Thiol-disulfide exchanges modulate aldo–keto reductase family 1 member B10 activity and sensitivity to inhibitors

The reversible thiol/disulfide exchange is an important regulatory mechanism of protein enzymatic activity. Many protein enzymes are susceptible to S-thiolation induced by reactive oxygen species (ROS); and the glutathione (GSH) and free amino acid cysteine (Cys) are critical cellular thiol anti-oxidants, protecting proteins from irreversible oxidative damage. In this study, we found that aldo–keto reductase family 1 member B10 (AKR1B10) contains 4 Cys residues, i.e., Cys45, Cys187, Cys200, and Cys299. Exposing AKR1B10 to ROS mixtures resulted in significant decrease of its free sulfhydryl groups, up to 40–50% in the presence of physiological thiol cysteine at 0.5 or 1.0 mM; and accordingly, AKR1B10 enzymatic activity was reversibly decreased, in parallel with the oxidation of the sulfhydryl groups. ROS-induced thiolation also affected the sensitivity of AKR1B10 to inhibitors EBPC, epalrestat, and statil. Together our results showed for the first time that AKR1B10's enzymatic activity and inhibitor sensitivity are modulated by thiol/disulfide exchanges.     

Synthesis and structure–activity relationship of thiobarbituric acid derivatives as potent inhibitors of urease

A series of thiobarbituric acid derivatives 1–27 were synthesized and evaluated for their urease inhibitory potential. Exciting results were obtained from the screening of these compounds 1–27. Compounds 5, 7, 8, 11, 16, 17, 22, 23 and 24 showed excellent urease inhibition with IC₅₀ values 18.1 ± 0.52, 16.0 ± 0.45, 16.0 ± 0.22, 14.3 ± 0.27, 6.7 ± 0.27, 10.6 ± 0.17, 19.2 ± 0.29, 18.2 ± 0.76 and 1.61 ± 0.18 μM, respectively, much better than the standard urease inhibitor thiourea (IC₅₀ = 21 ± 0.11 μM). Compound 3, 4, 10, and 26 exhibited comparable activities to the standard with IC₅₀ values 21.4 ± 1.04 and 21.5 ± 0.61μM, 22.8 ± 0.32, 25.2 ± 0.63, respectively. However the remaining compounds also showed prominent inhibitory potential The structure–activity relationship was established for these compounds. This study identified a novel class of urease inhibitors. The structures of all compounds were confirmed through spectroscopic techniques such as EI-MS and ¹H NMR.     

Synthesis and structure–activity relationship studies of phenolic hydroxyl derivatives based on quinoxalinone as aldose reductase inhibitors with antioxidant activity

To enhance aldose reductase (ALR2) inhibition and add antioxidant ability, phenolic hydroxyl was introduced both to the quinoxalinone core and C3 side chain, resulting in a series of derivatives as ALR2 inhibitors. Biological activity tests suggested that most of the derivatives were potent and selective inhibitors with IC₅₀ values ranging from 0.059 to 6.825 μM, and 2-(3-(4-hydroxystyryl)-7-methoxy-2-oxoquinoxalin-1(2H)-yl)acetic acid (6b) was the most active. Particularly, it was encouraging to find that some derivatives endowed with obvious antioxidant activity, and among them the phenolic 3,4-dihydroxyl compound 6f with 7-hydroxyl in the quinoxalinone core showed the most potent activity, even comparable with the well-known antioxidant Trolox. Structure-activity relationship and docking studies highlighted the importance of phenolic hydroxyl both in C3 side chain and the core structure for constructing potent ALR2 inhibitors with antioxidant activity.     

Inhibitor selectivity between aldo–keto reductase superfamily members AKR1B10 and AKR1B1: Role of Trp112 (Trp111)

The antineoplastic target aldo–keto reductase family member 1B10 (AKR1B10) and the critical polyol pathway enzyme aldose reductase (AKR1B1) share high structural similarity. Crystal structures reported here reveal a surprising Trp112 native conformation stabilized by a specific Gln114-centered hydrogen bond network in the AKR1B10 holoenzyme, and suggest that AKR1B1 inhibitors could retain their binding affinities toward AKR1B10 by inducing Trp112 flip to result in an “AKR1B1-like” active site in AKR1B10, while selective AKR1B10 inhibitors can take advantage of the broader active site of AKR1B10 provided by the native Trp112 side-chain orientation.     

