In vitro screening of angiotensin I-converting enzyme inhibitors from Japanese cedar (Cryptomeria japonica)

Screening and isolation of angiotensin I-converting enzyme (ACE) inhibitors from Japanese cedar (Cryptomeria japonica) based on the in vitro ACE inhib itory assay were attempted. The ethanol extract from outer bark showed the highest inhibitory activity (IC50 is 16 mu g/ml) among 24 extracts prepared from roots, leaves, heartwood, sapwood, inner bark, and outer bark by succ essive extraction with four solvents. The fractionation of the outer bark e thanol extract followed by the bioassay resulted in the isolation of two st rong ACE inhibitors, catechin and dimeric procyanidin B3. The bioassay of t hree flavan-3-ols including (+)-catechin and six flavones revealed that mos t of these compounds have high ACE inhibitory activity. The results suggest that the phenolic hydroxyl group at the C7 position and heterocyclic oxyge n atom of these compounds are important for expressing the inhibitory activ ity.