ISOLATION AND STRUCTURE OF LONG-CHAIN ALKYLPHENOLS AND LONG-CATECHOLS FROM PLECTRANTHUS-ALBIDUS (LABIATAE)

From the title plant, a series of even-numbered long-chain, phenol- or pyrocatechol-derived 1-arylalkan-5-ones was isolated by classical chromatography and preparative reversed phase HPLC. By chemical and spectroscopic methods, including coupled chromatographic techniques(GC/MS/FT-IR, HPLC/MS), their structures were established to be 1-(4'-hydroxyphenyl)tetradecan-5-one (2a), 1-(4'-hydroxyphenyl)hexadecan-5-one (2b), 1-(4'-hy-droxyphenyl)octadecan-5-one (2c), and (Z)-1-(4'-hydroxyphenyl)octadec-13-en-5-one (2d); (E,E)-1-(3',4'-dihy-droxyphenyl)deca-1,3-dien-5-one (1a), 1-(3',4'-dihydroxyphenyl)dodecan-5-one (3a), 1-(3',4'-dihydroxyphenyl)-tetradecan-5-one (3b), 1-(3',4'-dihydroxyphenyl)hexadecan-5-one (3c), 1-(3',4'-dihydroxyphenyl)octadecan-5-one (3d), 1-(3',4'-dihydroxyphenyl)icosan-5-one (3e), and (Z)-1-(3',4'-dihydroxyphenyl)octadec-13-en-5-one (3f). In vitro, the compounds show significant antioxidant activity, the inhibitory concentration of the most potent one, la, being slightly lower than for 2-(tert-butyl)-4-methoxyphenol (BHA) and 2,6-di(tert-butyl)-4-methylphenol (BHT) in the Fe2+-catalysed autooxidation of linoleic acid, whereas the activities of phenols 2a-d are in the same order of magnitude as alpha-tocopherol.