Aspartic Acid Analogues Research Articles

A Tar aspartate receptor and Rubisco-like protein substitute biotin in the growth of rhizobial strains.

Biotin is a key cofactor of metabolic carboxylases, although many rhizobial strains are biotin auxotrophs. When some of these strains were serially subcultured in minimal medium, they showed diminished growth and increased excretion of metabolites. The addition of biotin, or genetic complementation with biotin synthesis genes resulted in full growth of Rhizobium etli CFN42 and Rhizobium phaseoli CIAT652 strains. Half of rhizobial genomes did not show genes for biotin biosynthesis, but three-quarters had genes for biotin transport. Some strains had genes for an avidin homologue (rhizavidin), a protein with high affinity for biotin but an unknown role in bacteria. A CFN42-derived rhizavidin mutant showed a sharper growth decrease in subcultures, revealing a role in biotin storage. In the search of biotin-independent growth of subcultures, CFN42 and CIAT652 strains with excess aeration showed optimal growth, as they also did, unexpectedly, with the addition of aspartic acid analogues α- and N-methyl aspartate. Aspartate analogues can be sensed by the chemotaxis aspartate receptor Tar. A tar homologue was identified and its mutants showed no growth recovery with aspartate analogues, indicating requirement of the Tar receptor in such a phenotype. Additionally, tar mutants did not recover full growth with excess aeration. A Rubisco-like protein was found to be necessary for growth as the corresponding mutants showed no recovery either with high aeration or aspartate analogues; also, diminished carboxylation was observed. Taken together, our results indicate a route of biotin-independent growth in rhizobial strains that included oxygen, a Tar receptor and a previously uncharacterized Rubisco-like protein.

Enantioselective Aza-Reformatsky Reaction with Ketimines.

Here, an enantioselective aza-Reformatsky reaction using acyclic ketimine substrates is presented. Using α-phosphorated ketimines as electrophilic substrates and a simple BINOL-derived ligand, phosphorated analogues of aspartic acid holding chiral tetrasubstituted carbons are efficiently obtained with excellent enantioselectivity through an asymmetric organocatalytic Reformatsky-type reaction. The phosphorated analogues of aspartic acid have been used for the synthesis of phosphorus-containing enantiopure tetrasubstituted β-lactams.

Cogitum in children's neurology and psychiatry (experience in the practical use)

The authors review current data on the role of the synthetic aspartic acid analogue N-acetyaspartate (NAA) in various biochemical metabolic reactions in the CNS. Its importance as a biomarker for neuropsychiatric disorders identified using magnetic resonance spectroscopy (MRS) is noted. The authors present their own results of the use of cogitum, a synthetic analogue of NAA, in children with the effects of traumatic brain injury, mental retardation, hyperactivity disorder and in the complex therapy of schizotypal disorder. Effects of cogitum on cognitive deficit, asthenia are evaluated. The neurotrophic effect of the drug, which specifically affects cognitive and asthenic disorders in these diseases, is shown.

Construction of adjacent spiro-quaternary and tertiary stereocenters through phosphine-catalyzed asymmetric [3+2] annulation of allenoates with alkylidene azlactones

A novel axially chiral spiro-phosphine-catalyzed highly regio-, diastereo- and enantioselective [3+2] cycloaddition of alkylidene azlactones with various allenic esters has been developed, affording the corresponding functionalized spirocyclic products in moderate to excellent yields under mild conditions. These spirocyclic products as masked amino acids can be easily transformed into aspartic amino acid analogues.

ChemInform Abstract: Phosphine‐Catalyzed [3 + 2] Cycloadditions of 2‐Phenyl‐4‐arylidene‐5(4H)‐oxazolones with Allenoate: A Concise Synthesis of Aspartic Acid Analogues.

AbstractA new family of aspartic acid derivatives is obtained through cycloaddition reactions of oxazolones (I) with allenoate (II), providing restricted cyclopentanyl aspartic acid analogues (III) and (IV) under mild conditions.

