Stilbene derivatives from two species of Gnetaceae.
Five new stilbene oligomers (gnemonols A, B and C, gnemonoside E and gnetal) were isolated together with 2b-hydroxyampelopsin F and gnetin E from Gnetum gnemon and G. gnemonoides. The structures of the compounds were elucidated on the basis of spectral evidence.
Gnetol as a Potent Tyrosinase Inhibitor from Genus Gnetum
Gnetol (2,3′,5′,6-tetrahydroxy-trans-stilbene), a naturally occurring compound particularly found in the genus Gnetum, had a strong inhibitory effect on murine tyrosinase activity. Gnetol (IC50, 4.5 μM) was stronger than kojic acid (IC50, 139 μM) as a standard inhibitor for murine tyrosinase activity. Moreover, gnetol significantly suppressed melanin biosynthesis in murine B16 melanoma cells.
Cholesterol synthesis from acetate in the diabetic liver.
Brady and Gurin (1) recently compared the ability of liver slices prepaped from both normal and diabetic rats to incorporate added acetate into cholesterol. They drew the conclusion that the conversion of acetate to cholesterol in the diabetic liver is “apparently unimpaired, although this process may be inhibited when diabetes is sufficiently prolonged and severe.” In view of our interest in the relation of cholesterol synthesis to arteriosclerosis, the development of which is generally regarded as being accelerated in diabetes (2), we have reinvestigated cholesterol synthesis from acetate in diabetes. A definite increase in cholesterol formation in the diabetic liver is demonstrated here. It is further shown that, as a result of insulin injections in a diabetic rat, slices subsequently prepared from its liver have a reduced capacity to synthesize cholesterol.