Angiotensin converting enzyme inhibitors from Cuscuta japonica Choisy

Bioassay-guided fractionation of the EtOAc-soluble extract of Cuscuta japonica afforded 3,5-Di-O-caffeoylquinic acid (1). methyl 3,5-Di-O-caffeoylquinate (2). 3,4-Di-O-caffeoylquinic acid (3). and methyl 3,4-Di-O-caffeoylquinate (4). Purification of these compounds was conducted with the application of various chromatographic methods. The structures of the compounds were elucidated on the basis of MS and NMR data analysis. Compounds 1-4 inhibited the angiotensin I converting enzyme activity in a dose-dependent manner. Compounds 1-4 showed the 50% inhibitory concentration values of 596, 483, 534, and 460 micro M, respectively. The presence of these active components may be responsible, at least in part, for the antihypertensive action of traditional crude drug Cuscuta Semen.