Substituted 2,3-Dihydro Imidazo[1,2-C]pyrimidines

The Ring Index, page 155 (second edition, American Chemical Society, 1960) gives the basic imidazo[1,2-c]pyrimidine structure with a reference to Ann., 432, 120 (1923). Substituted imidazo[1,2-c]pyrimidines are also referred to in the more recent literature; for example, Bartholomew, et al. J. Med. Chem., 19, 814 (1976) gives the preparation of the arabinosyl hypoxanthine and arabinosyl guanine analogs of the imidazo[1,2-c]pyrimidine series. The intermediate compound 7-chloroimidazo[1,2-c]pyrimidine-5(6H)-one is also referred to. None of the compounds disclosed in this publication exhibited significant anti-viral or anti-microbial activity in vitro. West German Pat. No. 2511316 issued Sept. 18, 1975, (Derwent Abstract 64314W/39, 1975) to Eisai KK discloses a group of 2-alkyl-5-alkylmercapto-7-hydroxyimidazo[1,2-c]pyrimidines. They are alleged to be useful as anti-inflammatory or analgesic agents.

A single reference to chloro substituted 2,3-dihydro-imidazo[1,2-c]pyrimidines is available;--see Yanai et al. Yakugaku Zasshi, 94, 1503, (1974). Compound XVII on page 1506 is 7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride. Both the hydrochloride salt and the free base are characterized in Tables I and Table V and analytical data are provided in Table VIII. The corresponding unhydrogenated compound, XXXII, is also disclosed. No utility is set forth therein for these compounds.

This invention provides substituted 2,3-dihydroimidazo[1,2-c]pyrimidines of the structure ##STR1## wherein R is C.sub.1 -C.sub.5 alkyl, phenylamino or methylmercapto, R.sup.1 is Cl, pyrrolidino, methylamino or N-methyl-benzylamino and R.sup.2, R.sup.3 and R.sup.4 individually are H, methyl or phenyl, and pharmaceutically-acceptable acid addition salts thereof formed with strong inorganic acids or strong organic acids such as the organic sulfonic acids.

The illustrative C.sub.1 -C.sub.5 alkyl groups which R can represent include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, n-amyl, isoamyl, 1,2-dimethylpropyl, sec-amyl, t-amyl, and the like.

Compounds according to formula I in which R.sup.1 is chlorine are weakly basic and form acid addition salts only with strong acids. Pharmaceutically-acceptable acid addition salts of the bases of formula I are thus derived from strong inorganic acids such as: hydrochloric acid, nitric acid, phosphoric acid, sulfuric acid, hydrobromic acid, hydriodic acid, nitrous acid, phosphorous acid and the like. Strong organic acids useful for forming pharmaceutically-acceptable acid addition salts with bases according to formula I when R.sup.1 is Cl including particularly the organic sulfonic acids. Pharmaceutically-acceptable salts of this invention thus include sulfate, pyrosulfate, bisulfate, sulfite, bisulfite, nitrate, phosphate, monohydrogenphosphate, dihydrogenphosphate, metaphosphate, pyrophosphate, chloride, bromide, iodide, benzenesulfonate, toluenesulfonate, chlorobenzenesulfonate, xylenesulfonate, methanesulfonate, trifluoromethyl sulfonate, propanesulfonate, naphthalene-1-sulfonate, naphthalene-2-sulfonate and the like salts.

When R.sup.1 in formula I is other than Cl, i.e., is methylamino, pyrrolidino or N-methylbenzylamino, this amine group is quite basic and readily forms acid addition salts with all types of acids, not just strong acids.

Illustrative compounds coming within the scope of this invention include:

5,8-Dimethyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine sulfate,

2,5-Dimethyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrobromide,

3,5-Dimethyl-7-pyrrolidino-2,3-dihydroimidazo[1,2-c]pyrimidine nitrate,

3-Methyl-5-methylmercapto-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride,

2-Phenyl-5-amino-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine dihydrogenphosphate,

2,3,5-Trimethyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine metaphosphate,

3-Phenyl-7-methylamino-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride,

N-methyl-N-benzyl-2-isopropyl-7-amino-2,3-dihydro-imidazo[1,2-c]pyrimidine hydrochloride,

N,5-dimethyl-8-phenyl-2,3-dihydroimidazo[1,2-c]pyrimidine-7-amine sulfate,

5-Isoamyl-7-methylamino-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride.

