Regiospecific and conformationally restrained analogs of melphalan and dl-2-NAM-7 and their affinities for the large neutral amino acid transporter (system LAT1) of the blood–brain barrier

Regiospecific and conformationally restrained analogs of melphalan and dl-2-NAM-7 have been synthesized and their affinities for the large neutral amino acid transporter (LAT1) of the blood–brain barrier have been determined to assess their potential for accessing the CNS via facilitated transport. Several analogs had K_i values in the range 2.1–8.5 μM with greater affinities than that of either l-phenylalanine (K_i = 11 μM) or melphalan (K_i = 55 μM), but lower than dl-2-NAM-7 (K_i = 0.08 μM). The results indicate that regiospecific positioning of the mustard moiety on the aromatic ring in these analogs is very important for optimal affinity for the large neutral amino acid transporter, and that conformational restriction of the dl-2-NAM-7 molecule in benzonorbornane and indane analogs leads to 25- to 60-fold loss, respectively, in affinity.     

SAR studies of differently functionalized chalcones based hydrazones and their cyclized derivatives as inhibitors of mammalian cathepsin B and cathepsin H

Cathepsins have emerged as potential drug targets for melanoma therapy and engrossed attention of researchers for development and evaluation of cysteine cathepsin inhibitors as cancer therapeutics. In this direction, we have designed, synthesized, and assayed in vitro a small library of 30 low molecular weight functionalized analogs of chalcone hydrazones for evaluating structure–activity relationship aspects and inhibitory potency against cathepsin B and H. The maximum inhibitory effect was exerted by chalcone hydrazones, which are open chain analogues followed by their cyclized derivatives, pyrazolines and pyrazoles. All the synthesized compounds were established as reversible inhibitors of these enzymes. Cathepsin B was selectively inhibited by the compounds in each series. Compounds 1d, 2d and 4d were recognized as most potent inhibitors of cathepsin B in this study with K_i values of 0.042 μM, 0.053 μM and 0.131 μM whereas 1b (K_i = 1.111 μM), 2b (K_i = 1.174 μM) and 4b (K_i = 1.562 μM) inhibited cathepsin H activity effectively. And, preeminent cathepsin B inhibitors were –NO₂ functionalized however, –Cl substituted moieties were the most persuasive inhibitors for cathepsin H among all the designed compounds. Molecular docking studies performed using iGemdock provided valuable insights.     

Antitrypanosomal alkaloids from Polyalthia suaveolens (Annonaceae): Their effects on three selected glycolytic enzymes of Trypanosoma brucei

In continuation of our study on medicinal plants of Cameroon, stem barks of Polyalthia suaveolens were phytochemically studied. This investigation yielded a new indolosesquiterpene alkaloid, named polysin (1) and four hitherto known alkaloids (2–5). Polysin (1) appeared as a competitive reversible inhibitor (K_i = 10 μM) of phosphofructo kinase (PFK) of Trypanosoma brucei with respect to fructose-6-phosphate (K_i/K_M = 0.05) and could be used in the design of new trypanocidal drugs. The other isolated compounds (2–5) also exhibited interesting inhibitory effects on selected glycolytic enzymes (PFK, glyceraldehyde-3-phosphate dehydrogenase and aldolase).     

Synthesis and evaluation of novel ligands for the histamine H4 receptor based on a pyrrolo[2,3-d]pyrimidine scaffold

Starting from a known H₄R ligand based on a pyrimidine skeleton, a series of novel analogues based on a pyrrolo[2,3-d]pyrimidine scaffold have been prepared. Whereas the original pyrimidine congener shows good affinity at hH₄R (K_i = 0.5 μM), its lacks selectivity with a K_i value for the hH₃R of 1 μM. Within the newly synthesized pyrrolo[2,3-d]pyrimidines, several congeners show K_i values of less than 1 μM at the hH₄R and show a much improved selectivity profile. Therefore, these series represent an interesting starting point for the discovery of novel hH₄R ligands.     

