Reaction Steps
(2R)-2-({[(1,1-Dimethylethyl)oxy]carbonyl}amino)propyl methanesulfonate. To a stirred solution of 1,1-dimethylethyl[(1R)-2-hydroxy-1-methylethyl]carbamate (5.00 g, 28.5 mmol) and triethylamine (5.92 mL, 42.9 mmol) in CH2Cl2 (30 mL) cooled to 0° C. and under a nitrogen atmosphere was added dropwise a solution of methanesulfonyl chloride (2.43 mL, 31.5 mmol) in CH2Cl2 (25 mL). Stirring was continued for 20 minutes at 0° C., after which time the reaction was judged complete by TLC analysis (1:1 hexanes/EtOAc). The solution was poured into water and the layers were separated. The organic phase was washed with 0.1 N HCl and then with 5% NaHCO3, dried over Na2SO4, filtered and concentrated to give (2R)-2-({[(1,1-dimethylethyl)oxy]carbonyl}amino)propyl methanesulfonate (7.08 g, 98%) as a white solid. 1H NMR (400 MHz, CDCl3) δ 1.23 (d, J=6.8 Hz, 3H), 1.44 (s, 9H), 3.03 (s, 3H), 3.97 (m, 1H), 4.15 (dd, J=4.2, 9.8 Hz, 1H), 4.21 (m, 1H), 4.61 (br s, 1H). b) 1,1-Dimethylethyl[(1R)-2-cyano-1-methylethyl]carbamate. To a stirred solution of (2R)-2-({[(1,1-dimethylethyl)oxy]carbonyl}amino)propyl methanesulfonate (7.08 g, 27.9 mmol) in DMSO (50 mL) was added NaCN (3.78 g, 84.0 mmol). The solution was stirred at 70° C. for 2 hours, over which time the formation of a precipitate was observed. After cooling at room temperature, water was added and the mixture was extracted with Et2O. The ethereal layers were washed with a brine solution, dried over Na2SO4, filtered and concentrated to give 1,1-dimethylethyl [(1R)-2-cyano-1-methylethyl]carbamate (3.81 g, 73%) as a pale yellow solid. 1H NMR (400 MHz, CDCl3) δ 1.30 (d, J=6.8 Hz, 3H), 1.42 (s, 9H), 2.51 (dd, J=3.8, 16.6 Hz, 1H), 2.73 (m, 1H), 3.93 (m, 1H), 4.63 (br s, 1H). c) 1,1-Dimethylethyl[(1R)-3-amino-1-methylpropyl]carbamate. A solution of 1,1-dimethylethyl[(1R)-2-cyano-1-methylethyl]carbamate (1.30 g, 7.1 mmol) in ethanol saturated with anhydrous ammonia was treated with Raney-Ni (1.5 mL of 50% aq. Suspension) and 55 psi of H2 overnight. The mixture was filtered through Celite and the filtrate was concentrated in vacuo. The residue was purified by flash chromatography (80:19:1 CH2Cl2/MeOH/NH4OH (37%) gradient elution) through a short plug of silica gel to give 1,1-dimethylethyl [(1R)-3-amino-1-methylpropyl]carbamate (1.37 g, 100%) as a clear oil that solidified. 1H NMR (400 MHz, CDCl3) δ 1.14 (d, J=6.8 Hz, 3H), 1.43-1.62 (m, 13H), 2.76 (m, 2H), 3.77 (m, 1H), 4.57 (m, 1H). d) 1,1-Dimethylethyl {(1R)-1-methyl-3-[(2-methylpropyl)amino]propyl}carbamate. 1,1-dimethylethyl[(1R)-3-amino-1 methylpropyl]carbamate (0.320 g, 1.70 mmol), isobutyraldehyde (150 μL, 1.62 mmol), and sodium triacetoxyborohydride (0.512 g, 2.42 mmol) were stirred in anhydrous dichloroethane (10 mL) at ambient temperature overnight. The reaction was quenched by the addition of saturated NaHCO3 and then extracted with dichloromethane. The combined extracts were washed with water, dried over Na2SO4, filtered and concentrated. The residue was purified by flash chromatography (80:19:1 CH2Cl2/MeOH/NH4OH (37%) gradient elution) through a short plug of silica gel to afford 1,1-dimethylethyl {(1R)-1-methyl-3-[(2-methylpropyl)amino]propyl}carbamate (0.158 g, 40%) as a clear oil. 1H NMR (400 MHz, CDCl3) δ 0.90 (d, J=6.4 Hz, 6H), 1.13 (d, J=6.4 Hz, 3H), 1.42-1.51 (m, 11H), 1.67-1.75 (m, 2H), 2.33-2.42 (m, 2H), 2.58-2.72 (m, 2H), 3.72 (m, 1H), 5.20 (m, 1H). e) [(3R)-3-Aminobutyl](2-methylpropyl)amine. An ice cold solution of 1,1-dimethylethyl {(1R)-1-methyl-3-[(2-methylpropyl)amino]propyl}carbamate (0.158 g, 0.65 mmol) in THF (8 mL) was treated with 4 N HCl (aq) (2 mL) and then stirred at room temperature for 2 h. The mixture was concentrated in vacuo to give [(3R)-3-aminobutyl](2-methylpropyl)amine dihydrochloride. The HCl salt, was then dissolved in dichloromethane and a minimal amount of methanol and treated with solid supported carbonate resin (MP-Carbonate, Argonaut Technologies). After 30 minutes, the solution was filtered through a fritted tube and the solvents removed carefully in vacuo to give [(3R)-3-aminobutyl](2-methylpropyl)amine (65 mg). 1H NMR (400 MHz, CDCl3) δ 0.88 (d, J=6.0 Hz, 6H), 1.06 (d, J=5.6 Hz, 3H), 1.23-1.53 (m, 5H), 1.71-1.74 (m, 1H), 2.39 (m, 2H), 2.65 (m, 2H), 2.97 (m, 1H), f)
