ISOLATION, STRUCTURE, AND BIOLOGICAL-ACTIVITIES OF LONG-CHAIN CATECHOLS OF PLECTRANTHUS-SYLVESTRIS (LABIATAE)

Antioxidant activity guided fractionation of extracts of the aerial pa rts of the title plant and HPLC separation yielded a series of oxygena ted long-chain alkylcatechols. Their structures were inferred by spect roscopic methods and chemical transformations to be the novel tetrahyd ro-6-pentyl-2H-pyran-2-yl]benzene-1,2-diol (1a), -4-hydroxy-6-pentyl-2 H-pyran-2-yl]benzene-1,2-diol (1b), ,5S)-5-(acetyloxy)-3-hydroxydecyl] benzene-1,2-diol (2a), ,5S)-3-(acetyloxy)-5-hydroxydecyl]benzene-1,2-d iol (2b), 1-(3,4-dihydroxyphenyl)-3-hydroxydocos-13-en-5-one (3a), (Z) -1-(3,4-dihydroxyphenyl)docos-13-en-5-one (4), besides the known 1-(3, 4-dihydroxyphenyl)icosan-5-one (5). The absolute configurations of the optically active compounds which are structurally related to the [n]- gingerols (6) and -diols (7) were established by the high-field H-1-NM R application of Mosher's method. All compounds are in vitro potent an tioxidants, inhibiting the Fe2+-catalysed autooxidation of linoleic ac id in the same order of magnitude as the commercial antioxidant 2,6-di (tert-butyl)-4-methylphenol (BHT). The dose-dependent inhibitory effec ts on soybean-lipoxygenase are in the mu mol range, that of the most e ffective compound (3a) in the nmol range, hence being significantly mo re potent than the known anti-inflammatory and analgesic drugs indomet hacin and nordihydroguaiaretic acid.