人参属植物中水溶性非蛋白氨基酸与寡肽的研究

从人参属植物水提取液中分离鉴定了若干具有生物活性的非蛋白氨基酸,如神经抑制性递质,γ－氨基丁酸（GABA）,神经兴奋毒素,β－N－草酰基－L－α,β－二氨基丙酸（β－N－ODAP）。首次从人参根的水提取液中分离纯化与鉴定了一组N－末端为从谷氨酸,并以其γ－羧基形成肽键为特征的七个寡肽;其结构为P－Ⅰ（氧化型谷胱甘肽,GSSG）P－Ⅱ（氧化型谷胱甘酰胺）,P－Ⅲ[N, N‘-双－（γ－谷氨酰甘氨酰）胱氨酸,IGSSG]与P－Ⅳ（N－γ－谷氨酰胱氨酰－双－甘氨酸）,P－Ⅴ-（N,N‘-双－γ－谷氨酰胱氨酰甘氨酸）,P－Ⅵ（γ-谷氨酰精氨酸）与P－Ⅶ（还原型谷胱甘肽）。化合物P－Ⅱ至P－Ⅴ与P－Ⅶ均与氧化型谷胱甘肽有关。P－Ⅱ至P－Ⅵ的结构均经化学合成确证。化 合物P－Ⅲ为未见报道的新生物活性肽,具有比化合物P－Ⅰ强的促睡眠活性。同时还讨论了β－N－ODAP与GABA以及其它化合物的生物活性。     

一种基于共保护策略合成谷胱甘肽的新方法

报道了一种采用谷氨酸席夫碱Ni(II)配合物共保护L-谷氨酸α-氨基和α-羧基合成谷胱甘肽(γ-L-谷氨酰-L-半胱氨酰-甘氨酸)的新方法. 首先由手性助剂——2-[N-(N’-苄基-脯氨酰)氨基]二苯甲酮(1)、六水合氯化镍和L-谷氨酸反应, 得到谷氨酸席夫碱Ni(II)配合物2, 产率为98%; 进而采用二异丙基碳二亚胺(DIC)/1-羟基-苯并三氮唑(HOBt)复合缩合剂法与S-苄基-L-半胱氨酸反应, 得到S-苄基-γ-L-谷氨酰-L-半胱氨酸席夫碱Ni(II)配合物3, 产率为90%; 接着同样采用DIC/HOBt复合缩合剂法与甘氨酸反应, 得到S-苄基-γ-L-谷氨酰-L-半胱氨酰-甘氨酸席夫碱Ni(II)配合物4, 产率为95%; 然后稀酸水解配合物4, 得到S-苄基-γ-L-谷氨酰-L-半胱氨酰-甘氨酸(5), 产率为70%; 最后采用甲酸铵催化转移氢化脱除S-苄基, 得到谷胱甘肽(6), 产率为87%. 中间产物和终产物的结构经由旋光, 1H NMR, 13C NMR和HRMS表征.     

