Novel inhibitors of beta-ketoacyl-ACP reductase from Escherichia coli

Bacterial beta-ketoacyl-[acyl carrier protein] (beta-ketoacyl-ACP) reductase (FabG) is a highly conserved and ubiquitously expressed enzyme of the fatty-acid biosynthetic pathway of prokaryotic organisms that catalyzes NADPH-dependent reduction of beta-ketoacyl-ACP intermediates. Therefore, FabG represents an appealing target for the development of new antimicrobial agents. A number of trans-cinnamic acid derivatives were designed and screened for inhibitory activities against FabG from Escherichia coli. These inhibited FabG enzymatic activity with IC(50) values in the microM range, and were used as templates for the subsequent diversification of the chemotype. Introduction of an electron-withdrawing 4-cyano group to the phenol substituent showed improved inhibition over the non-substituted compound. The benzo-[1,3]-dioxol moiety also appeared to be essential for inhibitory activity of trans-cinnamic acid derivatives against FabG from E. coli. To explain the possible binding position, the best inhibitor from the present study was docked in the active site of FabG. The results for the best scoring conformers chosen by the docking programme revealed that cinnamic acid derivatives can be accommodated in the substrate-binding region of the active site, above the nicotinamide moiety of the NADPH cofactor. Additionally, a phage-displayed library of random linear 15-mer peptides was screened against FabG, to identify ligands with the common PPLTXY motif.     

Synthesis and biological evaluation of deoxy salacinols, the role of polar substituents in the side chain on the alpha-glucosidase inhibitory activity

Three analogs (5, 6, and 7) lacking polar substituents in the side chain of a naturally occurring alpha-glucosidase inhibitor, salacinol (1a), were synthesized by the coupling reaction of a thiosugar, 1,4-dideoxy-1,4-epithio-D-arabinitol (3), with cyclic sulfates (8, 9, and 10), and their alpha-glucosidase inhibitory activities were examined. All these simpler analogs (5, 6, and 7) showed less inhibitory activity compared to 1a, and proved the importance of cooperative role of the polar substituents for the alpha-glucosidase inhibitory activity. A practical synthetic route to 3 starting from D-xylose is also described.     

Hibiscus acid as an inhibitor of starch digestion in the Caco-2 cell model system.

Hibiscus acid, an alpha-amylase inhibitor isolated from roselle tea, and its derivatives were compared in an inhibition test for starch digestion. An alpha-amylase-added Caco-2 system was established as a useful model to evaluate the effects of alpha-glucosidase inhibitors on starch digestion. Hibiscus acid showed weak inhibition in this model system, and the methyl ester derivatives showed even weaker or no acitivity.     

Structure-activity relationships of bergenin derivatives effect on α-glucosidase inhibition

The α-glucosidase inhibitory activities of bergenin derivatives were evaluated. Bergenin derivatives were synthesized from bergenin which is a characteristic compound of B. ligulata. A new bergenin derivative, 11-O-(3′,4′-dimethoxybenzoyl)-bergenin showed the highest potent inhibitory activity among those of bergenin derivatives. The presence of substituents at 3′,4′-position in bergenin derivatives altered the α-glucosidase inhibitory activity. 11-O-(3′,4′-dimethoxybenzoyl)-bergenin was noncompetitive inhibitor for α-glucosidase. The present study reveals that bergenin derivatives could be classified as a new group of α-glucosidase inhibitors.     

Evaluation of glycolamide esters of indomethacin as potential cyclooxygenase-2 (COX-2) inhibitors

A number of novel indomethacin glycolamide esters were synthesized and tested for their cyclooxygenase (COX-1 and COX-2) inhibition properties in vitro. Many of these compounds proved to be selective COX-2 inhibitors, and subtle structural changes in the substituents on the glycolamide ester moiety altered the inhibitory properties as well as potencies significantly. Their in vitro data were rationalized through molecular modeling studies. Few of them displayed anti-inflammatory activity in vivo. Compound 32, [1-(4-chlorobenzoyl)-5-methoxy-2-methyl-1H-indol-3-yl]acetic acid 2-morpholin-4-yl-2-oxo ethyl ester, was identified as a promising compound in this class and its good anti-inflammatory activity was demonstrated in the in vivo model.     

