To a solution of 4-nitrophenylalanine, ethyl ester, hydrochloride (54.0 g) in dry dimethylformamide (400 ml), add t-butyl 2-bromopropionate (112.3 g) and triethylamine (76 ml) and heat the resulting mixture at 70° for 18 hours under a nitrogen atmosphere. Pour the reaction mixture into water and extract with methylene chloride (6×300 ml). Combine the organic layers, dry over magnesium sulfate and concentrate in vacuo to give a liquid (contains DMF). Chromatograph this liquid on a Prep 500 (3 silica gel cartridges) using hexane (8 l) then hexane:ethylacetate 4:1 and isolate N-[1(S)-ethoxycarbonyl-2-(4-nitrophenyl)ethyl]-(R)alanine, t-butyl ester, [α]D26 =+24.7° (methanol), and N-1(S)-ethoxycarbonyl-2-(4-nitrophenyl)ethyl]-(S)alanine, t-butyl ester.
