N-[7-(2,4-dichlorophenyl)-2-methylthiopyrazolo[1,5-a]pyridin-3-yl]-N-propylamine (59 mg) was dissolved in tetrahydrofuran (1 mL), and after adding propionaldehyde (0.035 mL) and 3 M aqueous sulfuric acid (0.16 mL), sodium borohydride (12 mg) was added in five portions while vigorously stirring on ice, and stirring was continued for 30 minutes. Water was added to the reaction mixture, extraction was performed with diethyl ether and the extract was washed with saturated aqueous sodium hydrogencarbonate and brine. After drying over anhydrous magnesium sulfate and filtration, the solvent was concentrated under reduced pressure, the residue was purified by silica gel column chromatography, and the title compound (49 mg) was obtained from the n-hexane:ethyl acetate (100:1) fraction as a yellow oil.