Inhibition of alkaline phosphatase by thioureido derivatives of methylenebisphosphonic acid

A series of thioureido derivatives of methylenebisphosphonic acid were synthesized by the reaction of aminomethylenebisphosphonic acid with the corresponding isothiocyanates, and their effect on the activity of alkaline phosphatases from bovine small intestine mucosa (BSIM) and human placenta was studied. It was found that (3-phenylthioureido)methylenebisphosphonate is approximately one order of magnitude more effective in inhibiting the activity of alkaline phosphatase from BSIM than the alkyl derivatives of thioureidomethylenebisphosphonic acid with methyl, ethyl, tert-butyl, or cyclohexyl substituents. The introduction of substituents into the benzene ring of (3-phenylthioureido)methylenebisphosphonate decreased the effect of the inhibitor on the activity of the enzyme. The affinity of (3-phenylureido)methylenebisphosphonate to the alkaline phosphatase of BSIM was also weaker as compared with the corresponding thioureidomethylenebisphosphonate. The insertion of thioureidobisphosphonates into the active site of alkaline phosphatase of human placenta by the method of molecular docking indicated that the methylenebisphosphonate residue and the substituted amino groups of the inhibitor are involved in the mechanisms of complex formation with the enzyme. It is supposed that the improvement of the inhibitory activity of (3-phenylthioureido)methylenebisphosphonate toward alkaline phosphatase of BSIM is due to the additional fixation of the phenyl substituent in the active site of the enzyme.     

Synthesis and SAR of thiazolidinedione derivatives as 15-PGDH inhibitors

Prostaglandins have a short life in vivo because they are metabolized rapidly by oxidation to 15-ketoprostaglandins catalyzed by a cytosolic enzyme known as NAD⁺-dependent 15-hydroxyprostaglandin dehydrogenase (15-PGDH). Previously, CT-8, a thiazolidinedione analogue, was found to be a potent inhibitor of 15-PGDH. Structure–activity analysis indicated that the N-methylation of thiazolidine-2,4-dione, CT-8, abolished the inhibitory activity, whereas the introduction of an ethyl hydroxyl group at amine in CT-8 still had a good inhibitory effect. Based on the structures of the thiazolidinediones analogues and inhibitory activity, a range of benzylidene thiazolidinedione derivatives were synthesized with different substituents on the phenyl ring and their inhibitory activity was evaluated. Replacement of the cyclohexylethyl group of CT-8 with the hetero five-member ring increased the inhibitory potency. However, replacement of the cyclohexylethyl group with a hetero six-member ring decreased the inhibitory potency significantly. It was found that compound 2 (5-(4-(2-(thiophen-2-yl)ethoxy)benzylidene)thiazolidine-2,4-dione) was the most potent inhibitor that was effective in the nanomolar range.     

Synthesis of 2-methyl and 2-carboxymethyl derivatives of ornithine and arginine

Synthesis and characterization of a dozen derivatives of ornithine and arginine bearing 2-methyl or 2-carboxymethyl substituents are described. These substituents were introduced by dilithiation of 3-(4-methoxybenzylidineamino)-2-piperidinone with lithium diisopropylamide followed by regiospecific alkylation at C-3 with iodomethane or ethyl bromoacetate. 2-Methyl-D,L-ornithine was obtained in three steps from 3-amino-2-piperidinone in 68% overall yield, and 2-carboxymethyl-D,L-ornithine was isolated in 56% overall yield. 2-Methyl- and 2-carboxymethyl-D,L-arginine were obtained by mild acid hydrolysis to remove the 4-methoxybenzylidine group, N-acylation with 4-toluenesulfonyl chloride, mild alkaline hydrolysis of the lactam ring and the ester group, guanidination of the 5-amino group with O-methylisourea, and strong acid hydrolysis to remove the 4-tolunenesulfonyl group. Several of these compounds are inhibitors of carboxypeptidase B.     

