2,3,7-Trisubstituted pyrazolo[1,5-d][1,2,4]triazines: functionally selective GABAA alpha3-subtype agonists

Novel synthetic routes have been devised for the preparation of previously inaccessible 2,3,7-trisubstituted pyrazolo[1,5-d][1,2,4]triazines 2. These compounds are high affinity ligands for the GABA(A) benzodiazepine binding site and some analogues show functional selectivity for agonism at alpha3-containing receptors over alpha1-containing receptors with the lead compound being 32.     

Synthesis and SAR of 4-(3-hydroxyphenylamino)pyrrolo[2,1-f][1,2,4]triazine based VEGFR-2 kinase inhibitors

A versatile synthesis of the suitably functionalized pyrrolo[2,1-f][1,2,4]triazine nucleus is described. SAR at the C-5 and C-6 positions of the 4-(3-hydroxy-4-methylphenylamino)pyrrolo[2,1-f][1,2,4]triazine template led to compounds with good in vitro potency against VEGFR-2 kinase. Glucuronidation of the phenol group is mitigated by incorporation of a basic amino group on the C-6 side chain of the pyrrolotriazine nucleus.     

Microwave-assisted synthesis and anti-HIV activity of new acyclic C-nucleosides of 3-(D-ribo-tetritol-1-yl)-5-mercapto-1,2,4-triazoles. Part 1

Microwave-assisted synthesis of novel acyclic C-nucleosides of 6-alkyl/aryl-3-(1,2-O-isopropylidene-D-ribo-tetritol-1-yl)[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles (5-12) and the 6-aryl-thiomethyl analogues 25-27 has been described. Deblocking of 5-12 and 25-27 afforded the free acyclic C-nucleosides 13-20, and 28-30, respectively. All of the synthesized compounds showed no inhibition against HIV-1 and HIV-2 replication in MT-4 cells. However, 6-(3,4-dichlorophenyl)-3-(1,2-O-isopropylidene-D-ribo-tetritol-1-yl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazole (6) is a potent inhibitor, in vitro, of the replication of HIV-2. These results suggest that compound 6 should be considered as a new lead in the development of antiviral agent.     

Pyrrolo- and pyrazolo-[3,4-e][1,2,4]triazolo[1,5-c]pyrimidines as adenosine receptor antagonists

The discovery and development of adenosine receptor antagonists have represented for years an attractive field of research from the perspective of identifying new drugs for the treatment of widespread disorders such as inflammation, asthma and Parkinson's disease. The present work can be considered as an extension of our structure-activity relationship studies on the pyrazolo[4,3-e][1,2,4]triazolo[1,5-c]pyrimidine (PTP) nucleus, extensively investigated by us as a useful template, in particular, for the identification of A(2A) and A(3) adenosine receptor antagonists. In order to explore the role of the nitrogen at the 7-position, we performed a new synthetic strategy for the preparation of pyrrolo[3,4-e][1,2,4]triazolo[1,5-c]pyrimidine derivatives which can be considered as 7-deaza analogues of the parent PTPs. We also synthesised a novel series of pyrazolo[3,4-e][1,2,4]triazolo[1,5-c]pyrimidines as junction isomers of the reference compounds. In both cases we obtained some examples of potent antagonists (K(i) in the low nanomolar range) with variable selectivity profiles in relation to the nature of substituents introduced at the C(5)-, N(8)- and/or N(9)-positions. The pyrrolo-triazolo-pyrimidine derivative 9b appeared to be a potent A(3) adenosine receptor antagonist (K(i)=10 nM) with good selectivity over hA(1) (74-fold) and hA(2A) (20-fold) adenosine receptors combined with low activity at the hA(2B) subtype (IC(50)=906 nM). Moreover, some examples of high-affinity A(1)/A(2A) dual antagonists have been identified in both series. This work constitutes a new and important contribution for the comprehension of the interaction between PTPs and adenosine receptors.     

Synthesis of pyrrolo[2,1-f][1,2,4]triazine C-nucleosides. Isosteres of sangivamycin, tubercidin, and toyocamycin