Synthesis and structure–activity relationship studies of MI-2 analogues as MALT1 inhibitors

Recent studies revealed that MALT1 is a promising therapeutic target for the treatment of ABC-DLBCL. Among several reported MALT1 inhibitors, MI-2 as an irreversible inhibitor represents a new class of ABC-DLBCL therapeutics. Due to its inherent potential cross-reactivity, further structure–activity relationship (SAR) study is imperative. In this work, five focused compound libraries based on the chemical structure of MI-2 are designed and synthesized. The systematic SARs revealed that the side chain of 2-methoxyethoxy has little impact on the activity and can be replaced by other functionalized groups, providing new MI-2 analogues with retained or enhanced potency. Compounds 81–83 with terminal hydroxyl group as side chain displayed enhanced activities against MALT1. Replacement of triazole core with pyrazole is also tolerant, while structural modifications on other sites are detrimental. These findings will facilitate further development of small-molecule MALT1 inhibitors.     

Synthesis and structure–activity relationship of 2-arylamino-4-aryl-pyrimidines as potent PAK1 inhibitors

2-Arylamino-4-aryl-pyrimidines were found to be potent inhibitors of PAK1 kinase. The synthesis and SAR are described. The incorporation of a bromide at the 5-position of the pyrimidine core and in combination with a 1,2-dimethylpiperazine pendant domain yielded a lead compound with potent PAK1 inhibition and anti-proliferative activity in various colon cancer cell lines.     

Synthesis and structure–activity relationship of novel cinnamamide derivatives as antidepressant agents

Cinnamamide 3a, a leading compound with antidepressant-like activity, and its derivatives were synthesized and their antidepressant activity and structure–activity relationship were investigated. Most of the compounds with trifluoromethyl group in methylenedioxyphenyl moiety (3f, 4b–c and 6a–b) exhibited significant antidepressant activity, measured in terms of percentage decrease in immobility duration by tail suspension test. In addition, the dose-dependent antidepressant effect of the most potent compound 3f was subsequently confirmed in tail suspension test and forced swim test. The test results showed that 3f was equal to or more effective than the standard drug fluoxetine at a concentration of 10 mg/kg. Furthermore, compound 3f did not show any central nervous system stimulant properties in the open-field test and the preliminary results were promising enough to warrant further detailed antidepressant research around this scaffold.     

Synthesis and structure–activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: Part 1

In an effort to develop potent and selective inhibitors toward ACAT2, structure–activity relationship studies were carried out using derivatives based on pyripyropene A (PPPA, 1). We have successfully developed novel PPPA derivatives with a 7-O-substituted benzoyl substituent that significantly exhibit more potent ACAT2 inhibitory activity and higher ACAT2 isozyme selectivity than 1.     

Synthesis and structure–activity relationship of 16,17-modified gibberellin derivatives

Gibberellins (GAs) are a group of diterpenoid plant hormones that control plant growth and development at various stages. Biologically active GAs share the common structures of a 3β-hydroxy group, a carboxy group at C-6, and a γ-lactone between C-4 and C-10. Hydroxylation at C-2β is a major deactivation step in many plant species, and hydroxylation at C-13 has been shown to weaken the binding affinity of GAs to their receptor proteins. In rice, bioactive GA₄ has also been shown to be deactivated through 16α,17-epoxidation. Moreover, 16,17-dihydro-16α,17-dihydroxy GA₄ has been identified as an aglycon of its glucoside from rice. However, our knowledge on the biological activity of 16,17-epoxidized GAs is currently limited to 16,17-dihydro-16α,17-epoxy GA₄. Moreover, the bioactivity of 16,17-dihydro-16α,17-dihydroxy GA₄ remains unknown. Here, we synthesized 16,17-epoxidized or dihydroxylated GA derivatives and performed a structure–activity relationship study using rice seedlings. 16,17-Epoxidation of bioactive GA₁ and GA₄ reduced their activity to promote elongation of rice leaf sheaths. Moreover, 16,17-dihydroxylation significantly decreased the activities of 16,17-dihydro-16α,17-epoxy GAs. These results suggest that GAs are deactivated in a stepwise manner via 16,17-epoxidation and hydrolysis of these epoxy groups.     

Synthesis and structure–activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: Part 2

Synthesis and structure–activity relationships of 7-O-p-cyanobenzoyl pyripyropene A derivatives with modification at C1 and 11 are described. Regioselective mono-deprotection of di-tert-butylsilylene acetal was critical in their synthesis.     

