Helically shaped bilirubins: natural optical activity and chemical correlation of M and P backbone helicity with biliverdins

Abstract

The natural optical activity of 2,18-bridged helically shaped bilirubins 2 and an unambigous chemical correlation of the M and P backbone helicity with the corresponding biliverdins 1 is reported. Complete resolution of the four component stereoisomeric mixture of (M,1′S), (M,1′R), (P,1′S) and (P,1′R) chirality was performed at the biliverdin stage 1. The optical activity of compounds is discussed in terms of the diagnostic value of CD spectra in the conformational analysis of non-restricted bilirubins.