron-withdrawing properties are found to decrease the addition barrier in para-position. A new structure-reactivity relationship is developed by correlating the calculated barrier heights with a combination of radical and cationic Hammett s-parameters [2]. A similar relationship is obtained when using theoretical scales based on bond dissociation energies for the addition of the hydroxyl radical and cation to substituted benzenes.

 

More complex substituent effects involving di- and tri-substituted benzenes are explored and compared to kinetic data from experimental studies. This work provides insight into the detailed mechanism and helps explain and predict the electronic contribution of substituents to reactivity in this enzymatic process.

 

[1] Anzenbacher, P.; Anzenbacherova, E. Cell. Mol. Life Sci. 2001, 58, 737-747.

[2] Bathelt, C. M.; Mulholland, A. J.; Harvey, J. N. J. Am. Chem. Soc. 2003, manuscript ja035590q accepted

 

 

2.     Development of Novel Methods for Protein Surface Representation & Comparison

 

Martin J Bayley1,2, Eleanor J. Gardiner1, Peter Willett1 and Peter J. Artymiuk2

1Department of Information Studies, University of Sheffield, Regent Court,  Sheffield, S1 4DP, UK

2Department of Molecular Biology and Biotechnology, Krebs Institute, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK

This work is funded by the BBSRC.

 

The aim of this project is to develop novel methodologies for the representation and comparison of protein surfaces and surface interface regions. This will be of great value in the assignment of function, and potential inhibitor and drug- binding capabilities, to novel protein structures solved under the auspices of structural proteomics / genomics initiatives. The broad remit of this project was taken to justify a philosophy of trailing as many novel methods as possible to cover maximum ground within this extremely complex problem area.   

 

The methods trailed fell into two general categories: those that attempted to summarise the local surface shape by the parameter set of a canonical local model and those attempting to create sufficiently reduced but rich sample point sets capable of being used in conjunction with pattern matching algorithms.

 

This poster presents brief explanations of five methods investigated and reports on the results and limitations discovered.    

3.     A Neural Network System for the Prediction of 1H NMR Spectra from the Molecular Structure

 

Yuri Binev and João Aires-de-Sousa

Departamento de Química, CQFB and REQUIMTE, Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Monte de Caparica, Portugal

 

Fast and accurate predictions of 1H NMR spectra of organic compounds are highly desired for automatic structure elucidation, for the analysis of combinatorial libraries, for spectra-activity relationships or for the interpretation of spectra by chemists and spectroscopists.

 

We developed a neural networks-based system to predict 1H NMR chemical shifts of organic compounds from their molecular structures. The neural networks were trained with 744 protons and their experimental chemical shifts. The protons were represented by a set of descriptors, selected from a pool of 120 topological, physico-chemical and geometric descriptors.1

 

For an independent test set of 952 protons, predictions could be obtained with an average error of 0.29 ppm. The quality of the predictions could be significantly improved when the trained networks were integrated into a system of associative neural networks2 with an additional memory of 4679 experimental chemical shifts – the average error for the same test set decreased to 0.19 ppm. This procedure avoided retraining the networks with the new data.

 

In this poster the procedure for prediction will be illustrated, and the predictions will be compared with those from commercial packages. A web-based tool3 for online prediction of 1H NMR chemical shifts will be presented.

 

[1] J. Aires-de-Sousa, M. Hemmer, J. Gasteiger, Analytical Chemistry, 2002, 74(1), 80-90.

[2] I. V. Tetko, J. Chem. Inf. Comput. Sci., 2002, 42(3), 717-728.

[3]. http://www2.chemie.uni-erlangen.de/services/spinus or http://www.dq.fct.unl.pt/spinus

 

4.     Classifying “Kinase Inhibitor-likeness” using Machine Learning Methods

 

Hans Briem and Judith Günther

Schering AG, CDCC/Computational Chemistry, 13342 Berlin, Germany

 

In recent years, drug research has increasingly focused on targeting whole gene families, such as kinases, GPCRs, proteases and ion channels rather than on isolated targets. Medicinal Chemistry has responded to this paradigm shift by generating target-family specific libraries of small molecules, either by using combinatorial synthesis or purchasing from vendors’ catalogues. For both activities, there is a strong demand for supporting compound selection by fast descriptor-based in-silico methods.

 

Here we describe the development of classifiers which are able to distinguish potential kinase inhibitors from non-actives. The learning set used for training the systems is comprised of both compounds showing activity in at least one of eight inhouse kinase assays as well as compounds devoid of any kinase activity. Each compound was encoded by the standard Ghose-Crippen fragment descriptors. Four different machine learning methods were employed: support vector machines (SVM), artificial neural networks (ANN), k-nearest neighbors with genetic algorithm-based variable selection (GA/kNN) and recursive partitioning (RP). We will demonstrate the predictive power of each approach and discuss their strengths and weaknesses.

 

 

5.     Performance Analysis of Similarity Measures for Improved Searching

 

Jenny Chen1, John Holliday1 and John Bradshaw2

1Department of Information Studies, University of Sheffield, Regent Court, Sheffield S1 4DP, UK

2Daylight Chemical Information Systems Inc., Sheraton House, Castle Park, Cambridge, CB3 0AX, UK

 

Recent studies compared the performance of 22 similarity coefficients, most of which are unknown in the chemoinformatics field, and identified a subset of 13 which perform very differently when applied to similarity searches of several databases. The results of several such searches show that these coefficients tend to retrieve different sets of compounds; the difference being dependent mainly on the density of the bitstrings. It is expected that suitable selection of a combination of these coefficients would complement their performance for similarity searching.

 

There is, however, no one optimum combination of coefficients as the selection is dependent on the characteristics of the database and of the query compound. A machine learning approach has been used to identify the optimum group of coefficients whose combination, using data fusion methods, should improve retrieval based on these characteristics.

 

 

6.     The Virtues of Working in Sample Space

 

Robert D. Clark
Tripos, Inc., 1699 S. Hanley Road, St. Louis MO 63144, USA

 

When linear regression is used in analyzing quantitative structure-activity relationships (QSARs) or quantitative structure-property relationships (QSPRs), the work is usually carried out in descriptor space – i.e., the analyst tries to rationalize variations in biological response in terms of relationships between descriptors.  There are some philosophical reasons for doing so, but practical and historical considerations are also key.  Regression coefficients must be extracted from some square derivative of the descriptor matrix, and XTX is used for this purpose in classical multiple linear regression (MLR) because the alternative XXT matrix is larger (nxn rather than kxk, where n is the number of observations and k is the number of descriptors) and is not singular.  This approach carried over into partial least squares by projection onto latent structures (PLS) analysis, where the NIPALS method was introduced to handle singularity caused by k being greater (often much greater) than n.  Bush and Nachbar (J. Comput.-Aided Mol. Design 1993, 7, 587) later introduced sample-based PLS (SAMPLS) as a way to speed computation by working from the distance matrix XXT.  The predicted response values obtained are the same for either approach, but in SAMPLS the predictions are a linear combination of the distances between observations (structures, for QSAR) rather than of individual descriptor values. Though this sample-based approach was originally taken simply to speed up analysis, it can, if taken further, help analysts avoid some of the most common mistakes made in inter­preting PLS results, be extended to quantitate confidence in predictions and – via kernel functions – incorporate non-linearity into PLS in a very intuitive and relatively robust way.

7.     Developments to the GOLD Docking Program

 

Jason Cole

Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK

 

GOLD (1) is a well validated (2) docking program widely used in the pharmaceutical industry for de-novo drug design and virtual screening. The program allows a user to dock using either Gold’s own scoring function (GoldScore), via the ChemScore scoring function, or to extend existing scoring via an application programming interface.

 

Recent work has been undertaken to include the ability to include water molecules as a component in docking, to extend the range of constraints available to the user, to allow for re-scoring of previously docked poses and to generally improve the usability of the program when used for virtual screening.

 

Further work is underway to develop a flexible suite of descriptor calculation tools that can be used for selection of hits with specific properties from large numbers of docked poses. The descriptors generated can be combined via an XML-based command language which allows a user to extract poses that conform to very specific user requirements.

 

A review of recent developments will be presented.

 

[1] G Jones, P Willett, RC Glen, AR Leach, R Taylor. Development and validation of a genetic algorithm for flexible docking. J Mol Biol 267:727-748, 1997.