肽的研究 Ⅰ.带保护基的胰岛素A鏈氨端五肽的合成

本文报告三种带不同保护基的胰岛素A键氨端五肽的合成。它们是N-苄氧羰基甘氨酰-异亮氨酰-缬氨酰-γ-甲酯-谷氨酰-谷氨酰胺(Ⅰ)、N-苄氧羰基甘氨酰-异亮氨酰-缬氨酰-γ-甲酯-谷氨酰-谷氨酰胺酰肼基甲酸叔丁酯(Ⅱ)和N-苄氧羰基甘氨酰-异亮氨酰-纈氨酰-谷氨酰-谷氨酰胺甲酯(Ⅲ)。五肽Ⅰ是由初次合成的N-苄氧羰基甘氨酰-异亮氨酰-纈氨酸(Ⅵ)与γ-甲酯-谷氨酰-谷氨酰胺(Ⅸ)经羧酸碳酸混合酸酐法,或Ⅵ的酰肼衍生物与Ⅸ经迭氮化物法缩合而成。五肽Ⅱ是由Ⅵ与γ-甲酯-谷氢酰-谷氨酰胺酰肼基甲酸叔丁酯(Ⅺ)经混合酸酐法合成。五肽Ⅲ则系用活化酯法由谷氨酰胺甲酯的氨端开始,逐步与相应的N-保护的氨基酸对硝基苯酯缩合、延伸而得。在用混合酸酐法合成五肽Ⅰ中,从反应混合物分离得N-苄氧羰基甘氯酰-异亮氨酰-D-纈氨酸(ⅩⅫ)。由ⅩⅫ与Ⅸ合成五肽Ⅰ的立体异构体,N-苄氧羰基甘氨酰-异亮氢酰-D-纈氨酰-γ-甲酯-谷氨酰一谷氨酰胺(ⅩⅩⅢ)。由N-苄氧羰基-γ-甲酯-谷氧酰-谷氨酰胺酰肼基甲酸叔丁酯(Ⅹ)经脱去酰肼上的保护基后,用迭氮法与S-苄基-半胱氨酰-S-苄基-半胱氨酸缩合而得N-苄氧羰基-γ-甲酯-谷氨酰-谷氨酰胺酰-S-苄基-半胱氨酰-S-苄基-半胱氨酸(四肽ⅩⅩⅤ)。五肽Ⅰ、Ⅱ、Ⅲ,四肽ⅩⅩⅤ及其主要的合成中间肽的光学纯度均经亮氨酸氨肽酶、胰羧肽酶法或旋光法检定。在五肽的酶水解的条件下有部分的谷氨酰胺和谷氨酸变为四氢吡咯酮-(5)-羧酸-(2),致使该二氨基酸的测定值偏低。     

肽的研究——Ⅴ.新的带保护基牛胰岛素A链氨端五肽和九肽的合成

本文叙述带保护基的牛胰岛素A链氨端五肽Ⅰ(N-苄氧羰基甘氨酰-异亮氨酰-缬氨酰-γ-叔丁酯谷氨酰-谷氨酰胺酰肼基甲酸叔丁酯)及九肽Ⅱ(N-苄氧羰基甘氨酰-异亮氨酰-缬氨酰-谷氨酰-谷氨酰胺酰-S-苄基半胱氨酰-S-苄基半胱氨酰-丙氨酰-丝氨酰脐)的合成。Ⅰ是由已知三肽Ⅲ(N-苄氧羰基异亮氨酰-缬氨酰-γ-叔丁酯谷氨酸乙酯)经二种不同的合成步骤分别缩合而得,五肽Ⅰ经三氟乙酸脱去γ-叔丁基和N-叔丁氧羰基后与已知四肽Ⅷ(S-苄基半胱氨酰-S-苄基半胱氨酰-丙氨酰-O-乙酰丝氨酸甲酯溴氢酸盐)借迭氮法缩合而得九肽酯Ⅸ再经肼解而得九肽肼Ⅱ。合成的三肽、四肽、五肽和九肽的化学纯度曾经纸层析、纸电泳、元素分析及氨基酸组成分析证明,其光学纯度(除九肽Ⅱ和Ⅸ外)皆曾经亮氨酸氨肽酶水解及水解物的氨基酸组成测定证明为L型,九肽Ⅸ是由光学纯L型的肽Ⅰ与Ⅷ经迭氦法缩合而成,因此Ⅸ以及Ⅱ很可能为光学纯L型。     

