A Facile Method for Asymmetric Synthesis of β-Hydroxy-α-amino Acids

β-Hydroxy-a-amino acids are an important class of amino acids due to their inherent biological investigations[1] and as structural components of more complex biomolecules.[2] β-Hydroxy-a-amino acids have been used as intermediates in the asymmetric synthesis of other compounds.[3] An efficient and convenient concise method for the preparation of optically pure enantiomers of β-hydroxy-α-amino acids would be of general interest.     

Synthesis of Trisaccharide of Incanosides from Caryopteris incana

Recent evidence has accumulated suggesting that free radicals are involved in many deterioration processes. They attack the unsaturated fatty acids in the biomembranes resulting in membrane lipid peroxidation, which is strongly connected with aging, carcinogenesis and atherosclerosis.[1] Free radicals also attack DNA and cause mutation leading to cancer.[2] Thus it is desirable to look for effective radical scavengers. In 1999, Gao et al.[3] isolated incanosides C, D and E from the whole plant of Caryopteris incana (THUNB.). These natural products were proved to exhibit good radical scavenging activities against DPPH radical and inhibitory activities against the oxidation of linoleic acid.[4] Herein, for the first time we report the synthesis of trisaccharide phenyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl-(1→2)-3,4-di-O-benzoyl-α-L-rhamno-pyranosyl-(1→3)-2-O-acetyl-4,6-O-benzylidene-1-thio-β-D-glucopyranoside (1), which is the common carbohydrate moiety of incanosides C, D and E.     

Efficient and Stereoselective Synthesis of C-(β-2''-Deoxynucleosides)

The formation of triplex DNA is, in principle, an effective way of regulating the expression of selected genes.[1]Many cytosine mimics were investigated to form triplex DNA, e.g., 2-amino-(2'-deoxy-β-D-ribofuranosyl)pyridine (9)was proved to have some effectiveness in stabilizing triplex DNA under neutral conditions.[2] Stereoselective synthesis of 9 was achieved starting from 2-deoxyribose.     

Preparation and Reactions of Amino Acid Ester Sulfones as New Remote Asymmetrical Induced Reagents

The development of chiral auxiliary-controlled asymmetric synthesis has been receiving increasing interest in recent yearsfi,2] Various chiral auxiliary reagents have been observed[3] and a lot of results showed that variation of the chiral auxiliary could influence asymmetric induction. Recently, it has been reported the reaction of the aminated sulfones as a remote chiral auxiliary with α,β-unsaturated carbonyl compounds.[4] Here we would like to report the preparation of amino acid ester sulfones as new remote asymmetrical induced reagents and their reactions with α,β-unsaturated esters.     

Stereoselective Synthesis of (+)-Boronolide

(+)-Boronolide (1) and its deacetylated products have attracted much attention of synthetic chemists due to their diverse biological properties as well as their structural complexities.[1] Many of these reported synthesis involved dehydrogenation of δ-lactone by using benzeneseleninic anhydride or ring-closing olefin metathesis (RCM) to introduce the requisite α,β-unsaturated δ-lactone in boronolide. Here, we report the synthesis of boronolide with diastereoselective propargylation of α-hydroxy aldehyde as the key step and D-gluconolactone as the starting material.     

Mild One-Pot Deoximation and Conjugate Reduction of α, β-Unsaturated Ketoximes with Hydrosilane and I2O5

The organic chemistry of polyvalent iodine compounds has experienced an unprecedented development during the last decade of 20th century.[1,2] On the other hand, despite its extensive use in industry, I2O5 (iodine pentoxide, IP) has rarely been employed in organic synthesis except as an alternative to iodoxybenzoic acid (IBX) for the dehydrogenation of aldehydes and ketones.[3] Generally, pentavalent iodine reagents, such as IBX and Dess-Martin periodinane (DMP)were used as mild and selective oxidants for oxidation of alcohols[1,2] and dehydrogenation of carbonyl compounds.[3] We wish to report herein that IP can serve as a mild and efficient reagent for the oxidative cleavage of oximes to aldehydes and ketones (Eq. 1). Most interestingly, IP can also activate hydrosilanes for reduction of alkenes. Hence, simultaneous deoximation and conjugate reduction of α,β-unsaturated ketoximes can be achieved by using IP and phenyldimethylsilane (Eq. 2).     

