Conformational analysis of thiopeptides: (φ, ψ) maps of thio-substituted dipeptides

Abstract

Noncoded amino acids such as isobutyric acid have been used extensively in the process of drug design and protein engineering. This article focuses on a noncoded amino acid where the oxygen in the peptide unit is replaced with a sp2 sulfur. It was hypothesized that the conformational space as well as the conformational preferences of thiopeptides will be more restricted and altered by the bulkier atom with different electrostatic properties. In vacuo conformational minima as well as associated energies for the thio-substituted alanine dipeptides were calculated at the ab initio HF/6-31G* level. When the bulkier sulfur atom acts as a hydrogen bond acceptor in the C5 conformation or in the C7a..