Synthesis and antifungal activity of a novel series of 13-(4-isopropylbenzyl)berberine derivatives

By replacing the methyl group of 13-(4-isopropylbenzyl)berberine 2 with various acyl, alkyl, and benzyl groups via the demethylated intermediate, 13-(4-isopropylbenzyl)berberrubine 4, a novel series of 9-O-alkyl-13-(4-isopropylbenzyl)berberine derivatives was synthesized and examined for antifungal activities against various human pathogenic fungi. The introduction of various alkyl groups led to enhanced antifungal activity but that of acyl groups resulted in decrease of the activity. Among them, 9-O-butyl-13-(4-isopropylbenzyl)berberine 6d exhibited the most potent antifungal activities against Cryptococcus neoformans, Candida species (MIC=0.25-1 μg/ml), and Aspergillus species (MIC=2-4 μg/ml). The compound was found to be relatively safe up to 900 mg/kg in oral administration to mice.