Vincan- and eburnan-type alkaloids from Tabernaemontana bovina and their hypoglycemic activity.

Thirty-one Vincan- and two Eburnan-type alkaloids were isolated from the aerial parts of Tabernaemontana bovina, whereas 20 of them are described the first time. Within the purified alkaloids, the firstly described taberbovcamine A features a 6/5/6/6/5 ring system. All the chemical structures were elucidated by employing extensive spectroscopic, computational electronic circular dichroism and X-ray diffraction methods. The two Eburnan-type alkaloids, 10,11-dimethoxy-16-O-methyllisoeburnamenine and 10,11-dimethoxy-isoeburnamenine were simultaneously identified by using the mentioned spectroscopic methods. Within the identified alkaloids, 10-hydroxy-14,15-didehydrovincanmine, 14,15-didehydrovincanmine, 14,15-didehydroapovincanmine, and criocerine increased the glucose consumption in a L6 myotube model.