On the conformation of the biotin molecule

Theoretical conformational study of the biotin molecule is divided into two parts. In the first step, various conformers of the model compound for the biotin molecule (D(+)-hexahydro-2 ' -oxo-2H-thieno[3,4-d] imidazole-4-pent anoic acid), with the methyl group replacing the side pentanoic substituent , have been optimized within the semiempirical and ah initio frameworks. Si xteen different biotin conformers resulting from three centers of asymmetry , non-planarity of two NH groups of imidazole ring, and energetical identit y of enantiomers, fall into two categories: trans and cis with respect to t he position of two hydrogen atoms at the carbon atoms bounding two rings. A ll the cis molecules are much more stable than the trans conformers and may exist in real systems. The second part of this study was devoted to the in fluence of conformation of pentanoic acid substituent in the biotin molecul e. (C) 2001 Elsevier Science B.V. All rights reserved.