EP0568540A1

EP0568540A1 - 2,4-DIOXO-PYRIDO 2,3-d]PYRIMIDINE-3-ACETIC ACIDS AND ESTERS AND SALTS THEREOF

Info

Publication number: EP0568540A1
Application number: EP92900341A
Authority: EP
Inventors: Harry R. Howard
Original assignee: Pfizer Inc
Current assignee: Pfizer Inc
Priority date: 1991-01-17
Filing date: 1991-11-05
Publication date: 1993-11-10
Also published as: IE920120A1; PT100013A; JPH05509108A; FI933244A0; WO1992012979A1; CA2100164A1; FI933244A

Abstract

Cette invention concerne une série de nouveaux acides acétiques 2,4-dioxo-pyrido 2,3-d pyrimidine-3- ainsi que leurs esters et leurs sels d'addition basiques pharmaceutiquement acceptables. Ces composés sont utiles dans le domaine de la thérapie en tant qu'inhibiteurs de l'aldose réductase, afin de maîtriser certaines complications chroniques du diabète sucré. Sont également présentés des procédés permettant de préparer ces composés à partir de substances de départ déjà connues.This invention relates to a series of novel 2,4-dioxo-pyrido 2,3-d pyrimidine-3- acetic acids and their pharmaceutically acceptable esters and basic addition salts. These compounds are useful in the field of therapy as aldose reductase inhibitors, in order to control certain chronic complications of diabetes mellitus. Also disclosed are methods of preparing these compounds from starting materials already known.

Description

2.4-DIOXO-PYRIDO \ 2 .3-d1PYRIMIDINE-3-ACETIC ACIDS

AND ESTERS AND SALTS THEREOF This invention relates to 2,4-dioxo-pyrido[2,3- d]pyrimidine-3-acetic acids. The compounds are useful for the control of certain chronic complications arising from diabetes mellitus (e.g., diabetic cataracts, retinopathy and neuropathy . The present invention also relates to pharmaceutical compositions comprising such compounds and to the use of such compounds in treating complications arising from diabetes mellitus. Past attempts to obtain new and better oral antidiabetic agents have, for the most part, involved an endeavor to synthesize new compounds that lower blood sugar levels. More recently, several studies have been conducted concerning the effect of various organic compounds in preventing or arresting certain chronic complications of diabetes, such as diabetic cataracts, neuropathy and retinopathy, etc. For instance, K. Sestanj et al. in U.S. Patent No. 3,821,383 disclose that certain aldose reductase inhibitors like l,3-dioxo-lH-benz[d,e]isoquinoline-2(3H)- acetic acid and some closely-related derivatives thereof are useful for these purposes even though they are not known to be hypoglycemic. These compounds function by inhibiting the activity of the enzyme aldose reductase, which is primarily responsible for catalyzing the reduction of aldoses (like glucose and galactose) to the corresponding polyols (such as sorbitol and galactitol) in the human body. In this way, unwanted accumulations of galactitol in the lens of galactosemic subjects and of sorbitol in the lens, retina, peripheral nervous system and kidney of diabetic subjects are prevented or reduced. As a result, these compounds control certain chronic diabetic complications, including those of an ocular nature, since it is already known in the art that the presence of polyols in the lens of the eye leads to cataract formation and concomitant loss of lens clarity. Two patent applications to Fujisawa Pharm. K. K. , U.S. Pat 4,734,419 and European Patent Application No. 331,059 relate to isomeric 3-substituted 2,4-dioxo-l(2H)- quinazolineacetic acids and claim aldose reductase inhibitory activity and diuretic or antihypertensive activity, respectively.

1,2,3,4-tetrahydro-2,4-dioxo-3-quinazoline-alkanoic acids and their use as plant growth regulators, fungicides and anti-allergenic agents are described by Akademie der Wissenschaften der DDR in Ger. (East) DD 250,118.

E. Papadopoulous (Journal of Heterocyclic Chemistry, 1981, vol. 15, 515) describes procedures for the preparation of 2,4-quinazolinedione-3-acetic acids.

Additionally, a series of 3-aryl-2,4-dioxo-l(2H)- quinazoline acetic acids and derivatives as potential inhibitors of bovine serum albumin denaturation are discussed by Bompart, J. et al, Ann. Pharm. Fr.. 1988, Vol. 46(6), 361-370; and Montginoul C. et al, Ann. Pharm. Fr.. 1988, Vol. 46(4), pp. 223-232.

Further, 6,8-Dihaloquinazolinon-3-acetic acids are described by Akademie der Wissenschaften der DDR in Ger. (East) DD 155,853.

