# Patent

## Title
Imidazo[1,2-b]pyridazines, processes, uses, intermediates and compositions

## Abstract

The invention provides novel imidazo[1,2-b]pyridazines of formula (I) and pharmaceutically acceptable salts, polymorphs, hydrates, tautomers, solvates and stereoisomers thereof.
Compounds of formula (I) are useful for treating or preventing diseases associated with GABAA receptors modulation, anxiety, epilepsy, sleep disorders including insomnia, and for inducing sedation-hypnosis, anesthesia, sleep and muscle relaxation.
The invention also provides synthetic procedures for preparing said compounds and certain intermediates, as well as intermediates themselves.

## Background
This invention is directed to agents with affinity for GABAA receptor, specifically to imidazo[1,2-b]pyridazine compounds.
BACKGROUND OF THE INVENTION
GABAA receptor (γ-aminobutyric acidA) is a pentameric protein which forms a membrane ion channel. GABAA receptor is implicated in the regulation of sedation, anxiety, muscle tone, epileptogenic activity and memory functions. These actions are due to defined subunits of GABAA receptor, particularly the α1- and α2-subunits.
Sedation is modulated by the α1-subunit. Zolpidem is characterized by a high affinity for the α1-receptors and its sedative and hypnotic action is mediated by these receptors in vivo. Similarly, the hypnotic action of zaleplon is also mediated by the α1-receptors.
The anxiolytic action of diazepam is mediated by the enhancement of GABAergic transmission in a population of neurons expressing the α2-receptors. This indicates that the α2-receptors are highly specific targets for the treatment of anxiety.
Muscle relaxation in diazepam is mainly mediated by α2-receptors, since these receptors exhibit a highly specific expression in spinal cord.
The anticonvulsant effect of diazepam is partly due to α1-receptors. In diazepam, a memory-impairing compound, anterograde amnesia is mediated by α1-receptors.
GABAA receptor and its α1- and α2-subunits have been widely reviewed by H. Möhler et al. (J. Pharmacol. Exp. Ther., 300, 2-8, 2002); H. Mohler et al. (Curr. Opin. Pharmacol., 1, 22-25, 2001); U. Rudolph et al. (Nature, 401, 796-800, 1999); and D. J. Nutt et al. (Br. J. Psychiatry, 179, 390-396, 2001).
Diazepam and other classical benzodiazepines are extensively used as anxiolytic agents, hypnotic agents, anticonvulsants and muscle relaxants.
Their side effects include anterograde amnesia, decrease in motor activity and potentiation of ethanol effects.
In this context, the compounds of this invention are ligands of α1- and α2-GABAA receptor for their clinical application in sleep disorders, preferably insomnia, anxiety and epilepsy.
Insomnia is a highly prevalent disease. Its chronicity affects 10% of the population and 30% when transitory insomnia is computed as well. Insomnia describes the trouble in getting to sleep or staying asleep and is associated with next-day hangover effects such as weariness, lack of energy, low concentration and irritability. The social and health impact of this complaint is important and results in evident socioeconomic repercussions.
Pharmacological therapy in the management of insomnia firstly included barbiturates and chloral hydrate, but these drugs elicit numerous known adverse effects, for example, overdose toxicity, metabolic induction, and enhanced dependence and tolerance. In addition, they affect the architecture of sleep by decreasing above all the duration and the number of REM sleep stages. Later, benzodiazepines meant an important therapeutic advance because of their lower toxicity, but they still showed serious problems of dependence, muscle relaxation, amnesia and rebound insomnia following discontinuation of medication.
The latest known therapeutic approach has been the introduction of non-benzodiazepine hypnotics, such as pyrrolo[3,4-b]pyrazines (zopiclone), imidazo[1,2-a]pyridines (zolpidem) and, finally, pyrazolo[1,5-a]pyrimidines (zaleplon). Later, two new pyrazolo[1,5-a]pyrimidines, indiplon and ocinaplon, have entered into development, the latter with rather anxiolytic action. All these compounds show a rapid sleep induction and have less next-day hangover effects, lower potential for abuse and lower risk of rebound insomnia than benzodiazepines. The mechanism of action of these compounds is the alosteric activation of GABAA receptor through its binding to benzodiazepine binding site (C. F. P. George, The Lancet, 358, 1623-1626, 2001). While benzodiazepines are unspecific ligands at GABAA receptor binding site, zolpidem and zaleplon show a greater selectivity for α1-subunit.
Notwithstanding that, these drugs still affect the architecture of sleep and may induce dependence in long-term treatments.
Some N-imidazo[1,2-b]pyridazin-3-yl-methyl-alkanamides and N-imidazo[1,2-b]pyridazin-3-yl-methyl-benzamides, wherein the phenyl ring from the benzamide group can be optionally substituted, have been disclosed in WO 89/01333.
The compounds of the present invention are structurally related to, but distinct from the compound N,N,6-trimethyl-2-p-tolylimidazo[1,2-a]pyridine-3-acetamide, zolpidem, which is described in U.S. Pat. No. 4,382,938, because of their improved properties as shown in the Detailed Description of the Invention.
Research for new active compounds in the management of insomnia answers an underlying health need, because even recently introduced hypnotics still affect the architecture of sleep and may induce dependence in long-term treatments.
It is therefore desirable to focus on the development of new hypnotic agents with a lower risk of side effects.
SUMMARY OF THE INVENTION
The present invention provides new imidazo[1,2-b]pyridazines which are active versus GABAA and, particularly, versus its α1- and α2-subunits. Consequently, the compounds of this invention are useful in the treatment and prevention of all those diseases mediated by GABAA receptor α1- and α2-subunits. Non-limitative examples of such diseases are sleep disorders, preferably insomnia, anxiety and epilepsy. Non-limitative examples of the relevant indications of the compounds of this invention are all those diseases or conditions, such as insomnia or anesthesia, in which an induction of sleep, an induction of sedation or an induction of muscle relaxation are needed.
Thus, the present invention describes a novel class of compounds represented by formula (I):




and pharmaceutically acceptable salts, polymorphs, hydrates, tautomers, solvates and stereoisomers thereof, wherein R1 to R4, and Y are defined below, which are ligands of GABAA receptor.

It is another object of this invention to provide synthetic procedures for preparing the compounds of formula (I), certain intermediates thereof, as well as intermediates themselves. Novel methods of treating or preventing diseases associated with GABAA receptors modulation such as anxiety, epilepsy and sleep disorders including insomnia, and for inducing sedation-hypnosis, anesthesia, sleep and muscle relaxation by administering a therapeutically effective amount of said compounds are also within the scope of the invention.