5-Phenyl-7-pyrrolidino-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride.

The above compounds as well as other compounds coming within the scope of formula I above wherein R.sup.1 is chlorine are prepared by the following reaction scheme: ##STR2## wherein R, R.sup.2, R.sup.3 and R.sup.4 have the same meaning as hereinabove.

According to the above reaction scheme, a 4,6-dichloropyrimidine substituted at C-2 with an alkylamino or methylmercapto group and optionally substituted at C-5 with methyl or phenyl (formula II) is reacted with an ethanol amine (formula III) in an inert non-hydroxylic solvent in the presence of a suitable alkali. Useful solvents for this reaction include ethers such as THF, dioxane, and the like, and amides such as DMA and DMF. Mild alkaline conditions should be employed, such as the presence of sodium bicarbonate, in order to avoid replacing the second chlorine atom in the pyrimidine by hydroxy. Ordinarily, equimolar quantities of ethanolamine and pyrimidine are employed. In addition, it is preferred to add the ethanolamine to the pyrimidine solution so as to minimize the production of diamino-substituted pyrimidine by-products. The 4-chloro-6-(.beta.-hydroxyethyl)amino pyrimidine thus produced is cyclized using trifluoromethyl sulfonic acid or thionyl chloride to yield the dihydroimidazopyrimidine (formula V) of this invention wherein R.sup.1 is chloro. In carrying out the cyclization reaction, it is important that the solvent not react under Friedel-Craft conditions with the hydroxylethyl group. Solvents including benzene or deactivated benzenes such as nitrobenzene and chlorobenzene, should be employed. Preferably, if avoidance of this by-product is overwhelmingly important, a solvent such as cyclohexane which does not undergo the Friedel-Craft reaction under any conditions should be used. Activated benzenes such as toluene, anisole and the like should be avoided as solvents. In cyclizing with thionyl chloride, a solvent such as THF is customarily employed. Both of the above cyclization reactions require heating for their rapid completion and it is customary to employ temperatures in the range 50.degree. C. to the boiling point of the particular solvent employed, or to about 110.degree. C. whichever temperature is lower.

The compounds of this invention wherein R.sup.1 is pyrrolidino, methylamino, or N-methyl benzylamino are prepared by reacting a compound according to formula I above wherein R.sup.1 is chloro with pyrrolidine, methylamine, or N-methyl benzylamine. This replacement reaction is carried out by simply mixing the amine and the 7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine in the form of an acid addition salt thereof in aqueous solution in the presence of base. Saturated sodium bicarbonate solution is an ideal reaction medium for this reaction. Heating is not required and the reaction ordinarily takes place at ambient temperature.

The compounds of this invention according to Formula I above wherein R.sup.3 or R.sup.4 are other than hydrogen, contain an asymmetric carbon atom. For example, 2,5-dimethyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine is produced in the above synthetic procedure as a dl mixture or racemate, the asymmetric carbon giving rise to optical isomers, in this case at C-2. This dl mixture can be resolved into its optical antipodes by methods known to the art or, alternatively, an optically active amine can be used as the reactant (III) in the above Reaction Scheme.

This invention is further illustrated by the following specific examples:

One hundred grams of 4,6-dichloro-2-methylpyrimidine and 37.40 g. of .beta.-aminoethanol were refluxed overnight in THF in the presence of an excess of sodium bicarbonate. The reaction mixture was filtered after cooling and the solvent removed in vacuo. The reaction product remaining as a residue was slurried in ether and the slurry filtered. A yield of 98 g. of 2-methyl-4-chloro-6-.beta.-hydroxyethylaminopyrimidine were collected. The compound was dissolved in benzene without further purification and 238.5 g. of trifluoromethylsulfonic acid were added. The consequent 2-phase reaction system was heated to refluxing temperature overnight. After cooling, water was added to the reaction mixture and the aqueous phase separated. The aqueous phase was evaporated in vacuo, leaving a residual oil comprising 5-methyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine formed in the above reaction as the trifluoromethylsulfonate salt; weight=92 g. The salt was crystallized from an etherethyl acetate solvent mixture. The crystalline salt was dissolved in water and treated with the chloride form of an ion exchange resin, thus forming 5-methyl-7-chloro-2,3-dihydroimidazo[1,2 -c]pyrimidine hydrochloride. The compound melted about 230.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture; yield=17 g.

