Synthesis and biological evaluation of 2-substituted-4-(3′,4′,5′-trimethoxyphenyl)-5-aryl thiazoles as anticancer agents

Antitumor agents that bind to tubulin and disrupt microtubule dynamics have attracted considerable attention in the last few years. To extend our knowledge of the thiazole ring as a suitable mimic for the cis-olefin present in combretastatin A-4, we fixed the 3,4,5-trimethoxyphenyl at the C4-position of the thiazole core. We found that the substituents at the C2- and C5-positions had a profound effect on antiproliferative activity. Comparing compounds with the same substituents at the C5-position of the thiazole ring, the moiety at the C2-position influenced antiproliferative activities, with the order of potency being NHCH₃ > Me ? N(CH₃)₂. The N-methylamino substituent significantly improved antiproliferative activity on MCF-7 cells with respect to C2-amino counterparts. Increasing steric bulk at the C2-position from N-methylamino to N,N-dimethylamino caused a 1–2 log decrease in activity. The 2-N-methylamino thiazole derivatives 3b, 3d and 3e were the most active compounds as antiproliferative agents, with IC₅₀ values from low micromolar to single digit nanomolar, and, in addition, they are also active on multidrug-resistant cell lines over-expressing P-glycoprotein. Antiproliferative activity was probably caused by the compounds binding to the colchicines site of tubulin polymerization and disrupting microtubule dynamics. Moreover, the most active compound 3e induced apoptosis through the activation of caspase-2, -3 and -8, but 3e did not cause mitochondrial depolarization.     

Target ROS to induce apoptosis and cell cycle arrest by 5,7-dimethoxy-1,4-naphthoquinone derivative

The 1,4-naphthoquinone derivatives bearing 5,7-dimethoxyl moiety were designed, synthesized, and tested as the antitumor agents against five human cancer cell lines (A549, Hela, HepG2, NCI-H460 and HL-60). All the compounds are described herein for the first time. The structure-activity relationships indicated that the presence of chlorine atom at the 2-position was crucial for the antiproliferative activity. Further, the electrochemical properties of the representative compounds (7e, 8e and 9e) were evaluated and a definite correlation between the redox potential and the antiproliferative activity. The most potent compound 9e displayed significant anti-leukemic activity with IC₅₀ value of 3.8?μM in HL-60 cells and weak cytotoxicity with IC₅₀ of 40.7?μM in normal cells WI-38. In mechanistic study for 9e, the increased numbers of apoptotic cells and increased cell population at G2/M phase correlated with ROS generation. Together, our results suggested that the derivatives of 2-chlorine-1,4-naphthoquinone might be the promising candidates for the treatment of promyelocytic leukemia.     

Synthesis of new antimicrobial pyrrolo[2,1-a]isoquinolin-3-ones

The attractive structure of the pyrroloisoquinoline moiety, together with its potential antimicrobial activity, encouraged us to prepare six 8-substituted and seven 8,9-disubstituted-1,2,3,5,6,10b-hexahydropyrrolo[2,1-a]isoquinolin-3-ones in a few steps with good yields. We applied a convenient methodology via double intramolecular cyclization conducted by a Bischler-Napieralski cyclodehydration-imine reduction sequence, which is widely employed in the synthesis of isoquinoline alkaloids. Therefore, we synthesized three series of these pyrrolo[2,1-a]isoquinolin-3-ones characterized by the substituent at the 8-position or 8,9-positions of the aromatic ring: (a) different side chains are attached to an 8-OH group (series 1); (b) a chlorine atom is attached to the 8-position (series 2); and (c) 8- and 9-carbons are bearing an identical group (series 3). The compounds bearing a benzylic moiety at the 8-position, for example, 8-benzyloxy-pyrrolo[2,1-a]isoquinolin-3-one (1a) and 8-(4-fluorobenzyloxy)-pyrrolo[2,1-a]isoquinolin-3-one (1e), as well as, a 8-chloro-9-methoxy moiety including the 8-chloro-9-methoxy-pyrrolo[2,1-a]isoquinolin-3-one (2a), provided the most fungicide and bactericide agents, respectively.     

