Crystal and molecular structure of N-α-acetyl-L-arginine-methyl ester hydrochloride

The crystal structure of N-α-acetyl-L-arginine-methyl ester hydrochloride has been determined from X-ray diffraction data. The crystals are orthorhombic, space group P212121, a = 15.746 (4), b = 11.569 (4), c = 7.158 (3) A, Z = 4. The structure was solved by direct methods (MULTAN) and refined by fullmatrix least-squares to an R = 0.070 for all observed reflections. The molecule shows a planar peptidic unit, with a distortion of H(N1) due to hydrogen bond interaction. The side chain is in the low energy all-trans conformation. The guanidinium group forms three hydrogen bonds with the carbonyl oxygens of two neighbouring molecules. A direct interaction of the peptidic NH with the chloride ions is observed. The latter ions also interact with the guanidinium groups, neutralizing their charges.