Title of Invention


Abstract Heterocyclic compounds of formula (I) wherein; R1 represents a hydrogen atom or a -(CH2)m-Y group, wherein m is an integer from 0 to 4 and Y represents an alkyl, haloalKyl, alkoxy, alkoxycarbonyl, C3-C7 cycloalkyl, norbornyl or phenylalkenyl group, or an aromatic group which aromatic group Y may optionally be substituted by one or more halogen atoms; R2 represents an aromatic group which aromatic group may optionally be substituted by one or more halogen atoms or alkyl, alkoxy, C3-C6 cycloalkoxy, methylenedioxy, nitro, dialkylamino or trifluoromethyl groups; and R3 represents a hydrogen or halogen atom or an alkyl group, and pharmaceutically acceptable salts thereof, processes for preparing the same and their use in medica1 treatment.
This invention relates to new therapeutically useful heterocyclic compounds, to process for their preparation and to pharmaceutical compositions containing them.
It is known that inhibitors of phosphodiesterase 4 (PDE 4) are useful in the treatment of inflammatory and allergic processes such as asthma, non-steroidal antiinflammatory drugs-induced gastrointestinal damage and atopic dermatitis.
EP-A-85,840 discloses a series of triazolo-phthalazine derivatives of formula:
(Figure Removed)
which are useful as anxiolytic agents.
We have now found that the presence of a pyridine ring instead of the benzo ring in the above structure, provides new compounds which inhibit cyclic phosphodiesterases, in particular type 4 cyclic phosphodiesterases and have a very low emetic activity (10-100 times less active than rolipram in inducing emesis in dogs).
Accordingly, the present invention provides a compound which is a heterocycle of formula (I):

(Figure Removed)
R1 represents a hydrogen atom or a -(CH2)m-Y group,
(Formula Removed)
wherein m is an integer rrom 0 to 4 and Y represents an alkyl, haloaikyl (preferably trifluoromethyl), alkoxy, alkoxycarbony], C3-C7 cycloalkyl, norbornyl (preferably 2-norbornyl) or phenylalkenyl group, or an aromatic group (preferably phenyl or pyridyl) which aromatic group Y may optionally be substituted by one or more halogen atoms;
R2 represents an aromatic group (preferably phenyl, naphthyl or thienyl) which aromatic group may optionally be substituted by one or more halogen atoms or alkyl, alkoxy, C3-C6 cycloalkoxy, methylenedioxy, nitro, dialkylamino or trifluoromethyl groups; and
R3 represents a hydrogen or halogen atom (preferably chloro) or an alkyl group,
and pharmaceutically acceptable salts thereof.
The alkyl, haioalkyl, alkenyl or alkynyl groups and moieties, such as in the alkoxy groups, mentioned in relation to the groups R1 - R3 in compounds of the invention are usually "lower" alkyl, that is containing up to 6 and particularly up to 4 carbon atoms, the hydrocarbon chain being branched or straight. Examples of alkyl groups and moieties are CH.,, C2H5, C3H7, i-C3H7, n-C4H9, i-C4H9, isoamyl and neopentyl.

When any of the groups, such as R1 or R2 has a chiral centre, trie compounds of formula (I) exhibit optical isomerism and Iho Lsomers are within the scope of the present. 1 nven t~ ion .
Examples of R1 are the preferred alkyl groups mentioned above, eye i.opropy 1, cyclopropylmethyl, cyclobutyl, cyclobutylmet hy 1, cyclopentyl and cyclopenthylmethyl.
Examples of R- are phenyl, 3-chlorophenyl, 4 -chloropheriy.I , 3-fluorophenyl, 4-f luorophenyl and 3-nitropheny.I ,
Examples of R' are hydrogen, alkyl or chloro, preferably in the 8- or ')- positions.
The most preferred compounds of the invention are
6- (4-f luorophenyl)-3-isobutyl-l,2,4-triazolo[4, 3 -b]pyrido[3,2-djpyridazine, 3-cyclopropylmethyl-6- ( 3-nit rophen y.i.) -1, 2, 4-triazolo[4, 3-b]pyrido[3,2-d]pyridazine, '3-cyclopropyl-6-phenyl-l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyr idazine, and 3-cyclobutylmethyl-6-(3-nitrophenyl)-i,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine.
According to a further feature of the present invention, the heterocyclic compounds of formula (I) can be prepared from the corresponding hydrazine derivative of formula (II):
(Formula Removed)

