Caffeoyl Phenylethanoid Glycosides from Unripe Fruits of Forsythia Suspensa

Chemical investigations of the 70% alcohol extract of F. suspensa have afforded a new caffeoyl phenylethanoid glycoside, lianqiaoxinoside C (1), together with the known calceolarioside C (2). A practical H-1 NMR spectrum rule was firstly summarized for assisting determination of lianqiaoxinoside C, whose structure was unambiguously determined as 3,4-dihydroxy-beta-phenethyl-O-beta-xylopyranosyl-(1 -> 6)-3-O-caffeoyl-beta- glucopyranoside on the basis of H-1 NMR spectrum and HR-ESI-MS. The H-1 NMR rule summarized here may be very helpful for assisting analysis and identification of the analogous caffeoyl phenylethanoid glycosides in the genus Forsythia. Calceolarioside C was also first reported from the genus Forsythia and showed obvious antioxidant activities in vitro by the 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonate (ABTS) radical-scavenging assay.