Synthesis and structure–activity relationships of dehydroaltenusin derivatives as selective DNA polymerase α inhibitors

Herein, we describe the synthesis and structure–activity relationships of dehydroaltenusin derivatives as inhibitors of a mammalian DNA polymerase α. We have newly synthesized nine dehydroaltenusin derivatives modified at the side chains or benzoquinone moiety. We also achieved the first synthesis of desmethylaltenusin and desmethyldehydroaltenusin, metabolites of Alternaria sp. or Talaromyces flavus, respectively. Among all synthesized derivatives, demethoxydehydroaltenusin was the most selective inhibitor of DNA polymerase α. The o-hydroxy-p-benzoquinone (2-hydroxycyclohexa-2,5-dienone) moiety is essential for the inhibition of DNA polymerases. Substitution at the 5-position of dehydroaltenusin is important for the inhibitory potency. Because dehydroaltenusin is conjugated with N-acetylcysteine methyl ester at the o-hydroxy-p-benzoquinone moiety, one or more cysteine residues of DNA polymerase α may act as a target for this compound.     

Synthesis and structure–activity relationship of 4-azaheterocycle benzenesulfonamide derivatives as new microtubule-targeting agents

A series of 1-sulfonyl indolines was synthesized and evaluated for antiproliferative activity. The most potent compounds 9a and 9e showed significant cytotoxicity (IC₅₀ in the range of 0.055–0.105 and 0.039–0.112 μM, respectively) against four human cancer cell lines HCT116, PC3, HepG2 and SK-OV-3. The structure–activity relationship of this series of sulfonamides, including the influence of azaheterocycle rings, substituent at the different positions of indoline, and the cyclopropane moiety, was described.     

Synthesis and structure–activity relationship of dihydrobenzofuran derivatives as novel human GPR119 agonists

Through appropriate medicinal chemistry design tactics and computer-assisted conformational modeling, the initial lead A was evolved into a series of dihydrobenzofuran derivatives 3 as potent GPR119 agonists. This Letter describes the optimization of general structure 3, including the substituent(s) on dihydrobenzofuran, the R¹ attachment on right-hand piperidine nitrogen, and the left-hand piperidine/piperazine and its attachment R². The efforts led to the identification of compounds 13c and 24 as potent human GPR119 modulators with favorable metabolic stability, ion channel activity, and PXR profiles.     

Identification and structure–activity relationship study of carvacrol derivatives as Mycobacterium tuberculosis chorismate mutase inhibitors

Abstract

In the present study, we identified carvacrol, a major phenolic component of oregano oil as a novel small molecule inhibitor of Mycobacterium tuberculosis (MTB) chorismate mutase (CM) enzyme with IC₅₀ of 1.06?±?0.4?µM. Virtual screening of the BITS-Pilani in-house database using the crystal structure of the MTB CM bound transition state intermediate (PDB: 2FP2) as framework identified carvacrol as a potential lead. Further various carvacrol derivatives were evaluated in vitro for their ability to inhibit MTB CM enzyme, whole cell MTB and cytotoxicity as steps toward the derivation of structure–activity relationships (SAR) and lead optimization.     

Synthesis and structure–activity relationship of pyripyropene A derivatives as potent and selective acyl-CoA:cholesterol acyltransferase 2 (ACAT2) inhibitors: Part 3

In an effort to develop potent and selective inhibitors toward ACAT2, structure–activity relationship studies were carried out using derivatives based on pyripyropene A (PPPA, 1). In particular, we investigated the possibility of introducing appropriate 1,11-O-benzylidene and 7-O-substituted benzoyl moieties into PPPA (1). The new o-substituted benzylidene derivatives showed higher selectivity for ACAT2 than PPPA (1). Among them, 1,11-O-o-methylbenzylidene-7-O-p-cyanobenzoyl PPPA derivative 7q and 1,11-O-o,o-dimethylbenzylidene-7-O-p-cyanobenzoyl PPPA derivative 7z proved to be potent ACAT2 inhibitors with unprecedented high isozyme selectivity.     

Synthesis and structure–activity relationship study of novel quinazolinone-based inhibitors of MurA

MurA is an intracellular bacterial enzyme that is essential for peptidoglycan biosynthesis, and is therefore an important target for antibacterial drug discovery. We report the synthesis, in silico studies and extensive structure–activity relationships of a series of quinazolinone-based inhibitors of MurA from Escherichia coli. 3-Benzyloxyphenylquinazolinones showed promising inhibitory potencies against MurA, in the low micromolar range, with an IC₅₀ of 8 µM for the most potent derivative (58). Furthermore, furan-substituted quinazolinones (38, 46) showed promising antibacterial activities, with MICs from 1 µg/mL to 8 µg/mL, concomitant with their MurA inhibitory potencies. These data represent an important step towards the development of novel antimicrobial agents to combat increasing bacterial resistance.     