Stereoselective Synthesis of C-Glycosides by Suzuki Cross-coupling Reaction

Carbohydrates and their conjugates have been recognized to play a wide variety of metabolic roles in numerous biological processes.[1] Various modified sugars and analogues have been recently synthesized for further investigation of glycosidase reactions and for the development of specific glycosidase inhibitors.[2] As one of the most important carbohydrate mimics, C-glycosides have attracted great attention due to their stability to chemical or enzymatic hydrolysis of the glycosidic linkage. A number of methodologies for the preparation of C-glycosides have been extensively investigated.[3] We have recently reported the syntheses of novel C-glycosyl amino acids and amino-C-disaccharides possessing a ketose form via the stereoselective 1,3-dipolar cycloaddition of exo-methylenesugars (1) and nitrones.[4,5] As a continuation of our research on the synthesis of C-glycosides using exo-methylenesugar as the precursor, we wish to describe here a stereoselective synthesis of C-glycosides by Suzuki cross-coupling reaction.     

Facile Synthesis of 6-Oxo-5,6,6αβ,7,8,9,10,10αβ-Octahydroindeno[2,1-b] Indole System

A facile stereoselective synthesis of 6-oxo-5,6,6aβ,7,8,9,10,10aβ-octahydroindeno[2,l-b]indole, the key intermediate for yuehchukene analogues synthesis, is described.     

Asymmetric Addition of Diethylzinc to Aldehydes Using SPINOL Derivatives

Lewis acid catalyzed enantioselective carbon-carbon bond formation is one of the most interesting challenges in catalytic asymmetric synthesis. A convenient route for this synthesis is the addition of organozinc to aldehydes.[1]1,1'-Spirobiindane-7,7'-diol (SPINOL), a new reported C2 symmetrical diol, was recently proven to be an excellent framework for chiral ligands.[2] In this paper, interestingly, we describe the preparation of SPINOL derivatives and application of these ligands to asymmetric addition of diethylzinc to aldehydes as model reaction. Previously, an improved method for the resolution of C2-symmetric spirocyclic SPINOL was presented with crude menthyl chloroformate as resolving reagent.[3] Then (R)-SPINOL with C2-symmetric spirocyclic framework was applied in the asymmetric diethylzinc addition to aromatic aldehydes, which induced high conversions and moderate enantioselectivities for the production of chiral secondary alcohols. Further work of other SPINOL derivative ligands for asymmetric diethylzinc addition to aromatic aldehydes and developing further new SPINOL-based Lewis acid catalyzed asymmetric synthesis are underway.     

Stereoselective Synthesis of 2,3,4,6-Tetrasubstituted Tetrahydropyrans

The construction of stereodefined, highly substituted tetrahydropyrans has attracted a lot of interest over the years since they constitute ubiquitous fragments of numerous biologically active natural products.[1] During the course of our synthetic studies toward ambruticin, a fascinating antibiotic[2] which came back in the front scene with three recent total synthesis, [3] we have been interested in the synthesis of 2,3,4,6-tetrasubstituted tetrahydropyrans 5 (Scheme 1). [4] Moreover, this kind of subunit is found to be embedded in several other natural products such as lasonolide A, polycavernoside A, ratjadone, or concanamycin A.     

lipase-catalyzed regioselective esterification of rapamycin: synthesis of temsirolimus (CCI-779)

A lipase-catalyzed acylation of the immunosuppressant rapamycin with complete regioselectivity is described. The method was successfully applied to the synthesis of 42-hemiesters and temsirolimus (CCI-779), an investigational oncology drug.[reaction: see text]     

Asymmetric Michael Addition of Activated Alkenes to Nitro Alkenes Catalyzed by Organic Catalyst

Enantioselective Michael addition is one of the most powerfulbond-forming reaction in organic synthesis. [1] A mong the Michael acceptors, nitro alkenes are very attractive, because the nitro group is the most electron-withdrawing group known and it can serve as masked functionality to be further transformed after the addition has taken place. [2] Recently, asymmetric Michael reactions catalyzed by organic catalyst have draw much attention.[3]     

Synthesis of the Anionic Fluororeceptors and Recognition Property for α,ω-Dicarboxylate

Anions, especially dicarboxylates, play an important role in chemical and biological processes,[1] dicarboxylates are critical components of numerous metabolic processes including, for instance, the citric acid and glyoxylate cycles.[1a]They also play an important role in the generation of high-energy phosphate bonds and in the biosynthesis of important intermediates.[1b] To date, several receptors containing different functional groups for selective binding of dicarboxylate anions have been reported.[2,3] However, the sensors based on the fluorescence emission for dicarboxylate anions are still rare.3 In this paper, we report the synthesis and binding properties of two new neutral anion receptors (1 and 2).     

