Piperazine derivatives of [1,2,4]triazolo[1,5-a][1,3,5]triazine as potent and selective adenosine A2a receptor antagonists

The [1,2,4]triazolo[1,5-a]triazine derivative 3, more commonly known in the field of adenosine research as ZM-241385, has previously been demonstrated to be a potent and selective adenosine A2a receptor antagonist, although with limited oral bioavailability. This [1,2,4]triazolo[1,5-a]triazine core structure has now been improved by incorporating various piperazine derivatives. With some preliminary optimization, the A2a binding affinity of some of the best piperazine derivatives is almost as good as that of compound 3. The selectivity level over the adenosine A1 receptor subtype for some of the more active analogues is also fairly high, > 400-fold in some cases. Many compounds within this piperazine series of [1,2,4]triazolo[1,5-a]triazine have now been shown to have good oral bioavailability in the rat, with some as high as 89% (compound 35). More significantly, some piperazines derivatives of [1,2,4]triazolo[1,5-a]triazine also possessed good oral efficacy in rodent models of Parkinson's disease. For instance, compound 34 was orally active in the rat catalepsy model at 3 mg/kg. In the 6-hydroxydopamine-lesioned rat model, this compound was also quite effective, with a minimum effective dose of 3 mg/kg po.     

5-amino-2-phenyl[1,2,3]triazolo[1,2-a][1,2,4]benzotriazin-1-one: a versatile scaffold to obtain potent and selective A3 adenosine receptor antagonists

Binding assays on human A1, A2A, and A3 adenosine receptors (ARs) and functional studies on A2B ARs revealed that various 2-phenyl[1,2,3]triazolo[1,2-a][1,2,4]benzotriazin-1,5(6H)-diones VIII, previously reported as ligands at the central benzodiazepine receptor (BzR), possess nanomolar affinity at the A3 AR. Replacement of the amide of VIII with an amidine moiety gave the 5-amino-2-phenyl[1,2,3]triazolo[1,2-a][1,2,4]benzotriazin-1-ones IX, which maintain a nanomolar potency at the A3 AR with selectivity over the BzR. Insertion of a p-methoxybenzoyl at the 5-amino moiety enhanced A3 AR affinity and selectivity over the A1, A2A, and A2B ARs. The best result of our lead optimization efforts is 9-chloro-5-(4-methoxybenzoyl)amino-2-phenyl[1,2,3]triazolo[1,2-a][1,2,4]benzotriazin-1-one (23), which displayed a Ki of 1.6 nM at the A3 AR and no significant affinity at the other ARs or the BzR. Docking simulations on selected ligands into a model of the A3 AR allowed us to rationalize the structure-activity relationships of phenyltriazolobenzotriazindiones VIII and aminophenyltriazolobenzotriazinones IX at the molecular level.     

1,2,4-Triazolo[1,5-a]quinoxaline derivatives: synthesis and biological evaluation as adenosine receptor antagonists

Since most of the reported adenosine receptor antagonists are 2-(hetero)aryl-substituted tricyclic heteroaromatic derivatives, in the present study we report the synthesis and the biological evaluation of a new set of 4-amino-1,2,4-triazolo[1,5-a]quinoxalines containing at position-2 an ethyl carboxylate group or a hydrogen atom. The structure-activity relationships on these compounds were in accordance with those of a previously reported series of analogous size and shape, thus suggesting a similar A(1)-binding mode. In particular, the binding data indicate that alkylation of the 4-amino group of these derivatives lead to potent A(1)-receptor antagonists. Moreover, as new results, this study has pointed out that the ethyl 2-carboxylate group can advantageously replace the 2-(hetero)aryl ring of previously reported triazoloquinoxaline derivatives, affording an ameliorated interaction with the A(1)-receptor subtype.     

