Three polyene antibiotics,mediomycins A (1),B (2),and clethramycin (3),were isolated from Streptomyces mediocidicus ATCC23936.Their structures were elucidated through extensive NMR study coupled with chemical reactions and MS/ MS fragmentation analys

摘要

In the course of our studies on antidiabetogenic compounds from natural medicines and medicinal foodstuffs,a methanolic extract of the fruits of Solanum lycocarpum showed an inhibitory effect on the increase of serum glucose levels in oral sucrose-loaded rats.Through bioassay-guided separation,three known steroidal alkaloid oligoglycosides,solamargine (1),solasonine (3),and 12-hydroxysolasonine (5),were isolated from the active fraction together with two new steroidal alkaloid oligoglycosides,robeneosides A (2) and B (4).The major constituents,solamargine (1) and solasonine (3),exhibited an inhibitory effect on the increase of serum glucose levels in oral sucrose-loaded rats.In addition,these compounds suppressed gastric emptying in mice.However,this methanolic extract from S.lycocarpum fruits did not have any effect on intestinal alpha-glucosidase (sucrase and maltase) in vitro.It was concluded that these steroidal alkaloid oligoglycosides,1 and 3,inhibited the increase of rat serum glucose levels by suppressing the transfer of sucrose from the stomach to the small intestine.