tert-butyl N-[(2S)-4-methyl-1-oxopentan-2-yl]carbamate → (1-{[2-(4-Benzyloxy-phenyl)-1-tert-butylcarbamoyl-ethylamino]-methyl}-3-methyl-butyl)-carbamic acid tert-butyl ester

Participants

Reaction Steps

A solution consisting of 1.00 g (4.64 mmol) N-tert-butoxycarbonyl-L-leucinal and 1.52 g (4.64 mmol) 2-amino-3-(4-benzyloxy-phenyl)-N-tert-butyl-propionamide (Example 2, Step C) in 20 mL methanol containing 1% acetic acid was stirred at 25° C. for 20 minutes, at which time a solution of 0.614 g (9.29 mmol) sodium cyanotrihydridoborate (Aldrich, Milwaukee, Wis.) in 12 mL methanol was added and the resulting mixture stirred for 24 hours. The reaction was quenched by the addition of 3 M HCl in 3 mL increments until the vigorous bubbling subsided. The mixture was neutralized with saturated NaHCO3 solution then extracted with three 50 mL portions of ethyl acetate. The combined extracts were washed with 100 mL brine, dried over anhydrous sodium sulphate, and evaporated at reduced pressure to give a clear, colorless oil which was chromatographed on a silica gel column using 30% to 40% ethyl acetate:hexane to give 735 mg (30%) of [S-(R*,S*)]-(1-{[2-(4-benzyloxy-phenyl)-1-tert-butylcarbamoyl-ethylamino]-methyl}-3-methyl-butyl)-carbamic acid tert-butyl ester as a clear foam.

Provenance & Evidence