Direct high-performance liquid chromatographic enantioseparation of apolar beta-amino acids on a quinine-derived chiral anion-exchanger stationary phase

A quinine-derived chiral anion-exchanger stationary phase was applied for the direct high-performance liquid chromatographic separation of the enantiomers of N-protected unusual beta-amino acids, i.e. 3-aminobutanoic acid, 3-aminopentanoic acid, 3-amino-4-methylpentanoic acid, 3-amino-4,4-dimethylpentanoic acid, 3-amino-4-methylhexanoic acid, 3-amino-4-ethylhexanoic acid, 3-amino-3-cyclohexylpropanoic acid, 3-amino-3-(3-cyclohexen-1-yl)propanoic acid and 3-amino-3-phenylpropanoic acid. The readily prepared N-2,4-dinitrophenyl derivatives were well separable, with good efficiency and high resolution. The chromatographic conditions (eluent composition, pH and buffer concentration) were varied to achieve optimal separation. In some cases, the elution sequences of the enantiomers of the derivatives were determined.     

Preparation of the both enantiomers of threo-2-amino-3-methylhexanoic acid by enzymatic resolution and their conversion to optically active forms of threo-4-methylheptan-3-ol,a pheromone component of the smaller european elm bark beetle

The both enantiomers of threo-2-amino-3-methylhexanoic acid were prepared by resolving its racemic N-acetate with Aspergillus acylase. The amino acid enantiomers were converted to optically active forms of threo-4-methylheptan-3-ol, a pheromone component of Scolytus multistriatus.     

Synthesis of substituted 2-(2-oxopyrrolidin-1-yl)acetamides

The reaction of chloroacetamide with 2 equiv of γ-aminobutyric acid potassium salts provides a convenient method for the synthesis of substituted 4-[(2-amino-2-oxoethyl)amino]butanoic acids. Alkylation products of 2-aminoacetic and 3-aminopropanoic acid with chloroacetamide were isolated. Thermal cyclization of substituted 4-[(2-amino-2-oxoethyl)amino]butanoic acids afforded 2-(2-oxopyrrolidin-1-yl)acetamides.     

Homophymine A, an anti-HIV cyclodepsipeptide from the sponge Homophymia sp

A new anti-HIV cyclodepsipeptide, homophymine A, was isolated from a New Caledonian collection of the marine sponge Homophymia sp. The structure of homophymine A was determined by interpretation of spectroscopic data, acid hydrolysis, and LC-MS analysis. Homophymine A contains 11 amino acid residues and an amide-linked 3-hydroxy-2,4,6-trimethyloctanoic acid moiety. Along with four D-, two L-, and one N-methyl amino acids, it also contains four unusual amino acid residues: (2S,3S,4R)-3,4-diMe-Gln, (2R,3R,4S)-4-amino-2,3-dihydroxy-1,7-heptandioic acid, L-ThrOMe, and (2R,3R,4R)-2-amino-3-hydroxy-4,5-dimethylhexanoic acid. In a cell-based XTT assay, homophymine A exhibited cytoprotective activity against HIV-1 infection with a IC50 of 75 nM.     

Aspergillicins A-E: five novel depsipeptides from the marine-derived fungus Aspergillus carneus

A search for new antiparasitic agents from a strain of the fungus Aspergillus carneus isolated from an estuarine sediment collected in Tasmania, Australia, yielded the known terrestrial fungal metabolite marcfortine A (1) as an exceptionally potent antiparasitic agent. This study also yielded a series of new depsipeptides, aspergillicins A-E (2-6) and the known terrestrial fungal metabolite acyl aszonalenin (7). Marcfortine A (1) and acyl aszonalenin (7) were identified by spectroscopic analysis, with comparison to literature data. Complete stereostructures were assigned to aspergillicins A-E (2-6) on the basis of detailed spectroscopic analysis, together with ESIMS analysis of the free amino acids generated by acid hydrolysis, and HPLC analysis of Marfey derivatives prepared from the acid hydrolysate. The peptide amino acid sequence for all aspergillicins was unambiguously assigned by MS(n) ion-trap ESI mass spectrometry.     