Discovery of N-methyl-4-(4-methoxyanilino)quinazolines as potent apoptosis inducers. Structure–activity relationship of the quinazoline ring

As a continuation of our efforts to discover and develop apoptosis inducing N-methyl-4-(4-methoxyanilino)quinazolines as novel anticancer agents, we explored substitution at the 5-, 6-, 7-positions of the quinazoline and replacement of the quinazoline by other nitrogen-containing heterocycles. A small group at the 5-position was found to be well tolerated. At the 6-position a small group like an amino was preferred. Substitution at the 7-position was tolerated much less than at the 6-position. Replacing the carbon at the 8-position or both the 5- and 8-positions with nitrogen led to about 10-fold reductions in potency. Replacement of the quinazoline ring with a quinoline, a benzo[d][1,2,3]triazine, or an isoquinoline ring showed that the nitrogen at the 1-position is important for activity, while the carbon at the 2-position can be replaced by a nitrogen and the nitrogen at the 3-position can be replaced by a carbon. Through the SAR study, several 5- or 6-substituted analogs, such as 2a and 2c, were found to have potencies approaching that of lead compound N-(4-methoxyphenyl)-N,2-dimethylquinazolin-4-amine (1g, EP128495, MPC-6827, Azixa®).     

Synthesis and antitumor activity of novel 1-substituted phenyl 3-(2-oxo-1,3,4-oxadiazol-5-yl) β-carbolines and their Mannich bases

A series of novel 1-(substituted phenyl)-3-(2-oxo-1,3,4-oxadiazol-5-yl) β-carbolines (4a–e) and the corresponding Mannich bases 5–9(a–c) were synthesized and evaluated for their in vitro antitumor activity against seven human cancer cell lines. Compounds of 4a–e series showed a broad spectrum of antitumor activity, with GI₅₀ values lower than 15 μM for five cell lines. The derivative 4b, having the N,N-dimethylaminophenyl group at C-1, displayed the highest activity with GI₅₀ in the range of 0.67–3.20 μM. A high selectivity and potent activity were observed for some Mannich bases, particularly towards resistant ovarian (NCI-ADR/RES) cell lines (5a, 5b, 6a, 6c and 9b), and ovarian (OVCAR-03) cell lines (5b, 6a, 6c, 9a, 9b and 9c). In addition, the interaction of compound 4b with DNA was investigated by using UV and fluorescence spectroscopic analysis. These studies indicated that 4b interact with ctDNA by intercalation binding.     

Design,synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of replacement of the 3-hydroxyphenyl group with pyridine or thiophene bioisosteres

The potent and selective KOR antagonist JDTic was derived from the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of pure opioid antagonists. In previous studies we reported that compounds that did not have a hydroxyl on the 3-hydroxyphenyl group and did not have methyl groups at the 3- and 4-position of the piperidine ring were still potent and selective KOR antagonists. In this study we report JDTic analogs 2, 3a–b, 4a–b, and 5, where the 3-hydroxyphenyl ring has been replaced by a 2-, 3-, or 4-pyridyl or 3-thienyl group and do not have the 3-methyl or 3,4-dimethyl groups, remain potent and selective KOR antagonists. Of these, (3R)-7-hydroxy-N-(1S)-2-methyl-[4-methyl-4-pyridine-3-yl-carboxamide (3b) had the best overall binding potency and selectivity in a [³⁵S]GTPγS functional assay, with a K_e = 0.18 nM at the KOR and 273- and 16,700-fold selectivity for the KOR relative to the MOR and DOR, respectively. Calculated physiochemical properties for 3b suggest that it will cross the blood–brain barrier.     

