Sugar-assisted glycopeptide ligation

The chemical synthesis of glycopeptides and glycoproteins from readily available materials presents an attractive route to homogeneous products for structural and functional studies. Chemical synthesis of glycopeptides and glycoproteins based on native chemical ligation represents one of the useful methods for the synthesis of natural glycopeptide structures. Here we describe a method that allows for the synthesis of glycopeptides from cysteine-free peptides. This method utilizes a peptide thioester and a glycopeptide in which the sugar moiety is modified with a thiol handle at the C-2 position. Upon completion of the ligation reaction, the thiol handle can be reduced with H2/metal to the acetamide moiety, furnishing the unmodified glycopeptides. Together, this sequence of reactions displays an attractive potential in glycopeptides and glycoproteins synthesis.     

离子热法合成分子筛的研究进展

离子热法是以离子液体或低共熔混合物为介质的一种新型的分子筛合成方法, 它提供了一种离子态的独特合成环境, 为合成新型分子筛及研究分子筛的生成机理提供了机会. 本文综述了离子热法在分子筛合成方面取得的一些进展, 包括合成方法的创新、合成机理的研究、新材料的合成以及新型催化剂的制备等, 并展望了其发展前景.     

A short enantioselective synthesis of (+)-eleutherin, (+)-allo-eleutherin and a formal synthesis of (+)-nocardione B

A short enantioselective synthesis of (+)-eleutherin, (+)-allo-eleutherin and the formal synthesis of (+)-nocardione B is described. The synthesis is completed in six steps in overall yields of 8% for eleutherin and 14% for allo-eleutherin. The synthetic strategy features an efficient combination of the Dötz annulation reaction with a chiral alkyne and an oxa-Pictet Spengler reaction as the keys steps in the stereodivergent synthesis of (+)-eleutherin and (+)-allo-eleutherin. The synthesis of (S)-(+)-2-(2′-hydroxypropyl)-5-methoxy-1,4-naphthoquinone entails the formal synthesis of (+)-nocardione B.     

New perspective for natural products synthesis: concise synthesis of (+)-sch 642305 by chiral auxiliary multiuse methodology

The synthesis of (+)-Sch 642305 is an example of chiral auxiliary multiuse methodology, which shows a new perspective for the synthesis of compounds with multiple asymmetric centers. Thus, (+)-Sch 642305 was concisely synthesized from the known compound. Every reaction is stereoselective, and the chiral nonracemic hydrobenzoin worked as chiral auxiliary for desymmetrization of diene, as a template for attaining regio- and stereoselective reactions, as an oxygen source at the C4-position, and as a protecting group of hydroxyl functions. Namely, the chiral auxiliary played a role in every step throughout the synthesis. Furthermore, the synthesis contains a new protocol for obtaining alpha'-alkylated enone compounds.     

Intermediacy of silylene and germylene in direct synthesis of organosilanes and organogermanes

In the direct synthesis of silicon compounds by reactions of elemental silicon with methyl chloride, methanol and hydrogen chloride, silylene formed on surface of silicon grains during the reaction is an intermediate. The reaction of surface silylene with a variety of unsaturated hydrocarbons provides new direct synthesis of organosilanes. In the direct synthesis of methylchlorogermanes from elemental germanium, surface germylene is not an intermediate, while tetrachlorogermane is synthesized by the direct reaction of germanium with hydrogen chloride via dichlorogermylene intermediate. Various unsaturated hydrocarbons or organic chlorides added to the system of tetrachlorogermane synthesis give new methods for the synthesis of organogermanes.     

Directed evolution of new glycosynthases from Agrobacterium beta-glucosidase: a general screen to detect enzymes for oligosaccharide synthesis

BACKGROUND: Oligosaccharide synthesis is becoming increasingly important to industry as diverse therapeutic roles for these molecules are discovered. The chemical synthesis of oligosaccharides on an industrial scale is often prohibitively complex and costly. An alternative, that of enzymatic synthesis, is limited by the difficulty of obtaining an appropriate enzyme. A general screen for enzymes that catalyze the synthesis of the glycosidic bond would enable the identification and engineering of new or improved enzymes. RESULTS: Glycosynthases are nucleophile mutants of retaining glycosidases that efficiently catalyze the synthesis of the glycosidic linkage by condensing an activated glycosyl fluoride donor with a suitable acceptor sugar. A novel agar plate-based coupled-enzyme screen was developed (using a two-plasmid system) and used to select an improved glycosynthase from a library of mutants. CONCLUSIONS: Plate-based coupled-enzyme screens of this type are extremely valuable for identification of functional synthetic enzymes and can be applied to the evolution of a range of glycosyl transferases.     

The first total synthesis of +-ratjadone

The first total synthesis of ratjadone was achieved using a highly convergent approach joining three subunits together with a Wittig olefination and a selective Heck reaction as the pivotal steps. Besides establishing a robust and reliable route for the synthesis of this orphan ligand, the configuration of unknown stereocenters could also be determined. This synthesis not only provides an additional access to a biologically important compound but also enables the synthesis of structural analogues for biological target identification.     

