NMR (CDCl3) δ: 1.44 (s, 18H, 2 x (CH3)3C), 2.46 (s, 3H, CH3), 7.29 (d, 1H, H-5, J5,6=5.12 Hz), 8.50 (d,
1H, H-6, J6,5=5.12 Hz); 13C-NMR (CDCl3) δ: 17.8 (4-CH3), 27.7 [2 x (CH3)3C], 84.1 [2 x (CH3)3C],
126.5 (C-5), 142.2 (C-4), 144.0 (C-3), 149.6 (C-2), 149.8 (C-6), 150.2 (2 x C=O). Anal. Calcd for
C16H23N3O6: C, 54.38; H, 6.56; N, 11.89. Found: C, 54.47; H, 6.45; N, 11.67.
tert-Butyl-N-(3-amino-4-methylpyridin-2-yl) carbamate (6a)
A solution of 4b (8 g, 31.6 mmol) in dry ethanol (150 mL) was hydrogenated in the presence of 10% Pd/C
(500 mg) under a pressure of 45 psi at rt for 3 h. The solution was filtered through a celite pad to remove
the catalyst and the filtrate was evaporated to dryness to give pure 6a (7 g, 99%), mp >250 oC (EtOH); 1H-
NMR (CDCl3) δ: 1.49 [s, 9H, (CH3)3C], 2.20 (s, 3H, CH3), 4.24 (br s, 2H, -NH2, D2O exchangeable), 6.88
(d, 1H, H-5, J5,6=4.76 Hz), 7.74 (d, 1H, H-6, J6,5=4.76 Hz), 8.37 (br s, 1H, -NHBoc, D2O exchangeable);
13C-NMR (CDCl3) δ: 17.4 (4-CH3), 28.4 [(CH3)3C], 81.0 [(CH3)3C], 123.2 (C-5), 133.6 (C-3), 135.0 (C-
4), 137.2 (C-6) 138.6 (C-2), 154.3 (C=O). Anal. Calcd for C11H17N3O2: C, 59.17; H, 7.67; N, 18.82.
Found: C, 59.03; H, 7.71; N, 18.63.
tert-Butyl-N-(3-acetamido-4-methylpyridin-2-yl) carbamate (6b)
To a solution of 6a (7 g, 31.4 mmol) in dry toluene (120 mL) acetic anhydride (6 mL, 65 mmol) was
added and the resulting solution was stirred at rt for 1 h. The solvent was vacuum-evaporated and the
residue was purified by column chromatography (silica gel) with cyclohexane/ethyl acetate (60/40, v/v) as
the eluent to give pure 6b (8.15 g, 98 %), mp 148 oC (Et2O/n-pentane); 1H-NMR (CDCl3) δ: 1.53 (s, 9H,
(CH3)3C), 2.13 (s, 3H, CH3), 2.29 (s, 3H, COCH3), 7.04 (d, 1H, H-5, J5,6=4.73 Hz), 7.65 (br s, 1H, -
NHBoc, D2O exchangeable), 8.15 (d, 1H, H-6, J6,5=4.73 Hz), 8.72 (br s, 1H, -NHAc, D2O exchangeable);
13C-NMR (CDCl3) δ: 18.7 (4-CH3), 23.5 (CH3-CO), 28.3 [(CH3)3C], 81.9 [(CH3)3C], 123.1 (C-5), 124.9
(C-3), 145.5 (C-6), 146.6 (C-4), 148.5 (C-2), 154.8 (t-BuOCO), 168.3 (NHCOCH3). Anal. Calcd for
C13H19N3O3: C, 58.85; H, 7.22; N, 15.84. Found: C, 59.06; H, 7.17; N, 15.59.
7-Methylimidazolo[4,5-b]pyridin-2-one (7)
Potassium acetate (56 mg, 0.57 mmol) and acetic anhydride (0.11mL, 1.14 mmol) were added under
argon to a solution of 6b (100 mg, 0.38 mmol) in dry benzene (30 mL) and the reaction mixture was
refluxed for 6 h. The precipitate was filtered off, the filtrate was concentrated to dryness and the residue
was treated with methanolic ammonia at 0οC for 15 min. The solvent was then vacuum-evaporated and
the solid residue was purified by flash chromatography on silica gel (dichloromethane/methanol: 90/10,
v/v, as eluent) to afford 7 (47 mg, 83%), mp >250 oC (EtOH/H2O); 1H-NMR (DMSO-d6) δ: 2.24 (s, 3H,
CH3), 6.78 (d, 1H, H-6, J6,5=5.37 Hz), 7.73 (d, 1H, H-5, J5,6=5.37 Hz), 10.92 (br s, 1H, NH, D2O