Synthetic UDP-galactofuranose analogs reveal critical enzyme-substrate interactions in GlfT2-catalyzed mycobacterial galactan assembly

Mycobacterial cell wall galactan, composed of alternating β-(1→5) and β-(1→6) galactofuranosyl residues, is assembled by the action of two bifunctional galactofuranosyltransferases, GlfT1 and GlfT2, which use UDP-galactofuranose (UDP-Galf) as the donor substrate. Kinetic analysis of synthetic UDP-Galf analogs identified critical interactions involved in donor substrate recognition by GlfT2, a processive polymerizing glycosyltransferase. Testing of methylated UDP-Galf analogs showed the donor substrate-binding pocket is sterically crowded. Evaluation of deoxy UDP-Galf analogs revealed that the C-6 hydroxyl group is not essential for substrate activity, and that interactions with the UDP-Galf C-3 hydroxyl group orient the substrate for turnover but appears to play no role in substrate recognition, making the 3-deoxy-analog a moderate competitive inhibitor of the enzyme. Moreover, the addition of a Galf residue deoxygenated at C-5 or C-6, or an l-arabinofuranose residue, to the growing galactan chain resulted in "dead end" reaction products, which no longer act as an acceptor for the enzyme. This finding shows dual recognition of both the terminal C-5 and C-6 hydroxyl groups of the acceptor substrate are required for GlfT2 activity, which is consistent with a recent model developed based upon a crystal structure of the enzyme. These observations provide insight into specific protein-carbohydrate interactions in the GlfT2 active site and may facilitate the design of future inhibitors.     

Synthetic routes and biological evaluation of largazole and its analogues as potent histone deacetylase inhibitors

Natural products with interesting biological properties and structural diversity have often served as valuable lead drug candidates for the treatment of various human diseases. Largazole, isolated from the marine cyanobacterium Symploca sp. has exhibited potent inhibitory activity against many cancer cell lines. Besides, it shows remarkable selectivity between transformed and nontransformed cells, which is the main disadvantage of other antitumor natural products such as paclitaxel and actinomycin D. Due to its potential as a potent and selective anticancer drug candidate, a great deal of attention has been focused on largazole and its analogues. It is the aim of this review to highlight synthetic aspects of largazole and its analogues as well as their preliminary structure-activity relationship studies.     

Synthetic disaccharide analogs as potential substrates and inhibitors of a mycobacterial polyprenol monophosphomannose-dependent α-(1→6)-mannosyltransferase

Analogs of the α-d-Manp-(1→6)-α-d-Manp-O(CH₂)₇CH₃ disaccharide 4, a known substrate for a polyprenol monophosphomannose-dependent α-(1→6)-mannosyltransferase involved in mycobacterial LAM biosynthesis, have been synthesized and screened as potential substrates and inhibitors of the enzyme. In the disaccharides synthesized, the hydroxyl groups at C-2 and C-6 on the reducing end residue have been replaced by combinations of amino, fluoro, and methoxy functionalities 9–14. In addition, a disaccharide in which the nonreducing mannopyranose residue was replaced with a 3,6-anhydromannopyranose residue 34 was synthesized from a byproduct formed during one of the reactions leading to 14. When tested against the enzyme, none were active as substrates, as would be expected as all lack the C-6′ hydroxyl group to which an additional sugar residue would be transferred. Evaluation of these compounds as inhibitors of the enzyme revealed that only three, 11, 12, and 13, all of which contain one or more amino groups, inhibited the enzyme. The most potent inhibitor was the diamino-disaccharide, 11.     

Synthetic inhibitors of proline-rich ligand-mediated protein-protein interaction: potent analogs of UCS15A

The proline-rich motif in proteins is known to function as a ligand sequence that binds to protein modules such as SH3, WW, and several other protein interaction domains. These proline-rich ligand-mediated protein-protein interactions (abbreviated PLPI) are important in many signaling pathways that are involved in various diseases. Our previous studies showed that UCS15A, produced by Streptomyces species, inhibited PLPI. Here we report on synthetic analogs of UCS15A that show more potent activity than UCS15A in inhibiting PLPI. A synthetic analog, compound 2c, blocked in vitro PLPI of Sam68-Fyn-SH3 as well as in vivo PLPI of Grb2-Sam68 and Grb2-Sos1. Activation of MEK was also inhibited by compound 2c. Unlike UCS15A, compound 2c was an order of magnitude less cytotoxic and did not cause morphological changes in treated cells.     

