Chemistry

"Adenosine receptors (ARs) are members of the superfamily of G protein-coupled receptors. The homology models of adenosine A1 and A2A receptors were constructed. The high-resolution X-ray structure of bovine rhodopsin and crystal structure of beta2-adrenergic receptor were used as templates. The binding sites of the A1 and A2A ARs were constructed by using data obtained from mutagenesis experiments as well as docking simulations of the respective AR antagonsists DPCPX and XAC. To compare rhodopsin- and beta2-adrenergic-based models, the binding mode of A1 (KW-3902, LUF-5437) and A2A (KW-6002, ZM-241385) ARs antagonists were also examined. The differences in the binding ability of both models were noted during the study. The beta2-adrenergic-based A2A AR model was much more capable to stabilize the ligand in the binding site cavity than the corresponding rhodopsin-based A2A AR model, however, such differences were not so clear in case of A1 AR models. It was suggested that for the A1 AR it is possible to use the crystal structure of rhodopsin as a template as well as beta2-adrenergic receptor, but for A2A AR, with the now available beta2-adrenergic receptor X-ray structure, docking studies should be avoided on the rhodopsin-based model. However, taking into account that the beta2AR shares about 31% of the residues with the AR in comparison to 21% in case of bRho, we suggest using beta2-adrenergic-based models for the A1 and A2A ARs for further in silico ligand screening also because of their generally better ability to stabilize ligands inside the binding pocket."

"Syntheses and physicochemical properties of N-aryl-substituted imidazo-, pyrimido-, and 1,3-diazepino[2,1-f]purinediones are described. These derivatives were synthesized by the cyclization of 7-haloalkyl-8-bromo-1,3-dimethyl- or 1,3-dipropyl-xanthine derivatives with corresponding arylamines. The obtained compounds (1-40), which can be envisaged as sterically fixed and configurationally stable analogs of 8-styrylxanthines, were evaluated for their affinity to adenosine A(1) and A(2A) receptors, the receptor subtypes that are predominant in the brain. Selected compounds were additionally investigated for affinity to the A(2B) and A(3) receptor subtypes. Many of the compounds showed adenosine A(2A) receptor affinity at micromolar or submicromolar concentrations and were A(2A)-selective, for example, compound 23 with p-fluoro substituent displayed K(i) value of 0.147 microM at the rat A(2A) receptor and more than 170-fold-A(2A) selectivity, compound 17 with naphthyl substituent had K(i) value of 0.219 microM and a more than 114-fold-A(2A) selectivity. The compounds were somewhat weaker and less selective at the human receptor subtypes. Elongation of the dimethyl substituent to dipropyl in xanthine moiety improved affinity but reduced selectivity. 1,3-Dimethylimidazo-, pyrimido-, and diazepinopurinediones were evaluated in vivo as anticonvulsants in MES, ScMet, TTE tests and examined for neurotoxicity in mice (ip). Substances with pyrimido ring displayed protective activity in ScMet or in MES and ScMet tests, showing also neurotoxicity. The pyrimidine annelated ring is beneficial for both receptor affinity and anticonvulsant activity."

"The synthesis of N-(un)substituted-phenylalkylpyrimido[2,1-f]purinediones was performed starting with 7-(3-chloropropyl)-8-bromotheophylline and 7-(3-chloropropyl)-8-bromo-1,3-dipropylxanthine. Compounds with unsubstituted or substituted ethylene spacer to an aromatic ring were synthesized. Additionally variations in the spacer-elongation of the linker containing more than two atoms, introduction of a double bond or heteroatoms were performed. Physicochemical properties of the synthesized compounds were described. The obtained compounds envisaged as sterically fixed and configurationally stable analogs of 8-styrylxanthines, were evaluated for their affinity to adenosine A(1) and A(2A) receptors, the receptor subtypes that are predominant in the brain. Selected compounds were also investigated for the affinity to the A(2B) and A(3) receptor subtypes. It was stated that phenylethyl pyrimido[2,1-f]purinediones and their analogs with variations of the ethylene spacer (substituted or extended) exhibit micromolar or submicromolar affinity for A(2A) ARs (adenosine receptors); for example compound 2Ac with p-hydroxy substituent displayed a K(i) value of 0.23 microM at the rat A(2A) receptor. In comparison to the previously obtained phenyl and benzyl pyrimido[2,1-f]purinediones compounds with a shorter spacer, phenethyl derivatives were optimal for A(2A) AR. The kind of substituent at the aromatic ring was important for the affinity. Oxygen and nitrogen atoms in the spacer resulted frequently in a slight decrease of the A(2A) AR affinity, introduction of more heteroatoms into the spacer-in carbamates-caused distinctly negative effect on the activity. In this series of compounds more frequently the adenosine A(1) activity was observed, also in submicromolar range as for dipropyl derivative 2Ba with K(i) value of 0.62 microM at the rat A(2A) AR. 3D-QSAR models were developed for the compounds presented in this paper as well as in the previous publications showing activity at adenosine A(1) and A(2A) ARs. It was concluded that for the activity at adenosine A(1) and A(2A) receptors lipophilicity, steric effects along with the molecule's electrostatic surface properties had greatest value. Chosen compounds were evaluated in vivo as anticonvulsants in MES, scMet tests and examined for neurotoxicity. Contrary to previously obtained phenyl and benzyl pyrimido[2,1-f]purinediones, all tested compounds were inactive as anticonvulsants."

