Discovery of novel small molecule activators of β-catenin signaling

Wnt/β-catenin signaling plays a major role in embryonic development and adult stem cell maintenance. Reduced activation of the Wnt/β-catenin pathway underlies neurodegenerative disorders and aberrations in bone formation. Screening of a small molecule compound library with a β-galactosidase fragment complementation assay measuring β-catenin nuclear entry revealed bona fide activators of β-catenin signaling. The compounds stabilized cytoplasmic β-catenin and activated β-catenin-dependent reporter gene activity. Although the mechanism through which the compounds activate β-catenin signaling has yet to be determined, several key regulators of Wnt/β-catenin signaling, including glycogen synthase kinase 3 and Frizzled receptors, were excluded as the molecular target. The compounds displayed remarkable selectivity, as they only induced β-catenin signaling in a human osteosarcoma U2OS cell line and not in a variety of other cell lines examined. Our data indicate that differences in cellular Wnt/β-catenin signaling machinery can be exploited to identify cell type-specific activators of Wnt/β-catenin signaling.     

Discovery and structure–activity relationships of a novel class of quinazoline glucokinase activators

We describe design, syntheses and structure–activity relationships of a novel class of 4,6-disubstituted quinazoline glucokinase activators. Prototype quinazoline leads (4 and 5) were designed based on the X-ray analyses of the previous 2-aminobenzamide lead classes. Modifications of the quinazoline leads led to the identification of a potent GK activator (21d).     

Synthesis and structure–activity relationships of small molecule inhibitors of the simian virus 40 T antigen oncoprotein,an anti-polyomaviral target

Polyomavirus infections are common and relatively benign in the general human population but can become pathogenic in immunosuppressed patients. Because most treatments for polyomavirus-associated diseases nonspecifically target DNA replication, existing treatments for polyomavirus infection possess undesirable side effects. However, all polyomaviruses express Large Tumor Antigen (T Ag), which is unique to this virus family and may serve as a therapeutic target. Previous screening of pyrimidinone–peptoid hybrid compounds identified MAL2-11B and a MAL2-11B tetrazole derivative as inhibitors of viral replication and T Ag ATPase activity (IC₅₀ of ∼20–50 μM). To improve upon this scaffold and to develop a structure–activity relationship for this new class of antiviral agents, several iterative series of MAL2-11B derivatives were synthesized. The replacement of a flexible methylene chain linker with a benzyl group or, alternatively, the addition of an ortho-methyl substituent on the biphenyl side chain in MAL2-11B yielded an IC₅₀ of ∼50 μM, which retained antiviral activity. After combining both structural motifs, a new lead compound was identified that inhibited T Ag ATPase activity with an IC₅₀ of ∼5 μM. We suggest that the knowledge gained from the structure–activity relationship and a further refinement cycle of the MAL2-11B scaffold will provide a specific, novel therapeutic treatment option for polyomavirus infections and their associated diseases.     

Novel glitazones: Design,synthesis, glucose uptake and structure–activity relationships

Glitazones are known to exhibit antihyperglycemic activity by decreasing peripheral insulin resistance. In the present study, we have designed some novel glitazones based on the structure–activity relationships as possible PPAR-γ agonists. The manually designed glitazones were synthesized by using the appropriate synthetic schemes and screened for their in vitro antihyperglycemic activity by estimating glucose uptake by rat hemi-diaphragm, both in the absence and in the presence of external insulin. Some of the glitazones exhibited good antihyperglycemic activity in presence of insulin. Illustration about their design, synthesis, evaluation, and structure–activity relationships is described.     

