Structure–activity relationships of diphenylpiperazine N-type calcium channel inhibitors

A novel series of compounds derived from the previously reported N-type calcium channel blocker NP118809 (1-(4-benzhydrylpiperazin-1-yl)-3,3-diphenylpropan-1-one) is described. Extensive SAR studies resulted in compounds with IC₅₀ values in the range of 10–150 nM and selectivity over the L-type channels up to nearly 1200-fold. Orally administered compounds 5 and 21 exhibited both anti-allodynic and anti-hyperalgesic activity in the spinal nerve ligation model of neuropathic pain.     

Structure–activity relationships of lanostane-type triterpenoids from Ganoderma lingzhi as α-glucosidase inhibitors

A series of lanostane-type triterpenoids, identified as ganoderma alcohols and ganoderma acids, were isolated from the fruiting body of Ganoderma lingzhi. Some of these compounds were confirmed as active inhibitors of the in vitro human recombinant aldose reductase. This paper aims to explain the structural requirement for α-glucosidase inhibition. Our structure–activity studies of ganoderma alcohols showed that the OH substituent at C-3 and the double-bond moiety at C-24 and C-25 are necessary to increase α-glucosidase inhibitory activity. The structure–activity relationships of ganoderma acids revealed that the OH substituent at C-11 is an important feature and that the carboxylic group in the side chain is essential for the recognition of α-glucosidase inhibitory activity. Moreover, the double-bond moiety at C-20 and C-22 in the side chain and the OH substituent at C-3 of ganoderma acids improve α-glucosidase inhibitory activity.These results provide an approach with which to consider the structural requirements of lanostane-type triterpenoids from G. lingzhi. An understanding of these requirements is considered necessary in order to improve a new type of α-glucosidase inhibitor.     

Structure–activity relationships of heteroaromatic esters as human rhinovirus 3C protease inhibitors

Human rhinovirus 3C protease (HRV 3C^pro) is known to be a promising target for development of therapeutic agents against the common cold because of the importance of the protease in viral replication as well as its expression in a large number of serotypes. To explore non-peptidic inhibitors of HRV 3C^pro, a series of novel heteroaromatic esters was synthesized and evaluated for inhibitory activity against HRV 3C^pro, to determine the structure–activity relationships. The most potent inhibitor, 7, with a 5-bromopyridinyl group, had an IC₅₀ value of 80 nM. In addition, the binding mode of a novel analog, 19, with the 4-hydroxyquinolinone moiety, was explored by molecular docking, suggesting a new interaction in the S1 pocket.     

Structure–activity relationships of substituted oxyoxalamides as inhibitors of the human soluble epoxide hydrolase

We explored both structure–activity relationships among substituted oxyoxalamides used as the primary pharmacophore of inhibitors of the human sEH and as a secondary pharmacophore to improve water solubility of inhibitors. When the oxyoxalamide function was modified with a variety of alkyls or substituted alkyls, compound 6 with a 2-adamantyl group and a benzyl group was found to be a potent sEH inhibitor, suggesting that the substituted oxyoxalamide function is a promising primary pharmacophore for the human sEH, and compound 6 can be a novel lead structure for the development of further improved oxyoxalamide or other related derivatives. In addition, introduction of substituted oxyoxalamide to inhibitors with an amide or urea primary pharmacophore produced significant improvements in inhibition potency and water solubility. In particular, the N,N,O-trimethyloxyoxalamide group in amide or urea inhibitors (26 and 31) was most effective among those tested for both inhibition and solubility. The results indicate that substituted oxyoxalamide function incorporated into amide or urea inhibitors is a useful secondary pharmacophore, and the resulting structures will be an important basis for the development of bioavailable sEH inhibitors.     

