Microbiological systems in organic synthesis: preparation of racemic prenalterol utilizing Cunninghamella echinulata

The fungal microorganism Cunninghamella echinulata was utilized to para-hydroxylate the synthetic substrate (+/-)-1-isopropylamino-3-phenoxy-propan-2-ol (1). The resulting product, (+/-)-1-(4-hydroxyphenoxy)-3-isopropylamino-propan-2-ol, or (+/-)-prenalterol, (2) was formed in greater than 85% yield. Extracts from incubates were derivatized with trifluoroacetic anhydride and the concentrations of 1 and 2 were determined by GC on a fused silica methyl silicone capillary column with nitrogen-phosphorus detection. At substrate concentrations of 100 and 200 mg/L, the biotransformation proceeds with apparent first-order kinetics. With higher concentrations, the kinetics of prenalterol formation and substrate uptake appear to be nonlinear with a Km value of 427.8 micrograms/mL and a Vmax value of 232.3 micrograms/mL/d. This suggests that the biotransformation may proceed through a single-capacity limited pathway. The microbial product was isolated and identified as (+/-)-prenalterol by comparison (mp, IR, MS, 1H NMR) with an authentic specimen.