Iridoids from the stems of Viburnum erosum

Two new iridoids were isolated and identified to three known ones, namely, loganic acid (2), sweroside (3), and 7-O-tigloylsecologanol (4), from the stems of Viburnum erosum. Dried stems of V. erosum were extracted with 80% methanol (MeOH), and the concentrated extract was partitioned successively with ethyl acetate (EtOAc), n-butyl alcohol (n-BuOH), and H2O. Five compounds were isolated after repeated silica gel (SiO2), octadecyl SiO2 (ODS), and Sephadex LH-20 column chromatography of the EtOAc fraction. The chemical structures of the compounds were determined based on spectroscopic data from H-1- and C-13-NMR, DEPT, and 2D-NMR (gCOSY, gHSQC, gHMBC) data. The new iridoids were identified as 3,7-dihydroxy-8-methyl-cyclopenta[c] pyran-4-carboxylic acid (1) and rel-(1S,5R,9S)-9-ethenyl-1-(beta-D-glucopyrinosyloxy)-5,9-dihydro-5-{2-[(2-methylbut-2-enoyl)oxy]ethyl}-1H-pyran-4-carboxylic acid (5) and named viburnin and epi-7-O-tigloylsecologanolic acid, respectively. This is the first report of the isolation of these five iridoids from V. erosum.