Phosphine-Catalyzed [3+2] Cycloadditions of 2-Phenyl-4-Arylidene-5(4H)-Oxazolones with Allenoate: A Concise Synthesis of Aspartic Acid Analogues

A Ph3P-catalyzed (3+2) cycloaddition of 2-phenyl-4- arylidene-5(4H)-oxazolones with benzyl 2,3-butadienoate has been developed for the efficient synthesis of structurally diverse and con- formationally constrained aspartic acid analogues.

How the MccB bacterial ancestor of ubiquitin E1 initiates biosynthesis of the microcin C7 antibiotic

The 39-kDa Escherichia coli enzyme MccB catalyses a remarkable posttranslational modification of the MccA heptapeptide during the biosynthesis of microcin C7 (MccC7), a 'Trojan horse' antibiotic. The approximately 260-residue C-terminal region of MccB is homologous to ubiquitin-like protein (UBL) activating enzyme (E1) adenylation domains. Accordingly, MccB-catalysed C-terminal MccA-acyl-adenylation is reminiscent of the E1-catalysed activation reaction. However, unlike E1 substrates, which are UBLs with a C-terminal di-glycine sequence, MccB's substrate, MccA, is a short peptide with an essential C-terminal Asn. Furthermore, after an intramolecular rearrangement of MccA-acyl-adenylate, MccB catalyses a second, unique reaction, producing a stable phosphoramidate-linked analogue of acyl-adenylated aspartic acid. We report six-crystal structures of MccB in apo, substrate-, intermediate-, and inhibitor-bound forms. Structural and kinetic analyses reveal a novel-peptide clamping mechanism for MccB binding to heptapeptide substrates and a dynamic-active site for catalysing dual adenosine triphosphate-consuming reactions. The results provide insight into how a distinctive member of the E1 superfamily carries out two-step activation for generating the peptidyl-antibiotic MccC7.

Stereoselective Synthesis of 4-Amino-3-hydroxy-4,5,6,6a-tetrahydro-3aH-cyclopenta[d]isoxazole-4-carboxylic Acid, a Conformationally Constrained Analogue of Aspartic Acid

An alternative synthesis of 4-amino-3-hydroxy-4,5,6,6a-tetrahydro-3aH-cyclopenta[d]isoxazole-4-carboxylic acid, a conformationally constrained analogue of aspartic acid, is described. The synthetic strategy is based on a regioselective 1,3-dipolar cycloaddition to give the cyclopenta[d]isoxazoline framework; subsequent condensation of this 4-oxocyclopenta[d]isoxazoline with 4-methoxybenzylamine gives a 4-imino derivative, which undergoes a highly stereoselective nucleophilic attack by the cyanide ion. This gives a 4-(methoxybenzylamino)-4-cyano derivative, which is oxidized to the corresponding 4-amino-4-cyano derivative, which itself is transformed into the target 4-carboxylic acid. This amino acid is obtained in 27% overall yield in five steps, whereas the previously described synthetic strategy gave the target derivative in only 0.5% overall yield over 15 steps.

Quantitative Structure–Activity Relationship Study of Some Aspartic Acid Analogues to Correlate and Predict their Sweetness Potency

AbstractA series of aspartame analogues and chemically modified derivatives was evaluated for their structure–activity relationship, as artificial sweeteners using Three Dimensional Quantitative Structure–Activity Relationship (3D‐QSAR) with Genetic Functional Algorithm (GFA). A four‐term equation was developed with conventional and cross‐validated coefficients of 0.753 and 0.660, respectively. 3D‐QSAR studies of the same series were also performed by Comparative Molecular Field Analysis (CoMFA) and Comparative Molecular Similarity Indices Analysis (CoMSIA). The CoMFA model produced modest statistical significance with conventional and cross‐validated correlation coefficients of 0.768 and 0.390, respectively. The combination of steric, electrostatic, hydrophobic, and H‐bond acceptor fields in CoMSIA gave better results with conventional and cross‐validated correlation coefficients of 0.927 and 0.585, respectively. The predictive ability of 3D‐QSAR with GFA, CoMFA, and CoMSIA were determined using a test set of ten molecules giving predictive correlation coefficients of 0.375, 0.535, and 0.596, respectively, indicating better predictivity of CoMSIA compared to the other methods. Based on this information, some key features that may be used to design new sweeteners and predict their sweetness value have been identified.

