61(PA2-1) チルシフェリル-23アセタートの合成研究(ポスター発表の部)

概要

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Thytrsiferyl-23 acetate(1) isolated from Laurencia obutsa is a tetracyclic triterpene polyether and has strong cytotoxicity against P388. The related compounds 2 and 3 are shown to have a strained tetrahydropyrane ring (C-ring) as a boat form by X-ray analysis. The remarkable bioactivity and its unique shape of this molecule prompted us to study a synthesis of thyrsiferyl-23 acetate. The optically active epoxide 14 was coupled to the sulfide 15 with n-BuLi and DABCO and then phenylthio group was removed by reduction to give 16. The alcohol 16 was next coverted to epoxide 20 whose tetrahydropyrane ring was corresponding to the B-ring of thyrsiferol. Construction of the strained C-ring was successfully achieved by treatment of the epoxide 20 with Ti(O^iPr)_4 in toluene at 50℃ over night. The bicyclic ether 21 was obtained and newly equipped C-ring was revealed to take a distored boat form by NMR experiments. The A-ring was formed by bromocyclization. The properly protected 21, namely, 23 was cyclized by TBCO in nitrometane to yield 24 which contained seven of ten asymmetric carbons of thyrsiferol. The stereochemistry was confirmed in comparison with a natural product. The bromoether 24 was converted to methyl ketone 25 which was identical with 25' derived from 15-anhydrothyrsiferyl diacetate(26) in all respects.
天然有機化合物討論会の論文
1987-07-25