Highly trans-1,4 selective polymerization of 1,3-butadiene initiated by iron(III) bis(imino)pyridyl complexes

A series of 2,6-bis(imino)pyridyl iron(III) complexes of the general formula [2,6-(ArNCMe)₂C₅H₃N]FeCl₃ (Ar = -C₆H₅, 3a; 2-MeC₆H₄, 3b; 2-EtC₆H₄, 3c; 2-ⁱPrC₆H₄, 3d; cyclohexyl, 3e; 4-MeC₆H₄, 3f; 4-ⁱPrC₆H₄, 3g; 4-FC₆H₄, 3h and 4-CF₃C₆H₄, 3i), activated by alkylaluminum, MAO or MMAO, have been investigated in 1,3-butadiene polymerization. Iron(III) complex (3a), with the least steric hindrance around the metal center, gives polymer up to 99% in yield in 4 h (butadiene to iron ratio = 1000), and trans-1,4 selectivity about 94.7% at room temperature in toluene, while those (3b-3d) bearing alkyl substituents at the 2-position of each N-aryl ring exhibit much lower catalytic activity and tunable trans-1,4 selectivity. Introduction of an alkyl group at the 4-position (para-position, 3f and 3g) exerts a slightly beneficial effect on the trans-1,4 selectivity, while electronegative groups at the same position (3h and 3i) affect negatively on the activity. The effects of temperature, types of cocatalyst and Al/Fe molar ratio on the polymerization behavior are investigated. More importantly, a mechanism for forming trans-1,4 structure is also proposed.     

Exploration of the 5-bromopyrimidin-4(3H)-ones as potent inhibitors of PDE5

The substituents both at the 6-position of the 5-bromopyrimidinone ring and at the 5′-position of the phenyl ring of 5-bromopyrimidin-4(3H)-ones were explored. 5-Bromo-6-isopropyl-2-(2-propoxy-phenyl)pyrimidin-4(3H)-one was identified as a new scaffold for potent PDE5 inhibitors. The crystal structures of PDE5/2e and PDE5/10a complexes provided a structural basis for the inhibition of 5-bromopyrimidinones to PDE5. In addition, it was also found that there is a great tolerance for the substitution at the 5′-position of the phenyl ring of 5-bormopyrimidinones and the resulted compound 13a has the highest inhibition activity to PDE5 (IC₅₀, 1.7 nM).     

3-Aryl/Heteroaryl-5-amino-1-(3′,4′,5′-trimethoxybenzoyl)-1,2,4-triazoles as antimicrotubule agents. Design,synthesis, antiproliferative activity and inhibition of tubulin polymerization

Many natural and synthetic substances are known to interfere with the dynamic assembly of tubulin, preventing the formation of microtubules. In our search for potent and selective antitumor agents, a novel series of 1-(3′,4′,5′-trimethoxybenzoyl)-5-amino-1,2,4-triazoles were synthesized. The compounds had different heterocycles, including thiophene, furan or the three isomeric pyridines, and they possessed a phenyl ring bearing electron-releasing or electron-withdrawing substituents at the 3-position of the 5-amino-1,2,4-triazole system. Most of the twenty-two tested compounds showed moderate to potent antiproliferative activities against a panel of solid tumor and leukemic cell lines, with four (5j, 5k, 5o and 5p) showing strong antiproliferative activity (IC₅₀ < 1 μM) against selected cancer cells. Among them, several molecules preferentially inhibited the proliferation of leukemic cell lines, showing IC₅₀ values 2-100-fold lower for Jurkat and RS4;11 cells than those for the three lines derived from solid tumors (HeLa, HT-29 and MCF-7 cells). Compound 5k strongly inhibited tubulin assembly, with an IC₅₀ value of 0.66 μM, half that obtained in simultaneous experiments with CA-4 (IC₅₀ = 1.3 μM).     

Discovery of novel heat shock protein (Hsp90) inhibitors based on luminespib with potent antitumor activity

A series of isosteric surrogates of the 4-phenyl group in luminespib were investigated as new scaffolds of the Hsp90 inhibitor for the discovery of novel antitumor agents. Among the synthesized surrogates of isoxazole and pyrazole, compounds 4a, 5e and 12b exhibited potent Hsp90 inhibition in ATPase activity and Her2 degradation assays and significant antitumor activity in A2780 and HCT116 cell lines. Animal studies indicated that compared to luminespib, their activities were superior in A2780 or NCI-H1975 tumor xenograft models. A molecular modeling study demonstrated that compound 4a could fit nicely into the N-terminal ATP binding pocket.     

