Antioxidant activities of natural and synthetic carbazoles.

The antioxidant activities of various natural and synthetic carbazoles were studied in the oxidations of methyl linoleate in homogeneous solution and soybean phosphatidylcholine (PC) liposomes in aqueous dispersion induced by free radicals. Carazostatin, 1-heptyl-3-hydroxy-2-methyl carbazole, which was isolated from a culture of Streptomyces chromofuscus, was found to be a strong antioxidant in both oxidation systems. Carbazomycin B, 4-hydroxy-3-methoxy-1,2-dimethylcarbazole, showed a moderate antioxidant activity. Other derivatives from these carbazoles without a free hydroxy group did not suppress the oxidation appreciably. The antioxidant activity of carazostatin in the oxidation of soybean PC liposome was stronger than that of alpha-tocopherol, although the latter exhibited stronger antioxidant activity than carazostatin in the oxidation in homogeneous solution. Vitamin C acted as a synergist in combination with carazostatin in the oxidation of soybean PC liposomes.