Novel small molecules as apoptosis inducers: Synthesis,preliminary structure–activity relationships,and in vitro biological evaluation

Inducing apoptosis is a promising therapeutic approach to overcome cancer. In this study, 30 compounds were synthesized and evaluated for their antiproliferative activity against three tumor cell lines in vitro: A875, H460 and Hela cancer cells by the MTT assay. The most potent analogue 7a, a novel compound was first reported by our group, inhibited the proliferation of A875 cells with an IC₅₀ value of 98 nM. Flow cytometry analysis and morphological analysis suggested that compound 7a had potential anticancer efficacy via G₂/M cell cycle arrest, which could be attributed to its proliferation and apoptosis, and also in a concentration-dependent manner. The SAR analysis indicated that the substituents R² played a crucial role in the antiproliferation activity.     

Synthesis,cytotoxic activity and structure–activity relationships of hedychenone analogues

Hedychenone, a plant-derived labdane diterpenoid, showed potent in vitro cytotoxic activity against cancerous cells. In the present study, a series of analogues have been synthesized by modification of the furanoid ring, double bond and the vinylic methyl functionality of this natural product lead and evaluated for their cytotoxic activities against human cancer cell lines. The structures of the target compounds were established by IR, ¹H NMR and mass spectral analysis. Majority of the analogues displayed potent activity than the parent compound, hedychenone. Preliminary structure–activity relationship studies indicated that furanoid ring has a greater impact on cytotoxicity than that of the decalone nucleus. However, dimerization through C-8 significantly enhanced the cytotoxic activity of the hedychenone.     

Novel approaches to map small molecule–target interactions

The quest for small molecule perturbators of protein function or a given cellular process lies at the heart of chemical biology and pharmaceutical research. Bioactive compounds need to be extensively characterized in the context of the modulated protein(s) or process(es) in living systems to unravel and confirm their mode of action. A crucial step in this workflow is the identification of the molecular targets for these small molecules, for which a generic methodology is lacking. Herein we summarize recently developed approaches for target identification spurred by advances in omics techniques and chemo- and bioinformatics analysis.     

Larkspur poisoning: toxicology and alkaloid structure–activity relationships

Systematic approaches to taxonomic classifications of the tall larkspur spp. have been developed using traditional chemical methods to profile alkaloids, comparison of relative toxicity of individual alkaloids, plant morphology/taxonomy and molecular genetics. Using these methods (papers published in this series) toxicology of three distinct species of tall larkspurs including Delphinium glaucum, Delphinium barbeyi and Delphinium occidentale is described. Tall larkspurs (Delphinium spp.) continue to be the most serious cause of cattle losses on mountain rangelands in the western US. Over 40 norditerpenoid alkaloids have been reported in species of larkspurs and toxicology data on 25 of these have been reported by the authors. These alkaloids can be classified into three general types based on their structural characteristics and toxicity: the N-(methylsuccinyl) anthranoyl lycoctonine (MSAL)-type, having high toxicity; the lycoctonine-type, with moderate toxicity; and the 7,8-methylenedioxylycoctonine (MDL)-type, of low toxicity. The structural importance of the methylsuccinimido anthranilic acid ester group at the C18 position is evident in the high toxicity of MSAL alkaloids, particularly methyllycaconitine (MLA), Nudicauline (NUD) and 14-deacetylnudicauline (14-DAN). Other structural aspects of these alkaloids such as the C14 functionality are also important, as demonstrated by the reduced toxicity of barbinine. MLA is the alkaloid of most importance in toxicity of larkspurs on mountain rangelands because of its prevalence in most larkspurs and high toxicity. While NUD and 14-DAN also possess high toxicity, they are relatively minor components in few larkspur species (generally the plains and low larkspurs), but when present at concentrations approaching 1 mg/g dry weight they contribute significantly to overall toxicity. Deltaline (DLT) is often found in high concentrations in many larkspurs but because of low toxicity, its contribution to larkspur poisoning in the field is relatively minor and it will probably not cause toxicosis in the absence of the MSAL-type alkaloids.     

Synthesis and structure–activity relationships of novel benzofuran farnesyltransferase inhibitors

A series of benzofuran-based farnesyltransferase inhibitors have been designed and synthesized as antitumor agents. Among them, 11f showed the most potent enzyme inhibitory activity (IC₅₀ = 1.1 nM) and antitumor activity in human cancer xenografts in mice.     

