42 ヒカゲノカズラ中の16-Oxoserratene系トリテルペノイド

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  • 42 TRITERENOIDS OF 16-OXOSERRATENE GROUP OCCURRING IN LYCOPODIUM CLAVATUM

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説明

Five triterpenoids containing conjugated ketone chromophor were newly isolated-four (A, B, C, and E) from L. clavatum and one (D) from L. serratum, -and characterized. Their structures and stereochemistry were elucidated as 16-oxodiepiserratenediol (1), 16-oxoepiserratenediol (2), 16-oxoserratenediol (3), 16-oxoserratriol (4), and 16-oxolycoclavanol(5), respectively, based on spectroscopic and chemical evidence, wherein several new methods in solving the structural and steric problems were discussed: i.e., i) Application of TH-effect, ii) NMR classification of acetonide types, iii) Alkaline treatment and LAH reduction of 23 or 24-monotosylate. Particularly, the last method had a great advantage to elucidate the stereochemistry of substituents at ring A of poly-hydroxylated triterpenoid by noticing the key-product, an oxetane (18) or a seco-compound (20). 3-Keto-23 or 24-tosylate, (23) and (24), on treatment with t-BuOK, gave novel cyclobutanone derivatives, (25) and (26), which showed strong positive and negative Cotton effect corresponding to its stereochemistry, thus giving a new chemical method for determination of the position of tosyloxy group.

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