Synthesis and structure-activity relationship of 5-pyridazin-3-one phenoxypiperidines as potent, selective histamine H(3) receptor inverse agonists

Synthesis of Spiro[cycloalkane-pyridazinones] with High Fsp3 Character Part 2*

Abstract:

An extended compound library of spiro[cycloalkane-pyridazinones] with a high Fsp3 character is targeted. There are two possibilities to improve the physicochemical parameters of a drug candidate molecules or building blocks, either to replace the aromatic systems with bioisoster heteroaromatic moieties, e.g. with one or two nitrogen containing ring systems (pyridines, pyridazines, pyrimidines, etc.), or to increase the Fsp3 character of the compounds. Using a new synthetic approach, the Grignard reaction of 2-oxaspiro[4.5]decane-1,3-dione and 2-oxaspiro[4.4]nonane-1,3-dione with p-halophenyl- or p-alkylphenyl-magnesium bromide resulted in the formation of the corresponding 2-oxoethyl-cycloalkanecarboxylic acids, which served as starting materials for the pyridazinones by reaction with hydrazine or phenylhydrazine. The pyridazinones obtained were alkylated with methyliodide or benzylbromide. 16 Novel 4-tolyl- or 4-halophenyl-2,3-diazaspiro[5.5]undec-3-en-1-one and 4-tolyl- or 4-halopyhenyl-7,8-diazaspiro[4.5]dec-8-en-6-one, and their N-methyl, N-benzyl, and N-phenyl derivatives were synthetized. The physicochemical parameters and the Fsp3 character of the novel compounds obtained were studied. A few of them showed excellent logP and clogP values, but the introduction of a further phenyl group seemed to be disadvantageous.

Crystal structure and Hirshfeld surface analysis of 4-(2,6-di-chloro-benz-yl)-6-[(E)-2-phenyl-ethen-yl]pyridazin-3(2H)-one

The title pyridazinone derivative, C19H14Cl2N2O, an important pharmacophore with a wide variety of biological applications is not planar, the chloro-phenyl and pyridazinone rings being almost perpendicular, subtending a dihedral angle of 85.73 (11)°. The phenyl ring of the styryl group is coplanar with the pyridazinone ring [1.47 (12)°]. In the crystal, N-H⋯O hydrogen bonds form inversion dimers with an R 2 2(8) ring motif and C-H⋯Cl hydrogen bonds also occur. The roles of the inter-molecular inter-actions in the crystal packing were clarified using Hirshfeld surface analysis, and two-dimensional fingerprint plots indicate that the most important contributions to the crystal packing are from H⋯H (37.9%), C⋯H/H⋯C (18.7%), Cl⋯H/ H⋯Cl (16.4%) and Cl⋯C/C⋯Cl (6.7%) contacts.

Crystal structure, Hirshfeld surface analysis and DFT studies of 6-[(E)-2-(thio-phen-2-yl)ethenyl]-4,5-di-hydro-pyridazin-3(2H)-one

In the title compound, C10H10N2OS, the five atoms of the thio-phene ring are essentially coplanar (r.m.s. deviation = 0.0037 Å) and the pyridazine ring is non-planar. In the crystal, pairs of N-H⋯O hydrogen bonds link the mol-ecules into dimers with an R 2 2(8) ring motif. The dimers are linked by C-H⋯O inter-actions, forming layers parallel to the bc plane. The theoretical geometric parameters are in good agreement with XRD results. The inter-molecular inter-actions were investigated using a Hirshfeld surface analysis and two-dimensional fingerprint plots. The Hirshfeld surface analysis of the title compound suggests that the most significant contributions to the crystal packing are by H⋯H (39.7%), C⋯H/H⋯C (17.3%) and O⋯H/H⋯O (16.8%) contacts.

Crystal structure and Hirshfeld surface analysis of (E)-6-(4-hy-droxy-3-meth-oxy-styr-yl)-4,5-di-hydro-pyridazin-3(2H)-one

In the title com­pound, inter­molecular C—H⋯O, O—H⋯O and N—H⋯O hydrogen bonds link the mol­ecules into a three-dimensional supra­molecular network.

