Structure of Forsythoside A, a Antibacterial Principle of Forsythia suspensa Leaves

iibrtract -A new glycoside, forsythoside A, exhibiting antibacterial activity, has been lsolated from Frosythia suspensa leaves.Degradative and ~pectroscopic studies have established the structure of forsythoside A as s h a m in formula I. Forsythia svrpensa vahl Ioleaceael 1s an important original plant of the crude drug "rengyo" (Forsythlae Fructus) which has been used for antilnflammatory, diuretic, drainage and antidotal purposes in Oriental medicine.The crude drug has also been known to exhibit antibacterial activlty which has hltherto been attributed to a lignan-glycoside, p h i ~l y r i n .~ pvite recently d- pinoresin01 was assigned as the phosphodiesterase mhibiting component of the crude drug.3 m r i n g our chmical and pharmacological studies on the crude drug, antibacterial activity against s t a p h y l o c o ~~~s aureu.9 was found in the methanol extract.A survey indicated that the principal activity was observed only in a fraction where phillyrin was not detected.b r o a d ) , 7.80 (1" d o u b l e t , J 16.0 Hz); MS: m / e 208.191, t h e e e d a t a b e l n y consistent w i t h t h o s e of t h e m e t h y l a t l o " p r o d u c t o f c a f f e i c a c i d w i t h d i m e t h y l s u l f a t e and sodium hydraxlde.The y " p o u n d was i d e n t i f i e d by d i r e c t comparison with an a u t h e n t i c sample.5 ) H NMR (CDCl31 6: 2.77 (2H t r i p l e t , J 7.5 Hz), 3 .8 1 (2H t r i p l e t , J 7 .5 Hz), 3.84 (6H s i n g l e t ) , 6.73 (3H b r o a d ) ; MS: m/e 182, 151, t h e s e d a t a b e i n g i n a c c o r d wxth t h o s e of t h e r e d u c t i o n prod u c t o f h o m o v e r a t r i c a c i d w i t h l i t h l u m aluminum h y d r i d e .The compound was i d e n t r f i e d by d i r e c t comparison w i t h an a u t h e n t i c sample.