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|Type:||Artigo de periódico|
|Title:||The C-13 Configuration Of The Bromine-containing Diterpene Isoaplysin-20. Synthesis Of Debromoisoaplysin-20 And Its C-13 Epimer|
|Abstract:||Syntheses of the tricyclic diterpenes 13-epidebromoisoaplysin-20 (14) and debromoisoaplysin-20 (15) from methyl copalate (3) are described. Methyl isocopalate (4) prepared from 3 was converted into the corresponding alcohol 8. By epoxidation of 8 a 1:1 mixture of isomeric epoxides was obtained; the reductive opening of the α-epoxide (13) afforded 14. Hydroxylation of 4 gave the diol ester 16, which on oxidation with dimethyl sulfoxide-acetic anhydride yielded 18a. Transformation of 18a into the ethylene thioketals 20 and 20a, followed by desulfuration of the mixture to the hydroxy ester 21, and subsequent lithium aluminium hydride reduction afforded 15. The stereochemical features of the epoxides 9 and 13 and the diol ester 16 as well as those at C-13 of 14 and 15 were determined by analysis of their 13C NMR spectra. On the basis of the comparison of the 1H NMR signals of the methyl groups of 14 and 15 and the ones of the acetoxymethylene groups of their monoacetates 14a and 15a with those reported for the methyls of the bromine-containing diterpene isoaplysin-20 (1) and the acetoxymethylene of its monoacetate (1a), the stereochemistry of the natural product was established. © 1980 American Chemical Society.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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