Synthesis and Biological Activity of New Potential Agonists for the Human Adenosine A_2A Receptor

Abstract

New adenosine derivatives have been synthesized and tested as putative agonists of adenosine receptors. Compounds 2-6 derive from the introduction of several types of substituents (electron donating, electron withdrawing, and halogens) in the para-position of the phenyl ring of the parent compound 1, and compound 7 lacks the hydroxyl group of amino alcohol 1. In radioligand binding assays using recombinant human A(1), A(2A), A(2B), and A(3) receptors, all compounds showed very low or negligible affinity for A(1) and A(2B) receptors but compounds 3, 5, and 7 displayed a remarkably potent affinity for the A(2A) receptor with K(i) values of 1-5 nM. Bromo derivative 3 displayed a selectivity A(1)/A(2A) = 62 and A(3)/A(2A) = 16 whereas the presence of a hydroxyl group (compound 5) improved the selectivity of A(1)/A(2A) and A(3)/A(2A) to 120- and 28-fold, respectively. When the methoxy derivative 4 lacks the hydroxyl group on the side chain (compound 7), the binding affinity for A(2A) is increased to 1 nM, improving selectivity ratios to 356- and 100-fold against A(1) and A(3), respectively. In Chinese hamster ovary cells transfected with human A(2A) and A(2B) receptors, most compounds showed a remarkable activity for the A(2A) receptor, except chloro derivative 2, with EC(50) values ranging from 1.4 to 8.8 nM. The compounds behaved as good A(2A) agonists, and all were more selective than 5'-(N-ethylcarboxamino)adenosine (NECA), with A(2B)/A(2A) ratios of cAMP accumulation ranging from 48 for compound 2 to 666 for compound 7 while the corresponding A(2B)/A(2A) ratio for NECA was only 9. Compounds 1, 3, 5, and 7 also displayed higher selectivities than NECA up to 100-fold in isolated aortas of rat and guinea pig. In guinea pig tracheal rings precontracted by carbachol, compounds 2 and 4 were more potent than adenosine (100-fold) and NECA (10-fold), whereas compounds 1 and 7 displayed similar effects to NECA. Pretreatment of the tracheal rings with A(2), A(2A), and A(2B) receptor antagonists 3,7-dimethyl-l-propargylxanthine, 8-(3-chlorostyryl)caffeine, and alloxazine produced a marked inhibition of the tracheal relaxations induced by compounds 1, 2, and 4, but none of the compounds showed selectivity toward any of the adenosine receptors.

Expression of human melanocortin 4 receptor in Saccharomyces cerevisiae

“…However, the potency of activation in yeasts was 30-40 times lower compared to mammalian cells (Table 1). A similar difference in ligand affinities between two expression systems has been observed also for adenosine A2b receptors [27,36]. One of the main differences between mammalian and yeast expression systems is the presence of the polysaccharide-rich yeast cell wall that has to be crossed by ligands in order to reach the receptors located in a plasma membrane.…”

Highlights on the Development of A2A Adenosine Receptor Agonists and Antagonists

“…The compounds have also been profiled in cAMP assays using human receptors expressed on transfected CHO cells, and in functional assays using rat aorta, guinea pig aorta, and guinea pig tracheal rings. [88] Results of these sets of experiments show that substitution at the para-position of the phenyl ring at the 2-side chain by different groups greatly increases the binding affinity for the A 2A AR. At the same time, the tested substituted derivatives have reduced affinity for A 1 and A 3 receptors, thus remarkably improving the A 1 /A 2A and A 3 /A 2A selectivity.…”

“…[58] Recently the synthesis and biological activity as potential agonists for human A 2A receptors of adenosine derivatives containing an ethyl-substituted tetrazole moiety at the 4'-position of the ribose and an amino alcohol at the 2-position of the adenine core were reported. [87,88] The activity of these compounds has been evaluated in radioligand binding assays using the four cloned human ARs. The compounds have also been profiled in cAMP assays using human receptors expressed on transfected CHO cells, and in functional assays using rat aorta, guinea pig aorta, and guinea pig tracheal rings.…”

Design and Synthesis of Novel Dual‐Action Compounds Targeting the Adenosine A2A Receptor and Adenosine Transporter for Neuroprotection

“…The chemical structures of the training set compounds and their binding affinities to the hA 2A R (or hENT1) were collected from published sources (see Supporting Information). [27,28] It is important to ensure that the activity of the training compounds cover at least four orders of magnitude, with at least three compounds in each log scale. [15,29] It is also recommended to select compounds with greater chemical diversity for constructing the training set.…”

“…On the other hand, amide 20 was converted into nitrile 21 upon treatment with DMSO, oxalyl chloride, and N,N-diisopropylethylamine. [26] After the substitution of the chlorine atom by 4-methoxybenzylamine, a 1,3-dipolar cycloaddition of the cyano group with sodium azide introduced the desired tetrazole moiety at the C5' position, [27] giving 16 after removal of the 2',3'-isopropylidene group under acidic conditions.…”