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|Title:||Crystal structure and conformation of two N-tosyl-protected dipeptides containing amino acids with polar side-chains|
|Keywords:||dipeptide; conformation; crystal structure; protein structure; X ray analysis; Amino Acid Sequence; Amino Acids; Chemistry, Physical; Comparative Study; Dipeptides; Molecular Sequence Data; Molecular Structure; Protein Conformation; Support, Non-U.S. Gov't; Thermodynamics; Tosyl Compounds; X-Ray Diffraction|
|Citation:||International Journal of Peptide and Protein Research, 42(3), 294-299|
|Abstract:||X-Ray diffraction studies and energy-minimization calculations were carried out on two dipeptides, N-tosyl-L-Ser-Gly-OMe monohydrate (C13H18N2O6S � H2O, compound A) and N-tosyl-L-Thr-Gly-OMe (C14H20N2O6, compound B). Compound A crystallized in the monoclinic system, space group P21 with unit cell parameters a = 4.915(1), b = 15.625(4), c = 11.003(1) �, ? = 91.28(1)�, V = 844.8 �3. M(r) = 348.4, d = 1.37(2) g cm-3, Z = 2, ?(Cu K�) = 1.5418 �, ? = 1.99 mm-1, T = 293 K. P = 0.032 for 1451 unique reflections with I > 2�(I). Compound B crystallized in the orthorhombic system, space group P212121, with unit cell parameters a = 5.050(2), b = 16.483(3), c = 20.769(5) �, V = 1729.3 �3, Z = 4. M(r) = 344.4, d = 1.32(2) g cm-3, ?(Cu K�) = 1.90 mm-1. R = 0.040 for 1060 unique reflections with I > 2�(I). The major difference in the backbone conformation of the two compounds is in their glycine residues, with the glycine residue in compound A adopting an extended conformation with ? = -132.6(3)� and ? = 175.3(3)� and that in compound B having a folded conformation with ? = -56.3(6)� and ? = -42.6(7)�. In compound A the oxygen atom of the Ser side-chain and the carbonyl oxygen atom of glycine are bridged by the water of crystallization through O-H ��� O hydrogen bonds, resulting in the relatively rare trans conformation [? = -175.7(2)�] for this side-chain. The Thr side-chain in compound B is in the sterically preferred (tg-) conformation [?1,1 = -179.4(4)� and ?1,2 = -62.3(5)�]. The conformations were found to be in general agreement with those obtained by an energy-minimization procedure. The energy-minimized structure of N-tosyl-L-Ser-Gly-Ome (anhydrous) showed a strong hydrophobic interaction between the methyl substituents of the tosyl group and the methyl ester (C-C = 4.08 �).|
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