Binding of 3-alkyl-1,4-benzodiazepin-2-one stereoisomers to human serum albumin

Conformation selectivity in the binding of diazepam and analogues to α1-acid glycoprotein

Diazepam, a 1,4-benzodiazepine lacking chiral centre, exists in an equimolar mixture of two chiral conformers. Induced circular dichroism spectra for the binding of diazepam and its 3,3-dimethyl substituted analogues to alpha1-acid glycoprotein (AGP) revealed that opposite to human serum albumin, AGP preferably binds the P-conformers. Accordingly, slightly favoured binding of (R)-enantiomers of 3-alkyl derivatives having P-conformation was found. In case of 3-acyloxy derivatives, however, AGP preferably binds the (S)-enantiomers. Studies with the separated genetic variants of AGP proved similar binding affinities, but markedly different conformation selectivities. For diazepam bound by the F1-S variant, a P/M selectivity of about 2 could be estimated.

Direct resolution, characterization, and stereospecific binding properties of an atropisomeric 1,4-benzodiazepine

The chromatographic resolution of 7-chloro-1,3-dihydro-1-(1,1-dimethylethyl)-5- (2-fluorophenyl)-2H-1,4-benzodiazepin-2-on (7), the 2'-fluoro, N1-tertbutyl analogue of diazepam, was attained on both analytical and preparative (mgs) scales, by using several chiral stationary phases (CSPs). The stereochemistry of this compound was characterized by means of 1H-NMR Nuclear Overhauser Effect (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) benzodiazepine receptor was assayed, showing a significant difference in their binding affinities. 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 one stereoisomer of 7. However, both on line CD detection and stereospecific interaction with other common drugs clearly demonstrated that the stereoselectivity of immobilized HSA for 7 is opposite to that for all the other studied benzodiazepines. In addition, HSA stereoselectivity for 7 is opposite to CNS receptor binding stereoselectivity for the same compound. Such HSA anomalous stereoselectivity for 7 was also confirmed in aqueous buffer solution by competitive displacement studies. Compared to other chiral 1,4-benzodiazepines, compound 7 thus shows several anomalous binding properties: HSA and the CNS receptor demonstrated opposite enantioselective discrimination; HSA has reversed enantioselectivity for compound 7; and HSA stereospecifically binds the low-affinity enantiomer.

Stereospecific and competitive binding of drugs to human serum albumin: a difference circular dichroism approach

Simultaneous binding of two drugs to human serum albumin (HSA) was investigated by difference circular dichroism (delta CD) spectroscopy. Phenylbutazone and diazepam were chosen as specific markers for binding areas I (cumarines) and II (indoles), respectively, and their stereospecific interactions with protein were selectively characterized. Displacers were drugs known to specifically bind to areas I (salicylate) and II (racemic ibuprofen). The results indicate two different interaction mechanisms: a direct competition one (diazepam-ibuprofen and phenylbutazone-salicylate) and an indirect competition one (diazepam-salicylate and phenylbutazone-ibuprofen). The two major binding areas on HSA are distinct, but not independent, entities. Finally, the dissociation constants of marker ligands and competitors complexed to HSA were determined by quantitative analysis of CD data.

Protein binding investigation by difference circular dichroism: native and acetylated human serum albumins

A modified albumin was prepared by selective reaction of Lys199 with acetyl salicylic acid. Protein binding investigation was carried out on native and modified proteins by difference circular dichroism (delta CD). Acetylation of Lys199 reduces significantly the effects of the interaction between drugs in the stereoselective HSA binding at specific binding areas.

Stereoselective effect of warfarin and bilirubin on the binding of 5-(o-chlorophenyl)-1,3-dihydro-3-methyl-7-nitro-2H-1,4-benzodiazepin-2- one enantiomers to human serum albumin

The binding of the title benzodiazepine enantiomers and its modulation by warfarin and bilirubin were studied by chromatography on human serum albumin (HSA) immobilized on Sepharose 4B, and also by a combination of ultrafiltration and circular dichroism (UF-CD) methods. In the absence of warfarin and bilirubin the binding of the benzodiazepine was not stereoselective. (S)-Benzodiazepine and (S)-warfarin mutually increased the binding of each other, while the binding of (R)-benzodiazepine was preferentially enhanced on HSA saturated with bilirubin.

Stereochemical features of 1,4-benzodiazepin-2-ones bound to human serum albumin: difference CD and UV studies

The stereochemistry of an achiral (Diazepam) and two chiral (3-methyl and 3-succinyloxy substituted) 1,4-benzodiazepin-2-ones interacting with human serum albumin (HSA) has been investigated by making use of difference absorption (UV) and circular dichroism (CD) spectroscopies. Evidence is obtained for a higher affinity with HSA for one of the two possible conformations of the seven-membered benzodiazepine ring. The red shift revealed by the absorption difference spectrum between the free and the bound drug accounts for the CD difference spectra observed.

The role of configuration and conformation in the binding of 2,3-benzodiazepines to human serum albumin

2,3-Benzodiazepines containing a centre of asymmetry at C-5 possess both central and helical chiralities, and the solution of their racemates contains four molecular species. The binding of these compounds to human serum albumin (HSA) was studied by affinity chromatography. The binding strength depended both on the steric orientation of the 5-ethyl substituent and on the conformation of the diazepine ring. Conformation P (defined by the positive sign of C-1-N-2-N-3-C-4 torsion angle) is favoured, while the quasiaxial orientation of the 5-ethyl substituent is not favoured by the albumin molecule.

Selective effect of clonazepam and (S)-uxepam on the binding of warfarin enantiomers to human serum albumin

Both clonazepam and (S)-uxepam selectively increase the binding of (S)-warfarin to human serum albumin. By liquid affinity chromatography, improved resolution of rac-warfarin was achieved.