Stereoselective Characterization of the 1,4-Dihydropyridine Binding Site at L-Type Calcium Channels in the Resting State and the Opened/Inactivated State

Via a 3D-QSAR pseudoreceptor modeling approach, atomistic binding site models for pharmacologically active 1,4-dihydropyridines (DHPs) were developed. Applying a training set of pure DHP enantiomers a pseudoreceptor model representing the resting state of voltage-gated calcium channels (VGCCs) was generated by correlating experimental versus predicted free energies of binding (ΔG°). For validation further test set derivativesnot used for receptor generationwere predicted yielding root-mean-square (rms) deviation of 0.532 kcal/mol. Selectivity of the resting state model was checked by using the same DHP training set compounds but experimental data for the inactivated channel mode. Although there was found an almost perfect correlation for the training set, the following free relaxation of the corresponding test set applying a Monte Carlo protocol showed rms of 2.033 kcal/mol, clearly demonstrating the lack of any predicting character of the hybrid model. Taking into consideration 19 additional nifedipine analogues, a further verification of the model was performed. This yielded a good correlation for the 12 training set compounds and a satisfactory prediction for the test set molecules with rms of 0.409 kcal/mol. The generation of a pseudoreceptor model depicting the opened/inactivated state of VGCCs required one single additional residue to achieve a rms of 0.848 kcal/mol for the prediction of the test set derivatives. Since all pseudoreceptor models are composed of the same six amino acid residuesThr, Phe, Gly, Met, Tyr, Tyrtransition from resting to open/inactivated state may be described by one additional hydrogen bond donor interaction (Thr) at the left-hand side of DHPs. Furthermore, a potential charge-transfer interaction for all electron-deficient 4-phenyl DHPs is postulated, because significant correlation between quantum chemically AM1 (R = 0.91) and RHF 6-31G** (R = 0.84) computed LUMO* energies and experimentally detected ΔG°exp values was found.