Structure and conformation of peptides involving prolyl residue III. L-Prolyl-L-isoleucine monohydrate

The dipeptide, L‐prolyl‐L‐isoleucine monohydrate (C11 H20N2O3· H2O, molecular weight 246.3) crystallizes in the monoclinic space group P21, with a = 6.601(3)Å, b = 5.413(3) Å, c = 19.128(6) Å, β= 98.1(1)°, Z = 2, Do = 1.20g·cm‐3 and Dc = 1.208g·cm‐3. The structure was solved by MULTAN–80 and refined to a final R‐factor of 0.081 for 594 reflections measured on a Enraf Nonius CAD‐4 diffractometer. The peptide linkage exists in the trans conformation. The pyrrolidine ring is disordered with two alternate envelope conformations for the Cγ atom. The values of the sidechain torsion angles are: χ11=– 63.6(17)°, χ12= 171.1(16)° and χ2=– 59.6(21)° for isoleucine (C‐terminal). The crystal structure is stabilized by a three‐dimensional network of N—H ⋯ O, O—H ⋯ O and C—H ⋯ O hydrogen bonds. The dipeptide exists in the extended Conformation.