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.     

Synthesis and biological evaluation of salicylic acid and N-acetyl-2-carboxybenzenesulfonamide regioisomers possessing a N-difluoromethyl-1,2-dihydropyrid-2-one pharmacophore: Dual inhibitors of cyclooxygenases and 5-lipoxygenase with anti-inflammatory activity

A novel class of salicylic acid and N-acetyl-2-carboxybenzenesulfonamide regioisomers possessing a N-difluoromethyl-1,2-dihydropyrid-2-one pharmacophore attached to its C-4 or C-5 position was designed for evaluation as anti-inflammatory (AI) agents. Replacement of the 2,4-difluorophenyl ring in diflunisal by the N-difluoromethyl-1,2-dihydropyrid-2-one moiety provided compounds showing dual selective cyclooxygenase-2 (COX-2)/5-lipoxygenase (5-LOX) inhibitory activities. AI structure–activity studies showed that the C-4 (14a) and C-5 (14b) salicylate regioisomers were 1.4- and 1.6-fold more potent than aspirin, and the C-5 N-acetyl-2-carboxybenzenesulfonamide regioisomer (22b) was 1.3- and 2.8-fold more potent than ibuprofen and aspirin, respectively. In vivo ulcer index (UI) studies showed that the 4- and 5-(N-difluoromethyl-1,2-dihydropyrid-2-one-4-yl)salicylic acids (14a and 14b) were completely non-ulcerogenic since no gastric lesions were present (UI = 0) relative to aspirin (UI = 57) at an equivalent μmol/kg oral dose. The N-difluoromethyl-1,2-dihydropyridin-2-one moiety provides a novel 5-LOX pharmacophore for the design of cyclic hydroxamic mimetics for exploitation in the development of dual COX-2/5-LOX inhibitory AI drugs.     

Design and synthesis of N-methylmaleimide indolocarbazole bearing modified 2-acetamino acid moieties as Topoisomerase I inhibitors

A novel series of N-methylmaleimide indolocarbazole derivatives bearing modified 2-acetamino acid moieties are first reported. The cytotoxic effects of these compounds were tested in five human tumor cell lines. The potent compounds 9a, 9b, 9d, and 9e have been further evaluated for their effect on Topoisomerase I (TOPO I) and cancer cell cycle. It is concluded that the indolocarbazoles with alkyl piperazine or morpholine substituent groups instead of esters or glycosyl residues would have better activities against tumors.     

Effect of carbohydrate amino group modifications on the cytotoxicity of glycosylated 2-phenyl-benzo[b]thiophenes and 2-phenyl-benzo[b]furans

In previous studies, we have identified a family of benzo[b]furan and benzo[b]thiophene derivatives linked to amino sugars (1-6) that are cytotoxic to a range of cancer cell lines. We describe here an exploration of the effect of structural modification of the amino group on one of the carbohydrate residues (4-amino-2,3,4,6-tetradeoxy-α-l-threo-hexopyranoside) on in vitro cytotoxicity. It has been found that maintaining at least one basic functional group around the C-4 position in the carbohydrate moiety is crucial for cytotoxicity. Furthermore, it appears that modifications around the C-4 position are limited by suitable hydrophilic/hydrophobic and/or ionic interactions, as well as steric constraints.     

Synthesis,in vitro and in vivo evaluation of 3-arylisoquinolinamines as potent antitumor agents

In the search for potent water-soluble 3-arylisoquinolines, several 3-arylisoquinolinamines were designed and synthesized. Various substituted 3-arylisoquinolinamines exhibited strong cytotoxic activity against eight different human cancer cell lines. In particular, C-6 or C-7 dimethylamino-substituted 3-arylisoquinolinamines displayed stronger potency than the lead compound 7a. Interestingly, compounds 7b and 7c showed more effective activity against paclitaxel-resistant HCT-15 human colorectal cancer cell lines when compared to the original cytotoxic cancer drug, paclitaxel. We analyzed the cell cycle dynamics by flow cytometry and found that treatment of human HCT-15 cells with 3-arylisoquinolinamine 7b blocked or delayed the progression of cells from G0/G1 phase into S phase, and induced cell death. Treatment with compound 7b also significantly inhibited the growth of tumors and enhanced tumor regression in a paclitaxel-resistant HCT-15 xenograft model.     

