A-Methylenecyclopentanone moiety

The diterpenoids of Isodon (Labiatae) species have been reviewed. The presence of an a-methylenecyclopentanone moiety in these diterpenoids is important for their anti-tumour and anti-bacterial activity. " Inflexin (79) is a cytotoxin and insect antifeedant which has been isolated from Isodon inflexus. Isodomedin (80) is another member of this series, isolated from /. shikokianus, which shows this type of biological activity. Its structure was assigned on the basis of its H and C n.m.r. spectra and on an interrelationship with kamebanin (81), isolated from /. kameba. 

The first report on antibacterial activity of Rabdosia constituents appeared in 1954, when it was discovered that a crystalline substance isolated from the ethanolic extract of Rabdosia japonica inhibited the growth of Gram-positive bacteria (i). Later two groups found that an extract of R, trichocarpa also had antibacterial and antitumor activities 131, 132). It was shown (133) that the activity was due to enmein. Dihydroenmein was inactive, while (9,(9-diacetylenmein remained active. Hence it was assumed that the biologically active site of enmein was the a-methylenecyclopentanone moiety (133). 

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