Syntheses of pyrrolo[2,1-f][1,2,4]triazine C-nucleosides are reported. Treatment of pyranulose glycoside with aminoguanidine in acetic acid gave the corresponding semicarbazone in 96% yield. The ring transformation of the semicarbazone in dioxane afforded a 51% yield of 2-amino-7-(2,3,5-tri-O-benzoyl-beta-D-ribofuranosyl)pyrrolo[2,1-f]-[1,2,4]triazine. Vilsmeier formylation of the pyrrolotriazine gave the major product, 5-formylpyrrolo[2,1-f][1,2,4]triazine, in 69% yield. The aldehyde was treated with hydroxylamine hydrochloride in methanol to give aldoximes. Dehydration of aldoxime with trifluoromethanesulfonic anhydride and triethylamine in dichloromethane afforded 5-cyanopyrrolo[2,1-f][1,2,4]triazine in 44% yield. Conversion of the nitrile to the deprotected amide, 2-amino-7-(beta-D-ribofuranosyl)pyrrolo[2,1-f][1,2,4]triazine-5-carboxamide, was accomplished in 96% yield on treatment with 30% H2O2 in ethanol for 1 day at room temperature. Debenzoylation with sodium hydroxide solution produced deprotected C-nucleosides.     

Synthesis and structure elucidation of novel fused 1,2,4-triazine derivatives as potent inhibitors targeting CYP1A1 activity

Synthesis and structure elucidation of new series of novel fused 1,2,4-triazine derivatives 3a-3f, 4a-4i and 6a-6b and their inhibitory activities are presented. Molecular structures of the synthesized compounds were confirmed by (1)H NMR, (13)C NMR, MS spectra and elemental analyses. X-ray crystallographic analysis was performed on 2-acetyl-8-(N,N-diacetylamino)-6-(4-methoxybenzyl)-3-(4-methoxy-phenyl)-7-oxo-2,3-dihydro-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazine 3d and 2-acetyl-8-(N-acetylamino)-6-benzyl-3-(4-chlorophenyl)-3-methyl-7-oxo-2,3-dihydro-7H-[1,2,4]triazolo[4,3-b][1,2,4]triazine 4e to secure their structures. The inhibitory effect of these compounds toward the CPY1A1 activity was screened to determine their potential as promising anticancer drugs. Our data showed that compounds 4e, 5a, 5b and 6b possess the highest inhibitory effects among all tested compounds. Furthermore, analysis of triazolotriazine derivatives docking showed that these compounds bind only at the interface of substrate recognition site 2 (SRS2) and (SRS6) at the outer surface of the protein. Amino-acids ASN214, SER216 and ILE462 participate in the binding of these compounds through H-bonds.     

Microwave-Assisted Synthesis and Anti-HIV Activity of New Acyclic C-Nucleosides of 3-(D-Ribo-Tetritol-1-yl)-5-Mercapto-1,2,4-Triazoles. Part 1

Microwave-assisted synthesis of novel acyclic C-nucleosides of 6-alkyl/aryl-3-(1,2-O-isopropylidene-D-ribo-tetritol-1-yl)[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles (5–12) and the 6-aryl-thiomethyl analogues 25–27 has been described. Deblocking of 5–12 and 25–27 afforded the free acyclic C-nucleosides 13–20, and 28–30, respectively. All of the synthesized compounds showed no inhibition against HIV-1 and HIV-2 replication in MT-4 cells. However, 6-(3,4-dichlorophenyl)-3-(1,2-O-isopropylidene-D-ribo-tetritol-1-yl)-7H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazole (6) is a potent inhibitor, in vitro, of the replication of HIV-2. These results suggest that compound 6 should be considered as a new lead in the development of antiviral agent.     

Double-headed acyclo C-nucleoside analogues. Functionalized 1,2-bis-(1,2,4-triazol-3-yl)ethane-1,2-diol

Reaction of L-tartaric acid with thiocarbohydcrazide afforded (1R, 2S)-1,2-bis(4-amino-5-mercapto-1,2,4-triazol-3-yl)-ethane-1,2-diol (3). The functional groups in 3 allowed the construction of fused heterocycles on the 1,2,4-triazole rings, mainly of the 1,2,4-triazolo[3,4-b][1,3,4]thiadiazine type as in 4, 5, 7, 10, 13 and 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole type as in 14.     

Studies on adenosine A2a receptor antagonists: comparison of three core heterocycles

Piperazine and (R)-2-(aminomethyl)pyrrolidine derivatives of [1,2,4]triazolo[1,5-a][1,3,5]triazine have recently been shown to be potent and selective adenosine A(2a) receptor antagonists. We have replaced the triazolotriazine core structure with two different heterocyclic cores. One of these, the one deriving from [1,2,4]triazolo[1,5-c]pyrimidine, appears to be particularly effective and selected analogs from this series have been shown to be orally active in a mouse catalepsy model of Parkinson's disease.     

