A suspension of 81 mg (0.24 mmol) of 4-amino-2-mesityl-7H,9H-thieno[3′,4′:3,4]pyrazolo[1,5-a]pyrimidine-3-carbonitrile from Step A in 1.2 mL of anhydrous tetrahydrofuran was stirred under nitrogen in an ultrasound bath as 1.2 mL (1.2 mmol) of 1M borane-tetrahydrofuran complex in tetrahydrofuran was added gradually by syringe. The mixture was stirred overnight with intermittent sonication. Next, the mixture was quenched by cautious gradual addition of 0.36 mL (4.32 mmol) of concentrated hydrochloric acid (gas evolution) followed by addition of 1.2 mL of methanol. The resulting solution was stirred in a sealed tube with heating in an oil bath at 80° C. for 4 h. The solution was evaporated to dryness and re-concentrated twice from methanol. The residue was converted to free base form by passage through a pre-washed SCX ion exchange cartridge. After flushing the column with methanol to remove trifluoroacetic acid, elution with 1M ammonia in methanol afforded the crude product. Further purification by flash chromatography on silica gel (elution with 98:2:0.4 dichloromethane:methanol:concentrated ammonium hydroxide) yielded the title compound. LC-MS 340 (M+1).
