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 novel furazan-3,4-diamide analogs as potent anti-cancer agents

This study describes the synthesis and structure–activity relationships of a series of furazan-3,4-diamide analogs. 1,2,5-Oxadiazole ring and electron-withdrawing substituent on the phenyl ring are proposed to be the important elements which contribute to a significant extent maximal potency of anti-proliferation effect.     

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.     

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.     

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.     

Structure–activity relationships of norepinephrine reuptake inhibitors with benzothiadiazine dioxide or dihydrosulfostyril cores

Two related series of selective norepinephrine reuptake inhibitors were synthesized based on 3,4-dihydro-1H-2,1,3-benzothiadiazine 2,2-dioxide or 3,4-dihydrosulfostyril cores, and screened for monoamine reuptake inhibition. Structure–activity relationships were determined for the series’ in vitro potency and selectivity versus serotonin or dopamine transporter inhibition, and analogs based on both cores were identified as potent and selective NRIs. The 3,4-dihydrosulfostyril series was further tested for microsome stability, and compound 16j, which was optimized for both potency and stability, showed efficacy in an in vivo model of thermoregulatory dysfunction.     

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.     

Optimization and structure–activity relationships of a series of potent inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase as novel antimicrobial agents

A novel series of hydrazones were synthesized and evaluated as inhibitors of methicillin-resistant Staphylococcus aureus (MRSA) pyruvate kinase (PK). PK has been identified as one of the most highly connected ‘hub proteins’ in MRSA. PK has been shown to be critical for bacterial survival which makes it a potential target for development of novel antibiotics and the high degree of connectivity implies it should be very sensitive to mutations and thus less able to develop resistance. PK is not unique to bacteria and thus a critical requirement for such a PK inhibitor would be that it does not inhibit the homologous human enzyme(s) at therapeutic concentrations. Several MRSA PK inhibitors (including 8d) were identified using in silico screening combined with enzyme assays and were found to be selective for bacterial enzyme compared to four human PK isoforms (M1, M2, R and L). However these lead compounds did not show significant inhibitory activity for MRSA growth presumably due to poor bacterial cell penetration. Structure–activity relationship (SAR) studies were carried out on 8d and led us to discover more potent compounds with enzyme inhibiting activities in the low nanomolar range and some were found to effectively inhibit bacteria growth in culture with minimum inhibitory concentrations (MIC) as low as 1 μg/mL. These inhibitors bind in two elongated flat clefts found at the minor interfaces in the homo-tetrameric enzyme complex and the observed SAR is in keeping with the size and electronic constraints of these binding sites. Access to the corresponding sites in the human enzyme is blocked.     

Discovery and structure–activity relationships of (2-(arylthio)benzylideneamino)guanidines as a novel series of potent apoptosis inducers

1-(2-(2,5-Dimethoxyphenylthio)benzylidene)semicarbazide (2a) was discovered as a potent apoptosis inducer through our cell based HTS assay. SAR study led to the discovery of a more aqueous soluble analog (2-(2,5-dimethoxyphenylthio)-6-methoxybenzylideneamino)guanidine (5e) with EC₅₀ value of 60 nM in the caspase activation assay and GI₅₀ value of 62 nM in the growth inhibition assay in T47D cells. Compound 5e was found to be an inhibitor of tubulin polymerization and efficacious in a MX-1 breast tumor model.     

Synthesis and structure–activity relationships of N-aryl-piperidine derivatives as potent (partial) agonists for human histamine H3 receptor

4-((1H-Imidazol-4-yl)methyl)-1-aryl-piperazine and piperidine derivatives were designed and synthesized as candidate human histamine type 3 agonists. The piperazine derivatives were found to have low (or no) affinity for human histamine H3 receptor, whereas the piperidine derivatives showed moderate to high affinity, and their agonistic activity was greatly influenced by substituents on the aromatic ring. Among the piperidine-containing compounds, 17d and 17h were potent human histamine H3 receptor agonists with high selectivity over the closely related human H4 receptor. Our results indicate that appropriate conformational restriction, that is, by the piperidine spacer moiety, favors specific binding to the human histamine H3 receptor.     

