Catalpol and methylcatalpol: naturally occurring glycosides in Plantago and Buddleia species

1. A glycoside of the aucubin type has been isolated in crystalline form from Plantago and Buddleia species, and has been shown to be identical with catalpol (Lunn, Edward & Edward, 1962). Catalpol has not been found in the free state before, but occurs as its p-hydroxybenzoyl ester, catalposide, in the genus Catalpa. 2. A second glycoside of this type has been obtained in crystalline form from Buddleia, and has been shown to be a mono-O-methyl derivative of catalpol, for which the name `methylcatalpol' is proposed. 3. Both Plantago and Buddleia species are known to contain aucubin. The concentrations of this glycoside and catalpol are comparable in Plantago. In Buddleia methylcatalpol predominates somewhat over catalpol. Yields of the individual glycosides were about 0·1% of the fresh weight of the leaves. 4. Bobbitt, Spiggle, Mahboob, Philipsborn & Schmid (1962) have suggested structures for catalposide and catalpol based on chemical and physical evidence, in particular on n.m.r. spectra. Reappraisal of this evidence and additional measurements have now confirmed these structures and show that the Buddleia glycoside is the 6-O-methyl derivative of catalpol.