Identification of cytidine-5-triphosphate synthase1-selective inhibitory peptide from random peptide library displayed on T7 phage

Cytidine triphosphate synthase 1 (CTPS1) is an enzyme expressed in activated lymphocytes that catalyzes the conversion of uridine triphosphate (UTP) to cytidine triphosphate (CTP) with ATP-dependent amination, using either L-glutamine or ammonia as the nitrogen source. Since CTP plays an important role in DNA/RNA synthesis, phospholipid synthesis, and protein sialyation, CTPS1-inhibition is expected to control lymphocyte proliferation and size expansion in inflammatory diseases. In contrast, CTPS2, an isozyme of CTPS1 possessing 74% amino acid sequence homology, is expressed in normal lymphocytes. Thus, CTPS1-selective inhibition is important to avoid undesirable side effects. Here, we report the discovery of CTpep-3: Ac-FRLGLLKAFRRLF-OH from random peptide libraries displayed on T7 phage, which exhibited CTPS1-selective binding with a K_D value of 210 nM in SPR analysis and CTPS1-selective inhibition with an IC₅₀ value of 110 nM in the enzyme assay. Furthermore, two fundamentally different approaches, enzyme inhibition assay and HDX-MS, provided the same conclusion that CTpep-3 acts by binding to the amidoligase (ALase) domain on CTPS1. To our knowledge, CTpep-3 is the first CTPS1-selective inhibitor.     

Design and synthesis of biphenyl derivatives as mushroom tyrosinase inhibitors

Two new series of biphenyls, analogs of aglycone of natural product fortuneanoside E, were prepared using Suzuki–Miyaura cross-coupling and selective magnesium iodide demethylation/debenzylation, and their mushroom tyrosinase inhibitory activity was evaluated. Most of the 4-hydroxy-3,5-dimethoxyphenyl biphenyl compounds (series II, 20–36) were in general more active than 3,4,5-trimethoxyphenyl biphenyl compounds (series I, 1–19). Structure–activity relationships study showed that monosaccharide substituents, such as glucose, were not necessary and the presence of 4-hydroxy-3,5-dimethoxyphenyl moiety was crucial for inhibitory activity. Among the compounds synthesised, compound 21 (IC₅₀ = 0.02 mM) was found to be the most active one, which exhibited an activity that was 7 times higher than that of fortuneanoside E (IC₅₀ = 0.14 mM) and 10 times higher than that of arbutin (IC₅₀ = 0.21 mM), known as potent tyrosinase inhibitors. The inhibition kinetics analyzed by Lineweaver–Burk plots revealed that compound 21 was a competitive inhibitor (K_i = 0.015 mM).     

Kojic acid derived hydroxypyridinone–chloroquine hybrids: Synthesis,crystal structure,antiplasmodial activity and β-haematin inhibition

Aminochloroquinoline–kojic acid hybrids were synthesized and evaluated for β-haematin inhibition and antiplasmodial activity against drug resistant (K1) and sensitive (3D7) strains of Plasmodium falciparum. Compound 7j was the most potent compound in both strains (IC₅₀^3D7 = 0.004 μM; IC₅₀^K1 = 0.03 μM) and had the best β-haematin inhibition activity (0.07 IC₅₀ equiv vs 1.91 IC₅₀ equiv for chloroquine). One compound 8c was found to be equipotent in both strains (IC₅₀ = 0.04 μM).     

Inhibition of tyrosinase activity by polyphenol compounds from Flemingia philippinensis roots

Flemingia philippinensis is used as a foodstuff or medicinal plant in the tropical regions of China. The methanol (95%) extract of the roots of this plant showed potent tyrosinase inhibition (80% inhibition at 30 μg/ml). Activity-guided isolation yielded six polyphenols that inhibited both the monophenolase (IC₅₀ = 1.01–18.4 μM) and diphenolase (IC₅₀ = 5.22–84.1 μM) actions of tyrosinase. Compounds 1–6 emerged to be three new polyphenols and three known flavanones, flemichin D, lupinifolin and khonklonginol H. The new compounds (1–3) were identified as dihydrochalcones which we named fleminchalcones (A–C), respectively. The most potent inhibitor, dihydrochalcone (3) showed significant inhibitions against both the monophenolase (IC₅₀ = 1.28 μM) and diphenolase (IC₅₀ = 5.22 μM) activities of tyrosinase. Flavanone (4) possessing a resorcinol group also inhibited monophenolase (IC₅₀ = 1.79 μM) and diphenolase (IC₅₀ = 7.48 μM) significantly. In kinetic studies, all isolated compounds behaved as competitive inhibitors. Fleminchalcone A was found to have simple reversible slow-binding inhibition against monophenolase.     

