Chemical Constituents of the Seeds of Pharbitis purpurea and Laxative Effect of Methyl Caffeate on Rats

The chemical constituents of the seeds of Pharbitis purpurea belonging to the Convolvulaceae family were studied. The anti-tumor activities of all isolated compounds on A549 and HepG2 tumor cell lines and effect of methyl caffeate (8) on intestinal excretion in rats were also studied. Fourteen compounds were isolated from the seeds of P. purpurea by column chromatography using silica gel, ODS, Sephadex LH-20 and HPLC. Their structures were determined by 1D and 2D NMR and HRMS. They were identified as (2S,3S)-5-[(1E)-2-carboxyethenyl]-2-(3,4-dihydroxyphenyl)-2,3-dihydro-7-hydroxy-3-benzofurancarboxylic acid dimethyl ester (1), 8-epiblechnic acid (2), dimethyl (1R,2S)-6,7-dihydroxy-l-(3,4-dihydroxy)-phenyl-1,2-dihydronaphthalene-2,3-dicarboxylate (3), dimethyl 6,9,10-trihydroxybenzo[kl]xanthene-1,2-dicarboxylate (4), syringaresinol-4’-O-β-D-glucopyranoside (5), (+)-syringaresinol (6), (+)-pinoresinol (7), methyl caffeate (8), ethyl caffeate (9), osmanthuside J (10), methyl 6β,7β,16β,17-tetrahydroxy ent-kauran-18-oate (11), β-sitosterol (12), 1-O-linoleoyl-glycol (13) and 1-O-linoleoyl-glycerol (14). Compounds 1 and 3 are new natural products. 4 is reported from the family Convolvulaceae for the first time and 8, 10 and 11 from P. purpurea for the first time. Methyl caffeate (8), 10 and 30 mg/kg, significantly promote intestinal peristalsis in rats. Methyl caffeate (8) has no acute toxicity to rats at 5000 mg/kg.