Analysis Calc.: C, 40.80; H, 4.40; N, 20.39; Found: C, 41.05; H, 4.44; N, 20.67.

Other compounds preparable by the above procedure include 5-phenyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride which decomposed at about 230.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 53.75; H, 4.14; N, 15.67; Cl, 26.44. Found: C, 53.55; H, 4.07; N, 15.72; Cl, 26.85.

5-Ethyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride decomposing above 220.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 43.66; H, 5.04; N, 19.09; Cl, 32.21. Found: C, 43.63; H, 4.93; N, 19.20; Cl, 32.45.

5-Amino-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride decomposing above 260.degree. C. after recrystallization from ethanol.

Analysis Calc.: C, 34.80; H, 3.89; N, 27.06; Cl, 34.24. Found: C, 34.70; H, 3.99; N, 26.98; Cl, 34.01.

5-n-Amyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride melting above 170.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 50.39; H, 6.54; N, 16.03. Found: C, 50.30; H, 6.64; N, 15.83.

5-Methylthio-7-chloro-8-phenyl-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride melting above 212.degree. C. with decomposition after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 49.69; H, 4.17; N, 13.37; Cl, 22.56. Found: C, 49.76; H, 3.95; N, 13.16; Cl, 22.71.

5-Methylthio-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride decomposing above 220.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 35.31; H, 3.81; N, 17.65; Cl, 29.77. Found: C, 35.56; H, 3.85; N, 17.64; Cl, 29.98.

By substituting .beta.-hydroxypropylamine for .beta.-hydroxyethylamine in the above example, dl-3,5-dimethyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride was prepared melting above 150.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 43.66; H, 5.04; N, 19.09; Cl, 32.21. Found: C, 43.44; H, 4.90; N, 18.22; Cl, 31.93.

By substituting .beta.-phenyl-.beta.-hydroxyethylamine for .beta.-hydroxyethylamine in the above procedure, dl-3-phenyl-5-methyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride was prepared decomposing above 180.degree. C. after recrystallization from an ethyl acetate ether solvent mixture.

Analysis Calc.: C, 55.34; H, 4.64; N, 14.89; Cl, 25.13. Found: C, 54.96; H, 4.34; N, 14.80; Cl, 25.37.

Also dl-3-phenyl-5-methylthio-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride decomposing above 200.degree. C. after recrystallization from an ethanol ethyl acetate solvent mixture.

Analysis Calc.: C, 49.69; H, 4.17; N, 13.37; L Cl, 22.56. Found: C, 49.78; H, 4.11; N, 13.08; Cl, 22.76.

By substituting .alpha.-phenyl-.beta.-hydroxyethylamine for .beta.-hydroxyethylamine in the above procedure, 2-phenyl-5-methyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride was prepared decomposing about 150.degree. C. after recrystallization from an ethanol-ethyl acetate ether solvent mixture.

Analysis Calc.: C, 55.35; H, 4.64; N, 14.89; Cl, 25.13. Found: C, 55.16; H, 4.60; N, 14.68; Cl, 25.12.

A reaction mixture was prepared from 2.0 g. of 5-methyl-7-chloro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride and 0.7 g. of pyrrolidine in a saturated aqueous sodium bicarbonate solution. The reaction mixture was allowed to remain at ambient temperature for about three hours, after which time the solvent was removed in vacuo. The resulting residue was heated in ethanol. Solids were separated by filtration and dilute aqueous hydrochloric acid was added to the ethanolic filtrate. The solvent was removed from the filtrate in vacuo to yield 5-methyl-7-pyrrolidino-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride formed in the above reaction which decomposed above 245.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 54.88; H, 7.12; N, 23.27; Cl, 14.73. Found: C, 54.73; H, 7.07; N, 23.03; Cl, 14.97.