肽的研究 Ⅳ.带保护基的牛胰岛素A链羧基末端十二肽及十六肽的合成

本文报告带保护基的牛胰岛素A链羧端的十二肽Ⅰ(N-苄氧羰基缬氨酰-S-苄基半胱氨酰-丝氨酰-亮氨酰-酪氨酰-谷氨酰胺酰-亮氨酰-γ-甲酯谷氨酰-天冬酰胺酰-酪氨酰-S-苄基半胱氨酰-天冬酰胺甲酯)和十六肽Ⅱ(N-苄氧羰基-S-苄基半胱氨酰-S-苄基半胱氨酰-丙氨酰-丝氨酰-缬氨酰-S-苄基半胱氨酰-丝氨酰-亮氨酰-酪氨酰-谷氨酰胺酰-亮氨酰-γ-甲酯谷氨酰-天冬酰胺酰-酪氨酰-S-苄基半胱氨酰-天冬酰胺甲酯)的合成. 肽Ⅰ和Ⅱ是由前文合成的带保护基的九肽Ⅳ(N-苄氧羰基亮氨酰-酪氨酰-谷氨酰胺酰-亮氨酰-γ-甲酶谷氨酰-天冬酰胺酰-酪氨酰-S-苄基半胱氨酰-天冬酰胺甲酯)经溴化氢-乙酸法脱去N-保护基后按迭氮化合物法分别与三肽酰肼Ⅴ(N-苄氧羰基缬氨酰-S-苄基半胱氨酰-丝氨酰肼)和七肽酰肼Ⅷ(N-苄氧羰基-S-苄基半胱氨酰-S-苄基半胱氮酰-丙氨酰-丝氨酰-缬氨酰-S-苄基半胱氨酰-丝氨酰肼)缩合而得. 肽Ⅰ和Ⅱ经元素分析及氨基酸组成分析证明为分析纯.由于它们是由光学纯L型的肽Ⅳ,Ⅴ,Ⅷ等经迭氮化合物法缩合而成,因此肽Ⅰ和Ⅱ很可能皆为光学纯L型.肽Ⅰ能被亮氨酸氨肽酶水解为相应的组成氨基酸而不留显著的茚三酮阳性的残肽.     

模拟谷胱甘肽过氧化物酶活性三肽的合成及表征

用Ｂ，Ｂ－二氟硼杂唑烷酮保护谷氨酸的α－氨基和α－羧基，通过液相合成法制得谷氨酰－γ－丝氨酰－甘氨酸三肽。结合苯甲基磺酰氟（ＰＭＳＦ）与硒化氢（Ｈ２Ｓｅ）的突变，再经纯化制得具有谷胱甘肽过氧化物酶活性的三肽模拟物，即γ－谷氨酰－硒代半腕氨酰－甘氨酸。元素分析、氨基酸分析均证明了两种三肽的结构。电子能谱技术分析测得硒的价态及含量。     

含半胱氨酸多肽的研究——Ⅲ.牛胰岛素A链带保护基的氨端九肽的合成

本文报告带保护基的牛胰岛素A链氨端九肽酯■和相应的九肽酰肼■与九肽酸■的合成.苄氧羰基甘氨酰-异亮氨酰-缬氨酰-γ-叔丁酯谷氨酸乙酯(III)分别由已知的苄氧羰基缬氨酰-γ-叔丁酯谷氨酸乙酯经催化氢解法脱去N-保护基后与苄氧羰基甘氨酰-异亮氨酰肼(VIII)按迭氮化合物法缩合,以及由已知的苄氧羰基甘氨酰-异亮氨酰-缬氨酸(VIII)与γ-叔丁酯谷氨酸乙酯按碳二亚胺法合成.III经肼解或皂化分别得四肽酰肼■和四肽酸■.苄氧羰基谷氨酰胺酰-S-苄基半胱氨酰-S-苄基半胱氨酰-丙氨酰-O-乙酰丝氨酸甲酯(V)分别由已知的苄氧羰基-S-苄基半胱氨酰-S-苄基半胱氨酰-丙氨酰-丝氨酸甲酯XII_a或苄氧羰基-S-苄基半胱氨酰-S-苄基半胱氨酰-丙氨酰-O-乙酰基丝氨酸甲酯XII以溴化氢-乙酸脱去N-保护基后与苄氧羰基谷氨酰胺对硝基苯酯(XIII)按活化酯法缩合而得.如以溴化氢-三氟乙酸脱去XIIa的N-保护基后与XIII按活化酯法缩合则得Va,合成Va的另一方法是将已知的苄氧羰基谷氨酰胺酰-S-苄基半胱氨酰-S-苄基半胱氨酰肼XIV通过迭氮化物法与丙氨酰-丝氨酸甲酯(X)缩合而得.五肽V经溴化氢-乙酸脱去N-保护基后与四肽酰肼IV或四肽酸IV_a分别通过迭氮化物法和碳二亚胺法缩合得到同一的九肽甲酯(I).化合物I用三氟乙酸脱去叔丁酯后肼解得九肽肼(II).化合物I经皂化得相应的九肽酸IIa.     

