Synthese von diastereo‐ und enantio‐selektiv deuterierten β,ε‐, β,β‐, β,γ‐ und γ,γ‐Carotinen

Synthesis of Diastereo‐ and Enantioselectively Deuterated β,ε‐, β,β‐, β,γ‐ and γ,γ‐Carotenes We describe the synthesis of (1′ R , 6′ S )‐[16′, 16′, 16′‐ 2 H 3 ]‐β, εcarotene, (1 R , 1′ R )‐[16, 16, 16, 16′, 16′, 16′‐ 2 H 6 ]‐β, β‐carotene, (1′ R , 6′ S )‐[16′, 16′, 16′‐ 2 H 3 ]‐γ, γ‐carotene and (1 R , 1′ R , 6 S , 6′ S )‐[16, 16, 16, 16′, 16′, 16′‐ 2 H 6 ]‐γ, γ‐carotene by a multistep degradation of (4 R , 5 S , 10 S )‐[18, 18, 18‐ 2 H 3 ]‐didehydroabietane to optically active deuterated β‐, ε‐ and γ‐C 11 ‐endgroups and subsequent building up according to schemes {article}{empty}{document}C₁₁ → C₁₄^C_ 26_ → → C₄₀{document} and C 11 → C 14 ; C 14 +C 12 +C 14 →C 40 . NMR.‐ and chiroptical data allow the identification of the geminal methyl groups in all these compounds. The optical activity of all‐( E )‐[ 2 H 6 ]‐β,β‐carotene, which is solely due to the isotopically different substituent not directly attached to the chiral centres, is demonstrated by a significant CD.‐effect at low temperature. Therefore, if an enzymatic cyclization of [17, 17, 17, 17′, 17′, 17′‐ 2 H 6 ]lycopine can be achieved, the steric course of the cyclization step would be derivable from NMR.‐ and CD.‐spectra with very small samples of the isolated cyclic carotenes. A general scheme for the possible course of the cyclization steps is presented.