Isolation of antiplasmodial anthraquinones from Kniphofia ensifolia,and synthesis and structure–activity relationships of related compounds

Bioassay-guided separation of the South African plant Kniphofia ensifolia for antiplasmodial activity led to the isolation of two new anthraquinones, named kniphofiones A and B (3 and 4), together with three known bioactive anthraquinone monomers (1, 2 and 5), and four known bisanthraquinones (6–9). The structures of the two new compounds were elucidated based on analyses of their 1D and 2D NMR spectra and mass spectrometric data. The dimeric compounds 6 and 7 displayed the strongest antiplasmodial activity among all the isolated compounds, with IC₅₀ values of 0.4 ± 0.1 and 0.2 ± 0.1 μM, respectively. The two new compounds displayed modest activities, with IC₅₀ values of 26 ± 4 and 9 ± 1 μM, respectively. Due to the synthetic accessibility of the new compounds and the increased activity shown by the dimeric compounds, a structure–activity relationship study was conducted. As a result, one analogue of kniphofione B (4), the caffeic acid derivative of aloe-emodin, was found to have the highest activity among all the aloe-emodin derivatives, with an IC₅₀ value of 1.3 ± 0.2 μM.     

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.     

Design,synthesis, and structure–activity relationships of pyrazole derivatives as potential FabH inhibitors

Fatty acid biosynthesis is essential for bacterial survival. FabH, β-ketoacyl-acyl carrier protein (ACP) synthase III, is a particularly attractive target, since it is central to the initiation of fatty acid biosynthesis and is highly conserved among Gram-positive and -negative bacteria. Fifty-six 1-acetyl-3,5-diphenyl-4,5-dihydro-(1H)-pyrazole derivatives were synthesized and developed as potent inhibitors of FabH. This inhibitor class demonstrates strong antibacterial activity. Escherichia coli FabH inhibitory assay and docking simulation indicated that the compounds 1-(5-(4-fluorophenyl)-3-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone (12) and 1-(5-(4-chlorophenyl)-3-(4-methoxyphenyl)-4,5-dihydro-1H-pyrazol-1-yl)ethanone (13) were potent inhibitors of E. coli FabH.     

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.     

Structure–activity relationships of various amino-hydroxy-benzenesulfonic acids and sulfonamides as tyrosinase substrates

Background

o-Aminophenols have been long recognised as tyrosinase substrates. However their exact mode of interaction with the enzyme's active site is unclear. Properly vic-substituted o-aminophenols could help gain some insight into tyrosinase catalytic mechanism.

Methods

Eight vic-substituted o-aminophenols belonging to two isomeric series were systematically evaluated as tyrosinase substrates and/or activators and/or inhibitors, by means of spectrophotometric techniques and HPLC-MS analysis. Some relevant kinetic parameters have also been obtained.

Results

Four o-aminophenolic compounds derived from 3-hydroxyorthanilic acid (2-amino-3-hydroxybenzenesulfonic acid) and their four counterparts derived from the isomeric 2-hydroxymetanilic acid (3-amino-2-hydroxybenzenesulfonic acid) were synthesised and tested as putative substrates for mushroom tyrosinase. While the hydroxyorthanilic derivatives were quite inactive as both substrates and inhibitors, the hydroxymetanilic compounds on the contrary all acted as substrates for the enzyme, which oxidised them to the corresponding phenoxazinone derivatives.

General significance

Based on the available structures of the active sites of tyrosinases, the different affinities of the four metanilic derivatives for the enzyme, and their oxidation rates, we propose a new hypothesis regarding the interaction between o-aminophenols and the active site of tyrosinase that is in agreement with the obtained experimental results.     

Structure–activity relationships of antibacterial peptides

Antimicrobial peptides play a crucial role in innate immunity, whose components are mainly peptide-based molecules with antibacterial properties. Indeed, the exploration of the immune system over the past 40 years has revealed a number of natural peptides playing a pivotal role in the defence mechanisms of vertebrates and invertebrates, including amphibians, insects, and mammalians. This review provides a discussion regarding the antibacterial mechanisms of peptide-based agents and their structure–activity relationships (SARs) with the aim of describing a topic that is not yet fully explored. Some growing evidence suggests that innate immunity should be strongly considered for the development of novel antibiotic peptide-based libraries. Also, due to the constantly rising concern of antibiotic resistance, the development of new antibiotic drugs is becoming a priority of global importance. Hence, the study and the understanding of defence phenomena occurring in the immune system may inspire the development of novel antibiotic compound libraries and set the stage to overcome drug-resistant pathogens. Here, we provide an overview of the importance of peptide-based antibacterial sources, focusing on accurately selected molecular structures, their SARs including recently introduced modifications, their latest biotechnology applications, and their potential against multi-drug resistant pathogens. Last, we provide cues to describe how antibacterial peptides show a better scope of action selectivity than several anti-infective agents, which are characterized by non-selective activities and non-targeted actions toward pathogens.     