R' and R1 are as defined above, by reaction with a react.ive derivative of a carboxylic acid of the general
(Formula Removed)
wherein R' is as defined above. The reactive derivative of the said cat boxylie acid may be, for example, a halide (preferably chloride), an anhydride or a mixed anhydride.
The reaction is preferably carried out in an inert organic soJvent such as methylene chloride, dioxane or tetrahydroturan, in the presence of an organic nitrogen-containing base, e.g. triethylamine and at a temperature between -10°C and +60°C. In the reaction, the corresponding hydrazide of general formula (IV) is first formed:
(Formula Removed)
wherein R1, R:' and R3 are as defined above. A suspension of this hydrazide (IV) in an organic solvent such as dioxane, tetrahydrofuran, isopropanol or n-butanol, is heated, for example at the boiling point of the solvent, to give the corresponding heterocyclic compound of formula (I).
The hydrazine derivative of formula (II) may be prepared by:
1) reacting a hydrazone of formula (V):
(Formula Removed)
wherein R- and Rj are as defined above and R4 is an alkyl group, with a phosphorus halide or phosphorus oxyhalide (preferably phosphorus oxychloride) , to form the intermediate compound of formula (VI):
(Formula Removed)
wherein R' and RJ are as defined above and X is a chlorine or bromine a torn;
2) reacting compound (VI) with an alkyl carbazate (preferably t-butyl carbazate) of formula (VII):

wherein R5 is an alkyl group, to give the alkoxycarbonyjhydrazine derivative (VIII) (Formula Removed)

wherein P/, R' and R' are as defined above; and
3) tiea! ing compound (VIII) with hydrogen chloride in an anhydrous solvent as ethanol.
The reaction between the hydrazone of formula (V) arid a phosphorus ha 1 Lde or phosphorus oxyhalicle is carried out with an excess of reagent at a temperature from 80°C to 120°C, then removed the excess of reagent and poured into cold water, in this way the compound (VI) is obtained.
The reaction of (VI) with the alkyl carbazate of formula (VII) to obtain the corresponding alkoxycarbonyLhydrazine derivative (VIII), is preferably carried out: in the presence of an organic solvent as tetrahydrofuran or dioxan at a temperature of from 60°C to the boiling point of the reaction medium.
The a 1koxycarbonylhydrazine derivative (VIII) may, for example, be transformed into the hydrazine derivative (II) at room temperature in hydrogen chloride-ethanol saturated solution.
The hydrazone derivatives of formula (V) are known compounds whicn can be prepared from the corresponding 2-acylnicotinic acid by known methods described in the literature.
The inhibition of cyclic nucleotide phosphodiesterase 4 from guinea-pig hearts was performed using 96-well microtiter: plates as described by Verghese et al., (Molecular Pharmacology, 47, 1164-1171 (1995)).
The results from such test are shown in Table 1.