"Synthesis and physicochemical properties of N-benzyl pyrimido[2,1-f]purinediones are described. These derivatives were synthesized by the cyclization of 7-chloropropylo-8-bromo-1,3-dimethyl- or 1,3-dipropyl xanthine derivatives with corresponding (un)substituted benzylamines. Dipropyl derivatives were obtained under microwave irradiation conditions either. The obtained compounds (1-20) were evaluated for their affinity to adenosine A1 and A2A receptors, selected compounds were additionally investigated for affinity to the A3 receptor subtype. The results of the radioligand binding assays to A1 and A2A adenosine receptors showed that most of the 1,3-dimethyl-9-benzylpyrimidopurinediones exhibited selective affinity to A2A receptors at micromolar or submicromolar concentrations (for example, derivative 9 with o-methoxy substituent displayed a Ki value of 0.699 microM at rat A2A receptor with more than 36-fold selectivity). Contrary to previously described arylpyrimido[2,1-f]purinediones dipropyl derivatives (compounds 15-20) showed affinity to both kinds of receptors increased, however A1 affinity increased to a larger extent, with the result that A2A selectivity was abolished. The best adenosine A1 receptor ligand was m-chlorobenzyl derivative 18 (Ki=0.089 microM and 5-fold A1 selectivity). Structure-activity relationships were discussed with the analysis of lipophilic and spatial properties of the investigated compounds. Pharmacophore model of adenosine A1 receptor antagonist was adopted for this purpose."

"Syntheses and physicochemical properties of N-cycloalkyl-substituted imidazo-, pyrimido- and 1,3-diazepino[2,1-f]purinediones are described. These derivatives were synthesized by cyclization of 7-halogenoalkyl-8-bromo-1,3-dimethylxanthine derivatives with aminocycloalkanes. The obtained compounds (1-33) were evaluated for their affinity to rat adenosine A(1) and A(2A) receptors. Selected compounds were additionally investigated for affinity to the human A(1), A(2A), A(2B) and A(3) receptor subtypes. The results of the radioligand binding assays at adenosine A(1) and A(2A) receptors showed that most of the compounds exhibited adenosine A(2A) receptor affinity at micromolar or submicromolar concentrations; an annelated pyrimidine ring was beneficial for A(2A) affinity. The most potent A(2A) ligands of the present series were compounds 6 (K(i) 0.33 μM rat A(2A), 0.31 μM human A(2A)), 8 (K(i) 0.98 μM rat A(2A), 0.42 μM human A(2A)) and 15 (K(i) 0.24 μM rat A(2A), 0.61 μM human A(2A)) with the latter one showing high A(2A) selectivity. In NaCl shift assay, 15 was shown to be an antagonist at A(2A) receptors. This result was confirmed for the best compounds 6, 8, 15 in cAMP accumulation studies. A 3D-QSAR equation with a good predicting power (q(2) = 0.88) for A(2A) AR affinity was obtained. The compounds were evaluated in vivo as anticonvulsants in MES and ScMet tests and examined for neurotoxicity in mice (i.p.). Most of them showed anticonvulsant activity in chemically induced seizures; among them the diazepinopurinediones were the best (e.g. 31) showing protection in both tests on short time symptoms, without signs of neurotoxicity. Five compounds, 8, 17, 20, 29, and 31, exhibited anticonvulsant activity after peroral application in rats. Structure-activity relationships are discussed including the analysis of lipophilic and spatial properties. The new compounds, which contain a basic nitrogen atom and can therefore be protonated, may be good starting points for obtaining A(2A) antagonists with good water-solubility."

