Synthesis and structure activity relationships of novel non-peptidic metallo-aminopeptidase inhibitors

Racemic derivatives of 3-amino-2-tetralone were synthesised and evaluated for their ability to inhibit metallo-aminopeptidase activities. New compounds substituted in position 2 by methyl ketone, substituted oximes or hydroxamic acids as well as heterocyclic derivatives were evaluated against representative members of zinc-dependent aminopeptidases: leucine aminopeptidase (E.C. 3.4.11.1), aminopeptidase-N (E.C. 3.4.11.2), Aeromonas proteolytica aminopeptidase (E.C. 3.4.11.10), and the aminopeptidase activity of leukotriene A(4) hydrolase (E.C. 3.3.2.6). Several compounds showed K(i) values in the low micromolar range against the 'one-zinc' aminopeptidases, while most of them were rather poor inhibitors of the 'two-zinc' enzymes. This interesting selectivity profile may guide the design of new, specific inhibitors of target mammalian aminopeptidases with one active site zinc.     

A novel amino-benzosuberone derivative is a picomolar inhibitor of mammalian aminopeptidase N/CD13

A new class of low molecular weight, highly potent and selective non peptidic inhibitors of aminopeptidase N (APN/CD13) is described. We report the synthesis and in vitro evaluation of racemic substituted analogues of 7-amino-benzocyclohepten-6-one 1a. We investigated various substitutions on the aromatic ring with phenyl and halogen groups. In vitro kinetic studies revealed that these compounds are among the most effective APN/CD13 inhibitors found so far. Hydrophobic substituents placed at position 1 or 4 on the cycloheptenone 1a led to the potent compounds 1c-h,b'-c',f',h' with K(i) in the nanomolar range. The key finding of the present work was the observed additive effect of 1,4-disubstitutions which led to the discovery of the picomolar inhibitor 1d' (K(i)=60 pM). The designed inhibitors retain the selectivity of our lead structure 1a towards selected members of the aminopeptidase family, combined with an impressive increase in inhibitory potency and a conserved stability.     

Novel β-dicarbonyl derivatives as inhibitors of aminopeptidase N (APN)

Most zinc metalloproteases are over-expressed in tumor cells and play a critical role in the genesis, development, and metastasis of tumors. Novel zinc binding groups (ZBGs) represent a novel strategy to obtain optimal potency and selectivity for zinc metalloproteases inhibitors. Here we described the design, synthesis, and biological studies of novel β-dicarbonyl derivatives as aminopeptidase N (APN/CD13) inhibitors. The results demonstrated that some compounds exhibited moderate to good inhibitory activities against APN with compound 5c being the most potent, suggesting that 5c could serve as new lead for the future APN inhibitor development. The results further confirm our design rationale of β-dicarbonyl moiety as a new ZBG, which may provide a new direction for the design and discovery of zinc metalloproteases inhibitors as new anti-tumor agents.     

Design, synthesis and biological evaluation of novel 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives as aminopeptidase N/CD13 inhibitors

A series of novel 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives were designed, synthesized and assayed for their activities against aminopeptidase N (APN/CD13) and MMP-2. The results showed that most compounds exhibited higher inhibitory activities against APN than that of MMP-2. Within this series, compound 12h (IC(50)=6.28 ± 0.11 μM) showed similar inhibitory activities compared with Bestatin (IC(50)=5.55 ± 0.01 μM), and it could be used as novel lead compound for the future APN inhibitors development as anticancer agents.     

Structural basis for herbicidal inhibitor selectivity revealed by comparison of crystal structures of plant and mammalian 4-hydroxyphenylpyruvate dioxygenases

A high degree of selectivity toward the target site of the pest organism is a desirable attribute for new safer agrochemicals. To assist in the design of novel herbicides, we determined the crystal structures of the herbicidal target enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD; EC 1.13.11.27) from the plant Arabidopsis thaliana with and without an herbicidal benzoylpyrazole inhibitor that potently inhibits both plant and mammalian HPPDs. We also determined the structure of a mammalian (rat) HPPD in complex with the same nonselective inhibitor. From a screening campaign of over 1000 HPPD inhibitors, six highly plant-selective inhibitors were found. One of these had remarkable (>1600-fold) selectivity toward the plant enzyme and was cocrystallized with Arabidopsis HPPD. Detailed comparisons of the plant and mammalian HPPD-ligand structures suggest a structural basis for the high degree of plant selectivity of certain HPPD inhibitors and point to design strategies to obtain potent and selective inhibitors of plant HPPD as agrochemical leads.     