(Table Removed)
(*) See structures in Table 2.
Compound A is 3-isobutyl-6-phenyl-l,2,4-triazolo[3,4-a] phthalazine, a compound included in EP-A-85,840.
As it can be seen from Table 1, the compounds of formula (I) are cyclic phosphodiesterase inhibitors, in particular type 4 cyc.l ic AMP phosphodiesterase inhibitors. The compounds are also capable of blocking the production of some pro-inflammatory cytokines such as, for example, TNFa. Thus, they can be used in the treatment of allergic, inflammatory and immunological diseases, as well as those diseases or conditions where the blockade of pro-i n f lammat.ory cylokines or the selective inhibition of PDE 4 . :ould be of benefit.
These diseases states include asthma, rheumatoid
arthrit -is, osteoarthritis, osteoporosis, bone-formation disorders, g J outer ulonephntis, multiple sclerosis, Graves ophtalrnopat hy, myasthenia gravis, insulin-dependent diabetes rneilitus, graft rejection, gastrointestinal disorders such as ulcerative colitis or Crohn disease, septic shock, adult distress respiratory syndrome, and skin diseases such as atopic dermatitis, contact dermatitis, acute dermatomyositis arid psoriasis .
They can also be used as improvers of cerebrovascular function as well as in the treatment of other CNS related diseases such as dementia, Alzheimer' s disease, depression, and as noot ropic agents.
The compounds of the present invention are also of benefit when administered in combination with other drugs such as steroids and immunosuppressive agents, such as cyclosporin A, rapamycin or T-cell receptor blockers. In this case the administration of the compounds allows a reduction of the dosage of the other drugs, thus preventing the appearance of the undesired side effects associated with both steroids arid immunosuppressants.
The compounds of the invention have also shown their efficacy in blocking, after preventive and/or curative treatment, the erosive and ulcerogenic effects induced by a variety of etiological agents, such as antiinflammatory drugs (steroidal or non-steroidal antiinflammatory agents), stress, ammonia, ethanol arid concentrated acids. They can be used alone or in combination with antacids and/or antisecretory drugs in the preventive and/or curative treatment of gastrointestinal pathologies like drug-induced ulcers, peptic ulcers, H. Pylori-related ulcers, esophagitis and gastro-esophageal reflux disease.
They can also be used in the treatment of pathological situations where damage to the cells or tissues is produced
through condit ions like anoxia or the production of an excess of free radicals. Examples of such beneficial effects •lire the protection of cardiac tissue after coronary artery oocJusion or the prolongation of cell and tissue viability when the compounds of the invention are added to preserving solutions intended for storage of transplant organs or fluids such as blood or sperm. They are also of benefit on t :i s s u e r e p air a n d wound healing.
The present: invention also provides a heterocyclic compound of formula (I) for use in a method of treatment of the human or animal body by therapy, particularly for use as a PDE 4 inhibitor or to block the production of a pro-inflammatcry eytokine such as TNFa.
The present invention additionally provides a pharmaceutical composition which comprises, as active ingredient, ac least one heterocyclic compound of formula (I), and a pharmaceutically acceptable carrier or diluent.
Preferably the compositions are in a form suitable for oral, inhalation, rectal, transdermal, nasal, topical or parenteral administration.
The pharmaceutically-acceptable carriers or diluents which are admixed with the active compound or compounds to form the compositions of this invention are well known per se and the actual excipients used depend inter alia on the intended method of administration of the compositions.
Compositions of this invention are preferably adapted for administration per os. The compositions for oral administration may take the form of tablets, capsules, lozenges or (effervescent granules or liquid preparations such as elixirs, syrups or suspensions, all containing one or more compounds of the invention. Such preparations may be made by methods well known in the art, for instance by mixing the heterocyclic compound of formula (I) with the
pharmaceut i ca ily acceptable carrier or diluent.
The diluents which may be used in the preparation of the compositions include those liquid and solid diluents which are compatible with the active ingredient, together with colouring or flavouring agents if desided. Tablets or capsules may conveniently contain from 1 to 100 mg and preferably from 5 to 50 mg of active ingredient. The compounds may also be incorporated into pellets coated with appropriate; natural or synthetic polymers known in the art to produce sustained release characteristics or incorporated with polymers into tablet form to produce the same characteristics.
