Synthesis of optically active natural carotenoids and structurally related compounds.I. Synthesis of the chiral key compound (4R,6 R)-4-hydroxy-2,2,6-trimethylcyclohexanone. -Summary. A technical synthesis of (4 A', 6 K)-4-hydroxy-2,2, h-trimethylcyclohexanone (7) starting from the readily available 0x0-isophorone (2) is described. 7 is an ideal precursor for the synthesis of naturally occurring, optically active hydroxylated carotenoids (a.g. zcaxanthin, cryptoxanthin and structurally related compounds).Chirality is introduced at C(6) by a stereoselective fermentative hydrogenation ol the doublc bond using baker's yeast as the biocatalyst. Thereafter the carbonyl group at C(4) is reduced selectively and stereospecifically by chemical methods to the corresponding alcohol. Chemical reduction is preferably carried out by hydrogenation in the prcsvnce of a nickel catalyst or using triisobutylaluminiuni as the rcducing agent. Stability, stereochemistry and physical properties of 7 and the stcrcoisomcrs thereof are discussed. 1) Die systematische Nomenklatur von 1 und 2 ist : 3,5,5-Tritnethyl-2-cyclohexenon (1) bzw.3,5,5-Trimcthyl-2-cyclohexen-l, 4-dion (2).

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Developmental efforts to improve the yield of the chemical synthesis of (3R,3'R)-zeaxanthin resulted in the isolation, partly by chromatography from reaction mixtures, and full spectroscopic characterization by 'H-NMR, UVjVIS, and CD spectrosocpy of eleven (Z/E)-isomers of zeaxanthin: (72)

Technical Procedures for the Synthesis of Carotenoids and RelatedCompounds from 6-0x0-isophorone. I. Modification of the Kienzfe-Mayer-Synthesis of (3S, 3'S)-Astaxanthin SummaryAn efficient synthesis of (3S, 3's)-astaxanthin (la) in high yield and optical purity starting from (4R, 6R)-4-hydroxy-2,2,6-trimethylcyclohexanone (4) is reported. The absolute configuration of la, previously derived from ORD. data, has been confirmed by X-ray analysis of 5, a derivative of 6-0x0-isophorone (2). The key features of the improved synthesis are the two-step conversion of 4 to the key intermediate (4S)-2,6,6-trimethyl-4-hydroxy-2-cyclohexen-1-one (14), a new method for the partial reduction of the sterically hindered triple bond of (S)-6-hydroxy-3-(5-hydroxy-3-methyl-3-penten-l-ynyl)-2,4,4-trimethyl-2-cyclohexen-1-one (32), and Wittig olefination of the dialdehyde l,6-dimethyl-1,3, Soctatrienedial (38) using phosphonium salt 37 with a free hydroxyl group.

Dedicated to Dr. Otfo Isler on the occasion of his 80th birthday (23.1V.90) Starting from the readily available, optically active (4R)-4-hydroxy-2,2,6-trimethylcyclohexanone (I), a new technical synthesis of (3R,3'R)-zeaxanthin is described. According to a 2(C9 + C,) + C,, = C,, construction scheme, the ketone 1 was first transformed with (E)-3-methylpent-2-en-4-yn-l-o1(5) into a CIS-intermediate which,by a three-step sequence, could be converted into the known olefinic CI5-Wittig salt 4. Optimized conditions for the final Wittig reaction of4 with the Clo-dialdehyde 3 are discussed. Based on 1, the overall yield of the entire technical process is ca. 40 %.