The mimicry of protein‐sized β‐sheet structures with unnatural peptidic sequences (foldamers) is a considerable challenge. In this work, the de novo designed betabellin‐14 β‐sheet has been used as a template, and α→β residue mutations were carried out in the hydrophobic core (positions 12 and 19). β‐Residues with diverse structural properties were utilized: Homologous β3‐amino acids, (1R,2S)‐2‐aminocyclopentanecarboxylic acid (ACPC), (1R,2S)‐2‐aminocyclohexanecarboxylic acid (ACHC), (1R,2S)‐2‐aminocyclohex‐3‐enecarboxylic acid (ACEC), and (1S,2S,3R,5S)‐2‐amino‐6,6‐dimethylbicyclo[3.1.1]heptane‐3‐carboxylic acid (ABHC). Six α/β‐peptidic chains were constructed in both monomeric and disulfide‐linked dimeric forms. Structural studies based on circular dichroism spectroscopy, the analysis of NMR chemical shifts, and molecular dynamics simulations revealed that dimerization induced β‐sheet formation in the 64‐residue foldameric systems. Core replacement with (1R,2S)‐ACHC was found to be unique among the β‐amino acid building blocks studied because it was simultaneously able to maintain the interstrand hydrogen‐bonding network and to fit sterically into the hydrophobic interior of the β‐sandwich. The novel β‐sandwich model containing 25 % unnatural building blocks afforded protein‐like thermal denaturation behavior. 相似文献
An amperometric method for the determination of the neurotoxic amino acid β‐N‐oxalyl‐L ‐α,β‐diaminopropionic acid (β‐ODAP) using a screen printed carbon electrode (SPCE) is reported. The electrode material was bulk‐modified with manganese dioxide and used as a detector in flow injection analysis (FIA). The enzyme glutamate oxidase (GlOx) was immobilized in a Nafion‐film on the electrode surface. The performance of the biosensor was optimized using glutamate as an analyte. Optimum parameters were found as: operational potential 440 mV (vs. Ag/AgCl), flow rate 0.2 mL min?1, and carrier composition 0.1 mol L?1 phosphate buffer (pH 7.75). The same conditions were used for the determination of β‐ODAP. The signal was linear within the concentration range 53–855 μmol L?1 glutamate and 195–1950 μmol L?1 β‐ODAP. Detection limits (as 3σ value) for both analytes were 9.12 and 111.0 μmol L?1, respectively, with corresponding relative standard deviations of 3.3 and 4.5%. The biosensor retained more than 73% of its activity after 40 days of on‐line use. 相似文献
A series of β‐amino esters were synthesized by the reaction of N‐tosyl aldimine or N‐hydroxy aldimine with bromoacetate by sonochemical Reformatsky reaction. The β‐N‐hydroxyamino ester was obtained and the formed sensitive hydroxylamino functionality was resistant under the reaction condition. The β‐lactam also was synthesized by the reaction of N‐p‐methoxy aldimine as reacting substrate under this sonochemical Reformatsky reaction condition. 相似文献
Different cyclo‐β‐dipeptides were prepared from corresponding N‐substituted β‐alanine derivatives under mild conditions using PhPOCl2 as activating agent in benzene and Et3N as base. To evaluate β3‐substituent influence, the amino acids 7 – 26 were synthesized, and a β‐lactam formation reaction was carried out instead of cyclo‐β‐dipeptide formation. The crystal structures of three derivatives of cyclo‐β‐peptides and one β‐lactam are presented. 相似文献
