Benzyloxycarbonyl-L-ornithine tert-butyl ester → tert-Butyl (2S)-5-{[(benzyloxy)carbonyl]amino}-2-{[(tert-butoxy)carbonyl]amino}pentanoate

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Nδ -(Benzyloxycarbonyl-L-ornithine tert-butyl ester (7.50 g, 23.3 mmol) was dissolved in 27 ml of methylene chloride, and the solution was cooled to 0° C. To that solution was added dropwise tert-butyl pyrocarbonate (5.87 g, 26.9 mmol) in 10 ml of methylene chloride. The reaction mixture was stirred at 0° C. for 1 hour, and stirring was continued for 3 additional hours at room temperature. The solvent was evaporated at reduced pressure and the oily residue was chromatographed on a column of silica gel (25 cm×30 mm) using hexane:ethyl acetate (3:1) as solvent. Fractions of approximately 5 ml were collected, and those containing product were identified by thin layer chromatography (see below). Chromatographic fractions containing product were pooled and evaporated to a thick oil by rotary evaporation at reduced pressure. The yield was 8.63 gm (93.5%). 1H NMR (DCCl3) δ1.44 (s,9H), 1.46 (s,9H), 1.5-1.9 (m,4H), 3.23 (t,2H), 4.17 (t,1H), 4.88 (s,1H broad), 5.09 (s,2H and s,1H broad) 7.35 (s,5H).

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