To a solution of compound 163A (164 mg, 0.472 mmol) in pyridine (1 mL) and CH2Cl2 (1 mL) at RT was added benzoyl chloride (82 μL, 0.71 mmol), and the mixture was then stirred at 50° C. for 16 h. After cooling to RT, the reaction was concentrated in vacuo and the resultant residue was taken into MeOH (4 mL), and Et3N (1 mL) added. The reaction was stirred at 70° C. for 1 h. After cooling to RT, the reaction was concentrated. The residue was diluted with 10% aqueous citric acid, then extracted with EtOAc (3×15 mL). The combined EtOAc extracts were concentrated. The resulting residue was purified using preparative HPLC (YMC S5 ODS 20×100 mm) eluting with MeOH (50-80%) in H2O for 8 min, and then 80% MeOH in H2O for 7 min to give the title compound (60 mg, 28%) as a white solid. HPLC: 99% at 6.2 min (retention time) (Conditions: Zorbax SB C18 (4.6×75 mm); Eluted with 0% to 100% B, 8 min gradient. (A=90% H2O−10% MeOH−0.1% H3PO4 and B=10% H2O−90% MeOH−0.1% H3PO4); Flow rate at 2.5 mL/min. UV detection at 220 nm). MS (ES): m/z 452 [M+H]+.
