To a solution of 2-(2,6-diethylphenyl)-4-methyl-5,6,7,8-tetrahydro-1,6-naphthyridine dihydrochloride (21.7 mg, 0.061 mmol) in THF (0.5 mL), 1.6 M n-BuLi in hexanes (0.119 mL, 0.190 mmol) was added at −78° C. under nitrogen. After stirring for 10 min. at the same temperature, 1-methyl-5-(methylsulfonyl)-1H-tetrazole (24.90 mg, 0.154 mmol) was added. The mixture was warmed up to rt and stirred for 19 h. The mixture was diluted with brine and EtOAc. The products were extracted with EtOAc, and the organic layer was concentrated. The crude was purified by RP-HPLC (X-Bridge Phenyl®, H2O (0.1% NH4OH)/CH3CN), then the fractions including the desired product were lyophilized to give the desired product. 1H NMR (400 MHz, CDCl3) δ ppm 7.26-7.30 (m, 2 H), 7.14 (d, J=7.58 Hz, 1 H), 6.98 (s, 1 H), 4.58 (s, 2 H), 4.01 (s, 3 H), 3.68 (t, J=5.94 Hz, 2 H), 3.25 (br t, J=5.94 Hz, 2 H), 2.30-2.37 (m, 7 H), 1.06 (t, J=7.58 Hz, 6 H); MS (ESI+) m/z 363.27 (M+H)+.