肽的研究——Ⅱ.带保护基的胰岛素A鏈羧端九肽的合成

本文报告带保护基的胰島素A鏈羧端九肽Ⅰ(N-苄氧羰基亮氨酰-酪氨酰-谷氨酰胺酰-亮氨酰-γ-甲酯-谷氨酰-天冬酰胺酰-酪氨酰-S-苄基半胱氨酰-天冬酰胺甲酯)的合成。Ⅰ是由N-苄氧羰基亮氨酰-酪氨酰-谷氨酰胺酰-亮氨酸(四肽Ⅱ)和由N-苄氧羰基-γ-甲酯谷氨酰-天冬酰胺酰-酪氨酰-S-苄基牛胱氨酰-天冬酰胺甲酯(五肽Ⅲ)脫N-保护基所得氨端自由的五肽(Ⅲa)經二环己基碳二亚胺法縮合而成。四肽Ⅱ和五肽Ⅲ分別由二种不同方法合成。多肽Ⅰ,Ⅱ和Ⅲ皆經元素分析、紙层析、紙电泳、酶水解分析証明系純粹,均一的L-型。在合50％的二甲基亚碸的三(羥甲基)甲胺緩冲液中亮氨酸氨肽酶仍能将脫N-保护基的四肽与九肽完全水解为相应的氨基酸。     

288.15, 298.15和308.15 K温度条件下甘氨酰甘氨酸在蔗糖-水混合溶剂中的体积性质研究

利用Anton Paar DMA55精密数字密度计测定了288.15, 298.15和308.15 K甘氨酰甘氨酸在蔗糖-水混合溶剂中的密度, 计算了甘氨酰甘氨酸的表观摩尔体积VΦ和极限偏摩尔体积 , 得到了其由纯水溶剂转移至混合溶剂中的迁移偏摩尔体积Δtrs 和理论水化数Nh．根据共球交盖模型, 讨论了迁移偏摩尔体积和水化数的变化规律．结果表明, 甘氨酰甘氨酸带电中心与蔗糖之间的结构相互作用对其迁移体积有正贡献, 且占主导地位．甘氨酰甘氨酸的迁移偏摩尔体积为正值, 且随着蔗糖浓度的增大而增大; 理论水化数随温度升高、蔗糖浓度的增大而减小; 温度升高, 极限偏摩尔体积增大, 迁移偏摩尔体积变化很小．     

298.15 K甘氨酰二肽在乙酸钠水溶液中的体积性质

测定了298.15 K三种甘氨酰二肽(甘氨酰甘氨酸、甘氨酰-L-缬氨酸和甘氨酰-L-亮氨酸)在0.5, 1.0, 1.5和2.0 mol•kg－1乙酸钠水溶液中的密度, 计算了这些肽在乙酸钠水溶液中的表观摩尔体积, 标准偏摩尔体积, 标准偏摩尔转移体积, 理论水化数和体积相互作用参数. 结果表明: 甘氨酰二肽的标准偏摩尔体积和标准偏摩尔转移体积均随乙酸钠浓度的增加而增大, 溶液中离子与肽带电基团/甘氨酰基团(CH2CONH)之间的相互作用大于离子与肽的非极性基团间的相互作用, 乙酸钠和甘氨酰二肽之间主要是对相互作用. 利用共球交盖模型对所研究的肽与乙酸钠之间的体积相互作用进行了解释. 利用氨基酸的标准偏摩尔体积值, 对二肽的标准偏摩尔体积进行了估算, 发现计算值与实验值一致.     

