Stereochemistry of Formation of theβ-Ring of Lycopene: Biosynthesis of (1R,1′R)-β,β-[16,16,16,16′,16′,16′-2H6]Carotene from [16,16,16,16′,16′,16′-2H6]Lycopene inFlavobacterium R 1560

Incubation of deuteriated precursors in cultures of Flavobacterium produced specifically deuteriated carotenoids. Analysis of these led to several conclusions: i) Lycopene is a direct precursor of β,β-carotene. ii) Its terminal Me groups retain their integrity during cyclization: there is a stereospecific folding of the 1,5-diene. The Me(16,16′) groups of lycopene become the Me(16,16′) of β,β-carotene. Consequently, the folding must follow the C2(E,E) mode. iii) Incorporation of deuterium was sufficiently extensive to permit CD measurements on the isolated β,β-carotene, allowing its centers of chirality to be assigned as (1S,1′S). iv) The same chirality resulted from incorporation of [2H3]mevalonate into zeaxanthin. The syntheses of specifically deuteriated [2H3]GPP, [2H3]FPP, and [2H3]GG are described.