Enantioselective syntheses of both enantiomers of 9′-dehydroxyimperanene and 7,8-dihydro-9′-dehydroxyimperanene and the comparison of biological activity between 9-norlignans and dihydroguaiaretic acids

To estimate the effect of methyl group of dihydroguaiaretic acid, which shows many kinds of biological activities, on biological activity, both enantiomers of 9′-dehydroxyimperanene (5, 6) and 7,8-dihydro-9′-dehydroxyimperanene (7, 8) lacking one of the methyl groups of dihydroguaiaretic acid were synthesized. (S)-7,8-Dihydro-9′-dehydroxyimperanene (7) showed 4–6-fold higher cytotoxic activity than all stereoisomers of dihydroguaiaretic acid (2–4). The IC50 values of (S)-7,8-dihydro-9′-dehydroxyimperanene (7) against HL-60 and HeLa cells were 6.1 μM and 5.6 μM, respectively. Though only one of three stereoisomers of dihydroguaiaretic acid showed antibacterial activity against a gram negative bacterium, both enantiomers of 5–8 showed antibacterial activity against a gram negative bacterium. This is a Letter on biological activity of 9-norlignan, in which one of methyl groups of lignan is absent.

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