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Reference H Synthesis of 2 [(S)-(TERT-BUTOXYCARBONYL) AMINO-L-(OXAZOLO] [4, [5-B] PYRIDIN-2-YL) BUTAN-1-OL] Step 1 A mixture of 2-amino-3-hydroxypyridine (11 g, 100 mmol), triethylorthoformate (80 mL) and p-toluenesulfonic acid (61 mg) was heated at [140 C] for 8 h. Excess triethylorthoformate was removed under vacuum and oxazolo [4, [5-B]] pyridine was crystalized from ethyl acetate (9 g). Step 2 In a clean roundbottom flask equipped with stir bar was placed oxazolo [4,5- [B]] pyridine (600 mg, 5 mmol) in THF (30 mL) and the reaction mixture was cooled to [0 C] under N2 atomosphere. Isopropylmagnesium chloride (2 M in THF, 2.5 mL, 5 mmol) was added. After stirring for 1 h at 0 [C,] [(USD)-2-(TERT-BUTOXYCARBONYL)] aminobutyraldehyde (573 mg, 3 mmol) in THF (20 mL) was added. The ice bath was removed and the reaction mixture was allowed to warm to room temperature. After 2 h, the reaction mixture was quenched with saturated ammonium chloride solution and concentrated to dryness. The residue was extracted with EtOAc, then washed with brine, dried with anhyd. [MGS04,] filtered and concentrated. The crude product was purified by chromatograph to yield 383 mg of the desired compound.
Reference H Synthesis of 2 [(S)-(TERT-BUTOXYCARBONYL) AMINO-L-(OXAZOLO] [4, [5-B] PYRIDIN-2-YL) BUTAN-1-OL] Step 1 A mixture of 2-amino-3-hydroxypyridine (11 g, 100 mmol), triethylorthoformate (80 mL) and p-toluenesulfonic acid (61 mg) was heated at [140 C] for 8 h. Excess triethylorthoformate was removed under vacuum and oxazolo [4, [5-B]] pyridine was crystalized from ethyl acetate (9 g). Step 2 In a clean roundbottom flask equipped with stir bar was placed oxazolo [4,5- [B]] pyridine (600 mg, 5 mmol) in THF (30 mL) and the reaction mixture was cooled to [0 C] under N2 atomosphere. Isopropylmagnesium chloride (2 M in THF, 2.5 mL, 5 mmol) was added. After stirring for 1 h at 0 [C,] [(USD)-2-(TERT-BUTOXYCARBONYL)] aminobutyraldehyde (573 mg, 3 mmol) in THF (20 mL) was added. The ice bath was removed and the reaction mixture was allowed to warm to room temperature. After 2 h, the reaction mixture was quenched with saturated ammonium chloride solution and concentrated to dryness. The residue was extracted with EtOAc, then washed with brine, dried with anhyd. [MGS04,] filtered and concentrated. The crude product was purified by chromatograph to yield 383 mg of the desired compound.
Reference R Synthesis of [(S)-2-AMINO-1-OXAZOLO] [4,5-b] pyridin-2-yl-butan-1-ol Step 1 A mixture of 2-amino-3-hydroxypyridine (25 g, 227 mmol), triethylorthoformate (75 mL) and p-toluenesulfonic acid (61 mg) was heated at [140 C] for 8 h. Excess triethylorthoformate was removed under vacuum. The product was crystallized from ethyl acetate to yield 22.5 g of oxazolo [4,5-b] pyridine. Step 2 To a stirred solution of the oxazolo [4,5-b] pyridine (12 g, 100 mmol) in THF (300 mL) was added n-BuLi (1.6 M solution in 62.5 mL of hexane) drop wise under N2 at-78 [C.] After 1 h, MgBr. [ET20] (25.8 g, 100 mmol) was added and the reaction mixture was allowed to warm [TO-45 C] for 1 h before being treated with [(S)-2-BOC-AMINO-BUTYLALDEHYDE] (11.46 g, 60 mmol) in THF (50 mL). The reaction mixture was stirred for 1 h, quenched with saturated [NH4C1,] and extracted with ethyl acetate. The organic layer was washed with brine, dried with MgS04 and concentrated. The residue was purified by silica gel column chromatography to yield (S)-2-Boc-amino-l-(oxazolo [4,5-b] pyridin-2-yl)-1-butanol (14.1 g). Step 3 [(S)-2-BOC-AMINO-L-(OXAZOLO] [4,5-b] pyridin-2-yl)-1-butanol (311 mg, 1 mmol) and MeCl2 (5mL) were mixed and TFA [(LML)] was added at room temperature. After stirring for 1 h, the solvent and excess TFA were removed under vacuum to produce 355 mg of [(USD)-2-] [AMINO-L-OXAZOLO] [4,5-b] [PYRIDIN-2-YL-BUTAN-1-OL.] TFA salt.
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