Pyridine-sugar conjugates as potent inhibitors of enzyme-catalysed glycoside hydrolysis

A series of O- and N-linked pseudo-disaccharides incorporating simple functionalised pyridines were synthesized and demonstrated potent inhibition of the glucoamylase-catalysed reaction.     

C-linked galactosyl serine AFGP analogues as potent recrystallization inhibitors

[reaction: see text] A series of C-linked antifreeze glycoprotein analogues have been prepared to evaluate antifreeze activity as a function of distance between the carbohydrate moiety and polypeptide backbone. The building blocks for these analogues were prepared using either an olefin cross-metathesis or catalytic asymmetric hydrogenation. Analysis of antifreeze protein-specific activity revealed that only analogue 2a (n = 1) was a potent recrystallization inhibitor and thus has potential medical and industrial applications.     

Bromoenterobactins as potent inhibitors of a pathogen-associated, siderophore-modifying C-glycosyltransferase

IroB is a C-glycosyltransferase encoded in the iroA cluster. C-Glucosylation of the bacterial siderophore enterobactin by IroB is a strategy some pathogenic bacteria use to evade the host's innate immunity mediated by lipocalin 2 (Lcn2). Without this modification, enterobactin can be tightly bound by host Lcn2, rendering it ineffective as a siderophore. Therefore, IroB inhibitors could be potential antibiotics against iroA-harboring pathogenic bacteria. We used enterobactin analogues to probe the properties of the active site of IroB and found that enterobactin analogues brominated at the C5 positions of the 2,3-dihydroxybenzoyl rings are potent inhibitors of IroB. This finding could lead to the discovery of effective antibiotics targeting iroA-containing bacteria.     

Design and synthesis of chitin synthase inhibitors as potent fungicides

Chitin is a structural component of fungal cell walls but is absent in vertebrates,mammals,and humans.Chitin synthase is thus an attractive molecular target for developing fungicides.Based on the structure of its donor substrate,UDP-N-acetyl-glucosamine,as well as the modelled structure of the bacterial chitin synthase NodC,we designed a novel scaffold which was then further optimized into a series of chitin synthase inhibitors.The most potent inhibitor,compound 13,exhibited high chitin synthase inhibitory activity with an IC_(50) value of 64.5 μmol/L All of the inhibitors exhibited antifungal activities against the growth of agriculturally-destructive fungi,Fusarium graminearum,Botrytis cinerea.and Colletotrichum lagenarium.This work presents a new scaffold which can be used for the development of novel fungicides.     

Cyclic amidine sugars as transition-state analogue inhibitors of glycosidases: potent competitive inhibitors of mannosidases

A series of monocyclic glycoamidines bearing different exocyclic amine, alcohol, or alkyl functionalities and bicyclic amidines derived from D-glucose and D-mannose were synthesized and tested as inhibitors of various glycosidases. All the prepared compounds demonstrated good to excellent inhibition toward glycosidases. In particular, the biscationic D-mannoamidine 9b bearing an exocyclic ethylamine moiety proved to be a selective competitive inhibitor of alpha- and beta-mannosidases (K(i) = 6 nM) making it the most potent inhibitor of these glycosidases reported to date. A favorable B(2,5) boat conformation might explain the selectivity of mannosidase inhibition compared to other glycosidases.     

Sterically hindered triacylglycerol analogues as potent inhibitors of human digestive lipases

A novel class of inhibitors of human digestive lipases have been developed. Various sterically hindered triacylglycerols based on 2-methyl- and 2-butylglycerol, and/or 2-methyl fatty acids were synthesized. The triacylglycerol analogues were tested for their ability to form stable monomolecular films at the air/water interface by recording their surface-pressure/molecular-area compression isotherms. The inhibition of human pancreatic and gastric lipases by the sterically hindered triacylglycerol analogues was studied by using the monolayer technique with mixed films of 1,2-dicaprin, which contained variable proportions of each inhibitor. Triolein analogues that contain a butyl group at the 2-position of the glycerol backbone or methyl groups both at the 2-position of glycerol, and the alpha-position of each oleic acid residue were potent inhibitors; this caused a 50% decrease in HPL activity at 0.003 molar fraction.     