4-Amino[1,2,4]triazolo[4,3-a]quinoxalines. A novel class of potent adenosine receptor antagonists and potential rapid-onset antidepressants

A series of 4-amino[1,2,4]triazolo[4,3-a]quinoxalines has been prepared. Many compounds from this class reduce immobility in Porsolt's behavioral despair model in rats upon acute administration and may therefore have therapeutic potential as novel and rapid acting antidepressant agents. Optimal activity in this test is associated with hydrogen, CF3, or small alkyl groups in the 1-position, with NH2, NH-acetyl, or amines substituted with small alkyl groups in the 4-position, and with hydrogen or 8-halogen substituents in the aromatic ring. Furthermore, many of these 4-amino[1,2,4]triazolo[4,3-a]quinoxalines bind avidly, and in some cases very selectively, to adenosine A1 and A2 receptors. A1 affinity of these compounds was measured by their inhibition of tritiated CHA (N6-cyclohexyladenosine) binding in rat cerebral cortex membranes and A2 affinity by their inhibition of tritiated NECA (5'-(N-ethylcarbamoyl)adenosine) binding to rat striatal homogenate in the presence of cold N6-cyclopentyladenosine. Structure-activity relationship (SAR) studies show that best A1 affinity is associated with ethyl, CF3, or C2F5 in the 1-position, NH-iPr or NH-cycloalkyl in the 4-position, and with an 8-chloro substituent. Affinity at the A2 receptor is mostly dependent on the presence of an NH2 group in the 4-position and is enhanced by phenyl, CF3, or ethyl in the 1-position. The most selective A1 ligand by a factor of greater than 3000 is 121 (CP-68,247; 8-chloro-4-(cyclohexyl-amino)-1- (trifluoromethyl)[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 28 nM at the A1 receptor. The most potent A2 ligand is 128 (CP-66,713; 4-amino-8-chloro-1- phenyl[1,2,4]triazolo[4,3-a]quinoxaline) with an IC50 of 21 nM at the A2 receptor and a 13-fold selectivity for this receptor. Representatives from this series appear to act as antagonists at both A1 and A2 receptors since they antagonize the inhibiting action of CHA on norepinephrine-stimulated cAMP formation in fat cells and they decrease cAMP accumulation induced by adenosine in limbic forebrain slices. Thus certain members of this 4-amino[1,2,4]triazolo[4,3-a]quinoxaline series are among the most potent and A1 or A2 selective non-xanthine adenosine antagonists known.     

Antimicrobial activity of nitro derivatives of azolo[1,5-a]-pyrimidine and azolo[5,1-c][1,2,4]triazine

Translated from Khimiko-farmatsevticheskii Zhurnal, Vol. 24, No. 1, pp. 39–40, January, 1990.     

New 2-arylpyrazolo[4,3-c]quinoline derivatives as potent and selective human A3 adenosine receptor antagonists

In this paper we report the synthesis and biological evaluation of a new class of 2-phenyl-2,5-dihydro-pyrazolo[4,3-c]quinolin-4-ones as A(3) adenosine receptor antagonists. We designed a new route based on the Kira-Vilsmeier reaction for the synthesis of this class of compounds. Some of the synthesized compounds showed A(3) adenosine receptor affinity in the nanomolar range and good selectivity as evaluated in radioligand binding assays at human (h) A(1), A(2A), A(2B), and A(3) adenosine receptor subtypes. We introduced several substituents on the 2-phenyl ring. In particular substitution at the 4-position by methyl, methoxy, and chlorine gave optimal activity and selectivity 6c (K(i)hA(1), A(2A)>1000 nM, EC(50)hA(2B)>1000 nM, K(i)hA(3) = 9 nM), 6d (K(i)hA(1), A(2A)>1000 nM, EC(50)hA(2B)>1000 nM, K(i)hA(3) = 16 nM), 6b (K(i)hA(1), A(2A) >1000 nM, EC(50)hA(2B)>1000 nM, K(i)hA(3) = 19 nM). In conclusion, the 2-phenyl-2,5-dihydro-pyrazolo[4,3-c]quinolin-4-one derivatives described herein represent a new family of in vitro selective antagonists for the adenosine A(3) receptor.     

