Bicyclic γ-amino acids as inhibitors of γ-aminobutyrate aminotransferase

The γ-aminobutyrate (GABA)-degradative enzyme GABA aminotransferase (GABA-AT) is regarded as an attractive target to control GABA levels in the central nervous system: this has important implications in the treatment of several neurological disorders and drug dependencies. We have investigated the ability of newly synthesized compounds to act as GABA-AT inhibitors. These compounds have a unique bicyclic structure: the carbocyclic ring bears the GABA skeleton, while the fused 3-Br-isoxazoline ring contains an electrophilic warhead susceptible of nucleophilic attack by an active site residue of the target enzyme. Out of the four compounds tested, only the one named (+)-3 was found to significantly inhibit mammalian GABA-AT in vitro. Docking studies, performed on the available structures of GABA-AT, support the experimental findings: out of the four tested compounds, only (+)-3 suitably orients the electrophilic 3-Br-isoxazoline warhead towards the active site nucleophilic residue Lys329, thereby explaining the irreversible inhibition of GABA-AT observed experimentally.     

A preparation of N-Fmoc-N-methyl-α-amino acids and N-nosyl-N-methyl-α-amino acids

A convenient route for the synthesis of lipophilic N-Fmoc-N-methyl-α-amino acids and N-nosyl-N-methyl-α-amino acids, interesting building blocks to be used for the preparation of N-methylated peptides, is presented. Both nosyl- and Fmoc-protected monomers are accessible, so these compounds can be used in solution as well as in solid phase peptide synthesis. The methodology is based on the use of benzhydryl group to protect temporarily the carboxyl function of N-nosyl-α-amino acids and on the subsequent methylation of the N-nosyl-α-amino acid benzhydryl esters with diazomethane. The benzhydryl esters offer several beneficial features such as simple preparation, stability to methylation and selective deprotection under mild conditions. The overall procedure is highly efficient in that the adopted conditions keep the chiral integrity of amino acid precursors and the process does not require chromatographic purification of the methylated products.     

Synthesis of biheterocyclicα-amino acids

Summary We report here the synthesis of biheterocyclic-amino acids by 1,3 dipolar cycloaddition of acetylenic compounds on-azido-amino esters.     

Syntheses ofγ-fluoro-α-amino acids

Summary Methods for the synthesis of racemic and optically active title compounds are presented. Key step of these four-step procedures is the alkylation with 1-bromo-2-fluoroalkanes of glycine-ester-derived imines in anhydrous medium using lithium diisopropylamide as a base at low temperature or phase transfer catalyzed alkylation with 50% NaOH and triethylbenzylammoniumchloride as the phase transfer catalyst, respectively. Subsequent three-step deprotection gave the free acids in 13–33% overall yield. Deracemization of-fluoro--aminobutyric acid methyl and ethyl esters with-chymotrypsin was shown to give the (–)-enantiomers of the esters and (+)--fluoro--aminobutyric acid in >98% ee, while from thetert-butylester the opposite stereochemical result was observed giving the (–)-acid with 88% ee. Optically active-fluoro--amino acids were synthesized alternatively by phase transfer catalysis with N-benzyl-cinchonium chloride or using an auxiliary-directed asymmetric alkylation of the imine derived from (R)-(+)-camphor or (R)-(+)-2-hydroxypinan-3-one. These processes gave different enantiomers of-fluoro--aminobutyric acid via a monomeric lithium enolate in the first or a dimeric lithium enolate in the second case, respectively. The enantiomeric excess can be improved by lithium/magnesium exchange.     

Synthesis and SAR of novel benzoxaboroles as a new class of β-lactamase inhibitors

A new class of benzoxaborole β-lactamase inhibitors were designed and synthesized. 6-Aryloxy benzoxaborole 22 inhibited AmpC P99 and CMY-2 with K_i values in the low nanomolar range. Compound 22 restored antibacterial activity of ceftazidime against Enterobacter cloacae P99 expressing AmpC, a class C β-lactamase enzyme. The SAR around the arylbenzoxaboroles, which included the influence of linker and substitutions was also established.     

