Abstract
Reduction of hypoepistephanine (I:R=H), a kind of tertiary phenolic base contained in Stephania japonica MIERS (Menispermaceae), as a free base or its dihydrochloride, with sodium borohydride in methanol solution results in selective hydrogenation to form dihydrohypoepistephanine-B (V:R=H), m. p. 223-224°, [α]D24 +87.71°, alone. Methylation of this product gives N-methyldihydrohypoepistephanine-B (VI:R=H) (asymmetric centers: -, -), m. p. 257-258°, [α]D21+82.19°, an antipode of repandine (VII:R=H) (asymmetric centers, +, +), m. p. 248-250°, [α]D21-93.85°. Reduction of (I:R=H) with zinc dust and dil. sulfuric acid results in preferential formation of dihydrohypoepistephanine-A (VIII), m. p. 217-218°, [α]D20+263.15°, accompanied with dihydrohypoepistephanine-B (V:R=H). Formation ratio of A and B is 3:1. Methylation of (VIII) gives oxyacanthine (IX).
Reduction of epistephanine (I:R=Me) or its dihydrochloride with sodium borohydride in methanol also results in selective hydrogenation and dihydroepistephanine-B (V:R=Me), m. p. 225-226°, [α]D25+101.01°, alone and its methylation gives N-methyl-dihydroepistephanine-B (VI:R=Me) (asymmetric centers, -, -), m. p. 213°, [α]D19+80.00, an antipode of O-methylrepandine (VII:R=Me) (asynmetric centers, +, +), m. p. 212-213°, [α]D19-79.93°.