The present invention relates to compounds of the formula

0

wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, Cj-Q, alkyl, C₁-C₄ alkoxy or Cι~C₄ alkylthio; Q is a divalent alkylene radical having from one to three carbon atoms; and R¹ is phenyl, thiazolophenyl, trifluoromethyl- thiazolophenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl, phenyloxadiazolyl, thiazolopyridinyl, oxazolopyridinyl, imidazopyridinyl, triazolopyridinyl or indolyl, wherein said phenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl and phenyloxadiozolyl groups are each optionally substituted with up to two identical or non- identical substituents on the benzene ring, said identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, C,-C alkyl and alkoxy and said non-identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, methyl and methoxy;

R² is hydrogen or C,-C₆ alkyl; and the pharmaceutically acceptable base addition salts thereof.

In a preferred embodiment of the invention, R¹ is phenyl or benzothiazol-2-yl or a ring-substituted derivative of phenyl or benzothiazol-2-yl. More preferably, R¹ is 3,4- dichlorophenyl or 4-bromo-2-fluorophenyl. Preferred compounds of the invention are:

1-(4-Bromo-2-fluorophenylmethyl)-1,4-dihydro-2,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

1-(4-Bromo-2-fluorophenylmethyl)-6-chloro-l,4-dihydro- 2,4-dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid; 1-(3,4-Dichlorophenylmethyl) -1,4-dihydro-2,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid.

Specific compounds of the present invention include the following:

1-((6-Chlorobenzothiazol-2-yl)methyl)-1,4-dihydro-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid; l-((6-Fluorobenzothiazol-2-yl)methyl)-l,4-dihydro-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid; l-( (6-(trifluoromethyl)benzothiazol-2-yl)methyl)-1,4- dihydro-2,4-dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid; 6-Fluoro-l- ( (6- (trifluoromethyl) benzothiazol-2- yl)methyl) -1, 4-dihydro-2 , 4-dioxo-3 (2H) -pyrido[2 , 3- d]pyrimidineacetic acid; l-( (5-Fluorobenzoxazol-2-yl)methyl)-l,4-dihydro-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

1-(2 ,4-Dichlorophenylmethyl)-1,4-dihydro-2, -dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

6-Chloro-l-(3 ,4-dichlorophenylmethyl)-1,4-dihydro-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid; 1-(3 ,4-Dichlorophenylmethyl)-1,4-dihydro-6-methoxy-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

1-(3 ,4-Dichlorophenylmethyl)-l,4-dihydro-6-methyl-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

1-(4-Bromo-2-fluorophenylmethyl)-6-fluoro-1,4-dihydro- 2,4-dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

1-(4-Bromo-2-fluorophenylmethyl)-1,4-dihydro-6-methoxy- 2,4-dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid;

1-(4-Bromo-2-fluorophenylmethyl)-1,4-dihydro-6-methyl- 2,4-dioxo-3(2H)-pyrido[2 ,3-d]pyrimidineacetic acid. The present invention also relates to a pharmaceutical composition for the treatment of chronic complications associated with diabetes comprising a compound of the formula I or a pharmaceutically acceptable base addition salt thereof in an amount effective to prevent or alleviate such chronic complications and a pharmaceutically acceptable carrier. Specific and preferred compositions of the present invention comprise the foregoing specific and preferred compounds.

The present invention also relates to a method for treating a diabetic subject to prevent or alleviate chronic complications arising in said subject, which comprises administering to said diabetic subject an amount of a compound of the formula I or a pharmaceutically acceptable base addition salt thereof effective to prevent or alleviate such complications. The present invention also relates to compounds of the following formulae IV, V and VI:

( where i n ^ε i s C^-Cg al ky l )

and

V I

(wherein R² is C_j-Cg alkyl)

which are alkyl 5-halo-2-(3-alkoxycarbonylmethylureido) pyridine-3-carboxylates, alkyl l,4-dihydro-2,4-dioxo-3 (2H)- pyrido[2,3-d]pyrimidine acetates, and alkyl 1-(substituted benzyl) l,4-dihydro-2,4-dioxo-3 (2H)-pyrido[2,3- d]pyrimidineacetates, respectively, wherein X, Q, R¹ and R² are as defined above. These compounds are useful as intermediates for preparing the compounds of the formula I.