Intermediacy of silylene and germylene in direct synthesis of organosilanes and organogermanes

In the direct synthesis of silicon compounds by reactions of elemental silicon with methyl chloride, methanol and hydrogen chloride, silylene formed on surface of silicon grains during the reaction is an intermediate. The reaction of surface silylene with a variety of unsaturated hydrocarbons provides new direct synthesis of organosilanes. In the direct synthesis of methylchlorogermanes from elemental germanium, surface germylene is not an intermediate, while tetrachlorogermane is synthesized by the direct reaction of germanium with hydrogen chloride via dichlorogermylene intermediate. Various unsaturated hydrocarbons or organic chlorides added to the system of tetrachlorogermane synthesis give new methods for the synthesis of organogermanes.     

Rapid synthesis of gold nanorods using a one-step photochemical strategy

Rapid synthesis of gold nanorods of controlled dimensions is one of the desired aspects of nanotechnology as a result of the potential of these nanomaterials for biomedical applications. The synthesis of gold nanorods has been achieved using a photoinitiator as an instant source of ketyl radicals, which allows the synthesis of gold nanorods in minutes. This is the first report providing a one-step synthesis of nanorods of controlled dimensions in 20-30 min using photoinitiator I-2959 as a source of ketyl radicals. Furthermore, the role of UV intensity, the concentration of silver ions, and the presence of cosolvents and a cosurfactant have been studied in detail in an effort to produce nanorods with controlled dimensions in higher yields. The role of acetone in nanorod synthesis has been explored in detail, and it has been demonstrated that, for the photochemical synthesis of nanorods using a photoinitiator, acetone is not a critical component and can be replaced by other water-miscible solvents, thus the successful synthesis of nanorods in tetrahydrofuran (THF) has been demonstrated. It has also been found that a cosurfactant and an organic solvent are not required for the synthesis of nanorods; however, their presence is found to improve the monodispersity of nanorod samples, in addition to providing a higher yield.     

Stereocontrolled synthesis and alkylation of cyclic beta-amino esters: asymmetric synthesis of a (-)-sparteine surrogate

A convenient method for the stereoselective synthesis of cyclic beta-amino esters from an iodo alphabeta-unsaturated ester and alpha-methylbenzylamine is described. Subsequent enolate generation and alkylation proceeds with complete stereocontrol, with the two stereogenic centres working together. In this way, a functionalised piperidine suitable for alkaloid natural product synthesis was prepared. The usefulness of the methodology is exemplified with the concise synthesis of a (-)-sparteine surrogate.     

Highly efficient diastereoselective biocatalytic acylation of a diastereotopic furanose diol and synthesis of key intermediates for amino derivatized bicyclonucleosides

The selectivity of Candida antarctica lipase has been demonstrated and employed in the manipulation of a diastereotopic furanose diol as the key step in the synthesis of a novel bicyclo 3-amino-3-deoxy furanose derivative, which is an important intermediate for the synthesis of bicyclic analogs of AZT. The asymmetrization of the diol has been achieved with preferred formation of a monoacylated product with 100% diastereoselectivity. An efficient synthesis of an intermediate in the synthesis of amino derivatized bicyclonucleosides is also described, two such novel compounds containing cycloamino residues have been prepared.     

A New Method of Low Temperature Methanol Synthesis

Low temperature methanol synthesis is a promising technique for the practical methanol industry. New developments of a new kind of low temperature methanol synthesis were reviewed, including the effects of feed gas, reaction solvent, supercritical media and catalyst modification. The reaction mechanism and kinetics were also summarized primarily. Carbon dioxide played an important role in this new kind of low temperature methanol synthesis. It reacted with hydrogen adsorbed on catalyst surface to form HCOOM, an important reaction intermediate. Alcohol solvent in the low temperature methanol synthesis performed not only a media, but also a homogeneous catalyst. The reaction of the adsorbed formate species with alcohol on Cu/ZnO catalyst surface proceeded according to the Rideal mechanism rather than Langmuir–Hinshelwood mechanism to form alkyl formate. The formation of alkyl formate from alcohol solvent and hydrogenation of such an alkyl formate were the key steps in low temperature methanol synthesis reaction. These results provided new insights into low temperature methanol synthesis.     

A practical and improved process for the synthesis of Hagen’s gland lactones by catalytic hydro-deiodination

Catalytic hydro-deiodination has been efficiently employed in the development of a benign process for the synthesis of Hagen’s gland lactones. The process was developed with only two column chromatographic purifications and is applicable for gram scale synthesis. No protecting groups were used in the synthesis which is an added advantage.     