Biological activity of novel N-substituted amides of endo-3-(3-methylthio-1,2,4-triazol-5-yl)bicyclo[2.2.1]hept-5-ene-2-carboxylic acid and N-substituted amides of 1-(5-methylthio-1,2,4-triazol-3-yl)cyclohexane-2-carboxylic acids

N-Substituted amides of endo-3-(3-methylthio-1,2,4-triazol-5-yl)bicyclo[2.2.1]hept-5-ene-2-carboxylic acid and 1-(5-methylthio-1,2,4-triazol-3-yl)cyclohexane-2-carboxylic acid were prepared by the condensation reaction of endo-S-methyl-N1-(bicyclo[2.2.1]hept-5-ene-2,3-dicarbonyl)isothiosemicarbazide and S-methyl-N1-(cyclohexane-2,3-dicarbonyl)isothiosemicarbazide with primary amines. The synthesized compounds were screened for their microbiological and pharmacological activities.     

Synthesis of 5-chloroformycin A, 5-chloro-2''-deoxyformycin A and certain related 5,7-disubstituted 3-beta-D-ribofuranosylpyrazolo[4,3-d] pyrimidines from formycin A.

A facile synthesis of 7-amino-5-chloro-3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine (5-chloroformycin A, 6), 7-amino-5-chloro-3-(2-deoxy-beta-D-erythro-pentofuranosyl) pyrazolo [4,3-d]-pyrimidine (5-chloro-2'-deoxyformycin A, 13) and certain related 5,7-disubstituted pyrazolo[4,3-d]pyrimidine ribonucleosides is described starting with formycin A. Thiation of tri-O-acetyloxoformycin B (4b) with phosphorus pentasulfide, followed 3-beta-D-ribofuranosyl-7-thioxopyrazolo[4,3-d] pyrimidin-5(1H,4H,6H)-one (3b) in excellent yield. Chlorination of 4b with either phosphorus oxychloride or phenyl phosphonicdichloride furnished the key intermediate 5,7-dichloro-3-(2,3, 5-tri-O-acetyl-beta-D-ribofuranosyl)pyrazolo[4,3-d]pyrimidine (5a), which on deacetylation afforded 5,7-dichloro-3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine (5b). Ammonolysis of 5a with liquid ammonia gave 6, whereas with MeOH/NH3, a mixture of 6 and 7-methoxy-5-chloro-3-beta-D-ribofuranosylpyrazolo[4,3-d]pyrimidine (7) was obtained. Reaction of 6 with lithium azide and subsequent hydrogenation afforded 5-aminoformycin A (10). Treatment of 5a with thiourea gave 5-chloro-3-(2,3,5-tri-O-acetyl-beta-D-ribofuranosyl) pyrazolo[4,3-d]pyrimidine-7(1H,6H)-thione (8a), which on further reaction with sodium hydrosulfide furnished 3-beta-D-ribofuranosylpyrazolo [4,3-d]pyrimidine-5,7(1H,4H,6H)-dithione (11). The four-step deoxygenation procedure using phenoxythiocarbonylation of the 2'-hydroxy group of the 3', 5'-protected 6 gave 5-chloro-2'-deoxyformycin A (13).     

Synthesis of Acyclo C-Nucleosides OF Phenanthro[9,10-e][1,2,4]Triazino[3,4-c]-[1,2,4] Triazoles,and Their Precursors

ABSTRACT

Reaction of 3-hydrazinophenanthro[9,10-e][1,2,4]triazine (1) with aliphatic and aromatic aldehydes as well as monosaccharides gave the corresponding hydrazones 2a-g. The D-glucose analogue exists in the cyclic pyranosyl structure 5. Acetylation and partial acetylation of the sugar hydrazones were carried out. Cyclization of a number of hydrazones including the partially acetylated sugar hydrazones by thionyl chloride gave regioselectively the respective angular isomer 1-substituted phenanthro[9,10-e][1,2,4]triazino[3,4-c][1,2,4]triazoles 16i-I, and not the linear isomer. The cyclization of 1 with acetic acid, however, gave regioselectively the linear isomer 19. The structural assignments were based on a model study whereby the angular 16a was found to be different from the linear isomer 19a obtained by the condensation of 4,5-diamino-3-methyl-1,2,4-triazole with 9,10-phenanthraquinone. Periodate oxidation of 2d gave 20 whose reaction with 1 gave 21.     

