α-methyl amino acids by catalytic phase-transfer alkylations

The α-methyl amino acids, α-methyl p-chlorophenylalanine, α-methyl p-tyrosine, α-methyl m-tyrosine and α-methyl DOPA have been prepared in good yields from amino ester hydrochlorides. The key step in the method is the catalytic phase-transfer alkylation of Schiff base derivatives of mono alkyl amino acids.     

Synthesis of alkylated sugar amino acids: conformationally restricted L-Xaa-L-Ser/Thr mimics

Two synthetic strategies for the generation of delta-substituted pyranoid sugar amino acids (SAAs) are evaluated. The first employs chiral nonracemic tert-butane sulfinamides as key reagents. Regardless of the stereochemistry of the applied sulfinamide, the product formed has a stereochemistry resembling that of a d amino acid at C7. Direct Grignard reaction on formyl-tetra-O-benzyl-beta-D-C-glucopyranoside in the second strategy and subsequent Mitsunobu inversion, yields the l,l-dipeptide isosters.     

Diastereoselective alkylations of β-tetrazolyl propionic acids

A new procedure for the diastereoselective alkylations of β-tetrazolyl propionic acids is described. A seven-membered chelation model is proposed to rationalize the observed high level of syn selectivity.     

糖类化学催化转化为氨基酸（英文）

在著名的1953年米勒实验中,甲烷、氨气、氢气和水在持续电火花的作用下被转换成一系列天然氨基酸混合物,包括甘氨酸、丙氨酸、天冬氨酸和α-氨基丁酸等等.这种化学转化过程奠定了现代人们对地球生命起源的认知基础.氨基酸作为蛋白质的基本组成成分,在生产生活中有广泛的应用,扮演着不可或缺的角色.目前,微生物发酵过程是氨基酸的主要生产途径,其生产受到许多限制.通过高效的催化方法将氨气和丰富的可再生碳资源直接转化成一系列氨基酸的化学路径尚未实现.近日,新加坡国立大学颜宁教授课题组与厦门大学王野教授课题组等数个国内外研究小组合作,开辟了一种用化学方法将木质生物质转化成一系列氨基酸的新路径.转化策略分两步:首先将纤维素、葡萄糖等转化为α-羟基酸,再将α-羟基酸在氨水和氢气作用下制备对应的氨基酸.第二步是核心步骤,可以被看作是一种改进版的米勒实验:即采用特定的木质生物质衍生物替代甲烷作为底物,而负载的钌催化剂则取代电火花实现定向高效转化.该系统已经成功用于6种氨基酸制备,包括丙氨酸、亮氨酸、缬氨酸、天冬氨酸和苯丙氨酸等.将α-羟基酸转化成氨基酸的反应遵循先脱氢再还原胺化途径,其中脱氢是速率控制步骤.在该反应中,碳纳米管上负载的钌催化剂比其他贵金属催化剂表现出显著优异的活性.这主要得益于氨分子对钌纳米颗粒的配位作用增强了钌脱氢反应的活性.基于新开发的催化体系,葡萄糖经由两步化学反应转化成43%丙氨酸,产率与微生物发酵过程相当.文章作者还使用膜蒸馏作为产物分离提纯技术,完成了概念性工艺设计,并用实验加以验证.考虑到氨基酸的高价值,这项报道不仅代表了近年来生物质催化转化的一项重要学术突破,在进一步开发和优化后还具有很好的应用潜力.     

Enzymatic transformations of 3-chloroalanine into useful amino acids

The investigation of the combination of enzymatic and chemical synthetic processes for the production of useful compounds has been carried out. This review focuses on the enzymatic transformation of chemically synthesized 3-chloroalanine into useful amino acids.     

A possible approach to site-specific insertion of two different unnatural amino acids into proteins in mammalian cells via nonsense suppression

The site-specific insertion of an unnatural amino acid into proteins in vivo via nonsense suppression has resulted in major advances in recent years. The ability to incorporate two different unnatural amino acids in vivo would greatly increase the scope and impact of unnatural amino acid mutagenesis. Here, we show the concomitant suppression of an amber and an ochre codon in a single mRNA in mammalian cells by importing a mixture of aminoacylated amber and ochre suppressor tRNAs. This result provides a possible approach to site-specific insertion of two different unnatural amino acids into any protein of interest in mammalian cells. To our knowledge, this result also represents the only demonstration of concomitant suppression of two different termination codons in a single gene in vivo.     

In vivo incorporation of multiple noncanonical amino acids into proteins

Expansion of the standard genetic code enables the design of recombinant proteins with novel and unusual properties. Traditionally, such proteins have contained only a single type of noncanonical amino acid (NCAA) in their amino acid sequence. However, recently reported initial efforts demonstrate that it is possible with suppression-based methods to translate two chemically distinct NCAAs into a single recombinant protein by combining the suppression of different termination codons and nontriplet coding units (such as quadruplets). The possibility of expanding the code with various NCAAs simultaneously further increases the toolkit for the generation of multifunctionalized proteins.     