Rhodium-catalyzed direct C-H addition of 3,4-dihydroquinazolines to alkenes and their use in the total synthesis of vasicoline

The inter- and intramolecular couplings of unactivated alkenes to 3,4-dihydroquinazolines with a Rh(I) catalyst are reported. Coupling between olefins and NH-3,4-dihydroquinazoline was found to occur consecutively with heterocycle dehydrogenation in the presence of a Rh(I)/PCy3/HCl catalyst. The reaction was used to develop an effective method for the synthesis of 2-substituted quinazolines through an oxidative workup step. The regiocontrolled synthesis and Rh-catalyzed cyclization of alkene-tethered 3,4-dihydroquinazolines are also described. Applying this method, the second total synthesis of vasicoline was achieved. The key Rh-catalyzed cyclization step was made possible by the use of a rigid bicyclic phosphine ligand. The synthesis further demonstrates a challenging Cu-catalyzed amidation of an ortho-substituted aryl chloride.     

Towards green synthesis of nanoparticles: From bio-assisted sources to benign solvents. A review

Current advancements in green synthesis of materials especially nanoparticles have led to conservation of natural and non-renewable resources along with reduction in environmental pollution. Development of cost-effective, simple and eco-friendly routes for the synthesis of nanoparticles is very important. All over the world, a wide variety of biogenic sources have been put to trial as a source of green agents to facilitate synthesis process. In addition to this, environmentally benign solvents are also being used these days in order to promote green synthesis. In this review, an attempt has been made to familiarise the readers with the different green routes for the synthesis of nanoparticles.     

Asymmetric Total Synthesis of Propindilactone G,Part 2: Enantioselective Construction of the Fully Functionalized BCDE Ring System

The enantioselective synthesis of the fully functionalized BCDE tetracyclic ring system of propindilactone G ( A ) is reported. Several synthetic methods were developed and applied to achieve this goal, including: 1) an asymmetric Diels–Alder reaction in the presence of Hayashi′s catalyst for the synthesis of optically pure key intermediate 3 ; 2) an intramolecular Pauson–Khand reaction (PKR) for the stereoselective synthesis of the BCDE ring with an all‐carbon chiral quaternary center at the C13 position by using the TMS‐substituted acetylene as the substrate; and 3) Pd‐catalyzed reductive hydrogenolysis for the stereoselective synthesis of the fully functionalized BCDE tetracyclic ring system. The chemistry developed herein provided a greater understanding of the total synthesis propindilactone G ( A ) and its analogues.     

Light-mediated inhibition of protein synthesis

The regulation of protein synthesis is vital for a host of cell biological processes, but investigating roles for protein synthesis have been hindered by the inability to selectively interfere with it. To inhibit protein synthesis with spatial and temporal control, we have developed a photo-releasable anisomycin compound, N-([6-bromo-7-hydroxycoumarin-4-yl]methyloxycarbonyl)anisomycin (Bhc-Aniso), that can be removed through exposure to UV light. The area of protein synthesis inhibition can be restricted to a small light-exposed region or, potentially, the volume of two-photon excitation if a pulsed IR laser is the light source. We have tested the compound's effectiveness with an in vitro protein-translation system, CHO cells, HEK293 cells, and neurons. The photo-released anisomycin can inhibit protein synthesis in a spatially restricted manner, which will enable the specific inhibition of protein synthesis in subsets of cells with temporal and spatial precision.     

An expedient synthesis of orthogonally protected lysinoalanine from Aloc-protected Garner’s aldehyde

An expedient synthesis of orthogonally protected lysinoalanine has been developed. We have prepared a novel Garner’s aldehyde derivative bearing an Aloc group; reductive amination of this aldehyde with Fmoc-Lys-OPMB gave the lysinoalanine skeleton. This was then transformed into an orthogonally protected lysinoalanine derivative suitable for the synthesis of side-chain bridged cyclic peptides by solid phase peptide synthesis methods.     

The furan approach to oxacycles: synthesis of medium-size 2,3-disubstituted oxacycles

We describe an efficient new approach for the synthesis of medium-size oxacycles that is based on the oxidation of a furan ring with singlet oxygen followed by an intramolecular Michael addition. This present study enlarges the scope of the furan approach strategy for the synthesis of oxepanes.     

A new reactivity-based one-pot synthesis of N-acetyllactosamine oligomers

Poly-N-acetyllactosamine oligomer is a type-2 glycan core from which a number of important bioactive glycoconjugates are assembled in vivo. Development of an effective synthesis of N-acetyllactosamine oligomers will therefore provide a new chemoenzymatic entry to this class of complex saccharides. This paper describes the design and synthesis of thioglycoside building blocks, determination of their relative reactivity values, and demonstration of their use in the programmable one-pot synthesis of various N-acetyllactosamine oligomers. Through a combination of segment condensation, the strategy allows for the preparation of larger oligosaccharides with minimal protecting group manipulation, as illustrated in the synthesis of an octasaccharide in a very short period of time.