The Crystal and Molecular Structure of tert - Butoxycarbonyl - a-aminoisobutyryl- leucyl - methyl ester

The crystal structure of a dipeptide Boc - Aib - Leu - OMe (C16H30N2O5) has been determined by X - ray diffraction analysis (CCDC # 144425). The crystals are orthorhombic, space group P212121 with a = 9.674(5), b = 13.642(2), c = 30.496(6) A, V = 4025(2) A3, Z = 8, Dcalc = 1.09 Mgm-3. Crystal structure was solved by direct methods and refined by full-matrix least-squares method to an R value of 0.067 (=1.5418 A) for 2389 reflections with I 3 (I). The dihedral angles of the peptide backbone show that the Aib residue adopts a right handed (R) and a left handed (L) helical conformation in molecules A and B respectively, whereas the Leucine residue takes an extended and folded conformation in molecules A and B respectively.