The product was obtained as white powder after lyophilization of the product containing fractions were dissolved in dimethylformamide (dry, 2 mL). DIPEA (39.5 μL, 0.23 mmol) was added and the reaction mixture was stirred at ambient temperature for 24 h. The reaction mixture was diluted with ethyl acetate and washed with saturated aqueous sodium bicarbonate solution (3×) and brine (1×). The organic layer was dried over sodium sulfate, filtered and concentrated under reduced pressure. The crude product was purified using a preparative HPLC (gradient of 5% to 95% methanol in water with 0.1% formic acid). Compund 1e was obtained as white powder after lyophilization (6.5 mg, According to general procedure A, 2a (208 mg, 434 µmol, 1 eq) was converted into the corresponding boronic acid pinacol ester 3a.