The role of cystine knots in collagen folding and stability,part II. Conformational properties of (Pro-Hyp-Gly)n model trimers with N- and C-terminal collagen type III cystine knots

In mature collagen type III the homotrimer is C-terminally cross-linked by an interchain cystine knot consisting of three disulfide bridges of unknown connectivity. This cystine knot with two adjacent cysteine residues on each of the three alpha chains has recently been used for the synthesis and expression of model homotrimers. To investigate the origin of correct interchain cysteine pairings, (Pro-Hyp-Gly)(n) peptides of increasing triplet number and containing the biscysteinyl sequence C- and N-terminally were synthesised. The possibilities were that this origin may be thermodynamically coupled to the formation of the collagen triple helix as happens in the oxidative folding of proteins, or it could represent a post-folding event. Only with five triplets, which is known to represent the minimum number for self-association of collagenous peptides into a triple helix, air-oxidation produces the homotrimer in good yields (70 %), the rest being intrachain oxidised monomers. Increasing the number of triplets has no effect on yield suggesting the formation of kinetically trapped intermediates, which are not reshuffled by the glutathione redox buffer. N-terminal incorporation of the cystine knot is significantly less efficient in the homotrimerisation step and also in terms of triple-helix stabilisation. Compared to an artificial C-terminal cystine knot consisting of two interchain disulfide bridges, the collagen type III cystine knot produces collagenous homotrimers of remarkably high thermostability, although the concentration-independent refolding rates are not affected by the type of disulfide bridging. Since the natural cystine knot allows ready access to homotrimeric collagenous peptides of significantly enhanced triple-helix thermostability it may well represent a promising approach for the preparation of collagen-like innovative biomaterials. Conversely, the more laborious regioselectively formed artificial cystine knot still represents the only synthetic strategy for heterotrimeric collagenous peptides.     

棒丝氨酸的全合成研究I. 从D-葡萄糖合成3-[3'R, 5'S)-7'-氧代-1'-氮杂-4'-氧杂双环[3.2.0]-庚-3'-基]-3-O-苄基-(2S, 3S)-丝氨酸及其(3'R, 5'R)-差向异构体

以D-葡萄糖为原料经侧链氨基酸合成, 与β-内酰胺缩合, 唑烷环合和除保护基等反应合成了棒丝氨酸的O-苄基衍生物, 3-[3'R, 5'S)-7'-氧代-1'-氮杂-4'-氧杂双环[3.2.0]-庚-3'-基]-3-O-苄基-(2S, 3S)-丝氨酸及其(3'R, 5'R)-差向异构体(18)。     

Contributions to the Chemistry of Silicon-Sulfur Compounds. 65 synthesis,crystal and molecular structure of cyclo-tetrakis[tri-tert-butoxysilanethiolatogold(I)], [(t-C4H9O)3SiSAu]4, the first example of an Au4S4 ring System

The preparation of the first silanethiolate complex of gold, cyclo-tetrakis[tri-tert-butoxysilanethiolatogold(I)] from tri-tert-butoxysilanethiol and tetrachloroauric acid is described. The compound forms colorless orthorhombic crystals, and the molecular structure was determined at 200 K by single crystal X-ray diffraction. At 187 K, a possible, reversible phase transition is observed. The center of the molecule is a distinctly folded eight-membered Au₄S₄ ring of alternating three-fold coordinated sulfur and two-fold coordinated gold atoms. The relevant bond lengths and angles are: Au? S 228.4 and 229.6 pm, Si? S 216.9 pm, S? Au? S 178.8° and 178.3°, Au? S? Au 90.3°, Si? S? Au 103.7° and 101.9°. The gold atoms are separated by 324.8 pm.     

Synthesis, structures, and spectral properties of biomimetic azomethine metal chelates with chromophores CuN2S2, CuN2O2, and CuN2Se2. Crystal structure of bis[4-(benzyl)aldimino-3-methyl-1-phenyl-5-pyrazolothiolato]copper(II)

Copper(II) chelates of composition CuL₂ were synthesized based on 4-aminomethylene derivatives of 5-thiopyrazoles (LH). The complexes were studied by UV, IR, ESR, and EXAFS spectroscopy, magnetochemistry, and X-ray diffraction analysis. The coordination polyhedra in the complexes are pseudotetrahedra or octahedra of the types CuN₂S₂ or CuN₄S₂, respectively, which are distorted due to the Jahn—Teller effect. The UV and ESR spectra of copper chelates with a six-coordinate metallocycle formed by the N and S atoms of the azomethine ligand and the nitrogen atom of the quinoline substituent (R) of the C=N−R fragment are most similar to the spectra observed for metals involved in the active centers of natural metalloenzymes (“blue” copper proteins). Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1891–1896, November, 2000.