Enantiospecific Synthesis Of Bioactive Styryllactones

Abstract

The thesis entitled “Enantiospecific synthesis of bio-active stryllactones” comprise an introduction about stryllactone and two chapters describes the synthesis of stryllactones. Trees of the genus Goniothalamus of the plant family Annonaceae in South East Asia has been known for a long time for their proven as folkloric medicine. Stryryllactones were found to exhibit moderate to significant biological activity including antitumour, antifungal as well as antibiotic properties. Because of their unique and intriguing structures and the activity associated much effort has been centered on the development of methodology for the synthesis of these compounds. The structures and relative configurations of these compounds were determined either by X-ray crystallography or by extensive NMR spectral analysis and by mass spectroscopic techniques. The research group of McLaughlin isolated and characterized a series of styryllactones, possessing significant to marginal cytotoxic activity against human tumor cell lines. The structures and relative configurations of these compounds were determined either by X-ray crystallography or by extensive NMR spectral analysis. Classification of these styryllactones is based on the structural characteristics of the six different skeletons as shown in Figure 1. Figure 1:features styryllactone the genus In this thesis, enantioselective total synthesis of styryllactones ()-9-deoxygoniopypyrone 1, ()-goniopypyrone 2, ()-7-epi-goniofufurone 3, ()-7-epigoniodiol 4 and the putative structure of ()-etharvendiol 5 is presented. a) Total synthesis of ()-9-deoxygoniopypyrone, ()-goniopypyrone, ()-7-epigoniofufurone and ()-7-epi-goniodiol: Synthesis of the styrylalctones is relied on elaboration of the trihydroxy ester 11 derived from tartaric acid. Appropriate protection of the hydroxy groups and further modifications of the ester functionality (which can be transformed into the corresponding alcohol or aldehyde) is planned for the synthesis of the styryllactones 1-5. Accordingly, the bis-dimethylamide 9 derived from D-()-tartaric acid, was transformed to the -hydroxy amide 10 using a combination of Grignard reagent addition followed by reduction of the resultant ketone. Acid mediated deprotection of the acetonide with concomitant hydrolysis of the amide to the ester is accomplished in one pot by treating 10 with p-TSA in benzene/MeOH mixture Treatment of the trihydroxy ester with 2,2-dimethoxy propane in presence of p-TSA afforded the hydroxy ester 12 which was elaborated to the styrylalctones 9deoxygoniopypyrone, 7-epi-goniodiol, 7-epi-goniofufurone and goniopypyrone (Scheme-2). (Part of this work is published: Prasad, K. R.; Dhaware, M.G. Synlett. 2007, 11121114.; Prasad, K.R.; Dhaware, M.G. Synthesis 2007, 3697) b) Stereoselective synthesis of the putative structure of (+)-etharvendiol: In 1997, Bermejo et al isolated the styryl pyrone etharvendiol 5 from the ethanolic extract of stem bark from Goniothalamus arvensis. Hitherto, no synthesis of etharvendiol is reported in the literature. In this section, approach towards the synthesis of putative structure of etharvendiol will be discussed. Synthesis of etharvendiol 5 is anticipated by the elaboration of masked tetrol 15, comprising an alkene tether and four contiguous hydroxy groups installed with definite configuration. It is relied on exploiting the hydroxy directed lactonization via the oxidation of alkene in 15, and subsequent elaboration to 7. Bis-dimethylamide 9, derived from D-()-tartaric acid was identified as the suitable precursor for the synthesis of 15. Synthesis of masked tetrol 15 is accomplished from 9 involving a combination of selective Grignard additions and stereoselective reduction (Scheme 3). (For structural formula pl see the pdf file)