Configurational studies on red algae carotenoids

Abstract

The configurations of (6′ R)-β,ε-carotene, (3′ R,6′ R)-β,ε-caroten-3′-ol (α-cryptoxanthin), (3 R,3′ R,6′ R)-β,ε-carotene-3,3′-diol (lutein), (3 R)-β,β-caroten-3-ol (β-cryptoxanthin), (3 R,3′ R)-β,β-carotene-3,3′-diol (zeaxanthin) and all- trans (3 S,5 R,6 S,3′ R)-5,6-epoxy-5,6-dihydro-β,β-carotene-3,3′-diol (antheraxanthin) were established by CD and 1H NMR studies. The red algal carotenoids consequently possessed chiralities at each chiral center (C-3, C-5, C-6, C-3′, C-6′), corresponding to the chiralities established for the same carotenoids in higher plants. Two post mortem artifacts from Erythrotrichia carnea were assigned the chiral structures (3 S,5 R,8 R,3′ R)-5,8-epoxy-5,8-dihydro-β,β-carotene-3,3′-diol [(8 R)-mutatoxanthin] and (3 S,5 R,8 S,3′ R)-5,8-epoxy-5,8-dihydro-β,β-carotene-3,3′-diol [(8 S)-mutatoxanthin]. This is the first well documented report of a naturally occurring β,ε-caroten-3′-ol ( 1H NMR, CD, chemical derivatization).