The liquid compositions adapted for oral use may be in the form oi solutions, suspensions or aerosols. The solutions may be aqueous or aqueous-alcoholic solutions in association with, for example, sucrose or sorbitol to form a syrup. The suspensions may comprise an insoluble or microencapsulated form of an active compound of the invention in association with water and other acceptable solvents together with a suspending agent or flavouring agent.
Compositions for inhalation administration may be in the form of solutions, suspensions or rnicronized powder, contained in an appropriate inhaler.
Compositions for parenteral injection may be prepared, which may or may not be freeze-dried and which may be dissolved in water or an appropriate parenteral injection fluid.
In human therapy, the doses of the heterocyclic compound depend on the desired effect and duration of the treatment; adult doses are generally from Img to 100 mg per day. In general the physician will decide the posology, taking into account the aqe arid weight of the patient being treated.
The following Examples further illustrate the invention.
d) A mixture of t-butoxycarbonylhydrazone of 2-benzoyinicotinic acid (45 g; 13.2 mols) in phosphorus oxychlorjde (f:>00 ml) was boiled under reflux for one hour, then the excess of phosphorus oxychloride was removed under: reduced pressure, the residue treated with ice-water and extracted twice with methylene chloride. The organic solution was washed with 4% sodium bicarbonate aqueous solution, with brine and after drying (Na2S04) , the solvent removed in vacua. The obtained solid was collected with a mixture of diethyl ether-petrol ether 1:1 to give 5-chloro-8-phenylpyrido[2,3-d]pyridazine as a red solid, (25.4 g; 80% yield).
b) To a suspension of the above compound (18.2; 0.075
mols) in anhydrous tetrahydrofuran (180 ml), t-butyl
carbazate (10.0 g; 0.075 mols) was added and the mixture was
boiled under reflux for one hour. After cooling the
crystallized solid was collected by filtration when 5-t-
butoxycarbonylhydrazino-8-phenylpyrido[2,3-d]pyridazine was
obtained (28.5 g) . This compound was solved in ethanol (150
ml), hydrogen chloride in ethanol saturated solution (100
ml) was added and the resulting mixture stirred at room
temperature for 15 hours. A solid was formed which was
collected by filtration and washed with diethyl ether to
give 5-hydrazino-8-phenylpyrido[2,3-d]pyridazine
dihydrochloride (21.6 g; 92% yield).
c) To a suspension of 5-hydrazino-8-phenylpyrido[2,3-
d]pyridazine dihydrochloride (1.24 g; 0.004 mols) in
methylene chloride (30 ml), triethylamine (1.9 ml; 0.013
mols) was added, then stirred at room temperature for 15
minutes and pivaloyl chloride (0.5 ml; 0.0044 moles) slowly
added. After' stirring at room temperature for two hours, water (30 ml) was added, the formed yellow solid, collected by filtration and washed with diethyl ether to give the intermediate nydrazide. This compound was suspended in n-butanol (30 ml), boiled under reflux for 15 hours and on cooling, crystallized a white solid which was collected by filtration and washed with diethyl ether. The obtained solid was purified by flash column chromatography with silica gel and methyl one chloride-ethanol-ammonium hydroxide 200:8:1 as eluent. 3-f-butyl-6-phenyl-l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine was obtained (0.83 g; 69% yield), m.p. 188.1 (determined by Differential Scanning Calorimetry, Perkin-Elmer DSC-7 (compound 8 in Table 2).
The heterocyclic compounds of formula (I) in Table 2 were prepared according to the processes disclosed in this Example, but with the appropriate starting materials.
(Table Removed)
The following Examples illustrate pharmaceutical compositions according to the invention.
3,000 inhalation-flasks each containing 40 mg of 3-t-butyl-6-phenyl~l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine (active compound) were prepared as follows:
Active compound Sorbitari 1: rioleate propellent q.s.
120 g
4 g
60 1
The microcrystalline suspension prepared with these ingredients was introduced in the inhalation-flasks at a volume of 20 ml per flask with a filling machine. The flasks
were furnJshod with an appropriate valve which released 0.2 ml of suspension for each activation (0.4 mg of active compound) .
15,000 capsules each containing 20 mg of 3-t-butyl-6-phenyl-1,2,4-t r iazolo[4,3-b]pyrido[3,2-d]pyridazine (active compound) were prepared from the following formulation:
A c t i v e c o m p o u n d 3 0 0 g
Sodium carboxymethyl starch 330 g
Talc 195 g
Hydrogenated castor oil 165 g
Corn starch 495 g
The above ingredients were sieved through a 60 mesh sieve, then mixed in a suitable mixer and filled into 15,000 gelatine capsules.

