STUDIES ON THE FLAVONOIDS PRESENT IN CHINESE DRUGS Ⅸ. A NEW FLAVONE GLYCOSIDE ISOLATED FROM WIKSTROEMIA VIRIDIFLORA

The Chinese folk medicine called Nan-Lin-Yao-Hua is a botanical drug (Wikstroemia viridiflora Meisen) family Thymelaeceae, which has been used as a remedy for ascites of the late stage Schistosomiasis. From its root bark or cortex radicis, a yellowish needle crystalline substance was isolated, and it is a new flavone glycoside and hence named wikstroemin. The new glycoside showed a diuretic action when intravenously injected at a dosage of 2—4mg/kg on anaesthetized dogs. This may respond a part of its effectiveness. The wikstroemin (C₂₈H₃₂O₁₅) was obtained in light yellow needles and possesses a characteristic double melting point, melting at 200—202℃ into transparent yellow liquid and resolidified at 210℃ and finally decomposed at 270—272℃. The pure substance was obtained in 0.05%. It is insoluble in ordinary organic solvents, but sparingly soluble in hot water or warmed ethanol and methanol. It exhibits no color reaction with FeCl₃, but developes a deep red coloration with Mg-HCl. It gave a positive color test with Molisch's reagent and produced a golden yellow coloration in alkali solution. Its paper chromatography showed R_f=0.46 (BuOH:HOAc:H₂O=4:1:5). U. V. spectra in absolute ethanol shows peaks λ_max 262 and 333mμ (log ε=4.45 and 4.50). On acid hydrolysis, the wikstroemin gave an aglycone (C₁₆H₁₂O₅ m. p. 290—293°) and two moles of glucose. Although the wikseroemin gave a negative color reaction with FeCl₃, but its aglycone developed a violet brown coloration. This proves that the 5-position hydroxy group has been opened on hydrolysis. From the above properties, wikstroemin has been identified as a flavone glycoside and its aglycone as genkwanin by the comparison of U. V. spectra and mixed melting point with authentic sample. The digluconide has been proved to be linked on the 5-position in A ring as a known compound genkwanin-4'-methylether (C₁₇H₁₄O₅, m. p. 169—171℃) which was successively isolated on mild methylation and then hydrolysis. From this fact, there is ample reason to explain that the aglycone is not linked separately both in 5 and 4'-positions. Wikstroemin will not be hydrolysed by the emulsin which was freshly prepared from bitter almond. The structure formula, therefore, has been confirmed to be (Ib), as genkwanin-5-α-D-glucosido-α-D-glucose.