Reaction Steps
(3R,11aS)—N-[(2,4-Difluorophenyl)methyl]-3-methyl-5,7-dioxo-6-[(phenylmethyl)oxy]-2,3,5,7,11,11a-hexahydro[1,3]oxazolo[3,2-a]pyrido[1,2-d]pyrazine-8-carboxamido. To a solution of 16a (409 mg, 0.87 mmol) in dichloroethane (20 mL) was added (2R)-2-amino-1-propanol (0.14 mL, 1.74 mmol) and 10 drops of glacial acetic acid. The resultant solution was heated at reflux for 2 h. Upon cooling, Celite was added to the mixture and the solvents removed in vacuo and the material was purified via silica gel chromatography (2% CH3OH/CH2Cl2 gradient elution) to give (3R,11aS)—N-[(2,4-difluorophenyl)methyl]-3-methyl-5,7-dioxo-6-[(phenylmethyl)oxy]-2,3,5,7,11,11a-hexahydro[1,3]oxazolo[3,2-a]pyrido[1,2-d]pyrazine-8-carboxamide (396 mg, 92%) as a glass. 1H NMR (CDCl3) δ 10.38 (m, 1H), 8.42 (s, 1H), 7.54-7.53 (m, 2H), 7.37-7.24 (m, 4H), 6.83-6.76 (m, 2H), 5.40 (d, J=10.0 Hz, 1H), 5.22 (d, J=10.0 Hz, 1H), 5.16 (dd, J=9.6, 6.0 Hz, 1H), 4.62 (m, 2H), 4.41 (m, 1H), 4.33-4.30 (m, 2H), 3.84 (dd, J=12.0, 10.0 Hz, 1H), 3.63 (dd, J=8.4, 7.2 Hz, 1H), 1.37 (d, J=6.0 Hz, 3H); ES+ MS: 496 (M+1). b) (3R,11aS)—N-[(2,4-Difluorophenyl)methyl]-6-hydroxy-3-methyl-5,7-dioxo-2,3,5,7,11,11a-hexahydro[1,3]oxazolo[3,2-a]pyrido[1,2-d]pyrazine-8-carboxamide sodium salt. To a solution of (3R,11aS)—N-[(2,4-difluorophenyl)methyl]-3-methyl-5,7-dioxo-6-[(phenylmethyl)oxy]-2,3,5,7,11,11a-hexahydro[1,3]oxazolo[3,2-a]pyrido[1,2-d]pyrazine-8-carboxamide (396 mg, 0.80 mmol) in methanol (30 mL) was added 10% Pd/C (25 mg). Hydrogen was bubbled through the reaction mixture via a balloon for 2 h. The resultant mixture was filtered through Celite with methanol and dichloromethane. The filtrate was concentrated III vacuo to give (3R,11aS)—N-[(2,4-difluorophenyl)methyl]-6-hydroxy-3-methyl-5,7-dioxo-2,3,5,7,11,11a-hexahydro[1,3]oxazolo[3,2-a]pyrido[1,2-d]pyrazine-8-carboxamide as a pink tinted white solid (278 mg, 86%). 1H NMR (CDCl3) δ 11.47 (m, 1H), 10.29 (m, 1H), 8.32 (s, 1H), 7.36 (m, 1H), 6.82 (m, 2H), 5.31 (dd, J=9.6, 3.6 Hz, 1H), 4.65 (m, 2H), 4.47-4.38 (m, 3H), 3.93 (dd, J=12.0, 10.0 Hz, 1H), 3.75 (m, 1H), 1.49 (d, J=5.6 Hz, 3H); ES+ MS: 406 (M+1). The above material (278 mg, 0.66 mmol) was taken up in ethanol (10 mL) and treated with 1 N sodium hydroxide (aq) (0.66 mL, 0.66 mmol). The resulting suspension was stirred at room temperature for 30 min. Ether was added and the liquids wore collected to provide the sodium salt of the title compound as a white powder (291 mg, 99%). 1H NMR (DMSO-d6) δ 10.68 (m, 1H), 7.90 (s, 1H), 7.35 (m, 1H), 7.20 (m, 1H), 7.01 (m, 1H), 5.20 (m, 1H), 4.58 (m, 1H), 4.49 (m, 2H), 4.22 (m, 2H), 3.74 (dd, J=11.2, 10.4 Hz, 1H), 3.58 (m, 1H), 1.25 (d, J=4.4 Hz, 3H).
