Synthesis of Carotenoids in the Gliding Bacteria Taxeobacter: (all-E,2′R)-3-deoxy-2′-hydroxyflexixanthin

The c₄₀-carotenoid (all-E, 2′R)-deoxy-2′-hydroxyflexixanthin (=1′,2′-dihydroxy-3′,4′-didehydro-1′,2′-dihydro-β,ψ-caroten-4-one;(2′R)- 2 ) was synthesized according to a C₁₅ + C₁₀ + C₁₀ = C₄₀ strategy. The chiral centre was introduced into the C₁₀-end group by the enantioselective Sharpless dihydroxylation. The four building blocks were coupled by applying four consecutive Witting reactions. By comparison of the CD spectra of the synthetic (2′R)- 2 with those of 2 isolated from the gliding bacteria Taxeobacter, the configuration of natural 2 was determined as (2′R).