3.5. Microbial transformation using Aspergillus niger NRRL 322

Biotransformation of papaverine using Aspergillus niger NRRL 322 afforded to two metabolites (2 and 3). The residue (1 gm) was dissolved in 50 ml of methanol/dichloromethane mixture (1:1) and adsorbed onto 1 gm Celite and dried. The adsorbed sample was placed onto a glass column (50 × 2.5 cm) packed with silica after making a slurry in dichloromethane. The column was isocratically eluted with dichloromethane: methanol (97.5:2.5) and 10 ml fractions were collected. Fractions 20–44 were pooled together to give mixture of 2 and 3 as determined by TLC. The metabolites were obtained in the form of yellowish residue (80 mg, R f 0.3 S 2).

The mixture was loaded in silica biotage column (18 × 150 mm). The column was gradiently eluted with dichloromethane 100% then dichloromethane:2-propanol (98:2, 97:3,95:5) and 20 ml fractions were collected. Fractions 27–31 were pooled together to give pure 2, in the form of white powder (7 mg, Rf 0.70 S 1). Fractions 65–85 were pooled together to give pure 3, in the form of white powder (30 mg, R f 0.61 S 1).