In the title com­pound, C₁₃H₁₄N₂O₃, the dihydropyridazine ring (r.m.s. deviation = 0.166 Å) has a screw-boat conformation. The dihedral angle between its mean plane and the benzene ring is 0.77 (12)°. In the crystal, inter­molecular O—H⋯O hydrogen bonds generate C(5) chains and N—H⋯O hydrogen bonds produce R₂²(8) motifs. These types of inter­actions lead to the formation of layers parallel to (12). The three-dimensional network is achieved by C—H⋯O inter­actions, including R₂⁴(8) motifs. Inter­molecular inter­actions were additionally investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots. The most significant contributions to the crystal packing are by H⋯H (43.3%), H⋯C/C⋯H (19.3%), H⋯O/H⋯O (22.6%), C⋯N/N⋯C (3.0%) and H⋯N/N⋯H (5.8%) contacts. C—H⋯π inter­actions and aromatic π–π stacking inter­actions are not observed.

Crystal structure and Hirshfeld surface analysis of 4-(4-methyl-benz-yl)-6-phenyl-pyridazin-3(2H)-one

In this paper, we describe the synthesis of a new di-hydro-2H-pyridazin-3-one derivative. The mol-ecule, C18H16N2O, is not planar; the benzene and pyridazine rings are twisted with respect to each other, making a dihedral angle of 11.47 (2)°, and the toluene ring is nearly perpendicular to the pyridazine ring, with a dihedral angle of 89.624 (1)°. The mol-ecular conformation is stabilized by weak intra-molecular C-H⋯N contacts. In the crystal, pairs of N-H⋯O hydrogen bonds link the mol-ecules into inversion dimers with an R 2 2(8) ring motif. The inter-molecular inter-actions were investigated using Hirshfeld surface analysis and two-dimensional (2D) fingerprint plots, revealing that the most important contributions for the crystal packing are from H⋯H (56.6%), H⋯C/C⋯H (22.6%), O⋯H/H⋯O (10.0%) and N⋯C/C⋯N (3.5%) inter-actions.

Crystal structure and Hirshfeld surface analysis of ethyl 2-[5-(3-chloro-benz-yl)-6-oxo-3-phenyl-1,6-di-hydro-pyridazin-1-yl]acetate

The title pyridazinone derivative, C21H19ClN2O3, is not planar. The unsubstituted phenyl ring and the pyridazine ring are inclined to each other, making a dihedral angle of 17.41 (13)° whereas the Cl-substituted phenyl ring is nearly orthogonal to the pyridazine ring [88.19 (13)°]. In the crystal, C-H⋯O hydrogen bonds generate dimers with R 2 2(10) and R 2 2(24) ring motifs which are linked by C-H⋯O inter-actions, forming chains extending parallel to the c-axis direction. The inter-molecular inter-actions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, revealing that the most significant contributions to the crystal packing are from H⋯H (44.5%), C⋯H/H⋯C (18.5%), H⋯O/H⋯O (15.6%), Cl⋯H/H⋯Cl (10.6%) and C⋯C (2.8%) contacts.

Crystal structure and Hirshfeld surface analysis of 4-(2,6-di-chloro-benz-yl)-6-phenyl-pyridazin-3(2H)-one

The asymmetric unit of the title compound, C₁₇H₁₂Cl₂N₂O, contains one independent mol-ecule. The mol-ecule is not planar, the phenyl and pyridazine rings are twisted with respect to each other, making a dihedral angle of 29.96 (2)° and the di-chloro-phenyl ring is nearly perpendicular to the pyridazine ring, with a dihedral angle of 82.38 (11)°. In the crystal, pairs of N-H⋯O hydrogen bonds link the mol-ecules to form inversion dimers with an R ₂ ²(8) ring motif. The dimers are linked by C-H⋯O inter-actions, forming layers parallel to the bc plane. The inter-molecular inter-actions were investigated using Hirshfeld surface analysis and two-dimensional fingerprint plots, and the mol-ecular electrostatic potential surface was also analysed. The Hirshfeld surface analysis of the title compound suggests that the most significant contributions to the crystal packing are by H⋯H (31.4%), Cl⋯H/H⋯Cl (19.9%) and C⋯H/H⋯C (19%) contacts.

Pyridazinone: an attractive lead for anti-inflammatory and analgesic drug discovery

In spite of the availability of a large number of anti-inflammatory and analgesic agents, fighting pain and inflammation remains a common problem. The current review article discusses the need of novel therapeutic targets for risk-free anti-inflammatory and analgesic therapy and summarizes some new agents in various stages of drug discovery pipeline. Pyridazin-3(2H)-ones are nitrogen-rich heterocyclic compounds of considerable medicinal interest due to their diverse biological activities. The current review article focuses on progressive development of this attractive scaffold for the design and synthesis of new pyridazinone-based anti-inflammatory and analgesic agents. Mechanistic insights into the anti-inflammatory and analgesic properties of pyridazinone derivatives and various synthetic techniques used for their synthesis are also described.

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.