By substituting methylamine for pyrrolidine in the above procedure, there was prepared 5-methyl-7-methylamino-2,3-dihydroimidazo[1,2-c]pyrimidine dihydrochloride melting at 250.degree.-253.degree. C. after recrystallization from an ethanol-ethyl acetate solvent mixture.

Analysis Calc.: C, 40.05; H, 5.09; N, 23.06; Cl, 29.09. Found: C, 40.42; H, 5.68; N, 23.70; Cl, 29.50.

Following the above procedure, but substituting N-methyl benzylamine for pyrrolidine, there was prepared N,5-dimethyl-7-benzylamino-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride decomposing at 213.degree. C. after recrystallization from ether.

A solution of 20 g. of 4,6-dichloro-5-nitropyrimidine was prepared in ether. An aqueous solution containing 14 g. of .beta.-chloroethylamine hydrochloride and 24 g. of sodium bicarbonate were added thereto and the subsequent mixture agitated for about 30 minutes. The ether layer was separated, and the separated layer washed with water and dried. Removal of the ether in vacuo yielded an oil containing chiefly 4-(.beta.-chloroethylamino)-5-nitro-6-chloropyrimidine plus a small quantity of 5-nitro-4,6-bis(.beta.-chloroethyl)pyrimidine (the disubstituted product) and a very small quantity of starting material. The oily residue was allowed to stand in chloroform for about one day. A solid comprising 7-(.beta.-chloroethylamino)-8-nitro-2,3-dihydroimidazo[1,2-c]pyrimidine hydrochloride precipitated and the precipitate was separated by filtration, 7-(.beta.-chloroethyl)amino-8-nitro-2,3-dihydroimidazo[1,2-c]p yrimidine hydrochloride thus prepared decomposed at 135.degree. C. after recrystallization from chloroform; yield=5.378 g.

Analysis Calc.: C, 34.30; H, 3.96; N, 25.00; Cl, 25.31. Found: C, 34.42; H, 3.82; N, 25.08; Cl, 25.59.

The compounds of this invention prepared according to the above procedures were isolated and characterized in the form of the hydrochloride salts. Other salts are prepared by substituting the desired anion for the chloride anion in the particular ion exchange resin employed during the metathetic reaction to replace the trifluoromethylsulfonic acid group.

The compounds of this invention are anti-viral agents and have demonstrated their activity against cutaneous Herpes simplex virus type 1 (HSU-1) in guinea pigs according to the following tests. Three epilated areas on each guinea pig back were inoculated with approximately 1.times.10.sup.5 plaque forming units of virus using a Sterneedle triggered 10 times for each area. Untreated guinea pigs so inoculated developed consistent rosette lesions in about 96 hours. All three areas on the back of each guinea pig were drug-treated and these compared with separate control animals which were treated with the particular vehicle employed for administering the drug. The positive control animals were treated with 0.5-1.0 percent phosphonoacetic acid (PAA) suspended in the same vehicle as the drug. Animals were inoculated on the morning of day 1 and treated on the afternoon of day 1. Two treatments per day were administered through day 5 for a total of 10 treatments. Hair was again epilated on day 5 and readings were begun then and taken daily through day 10. Lesions for each area were scored from 0 to 4+, which was a fully developed herpatic lesion with inflammation vesicles and pustules. An average score was then calculated for each drug for each day for the number of treated areas and control areas. Usually 3-6 guinea pigs were used per drug. After scoring, a final score or mean of means was calculated for drug-treated and for control areas. Table I which follows gives the results of determinations carried out as outlined above on compounds coming within the scope of this invention. In the table, column 1 gives the name of the drugs, column 2, the vehicle, column 3, the concentration; column 4, the number of animals used; and columns 5, the final score.

