The crystal structure of N,N′-bismethoxycarbonyl-L-valyl-L-valine, a product of the rearrangement of the symmetrical anhydride of N-methoxycarbonyl-L-valine

Abstract

A side product accompanying the reaction of N-methoxycarbonyl-L-valine anhydride with an amino acid anion in aqueous dimethylformamide has been characterized by an X-ray analysis as N,N′-bismethoxycarbonyl-L-valyl-L-valine, C₁₄H₂₄N₂O₇. The crystals are orthorhombic, space group P2₁2₁2₁, a = 14.581(2), b = 17.110(2), c = 6.970(1) Å, Z = 4. The structure was determined by the direct method, and refined by block-diagonal least squares to R = 0.046, R_w = 0.053 for 1759 reflections with I ≥ 3σ(i). The carboxy-terminal part of the dimer is in the gauche conformation while the other part is trans. Each molecule at (x, y, z) makes two hydrogen bonds O … H—O and N—H … O to the molecule at (1 − x, y − 1/2, 1/2 − z) and similarly to that at (1 − x, 1/2 + y, 1/2 − z) to form infinite ribbons along y.