Carotenoids with two chromophores: carotenoid retinoates

Abstract

In this study, carotenoid retinoates are described for the first time. The preparation was achieved by the azolide method. Various sec carotenols reacted with N-retinoylimidazol in the presence of catalytic amounts of sodium hydride. Mono- and diretinoates of (3R,3′R)-zeaxanthin and its (3S,3′S)-enantiomer, (9Z,9′Z; 3R,3′R)-alloxanthin, (3R,3′R)-7,8,7′,8′-tetrahydro-3,3′-dihydroxy-β,β-carotene-8,8′-dione and (3R,6R,3′R,6′R)-ε,ε-carotene-3,3′-diol (lactucaxanthin), as well as monoretinoates of (3R,3′RS,6′R)-3′-methoxy-β,ε-caroten-3-ol, (3R,3′RS,6′R)-3-methoxy-β,ε-caroten-3′-ol, (2R,6′RS)-β,ε-caroten-2-ol, (3R,3′S; meso)-astaxanthin and (2′R)-aleuriaxanthin are reported in this study. Spectroscopic properties (¹H-NMR mass spectrometry, visible and circular dichroism spectra) are discussed. Studies on other carotenoid derivatives with two chromophores are referred to here.

Keywords:

• carotenoids
• retinol
• retinoates
• chromophores
• chirality

Acknowledgements

We thank Professor K. Nakanishi, Columbia University, for suggesting this study. Skilled technical assistance including CD spectra was provided by student Einar Egeland. Vitamin A acid and the synthetic carotenoids were mainly gifts from Dr H. Mayer, Hoffmann-La Roche, Basel, except synthetic alloxanthin and 3,3′-dihydroxy-7,8,7′,8′-tetrahydro-β,β-carotene-8,8′-dione, which were gifts from Dr G. Saucy, formerly of Hoffmann-La Roche, Nutley. Sissel Hertzberg and Einar Egeland were supported by a research grant from Hoffmann-La-Roche, Basel, to Synnøve Liaaen-Jensen.