Microwave assisted synthesis of novel hybrid tacrine-sulfonamide derivatives and investigation of their antioxidant and anticholinesterase activities

A novel series of tacrine derivatives containing sulfonamide group were synthesized and their inhibitory effects on acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were evaluated. The result showed that all the synthesized tacrine-sulfonamides (VIIIa–o) exhibited inhibitory activity on both cholinesterases. VIIIg showed the highest inhibitory activity on AChE IC₅₀ = 0.009 μM. This value is 220-fold greater than that of galantamine (IC₅₀ = 2.054 μM) and 6-fold greater than tacrine (IC₅₀ = 0.055 μM). VIIIf displayed the strongest inhibition of BuChE (IC₅₀ = 2.250 μM), which is close to donepezil (IC₅₀ = 2.680 μM) and 8-fold greater than that of galantamine (IC₅₀ = 18.130 μM) Furthermore, all of the synthesized tacrine derivatives showed higher inhibition of BuChE than that of galantamine. In addition, the cupric reducing antioxidant capacities (CUPRAC) and ABTS cation radical scavenging abilities of the synthesized compounds were investigated for the antioxidant activity. Among them, VIIIb (IC₅₀ = 94.390 ± 2.310 μM) showed significantly better ABTS cation radical scavenging ability than all of the new synthesized compounds.     

Pyrazole-based arylalkyne cathepsin S inhibitors. Part II: Optimization of cellular potency

Basic lipophilic substituents dramatically improved the cellular potency of a previously disclosed series of pyrazole-based arylalkyne cathepsin S inhibitors. The incorporation of substituted benzylamines in the para position of the arylalkyne maintained enzymatic activity (hCatS IC₅₀ = 80–420 nM) and imparted cellular potency (IC₅₀ = 0.8–4.0 μM). Further refinement of the morpholine portion of the pharmacophore enabled the identification of bicyclic piperidines with enhanced affinity for CatS (IC₅₀ = 10–30 nM) and sub-micromolar cellular potency (JY Ii IC₅₀ = 200–720 nM).     

Anti-HBV agents. Part 2: Synthesis and in vitro anti-hepatitis B virus activities of alisol A derivatives

Chemical modifications were performed on hydroxyl groups at C-11,23,24,25 positions and C-13(17) double bond of alisol A for structure–activity relationship study. Forty-one derivatives of alisol A were synthesized and assayed for their in vitro anti-hepatitis B virus (HBV) activities and cytotoxicities. Of them, 14 compounds were active against HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) secretion in HepG 2.2.15 cells, and the most promising compound 25 exhibited high activities against secretion of HBsAg (IC₅₀ = 0.028 mM), HBeAg (IC₅₀ = 0.027 mM) and remarkable selective indices (SI_HBsAg >90, SI_HBeAg >93).     

Synthesis and α-glucosidase inhibitory activity evaluation of N-substituted aminomethyl-β-d-glucopyranosides

A series of N-substituted 1-aminomethyl-β-d-glucopyranoside derivatives was prepared. These novel synthetic compounds were assessed in vitro for inhibitory activity against yeast α-glucosidase and both rat intestinal α-glucosidases maltase and sucrase. Most of the compounds displayed α-glucosidase inhibitory activity, with IC₅₀ values covering the wide range from 2.3 μM to 2.0 mM. Compounds 19a (IC₅₀ = 2.3 μM) and 19b (IC₅₀ = 5.6 μM) were identified as the most potent inhibitors for yeast α-glucosidase, while compounds 16 (IC₅₀ = 7.7 and 15.6 μM) and 19e (IC₅₀ = 5.1 and 10.4 μM) were the strongest inhibitors of rat intestinal maltase and sucrase. Analysis of the kinetics of enzyme inhibition indicated that 19e inhibited maltase and sucrase in a competitive manner. The results suggest that the aminomethyl-β-d-glucopyranoside moiety can mimic the substrates of α-glucosidase in the enzyme catalytic site, leading to competitive enzyme inhibition. Moreover, the nature of the N-substituent has considerable influence on inhibitory potency.     

