Synthesis and structure–activity relationships of 4,5-fused pyridazinones as histamine H3 receptor antagonists

Chemo-, Regio-, and Enantioselective Rhodium-Catalyzed Allylation of Pyridazinones with Terminal Allenes

The rhodium-catalyzed addition of pyridazinones to terminal allenes furnished the corresponding branched N²-allylated products in good yields with high regio- and enantioselectivities. A broad functional group compatibility was observed, and assorted synthetic transformations of the N-allylpyridazinones led to the preparation of a small library of N²-functionalized pyridazinones. Labeling experiments with deuterated substrates provided insights into the underlying reaction mechanism.

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-[(tert-Butyl-diphenyl-sil-yloxy)meth-yl]pyridazin-3(2H)-one

In the title compound, C₂₁H₂₄N₂O₂Si, the carbonyl group of the heterocyclic ring and the O atom of the silyl ether group are placed toward opposite sides and the tert-butyl and pyridazinone moieties are anti-oriented across the Si—O bond [torsion angle = −168.44 (19)°]. In the crystal, mol­ecules are assembled into inversion dimers through co-operative N—H⋯O hydrogen bonds between the NH groups and O atoms of the pyridazinone rings of neighbouring mol­ecules. The dimers are linked by π–π inter­actions involving adjacent pyridazinone rings [centroid–centroid distance = 3.8095 (19) Å], generating ladder-like chains along the b-axis direction. The chains are further linked into a two-dimensional network parallel to the ab plane through weak C—H⋯π inter­actions.

5-[(tert-Butyl-diphenyl-sil-yloxy)meth-yl]pyridazin-3(2H)-one

In the title compound, C₂₁H₂₄N₂O₂Si, a new pyridazin-3(2H)-one derivative, the carbonyl group of the heterocyclic ring and the O atom of the silyl ether are located on the same side of the pyridazinone ring and the C—C—O—Si torsion angle is −140.69 (17)°. In the crystal, mol­ecules are linked by pairs of strong N—H⋯O hydrogen bonds into centrosymmetric dimers with graph-set notation R₂²(8). Weak C—H⋯π inter­actions are also observed.

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.