手性亚砜合成*

手性亚砜及其衍生物广泛作为重要手性中间体和辅剂、手性配体和催化剂、手性药物。手性亚砜可以采用生物方法和化学方法来合成,化学方法包括手性辅剂诱导、手性氧化剂氧化、手性拆分和不对称催化等。本文简要综述了手性亚砜的各种用途和各种合成方法的研究进展,主要介绍了钛和钒催化的不对称硫醚氧化反应,也介绍了作者最近在钒催化的不对称硫醚氧化反应方面所做的研究工作。     

蜈蚣毒素多肽RhTx的高效化学合成及复性折叠研究

二硫键的氧化折叠是合成二硫键构象锁定多肽的关键步骤.前人发展的二硫键氧化折叠策略主要有一次氧化折叠、多次氧化折叠和一锅法氧化折叠.目前对三种策略复性效率和收率等的比较性研究较少.分别采用三种氧化折叠策略制备目标蜈蚣毒素多肽RhTx.结果表明,两次氧化折叠策略的分离收率高于一次和一锅法氧化折叠策略,一锅法氧化折叠策略可能会导致较大比例的错误折叠.探索了数十毫克量级RhTx的高效制备方法,为进一步探索RhTx靶向TRPV1的结构机制等研究提供了工具分子.此外,对三种氧化折叠策略进行了系统比较,为二硫键构象锁定多肽的合成提供了参考.     

糖类化合物中羟基的常用氧化方法

介绍了在糖化学中常用的几种氧化方法，包括二甲亚砜法，改进ＰＤＣ法，金属有机锡／溴法，碘化法等。参考文献９篇。     

过氧化氢选择性氧化硫醚的研究进展

亚砜和砜类化合物具有广谱生物活性而有广泛的应用前景,同时作为有机合成的重要中间体广泛应用于碳-碳键形成、分子重组反应中.硫醚直接氧化是制备亚砜和砜的主要方法之一.在众多关于硫醚选择性氧化反应的研究中,过氧化氢作为清洁氧化剂备受关注.鉴于此,就过氧化氢选择性氧化硫醚反应中的重要金属催化体系和一些非金属催化体系的研究状况作一综述,简要介绍各类催化氧化体系的催化效果.     

亚砜的合成及其含量的确定

亚砜类物质是重要的化工原料,在医药、冶金和合成等方面得到广泛应用.为了研究亚砜在贵金属中的萃取机理,实验合成了对称及不对称的亚砜,本文介绍了一种不对称亚砜的合成及其结构表征.并用MS、FT-IR、1H NMR和13C NMR手段确定了它的结构是正丁基正辛基亚砜(BOSO).在合成中,亚砜易氧化成砜,不易控制,在硫醚氧化生成亚砜与砜后,必须有简捷的方法测出它们的含量,以便优化合成条件,减少生成砜的副反应,提高亚砜的产率,并保证所获亚砜的纯度.传统的方法是利用自动电位滴定法测定亚砜硫含量[1],此方法烦琐,时间长,重复性差;近年来也有用气液色谱[2],其原理是用内标法,实验条件要求是易挥发,难分解的样品,但此方法标样不易获得,并且样品要求高.1H NMR方法的原理是:积分曲线面积与引起该组峰的核数成正比关系,其优点是,不需要引进任何校正因子或绘制工作曲线,可直接根据各共振峰的积分面积的比值,得到两者含量之比,并且在有其他杂质存在且不与亚砜和砜的特征峰相重合的情况下,采用标准加入法可得到亚砜和砜的各自含量.为此,本文介绍了在BOSO的合成中的应用实例.     

选择性氧化形成三对二硫键合成齐考诺肽

利用不同保护基保护的巯基的氧化反应性不同,分别以空气和碘作为氧化剂,通过选择性氧化工艺使齐考诺肽线性肽的1,8,16,20-位两对Trt保护巯基先形成两对二硫键,然后用碘氧化15,25-位Acm保护的巯基,成功地生成第三对二硫键,合成了齐考诺肽.     