NAD-based inhibitors with anticancer potential

Three classes of novel inhibitors of inosine monophosphate dehydrogenase have been prepared and their anti-proliferative properties were evaluated against several cancer cell lines.(1) Mycophenolic adenine dinucleotide analogues (8–13) containing a substituent at the C2 of adenine ring were found to be potent inhibitors of IMPDH (K_i’s in range of 0.6–82 nM) and sub-μM inhibitors of leukemic K562 cell proliferation. (2) Mycophenolic adenosine (d and l) esters (20 and 21) showed a potent inhibition of IMPDH2 (K_i = 102 and K_i = 231 nM, respectively) and inhibition of K562 cell growth (IC₅₀ = 0.5 and IC₅₀ = 1.6 μM). These compounds serve both as inhibitors of the enzyme and as a depot form of mycophenolic acid. The corresponding amide analogue 22, also a potent inhibitor of IMPDH (K_i = 84 nM), did not inhibit cancer cell proliferation. (3) Mycophenolic-(l)- and (d)-valine adenine di-amide derivatives 25 (K_i = 9 nM) and 28 (K_i = 3 nM) were found to be very potent enzymatically, but did not inhibit proliferation of cancer cells.     

Tea catechins’ affinity for human cannabinoid receptors

Among the many known health benefits of tea catechins count anti-inflammatory and neuroprotective activities, as well as effects on the regulation of food intake. Here we address cannabimimetic bioactivity of catechin derivatives occurring in tea leaves as a possible cellular effector of these functionalities. Competitive radioligand binding assays using recombinant human cannabinoid receptors expressed in Chem-1 and CHO cells identified (–)-epigallocatechin-3-O-gallate, EGCG (K_i=33.6 μM), (–)-epigallocatechin, EGC (K_i=35.7 μM), and (–)-epicatechin-3-O-gallate, ECG (K_i=47.3 μM) as ligands with moderate affinity for type 1 cannabinoid receptors, CB1. Binding to CB2 was weaker with inhibition constants exceeding 50 μM for EGC and ECG. The epimers (+)-catechin and (–)-epicatechin exhibited negligible affinities for both CB1 and CB2. It can be concluded that central nervous cannabinoid receptors may be targeted by selected tea catechins but signaling via peripheral type receptors is less likely to play a major role in vivo.     

Lobeline esters as novel ligands for neuronal nicotinic acetylcholine receptors and neurotransmitter transporters

Vesicular monoamine transporter-2 (VMAT2) is a viable target for development of pharmacotherapies for psychostimulant abuse. Lobeline (1) is a potent antagonist at α4β21 nicotinic acetylcholine receptors, has moderate affinity (K_i = 5.46 μM) for VMAT2, and is being investigated currently as a clinical candidate for treatment of psychostimulant abuse. A series of carboxylic acid and sulfonic acid ester analogs 2–20 of lobeline were synthesized and evaluated for interaction with α4β21 and α71 neuronal nicotinic acetylcholine receptors (nAChRs), the dopamine transporter (DAT), serotonin transporter (SERT) and VMAT2. Both carboxylic acid and sulfonic acid esters had low affinity at α71 nAChRs. Similar to lobeline (K_i = 4 nM), sulfonic acid esters had high affinity at α4β21 (K_i = 5–17 nM). Aromatic carboxylic acid ester analogs of lobeline (2–4) were 100–1000-fold less potent than lobeline at α4β21 nAChRs, whereas aliphatic carboxylic acid ester analogs were 10–100-fold less potent than lobeline at α4β21. Two representative lobeline esters, the 10-O-benzoate (2) and the 10-O-benzenesulfonate (10) were evaluated in the ³⁶Rb⁺ efflux assay using rat thalamic synaptosomes, and were shown to be antagonists with IC₅₀ values of 0.85 μM and 1.60 μM, respectively. Both carboxylic and sulfonic acid esters exhibited a range of potencies (equipotent to 13–45-fold greater potency compared to lobeline) for inhibiting DAT and SERT, respectively, and like lobeline, had moderate affinity (K_i = 1.98–10.8 μM) for VMAT2. One of the more interesting analogs, p-methoxybenzoic acid ester 4, had low affinity at α4β21 nAChRs (K_i = 19.3 μM) and was equipotent with lobeline, at VMAT2 (K_i = 2.98 μM), exhibiting a 6.5-fold selectivity for VMAT2 over α4β2 nAChRs. Thus, esterification of the lobeline molecule may be a useful structural modification for the development of lobeline analogs with improved selectivity at VMAT2.     