Approaches to novel AB heteroaromatic polyamides based on cyanoimidazoles

We report the synthesis of several AB monomers based on 2-amino-4,5-dicyanoimidazole. Polymerization of the monomers to poly(imidazoleamide)s, by several methods is described. Amino acids 2-amino-4-cyano-1-methyl-5-imidazolecarboxylic acid and 2-amino-5-cyano-1-methyl-4-imidazolecarboxylic acid were prepared by mono-ethanolysis of 2-amino-4,5-dicyanoimidazole followed by methylation of the 1-nitrogen. The resulting regioisomeric mixture of ethyl esters was separated by fractional crystallization and hydrolyzed to the desired amino acids. The regioisomeric structure was determined by NOE studies of the decarboxylated amino acids. The corresponding acid chlorides were prepared with thionyl chloride and isolated as the HCl salts. Activated esters were prepared by reacting the acid chlorides with alcohols such as 1,1,1-trifluoroethanol and 2-chlorophenol. Model compounds were prepared by the acylation of aminocyanoimidazoles but yields were low. The low nucleophilicity of the aminocyanoimidazolecarboxylic acids was partially overcome by the use of the acylation catalyst 4-dimethylaminopyridine (DMAP) and the activating agent silicon tetrachloride. The acid chlorides were polymerized in amide solvents such as hexamethyl phosphoramide with pyridine and DMAP. A copolyamide consisting of both regioisomers was prepared from a regioisomeric mixture of the acid chlorides. In addition, aminolysis of 2-chlorophenyl 2-amino-4-cyano-1-methyl-5-imidazolecarboxylate resulted in a low yield of poly(imidazoleamide). Poly(imidazoleamide)s were red to tan which suggest conjugation along the polymer backbone. The solubility of the polyamides varied from amide solvents to sulfuric acid depending on the regioisomeric structure and molecular weight. The molecular weight of the heteroaramids was in the range from 1500 to 4000 based on viscosity measurements in sulfuric acid. The poly(imidazoleamide)s were thermally stable in excess of 300°C under air and nitrogen atmosphere. © 1993 John Wiley & Sons, Inc.     

Cyclodysidins A–D,cyclic lipopeptides from the marine sponge-derived Streptomyces strain RV15

Four new cyclic lipopeptides, cyclo-(AFA-Ser-Gln-Asn-Tyr-Asn-Ser-Thr), named cyclodysidins A–D, were isolated from the broth culture of Streptomyces strain RV15 associated with the marine sponge Dysidea tupha. The sequences of the amino acid building blocks in the compounds and their structures were determined by 1D- and 2D-NMR techniques and CID-MS/MS experiments. The absolute configurations of all α-amino acids were determined by HPLC analysis after derivatization with Marfey’s reagent and comparison with commercially available reference samples, while those two of the β-amino fatty acids were determined by using racemic and enantiopure reference samples synthetically prepared.     

3－苄基－6－（1－氨基烃基）－1，2，4－三唑并[3,4-b]-1,3,4-噻二唑的合成与波谱表征

3－苄基－4－氨基－5－巯基－1，2，4－三唑与氨基酸在三氯氧磷存在下反应 ，合成3－苄基－6－（1－氨基烃基）－1，2，4－三唑并[3,4-b]－1，3，4－噻二 唑，其结构经元素分析、红外光谱、核磁共振氢谱、碳谱、质谱等确证。这是稠杂 环接氨基酸残基的首次报道。     

A solid-phase total synthesis of the cyclic depsipeptide HDAC inhibitor spiruchostatin A

Spiruchostatin A, a potent histone deacetylase inhibitor, was efficiently synthesized from (3S,4R)-4-amino-3-hydroxy-5-methylhexanoic acid utilizing solid-phase peptide elongation with d-cysteine, d-alanine, and (E)-3-hydroxy-7-thio-4-heptenoic acid and solution-phase macrolactonization, followed by intramolecular disulfide formation.     

Revised absolute stereochemistry of natural kulokekahilide-2

Kulokekahilide-2 is a potent cytotoxic depsipeptide isolated from the Hawaiian marine mollusk Philinopsis speciosa. The structure of kulokekahilide-2 was reported to be composed of five amino acids (l-Ala, l-Ile, MeGly, l-MePhe, d-Ala) and two hydroxy acids (d-Hica, 5S,6S,7S-Dtda); however, following its total synthesis, the ¹H NMR spectrum of the synthetic compound was found to be different from that of the natural one, suggesting that the stereochemistry of the reported structure was incorrect. To determine the stereochemistry of the natural compound, arrays of analogues have been prepared using different sets of chiral amino acids, and the absolute stereochemistry of kulokekahilide-2 has been unambiguously confirmed to involve the combination 21-l-Ala, 24-d-MePhe, and 43-d-Ala.     

