Synthesis and antioxidant activities of berberine 9--benzoic acid derivatives.

Although berberine (BBR) shows antioxidant activity, its activity is limited. We synthesized 9--benzoic acid berberine derivatives, and their antioxidant activities were screened ABTS, DPPH, HOSC and FRAP assays. The -position was modified with halogen elements on the benzoic acid ring, which led to an enhanced antioxidant activity and the substituent on the -position was found to be better than the -position. Compounds 8p, 8c, 8d, 8i, 8j, 8l, and especially 8p showed significantly higher antioxidant activities, which could be attributed to the electronic donating groups. All the berberine derivatives possessed proper lipophilicities. In conclusion, compound 8p is a promising antioxidant candidate with remarkable elevated antioxidant activity and moderate lipophilicity.