Microbial transformation of some simple β-carboline alkaloids

Abstract

Microbial transformation of some simple β-carboline alkaloids e.g.: harmaline, harmalol, harman and harmine was carried out. The study resulted in isolation of ten metabolites. The structures of these metabolites were established using physical and spectroscopic techniques including: melting points, UV, IR, ¹H NMR, ¹³C NMR and mass spectrometry. The metabolites were identified as: 1 (2-acetyl-3-(2-acetamidoethyl)-7-methoxyindole), 2 (acetamide), 3 (harmalol), 4 (2-acetyl-3-(2-acetamidoethyl)-7-hydroxyindole), 5 (harman-2-oxide), 6 (6-hydroxy-harman), 7 (acetamide), 8 (6-hydroxy harmine), 9 (harmine-2-oxide), and 10 (harmol). The antioxidant and cytotoxic activities of the substrates and their metabolites were investigated. The results revealed that harman-2-oxide presented strong free radical scavenging activity, which was much more potent than the positive control (IC₅₀= 18±1.2 µg/ml). Harmine, 6-hydroxy-harmine, harman-2-oxide, harmine-2-oxide, harmalol and 6-hydroxy harman presented the highest cytotoxic activity comparable to doxorubicin (IC ₅₀= 0.60 µg/ml).