(S)-α-methyl,α-amino acids: a new stereocontrolled synthesis

A new and convenient stereocontrolled synthesis of the optically pure (S)-α-methyl,α-amino acids 6(a–d) that exploits the chiral synthon 1,4-N,N-[(S)-1-phenylethyl]-piperazine-2,5-dione (1) is described. The (S)-1-phenylethyl group, bonded to each of the N-atoms of the 2,5-diketopiperazine, acts as a chiral inductor in the first alkylation, while the steric hindrance appears to be the determining factor of stereocontrol in third and forth alkylation.     

Discovery of 4-functionalized phenyl-O-β-d-glycosides as a new class of mushroom tyrosinase inhibitors

A series of 4-functionalized phenyl-O-β-d-glycosides were designed, synthesized and evaluated as a new class of mushroom tyrosinase inhibitors. The results demonstrated that compounds 6a–13a bearing a thiosemicarbazide moiety exhibited potent activities with IC₅₀ values range from 0.31 to 52.8 μM. Particularly, compound 9a containing acetylated glucose moiety was found to be the most active molecule with an IC₅₀ value of 0.31 μM. SARs analysis suggested that (1) the thiosemicarbazide moiety remarkably contributed to the increase of inhibitory effects on tyrosinase; (2) the configuration and bond type of sugar moiety also played a very important role in determining their inhibitory activities. The inhibition kinetics and inhibition mechanism study revealed that compound 9a was reversible and competitive type inhibitor, whereas compound 13a was reversible and competitive–uncompetitive mixed-II type inhibitor.     

ω-3 Polyunsaturated fatty acids and their metabolites as inhibitors of mammalian tumorigenesis

Components of tumorigenesis include uncontrolled proliferation and defects in cell death pathways, as well as increased angiogenesis, in which tumors develop their own blood supply, and metastasis, which enables tumor dissemination. Most anticancer drugs are designed to kill cancer cells but are relatively ineffective against some phases of tumorigenesis. Alternate strategies to prevent tumorigenesis are urgently required and considerable evidence has emerged that ω-3 polyunsaturated fatty acids (PUFAs) derived from certain plants and oily fish are important modulators of tumor cell proliferation, apoptosis, angiogenesis and metastasis. Epidemiological studies in man, as well as experimental studies in animal models and cells, have reported that while ω-6 PUFA accelerate tumorigenesis, ω-3 PUFA have anticancer properties. The over-expression of certain PUFA-metabolizing enzymes in tumors, including cyclooxygenases, lipoxygenases and cytochromes P450 (CYP), has provided the impetus for studies on the roles of biotransformation products in the cancer-modulatory actions of PUFAs. Some ω-6 PUFA metabolites, including PGE₂, 5-HETE and the CYP-derived EETs, stimulate tumorigenesis by activating prostanoid receptors, nuclear receptors and intracellular signal transduction cascades. In contrast, ω-3 PUFA both inhibit the formation of pro-tumorigenic ω-6 PUFA metabolites and generate ω-3 metabolites that are anti-tumorigenic in their own right, including PGE₃ and the 17,18-epoxide of epoxyeicosapentaenoic acid (HETE). Some of these naturally occurring metabolites of ω-3 PUFA formed in human cells may be useful lead compounds for the development of novel agents that inhibit cancer.     

Tetra-substituted imidazoles as a new class of inhibitors of the p53–MDM2 interaction

Capitalizing on crystal structure information obtained from a previous effort in the search for non peptide inhibitors of the p53–MDM2 interaction, we have discovered another new class of compounds able to disrupt this protein–protein interaction, an important target in oncology drug research. The new inhibitors, based on a tetra-substituted imidazole scaffold, have been optimized to low nanomolar potency in a biochemical assay following a structure-guided approach. An appropriate strategy has allowed us to translate the high biochemical potency in significant anti-proliferative activity on a p53-dependent MDM2 amplified cell line.     