Synthesis and characterization of ampelopsin glucosides using dextransucrase from Leuconostoc mesenteroides B-1299CB4: Glucosylation enhancing physicochemical properties

Novel ampelopsin glucosides (AMPLS-Gs) were enzymatically synthesized and purified using a Sephadex LH-20 column. Each structure of the purified AMPLS-Gs was determined by nuclear magnetic resonance, and the ionic product of AMPLS-G1 was observed at m/z 505 (C₂₁H₂₂O₁₃·Na)⁺ using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. AMPLS-G1 was identified as ampelopsin-4′-O-α-d-glucopyranoside. The optimum condition for AMPLS-G1, determined using response surface methodology, was 70 mM ampelopsin, 150 mM sucrose, and 1 U/mL dextransucrase, which resulted in an AMPLS-G1 yield of 34 g/L. The purified AMPLS-G1 displayed 89-fold increased water solubility and 14.5-fold browning resistance compared to those of AMPLS and competitive inhibition against tyrosinase with a K_i value of 40.16 μM. This value was smaller than that of AMPLS (K_i = 62.56 μM) and much smaller than that of β-arbutin (K_i = 514.84 μM), a commercial active ingredient of whitening cosmetics. These results indicate the potential of AMPLS and AMPLS-G1 as superior ingredients for functional cosmetics.     

Design and synthesis of 1-(benzothiazol-5-yl)-1H-1,2,4-triazol-5-ones as protoporphyrinogen oxidase inhibitors

Protoporphyrinogen oxidase (PPO, E.C. 1.3.3.4) is the action target for several structurally diverse herbicides. A series of novel 4-(difluoromethyl)-1-(6-halo-2-substituted-benzothiazol-5-yl)-3-methyl-1H-1,2,4-triazol-5(4H)-ones 2a–z were designed and synthesized via the ring-closure of two ortho-substituents. The in vitro bioassay results indicated that the 26 newly synthesized compounds exhibited good PPO inhibition effects with K_i values ranging from 0.06 to 17.79 μM. Compound 2e, ethyl 2-{[5-(4-(difluoromethyl)-3-methyl-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)-6-fluorobenzo-thiazol-2-yl]thio}acetate, was the most potent inhibitor with K_i value of 0.06 μM against mtPPO, comparable to (K_i = 0.03 μM) sulfentrazone. Further green house assays showed that compound 2f (K_i = 0.24 μM, mtPPO), ethyl 2-{[5-(4-(difluoromethyl)-3-methyl-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl)-6-fluorobenzothiazol-2-yl]thio}propanoate, showed the most promising post-emergence herbicidal activity with broad spectrum even at concentrations as low as 37.5 g ai/ha. Soybean exhibited tolerance to compound 2f at the dosages of 150 g ai/ha, whereas they are susceptible to sulfentrazone even at 75 g ai/ha. Thus, compound 2f might be a potential candidate as a new herbicide for soybean fields.     

Synthesis,enzyme kinetics and computational evaluation of N-(β-d-glucopyranosyl) oxadiazolecarboxamides as glycogen phosphorylase inhibitors

All possible isomers of N-β-d-glucopyranosyl aryl-substituted oxadiazolecarboxamides were synthesised. O-Peracetylated N-cyanocarbonyl-β-d-glucopyranosylamine was transformed into the corresponding N-glucosyl tetrazole-5-carboxamide, which upon acylation gave N-glucosyl 5-aryl-1,3,4-oxadiazole-2-carboxamides. The nitrile group of the N-cyanocarbonyl derivative was converted to amidoxime which was ring closed by acylation to N-glucosyl 5-aryl-1,2,4-oxadiazole-3-carboxamides. A one-pot reaction of protected β-d-glucopyranosylamine with oxalyl chloride and then with arenecarboxamidoximes furnished N-glucosyl 3-aryl-1,2,4-oxadiazole-5-carboxamides. Removal of the O-acetyl protecting groups by the Zemplén method produced test compounds which were evaluated as inhibitors of glycogen phosphorylase. Best inhibitors of these series were N-(β-d-glucopyranosyl) 5-(naphth-1-yl)-1,2,4-oxadiazol-3-carboxamide (K_i = 30 μM), N-(β-d-glucopyranosyl) 5-(naphth-2-yl)-1,3,4-oxadiazol-2-carboxamide (K_i = 33 μM), and N-(β-d-glucopyranosyl) 3-phenyl-1,2,4-oxadiazol-5-carboxamide (K_i = 104 μM). ADMET property predictions revealed these compounds to have promising oral drug-like properties without any toxicity.     