The following reaction scheme illustrates the preparation of the compounds of the present invention.

kyl)

IV V

(uherein R₂=C₁-C₆ al kyl ) (uherein R₂=H)

VI I

In accordance with the process employed for preparing the compounds of the present invention, an appropriately substituted carboxylic acid ester of formula VI is converted by means of a suitable reagent or reagents into the title compounds of formula I. Such reagents which may be useful for this transformation are those which are often employed by those skilled in the art for converting carboxylic acid esters to the corresponding carboxylic acids and may include sodium or potassium hydroxides, hydrochloric acid, trifluoroacetic acid and the like. These reagents may be used in the presence or absence of a reaction-inert solvent such as water, lower alcohol, lower ether or cyclic ether, or an organic acid (such as acetic acid) . A solution of sodium hydroxide in water is preferred for this step. Furthermore, these reactions may be carried out at a temperature that is in the range of about 0°C up to the boiling point of the solvent employed, and is preferably conducted in the range of about 20°C to about 40°C. Isolation of the desired products of formula I may be effected by adjusting the pH of the reaction mixture to within the range of about 1 to about 7, followed by filtration of the precipitated acidic product I or by extraction of the crude product into a water-immiscible solvent which may be subsequently dried and evaporated to obtain product acid I. Further purification may then be accomplished by crystallization/recrystallization of the crude product I from a suitable solvent system or by chromatographic methods.

The appropriately substituted carboxylic acid esters of formula VI (in which Q R¹ and R² are as previously defined) , the immediate precursors to the title compounds of formula I, are themselves all novel compounds and are readily prepared by the N-alkylation of the N-l unsubstituted compounds of formula V by analogy with methods reported in the scientific literature and familiar to those skilled in the art. Thus, the intermediates of formula V, which possess a removable hydrogen atom at the 1-position of the pyrido[2,3-d]pyrimidineacetate may be alkylated with a variety of activated arylalkyl or heteroarylalkyl compounds of general formula Z-Q-R¹, where Q and R¹ are as previously defined and Z is a leaving group such as halogen or lower alkane-sulfonate. This particular reaction is normally carried out in the presence of a base condensing agent, such as an alkali metal hydride, alkanoate or amide, or an alkali metal-alky1 or metal-aryl compound, as the case may be. Furthermore, the reaction is usually conducted in a reaction-inert organic solvent, preferably using N,N-di- (lower alkyl) lower alkanoamide for the best results; preferred agents in this connection would include sodium hydride as the base condensing agent and N,N- dimethylformamide as the solvent. In general, substantially equimolar quantities of the reactants are employed. The preferred temperature range is from about 0°C up to about the boiling point of the solvent employed for a period of about 0.5 hours to about 48 hours. In practice, the reaction is usually conducted at room temperature for a period of time which is often less than 24 hours. In addition, while this reaction may be conducted at pressures up to 5 atmospheres, in practice it is adequate to perform this step at atmospheric pressure, usually under an inert atmosphere such as nitrogen or argon gas and with suitable exclusion of moisture which could decrease the yield of intermediate product VI. Upon completion of the reaction, as determined using any of a variety of methods (such as thin layer chromatography) , the desired N-l substituted esters of formula VI are recovered from the reaction mixture by the use of any number of standard techniques known to those skilled in the art. In practice, the reaction mixture is first diluted with water and the crude reaction product is then filtered (in the case of a precipitated solid product) or extracted into a suitable, water-immiscible solvent from which the crude intermediate of formula VI may be isolated by evaporation of the solvent to dryness. Further purification of these compounds may best be accomplished as in the case of the final acid products of formula I, i.e., by crystallization /recrystallization from a suitable solvent system, or by chromatography of the crude reaction product.

Finally, the N-l unsubstituted esters of formula V are themselves novel compounds and they may be prepared by one of several methods reported in the scientific literature. For example, E. Papadopoulos (Journal of Heterocvclic Chemistry. 1981, vol. 18, 515) has described a procedure for the conversion of a ureido ester into a 2,4- quinazolinedione-3-acetic acid by treating the former with concentrated ammonium hydroxide in ethanol at 25°C. In the examples described within the present invention, the novel ureido esters of formula IV are similarly best converted to the compounds of formula V by the action of concentrated ammonium hydroxide in ethanol at 50°C. The same ureido esters of formula IV are prepared by the condensation of the appropriate methyl nicotinate III with an ester of isocyanoacetic acid, this condensation taking place with equimolar amounts of the two components in the presence or absence of a reaction-inert solvent. In all cases, the compounds of formula III, the starting materials for the preparation of the ureido esters of formula IV are either commercially available or are readily prepared using methods and procedures found in the scientific literature. Esters of the general structural type VI may be isolated prior to conversion to the acids of structure I. In instances when a different ester is desired, the acid I may be esterified using any variety of procedures known to those skilled in the art of organic chemistry. For example, the acid I may be suspended in the appropriate C,-C₆ alcohol and treated with a suitable inorganic acid (e.g., hydrochloric acid or sulfuric acid) and then stirred under an inert atmosphere with the exclusion of moisture at a temperature within the range of room temperature to about the boiling point of the alcohol employed. The crude ester VI so obtained may be isolated by removal of the solvent alcohol and purification by recrystallization, chromatography, distillation or other suitable technique.

