ISSN:
0899-0042
Keywords:
circular dichroism
;
mesobilirubins
;
conformation
;
ridge-tile shape
;
molecular helicity
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Bilirubin, the yellow pigment of jaundice, is a bichromophoric tetrapyrrole that readily adopts either of two enantiomeric, folded conformations shaped like ridge-tiles and stabilized by a network of six intramolecular hydrogen bonds. Interconversion of these M and P helical chirality conformational enantiomers is rapid at room temperature but may be displaced toward either enantiomer by intramolecular nonbonded steric interactions. Introduction of a methyl group at the β and β′ carbons of the propionic acid chains on the symmetric bilirubin analog, mesobilirubin-XIIIα, shifts the conformational equilibrium toward the M or the P-chirality intramolecularly hydrogen-bonded conformer, depending only on the S or R stereochemistry at β and β′, resulting in pigments with intense exciton coupling circular dichroism (CD) for the ∼430 nm transition(s). Optically active synthetic analogs of bilirubin with propionic acid groups lengthened systematically to heptanoic acid (1-5) were synthesized and examined by spectroscopy to explore the influence of alkanoic acid chain length on conformation and intramolecular hydrogen bonding. In these diacids and their dimethyl esters (6-10), strong exciton chirality CD spectra are observed, and the data are correlated with molecular helicity. Chirality 9:604-615, 1997. © 1997 Wiley-Liss, Inc.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
