Anilide derivatives of an 8-phenylxanthine carboxylic congener are highly potent and selective antagonists at human A(2B) adenosine receptors.
No highly selective antagonists of the A(2B) adenosine receptor (AR) have been reported; however such antagonists have therapeutic potential as antiasthmatic agents. Here we report the synthesis of potent and selective A(2B) receptor antagonists. The structure-activity relationships (SAR) of 8-phenyl-1, 3-di-(n-propyl)xanthine derivatives in binding to recombinant human A(2B) ARs in HEK-293 cells (HEK-A(2B)) and at other AR subtypes were explored. Various amide derivatives of 8-[4-[[carboxymethyl]oxy]phenyl]-1,3-di-(n-propyl)xanthine, 4a, were synthesized. A comparison of aryl, alkyl, and aralkyl amides demonstrated that simple anilides, particularly those substituted in the para-position with electron-withdrawing groups, such as nitro, cyano, and acetyl, bind selectively to human A(2B) receptors in the range of 1-3 nM. The unsubstituted anilide 12 had a K(i) value at A(2B) receptors of 1.48 nM but was only moderately selective versus human A(1)/A(2A) receptors and nonselective versus rat A(1) receptors. Highly potent and selective A(2B) antagonists were a p-aminoacetophenone derivative 20 (K(i) value 1.39 nM) and ap-cyanoanilide 27 (K(i) value 1.97 nM). Compound 27 was 400-, 245-, and 123-fold selective for human A(2B) receptors versus human A(1)/A(2A)/A(3) receptors, respectively, and 8.5- and 310-fold selective versus rat A(1)/A(2A) receptors, respectively. Substitution of the 1,3-dipropyl groups with 1,3-diethyl offered no disadvantage for selectivity, and high affinities at A(2B) receptors were maintained. Substitution of the p-carboxymethyloxy group of 4a and its amides with acrylic acid decreased affinity at A(2B) receptors while increasing affinity at A(1) receptors. 1, 3-Di(cyclohexylmethyl) groups greatly reduced affinity at ARs, although the p-carboxymethyloxy derivative 9 was moderately selective for A(2B) receptors. Several selective A(2B) antagonists inhibited NECA-stimulated calcium mobilization in HEK-A(2B) cells.
Kim
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Molecular Recognition Section, Laboratory of Bioorganic Chemistry, National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0810, USA.
Ji
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Melman
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Linden
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Jacobson
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D000813:Anilides / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D058915:Purinergic P1 Receptor Antagonists; D011869:Radioligand Assay; D051381:Rats; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1 / Q000378:metabolism; D013329:Structure-Activity Relationship; D014970:Xanthines / Q000138:chemical synthesis* / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
D000813:Anilides; C406351:MRS 1204; C406352:MRS 1595; D058915:Purinergic P1 Receptor Antagonists; D043705:Receptor, Adenosine A2A; D043704:Receptor, Adenosine A2B; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1; D014970:Xanthines; D002118:Calcium