The adenosine A(2B) receptor is the least well characterized of the four known adenosine receptor subtypes because of the absence of potent, selective agonists. Here, we present five non-adenosine agonists. Among them, 2-amino-4-(4-hydroxyphenyl)-6-(1H-imidazol-2-ylmethylsulfanyl)pyridine-3,5-dicarbonitrile, 17, LUF5834, is a high-efficacy partial agonist with EC(50) = 12 nM and 45-fold selectivity over the adenosine A(3) receptor but lacking selectivity versus the A(1) and A(2A) subtypes. Compound 18, LUF5835, the 3-hydroxyphenyl analogue, is a full agonist with EC(50) = 10 nM.

Adenosine receptor antagonists usually possess a bi- or tricyclic heteroaromatic structure at their core with varying substitution patterns to achieve selectivity and/or greater affinity. Taking into account molecular modeling results from a series of potent adenosine A1 receptor antagonists, a pharmacophore was derived from which we show that a monocyclic core can be equally effective. To achieve a compound that may act at the CNS we propose imposing a restriction related to its polar surface area (PSA). In consequence, we have synthesized two novel series of pyrimidines, possessing good potency at the adenosine A1 receptor and desirable PSA values. In particular, compound 30 (LUF 5735) displays excellent A1 affinity (Ki = 4 nM) and selectivity (< or =50% displacement of 1 muM concentrations of the radioligand at the other three adenosine receptors) and has a PSA value of 53 A2.

Adenosine receptor agonists are usually variations of the natural ligand, adenosine. The ribose moiety in the ligand has previously been shown to be of great importance for the agonistic effects of the compound. In this paper, we present a series of nonadenosine ligands selective for the adenosine A(1) receptor with an extraordinary pharmacological profile. 2-Amino-4-benzo[1,3]dioxol-5-yl-6-(2-hydroxyethylsulfanyl)pyridine-3,5-dicarbonitrile (70, LUF 5853) shows full agonistic behavior comparable with the reference compound CPA, while also displaying comparable receptor binding affinity (K(i) = 11 nM). In contrast, compound 58 (2-amino-4-(3-trifluoromethylphenyl)-6-(2-hydroxyethylsulfanyl)pyridine-3,5-dicarbonitrile, LUF 5948) has a binding affinity of 14 nM and acts as an inverse agonist. Also present within this same series are compounds that show neutral antagonism of the adenosine A(1) receptor, for example compound 65 (2-amino-4-(4-difluoromethoxyphenyl)-6-(2-hydroxyethylsulfanyl)pyridine-3,5-dicarbonitrile, LUF 5826).

Purines have long been exploited as adenosine receptor antagonists. The substitution pattern about the purine ring has been well investigated, and certain criteria have become almost a prerequisite for good affinity at the adenosine A(1) receptor. The adaptation of the pharmacophore and the initial series of pyrimidines developed in an earlier publication resulted in a series of purines with an entirely new substitution pattern. One compound in particular, 8-cyclopentyl-2,6-diphenylpurine (31, LUF 5962) has been shown to be very promising with an affinity of 0.29 nM at the human adenosine A(1) receptor.

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