Synthesis and biological evaluation of a new series of 1,2,4-triazolo[1,5-a]-1,3,5-triazines as human A(2A) adenosine receptor antagonists with improved water solubility

The structure-activity relationship (SAR) of 1,2,4-triazolo[1,5-a]-1,3,5-triazine derivatives related to ZM241385 as antagonists of the A(2A) adenosine receptor (AR) was explored through the synthesis of analogues substituted at the 5 position. The A(2A) AR X-ray structure was used to propose a structural basis for the activity and selectivity of the analogues and to direct the synthetic design strategy to provide access to solvent-exposed regions. Thus, we have identified a point of substitution for the attachment of solubilizing groups to enhance both aqueous solubility and physicochemical properties, maintaining potent interactions with the A(2A) AR and, in some cases, receptor subtype selectivity. Among the most potent and selective novel compounds were a long-chain ether-containing amine congener 20 (K(i) 11.5 nM) and its urethane-protected derivative 14 (K(i) 17.8 nM). Compounds 20 and 31 (K(i) 11.5 and 16.9 nM, respectively) were readily water-soluble up to 10 mM. The analogues were docked in the crystallographic structure of the hA(2A) AR and in a homology model of the hA(3) AR, and the per residue electrostatic and hydrophobic contributions to the binding were assessed and stabilizing factors were proposed.     

1,2,4-Triazolo[4,3-a]quinoxalin-1-one: a versatile tool for the synthesis of potent and selective adenosine receptor antagonists

4-Amino-6-benzylamino-1,2-dihydro-2-phenyl-1,2,4-triazolo[4, 3-a]quinoxalin-1-one (1) has been found to be an A(2A) versus A(1) selective antagonist (Colotta et al. Arch. Pharm. Pharm. Med. Chem. 1999, 332, 39-41). In this paper some novel triazoloquinoxalin-1-ones 4-25 bearing different substituents on the 2-phenyl and/or 4-amino moiety of the parent 4-amino-1, 2-dihydro-2-phenyl-1,2,4-triazolo[4,3-a]quinoxalin-1-one (3) have been synthesized and tested in radioligand binding assays at bovine A(1) and A(2A) and cloned human A(3) adenosine receptors (AR). Moreover, the binding activities at the above-mentioned AR subtypes of the 1,4-dione parent compounds 26-31 and their 5-N-alkyl derivatives 33-37 were also evaluated. The substituent on the 2-phenyl ring exerted a different effect on AR subtypes, while replacement of a hydrogen atom of the 4-amino group with suitable substituents yielded selective A(1) or A(3) antagonists. Replacement of a hydrogen atom of the 4-NH(2) with an acyl group, or replacement of the whole 4-NH(2) with a 4-oxo moiety, shifted the binding activity toward the A(3) AR. The binding results allowed elucidation of the structural requirements for the binding of these novel tricyclic derivatives at each receptor subtype. In particular, A(1) and A(2A) binding required the presence of a proton donor group at position-4, while for A(3) affinity the presence of a proton acceptor in this same region was of paramount importance.     

Novel bicyclic piperazine derivatives of triazolotriazine and triazolopyrimidines as highly potent and selective adenosine A2A receptor antagonists

A series of bicyclic piperazine derivatives of triazolotriazine and triazolopyrimidines was synthesized. Some of these analogues show high affinity and excellent selectivity for adenosine A(2a) receptor versus the adenosine A(1) receptor. Structure-activity-relationship (SAR) studies based on octahydropyrrolo[1,2-a]pyrazine and octahydropyrido[1,2-a]pyrazine with various capping groups are reported. Among these analogues, the most potent and selective A(2a) antagonist 26 h has a K(i) value of 0.2 nM and is 16 500-fold selective with respect to the A(1) receptor. Among a number of compounds tested, compounds 21a and 21c exhibited significantly improved metabolic stability. Compounds 21a, 21c, and 18a showed good oral efficacy in rodent catalepsy models of Parkinson's disease.     