DETAILED DESCRIPTION OF THE INVENTION
The present invention relates to novel imidazo[1,2-b]pyridazine compound of formula (I):




wherein

R1 and R2 are independently selected from the group consisting of hydrogen, linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C2-C6), cycloalkyl(C3-C6), haloalkyl(C2-C6), hydroxy, —O-alkyl(C1-C6), phenoxy, —S-alkyl(C1-C6), phenylthio, halogen, nitro, cyano, amino, alkylamino(C1-C6), dialkylamino(C1-C6), pyrrolidinyl, morpholinyl, piperidinyl, N-alkyl(C1-C6)piperazinyl, phenyl optionally substituted by 1 to 5 Z groups and heteroaryl optionally substituted by 1 to 5 Z groups; R3 and R4 are independently selected from the group consisting of hydrogen, linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C2-C6), cycloalkyl(C3-C6), hydroxyalkyl(C1-C6), amino, —NH-alkyl(C1-C6), —N-dialkyl(C1-C6), pyrrolidinyl, morpholinyl, piperidinyl, —N-alkyl(C1-C6)piperazinyl, —N-acyl(C1-C6)piperazinyl, phenyl optionally substituted by 1 to 5 Z groups and heteroaryl optionally substituted by 1 to 5 Z groups, or both R3 and R4 can form, together with the nitrogen atom to which they are attached, a 5-6 membered heterocyclic ring optionally substituted by 1 to 5 Z groups, with the proviso that R3 and R4 may not be simultaneously hydrogen;

X is selected from CO and SO2;

Z is selected from the group consisting of linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C2-C6), cycloalkyl(C3-C6), haloalkyl(C2-C6), hydroxy, —O-alkyl(C1-C6), phenoxy, —S-alkyl(C1-C6), phenylthio, halogen, nitro, cyano, amino, alkylamino(C1-C6) and dialkylamino(C1-C6); and

pharmaceutically acceptable salts, polymorphs, hydrates, tautomers, solvates and stereoisomers thereof.

Preferably R1 is selected from methyl, chlorine, methoxy, ethoxy, phenylthio or 1-pyrrolidinyl group and R2 is a phenyl group or a phenyl group substituted in para-position by methyl, halogen, methoxy, nitro or trifluoromethyl.
Preferably, X is CO; R3 is selected from the group consisting of hydrogen, linear alkyl(C1-C6), phenyl optionally substituted by 1 to 5 Z groups, heteroaryl optionally substituted by 1 to 5 Z groups, amino, —NH-alkyl(C1-C6), —N-dialkyl(C1-C6), 1-pyrrolidinyl, 4-morpholinyl and 1-piperidinyl; and R4 is selected from the group consisting of hydrogen, linear alkyl(C1-C6), phenyl optionally substituted by 1 to 5 Z groups and heteroaryl optionally substituted by 1 to 5 Z groups; or both R3 and R4 can form, together with the nitrogen atom to which they are attached, a 5-6 membered heterocyclic ring optionally substituted by 1 to 5 Z groups; and Z is selected from the group consisting of methyl and methoxy.
The term “pharmaceutically acceptable salt” used herein encompasses any salt formed from organic and inorganic acids, such as hydrobromic, hydrochloric, phosphoric, nitric, sulfuric, acetic, adipic, aspartic, benzenesulfonic, benzoic, citric, ethanesulfonic, formic, fumaric, glutamic, lactic, maleic, malic, malonic, mandelic, methanesulfonic, 1,5-naphthalendisulfonic, oxalic, pivalic, propionic, p-toluenesulfonic, succinic, tartaric acids and the like.
Preferred compounds of formula (I) include:

    2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-diethyl-acetamide;
    2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone;
    2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone;
    2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-pyrrolidin-1-yl-ethanone;
    N,N-Diethyl-2-(6-pyrrolidin-1-yl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N,N-Diethyl-2-(6-methoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-N,N-dibutyl-acetamide;
    2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-N,N-diethyl-acetamide;
    2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-dibutyl-acetamide;
    2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-diethyl-acetamide;
    2-[2-(4-Chloro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-diethyl-acetamide;
    2-[2-(4-Chloro-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-N,N-diethyl-acetamide;
    2-[2-(4-Chloro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-[2-(4-chloro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[2-(4-Chloro-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-[2-(4-chloro-phenyl)-6-ethoxy-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    N,N-Diethyl-2-(6-methoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-methoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone;
    2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-diethyl-acetamide;
    2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone;
    2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone;
    N,N-Diethyl-2-(6-methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone;
    2-(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone;
    2-[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-[2-(4-fluoro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[2-(4-Fluoro-phenyl)-6-methoxy-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-[2-(4-fluoro-phenyl)-6-methoxy-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-[6-ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    N,N-Diethyl-2-(6-methoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-methoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone;
    2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-diethyl-acetamide;
    2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-pyrrolidin-1-yl-ethanone;
    2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone;
    2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone;
    N,N-Diethyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-pyrrolidin-1-yl-ethanone;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone;
    N,N-Diethyl-2-[2-(4-fluoro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    N,N-Diethyl-2-[2-(4-fluoro-phenyl)-6-methoxy-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[2-(4-Fluoro-phenyl)-6-methoxy-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-N,N-diethyl-acetamide;
    2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    2-[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    2-[2-(4-Fluoro-phenyl)-6-methoxy-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    N,N-Diethyl-2-[2-(4-methoxy-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N,N-Dibutyl-2-[2-(4-methoxy-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    2-[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    N,N-Diethyl-2-[6-methoxy-2-(4-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[6-Methoxy-2-(4-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-acetamide;
    N N-Dibutyl-2-[6-methoxy-2-(4-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-acetamide;
    2-[6-Methoxy-2-(4-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone;
    2-[6-Methoxy-2-(4-methoxy-phenyl)-imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone;
    Acetic acid 2-{[2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetyl]-propyl-amino}-ethyl ester;
    1-(3,5-Dimethyl-piperidin-1-yl)-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-ethanone;
    N-Cyclopropyl methyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-propyl-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-thiazol-2-yl-acetamide;
    N,N-Diisopropyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N-Cyclohexyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-phenyl-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-p-tolyl-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-pyridin-2-yl-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-pyridin-2-ylmethyl-acetamide;
    N-(3,5-Dimethyl-isoxazol-4-yl)-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N-Cyclopentyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N,N-Diallyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N-Cyclopropyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-quinolin-2-yl-acetamide;
    N-(5-Methyl-isoxazol-3-yl)-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N-(4-Methoxy-phenyl)-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    N-(3-Methyl-isoxazol-5-yl)-2-(6-methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-[1,3,4]thiadiazol-2-yl-acetamide;
    [2-(4-Fluoro-phenyl)-6-pyrrolidin-1-yl-imidazo[1,2-b]pyridazin-3-yl]-acetic acid hydrazide;
    [2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetic acid hydrazide;
    [2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetic acid hydrazide;
    [2-(4-Chloro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetic acid hydrazide;
    [2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-b]pyridazin-3-yl]-acetic acid hydrazide;
    (6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-yl)-acetic acid hydrazide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-morpholin-4-yl-acetamide;
    2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-N-piperidin-1-yl-acetamide; and
    (6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetic acid N′,N′-dimethyl-hydrazide.


