5 One pot synthesis towards pharmaceutical precursor
Ethyl 2-[(4-chlorophenyl)methyl]-3-oxobutanoate (3g ) is the precursor of antituberculosis drugs[3] and can be produced by tandem reaction optimized above. Motivated by the pharmaceutical application, we tried to scale up the synthesis of3g . To avoid enzyme deactivation at high concentrations ofp -chlorobenzaldehyde, fed-batch was selected. 50 mM 1g , 50 mM EAA and 50 mM glucose were added at 2 h, 4 h, 7 h, 10 h, 13 h, 17 h and 20 h, respectively. The reaction progress was monitored by GC and the result was shown in Figure 5, the product was continuously synthesized within 13 hours. Then, 1.5 mg mL-1 NerA and 1 mg mL-1 GDH were compensated for the loss of enzyme activity. At 20 hours, the rate of reaction slowed down again and stopped feeding. The synthesis of 3g was completed at 28 hours, and the yield of 1g was 91%. Isolation of most products was simply extracted by ethyl acetate, resulting in 88% yield (880 mg). The transformation could be applied in preparative-scale synthesis without sacrificing yield.