Synthesis and pharmacological characterization at glutamate receptors of erythro- and threo-tricholomic acid and homologues thereof

The erythro- and threo-amino-(3′-hydroxy-4′,5′-dihydro-isoxazol-5′-yl)-acetic acids, stereoisomers of tricholomic acid, were synthesized along with the corresponding higher homologues erythro- and threo-amino-(3′-carboxy-4′,5′-dihydro-isoxazol-5′-yl)-acetic acids. The target compounds were prepared via the 1,3-dipolar cycloaddition of a suitable nitrile oxide to (±)-2-tert-butoxycarbonylamino-3-buten-1-ol. Such a strategy allowed the synthesis of the two stereoisomeric amino acids in comparable amounts. The pharmacological activity of these compounds was investigated at ionotropic and metabotropic glutamate receptors (iGluRs and mGluRs) by means of receptor binding assays to rat cortical membranes, electrophysiological tests and second messenger assays at cloned receptors expressed in CHO cells. Their pharmacological profiles were compared to those of l-glutamate and of the previously described selective NMDA receptor antagonists 5-(2-amino-2-carboxyethyl)-4,5-dihydroisoxazole-3-carboxylic acids in order to highlight the effect of increasing/reducing the distance between the amino acid moiety and the distal acid group, which represent the two pharmacophoric entities.     

Koshikamide B, a cytotoxic peptide lactone from a marine sponge Theonella sp

Koshikamide B (1) has been isolated from two separate collections of the marine sponge Theonella sp. as the major cytotoxic constituent. Koshikamide B is a 17-residue peptide lactone composed of six proteinogenic amino acids, two D-isomers of proteinogenic amino acids, seven N-methylated amino acids, and two unusual amino acid residues. The unusual amino acids are N(delta)-carbamoylasparagine and 2-(3-amino-2-hydroxy-5-oxopyrrolidin-2-yl)propionic acid (AHPP); the former is first found as the constituent of peptides, whereas the latter is a new amino acid residue. The N-terminus of koshikamide B is blocked by a methoxyacetyl group. The structure of koshikamide B (1) has been determined by interpretation of spectral data and analysis of chemical degradation products. Koshikamide B (1) exhibits cytotoxicity against P388 murine leukemia cells and the human colon tumor (HCT-116) cell line with an IC50 value of 0.45 and 7.5 microg/mL, respectively.     

Synthesis of the 3-methyl and 4-methyl derivatives of 3-amino-3,4-dihydro-1-hydroxycarbostyril and related compounds

The 3-methyl and 4-methyl derivatives of 3-amino-3,4-dihydro-1-hydroxycarbostyril were synthesized by the reductive cyclization of α-methyl-β-(o-nitrophenyl)alanine and α-amino-β-(o-nitrophenyl)butyric acid hydrohalides, respectively, under conditions of catalytic hydrogenation in acidic solution. The free bases of the latter two o-nitroaromatic amino acids were also catalytically hydrogenated under neutral conditions to yield the respective α-methyl-β-(o-aminophenyl)alanine and α-amino-β-(o-aminophenyl)butyric acid which were converted to the corresponding lactams, 3-methyl- and 4-methyl-3-amino-3,4-dihydrocarbostyrils. α-Methyl-β-(o-nitrophenyl)alanine was obtained by acid hydrolysis of 5-methy)-5-(o-nitrobenzyl)hydantoin which was prepared by treatment of o-nitrophenylacetone with potassium cyanide and ammonium carbonate. α-Amino-β-(o-nitrophenyl)butyric acid was synthesized by condensation of α-bromo-o-nitroethylbenzene with diethyl acetamidomalonate, followed by acid hydrolysis of the condensation product. The 4-methylated compounds were obtained as synthetic mixtures of two diasteromeric racemates in nearly the same amounts as shown by nmr spectral analysis. Unlike the demethylated parent compound, 3-amino-3,4-dihydro-1-hydroxycarbostyril, neither the 3-methyl nor 4-methyl analog was found to possess any antibacterial activity.     