The chemical bases which are used in this invention to prepare the aforementioned pharmaceutically acceptable base addition salts are those which form non-toxic base salts with the herein described 1-substituted 2,4-dioxo- pyrido[2,3-d]pyrimidine-3-acetic acids, such as l-(4-bromo- 2-flurophenylmethyl)-6-chloro-l,4-dihydro-2,4-dioxo-3(2H)- pyrido[2,3-d]pyrimidineacetic acid. These particular non- toxic base salts include those derived from such pharmacologically acceptable cations as sodium, potassium, calcium, magnesium, etc. These salts can be easily prepared by treating the aforementioned acid compounds with an aqueous solution of the pharmacologically acceptable cation and then evaporating the resulting solution to dryness, preferably under reduced pressure. Alternatively, they may also be prepared by mixing lower alkanolic solutions of the acidic compounds and the desired alkali metal alkoxide together, and then evaporating the resulting solution to dryness in the same manner as above. In either case, stoichiometric quantities of the reagents must be employed to ensure completeness of the reaction and maximum production of yields of the desired final base addition salts. Also, salts of the title compounds may be prepared using pharmacologically acceptable organic bases to form the salts, these organic bases including compounds such as diethanolamine, meglumine, cyclohexylamine, dicyclo- hexylamine and the like. The salts derived from these organic bases may be prepared by combining the two reagents in essentially equimolar amounts in a suitable solvent from which the derived base addition salt can be isolated by virtue of its reduced solubility in the solvent system, or by concentration of the solvent system to dryness followed by crystallization/recrystallization of the crude salt in a suitable solvent system. The starting materials required for preparing the compounds of formula I are either known compounds which are readily available commercially or they are described in the literature or else they can easily be synthesized by those skilled in the art starting from common chemical reagents and using conventional methods of organic synthesis. For instance, 2-aminonicotinic acid is readily prepared from the known 2-aminonicotinonitrile (Beilstein, 22., 542).

The compounds of the formula I and the pharmaceutically acceptable salts thereof (hereinafter also referred to as the active compounds of the present invention) are readily adapted to therapeutic use as aldose reductase inhibitors for the control of certain chronic diabetic complications, in view of their ability to reduce lens and peripheral nerve (e.g., the sciatic nerve) sorbitol levels in diabetic subjects. The active compounds of the present invention can be administered to affected mammals (including humans) by either the oral, topical or parenteral routes of administration. In general, these compounds are ordinarily administered in dosages ranging from about 0.50 mg to about 50 mg per kg of body weight per day, although variations will necessarily occur depending upon the weight and condition of the subject being treated and the particular route of administration chosen. These compounds may be administered either alone or in combination with pharmaceutically acceptable carriers by the various routes previously indicated, and such administration can be carried out in either single or multiple dosages. More particularly, the active compounds of this invention can be administered in a wide variety of different dosage forms, i.e., they may be combined with various pharmaceutically-acceptable inert carriers in the form of tablets, capsules, lozenges, troches, hard candies, powders, sprays, aqueous suspensions, injectable solutions, elixirs, syrups, and the like. Such carriers include solid diluents or fillers, sterile aqueous media and various non-toxic organic solvents. In general, the active compounds of the invention will be present in such dosage forms at concentration levels ranging from about 0.5% to about 90% by weight of the total composition to provide the desired unit dosage.

For oral administration, tablets containing various excipients such as sodium citrate, calcium carbonate and calcium phosphate may be employed along with various disintegrants such as starch and preferably potato or tapioca starch, alginic acid and certain complex silicates, together with binding agents such as polyvinylpyrrolidone, gelatin and acacia. Additionally, lubricating agents such as magnesium stearate, sodium lauryl sulfate and talc are often very useful for tabletting purposes. Solid compositions of a similar type may also be employed as fillers in soft and hard-filled gelatin capsules; preferred materials in this connection also include the high molecular weight polyethylene glycols. When aqueous suspensions and/or elixirs are desired for oral administration, the essential active ingredient therein may be combined with various sweetening or flavoring agents, coloring matter or dyes, and if so desired, emulsifying and/or suspending agents as well, together with such diluents as water, ethanol, propylene glycol, glycerin and various combinations thereof.

For parenteral administration, solutions of the active compounds of the present invention may be prepared, taking into account the solubility of the compound or salt to be utilized. Thus, solutions in sesame or peanut oil or in aqueous propylene glycol or N,N-dimethyIformamide as well as sterile aqueous solutions may be employed. Such aqueous solutions should be suitably buffered if necessary and the liquid diluent first rendered isotonic with sufficient saline or glucose. These particular aqueous solutions are especially suitable for intravenous, intramuscular, subcutaneous and intraperitoneal injection. In this connection, the sterile aqueous media employed are all readily obtainable by standard techniques well-known to those skilled in the art. Additionally, it is also possible to administer the compounds topically via an appropriate ophthalmic solution (e.g., 0.5-2.0%) applied dropwise to the eye.

