DIRECT RESOLUTION, CHARACTERIZATION, AND STEREOSPECIFIC BINDING-PROPERTIES OF AN ATROPISOMERIC 1,4-BENZODIAZEPINE

The chromatographic resolution of thyl)-5-(2-fluorophenyl)-2H-1,4-benz odiazepin-2-on (7), the 2'-fluoro, N-1-tert-butyl analogue of diazepam , was attained on both analytical and preparative (mgs) scales, by usi ng several chiral stationary phases (CSPs). The stereochemistry of thi s compound was characterized by means of H-1-NMR Nuclear Overhauser Ef fect (NOE) analysis. The single enantiomers of 7 were tested for their configuration and stereochemical stability by circular dichroism (CD) , and their interaction with the central nervous system (CNS) benzodia zepine receptor was assayed, showing a significant difference in their binding affiities. Protein binding studies with human serum albumin ( HSA, the main benzodiazepine carrier in human plasma) immobilized on a silica stationary phase revealed that HSA also preferentially binds o ne stereoisomer of 7. However, both on line CD detection and stereospe cific interaction with other common drugs clearly demonstrated that th e stereoselectivity of immobilized HSA for 7 is opposite to that for a ll the other studied benzodiazepines. In addition, HSA stereoselectivi ty for 7 is opposite to CNS receptor binding stereoselectivity for the same compound. Such HSA anomalous stereoselectivity for 7 was also co nfirmed in aqueous buffer solution by competitive displacement studies . Compared to other chiral 1,4-benzodiazepines, com pound 7 thus shows several anomalous binding properties: HSA and the CNS receptor demons trated opposite enantioselective discrimination; HSA has reversed enan tioselectivity for compound 7; and HSA stereospecifically binds the lo w-affinity enantiomer. (C) 1997 Wiley-Liss, Inc.