Cristiano R. W. Guimarães

MM-GB/SA Rescoring of Docking Poses in Structure-Based Lead Optimization

The critical issues in docking include the prediction of the correct binding pose and the accurate estimation of the corresponding binding affinity. Different docking methodologies have all been successful in reproducing the crystallographic binding modes but struggle when predicting the corresponding binding affinities. The aim of this work is to evaluate the performance of the MM-GB/SA rescoring of docking poses in structure-based lead optimization. To accomplish that, a diverse set of pharmaceutically relevant targets, including CDK2, FactorXa, Thrombin, and HIV-RT were selected. The correlation between the MM-GB/SA results and experimental data in all cases is remarkable. It even qualifies this approach as a more attractive alternative for rank-ordering than the Free Energy Perturbation and Thermodynamic Integration methodologies because, while as accurate, it can handle more structurally dissimilar ligands and provides results at a fraction of the computational cost. On the technical side, the benefit of performing a conformational analysis and having an ensemble of conformers to represent each ligand in the unbound state during the MM-GB/SA rescoring procedure was investigated. In addition, the estimation of conformational entropy penalties for the ligands upon binding, computed from the Boltzmann distribution in water, was evaluated and compared to a commonly used approach employed by many docking scoring functions.

Extension of the PDDG/PM3 and PDDG/MNDO semiempirical molecular orbital methods to the halogens

The new semiempirical methods, PDDG/PM3 and PDDG/MNDO, have been parameterized for halogens. For comparison, the original MNDO and PM3 were also reoptimized for the halogens using the same training set; these modified methods are referred to as MNDO′ and PM3′. For 442 halogen‐containing molecules, the smallest mean absolute error (MAE) in heats of formation is obtained with PDDG/PM3 (5.6 kcal/mol), followed by PM3′ (6.1 kcal/mol), PDDG/MNDO (6.6 kcal/mol), PM3 (8.1 kcal/mol), MNDO′ (8.5 kcal/mol), AM1 (11.1 kcal/mol), and MNDO (14.0 kcal/mol). For normal‐valent halogen‐containing molecules, the PDDG methods also provide improved heats of formation over MNDO/d. Hypervalent compounds were not included in the training set and improvements over the standard NDDO methods with sp basis sets were not obtained. For small haloalkanes, the PDDG methods yield more accurate heats of formation than are obtained from density functional theory (DFT) with the B3LYP and B3PW91 functionals using large basis sets. PDDG/PM3 and PM3′ also give improved binding energies over the standard NDDO methods for complexes involving halide anions, and they are competitive with B3LYP/6‐311++G(d,p) results including thermal corrections. Among the semiempirical methods studied, PDDG/PM3 also generates the best agreement with high‐level ab initio G2 and CCSD(T) intrinsic activation energies for SN2 reactions involving methyl halides and halide anions. Finally, the MAEs in ionization potentials, dipole moments, and molecular geometries show that the parameter sets for the PDDG and reoptimized NDDO methods reduce the MAEs in heats of formation without compromising the other important QM observables.

Addressing Limitations with the MM-GB/SA Scoring Procedure using the WaterMap Method and Free Energy Perturbation Calculations

The MM-GB/SA scoring technique has become an important computational approach in drug design. We, and others, have demonstrated that for congeneric molecules the correlation with experimental data obtained with the physics-based scoring is usually superior to scoring functions from typical docking algorithms. Despite showing good accuracy when applied within a series, much work is necessary to improve the MM-GB/SA method in order to gain greater efficiency in drug design. Here, we investigate the poor estimation of protein desolvation provided by the GB/SA solvation model and the large dynamic range observed in the MM-GB/SA scoring compared to that of the experimental data. In the former, replacing the GB/SA protein desolvation in the MM-GB/SA method by the free energy associated with displacing binding site waters upon ligand binding estimated by WaterMap provides the best results when ranking congeneric series of factor Xa and cyclin-dependent kinase 2 (CDK2) inhibitors. However, the improvement is modest over results obtained with the MM-GB/SA and WaterMap methods individually, apparently due to the high correlation between the free energy liberation of the displaced solvent and the protein-ligand van der Waals interactions, which in turn may be interpretable as estimates of the hydrophobic effect and hydrophobic-like interactions, respectively. As for the large dynamic range, comparisons between MM-GB/SA and FEP calculations indicate that for the factor Xa test set this problem has its origin in the lack of shielding effects of protein--ligand electrostatic interactions; that overly favors ligands that engage in hydrogen bonds with the protein.

Understanding the Impact of the P-loop Conformation on Kinase Selectivity

This work addresses the link between selectivity and an unusual, folded conformation for the P-loop observed initially for MAP4K4 and subsequently for other kinases. Statistical and computational analyses of our crystal structure database demonstrate that inhibitors that induce the P-loop folded conformation tend to be more selective, especially if they take advantage of this specific conformation by interacting more favorably with a conserved Tyr or Phe residue from the P-loop.