"The use of QSAR applications to develop adenosine receptor (AR) antagonists is not so common. A library of all xanthine derivatives, obtained at the Department of Technology and Biotechnology of Drugs, was created. Sixty-three active adenosine A1 receptor ligands and one hundred thirty nine active adenosine A2A receptor ligands were used for 3D-QSAR investigation. The 3D-QSAR equations with a high predictive power in estimating the binding affinity values of potential A1 and A2A ARs ligands were derived. For the first time, hybrid shape-property descriptors were used in 3D-QSAR for xanthine ARs ligands. The obtained models were characterized by a high regression and cross-validation coefficients. Two types of the model validation were tested – dividing the library into the training set for model development and external set for model validation and increasing the number of library components and checking the model by cross-validated regression coefficient. The analysis of the results depicts that for the A1 AR binding activity it is important for ligands to possess R1-propyl substituents along with the phenyl or benzyl substituents bearing halogen atom and phenethyl moiety. For A2A AR affinity it could be favorable to introduce phenethyl or phenyl substituent connected with the tricyclic ring by the alkoxy chain. The nature of R1 group may not significantly affect the A2A AR affinity. High predictive power of the equations suggests their use for further development of adenosine receptor antagonists within xanthine derivatives."

"This review summarizes the current tendencies observed in the past 5 years in the development of A(1) and A(2A) adenosine receptor antagonists performed in various academia and industry. A(1) and A(2A) AR antagonists are as well xanthines as heteroaromatic derivatives and are most commonly 6:5 fused heteroatomic compounds. Among xanthine-based compounds, some common features could be pointed out. The recent A(1) AR ligands which show good biological profile, possess long alkyl chains in position 1 and 3 as well as bulky C(8)-substituent, while A(2A) AR antagonists with a high A(2A) AR affinity are C(8)-styryl substituted with N(1)-alkyl/alkynyl moiety or fused tricyclic xanthines possessing heteroatom(s) in the third cycle. The research in the field of heteroaromatic A(1) and A(2A) ARs antagonists impressively has a wide range. Ligands are as well non-fused monocyclic substituted compounds as fused bi- and tricyclic derivatives with the nitrogen, oxygen and sulfur heteroatoms. Most often, adenosine A(1) receptor non-xanthine antagonists are adenine-based, having substituted amino group and variable nitrogen atoms positions in the molecules. A(2A) AR ligands show good affinity when furanyl function, which is crucial for binding, is present in the fused bicyclic and tricyclic analogs. Moreover, tricyclic nitrogen containing antagonists in order to be active, frequently possess long-alkylphenyl moiety."

"Syntheses and biological activities of imidazo-, pyrimido- and diazepino[2,1-f]purinediones containing N-alkyl substituents (with straight, branched or unsaturated chains) are described. Tricyclic derivatives were synthesized by the cyclization of 8-bromo-substituted 7-(2-bromoethyl)-, 7-(3-chloropropyl)- or 7-(4-bromobutyl)-theophylline with primary amines under various conditions. Compound 22 with an ethenyl substituent was synthesized by dehydrohalogenation of 9-(2-bromoethyl)-1,3-dimethyltetrahydropyrimido[2,1-f]purinedione. The obtained derivatives (5–35) were initially evaluated for their affinity at rat A1 and A2A adenosine receptors (AR), showing moderate affinity for both adenosine receptor subtypes. The best ligands were diazepinopurinedione 28 (K i = 0.28 μM) with fivefold A2A selectivity and the non-selective A1/A2A AR ligand pyrimidopurinedione 35 (K i A1 = 0.28 μM and K i A2A = 0.30 μM). The compounds were also evaluated for their affinity at human A1, A2A, A2B and A3 ARs. All of the obtained compounds were docked to the A2A AR X-ray structure in complex with the xanthine-based, potent adenosine receptor antagonist—XAC. The likely interactions of imidazo-, pyrimido- and diazepino[2,1-f]purinediones with the residues forming the A2A binding pocket were discussed. Furthermore, the new compounds were tested in vivo as anticonvulsants in maximal electroshock, subcutaneous pentylenetetrazole (ScMet) and TOX tests in mice (i.p.). Pyrimidopurinediones showed anticonvulsant activity mainly in the ScMet test. The best derivative was compound 11, showing 100 % protection at a dose of 100 mg/kg without symptoms of neurotoxicity. Compounds 6, 7, 8 and 14 with short substituents showed neurotoxicity and caused death. In rat tests (p.o.), 9 was characterized by a high protection index (>13.3). AR affinity did not apparently correlate with the antiepileptic potency of the compounds."