Chiral Discrimination in Biliverdin (S)-Amino Acids, II : Structural Variations of the Amino Acid Functional Groups

Article abstract of DOI:10.1007/BF00811333

The Biliverdin-(S)-amino acid derivatives 2-21 have been synthesized, and are subject to a thorough c.d. and u.v.-vis. electronic absorption analysis in the bilatriene chromophoric region.It is shown that the extent of chiral discrimination of the bilatriene helices is particularly sensitive towards structural variations of the amino acids bound to the propionic side chains.Thus, a pronounced decrease of chiral induction occurs if hydrogen bonding between one of the two essential coordination sites of the amino acid entity and the bilatriene backbone is disturbed.Acco rdingly, derivatives of (S)-amino acid t-butyl esters (3,5,7,16, and 17) and N-substituted (S)-amino acids (8-10, 20, and 21) generally display weak c.d. spectra.If additional polar groups are present in bis(amino acid) derivatives mutual interferences of the adjacent side chains must be taken into account.The attenuations of Δε-values observed for the bis(serine) and bis(aspartic acid) compounds 14 and 15 thus are mainly due to intramolecular interchain interactions.The results provide evidence in support of the proposed mechanism of chiral discrimination in biliverdin amino acids. - Keywords: Biliverdins; Chiral discrimination; Amino acids; C.d.; U.v.-vis