Design,synthesis and structure–activity relationships of 3,5-diaryl-1H-pyrazoles as inhibitors of arylamine N-acetyltransferase

The synthesis and inhibitory potencies of a novel series of 3,5-diaryl-1H-pyrazoles as specific inhibitors of prokaryotic arylamine N-acetyltransferase enzymes is described. The series is based on hit compound 1 3,5-diaryl-1H-pyrazole identified from a high-throughout screen that has been carried out previously and found to inhibit the growth of Mycobacterium tuberculosis.     

Design,synthesis and structure–activity relationships of zwitterionic spirocyclic compounds as potent CCR1 antagonists

A series of zwitterionic spirocyclic compounds were synthesised. In vitro data revealed that these compounds were potent CCR1 antagonists. In particular, 2, 4, 11 and 20 inhibited CCR1 mediated chemotaxis of THP-1 cells in a functional assay.     

Structure–activity relationships for 4-anilinoquinoline derivatives as inhibitors of the DNA methyltransferase enzyme DNMT1

A series of 4-anilinoquinoline derivatives related to the known inhibitor SGI-1027, containing side chains of varying pK_a, were prepared by acid-catalysed coupling of the pre-formed side chains with 4-chloroquinolines. The compounds were evaluated for their ability to reduce the level of DNMT1 protein in HCT116 human colon carcinoma cells by Western blotting. With a very strongly basic N-methylpyridinium side chain, only NHCO-linked compounds were effective, whereas less strongly basic ((diaminomethylene)hydrazono)ethyl or 3-methylpyrimidine-2,4-diamine side chains allowed both NHCO- and CONH-linked compounds to show activity. In contrast, the pK_a of the quinoline unit had little apparent influence on activity.     

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.     

Discovery and structure–activity relationships of phenyl benzenesulfonylhydrazides as novel indoleamine 2,3-dioxygenase inhibitors

A novel class of phenyl benzenesulfonylhydrazides has been identified as potent inhibitors of indoleamine 2,3-dioxygenase (IDO), and their structure–activity relationship was explored. Coupling reactions between various benzenesulfonyl chlorides and phenylhydrazides were utilized to synthesize the sulfonylhydrazides bearing various substituents. Compound 3i exhibited 61 nM of IC₅₀ in enzymatic assay and 172 nM of EC₅₀ in the HeLa cell. The computational study of 3i suggested that the major interactions between 3i and IDO protein are the coordination of sulfone and heme iron, the hydrogen bonding and hydrophobic interactions between 3i and IDO. This novel class of IDO inhibitor provides a new direction to discover effective anti-cancer agents.     

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.     

Structure–activity relationships of fraxamoside as an unusual xanthine oxidase inhibitor

Fraxamoside, a macrocyclic secoiridoid glucoside featuring a hydroxytyrosol group, was recently identified as a xanthine oxidase inhibitor (XOI) comparable in potency in vitro to the standard antigout drug allopurinol. However, this activity and its considerably higher value than its derivatives oleuropein, oleoside 11-methyl ester, and hydroxytyrosol are not explained by structure–activity relationships (SARs) of known XOIs. To exclude allosteric mechanisms, we first determined the inhibition kinetic of fraxamoside. The resulting competitive mechanism prompted a computational SAR characterization, combining molecular docking and dynamics, which fully explained the behavior of fraxamoside and its derivatives, attributed the higher activity of the former to conformational properties of its macrocycle, and showed a substantial contribution of the glycosidic moiety to binding, in striking contrast with glycoside derivatives of most other XOIs. Overall, fraxamoside emerged as a lead compound for a new class of XOIs potentially characterized by reduced interference with purine metabolism.     