Another aspect of the present invention is to provide a process for preparing compounds of formula (I) as well as an imidazo[1,2-b]pyridazine intermediate of formula (II):




wherein R is methyl, R1 is a methyl, chlorine, methoxy, ethoxy, thiophenoxy or 1-pyrrolidinyl group and R2 is a phenyl group or a phenyl group substituted in para-position by methyl, halogen, methoxy, nitro or trifluoromethyl.

The compounds of general formula (I), when X is CO, can be obtained following the synthetic strategy showed in Scheme 1.




Starting from ketoacids (III), ketoamides (IV) can be obtained by using conventional coupling conditions. These ketoamides (IV) can be brominated in α-position of the reacting carbonyl group with bromine in acetic acid, to yield the bromoketoamides (V). Finally, cyclization of aminopyridazines (VI) in acetonitrile at reflux affords the imidazopyridazines (I, X═CO).
On the other hand, if R3 or R4 are optionally substituted amino groups, then the molecule obtained is not an amide but an hydrazide. The synthetic pathway has to be slightly modified for that proposal (Scheme 2).




A Fischer esterification of the same ketoacid (III) is carried out with an alcohol ROH to afford the corresponding ester (VII). This ester is brominated under similar conditions as the amide (IV) described above, to yield bromoketoesters (VIII). A cyclization with aminopyridazines (VI) allows the preparation of the imidazopyridazines (II) substituted with an ester group. Finally, acylic substitution by using a substituted hydrazine in a suitable solvent at reflux provides the corresponding hydrazides (I, X═CO, R3 or R4 are optionally substituted amino groups). Suitable solvents to be used in this reaction are selected preferably from linear or branched alkanols (C1-C6), more preferably methanol, or mixtures thereof.
The compounds of the present invention or their pharmaceutically acceptable salts, polymorphs, hydrates, tautomers, solvates and stereoisomers can be used for the preparation of a medicament for treating or preventing diseases associated with GABAA receptor modulation in a human or non-human mammal. More specifically, diseases associated with GABAA receptor modulation comprise diseases associated with α1-GABAA receptor modulation and/or α2-GABAA receptor modulation. It is well-known for the skill in the art which diseases associated with GABAA receptor modulation are (cf. Kaufmann W. A. et al., “Compartmentation of alpha 1 and alpha 2 GABAA receptor subunits within rat extended amygdala: implications for benzodiazepine action”, Science 2003, vol. 964 p. 91-99; Möhler H. et al., “GABAA-receptor subtypes: a new pharmacology”, Current Opinion in Pharmacology 2001, vol. 1:22-25). A non-limitative list of such diseases comprises anxiety, epilepsy, sleep disorders, including insomnia, and the like.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate and stereoisomer thereof for the preparation of a medicament for treating or preventing anxiety in a human or non-human mammal.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomers thereof for the preparation of a medicament for treating or preventing epilepsy in a human or non-human mammal in need thereof.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomer thereof for the preparation of a medicament for treating or preventing sleep disorders in a human or non-human mammal in need thereof.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomer thereof for the preparation of a medicament for treating or preventing insomnia in a human or non-human mammal in need thereof.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomer thereof for the preparation of a medicament for inducing sedation-hypnosis in a human or non-human mammal in need thereof.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomer thereof for the preparation of a medicament for inducing anesthesia in a human or non-human mammal in need thereof.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomer thereof for the preparation of a medicament for modulating the necessary time to induce sleep and its duration in a human or non-human mammal in need thereof.
Another embodiment of the present invention is to provide the use of a compound of formula (I) or a pharmaceutically acceptable salt, polymorph, hydrate, tautomer, solvate or stereoisomer thereof for the preparation of a medicament for inducing muscle relaxation in a human or non-human mammal in need thereof.
The present invention also relates to a method of treatment or prevention of a human or non-human mammal suffering from diseases associated with GABAA receptor modulation in a human or non-human mammal, which comprises administering to said human or non-human mammal in need thereof a therapeutically effective amount of a compound of formula (I) or pharmaceutically acceptable salts, polymorphs, hydrates, tautomers, solvates and stereoisomers thereof, together with pharmaceutically acceptable diluents or carriers. More specifically, diseases associated with GABAA receptor modulation comprise diseases associated with α1-GABAA receptor modulation and/or α2-GABAA receptor modulation. A non-limitative list of such diseases comprises anxiety, epilepsy, sleep disorders, including insomnia, and the like.
As used herein, the term “mammal” shall refer to the Mammalian class of higher vertebrates. The term “mammal” includes, but is not limited to, a human.
Another embodiment of the present invention is to provide a pharmaceutical composition containing a compound of formula (I) or pharmaceutically acceptable salts, polymorphs, hydrates, tautomers, solvates and stereoisomers thereof, in association with therapeutically inert carriers.
The compositions include those suitable for oral, rectal and parenteral (including subcutaneous, intramuscular, and intravenous) administration, although the most suitable route will depend on the nature and severity of the condition being treated. The most preferred route of the present invention is the oral route. The compositions may be conveniently presented in unit dosage form, and prepared by any of the methods well known in the art of pharmacy.
The active compound can be combined with a pharmaceutical carrier according to conventional pharmaceutical compounding techniques. The carrier may take a wide variety of forms depending on the form of the preparation desired for administration, e.g. oral or parenteral (including intravenous injections or infusions). In preparing the compositions for oral dosage form any of the usual pharmaceutical media may be employed. Usual pharmaceutical media include, for example, water, glycols, oils, alcohols, flavoring agents, preservatives, coloring agents, and the like in the case of oral liquid preparations (such as for example, suspensions, solutions, emulsions and elixirs); aerosols; or carriers such as starches, sugars, micro-crystalline cellulose, diluents, granulating agents, lubricants, binders, disintegrating agents and the like, in the case of oral solid preparations (such as for example, powders, capsules, and tablets) with the oral solid preparations being preferred over the oral liquid preparations.
Because of their ease of administration, tablets and capsules represent the most advantageous oral dosage unit form, in which case solid pharmaceutical carriers are employed. If desired, tablets may be coated by standard aqueous or non-aqueous techniques.
A suitable dosage range for use is from about 0.01 mg to about 100.00 mg total daily dose, given as a once daily administration or in divided doses if required.
The compounds of the present invention have a high affinity for α1- and α2-GABAA receptors. These in vitro results are consistent with those in vivo results obtained in sedation-hypnosis tests.
In accordance with the results obtained, certain compounds of the present invention have evidenced pharmacological activity both in vitro and in vivo, which has been similar to or higher than that of prior-art compound zolpidem. All these results support their use in diseases or conditions modulated by α1- and α2-GABAA receptors, such as insomnia or anesthesia, in which an induction of sleep, an induction of sedation or an induction of muscle relaxation are needed.
The pharmacological activity of the compounds of the present invention has been determined as shown below.
a) Ligand-Binding Assays. Determination of the Affinity of Test Compounds for α1- and α2-GABAA Receptor
Male Sprague-Dawley rats weighing 200-250 g at the time of experiment were used. After decapitation of the animal, the cerebellum (tissue that mostly contains α1-GABAA receptor) and spinal cord (tissue that mostly contains α2-GABAA receptor) were removed. The membranes were prepared according to the method by J. Lameh et al. (Prog. Neuro-Psychopharmacol. Biol. Psychiatry, 24, 979-991, 2000) and H. Noguchi et al. (Eur J Pharm, 434, 21-28, 2002) with slight modifications. Once the tissues weighed, they were suspended in 50 mM Tris.HCl (pH 7.4), 1:40 (v/v), or sucrose 0.32 M in the case of spinal cord, homogenized and then centrifuged at 20000 g for 10 minutes at 7° C. The resulting pellet was resuspended under the same conditions and centrifuged again. The pellet was finally resuspended on a minimum volume and kept at −80° C. overnight. A slight modification was used in the case of spinal cord at the first centrifugation step. Centrifugation speed was at 1000 g and the supernatant was collected instead of discarded as in cerebellum. Then, supernatant was centrifuged at 20000 g and resuspended twice more under the same conditions described above for cerebellum. On the next day, the process was repeated until the final pellet was resuspended at a ratio of 1:10 (v/v) in the case of cerebellum and at a ratio of 1:5 (v/v) in the case of spinal cord.
Affinity was determined by competitive tests using radiolabeled flumazenil as ligand. The tests were performed according to the methods described by S. Arbilla et al. (Eur. J. Pharmacol., 130, 257-263, 1986); and Y. Wu et al. (Eur. J. Pharmacol., 278,125-132, 1995) using 96-well microtiter plates. The membranes containing the study receptors, flumazenil (radiolabeling at a final concentration of 1 nM) and ascending concentrations of test compounds (in a total volume of 230 μl in 50 mM [pH 7.4] Tris.HCl buffer) were incubated. Simultaneously, the membranes were only incubated with the radiolabeled flumazenil (total binding, 100%) and in the presence of an elevated concentration of unradiolabeled flumazenil (non-specific binding, % estimation of radiolabeled ligand). The reactions started on adding the radiolabeled ligand followed by incubation for 60 minutes at 4° C. At the end of the incubation period, 200 μl of reaction were transferred to a multiscreen plate (Millipore) and filtered using a vacuum manifold and then washed three times with cold test buffer. The multiscreen plates were equipped with a GF/B filter that retained the membranes containing the receptors and the radiolabeled ligand which had been bound to the receptors. After washing, the plates were left till dry. Once dried, scintillation liquid was added and left under stirring overnight. The next day the plates were counted using a Perkin-Elmer Microbeta scintillation counter.
For analysis of the results the percentage of specific binding for every concentration of test compound was calculated as follows:

% specific binding=(X−N/T−N)×100

where,

X: amount of bound ligand for every concentration of compound.

T: total binding, maximum amount bound to the radiolabeled ligand.

N: non-specific binding, amount of radiolabeled ligand bound in a non-specific way irrespective of the receptor used.

Every concentrations of compound were tested in triplicate and their mean values were used to determine the experimental values of % specific binding versus the concentration of compound. Affinity data are expressed as % inhibition at 10−5M and 10−7M concentrations. The results of these tests are given in Tables 1 and 2.







TABLE 1







Affinity for the α1-subunit of the GABAA receptor











Compound
% inhib 10−5M
% inhib 10−7M















Example 1
100.1
98.2



Example 2
100.3
99.6



Example 3
100.2
99.4



Example 4
99.9
98.3



Example 5
100.3
97.5



Example 6
100.0
97.4



Example 9
96.8
11.4



Example 10
99.1
39.3



Example 11
96.0
22.0



Example 12
96.9
34.6



Example 13
99.7
58.3



Example 14
99.5
80.6



Example 17
99.5
97.1



Example 20
99.6
73.7



Example 22
100.0
97.6



Example 23
99.1
61.7



Example 24
98.4
57.7



Example 26
100.0
73.5



Example 35
100.2
97.5



Example 40
100.3
98.0



Example 41
99.8
75.4



Example 42
99.7
62.2



Example 43
99.5
49.9



Example 65
99.5
58.5



Example 66
98.3
50.4



Example 67
98.9
42.2



Example 70
99.9
84.5



Example 71
100.2
95.0



Example 72
100.4
91.5



Example 73
99.9
76.5



Example 75
99.4
52.1



Example 77
100.1
42.2



Example 78
98.3
26.5



Example 80
99.7
85.2



Example 81
100.1
98.5



Example 82
100.1
99.2



Example 83
99.6
97.6



Example 84
100.0
91.7



Example 86
99.5
75.9



Example 87
99.3
57.2



Example 88
100.2
83.9



Example 91
99.1
45.8



Example 93
100.0
78.2



Example 94
100.1
65.1



Example 100
99.5
62.4



Example 102
99.1
66.7



Example 105
98.8
56.0



Example 106
99.5
53.7



zolpidem
99.4
73.6

















TABLE 2







Affinity for the α2-subunit of the GABAA receptor











Compound
% inhib 10−5M
% inhib 10−7M















Example 1
94.3
49.0



Example 2
98.6
66.1



Example 3
91.3
60.8



Example 4
97.6
53.2



Example 5
97.7
45.0



Example 6
97.5
49.4



Example 9
61.7
5.9



Example 10
72.0
19.1



Example 11
47.0
1.7



Example 12
71.9
2.2



Example 13
76.7
15.5



Example 14
76.9
10.8



Example 17
83.0
36.8



Example 20
82.0
20.8



Example 22
86.6
61.2



Example 23
80.0
0.0



Example 24
77.4
13.6



Example 26
84.5
27.4



Example 35
92.5
57.9



Example 40
91.5
60.7



Example 41
85.3
17.0



Example 42
79.4
16.3



Example 43
80.3
20.1



Example 65
78.5
16.3



Example 66
79.4
7.8



Example 67
83.7
8.8



Example 70
80.3
23.6



Example 71
88.5
50.6



Example 72
85.6
51.7



Example 73
77.0
20.6



Example 75
68.8
9.3



Example 77
83.4
23.6



Example 80
84.3
37.0



Example 83
93.1
57.7



Example 84
63.9
3.1



Example 86
80.9
23.0



Example 100
73.0
2.3



Example 102
77.9
13.7



zolpidem
74.1
19.9










b) In Vivo Determination of Predictive Sedative-Hypnotic Action

The in vivo effects of these compounds were assessed by a predictive sedation-hypnosis test in mice (D. J. Sanger et al., Eur. J. Pharmacol., 313, 35-42, 1996; and G. Griebel et al., Psychopharmacology, 146, 205-213, 1999).
Groups of 5-8 male CD1 mice, weighing 22-26 g at the time of test, were used. The test compounds were administered at 98.0 μmol/kg by mean of intraperitoneal injection. Compounds were suspended in 0.25% agar with one drop of Tween in a volume of 10 mL/kg. Control animals were given the vehicle alone. Using a Smart System (Panlab, S. L., Spain) the traveled distance in cm is recorded for each mouse at 5-minutes intervals during a period of 30 minutes after dosing. The inhibition percentage of traveled distance of treated animals versus control animals (the first 5 minutes were discarded) was calculated. Some compounds were also tested in a lower dose—0.98 μmol/kg—to further discriminate the potency of sedation induction. The results of this test are given in Table 3 and Table 4.