Synthesis of protected 2-pyrrolylalanine for Peptide chemistry and examination of its influence on prolyl amide isomer equilibrium

Protected enantiopure 2-pyrrolylalanine was synthesized for application in peptide science as an electron-rich arylalanine (histidine) analog with π-donor capability. (2S)-N-(Boc)-N'-(Phenylsulfonyl)-, (2S)-N,N'-bis-(phenylsulfonyl)-, and (2S)-N,N'-bis-(Boc)-3-(2-pyrrolyl)alanines (10, 3, and 14, respectively) were made in 13-17% overall yields and six to seven steps from oxazolidine β-methyl ester 4. Homoallylic ketone 5 was prepared by a copper-catalyzed cascade addition of vinylmagnesium bromide to ester 4 and converted to pyrrolyl amino alcohol 7 by olefin oxidation and Paal-Knorr condensation. Protecting group shuffle and oxidation of the primary alcohol enabled the synthesis of pyrrolylalanines. The bis-Boc analog 14 proved useful in peptide chemistry and was employed to make N-acetyl-pyrrolylalaninyl-proline N'-methylamide 25. A study of the influence of the pyrrole moiety on the prolyl amide isomer equilibrium of 25 using (1)H NMR spectroscopy in chloroform, DMSO, and water demonstrated that the pyrrolylalanine peptide exhibited behavior and conformations different from those of other arylalanine analogs.     

Efficient Access to Enantiopure γ4‐Amino Acids with Proteinogenic Side‐Chains and Structural Investigation of γ4‐Asn and γ4‐Ser in Hybrid Peptide Helices

Hybrid peptides composed of α‐ and β‐amino acids have recently emerged as new class of peptide foldamers. Comparatively, γ‐ and hybrid γ‐peptides composed of γ⁴‐amino acids are less studied than their β‐counterparts. However, recent investigations reveal that γ⁴‐amino acids have a higher propensity to fold into ordered helical structures. As amino acid side‐chain functional groups play a crucial role in the biological context, the objective of this study was to investigate efficient synthesis of γ⁴‐residues with functional proteinogenic side‐chains and their structural analysis in hybrid‐peptide sequences. Here, the efficient and enantiopure synthesis of various N‐ and C‐terminal free‐γ⁴‐residues, starting from the benzyl esters (COOBzl) of N‐Cbz‐protected (E)‐α,β‐unsaturated γ‐amino acids through multiple hydrogenolysis and double‐bond reduction in a single‐pot catalytic hydrogenation is reported. The crystal conformations of eight unprotected γ⁴‐amino acids (γ⁴‐Val, γ⁴‐Leu, γ⁴‐Ile, γ⁴‐Thr(OtBu), γ⁴‐Tyr, γ⁴‐Asp(OtBu), γ⁴‐Glu(OtBu), and γ‐Aib) reveals that these amino acids adopted a helix favoring gauche conformations along the central C^γ? C^β bond. To study the behavior of γ⁴‐residues with functional side chains in peptide sequences, two short hybrid γ‐peptides P1 (Ac‐Aib‐γ⁴‐Asn‐Aib‐γ⁴‐Leu‐Aib‐γ⁴‐Leu‐CONH₂) and P2 (Ac‐Aib‐γ⁴‐Ser‐Aib‐γ⁴‐Val‐Aib‐γ⁴‐Val‐CONH₂) were designed, synthesized on solid phase, and their 12‐helical conformation in single crystals were studied. Remarkably, the γ⁴‐Asn residue in P1 facilitates the tetrameric helical aggregations through interhelical H bonding between the side‐chain amide groups. Furthermore, the hydroxyl side‐chain of γ⁴‐Ser in P2 is involved in the interhelical H bonding with the backbone amide group. In addition, the analysis of 87 γ⁴‐residues in peptide single‐crystals reveal that the γ⁴‐residues in 12‐helices are more ordered as compared with the 10/12‐ and 12/14‐helices.     