Synthesis and structure–activity relationships of fibrate-based analogues inside PPARs

In an effort to develop safe and efficacious compounds for the treatment of metabolic disorders, new compounds based on a combination of clofibric acid, the active metabolite of clofibrate, and lipophilic groups derived from natural products chalcone and stilbene were synthesised. Some of them were found to be active at micromolar concentrations only on PPARα or PPARγ, while others were identified as dual agonists PPARα/γ.     

Synthesis,characterization, antimicrobial activity and structure–activity relationships of new aryldisulfonamides

A series of aromatic disulfonamide (1-8) derivatives and 4-methylbenzenesulfonyl hydrazide (9) were synthesized and characterized. All compounds were evaluated in vitro for their antimicrobial activity against Staphylococcus aureus ATCC 25953, Bacillus cereus ATCC 6633, Bacillus magaterium RSKK 5117, Escherichia coli ATCC 11230, Salmonella enterititis ATCC 13076 by microdilution and disc diffusion methods. Antimicrobial activity of the aromatic disulfonamides decreased as the length of the carbon chain increased. An analysis of the structure- activity relationship (SAR) along with computational studies showed that the most active compound (9) possessed low lipophilicity (AlogP=0.59) and high solubility (logS = -1.33).     

Cationic membrane peptides: atomic-level insight of structure–activity relationships from solid-state NMR

Many membrane-active peptides, such as cationic cell-penetrating peptides (CPPs) and antimicrobial peptides (AMPs), conduct their biological functions by interacting with the cell membrane. The interactions of charged residues with lipids and water facilitate membrane insertion, translocation or disruption of these highly hydrophobic species. In this review, we will summarize high-resolution structural and dynamic findings towards the understanding of the structure–activity relationship of lipid membrane-bound CPPs and AMPs, as examples of the current development of solid-state NMR (SSNMR) techniques for studying membrane peptides. We will present the most recent atomic-resolution structure of the guanidinium-phosphate complex, as constrained from experimentally measured site-specific distances. These SSNMR results will be valuable specifically for understanding the intracellular translocation pathway of CPPs and antimicrobial mechanism of AMPs, and more generally broaden our insight into how cationic macromolecules interact with and cross the lipid membrane.     

Autotaxin structure–activity relationships revealed through lysophosphatidylcholine analogs

Autotaxin (ATX) catalyzes the hydrolysis of lysophosphatidylcholine (LPC) to form the bioactive lipid lysophosphatidic acid (LPA). LPA stimulates cell proliferation, cell survival, and cell migration and is involved in obesity, rheumatoid arthritis, neuropathic pain, atherosclerosis and various cancers, suggesting that ATX inhibitors have broad therapeutic potential. Product feedback inhibition of ATX by LPA has stimulated structure–activity studies focused on LPA analogs. However, LPA displays mixed mode inhibition, indicating that it can bind to both the enzyme and the enzyme–substrate complex. This suggests that LPA may not interact solely with the catalytic site. In this report we have prepared LPC analogs to help map out substrate structure–activity relationships. The structural variances include length and unsaturation of the fatty tail, choline and polar linker presence, acyl versus ether linkage of the hydrocarbon chain, and methylene and nitrogen replacement of the choline oxygen. All LPC analogs were assayed in competition with the synthetic substrate, FS-3, to show the preference ATX has for each alteration. Choline presence and methylene replacement of the choline oxygen were detrimental to ATX recognition. These findings provide insights into the structure of the enzyme in the vicinity of the catalytic site as well as suggesting that ATX produces rate enhancement, at least in part, by substrate destabilization.     