[2] JW Nissink, C Murray, M Hartshorn, ML Verdonk, JC Cole, R Taylor. A new test set for validating predictions of protein-ligand interaction. Proteins 49:457-471, 2002

 

 

8.     Generation of Multiple Pharmacophore Hypotheses Using a Multiobjective Genetic Algorithm

 

Simon J. Cottrell1, Valerie J. Gillet1 and Robin Taylor2

1Department of Information Studies, University of Sheffield, Regent Court, Sheffield, S1 4DP, UK

2Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK

 

A pharmacophore is the three-dimensional arrangement of functional groups required for activity at a receptor.  Pharmacophore elucidation is the process of inferring the pharmacophore for a receptor, whose three-dimensional structure is not known, from the structures of several ligands that are known to be active at that receptor.  The process involves finding an alignment of the molecules such that relevant functional groups are overlaid in the most plausible way.

 

Several programs exist for generating pharmacophore hypotheses automatically, such as the GASP program by Jones et al.[1].  GASP uses a genetic algorithm to explore the conformational space of the ligands while attempting to align them based on their pharmacophore features. Three objectives are taken into account in evaluating potential solutions: the goodness of fit of the pharmacophoric features, the volume overlay and the internal strain energy of the ligands. These are combined into a single function and GASP returns a single pharmacophore hypothesis which maximises the function.  However, for many datasets, there are several plausible pharmacophore hypotheses which represent different compromises in the objectives.  Which one of these corresponds to the actual binding mode will depend on the structure of the receptor as well as the ligands.  It is therefore unreasonable to make a single prediction of the pharmacophore based solely on the structure of the ligands.

 

In this work, a multiobjective genetic algorithm (MOGA) has been applied to the problem.  The MOGA suggests several pharmacophore hypotheses for each dataset, which represent different compromises between the different objectives.  It does not attempt to rank these hypotheses against each other, but presents each of them as an equally valid alternative.  Thus, the MOGA takes a more realistic view of the uncertainty inherent in the search problem, and it therefore provides a substantial improvement over GASP.

 

[1] Jones, G.; Willett, P.; Glen, R.C.  A genetic algorithm for flexible molecular overlay and pharmacophore elucidation.  Journal of Computer-Aided Molecular Design, 1995, 9, 532-549

 

 

9.     Reaction Plausibility Checking: Trapping Input Errors in Reaction Databases

 

Joseph L. Durant1, Burton A. Leland1, James G. Nourse1, Bernhard Roth2 and Alexander Lawson2

1MDL Information Systems, Inc. 14600 Catalina Street San Leandro, CA 94577, USA

2MDL GmbH, Theodor Heuss Allee 108, D-60486 Frankfurt, Germany

 

Chemical reaction databases continue to be of interest to diverse applications, ranging from, for example, synthesis design to metabolite prediction.  However, the utility of these databases is adversely affected by the presence of bad data.  Such bad data can result from problems in data entry (manual or automated) or conversion of various names and internal formats among many other causes. Whatever the source, the result is inclusion of incorrect reactions in the database.  Trapping such errors in "real world" reaction databases is a complex task.

 

On problem is that the study of chemical reactivity lacks a simple and systematic way to partition possible reactions into plausible and implausible sets.  Instead, one is presented with a wealth of rules and examples which make construction of an expert system for reaction planning a challenging endeavour.

 

Further complicating the task are the properties of real world data. For example, it is common to represent a reaction as an unbalanced reaction, where one or more products (the "uninteresting ones") are not represented, as well as suppressing inclusion of compounds which do not contribute carbon atoms to the product for organic reactions. In this way the reaction representation can highlight the important features of the reactions.  However, the increased usability resulting from this flexibility in reaction representation introduces ambiguity into the interpretation of the reaction, and complicate the evaluation of its plausibility.

 

In order to support creation of new reaction databases we have created a program to evaluate the plausibility of chemical reactions to be included in the database.  This method focuses on trapping common classes of input and representation errors and minimizing the occurrence of false positives (incorrect reactions) allowed into the database.

 

We will discuss the various strategies developed, as well as their relative strengths and weaknesses.

10.   Web-based Cheminformatics Tools at Novartis

 

Peter Ertl, Paul Selzer and Jörg Mühlbacher

Novartis Institutes for BioMedical Research, Cheminformatics, CH-4002 Basel, Switzerland

 

The Novartis web-based cheminformatics and molecular processing system was launched in 1995. Thank to its ease of use and user friendliness the system was immediately accepted by bench chemists and has become an integral part of their decision making process. Novartis cheminformatics web tools offer easy access to a broad range of molecular processing services, including calculation of molecular physicochemical properties and drug transport characteristics, toxicology alerting, and structure visualization. In addition, automatic bioisosteric design, diversity analysis, and creation of virtual combinatorial libraries is supported. The system is used currently by more than 1000 chemists and biologists from all Novartis research sites.

In this poster several new modules of the Novartis cheminformatics system will be presented, including:

In silico ToxCheck – user friendly toxicity alerting system.

Molecular Minesweeper – interactive analysis of molecular diversity including property-based or structure-based clustering.

Visualization of Bioavailability Potential – visualization of drug bioavailability using simple radar plots.

Substituent Bioisosteric Design – automatic selection of bioisosteric drug-like substituents based on compatibility in physicochemical properties.

 

[1] P. Ertl, World Wide Web-based system for the calculation of substituent parameters and substituent similarity searches, J. Mol. Graph. Model. 16, 11-13 (1998).

[2] P. Ertl, J. Mühlbacher. B. Rohde, P. Selzer, Web-based cheminformatics and molecular property prediction tools supporting drug design and development at Novartis, SAR and QSAR Env. Res. 14, 321-328 (2003).

[3] P. Ertl, Cheminformatics Analysis of Organic Substituents, J. Chem. Inf. Comp. Sci. 43, 374-380 (2003).

[4] J. Mühlbacher et al. Toxizitätsvorhersage im Intranet, Nachr. Chem. 52, 162-164 (2004).

[5] T. Ritchie, P. Ertl, J. Mühlbacher, P. Selzer, T. Hart, A Rapid Visualisation of Bioavailability Using Simple Radar Plots, J. Med. Chem. submitted.

 

 

11.   "FitoMyMol: a Web-Oriented Molecular Database and its Interaction with MOE/web"

 

Matteo Floris and Stefano Moro

Molecular Modeling Section, Department of Pharmaceutical Sciences, University of Padova, Via Marzolo 5, 35131 Padova,  Italy

 

Modern chemistry techniques cause a continuous increase of the number of compounds and data. Consequently, the new scientific field of cheminformatics must improve its solutions and experience new ways for analysis and management of molecular data.

The world of the open source can give an important contribution in this process.

 

With this study, we have upgraded MyMol, a simple molecular web-based database for small molecules, implemented by using in tandem PHP and Mysql. This tool transforms chemical/structural data into chemical information. We have modified some SVL files of the MOE/web tool, so as to allow the calculation of the properties of structures recorded in the Mysql database. Therefore we have created FitoMyMol, an effective and reliable tool that joins the flexibility of the PHP and the power of MOE/web. The PHP code of FitoMyMol contains some new functions for the input/output of Molfile/SDFile and for the generation of PHP-fingerprints. With this study, the PHP language demonstrates its usefulness in the development of web-oriented cheminformatics tools. We are hoping to use FitoMyMol to allow the mining of very large datasets of chemical compounds to look for new drug leads or drug design ideas, thereby speeding the discovery and development of new drug candidates.

 

 

12.   DNA Sequence-Structure Relationships

 

Eleanor Gardiner1,2, Linda Hirons1,2, Chris Hunter1 and Peter Willett2

1Centre for Chemical Biology, Krebs Institute for Biomolecular Science, Department of Chemistry, University of Sheffield, Sheffield, S3 7HF, UK

2Department of Information Studies, University of Sheffield, Regent Court, Sheffield, S1 4DP, UK

 

A database of the structural properties of all 32,896 unique DNA octamer sequences has been compiled.  The calculated descriptors include the 6 step parameters that collectively describe the energy minima conformations, the force constants and partition coefficients that describe the flexibility of an octamer and several ground state properties such as the RMSD, which measures the straightness of an octamer’s path.

 

Use of these structural properties to identify patterns within families of DNA sequences has been justified by the discovery that many very different sequences have similar structural properties.  This means that by looking at the information hidden within the structure, similarities between DNA sequences will be found that would otherwise be unrecognised.

