Soluble Polymer-Supported Synthesis of α-Amino Acid Derivatives

Due to the central role played by α-amino acid in chemistry and biology, the development of versatile and new methodology for the synthesis of natural and unnatural α-amino acid has emerged as an important and challenging synthetic endeavour for organic chemists.[1] Among the various methodologies reported for α-amino acid synthesis, [2,3] the solid-phase organic synthesis (SPOS) has served as an important approach. [4] However, inherent prob lems on solid supports are reactive site accessibility, site-site interaction and monitoring of the reaction.     

A new general, practical and enantioselective synthesis of α-amino acids

In recent years, considerable efforts have been expended to the development ofenantioselective synthesis of α-amino acids and the use of α-amino acids as chiralbuilding blocks for the synthesis of complex molecules. Numerous unnatural aminoacids which are often the characteristic units of biologically active peptides, have alsobeen discovered. Herein we describe a convenient and general access to natural andunnatural α-amino acids which are based on the use of the chiral building blocks,(S)-1a-e and (R)-1a-e from kinetic resolution of α-furfuryl amines (Scheme 1).     

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.     

THE ASYMMETRIC SYNTHESIS OF AMINO ACIDS UNDER POLYMER-SUPPORTED PHASE TRANSFER CATALYTIC CONDITION

The optical α-amino acids were synthesized under room temperature byalkylation of N-(diphenyl methylene) glycine t-butyl ester under polymer-supported phasetransfer conditions using polymer-supported cinchonine (or quinine) alkaloids as chiralphase transfer catalysts and dichloromethane as solvent, followed by hydrolysis of theabove intermediates introduced to the final products-optical α-amino acids. This is anew method for the asymmetric synthesis of α-amino acids. The influences of catalyst,temperature, substrates, and organic solvents on the chemical yield and optical purities ofproducts were studied.     

Synthesis of (s)-(-)-Benzyl-2-tert-butoxycarbonyl amino-4-iodobutyrate

The proteinogenic (-amino acids constitute an important section of the "chiral pool", being inexpensive in the L-form (but available if necessary as the D enantiomers), structurally varied and chemically versatile1, they are useful starting materials for chiral reagents, auxiliaries and ligands2. Any high-yielding transformation of an (-amino acids which proceeds without racemization is thus of potential importance, especially if it generates another reactive center and may be applied to the s…     

Synthesis and Crystal Structure of 2-Ethoxy-spiro[2H-1, 4,2-benzoxazaphosphorine-3（4H）, 1＇-Cycloheptane] 2-Oxide

1 INTRODUCTION α-Aminophosphonates are an important class of compounds since they are considered as structural analogues of the corresponding α-amino acids. Their utilities as enzyme inhibitors, antibiotics, pharma- cological agents and many other applications are well documented[1~5]. Moreover, cyclic α-amino- phosphonates, one important kind of α-aminopho- sphonates, have attracted chemists’ interests for a long time[6~11]. In order to search for potent and selec- tive herbicides a…     

Synthesis of Novel C2-Symmetrical Bidentate Phosphoramidite Ligands for Rh-catalyzed Asymmetric Hydrogenation of β-（Acylamino）acrylates

Enantiomerically pure β-amino acids and their derivatives are especially attractive due to their vital importance for biochemical and medicinal applications1. One of the most convenient paths to β-amino acids involves the asymmetric hydrogenation of the…     

Concise synthesis of valuable chiral N-Boc-β-benzyl-β-amino acid via construction of chiral N-Boc-3-benzyl-5-oxoisoxazolidine through cross-metathesis/conjugate addition/oxidation

Valuable chiral N-Boc-β-benzyl-β-amino acid was concisely synthesized via construction of chiral NBoc-3-benzyl-5-oxoisoxazolidine through cross-metathesis/conjugate addition/oxidation.All of the starting materials for the synthesis of chiral N-Boc-β-benzyl-β-amino acid are cheap,and two-step short procedure make it easy for the rapid construction of various chiral β-arylmethyl-β-amino acids and important drugs,such as sitagliptin phosphate.     

