Synthesis of mangiferin derivatives as protein tyrosine phosphatase 1B inhibitors

Protein tyrosine phosphatase 1B (PTP1B) has received much attention due to its pivotal role in type 2 diabetes and obesity as a negative regulator of the insulin signaling pathway. Mangiferin, a xanthone glucoside, has been reported to possess significant antidiabetic activity. In the present study, a series of mangiferin derivatives was synthesized and evaluated for their PTP1B inhibitory activity. Some of the screened compounds displayed good PTP1B inhibitory activity. Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 549–551, November–December, 2007.     

Porphyrin-aminoquinoline conjugates as telomerase inhibitors

A series of metalloporphyrins was prepared in order to target the G-quadruplex structure of telomeric DNA for the design of antitelomerase compounds. The initial cationic tetramethylpyridiniumyl porphyrin was modified by the replacement of one or two methylpyridiniumyl groups by one or two 4-aminoquinoline moieties, at the meso position, in order to increase the cell penetration and the quadruplex affinity. The porphyrins were either metallated by manganese or by nickel. The degradation of quadruplex DNA was assayed in vitro with the manganese redox-active derivatives. All porphyrins complexes were capable of inhibiting the telomerase enzyme with IC50 values in the micromolar range (TRAP assay).     

Identification of protein tyrosine phosphatase 1B and casein as substrates for 124-v-Mos

Background  

The mos proto-oncogene encodes a cytoplasmic serine/threonine-specific protein kinase with crucial function during meiotic cell division in vertebrates. Based on oncogenic amino acid substitutions the viral derivative, 124-v-Mos, displays constitutive protein kinase activity and functions independent of unknown upstream effectors of mos protein kinase. We have utilized this property of 124-v-Mos and screened for novel mos substrates in immunocomplex kinase assays in vitro.     

Mannose-pepstatin conjugates as targeted inhibitors of antigen processing

The molecular details of antigen processing, including the identity of the enzymes involved, their intracellular location and their substrate specificity, are still incompletely understood. Selective inhibition of proteolytic antigen processing enzymes such as cathepsins D and E, using small molecular inhibitors such as pepstatin, has proven to be a valuable tool in investigating these pathways. However, pepstatin is poorly soluble in water and has limited access to the antigen processing compartment in antigen presenting cells. We have synthesised mannose-pepstatin conjugates, and neomannosylated BSA-pepstatin conjugates, as tools for the in vivo study of the antigen processing pathway. Conjugation to mannose and to neomannosylated BSA substantially improved the solubility of the conjugates relative to pepstatin. The mannose-pepstatin conjugates showed no reduction in inhibition of cathepsin E, whereas the neomannosylated BSA-pepstatin conjugates showed some loss of inhibition, probably due to steric factors. However, a neomannosylated BSA-pepstatin conjugate incorporating a cleavable disulfide linkage between the pepstatin and the BSA showed the best uptake to dendritic cells and the best inhibition of antigen processing.     

Solid-phase assembly and in situ screening of protein tyrosine phosphatase inhibitors

A highly efficient solid-phase strategy for assembly of small molecule inhibitors against protein tyrosine phosphatase 1B (PTP1B) is described. The method is highlighted by its simplicity and product purity. A 70-member combinatorial library of analogues of a known PTP1B inhibitor has been synthesized, which upon direct in situ screening revealed a potent inhibitor ( Ki = 7.0 microM) against PTP1B.     

Identification and further development of thiazolidinones spiro-fused to indolin-2-ones as potent and selective inhibitors of Mycobacterium tuberculosis protein tyrosine phosphatase B