Design,synthesis and preliminary evaluation of α-sulfonyl γ-(glycinyl-amino)proline peptidomimetics as matrix metalloproteinase inhibitors

A series of novel α-sulfonyl γ-(glycinyl-amino)proline peptidomimetic derivatives were designed, synthesized and assayed for their activities against matrix metalloproteinase-2 (MMP-2), aminopeptidase N (APN)/CD13 and HDACs. The results indicated that all the compounds exhibited highly selective inhibition against MMP-2 as compared with APN and HDACs. The antiproliferative activities of some compounds against SKOV3, HL60 and A549 cells were also investigated. Comparing with the control LY52, compound 12u, with excellent activity both in the enzymatic inhibition assay and cell-based assay, could be used as lead compound for the further development of MMP inhibitors.     

Role of CD13/aminopeptidase N in rat lymphocytic alveolitis caused by thoracic irradiation

CD13/aminopeptidase N is a cell surface glycoprotein that is widely distributed in a variety of mammalian cells. It was recently shown to have chemotactic activity for T lymphocytes. This study examined the role of CD13/aminopeptidase N in lymphocytic alveolitis in radiation-induced lung injury caused by a single-dose thoracic irradiation (15 Gy) in rats. Significantly increased aminopeptidase activity was detected in bronchoalveolar lavage fluid obtained from irradiated rats at 4 weeks after irradiation compared to the activity in unirradiated rats. Significantly higher aminopeptidase activity was detected on alveolar macrophages from irradiated rats at 2 and 4 weeks than on those from unirradiated rats. Western blot analysis showed an increased expression of CD13/aminopeptidase N protein in alveolar macrophages from irradiated rats at 4 weeks. Chemotactic activity for normal rat lymphocytes was detected in bronchoalveolar lavage fluid from irradiated rats at 4 weeks, and approximately 60% of the activity was inhibited by pretreatment of bronchoalveolar lavage fluid with bestatin, a specific aminopeptidase inhibitor. This study suggests that CD13/aminopeptidase N may play an important role as a lymphocyte chemoattractant in lymphocyte-mediated alveolitis in experimental radiation-induced lung injury.     

Synthesis and biological evaluation of salicylate-based compounds as a novel class of methionine aminopeptidase inhibitors

A series of salicylate-based compounds were designed and synthesized based on the simple function group replacement from our previously reported catechol-containing inhibitors of methionine aminopeptidase (MetAP). Some of these salicylate derivatives showed similar potency and metalloform selectivity, and some showed considerable antibacterial activity. These findings are consistent with our previous conclusion that Fe(II) is the likely metal used by MetAP in bacterial cells and provide new lead structures that can be further developed as novel antibacterial agents.     

Carbonic anhydrase inhibitors: guaiacol and catechol derivatives effectively inhibit certain human carbonic anhydrase isoenzymes (hCA I,II, IX and XII)

Abstract

Carbonic anhydrases (CAs) are widespread metalloenzymes in higher vertebrates including humans. A series of phenolic compounds, including guaiacol, 4-methylguaiacol, 4-propylguaiacol, eugenol, isoeugenol, vanillin, syringaldehyde, catechol, 3-methyl catechol, 4-methyl catechol and 3-methoxy catechol were investigated for their inhibition of all the catalytically active mammalian isozymes of the Zn²⁺-containing CA (EC 4.2.1.1). All the phenolic compounds effectively inhibited human carbonic anhydrase isoenzymes (hCA I, II, IX and XII), with K_is in the range of 2.20–515.98?μM. The various isozymes showed diverse inhibition profiles. Among the tested phenolic derivatives, compounds 4-methyl catechol and 3-methoxy catechol showed potent activity as inhibitors of the tumour-associated transmembrane isoforms (hCA IX and XII) in the submicromolar range, with high selectivity. The results obtained from this research may lead to the design of more effective carbonic anhydrase isoenzyme inhibitors (CAIs) based on such phenolic compound scaffolds.     

Quinazoline–sulfonamides with potent inhibitory activity against the α-carbonic anhydrase from Vibrio cholerae

Thirteen novel sulfonamide derivatives incorporating the quinazoline scaffold were synthesized by simple, eco-friendly procedures. These compounds were tested for their ability to inhibit the α-carbonic anhydrases (CA, EC 4.2.1.1) from Vibrio cholerae (VchCA) as well as the human α-CA isoforms, hCA I and hCA II. Nine compounds were highly effective, nanomolar inhibitors of the pathogenic enzyme VchCA. Three of them were also highly effective sub-nanomolar inhibitors of the cytosolic isoform II. The best VchCA inhibitor had a K_I of 2.7 nM. Many of these developed compounds showed high selectivity for inhibition of the bacterial over the mammalian CA isoforms, with one compound possessing selectivity ratios as high as 97.9 against hCA I and 9.7 against hCA II. Compound 9d was another highly effective VchCA inhibitor presenting a selectivity ratio of 99.1 and 8.1 against hCA I and hCA II, respectively. These results suggest that sulfonamides with quinazoline backbone could be considered suitable tools to better understand the role of bacterial CAs in pathogenesis.     

