2,9-disubstituted-N6-(arylcarbamoyl)-8-azaadenines as new selective A3 adenosine receptor antagonists: synthesis, biochemical and molecular modelling studies.

A number of N6-(N-arylcarbamoyl)-2-substituted-9-benzyl-8-azaadenines, obtained by a modification of the synthetic scheme used to prepare selective A1 ligands, by only three or two steps, are described. At first we prepared a series of 2-phenyl-9-benzyl-8-azaadenines having as N6 substituent a variously substituted N-phenylcarbamoyl group. Some of these derivatives demonstrated good affinity towards the A3 subtype but low selectivity. Compounds having p-CF3, p-F and p-OCH3, as substituents on the phenylcarbamoyl group were selected as lead compounds for the second part of this study. Without modifying the N6 substituent, which would assure A3 affinity, we varied the 9 and 2 positions on these molecules to enhance selectivity. Some compounds having a p-methyl group on the 2-phenyl substituent showed a very good affinity and selectivity for the A3 subtype, revealing the first class of A3 adenosine receptor selective antagonists with a bicyclic structure strictly correlated to the adenine nucleus. The molecular modelling work, carried out using the DOCK program, supplied two models which may be useful for a better understanding of the binding modes. Both models highlighted the preferred interacting tautomeric forms of the antagonists for human A1 and A3 receptors.

N6-cycloalkyl-2-phenyl-3-deaza-8-azaadenines: a new class of A1 adenosine receptor ligands. A comparison with the corresponding adenines and 8-azaadenines.

Several 9-benzyl-N6-cycloalkyl-2-phenyladenines, 9-benzyl-N6-cycloalkyl-2-phenyl-8-azaadenines and 4-cycloalkylamino-1-benzyl-6-phenyl-1H-1,2,3-triazolo[4,5-c]pyridines were prepared and assayed as A1 adenosine receptor ligands. The 1H-1,2,3-triazolo[4,5-c]pyridines were obtained starting from N,N-diethyl-1-benzyl-4-carboxyamido-5-methyl-1H-1,2,3-triazole by lithiation in anhydrous tetrahydrofurane in the presence of benzonitrile. The usual work up afforded the isolation of 1-benzyl-6-phenyl-1H-1,2,3-triazolo[4,5-c]pyridin-4-one which was treated with phosphorous oxychloride and cycloalkylamines. Some compounds showed high affinity and selectivity and the trend of Ki values corresponds to the series of 9-benzyl-N6-cycloalkyl-2-phenyladenines and 9-benzyl-N6-cycloalkyl-2-phenyl-8-azaadenines, therefore they can be considered bioisosteres. The affinity data permitted us to ascertain the role and the importance of the N3 in the adenine or 8-azaadenine moiety in the receptor binding and to study the dimension of the receptor lipophilic pocket which is filled by the N6 substituent of adenosine derivatives.

New N6- or N(9)-hydroxyalkyl substituted 8-azaadenines or adenines as effective A1 adenosine receptor ligands.

In this paper we describe synthesis and biological assays of some A(1) ligands more water-soluble than the effective, but very lipophilic, 8-azaadenines and adenines discovered in the past and obtained introducing on N(6) or N(9) substituent a hydroxy group. Five of the new N(6)-hydroxyalkyl- and N(6)-hydroxycycloalkyl-2-phenyl-9-benzyl-8-azaadenines showed very high affinity (Ki<40 nM) and selectivity for A(1) adenosine receptors. Among the 2-phenyl-9-(2-hydroxy-3-alkyl)-8-azaadenines or adenines prepared, the compounds with the higher A(1) affinity and selectivity resulted 2-phenyl-9-(2-hydroxy-3-propyl)-N(6)-cyclopentyl- and cyclohexyl-8-azaadenine with Ki 2.2+/-0.2 nM and 2.8+/-0.3 nM respectively. From the point of view of water-solubility, 2-phenyl-9-(2-hydroxy-3-propyl)-8-azaadenine was the most interesting compound, having a CLogP of 1.066991 and a water-solubility of 1.2 mg mL(-1).

Erythro- and threo-2-hydroxynonyl substituted 2-phenyladenines and 2-phenyl-8-azaadenines: ligands for A1 adenosine receptors and adenosine deaminase.

erythro-2-Phenyl-9-(2-hydroxy-3-nonyl)adenine and its 8-aza analog were prepared and showed a very high inhibitory activity towards adenosine deaminase (ADA), with Ki 0.55 and 1.67 nM, respectively, and high affinity for A1 adenosine receptors, with Ki 28 and 2.8 nM, respectively. To increase affinity for A1 receptors we introduced a substituent on the N6 position such as alkyl or cycloalkyl groups, which are present in effective agonists or antagonists. Furthermore, for some compounds, we prepared the two diastereoisomers erythro and threo to verify whether the binding with A1 receptors is stereoselective, as in ADA. Results show that some of the synthesised compounds are good inhibitors for ADA and good ligands for A1, and the erythro diastereoisomers are more active than the threo ones. The experimental evidence allows us to hypothesise some similarity in the three dimensional structures of the binding site of the two proteins, ADA and A1 adenosine receptor, in spite of lacking any homologies in the amino acid sequences.