Chemoenzymatic synthesis of conformationally rigid glutamic acid analogues

Bicyclic glutamic acid derivatives

For the second-generation asymmetric synthesis of the trans-tris(homoglutamic) acids via Strecker reaction of chiral ketimines, the cyanide addition as the key stereodifferentiating step produces mixtures of diastereomeric alpha-amino nitrile esters the composition of which is independent of the reaction temperature and the type of the solvent, respectively. The subsequent hydrolysis is exclusively achieved with concentrated H(2)SO(4) yielding diastereomeric mixtures of three secondary alpha-amino alpha-carbamoyl-gamma-esters and two diastereomeric cis-fused angular alpha-carbamoyl gamma-lactams as bicyclic glutamic acid derivatives, gained from in situ stereomer differentiating cyclisation of the secondary cis-alpha-amino alpha-carbamoyl-gamma-esters. Separation was achieved by CC. The pure secondary trans-alpha-amino alpha-carbamoyl-gamma-esters cyclise on heating and treatment with concentrated H(2)SO(4), respectively, to diastereomeric cis-fused angular secondary alpha-amino imides. Their hydrogenolysis led to the enantiomeric cis-fused angular primary alpha-amino imides. The configuration of all compounds was completely established by NMR methods, CD-spectra, and by X-ray analyses of the (alphaR,1R,5R)-1-carbamoyl-2-(1-phenylethyl)-2-azabicyclo[3.3.0]octan-3-one and of the trans-alphaS,1S,2R-2-ethoxycarbonylmethyl-1-(1-phenylethylamino)cyclopentanecarboxamide.

Rigid nonproteinogenic cyclic amino acids as ligands for glutamate receptors:trans-Tris(homoglutamic) acids

The second-generation asymmetric synthesis of the trans-tris(homoglutamic) acids reported herein proceeds via Strecker reaction of chiral ketimines, obtained from condensation of racemic 2-ethoxycarbonylmethylcyclopentanone and commercially available (S)- and (R)-1-phenylethylamine, respectively. In the key stereodifferentiating step, the cyanide addition leads to mixtures of diastereomeric alpha-amino nitrile-esters, the composition of which is independent of the reaction temperature and the type of the solvent, respectively. Hydrolysis of the alpha-amino nitrile-esters with concentrated H(2)SO(4) yielded diastereomeric mixtures of secondary alpha-amino amido-esters, which after separation were hydrogenolyzed and hydrolyzed each to the enantiomeric trans-1-amino-2-carboxymethylcyclopentanecarboxylic acids. Their configuration was completely established by NMR methods, CD spectra, and X-ray analysis of the trans-1S,2R-configured secondary alpha-amino amido-ester. In receptor binding assays and functional tests, trans-1S,2R-1-amino-2-carboxymethylcyclopentanecarboxylic acid hydrochloride was found to behave as a selective mGluR(2)-antagonist without relevant binding properties at iGluRs.

Enantioselective synthesis of the excitatory amino acid (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid

An enantioselective synthesis of the alpha,alpha-dialkyl-alpha-amino acid (1S,3R)-ACPD has been achieved using an alkylidene carbene 1,5-CH insertion reaction as a key step. The ketone cyclization precursor was synthesized from Garner's aldehyde in high yield via a Wittig homologation and subsequent catalytic hydrogenation. Treatment of the ketone with 1.2 equiv of lithio(trimethylsilyl)diazomethane in THF resulted in the formation of the corresponding cyclopentene-containing CH-insertion product in 62-69% yield in high enantiomeric excess. Subsequent functional group manipulation allowed the synthesis of the amino acid (1S,3R)-ACPD to be completed.

Synthesis of constrained phenylalanine derivatives via a [2+2+2] cycloaddition strategy

A simple synthesis of dialkyne building blocks (6, 7, 8 and 9) embodying amino acid moiety is described. The dialkyne 6 participated in a [2+2+2] cycloaddition reaction with various monoalkynes in presence of Wilkinson's catalyst to give 5- and 5,6-disubstituted indan-based -amino acid derivatives. Cobalt catalyst [e.g., CpCo(CO)2] has also been employed in the synthesis of various 2-indanyl glycine derivatives via co-trimerization reaction of the diyne building blocks 6 and 7 with several monoalkynes.

Diels-Alder approach to tetralin-based constrained alpha-amino acid derivatives

Tetralin-based constrained alpha-amino acid derivatives were prepared via [4 + 2]-cycloaddition reaction as a key step. Here sultine is used as a latent diene and 2-acetamidoacrylate serves as a dienophile component.

Aminobicyclo[2.2.1.]heptane dicarboxylic acids (ABHD), rigid analogs of ACPD and glutamic acid: synthesis and pharmacological activity on metabotropic receptors mGluR1 and mGluR2

Isomeric norbornane-derived rigid analogs mimicking different potential conformations of ACPD (1-aminocyclopentane-1,3-dicarboxylic acid) and glutamic acid have been synthesized, via the hydantoin route, to be used as conformational probes for bioactive conformations at the glutamatergic receptors of the central nervous system. Activities on metabotropic receptors mGluR1 and mGluR2 are reported and discussed.

Effect of various analogues of D-glutamic acid on the D-glutamate-adding enzyme from Escherichia coli

Twenty-four analogues of D-glutamic acid were tested as substrates or inhibitors of the D-glutamate-adding enzyme from Escherichia coli. The best substrates were, in decreasing order of specific activity, D-erythro-4-methylglutamic acid, D-erythro-3-methylglutamic acid, DL-homocysteic acid, (+/-)-trans-1-amino-3-carboxy-cyclopentanecarboxylic acid and (+/-)-trans-1-amino-3-carboxy-cyclohexanecarboxylic acid. Among the different stereoisomers, only the D-erythro isomers for methylglutamic acids, and the trans isomers for the cyclic analogs, were substrates. Apart from the D-erythro-3- and 4-methylglutamic acids and DL-homocysteic acid, none of the examined compounds significantly inhibited the addition of radioactive D-glutamic acid to UDP-N-acetylmuramyl-L-alanine.

Synthesis of diastereoisomeric peptides incorporating cycloglutamic acids. Substrate specificity of vitamin K-dependent carboxylation

Tripeptides Boc-X-Glu-Val where X is alpha-methyl glutamic acid or various cyclic analogues of glutamic acid, such as 1-amino-1,3-dicarboxycyclohexane (cis or trans-CHGA) or -cyclopentane (cis or trans-CPGA) have been synthesized. Methods for the selective protection, activation, and coupling of such unnatural amino acids are described. The peptides, which are potential competitive inhibitors of the vitamin K-dependent carboxylation, have been preliminarily tested with the rat liver microsomal carboxylase and found to be effective substrates of the carboxylation reaction.