25-Methoxylprotopanaxadiol derivatives and their anti-proliferative activities

(20R)-25-Methoxyl-dammarane-3β,12β,20-triol (25-OCH₃-PPD) is a dammarane-type sapogenin showing anti-proliferative potential. In our study, two series of analogs substituted at the C-3 or C-3 and C-12 positions with fatty acids were prepared conveniently. The cytotoxic activity of these compounds was evaluated using four different human tumor cell lines (A549, Hela, HT-29 and MCF-7) and a normal cell line (IOSE144). As compared with 25-OCH₃-PPD, compounds 1a, 1b, 2a and 2b showed better anti-proliferative activities against all tumor cell lines and all the derivatives, with low toxicities in the normal cell line. Compound 1a (C-3 monoformiate) exhibited the strongest activity with the IC₅₀ value of 5.2 μM towards HT29 cells. The results indicated that the difference in the substituents may affect the anti-proliferative activity of the compounds. The longer the side chain of 25-OCH₃-PPD is, the lower the anti-proliferative activity would be. This information may be useful for evaluating the structure–activity relationship of other dammarane-type sapogenins and for development of novel antineoplastic agents.     

Synthesis of N4-(substituted phenyl)-N4-alkyl/desalkyl-9H-pyrimido[4,5-b]indole-2,4-diamines and identification of new microtubule disrupting compounds that are effective against multidrug resistant cells

A series of fourteen N⁴-(substituted phenyl)-N⁴-alkyl/desalkyl-9H-pyrimido[4,5-b]indole-2,4-diamines was synthesized as potential microtubule targeting agents. The synthesis involved a Fisher indole cyclization of 2-amino-6-hydrazinylpyrimidin-4(3H)-one with cyclohexanone, followed by oxidation, chlorination and displacement with appropriate anilines. Compounds 6, 14 and 15 had low nanomolar potency against MDA-MB-435 tumor cells and depolymerized microtubules. Compound 6 additionally had nanomolar GI₅₀ values against 57 of the NCI 60-tumor panel cell lines. Mechanistic studies showed that 6 inhibited tubulin polymerization and [³H]colchicine binding to tubulin. The most potent compounds were all effective in cells expressing P-glycoprotein or the βIII isotype of tubulin, which have been associated with clinical drug resistance. Modeling studies provided the potential interactions of 6, 14 and 15 within the colchicine site.     

Synthesis and evaluation of bioactive naphthoquinones from the Brazilian medicinal plant, Tabebuia avellanedae

A series of naphthoquinones based on the naphtho[2,3-b]furan-4,9-dione skeleton such as (−)-5-hydroxy-2-(1′-hydoxyethyl)naphtho[2,3-b]furan-4,9-dione (1) and its positional isomer, (−)-8-hydroxy-2-(1′-hydoxyethyl)naphtho[2,3-b]furan-4,9-dione (2), which are secondary metabolites found in the inner bark of Tabebuia avellanedae, were stereoselectively synthesized and their biological activities were evaluated in conjunction with those of their corresponding enantiomers. Compound 1 exhibited potent antiproliferative effect against several human tumor cell lines, but its effect against some human normal cell lines was much lower than that of mitomycin. On the other hand, its enantiomer (R)-1 was less active toward the above tumor cell lines than 1. The antiproliferative effect of 2 against all tumor cell lines was significantly reduced. These results indicated the presence of the phenolic hydroxy group at C-5 is of great important for increasing antiproliferative effect. In addition, 1 also showed higher cancer chemopreventive activity than 2, while there were no significant differences between 1 and 2 in antimicrobial activity. Both compounds displayed modest antifungal and antibacterial activity (Gram-positive bacteria), whereas they were inactive against Gram-negative bacteria.     