 

Patterns in flexibility with respect to rotations in both roll and twist have been investigated for a set of human promoters with low sequence homology.  The results show that these promoters contain a large variation in their twist flexibility around their transcription start site.  It has been confirmed that this pattern is not present within sets of random sequences and therefore not due to chance.  The patterns found agree with the findings of previous analogous work on the same dataset.

 

 

13.   Computational Studies of Asymmetric Organocatalysis

 

David Joseph Harriman and Ghislian Deslongchamps

Department of Chemistry, University of New Brunswick, Fredericton, New Brunswick, E3B 6E2, Canada

My current research is in the field of asymmetric organocatalysis.  This involves the use of a chiral organic molecule to catalyze an enantioselective transformation.  Peptide catalysts have re-emerged in the last decade as viable approach to catalysis.  In particular the work of Scott Miller at Boston College has focused on developing peptide-based catalysts for asymmetric reactions.  These peptide-based catalysts have good enantiomeric excess for a given product, however there is little known of their mechanism. 

 

Miller found that an azide molecule could be added catalytically using a tertiary amine base.  This could then be rendered asymmetric by using peptide catalysts that possesses histidine derivative as a general base.

 

 

 

 

 

 

 

 


           

 

These asymmetric additions of azide by Miller et al. on a variety of ketone substrates show very good enantiomeric excesses.  However, the mechanism by which this addition is facilitated through the peptide catalyst is still unknown.  This research project was undertaken in an effort to determine the mechanism of the asymmetric addition of azide via the shown peptide catalyst. 

 

Our group has developed a de novo methodology for docking simulations specifically for this project.  Normal docking runs involve a rigid receptor (usually a portion of a large protein) and a small, flexible ligand.  However, in our reverse docking approach we allow our peptide to be flexible and rigidify the substrate.  Due to the conjugation of the substrates they are inherently rigid; this allows us to make them completely rigid in our trials at a minimal penalty.  Using ab initio calculations to determine the transition state geometry of the substrate-azide complex, we can then dock the flexible peptide-catalyst around the complex.  The resulting poses from the docking simulation are then post-processed (MOE) to account for VdW, electrostatic, solvent, and potential energy considerations.  The ultimate goal of this research is to provide a basis for the rational design of peptide-based catalysts that give enantiomeric excess of a specified product.  This research project is the first of its kind in the field of computational organocatalyst design.   This computational approach which combines molecular mechanics, molecular dynamics and quantum chemistry calculations may lead to some insight into the mechanisms of such reactions.

           

For this project the following methodology/programs were used:

 

·                     Molecular Modeling (MOE 2003.02)

·                     Molecular Dynamics (Amber7.0)

·                     Gaussian 98 and Gaussian03

·                     Docking Simulations (MOE 2003.02 and Autodock3.0)

 

[1] Horstmann, T. E.; Guerin, D. J.; Miller, S. J. Angew.Chem.Int.Ed. 2000, 39, 3635.

[2] Jarvo, E. R.; Miller, S. J. Tetrahedron 2002, 58, 2481.

[3] Guerin, D. J.; Horstmann, T. E.; Miller, S. J. Organic Letters 1999, 1, 1107.

 

 

14.   2D-Based Virtual Screening using Multiple Bioactive Reference Structures

 

Jérôme Hert1, Peter Willett1, David Wilton1, Pierre Acklin2, Kamal Azzaoui2, Edgar Jacoby2 and Ansgar Schuffenhauer2

1Krebs Institute for Biomolecular Research and Department of Information  Studies, University of Sheffield, Regent Court, Sheffield S1 4DP, UK

2Novartis Institutes for Biomedical Research, Discovery Technologies, Compound Logistics and Properties Unit, Molecular and Library Informatics Program, CH-4002 Basel, Switzerland

 

Virtual Screening (VS) methods can be classified according to the amount of chemical and biological data that they require. When several active compounds are available, the normal screening approach is pharmacophore mapping followed by 3D database search. However, the technique is not always applicable given the heterogeneity that characterises typical HTS hits. This study hence describes several approaches to the combination of the structural information that can be gleaned from multiple reference structures, and evaluates their effectiveness, as well as the effectiveness of several descriptors, by means of simulated VS experiments.

 

 

15.   Discovery of Novel and Potent MCH-1 Receptor Antagonists by Virtual Screening

 

Christopher Higgs*, David E. Clark, Stephen P. Wren, Hazel J. Hunt, Melanie Wong, Dennis Norman, Peter M. Lockey and Alan G. Roach

Argenta Discovery Ltd., 8/9 Spire Green Centre, Flex Meadow, Harlow, Essex, CM19 5TR, UK

 

Melanin-concentrating hormone (MCH) has been known to be an appetite-stimulating peptide for a number of years. However, it has been discovered recently that MCH is the ligand for a previously “orphan” G-protein coupled receptor, now designated MCH-1R. This receptor located in the CNS mediates the effects of MCH on appetite and body weight. Consequently, recent drug discovery programmes have begun to exploit this information to look for MCH-1R antagonists for the treatment of obesity. Here we report the rapid discovery of multiple, structurally-distinct series of MCH-1R antagonists using a variety of virtual screening techniques. The most potent of these compounds had an IC50 value of 55nM in the primary screen, exhibited competitive interaction with the MCH radioligand in the binding assay and demonstrated antagonist properties in a functional cellular assay measuring Ca2+ release. More potent compounds were identified by follow-up searches around this initial hit. A proposed binding mode for the most potent compound in a homology model of the MCH-1R will be presented.

 

 

16.   Rational Design of Small-Sized Diverse Libraries

 

Mireille Krier and Didier Rognan

Bioinformatics Group, UMR CNRS 7081, F-67401 Illkirch Cedex, France

 

The design of a screening library making the compromise between reasonable size for bench chemists and maximal molecular diversity is an ongoing quest. Our approach is reversing Bemis and Murcko[1, 2] decomposition of molecules into frameworks, sidechains and linkers.

 

In the present work, a C++ program called SLF_LibMaker which, by complete enumeration, constructs the molecules composed of user-defined building blocks, has been implemented. The molecular framework is given by the medicinal chemist. At each diversity point a combination of a spacer fragment and a functional group is added. Thus the linkers are chosen among a linker database and the functional groups represent a given pharmacophore property.

 

An application for validating the approach is a realised lead optimisation. Thus we applied virtual screening to a focalised library targeting PDE4 and selected best scored molecules for synthesis.

 

[1] Bemis, G.W. and M.A. Murcko, The properties of known drugs. 1. Molecular frameworks. Journal of Medicinal Chemistry, 1996. 39(15): p. 2887-93.

[2] Bemis, G.W. and M.A. Murcko, Properties of known drugs. 2. Side chains. Journal of Medicinal Chemistry, 1999. 42(25): p. 5095-9

17.   Drug Rings Database with Web Interface: A Tool to Aid in Ring Replacement

 

Xiao Q Lewell1, Andrew C Jones1, Craig L Bruce1, Gavin Harper1,  Matthew M Jones1, Iain M Mclay1 and John Bradshaw2

1Computational and Structural Sciences, GlaxoSmithKline Research and Development, Gunnels Wood Road, Stevenage, Hertfordshire, SG1 2NY, UK

2Daylight Chemical Information Systems Inc., Sheraton House, Castle Park, Cambridge, CB3 0AX, UK

 

The effort to replace chemical rings forms a large part of the medicinal chemistry practice. This poster describes our effort in developing a comprehensive database of drug rings supported by a web-enabled searching system. Analysis of the rings found in several major chemical databases is mentioned. The use of the database is illustrated through application to lead discovery programs for which bioisosteres and geometric isosteres were sought.

 

 

18.   Molecule Classification with Support Vector Machines and Graph Kernels

Pierre Mahé1, Nobuhisa Ueda2, Tatsuya Akutsu2, Jean-Luc Perret2 and Jean-Philippe Vert1
1Ecole des Mines de Paris, France
2Kyoto University, Japan

We propose a new approach to QSAR based on support vector machines (SVM), an algorithm for classification and regression that recently attracted a lot of attention in the machine learning community. SVMs have the particularity not to require an explicit vectorial representation of each molecule. Instead, molecules are represented through pairwise comparisons computed by a function called the kernel. Developing valid kernels for non-vectorial data such as strings has greatly extended the scope of machine learning techniques in computational biology, for example. A valid kernel for graphs has recently been proposed. It is based on a random walk model on each graphs, and involves an implicit projection of each graph onto an infinite-dimensional vector space, where each dimension corresponds to a particular path in the graph. The similarity between two graphs computed by this kernel is based on the detection of common paths

The use of such kernels allows the comparison and efficient classification of graphs without any explicit feature extraction. Furthermore, the general graph kernel formulation can be customized using prior knowledge to deal with specific data, such as molecules. We suggest such customizations and test our approach in a toxicology prediction context, with very encouraging results.