Inhibition of alkaline phosphatase by thioureido derivatives of methylenebisphosphonic acid

A series of thioureido derivatives of methylenebisphosphonic acid were synthesized by the reaction of aminomethylenebisphosphonic acid with the corresponding isothiocyanates, and their effect on the activity of alkaline phosphatases from bovine small intestine mucosa (BSIM) and human placenta was studied. It was found that (3-phenylthioureido)methylenebisphosphonate is approximately one order of magnitude more effective in inhibiting the activity of alkaline phosphatase from BSIM than the alkyl derivatives of thioureidomethylenebisphosphonic acid with methyl, ethyl, tert-butyl, or cyclohexyl substituents. The introduction of substituents into the benzene ring of (3-phenylthioureido)methylenebisphosphonate decreased the effect of the inhibitor on the activity of the enzyme. The affinity of (3-phenylureido)methylenebisphosphonate to the alkaline phosphatase of BSIM was also weaker as compared with the corresponding thioureidomethylenebisphosphonate. The insertion of thioureidobisphosphonates into the active site of alkaline phosphatase of human placenta by the method of molecular docking indicated that the methylenebisphosphonate residue and the substituted amino groups of the inhibitor are involved in the mechanisms of complex formation with the enzyme. It is supposed that the improvement of the inhibitory activity of (3-phenylthioureido)methylenebisphosphonate toward alkaline phosphatase of BSIM is due to the additional fixation of the phenyl substituent in the active site of the enzyme.     

A new class of potential anti-tuberculosis agents: Synthesis and preliminary evaluation of novel acrylic acid ethyl ester derivatives

Novel acrylic acid ethyl ester derivatives were synthesized and evaluated as potential agents against Mycobacterium species. A versatile and efficient copper-catalyzed coupling process was developed and used to prepare a library of substituted acrylic acid ethyl ester analogs. Minimum inhibitory concentration assays indicated that two of these compounds 3 and 4 have greater in vitro activity against Mycobacterium smegmatis than rifampin, one of the current, first-line anti-mycobacterial chemotherapeutic agents. Moreover, members of this new class of compounds appear to exhibit a specific anti-mycobacterial effect and do not inhibit the growth of the other Gram-positive or Gram-negative species tested.     

Inhibitory effect of the alkyl side chain of caffeic acid analogues on lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophages

Caffeic acid esters, one of the components of propolis, are known to show a variety of biological effects such as anti-tumor, anti-oxidant, and anti-inflammatory activities. Although, the anti-inflammatory activities of caffeic acid esters have been studied by analyzing their structure, the detailed mechanisms of their activities remain unclear. Thus, in this study, we examined the function of the ester functional group and the alkyl side chain (alcoholic part) and transformed caffeic acid to several derivatives. The inhibitory effect of these derivatives on NO production in murine macrophage RAW264.7 cells was dependent on the length and size of the alkyl moiety, and undecyl caffeate was the most potent inhibitor of NO production. In addition, individual experiments using undecanol, caffeic acid, undecanol plus caffeic acid, and undecyl caffeate showed that the connection between caffeic acid and the alkyl chain is critical for activity. Amide and ketone derivatives showed that not only the ester functional group but also the amide and ketone functional groups exhibit an inhibitory effect on NO production.     

