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Photoaffinity labeling (PAL) is widely used for the identification of ligand-binding proteins and elucidation of ligand-binding sites. PAL has also been employed for the characterization of G protein-coupled receptors (GPCRs); however, a limited number of reports has successfully identified their cross-linked amino acids. This report is the first of its kind to determine the cross-link position of the human A adenosine receptor by PAL with the novel diazirine-based photoaffinity probe .

With a novel assay using isolated ferret detrusor to estimate beta(3)-adrenoceptor agonistic activity, we found that a series of glycine derivatives of ritodrine, a beta(2)-adrenoceptor agonist, are potent beta(3)-adrenoceptor agonists, with excellent selectivity versus beta(1) and beta(2) subtypes. Substitution of halogens in the phenyl ring increased potency and selectivity for the beta(3)-adrenoceptor, and this was dependent upon the position of the halogens. The chlorine-substituted derivatives 3f-i exhibited potent beta(3)-adrenoceptor-mediated relaxation of ferret detrusor (EC(50) = 0.93, 11, 14, and 160 nM) and higher potency at beta(3)-adrenoceptors than at beta(1) or beta(2). The intravenous administration of 3h significantly reduced the urinary bladder pressure in anesthetized male rats (ED(50) = 48 microg/kg) without cardiovascular side effects. This article is the first report of structure-activity relationships (SAR) concerning beta(3)-adrenoceptor agonists as agents for the treatment of urinary frequency and incontinence.

This report proposes a beta(3)-adrenoceptor (AR) selective agonist, 2-[2-chloro-4-(2-([(1S,2R)-2-hydroxy-2-(4-hydroxyphenyl)-1-methylethyl]amino)ethyl)phenoxy]acetic acid (1a), as a novel agent for treating urinary bladder dysfunction. This compound and its relatives have a unique feature among beta(3)-AR agonists: two chiral carbons are adjacently structured on the left side of the molecule. To study the relationship between the stereoconfiguration of the vicinal chiral carbons in 1a and beta-AR agonistic activity, the four stereoisomers were synthesized via oxazolidinone prepared by intracyclization involving inversion of the beta-hydroxy group. The in vitro assays using rat atria for beta(1)-AR, rat uteri for beta(2)-AR, and ferret detrusor for beta(3)-AR showed that 1a possessed potent beta(3)-AR agonistic activity (EC(50) = 3.85 nM) and 3700- and 1700-fold selectivity for beta(3)-AR relative to beta(1)- and beta(2)-AR, respectively. Comparison of the four isomers revealed that the (alphaS,betaR)-compound (1a) was not only the most potent agonist but was also the most selective for beta(3)-AR. In the anesthetized rat, intravenous administration of 1a brought about a sufficient decrement of the intrabladder pressure (ED(50) = 12 microg/kg), and intraduodenal administration of 2a, which is the ethyl ester of 1a, led to same result (ED(50) = 0.65 mg/kg). Moreover, no effects on the cardiovascular system were observed in either test.

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