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Synthesis of 13C-labelled (all-E,3R,3′R)-β,β-carotene-3,3′-diol (zeaxanthin) at C(12), C(13), C(12′), and C(13′) via all-E-2,7-dimethylocta-2,4,6-triene-1,8-dial-13C4

✍ Scribed by Frederick Khachik; Gary R. Beecher; Betty W. Li; Gerhard Englert

Publisher
John Wiley and Sons
Year
1995
Tongue
French
Weight
668 KB
Volume
36
Category
Article
ISSN
0022-2135

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✦ Synopsis

Abstract

The title compound (10) has been synthesized from all‐E‐2,7‐ dimethylocta‐2,4,6‐triene‐1,8‐dial (C~10~‐dialdehyde, 8) labelled with four ^13^C from commercially available and relatively inexpensive starting materials. The key starting material in this synthesis, (EtO)~2~P(O)^13^CHMe^13^CO~2~Et (2), has been prepared from triethyl phosphonoacetate‐^13^C~2~. The sodium salt of 2 reacted with fumarylaldehyde dimethylacetal to give ethyl 6,6‐dimethoxy‐2‐methyl‐E, E‐2,4‐hexadienoate (4) which was converted to 8 in four steps [(1) acid hydrolysis, (2) 2/NaH, (3) LiAlH~4~ reduction, (4) MnO~2~ oxidation]. The overall yield of 8 based on phosphonate 1 is 43‐46%. The double Wittig reaction of 8 with [(3R‐3‐hydroxy‐β‐ionylidene)ethyl]triphenylphosphonium chloride afforded 10 also known as (all‐E,3R,3′R)‐zeaxanthin‐^13^C~4~ (39% based on phosphonate 1) in high purity. This synthetic method may be extended to prepare other ^13^C‐labelled carotenoids.

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