Synthesis and biological evaluation of substituted 2-benzoylpyridine thiosemicarbazones: Novel structure–activity relationships underpinning their anti-proliferative and chelation efficacy

The 2-benzoylpyridine thiosemicarbazone (BpT) chelators demonstrate potent anti-proliferative effects against tumor cells. To understand their structure–activity relationships, BpT analogues incorporating electron-donating substituents on the pyridine and phenyl rings of the BpT scaffold were designed and represent the first attempts to modify the pyridine ring of these thiosemicarbazones. Eight analogues showed significantly (p <0.001) greater anti-proliferative activity than the ‘gold-standard’ chelator, desferrioxamine. Structure–activity analysis revealed that mono- or di-methoxy substitution at the phenyl ring resulted in lower anti-proliferative activity, while methoxy substitutions at the phenyl ring enhanced iron chelation efficacy. These important findings facilitate the design of thiosemicarbazones with greater anti-tumor activity.     

Synthesis and structure–activity relationships of cassiarin A as potential antimalarials with vasorelaxant activity

Cassiarin A 1, a tricyclic alkaloid, isolated from the leaves of Cassia siamea (Leguminosae), shows powerful antimalarial activity against Plasmodium falciparum in vitro as well as P. berghei in vivo, which may be valuable leads for novel antimalarials. Interactions of parasitized red blood cells (pRBCs) with endothelium in aorta are especially important in the processes contribute to the pathogenesis of severe malaria. Nitric oxide (NO) reduces endothelial expression of receptors/adhesion molecules used by pRBC to adhere to vascular endothelium, and reduces cytoadherence of pRBC to vascular endothelium. Cassiarin A 1 showed vasorelaxation activity against rat aortic ring, which may be related with NO production. A series of a hydroxyl and a nitrogen-substituted derivatives and a dehydroxy derivative of 1 have been synthesized as having potent antimalarials against P. falciparum with vasodilator activity, which may reduce cytoadherence of pRBC to vascular endothelium. Cassiarin A 1 exhibited a potent antimalarial activity and a high selectivity index in vitro, suggesting that the presence of a hydroxyl and a nitrogen atom without any substituents may be important to show antimalarial activity. Relative to cassiarin A, a methoxy derivative showed more potent vasorelaxant activity, although it did not show improvement for inhibition of P. falciparum in vitro. These cassiarin derivatives may be promising candidates as antimalarials with different mode of actions.     

Motualevic acids and analogs: Synthesis and antimicrobial structure–activity relationships

Synthesis of the marine natural products motualevic acids A, E, and analogs in which modifications have been made to the ω-brominated lipid (E)-14,14-dibromotetra-deca-2,13-dienoic acid or amino acid unit are reported, together with antimicrobial activities against Staphylococcus aureus, methicillin-resistant S. aureus, Enterococcus faecium, and vancomycin-resistant Enterococcus.     

Synthesis and structure–activity relationships of C-glycosylated oxadiazoles as inhibitors of glycogen phosphorylase

A series of per-O-benzoylated 5-β-d-glucopyranosyl-2-substituted-1,3,4-oxadiazoles was prepared by acylation of the corresponding 5-(β-d-glucopyranosyl)tetrazole. As an alternative, oxidation of 2,6-anhydro-aldose benzoylhydrazones by iodobenzene I,I-diacetate afforded the same oxadiazoles. 1,3-Dipolar cycloaddition of nitrile oxides to per-O-benzoylated β-d-glucopyranosyl cyanide gave the corresponding 5-β-d-glucopyranosyl-3-substituted-1,2,4-oxadiazoles. The O-benzoyl protecting groups were removed by base-catalyzed transesterification. The 1,3,4-oxadiazoles were practically inefficient as inhibitors of rabbit muscle glycogen phosphorylase b while the 1,2,4-oxadiazoles displayed inhibitory activities in the micromolar range. The best inhibitors were the 5-β-d-glucopyranosyl-3-(4-methylphenyl- and -2-naphthyl)-1,2,4-oxadiazoles (K_i = 8.8 and 11.6 μM, respectively). A detailed analysis of the structure–activity relationships is presented.