Ca-mediated thiolysis of peptide–resin linkage as an option for preparing protected peptide thioesters

A mild new procedure for preparing protected peptide thioesters, based on Ca²⁺-assisted thiolysis of peptide–Kaiser oxime resin (KOR) linkage, is described. Ac-Ile-Ser(Bzl)-Asp(OcHx)-SR (Ac: acetyl; Bzl: benzyl; cHx: cyclohexyl), model peptide, was readily released from the resin by incubating the peptide–KOR at 60 °C in mixtures of DMF with n-butanethiol [R = (CH₂)₃CH₃] or ethyl 3-mercaptopropionate [R = (CH₂)₂COOCH₂CH₃] containing Ca(CH₃COO)₂. After serine and aspartic acid side-chain deprotection under acid conditions, Ac-Ile-Ser-Asp-S(CH₂)₂COOCH₂CH₃ was successfully obtained with good quality and high yield. This type of C-terminal modified peptide may act as an excellent acyl donor in peptide segment condensation by the thioester method, native chemical ligation and enzymatic methods.     

A DFT study of the enantioselective reduction of oxime ethers promoted by chiral spiroborate esters

Mechanisms of borane reduction of the (E)‐acetophenone O‐methyl oxime catalyzed by the easily prepared and stable spiroborate ester 1, derived from diphenylvalinol has been reported for the first time using density functional theory. Two reaction pathways are investigated at the B3LYP/6‐31G(d,p) level of theory. The calculated results reveal that this reaction is accomplished via four steps. All the reactants, products, transition states, and intermediates have been optimized at the B3LYP/6‐31G (d,p) level. The analysis of these results reveals that one pathway is more energetically favorable than the other, and its associated product is in good agreement with the experimental result. The solvent effect has been further considered at the B3LYP/6‐31G(d,p) level in the solvent THF using the PCM model, and the results indicate that it has no great influence on the enantioselectivity of this reduction. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Syntheses and characterizations of a novel 1,2,3,4-tetrahydroquinazoline and a Co(III) complex

The 2-furan-2-yl-1,2,3,4-tetrahydroquinazoline-2-carbaldehyde oxime (HL) and complex of tridentate ligand containing oxime, imine, and amine donors resulting from reactions with cobalt(II) salt have been synthesized and characterized by spectral methods (FT-IR, NMR, UV-Vis, mass), elemental analysis, magnetic susceptibility, molar conductivity, and thermal analysis (TG, DTA) techniques. The molecular structure of HL was elucidated from single-crystal X-ray diffraction. X-ray crystallographic analysis shows that the molecule crystallizes in the monoclinic system, space group C2/c. In the complex, chloride was not coordinated as confirmed by conductivity measurements. The metal is coordinated to the oxime, imine, and amine nitrogen atoms and decomposes with loss of the organic ligand and halogen to leave metal oxide. The metal to ligand ratio was 1?:?2 by elemental analysis and mass spectrum.     

Synthesis of sterically hindered ketones from aldehydes via O-silyl oximes

A mild and efficient method to synthesize sterically hindered ketones from aldehydes via O-silyl oximes was developed. Treatment of O-triphenylsilylated oximes with alkyl iodides in the presence of triethyl borane afforded the corresponding ketones.     

TS-1/H_2O_2体系催化香茅醛肟化反应

将TS-1/H2O2催化体系用于催化香茅醛氨肟化制备香茅醛肟反应中,结果表明,在优化的反应条件下,香茅醛转化率和香茅醛肟选择性分别达99.9%和99.2%以上.反应过程中主要存在两对竞争反应:TS-1催化的醛肟化反应和碱催化的羟醛缩合反应;TS-1催化的醛肟化反应和双键环氧反应.通过调节体系中氨含量可有效抑制副反应.     

Synthesis of Cobalt Doped Mesoporous Silica with high Cyclohexanone Selectivity for Catalytic Oxidation of Cyclohexane by the wild Sugarcane-grass Stems Bio-template Route

以野生滇蔗茅为生物模板剂合成Co掺杂的介孔SiO2催化氧化环己烷.并用X射线衍射、N2-物理吸附和解吸附、紫外-可见光光度计、傅里叶红外光谱仪和扫描电镜对材料进行了表征.X射线衍射、N2-物理吸附和解吸附研究结果表明该材料为介孔材料且氧化钴高分散于介孔材料的表面.紫外-可见光光谱表明钴离子以Co2＋和Co3＋的形态存在.环己烷的催化氧化结果表明催化剂能高效催化环己烷（环己烷的转化率为71.0%）转化为环己酮（选择性高达76.7%）.催化剂的重复性试验表明该催化剂具有较高的稳定性,循环使用3次后,催化活性仅有微小的改变.     

离子液体中酮肟O-烷基化反应的研究

以[Bmim]PF6,[Bmim]BF4,[Bmim]OH为介质,以NaOH为缚酸剂,由酮肟与卤烷、硫酸酯等烷基化剂在20～40℃反应1～2h,以52%～94%的收率制备了酮肟醚衍生物,产物结构经1HNMR,GC-MS表征.结果表明,该方法简便易操作,所用离子液体对环境友好,并可循环使用.     

Pillared clays as efficient catalysts for cyclohexanol oxidation

Summary Iron, aluminium and mixed iron aluminium pillared clays were prepared by partial hydrolysis method and doped with 10% V and Mo. The samples were characterised by XRD, FTIR and surface area and pore volume measurements. Oxidation of cyclohexanol with hydrogen peroxide was done as probe reaction to test catalytic activity. Iron pillared systems exhibited maximum activity. The effects of various reaction variables on the reaction were studied.     

Unprecedented chemo-enzymatic synthesis of stereochemically pure 3-acetoxy-2-methyl-2-vinylcycloalkanones

A new approach to 3-acetoxy-2-methyl-2-vinylcyclohexanone and 3-acetoxy-2-methyl-2-vinylcyclopentanone in stereochemically pure state, by means of a combination of yeast-catalyzed reduction and subsequent radical β-fragmentation is described.