Circular dichroism and gel filtration study of binding of prochiral and chiral 1,4-benzodiazepin-2-ones to human serum albumin

Abstract

Combining circular dichroism (c.d.) and gel filtration method in studying the binding of chiral ((S)/R)- 1) and prochiral ( 2. diazepam and 3 . desmethyldiazepam) benzodiazepines to human serum albumin (HSA), the following results were obtained: c.d. measurements revealed that both enantiomers of 1 are bound by HSA with different affinities. Gel filtration measurements revealed the following data on binding; (a) the HSA affinity for ( S)- 1 is about 40 times higher than for ( R)- 1 , (b) for ( S)- 1 exist two independent and nonequivalent sites of high affinity and for ( R)- 1 two independent equivalent sites of low affinity, (c) at equimolar concentrations of 1 and HSA, ( S)-enantiomer is bound up to 5 3 per cent, but ( R)-enantiomer up to 18 per cent only; at the same ratio of ligand to protein prochiral 3 was bound up to 56 per cent.