Studies of peptide antibiotics. XLVI. Syntheses of gramicidin S analogs containing D-α, β-diaminopropionic acid or α,β-dehydroalanine*

A gramicidin S (GS) analog ([d -Dpr^4,4] GS) containing d -α,β-diaminopropionic acid (D-Dpr) in place of D-Phe at 4,4′ positions was derived from [l -Orn(δ-formyl)^2,2, d -Dpr(β-Z)^4,4′]GS, which was synthesized by conventional method in solution. An analog [ΔAla^4,4′]GS was synthesized from [l -Orn(δ-Boc)^2,2′, d -Dpr^4,4′]GS through Hofmann degradation of the d -Dpr residues. Antimicrobial activities of these analogs were tested; [d -Dpr(β-Z)^4,4′]GS and [ΔAla^4,4′]GS showed high antimicrobial activities against Gram-positive bacteria. [d -Dpr^4,4′]-GS showed an appreciable activity against Gram-negative bacteria such as Escherichia coli. Four semigramicidin S (semiGS) analogs such as [ΔAla⁴]semiGS were synthesized; these had no antimicrobial activity. Analogs containing ΔAla residues were hydrogenated, and the formation of l -Ala or d -Ala residues was determined. The ΔAla residues in [ΔAla^4,4′] GS were reduced to dl -Ala, and ΔAla in [ΔAla⁴]semiGS mostly to l -Ala. The relationships of the antimicrobial activity, CD curves and asymmetric hydrogenation to the structure were discussed.     

贵金属-壳聚糖催化苯乙酮不对称转移加氢反应

将天然手性高分子聚合物壳聚糖(CS)负载到SiO2上后,再络合M(Pd、Pt、Pu和Ph)金属,制得了多相手性加氢催化剂M-CS-SiO2.在空气氛围下,以异丙醇为氢源,考察了M-CS-SiO2对苯乙酮不对称催化氢转移加氢反应的催化活性.研究了活性金属(Pd、Pt、Rh和Ru)、载体(ZSM-5、β、MCM-41、SiO2),及钯的前驱物对多相手性加氢催化剂性能的影响.结果表明:Pd-CS-SiO2对苯乙酮不对称转移加氢反应具有较好的催化加氢性能和对R-1-苯乙醇的对映选择性;Pd的前驱物对Pd-CS-SiO2的催化活性和对映选择性的影响较小;载体对Pd催化剂的催化活性和对映选择性的影响很大;在苯乙酮不对称转移加氢反应中,Pd-CS-β分子筛对R-1-苯乙醇的对映体过量值可达到65.7%.     

对苯二甲酸的加氢精制过程Ⅱ.不同粒度催化剂上4-CBA表观加氢动力学

对Pd/AC催化剂上对苯二甲酸(TA)加氢精制过程中的对羧基苯甲醛(4-CBA)加氢反应进行了研究。考察了氢分压、反应温度、催化剂颗粒大小对4-CBA消逝速率的影响,结果表明:在高于0.35 M Pa时,氢分压对4-CBA加氢反应速率的影响很小,而温度和催化剂粒度大小对加氢反应的影响显著。同时,工业条件下的TA加氢精制过程存在着严重的内外扩散。采用幂函数动力学模型方程利用M atlab拟合得到了不同粒度催化剂上的表观动力学方程。     

新型手性配体的合成及其在沙美特罗关键中间体合成中的应用

目的合成沙美特罗的关键手性中间体。方法设计合成新型手性配体单磺酰化1，2-双-（3，5-二甲基苯基）乙二胺，通过与金属铑配合生成手性催化剂，利用该催化剂催化沙美特罗的关键手性中间体的不对称氢转移反应。结果与结论新型手性配体具有良好的催化活性和对映体选择性，催化合成得到的沙美特罗中间体的对映体选择性的ee％值为91％。     

Industrially viable processes for synthesis of biologically active hydroxycarotenoids commonly found in fruits and vegetables