Tuberculosis continues to be a major cause of morbidity and mortality throughout the world. Protein tyrosine phosphatases from Mycobacterium tuberculosis are attractive targets for developing novel strategies in battling tuberculosis due to their role in the intracellular survival of M. tuberculosis in various infection models. Here, we report on the identification and further development of thiazolidinones spiro-fused to indolin-2-ones as a new class of potent and selective inhibitors of M. tuberculosis protein tyrosine phosphatase B. Detailed structure-activity relationship (SAR) studies revealed that a nitro-substituted 2-oxoindole core together with a dihalogenated anilide and a halogenated N-benzyl moiety are essential for strong inhibitory activity against MptpB (M. tuberculosis protein tyrosine phosphatase B). Small structural modification of the identified compounds led to significant improvement of compound solubility and cell permeability retaining inhibitory activity in the micromolar range. The configuration of the spiro-center was found to be crucial for the inhibitory activity and the separation of the racemate revealed the R-(−)-enantiomers as the biologically active component. The reported MptpB inhibitors show excellent selectivity against a selected panel of protein tyrosine phosphatases, including MptpA (M. tuberculosis protein tyrosine phosphatase A), PTP1B (protein tyrosine phosphatase 1B), SHP-2 (Src homology 2 domain-containing protein tyrosine phosphatase), PTPN2, h-PTPβ (human protein tyrosine phosphatase β), and VHR (Vaccinia virus VH1-related dual-specific protein phosphatase) and further highlight the identified thiazolidinones spiro-fused to indolin-2-ones as a promising class of new compounds that might prove useful for chemical biology research to dissect MptpB function and eventually foster the development of next generation antibiotics.     

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.     

Hypervalent organochalcogenanes as inhibitors of protein tyrosine phosphatases

A series of organochalcogenanes was synthesized and evaluated as protein tyrosine phosphatases (PTPs) inhibitors. The results indicate that organochalcogenanes inactivate the PTPs in a time- and concentration-dependent fashion, most likely through covalent modification of the active site sulfur-moiety by the chalcogen atom. Consequently, organochalcogenanes represent a new class of mechanism-based probes to modulate the PTP-mediated cellular processes.     

Protein‐oligosaccharide conjugates as novel prebiotics

Maintaining a good proportion of gut probiotic bacteria is imperative to health. This may be achieved by consuming “prebiotics,” e.g., galacto‐oligosaccharides (GOS) that selectively promote probiotic bacteria, as they often uniquely express transporters for such oligosaccharides. Proteins are an important source for amino acids essential to probiotic bacteria. As most protein digestion products are absorbed in the small intestine, and there is great competition on the residuals by colonic bacteria, amino acids are scarce (<0.01 mM) in the colonic intercellular fluid, thus limiting probiotics' proliferation. However, no existing prebiotic product contains protein. Herein, we propose a new type of prebiotics: protein‐oligosaccharide conjugates. These conjugates were designed to be selectively targeted to probiotic bacteria in the colon, for enhancing their competitive advantage over undesired microorganisms. The approach was inspired by active targeting of chemotherapy, achieved by conjugating drugs to ligands, which selectively bind to proteins uniquely expressed on cancer cells; except here, we aimed to promote, not eliminate, the targeted cells. We formed these conjugates by mild Maillard‐reaction‐based covalent conjugation of GOS to lactoferrin hydrolysate (LFH), formed by peptic digestion, hence it resists gastric digestion. LFH‐GOS conjugates comprised 76% ± 1% LFH and 25% ± 4% GOS, and self‐assembled into 0.2 to 1.5‐μm microparticles. Most of the conjugates' protein content endured simulated gastrointestinal digestion, hence is expected to reach the colon. Remarkably, we found that the growth rate of a model probiotic bacterium (Lactobacillus casei) on the conjugates was double that on the unconjugated components (0.082 and 0.041 h^?1, respectively). This study proposes the next generation of prebiotics.     

Synthesis and biological evaluation of a series of novel salicylanilides as inhibitors of EGFR protein tyrosine kinases

The synthesis and biological evaluation of two series of salicylanilide derivatives on the EGFR and ErbB-2 tyrosine kinases inhibitory activities were conducted.Of the tested compounds those having an additional aryl group substituted on the anilino ring were active on the EGFR tyrosine kinase inhibition(7a-c and 13a,13c,13d,13f).The inhibitory activities were all in the low micromolar or submicromolar range.In addition,compound 13a was found to have dual inhibitory activities both on EGFR and ErbB-2 tyrosine kinases(1.654±1.280 and 7.134±1.265μmol/L).     

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.     