Search for Non-nucleoside Inhibitors of HIV-1 Reverse Transcriptase using Chemical Similarity, Molecular Docking, and MM-GB/SA Scoring

A virtual screening protocol has been applied to seek non-nucleoside inhibitors of HIV-1 reverse transcriptase (NNRTIs) and its K103N mutant. First, a chemical similarity search on the Maybridge library was performed using known NNRTIs as reference structures. The top-ranked molecules obtained from this procedure plus 26 known NNRTIs were then docked into the binding sites of the wild-type reverse transcriptase (HIV-RT) and its K103N variant (K103N-RT) using Glide 3.5. The top-ranked 100 compounds from the docking for both proteins were post-scored with a procedure using molecular mechanics and continuum solvation (MM-GB/SA). The validity of the virtual screening protocol was supported by (i) testing of the MM-GB/SA procedure, (ii) agreement between predicted and crystallographic binding poses, (iii) recovery of known potent NNRTIs at the top of both rankings, and (iv) identification of top-scoring library compounds that are close in structure to recently reported NNRTI HTS hits. However, purchase and assaying of selected top-scoring compounds from the library failed to yield active anti-HIV agents. Nevertheless, the highest-ranked database compound, S10087, was pursued as containing a potentially viable core. Subsequent synthesis and assaying of S10087 analogues proposed by further computational analysis yielded anti-HIV agents with EC50 values as low as 310 nM. Thus, with the aid of computational tools, it was possible to evolve a false positive into a true active.

Use of 3D Properties to Characterize Beyond Rule-of-5 Property Space for Passive Permeation

The application of conformationally dependent measures of size and polarity to characterize beyond rule-of-5 (Ro5) space for passive permeation was investigated. Specifically, radius of gyration, an alternative to molecular weight, and three-dimensional polar surface area and the generalized Born/surface area dehydration free energy, alternatives to hydrogen-bond donor and acceptor counts, were computed on models of the permeating conformations of over 35 000 molecules. The resulting guidelines for size and polarity, described by the 3D properties, should aid the design of Ro5 violators with passive permeability.

Activation of the G-protein-coupled receptor 119: a conformation-based hypothesis for understanding agonist response.

The synthesis and properties of the bridged piperidine (oxaazabicyclo) compounds 8, 9, and 11 are described. A conformational analysis of these structures is compared with the representative GPR119 ligand 1. These results and the differences in agonist pharmacology are used to formulate a conformation-based hypothesis to understand activation of the GPR119 receptor. We also show for these structures that the agonist pharmacology in rat masks the important differences in human pharmacology.

Design and evaluation of a 2-(2,3,6-trifluorophenyl)acetamide derivative as an agonist of the GPR119 receptor.

The design and synthesis of a GPR119 agonist bearing a 2-(2,3,6-trifluorophenyl)acetamide group is described. The design capitalized on the conformational restriction found in N-β-fluoroethylamide derivatives to help maintain good levels of potency while driving down both lipophilicity and oxidative metabolism in human liver microsomes. The chemical stability and bioactivation potential are discussed.

Effects of Arg90 Neutralization on the Enzyme-Catalyzed Rearrangement of Chorismate to Prephenate.

Chorismate mutase (CM) is an enzyme that catalyzes the Claisen rearrangement of chorismate to prephenate. In a recent effort to understand the basis for catalysis by CM, Kienhöfer and co-workers (J. Am. Chem. Soc. 2003, 125, 3206-3207) reported results on the mutation of Arg90 in Bacillus subtilis CM (BsCM) to citrulline (Cit), an isosteric but neutral arginine analogue. An ca. 10(4)-fold decrease in kcat or 5.9 kcal/mol increase in the free-energy barrier (ΔG(‡)) for the overall catalysis was observed upon mutation. In this work, attention is turned to determining the key factors that contribute to the reduced catalytic efficiency of Arg90Cit BsCM. Using a combined QM/MM Monte Carlo/Free-Energy Perturbation method, a ΔΔG(‡) value of 3.3 kcal/mol is obtained. The higher free-energy barrier for the mutant is exclusively related to inferior stabilization of the TS, particularly one of its carboxylate groups, by neutral Cit. In addition, the reaction becomes 2.0 kcal/mol more exergonic. As BsCM is limited by product release, this step contributes to the remainder of the 10(4)-fold decrease in the rate constant in going from Arg90 to Cit.

On the application of simple explicit water models to the simulations of biomolecules

Computer simulations of biomolecular systems have achieved a significant importance in science as they provide information regarding structure, dynamics, and energetics of biomolecules that are inaccessible to experimental measuring techniques. In this work, some important aspects of the simulation of biomolecular systems are described. An overview of the most popular protein force fields, simple explicit water models for the simulation of liquid water, and different approaches to treat the boundaries of the system is presented. Also, studies conducted in our group illustrating successful simulations of three biomolecules (thrombin, L-type calcium channel and human Cytomegalovirus protease) through the application of simple explicit water models combined with protein force fields are discussed.