19.   A Comparison of Optimized Machine Learning Methods on HTS and ADMET Datasets

 

Ravi Mallela and Hamilton Hitchings

Equbits LLC, PO Box 51977 Palo Alto, CA 94303, USA

 

Many pharmaceutical firms use a variety of machine learning techniques for predictive modeling on HTS and ADMET datasets. These techniques include ANN, Naïve Bayes, PLS, Decision Trees, and Suppor Vector Machines. This poster will present a framework for comparison of techniques and results on well described public data sets and data sets internal to pharmaceutical firms. Tradeoffs, pro and cons, and new directions for improving results with current algorithms will presented.

 

 

20.   Enhancing Hit Quality and Diversity within Assay Throughput Constraints

 

Iain McFadyen, Gary Walker*, Diane Joseph-McCarthy and Juan Alvarez

Wyeth Research, Computational Chemistry, Chemical and Screening Sciences, Cambridge, MA, USA (* Pearl River)

 

The selection of hits from an HTS assay is a critical step in the lead discovery process. A ‘Top X’ selection method is commonly used where the activity threshold defining a ‘hit’ is chosen to meet the throughput limits of the confirmation assay. We have investigated an alternative hit selection scheme where; a) the activity threshold is determined by rigorous statistical analysis of primary assay data; b) all hits are considered, regardless of quantity; c) duplicates, undesirable compounds, and uninteresting scaffolds are eliminated as early as possible; and d) the details of the workflow are easily customized to the individual needs of the project. In cases where the number of hits is large relative to the throughput limit of the confirmation assay, clustering techniques allow the selection of representatives from clusters enriched with actives, achieving reduction in numbers whilst minimizing loss of diversity and simultaneously reducing the false negative rate. Carefully implemented filters retain only those hits interesting to the project team, having physiochemical properties suited to optimization from low affinity HTS hits into drug-like development candidates. We present results from 3 diverse projects, and show significant improvements in the diversity and quality of the selected hits as well as in the observed confirmation rates.

 

 

21.   Descriptor Selection for Non-Parametric QSAR Using Internal Validation Sets

 

John McNeany and Jonathan Hirst

Department of Physical Chemistry, School of Chemistry, University of Nottingham, University Park, Nottingham,  NG7 2RD, UK

A greedy algorithm with internal validation, and external cross validation, has been implemented for descriptor selection for non-parametric regression approaches to quantitative structure activity relationships (QSAR).  Models are selected in a stepwise fashion, with the descriptor which gives the greatest improvement in an objective function being included in the current model.  The objective function chosen in this case is a weighted sum of internal training set r2 and the internal validation set r2.  The inclusion of internal validation set performance in the objective function, prevents the inclusion of descriptors which overfit the training data, and allows predictive models to be selected independently of external validation performance.  This approach has been applied to several datasets, and resulting models are low dimensional, with a 5-fold cross validated q2=0.37 for the largest dataset, and a leave-one-out cross validated q2=0.71 for the second smallest dataset.  This approach provides a reliable and unbiased approach to descriptor selection for non-parametric regression, and is computationally cheap compared to other optimisation approaches.

 

 

22.   Comparison of Field-based Similarity Searching Methods

 

Kirstin Moffat1, Val Gillet1, Gianpaolo Bravi2 and Andrew Leach2

1Krebs Institute for Biomolecular Research and Department of Information Studies, University of Sheffield, Regent Court, Sheffield S1 4DP, UK

2GlaxoSmithKline, Gunnels Wood Road, Stevenage, SG1 2NY, UK

 

 

 

A comparison of three field-based similarity-searching methods was carried out.  These methods were ROCS (OpenEye), CatShape (Accelrys) and FBSS (Sheffield University).  Seven datasets were identified, with the compounds within each set exhibiting the same biological activity.  Between 7 and 10 compounds from each of the active sets were chosen as query compounds.  1000 compounds, that did not display the activities under consideration, were selected randomly from the MDDR.  For each activity class the active compounds were seeded into this 1000 inactive dataset.  Each similarity method was then used to calculate the similarities between each of the query compounds and all of the compounds in the seeded dataset.  The dataset was then ranked on similarity score and the ranking of each of the actives in the dataset was used to calculated enrichments.  Each method was tested in rigid mode and in flexible mode.

 

 

23.   Using Small-Molecule Crystallographic Data to Predict Protein-Ligand Interactions.

 

J. Willem M. Nissink and Robin Taylor

Cambridge Crystallographic Data Centre 12 Union Road, Cambridge, CB2 1EZ, UK

Crystallographic data on intermolecular interactions mined from the CSD or PDB databases can be used to predict interactions in binding sites, or to build scoring functions [1,2]. There are several problems that one has to overcome to end up with a usable result.

 

Two issues must be addressed when compiling interaction data for use in a knowledge-based predictive tool. The first has to do with data selection: it is important to have a diverse set of data to start with, and one has to check for, and if need be, eliminate, unwanted interactions. Such cases can be those where secondary contacts are observed, or solvents are involved.

 

The second issue arises from the very nature of the data used. The environment of ligands in protein crystals from the PDB is decidedly different from that of small molecules in the CSD, and although chemical interaction patterns from CSD data are largely similar, the relative importance of different types of interactions (polar, hydrophobic) is skewed as a result.

 

We will highlight problems that were encountered when applying both CSD and PDB data in SuperStar, a tool for the analysis of binding sites, and show the corrections that are applied.

 

SuperStar calculates maps that reflect the probability of a probe group occurring at a certain location. Results of prediction of ligand groups in binding sites by these maps will be discussed, focussing on predictions of groups by their most suited map probes, and by different probes with similar physicochemical properties.

 

[1] Verdonk et al., J.Mol.Biol 307 (2001) 841 ; Bruno et al., J. Comput.-Aided Mol. Design 11 (1997) 525; Ischchenko et al, J.Med.Chem. 45 (2002) 2770

[2] Laskowski et al., J.Mol.Biol 259 (1996) 175 ; Gohlke et al., J.Mol.Biol. 295 (2000) 337

 

24.   Flexligdock: A Flexible Ligand Docking Tool

 

P.R. Oledzki, P.C. Lyon and R.M. Jackson

School of Biochemistry and Molecular Biology, University of Leeds, Leeds LS2 9JT, UK

 

 

The algorithm Flexligdock is being developed to provide a comprehensive flexible ligand docking tool for small molecule docking to proteins. The program is based on QFIT and uses a probabilistic sampling method [1] in conjunction with the GRID molecular mechanics force field [3] to predict ligand binding modes.

 

The method fragments a ligand to produce a series of rigid fragments and utilises an interaction point methodology to map the ligand fragments onto an interaction energy grid map of the protein target. The method then uses an incremental construction method to build the ligand fragment by fragment in the protein binding site. This stage uses torsion angle sampling to search for low energy ligand conformations.

 

The algorithm has been parameterised on a data set of 46 protein-ligand complexes obtained from a recently released docking data set [3]. The parameterisation data set contained a structurally diverse set of proteins and a variety of ligands that contained between 0-23 torsion angles.

 

Currently, a validation data set of 200 protein-ligand complexes is being used to validate Flexligdock and allow comparison against other existing protein-ligand docking algorithms.

 

[1] Jackson, R.M. (2002). Q-fit: a probabilistic method for docking molecular fragments by sampling low energy conformational space. J Comput Aided Mol Des. Jan;16(1):43-57.

[2] Goodford, P.J. (1985). A computational procedure for determining energetically favourable binding sites on biologically important macromolecules. J. Med. Chem 28, 849-857.

[3] Nissink, J.W. Murray, C. Hartshorn, M. Verdonk, M.L. Cole, J.C. Taylor, R. (2002).A new test set for validating predictions of protein-ligand interaction. Proteins. Dec 1;49(4):457-71.

