Reaction Steps
1,1-Dimethylethyl (2R)-2-(aminocarbonyl)-1-piperidinecarboxylate. To a cold (0° C.) solution of (2R)-1-{[(1,1-dimethylethyl)oxy]carbonyl}-2-piperidinecarboxylic acid (1.0 g, 4.36 mmol) in THF (20 mL) was added triethylamine (0.60 mL, 4.36 mmol) followed by slow addition of methyl chloroformate (0.34 mL, 4.36 mmol). After a few minutes a suspension had formed. To this mixture was added concentrated NH4OH (1.5 mL) and the solution was allowed to warm to rt as the bath warmed and stirred for a total of 4 h. The mixture was concentrated in vacuo and the residue was taken up in EtOAc. The organic layer was washed with citric acid, sodium bicarbonate and then brine, dried over Na2SO4. Filtration and concentration gave 1,1-dimethylethyl (2R)-2-(aminocarbonyl)-1-piperidinecarboxylate (1.0 g, 99%). 1H NMR (CDCl3) δ 6.03 (br, 1H), 5.45 (br, 1H), 4.77 (br, 1H), 4.06 (br, 1H), 2.82 (m, 1H), 2.29 (m, 1H), 1.67-1.43 (m, 13H). b) 1,1-Dimethylethyl (2R)-2-cyano-1-piperidinecarboxylate. To a cold (0° C.) solution of 1,1-dimethylethyl (2R)-2-(aminocarbonyl)-1-piperidinecarboxylate (269 mg, 1.17 mmol) in THF (10 mL) was added triethylamine (0.33 mL, 2.34 mmol) and then trifluoroacetic anhydride (0.17 mL, 1.17 mmol). The mixture was stirred at 0° C. for 1 h and concentrated in vacuo. The residue was taken up in EtOAc and washed successively with sodium bicarbonate, 0.5 N HCl and brine. The organics were dried over Na3SO4, filtered and concentrated to give 1,1-dimethylethyl (2R)-2-cyano-1-piperidinecarboxylate (255 mg, 99%) as a crystalline solid upon standing, 1H NMR (CDCla) δ 5.23 (br, 1H), 4.05 (br, 1H), 2.93 (br, 1H), 1.93-1.39 (m, 6H), 1.46 (s, 9H). c) 1,1-Dimethylethyl (2R)-2-(aminomethyl)-1-piperidinecarboxylate. An ammonia saturated ethanol solution of 1,1-dimethylethyl (2R)-2-cyano-1-piperidinecarboxylate (255 mg, 1.19 mmol) was reduced with Raney-Ni in a similar manner to that described in example Z-3 to give after filtration through a short plug of silica, 1,1-dimethylethyl (2R)-2-(aminomethyl)-1-piperidinecarboxylate (236 mg, 91%), as an oil, 1H NMR (CDCl3/CD3OD) δ 4.15 (br, 1H), 3.97 (m, 1 h), 2.96 (m, 1H), 2.75-2.69 (m, 2H), 2.23-2.08 (m, 3H), 1.59-1.55 (m, 3 II), 1.4.3 (s, 9H). d) [(2R)-2-Piperidinylmethyl]amine bis HCl salt. A solution of 1,1-dimethylethyl (2R)-2-(aminomethyl)-1-piperidinecarboxylate (236 mg, 1.08 mmol) in THF (10 mL) was treated with 4 N HCl (3 mL) as described in example Z-3 to give the bis HCl salt of [(2R)-2-Piperidinylmethyl]amine. 1H NMR (DMSO-d6) δ 9.67 (br, 1H), 9.48 (hr, 1H), 8.48 (br, 2H), 3.70 (br, 2H), 3.20 (m, 1H), 3.04 (m, 1H), 2.86 (m, 1H), 1.89-1.41 (m, 6H), e) (5aR,14aR)—N-[(2,4-Difluorophenyl)methyl]-11-hydroxy-10,12-dioxo-1,2,3,4,5a,6,10,12,14,14a-decahydropyrido[1,2-a]pyrido[1′,2′:3,4]imidazo[1,2-d]pyrazine-9-carboxamide. The title compound was made in two steps using a similar process to that described in example Z-2. 16a (50 mg, 0.11 mmol) and [(2R)-2-Piperidinylmethyl]amine (150 mg, 1.31 mmol) (free based using carbonate resin as described in example Z-3) were reacted in dichloromethane (2 mL) with acetic acid to give (5aR,14aR)—N-[(2,4-difluorophenyl)methyl]-10,12-dioxo-11-[(phenylmethyl)oxy]-1,2,3,4,5a,6,10,12,14,14a-decahydropyrido[1,2-a]pyrido[1′,2′:3,4]imidazo[1,2-a]pyrazine-9-carboxamide (50 mg, 88%). This material was hydrogenated in a second step as described in example Z-2 to give (5aR,14aR)—N-[(2,4-difluorophenyl)methyl]-11-hydroxy-10,12-dioxo-1,2,3,4,5a,6,10,12,14,14a-decahydropyrido[1,2-a]pyrido[1′,2′:3,4]imidazo[1,2-d]pyrazine-9-carboxamide (11 mg, 44%) as a white solid, NMR (CD3OD/CDCl3) 10.46 (m, 1H), 8.32 (s, 1H), 7.31 (m, 1H), 6.80 (m, 2H), 4.64-4.52 (m, 3H), 4.14 (dd, J=10.4, 2.8 Hz, 1H), 3.91-3.82 (m, 2H), 3.19 (apparent t, J=10.8 Hz, 1H), 3.08 (d, J=1.0.4 Hz, 1H), 2.50 (m, 1H), 2.27 (m, 1H), 1.99-1.30 m, 6H); ES+ MS: 445 (M+1).