4-Amino-3-(2,3,5-tri-O-benzyl-beta-D-ribofuranosyl)-5-pyrazole-carb oni trile. Synthesis and conversion into a sugar-blocked 5,7-disubstituted formycin analog

The title compound, a potential intermediate to protected C-nucleoside analogs related to formycin A, was synthesized via a new route wherein 2,3,5-tri-O-benzyl-1-O-p-nitrophenyl)-D-ribofuranose was converted to 2,5-anhydro-3,4,6-tri-O-benzyl-D-allonic acid, and further transformed into 4-(tert-butyloxycarbonyl)-5-ethoxycarbonyl-3-(2,3,5-tri-O-benzyl-beta-D- ribofuranosyl)pyrazole. After amidation and dehydration to form the 4-(tert-butyloxycarbonyl)-5-pyrazolecarbonitrile, acidolysis followed by a Curtius-type sequence afforded the 4-amino-5-pyrazole-carbonitrile nucleoside. Treatment of the latter with nitrous acid and copper chloride in a Sandmeyer-type reaction gave a diazonitrile rather than a chloronitrile. Attempts to convert either the aminonitrile or the diazonitrile to 5,7-diamino-3-(2,3,5-tri-O-benzyl-beta-D-ribofuranosyl)pyrazolo[4,3-d] pyrimidine (5-aminoformycin A) by condensation with guanidine or N,N-dimethylguanidine were unsuccessful. Condensation of the aminonitrile with carbon disulfide in pyridine provided access to the formycin system in the form of 3-(2,3,5-tri-O-benzyl-beta-D-ribofuranosyl)pyrazolo[4,3-d]pyrimidine-5,7 - dithione.     

Synthesis, SAR, and Evaluation of 4-[2,4-Difluoro-5-(cyclopropylcarbamoyl)phenylamino]pyrrolo[2,1-f][1,2,4]triazine-based VEGFR-2 kinase inhibitors

Introduction of the 2,4-difluoro-5-(cyclopropylcarbamoyl)phenylamino group at the C-4 position of the pyrrolo[2,1-f][1,2,4] triazine scaffold led to the discovery of a novel sub-series of inhibitors of VEGFR-2 kinase activity. Subsequent SAR studies on the 1,3,5-oxadiazole ring appended to the C-6 position of this new sub-family of pyrrolotriazines resulted in the identification of low nanomolar inhibitors of VEGFR-2. Antitumor efficacy was observed with compound 37 against L2987 human lung carcinoma xenografts in athymic mice.     

1,2,4]Triazole derivatives as 5-HT(1A) serotonin receptor ligands.

A series of new 4-amino-3-[3-[4-(2-methoxy or nitro phenyl)-1-piperazinyl] propyl]thio]-5-(substitutedphenyl)[1,2,4]triazoles 11a-t was synthesized in order to obtain compounds with high affinity and selectivity for 5-HT(1A) receptor over the alpha(1)-adrenoceptor. A series of isomeric 4-amino-2-[3-[4-(2-methoxy or nitro phenyl)-1-piperazinyl]propyl]-5-(substitutedphenyl)-2,4-dihydro-3H[1,2,4]triazole-3-thiones 12a-r was also isolated and characterized. New compounds were tested to evaluate their affinity for 5-HT(1A) receptor and alpha(1)-adrenoceptor in radioligand binding experiments. As a general trend, triazoles 11a-t showed a preferential affinity for the 5-HT(1A) receptor whereas isomeric 2,4-dihydro-3H[1,2,4]triazole-3-thiones 12a-r preferentially bind to the alpha(1)-adrenoceptor site. Several molecules showed affinities in the nanomolar range and 4-amino-3-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]thio]-5-(4-propyloxy-phenyl)[1,2,4]triazole (11o) was the most selective derivative for the 5-HT(1A) receptor (K(i) alpha(1)/K(i) 5-HT(1A)=55). The decrease in 5-HT(1A) receptor selectivity in 3-[3-[4-(2-methoxyphenyl)-1-piperazinyl]propyl]thio]-5-(substitutedphenyl)[1,2,4] triazole 14a-b, lacking in the amino group in 4-position of the triazole ring, in comparison with their analogues in the series 11a-t, suggest that the amino function represents a critical structural feature in determining 5-HT(1A) receptor selectivity in this class of compounds.     

