Benzaldehyde → (+/-)-tert-butyl ((1R,2S,3S,5R)-5-(3-((tert-butoxycarbonyl)amino)pyridin-4-yl)-3-methyl-2-(methylamino)cyclohexyl)carbamate

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To a solution of (+/−)-tert-butyl ((1R,2S,3S,5R)-5-(3-((tert-butoxycarbonyl)amino)pyridin-4-yl)-2-amino-3-methylcyclohexyl)carbamate (1.0 equiv.) in MeOH (0.10 M) was added benzaldehyde (1.3 equiv.). After 3 hrs, sodium cyanotrihydroborate (2.5 equiv.) was added and the mixture was stirred at rt for 16 hrs. The reaction mixture was quenched by the addition of water, and volatiles were removed in vacuo. The mixture was extracted with ethyl acetate. The combined organic phases were dried with sodium sulfate, filtered and concentrated. The residue was dissolved in MeOH (0.10 M) and paraformaldehyde (5.0 equiv.) was added. After 16 hrs, sodium cyanotrihydroborate (5.0 equiv.) was added and the mixture was left stirred at rt for 16 hrs. The reaction was quenched by the addition of water, and volatiles were removed in vacuo. The mixture was extracted with DCM. The combined organic phases were dried with sodium sulfate, filtered, concentrated and purified by ISCO Chromatography. The product was dissolved in MeOH (0.10 M) and treated with Pd(OH)2 (0.50 equiv.) under H2 for 5 hrs at RT. The reaction was filtered through a pad of celite and the cake was washed with MeOH. The organics were concentrated to yield (+/−)-tert-butyl ((1R,2S,3S,5R)-5-(3-((tert-butoxycarbonyl)amino)pyridin-4-yl)-3-methyl-2-(methylamino)cyclohexyl)carbamate in 75% yield. LC/MS (m/z)=435.2 (MH+), Rt=0.64 min.

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