Molecular basis of peripheral vs central benzodiazepine receptor selectivity in a new class of peripheral benzodiazepine receptor ligands related to alpidem.

Alpidem (1), the anxiolytic imidazopyridine, has nanomolar binding affinity for both the central benzodiazepine receptor (CBR) and the peripheral benzodiazepine receptor (PBR). A novel class of PBR ligands related to alpidem has been designed by comparing the interaction models of alpidem with PBR and CBR. Several compounds in this class have shown high selectivity for PBR vs CBR, and the selectivity has been discussed in terms of interaction models. The binding behavior of the three selected compounds was extensively studied by competition and saturation assays, and the results suggest that they are capable of recognizing two sites labeled by [3H]PK11195. The molecular structure of one of the most active compounds (4e) has been determined by X-ray diffraction and compared with that of alpidem. Molecular modeling studies suggest that the bioactive conformation of 4e is likely to be very similar to the conformation found in the crystal.