Transforming natural amino acids into alpha-alkyl-substituted amino acids with the help of the HOF.CH3CN complex

Alpha-alkyl amino acids can be efficiently prepared in high yields from the respective amino acids themselves. The key step is the oxidation of the amine function to create the corresponding alpha-nitro acid in a fast and very high yield reaction followed by phase-transfer alkylation and finally reduction to the desired alpha-alkyl amino acid. Several such acids containing aromatic rings or additional carboxylic groups and acids with steric hindrance at the alpha-position are suitable substrates. Several alkyl halides were examined as alkylating agents.     

A likely possible origin of homochirality in amino acids and sugars on prebiotic earth

For life to start on earth and elsewhere, it is critical that the building blocks—amino acids and sugars—be in predominant homochiral form. Over the past century, the origin of terrestrial prebiotic homochirality has been the subject of many speculations. In this Letter I summarize the experimental evidence for ways in which some meteoritic components could have led to the dominance of l amino acids and d sugars on earth, and the most likely way in which the original chiral excesses in the meteorites were formed.     

Partial transfer of enantioselective chiralities from α-methylated amino acids, known to be of meteoritic origin, into normal amino acids

There is overwhelming evidence that meteorites bring α-methylated amino acids to earth with some l(S) enantiomeric excess. How does that get transferred into normal biological molecules? In this brief account, we show that an α-methylated amino acid, d(R)-α-methylvaline, can react with pyruvate and phenylpyruvate salts in dry mixtures to form alanine and phenylalanine with l enantiomeric excesses, under sensible prebiotic conditions. Thus the meteoritic l(S) excesses of this compound would produce excess d-alanine and d-phenylalanine, which are found in some organisms.     

Unconventional titania photocatalysis: direct deployment of carboxylic acids in alkylations and annulations

Under dry, anaerobic conditions, TiO(2) photocatalysis of carboxylic acid precursors resulted in carbon-carbon bond-forming processes. High yields of dimers were obtained from TiO(2) treatment of carboxylic acids alone. On inclusion of electron-deficient alkenes, efficient alkylations were achieved with methoxymethyl and phenoxymethyl radicals. In reactions with maleic anhydride or maleimides, phenoxyacetic acid produced chromenedione derivatives in addition to adducts. These photocatalytic reactions are simple and cheap to perform, and the TiO(2) is easily removed by filtration. The anaerobic photocatalysis strategy offers a range of synthetic possibilities.     

Site-specific incorporation of photo-cross-linker and bioorthogonal amino acids into enteric bacterial pathogens

Enteric bacterial pathogens are known to effectively pass through the extremely acidic mammalian stomachs and cause infections in the small and/or large intestine of human hosts. However, their acid-survival strategy and pathogenesis mechanisms remain elusive, largely due to the lack of tools to directly monitor and manipulate essential components (e.g., defense proteins or invasive toxins) participating in these processes. Herein, we have extended the pyrrolysine-based genetic code expansion strategy for encoding unnatural amino acids in enteric bacterial species, including enteropathogenic Escherichia coli , Shigella , and Salmonella . Using this system, a photo-cross-linking amino acid was incorporated into a Shigella acid chaperone HdeA (shHdeA), which allowed the identification of a comprehensive list of in vivo client proteins that are protected by shHdeA upon acid stress. To further demonstrate the application of our strategy, an azide-bearing amino acid was introduced into a Shigella type 3 secretion effector, OspF, without interruption of its secretion efficiency. This site-specifically installed azide handle allowed the facile detection of OspF's secretion in bacterial extracellular space. Taken together, these bioorthogonal functionalities we incorporated into enteric pathogens were shown to facilitate the investigation of unique and important proteins involved in the pathogenesis and stress-defense mechanisms of pathogenic bacteria that remain exceedingly difficult to study using conventional methodologies.     

Site-specific incorporation of unnatural amino acids into receptors expressed in Mammalian cells

We describe an approach to achieve unnatural amino acid incorporation into channels and receptors expressed in mammalian cells. We show that microelectroporation provides a general method to deliver DNA, mRNA, and tRNA simultaneously. In both CHO cells and cultured neurons, microelectroporation efficiently delivers an in vitro transcribed, serine amber suppressor tRNA, leading to nonsense suppression in a mutant EGFP gene. In CHO cells, both natural and unnatural amino acids chemically appended to a suppressor tRNA are site specifically incorporated into the nicotinic acetylcholine receptor (nAChR). Electrophysiology confirms the expected functional consequences of the unnatural residue. The microelectroporation strategy described here is more general, less tedious, and less damaging to mammalian neuronal and nonneuronal cells than previous approaches to nonsense suppression in small cells and provides the first example of unnatural amino acid incorporation in mammalian cells using chemically aminoacylated tRNA.     