Synthesis and biological evaluation of novel synthetic chalcone derivatives as anti-tumor agents targeting Cat L and Cat K

A series of chalcone derivatives bearing benzamide or benzenesulfonamide moieties were synthesized and evaluated for their anti-tumor effect on HCT116, MCF7 and 143B cell lines in vitro. SAR analysis showed that compounds bearing a benzenesulfonamide group had greater potency than those bearing a benzamide group. It was also shown that compounds with a mono-methyl or mono-halogen group at the 3-position on the terminal phenyl ring were more effective than those with trifluoromethyl or methoxy groups. Compound 8e exhibited the most potent anti-tumor activities against HCT116, MCF7 and 143B cell lines, with IC₅₀ values of 0.597, 0.886 and 0.791 μM, respectively. Molecular docking studies and enzymatic assays demonstrated that the anti-tumor activity of compound 8e might be regulated by Cat L and Cat K.     

2-Aryl-4,5,6,7-tetrahydro-1,3-benzothiazol-7-ols as a class of antitumor agents selectively active in securin−/− cells

A series of 2-(4-aminophenyl)-4,5,6,7-tetrahydro-1,3-benzothiazol-7-ols have been developed as antitumor agents that showed high selectivity against aneuploid cell lines (vs diploid cell lines). Structure–activity relationship studies showed that a hydroxymethyl group at the 2-position of the phenyl ring increased potency and selectivity. A pyrrolidinyl group at the 4-position of the phenyl ring was comparable to a dimethylamino group. The corresponding 5-aza analogs, 2-(4-aminophenyl)-4,5,6,7-tetrahydro[1,3]thiazolo[4,5-c]pyridin-7-ols, retained potency and high level of selectivity against aneuploid cell growth (vs diploid cells). These 5-aza compounds exhibited higher water solubility and higher metabolic stability than the corresponding carba analogs. Compound 19 showed the highest potency against MCF-7 and MDA-MB-361 lines and was selected for further evaluation.     

Design,synthesis and biological evaluation of isochroman-4-one hybrids bearing piperazine moiety as antihypertensive agent candidates

7,8-Dihydroxy-3-methyl-isochromanone-4 (XJP), is a polyphenolic natural product with moderate antihypertensive activity. To obtain new agents with stronger potency and safer profile, we employed XJP and naftopidil as the lead compounds to design and synthesize a novel class of hybrids as antihypertensive agent candidates. In the present study, a series of hybrids (6a–r) of XJP bearing arylpiperazine moiety, which is identified as the pharmacophore of naftopidil, were designed and synthesized as novel α₁-adrenergic receptor antagonists. The biological evaluation showed that target compounds 6c, 6e, 6f, 6g, 6h, 6m and 6q possessed potent in vitro vasodilation potency and α₁-adrenergic receptor antagonistic activity. Furthermore, the most potent compound 6e significantly reduced the systolic and diastolic blood pressure in spontaneously hypertensive rats (SHRs), which was comparable to that of naftopidil, and it had no observable effects on the basal heart rate, suggesting that 6e deserves to be further investigated as a potential clinical candidate for the treatment of hypertension.     

Discovery of 1-benzoyl-3-cyanopyrrolo[1,2-a]quinolines as a new series of apoptosis inducers using a cell- and caspase-based high-throughput screening assay. 2: Structure–activity relationships of the 4-, 5-, 6-, 7- and 8-positions

As a continuation of our efforts to discover and develop the apoptosis inducing 1-benzoyl-3-cyanopyrrolo[1,2-a]quinolines as potential anticancer agents, we explored substitutions at the 4-, 5-, 6-, 7- and 8-positions of pyrrolo[1,2-a]quinoline. SAR studies showed that substitution at the 6-position by a small group such as Cl resulted in potent compounds. Substitutions at the 5- and 8-positions were tolerated while substitutions at the 4- and 7-position led to inactive compounds. Several compounds, including 2c, 3a, 3b and 3f, were found to be highly active against human breast cancer cells T47D with EC₅₀ values of 0.053–0.080 μM, but much less active against human colon cancer cells HCT116 and hepatocellular carcinoma cancer cells SNU398 in the caspase activation assay. Compound 3f also was found to be highly active with a GI₅₀ value of 0.018 μM against T47D cells in a growth inhibition assay.     

