Neighboring group participation in epoxide ring cleavage in reactions of some 16 alpha, 17 alpha-oxidosteroids with lithium hydroperoxide

In order to work out a new approach to the synthesis of the potent anti-tumor saponin OSW-1 aglycone, 16 alpha ,17 alpha -oxidosteroids were treated with acids, bases and lithium hydroperoxide. Acids caused Wagner-Meerwein type rearrangements irrespective of the sidechain structure. 16 alpha ,17 alp...

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Published inTetrahedron Vol. 57; no. 11; pp. 2185 - 2193
Main Authors Morzycki, JW, Gryszkiewicz, A, Jastrzebska
Format Journal Article
LanguageEnglish
Published OXFORD Elsevier 10.03.2001
Subjects
Chemistry
Chemistry, Organic
Physical Sciences
Science & Technology
PYRAZINE MARINE ALKALOIDS
ORNITHOGALUM-SAUNDERSIAE
BULBS
ANALOG
lithium compounds
AGLYCONE
POTENT ANTITUMOR SAPONIN
neighboring group effects
OSW-1
ESTERS
steroids
CHOLESTANE GLYCOSIDES
epoxides
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Summary:In order to work out a new approach to the synthesis of the potent anti-tumor saponin OSW-1 aglycone, 16 alpha ,17 alpha -oxidosteroids were treated with acids, bases and lithium hydroperoxide. Acids caused Wagner-Meerwein type rearrangements irrespective of the sidechain structure. 16 alpha ,17 alpha -Epoxides proved resistant to bases unless a 22-carbonyl group was present; in the case of 22-esters or 22-ketones the epoxide rings were cleaved with base and the corresponding allylic alcohols were formed. The epoxide ring cleavage of 16 alpha ,17 alpha -oxido-22-ester with lithium hydroperoxide was followed by lactonization of the intermediate 16 beta ,17 alpha -dihydroxy acid. The saponin OSW-1 aglycone was obtained by reaction of the lactone with isoamyllithium. (C) 2001 Published by Elsevier Science Ltd.
ISSN:0040-4020
DOI:10.1016/S0040-4020(01)00051-5