82 g of carbobenzoxy-L-alanine are dissolved in 100 ml of absolute tetrahydrofuran, the solution is cooled to -40° C and treated with 80 g of phosphorus pentachloride. The mixture is stirred at -30° C for 20 minutes and subsequently added to a shaken solution of 80 g of 2-amino-5-nitro-2'-chlorobenzophenone in 100 ml of absolute tetrahydrofuran. The solution is concentrated on a rotary evaporator at 50°-60° C, treated twice with toluene and evaporated each time. By crystallisation of the residue from ether, there is obtained (-)-benzyl-[1-[{2-(o-chlorobenzoyl)4-nitrophenyl}carbamoyl]-ethyl]carbamate which melts at 147° C and exhibits a rotation of [α]25D =-18.2° (in methylene chloride, 1%).
