Antimycobacterial activity of natural products and synthetic agents: pyrrolodiquinolines and vermelhotin as anti-tubercular leads against clinical multidrug resistant isolates of Mycobacterium tuberculosis.

Various classes of natural products and synthetic compounds were tested against reference strains and clinical multidrug resistant isolates of Mycobacterium tuberculosis. Vermelhotin (19), a natural tetramic acid from fungi, was the most active toward clinical MDR TB isolates (MIC 1.5-12.5 μg/mL). Synthetic compounds (i.e. benzoxazocines, coumarins, chromenes, and pyrrolodiquinoline derivatives) were prepared by green chemistry approaches. Under microwave irradiation, a one-pot synthesis of pyrrolodiquinoline 85 was achieved by homocoupling of 1-methylquinolinium iodide; the structure of 85 was confirmed by single-crystal X-ray analysis. Compound 85 and its derivative 86 exhibited potent anti-tubercular activity (MIC 0.3-6.2 μg/mL) against clinical MDR TB isolates, and they displayed weak cytotoxicity toward normal cell line. The scaffold of 85 and 86 is potential for antimycobacterial activity.