New and Concise Approach to (R)-α-Lipoic Acid

A concise enantiospecific synthesis of (S)-6,8-bis(methylsulfonyloxy)-octanoic acid (2), a ready precursor of (R)-(+)-α-lipoic acid (1), is reported. The key step of the synthesis is the coupling of the tosylate derived from (R)-malic acid with phenylpropyl magnesium bromide. A recently reported green procedure was used for the oxidative unmasking of the phenyl group, used as a latent carboxyl group.     

Oxidative ring opening of 2-pyrazolines. Application to lactamisation and formylation of 1,3-6h-thiazines.

Benzeneseleninic anhydride allows oxidative ring opening of 2-pyrazolines to α,β-unsaturated carbonyl compounds. Thus, a pyrazoline ring may be used as a masking, a stereodirecting and a latent formyl group in the synthesis of 7-amino 4-formyl cephem from 1,3-6H-thiazine.     

钐钆共掺杂荧光配合物的合成及在潜手印显现中的应用

以2-噻吩甲酰三氟丙酮(TTA)为第一配体,邻菲罗啉(o-Phen)为第二配体,利用共沉淀法合成一系列钐钆共掺杂荧光配合物,并优化了该系列荧光配合物的合成条件(反应温度、体系pH、稀土离子相对含量).将最优条件合成的Sm0.5 Gd0.5 TTA3(o-Phen)荧光配合物粉末用于常见光滑非渗透性客体表面潜在手印的显现...     

A latent entanglement model for the draw of semicrystalline polymers

A novel molecular model, the latent entanglement, is proposed to explain the relationships between ductilities of polyethylene reactor powders and different conditions of synthesis. According to Hoffman's variable cluster model, irregularities in the crystallite fold surface increase as the synthesis temperature is decreased. The concept of latent entanglement stems from the potentiality of these defects to convert into active entanglements when the involved chain segments are drawn out of the crystals.     

Exploration of the interrupted Fischer indolization reaction

A convergent method to access the fused indoline ring system present in a multitude of bioactive molecules has been developed. The strategy involves the condensation of hydrazines with latent aldehydes to ultimately deliver indoline-containing products by way of an interrupted Fischer indolization sequence. The method is convergent, mild, operationally simple, broad in scope, and can be used to access enantioenriched products. In addition, our approach is amenable to the synthesis of furoindoline and pyrrolidinoindoline natural products as demonstrated by the concise formal total syntheses of physovenine and debromoflustramine B. The strategy will likely enable the synthesis of more complex targets such as the communesin alkaloids.     

卤代苯丙氨酸衍生物的合成与拆分

以苯胺类化合物为起始原料,经重氮化、丙烯酸加成、氨解等过程合成了5种消旋苯环取代苯丙氨酸衍生物,并采用α-糜蛋白酶和枯草杆菌蛋白酶对所有氨基酸进行了拆分,通过IR,¹HNMR,元素分析和旋光等技术进行表征.其中4种氨基酸未见文献报道.     

Dual catalysis with an N-heterocyclic carbene and a Lewis acid: Thermally latent precatalyst for the polymerization of ε-caprolactam

So far, the earlier reported strong correlation between basicity of an N-heterocyclic carbene (NHC) and its reactivity in poly(ε-caprolactam) (PA6) synthesis resulted in a substantial limitation of applicable carbenes. Here, to overcome this issue, 1,3-dimethylimidazolium-2-carboxylate, an easily accessible, air and moisture-stable NHC, was applied as thermally latent initiator. In order to compensate for its low basicity, reactivity was enhanced by the addition of both a Lewis acid and an activator to ease the initial polymerization step. The resulting mixtures of ε-caprolactam, the CO₂-protected NHC, a Lewis acid and N-acylazepan-2-one constitute homogeneous, thermally fully latent “single-component” blends for the anionic polymerization-based synthesis of PA6. They can be stored both in the liquid and solid state for days and months, respectively, without any loss in activity. The role of the Lewis acid as well as technical implications of the prolonged pot-times are discussed.     

vic‐Tricarbonyl Compounds of Quinolines: Analogues of Ninhydrin: A Short Review

Derivatives of ninhydrin are extensively used in the field of forensic sciences as important latent fingerprint reagents. Many works have been performed upon their synthesis and reactivity, but there are many spaces to work on the compounds of quinoline‐2,3,4(1H)‐triones—analogues of ninhydrin, in both dimensions: synthesis and reactivity, and according to the best of our knowledge, not a single detailed or short compiled article has been published for these compounds. This review briefly summarizes the chemistry of quinoline‐2,3,4(1H)‐triones.     