Tricyclic imidazoline derivatives as potent and selective adenosine A1 receptor antagonists

Novel tricyclic imidazoline antagonists of the adenosine A1 receptor are described. For key compounds, the selectivity level over other adenosine receptor subtypes is examined along with their in vivo effects in a rat diuresis model. Compound 14, the (R)-isomer of 7,8-dihydro-8-ethyl-2-(4-bicyclo[2.2.2]octan-1-ol)-4-propyl-1H-imidazo[2,1-i]purin-5(4H)-one, is a particularly potent adenosine A1 receptor antagonist with good selectivity over the other three adenosine receptor subtypes: A1 (human) Ki=22 nM; A2A (human) Ki=4400 nM; A2B (human) Ki=580 nM; A3 (human) Ki>or=10,000 nM. Imidazoline 14 is a competitive adenosine A1 receptor antagonist with a pA2 value of 8.88 and is highly soluble in water (>100 mg/mL). In addition, it has an oral bioavailability of 84% and an oral half-life of 3.8 h in rats. When orally administered in a rat diuresis model, compound 14 promoted sodium excretion (ED50=0.01 mg/kg). This level of efficacy is comparable to that of BG9928, a selective adenosine A1 receptor antagonist that is currently in clinical trials as a treatment for congestive heart failure. Additional modifications to 14 also showed that the bridgehead hydroxyl group could be replaced with a propionic acid (compound 36) without a significant loss in binding affinity or in vivo activity.     

1,2,4]Triazolo[4,3-a]quinoxalin-4-amines: a new class of A1 receptor selective adenosine antagonists

Several [1,2,4]triazolo[4,3-a]quinoxalines that were reported as antidepressants in the patent literature were found to possess moderate affinity for the adenosine A1 and A2 receptors. On the basis of structural parallels with adenine and adenosine, the N-cyclopentyl derivative was synthesized and found to have improved affinity and selectivity for the A1 receptor. In the N-cyclopentyl series, affinity was optimal with trifluoromethyl substitution at the 1-position, resulting in a compound (9) with 7.3 nM A1 affinity and 138-fold selectivity for the A1 receptor.     

1,5-Benzodiazepines. X. Dialkylamino substituted 1,5-benzodiazepine and [1,2,4]triazolo [4,3-a][1,5] benzodiazepine derivatives with inhibitory activity on PAF-induced platelet aggregation.

Novel 4-(dialkylamino) substituted (4, 5 c, 8) and 2,4-bis(dialkylamino) substituted (6) 1,5-benzodiazepine derivatives were synthesized. Both these new compounds and the substituted 4H-[1,2,4]triazolo[4,3-a][1,5]benzodiazepine-5-amines 2 a-h, recently described by us, were tested in vitro for their inhibitory activity on the PAF-induced aggregation of human platelets. Actually, bicyclic compounds 4 d, 5 c and tricyclic compounds 2 g, h showed a significant activity: in all them the dialkylamino substituent was the 4-(ethoxycarbonyl)-1-piperazinyl group. On the contrary, compounds 4 d, 5 c, 2 g,h showed practically no inhibitory activity when platelet aggregation was induced by ADP, A23187, or collagen.     

New 2-heterocyclyl-imidazo[2,1-i]purin-5-one derivatives as potent and selective human A3 adenosine receptor antagonists