Synthesis of some racemicγ-fluoro-α-amino acids

Summary Versatile three-step procedures for syntheses of seven racemi-fluoro-a-amino acids are described. Alkylation oftert-butyl N-(diphenylmethylene) glycinate with 1-bromo-2-fluoroalkanes gave N-protected aminoacid esters both in anhydrous medium using lithium-diisopropylamide as base at low temperature or in a two phase system of 50% aqueous sodium hydroxide and methylene chloride with triethylbenzylammonium chloride as the phase transfer catalyst at room temperature. Subsequent two-step deprotection with citric acid and hydrochloric acid gave the title compounds in 13–33% overall yields.Dedicated to Professor Dr.mult., Dr.h.c. Alois Haas on the occasion of his 65th birthday     

New aromatic monoesters of α-aminoaralkylphosphonic acids as inhibitors of aminopeptidase N/CD13

A series of new aromatic monoesters of α-aminoaralkylphosphonic acids were synthesized by selective hydrolysis of corresponding aromatic diesters of α-aminoaralkylphosphonic acids. New potential inhibitors of aminopeptidase N/CD13, an enzyme important in tumour angiogenesis, were developed. Some derivatives of the homophenylalanine and norleucine related monoaryl phosphonates displayed higher inhibition potency than corresponding α-aminoaralkylphosphonic acids toward aminopeptidase N/CD13. The effect of one of the new inhibitors on the growth of human PANC-1 and HT-1080 cell lines was examined, either alone or in combination with TNF-α.     

Evaluation of α-hydroxycinnamic acids as pyruvate carboxylase inhibitors

Through a structure-based drug design project (SBDD), potent small molecule inhibitors of pyruvate carboxylase (PC) have been discovered. A series of α-keto acids (7) and α-hydroxycinnamic acids (8) were prepared and evaluated for inhibition of PC in two assays. The two most potent inhibitors were 3,3′-(1,4-phenylene)bis[2-hydroxy-2-propenoic acid] (8u) and 2-hydroxy-3-(quinoline-2-yl)propenoic acid (8v) with IC₅₀ values of 3.0 ± 1.0 μM and 4.3 ± 1.5 μM respectively. Compound 8v is a competitive inhibitor with respect to pyruvate (K_i = 0.74 μM) and a mixed-type inhibitor with respect to ATP, indicating that it targets the unique carboxyltransferase (CT) domain of PC. Furthermore, compound 8v does not significantly inhibit human carbonic anhydrase II, matrix metalloproteinase-2, malate dehydrogenase or lactate dehydrogenase.     

Synthesis of optically active lipidicα-amino acids and lipidic 2-amino alcohols

Summary Lipidic-amino acids (LAAs) are a class of compounds combining structural features of amino acids with those of fatty acids. They are non-natural-amino acids with saturated or unsaturated long aliphatic side chains. Synthetic approaches to optically active LAAs and lipidic 2-amino alcohols (LAALs) are summarized in this review. A general approach to enantioselective synthesis of saturated LAAs is based on the oxidative cleavage of 3-amino -1,2-diols obtained by the regioselective opening of enantiomerically enriched long chain 2,3-epoxy alcohols. Unsaturated LAAs are prepared in their enantiomeric forms by Wittig reactionvia methyl (S)-2di-tert-butoxycarbonylamino-5-oxo-pentanoate. This key intermediate aldehyde is obtained by selective reduction of dimethyl N,N-di-Boc glutamate with DIBAL. (R) or (S) LAALs may be prepared starting from D-mannitol or L-serine. LAAs are converted into LAALs by chemoselective reduction of their fluorides using sodium borohydride with retention of optical purity. Replacement of the hydroxyl group of LAALs by the azido group, followed by selective reduction leads to unsaturated optically active lipidic 1,2-diamines.Abbreviations Bn benzyl - Boc tert-butoxycarbonyl - DDQ 2,3-dichloro-5,6-dicyano-1,4-benzoquinone - DET diethyl tartrate - DIBAL diisobutyl aluminum hydride - DMAP 4-dimethylaminopyridine - DMF N,N-dimethylformamide - DMSO dimethyl sulfoxide - EDC N-ethyl-N-(3-dimethylaminopropyl)carbodiimide - Et₃N triethylamine - HMPA hexamethylphosphoramide - HOBt 1-hydroxybenzotriazole - KN(TMS)₂ potassium bis(trimethylsilyl)-amide - LAA lipidic-amino acid - LAAAl lipidic 2-amino alcohol - LDA lipidic 1,2-diamine - LP lipidic peptide - MPM-Cl p-methoxybenzyl chloride - MsCl methanesulphonyl chloride - MTPA -methoxy--(trifluoromethyl)phenylaccitc - PLA₂ phospholipase A₂ - TBIIP tert-butyl hydroperoxide - THF tetrahydrofuran - TMSCl trimethylsilyl chloride - Tr trityl - Z benzyloxycarbonyl     

Discovery of Strecker-type α-aminonitriles as a new class of human carbonic anhydrase inhibitors using differential scanning fluorimetry

A new type of carbonic anhydrase inhibitors was identified via differential scanning fluorimetry (DSF) screening. The compounds displayed interesting inhibition profile against human carbonic anhydrase isoforms I, II, IX and XII with an obvious selectivity displayed by one compound toward carbonic anhydrase (CA) IX, an established anti-cancer target. A hypothetical mechanism of inhibitory action by the Strecker-type α-aminonitriles has been proposed.     