Novel DNA-directed alkylating agents: Design,synthesis and potent antitumor effect of phenyl N-mustard-9-anilinoacridine conjugates via a carbamate or carbonate linker

A series of phenyl N-mustard-9-anilinoacridine conjugates via a carbamate or carbonate linker was synthesized for antitumor evaluation. The carbamate or carbonate linker is able to lower the reactivity of the phenyl N-mustard pharmacophore and thus, these conjugates are rather chemically stable. The in vitro studies revealed that these derivatives possessed significant cytotoxicity with IC₅₀ in sub-micromolar range in inhibiting human lymphoblastic leukemia (CCRF-CEM), breast carcinoma (MX-1), colon carcinoma (HCT-116) and human non-small cell lung cancer (H1299) cell growth in vitro. Compounds 10a, 10b, 10e, 10i, and 15a were selected for evaluating their antitumor activity in nude mice bearing MX-1 and HCT-116 xenografts. Remarkably, total tumor remission was achieved by these agents with only one cycle of treatment. Interestingly, no tumor relapse was found in mice treated with 10a over 129 days. This agent is capable of inducing DNA interstrand cross-linking in human non-small lung cancer H1299 cells in a dose dependent manner by modified comet assay and has a long half-life in rat plasma.     

Imidazolylchromanone oxime ethers as potential anticonvulsant agents: Anticonvulsive evaluation in PTZ-kindling model of epilepsy and SAR study

As a continuation of our efforts to develop the azolylchromanone derivatives as potential anticonvulsant agents, we explored (Z)- and (E)-oxime ether derivatives of imidazolylchromanones bearing different lipophilic O-benzyl groups and tested their anticonvulsant activities in PTZ-kindling model of epilepsy. O-(2,4-Dichlorobenzyl) oximes 8a, 16a and 20a were significantly effective in delaying the onset of the PTZ-evoked seizures at the dose of 30 mg/kg in kindled animals. The most effective compounds in delaying seizures were 7-chlorochromanone-O-(2,4-dichlorobenzyl) oximes 8a and 20a. SAR studies showed that introduction of a chlorine atom to the 7-position and/or a methyl group to the 2-position of the chroman ring resulted in an improvement of anti-seizure efficacy in O-(2,4-dichlorobenzyl) oxime series.     

Discovery of 1,2,3,4-tetrahydropyrimido[1,2-a]benzimidazoles as novel class of corticotropin releasing factor 1 receptor antagonists

A new class of corticotropin releasing factor 1 (CRF₁) receptor antagonists characterized by a tricyclic core ring was designed and synthesized. Novel tricyclic derivatives 2a–e were designed as CRF₁ receptor antagonists based on conformation analysis of our original 2-anilinobenzimidazole CRF₁ receptor antagonist. The synthesized tricyclic derivatives 2a–e showed CRF₁ receptor binding activity with IC₅₀ values of less than 400?nM, and the 1,2,3,4-tetrahydropyrimido-[1,2-a]benzimidazole derivative 2e was selected as a lead compound with potent in vitro CRF₁ receptor binding activity (IC₅₀?=?7.1?nM). To optimize the pharmacokinetic profiles of lead compound 2e, we explored suitable substituents on the 1-position and 6-position, leading to the identification of compound 42c-R, which exhibited potent CRF₁ receptor binding activity (IC₅₀?=?58?nM) with good oral bioavailability (F?=?68% in rats). Compound 42c-R exhibited dose-dependent inhibition of [¹²⁵I]-CRF binding in the frontal cortex (5 and 10?mg/kg, p.o.) as well as suppression of locomotor activation induced by intracerebroventricular administration of CRF in rats (10?mg/kg, p.o.). These results suggest that compound 42c-R successfully binds CRF₁ receptors in the brain and exhibits the potential to be further examined for clinical studies.     