Can a consecutive double turn conformation be considered as a peptide based molecular scaffold for supramolecular helix in the solid state?

Helices and sheets are ubiquitous in nature. However, there are also some examples of self-assembling molecules forming supramolecular helices and sheets in unnatural systems. Unlike supramolecular sheets there are a very few examples of peptide sub-units that can be used to construct supramolecular helical architectures using the backbone hydrogen bonding functionalities of peptides. In this report we describe the design and synthesis of two single turn/bend forming peptides (Boc-Phe-Aib-Ile-OMe 1 and Boc-Ala-Leu-Aib-OMe 2) (Aib: α-aminoisobutyric acid) and a series of double-turn forming peptides (Boc-Phe-Aib-Ile-Aib-OMe 3, Boc-Leu-Aib-Gly-Aib-OMe 4 and Boc-γ-Abu-Aib-Leu-Aib-OMe 5) (γ-Abu: γ-aminobutyric acid). It has been found that, in crystals, on self-assembly, single turn/bend forming peptides form either a supramolecular sheet (peptide 1) or a supramolecular helix (peptide 2), unlike self-associating double turn forming peptides, which have only the option of forming supramolecular helical assemblages.     

Searching for new cell-penetrating agents: hybrid cyclobutane-proline γ,γ-peptides

Two generations of hybrid γ,γ-peptides containing cyclobutane amino acids and cis-γ-amino-L-proline joined in alternation have been synthesized and their capacity to cross the eukaryotic cell membrane has been evaluated. The first generation consists of di-, tetra- and hexapeptides, and their properties have been analyzed as well as the influence of peptide length and chirality of the cyclobutane residues. Results have shown that the absolute configuration of the cyclobutane amino acid does not have a relevant influence. The second generation consists of hybrid γ,γ-hexapeptides with a common backbone and distinct side chains introduced with different linkage types through the α-amino group (N(α)) of the proline monomers. These peptides have been shown to be non-toxic towards HeLa cells and to internalize them effectively, the best results being obtained for the peptides with a spacer of five carbons between the N(α) atom and the guanidinium group. The introduction of cyclobutane residues inside the sequence affords a good balance between charge and hydrophobicity, reducing the number of positive charges. This results in lower toxicity and similar cell-uptake properties when compared to previously described peptide agents.     

Application of DEPBT on the Synthesis of the Protected Dipeptides Containing Histidine with Unprotected Imidazole Group by Solution Method

3- (Diethoxyphosphoryloxy)- 1,2,3-benzotriazln-4 (3H)-one (DE-PBT) was an organophosphorus coupling reagent developed by our group. It was an effective coupling reagent for the synthesis of protected peptides containing Tyr, Ser and Thr with unprotected hydroxy group on their side chain. The further study of the synthesis of a series of protected dipeptides containing hisfidine with unprotected imidazole group using DEPBT is reported. During the synthetic procedure, the imidazole group of histidine did not need to be protected. When the carboxyl components were N-protected aromatic amino acids or basic amino acids, the yields were relatively high (63%--81%). However,when the carboxyl components were N-protected acidic amino acids, the yields were relatively low (47%--48%). The results expanded the application of DEPBT on the synthesis of bioactive peptides containing histidine.     

Preparation of DL-N-benzyloxycarbonyl-gamma-carboxy-glutamic acid-gamma, gamma'-di-t-butyl-alpha-methyl ester, a suitable derivative for peptide synthesis with the new aminotricarboxylic acid from prothrombin]

The first synthesis of a selectively, fully protected derivative of the new aminotricarboxylic acid found in prothrombin and other homologous blood-clotting factors, γ-carboxy-glutamic acid (Gla), is described. The compound DL -N-benzyloxycarbonyl-γ-carboxy-glutamic acid γ,γ′-di-t-butyl-γ-methyl-ester is potentially useful for peptide synthesis. The free amino-acid (DL -Gla) and DL -pyro-γ-carboxy-glutamic acid dimethyl-ester were also prepared.     