Intercalation behavior of amino acids into Zn-Al-layered double hydroxide by calcination-rehydration reaction

The intercalation of amino acids for the Zn-Al-layered double hydroxide (LDH) has been investigated by the calcination-rehydration reaction at 298 K using mainly phenylalanine (Phe) as a guest amino acid. The Zn-Al oxide precursor prepared by the calcination of Zn-Al-carbonated LDH at 773 K for 2 h was used as the host material. The amount of Phe intercalated by the rehydration was remarkably influenced by the initial solution pH and reached ca. 2.7 times for anion exchange capacity (AEC) of the LDH at neutral and weak alkaline solutions, suggesting that Phe was intercalated as amphoteric ion form into the LDH interlayer. As Phe is intercalated for the LDH as monovalent anion in alkaline solution, the amount of Phe intercalated at pH 10.5 corresponded with AEC of the LDH. The solid products were found to have the expanded LDH structure, which confirmed that Phe was intercalated into the LDH interlayer as amphoteric ion or anion form. The basal spacing, d₀₀₃, of the Phe/LDH was 1.58 nm at pH 7.0 and 0.80 nm at pH 10.5; two kinds of expansion suggested for Phe in the interlayer space as vertical (pH 7.0) and horizontal (pH 10.5) orientations. The intercalation behavior of various amino acids for the LDH was also found to be greatly influenced by the feature of the amino acid side-chain, namely, its carbon-chain length, structure and physicochemical property. In particular, α-amino acids possessing a hydrophobic or negative-charged side-chain were preferentially intercalated for the LDH.     

Chiral separation of dansyl amino acids by capillary electrophoresis: Comparison of formamide andN-Methylformamide as background electrolytes

Summary Chiral separation of 12 dansyl amino acids has been achieved by capillary electrophoresis using -cyclodextrin dissolved inN-methylformamide or formamide. The viscosity and the dielectric constants of these two solvents are very different, giving them disimilar electrophoretic properties. Intense electroosmotic flow, high electrophoretic mobilities and high efficiency were achieved inN-methylformamide, but high chiral selector concentration was needed for sufficient resolution. In contrast, the separation of dansyl amino acids in formamide was characterized by longer analysis time and lower efficiency, but the resolution and selectivity of the separation were better and baseline separation could be achieved at lower -cyclodextrin concentrations.     

Engineering dehydro amino acids and thioethers into peptides using lacticin 481 synthetase

Lantibiotics are peptide antimicrobials containing the thioether-bridged amino acids lanthionine (Lan) and methyllanthionine (MeLan) and often the dehydrated residues dehydroalanine (Dha) and dehydrobutyrine (Dhb). While biologically advantageous, the incorporation of these residues into peptides is synthetically daunting, and their production in vivo is limited to peptides containing proteinogenic amino acids. The lacticin 481 synthetase LctM offers versatile control over the installation of dehydro amino acids and thioether rings into peptides. In vitro processing of semisynthetic substrates unrelated to the prelacticin 481 peptide demonstrated the broad substrate tolerance of LctM. Furthermore, a chemoenzymatic strategy was employed to generate novel thioether linkages by cyclization of peptidic substrates containing the nonproteinogenic cysteine analogs homocysteine and beta-homocysteine. These findings are promising with respect to the utility of LctM toward preparation of conformationally constrained peptide therapeutics.     

Method for clustering proteins by use of all possible pairs of amino acids as structural descriptors

Proteins were represented as vectors, of which components were all possible pairs of amino acids. From a distance matrix between any pairs of proteins thus represented, several clusters corresponding to connected components were generated. Application of this method to three different sets of proteins showed that it was suitable for clustering closely related proteins with respect to the sequential similarity defined by Dayhoff.     

Protease-catalyzed peptide synthesis for the site-specific incorporation of alpha-fluoroalkyl amino acids into peptides

Substitution of native amino acids by fluoroalkyl analogues represents a new approach for the design of biologically active peptides with increased metabolic stability as well as defined secondary structure and provides a powerful label for spectroscopic investigations. Here, we introduce a methodology for the incorporation of sterically demanding C(alpha)-fluoroalkyl amino acids into the P(1) position of peptides catalyzed by the commercially available proteases trypsin and alpha-chymotrypsin. The combination of 4-guanidinophenyl ester of C(alpha)-fluoroalkyl amino acids as substrate mimetics with frozen-state reaction conditions provided the most efficient strategy for protease-catalyzed site-specific introduction of this kind of nonnatural amino acids into peptide sequences. Consequently, a library of di-, tri-, and tetrapeptides containing alpha-methyl, alpha-difluoromethyl, and alpha-trifluoromethyl alanine, leucine, and phenylalanine in the P(1) position was synthesized catalyzed by trypsin as well as alpha-chymotrypsin. Trypsin was shown to be the more versatile protease.