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 inhibitory assay were attempted. The ethanol extract from outer bark showed the highest inhibitory activity (IC₅₀ is 16g/ml) among 24 extracts prepared from roots, leaves, heartwood, sapwood, inner bark, and outer bark by successive extraction with four solvents. The fractionation of the outer bark ethanol extract followed by the bioassay resulted in the isolation of two strong ACE inhibitors, catechin and dimeric procyanidin B3. The bioassay of three flavan-3-ols including (+)-catechin and six flavones revealed that most of these compounds have high ACE inhibitory activity. The results suggest that the phenolic hydroxyl group at the C7 position and heterocyclic oxygen atom of these compounds are important for expressing the inhibitory activity.