Structure and conformation of peptides involving prolyl residue. IV. L-Prolyl-L-leucine 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)A, b = 5.413(3) A, c = 19.128(6) A, 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.