An efficient chiral synthesis of fluoro-containing amino acids: N-benzyloxycarbonyl-2-amino-4,4-difluorobutyric acid methyl ester and its analogs

Fluoro-containing amino acids, N-benzyloxycarbonyl-2-amino-4,4-difluorobutyric acid methyl ester and analogs, were prepared in high enantiomeric excess. Incorporation of 2-amino-4,4-difluoro butyric acid as P1 group provided a potent HCV NS3 protease inhibitor.     

IB-01212, a new cytotoxic cyclodepsipeptide isolated from the marine fungus Clonostachys sp. ESNA-A009

IB-01212, a new cytotoxic cyclodepsipeptide featuring C2 symmetry, was isolated from the mycelium extract of Clonostachys sp. ESNA-A009. The amino acid sequence of the compound was determined by spectroscopy techniques. The absolute configuration of the amino acids was determined by a combination of the Marfey and menthol methods. The structure, which was confirmed by comparison of the analytical data for the natural product with a sample obtained by solid-phase peptide synthesis, was revealed to be a cyclic dimer formed by two chains of L-N,N-Me2Leu-L-Ser-L-N-MeLeu-L-N-MePhe bound by the two esters formed between the carboxylic acid of the L-N-MePhe and the hydroxyl function of the L-Ser. IB-01212 is highly cytotoxic to different tumor cell lines.     

Directed resolution of 2-fluoro-2-methylhexanoic acid

The applicability of Helmchen's methods for the separation and determination of absolute configuration of enantiomers via diastereoisomeric phenylethylamides has been tested with 2-fluoro-and 2-methylhexanoic acids, then successfully applied to 2-fluoro-2-methylhexanoic acid.     

HPLC enantioseparation of amino acids and their protected derivatives used in peptide synthesis with pre-column chiral derivatization

Summary Indirect chiral separation methods based on enantiomeric derivatizations were developed in order to monitor optical purity of uncoded amino acids and a new series of amino acid derivatives. Marfey's reagent was used for derivatization of amino groups: whilst boxyl groups were derivatised with (1R, 2R)-or (1S, 2S)-2-amino-1(4-nitrophenyl)-1,3-propanediol reagents were used, respectively. The separations of diastereomeric derivatives formed via derivatization were optimized in RP-HPLC and NP-HPLC systems. Presented at Balaton Symposium on High Performance Separation Methods, Siófok, Hungary, September 1–3, 1999     

Synthesis of N-Substituted Derivatives of 2-(4-Amino-2-methyl-1H-indol-3-yl)- and 2-(6-Amino-2-methyl-1H-indol-3-yl)acetic Acids

A method was developed for the production of indole compounds containing an amino group at positions 4 and 6 of the benzene ring on the basis of the indolization of the 3-acetylaminophenylhydrazone of ethyl levulinate. A series of derivatives of 2-(4-amino-2-methyl-1H-indol-3-yl)- and 2-(6-amino-2-methyl-1H-indol-3-yl)acetic acids at the 4- and 6-amino group were synthesized.     

Synthesis of 2-methyl- and 2-methylenecyclobutane amino acids

An efficient and easy formal [2+2] cycloaddition (Michael-Dieckmann-type reaction) on methyl 2-acetamidoacrylate with ketene diethyl acetal gave the cyclobutane core. Two kinds of 2-substituted cyclobutane amino acids have been obtained from this compound by means of stereocontrolled interconversion of functional groups: 1-amino-2-methylcyclobutane-1-carboxylic acids (2,4-methanovalines) and 1-amino-2-methylenecyclobutane-1-carboxylic acid. The latter amino acid can be regarded as a restricted α-methyl-α-vinylglycine.     

Isolation and Characterization of Actinoramides A-C, Highly Modified Peptides from a Marine Streptomyces sp

Reported herein is the isolation and structure elucidation of three highly modified peptides, actinoramides A-C (1-3), which are produced by a marine bacterium closely related to the genus Streptomyces. The planar structures of the actinoramides, which are composed of the unusual amino acids 2-amino-4-ureidobutanoic acid and 4-amino-3-hydroxy-2-methyl-5-phenylpentanoic acid, were assigned by chemical transformations and by interpretation of spectroscopic data, while the absolute configuration of these new peptides were defined by application of the advanced Marfey’s and Mosher’s methods.