Synthesis and Catalytic Asymmetric Reaction of Chiral Pyridine Prolinol Derivatives

The enantioselective reduction of prochiral ketones with borane in the presence of a chiral ligand leading to enantiomerically pure secondary alcohols has received considerable attention in recent years. [1] Enantiomerically pure secondary alcohols are important intermediates for the synthesis of various other organic compounds such as halides, esters, ethers, ketones and amines. To the best of our knowledge, the use of pyridine prolinol derivatives in the reduction of ketones has not been reported so far. Thus, it should be of interest to investigate the catalytic a bility of such ligands. We have an ongoing project in the synthesis and application of chiral pyridine derivatives in chiral molecular recognition[2] and we want to evaluate the effect resulting from the introduction of a pyridinyl moiety onto the catalysts. We expect that the cooperation of pyridine unit and chiral prolinol unit in new ligands may result in unique properties for catalytic reaction.     

Catalytic enantioselective synthesis of β-amino alcohols by nitrene insertion

Chiral β-amino alcohols are important building blocks for the synthesis of drugs, natural products, chiral auxiliaries, chiral ligands and chiral organocatalysts. The catalytic asymmetric β-amination of alcohols offers a direct strategy to access this class of molecules. Herein, we report a general intramolecular C(sp³)–H nitrene insertion method for the synthesis of chiral oxazolidin-2-ones as precursors of chiral β-amino alcohols. Specifically, the ring-closing C(sp³)–H amination of N-benzoyloxycarbamates with 2 mol% of a chiral ruthenium catalyst provides cyclic carbamates in up to 99% yield and with up to 99% ee.The method is applicable to benzylic, allylic, and propargylic C–H bonds and can even be applied to completely non-activated C(sp³)–H bonds, although with somewhat reduced yields and stereoselectivities. The obtained cyclic carbamates can subsequently be hydrolyzed to obtain chiral β-amino alcohols. The method is very practical as the catalyst can be easily synthesized on a gram scale and can be recycled after the reaction for further use. The synthetic value of the new method is demonstrated with the asymmetric synthesis of a chiral oxazolidin-2-one as intermediate for the synthesis of the natural product aurantioclavine and chiral β-amino alcohols that are intermediates for the synthesis of chiral amino acids, indane-derived chiral Box-ligands, and the natural products dihydrohamacanthin A and dragmacidin A.     

Iodine-catalyzed Synthesis of α-Amino Phosphonates

α-Amino phosphonates are structural analogues of the corresponding α-amino acids. They are found to exhibit intriguing biological activities1, for example as enzyme inhibitors, peptidomimetics, antibacterial agents and other pharmacological agents. A va…     

Organic Reactions in Ionic Liquids： An Efficient Method for the Synthesis of Phenacyl Esters by Reaction of Carboxylic Acids with α-Bromoacetophenone Promoted by Potassium Fluoride

An efficient method is reported for the synthesis of phenacyl esters by reaction of carboxylic acids with a-bromoacetophenone promoted by potassium fluoride in ionic liquid [Bmim]PF6, the yield of the reaction is almost quantitative and the products are essentially pure.     

First One-step Enantioselective Reduction of á-Haloacetophenones into Styrene Oxides using Sodium Borohydride in Water

The synthesis of enantiomerically enriched epoxides especially styrene oxides is an interesting challenge1, since they are often valuable building blocks for various fine chemical 2 products and pharmaceuticals such as β2-, β3-, and α1-adrenergic receptor agonists3, . In recent years, 4 there has been a flood of papers describing the synthetical methods of the chiral non-racemic epoxides5, . Here we firstly developed a green, simple and potential epoxidation system by 6 enantioselecti…     

Study on Fmoc Solid-phase Synthesis and Activity of Thymosin α1

Thymosin α1 (Tα1), an immunologically polypeptide, [1] is highly acidic composed of 28 amino acid residues with acetylserine as the NH2 terminus. The MW of this peptide is 3108, with pI 4.2. There are many Asp and Glu in this molecule and the complete amino acid sequence of Tα1 is Ac-Ser-Asp-Ala-Ala-Val-Asp-Thr-Ser-Ser-Glu-IleThr-Thr-Lys-Asp-Leu-Lys-Glu-Lys-Lys-Glu-Val-Val-Glu-Glu-Ala-Glu-Asn-OH. This peptide has potent biological activity and has been found to be 10～ 1000 times as active as thymosin F5. In this paper, a Tα1 has been synthe sized by a solid-phase method. Peptide synthesis was performed manually by the stepwise solid-phase method using the base-labile Fmoc group for protecting the α-amino acid. [2]     