Design of the first highly potent and selective aminopeptidase N (EC 3.4.11.2) inhibitor.

A series of phosphinic compounds mimicking the transition state of substrates hydrolysed by aminopeptidase N (EC 3.4.11.2) were synthesized. These new compounds have potent inhibitory activities with Ki values in the nanomolar range. These derivatives behave as the most potent APN inhibitors designed to date.     

First synthesis of alpha-aminoalkyl-(N-substituted)thiocarbamoyl-phosphinates: inhibitors of aminopeptidase N (APN/CD13) with the new zinc-binding group

OO-Di-trimethylsilyl esters of alpha-N-benzyloxycarbonylaminoalkylphosphinates (III) undergo triethylamine catalyzed addition to isothiocyanates to give after hydrolysis, a series of new alpha-aminoalkyl-(N-substituted)thiocarbamoyl-phosphinates. Thiocarbamoyl-phosphinate moiety can be included in the structures of the metalloproteinase inhibitors as the zinc-binding group and the new compounds reported here are good inhibitors of important aminopeptidase N(CD13) with IC(50) in range of 10.56-0.25 microM.     

Novel inhibitors of enkephalin-degrading enzymes. II: N5'-substituted-4-thioxohydantoic acids as aminopeptidase inhibitors

Some 2-substituted-(2'-aminophenyl)-4-thioxohydantoic acids (o-amino PTC-amino acids) have antinociceptive activity when administered (icv) alone (IC50 = 0.04-0.87 microM/animal) and show a striking prolongation of the antinociceptive action of (D-Ala-2 D-Leu5)-enkephalin (DADL) in combination. The effects are thought to be mediated via opioid receptors since they are naloxone-reversible. Although inhibitors of the enkephalin degrading puromycin-insensitive, bestatin-sensitive aminopeptidase (possibly aminopeptidase M) their action is weak (IC50 = 32 microM leucine, 536 microM, glycine) and they might be considered to have a direct antinociceptive effect on opioid receptors. The titled compounds constitute novel 'lead' compounds for the development of potent aminopeptidase M inhibitors.     

alpha-Aminoboronic acid derivatives: effective inhibitors of aminopeptidases

alpha-Aminoboronic acids and their derivatives have been synthesized as stable white solids. These compounds are effective inhibitors of human enkephalin degrading aminopeptidase, microsomal leucine aminopeptidase (EC 3.4.11.2), and cytosolic leucine aminopeptidase (EC 3.4.11.1) at micro- to nanomolar concentrations. The inhibition of cytosolic leucine aminopeptidase has been studied in some detail. Kinetic data correspond to the mechanism for biphasic slow-binding inhibition: E + I in equilibrium E.I in equilibrium E.I*, in which a rapid initial binding is followed by a slow transformation to a stable enzyme inhibitor complex. The initial and final binding constants are dependent on the nature of the side chain at the alpha-carbon atom but are independent of the protecting group on the boronic acid moiety and follow the trend for the hydrolysis of the corresponding amino acid amides. The first-order rate constant for the transformation of E.I to E.I* is similar for all four compounds studied. These data suggest that the slow-binding step represents the formation of tetrahedral boronate species from trigonal boronic acid.     

Antifeedant C20 diterpene alkaloids

We have tested the insect antifeedant and toxic activity of 21 C20 diterpenoid alkaloids on Spodoptera littoralis and Leptinotarsa decemlineata. The antifeedant effects of the test compounds were structure- and species-dependent. The most active antifeedants to L. decemlineata and S. littoralis were the rearranged form of hetisine (20; EC50 = 1.7 microg/cm2) and 19-oxodihydroatisine (9; EC50 = 0.1 microg/cm2), resp. Glandulosine (8) moderately affected orally injected S. littoralis larvae. A few compounds (13-oxocardiopetamine (4), 9, and atisinium chloride (13)) had cytotoxic effects to insect-derived Sf9 cells with varying degrees of selectivity with respect to mammalian CHO cells. Compounds 4 and 15,22-O-diacetyl-19-oxodihydroatisine (10) increased Trypanosoma cruzi mortality. Our results support the plant protective role of C20 diterpenoid alkaloids and open a new field for parasite control strategies.     

