Structure of N-tert-butoxycarbonyl-L-phenylalanine benzyl ester.

C21H25NO4, Mr = 355.4, monoclinic, P2(1), a = 5.206 (2), b = 17.294 (4), c = 10.972 (2) A, beta = 98.91 (1) degrees, V = 976 (1) A3, Z = 2, Dx = 1.21 Mg m-3, lambda(Cu K alpha) = 1.5418 A, mu = 0.68 mm-1, F(000) = 380, T = 293 K, final R = 0.071 for 1186 observed reflections. The structure is stabilized in the a direction by means of intermolecular hydrogen bonds [N(1) ... O(2i) = 3.01 (1) A, (i) = x + 1, y, z]. The urethane amide bond adopts the trans conformation [H(1)-N(1)-C(5) = O(2) = 169 (3) degrees]. The butoxycarbonyl (Boc) moiety is directed away from both the phenylalanine aromatic ring and the benzyl ester ring, in contrast to the arrangement observed in Bocphenylalanine phenacyl ester [Vlassi, Germain, Matsoukas, Psachoulia, Voliotis & Leban (1987). Acta Cryst. C43, 2173-2175]. The orientation assumed by the Boc group may be the result of steric restrictions imposed by both rings.