Process for Preparing N-Cyanoguanidines

This invention relates to an improved chemical process. In particular it relates to an improved process for the production of certain pharmacologically active guanidine compounds.

In German OLS 2,344,779 and British Patent Specification No. 1,397,436 cyanoguanidine compounds have been described including, inter alia, compounds of the following formula: ##STR1## wherein R.sub.1 is lower alkyl such as methyl; and R.sub.2 is a grouping of the structure shown in Formula II:

wherein Het is a nitrogen-containing 5 or 6 membered heterocyclic ring such as imidazole, pyridine, thiazole, isothiazole, oxazole, isoxazole, triazole or thiadiazole which is optionally substituted by lower alkyl, hydroxyl, halogen or amino; Z is sulphur, oxygen, or a methylene group; and m is 0, 1 or 2 and n is 2 or 3 such that the sum of m and n is from 2 to 4. Processes for the production of these compounds have also been described therein. One process described was the treatment of a thiourea of formula: ##STR2## WITH A HEAVY METAL SALT OF CYANAMIDE.

The present invention provides an improved process for the production of these compounds. Throughout the specification by the term "lower alkyl" we refer to an alkyl group containing from one to four carbon atoms.

According to the present invention we provide a process for the production of compounds of Formula I wherein an isothiourea of Formula III: ##STR3## wherein R.sub.1 and A which may be the same or different are lower alkyl, for example methyl, is treated with a suitable heavy metal salt and an amine of formula R.sub.2 NH.sub.2, where R.sub.2 has the same significance as in Formula I. By suitable heavy metal salt we mean salts of heavy metals such as silver, mercury, lead or cadmium, and preferably silver nitrate or mercuric chloride. Preferably a base such as potassium carbonate is added to neutralise the acid generated by the reaction. The heavy metal mercaptide which is formed is conveniently removed by filtration. The process of our invention may be carried out in a suitable solvent such as pyridine or dimethylformamide and will proceed at room temperature. Our process therefore offers considerable advantage in terms of reaction rate over the process of the prior art which does not employ a heavy metal salt and may require elevated temperatures and/or extended reaction times. Methods for preparing the amines R.sub.2 NH.sub.2 are described in British Patent Specifications 1338169 and 1307539. The isothiourea of Formula III may be prepared by the reaction of the known di(lower alkyl)cyanodithioimidocarbonate and a lower alkylamine.

Although we do not wish the present invention to be in any way limited by the following theoretical explanation, we believe that our process proceeds by way of an intermediate carbodiimide of Formula IV:

wherein R.sub.1 has the same significance as in Formula I., (see McCarty et al., J. Org. Chem. 35, 2067, (1970)). On the basis of this belief, our invention also therefore includes a process for the production of compounds of Formula I wherein a carbodiimide of Formula IV is reacted with an amine of formula R.sub.2 NH.sub.2. Although the preferred method for the production of carbodiimides of Formula IV is from isothioureas of Formula III, we do not wish to be limited, in this aspect of our invention, to this method.

It will be understood that many of the compounds produced and used as starting materials in the process of our invention may exist in the form of an acid addition salt. The process of the present invention is advantageous for the production of compounds of Formula I wherein R.sub.2 is Het--CH.sub.2 S--(CH.sub. 2).sub.2 and is particularly preferred when Het is imidazole, thiazole, isothiazole or pyridine and is optionally substituted by methyl, hydroxyl, chlorine or bromine. Specific compounds which may be made by the present process are:

N-cyano-N'-methyl-N"[2-((5-methyl-4-imidazolyl)methylthio)-ethyl]guanidine

N-cyano-N'-ethyl-N"-[2-((5-methyl-4-imidazolyl)methylthio)-ethyl]guanidine

N-cyano-N'-methyl-N"-[2-((5-bromo-4-imidazolyl)methylthio)-ethyl]guanidine

N-cyano-N'-methyl-N"-[2-((2-thiazolyl)methylthio)ethyl]guanidine

N-cyano-N'-methyl-N"-[2-((3-isothiazolyl)methylthio)ethyl]-guanidine

N-cyano-N'-methyl-N"-[2-((3-hydroxyl-2-pyridyl)methylthio)-ethyl]guanidine

N-cyano-N'-methyl-N"-[2-((3-bromo-2-pyridyl)methylthio)ethyl]-guanidine

N-cyano-N'-methyl-N"-[4-(4-imidazolyl)butyl]guanidine

As stated in German OLS 2,344,779 and British Patent Specification No. 1,397,436 the compounds of Formula I (which may be produced by the present process) are pharmacologically active, for example as histamine H.sub.2 -antagonists (see Nature 1972, 236, 385), and they are useful for example as inhibitors of gastric acid secretion. For administration they will of course by made up in suitable pharmaceutically acceptable unit dosage forms.

The invention is illustrated but in no way limited by the following examples.