The utility of the compounds of the present invention, as agents for the control of chronic diabetic complications, may be predicted by measuring their ability to (1) inhibit the enzyme activity of isolated aldose reductase; (2) reduce or inhibit sorbitol accumulation in the sciatic nerve and lens of acutely streptozotocinized (i.e. diabetic) rats; (3) reverse already-elevated sorbitol levels in the sciatic nerve and/or lens of chronic streptozotocin-induced diabetic rats; (4) prevent or inhibit galactitol formation in the lens of acutely galactosemic rats, and/or (5) delay cataract formation and reduce the severity of lens opacities in chronic galactosemic rats.

The following Examples illustrate the preparation of the compounds of the present invention. All melting points are uncorrected. Ratios of solvents used in thin layer chromatography (TLC) are by volume.

Example 1 Ethyl 1-(4-bromo-2-fluorophenylmethyl)-6-chloro-l.4-dihydro- 2,4-dioxo-3(2H-pyridor2.3-dlpyrimidineacetate A. 2-Amino-5-chloro-nicotinic acid

A mixture of 10 g (72 mmol) of 2-aminonicotinic acid in 300 ml acetic acid was treated with chlorine gas for 1 hour at room temperature. During this time, the solution initially became homogeneous and then a yellow product precipitated. The reaction mixture was then poured into 1000 ml of ethyl ether, stirred for one half hour and then filtered. The solids were washed with ethyl ether and then dried to give 12.46 g (99%) of the title compound, .p. 250- 255°C. B. Methyl 2-amino-5-chloronicotinate A mixture of 6.2 g (36 mmol) of the title compound of Example 1A and 70 ml methanol was treated with HC1 gas for 2 hours, refluxed for 16 hours (a homogeneous solution resulted) and then treated with HC1 gas for an additional 2 hours. TLC (90 CHC1₃:10 methanol) then showed completion of reaction (RF 0.70 vs 0.10 for the title compound of Example 1A) . The solvent was removed in vacuo, the solids were washed with 5% NaHC0₃, and then with water, and were then dried overnight under vacuum to yield the title compound, 6.21 g (93%), m.p. 260-263°C, m/e: 186 (p⁺) , 188.

Similarly, 5.0 g (36 mmol) 2-aminonicotinic acid (Aldrich Chemical Co.) in 50 ml methanol was converted to 5.4 g (98%) methyl 2-aminonicotinate, m.p. 82-84°C. C. Ethyl 6-chloro-l.4-dihydro-2.4-dioxo-3 (2H)-pyrido- \2 .3-dTpyrimidineacetate

A mixture of 6.21 g (33 mmol) of the title compound of Example IB and 3.73 ml of (33 mmol) of ethyl isocyanatoacetate was heated until the mixture became homogeneous and heating was then continued for an additional 15 minutes. On cooling, the material became a hard, gummy solid which was then dissolved in 50 ml of absolute ethanol, treated with 20 ml concentrated NH₄0H and stirred 3 hours at 50°C. TLC (1 ethyl acetate:1 hexane) showed conversion to a product (at Rf 0.60). The solution was cooled, excess ethanol was removed in vacuo and the aqueous residue was acidified with about 100 ml of IN HC1. The resulting yellow-orange solid was filtered, washed with IN HC1 and dried to give 7.2 g crude product. Recrystallization from ethanol gave 2.33 g (25%) of the title compound, m.p. 112- 114°C; m/e 283 (p⁺) , 285; Analysis for C_uH_I0O₄Cl: Calc'd: C 46.57; H 3.55; N 14.81; Found: C 46.21, H 3.51; N 14.85.

Similarly, 5 g methyl 2-aminonicotinate and 4.66 ml ethyl isocyanatoacetate gave, after treatment with 60 ml ethanol and 20 ml concentrated NH₄OH at 50°C for 1 hour, acidification to pH3, extraction with ethyl acetate (2x100 l) and concentration of the organic extracts, 6.21 g of crude product. Recrystallization from ethanol gave 3.2 g (35.5%) of ethyl l,4-dihydro-2,4-dioxo-3(2H)-pyrido[2,3- d]pyrimidineacetate quarter hydrate, m.p. 109-113°C; m/e: 249 (p⁺) ; Analysis for Calc^,d: C 52.07; H 4.57; N 16.56; Found: C 52.15; H 4.43; N 16.62.