TABLE 3







Determination of in vivo sedative-hypnotic


activity in mice at 98.0 μmol/kg










Compound
% inhib motor activity














Example 1
94.66



Example 2
96.71



Example 3
90.94



Example 4
94.65



Example 5
93.65



Example 6
96.86



Example 9
93.85



Example 10
93.47



Example 11
79.82



Example 12
83.44



Example 13
92.08



Example 14
95.56



Example 17
93.08



Example 20
91.51



Example 22
87.97



Example 23
91.74



Example 24
86.54



Example 26
91.55



Example 35
80.60



Example 40
91.79



Example 41
91.18



Example 42
91.01



Example 43
95.72



Example 65
95.46



Example 66
95.95



Example 67
90.81



Example 70
86.98



Example 71
95.96



Example 72
93.35



Example 73
94.07



Example 75
92.56



Example 77
89.35



Example 78
91.14



Example 80
94.41



Example 81
90.83



Example 82
94.22



Example 83
88.93



Example 84
90.78



Example 86
92.62



Example 87
90.70



Example 88
88.51



Example 91
93.05



Example 93
93.20



Example 94
93.49



Example 100
93.71



Example 102
85.50



Example 105
94.02



Example 106
94.05



zolpidem
91.70

















TABLE 4







Determination of in vivo sedative-hypnotic


activity in mice at 0.98 μmol/kg











% inhib motor



Compound
activity














Example 1
27.56



Example 2
38.39



Example 3
14.61



Example 4
38.38



Example 5
41.15



Example 6
51.90



Example 9
19.94



Example 10
29.54



Example 11
15.29



Example 12
15.05



Example 13
15.11



Example 14
4.77



Example 17
9.91



Example 22
22.21



Example 23
12.37



Example 24
3.65



Example 26
19.19



Example 35
6.76



Example 41
15.73



zolpidem
18.30










c) In Vivo Determination of Predictive Anesthetic Activity

The in vivo effects of these compounds were assessed by a predictive anesthetic test in mice as the loss of righting reflex (Kralic et al., Neuropharmacology, 43(4), 685-689 2002; Belelli et al., Neuropharmacology, 45, 57-71, 2003).
Groups of 5-8 male CD1 mice, weighing 22-26 g at the time of test, were used. The test compounds were administered at 98.0 μmol/kg by mean of intraperitoneal injection. Compounds were suspended in 0.25% agar with one drop of Tween in a volume of 10 mL/kg. Percentage of treated mice which showed loss of righting reflex was calculated.
Interestingly, compounds of examples 2, 3, and 82 exhibited a 90%, 100% and 30% of animals with loss of righting reflex respectively. On the contrary, zolpidem, the prior art compound, exhibited lower anesthetic potential, being necessary to administer double dose than compounds of the present invention to achieve 80% of animals with loss of righting reflex.
d) Comparative Assay
In order to show that the compounds of the present invention are better than other known in the state of the art, particularly those described in the PCT application WO 89/01333, the IC50 value for compounds 22, 26, 88, 95, 96, 97 and 98 were calculated and compared to the structurally closest compounds described in said PCT application, i.e., compounds 317 and 318. All these compounds have in common that at 3-position, the imidazo[1,2-b]pyradizine ring have an acetamide. The rest of compounds disclosed in WO89/01333 are not structurally so related with the compounds of the present invention.
The IC50 values were estimated from Cheng-Prusoff equation (Cheng Y. C. and Prusoff W. H.; Biochem. Pharmacol. 22, 3099-3108, 1973)




  Ki
  =
  
    
      IC
      50
    
    
      1
      +
      
        
          [
          
            RL
            *
          
          ]
        
        Kd
      
    
  




where,

Ki is determined for each one of the compounds of the invention as described above (section (a)).

[RL*]: radiolabeled ligand concentration (1 nM).

Kd: affinity constant (cerebellum 1.34 nM/spinal cord 1.19 nM)

Table 5 shows the IC50 values obtained for the compounds of the present invention and includes the IC50 values for compounds 317 and 318 of the PCT application WO89/01333:







TABLE 5







Comparison of IC50 values










Example number
IC50 (nM)











COMPOUNDS OF THE INVENTION










22
17.2



88
13



95
17.1



97
14.6



98
12.2







COMPOUNDS OF WO89/01333










317
55



318
474










As it is derived from the results obtained, the compounds of the present invention have IC50 values lower than the IC50 values of WO89/01333, which means that a lower dose of the compounds of the present invention are needed in order to achieve the same therapeutic effect.
The following non-limiting examples illustrate the scope of the present invention.
Example A
General Method for the Preparation of Amides (IV)




To a solution of the acid (III) (1 eq) in dichloromethane was added a solution of water-soluble carbodiimide (1.5 eq) in dichloromethane. The mixture was stirred at room temperature for 30 minutes. After this period, a solution of 0.5 eq of 4-dimethylamino-pyridine and 1.5 eq of the corresponding amine in dichloromethane was added, and the mixture was stirred for 6 h. The crude was washed with HCl 1 N, the organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, to afford the ketoamide (IV).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 7.80-7.15 (m, 4H, Ar), 3.30 (t, 4H, CH2N), 2.87 (t, 2H, CH2CO), 2.47 (t, 2H, H2CON), 1.58-0.93 (m, 14H, CH2CH2CH3).
MS (ES) m/z=308 (MH+)
HPLC=100%
Yield=80%
Example B
General Method for the Preparation of Bromoamides (V, X═CO)




To a solution of (IV) (1 eq) in acetic acid was added dropwise a solution of bromine (2.2 eq) in acetic acid. The mixture was stirred at room temperature for 24 h. The solvent was removed in vacuo and the residue was extracted with dichloromethane/NaOH 1 N and with dichloromethane/water. The organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, thus affording the bromoketoamide (V).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 7.97-7.23 (m, 4H, Ar), 5.20 (t, 2H, CHBr), 3.24 (t, 4H, CH2N), 2.87 (d, 2H, CH2CON), 1.75-0.76 (m, 14H, CH2CH2CH3).
MS (ES) m/z=380 (M), 382 (M+2H)
HPLC=95%
Yield=34%
Example C
General Method for the Preparation of Imidazopyridazines (I, X═CO)




To a solution of (V) (1 eq) in acetonitrile was added a solution of (VI) (1.2 eq) in acetonitrile. The mixture was stirred at reflux for 2 h. The solvent was removed in vacuo and the residue was extracted with dichloromethane/HCl 1 N and with DCM/water. The organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, thus affording the imidazopyridazine (I).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 7.30-7.03 (m, 6H, Ar), 3.48 (s, 2H, CH2), 2.32 (s, 3H, CH3), 3.21-0.96 (m, 18H, CH2CH2CH2CH3).
MS (ES) m/z=397 (MH+)
HPLC=89%
Yield=60%
Compounds 1-98 were prepared following this methodology.













