Synthesis of the water-soluble adenosine A1 receptor antagonist FR166124 through a novel sequential Horner-Emmons / isomerization reaction

Design, synthesis and biological evaluation of a novel series of potent, orally active adenosine A1 receptor antagonists with high blood-brain barrier permeability

A novel series of 3-(2-substituted-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazolo[1,5-a]pyridines (5-38) were synthesized and evaluated for their in vitro adenosine A1 and A(2A) receptor binding activities, and in vitro metabolism by rat liver in order to search for orally active compounds. Most of the test compounds were potent adenosine A1 receptor antagonists with high A1 selectivity and the A1 affinity and A1 selectivity of carbonyl derivatives (5-11) was particularly high. In particular, compound 7 was an extremely potent and selective adenosine A1 antagonist with high A1 selectivity (Ki=0.026 nM, A(2A)/A1=5400). In terms of metabolic stability, 2-oxopropyl (5), 2-hydroxypropyl (12), N-methylacetamide (16), 2-(piperidin-1-yl)ethyl (28) and 1-methylpiperidin-4-yl (32, FR194921) were the most stable compounds in this series of analogues. Further in vivo evaluation indicated that compounds 5, 13, 17, 28 and 32 were detected in both plasma and brain after oral administration in rats. In particular, 32 displayed good plasma and brain concentrations (dose: 32 mg/kg (n=3); after 30 min, plasma conc.=3390+/-651nM, brain conc.=3670+/-496nM; after 60min, plasma conc.=1580+/-348nM, brain conc.=2143+/-434nM), and a good brain/plasma ratio (1.11+/-0.060 (30min), 1.39+/-0.172 (60min)). As a result, we could show that 32 is a good candidate for an orally active adenosine A1 receptor antagonist with high blood-brain barrier permeability and good bioavailability (Ki=6.6nM, A(2A)/A1=820, BA=60.6+/-4.9% (32 mg/kg)).

Novel adenosine A1 receptor antagonists. Synthesis and structure-activity relationships of a novel series of 3-(2-cyclohexenyl-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazolo[1,5 -a]pyridines

A novel series of 3-(2-cyclohexenyl-3-oxo-2,3-dihydropyridazin-6-yl)-2-phenylpyrazol o[1,5-a]pyridines was synthesized and evaluated for in vitro adenosine A1 and A2A receptor binding activities. Most of the cyclohexenyl derivatives (7a-e, 8a-s) were found to be potent adenosine A1 receptor antagonists. In a series of analogues of FR166124 (3a), alcohol 7c, nitrile 7e and amide derivatives (7d, 8c, 8r) were found to be more potent A1 antagonists with higher A2A/A1 selectivity than FR166124. Amongst them, 8r showed considerable water solubility (33.3 mg/mL), but lower than that of the sodium salt of FR166124 (> 200 mg/mL). Additionally, FR166124 had strong diuretic activity by both p.o. and iv administration in rats (minimum effective dose=0.1 and 0.032 mg/kg, respectively).