Latent fluorophore based on the trimethyl lock

Fluorescent molecules are essential for basic research in the biological sciences and have numerous practical applications. Herein is described the synthesis and use of a new class of latent fluorophores based on a novel design element, the trimethyl lock, that confers distinct advantages over extant fluorophores and pro-fluorophores. A diacetyl version of the latent fluorophore is stable in a biological environment, but rapidly yields rhodamine 110 upon acetyl-group hydrolysis by pig liver esterase or endogenous esterases in the cytosol and lysosomes of human cells. This design element is general and, hence, provides access to an ensemble of useful latent fluorophores.     

Enantioselective synthesis of (1E,3S)-1-iodoundec-1-en-5-yn-3-ol,the eicosanoid synthon

A synthesis of the title compound, the synthon for the constanolactones and other eicosanoids, has been developed from achiral starting compounds. The synthesis is based on the S-enantiodirected dihydroxylation of the double bond to introduce a chirality and on the use of conformational restriction of the triple bond (the latent Z-double bond) surroundings.     

硫增感的敏化中心和潜影中心的氧化还原性能的研究

本文采用Reinders的氧化还原缓冲液的方法研究硫敏化的立方体卤化银微晶的敏化中心和潜影中心的氧化还原性能.实验结果表明:1)Reinders的氧化还原缓冲液的方法,不仅可用于研究潜影中心,也可用于研究敏化中心;2)本实验条件下的硫化银敏化中心的氧化还原电位约略负于－220 mV(相对于饱和甘汞电极),潜影中心的氧化还原电位值是介于－220 mV与－190 mV之间(相对于饱和甘汞电极);3)潜影中心的氧化还原活性较敏化中心大得多.     

Synthesis of fused indolines by interrupted Fischer indolization in a microfluidic reactor

This study describes our development of a microfluidic reaction scheme for the synthesis of fused indoline ring systems found in several bioactive compounds. We have utilized a continuous-flow microfluidic reactor for the reaction of hydrazines with latent aldehydes through the interrupted Fischer indolization reaction to form fused indoline and azaindoline products. We have identified optimal conditions and evaluated the scope of this microfluidic reaction using various hydrazine and latent aldehyde surrogates. This green chemistry approach can be of general utility to rapidly produce indoline scaffolds and intermediates in a continuous manner.     

Recyclable fluorous-tag assisted two-directional oligosaccharide synthesis enabled by interrupted Pummerer reaction mediated glycosylation

Herein, we report a novel fluorous-tag assisted two-directional oligosaccharide assembly strategy, which maintained the high coupling efficiency of solution-phase synthesis and featured the advantage of an easy purification process comparable to solid-phase synthesis. A well-designed fluorous tag was decorated on the latent anomeric leaving group in interrupted Pummerer reaction mediated (IPRm) glycosylation. The high efficiency of the in-solution phase glycosylation and the unique affinity of the fluorous tag towards polytetrafluoroethylene (PTFE) particles allowed flexible assembly from the reducing end to the non-reducing end and fast purification by PTFE-assisted filtration. Moreover, the fluorous-tagged latent anomeric leaving group could be activated by oxidation and cleaved by IPRm glycosylation, thus enabling the elongation of the carbohydrate chain from the non-reducing end to the reducing end as well as the recovery of the fluorous tag. The present two-directional synthetic strategy is used to assemble the repeating unit of Streptococcus pneumoniae type 14 capsular polysaccharide.

Recyclable fluorous-tag assisted IPRm glycosylation enabled efficient solution-phase synthesis and rapid fluorous purification, thus promoting sustainable two-directional oligosaccharide assembly.     

Convenient route to enantiopure substituted butyrolactones: application in a formal synthesis of both enantiomers of enterolactone

A simple route for the synthesis of enantiopure substituted γ-butyrolactones involving a highly diastereoselective alkylation of an enantiomerically pure substituted latent succinate ester is described. This route provides entry into both enantiomers of 3,4-disubstituted butyrolactones from a single enantiomer, 2,3-di-O-cyclohexylidine-R-(+)-glyceraldehyde. The synthetic potential of this methodology has been demonstrated by a formal synthesis of both enantiomers of enterolactone.     