 

 

25.   Sequential Superparamagnetic Clustering for Unbiased Classification of High-dimensional Chemical Data

 

Thomas Ott, Pierre Acklin, Edgar Jacoby, Ansgar Schuffenhauer and Ruedi Stoop

Institute of Neuroinformaics University/ETH Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland

Clustering of chemical data is a non-trivial task. The goal of any clustering procedure is to find a best possible classification on the basis of the chemical description available. The challenge is to find classes of structurally similar substances in a, as much as possible, unbiased way. Such classes simplify the search for new pharmaceuticals obtained via combinatorical chemistry. Therefore, clustering is of utterly economical interest for the pharmaceutical industry. Traditional clustering methods often fail to work, mostly due to sparseness and high-dimensionality of the data. The task can further be complicated by inhomogeneous cluster densities. To overcome these difficulties we introduce a novel method based on  superparamagnetic clustering. This method relies on self-organizing processes of Potts-spin-systems, alternatively interpreted as stochastic neural networks. The method itself is completely unbiased as required. In order to solve the problem of inhomogeneous densities we designed a second level procedure (sequential clustering).

 

In this contribution, we introduce the method and report on results obtained from its applications to systems of known composition. Furthermore, we compare it to the performance of traditional methods such as single linkage hierarchical clustering and Ward`s method. The results show that our approach outperforms these alternative methods.

 

26.   Exploring Protein-Nucleic Acid Interactions at the Atomic Level

 

Jayshree Patel1,2, Peter Willett1 and Peter J. Artymiuk2

1Department of Information Studies, University of Sheffield, Regent Court, Sheffield, S1 4DP, UK

2 Krebs Institute, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, S10 2TN, UK

 

One function of proteins, the workhorses of cells, is to decode the genetic information stored within the nucleic acid material.  The way, in which a specific protein molecule correctly recognizes and interacts with its target nucleotide sequence from amongst the billions of nucleotide bases contained within a cell, is clearly of great interest. Increased knowledge of how these two types of molecules interact with one another can be applied as screens in docking experiments and rational drug design programs.

 

Here a computer program based on graph theory is used to carry out substructure searches within complexes of proteins and nucleic acids. Initial search patterns involve a pseudoatom representing an amino acid being placed in six positions around a base pair, three in the major groove and three in the minor groove. Standard base pairing patterns have been used in protein-DNA complexes and both standard and non-standard base pairing patterns in protein-RNA complexes. More complex patterns used consist of stacked base pairs. Additional features of the program, called Nassamj, include a planarity measure to explore how planar an amino acid is to a base pair, identification of which atoms are participating in hydrogen bonds formation based on distance and angle criteria, and  which atoms are forming van der Waals contacts.

 

The results obtained so far demonstrate that Nassamj can effectively locate substructures from within large structural complexes, and that there may be some correlation between the position and the nature of the interaction formed. 

 

 

27.   Assessing Models of the b2-adrenergic Receptor as Targets for Virtual Screening

 

George Psaroudakis and Christopher A. Reynolds

Department of Biological Sciences, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK

 

The determination of the crystal structure for dark-state (inactive) rhodopsin created a breakthrough in understanding the structure and function of G-protein coupled receptors (GPCRs) and offered new opportunities in rational drug design. A rational strategy for generating molecular models not only for the inactive form of the b2-adrenergic receptor, but also of the active form is assessed here. The validity of these models is established by assessing their usefulness as targets for virtual screening. The active and inactive targets were prepared by interactively docking norepinephrine and propranolol respectively; the binding sites were then defined from the region occupied by these ligands and the free space surrounding them. A series of 172 drug-like adrenergic and non-adrenergic drug-like GPCR ligands were retrieved form the Cambridge Structural Database and docked into the receptor using the ligandfit software. The active structure in particular showed a high hit rate, yield and enrichment factor, which is particularly remarkable because the false positives were also GPCR ligands. The results help to validate both the method for generating the structures and the quality of the structures themselves and suggest that GPCR homology models may soon be useful targets in virtual screening.

 

 

28.   MolMap: Visualisation of Sets of Structures in a Chemical Space with Meaningful Axes

 

Chris Pudney1 and Graham Mullier2

1Focal Technologies, Kensington, WA 6151, Australia

2Chemistry Design Group, Syngenta, Jealott's Hill, Bracknell, RG42 6EY, UK

 

Visualizing sets of compounds from large chemical databases or libraries usually requires the definition of a "chemical space" in which the compounds can be represented.  To be useful the chemical space can have only a few dimensions, and these dimensions must be chemically meaningful.  Choosing a small set of chemical properties with which to define the chemical space is difficult because of the vast number of properties that can be calculated and the correlation between them.

 

Building on previous work around Principal Components Analysis (PCA) [1, 3-5] and biased descriptor selection [2], we have developed a technique based on PCA and orthogonal rotations of the resulting components. This technique reduced a set of nine calculated properties to three (uncorrelated) properties that are related to molecular size, flexibility and lipophilicity, retaining >80% of the variation (information) of the original descriptors.  These three properties define the axes of a chemical space (MolMap) that we use to visualize sets of chemical structures (Fig 1).

Figure 1: 5 analogue sets projected into the MolMap chemical space.

[1] Basak, S.C.; Magnuson, V.R.; Niemi, G.J. and Regal, R.R. (1988) "Determining structural similarity of chemicals using graph-theoretic indices". In Discrete Applied Mathematics 19:17-44.

[2] Lewis, R.A.; Mason, J.S. and McLay, I.M. (1997) "Similarity measures for rational set selection and analysis of combinatorial libraries: the diverse property-derived (DPD) approach". In Journal of Chemical Information and Computer Sciences. 37(3):599-614.

[3] Oprea, T.I. and Gottfries, J. (2000) "ChemGPS: A chemical space navigation tool". In Proceedings of 13th European Symposium on Quantitative Structure-Activity Relationships.

[4] Oprea, T.I. and Gottfries, J (2000) "Chemography: the art of navigating in chemical space". In Journal of Combinatorial Chemistry. 3:157-166.

[5] Oprea, T.I.; Gottfries, J.; Sherbukhin, V.; Svensson, P. and Kuhler, T.C. (2000) "Chemical information management in drug discovery: optimizing the computational and combinatorial chemistry interfaces". In Journal of Molecular Graphics and Modelling. 18:512-524.

29.   An Automated Linker Replacement Technique

 

John Raymond1, Mehran Jalaie1 and Dan Holsworth2

1Discovery Technologies and 2Cardiovascular Chemistry, Pfizer Global R & D, Ann Arbor Labs, 2800 Plymouth Road, Ann Arbor MI 48105, USA

Given the current economic and political climate for drug research, there exists a definite desire to decrease the time and costs associated with early discovery stages. As a consequence, we have found an increasing need among medicinal chemists and project leaders for a mechanism to suggest alternative structural templates given a target series of interest. In this manner, an attempt is made to capitalize on prior research, thus reducing the amount of new capital expenditure.

 

This problem is analogous to the de novo design paradigm which has typically been applied in a build-up fashion using libraries of subfragments and/or more primitive constructs such as atoms and bonds in the presence of a protein binding site. This effort differs in that it operates solely on the ligand and generates new substructure linkers by extracting them en bloc from a database of existing molecular structures rather than by incrementally building them. First, the substructures that are to remain semi-fixed are specified. Then an existing database of molecular structures is searched and all possible candidate substructure linkers are identified from each database molecule. These candidate linkers are passed through a series of 2D and 3D filters. The filtered linker substructures are then grafted onto the fixed substructures and aligned to the reference molecule.

 

 

30.   Identification of Therapeutic Leads for Prion Disease by GOLD Docking Studies

 

Tummala R. Reddy1,2, Valerie J. Gillet1 and Beining Chen2

1Department of Information Studies, University of Sheffield, Regent Court, Sheffield, S1 4DP, UK

2Department of Chemistry, University of Sheffield, Sheffield, S10 2TN, UK

 

Prion diseases are a group of fatal neurodegenerative disorders caused by conformational change of cellular prion proteins in humans and a variety of other animals. Cellular prion proteins consist of a single polypeptide chain of 250 amino acids. When abnormal prion protein (PrPSc) entering the body, it is able to convert their cellular counterparts into the abnormal forms. The difference between the normal and abnormal proteins lies in their folding. The abnormal PrPSc proteins are folded in a way that resists normal protease degradation leading to the build-up of aggregates of PrPSc. Aggregation of PrPSc results in neurological dysfunction accompanied by neuronal vacuolation and astrocytic gliosis.