Structure-activity analysis of thiourea analogs as inhibitors of UT-A and UT-B urea transporters

Small-molecule inhibitors of urea transporter (UT) proteins in kidney have potential application as novel salt-sparing diuretics. The urea analog dimethylthiourea (DMTU) was recently found to inhibit the UT isoforms UT-A1 (expressed in kidney tubule epithelium) and UT-B (expressed in kidney vasa recta endothelium) with IC₅₀ of 2-3 mM, and was shown to have diuretic action when administered to rats. Here, we measured UT-A1 and UT-B inhibition activity of 36 thiourea analogs, with the goal of identifying more potent and isoform-selective inhibitors, and establishing structure-activity relationships. The analog set systematically explored modifications of substituents on the thiourea including alkyl, heterocycles and phenyl rings, with different steric and electronic features. The analogs had a wide range of inhibition activities and selectivities. The most potent inhibitor, 3-nitrophenyl-thiourea, had an IC₅₀ of ~ 0.2 mM for inhibition of both UT-A1 and UT-B. Some analogs such as 4-nitrophenyl-thiourea were relatively UT-A1 selective (IC₅₀ 1.3 vs. 10 mM), and others such as thioisonicotinamide were UT-B selective (IC₅₀ > 15 vs. 2.8 mM).     

Identification of substituted 2-thio-6-oxo-1,6-dihydropyrimidines as inhibitors of human lactate dehydrogenase

A novel 2-thio-6-oxo-1,6-dihydropyrimidine-containing inhibitor of human lactate dehydrogenase (LDH) was identified by high-throughput screening (IC₅₀ = 8.1 μM). Biochemical, surface plasmon resonance, and saturation transfer difference NMR experiments indicated that the compound specifically associated with human LDHA in a manner that required simultaneous binding of the NADH co-factor. Structural variation of the screening hit resulted in significant improvements in LDHA biochemical inhibition activity (best IC₅₀ = 0.48 μM). A crystal structure of an optimized compound bound to human LDHA was obtained and explained many of the observed structure–activity relationships.     

Microwave assisted synthesis of naphthopyrans catalysed by silica supported fluoroboric acid as a new class of non purine xanthine oxidase inhibitors

A series of naphthopyrans was synthesized employing silica supported fluoroboric acid under solvent free conditions in a microwave reactor. The catalytic influence of HBF₄–SiO₂ was investigated in detail to optimize the reaction conditions. The synthesised compounds were evaluated for in vitro xanthine oxidase inhibitory activity for the first time. Structure–activity relationship analyses have also been presented. Among the synthesised compounds, NP-17, NP-19, NP-20, NP-23, NP-24, NP-25 and NP-26 were the active inhibitors with an IC₅₀ ranging from 4 to 17 μM. Compound NP-19 with a thiophenyl ring at position 1 emerged as the most potent xanthine oxidase inhibitor (IC₅₀ = 4 μM) in comparison to allopurinol (IC₅₀ = 11.10 μM) and febuxostat (IC₅₀ = 0.025 μM). The basis of significant inhibition of xanthine oxidase by NP-19 was rationalized by its molecular docking at MTE binding site of xanthine oxidase.     

Design,modification and 3D QSAR studies of novel naphthalin-containing pyrazoline derivatives with/without thiourea skeleton as anticancer agents

Two series of novel naphthalin-containing pyrazoline derivatives C1–C14 and D1–D14 have been synthesized and evaluated for their EGFR/HER-2 inhibitory and anti-proliferation activities. Compound D14 displayed the most potent activity against EGFR and A549 cell line (IC₅₀ = 0.05 μM and GI₅₀ = 0.11 μM), being comparable with the positive control Erlotinib (IC₅₀ = 0.03 μM and GI₅₀ = 0.03 μM) and more potent than our previous compounds C0–A (IC₅₀ = 5.31 μM and GI₅₀ = 33.47 μM) and C0–B (IC₅₀ = 0.09 μM and GI₅₀ = 0.34 μM). Meanwhile, compound C14 displayed the most potent activity against HER-2 and MCF-7 cell line (IC₅₀ = 0.88 μM and GI₅₀ = 0.35 μM), being a little less potent than Erlotinib (IC₅₀ = 0.16 μM and GI₅₀ = 0.08 μM) but far more potent than C0–A (IC₅₀ = 6.58 μM and GI₅₀ = 27.62 μM) and C0–B (IC₅₀ = 2.77 μM and GI₅₀ = 3.79 μM). The docking simulation was performed to analyze the probable binding models and the QSAR models were built for reasonable design of EGFR/HER-2 inhibitors at present and in future. The structural modification of introducing naphthalin moiety reinforced the combination of our compounds and the receptor, resulting in progress of bioactivity. Moreover, the replacement of thiourea skeleton by using benzene ring resulted in the slight diversity of the two series towards specific targets.     

