[A new lupin alkaloid, (-)-leontalbinine N-oxide, in Sophora flavescens var. angustifolia seeds and its synthesis by biomimetic transformation from (+)-matrine N-oxide].

The possibility of the biomimetic transformation of (+)-matrine N-oxide, a main alkaloid in Sophora flavescens var. angustifolia, under various oxidative conditions was examined by the use of several metallic ions. When (+)-matrine N-oxide was warmed with FeSO4, or Fe(COOH)2 in MeOH-H2O at 40 degrees C, (-)-7, 11-didehydromatrine [(-)-leontalbinine], a minor alkaloid in the same plant, was obtained along with (+)-matrine. This selective formation of (-)-leontalbinine seems to be specific to the reaction of (+)-matrine N-oxide with ferrous reagents. In addition, the structure of the newly isolated minor lupin alkaloid from the seeds of S. flavescens. was determined as (-)-leontalbinine N-oxide from its spectral comparison with the authentic sample.