非手性PNNP型钌配合物催化仲醇的外消旋化研究

制备了两种非手性PNNP型钌配合物Ru(BF4)2P2N2(3a,P2N2=N,N'-双-[邻-(二苯基膦)苯哑甲基]乙二胺)和Ru(BF4)2P2H4(3b,P2N2H4=N,N'-双-[邻-(二苯基膦)苯甲基]乙二胺),并以(R)-苯乙醇的消旋化为探针反应,分别考察了添加剂、溶剂、催化剂用量及温度等对两种钌配合物催化反应的影响,得到了较理想的反应条件,即4%3a,2 mL甲苯,lequiv.Ag2O,70℃下,在氮气保护下反应12 h.反应结果发现钌配合物3a可以较好地催化仲醇的消旋化,其中(R)-和(S)-苯乙醇消旋化反应后,ee都为58%;另外(S)-对甲基苯乙醇和(S)-对氟苯乙醇消旋化反应后,ee值分别为85%和71%.并初步试探了以苯乙醇为探针底物,钌配合物结合脂肪酶Candida antarctica催化的动态动力学拆分.     

Effectiveness of the suzuki-miyaura cross-coupling reaction for solid-phase peptide modification

The Suzuki-Miyaura (SM) cross-coupling reaction has recently become one of the most efficient methods for C-C bond construction opening a wide range of opportunities in organic synthesis. This study focused on the evaluation of the use of the SM reaction to modify peptides using a solid-phase synthesis approach, an avenue that was still not investigated intensively. We used as a peptide model [Ala (1,2,3), Leu (8)]Enk linked to a polystyrene support on which it was previously assembled. The aromatic residues Tyr (4) and Phe (7) of [Ala (1,2,3), Leu (8)]Enk were respectively substituted with p-iodo-Phe, and an SM-related strategy was developed. Results indicated that the reaction conditions involving K 3PO 4 or Na 2CO 3 (base), DMF (solvent), Pd(PPh 3) 4 (catalyst), and temperatures ranging from 50 to 80 degrees C during 20 h were found as optimal. Finally applying those optimal conditions, a series of [Ala (1,2,3), Leu (8)]Enk analogs modified at Tyr (4) or Phe (7) positions was synthesized using diverse boronic acid derivatives.     

Effect of cobalt precursors on the dispersion, reduction, and CO oxidation of CoO(x)/γ-Al2O3 catalysts calcined in N2

The present work tentatively investigated the effect of cobalt precursors (cobalt acetate and cobalt nitrate) on the physicochemical properties of CoO(x)/γ-Al(2)O(3) catalysts calcined in N(2). XRD, Raman, XPS, FTIR, and UV-vis DRS results suggested that CoO/γ-Al(2)O(3) was obtained from cobalt acetate precursors and CoO was dispersed on γ-Al(2)O(3) below its dispersion capacity of 1.50 mmol/(100 m(2) γ-Al(2)O(3)), whereas Co(3)O(4)/γ-Al(2)O(3) was obtained from cobalt nitrate precursors and Co(3)O(4) preferred to agglomerate above the dispersion capacity of 0.15 mmol/(100m(2) γ-Al(2)O(3)). Compared with Co(3)O(4)/γ-Al(2)O(3), CoO/γ-Al(2)O(3) catalysts were difficult to be reduced and easy to desorb oxygen species at low temperatures and presented high activities for CO oxidation as proved by H(2)-TPR, O(2)-TPD, and CO oxidation model reaction results. A surface incorporation model was proposed to explain the dispersion and reduction properties of CoO/γ-Al(2)O(3) catalysts.