Amine-constrained pyridazinone histamine H3 receptor antagonists

Microwave-assisted synthesis of 4-oxo-2-butenoic acids by aldol-condensation of glyoxylic acid

4-Oxobutenoic acids are useful as biologically active species and as versatile intermediates for further derivatisation. Currently, routes to their synthesis can be problematic and lack generality. Reaction conditions for the synthesis of 4-oxo-2-butenoic acid by microwave-assisted aldol-condensation between methyl ketone derivatives and glyoxylic acid have been developed. They provide the desired products in moderate to excellent yields for a wide range of substrates, by applying a simple procedure to accessible starting materials. The investigation revealed different conditions are required depending on the nature of the methylketone substituent, with aryl derivatives proceeding best using tosic acid and aliphatic substrates reacting best with pyrrolidine and acetic acid. This substituent effect is rationalised by frontier orbital calculations. Overall, this work provides methods for synthesis of 4-oxo-butenoic acids across a broad range of substrates.

N-Heterocyclic Carbene-Catalyzed Oxidative Annulations of α,β-Unsaturated Aldehydes with Hydrazones: Selective Synthesis of Optically Active 4,5-Dihydropyridazin-3-ones and Pyridazin-3-ones

A novel and efficient method for the highly enantioselective synthesis of chiral 4,5-dihydropyridazin-3-one derivatives has been developed based on the chiral N-heterocyclic carbene-catalyzed oxidative annulation between α,β-unsaturated aldehydes and hydrazones. Meanwhile, the selective synthesis of either 4,5-dihydropyridazin-3-ones or pyridazin-3-one derivatives from the same reactants has been achieved by simply varying catalytic and reaction conditions.

Discovery of (1R,6S)-5-[4-(1-cyclobutyl-piperidin-4-yloxy)-phenyl]-3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one (R,S-4a): histamine H(3) receptor inverse agonist demonstrating potent cognitive enhancing and wake promoting activity

A series of fused cyclopropyl-4,5-dihydropyridazin-3-one (3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one) phenoxypiperidine analogs was designed and synthesized, leading to the identification of (1R,6S)-5-[4-(1-cyclobutyl-piperidin-4-yloxy)-phenyl]-3,4-diaza-bicyclo[4.1.0]hept-4-en-2-one (R,S-4a) as a second-generation pyridazin-3-one H3R antagonist. Compound R,S-4a was a potent H3R functional antagonist in vivo in the rat dipsogenia model, demonstrated potent wake activity in the rat EEG/EMG model, and enhanced short-term memory in the rat social recognition memory model at doses as low as 0.03-0.3 mg/kg po.

4-phenoxypiperidine pyridazin-3-one histamine H(3) receptor inverse agonists demonstrating potent and robust wake promoting activity

Structure-activity relationships for a series of phenoxypiperidine pyridazin-3-one H(3)R antagonists/inverse agonists are disclosed. The search for compounds with improved hERG and DAT selectivity without the formation of in vivo active metabolites identified 6-[4-(1-cyclobutyl-piperidin-4-yloxy)-phenyl]-4,4-dimethyl-4,5-dihydro-2H-pyridazin-3-one 17b. Compound 17b met discovery flow criteria, demonstrated potent H(3)R functional antagonism in vivo in the rat dipsogenia model and potent wake activity in the rat EEG/EMG model at doses as low as 0.1 mg/kg ip.