Carotenoids and related compounds. Part 41. Structure of mytiloxanthin and synthesis of a cis-isomer

Anti-Oxidative Activity of Mytiloxanthin, a Metabolite of Fucoxanthin in Shellfish and Tunicates

“…The compound 5 was converted into the methyl ketone 9 in four steps and this was condensed with the separately prepared conjugated ester 10 to give the desired β-diketone 11 . After hydrolysis of acetal moiety of 11 and subsequent desilylation, the resulting apocarotenal 12 [ 5 ] was condensed with the acetylenic phosphonium salt 13 [ 19 ] and then desilylated to preferentially provide all- E -mytiloxanthin ( 1 ) in a good yield. The total yield of 1 from epoxy alcohol 4 was 30% over 13 steps (21% from (–)-actinol over 18 steps).…”

“…Its structure was determined to be 3,3′,8′-trihydroxy-7,8-didehydro-β,κ-caroten-6′-one through chemical and spectroscopic studies by Khare et al , in 1973 [ 4 ]. Subsequently, Chopra et al synthesized 9 Z -(3 R ,3′ S ,5′ R )-mytiloxanthin [ 5 ]. Its absolute configuration was determined to be (3 R ,3′ S ,5′ R ) using a modified Mosher’s method by Maoka and Fujiwara [ 6 ].…”

Carotenoids and related polyenes. Part 7.1 Total synthesis of crassostreaxanthin B applying the stereoselective rearrangement of tetrasubstituted epoxidesWe have employed the numbering system used in carotenoids.

“…[α] 28 D ϩ10.1 (c 0.89, MeOH); ν max /cm Ϫ1 3611 and 3504 (OH), 1725 (OAc); δ H (300 MHz) 0.81, 1.16 and 1.31 (each 3H, s, Me × 3), 1.47 (1H, dd J 14.5 and 3, 4-H β ), 1.67 (1H, dd, J 13.5 and 4.5, 2-H β ), 1.86 (2H, m, 8-H 2 ), 1.98 (1H, dd, J 13.5 and 7.5, 2-H α ), 2.03 (3H, s, OAc), 2.47, 2.56 (each, 1H, dt, J 18 and 6.5, 7-H 2 ), 2.81 (1H, dd, J 14. 5…”

“…We assumed that the tetrasubstituted olefinic end group was formed in Nature from the epoxide end group of 5,6-epoxy carotenoids such as halocynthiaxanthin 3 2 by opening of the C-6-oxygen bond of the oxirane ring and subsequent rearrangement of the methyl group at C-1 (Scheme 1, route a). Thus, the absolute configuration at C-3Ј in 1 is considered to be S, since chiralities at C-3 in most of the known natural epoxy carotenoids are R. On the other hand, mytiloxanthin 3b,4 3 is also believed 5 to arise from 5,6-epoxy carotenoids by cleavage of the oxirane ring at C-5 and successive ring contraction (a pinacolic rearrangement) (Scheme 1, route b). In the previous communi- † We have employed the numbering system used in carotenoids.…”

Stereoselective rearrangement of 5,6-epoxy carotenoid model compounds

“…Scheme4 Reagents and conditions: i, (EtO),P(O)SCH(Et)CO,Me 24, LDA; ii, LiAIH,; iii, MsCl, py; iv, LiAlH,; v,p-TsOH; vi, LDA, acetone; vii, A c A PY…”