Modelling of a high pressure calorimeter

The evaluation of the latent heat and enthalpy of fusion of food systems in the case of high pressure–low temperature processing is important for modelling purposes as well as for technical applications. A high pressure calorimeter has been designed for this purpose. The high pressure calorimeter was used to evaluate the latent heat during a pressure scan at constant temperature. It permits to measure the heat of phase transitions and to obtain the relationship between the initial freezing temperature T _ifp and the average pressure while the phase transition is going on. This work presents a modelling of results obtained from an experimental approach using a high pressure calorimeter and from a mathematical model developed from existing data on the phase change of pure water. The modelling work consisted in evaluating the latent heat measured in previous tests from computations taking into account the dependence of the latent heat of fusion of water on pressure. Models predicting the amount of frozen water in a food matrix under atmospheric conditions were used to determine the initial amount of frozen water in the sample. Then a stepwise procedure was operated in a program to reproduce the pressure rise occurring during a high pressure calorimeter test. The amount of melted ice at each pressure step was calculated using conventional ice fraction models, which were adapted to pressure dependence of the initial freezing temperature and the dependence of the latent heat pressure. The comparison was satisfactory, especially at low temperatures.     

Toward fully synthetic glycoproteins by ultimately convergent routes: a solution to a long-standing problem

A method is disclosed for the convergent synthesis of multiply glycosylated peptides. The approach centers on a convergent technique for generating masked, complex glycopeptide-containing C-terminal acyl donors. Activation of the latent donor in situ and use directly in segment coupling with a second peptide bearing a complex carbohydrate produces a completely unprotected, bifunctional glycopeptide. The system demonstrates a minimum level of hydrolysis and epimerization at the C-terminal amino acid residue of the acyl donor during fully convergent segment coupling and is therefore a powerful tool for the synthesis of glycoproteins.     

One step to detect the latent fingermarks with gold nanoparticles

A simple and environment friendly chemical route for detecting latent fingermarks by one-step single-metal nanoparticles deposition method (SND) was achieved successfully on several non-porous items. Gold nanoparticles (AuNPs) synthesized using sodium borohydride as reducing agent in the presence of glucose, were used as working solution for latent fingermarks detection. The SND technique just needs one step to obtain clear ridge details in a wide pH range (2.5-5.0), whereas the standard multi-metal deposition (MMD) technique requires six baths in a narrow pH range (2.5-2.8). The SND is very convenient to detect latent fingermarks in forensic scene or laboratory for forensic operators. The SND technique provided sharp and clear development of latent fingermarks, without background staining, dramatically diminished the bath steps.     

几类4－取代苄基－2，6－哌嗪二酮的合成

介绍了４类具有络合性质或潜在的络合性质的４－取代苄基－２，６－哌嗪二酮化合物的合法。所合成的化合物中有些表现出明显的体外抑制白血细胞Ｐ３８８生长的活性。     

Synthesis of Functional Poly(disubstituted acetylene)s through the Post‐Polymerization Modification Route

We report the recent progress in the preparation of functional poly(disubstituted acetylene)s (PDSAs) through post‐polymerization modification routes. The metathesis polymerization of disubstituted acetylene monomers activated by Mo/W–Sn complex catalysts, which do not tolerate highly polar functionalities, was assumed to be a key step in the polymer synthetic procedures. We and other groups have explored several approaches to prepare PDSAs with latent reactive functionalities, which are inactive to Mo/W–Sn complex catalysts but can be used as highly reactive sites for post‐polymerization modification. Click chemistry, Michael‐type addition reactions, the use of activated esters and other strategies are demonstrated by recently published examples. These works indicate that post‐polymerization modification is an efficient route to the synthesis of various functional PDSAs.     

Stereoselective synthesis of vinylsilanes by a gold(I)-catalyzed acetylenic sila-cope rearrangement

Cationic tri-tert-butylphosphinegold(I) serves as a catalyst in the sila-Cope rearrangement of acetylenic allylsilanes. When phenol is employed as a nucleophile, the reaction allows for the stereoselective synthesis of vinylsilanes. Alternatively, use of methanol as a nucleophile leads to cyclic vinylsilanes, which can be viewed as latent vinylsilanes that are revealed on treatment with a mild Lewis acid. Thus, both of these reagents serve as useful reagents for stereoselective synthesis of trisubstituted olefins through transition-metal-catalyzed cross-coupling reactions.