蛋氨酸亚砜还原酶的结构特征及与神经退行性疾病的关系

蛋氨酸易被氧化为蛋氨酸亚砜,使生物体中氧化还原平衡失调,诱发各种疾病.蛋氨酸亚砜还原酶(Msrs)能将蛋氨酸亚砜还原成蛋氨酸,恢复蛋白的结构与功能,对调控多种氧化应激相关疾病具有重要作用.本文结合本课题组的研究结果,介绍了Msrs的分类进化、结构特征、催化机理和基因工程表达;综述了Msrs与衰老、帕金森病和阿尔茨海默病的关系,以探讨有关Msrs研究的发展方向和应用前景.     

高分子亚砜树脂的合成及XPS方法对萃金机理的研究

对氯甲基聚本乙烯树脂进行改性,与硫醇化合物反应氧化合成一种高分子亚砜树脂化合物,用FT-IR、XPS等方法表征了该化合物的结构组成.将亚砜物质直接用于含Au溶液的萃取,萃取率达95%.用一种新的研究方法XPS法研究了萃取机理.该亚砜树脂具有性能稳定、合成简便、固定相单一、萃取率高等特点.     

半选择性氧化形成三对二硫键合成利那洛肽

利用Fmoc固相合成策略,Wang树脂为载体,使用三苯甲基(Trt)和乙酰胺甲基(Acm)保护基的半胱氨酸合成了3条[4 Trt+2 Acm]和3条[2 Trt+4 Acm]利那洛肽的线性前体化合物.在此基础上,采用半选择性氧化策略合成含有三对二硫键的利那洛肽.首先使用含三氟乙酸(TFA)的裂解剂脱除线性前体肽中半胱氨酸的Trt保护基,并使用氯化血红素催化氧化半胱氨酸自由巯基形成二硫键.下一步使用Ph S(O)Ph/CH3Si Cl3试剂体系脱除剩余保护半胱氨酸的Acm保护基,并同时形成二硫键.使用这种策略,在6条线性前体肽中,有3条可以得到利那洛肽,转化率分别为71.9%、31.5%、81.4%.通过分析6条线性前体肽中二硫键形成的先后顺序对目标产物生成的影响,发现二硫键Cys5-Cys13的形成对利那洛肽的氧化折叠非常关键,在选择性氧化合成利那洛肽时应当优先形成这对二硫键.     

氯化血红素催化氧化巯基形成二硫键

对氯化血红素催化氧化巯基形成二硫键的反应进行了研究,发现N,N-二异丙基乙胺(DIEA)的加入可以提高氯化血红素的催化活性,并降低其在氧化过程中的自聚现象.在室温及少量DIEA存在下,将氯化血红素和巯基乙酸甲酯按摩尔比1∶4混合于p H=8.0的水溶液中,敞口搅拌反应20 min,可以催化空气氧化90%的巯基乙酸甲酯形成相应的分子间二硫键产物.该催化氧化体系还可应用于多肽合成中,在相同条件下,只需2 h即可完成还原型催产素和利那洛肽的氧化环合,生成高产率的催产素和利那洛肽环肽.与传统的氧化方法相比,氯化血红素催化氧化的方法具有高效、环保的优点,为多肽合成中二硫键的形成提供了一种新方法.     

The Action of Carbon Disulfide and Sulfur on Enamines,Ketimines, and CH Acids

The reaction of sulfur, carbon disulfide, and enamines at room temperature leads mainly or exclusively to 3H-1,2-dithiole-3-thiones; these are occasionally accompanied by 2H-1,3-dithiole-2-thiones, which can also be prepared by a modified procedure. Many enamines react with sulfur at room temperature to form thioamides. At about 50°C, enamines of acetophenone give 2-benzylidene-4-phenyl-2H-1,3-dithiol. The action of isothiocyanates and sulfur on enamines leads to the formation of thiazolidine-2-thiones. 2H-Thiopyran-2-thiones can be prepaAred from enamines or dienamines with carbon disulfide at room temperature. The reaction of ketimines (Schiff bases) with carbon disulfide and sulfur yields 3H-1,2-dithiole-3-thiones or isothiazoline-5-thiones. The reaction of alkynes with sulfur and carbon disulfide leads to 2H-1,3-dithiole-2-thiones. Nitriles containing active methylene groups react with carbon disulfide and sulfur to form 5-amino-3H-1,2-dithiole-3-thiones. When isothiocyanates are used instead of CS₂, the reaction leads to δ⁴-4-amino-thiazoline-2-thiones.     