Pyrrolidine analogs of GZ-793A: Synthesis and evaluation as inhibitors of the vesicular monoamine transporter-2 (VMAT2)

Central heterocyclic ring size reduction from piperidinyl to pyrrolidinyl in the vesicular monoamine transporter-2 (VMAT2) inhibitor GZ-793A and its analogs resulted in novel N-propane-1,2(R)-diol analogs 11a–i. These compounds were evaluated for their affinity for the dihydrotetrabenazine (DTBZ) binding site on VMAT2 and for their ability to inhibit vesicular dopamine (DA) uptake. The 4-difluoromethoxyphenethyl analog 11f was the most potent inhibitor of [³H]-DTBZ binding (K_i = 560 nM), with 15-fold greater affinity for this site than GZ-793A (K_i = 8.29 μM). Analog 11f also showed similar potency of inhibition of [³H]-DA uptake into vesicles (K_i = 45 nM) compared to that for GZ-793A (K_i = 29 nM). Thus, 11f represents a new water-soluble inhibitor of VMAT function.     

Syntheses and biological evaluation of 1-heteroaryl-2-aryl-1H-benzimidazole derivatives as c-Jun N-terminal kinase inhibitors with neuroprotective effects

1-Heteroaryl-2-aryl-1H-benzimidazole derivatives were synthesized as inhibitors of c-Jun N-terminal kinases, JNK3. Their activities were evaluated through measurement of K_d using SPR, JNK3 kinase assay, and cell-viability of human neuroblastoma cells. Most tested compounds showed high affinity (10 μM–46 nM) to JNK3. Among them, compound 16f exhibited potent activities (K_d = 46 nM). Especially, 16f was also found to present a potent cell protective effect (IC₅₀ = 1.09 μM) against toxicity induced by anisomycin, showing a possibility as protective therapeutics in neuronal cell apoptosis.     

Improved binding affinities of pyrrolidine derivatives as Mcl-1 inhibitors by modifying amino acid side chains

As an important member of anti-apoptotic Bcl-2 protein, myeloid cell leukemia sequence 1 (Mcl-1) protein is an attractive target for cancer therapy. In this study, a new series of pyrrolidine derivatives as Mcl-1 inhibitors were developed by mainly modifying the amino acid side chain of compound 1. Among them, compound 18 (K_i = 0.077 μM) exhibited better potent inhibitory activities towards Mcl-1 protein compared to positive control Gossypol (K_i = 0.18 μM). In addition, compound 40 possessed good antiproliferative activities against PC-3 cells (K_i = 8.45 μM), which was the same as positive control Gossypol (K_i = 7.54 μM).     

Synthesis and evaluation of N6-substituted apioadenosines as potential adenosine A3 receptor modulators

Adenosine receptors (ARs) trigger signal transduction pathways inside the cell when activated by extracellular adenosine. Selective modulation of the A₃AR subtype may be beneficial in controlling diseases such as colorectal cancer and rheumatoid arthritis. Here, we report the synthesis and evaluation of β-d-apio-d-furano- and α-d-apio-l-furanoadenosines and derivatives thereof. Introduction of a 2-methoxy-5-chlorobenzyl group at N⁶ of β-d-apio-d-furanoadenosine afforded an A₃AR antagonist (10c, K_i = 0.98 μM), while a similar modification of an α-d-apio-l-furanoadenosine gave rise to a partial agonist (11c, K_i = 3.07 μM). The structural basis for this difference was examined by docking to an A₃AR model; the antagonist lacked a crucial interaction with Thr94.     

Synthesis of substituted diphenyl sulfones and their structure–activity relationship with the antagonism of 5-НТ6 receptors

Substituted diphenyl sulfones (10a–n) were synthesised, and the structures were confirmed by NMR, LC–MS and X-ray crystallography. Their antagonistic activities towards 5-HT₆ receptor were assessed in a cell-based functional assay. Diphenyl sulfone 10a, in spite of being the smallest and simplest known sulfonyl-containing 5-HT₆R antagonist, showed a strong potency (K_i = 1.6 μM). Its derivative with a methylamine substituent, 10g (N-methyl-2-(phenylsulfonyl)aniline), was ～66-times as active as diphenyl sulfone (K_i = 24.3 nM). Addition of a piperazinyl moiety in the para-position relative to the sulfonyl group in compound 10m (N-methyl-2-(phenylsulfonyl)-5-piperazin-1-ylaniline) led to a further 150-fold increase in potency (K_i = 0.16 nM) to block the serotonin-induced response of HEK-293 cells that were stably transfected with the human recombinant 5-HT₆ receptor.     