A Novel Synthesis of β-Hydroxy-α-amino Acids

β-hydroxy-α-amino acids constitute an important class of compounds as naturally occurring amino acids and as components of many complex natural products possessing a wide range of biological activities. [1] As a consequence of the essential role played by these amino acids in the biological systems and their utility as synthetic building blocks, a number of useful strategies have been devised for their preparation. [2]     

Covalent Immobilization of Lipase on Poly（ acrylonitrile-co-maleic acid） Ultrafiltration Hollow Fiber Membrane

IntroductionLipases are biotechnologically important enzymes,which are able to catalyze the hydrolysis/synthesis of awide range of soluble or insoluble carboxylic acid estersand amides.In this way,the enzymes have been wide-ly used biotechnologically in dairy industry,oil pro-cessing,the production of surfactants,and the prepara-tion of enantiomerically pure pharmaceuticals[1,2].However,like mostenzymes for industrial applica-tions,lipases are unstable and easy to lose their cata-lytic activit…     

α-氨基酸与氯化铷在水溶液中焓相互作用参数

The mixing enthalpies of aqueous heavy rare alkali metal chloride RbC1 solutions with aqueous α-amino acid (Loglycine, L-alanine and α-aminobutyric acid) solutions, as well as the dilution enthalpies of RbC1 and α-amino acid solutions in pure water had been measured at 298.15K. The transfer enthalpies of RbCI from pure water to aqueous α-amino acid solutions could be obtained from these data. The enthalpic pair interaction parameters of RbC1 with α-amino acid in water have been evaluated according to the McMillan-Mayer theory and discussed in terms of the electrostatic interaction, structure interaction and Savage-wood group additivity mode.     

Enantioselective three-component Ugi reaction catalyzed by chiral phosphoric acid

A catalytic enantioselective three-component Ugi reaction was developed. SPINOL-derived phosphoric acid with bulky 2,4,6-tricyclohexylphenyl groups at the 6,6′ positions was found to be the best catalyst to afford α-amino amide derivatives in good to excellent yields(62% to 99%) and enantiocontrol(81% to 99% enantiomeric excess). This asymmetric reaction was applicable well to an array of aliphatic aldehydes. The gram-scale synthesis, modification of dapsone, and enantioselective synthesis of(R)-Lacosamide underline the general utility of this methodology. Influence of dihedral angles and substituents of the chiral phosphoric acids on the enantioselectivity was also discussed in this article.     

α-氨基酸在水-乙醇中羧基质子化热力学

Enthalpy changes for the protonation of carboxyl group of four α-amino acids(glycine,L-α-alanine,L-valine and L-serine) were measured in water-ethanol mixtures (10－ 70wt％) at 298.15K using LKB-2277 Bioactivity Monitor.The corresponding entropy and Gibbs energy changes were also calculated.The results show that both enthalpy changes and entropy changes are favorable to the protonation of carboxyl groups of the investigated amino acids in water-ethanol mixtures.However,the influence of the composition of ethanol in the mixed solvents on the enthalpy change and entropy changes is complicated.Both sδ and sδ ,the differences of enthalpy changes and entropy changes in mixed solvents and in pure water respectively,show a minimum approximately at xEtOH=0.1.The effects of side chains on the enthalpy change and entropy changes were also investigated using the proton transfer process between glycine and the other three amino acids.The results demonstrate that the proton transfer processes for alanine and valine are spontaneous but not for serine,which could be interpreted in terms of the electrostatic interaction between amino group and carboxyl group within the molecule and the interaction between carboxyl group and the solvent.     

H14[NaP5W29MoO110]: a Novel and Useful Catalyst for Aminolysis of Epoxides with Amines under Solvent-Free Conditions

A simple and efficient method has been developed for the synthesis of β-amino alcohols by ring opening of epoxides in the presence of a catalytic amount of H14[NaP5W29MoO110] at room temperature under solvent-free conditions. The reaction works well for both aromatic and aliphatic amines.