Kinetic analyses of disulfide formation between thiol groups attached to linear poly(acrylamide)

Kinetic analyses were carried out for formation of disulfide crosslinkages between thiol groups on linear polymers, poly(acrylamide‐co‐N‐acrylcysteamine) (P‐SH). Disulfide crosslinkages were formed by auto‐oxidation of pendant thiol groups or through the thiol‐disulfide exchange reaction induced by addition of disulfide compounds gluthathione. In the auto‐oxidation reaction, the rate constant for disulfide formation highly depended on pH values of the reaction mixtures and the P‐SH concentrations. Gelation rate is too slow to enclose living cells into hydrogel under physiological pH 7.4. The hydrogel formation rate can be accelerated by addition of disulfides, such as oxidized glutathione. In the later case, oxygen in the reaction mixture is not consumed. The thiol‐disulfide exchange reaction is much more suitable for the cell encapsulation than the thiol auto‐oxidation reaction. These findings give a basis for enclosure of living cells in a hydrogel. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Multiple Disulfide-Bonded States of Native Proteins: Estimate of Number Using Probabilities of Disulfide Bond Formation

The polypeptide backbone of proteins is held together by two main types of covalent bonds: the peptide bonds that link the amino acid residues and the disulfide bonds that link pairs of cysteine amino acids. Disulfide bonds form as a protein folds in the cell and formation was assumed to be complete when the mature protein emerges. This is not the case for some secreted human blood proteins. The blood clotting protein, fibrinogen, and the protease inhibitor, α2-macroglobulin, exist in multiple disulfide-bonded or covalent states in the circulation. Thousands of different states are predicted assuming no dependencies on disulfide bond formation. In this study, probabilities for disulfide bond formation are employed to estimate numbers of covalent states of a model polypeptide with reference to α2-macroglobulin. When disulfide formation is interdependent in a protein, the number of covalent states is greatly reduced. Theoretical estimates of the number of states will aid the conceptual and experimental challenges of investigating multiple disulfide-bonded states of a protein.     

UV‐Induced Disulfide Formation and Reduction for Dynamic Photopatterning

UV‐induced disulfide formation (UV‐DF) and disulfide reduction (UV‐DR) reactions for surface functionalization and dynamic photopatterning are presented. Both photochemical reactions allow for the spatially and temporally controlled, reversible transition between thiol‐ and disulfide‐functionalized surfaces. The dynamic photopatterning strategy was demonstrated by the UV‐induced attachment, exchange, and detachment on thiol‐modified substrates.     

A small-molecule catalyst of protein folding in vitro and in vivo

BACKGROUND: The formation of native disulfide bonds between cysteine residues often limits the rate and yield of protein folding. The enzyme protein disulfide isomerase (PDI) catalyzes the interchange of disulfide bonds in substrate proteins. The two -Cys-Gly-His-Cys- active sites of PDI provide a thiol that has a low pKa value and a disulfide bond of high reduction potential (Eo'). RESULTS: A synthetic small-molecule dithiol, (+/-)-trans-1,2-bis(2-mercaptoacetamido)cyclohexane (BMC), has a pKa value of 8.3 and an Eo' value of -0.24 V. These values are similar to those of the PDI active sites. BMC catalyzes the activation of scrambled ribonuclease A, an inactive enzyme with non-native disulfide bonds, and doubles the yield of active enzyme. A monothiol analog of BMC, N-methylmercaptoacetamide, is a less efficient catalyst than BMC. BMC in the growth medium of Saccharomyces cerevisiae cells increases by > threefold the heterologous secretion of Schizosaccharomyces pombe acid phosphatase, which has eight disulfide bonds. This effect is similar to that from the overproduction of PDI in the S. cerevisiae cells, indicating that BMC, like PDI, can catalyze protein folding in vivo. CONCLUSIONS: A small-molecule dithiol with a low thiol pKa value and high disulfide Eo' value can mimic PDI by catalyzing the formation of native disulfide bonds in proteins, both in vitro and in vivo.     