Synthesis of spirocyclic σ1 receptor ligands as potential PET radiotracers,structure–affinity relationships and in vitro metabolic stability

Several 3H-spiro[[2]benzofuran-1,4′-piperidines] bearing a p-fluorobenzyl residue at the N-atom and various substituents in position 3 of the benzofuran system were synthesized. The crucial reaction steps are the addition of a lithiated benzaldehyde derivative to the p-fluorobenzylpiperidone 5 and the BF₃·OEt₂ catalyzed substitution of the methoxy group of 2a by various nucleophiles. Structure–affinity relationship studies revealed that compounds with two protons (2d), a methoxy group (2a), and a cyano group (2e) in position 3 possess subnanomolar σ₁ affinity (K_i = 0.18 nM, 0.79 nM, 0.86 nM) and high selectivity against the σ₂ subtype. The metabolites of 2a, 2d, and 2e, which were formed upon incubation with rat liver microsomes, were identified. Additionally, the rate of metabolic degradation of 2a, 2d, and 2e was determined and compared with the degradation rate of the non-fluorinated spirocyclic compound 1. For the synthesis of the potential PET tracers [¹⁸F]2a and [¹⁸F]2e two different radiosynthetic approaches were followed.     

Synthesis,antitumor activity,and cytotoxicity of 4-substituted 1-benzyl-5-diphenylstibano-1H-1,2,3-triazoles

Trisubstituted 5-organostibano-1H-1,2,3-triazoles (3a–f) were synthesized by the Cu-catalyzed azide-alkyne cycloaddition of various ethynylstibanes (1) with benzylazide (2) in the presence of CuBr (5 mol%) under aerobic conditions. The reaction of 5-stibanotriazoles with HCl afforded C5-unsubstituted 1,2,3-triazoles (4a–f). The antitumor activity of trisubstituted 5-organostibano-1H-1,2,3-triazoles (3a–f) and their 5-unsubstituted 1,2,3-triazoles (4a–f) were evaluated in several tumor cell lines. All 5-stibanotriazoles (3a–f) exerted an excellent antitumor activity. On the contrary, 5-unsubstituted 1,2,3-triazoles (4a–f) without a diphenylantimony group in the molecule exhibited very low antitumor activity compared with 5-stibanotriazoles (3a–f). In compounds of both the series, the substituted 4-butyl group appeared to decrease antitumor activity. However, results suggested that organometal (antimony) in the molecule was required for greater antitumor activity. In addition, all 5-stibanotriazoles (3a–f), but not all 5-unsubstituted 1,2,3-triazoles (4a–f), exhibited cytotoxicity in normal vascular endothelial cells derived from bovine aorta. Among the compounds (3b–e) that exhibited excellent antitumor activity, those with 4-methylphenyl (3b) and 1-cyclohexenyl (3e) showed relatively low cytotoxicity to vascular endothelial cells. Together, these results suggest that trisubstituted 5-organostibano-1H-1,2,3-triazoles, including compounds 3b and 3e, may serve as potential anticancer therapeutic drugs in the future.     

Combination of 4-anilinoquinazoline,arylurea and tertiary amine moiety to discover novel anticancer agents

In present study, 4-anilinoquinazolines scaffold, arylurea and tertiary amine moiety were combined to design, synthesize gefitinib analogs and discover novel anticancer agents. A series of 4-anilinoquinazoline derivatives (1, 2, 3 and 4) bearing arylurea and tertiary amine moiety at its 6-position were synthesized. Their antiproliferative activities in vitro were evaluated via MTT assay against A431 cell and A549 cell. The SAR of the title compounds was discussed. The compounds 2d, 2i and 2j with potent antiproliferative activities were evaluated their inhibitory activity against EGFR-TK. Compound 2j displayed potent inhibitory activity against EGFR-TK. In addition, compound 2j, at 50 mg/kg, can completely inhibit cancer growth in established nude mouse A549 xenograft model in vivo. These results suggest that the 4-anilinoquinazoline derivatives bearing diarylurea and tertiary amino moiety at its 6-position can serve as anticancer agents and EGFR inhibitors.