Novel Inhibitors of Enkephalin-Degrading Enzymes II: N5-Substituted-4-Thioxohydantoic Acids as Aminopeptidase Inhibitors

Abstract

Some 2-substituted-(2′-aminophenyl)-4-thioxohydantoic acids (o-amino PTC-amino acids) have antinociceptive activity when administered (icv) alone (IC₅₀ = 0.04-0.87 μM/animal) and show a striking prolongation of the antinociceptive action of (D-Ala-² D-Leu⁵)-enkephalin (DADL) in combination. The effects are thought to be mediated via opioid receptors since they are naloxone-reversible. Although inhibitors of the enkephalin degrading puromycin-insensitive, bestatin-sensitive aminopeptidase (possibly aminopeptidase M) their action is weak (IC₅₀ = 32μM leucine, 536μM, glycine) and they might be considered to have a direct antinociceptive effect on opioid receptors. The titled compounds constitute novel ‘lead’ compounds for the development of potent aminopeptidase M inhibitors.     

Nonpeptide small-molecular inhibitors of dipeptidyl peptidase IV: N-phenylphthalimide analogs

A novel series of nonpeptide small-molecular dipeptidyl peptidase IV (DPP-IV) inhibitors with an N-phenylphthalimide skeleton has been developed. Some of the compounds, including 4-amino-(2,6-dimethylphenyl)phthalimides (7), 4- and 5-hydroxy-(2,6-diethylphenyl)phthalimide (11 and 14), 4-hydroxy-(2,6-diisopropylphenyl)phthalimide (12), and thiocarbonyl analogs of (2,6-diisopropylphenyl)phthalimide and their 4,5,6,7-tetrafluorinated derivative (18, 19 and 20), were more potent than the well-known DPP-IV-specific inhibitor, Pro-boroPro (PBP). Among them, 18 was revealed to be a DPP-IV-specific inhibitor, while the others also showed inhibitory activity toward another peptidase, aminopeptidase N (APN).     

Design, synthesis and biological evaluation of novel L-lysine ureido derivatives as aminopeptidase N inhibitors

As the exopeptidase over-expressed in the cell surface of endothelial cells, aminopeptidase N (APN/CD13) is an essential target for tumor angiogenesis and metastasis. Based on the previous work of L-lysine amide derivatives in our laboratory, we designed and synthesized two series of L-lysine ureido derivatives as APN inhibitors. Within these compounds, one compound, 5d (IC?? = 4.51 μM), showed similar inhibitory effect compared with Bestatin (IC?? = 5.87 μM).     

Sulfanylphthalonitrile analogues as selective and potent inhibitors of monoamine oxidase B

It has recently been reported that nitrile containing compounds frequently act as potent monoamine oxidase B (MAO-B) inhibitors. Modelling studies suggest that this high potency inhibition may rely, at least in part, on polar interactions between nitrile functional groups and polar moieties within the MAO-B substrate cavity. In an attempt to identify potent and selective inhibitors of MAO-B and to contribute to the known structure–activity relationships of MAO inhibition by nitrile containing compounds, the present study examined the MAO inhibitory properties of series of novel sulfanylphthalonitriles and sulfanylbenzonitriles. The results document that the evaluated compounds are potent and selective MAO-B inhibitors with most homologues possessing IC₅₀ values in the nanomolar range. In general, the sulfanylphthalonitriles exhibited higher binding affinities for MAO-B than the corresponding sulfanylbenzonitrile homologues. Among the compounds evaluated, 4-[(4-bromobenzyl)sulfanyl]phthalonitrile is a particularly promising inhibitor since it displayed a high degree of selectivity (8720-fold) for MAO-B over MAO-A, and potent MAO-B inhibition (IC₅₀ = 0.025 μM). Based on these observations, this structure may serve as a lead for the development of therapies for neurodegenerative disorders such as Parkinson’s disease.     

Identification of aminopeptidase M as an enkephalin-inactivating enzyme in rat cerebral membranes

Two membrane-bound enkephalin-hydrolyzing aminopeptidase activities were partially purified from rat brain membranes. The first, which represents 90% of the total activity, was highly sensitive to both puromycin (Ki = 1 microM) and bestatin (Ki = 0.5 microM). The second was inhibited much more by bestatin (Ki = 4 microM) than by puromycin (Ki = 100 microM). The latter puromycin-insensitive aminopeptidase was found to resemble aminopeptidase M purified from rat kidney brush border membranes. Both displayed the same purification pattern and the same kinetic constants of substrates and inhibitors, and both were similarly inactivated by metal chelating agents. Moreover, antibodies raised in rabbits against rat kidney aminopeptidase M inhibited the aminopeptidase activities of both kidney and brain puromycin-insensitive enzymes at similar dilutions, while the brain puromycin-sensitive aminopeptidase activity was not affected. Thus, aminopeptidase M (EC 3.4.11.2) was found to occur in brain, and the role of this enzyme in inactivating endogenous enkephalins released from their neuronal stores is suggested.