 

Effective therapeutics for prion disease are urgently needed taking into account that there is no therapeutic drug currently available in the market for vCJD. The aim of this project is to use extensive modelling to rationally design libraries of compounds and then synthesize for screening. Firstly, identification of possible lead compounds was performed using GOLD docking program. The NMR solution structure of prion protein [QM3(15)] was used for the docking studies of in-house collected compounds. These compounds were ranked using the fitness score produced by GOLD and compared with the experimental data.  Based on the fitness scores and screening data a lead has been identified, therefore its binding mode has been generated. The possible key amino acids involved in interaction with the ligands were also identified through docking studies.

31.   Correlation Vector Approaches for Ligand-Based Similarity Searching

 

Steffen Renner, Uli Fechner and Gisbert Schneider

Johann Wolfgang Goethe-Universität, Institut für Organische Chemie und Chemische Biologie, Marie-Curie-Str. 11, D-60439 Frankfurt, Germany

 

Correlation vector methods were tested for their usefulness in ligand-based virtual screening. Three molecular descriptors – two based on potential pharmacophore points (PPP) and one on partial atom charges – and three similarity measures, the Manhattan distance, the Euclidian distance and the Tanimoto coefficient, were compared. All datasets employed were subsets of the COBRA database, a non-redundant collection of reference molecules for ligand-based library design compiled from recent scientific literature. The alignment-free correlation vector descriptors seem to be particularly applicable when a course-grain filtering of data sets is required in combination with a high execution speed. Significant enrichment of actives was obtained by retrospective analysis. The cumulative percentages for all three descriptors allowed for the retrieval of up to 78% of the active molecules in the first five percent of the reference database. Different descriptors retrieved only weakly overlapping sets of active molecules among the top-ranking compounds. Generally, none of the three different descriptors tested in this study clearly outperformed the others. For ligand-based similarity searching it is recommended to exploit several descriptors in parallel and unite their respective information.

 

The correlation vector method based upon PPPs was further investigated by means of an “ideal ligand” approach. For this purpose we developed a new pharmacophore searching approach which takes into account information from explicit three-dimensional molecular alignments of known active ligands for the screening of correlation-vector-encoded molecular databases. Knowledge about the conservation and deviation of the spatial distribution of the ligands features is incorporated into the pharmacophore model. PPPs are represented by spheres of Gaussian-distributed feature densities, weighted by the conservation of the respective features. Different degrees of “fuzziness” can be introduced to influence the model’s resolution. The approach was validated by retrospective screening for cyclooxygenase-2 and thrombin ligands. A variety of models with different degrees of fuzziness were calculated and tested for both classes of molecules. Best performance was obtained with pharmacophore models reflecting an intermediate degree of fuzziness, yielding an enrichment factor of up to 35 for the first 1% of the ranked database. Appropriately weighted fuzzy pharmacophore models performed better in retrospective screening than similarity searching using only a single query molecule.

 

[1] Fechner, U., Franke, L., Renner, S., Schneider, P., Schneider, G., Comparison of correlation vector methods for ligand-based similarity searching J. Comput. Aided Mol. Des., 17 (2003), 687-698.

[2] Fechner, U., Schneider, G., Optimization of a Pharmacophore-based Correlation Vector Descriptor for Similarity Searching, QSAR Comb. Sci., 23 (2004), 19-22.

[3] Renner, S., Schneider, G., Fuzzy Pharmacophore Models from molecular alignments for correlation vector-based virtual screening, J. Med. Chem., manuscript submitted.

[4] Schneider, P., Schneider, G. Collection of bioactive reference compounds for focused library design, QSAR Comb. Sci., 22 (2003), 713-718.

 

 

32.   Topological Study of the Chemical Elements

 

Guillermo Restreppo and José Luis Villaveces

Facultad de Ciencias Basicas, Universidad de Pamplona, Norte de Santander, Pamplona, Columbia

 

We developed a mathematical study of the chemical elements Q using cluster analysis and topology. We defined each element by a point in a space of properties built up using 31 physico-chemical properties of the chemical elements. After, we apply cluster analysis on Q making use of 4 similarity functions and 4 clustering methods to obtain 16 dendrograms that lead further a consensual trees. Based on such trees, we carried on a topological study of Q introducing the concept of neighbourhood. Thus, we defined a basis for a topology for Q using the neighbourhoods mentioned above. Finally, we studied some topological properties such as the closure, the derived sets and the boundaries of particular subsets of elements. Among the results obtained, there is a robustness property of some of the better known families of elements, but also evidence of the Diagonal Effect and the Singularity Principle. Alkaline metals and Noble Gases appeared as sets whose neighbourhoods have no other elements besides themselves, whereas the topological boundary of the set of metals is formed by semi-metallic elements.

 

 

33.   Advancing In Silico ADME/Tox Consensus Modeling

 

Holgar Ruchatz,  Gregory Banik and Yann Bidault

Bio-Rad Laboratories, Informatics Division, 3316 Spring Garden Street, Philadelphia, PA 19104 USA

 

Consensus modeling involves the combination of multiple, complementary models to improve the accuracy of prediction over a single model.  Three types of consensus models (discrete variable, continuous variable, and mixed-mode) will be described.  An integrated system is described that utilizes an N-fold cross-validation technique for continuous variable consensus model creation and one of a number of Boolean combination mechanisms for discrete models.  Mixed mode models, in which one or more models are continuous variable and one or more models are discrete variable, are automatically normalized to the same discrete scale. Integrated validation statistics are included to assess the error and accuracy of each individual model as well as of the resulting consensus model.  The application of consensus modeling in ADME/Tox prediction will be described for a variety of endpoints, including log P, log D, mutagenicity, plasma protein binding, and others.  Examples will be shown that demonstrate the effectiveness of the consensus modeling approach for ADME/Tox, and guidelines for producing the best consensus models will be described.

 

 

34.   A Combinatorial DFT Study of How Cisplatin Binds to Purine Bases

 

Leah Sandvoss and Mookie Baik

Indiana University, 1200 Rolling Ridge Way #1311, Bloomington, Indiana, 47403, USA

Cisplatin (cis-diamminedichloroplatinum(II)) continues to attract much attention because of its therapeutic importance as an anticancer drug. It binds primarily to the N7 positions of adjacent guanine (G) sites in genomic DNA, causing intrastrand cross-links, which suppress replication and lead ultimately to cell death. Previous work showed both kinetic and thermodynamic preference of G over adenine for the platination reaction. The goal of this study is to obtain a chemically intuitive explanation for this selective behavior of cisplatin by systematically comparing the electronic structures of a diverse set of functionalized purine bases. A computational combinatorial library of over 1500 purine derivatives was designed based on density functional theory calculations and the changes of the most important molecular orbitals as a function of structural variance were examined in detail. This electronic profile for purine bases reveals how electronic hot spots control the reactivity at the N7 position (see figure).

 

Figure 1: Numbering system for purine bases

 

 

35.   Computational Studies on the Analysis of Organic Reactivity

 

Ingrid M. Socorro1, Jonathan M. Goodman1 and Keith T. Taylor2

1Unilever Centre for Molecular Informatics, Department of Chemistry, Lensfield Road, Cambridge, CB2, 1EW, UK

2MDL Information Systems Inc, 14600 Catalina Street, San Leandro,  CA 94577, USA

 

Organic chemistry is full of interesting and surprising reactions. The prediction of organic reactions is a challenging task for a chemist. Expert programs could be able to help chemists to anticipate, analyse and understand their results. The aim of our work is focused on the development of computational tools for the study of organic reactivity with the purpose of predicting and analysing organic reactions. We are developing a reaction prediction program based at a first stage on general knowledge of organic chemistry. The program is coded in Java programming language and makes use of MDL Cheshire scripts to analyse structures and transformations. ISIS/Draw software is used as the user interface.

The system developed arrives at its conclusions by application of a series of rules designed to consider different features in molecules for the determination of reactivity. In this way, the program makes decisions on primary aspects when considering a reaction such as the determination of reaction sites or which bonds are to be broken or made. Therefore, new reactivity should be found and analysed when considering unprecedented reactions. It will also be possible to predict and to analyse the reactivity of unknown reactions. Finally, we have made studies on some kind of reactions in which carbonyl groups are involved, such as aldol reactions. An example is given in the figure below.

 

 

 

 

 

 


 
 
      

 

 

 

 

 

 


                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                  

 

 

 

 

 

 

Figure: Results of the Reaction Prediction Program.

