Blocking of the α-Carboxyl Group

Abstract

The amino acid (10 mmol) is suspended in 2,2-dimethoxypropane [3] (100 to 150 ml) and concentrated hydrochloric acid (10 ml) is added. The mixture is allowed to stand [4] at room temperature overnight. The volatile reactants are removed in vacuo at a bath temperature not exceeding 60 °C, the residue dissolved in a minimum amount of dry methanol and the solution diluted with dry ether (250 ml). The crystalline methyl ester hydrochloride is collected on a filter, washed with ether and dried in vacuo over NaOH pellets. Recrystallization from methanol-ether affords the analytically pure ester hydrochloride [5]; yields range from 80 to 95%. The values of specific rotations agree with those reported in the literature.