Design and synthesis of novel spin-labeled camptothecin derivatives as potent cytotoxic agents

In our continuing search for natural product-based spin-labeled antitumor drugs, 20 novel spin-labeled camptothecin derivatives were synthesized via a Cu-catalyzed one pot reaction and evaluated for cytotoxicity against four human tumor cell lines (A-549, MDA-MB-231, KB, and KBvin). Eighteen of the target compounds (9a, 9b, 9d–9k, 9m–9t) exhibited significant in vitro antiproliferative activity against these four tested tumor cell lines. Compounds 9e and 9j (IC₅₀ 0.057 and 0.072 μM, respectively) displayed the greatest cytotoxicity against the multidrug-resistant (MDR) KBvin cell line and merit further development into preclinical and clinical drug candidates for treating cancer including MDR phenotype.     

Synthesis and cytotoxicity of novel imidazo[4,5-d]azepine compounds derived from marine natural product ceratamine A

A series of novel imidazo[4,5-d]azepine compounds derived from marine natural product ceratamine A were designed and synthesized in 7 steps. Most compounds exhibited comparable cytotoxicity against five human cancer cell lines (HCT-116, HepG2, BGC-823, A549 and A2780) to natural product ceratamine A. Compound 1k, bearing methoxy group at C-14, C-15 and C-16, showed the best in vitro cytotoxicity, which was better than ceratamine A. The structure and activity relationships study showed that the benzyloxymethyl group on N-3 played an important role on the cytotoxicity.     

Design,synthesis, and evaluation of a water-soluble antofine analogue with high antiproliferative and antitumor activity

New water soluble antofine C-13a analogues were designed, synthesized, and evaluated for antiproliferative activity against cancer cells. Particularly, (?)-(R)-13a-hydroxymethylantofine ((?)-(R)-4b) demonstrated notable growth inhibition against a panel of human cancer cell lines. This growth inhibition was associated with the arrest of the cell cycle in the G0/G1 phases and suppression of mTOR signaling in human lung A549 cancer cells. Compound (?)-(R)-4b also overcame paclitaxel-resistance in human lung cancer cells (A549-Pa) by suppressing P-glycoprotein expression. Furthermore, compound (?)-(R)-4b significantly inhibited the tumor growth of A549 and A549-Pa xenografts in a nude mouse model, which suggests it is a promising novel antitumor agent with sufficient aqueous solubility.     

Suzuki coupling based synthesis and in vitro cytotoxic evaluation of 7-heteroaryl-substituted camptothecin analogs

In an effort to discover potent antitumor agents, a series of novel C-7-heteroaryl-substituted camptothecin derivatives were designed and synthesized via microwave-promoted Suzuki coupling reaction. These analogs were then assessed for cytotoxicity against three human tumor cell lines, A549, HCT116, HT-29, and inhibitory effects on topoisomerase I. All of the new compounds showed potent inhibition of human tumor cell growth, among which compound 10a showed higher cytotoxic activity than that of SN-38. Furthermore, this series of compounds retained or enhanced Topo I inhibition.     

Novel C-6 substituted and unsubstituted pregnane derivatives as 5α-reductase inhibitors and their effect on hamster flank organs diameter size

The present study is addressed to ascertain the inhibitory effect of several progesterone derivatives having a chlorine substituent at C-6 (12a–12d), 15 with a bromine substituent at C-6 and 14a–14d, without any halogen atom at C-6 all having an ester side chain at C-17 (benzoate ester bearing a Cl, F and a Br atom at C-4 position of the phenyl ring) on the 5α-reductase enzyme activity present in human prostate. In addition, it was also of interest to investigate the pharmacological effect on hamster flank organs diameter size.In order to study the structure–activity relationships of steroids 12a–12d, 14a–14d and 15 we determined the concentration of these steroids that inhibited 50% of the activity of human prostate 5α-reductase enzyme (IC₅₀), as well as the in vivo effect of these compounds in the hamster flank organs diameter size. We also ascertained, the capacity of these steroids to bind to the androgen receptors present in the rat prostate cytosol using labeled mibolerone (MIB) for monitoring the binding to the androgen receptor.The results from this study indicated that compounds 12a–12d (having a chlorine substituent at C-6), 14a–14d (lacking a halogen atom at C-6), 13 and 15 (having a bromine atom at C-6) showed an increased antiandrogenic effect (lower value for the diameter of the flank organs) as compared to the flank organs from testosterone-treated hamsters. On the other hand, the series of compounds containing a chlorine substituent at C-6 compounds (12a–12d) showed a higher antiandrogenic activity as compared to the compounds lacking a halogen atom at C-6 (14a, 14b and 14d). Although compounds 13 and 15 decreased the flank organs diameter size, however, this increase was not statistically significant as compared to that of the commercially available product finasteride. The steroidal derivatives 13, 14a–14d (lacking the chlorine substituent at C-6) and 15 (having a bromine atom at C-6) exhibited a higher 5α-reductase inhibitory activity (lower IC₅₀ values) as compared to the series of compounds 12a–12d having the halogen substituent at C-6.Finasteride reduced the diameter size of the flank organs. The effect of this steroid and compounds 12a–12d, 13, 14a–14d and 15 on hamster flank organs can be explained by the fact that these steroids did not bind to the androgens receptor, which indicates that its mechanism of action is an inhibiting for the 5α-reductase activity. This enzyme is present in the hamster flank organs and was inhibited by the novel steroids in the human prostate homogenates.     

