Peptide-mediated chiral discrimination in bilipeptides: biliverdin di- and tri-peptides

Abstract

Synthetic biliverdin di- and tri-peptides (1)–(26) have been investigated by c.d. and u.v.–visible absorption spectroscopy with regard to the influence of their peptide chains on chiral discrimination of the helical, optically labile bilatriene backbone. In general, chiral discrimination increases with the number of amide groups per sidechain; the excess of population in bilitripeptides may exceed 85%. The preferred helicity of the bilatriene moiety is primarily determined by the presence of chiral centres between amide groups while the extent of discrimination depends on the steric requirements of all amino acid constituents present. In biliverdin bis(peptides) intramolecular interchain interactions may occur, lowering discriminatory efficiencies. Chiral discrimination is monitored by c.d. and its origin discussed in terms of intramolecular amide–bilatriene hydrogen bonding.