Isorenieratene synthesis

The synthetic principle of olefinating an a,co-bisfunctional synthon A, representing the later molecular centre of the carotenoid, with two reaction partners B, the future molecular ends, can easily be described by the equation A + 2B -> B—A—B. This method was used by Mayer et al.265> in the synthesis of rhodoxanthin 550, a ketonic carotenoid, which was isolated for the first time from the red berrys of the yew-tree Taxus baccata. The authors describe the conversion of two equivalents of the stable phosphorane 548 with one equivalent of the C12-dialdehyde 549 265) (Scheme 93). The analogous reaction of crocetindial 552 with substituted benzylidenephospho-ranes such as 551 gives carotenoids such as isorenieratene 553266,267) and related compounds 266> (Scheme 93). Condensation of the phosphoranes 554 and 555 with the Cjo-dialdehyde 539 yields carotenoids of the dihydro type 556 268) and such like 557 269), respectively (Scheme 93). 

The intermediate 4-(t-butylthio)-but-3-en-2-one has been used in a new synthesis of isorenieratene [0,0-carotene(69)]. Electroreduction of retinal (70) in the presence of diethyl malonate or diethyl ethylmalonate gave the pinacol 15,15 -dihydro-/S,/8- carotene-15,15 -diol (71)... 

The reagent has been used for synthesis of the natural carotenoid isorenieratene (2) (equation I). ... 

G. (1999) Functional analysis of genes from Streptomyces griseus involved in the synthesis of isorenieratene, a carotenoid with aromatic end groups, revealed a novel type of carotenoid desaturase. Biochim. Biophys. Acta 1439, 57-64. 

Certain bacteria are able to rearrange the normal carbon skeleton to give aromatic carotenoids. Phenolic examples were isolated from Streptomyces mediolani. As well as the hydrocarbon isorenieratene (43), 3-hydroxy- (44), and 3,3 -dihydroxy-isorenieratene (45) were present and their structures confirmed by synthesis. In Thiothece gelatinosa the major carotenoid was okenone... 

The < ) end group is found, for example, in the symmetrical carotene isorenieratene (24) and in renieratene (26). Three different strategies have been applied for the synthesis of these compounds. 

The 3-hydroxy-(t) end group occurs in 3,3 -dihydroxyisorenieratene (161) and 3-hydroxy-isorenieratene (87). The synthesis of the symmetrical compound 161 was carried out in an analogous way to the synthesis of isorenieratene (24), by the Cio + C2o + Cio = C4o strategy (Scheme 44) with the Wittig reaction for the olefination. As starting material for the Cio-building block, 4-hydroxy-2,3,6-trimethylbenzaldehyde was chosen and the hydroxy group was protected as the tetrahydropyranyl or methoxymethoxy ether [60,61]. 

Yamaguchi, M. (1959) Total synthesis of isorenieratene. Bull. Chem. Soc. Japan, 32, 1171-1173. 

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