A structure–activity relationship study of compounds with antihistamine activity

A structure-activity relationship (SAR) analysis of H(1)-, H(2)- and H(3)-antihistamine activity was carried out and chromatographic data of 2-[2-(phenylamino)thiazol-4-yl]ethanamine, 2-(2-benzyl-4-thiazolyl)ethanamine, 2-(2-benzhydrylthiazol4-yl)ethanamine, 2-(1-piperazinyl- and 2-(hexahydro-1H-1,4-diazepin-1-yl)benzothiazole, 2-(1-piperazinyl)benzothiazole, 2-[4-(1-alkyl)piperidinyl]benzothiazole, 2-(N,N',N'-dimethylalkyl-1,2-ethanediamino)benzothiazole, 2[1-(4-aminopiperidinyl)]benzothiazole, 2-[2-phenyl-4-thiazolyl]ethanamine derivatives and selected H(1)- and H(2)-antihistamine drugs were obtained. NP TLC and RP2 TLC plates (silica gel NP 60F(254) and silica gel RP2 60F(254) silanized precoated), impregnated with a solution of aspartic acid (L-Asp) and a solution of an analogue of aspartic acid (propionic acid), were used in two developing solvents as H(1)-, H(2)- and H(3)-antihistaminic interaction models. The lipophilicity data of the examined compounds were obtained and used in the SAR assay. Biochromatographic tests using TLC plates impregnated with solutions of asparic acid or propionic acid were found to be a source of useful data for the qualitative analysis of compounds with different structures, demonstrating activity to histamine H(1)-, H(2)- and H(3)-receptors. The four presented discriminant models based on biochromatographic studies are an efficient tool in the SAR analysis for initial prediction of compound activity direction within histamine receptors.

Sterically hindered C(alpha, alpha)-disubstituted alpha-amino acids: synthesis from alpha-nitroacetate and incorporation into peptides.

The preparation of sterically hindered and polyfunctional C(alpha,alpha)-disubstituted alpha-amino acids (alpha alpha AAs) via alkylation of ethyl nitroacetate and transformation into derivatives ready for incorporation into peptides are described. Treatment of ethyl nitroacetate with N,N-diisopropylethylamine (DIEA) in the presence of a catalytic amount of tetraalkylammonium salt, followed by the addition of an activated alkyl halide or Michael acceptor, gives the doubly C-alkylated product in good to excellent yields. Selective nitro reduction with Zn in acetic acid or hydrogen over Raney Ni gives the corresponding amino ester that, upon saponification, can be protected with the fluorenylmethyloxycarbonyl (Fmoc) group. The first synthesis of an orthogonally protected, tetrafunctional C(alpha,alpha)-disubstituted analogue of aspartic acid, 2,2-bis(tert-butylcarboxymethyl)glycine (Bcmg), is described. Also, the sterically demanding C(alpha,alpha)-dibenzylglycine (Dbg) has been incorporated into a peptide using solid-phase synthesis. It was found that once sterically congested Dbg is at the peptide N-terminus, further chain extension becomes very difficult using uronium or phosphonium salts (PyAOP, PyAOP/HOAt, HATU). However, preformed amino acid symmetrical anhydride couples to N-terminal Dbg in almost quantitative yield in nonpolar solvent (dichloroethane-DMF, 9:1).

Synthesis of boronic acid analogues of alpha-amino acids by introducing side chains as electrophiles.

