Synthesis and stereochemistry of bilirubin analogs lacking carboxylic acids

Article abstract of DOI:10.1016/S0040-4020(97)01066-1

Bilirubin analogs with propionic acid groups replaced by sec-butyl (1), 3-acetoxy-1-methylpropyl (2) or 3-acetamido-1-methylpropyl (3) were synthesized in enantiopure form and known absolute configuration. Although there are no propionic acid groups to act in stabilizing folded, ridge-tile conformations, the (S) stereogenic centers induce the pigments to adopt a left-handed (M) helicity - as evidenced by exciton circular dichroism spectra.