Selective inhibition of human acetylcholinesterase by xanthine derivatives: In vitro inhibition and molecular modeling investigations

The commonly used beverage and psychostimulant caffeine is known to inhibit human acetylcholinesterase enzyme. This pharmacological activity of caffeine is partly responsible for its cognition enhancing properties. However, the exact mechanisms of its binding to human cholinesterases (acetyl and butyrylcholinesterase; hAChE and hBuChE) are not well known. In this study, we investigated the cholinesterase inhibition by the xanthine derivatives caffeine, pentoxifylline, and propentofylline. Among them, propentofylline was the most potent AChE inhibitor (hAChE IC₅₀ = 6.40 μM). The hAChE inhibitory potency was of the order: caffeine (hAChE IC₅₀ = 7.25 μM) < pentoxifylline (hAChE IC₅₀ = 6.60 μM) ? propentofylline (hAChE IC₅₀ = 6.40 μM). These compounds were less potent relative to the reference agent donepezil (hAChE IC₅₀ = 0.04 μM). Moreover, they all exhibited selective inhibition of hAChE with no inhibition of hBuChE (IC₅₀ > 50 μM) relative to the reference agent donepezil (hBuChE IC₅₀ = 13.60 μM). Molecular modeling investigations indicate that caffeine binds primarily in the catalytic site (Ser203, Glu334 and His447) region of hAChE whereas pentoxifylline and propentofylline are able to bind to both the catalytic site and peripheral anionic site due to their increased bulk/size, thereby exhibiting superior AChE inhibition relative to caffeine. In contrast, their lack of hBuChE inhibition is due to a larger binding site and lack of key aromatic amino acids. In summary, our study has important implications in the development of novel caffeine derivatives as selective AChE inhibitors with potential application as cognitive enhancers and to treat various forms of dementia.     

Schiff’s base derivatives bearing nitroimidazole and quinoline nuclei: New class of anticancer agents and potential EGFR tyrosine kinase inhibitors

New Schiff’s base derivatives 5a–j have been synthesized by reaction between 2-phenoxyquinoline-3-carbaldehydes 3a–j and 2-(2-methyl-5-nitro-1H-imidazol-1-yl)acetohydrazide 4 in presence of nickel(II) nitrate as a catalyst in ethanol under reflux in good yield (78–92%). All compounds were tested for anticancer and inhibition of EGFR. Of the compounds studied, majority of the compounds showed effective antiproliferation and inhibition of EGFR and HER-2 activities. Compound 5h showed most effective inhibition (IC₅₀ = 0.12 ± 0.05 μM) by binding in to the active pocket of EGFR receptor with minimum binding energy (ΔG_b = −58.3691 kcal/mol). The binding was stabilized by two hydrogen bonds, two π–cation and one π–sigma interactions. Compound 5d showed most effective inhibition (IC₅₀ = 0.37 ± 0.04 μM).     

Design,synthesis and evaluation of novel metalloproteinase inhibitors based on l-tyrosine scaffold

A series of novel l-tyrosine derivatives were designed, synthesized and assayed for their inhibitory activities on matrix metalloproteinase 2 (MMP-2) and histone deacetylase 8 (HDAC-8). The results showed that these l-tyrosine derivatives exhibited inhibitory profiles against MMP-2 and HDAC-8. The compounds 6h (IC₅₀ = 0.013 ± 0.001 μM) and 6j (IC₅₀ = 0.017 ± 0.001 μM) were equal potent MMP-2 inhibitors to the positive control NNGH (IC₅₀ = 0.014 ± 0.001 μM). As for HDAC-8 inhibition, some of the hydroxamate compounds, such as 6d (IC₅₀ = 3.6 ± 0.2 μM) and 6c (IC₅₀ = 5.8 ± 0.5 μM), were equal potent to the positive control SAHA (IC₅₀ = 1.6 ± 0.1 μM). Structure–activity relationships were also briefly discussed.     