PDI-Regulated Disulfide Bond Formation in Protein Folding and Biomolecular Assembly

Disulfide bonds play a pivotal role in maintaining the natural structures of proteins to ensure their performance of normal biological functions. Moreover, biological molecular assembly, such as the gluten network, is also largely dependent on the intermolecular crosslinking via disulfide bonds. In eukaryotes, the formation and rearrangement of most intra- and intermolecular disulfide bonds in the endoplasmic reticulum (ER) are mediated by protein disulfide isomerases (PDIs), which consist of multiple thioredoxin-like domains. These domains assist correct folding of proteins, as well as effectively prevent the aggregation of misfolded ones. Protein misfolding often leads to the formation of pathological protein aggregations that cause many diseases. On the other hand, glutenin aggregation and subsequent crosslinking are required for the formation of a rheologically dominating gluten network. Herein, the mechanism of PDI-regulated disulfide bond formation is important for understanding not only protein folding and associated diseases, but also the formation of functional biomolecular assembly. This review systematically illustrated the process of human protein disulfide isomerase (hPDI) mediated disulfide bond formation and complemented this with the current mechanism of wheat protein disulfide isomerase (wPDI) catalyzed formation of gluten networks.     

富含二硫键的小分子肽合成研究进展

综述了目前多肽合成领域构建2-3个二硫键的策略和对二硫键排列方式给予定位的方法。     

Preliminary mechanistic information on disulfide-bond formation and the role of hydrogen bonds by nanoelectrospray mass spectrometry

The formation of disulfide-bonds is vital for the proper folding of most secreted proteins and the stabilization of the final protein structure, including many of medical importance. The determination of disulfide-bonds is an important aspect of gaining a comprehensive understanding of the chemical structure of a protein. A long-term goal of ours is to examine the mechanism of disulfide-bond formation in aqueous solution and the potential role hydrogen bonds play in this process. Here, we report preliminary results from a method that utilizes the oxidizing power of iodine to generate disulfide bonds from synthesized model compounds, which is followed by nanoelectrospray ionization (nanoESI)- mass spectrometry (MS). By continuously monitoring the reaction mixture during disulfide formation, this nanoESI approach provides insight on the sequence of intermediate species formed, and how hydrogen-bonding donor/acceptor pairs may promote disulfide bond formation.     

A Diaminodiacid (DADA) Strategy for the Development of Disulfide Surrogate Peptides

Disulfide bond‐containing peptides are useful molecular scaffolds with diagnostic and therapeutic applications due to their good biological activity and good target selectivity, but their utility is sometimes limited by the lability of the disulfide moiety under reducing conditions and in the presence of disulfide bond isomerase. The development of disulfide surrogates with improved redox stability has been an area of ongoing research; and one possible strategy is based on a diaminodiacid (DADA) moiety, which can be used to synthesize the disulfide bond replacement peptides with precise structures and enhanced stability through automated solid‐phase peptide synthesis (SPPS). This review summarizes recent developments in the DADA‐based SPPS of peptide disulfide surrogates. Some representative applications and structural studies on the DADA‐based disulfide surrogates are described.     

In silico identification of the protein disulfide isomerase family from a protozoan parasite

Protein disulfide isomerase (PDI) enzymes are eukaryotic oxidoreductases that catalyze the correct formation of disulfide bonds during protein folding. Structurally they are characterized by the presence of functional thioredoxin-like (Trx) domains. For the protozoan parasite causative of the human amebiasis (Entamoeba histolytica), the correct formation of disulfide bonds is important for an accurate folding of its proteins, including some virulence factors. However, little is known about the enzymes involved in this mechanism. We undertook a post-genomic approach to identify the PDI family of this parasite. The genome database survey revealed a set of 11 PDI-encoding sequences with predictable protein thiol/disulfide oxidoreductase activities.