The crystal and molecular structure of tert-butoxycarbonyl - α-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) Å, V = 4025(2) ų, Z = 8, D_calc = 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 (λ=1.5418 Å) for 2389 reflections with I ≥ 3σ (I). The dihedral angles of the peptide backbone show that the Aib residue adopts a right handed (α_R) and a left handed (α_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.