Structure–activity relationship study of 4-(thiazol-5-yl)benzoic acid derivatives as potent protein kinase CK2 inhibitors

Two classes of modified analogs of 4-(thiazol-5-yl)benzoic acid-type CK2 inhibitors were designed. The azabenzene analogs, pyridine- and pyridazine-carboxylic acid derivatives, showed potent protein kinase CK2 inhibitory activities [IC₅₀ (CK2α) = 0.014–0.017 μM; IC₅₀ (CK2α′) = 0.0046–0.010 μM]. Introduction of a 2-halo- or 2-methoxy-benzyloxy group at the 3-position of the benzoic acid moiety maintained the potent CK2 inhibitory activities [IC₅₀ (CK2α) = 0.014–0.016 μM; IC₅₀ (CK2α′) = 0.0088–0.014 μM] and led to antiproliferative activities [CC₅₀ (A549) = 1.5–3.3 μM] three to six times higher than those of the parent compound.     

Isoquinoline derivatives as potent CRTH2 antagonists: Design,synthesis and SAR

In this study, we describe the synthesis and structure–activity relationship (SAR) of a series of isoquinoline chemoattractant receptor–homologous molecule expressed on Th2 cells (CRTH2) antagonists. TASP0376377 (15-20), one of the most potent compounds, showed a potent binding affinity (IC₅₀ = 19 nM) in addition to the excellent functional antagonist activity (IC₅₀ = 13 nM). Moreover, the efficacy of this compound in a chemotaxis assay (IC₅₀ = 23 nM) was in good agreement with its potency as a CRTH2 antagonist. In addition, 15-20 exhibited greater selectivity in binding to CRTH2 than to the DP1 prostanoid receptor (IC₅₀ >1 μM) or the enzymes COX-1 and COX-2 (IC₅₀ >10 μM).     

Design,synthesis and biological evaluation of heterocyclic azoles derivatives containing pyrazine moiety as potential telomerase inhibitors

Three series of novel heterocyclic azoles derivatives containing pyrazine (5a–5k, 8a–8k and 11a–11k) have been designed, synthesized, structurally determined, and their biological activities were evaluated as potential telomerase inhibitors. Among the oxadiazole derivatives, compound 5c showed the most potent biological activity against SW1116 cancer cell line (IC₅₀ = 2.46 μM against SW1116 and IC₅₀ = 3.55 μM for telomerase). Compound 8h performed the best in the thiadiazole derivatives (IC₅₀ = 0.78 μM against HEPG2 and IC₅₀ = 1.24 μM for telomerase), which was comparable to the positive control. While compound 11f showed the most potent biological activity (IC₅₀ = 4.12 μM against SW1116 and IC₅₀ = 15.03 μM for telomerase) among the triazole derivatives. Docking simulation by positioning compounds 5c, 8h and 11f into the telomerase structure active site was performed to explore the possible binding model. The results of apoptosis demonstrated that compound 8h possessed good antitumor activity against HEPG2 cancer cell line. Therefore, compound 8h with potent inhibitory activity in tumor growth inhibition may be a potential antitumor agent against HEPG2 cancer cell. Therefore, the introduction of oxadiazole, thiadiazole and triazole structures reinforced the combination of our compounds and the receptor, resulting in progress of bioactivity.     

Structure–activity relationship studies of antiplasmodial aminomethylthiazoles

Structure–activity relationship (SAR) studies around a previously reported antimalarial aminomethylthiazole pyrazole carboxamide 1 are reported. Several analogues were synthesised and profiled for in vitro antiplasmodial activity against the drug-sensitive Plasmodium falciparum malaria parasite strain, NF54. Although all the reported analogues exhibited inferior in vitro antiplasmodial activity (IC₅₀ = 0.125–173 μM) relative to compound 1 (IC₅₀ = 0.0203 μM), one analogue, compound 5a, retained submicromolar activity (IC₅₀ = 0.125 μM).     

Synthesis and biological evaluation of novel thiadiazole amides as potent Cdc25B and PTP1B inhibitors

A series of novel thiadiazole amide derivatives have been synthesized and evaluated for inhibitory activities against Cdc25B and PTP1B. Most of them showed inhibitory activities against Cdc25B (IC₅₀ = 1.18–8.01 μg/mL) and PTP1B (IC₅₀ = 0.85–8.75 μg/mL), respectively. Moreover, compounds 5b and 4l were most potent with IC₅₀ values of 1.18 and 0.85 μg/mL for Cdc25B and PTP1B, respectively, compared with reference drugs Na₃VO₄ (IC₅₀ = 0.93 μg/mL) and oleanolic acid (IC₅₀ = 0.85 μg/mL). The results of selectivity experiments showed that the target compounds were selective inhibitors against PTP1B and Cdc25B. Enzyme kinetic experiments demonstrated that compound 5k was a specific inhibitor with the typical characteristics of a mixed inhibitor.