Potent in vitro anticancer activities of ring-expanded ("fat") nucleosides containing the imidazo[4,5-e][1,3]diazepine ring system

The ring-expanded ("fat") nucleoside, 4,8-diamino-6-imino-6H-1-beta-D-ribofuranosylimidazo[4,5-e][1,3]diazepine (1) and its 2',3',5'-tri-O-benzoyl derivative (2) exhibited potent broad spectrum anticancer activities in vitro against a wide variety of human tumor cell lines. The tribenzoyl derivative 2 was found to be considerably more active than the parent nucleoside 1. Further studies using human prostate cancer cells PC-3 and DU-145 suggest that the treatment of exponentially growing culture cells with 1 and 2 leads to marked loss of cell viability in a dose-dependent manner.     

Synthesis of 4-substituted imidazo[4,5-d][1,2,3]triazine (2-azapurine)nucleosides

Several methods for functionalization of the 4-position of imidazo[4,5-d][1,2,3]triazin-4-one were investigated. These investigations were successful and led to the preparation of 4-amino, 4-triazol-1-yl, 4-methoxy, 4-methylthio, 4-methylamino, 4-thio, 4-nitrobenzyl, and 4-unsubstituted 9-(beta-D-ribofuranosyl)-imidazo-[4,5-d][1,2,3]triazine (2-azapurine ribosides). The 4-unsubstituted compound (19) was slightly active against HCMV in plaque and yield reduction experiments and was not cytotoxic at 100 microM. The methylamino (15), hydrazino (16), and p-nitrobenzylthio (20) were inactive against HCMV but slightly cytotoxic. The thiomethyl-substituted analog (21) was the most active with activity comparable to ganciclovir but with greater cytotoxicity. We conclude that even though none of the tested compounds had antiviral activity superior to ganciclovir, the new synthetic methods will provide a route to more interesting compounds.     

Synthesis and anti-HIV evaluation of 2',3'-dideoxy imidazo- and nu-triazolo[4,5-d]pyridazine nucleosides

The syntheses of the 2'-deoxy and 2',3'-dideoxynucleosides of 2,8-diaza-3-deazainosine and the 2',3'-dideoxynucleoside of 2-aza-3-deazainosine were achieved and the pathways leading to these novel nucleosides are described. The preparation of the 2',3'-dideoxynucleoside (1) of 2-aza-3-deazainosine involved deoxygenation of the 2'-deoxy-3'-imidazolide intermediate with n-Bu3SnH and AlBN. The latter nucleoside was synthesized from the known 2'-deoxy derivative of 2-aza-3-deazainosine. The three-step synthesis of 1 from the 2'-deoxy analogue was accomplished in 40% overall yield. Rather than synthesize the corresponding 2',3'-dideoxynucleoside (2) of 2,8-diaza-3-deazainosine in the same manner, i.e. deoxygenation of the 2'-deoxynucleoside, a more cost-effective route was chosen. This pathway involved reductive cleavage of the 5'-protected, 2',3'-thiocarbonate derivative to furnish a mixture of the 2'- and 3'-deoxy isomers. This mixture was not separated, but was deoxygenated by the aforementioned imidazolide method. Using this methodology, 2 was prepared in 23% overall yield from 2,8-diaza-3-deazainosine. Nucleosides 1 and 2 were evaluated for antiretroviral activity and were found to be inactive.     

A novel,broad-spectrum anticancer compound containing the imidazo[4,5-e][1,3]diazepine ring system

Synthesis and broad-spectrum anticancer activity of a novel heterocyclic compound 1 containing the title imidazo[4,5-e][1,3]diazepine ring system have been reported. The compound shows potent in vitro antitumor activity with low micromolar IC₅₀’s against prostate, lung, breast, and ovarian cancer cell lines tested. The long alkyl chain attached to the six-position of the heterocyclic ring of 1 appears to be necessary for the observed biological activity.     

Synthesis and Biological Activity of Certain 4-Substituted Imidazo[4,5-d]Pyridazine Nucleosides

Abstract

Purine analogues and derivatives exhibit a broad range of pharmacological activities and are used in the chemotherapy of cancer, parasitic and viral infections, and for the suppression of immune responses. Undoubtedly, this wide range of biological activities reflect an equally wide number of biochemical sites of action, one of which is the purine de novo pathway. New agents which can either serve as inhibitors of enzymes involved in this pathway or as substrates are continually sought. The unique series of nucleosides described herein should meet these desired needs.