Synthesis and antimycobacterial evaluation of new trans-cinnamic acid hydrazide derivatives

In this work, we report the synthesis and the antimycobacterial evaluation of new trans-cinnamic acid derivatives of isonicotinic acid series (5) and benzoic acid series (6), designed by exploring the molecular hybridization approach between isoniazid (1) and trans-cinnamic acid derivative (3). The minimum inhibitory concentration (MIC) of the compounds 5a-d and 6c exhibited activity between 3.12 and 12.5 microg/mL and could be a good start point to find new lead compounds against multi-drug resistant tuberculosis.     

Structural insight into interaction between C20 phenylalanyl derivative of tylosin and ribosomal tunnel

Macrolides are clinically important antibiotics that inhibit protein biosynthesis on ribosomes by binding to ribosomal tunnel. Tylosin belongs to the group of 16-membered macrolides. It is a potent inhibitor of translation whose activity is largely due to reversible covalent binding of its aldehyde group with the base of A2062 in 23S ribosomal RNA. It is known that the conversion of the aldehyde group of tylosin to methyl or carbinol groups dramatically reduces its inhibitory activity. However, earlier we obtained several derivatives of tylosin having comparable activity in spite of the fact that the aldehyde group of tylosin in these compounds was substituted with an amino acid or a peptide residue. Details of the interaction of these compounds with the ribosome that underlies their high inhibitory activity were not known. In the present work, the structure of the complex of tylosin derivative containing in position 20 the residue of ethyl ester of 2-imino(oxy)acetylphenylalanine with the tunnel of the E. coli ribosome was identified by means of molecular dynamics simulations, which could explain high biological activity of this compound.     

alpha-Glucosidase inhibition of 6-hydroxyflavones. Part 3: Synthesis and evaluation of 2,3,4-trihydroxybenzoyl-containing flavonoid analogs and 6-aminoflavones as alpha-glucosidase inhibitors

The SAR studies suggested that the C-ring of baicalein (1) was not necessary for the activity, and validated the importance of 2,3,4-trihydroxybenzoyl structure of 1. Thus, a series of 2,3,4-trihydroxybenzoyl-containing flavonoid analogs were investigated for the alpha-glucosidase inhibitory activity. The results indicated that 5,6,7-trihydroxy-2-phenyl-4-quinolone (2) and 5,6,7-trihydroxyflavanone (4) showed the comparable activity to 1, while 3,5,6,7-tetrahydroxyflavone (7), 5,6,7-trihydroxyisoflavone (8), and 6-hydroxygenistein (9) showed moderate alpha-glucosidase inhibitory activity. In addition, it was found that 6-amino-5,7-dihydroxyflavone (16) was a more potent and specific rat intestinal alpha-glucosidase inhibitor than 1, and showed the comparable activity to acarbose. This is the first report on mammalian intestinal alpha-glucosidase inhibitory activity of 6-aminoflavones. Kinetic studies revealed that 16 inhibited both sucrose- and maltose-hydrolyzing activities of rat intestinal alpha-glucosidase uncompetitively.     

2-Aminoresorcinol is a potent alpha-glucosidase inhibitor

A series of aminoresorcinols and related compounds were tested for rat intestinal alpha-glucosidase inhibition and these results suggested that the 2-aminoresorcinol moiety of 6-amino-5,7-dihydroxyflavone (2) is important to exert the intestinal alpha-glucosidase inhibitory activity and 2-aminoresorcinol (4), itself, is a potent alpha-glucosidase inhibitor and inhibited sucrose-hydrolyzing activity of rat intestinal alpha-glucosidase uncompetitively.     

Amide and ester derivatives of N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid: the selective inhibitor of glucosamine-6-phosphate synthase

Several amide and ester derivatives of a glutamine analogue, N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid (FMDP) (1-8), were synthesized and evaluated for the inhibitory activity in regard to glucosamine-6-phosphate synthase from Candida albicans. The syntheses were accomplished by the reaction of N2-tert-butoxycarbonyl-N3-(4-methoxyfumaroyl)-(S)-2,3-diaminopropanoic acid (BocFMDP) with the corresponding amines to give the FMDP amides (1-4) or with alkyl halides to give corresponding esters of FMDP (5-8). Among the synthesized compounds, the acetoxymethyl ester of FMDP was the most active inhibitor of the enzyme. Its IC50 value compared to that of FMDP (4 microM) was equal to 11.5 microM. The methyl and allyl esters and the N-hexyl-N-methyl-amide of FMDP exhibited a moderate enzyme inhibitory activity.     