D. Ethyl 1-(4-bromo-2-fluorophenylmethyl)-6-chloro- 1.4-dihydro-2.4-dioxo-3 (2H)-pyridor2.3-dlpyrimidineacetate Under N₂ in a flame dried flask with magnetic stirrer, 0.310 g (7.8 mmol) of NaH (60% in oil dispersion) was washed with pentane. The resulting oil free solid was suspended in 35 ml of sieve-dried N,N-dimethylformamide (DMF), and 2.00 g (7.1 mmol) of the title compound of Example 1C was added portionwise with stirring. After H₂ evolution had ceased (about 0.5 hour), 4-bromo-2-fluorobenzyl bromide (1.89 g, 7.1 mmol) was added in one portion. After 2 hours, a thick suspension had formed, and an additional 10 ml DMF was added. After an additional 16 hours at room temperature, TLC (75 hexane: 25 ethyl acetate) showed product (RF 0.80) and no starting material (RF 0.30). The reaction mixture was poured over 200 ml ice/H₂0, stirred 30 minutes, filtered, washed well with H₂0 and then air dried to give 3.12 g crude product. Recrystallization from ethanol gave the title compound as a pure product, 2.85 g (86.1%), m.p. 145-147°C; m/e: 469 (p⁺) , 471.

Similarly, 3.0 g (12 mmol) ethyl l,4-dihydro-2,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetate, 0.529 g (13.2 mmol) 60% NaH and 3.22 g (12.0 mmol) 4-bromo-2-fluorobenzyl bromide in 50 ml dry DMF gave 2.65 g (50.5%) ethyl l-(4- bromo-2-fluorophenylmethyl)-1,4-dihydro-2,4-dioxo-3 (2H)- pyrido[2,3-d]pyrimidineacetate, m.p. 140-143°C.

Similarly, 1.74 g (7.0 mmol) ethyl l,4-dihydro-2,4- dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetate and 1.36 ml (7.0 mmol) alpha,3,4-trichlorotoluene (97%, Aldrich Chemical Co.) gave 2.61 g (91%) ethyl l-(3,4-dichlorophenylmethyl)-2,4- dioxo-3 (2H)-pyrido[2,3- ]pyrimidineacetate, m.p. 136-138°C. Example 2 1-(4-Bromo-2-fluorophenylmethyl)-6-chloro-l,4-dihydro-2,4- dioxo-3f2H)-pyridor2.3-dlpyrimidineacetic acid

A mixture of 1.40 g (2.97 mmol) of the title compound of Example ID, 15 ml concentrated HCl and 50 ml glacial acetic acid was refluxed for 16 hours. TLC (75 hexane:25 ethyl acetate) showed only a single spot at Rf 0.10. After concentration in vacuo. the residue was recrystallized from ethyl acetate:hexane (120:55 ml) to give the title compound as yellow crystals, 0.728 g (55.3%), m.p. 195-197^βC; Analysis for C₁₆HioBrClFN₃0₄, Calc'd: C 43.42; H 2.28; N 9.49; Found: C 43.36; H 2.34; N 9.35.

Example 3 1-f4-Bromo-2-fluorophenylmethyl)-1.4-dihydro-2.4-dioxo-3(2H- pyridor2.3-dlpyrimidineacetic acid hvdrochloride

A mixture of 2.30 g (5.27 mmole) ethyl l-(4-bromo-2- fluorophenylmethyl)-1,4-dihydro-2,4-dioxo-3(2H)-pyrido[2,3- d]pyrimidineacetate and 50 ml 2N NaOH in 100 ml absolute ethanol was stirred for 3 hours at room temperature, resulting in a homogeneous solution. The solution was acidified to pH 7 and extracted with ethyl acetate (2x100 ml) . The organics were washed with water, dried over Na₂S0₄ and concentrated in vacuo to a viscous oil. Trituration with hexanes gave 1.3 g of crude product, recrystalized from methanol to give the title compound, 0.60 g (26%), as the hydrochloride salt, m.p. >300°C; Analysis for C_j6H_nBrFN₃0₄«HCl: Calc'd: C 43.22; H 2.72; N 9.45; Found: C 43.60; H 2.33; N 9.10.

Similarly, 2.4 g (5.87 mmole) of ethyl l-(3,4-dichloro- phenylmethyl)-2,4-dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetate in 90 ml ethanol with 20 ml 2N NaOH gave 0.370 g (17%) 1- (3,4-dichlorophenylmethyl)-1,4-dihydro-2,4-dioxo-3 (2H)- pyrido[2,3-d] yrimidineacetic acid as white crystals from ethyl acetate:hexane) , m.p. 205-208°C; m/e 379 (p⁺) , 381; Analysis for C₁₆H_nCl,N₃0₄: Calc'd: C 50.55; H 2.92; N 11.05; Found: C 50.54; H 2.75; N 10.84. Example 4 The compounds of Examples 2 and 3 were tested for their ability to reduce or inhibit aldose reductase enzyme activity via the procedure of S. Hayman et al. , as described in the Journal of Biological Chemistry. Vol. 240, p.877 (1965) and as modified by K. Sestanj et al. in U.S. Patent No. 3,821,383. In each case, the substrate employed was partially purified aldose reductase enzyme obtained from human placenta. At a concentration of 10" the compounds showed a percent inhibition greater than 70%.

