To a solution of ethyl 5-(5-phenyl-4-((pyridin-2-ylmethyl)amino)phthalazin-1-yl)nicotinate (0.120 g, 0.260 mmol) in EtOH (6 mL) and THF (6 mL) was added LiOH (0.0620 g, 2.60 mmol) in water (3 mL) at room temperature. The reaction mixture was stirred at the same temperature for 16 h. Then the reaction mixture was concentrated under reduced pressure and the resulting residue was diluted with water (5 mL). The reaction mixture was extracted with EtOAc and the aqueous layer was separated. The aqueous layer was acidified to pH 5 with citric acid and extracted with EtOAc. The organic extract was dried over anhydrous Na2SO4, filtered and concentrated under reduced pressure. The resulting residue was purified by HPLC (Condition 13 as described in general methods) to afford 5-(5-phenyl-4-((pyridin-2-ylmethyl)amino)phthalazin-1-yl)nicotinic acid (0.0150 g, 13.3%). LCMS (Condition 2): retention time 1.54 min, [M-1]=432.0. HPLC (Condition 25): retention time=5.86 min, purity 95.51%. 1H NMR (400 MHz, DMSO-d6) δ 4.66 (d, J=4.4 Hz, 2 H), 6.25 (dd, J=4.0 Hz, J=4.4 Hz, 1 H), 7.20-7.24 (m, 1 H), 7.28 (d, J=7.6 Hz, 1 H), 7.52-7.59 (m, 5 H), 7.68-7.73 (m, 2 H), 7.82 (dd, J=1.2 Hz, J=8.4 Hz, 1 H), 7.91 (dd, J=7.2 Hz, J=8.4 Hz, 1 H), 8.22-8.25 (m, 1 H), 8.35 (dd, J=1.6 Hz, J=2.0 Hz, 1 H), 8.74 (d, J=2.0 Hz, 1 H), 9.09 (d, J=1.6 Hz, 1 H).
