Hemiphosphate hemihydrate of 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole

Abstract: The hemiphosphate hemihydrate salt of 2-(1-pentyl-­ 3-guanidino-4-imidazolyl)thiazole is the preferred salt of this antiulcer agent.

Description: The present invention is directed to a hemiphosphate hemihydrate salt of 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole having advantageous properties. U.S. Patent 4,560,690, which is herein included by reference, describes 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole and analogs as having antiulcer activity. The form of this preferred compound, reported in said patent is the anhydrous dihydrochloride salt, which is noncrystalline, difficult to purify and possesses properties which are generally less suitable for formulation and use as a medicinal agent in man. International Application No. PCT/US86/02308 reports a further improvement in salts of this preferred antiulcer agent and describes the preparation and properties of the dihydrochloride trihydrate salt. It has now been found that a yet unreported salt of 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole, namely, the hemiphosphate hemihydrate, offers many advantages especially a high weight percent of active agent. 2-(1-Pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole hemiphosphate hemihydrate is prepared by solubilizing the dihydrochloride trihydrate salt (10 mg free base equivalent) per ml in a pH 6.6, 0.2 M Phosphate buffer containing acetone in the ratio one part (weight) acetone to four parts (weight) buffer. After standing overnight at room temperature, the desired product is removed by filtration and dried under vacuum at room temperature. This hemiphosphate hemihydrate salt has all the characteristics desired in a drug to be formulated for human use; it is crystalline, stable, non-hygroscopic and contains a high weight percent of active agent. This latter characteristic is especially important in allowing the formulation of smaller tablets, capsules, etc., for oral administration. This can readily be seen from the following comparison of the various reported forms of 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole: Form Molecular Formula Molecular Wt.(gr/mole) %Potency free base C₁₃H₂₀N₆S₁ 292.4 100% dihydrochloride C₁₃H₂₀N₆S₁ 419.4 292.4/419.4 trihydrate 2HCl 3H₂O 69.7% hemiphosphate C₁₃H₂₀N₆S₁ 350.4 292.4/350.4 hemihydrate 1/2H₃PO₄ 1/2H₂O 83.4% The following example is given by way of illustration:- EXAMPLE 1 2-(1-Pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole Hemiphosphate Hemihydrate Salt Sufficient 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole dihydrochloride trihydrate was added to 100 ml. of a solution consisting, by weight, of 1 part acetone and 4 parts of a 0.2 M phosphate buffer to give a drug concentration of 10 mg free base equivalent/ml. The mixture was stirred until all the solids had dissolved and was then allowed to remain undisturbed at room temperature overnight. The precipitated crystals were filtered and dried at room temperature in vacuo for 24 hours. The DSC data gathered on this material shows it to possess two low temperature endotherms and one high temperature endotherm associated with melting. The TGA data shows a loss of approximately 3% of the total weight when heated to 170°C. This weight loss is likely due to water loss, since Karl Fischer readings show 3.2% water on the material. Samples of the hemiphosphate hemihydrate were submitted for elemental analysis. The amount of carbon, hydrogen and nitrogen are within 3% of the theoretical value whereas phosphorous is slightly higher that the theoretical value. The titratable water is slightly higher than the theoretical water content for a hemihydrate (2.6%). The slightly higher % water could be accounted for by the presence of some surface water on the bulk. The habit of the hemiphosphate hemihydrate crystals is more rod-like or bladed in character than the needle crystalline habit of the dihydrochloride trihydrate form. Single crystal studies showed that there are 8 molecules per unit cell. The single crystal data confirms that this is the hemiphosphate hemihydrate. X-ray powder diffraction patterns generated for the new form and for the dihydrochloride trihydrate form also verifies that these are two completely different forms. Samples of the hemiphosphate hemihydrate were stored at 50°C. After 55 days, TGA data still shows a weight loss of 2.7% up to 170°C and microscopically shows birefringence indicating that the form is physically stable under these conditions. A tabulation of this information is as follows:

Claims: Claims for the following Contracting States : AT BE CH DE FR GB IT LI LU NL SE 2-(1-Pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole hemiphosphate hemihydrate. A process for preparing 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole hemiphosphate hemihydrate characterized by the steps of (a) combining sufficient 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole dihydrochloride trihydrate with a solution comprising, by weight, 1 part acetone and 4 parts of a 0.2 M phosphate buffer such that the resulting solution contains 10mg. free base per ml. and (b) filtering and drying the precipitated product. Claim for the following Contracting States : ES GR A process for preparing 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole hemiphosphate hemihydrate characterized by the steps of (a) combining sufficient 2-(1-pentyl-3-guanidino)-4-(2-methyl-4-imidazolyl)thiazole dihydrochloride trihydrate with a solution comprising, by weight, 1 part acetone and 4 parts of a 0.2 M phosphate buffer such that the resulting solution contains 10mg. free base per ml. and (b) filtering and drying the precipitated product.

Inventors: APPLETON TROY ANTHONY, SMITH WARD MARVIN, APPLETON, TROY ANTHONY, SMITH, WARD MARVIN
Applicants: PFIZER, PFIZER INC.
Application year: 1989
Main classification: C07D417
IPC codes: C07D417, A61K31, A61P35