A solution of N-cyano-N', S-dimethylisothiourea (0.81 g) and silver nitrate (1.06 g) in pyridine (100 ml) was added to a stirred mixture of 2-((5-methyl-4-imidazolyl)methylthio)-ethylamine (1.07 g), anhydrous potassium carbonate (0.44 g) and anhydrous dimethylformamide (4ml). The mixture was stirred at room temperature for 18 hours and filtered. The filtrate was evaporated to dryness and the residue was eluted from a column of silica gel using isopropyl alcoholethylacetate (1:4) followed by isopropyl alcohol-ethyl acetate (1:3) to give N-cyano-N'-methyl-N"-[2-((5-methyl-4-imidazolyl)methylthio)ethyl]guanidine (0.71 g) m.p. 139.degree.-141.degree. C.

A mixture of N-cyano-N', S-dimethylisothiourea (0.81 g), silver nitrate (1.06 g), anhydrous potassium carbonate (0.44 g) and pyridine (100 ml) was stirred at room temperature for 18 hours and was filtered. The filtrate was evaporated to dryness and was treated with a solution of 2-((5-methyl-4-imidazolyl)methylthio)ethylamine (1.07 g) in dimethylformamide (4 ml) and the mixture was left at room temperature for 18 hours. The mixture was evaporated to dryness and the residue was chromatographed on a column of silica gel, eluting with isopropyl alcohol-ethyl acetate (1:3) to give N-cyano-N'-methyl-N"-[2-((5-methyl-4-imidazolyl)methylthio)ethyl]-guanidin e.

When N-cyano-N'-ethyl-S-methylisothiourea and N-cyano-N'-butyl-S-methylisothiourea are substituted for N-cyano-N' ,S-dimethylisothiourea in the procedure of Example 1 the products are

N-cyano-N'-ethyl-N"-[2-((5-methyl-4-imidazolyl)methylthio)-ethyl] guanidine and

N-cyano-N'-butyl-N"-[2-((5-methyl-4-imidazolyl)methylthio)-ethyl]guanidine respectively.

The starting materials may be prepared by treating dimethyldithiocyanoimidocarbonate with ethylamine and butylamine.

Substitution of 4-(5-methyl-4-imidazolyl)butylamine or 2-(4-imidazolylmethoxy)ethylamine for 2-((5-methyl-4-imidazolyl)-methylthio)ethylamine in the procedure of Example 1 gives N-cyano-N'-methyl-N"-[4-(5-methyl-4-imidazolyl)butyl]guanidine and N-cyano-N'-methyl-N"-[2-(4-imidazolylmethoxy)ethyl]-guanidine respectively.

Substitution of the following amines:

a. 2-(3-bromo-2-pyridylmethythio)ethylamine

b. 2-(3-chloro-2-pyridylmethylthio)ethylamine

c. 2-(3-hydroxy-2-pyridylmethylthio)ethylamine

d. 2-(2-thiazolylmethlthio)ethylamine

e. 2-(3-isothiazolylmethylthio)ethylamine

f. 3-(2-oxazolylthiopropyl)ethylamine

g. 2-(3-isoxazolylmethylthio)ethylamine

h. 2-(3-(1,2,4)-triazolylmethylthio)ethylamine

i. 2-(5-amino-2-(1,3,4-thiadiazolylmethylthio)ethylamine

j. 2-(5-bromo-4-imidazolylmethylthio)ethylamine for 2-(5-methyl-4-imidazolylmethylthio)ethylamine in the procedure of Example 1, gives

a. N-cyano-N'-methyl-N"-[2-((3-bromo-2-pyridyl)methylthio)-ethyl]guanidine

b. N-cyano-N'-methyl-N"-[2-((3-chloro-2-pyridyl)methylthio)-ethyl]guanidine

c. N-cyano-N'-methyl-N"-[2-((3-hydroxy-2-pyridyl)methylthio)-ethyl]guanidine

d. N-cyano-N'-methyl-N"-[2-((2-thiazolyl)methylthio)ethyl]-guanidine

e.N-cyano-N'-methyl-N"-[2-((3-isothiazolyl)methylthio)ethyl]-guanidine

f. N-cyano-N'-methyl-N"-[3-(2-oxazolyl)thiopropyl]guanidine

g. N-cyano-N'-methyl-N"-[2-((3-isoxazolyl)methylthio)ethyl]-guanidine

h. N-cyano-N'-methyl-N"-[2-(3-(1,2,4-triazolyl)methylthio)-ethyl]guanidine

i. N-cyano-N'-methyl-N"-[2-(2-(5-amino-1,3,4-thiadiazolyl)-methylthio)ethyl]g uanidine

j. N-cyano-N'-methyl-N"-[2-((5-bromo-4-imidazolyl)methylthio)-ethyl]guanidine .

Substitution of 3-(4-imidazolyl)propylamine and 2-(4-imidazolylethylthio)ethylamine for 2-(5-methyl-4-imidazolylmethylthio)ethylamine in the procedure of Example 1, leads to the preparation of N-cyano-N'-methyl-N"-[3-(4-imidazolyl)propyl]-guanidine and N-cyano-N'-methyl-N"-[2-(4-imidazolylethylthio)-ethyl] guanidine respectively.

When N-cyano-N' ,S-dimethylisothiourea is treated with mercuric chloride in pyridine and the mixture added to a mixture of 2-((5-methyl-4-imidazolyl)methylthio)ethylamine and potassium carbonate in dimethylformamide the product is N-cyano-N'-methyl-N"-[2((5-methyl-4-imidazolyl)methylthio)-ethyl]guanidine .