Human plasma and tissues contain in excess of 12 dietary carotenoids and several metabolites that originate from consumption of fruits and vegetables. The major hydroxycarotenoids absorbed by humans are: (3R,3′R,6′R)-lutein (1), (3R,3′R)-zeaxanthin (2), (3R,6′R)-α-cryptoxanthin (3), and (3R)-β-cryptoxanthin (4) and their E/Z-stereoisomers. In addition, several hydroxycarotenoids that result from metabolic transformation of 1 have also been identified in human plasma and ocular tissues. Epidemiological and experimental evidence to date suggest hydroxycarotenoids may protect against chronic diseases such as cancer, cardiovascular disease and age-related macular degeneration (AMD). Therefore, supplementation with these carotenoids in individuals with a low dietary intake of fruits and vegetables is essential. However, with the exception of 1 and 2, industrial production of 3 and 4 have not yet materialized. A relatively straightforward semisynthetic process has been developed that transform 1 into a mixture of 3 (12%) and 4 (80%). Hydroxycarotenoid 3 can also be directly prepared from allylic deoxygenation of 1 in a single step in an excellent yield. These two processes provide an easy access to optically active 3 and 4 that are normally prepared by numerous synthetic steps.     

The Effect of Sibunit Carbon Surface Modification with Diazonium Tosylate Salts of Pd and Pd-Au Catalysts on Furfural Hydrogenation

Herein, we investigated the effect of the support modification (Sibunit carbon) with diazonium salts of Pd and Pd-Au catalysts on furfural hydrogenation under 5 bars of H₂ and 50 °C. To this end, the surface of Sibunit (Cp) was modified with butyl (Cp-Butyl), carboxyl (Cp-COOH) and amino groups (Cp-NH₂) using corresponding diazonium salts. The catalysts were synthesized by the sol immobilization method. The catalysts as well as the corresponding supports were characterized by Fourier transform infrared spectroscopy, N₂ adsorption-desorption, inductively coupled plasma atomic emission spectroscopy, high resolution transmission electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Hammet indicator method and X-ray photoelectron spectroscopy. The analysis of the results allowed us to determine the crucial influence of surface chemistry on the catalytic behavior of the studied catalysts, especially regarding selectivity. At the same time, the structural, textural, electronic and acid–base properties of the catalysts were practically unaffected. Thus, it can be assumed that the modification of Sibunit with various functional groups leads to changes in the hydrophobic/hydrophilic and/or electrostatic properties of the surface, which influenced the selectivity of the process.     

2-巯基-5-甲氧基苯并咪唑合成工艺的研究

目的改进2-巯基-5-甲氧基苯并咪唑的合成工艺。方法以对氨基苯甲醚为起始原料,采用醋酸硝酰作硝化剂进行硝化;采用雷尼镍催化加氢法进行还原。结果制得了奥美拉唑中间体2-巯基-5-甲氧基苯并咪唑,总收率78.5%。结论值得推广到工业化生产。     

Highly selective catalytic transfer hydrodeuteration of cyclic alkenes

Selective deuterium installation into small molecules is becoming increasingly desirable not only for the elucidation of mechanistic pathways and studying biological processes but also because of deuterium's ability to favorably adjust the pharmacokinetic parameters of bioactive molecules. Fused bicyclic moieties, especially those containing heteroatoms, are prevalent in drug discovery and pharmaceuticals. Herein, we report a copper-catalyzed transfer hydrodeuteration of cyclic and heterocyclic alkenes, which enables the synthesis of chromans, quinolinones, and tetrahydronaphthalenes that are precisely deuterated at the benzylic position. We also demonstrate the ability to place one deuterium atom at the homobenzylic site of these scaffolds with high regioselectivity by swapping transfer reagents for their isotopic analogs. Furthermore, examples of chemoselective transfer hydrogenation and transfer deuteration are disclosed, allowing for the simultaneous incorporation of two vicinal hydrogen or deuterium atoms into a double bond.