Microbial transformation of (+)-heraclenin by Aspergillus niger and evaluation of its antiplasmodial and antimicrobial activities.

MICROBIOLOGICAL synthesis; ASPERGILLUS niger; GRAM-negative bacteria; PLASMODIUM falciparum; BACILLUS subtilis; ESCHERICHIA coli; CANDIDA albicans; CHLOROQUINE

Mangala Gowri, P.; Haribabu, K.; Kishore, Hara; Manjusha, O.; Biswas, Sukla; Murty, U. S. N.

Microbial transformation of (+)-heraclenin (1) by Aspergillus niger was studied in growth media to assess its antiplasmodial and antimicrobial activities. It was transformed to (–)-heraclenol (2) as the sole product in a stereospecific manner. The in vitro antiplasmodial activity of compounds 1 and 2 was tested with chloroquine-sensitive and chloroquine-resistant strains of Plasmodium falciparum. Further, the in vitro antibacterial activity of 1 and 2 against three Grampositive bacteria, Bacillus subtilis, Bacillus sphaericus and Staphylococcus aureus, and three Gram-negative bacteria, Pseudomonas aeruginosa, Escherichia coli and Chromobacterium violaceum was analysed using agar-plate diffusion assay. The same method was employed for the evaluation of antifungal activity against five pathogenic strains of fungi, A. niger, Rhizopus oryzae, Aspergillus flavus, Candida albicans and Saccharomyces cerevisiae. Both furanocoumarins 1 and 2 displayed significant levels of antiplasmodial and moderate levels of antimicrobial activities against the tested pathogenic strains. Compound 2 exhibited two-fold less potent antiplasmodial activity (IC50 = 6.0 μg/ml) than the parent compound 1 (IC50 = 2.5 μg/ml), whereas no difference was observed in the antimicrobial activity of both furanocoumarins. The oxirane ring was found to be beneficial in terms of antiplasmodial activity.