Synthesis and biological evaluation of indomethacin analogs possessing a N-difluoromethyl-1,2-dihydropyrid-2-one ring system: A search for novel cyclooxygenase and lipoxygenase inhibitors

A novel class of indomethacin analogs were synthesized wherein a N-difluoromethyl-1,2-dihydropyrid-2-one moiety (5-LOX pharmacophore) was attached at its C-4 or C-5 position via either a CO (14a–b) or CH₂ (19a–b) linker to the indole N¹-position. In this regard, replacement of the 4-chlorobenzoyl group present in indomethacin by N-difluoromethyl-1,2-dihydropyrid-2-one-4-(or 5-)carbonyl and N-difluoromethyl-1,2-dihydropyrid-2-one-4-yl(or 5-yl)methylene moieties furnished compounds showing no inhibitory activities against the COX-2/5-LOX enzymes (except for the weak but selective COX-2 inhibitor 19a, COX-2 IC₅₀ = 31 μM), and moderate in vivo anti-inflammatory activities (except for the methylene compound 19a that was inactive). These structure–activity data indicate replacement of the 4-chlorobenzoyl group present in indomethacin by a N-difluoromethyl-1,2-dihydropyrid-2-one ring system connected by a CO or CH₂ linker is not a suitable approach for the design of dual COX-2/5-LOX inhibitory analogs of indomethacin.     

Design and synthesis of anti-breast cancer agents from 4-piperazinylquinoline: A hybrid pharmacophore approach

A novel class of 4-piperazinylquinoline derivatives based on the isatin scaffold were designed by molecular hybridization approach and synthesized for biological evaluation. Subsequently, the compounds were examined for their cytotoxic effects on two human breast tumor cell lines, MDA-MB468 and MCF7, and two non-cancer breast epithelial cell lines, 184B5 and MCF10A. Although all compounds examined were quite effective on the breast cancer cell lines examined, the compound 4-bromo-1-[4-(7-chloro-quinolin-4-yl)-piperazin-1-ylmethyl]-1H-indole-2,3-dione (5b) and N¹-[4-(7-trifluoromethyl-quinolin-4-yl)]-piperazin-1-ylmethyl-4-chloro-1H-indole-2,3-dione-3-thiosemicarbazone (8a) emerged as the most active among this series. It appeared that both 5b and 8a caused apoptosis to MCF7 cancer cells, but not MCF10A non-cancer cells. Thus, 4-piperazinylquinoline linked isatin analog can serve as the prototype molecule for further development of a new class of anti-breast cancer agents.     

Furanoeremophilanes from Petasites niveus: High solvolytic reactivity at the C-6β position bearing an α,β-unsaturated ester group

Rhizomes and roots of Petasites niveus gave some new cis-fused, unstable furanoeremophilanes bearing the senecioyloxy group either at C-2β or at C-3β and C-6β, besides the known, unstable 2β-pangeloyloxy-10β-H-furanoeremophilane (furanojaponin) and 3β,6β-diangeloyloxy-10β-H-furanoeremophilane. The senecioyloxy or angeloyloxy group at C-6 was easily replaced in alcohols, by the alkoxyl group, leading in medium yields to the ethers with retention of configuration at C-6. Most of the above terpenes prefer the ‘non-steroid-like’ conformation.     