Example
MH+




Number
(LCMS)
Purity (UV)
IUPAC NAME


















1
358
99
2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-diethyl-acetamide


2
386
99
2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-dipropyl-acetamide


3
414
97
N,N-Dibutyl-2-(6-chloro-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


4
370
94
2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-piperidin-1-yl-ethanone


5
372
97
2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-morpholin-4-yl-ethanone


6
356
83
2-(6-Chloro-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-pyrrolidin-1-yl-ethanone


7
393
100
N,N-Diethyl-2-(6-pyrrolidin-1-yl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


8
353
84
N,N-Diethyl-2-(6-methoxy-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


9
446
84
2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone


10
444
100
2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone


11
488
100
2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dibutyl-acetamide


12
460
100
2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


13
432
80
2-[2-(4-Bromo-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-N,N-diethyl-acetamide


14
416
86
2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone


15
414
96
2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone


16
458
99
2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dibutyl-acetamide


17
430
99
2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


18
402
98
2-[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-diethyl-acetamide


19
358
94
2-[2-(4-Chloro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-diethyl-acetamide


20
388
87
2-[2-(4-Chloro-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-N,N-diethyl-acetamide


21
386
100
2-[2-(4-Chloro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


22
414
99
N,N-Dibutyl-2-[2-(4-chloro-phenyl)-6-methyl-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


23
416
98
2-[2-(4-Chloro-phenyl)-6-ethoxy-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


24
444
100
N,N-Dibutyl-2-[2-(4-chloro-phenyl)-6-ethoxy-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


25
339
80
N,N-Diethyl-2-(6-methoxy-2-phenyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


26
367
96
2-(6-Methoxy-2-phenyl-imidazo[1,2-





b]pyridazin-3-yl)-N,N-dipropyl-acetamide


27
396
87
N,N-Dibutyl-2-(6-methoxy-2-phenyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


28
353
100
2-(6-Methoxy-2-phenyl-imidazo[1,2-





b]pyridazin-3-yl)-1-morpholin-4-yl-ethanone


29
353
83
2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-diethyl-acetamide


30
381
100
2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-dipropyl-acetamide


31
410
100
N,N-Dibutyl-2-(6-ethoxy-2-phenyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


32
367
88
2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-1-morpholin-4-yl-ethanone


33
365
80
2-(6-Ethoxy-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-1-piperidin-1-yl-ethanone


34
323
80
N,N-Diethyl-2-(6-methyl-2-phenyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


35
351
100
2-(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-dipropyl-acetamide


36
380
88
N,N-Dibutyl-2-(6-methyl-2-phenyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


37
337
100
2-(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-1-morpholin-4-yl-ethanone


38
335
81
2-(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-





3-yl)-1-piperidin-1-yl-ethanone


39
369
89
2-[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


40
398
89
N,N-Dibutyl-2-[2-(4-fluoro-phenyl)-6-methyl-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


41
385
90
2-[2-(4-Fluoro-phenyl)-6-methoxy-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


42
414
92
N,N-Dibutyl-2-[2-(4-fluoro-phenyl)-6-methoxy-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


43
399
85
2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


44
428
93
N,N-Dibutyl-2-[6-ethoxy-2-(4-fluoro-phenyl)-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


45
385
80
2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-





b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone


46
353
97
N,N-Diethyl-2-(6-methoxy-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


47
381
82
2-(6-Methoxy-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-N,N-dipropyl-acetamide


48
410
90
N,N-Dibutyl-2-(6-methoxy-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


49
365
80
2-(6-Methoxy-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-1-piperidin-1-yl-ethanone


50
367
85
2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-diethyl-acetamide


51
396
80
2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-dipropyl-acetamide


52
424
89
N,N-Dibutyl-2-(6-ethoxy-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


53
365
81
2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-pyrrolidin-1-yl-ethanone


54
381
85
2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-morpholin-4-yl-ethanone


55
379
80
2-(6-Ethoxy-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-piperidin-1-yl-ethanone


56
337
90
N,N-Diethyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


57
365
90
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N,N-dipropyl-acetamide


58
394
90
N,N-Dibutyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


59
335
80
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-pyrrolidin-1-yl-ethanone


60
351
85
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-morpholin-4-yl-ethanone


61
349
85
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-1-piperidin-1-yl-ethanone


62
341
87
N,N-Diethyl-2-[2-(4-fluoro-phenyl)-6-methyl-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


63
353
81
2-[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone


64
357
90
N,N-Diethyl-2-[2-(4-fluoro-phenyl)-6-methoxy-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


65
369
94
2-[2-(4-Fluoro-phenyl)-6-methoxy-imidazo[1,2-





b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone


66
371
91
2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-





b]pyridazin-3-yl]-N,N-diethyl-acetamide


67
383
91
2-[6-Ethoxy-2-(4-fluoro-phenyl)-imidazo[1,2-





b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone


68
355
92
2-[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone


69
371
95
2-[2-(4-Fluoro-phenyl)-6-methoxy-imidazo[1,2-





b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone


70
353
99
N,N-Diethyl-2-[2-(4-methoxy-phenyl)-6-methyl-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


71
381
99
2-[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-N,N-dipropyl-acetamide


72
410
100
N,N-Dibutyl-2-[2-(4-methoxy-phenyl)-6-methyl-





imidazo[1,2-b]pyridazin-3-yl]-acetamide


73
365
100
2-[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-1-piperidin-1-yl-ethanone


74
367
92
2-[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-1-morpholin-4-yl-ethanone


