(±)-Metaphanine (49), which is a member of hasubanan alkaloids and possesses an intramolecular hemiketal ring, was synthesized. The keto-lactam (5)3) was derived to the diacetoxy-ketal (13) via the O-acetyl-ketolactam (11). The compound (13) was oxidized to the 10-oxo compound (16) which was reduced stereoselectively to the trans diol-lactam (22), a C10-hydroxy group of which was selectively protected by an acetyl group or by a tetrahydropyranyl group to give the trans 10-acetoxy compound (23) or the monotetrahydropyranyl ether (33), both of which were oxidized and hydrolyzed to provide (±)-7-ethyleneketal-16-oxo-metaphanine (36). The selective reduction of the lactam carbonyl group of the compound (36) by the Borch's method4) gave (±)-7-ethyleneketal-metaphanine (44) which was hydrolyzed to give (±)-metaphanine (49).
(±)-Metaphanine (49)是一种hasubanan
生物碱,具有分子内
半缩醛环,已合成。酮内酰胺(5)3)通过O-乙酰基-酮内酰胺(11)转化为
二乙酰氧基-
缩酮(13)。化合物(13)被氧化为10-氧代化合物(16),后者被立体选择性还原为反式二醇内酰胺(22),其中C10-羟基被乙酰基或
四氢吡喃基选择性保护,得到反式10-乙酰氧基化合物(23)或单
四氢吡喃基醚(33),两者均被氧化和
水解,得到(±)-7-
乙烯基缩酮-16-氧代-metaphanine (36)。通过Borch法4)选择性还原化合物(36)的内酰胺羰基,得到(±)-7-
乙烯基缩酮-metaphanine (44),后者被
水解得到(±)-metaphanine (49)。