Three naphthalenes from root bark of Hibiscus syriacus.

Three new naphthalenes, designated as syriacusins A-C, were isolated from the root bark of Hibiscus syriacus. These compounds were identified as 2,7-dihydroxy-6-methyl-8-methoxy-1-naphthalenecarbaldehyde, 2-hydroxy-6-hydroxymethyl-7,8-dimethoxy-1-naphthalenecarbaldehyde, 1-carboxy-2,8-dihydroxy-6-methyl-7-methoxynaphthalenecarbolactone (1-->8), respectively, on the basis of various spectral studies. The compounds inhibited lipid peroxidation with IC50s of 0.54, 5.90 and 1.02 micrograms ml-1, respectively. The first compound also showed cytotoxicity against some human cancer cell lines with an ED50 of 1.5-2.4 micrograms ml-1.