1. A l,2,4-triazolo[4,3-6]pyrido[3,2-d]pyridazine of formula (I)

(Formula Removed)
R1 represents a hydrogen atom or a-(CH2)m-Y group, wherein m is an integer from 0 to 4 and Y represents a C1-C6 alkyl group, C1-C6 halolkyl group, C1-C6 alkoxy grup, alkoxycarbonyl group having upto 7 carbon atoms, C3-C7 cycloalkyl group, norbornyl or phenylalkenyl group having up to 12 carbon atoms, or a phenyl or pyridyl group which may be unsubstituted or substituted by one or more halogen atoms;
R2 represent a phenyl, naphthyl or thienyl group which may be unsubstituted or substituted by one or more halogen atoms or C1-C6alkyl, C1-C6 alkoxy, C3-C6 cycloalkoxy, methylenedioxy, nitro, di-(C1-C6) alkylamino or trifluoromethyl groups; and
R3 represents a hydrogen or halogen atom or a C1-C6 alkyl group,
and pharmaceutically acceptable salts thereof.
2. A l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine as claimed in claim 1 wherein R1 represents -(CH2)m-Y wherein m is 0 or 1 and Y represents C1-C6 alkyl or C3-C7 cycloalkyl.

3. A l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine as claimed in any one of the preceeding claims wherein R2 represents a phenyl group, naphthyl group or thienyl group which group R2 may optionally be substituted by one or more halogen atoms, methyl groups, methoxy groups, cyclopentoxy groups, nitro groups or dimethyl amino groups.
4. A l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine as claimed in claim 3 wherein R2 represents a phenyl, 3-chlorophenyl, 4-chlorophenyl, 3-fluorophenyl, 4-fluorophenyl or 3 nitrophenyl group.
5. A l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine as' claimed in any one of the preceding claims wherein R3 represents a hydrogen atom, a C1-C6 alkyl group or a chlorine atom at the 8- or 9- position of the l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine skeleton.
6. A 1, 2, 4-triazolo[4, 3-b]pyrido[3,2-d]pyridazine as claimed in claim 1 which is 6-(4-fluorophenyl)-3-isobutyl-l,2,4-triazolo[4,3-b]pyrido[3,2-d] pyridazine, 3 -cyclopropylmethyl-6 - (3 -nitrophenyl) -1,2,4-triazolo [4,3 -b]pyrido[3,2-d]pyridazine, 3-cyclopropyl-6-phenyl-l,2,4-triazolo[4, 3-b)pyrido[3, 2-d]pyridazine and 3-cyclobutylmethyl-6-(3-nitrophenyl)-1,2,4-triazolo[4,3-b]pyrido [3, 2-d]pyridazine.
7. A composition comprising 1 to 99% by weight of a l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine as claimed in any one of claims 1 to 6 or pharmaceutically acceptable salt thereof and a pharmaceutically acceptable diluent or carrier of a kind such as herein defined, and wherein the ratio of said l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine to diluents or carrier is as herein defined.
8. A l,2,4-triazolo[4,3-b]pyrido[3,2-d]pyridazine as claimed in any one of claims 1 to 6 or pharmaceutically acceptable salt thereof used for the treatment of a condition whose known treatment is to inhibit phosphodiesterase 4

including allergic reaction and disease states, inflammation, ulcers and immunological disease.











2173-del-1998-description (complete)-04-09-2008.pdf

2173-del-1998-description (complete).pdf





















Patent Number 223364
Indian Patent Application Number 2173/DEL/1998
PG Journal Number 29/2008
Publication Date 26-Sep-2008
Grant Date 09-Sep-2008
Date of Filing 24-Jul-1998
Applicant Address GENERAL MITRE, 151, 08022 BARCELONA, SPAIN.
# Inventor's Name Inventor's Address
PCT International Classification Number C07D 487/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 9701670 1997-07-29 Spain