The synthesis of 1involved glycosylation of a suitably 4,5-disubstituted imidazole and subsequent cyclization of the imidazole nucleoside so formed to the imidazo[4,5-d]pyridazine nucleoside. Such methodology was successfully employed^1,2 in the preparation of certain 4,7-disubstituted imidazo[4,5-d]pyridazine nucleosides. Chlorination of 1furnished 4-chloro-1-(2,3,5-tri-O-acetyl-β-D-ribo-furanosyl)imidazo[4,5-dlpyridazine (2) in 80% yield. This versatile intermediate can now serve as a precursor to a variety of 4-substituted imidazo[4,5-d]pyridazine nucleosides.     

Novel imidazo[1,2-c]pyrimidine base-modified nucleosides: synthesis and antiviral evaluation

The preparation of a series of novel 6-(beta-D-ribofuranosyl)-2-alkyl/aryl-6H-imidazo[1,2-c]pyrimidin-5-one nucleosides and the 2-nitrile nucleosides, 6-(beta-D-ribofuranosyl)-5-oxo-5,6-dihydro-imidazo[1,2-c]pyrimidine-2-carbonitrile and 2R and 2S isomers of 6-(beta-D-ribofuranosyl)-5-oxo-2,3,5,6-tetrahydro-imidazo[1,2-c]pyrimidine-2-carbonitrile, is described using two synthetic approaches. The nucleoside mimetics described were evaluated against a wide range of viral types and strains in cell culture. With the exception of one nucleoside, which displayed anti-CMV activity at toxic concentrations, none of the compounds showed antiviral activity most likely due to a lack of substrate recognition by viral and/or cellular nucleoside kinases.     

Structure-activity relationship studies on anti-HCV activity of ring-expanded ('fat') nucleobase analogues containing the imidazo[4,5-e][1,3]diazepine-4,8-dione ring system

In continuation of our structure-activity relationship studies on anti-HCV activity of the title imidazo[4,5-e][1,3]diazepine ring system, we report here the synthesis and effect on biological activity of introducing hydrophobic substituents at the 2-position of the heterocycle. Our results suggest that there is no particular advantage to that end as the observed antiviral activity of the test compounds was lower than that of the unmodified 2-bromo derivative used for comparison. The activity/toxicity profile of all target compounds, however, was still better than that of the reference compound ribavirin used in the antiviral assay, but not as good as that of interferon-alpha, the other reference compound used in the assay.     

Solid-phase parallel synthesis of 4-beta-D-ribofuranosylpyrazolo[4,3-d]pyrimidine nucleosides

The synthesis of pyrazolo[4,3-d]pyrimidine nucleoside library using solid-phase parallel synthesis methodology is described. Glycosylation of the trimethylsilyl (TMS) derivative of 1- and 2-(methyl)-1H and 2H-pyrazolo[4,3-d]pyrimidine-5,7-(4H, 6H)-dione (5) with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose in the presence of TMS triflate provided two novel protected nucleosides 6 and 7. The structures of 6 and 7 were assigned by 1H and 2D NMR experiments. Nucleosides 6 and 7 were then transformed to the key intermediates 12 and 15 respectively. Reaction of 12 and 15 with MMTCl resin in the presence of 2,6-lutidine afforded the necessary scaffolds B and C. Different amines (96) were introduced selectively by nucleophilic substitution on scaffolds B and C using solid-phase parallel semi-automated synthesizer. Cleavage of the products from the solid support with 30% HFIP in a parallel fashion yielded nucleoside libraries simultaneously, and they were analyzed and characterized by high-throughput LC-MS.     

in vitro inhibition of the measles virus by novel ring-expanded ('fat') nucleoside analogues containing the imidazo[4,5-e]diazepine ring system

The synthesis and in vitro anti-measles virus (anti-MV) activity of a class of ring-expanded ('fat') nucleoside analogues (1-4) containing the title heterocyclic ring system are reported. The target compounds were synthesized by base-catalyzed condensations of 4,5-dicarboxylic acid esters of the appropriately substituted imidazole-1-ribosides with suitably substituted guanidine derivatives. Compounds were screened for anti-MV activity in African green monkey kidney cells (CV-1), employing ribavirin as the control standard. While the parent compound 1 itself failed to show any significant antiviral activity against MV, its analogues containing hydrophobic substituents at the 2-position (2) or the 6-position (4) showed promising antiviral activity at submicromolar or micromolar concentration levels with no apparent toxicity to the host cell line. Both compounds showed higher anti-MV activity than the control drug ribavirin.     

Synthesis of imidazo[4,5-d][1,3]thiazine ribosides and related compounds of biological interest

Several tri-O -acetyl-1-beta-D -ribofuranosyl- and 2-acetoxyethoxymethylimidazo[4,5-d][1,3]thiazine derivatives 5-10 were synthesized from imidazo[4,5-d][1,3]thiazine 4 and tetra-O -acetyl-beta-D -ribofuranose or 2-acetoxyethoxymethyl acetate by fusion method. In each case, depending on the substituent on position 5 of thiazine skeleton, only N3 isomer or both N1 and N3 isomers (in different ratios) were obtained.     