Inhibition of recombinant human maltase glucoamylase by salacinol and derivatives

Inhibitors targeting pancreatic alpha-amylase and intestinal alpha-glucosidases delay glucose production following digestion and are currently used in the treatment of Type II diabetes. Maltase-glucoamylase (MGA), a family 31 glycoside hydrolase, is an alpha-glucosidase anchored in the membrane of small intestinal epithelial cells responsible for the final step of mammalian starch digestion leading to the release of glucose. This paper reports the production and purification of active human recombinant MGA amino terminal catalytic domain (MGAnt) from two different eukaryotic cell culture systems. MGAnt overexpressed in Drosophila cells was of quality and quantity suitable for kinetic and inhibition studies as well as future structural studies. Inhibition of MGAnt was tested with a group of prospective alpha-glucosidase inhibitors modeled after salacinol, a naturally occurring alpha-glucosidase inhibitor, and acarbose, a currently prescribed antidiabetic agent. Four synthetic inhibitors that bind and inhibit MGAnt activity better than acarbose, and at comparable levels to salacinol, were found. The inhibitors are derivatives of salacinol that contain either a selenium atom in place of sulfur in the five-membered ring, or a longer polyhydroxylated, sulfated chain than salacinol. Six-membered ring derivatives of salacinol and compounds modeled after miglitol were much less effective as MGAnt inhibitors. These results provide information on the inhibitory profile of MGAnt that will guide the development of new compounds having antidiabetic activity.     

Sulfonamide chalcone as a new class of alpha-glucosidase inhibitors

Chalcones 1-20, a new class of glycosidase inhibitors, were synthesized, and their glycosidase inhibitory activities were investigated. Non-aminochalcones 1-12 had no inhibitory activity, however, aminochalcones 13-20 had strong glycosidase (alpha-glucosidase, alpha-amylase, and beta-amylase) inhibitory activities. In particular, sulfonamide chalcones 17-20 had more potent alpha-glucosidase inhibitory activity than aminated chalcone 13-16. 4'-(p-Toluenesulfonamide)-3,4-dihydroxy chalcone 20 (IC(50)=0.4microM) was the best inhibitor against alpha-glucosidase, and these sulfonamide chalcones showed non-competitive inhibition.     

Synthesis and CYP26A1 inhibitory activity of 1-[benzofuran-2-yl-(4-alkyl/aryl-phenyl)-methyl]-1H-triazoles

Methodology previously described by our group was applied to the preparation of a series of 4-alkyl/aryl-substituted 1-[benzofuran-2-yl-phenylmethyl]-1H-triazoles. The [1,2,4]-triazole derivatives were prepared for a range of alkyl and aryl substituents, and for the 4-methyl, 4-ethyl, 4-(i)propyl, 4-(t)butyl, 4-phenyl and 4-chlorophenyl derivatives, the minor [1,3,4]-triazole isomer also isolated. All the triazole derivatives were evaluated for CYP26A1 inhibitory activity using a MCF-7 cell-based assay. The 4-ethyl and 4-phenyl-1,2,4-triazole derivatives displayed inhibitory activity (IC(50) 4.5 and 7 microM, respectively) comparable with that of the CYP26 inhibitor liarozole (IC(50) 7 microM). Using a CYP26A1 homology model (based on CYP3A4) template, docking experiments were performed with MOE with multiple hydrophobic interactions observed in addition to coordination between the triazole nitrogen and the haem transition metal.