A second in-vivo test against Herpes simplex virus type I and Herpes simplex virus type II was carried out as follows. Guinea pigs were inoculated intravaginally by swabing the vagina with an absorbent cotton swab containing 2.times.10.sup.4 plaque forming units of the virus. Prior to the inoculation with the virus, the vagina was swabbed with physiological saline to remove potential virus inhibitors. Treatment was started four hours after inoculation and continued for four days. The drug in a suitable base was introduced into the vaginal area also with an absorbent cotton swab. Controls in which the vehicle only were swabbed were included. Beginning on day 5 after inoculation and continuing through day 10, each animal was examined and scored from 0 to 4+ for secretion, inflammation, vesiculation and necrosis, thus yielding a possible top score of +16 per guinea pig. The results of this determination are included in Table 2. In the table, column 1 gives the name of the compound; column 2, the vehicle; column 3, the concentration; column 4, the number of animals used; and columns 5, the final score.

The compounds of this invention also have anti-viral activity in vitro against Herpes simplex virus. In order to demonstrate this activity, the following test method was employed.

African green monkey kidney cells (BSC-1) or Hela cells (5-3) were grown in 25 cc. Falcon flasks at 37.degree. C. in medium 199 with 5 percent inactivated fetal bovine serum (FBS), penicillin (150 units 1 ml.) and streptomycin (150 mcg./ml.). When confluent monolayers were formed, the supernatant growth medium was removed and 0.3 ml. of an appropriate dilution of Herpes simplex virus was added to each flask. After adsorption for one hour at room temperature, the virus infected cell sheet was overlaid with a medium comprising one part of 1 percent Ionagar No. 2 and one part double strength medium 199 with FCS, (fetal calf serum) penicillin, and streptomycin and also containing drug at concentrations of 100, 50, 25, 12, 6 and 3 micrograms per milliliter (mcg./ml.). The flask containing no drug served as a control. The stock solutions of 2,3-dihydroimidazo[1,2-c]pyrimidine compounds were made up in dimethylsulfoxide dilution at a concentration of 10.sup.4 mcg./ml. The flasks were incubated for 72 hours at 37.degree. C. Plaques were seen in those areas where the virus infected and reproduced in the cells. A solution of 10 percent formalin and 2 percent sodium acetate was added to each flask to inactivate the virus and fix the cell sheet to the surface of the flask. The virus plaques, irrespective of size, were counted after staining the surrounding cell areas with crystal violet. The plaque count was compared to the control count at each drug concentration. The activity of the test compound was expressed as percentage plaque inhibition. Table 3, which follows, embodies the results of these determinations. In the table, column 1 gives the name of the compound, columns 2 through 6, the percent inhibition of herpes simplex plaques at various mcg./ml. levels of drug.

In accordance with the data presented in the above table, those compounds according to Formula I in which R.sup.1 is chloro, form a preferred class of the compounds of this invention and more particularly, those compounds according to Formula I in which R.sup.1 is chloro, and R is C.sub.1 -C.sub.5 alkyl or methylmercapto constitute a particularly preferred group of compounds.

Compounds coming within the scope of Formula I above are above to suppress the growth of Herpes simplex virus on various surfaces wherein said virus is multiplying. These surfaces include non-living surfaces such as hospital glassware, hospital working surfaces and the like. The compounds can also be administered to mammals topically both to skin surfaces and particularly to mucuosal membranes such as those present in the oral cavities and in the vagina. For such topical application, any of the vehicles listed in Table 4 below may be employed. A particularly useful vehicle for application to mucuosal membranes is vehicle R, a cream base.

The particular pharmaceutical vehicle or carrier for the antiviral agents of formula I should be nonirritating either to skin or mucosa. Obviously, in general, skin can tolerate a greater degree of irritation in a carrier than can mucosa, but care should be taken in selection of a carrier that it be non-irritating for the particular body surface, internal or external, to which it is to be applied.

For treatment of Herpes simplex infections of the skin or mucosal surfaces, a compound of this invention is applied to the infected area as a 0.5-2.5% solution or suspension of an antiviral drug in salt form according to formula I above. The concentration of drug should be such that an anti-Herpes quantity can readily be delivered by application to the infected site of a thin layer of drug-containing vehicle. Whether it be a cream base, a jelly, or a high-viscosity aqueous vehicle.