The reaction of the β‐diketoiminate lithium complex (dipp)NacNacLi · OEt2 ((dipp)NacNac = 2‐((2,6‐diisopropylphenyl)amino)‐4‐((2,6‐diisopropylphenyl)imino)‐pent‐2‐enyl) with iPrMgCl and MgI2 yield the corresponding (dipp)NacNacMgiPr · OEt2 ( 1 ) and (dipp)NacNacMgI · OEt2 ( 2 ). The reaction of 2 with NaBH4 in diethylether gives (dipp)NacNacMg(μ‐H)3BH · OEt2 ( 3 ). The core element of compounds 1 – 3 is a six‐membered ring formed by N(1)–C(1)–C(2)–C(3)–N(2) and magnesium. The structures of 1 and 2 show the β‐diketoiminate backbone in a boat‐conformation with the tetrahedrally coordinated metal center at the prow and the opposing carbon atom at the stern. The magnesium atom in 3 is octahedrally coordinated and out of the β‐diketoiminate plane. 相似文献
The photochemical behavior of various substituted epoxycarbonyl compounds consisting of more than one possible photo‐labile site (i.e. δ‐hydrogen, β‐hydrogen and epoxide ring) has been investigated. These compounds on photo‐irradiation produced the β‐hydroxyenones in an eco‐friendly green approach. Mechanistically, these photo‐transformations have been envisaged to occur via an intramolecular β‐hydrogen abstraction by the carbonyl group of benzoyl moiety to generate the 1,3‐biradical followed by epoxide ring opening that isomerizes into the photoproducts. The photolysis of the probed epoxy ketones didn’t furnish any photoproduct through δ‐hydrogen abstraction, whatsoever. This exclusive preference for β‐H abstraction over δ‐H abstraction by carbonyl group has been vindicated by the MM2 energy mini‐ mized program for the investigated photochemical substrates. The structures of these photoproducts were established from the analysis of their spectral parameters (IR, 1H/13C NMR and Mass) and single crystal X‐ray crystallography data. 相似文献
Hybrid peptidic oligomers comprising natural and unnatural amino acid residues that can exhibit biomolecular folding and hydrogen‐bonding mimicry have attracted considerable interest in recent years. While a variety of hybrid peptidic helices have been reported in the literature, other secondary structural patterns such as γ‐turns and ribbons have not been well explored so far. The present work reports the design of novel periodic γ‐turns in the oligomers of 1:1 natural‐α/unnatural trans‐β‐norborenene (TNAA) amino acid residues. Through DFT, NMR, and MD studies, it is convincingly shown that, in the mixed conformational pool, the heterogeneous backbone of the hybrid peptides preferentially adopt periodic 8‐membered (pseudo γ‐turn)/7‐membered (inverse γ‐turn) hydrogen bonds in both polar and non‐polar solvent media. It is observed that the stereochemistry and local conformational preference of the β‐amino acid building blocks have a profound influence on accessing the specific secondary fold. These findings may be of significant relevance for the development of molecular scaffolds that facilitate desired positioning of functional side‐chains. 相似文献
An addition to the family : The introduction of β‐amino acid residues into a modified amyloid β peptide fragment resulted in well‐defined helical nanoribbons (see cryo‐TEM image) comprising β strands mainly oriented perpendicular to the ribbon axis. The nanoribbons order into a flow‐aligning nematic phase at higher concentration. The β‐strand nanoribbon structure is an addition to the known set of secondary structures adopted by β‐peptides.