β,γ-Alkynylα-amino acids: a synthetic challenge

Summary Ethynyl glycine is a naturally occurring unusual-amino acid. Its known chemical and biological properties are summarized in the first part of this review. The second part is an overview on racemic syntheses of ethynyl glycine and other,-alkynyl-amino acid derivatives, including patent data. These small polyfunctional compounds revealed as being very labile and the synthesis of mainly fully or partially protected forms seemed to have been actually performed. The last part deals with the approaches to the enantioselective synthesis of,-alkynyl-amino acids derivatives, and details the only satisfactory strategy that has led to optically active,-alkynyl-amino acids derivatives up to now.     

The use of β-amino acids in the design of protease and peptidase inhibitors

Summary The use of β-amino acids as peptidomimetics has emerged in recent years with significant potential in a number of applications. The incorporation of β-amino acids has been successful in creating peptidomimetics that not only have potent biological activity, but are also resistant to proteolysis. This article reviews the recent applications of β-amino acids in the design of protease and peptidase inhibitors. Given their structural diversity, together with the ease of synthesis and incorporation into peptide sequences using standard solid-phase peptide synthesis techniques, β-amino acids have the potential to form a new platform technology for peptidomimetic design and synthesis.     

Serendipitous discovery of aryl boronic acids as β-lactamase inhibitors

High throughput screening for β-lactamase inhibitors afforded biphenyl hits such as 1. Hit confirmation and X-ray soaking experiments with Pseudomonas Aeruginosa AmpC enzyme led to the identification of an aryl boronic acid-serine complex 4, which was formed from phenyl boronic acid 8 (an impurity in compound 1) and ethylene glycol (the cryoprotectant in the soaking experiment).     

Synthesis of medicinally useful lipidicα-amino acids, 2-amino alcohols and diamines

Summary The lipidic-amino acids (LAAs) are non-natural-amino acids with saturated or unsaturated long aliphatic side chains. LAAs and their derivatives (lipid mimetics) together with the lipidic peptides represent a class of compounds which combine structural features of lipids with those of amino acids and peptides. Racemic LAAs may be prepared by classical methods and resolved by chemical or enzymatic methods. LAA amides and esters with saturated or unsaturated long chain amines and alcohols respectively, as well as lipidic dipeptide derivatives inhibit both pancreatic and human platelet phospholipase A₂. Lipophilic peptide derivatives are inhibitors of human neutrophil elastase. LAAs and their oligomers have been used as drug delivery system. A Lipid-Core-Peptide system has been designed and used as a combined adjuvant-carrier-vaccine system. A variety of lipid mimetics such as lipidic 2-amino alcohols, lipidic 1,2- and 1,3-diamines have been prepared based upon LAAs. Some of them are potent inhibitors of phospholipase A₂. A general approach to enantioselective synthesis of LAAs and lipid mimetics is based on the oxidative cleavage of 3-amino-1,2-diols obtained by the regioselective opening of enantiomerically enriched long chain 2,3-epoxy alcohols.Abbreviations Boc tert-butoxycarbonyl - BSA bovine serum albumin - CD circular dichroism - DET diethyl tartrate - DIBAL diisobutyl aluminum hydride - DMF N,N-dimethylformammide - HMPA hexamethylphosphoramide - HNE human neutophil elastase - LAA lipidic amino acid - LAAL lipidic amino alcohol - LH-RH luteinizing hormone-releasing hormone - LCP lipid-core-peptide - LDA lipidic diamine - LP lipidic peptide - MAP multiple antigenic peptide - PLA₂ phospholipase A₂ - TBHP tert-butyl hydroperoxide - THF tetrahydrofuran - TRH thyrotropin-releasing hormone - Z benzyloxycarbonyl