Synthesis of New 9,15-Cyclogibberellins from Developing Apple Seeds: Confirmation of Structure for GA105 and GA108

Abstract

The structures of two new gibberellins (GA105 and GA108) from developing apple seeds were confirmed as 2β- and 11β-hydroxy-9,15-cyclo-GA9, respectively, by synthesis of their methyl esters (7) and (8); the analogous 1α-, 2α- and 11α-isomers were also prepared, the last two being identified as metabolites of 9,15-cyclo-GA9 (2) formed in feeding experiments with fern prothallia of Lygodium circinnatum. The route to (7) began with the Birch reduction of gibberellic acid (GA3) methyl ester 3,13-dimesylate, thereby removing the oxygen substituents from C3 and C13. A series of iodolactonizations and elimination processes followed by ozonolysis of the 17-methylene group furnished (19) which, on treatment with potassium hydride, underwent intramolecular alkylation to afford the cyclogibberellin (20). Further functional group manipulation then led to (7) via its 2α-epimer (23). The previously prepared 11β-bromocyclogibberellin (28) was also subjected to a series of functional group manipulations and deletions to afford the 11α-hydroxy analogue (33), and thence the 11β-epimer (8) by means of an oxidation/reduction cycle; 1α-hydroxycyclo-GA9 methyl ester (26) was similarly prepared from the methyl ester of the known 1β-epimer (3).

Diterpenoids

“…85 from gibberellic acid, has been reported 120 in this context. Confirmation of the structures of GA 105 86 and GA 108 87 which are present in developing apple seeds, has also been made 121 by the synthesis of their methyl esters from gibberellic acid. The synthesis of the wheat gibberellins A 93 88 and A 94 89 from gibberellic acid and gibberellin A 7 has been described.…”

Twenty years of gibberellin researchElectronic supplementary information (ESI) available: functionality patterns for naturally occurring gibberellins (GAn). See http://www.rsc.org/suppdata/np/b0/b007744p/

“…This product could then be used to prepare the methyl ester of the 11-hydroxy-cycloGA, GA 108 (131). 205…”

Application of Carbohydrate-Templated Asymmetric Diels–Alder Reaction to the Syntheses of ent-Penicillones A and B

“…Replacing t -BuOK with n -BuLi as a base in the Wittig reaction was unsuccessful. Hydrogenation of the unsaturated dioxolane 15 over 5% Rh on alumina afforded aldol precursor 16 . Finally, aqueous acid-catalyzed hydrolysis and an aldol reaction were carried out in refluxing THF with 2 M H 2 SO 4 to generate the desired product, penicillone B ( 2 ) as an only epimer.…”