Emerging antifungal azoles and effects on Magnaporthe grisea

Derivatives of pyrazolo[1,5-a][1, 3, 5]triazine-2,4-dione,pyrazolo[1,5-c][1, 3, 5]thiadiazine-2-one, pyrazolo[3,4-d][1, 3]thiazine-4-one, and pyrazolo[3,4-d][1, 3]thiazine-4-thione were screened for antifungal activity against the causal agent of rice blast disease, Magnaporthe grisea. The compounds were tested at doses ranging from 10 to 200 μg ml⁻¹, using the commercial fungicide tricyclazole as reference compound. All triazine derivatives inhibited the growth and pigmentation of the mycelia less effectively than tricyclazole. The thiadiazine derivatives proved to be more effective than their triazine counterparts, but only 4-(butylimino)-7-methylpyrazolo[1,5-c][1,3,5]thiadiazine-2-one (2h) and 4-(cyclohexylimino)-7-methylpyrazolo[1,5-c][1,3,5]thiadiazine-2-one (2j) were more effective than tricyclazole. Pyrazolo[3,4-d][1,3]thiazine-4-one derivatives were active only at the highest doses, whereas members of the pyrazolo[3,4-d][1,3]thiazine-4-thione series inhibited fungal growth at the lowest concentrations used, at which tricyclazole had no effect. A dose-dependent mechanism might be responsible for this effect, with lipophilicity as the governing factor. Within a given set, the presence of a cyclohexyl or an n-butyl group generally increased antifungal activity, with respect to both growth inhibition and cell de-pigmentation of the mycelium, suggesting that a higher lipophilicity might improve transport inside the cells. SEM and TEM of M. grisea hyphae showed that treatment with the most active substance (2h) caused significant ultrastructural effects, particularly on the endomembrane system, suggesting a mechanism of action similar to that of most azole fungicides. Dissimilarities were also observed, with no alterations of the cell wall evident. In conclusion, several compounds showed greater inhibition than tricyclazole, and therefore provide useful new chemistry for control of M. grisea infections.     

Synthesis and biological evaluation of novel steroidal[17,16-d][1,2,4]triazolo[1,5-a]pyrimidines

The preparation of steroidal[17,16-d][1,2,4]triazolo[1,5-a]pyrimidines and their biological evaluation as potential anticancer agents are herein reported. These novel heterosteroids (2, 4) were prepared through the condensation reaction of 3-amino-1,2,4-triazole with 16-arylidene-17-ketosteroids (1, 3). All the synthesized compounds were evaluated for their anticancer activity in vitro against PC-3 (human prostatic carcinoma), MCF-7 (human breast carcinoma) and EC9706 (human esophageal carcinoma) cell lines. Among the screened compounds, 2i, 2n and 4f showed significant inhibitory activity against all the three human cell lines.     

Synthesis of some new [1,2,4]triazolo[3,4-b][1,3,4]thiadiazines and [1,2,4]triazolo[3,4-b][1,3,4] thiadiazoles starting from 5-nitro-2-furoic acid and evaluation of their antimicrobial activity

New series of fused 1,2,4-triazoles such as, 6-(aryl)-3-(5-nitrofuran-2-yl)-5,6-dihydro-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 4-8, 6-(alkyl/aryl amino)-3-(5-nitrofuran-2-yl)-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazoles 9-13 and 6-(4-substituted phenyl)-3-(5-nitrofuran-2-yl)-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines 14-18 have been synthesized via the reaction of 4-amino-5-(5-nitrofuran-2-yl)-4H-1,2,4-triazole-3-thiol 3 with various reagents such as hetero aromatic aldehydes, alkyl/aryl isothiocyanates and 4-substituted phenacyl bromides, respectively. The structures of the newly synthesized compounds have been confirmed on the basis of elemental analysis and spectral studies. The newly synthesized triazolo derivatives have been investigated for their in vitro antibacterial activity. Most of the tested compounds showed interesting antibacterial activity against Staphylococcus aureus. Furthermore, the most potent antibacterial compounds 11-13 were evaluated for their in vitro cytotoxic activity against human cancer cell lines. It was found that compounds 11 and 13 showed higher cytotoxicity against Hep-G2 cell line as compared to standard.     

4-Hydroxy-1-[3-(5-(1,2,4-triazol-4-yl)-1H-indol-3-yl)propyl]piperidines: selective h5-HT1D agonists for the treatment of migraine

A series of 4-hydroxy-1-[3-(5-(1,2,4-triazol-4-yl)-1H-indol-3-yl)propyl] piperidines was investigated as potential selective h5-HT1D agonists for the treatment of migraine. The 4-[(N-benzyl-N-methyl)amino]methyl analog 12a was found to be a full agonist at the h5-HT1D receptor with good binding selectivity over the h5-HT1B receptor.     

Potent and selective adenosine A(2A) receptor antagonists: [1,2,4]-triazolo[4,3-c]pyrimidin-3-ones

Antagonism of the adenosine A_2A receptor affords a possible treatment of Parkinson’s disease. In the course of investigating pyrazolo[4,3-e]-1,2,4-triazolo[1,5-c]pyrimidine A_2A antagonists, we prepared [1,2,4]-triazolo[4,3-c]pyrimidin-3-ones with potent and selective (vs A₁) A_2A antagonist activity. Structure-activity relationships are described for this series.