A Concise Total Synthesis of S-(+)-Tylophorine

Phenanthroindolizidine alkaloids, which exhibit extensively biological properties, are widely present at various plants of the Asclepiadaceae family.[1] The significantly biological importance of these natural products has attracted considerable synthetic efforts.[2] We herein report an efficiently asyinmetric synthesis of S-(+)-tylophorine (1), as a typically representative alkaloids.     

Development of a Novel, Oxidatively Activated, Safety-Catch Linker for Solid-Phase Asymmetric Organic Synthesis (SPOS)

Solid-phase asymmetric organic synthesis has become a very important synthetic strategy within the organic chemistry community.[1] Critical to success in SPOS is a linking strategy which allows both the substrate to be loaded and the product released efficiently from the polymeric support. A safety catch linker[2] (SCL) is in principle a linking molecule orthogonal to the reaction conditions of the library synthesis, which can be easily activated by a simple chemical transformation to allow efficient cleavage of the products from the polymer under mild conditions. In order to introduce the SuperQuat chiral auxiliaries[3] for SOPS, we report herein design and synthesis of a novel safety catch linker for asymmetric conjugate addition reactions.     

A Practical and Convenient Synthetic Process of 3-O-Decladinose-6-methyl 10,11-dehydrate-erythromycin-3-one-2''''-acetate, an Important Intermediate of Ketolides Synthesis

3-O-Decladinose-6-methyl-10,11-dehydrate-erythromycin-3-one-2'-acetate (5) is an important intermediate for the synthesis of ketolides antibiotics.[1] In the improved synthetic method of compound 5, the more common reagent PCC[2]was used instead of the expensive reagent EDC and methanesulfonic anhydride.[3～4] In this way, compound 5 was obtained efficiently and economically in five steps from clathromycin 1 without being further purfied by column chromatography.     

Synthesis of 1,7-Bis(4-hydroxyphenyl)hepta-4E,6E-dien-3-one

Diarylheptanoids, most of which appearing in the areas of anti-inflammatory, anti-oxidative, super-oxide scavenging and anti-hepatotoxic effects, constitute a distinct group of metabolites of natural plants characterized by two aromatic rings linked by a linear seven aliphatic chain. We have investigated this kind of compounds and made some progress.[1]1,7-Bis(4-hydroxy-phenyl)hepta-4E,6E-dien-3-one (1) was firstly isolated from the seeds of Alpinia blepharocalyx.[2] So far the synthesis of the compound has not been reported yet. Herein, we report the synthesis of compound 1. The synthetic route is outlined in Scheme 1.     

咪唑根碱性离子液体在水介质Knoevenagel反应中的催化作用

报道了咪唑根1-丁基-3-甲基咪唑([Bmim]Im)碱性离子液体的合成与表征,该离子液体具有强碱性和较好的热稳定性.碱性离子液体[Bmim]Im用于催化水介质中Knoevenagel反应,发挥了碱催化剂与相转移催化剂双重作用.此外,离子液体[Bmim]Im及其水溶液还具有良好的循环使用性能.水介质、低催化剂用量、室温...     

An Expeditious Synthesis of β-Indolylketones Catalyzed by p-Toluenesulfonic Acid (PTSA) Using Ultrasonic Irradiation

The investigation of the chemistry of indoles has been, and continues to be, one of the most active areas of heterocyclic chemistry.[1] In particular, β-indolylketones have received much attention as important building blocks for the synthesis of many natural products and other biologically active compounds.[2] In continuation of our work in the synthesis of indole derivates,[3] we describe the remarkable catalytic of PTSA as a cheaper catalyst in ultrasound-accelerated Michael reaction of indole with α, β-unsaturated ketones (2), which provide one of the most efficient routes to the synthesis of β-indolyketones. In all cases, the substitution on the indole nucleus occurred exclusively at the 3-position, and N-alkylation products have not been observed. In addition, the structure of 3a was further confirmed by single crystal X-ray crystallography.     

New Synthetic Method of Azuleno[1,2-c]thiophenes

On the viewpoints of physical and chemical properties and biological activities, syntheses of a variety of heterocycle-fused azulenes have been repoted.[1] Of them, thiophene-fused azulenes were prepared by using different types of stating materials as follows. Azuleno[2,1-b] thiophenes are readily obtained from the reactions of 2-chloroazulene derivatives with ethyl mercaptoacetate in a few steps in good yield by Matsui[2] and Yamane.[3] On the other hand, the first synthesis of azuleno[1,2-c]thiophenes was accomplished by the reaction of 3-methoxycarbonyl-2H-cyclohepta[b]furan2-one with morpholino enamine of 3-oxotetrahydro-thiophene followed by dehydrogenation in poor yield by Fujimori.