MOLECULAR-STRUCTURES OF L-LEU-L-TYR, GLY-D,L-MET P-TOLUENESULFONATE AND L-HIS-L-LEU

L-LeU-L-Tyr, (I), C15H22N2O4, M(r) = 294.35, crystallizes from MeOH/5% dimethyl sulfoxide in the orthorhombic space group P2(1)2(1)2(1). a = 5.644(l), b = 12.094 (3), c = 22.548 (4) angstrom, V = 1539.0 (5) angstrom3, Z = 4, D(x) = 1.270 g cm-3, Cu Kalpha, lambda = 1.54184 angstrom, mu = 7.228 cm-1, F(000) = 632, T = 173 K, final R (on F) = 0.033 for 1347 observations with I greater-than-or-equal-to 2sigma(I). (I) crystallizes as a zwitterion with the N-terminus protonated and the C-terminus ionized. The peptide backbone adopts a distorted trans antiparallel beta pleated-sheet conformation, with principal torsion angles psi1 = 163.7 (2), omega1 = 158.7 (2), phi2 = - 110.9 (3) and psi2 = 141.4 (2)-degrees. The leucyl residue is in the g-(tg-) conformation while the tyrosyl residue adopts the g- conformation, with the phenol ring twisted from the low-energy perpendicular position. Gly-D,L-Metp-toluenesulfonate, (II), C7H15N2O3S+.C7H7O3S, M(r) = 378.47, crystallizes from MeOH/EtOAc in the orthorhombic space group Pbca. a = 33.642(4), b = 15.951(1), c = 6.785 (1) angstrom, V = 3641.0 (4) angstrom3, Z = 8, D(x) = 1.381 g cm-3, Cu Kalpha, lambda = 1.5484 angstrom, mu = 28.865 cm-1, F(000) = 1600, T = 223 K, final R (on F) = 0.055 for 1669 observations with I greater-than-or-equal-to 3sigma(I). Gly-D,L-Met exists as a cation with the N- and C-termini protonated, the p-toluenesulfonate being the counterion. The peptide backbone conformation is a trans right-handed helical structure with psi1 = 172.8 (4), omega1 = - 178.9 (4), phi2 = - 80.6 (7) and psi2 = - 33.8 (8)-degrees. The methionine residue adopts the g-(tg-) conformation. L-HiS-L-LeU, (III), C12H20N4O3, M(r) = 268.32, crystallizes from aqueous ethanol in the monoclinic space group P2(1). a = 6.559 (1), b = 5.451 (1), c = 20.463 (2) angstrom, beta = 99.00 (1)-degrees, V = 722.7 (3) angstrom3, Z = 2, D(x) = 1.233 g cm-3, Cu Kalpha, lambda = 1.54184 angstrom, mu = 7.102 cm -1, F(000) = 288, T = 295 K, final R (on F) = 0.033 for 1237 observations with I greater-than-or-equal-to 3sigma(I). (III) crystallizes as a zwitterion with the N-terminus protonated and the C-terminus ionized. The peptide backbone extends to the C-terminus, which then coils in a helical conformation. Principal torsion angles are psi1 = 164.5 (2), omega1 = 174.8 (2), psi2 = -77.9 (3) and psi2 = -18.7 (3)-degrees. The histidyl side chain adopts a gauche orientation with the ring twisted slightly from a perpendicular orientation. The leucine residue adopts the g-(tg-) conformation. Two intramolecular hydrogen-bonding interactions are proposed, one from the imidazole ring to the ionized C-terminus and the other from the protonated N-terminus to the peptide carbonyl O atom.