Example 5 The compounds of Examples 2 and 3 were tested for their ability to reduce or inhibit sorbitol accumulation in the sciatic nerve and lens of streptozotocinized (i.e., diabetic) rats by the procedure described in U.S. Patent No. 3,821,383. In the present study, the amount of sorbitol accumulation in the sciatic nerve and lens of each test animal was measured 27 hours after the induction of diabetes. The compounds were the administered orally at 25 mg/kg at intervals of 4, 8 and 24 hours after the administration of streptozotocin. The results obtained in this manner are presented in terms of the percent inhibition (%) afforded by the test compound as compared to the case where no compound was administered (i.e., the control or untreated animal where sorbitol levels normally rise from approximately 50-100 nM/g tissue to as high as 400 nm/g tissue in the 27-hour test period) . In this manner, it was found that each compound afforded a reduction in the accumulated sorbitol levels in the sciatic nerve of diabetic rats of at least 60% and a reduction in the lens of at least 4%.

Claims

CLAIMS 1. A compound of the formula: o

wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, Cj-Q, alkyl, Cj-C₄ alkoxy or Cι~C₄ alkylthio; Q is a divalent alkylene radical having from one to three carbon atoms; and

R¹ is phenyl, thiazolophenyl, trifluorσmethyl- thiazolophenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl, phenyloxadiazolyl, thiazolopyridinyl, oxazolopyridinyl, imidazopyridinyl, triazolopyridinyl or indolyl, wherein said phenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl and phenyloxadiazolyl groups are each optionally substituted with up to two identical or non- identical substituents on the benzene ring, said identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, Cj-Q, alkyl and Cι~C₄ alkoxy and said non-identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, methyl and methoxy;

R² is hydrogen or Cj-Cg alkyl; and the pharmaceutically acceptable base addition salts thereof.

2. A compound as claimed in claim 1 which is an acid wherein R¹ is phenyl or benzothiazol-2-yl, or a ring- substituted derivative of phenyl or benzothiazol-2-yl.

3. A compound as claimed in claim 2 wherein X is hydrogen, Q is methylene and R¹ is unsubstituted benzothiazol-2-yl.

4. A compound as claimed in claim 2 wherein X is hydrogen, Q is methylene and R¹ is ring-substituted benzothiazol-2-yl.

5. A compound as claimed in claim 2 wherein X is hydrogen, Q is methylene and R¹ is ring-substituted phenyl.

6. A compound as claimed in claim 5 wherein R¹ is 4- bromo-2-fluorophenyl.

7. A compound as claimed in claim 5 wherein R¹ is 3,4- dichlorophenyl.

8. A compound as claimed in claim 2 wherein X is chlorine, Q is methylene and R¹ is ring-substituted phenyl.

9. A compound as claimed in claim 8 wherein X is chlorine at the 6-position of the molecule and R¹ is 4-bromo-

2-fluorophenyl.

10. A compound as claimed in claim 1 wherein R² is C,-C₆ alkyl.

11. A compound as claimed in claim 10 wherein R² is ethyl.

12. A compound according to claim 1, said compound being selected from the group consisting of:

1-(4-Bromo-2-fluorophenylmethyl)-1,4-dihydro-2 ,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid; l-(4-Bromo-2-fluorophenylmethyl)-6-chloro-l,4-dihydro- 2,4-dioxo-3(2H)-pyrido[2,3-d]pyrimidineacetic acid; and l-(3,4-Dichlorophenylmethyl) -1,4-dihydro-2,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid.

13. A pharmaceutical composition useful for preventing or alleviating chronic diabetic complications in a diabetic subject, said composition comprising an amount of a compound as claimed in claim 1 effective to prevent or alleviate such complications and a pharmaceutically-acceptable carrier.

14. A method for treating a diabetic subject to prevent or alleviate chronic complications arising in said diabetic subject, which comprises administering to said subject an amount of a compound as claimed in claim 1 effective to prevent or alleviate such complications.

15. A compound of the formula: wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, Cj-C₄ alkyl, Cj- , alkoxy or C_ι~C₄ alkylthio; and R² is hydrogen or alkyl; and the pharmaceutically acceptable base addition salts thereof.