We report a novel 1:1 cocrystal of β‐alanine with dl ‐tartaric acid, C3H7NO2·C4H6O6, (II), and three new molecular salts of dl ‐tartaric acid with β‐alanine {3‐azaniumylpropanoic acid–3‐azaniumylpropanoate dl ‐tartaric acid–dl ‐tartrate, [H(C3H7NO2)2]+·[H(C4H5O6)2]−, (III)}, γ‐aminobutyric acid [3‐carboxypropanaminium dl ‐tartrate, C4H10NO2+·C4H5O6−, (IV)] and dl ‐α‐aminobutyric acid {dl ‐2‐azaniumylbutanoic acid–dl ‐2‐azaniumylbutanoate dl ‐tartaric acid–dl ‐tartrate, [H(C4H9NO2)2]+·[H(C4H5O6)2]−, (V)}. The crystal structures of binary crystals of dl ‐tartaric acid with glycine, (I), β‐alanine, (II) and (III), GABA, (IV), and dl ‐AABA, (V), have similar molecular packing and crystallographic motifs. The shortest amino acid (i.e. glycine) forms a cocrystal, (I), with dl ‐tartaric acid, whereas the larger amino acids form molecular salts, viz. (IV) and (V). β‐Alanine is the only amino acid capable of forming both a cocrystal [i.e. (II)] and a molecular salt [i.e. (III)] with dl ‐tartaric acid. The cocrystals of glycine and β‐alanine with dl ‐tartaric acid, i.e. (I) and (II), respectively, contain chains of amino acid zwitterions, similar to the structure of pure glycine. In the structures of the molecular salts of amino acids, the amino acid cations form isolated dimers [of β‐alanine in (III), GABA in (IV) and dl ‐AABA in (V)], which are linked by strong O—H…O hydrogen bonds. Moreover, the three crystal structures comprise different types of dimeric cations, i.e. (A…A)+ in (III) and (V), and A+…A+ in (IV). Molecular salts (IV) and (V) are the first examples of molecular salts of GABA and dl ‐AABA that contain dimers of amino acid cations. The geometry of each investigated amino acid (except dl ‐AABA) correlates with the melting point of its mixed crystal. 相似文献
Conformational features of α,β‐disubstituted β2,3‐dipeptide models have been studied with quantum mechanics method. Geometries were optimized with the HF/6‐31G** method, and energies were evaluated with the B3LYP/6‐31G** method. Solvent effect was evaluated with the SCIPCM method. For (2S,3S)‐β2,3‐dipeptide model 1 , a six‐membered‐ring hydrogen bonded structure is most stable. However, the conformation corresponding to the formation of the 14‐helix is only about 1.7 kcal/mol less stable in methanol solution, indicating that the 14‐helix is favored if a (2S,3S)‐β2,3‐polypeptide contains more than 5 residues. On the other hand, the conformation corresponding to the formation of β‐sheet is most stable for (2R,3S)‐β2,3‐dipeptide model 2 , suggesting that this type of β‐peptides is intrinsically favored for the formation of β‐sheet secondary structure. 相似文献
A method is described to separate α‐ from β‐arylalanines by ligand exchange chromatography on a nickel nitrilotriacetate agarose column with UV monitoring of the effluent. Separate mixtures containing an α‐ and β‐arylalanine pair (1 mg of each) were individually loaded onto the nickel resin pre‐equilibrated with the mobile phase at room temperature, and the amino acids were eluted from the column with a gradient from pH 12.0–8.0. The β‐arylalanines eluted first, followed by the α‐isomers. The four α/β‐amino acid pairs tested were well separated with baseline resolution. An aliquot of each fraction was chemically treated to derivatize the amino acids to their N‐acyl methyl ester analogs, and their identities were confirmed by GC/MS analysis. The sample recovery was quantitative (>98%), and the column matrix was very resilient, as demonstrated by consistent separation of the solutes after ~100 preparative cycles. 相似文献
α‐Amino phosphonic acid derivatives are considered to be the most important structural analogues of α‐amino acids and have a very wide range of applications. However, approaches for the catalytic asymmetric synthesis of such useful compounds are very limited. In this work, simple, efficient, and versatile organocatalytic asymmetric 1,2‐addition reactions of α‐isothiocyanato phosphonate were developed. Through these processes, derivatives of β‐hydroxy‐α‐amino phosphonic acid and α,β‐diamino phosphonic acid, as well as highly functionalized phosphonate‐substituted spirooxindole, can be efficiently constructed (up to 99 % yield, d.r. >20:1, and >99 % ee). This novel method provides a new route for the enantioselective functionalization of α‐phosphonic acid derivatives. 相似文献