A new pyrrolizidine alkaloid, broussonetine N, as an inhibitor of glycosidase, from Broussonetia kazinoki SIEB-and absolute stereostructures of broussonetines A and B

A new pyrrolizidine alkaloid, broussonetine N, was isolated from the branch es of Broussonetia kazinoki SIEB. (Moraceae). Broussonetine IV was formulat ed as (1R,2R,3R,5S,8R)-1,2-dihydroxy-3-hydroxymethyl- 1-5-[(1R)-1,10-dihydr oxy-6-oxo-decyl] pyrrolizidine (1) by spectroscopic and chemical methods. 1 inhibited beta-glucosidase, beta-galactosidase, and beta-mannosidase. Abso lute stereostructures of broussonetines A (2) and B (3) as well as that of 1 were also determined by a new version of Mosher's method.