16. A compound of the formula:

0

wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, C^C^ alkyl, C_j-^ alkoxy or Cj- alkylthio;

Q is hydrogen or a divalent alkylene radical having from one to three carbon atoms; and

R¹ is phenyl, thiazolophenyl, trifluoromethyl- thiazolophenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl, phenyloxadiazolyl, thiazolopyridinyl, oxazolopyridinyl, imidazopyridinyl, triazolopyridinyl or indolyl, wherein said phenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl and phenyloxadiazolyl groups are each optionally substituted with up to two identical or non- identical substituents on the benzene ring, said identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, Cι~C₄ alkyl and Cι~C₄ alkoxy and said non-identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, methyl and methoxy;

R² is Cj-Cβ alkyl; and the pharmaceutically acceptable base addition salts thereof.

17. A process for the preparation of a compound of the formula:

wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, C_t-C₄ alkyl, Cj-C₄ alkoxy or C_j- alkylthio; Q is a divalent alkylene radical having from one to three carbon atoms; and

R¹ is phenyl, thiazolophenyl, trifluoromethyl- thiazolophenyl , benzothiophenyl, benzoxazolyl, benzothiazolyl, phenyloxadiazolyl, thiazolopyridinyl, oxazolopyridinyl, imidazopyridinyl, triazolopyridinyl or indolyl, wherein said phenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl and phenyloxadiazolyl groups are each optionally substituted with up to two identical or non- identical substituents on the benzene ring, said identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, Cι-C₄ alkyl and C,-C₄ alkoxy and said non-identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, methyl and methoxy;

R² is hydrogen or Cj-C₆ alkyl comprising reacting a compound of the formula

where X, R¹ are previously defined and R² is Cι-C₆ alkyl, with an acidic or basic reagent in the presence or absence of a reaction inert solvent to form a compound of formula I, and, if desired, converting a compound of the formula I to a pharmaceutically acceptable salt thereof.

18. A process as claimed in claim 17 wherein R¹ is phenyl or benzothiazol-2-yl, or a ring-substituted derivative of phenyl or benzothiazol-2-yl.

19. A process as claimed in claim 18 wherein X is hydrogen, Q is methylene and R¹ is unsubstituted benzothiazol-2-yl.

20. A process as claimed in claim 18 wherein X is hydrogen, Q is methylene and R¹ is ring-substituted benzothiazol-2-yl or ring-substituted phenyl.

21. A process as claimed in claim 20 wherein R¹ is 4- bromo-2-fluorophenyl or dichlorophenyl.

22. A process as claimed in claim 18 wherein X is chlorine, Q is methylene and R¹ is ring-substituted phenyl.

23. A process as claimed in claim 22 wherein X is chlorine at the 6-position of the molecule and R¹ is 4-bromo- 2-fluorophenyl.

24. A process as claimed in claim 17 wherein R² is C,-^ alkyl.

25. A process according to claim 17, said compound prepared by said process being selected from the group consisting of:

1-(4-Bromo-2-fluorophenylmethyl)-1,4-dihydro-2,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid; l-(4-Bromo-2-fluorophenylmethyl)-6-chloro-l,4-dihydro- 2 ,4-dioxo-3 (2H)-pyrido[2,3-d]pyrimidineacetic acid; and

1-(3,4-Dichlorophenylmethyl) -1,4-dihydro-2,4-dioxo- 3(2H)-pyrido[2,3-d]pyrimidineacetic acid.

26. A process for the preparation of a compound of the formula:

wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, C,-C₄ alkyl, C--C₄ alkoxy or C]-C₄ alkylthio; and R² is hydrogen or Cι~C₆ alkyl; comprising condensing a compound of the formula

with an ester of isocyano acetic acid in the presence or absence of a reaction inert solvent, and, if desired converting the resulting compound to a pharmaceutically acceptable salt thereof.

27. A process for the preparation of a compound of the formula:

wherein X is hydrogen, fluorine, chlorine, bromine, trifluoromethyl, C₁-C₄ alkyl, C^Q, alkoxy or C,-C₄ alkylthio; Q is hydrogen or a divalent alkylene radical having from one to three carbon atoms; and

R¹ is phenyl, thiazolophenyl, trifluoromethyl- thiazolophenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl, phenyloxadiazolyl, thiazolopyridinyl, oxazolopyridinyl, imidazopyridinyl, triazolopyridinyl or indolyl, wherein said phenyl, benzothiophenyl, benzoxazolyl, benzothiazolyl and phenyloxadiazolyl groups are each optionally substituted with up to two identical or non- identical substituents on the benzene ring, said identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, C_x-C₄ alkyl and C^ , alkoxy and said non-identical substituents being selected from fluorine, chlorine, bromine, trifluoromethyl, methyl and methoxy;

R² is Cι-C₆ alkyl; comprising alkylating a compound of the formula

wherein X is previously defined and R² is C_j-Cg alkyl, with an activated aryl alkyl or heteroarylalkyl compound in the presence of a base condensing agent and a reaction-inert solvent, and, if desired, converting the resulting compound to a pharmaceutically acceptable salt thereof.