Hybrid molecules containing benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazole and alpha-bromoacryloyl moieties as potent apoptosis inducers on human myeloid leukaemia cells

The synthesis and biological activity of a series of hybrids 1-5 prepared combining a benzo[4,5]imidazo[1,2-d][1,2,4]thiadiazole and different benzoheterocyclic alpha-bromoacryloyl amides have been described and their structure-activity relationships discussed. All these hetero-bifunctional compounds were highly cytotoxic against the human myeloid leukaemia cell lines HL-60 and U937 (IC(50) 0.24-1.72microM), significantly superior to that of both alkylating units alone. In human myeloid leukaemia HL-60 cells we observed that these compounds suppress survival and proliferation by triggering morphological changes and internucleosomal DNA fragmentation characteristic of apoptotic cell death. The apoptosis induced by these compounds is mediated by caspase-3 activation and is also associated to an early release of cytochrome c from the mitochondria.     

Design,synthesis and antiviral evaluation of novel acyclic phosphonate nucleotide analogs with triazolo[4,5-b]pyridine,imidazo[4,5-b]pyridine and imidazo[4,5-b]pyridin-2(3H)-one systems

Abstract

A new series of phosphonylated triazolo[4,5-b]pyridine (1-deaza-8-azapurine), imidazo[4,5-b]pyridine (1-deazapurine) and imidazo[4,5-b]pyridin-2(3H)-one (1-deazapurin-8-one) were synthesized from 2-chloro-3-nitropyridine and selected diethyl ?-aminoalkylphosphonates followed by reduction of the nitro group and cyclization. In the final step O,O-diethylphosphonates were transformed into the corresponding phosphonic acids. All synthesized compounds were evaluated in vitro for inhibitory activity against a broad variety of DNA and RNA viruses and their cytotoxic potencies were also established. Compound 12f showed marginal activity against cytomegalovirus Davis strain (EC₅₀?=?76.47?μM) in human embryonic lung (HEL) cells while compounds 10g (EC₅₀?=?52.53?μM) and 12l (EC₅₀?=?61.70?μM) were minimally active against the varicella-zoster virus Oka strain in HEL cells. Compounds under investigation were not cytotoxic at the maximum concentration evaluated (100?µM).     

Synthesis of 4-Substituted Imidazo[4,5-d][1,2,3]triazine (2-Azapurine)nucleosides

Abstract

Several methods for functionalization of the 4-position of imidazo[4,5-d][1,2,3]triazin-4-one were investigated. These investigations were successful and led to the preparation of 4-amino, 4-triazol-1-yl, 4-methoxy, 4-methylthio, 4-methylamino, 4-thio, 4-nitrobenzyl, and 4-unsubstituted 9-(β-D-ribofuranosyl)-imidazo-[4,5-d][1,2,3]triazine (2-azapurine ribosides). The 4-unsubstituted compound (19) was slightly active against HCMV in plaque and yield reduction experiments and was not cytotoxic at 100 μM. The methylamino (15), hydrazino (16), and p-nitrobenzylthio (20) were inactive against HCMV but slightly cytotoxic. The thiomethyl-substituted analog (21) was the most active with activity comparable to ganciclovir but with greater cytotoxicity. We conclude that even though none of the tested compounds had antiviral activity superior to ganciclovir, the new synthetic methods will provide a route to more interesting compounds.     

Ruthenium(II) mixed-ligand complex containing 2-(4'-benzyloxy-phenyl)imidazo[4,5-f][1,10]phenanthroline: synthesis, DNA-binding and photocleavage studies

A novel polypyridyl ligand 2-(4'-benzyloxyphenyl)imidazo[4,5-f][1,10]phenanthroline (BPIP) and its complex [Ru(bpy)2(BPIP)]2+ (1) (bpy=2,2'-bipyridine) and (2) [Ru(phen)2(BPIP)]2+) (phen=1,10-phenanthroline) have been synthesized and characterized by elemental analysis, electrospray mass spectra and 1H NMR. The DNA-binding properties of the two complexes were investigated by spectroscopic and viscosity measurements. The results suggest that both complexes bind to DNA via an intercalative mode. Both complexes can enantioselectively interact with calf thymus DNA (CT-DNA) in a way. The Lambda enantiomer of complex 1 is slightly predominant for binding to CT-DNA to the Delta enantiomer. Under irradiation at 365 nm, both complexes have also been found to promote the photocleavage of plasmid pBR 322 DNA. Inhibitors studies suggest that singlet oxygen ((1)O2) and hydroxyl radical (*OH) play a significant role in the cleavage mechanism for both complexes. Moreover, the DNA-binding and photocleavage properties of both complexes were compared with that of [Ru(bpy)2(BPIP)]2+ and [Ru(phen)2(BPIP)]2+. The experimental results indicate that methene group existence or not have a significant effect on the DNA-binding and cleavage mechanism of these complexes.     