A synthetic route has been developed which has allowed us to prepare novel alpha-aminoboronic acids as inhibitors of serine proteases. These compounds were prepared to study the roles of proteases in biological systems. This methodology affords alpha-aminoboronic acids with the general formula R'-NHCH(R)BO(2)-pinanediol, where R = -CH(2)CHF(2), -CH(2)CO(2)tBu, and -(CH(2))(2)CO(2)Me and R' = either H or C(O)R". The latter two compounds are the boronic acid analogues of the natural amino acids aspartic acid and glutamic acid with the side chain carboxylate protected as a tert-butyl or a methyl ester, respectively. Following acylation of the amino group, the side chain tert-butyl ester of boroaspartic acid was removed by treatment with TFA. Boroglutamic acid was obtained as the free boronic acid by hydrolysis with HCl. Prior syntheses of alpha-aminoboronic acids involve the initial addition of an organometallic reagent to a trialkyl borate ester. These conditions do not allow the preparation of compounds with functionalities that are not stable to the strongly basic reaction conditions. The methodology described here allows the preparation of alpha-aminoboronic acids by introducing side chains as electrophiles. This is particularly advantageous for side chains which are prone to elimination or unwanted enolate formation. Specifically, BrCH(2)CHF(2), BrCH(2)COO(t)Bu, and CH(2)=CHCOOMe were allowed to react with the stabilized anion of (phenylthio)methane boronate, PhSCH(2)BO(2)C(6)H(12), to give the substituted boronate. The substituted (phenylthio)methane boronate was converted to the corresponding sulfonium ion by treatment with methyl iodide and subsequently displaced with iodide. The alpha-iodo derivative was converted to the amine by conventional methods.

Probing the S1/S1' substrate binding pocket geometry of HIV-1 protease with modified aspartic acid analogues.

Aspartates 25 and 125, the active site residues of HIV-1 protease, participate functionally in proteolysis by what is believed to be a general acid-general base mechanism. However, the structural role that these residues may play in the formation and maintenance of the neighboring S1/S1' substrate binding pockets remains largely unstudied. Because the active site aspartic acids are essential for catalysis, alteration of these residues to any other naturally occurring amino acid by conventional site-directed mutagenesis renders the protease inactive, and hence impossible to characterize functionally. To investigate whether Asp-25 and Asp-125 may also play a structural role that influences substrate processing, a series of active site protease mutants has been produced in a cell-free protein synthesizing system via readthrough of mRNA nonsense (UAG) codons by chemically misacylated suppressor tRNAs. The suppressor tRNAs were activated with the unnatural aspartic acid analogues erythro-beta-methylaspartic acid, threo-beta-methylaspartic acid, or beta,beta-dimethylaspartic acid. On the basis of the specific activity measurements of the mutants that were produced, the introduction of the beta-methyl moiety was found to alter protease function to varying extents depending upon its orientation. While a beta-methyl group in the erythro orientation was the least deleterious to the specific activity of the protease, a beta-methyl group in the threo orientation, present in the modified proteins containing threo-beta-methylaspartate and beta,beta-dimethylaspartate, resulted in specific activities between 0 and 45% of that of the wild type depending upon the substrate and the substituted active site position. Titration studies of pH versus specific activity and inactivation studies, using an aspartyl protease specific suicide inhibitor, demonstrated that the mutant proteases maintained bell-shaped pH profiles, as well as suicide-inhibitor susceptibilities that are characteristic of aspartyl proteases. A molecular dynamics simulation of the beta-substituted aspartates in position 25 of HIV-1 protease indicated that the threo-beta-methyl moiety may partially obstruct the adjacent S1' binding pocket, and also cause reorganization within the pocket, especially with regard to residues Val-82 and Ile-84. This finding, in conjunction with the biochemical studies, suggests that the active site aspartate residues are in proximity to the S1/S1' binding pocket and may be spatially influenced by the residues presented in these pockets upon substrate binding. It thus seems possible that the catalytic residues cooperatively interact with the residues that constitute the S1/S1' binding pockets and can be repositioned during substrate binding to orient the active site carboxylates with respect to the scissile amide bond, a process that likely affects the facility of proteolysis.

1H NMR studies of rotational isomerism in phosphonic analogues of aspartic acid

Aspartic acid and its phosphonic acid analogues exhibit rotational isomerism around the C(2)-C(3) bond in solution. The characteristic vicinal proton-proton coupling constants in their H-1 NMR depend on the population of rotamers. By the use of these coupling constants, which are correlated with two different sets of parameters describing rotamer populations, namely (3)J(HH)(g) = 2.3 (or 2.4), (3)J(HH)(t) = 13.9 (or 13.3) and (3)J(HP)(g) = 4.2, (3)J(HP)(t) = 33.0 Hz, one can obtain full information on the population distribution of the rotamers in the examined compounds. Copyright (C) 2000 John Wiley & Sons, Ltd.

Synthesis and proteinase inhibitory properties of diphenyl phosphonate analogues of aspartic and glutamic acids.