β-Keto and β-hydroxyphosphonate analogs of biotin-5′-AMP are inhibitors of holocarboxylase synthetase

Holocarboxylase synthetase (HLCS) catalyzes the covalent attachment of biotin to cytoplasmic and mitochondrial carboxylases, nuclear histones, and over a hundred human proteins.Nonhydrolyzable ketophosphonate (β-ketoP) and hydroxyphosphonate (β-hydroxyP) analogs of biotin-5′-AMP inhibit holocarboxylase synthetase (HLCS) with IC₅₀ values of 39.7 μM and 203.7 μM. By comparison, an IC₅₀ value of 7 μM was observed with the previously reported biotinol-5′-AMP. The K_i values, 3.4 μM and 17.3 μM, respectively, are consistent with the IC₅₀ results, and close to the K_i obtained for biotinol-5′-AMP (7 μM). The β-ketoP and β-hydroxyP molecules are competitive inhibitors of HLCS while biotinol-5′-AMP inhibited HLCS by a mixed mechanism.     

Synthesis and biological evaluation of phloridzin analogs as human concentrative nucleoside transporter 3 (hCNT3) inhibitors

Nucleoside transporter inhibitors have potential therapeutic applications as anticancer, antiviral, cardioprotective and neuroprotective agents. Although quite a few potent inhibitors of the equilibrative nucleoside transporters are known, largely missing are the concentrative nucleoside transporter inhibitors. Phloridzin (3, K_i = 16.00 μM) is a known moderate inhibitor of the concentrative nucleoside transporters. We have synthesized and evaluated analogs of phloridzin at the hCNT3 nucleoside transporter. Within the series of synthesized analogs compound 16 (K_i = 2.88 μM), possessing a ribofuranose sugar unit instead of a glucopyranose as present in phloridzin, exhibited the highest binding affinity at the hCNT3 transporter. Phloridzin and compound 16 have also been shown to be selective for the hCNT3 transporter as compared with the hENT1 transporter. Compound 16 can serve as a new lead which after further modifications could yield selective and potent hCNT3 inhibitors.     

Elevation of cellular O-GlcNAcylation level by a potent and selective O-GlcNAcase inhibitor based on tetrahydroimidazopyridine scaffold

Protein O-GlcNAc glycosylation is a ubiquitous post-translational modification in metazoans. O-GlcNAcase (OGA), which is responsible for removing O-GlcNAc from serine or threonine residues, plays a key role in O-GlcNAc metabolism. Potent and selective O-GlcNAcase (OGA) inhibitors are useful tools for investigating the role of this modification in a broad range of cellular processes, and may also serve as drug candidates for treatment of neurodegenerative diseases. Biological screening of the gluco-configured tetrahydroimidazopyridine derivatives identified a compound as a potent and competitive inhibitor of human O-GlcNAcase (OGA) with a K_i of 5.9 μM, and it also displayed 28-fold selectivity for human OGA over human lysosomal β-hexosaminidase A (Hex A, K_i = 163 μM). In addition, cell-based assay revealed that this compound was cell-permeant and effectively induced cellular hyper-O-GlcNAcylation at 10 μM concentration.     

Synthesis of a d-Ala-d-Ala peptide isostere via olefin cross-metathesis and evaluation of vancomycin binding

The alkene peptide isostere for the d-Ala-d-Ala dipeptide was synthesized via a convergent approach utilizing olefin cross-metathesis. The new isostere was then evaluated for binding to the last resort antibiotic, vancomycin. The alkene isostere exhibited a K_D = 90 μM in comparison to the native peptide (K_D = 2.3 μM) and Lac mutant (K_D = 2300 μM). This study demonstrates that loss of binding in vancomycin resistant strains as a result of a d-Ala to d-Lac mutation is from both the loss of a crucial hydrogen bond and introduction of a repulsive lone pair interaction.