Bruno Traber

Carotenoid synthesis: A progress report

The present review covers the progress in chemical synthesis of carotenoids over the period 1990 - 1996 and is a continuation of the review given at the 9th International Symposium on Carotenoids held in Kyoto. Highlights presented at previous symposia will be reported briefly and some reflections on possible future developments in the field are made. HIGHLIGHTS PRESENTED AT PREVIOUS CAROTENOID SYMPOSIA

2,6-Cyclolycopene-1,5-diol: Total synthesis of a naturally occurring oxidation product of lycopene

Abstract 2,6-Cyclolycopene-1,5-diol (3) was synthesized in 9 steps starting from α-terpinyl acetate (11). This represents the first total synthesis of an oxidative metabolite of lycopene (2). The synthesis was performed according to a C15 + C10 + C15 = C40 strategy using the Wittig olefination to couple the end groups to the central building block. An intramolecular aldol addition was used to introduce two new stereocenters with a defined relative stereochemistry.

'Prenigroxanthin' [(all-E,3R,3′S,6′S) -β,γ-carotene-3,3′,6′-triol], a novel carotenoid from red paprika (Capsicum annuum)

From the ripe fruits of red paprika (Capsicum annuum) prenigroxanthin, a minor carotenoid was isolated and, based on the spectral data and the proposed biosynthesis, identified as (all-E,3R,3′S,6′S)-β,γ-carotene-3,3′,6′-triol.

Facile synthesis of the cyclopentane moiety of (all-E,2R,5R,6S)-2,6-cyclolycopene-1,5-diol

The carotenoid (2R,5R,6S)-2,6-cyclolycopene-1,5-diol (1) bears a tetrasubstituted cyclopentane ring with three neighbouring stereogenic centers. The cyclic aldehyde 2 with the correct substitution pattern was synthesized in four steps from (R)-α-terpineol (3). From 2 the carotenoid 1 was prepared and investigated by CD spectroscopy.

Synthesis of carotenoids

Publisher Summary This chapter focuses on the brightly colored carotenoids that have aroused the curiosity of scientists since the beginning of organic chemistry and the first publications to deal with the carotenoids date from the early part of the 19th century. Most of the carotenoids have a trivial name, which is often derived from its natural origin and which gives no information on the structure. Carotenoids also occur as glycosides, glycosyl esters, and carotenoproteins and a special case are the sulfates in which the hydroxy group of the carotenoid is esterified with sulphuric acid. In principle, an almost countless number of strategies can be developed for the preparation of a carotenoid, but in reality, only a few strategies and methods have been worked out successfully and they have since been used repeatedly. Since carotenoid synthesis began, the enol ether condensation has frequently been used for the formation of carbon–carbon double bonds and this reaction was also applied for large-scale industrial production of carotenoids.