Carbon-13 nmr spectra of carotenoids

Abstract

The 13 C-NMR spectrum of β-carotene has been assigned using data from deuterium labelled samples, and cis vitamin A. A study of methyl β-apo carotenoates is consistant with this result. Spectra of derivatives of β-carotene, such as zeaxanthin, isozeaxanthin, violaxanthin and alloxanthin, have been analysed. The stereochemistry of lutein is deduced from its spectrum to be trans between the 3’-hydroxyl group and the polyene chain at C-6' x2018;. It is suggested that isomytiloxanthin has the alkyl groups at C-5 and C-6 of the cyclohexanone ring trans. Cis double bonds give characteristic changes in the spectrum compared with that of the corresponding trans compound violeoxanthin is shown to be the 9-cis isomer of violaxanthin. 13 C- 31 P coupling over six bonds is observed with trans β-Ci 5 Wittig salt, but only over four bonds with the cis isomer. The 15, 15’ -β-carotene spectrum suggests a revision of the assignment of the phytoene spectrum. Using the data from appropriate apo esters and other model compounds the spectra of capsorubin and azafrin are analysed. The absence of suitable model compounds as yet prevents a complete assignment of the fucoxanthin spectrum. © 1976, Walter de Gruyter. All rights reserved.