Identification and structure–activity relationship of 8-hydroxy-quinoline-7-carboxylic acid derivatives as inhibitors of Pim-1 kinase

Pim-1 kinase is a cytoplasmic serine/threonine kinase that controls programmed cell death by phosphorylating substrates that regulate both apotosis and cellular metabolism. A series of 2-styrylquinolines and quinoline-2-carboxamides has been identified as potent inhibitors of the Pim-1 kinase. The 8-hydroxy-quinoline 7-carboxylic acid moiety appeared to be a crucial pharmacophore for activity. Molecular modeling indicated that interaction of this scaffold with Asp186 and Lys67 residues within the ATP-binding pocket might be responsible for the kinase inhibitory potency.     

Synthesis,evaluation and quantitative structure–activity relationship (QSAR) analysis of Wogonin derivatives as cytotoxic agents

A novel series of 49 wogonin derivatives were synthesized by introducing group at 7-, 8- or B ring of wogonin. The cytotoxic activities against HepG2, A549 and BCG-823 cancer cell lines were also investigated in vitro. Several of them showed obvious cytotoxic activities and compound 3h possessed the highest potency against HepG2, A549, and BCG-823 with IC₅₀ values of 1.07 μM, 1.74 μM and 0.98 μM, respectively. A quantitative structure-activity relationship (QSAR) study of these synthetic derivatives as well as wogonin indicated that high solubility and low octanol/water partition coefficient are favorable, and excessive electrostatic properties and refractivity are unfavorable for the cytotoxic activities of these wogonin derivatives. These findings and results provide a base for further investigations.     

Synthesis,biological activity and structure–activity relationship of endomorphin-1/substance P derivatives

Endomorphins have been shown to produce potent analgesia in various rodent models of pain. However, their central administration led to the development of tolerance and physical dependence. Conjugation of C-terminal substance P (SP) fragments to opioids and opioid peptides was previously shown to produce hybrid peptides with strong analgesic activity, with low or no propensity to develop tolerance. In this study, four peptides (2–5) comprised of endomorphin-1 (1) and C-terminal fragments of SP (four or five amino acids, SP_8–11 (2) or SP_7–11 (4), respectively), with an overlapping Phe residue, were synthesized. To overcome low metabolic stability and poor membrane permeability of the peptide, the N-terminus of 2 and 4 was further modified with a C10-carbon lipoamino acid (C10LAA) achieving 3 and 5, respectively. LAA-modification of the hybrid peptides resulted in a significant increase in metabolic stability and membrane permeability compared to peptides 1, 2 and 4. Compound 5 showed potent μ-opioid receptor binding affinity (K_iμ = 3.87 ± 0.51 nM) with dose-dependent agonist activity in the nanomolar range (IC₅₀ = 45 ± 13 nM). In silico modeling was used to investigate the binding modes and affinities of compounds 1–5 in the active site of μ-opioid receptors. The docking scores were in agreement with the K_iμ values obtained in the receptor binding affinity studies. The more active LAA-modified hybrid peptide showed a lower total interaction energy and higher negative value of MolDock score.     

Synthesis and structure–activity relationship of fused-pyrimidine derivatives as a series of novel GPR119 agonists

A series of fused-pyrimidine derivatives have been discovered as potent and orally active GPR119 agonists. A combination of the fused-pyrimidine structure and 4-chloro-2,5-difluorophenyl group provided the 5,7-dihydrothieno[3,4-d]pyrimidine 6,6-dioxide derivative 14a as a highly potent GPR119 agonist. Further optimization of the amino group at the 4-position in the pyrimidine ring led to the identification of 2-{1-[2-(4-chloro-2,5-difluorophenyl)-6,6-dioxido-5,7-dihydrothieno[3,4-d]pyrimidin-4-yl]piperidin-4-yl}acetamide (16b) as an advanced analog. Compound 16b was found to have extremely potent agonistic activity and improved glucose tolerance at 0.1 mg/kg po in mice. We consider compound 16b and its analogs to have clear utility in exploring the practicality of GPR119 agonists as potential therapeutic agents for the treatment of type 2 diabetes mellitus.