75
369
100
N,N-Diethyl-2-[6-methoxy-2-(4-methoxy-





phenyl)-imidazo[1,2-b]pyridazin-3-yl]-acetamide


76
397
98
2-[6-Methoxy-2-(4-methoxy-phenyl)-





imidazo[1,2-b]pyridazin-3-yl]-N,N-dipropyl-





acetamide


77
426
100
N,N-Dibutyl-2-[6-methoxy-2-(4-methoxy-





phenyl)-imidazo[1,2-b]pyridazin-3-yl]-





acetamide


78
381
100
2-[6-Methoxy-2-(4-methoxy-phenyl)-





imidazo[1,2-b]pyridazin-3-yl]-1-piperidin-1-yl-





ethanone


79
383
97
2-[6-Methoxy-2-(4-methoxy-phenyl)-





imidazo[1,2-b]pyridazin-3-yl]-1-morpholin-4-yl-





ethanone


80
410
94
Acetic acid 2-{[2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetyl]-propyl-





amino}-ethyl ester


81
378
89
1-(3,5-Dimethyl-piperidin-1-yl)-2-(6-methyl-2-





p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-ethanone


82
378
93
N-Cyclopropylmethyl-2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-N-propyl-acetamide


83
364
98
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-thiazol-2-yl-acetamide


84
365
97
N,N-Diisopropyl-2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


85
363
96
N-Cyclohexyl-2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


86
357
95
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-phenyl-acetamide


87
371
99
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-p-tolyl-acetamide


88
358
96
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-pyridin-2-yl-acetamide


89
372
94
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-pyridin-2-ylmethyl-acetamide


90
376
99
N-(3,5-Dimethyl-isoxazol-4-yl)-2-(6-methyl-2-





p-tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide


91
349
93
N-Cyclopentyl-2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


92
361
82
N,N-Diallyl-2-(6-methyl-2-p-tolyl-imidazo[1,2-





b]pyridazin-3-yl)-acetamide


93
321
97
N-Cyclopropyl-2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


94
408
95
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-quinolin-2-yl-acetamide


95
362
95
N-(5-Methyl-isoxazol-3-yl)-2-(6-methyl-2-p-





tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide


96
387
99
N-(4-Methoxy-phenyl)-2-(6-methyl-2-p-tolyl-





imidazo[1,2-b]pyridazin-3-yl)-acetamide


97
362
99
N-(3-Methyl-isoxazol-5-yl)-2-(6-methyl-2-p-





tolyl-imidazo[1,2-b]pyridazin-3-yl)-acetamide


98
365
99
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-[1,3,4]thiadiazol-2-yl-acetamide









Example D
General Method for the Preparation of Ketoesters (VII)




To a solution of (III) (1 eq) in methanol (ROH, R═CH3) was added dropwise a solution of concentrated H2SO4 (0.5 eq) in methanol. The mixture was stirred at reflux for 30 minutes. The solvent was removed in vacuo and the residue was extracted with dichloromethane/NaOH 1 N and with dichloromethane/water. The organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, thus affording the ketoester (VIII).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 7.89-6.88 (m, 4H, Ar), 3.75 (s, 3H, OCH3), 3.77 (s, 3H, OCH3), 2.65 (t, 2H, CH2CO), 2.25 (t, 2H, CH2COO).
MS (ES) m/z=223 (MH+)
HPLC=95%
Yield=93%
Example E
General Method for the Preparation of Bromoketoesters (VIII)




To a solution of (VII) (1 eq) in acetic acid was added dropwise a solution of bromine (2.2 eq) in acetic acid. The mixture was stirred at room temperature for 24 h. The solvent was removed in vacuo and the residue was extracted with dichloromethane/NaOH 1 N and with dichloromethane/water. The organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, thus affording the bromoketoester (VIII).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 7.98-6.82 (m, 4H, Ar), 5.38 (t, 1H, CHBr), 3.98 (s, 3H, OCH3), 3.54 (s, 3H, OCH3), 2.75 (t, 2H, CH2COO).
MS (ES) m/z=301 (M), 303 (M+2H)
HPLC=95%
Yield=35%
Example F
General Method for the Preparation of Imidazopyridazines (II)




To a solution of (VIII) (1 eq) in acetonitrile was added a solution of (VI) (1.2 eq) in acetonitrile. The mixture was stirred at reflux for 2 h. The solvent was removed in vacuo and the residue was extracted with dichloromethane/HCl 1 N and with dichloromethane/water. The organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, thus affording the imidazopyridazine (II).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 7.69-6.79 (m, 6H, Ar), 3.75 (s, 3H, OCH3), 3.67 (s, 3H, OCH3), 3.35 (s, 2H, CH2), 2.17 (s, 3H, CH3).
MS (ES) m/z=312 (MH+)
HPLC=90%
Yield=60%
Example G
General Method for the Preparation of Imidazopyridazines (I, X═CO, R3 or R4 are Substituted Amino Groups)




To a solution of (II) (1 eq) in methanol was added a solution of (substituted) hydrazine (5 eq) in methanol. The mixture was stirred at reflux for 24 h. The solvent was removed in vacuo and the residue was extracted with dichloromethane/HCl 1 N and with dichloromethane/water. The organic layer was dried over Na2SO4 and filtered off, and the solvent was removed in vacuo, thus affording the imidazopyridazine (I).
E.g. for




1H NMR (400 MHz, DMSO-d6): δ 8.00 (bs, 1H, NH), 7.50-6.93 (m, 6H, Ar), 3.78 (s, 3H, OCH3), 3.96 (s, 3H, OCH3), 3.28 (s, 2H, CH2), 2.12 (bs, 2H, NH2).
MS (ES) m/z=312 (MH+)
HPLC=93%
Yield=65%
Compounds 99-107 were prepared following this methodology.













Exam-

Pu-



ple
MH+
rity



Number
(LCMS)
(UV)
IUPAC NAME


















99
355
100
[2-(4-Fluoro-phenyl)-6-pyrrolidin-1-yl-





imidazo[1,2-b]pyridazin-3-yl]-acetic acid





hydrazide


100
361
100
[2-(4-Bromo-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-acetic acid hydrazide


101
312
93
[2-(4-Methoxy-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-acetic acid hydrazide


102
317
99
[2-(4-Chloro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-acetic acid hydrazide


103
300
92
[2-(4-Fluoro-phenyl)-6-methyl-imidazo[1,2-





b]pyridazin-3-yl]-acetic acid hydrazide


104
282
99
(6-Methyl-2-phenyl-imidazo[1,2-b]pyridazin-3-





yl)-acetic acid hydrazide


105
366
91
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-morpholin-4-yl-acetamide