A series of 4-allyl/benzyl-7,8-dihydro-8-methyl/ethyl-2-[(substituted)isoxazol/pyrazol-3/5-yl]-1H-imidazo[2,1-i]purin-5(4H)-ones has been synthesized and evaluated in radioligand binding assays to determine their affinities at the human A(1), A(2A), and A(3) adenosine receptors. Efficacy at the hA(2B) AR and antagonism of selected ligands at the hA(3) AR were also assessed through cAMP experiments. All of the synthesized molecules exhibited high affinity at the hA(3) AR (K(i) values ranging from 1.46 to 44.8 nM), as well as remarkable selectivity versus A(1), A(2A), and A(2B) AR subtypes. Compound (R)-4-allyl-8-ethyl-7,8-dihydro-2-(3-methoxy-1-methyl-1H-pyrazol-5-yl)-1H-imidazo[2,1-i]purin-5(4H)-one (R-33) was found to be the most potent and selective ligand of the series (K(i) hA(3) = 1.46 nM, K(i) hA(2A)/K(i) hA(3) > 3425; IC(50) hA(2B)/K(i) hA(3) > 3425; K(i) hA(1)/K(i) hA(3) = 1729). Molecular modeling studies were helpful in rationalizing the available structure-activity relationships along with the selectivity profiles of the new series of ligands.     

1,2,4-Triazolo[5,1-i]purine derivatives as highly potent and selective human adenosine A(3) receptor ligands

A series of triazolopurines showed structural similarity to human adenosine A(3) receptor antagonist, 9-chloro-2-(2-furanyl)-5-[(phenylacetyl)amino][1,2,4]triazolo[1,5-c]quinazoline (MRS 1220, 1). In this study, we found novel 1,2,4-triazolo[5,1-i]purine derivatives (2) showing human adenosine A(3) receptor affinities. The compounds were obtained in two steps from 5-amino-4-cyanoimidazole (33). The affinity was determined in radioligand binding assays for the cloned human adenosine A(1), A(2A), A(2B), and A(3) receptors. After the structure-activity relationship was analyzed, we determined that there was a mild parabolic relationship between the length of alkyl groups at the 5-position and the affinities at the A(3) receptor and positive correlation between the length of the substituents on phenyl groups at the 8-position and the affinities at the A(2A) receptor. These investigations led to potent and selective human adenosine A(3) receptor ligands. The most potent A(3) receptor ligand (5-n-butyl-8-(4-methoxyphenyl)-3H-[1,2,4]triazolo[5,1-i]purine (27, K(i) = 0.18 nM) and the most selective A(3) receptor ligand against A(1), A(2A), and A(2B) receptors, (5-n-butyl-8-(4-n-propoxyphenyl)-3H-[1,2,4]triazolo[5,1-i]purine (29, >19 600), were discovered.     

Cholecystokinin antagonists. Synthesis and biological evaluation of 4-substituted 4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepines

A series of 4-substituted 4H-[1,2,4]triazolo[4,3-a][1,4]benzodiazepines was prepared by standard methodology. These compounds were tested in vitro as antagonists of the binding of [125I]cholecystokinin (CCK) to rat pancreas and guinea pig brain receptors and of the binding of [125I]gastrin to guinea pig gastric glands. All compounds proved to have greater affinity for the peripheral CCK receptor with some analogues having IC50's in the subnanomolar range. In vivo activity of selected compounds in mice is presented and the structure/activity profile of this class of benzodiazepines as CCK antagonists is discussed.     

Design and synthesis of 4-substituted indolo[3,2-e][1,2,3]triazolo[1,5-a]pyrimidine derivatives with antitumor activity

New derivatives of the indolo[3,2- e][1,2,3]triazolo[1,5- a]pyrimidine system, substituted in the 4 position, were designed as novel antitumor agents because of their theoretical capability to form stable complexes with DNA fragments. The calculated free energies of binding were found in the range -12.76 --> -39.68 Kcal/mol. The docking studies revealed a common binding mode with the chromophore intercalated between GC base pairs, whereas the side chain lies along the minor groove. Compounds, selected on the basis of the docking studies and suitably synthesized, showed antiproliferative activity against each type of tumor cell line investigated, generally in the low micromolar range. The more active derivatives were shown to be 1eJ and 1eL, endowed with significant antiproliferative activity against the renal and CNS subpanels, respectively. A mechanism of action closely related to the DNA-interacting drugs can be supposed, although, alternative mechanisms, similar to those of the anthracyclines, can also operate.