Nitrogen heterocycles as potential monoamine oxidase inhibitors: Synthetic aspects

The present review highlights the synthetic methods of monoamine oxidase inhibitors (MAO) belonging to a group of nitrogen heterocycles such as pyrazoline, indole, xanthine, oxadiazole, benzimidazole, pyrrole, quinoxaline, thiazole and other related compounds (1990–2012). Moreover, it emphasizes salient findings related to chemical structures and the bioactivities of these heterocycles as MAO inhibitors. The aim of this review is to find out different methods for the synthesis of nitrogen containing heterocycles and their bioactivity related aspects as MAO inhibitors.     

Benzofuran-isatin conjugates as potent VEGFR-2 and cancer cell growth inhibitors

A series of benzofuran-isatin conjugates 6a-l and 7a,b tethered by various alkyl linkers were synthesized and evaluated for their VEGFR-2 inhibitory activity and in vitro activity against a panel of cancer cell lines. Seven of them were comparable with or better than Sunitinib against all tested cancer cells, demonstrating benzofuran-isatin conjugates were potential anticancer candidates. The mechanism study revealed that VEGFR-2 was at least one of the targets for this kind of conjugates. The structure-activity relationship demonstrated that the carbon spacer between benzofuran and isatin moieties, substituents on the C-2 position of benzofuran moiety, and substituents on C-3 as well as C-5 position of isatin motif influenced the anticancer activity significantly, and the enriched structure-activity relationship may provide an insight for rational design of more effective conjugates.     

Syntheses of mycobactin analogs as potent and selective inhibitors of Mycobacterium tuberculosis

Three analogs of mycobactin T, the siderophore secreted by Mycobacterium tuberculosis (Mtb) were synthesized and screened for their antibiotic activity against Mtb H(37)Rv and a broad panel of Gram-positive and Gram-negative bacteria. The synthetic mycobactins were potent (MIC(90) 0.02-0.88 μM in 7H12 media) and selective Mtb inhibitors, with no inhibitory activity observed against any other of the microorganisms tested. The maleimide-containing analog 40 represents a versatile platform for the development of mycobactin-drug conjugates, as well as other applications.     

Total synthesis of moniliformediquinone and calanquinone A as potent inhibitors for breast cancer

The first synthesis of moniliformediquinone has been achieved in which the longest linear sequence is only nine steps. The synthesis proceeds in 23% overall yield from commercially available 2,4,5-trimethoxybenzaldehyde. The key transformations include a Pd-catalyzed coupling between a phenyl triflate and an acetylene, and a TiCl₄-mediated cyclization of a benzoquinone intermediate. In addition, in vitro inhibitory effects of moniliformediquinone, denbinobin, moscatilin, and calanquinone A were determined to have IC₅₀ values of 0.7, 1.6, 2.5, and 1.5 μM, respectively.     

A new synthesis of fully phosphorylated flavones as potent pancreatic cholesterol esterase inhibitors

Five flavones possessing one to four phenolic groups were fully phosphorylated efficiently and the obtained compounds showed excellent pancreatic cholesterol esterase (CEase) inhibitory activities with IC(50) in the nanomolar range, which were much more potent than their parent compounds. The inhibition mechanism and kinetic characterization studies indicate that they are irreversible competitive inhibitors.     

Ethacrynic acid as a lead structure for the development of potent urease inhibitors

Ethacrynic acid and a series of its analogues were synthesized and subsequently evaluated for their inhibitory effect on jack bean urease. Ethacrynic acid showed, even at low concentrations, very potent inhibitory activity against the enzyme. For ethacrynic acid, the inhibition potential increased with increasing preincubation time of ethacrynic acid and enzyme, whereas for some other compounds a higher preincubation time lead to a significant reduction of their activity. We could demonstrate that the α,β-unsaturated carbonyl unit of our compounds is mandatory to inhibit the enzyme, possibly due to its ability to bind to cysteine residues in the active site of the jack bean urease.     

C-Alkyl 5-membered ring imino sugars as new potent cytotoxic glucosylceramide synthase inhibitors

The stereoselective preparation of novel C-alkyl 5-membered ring imino sugars and their biological evaluation with regard to GCS inhibition and cytotoxicity in a murine melanoma model are reported.