Furano- and pyrrolo [2,3-d] pyrimidine nucleosides and their 5'-O-triphospates: synthesis and enzymatic activity

A series of bicyclic [2,3-d]furano- and pyrrolopyrimidine ribonucleosides were synthesized and converted chemically into corresponding 5'-O-triphosphates. Substrate properties of the triphosphates toward some RNA and DNA polymerases are reported.     

Structure-based design,synthesis, and evaluation of imidazo[1,2-b]pyridazine and imidazo[1,2-a]pyridine derivatives as novel dual c-Met and VEGFR2 kinase inhibitors

To identify compounds with potent antitumor efficacy for various human cancers, we aimed to synthesize compounds that could inhibit c-mesenchymal epithelial transition factor (c-Met) and vascular endothelial growth factor receptor 2 (VEGFR2) kinases. We designed para-substituted inhibitors by using co-crystal structural information from c-Met and VEGFR2 in complex with known inhibitors. This led to the identification of compounds 3a and 3b, which were capable of suppressing both c-Met and VEGFR2 kinase activities. Further optimization resulted in pyrazolone and pyridone derivatives, which could form intramolecular hydrogen bonds to enforce a rigid conformation, thereby producing potent inhibition. One compound of particular note was the imidazo[1,2-a]pyridine derivative (26) bearing a 6-methylpyridone ring, which strongly inhibited both c-Met and VEGFR2 enzyme activities (IC₅₀ = 1.9, 2.2 nM), as well as proliferation of c-Met-addicted MKN45 cells and VEGF-stimulated human umbilical vein endothelial cells (IC₅₀ = 5.0, 1.8 nM). Compound 26 exhibited dose-dependent antitumor efficacy in vivo in MKN45 (treated/control ratio [T/C] = 4%, po, 5 mg/kg, once-daily) and COLO205 (T/C = 13%, po, 15 mg/kg, once-daily) mouse xenograft models.     

Synthesis of imidazo[4,5-e][1,4]diazepine and 3-substituted 3-deazapurine nucleosides from 1-substituted inosines.

New synthetic methods of imidazo[4,5-e][1,4]diazepine nucleosides 8-11 and 3-substituted 3-deazainosines 14 from inosine have been reported. Treatment of N1-substituted inosines 1-3 with aqueous NaOH gave 5-amino-4-(N-substituted carbamoyl)imidazole ribosides 5-7, followed by appropriate manipulations to afford ring-expanded guanosine, inosine, and xanthosine analogues. Additionally, the 5-amino group of 4-N-allylcarbamoyl derivative 12 was converted into corresponding 5-iodo nucleoside 13. We found that 13 was cyclized to form 3-deaza-3-methylinosine (14) in the presence of Pd catalysts.     

Pyrrolo[2,3-d]pyrimidine nucleosides: synthesis and antitumor activity of 7-substituted 7-deaza-2'-deoxyadenosines

A one step synthesis, using the nucleoside 7-iodo-2'-deoxytubercidin (2b) in a Pd(0)/Cu(I)-catalyzed cross coupling reaction furnished a series of 7-alkynyl-2'-deoxytubercidin derivatives. The 7-iodo-, 7-chloro- or 7-bromo 2'-deoxytubercidins 2b-d as well as certain 7-alkynyl derivatives show significant activity against several tumor cell lines, with 7-iodo-2'-deoxytubercidin (2b) as the most effective compound.     

Anticytokinin activity of 4-substituted triazolo[4,5-d]pyrimidines and 4-substituted pyrazolo[3,4-d]pyrimidines

The synthesis and physiological activity of some novel 4-substituted triazolo[4,5-d]pyrimidines and 4-substituted pyrazolo[3,4-d]pyrimidines are described. Most of the compounds possessed high anticytokinin activity towards purine (benzyladenine) and phenylurea (4-PU-30) type cytokinins. 1-Benzyl-4-ethoxycarbonylpiperazinyl-1H-1,2,3-triazolo[4,5-d]pyrimidine almost completely removed cytokinin stimulated effects—betacyanin synthesis in Amaranthus caudatus cotyledons; growth of radish cotyledons and retention of chlorophyll in leaf explants. Some chemical structurephysiological activity relationships have been established.