 

36.   Data Evaluation Tools for Affinity Information on a Large Scale (DETAILS)

 

Dirk Tomandl and Günther Metz

Graffinity Pharmaceuticals, Im Neuenheimer Feld 518-519, 69120 Heidelberg, Germany

Graffinity has developed a novel small molecule screening technology combining chemical microarrays and label-free affinity detection based on surface plasmon resonance (SPR) imaging. The technology is applied to the screening of lead-like, fragment-based compound collections against protein targets providing direct access to comprehensive structure-affinity maps. A typical screening campaign provides a large and complex dataset of 100,000 – 300,000 datapoints. Mapping and understanding such affinity fingerprints of molecular interactions is facilitated by a chemoinformatic data visualisation and analysis tool, which we developed based on in-house and commercial software [Unity (Tripos), ClassPharmer (BioReason), Feature Trees (BioSolveIT), Decision Site (Spotfire)].

 

The poster will highlight the basic database architecture, the procedures for quality control as well as the rigorous statistical measures for data standardisation and hit definition. We will also present how various chemical classifications allow to extract structure activity relationships from the array data. To simplify visual inspection of chemical arrays a number of coordinate systems have been implemented such as ordered educts of combinatorial libraries, fingerprint-based Kohonen-maps as well as compound classes based on common substructures and molecular frameworks. Pre-calculated molecular descriptors can be interactively merged with the screening data.

 

Subsets of compounds are defined by various criteria such as common substructures or descriptor based neighbourhood behaviour and ranked by statistical properties. The highest ranked subsets highlight interesting compounds and can reveal non-obvious structure activity relationships. These can be further processed for reports, shopping campaigns or virtual screening.

 

 

37.   Nonequilibrium Consideration of Interaction of Molecules with Water-Membrane Interface

 

Yegor Tourleigh and Konstantin Shaitan

Moscow Lomonosov State University, Dept. of Biophysics, 119899 Moscow, Russia

 

In this work two types of hydrated membrane (hydrocarbon and lipid) were modelled by method of molecular dynamics. As molecules which interaction with a membrane and possible transport through it were functional groups of atoms, molecular oxygen, aminoacid residues of variable degree of polarity and hydrophobicity, and also carbon nanotube. The calculations were carried out in Amber99© force field.

 

As it was found, spontaneous transport can be registered during a calculation only for oxygen. At room temperature the behaviour of the remaining molecules at the interface correlated with their size, polarizability and charge (for comparison experimental aminoacids hydropathy scale and Born law for transfer of spherically symmetrical particles to hydrophobic medium were applied). For speedup of transport processes a force (either stationary or alternating) was applied to the molecules under study. The relation of penetration speed to the frequency of external field tells about probable existence of a resonance frequency determining the characteristic time of necessary rearrangements of such structured medium as a membrane. Calculated from Stokes-Einstein relation characteristic viscosities and diffusion coefficients of molecules in the medium non-linearly depend on sizes of the latter and applied force that gives cause to suppose different nonequilibrium modes of molecules dynamics.

38.   Lone Pair Directionality in de novo drug design

 

Aniko Vigh

ICAMS, Chemistry Department, University of Leeds, Leeds, LS2 9JT, UK

 

SPROUT is a de novo molecular structure design software suite developed over many years at the University of Leeds. The system provides a set of modules offering automatic methods for solving numerous problems associated with the structure based rational drug design process.

 

In de novo drug design, structures are generated to fit a set of steric and functional constraints. The constraints are usually derived by characterizing the binding sites – or target sites in SPROUT terminology – in order to find a ligand with good binding properties. Hydrogen bonds are important in receptor-ligand interactions and have always played an important part in the SPROUT process. Until recently, constraints for hydrogen bonds in SPROUT have controlled the H-bond length and the H-bond angle, but have not taken into account directionality of lone pairs, and as a result some ligands were generated which displayed poor geometry at acceptor atoms in that the acceptor lone pairs pointed away from the hydrogen. In order to prevent such bad interactions, additional constraints have been introduced for hydrogen bonds, with special regard to the lone pair geometry of acceptor atoms. Results (which will be presented) show that using lone pair directionality constraints in structure generation greatly improves the quality of structures generated, not only by excluding poor structures, but also by causing the generation of structures which would not have been found using the old H-bond constraints.  The poster will include a detailed account of the constraints used for different hybridization patterns (sp2 etc) of lone pair bearing atoms.

 

 

39.   A Structural Hierarchy for Virtual Library Screening and as a Tool for Data Analysis

 

Shane Weaver, Peter Johnson and Andrew Leach

ICAMS, Chemistry Department, University of Leeds, Leeds, LS2 9JT, UK

 

Currently the pharmaceutical industry has at its disposal several computational techniques for the discovery of lead compounds.  These include methods such as library docking and structure based de novo drug design.  Inherent with many of these techniques is a large library of drug-like molecules which has to be processed sequentially each time a new drug is sought.  Reducing the number of molecules which need to be analysed in the library without missing any leads is the aim of this project.  This can be achieved by arranging the library of molecules into a hierarchy based on 3D structure.  The relationships can be used in several ways which are being investigated in this project.  The first was to implement the hierarchy into SynSPROUT1, a structure generation program for de novo design.  At each step of structure growth a synthetic reaction is used to join a new starting material from the library.  The result of the docking phase of the unified species decides if superstructures of that starting material should be joined or screened out.

The hierarchy is also being used for replacement of starting materials within the finished structure, i.e. where monomers of a generated or imported ligand are replaced by sub- and super-structures which may better complement the boundary of the protein cavity.

 

A tool has been developed that can organise a molecular series into a 2D structural hierarchy.  By allowing the medicinal chemist to visualise the structural relationships in the series, this tool can be useful for analysing structure-activity relationships and may also aid in activity prediction. 

Once the main hierarchy has been constructed an optimization step can be performed to detect relationships between root nodes (molecules that are not substructures of any other).  The optimization step was implemented in order to cluster those structures belonging to the same congeneric series.  This was achieved by recursively removing terminal atoms from all root nodes to create frameworks2.  A further optimization is a similarity test which groups those frameworks within a predefined tolerance. 

[1] Bodo, K.; SynSPROUT: Generating synthetically accessible ligands by de novo design, Ph.D. Thesis, University of Leeds, Chemistry Department, 2002

[2] Xu, J.; A New Approach to Finding Natural Chemical Structure Classes, J. Med. Chem., 2002, 45, 5311-5320

 

 

40.   Why Size Matters and the Tanimoto Coefficient Works

 

Martin Whittle1, Naomie Salim2, John Holliday1, Peter Willett1

1The Krebs Institute for Biomolecular Research, Department of Information Studies, University of Sheffield, Regent Court, Sheffield S1 4DP, UK

 

2Faculty of Computer Science and Information System, Universiti Teknologi Malaysia, 81310 Sekudai, Johor, Malaysia

 

 

 

Using a plot of similarity values against the relative bit size of target and comparison molecules we show how the size bias of similarity coefficients can be visualised in a graphical display.  These plots clearly show the well-known tendency of the Tanimoto coefficient to choose small molecules in a dissimilarity selection.  The Tanimoto coefficient is consistently the best performer when analysed using precision-recall plots.  Plots of similarity against relative bit size can also be used to suggest a reason for this success: the Tanimoto coefficient chooses the smallest range of comparison molecule size (measured as bit density) for any of the common coefficients tested.   It therefore seems possible that the Tanimoto coefficient is successful because it chooses molecules with best match to the size dispersion found in typical bioactive sets.

 

 

41.   New Virtual Screening Methods for the Prediction of Potential Pesticides

 

David J. Wilton1, John Delaney2, Kevin Lawson2, Graham Mullier2 and Peter Willett1

1The Krebs Institute for Biomolecular Research, Department of Information Studies, University of Sheffield, Regent Court, Sheffield, S1 4DP, UK

2Syngenta, Jealott’s Hill International Research Centre, Bracknell, RG42 6EY, UK

 

This poster discusses the use of two new virtual screening methods, based on the data mining techniques known as Binary Kernel Discrimination and Support Vector Machines, for identifying potential active compounds in pesticide-discovery programmes. Both methods use a training-set of compounds, for which structural data and qualitative activity data are available, to produce a model which can then be applied to the structural data of other compounds in order to predict their likely activity.  These new methods were compared to more established virtual screening methods in experiments using pesticide data from the Syngenta corporate database.  The new methods give similar results and outperform the established methods in the experiments we have carried out.