Synthesis and biological evaluation of 2-amino-5-aryl-3-benzylthiopyridine scaffold based potent c-Met inhibitors

A series of 2-amino-N-benzylpyridine-3-carboxnamides, 2-amino-N-benzylpyridine-3-sulfonamides and 2-amino-3-benzylthiopyridines against c-Met were designed by means of bioisosteric replacement and docking analysis. Optimization of the 2-amino-3-benzylthiopyridine scaffold led to the identification of compound (R)-10b displaying c-Met inhibition with an IC₅₀ up to 7.7 nM. In the cytotoxic evaluation, compound (R)-10b effectively inhibited the proliferation of c-Met addictive human cancer cell lines (IC₅₀ from 0.19 to 0.71 μM) and c-Met activation-mediated cell metastasis. At a dose of 100 mg/Kg, (R)-10b evidently inhibited tumor growth (45%) in NIH-3T3/TPR-Met xenograft model. Of note, (R)-10b could overcome c-Met-activation mediated gefitinib-resistance, which indicated its potential use for drug combination. Taken together, 2-amino-3-benzylthiopyridine scaffold was first disclosed and exhibited promising pharmacological profiles against c-Met, which left room for further exploration.     

Cytotoxicity of new pyrazino[1,2-b]isoquinoline and 6,15-iminoisoquino[3,2-b]3-benzazocine compounds

Looking for optimised analogues of compound 2 that might be useful in colon cancer therapy, we here explore the in vitro cytotoxicity against MDA-MB 231 human breast carcinoma, A-549 human lung carcinoma and HT-29 human colon carcinoma cell lines of several analogues and derivatives. The effect of the R₂-substituent and/or the introduction of an arylmethyl side-chain at C-3, as well as the presence of a double bond in the skeleton or a methoxy group at C-1 have been investigated. New 6,15-iminoisoquino[3,2-b]3-benzazocine compounds, related to the saframycin family, in which the C(7)–N(8)–C(9)-substructure contains a lactam function, a fused oxazolidine or an aminonitrile function were also studied, and many of them showed low micromolar GI₅₀ values.     

Facile synthesis of SSR180575 and discovery of 7-chloro-N,N,5-trimethyl-4-oxo-3(6-[18F]fluoropyridin-2-yl)-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide,a potent pyridazinoindole ligand for PET imaging of TSPO in cancer

A novel synthesis of the translocator protein (TSPO) ligand 7-chloro-N,N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide (SSR180575, 3) was achieved in four steps from commercially available starting materials. Focused structure–activity relationship development about the pyridazinoindole ring at the N3 position led to the discovery of 7-chloro-N,N,5-trimethyl-4-oxo-3(6-fluoropyridin-2-yl)-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide (14), a novel ligand of comparable affinity. Radiolabeling with fluorine-18 (¹⁸F) yielded 7-chloro-N,N,5-trimethyl-4-oxo-3(6-[¹⁸F]fluoropyridin-2-yl)-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide ([¹⁸F]-14) in high radiochemical yield and specific activity. In vivo studies of [¹⁸F]-14 revealed this agent as a promising probe for molecular imaging of glioma.     

A novel method for the methylation of heterocyclic amino groups. Conversion of guanosine into its 2-N-methyl- and 2-N,2-N-dimethyl derivatives

The heterocyclic amino-compounds 11a, 13a, 13b, and 17 reacted with formaldehyde and p-thiocresol (14) in alcoholic solution to give the corresponding N-methylphenylthiomethyl derivatives (16, 15a, 15b, and 18a, respectively) in satisfactory to good yields. The reactions were catalyzed by acetic acid. 2-N-Methylguanosine (6a) was obtained in good yield by treatment of 15b with sodium borohydride followed by acidic hydrolysis, or alternatively by Raney nickel desulfurization of 15a followed by ammonolysis of the product. Sodium borohydride reduction of 18a gave 21 in good yield. 2-N,2-N-Dimethylguanosine (6b) was obtained from 19a in three steps.