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 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.     

Synthesis and structure–activity relationships of γ-carboline derivatives as potent and selective cysLT1 antagonists

A γ-carboline series of cysLT₁ receptor antagonists has been prepared. Some of the compounds show good potencies both, in vitro and in vivo, compared to the standard compounds.     

Synthesis and structure–activity relationship of dicationic diaryl ethers as novel potent anti-MRSA and anti-VRE agents

A series of dicationic diaryl ethers have been synthesized and evaluated for in vitro antibacterial activities, including drug resistant bacterial strains. Most of these compounds have shown potent antibacterial activities. Several compounds, such as piperidinyl and thiomorpholinyl compounds 9e and 9l, improved the antimicrobial selectivity and kept potent anti-MRSA and anti-VRE activity. The most potent bis-indole diphenyl ether 19 exhibited anti-MRSA MIC value of ?0.06 μg/mL and enhanced antimicrobial selectivity.     

Anti-HBV agents. Part 3: Preliminary structure–activity relationships of tetra-acylalisol A derivatives as potent hepatitis B virus inhibitors

Thirty-two tetra-acylated derivatives of alisol A were synthesized and evaluated for their anti-hepatitis B virus (HBV) activities and cytotoxicities in vitro. Among the series of alisol A derivatives examined, five analogues were active against HBV surface antigen (HBsAg) and HBV e antigen (HBeAg) secretion in HepG 2.2.15 cells. These results also provide interesting structure–activity relationships of tetra-acylalisol A derivatives. Compounds tetra-acetyl alisol A (A1), tetra-methoxyacetyl alisol A (A23), and tetra-ethoxyacetyl alisol A (A24) exhibited high activities against secretion of HBsAg with IC₅₀ values of 0.0048, 0.0044, and 0.014 mM, respectively, HBeAg with IC₅₀ values of 0.011, 0.012, and 0.018 mM, respectively, and remarkable selective index values SI_HBsAg >333, SI_HBeAg >145; SI_HBsAg = 209, SI_HBeAg = 77; and SI_HBsAg >200, SI_HBeAg >156, respectively. Additional studies in rats showed that compound A1 has favorable pharmacokinetic prosperities for further development purpose, with elimination half-time (t_1/2) of 1.63 h and oral bioavailability (F) of 40.9%.     

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.     

Peptide deformylase inhibitors with retro-amide scaffold: Synthesis and structure–activity relationships

Peptide deformylase (PDF) is a metalloprotease catalyzing the removal of a formyl group from newly synthesized proteins. Thus inhibition of PDF activity is considered to be one of the most effective antibiotic strategies. Reported herein are the synthesis and structure–activity relationship studies of retro-amide inhibitors based on actinonin, a naturally occurring PDF inhibitor. Analysis of the structure–activity relationships led to the discovery of 7a, which exhibits potent enzyme inhibition and antibacterial activity against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis.     

Synthesis and structure–activity relationships of 1,2,3,4-tetrahydropyrido[2,3-b]pyrazines as potent and selective inhibitors of the anaplastic lymphoma kinase

Dysregulation of the anaplastic lymphoma kinase (ALK) is implicated in a variety of cancers. A series of tetrahydropyrido[2,3-b]pyrazines was constructed as ring-constrained analogs of a known aminopyridine kinase scaffold. Chemistry was developed to rapidly elaborate the SAR, structural elements impacting ALK inhibitory activity were exploited, and kinase selective analogs were identified that inhibit ALK with IC₅₀ values ～10 nM (enzyme) and ～150 nM (cell).     

Synthesis and structure–activity relationships of novel indazolyl glucocorticoid receptor partial agonists

SAR was used to further develop an indazole class of non-steroidal glucocorticoid receptor agonists aided by a GR LBD (ligand-binding domain)-agonist co-crystal structure described in the accompanying paper. Progress towards discovering a dissociated GR agonist guided by human in vitro assays biased the optimization of this compound series towards partial agonists that possessed excellent selectivity against other nuclear hormone receptors.     

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.