The synthesis of diphenyl phosphonate analogues of aspartic and glutamic acid, and their inhibitory activity against S. aureus V8 protease and granzyme B, is described. The study has revealed difficulties with protecting group compatibility in the synthesis of these analogues. Two analogues, Acetyl. AspP (OPh)2 and Acetyl.GluP (OPh)2 were found to function as irreversible inactivators of V8 proteinase, yet exhibit no activity against granzyme B.

Zinc(II) complexes of phosphonic acid analogues of aspartic acid and asparagine

An analogue of aspartic acid obtained by the replacement of the α-carboxylic group by a phosphonic acid group underwent chemical transformation upon the action of zinc(II) ions under neutral and slightly alkaline conditions yielding, most probably, a cyclic phosphonamidate composed of two ligand molecules. In contrast, an analogue obtained by the replacement of the β-carboxylic group by a phosphonic acid moiety did not undergo such a transformation. In order to determine which structural features are responsible for the observed cyclization a series of aminophosphonic acids was synthesized and their behaviour in zinc(II) solutions studied by means of NMR spectroscopy. Cyclization of 1-aminoalkylphosphonic acids upon the action of zinc(II) ions in neutral and slightly alkaline media seems to be a general property of these acids. The crystal structures of two of the studied compounds were also determined.

Probing the Role of an Active Site Aspartic Acid in Dihydrofolate Reductase

Analogues of E. coli dihydrofolate reductase (DHFR) containing modified amino acids at single, predetermined sites have been prepared. This was accomplished by the use of the DHFR gene containing an engineered nonsense codon (TAG) at the positions corresponding to Val-10 and Asp-27. Misacylated suppressor tRNAs activated with the modified amino acids of interest were employed for the suppression of the nonsense codons in a cell free protein biosynthesizing system, thereby permitting the elaboration of the desired protein analogues. In this fashion, the aspartic acid analogues erythro-carboxyproline, cysteic acid, β,β-dimethylaspartic acid, α-methylaspartic acid, erythro- and threo-β-methylaspartic acid, N-methylaspartic acid, and phosphonoalanine were incorporated into one or both of the aformentioned positions. Although a number of these analogues were incorporated only in low yield, a modification of the strategy has suggested how this might be improved significantly. The derived proteins were purified and then characterized by their mobility on polyacrylamide gels in comparison with wild-type DHFR. Representative DHFRs modified at position 10 were also degraded by defined proteolysis with Glu-C endoproteinase; the fragments containing the modified amino acids were shown to have the same chromatographic properties on reverse phase HPLC as authentic synthetic standards. Individual analogues were assayed for their abilities to bind to the substrate analogue methotrexate and to convert dihydrofolate to tetrahydrofolate. DHFR analogues containing erythro- and threo-β-methylaspartic acid and β,β-dimethylaspartic acid were all shown to mediate tetrahydrofolate production 74−86% as efficiently as wild-type DHFR under conditions of multiple substrate turnover. Analysis of the rates of tetrahydrofolate production in the presence of NADPH and NADPD at two pH values suggests that this was due to rate-limiting hydride transfer from NADPH bound to DHFR analogues whose active site had been altered structurally.

ChemInform Abstract: Synthesis of Phosphinic and Phosphonic Analogues of Aspartic Acid.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: A New Conformationally Restricted Aspartic Acid Analogue with a Bicyclo(2.2.2)octane Skeleton.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

A New Conformationally Restricted Aspartic Acid Analogue with a Cyclohexanone Skeleton

In the compound (1R,2S)-2-benzamido-2-methoxycarbonyl-5-oxo-1-cyclohexanecarboxylic acid, C16H17NO6, the cyclohexanone ring adopts a distorted chair conformation. The carboxylic acid and the methyl ester groups occupy the axial positions, while the benzamido group is equatorial. The values determined for the torsion angles about the N—Cα(ϕ) and Cα—CO(ψ) bonds correspond to a semi-extended conformation for the amino acid residue. The crystal structure is stabilized by two intermolecular hydrogen bonds (O-H⋯O and N-H⋯O) involving the carboxylic acid, the benzamido and the methyl ester groups.