Synthesis of uracil–coumarin conjugates as potential inhibitors of virus replication

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Negative regulation of a protein tyrosine phosphatase by tyrosine phosphorylation

The low molecular weight protein tyrosine phosphatase (LMW-PTP) is a ubiquitously expressed enzyme with several proposed roles in cell signaling. Previously, two tyrosine phosphorylation modifications of LMW-PTP at sites Tyr-131 and Tyr-132 in response to growth factor stimulation have been mapped and suggested to stimulate LMW-PTP phosphatase activity. Biochemical analysis of tyrosine phosphorylation of a tyrosine phosphatase is challenging because of the intrinsic instability of these modifications. Here we used expressed protein ligation to site-specifically incorporate a phosphotyrosine mimic (phosphonomethylenephenylalanine, Pmp) at the Tyr-131 and Tyr-132 positions and measured the catalytic activity of these semisynthetic LMW-PTPs. The phosphonate-modified LMW-PTPs were 10- to 23-fold less active in dephosphorylating phosphotyrosine peptides derived from the PDGF receptor and p190RhoGap, two putative cellular substrates. These findings suggest the first example of a tyrosine phosphatase that is inhibited by tyrosine phosphorylation and provide a new model for the regulation of LMW-PTP and its role in cell adhesion.     

Receptor-based virtual ligand screening for the identification of novel CDC25 phosphatase inhibitors

CDC25 phosphatases play critical roles in cell cycle regulation and are attractive targets for anticancer therapies. Several small non-peptide molecules are known to inhibit CDC25, but many of them appear to form a covalent bond with the enzyme or act through oxidation of the thiolate group of the catalytic cysteine. Structure-based virtual ligand screening computations were performed with FRED, Surflex, and LigandFit, a compound collection of over 310,000 druglike molecules and the crystal structure of CDC25B in order to identify novel classes of ligands. In vitro experiments carried out on a selected list of 1500 molecules led to the discovery of 99 compounds able to inhibit CDC25B activity at 100 microM. Further docking computations were applied, allowing us to propose a binding mode for the most potent molecule (IC50 = 13 microM). Our best compounds represent promising new classes of CDC25 inhibitors that also exhibit antiproliferative properties.     

Identification of protoberberine alkaloids as novel histone methyltransferase G9a inhibitors by structure-based virtual screening

The protein lysine methyltransferase G9a, which controls gene expression by epigenetic regulation of H3K9 methylation, is related to various human diseases, including cancer, drug addiction, and mental retardation. In recent years, genetic, biological, and physiological evidence has established G9a inhibitors as potential chemotherapeutic agents for cancer treatment. In this study, we identified protoberberine alkaloid pseudodehydrocorydaline (CT13) as a novel G9a inhibitor, by structure-based virtual screening of in-house library containing natural product compounds. The activity of CT13 was determined by biophysical analyses involving MALDI-TOF mass spectrometry and western blot analysis. CT13 showed selective inhibitory activity against G9a and suppressed the level of H3K9me2 in MCF7 human breast cancer cells. Molecular docking analysis suggested the binding mode of CT13 which occupies the binding site of histone H3 substrate. CT13 provides a novel scaffold for further development of analogous synthetic G9a inhibitors.

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3D QSAR analyses of novel tyrosine kinase inhibitors based on pharmacophore alignment

In an effort to develop a quantitative ligand-binding model for the receptor tyrosine kinases, a pharmacophore search was first used to identify structural features that are common in two novel sets of 12 molecules of the 3-substituted indolin-2-ones and 19 compounds of the benzylidene malononitriles with low-to-high affinity for HER2, a kind of receptor tyrosine kinase. The common pharmacophore model based on these 31 compounds was used as a template to obtain the aligned molecular aggregate, which provided a good starting point for 3D-QSAR analysis of only the 19 benzylidene malononitriles. Two molecular field analysis (MFA) techniques, including CoMFA and CoMSIA, were used to derive the quantitative structure-activity relationships of the studied molecules. From the studied results, it was obvious that the 3D-QSAR models based on the pharmacophore alignment were superior to those based on the simple atom-by-atom fits. Considering the flexibility of the studied molecules and the difference between the active conformers and the energy-lowest conformers, the pharmacophore model can usually provide the common features for the flexible regions. Moreover, the best CoMSIA model based on the pharmacophore hypothesis gave good statistical measure from partial least-squares analysis (PLS) (q(2) = 0.71), which was slightly better than the CoMFA one. Our study demonstrated that pharmacophore modeling and CoMSIA research could be effectively combined. Results obtained from both methods helped with understanding the specific activity of some compounds and designing new specific HER2 inhibitors.