Studies on the Asymmetric Synthesis of Stemona Alkaloids: Total Synthesis of ( --)-Stenine

摘要

Extracts from the roots and rhizomes of stemonaceous plants (Stemona and Croomia) have long been used in China and Japan as cough remedies for humans and as antheltnintics for domestic animals. A number of related Stemona alkaloids have been isolatedfrom these extracts and their structures have been determined, mostly by X-ray diffraction studies. The most prototypical members of this family of alkaloids are stenine (1). tuberostemonine(2), and tuberostemonine A (3), and of these 2. in particular, has been shown to possess inhibitory activity on the excitatory transmission at the crayfish neuromuscular junction. These pharmacological properties indicate that some of the effects of the crude extracts may be attributable to 2 and that this alkaloid may be a useful tool in the field of ncuropharmacology. These and other types of Stemona alkaloids have recently been the subject of several studies because of their stimulating structures and prominent physiological activities, and the total synthesis of( +-)-stenine (1) has already been accomplished by Hart and Chen. In the course of our investigations into the asymmetric syntheses of these alkaloids, we now report the highly stereocontrolled total synthesis of (--)-stenine (1).