 

 

 

 

42.   Docking a Supposed Ligand From Four Residues of E2F to the Retinoblastoma Tumor Suppressor Protein (pRb) and the Prediction of a Putative Inhibitor

 

Aixia Yan, Guy H. Grant and W. Graham Richards

Department of Chemistry, Central Chemistry Laboratory, South Parks Road, Oxford OX1 3QH, UK

 

The retinoblastoma tumor suppressor protein (pRb) is an important protein that regulates the cell cycle, facilitates differentiation, and restrains apoptosis. Many of the functions of pRb are mediated by its regulation of the E2F transcription factors. It seems plausible that the inhibitory effect of pRb overexpression on apoptosis may be mediated by E2F.

 

The structural relationship (interaction) between pRb and E2F can be understood from their crystal structures. The pRb pocket, comprising the A and B cyclin-like domains, is the major focus of tumourigenic mutations in the protein. The fragment of E2F used in the structural studies, residues 409-426 of E2F-1, represents the core of the pRb-binding region of the transcription factor.

 

By analyzing the crystal structure of chains of A and B of the retinoblastoma tumor suppressor protein (pRb) bound to E2F-1, it is likely that of the 18 residues 409-426 of E2F-1, four residues (422-425) play an important role based on the particular location of charged groups. This segment of four residues 422-425 (Arg-Asp-Leu-Phe) was selected and its formal charges were set. The terminus of arginine was set as a nitrogen cation with a formal positive charge of one and the terminal of phenylalanine was set as carboxylic anion with a negative charge of one. The structure of the proposed peptide compound (given name: E2Fresidues4) with molecular weight 549.6 was then used to dock the chains of A and B of the protein by applying the program of LigandFit in Cerius2. The active binding site of the protein with the ligand is determined by protein shape-based cavity detection method and by the docked ligand, which was also conformed by the crystal structures. The docking result of the supposed compound E2Fresidues4 to the protein pRb fits the crystal structure quite well.

 

After that, 80 other compounds that are similar to the ligand E2Fresidues4 were taken from the NCI database and also docked to the protein at the same binding site. By comparing the binding affinity of E2Fresidues4 (from the X-ray crystal structure) with affinity scores for the 80 compounds, it is hoped that a compound suitable for future drug design may be found. We are also intending to use this protein target for our Screensaver computing project.

 

 

43.   eHiTS (electronic High Throughput Screening): New Method for Fast, Exhaustive Flexible Ligand Docking

 

Zsolt Zsoldos

SimBioSys Inc. 135 Queen's Plate Dr. Unit 520,  Toronto, Ontario, M9W 6V1, Canada

The flexible ligand docking problem is divided into two subproblems: pose/conformation search and scoring function. For successful virtual screening the search algorithm must be fast and able to find the optimal binding pose and conformation of the ligand. The presentation will demonstrate on practical examples that algorithms employing stochastic elements or crude rotomer samplings are unable to cover the full search space with necessary resolution to reproduce experimentally observed binding geometries.

 

eHiTS is an exhaustive flexible docking method that systematically covers the conformational and positional search space, producing highly accurate docking poses at competitive speed (few minutes per ligand). The sampling rate of the systematic search can be controlled by parameters allowing fast search (few seconds per ligand) while maintaining an accuracy level comparable to results reached by other docking software that are slower.

 

The search algorithm of eHiTS is based on exhaustive graph matching that rapidly enumerates all possible mappings of geometric shape and chemical feature graph of the ligand onto similar graph representation of the receptor cavity. Dihedral angles of rotatable bonds are computed deterministically as required by the positioning of the interacting atoms. Consequently, the algorithm can find the optimal conformation even

if unusual rotomers are required.

 

eHiTS employs a new scoring approach based on local surface point contact evaluation. Surface point properties are assigned with fine granularity: e.g. properties of polar atoms

in aromatic rings are different along the edge and the faces of the ring. This overcomes the property ambiguity problems inherent to atom based scoring functions. Receptor surface points are also assigned pocket-depth information to express differences in dielectric constants on solvated surface points and deeply embedded cavity points.

 

Validation results of eHiTS on several hundreds of PDB complex structures will be presented to demonstrate the ability of the program to accurately reproduce known binding poses. 

 

 

 

 

 

44.   Active Binding Site Detection by Flood Docking a Library of Molecular Fragments

 

Tamas Lengyel and A. Peter Johnson

ICAMS, Chemistry Department University of Leeds Leeds LS2 9JT

An important step of de novo drug design methods is to find the binding sites on the receptor, which will act as starting points of the structure generation procedure.

SPROUT is a de novo ligand design program, that constructs putative ligands using a small library of generic templates in a stepwise fashion with the constraints of the receptor. Prior to the structure generation phase, the active pocket of the receptor is explored. The characterisation of the pocket is followed by docking fragments sequentially to a user-selected set of target sites, providing strong electrostatic constraints for structure generation.

For an average protein, SPROUT typically generates 10-40 acceptor or donor hydrogen bonding target sites, but even tightly binding ligands rarely make more than 5 H bonds to the receptor. Therefore, the user has to select manually a subset of all the sites and these are used in the growing phase. Appropriate site selection is a crucial step in the de novo design procedure - different selections represent different de novo design experiments and will give rise to different answers.

A novel flood docking method, presented here, has been implemented in SPROUT to assist target site selection by docking and scoring a large fragment library to each potential target site or pair of neighbouring sites. This library is obtained by selecting the most frequently occurring of the set of fragments, themselves obtained by fragmenting the MDDR database. After scoring the docked templates, an overall site score is calculated for each site taking into account the number of fragments docked to the site and the binding scores of each individual fragment. Our hypothesis is that this site score provides a good estimate of the ability of a particular target site to bind strongly to an appropriate ligand.

This hypothesis has been validated on six protein families, each containing 15-20 pdb complexes. This method also provides a good starting set of highly scored docked templates for connection.

 

 

 

45.   Relating Structures to Targets Through the Analysis of Quality-Controlled Large-Scale Screening Data

 

Michael Lindemann, Bernd Rinn, Oliver Duerr, Tim Wormus, Bernd Kappler, Swen Reimann, Christian Ribeaud, Tom Jung and Stephan Heyse

GeneData, AG

High-throughput screening operations systematically explore the space of drug-like molecules, measuring their activity on a variety of biological targets in standardized and well-controlled experiments, and providing a wealth of data which has so far rarely been fully exploited.

At Genedata, we are developing sophisticated methods and software for the systematic and highly automated analysis of the relationships between compound structures and their effects on biological targets. As an important first step in our analysis process we perform large-scale automated quality assurance and data standardization.

Here we present a case study from a pharmaceutical HTS setting. First, we perform rigorous quality assurance on screening data for a set of targets. Second, we relate the structural classes of compounds to their bioactivity and specificity by in silico compound profiling. We demonstrate that our analysis process provides early indications for mechanisms-of-action and structure-activity relationships, and allows an excellent selection of targets and sub-libraries for further screening.

 

 

 

46.   Chemetics: Drug Discovery by Evolution

 

Sanne Schrøder Glad and Mads Nørregaard-Madsen

Nuevolution A/S, Rønnegade 8, DK2100 Copenhagen, Denmark

Chemetics®-driven Drug Discovery is a radically different way of undertaking drug discovery. Today, drug discovery is based on the iterative synthesis and testing of small molecules in order to identify hits from which leads may be generated through further synthesis and screening. This is a very cumbersome and time-consuming process. Nuevolution takes a very different approach to drug discovery. This involves the upfront synthesis of an enormous and diverse library of drug-like molecules through the use of Chemetics® (Chemical Genetics). Such libraries (e.g. 1010-1012 drug-like molecules) will contain hundreds to thousands of leads. Current technologies do not allow the screening of such large libraries of small molecules, making it impossible to identify the leads. This identification, however, is possible when applying the Chemetics® technology. Moreover, the Chemetics® technology allows the direct selection for subtype selectivity, otherwise a very difficult task in medicinal chemistry.

Despite the large size of Chemetics libraries, the theoretical chemical space relevant to drug discovery is far bigger. Therefore, designing Chemetics libraries is dependent on skilled use of computational chemistry techniques. In this poster we describe the principles of Chemetics and in detail describe the in silico process of library design.