106
364
90
2-(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-





3-yl)-N-piperidin-1-yl-acetamide


107
324
91
(6-Methyl-2-p-tolyl-imidazo[1,2-b]pyridazin-3-





yl)-acetic acid N′,N′-dimethyl-hydrazide









Composition Example 1
5 mg Tablets
















Active ingredient
5.0 mg



Colloidal silicon dioxide
0.6 mg



Croscarmellose sodium
12.0 mg 



Talc
4.0 mg



Magnesium stearate
1.5 mg



Polysorbate 80
1.0 mg



Lactose
75.0 mg 



Hydroxypropyl methylcellulose
3.0 mg



Polyethylene glycol 4000
0.5 mg



Titanium dioxide E171
1.5 mg



Microcrystalline cellulose q.s. to
125.0 mg 










Composition Example 2
10 mg Capsules
















Active ingredient
10.0 mg



Colloidal silicon dioxide
 0.6 mg



Crospovidone
12.0 mg



Talc
 4.0 mg



Magnesium stearate
 1.5 mg



Lauryl sulfate sodium
 1.5 mg



Lactose
77.0 mg



Gelatin
28.5 mg



Titanium dioxide E171
 1.5 mg



Indigotin E132
0.02 mg



Microcrystalline cellulose q.s. to
155.0 mg 










Composition Example 3
Oral Drops

















Active ingredient
0.5
g



Propylene glycol
10.0
g



Glycerin
5.0
g



Saccharin sodium
0.1
g



Polysorbate 80
1.0
g



Lemon flavor
0.2
g



Ethanol
25.0
mL



Purified water q.s. to
100.0
mL










Composition Example 4
2.5 mg Tablets
















Active ingredient
2.5 mg



Colloidal silicon dioxide
0.6 mg



Croscaramellose sodium
12.0 mg 



Talc
4.0 mg



Magnesium stearate
1.5 mg



Polysorbate 80
1.0 mg



Lactose
75.0 mg 



Hydroxypropyl methylcellulose
3.0 mg



Polyethylene glycol 4000
0.5 mg



Titanium dioxide E171
1.5 mg



Microcrystalline cellulose q.s. to
125.0 mg 










Composition Example 5
5 mg Capsules
















Active ingredient
5.0 mg



Colloidal silicon dioxide
0.6 mg



Crospovidone
12.0 mg 



Talc
4.0 mg



Magnesium stearate
1.5 mg



Lauryl sulfate sodium
1.5 mg



Lactose
77.0 mg 



Gelatin
28.5 mg 



Titanium dioxide E171
1.5 mg



Indigotin E132
0.02 mg 



Microcrystalline q.s. to
155.0 mg 










Composition Example 6
Oral Drops

















Active ingredient
0.25
g



Propylene glycol
10.0
g



Glycerin
5.0
g



Saccharin sodium
0.1
g



Polysorbate 80
1.0
g



Lemon flavor
0.2
g



Ethanol
25.0
mL



Purified q.s. to
100.0
mL

## Claims

1. A process for preparing a compound of formula (I)




wherein:
X is CO or SO2;
R1 and R2 are independently selected from the group consisting of hydrogen, linear or branched alkyl(C1-C6), alkenyl(C1-C6), alkynyl(C1-C6), cycloalkyl(C3-C6), haloalkyl(C1-C6), hydroxy, —O-alkyl(C1-C6), phenoxy, —S-alkyl(C1-C6), phenylthio, halogen, nitro, cyano, amino, alkylamino(C1-C6), dialkylamino(C1-C6), pyrrolidinyl, morpholinyl, piperidinyl, N-alkyl(C1-C6)piperazinyl, phenyl optionally substituted by 1 to 5 Z groups, and heteroaryl optionally substituted by 1 to 5 Z groups;
R3 and R4 are independently selected from the group consisting of hydrogen, linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C1-C6), cycloalkyl(C3-C6), hydroxyalkyl(C1-C6), amino, —NH-alkyl(C1-C6), —N-dialkyl(C1-C6), pyrrolidinyl, morpholinyl, piperidinyl, —N-alkyl(C1-C6)piperazinyl, —N-acyl(C1-C6)piperazinyl, phenyl optionally substituted by 1 to 5 Z groups, and heteroaryl optionally substituted by 1 to 5 Z groups, or both R3 and R4 can form, together with the nitrogen atom to which they are attached, a 5-6 membered heterocyclic ring optionally substituted by 1 to 5 Z groups, with the proviso that R3 and R4 are not simultaneously hydrogen;
Z is selected from the group consisting of linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C1-C6), cycloalkyl(C3-C5), haloalkyl(C2-C6), hydroxy, —O-alkyl(C1-C6), phenoxy, —S-alkyl(C1-C6), phenylthio, halogen, nitro, cyano, amino, alkylamino(C1-C6), and dialkylamino(C1-C6),
comprising reacting an intermediate (V):





wherein R2, R3, R4, and X are as defined above, with a substituted 3-aminopyridazine (VI):




wherein R1 is as defined above.

2. A process for preparing a compound of formula (I),




wherein:
X is CO;
R1 and R2 are independently selected from the group consisting of hydrogen, linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C2-C6), cycloalkyl(C3-C6), haloalkyl(C2-C6), hydroxy, —O-alkyl(C1-C6), phenoxy, —S-alkyl(C1-C6), phenylthio, halogen, nitro, cyano, amino, alkylamino(C1-C6), dialkylamino(C1-C6), pyrrolidinyl, morpholinyl, piperidinyl, N-alkyl(C1-C6)piperazinyl, phenyl optionally substituted by 1 to 5 Z groups, and heteroaryl optionally substituted by 1 to 5 Z groups,
R3 and R4 are independently selected from the group consisting of hydrogen, linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C2-C6), cycloalkyl(C3-C6), hydroxyalkyl(C1-C6), amino, —NH-alkyl(C1-C6), —N-dialkyl(C1-C6), pyrrolidinyl, morpholinyl, piperidinyl, —N-alkyl(C1-C6)piperazinyl, —N-acyl(C1-C6)piperazinyl, phenyl optionally substituted by 1 to 5 Z groups, and heteroaryl optionally substituted by 1 to 5 Z groups, or both R3 and R4 can form, together with the nitrogen atom to which they are attached, a 5-6 membered heterocyclic ring optionally substituted by 1 to 5 Z groups, with the proviso that R3 and R4 are not simultaneously hydrogen;
Z is selected from the group consisting of linear or branched alkyl(C1-C6), alkenyl(C2-C6), alkynyl(C2-C6), cycloalkyl(C3-C6), haloalkyl(C2-C6), hydroxy, phenoxy, —O-alkyl(C1-C6), phenoxy, —S-alkyl(C1-C6), phenylthio, halogen, nitro, cyano, amino, alkylamino(C1-C6), and dialkylamino(C1-C6),
comprising reacting an intermediate (II):





wherein R is a linear or branched alkyl(C1-C6) group and R1 and R2 are as defined above with a compound HNR3R4 wherein R3 and R4 are as defined above.

3. The process of claim 2, wherein R is methyl.

4. An imidazo[1,2-b]pyridazine compound of formula (II):




as well as pharmaceutically acceptable salts thereof, wherein
R is methyl,
R1 is methyl, chlorine, methoxy, ethoxy, thiophenoxy or 1-pyrrolidinyl group and
R2 is a phenyl group or a phenyl group substituted in para-position by methyl, halogen, methoxy, nitro or trifluoromethyl.