Structure–activity relationships of new 4-hydroxy bis-coumarins as radical scavengers and chain-breaking antioxidants

The main antioxidant properties of five new 4-hydroxy-bis-coumarins during bulk lipid autoxidation at 80 °C and 0.1 mM and 1.0 mM concentrations were studied and compared with 4-hydroxy-2H-chromen-2-one (1). These compounds are: 3,3′-((3,4-dihydroxy-phenyl) methylene) bis (4-hydroxy-2H-chromen-2-one) (2), 3,3′-((3,4-dimethoxyphenyl) methylene) bis (4-hydroxy-2H-chromen-2-one) (3), 3,3′-((4-hydroxy-3,5-dimethoxy-phenyl) methylene) bis(4-hydroxy-2H-chromen-2-one) (4) 3,3′-((3,4,5- trimethoxyphenyl) methylene) bis (4-hydroxy-2H-chromen-2-one) (5) 3,3′-((4-hydroxy-3-methoxy-5-nitrophenyl) methylene) bis (4-hydroxy-2H-chromen-2-one) (6), It was found that compound 2 with a catecholic structure in the aromatic nucleus showed the strongest antioxidant activity. Compound 4 showed a moderate antioxidant activity, and all the other compounds didn't show any capacity as chain-breaking antioxidants. Both 4-hydroxy-bis-coumarins (2 and 4) demonstrated also stronger radical scavenging activity towards DPPH radical by using TLC DPPH rapid test, than compound 1. The other compounds (3, 5, 6) didn't show any capacity as radical scavengers. The structure–activity relationship was discussed on the base of comparable kinetic analysis of studied 4-hydroxy-bis-coumarins with the known and standard antioxidants as α-tocopherol (TOH), caffeic acid (CA), sinapic acid (SA), ferulic acid (FA), and p-coumaric acid (p-CumA). In order to study the possible synergism between two phenolic antioxidants, the antioxidant efficiency and reactivity of two equimolar binary mixtures of coumarins and TOH (2 + TOH and 4 + TOH) and of corresponding cinnamic acid with TOH (CA + TOH and SA + TOH) were also tested and compared. The oxidation stability of the lipid substrate in presence of binary mixtures CA + TOH, SA + TOH and 2 + TOH appeared to be higher than that of the individual antioxidants. However, no synergism was obtained for all tested binary mixtures.     

Benzothiophene inhibitors of MK2. Part 1: Structure–activity relationships,assessments of selectivity and cellular potency

Identification of potent benzothiophene inhibitors of mitogen activated protein kinase-activated protein kinase 2 (MK2), structure–activity relationship (SAR) studies, selectivity assessments against CDK2, cellular potency and mechanism of action are presented. Crystallographic data provide a rationale for the observed MK2 potency as well as selectivity over CDK2 for this class of inhibitors.     

Structure–activity relationship study of acridine analogs as haspin and DYRK2 kinase inhibitors

Haspin is a serine/threonine kinase required for completion of normal mitosis that is highly expressed during cell proliferation, including in a number of neoplasms. Consequently, it has emerged as a potential therapeutic target in oncology. A high throughput screen of approximately 140,000 compounds identified an acridine analog as a potent haspin kinase inhibitor. Profiling against a panel of 270 kinases revealed that the compound also exhibited potent inhibitory activity for DYRK2, another serine/threonine kinase. An optimization study of the acridine series revealed that the structure–activity relationship (SAR) of the acridine series for haspin and DYRK2 inhibition had many similarities. However, several structural differences were noted that allowed generation of a potent haspin kinase inhibitor (33, IC₅₀ <60 nM) with 180-fold selectivity over DYRK2. In addition, a moderately potent DYRK2 inhibitor (41, IC₅₀ <400 nM) with a 5.4-fold selectivity over haspin was also identified.