CHEMICAL PROCESS

Abstract: A process for preparing 2-[2-[(2-furylmethyl)­ thio]ethylamino]-5-[(6-methyl-3-pyridinyl)methyl]-4(1H)-­ pyrimidinone by reacting a guanidine and a 2-formyl-3-(6-­ methyl-3-pyridinyl)propionate ester. The pyrimidinone pro­ duct is particularly useful as an intermediate for a 5-­ dimethylaminomethylfuryl compound having histamine H₂- antagonist activity.

Description: CHEMICAL PROCESS This invention provides a process for preparing 2 [2-[(2-furylmethyl)thio]ethylamino]-5-[(6-methyl-3- pyridinyl)methyl]-4(1H)-pyrimidinone. This compound is disclosed in European Patent Specification 3677 and is particularly useful as an intermediate to prepare the corresponding 5-dime thy laminomethyl compound which has potent activity as a histamine H2-antagonist. The process of this invention is represented by the following reaction sequence: EMI1.1 In this reaction sequence, alk is a lower alkyl of 1-6 carbons, usually methyl or ethyl. According to the process of this invention substantially equimolar quanitities of 2-[(2-furyl- methyl)thio]ethylguanidine (I), conveniently generated in situ from one of its acid addition salts, and a lower alkyl 2-formyl-3-(6-methyl-3-pyridinyl)propionate (II) are reacted in the presence of a base, for example, an alkali metal hydroxide, carbonate or lower alkoxide. Sodium or potassium methoxides, ethoxides, n-propoxides or isopropoxides are most useful. The reaction is carried out in a solvent toward which the reactants are chemically inert and in which the reactants are soluble enough to react, for example, an alcoholic solvent of from 1-5 carbons such as methanol, ethanol, n-propanol, n-butanol or isopropanol, an aromatic solvent such as benzene, toluene or xylene, dimethylformamide, dimethylacetamide, dimethylsulfoxide, water, an ester solvent such as ethyl acetate or a halohydrocarbon solvent such as methylene chloride or chloroform. Preferably n-propanol or toluene are used. The solvents may also be used in various combinations. Preferably, the process is carried out using a sodium or potassium alkoxide in a lower alkanol solvent. If an acid addition salt of the guanidine (I) is used, at least one mole of a base is needed to generate the basic compound. For the condensation itself, less than one molar equivalent of a base, for example 1/4 molar equivalent, is satisfactory; however, an excess of base can be used. The reaction is allowed to proceed at from ambient up to reflux temperature until complete. Most conveniently the reaction described above is carried o--t in n-propanol at reflux temperature for from about 1-5 hours. When the reaction is complete, the volume of solvent is reduced. Water is added to the reaction mixture followed by cooling to separate the desired pyrimidinone (III). Unexpectedly, the condensation is selective and the desired product, i.e. the pyrimidinone of Formula III, is produced as a large proportion of the product of reaction with only a small proportion of the alternative isomeric condensation products (1- and 3-substituted-2 aminopyrimidinones), the ratio being about 9 to 10:1 of the desired product. The product can be purified as known to the art but preferably as described in the following example to give from 60-85% yields of isolated pure product. Alternatively, the impure product may be used as such or in situ to prepare the 5-dimethylaminomethyl derivative. The 5-dimethylaminomethyl derivative is prepared from 2-EE2-E( 2-furylmethyl)thio]ethyl)amino]-5-( (6-methyl- 3-pyridinyl)methyl-4(lH)-pyrimidinone (III) by reaction with a Mannich reagent to insert a dimethylaminomethyl group at the 5-position of the furyl ring by procedures described in European Patent Specification 3677. There are two unexpected features of the chemical process of this invention which are particularly advantageous in obtaining good purity of the products. The first is that this process, to form a specifically substituted pyrimidinone ring, has been found to be highly selective with only about 10% of the undesired isomers formed. The second concerns the purification of the furylpyrimidinone III to remove the unwanted isomers. Slurrying of the crude reaction product in an organic solvent for example a low molecular weight ester, ketone or ether, such as a lower alkyl acetate, methyl ethyl ketone, acetone or tetrahydrofuran, especially ethyl acetate or acetone, is very effective in removing the isomeric byproducts which are selectively more soluble in said solvents. This method of purification is surprisingly efficient considering the close structural relationship between the desired product and the alternative isomeric condensation products. The following example illustrates the process of this invention. EXAMPLE 1 A mixture of 1600 g (3.88 m) of 2-[(2-furylmethyl)thio]ethylamine hemisulfate and 2.8 L of n-propanol 0 was heated to 50 and 400 ml of 50% aqueous cyanamide added thereto. The pH was adjusted to 7.9 with 10N sodium hydroxide solution. The reaction mixture was heated to reflux. Additional 400 ml portions of aqueous cyanamide were added at 1 hour, 2 hours and 4 hours maintaining the pH at 8.3 t .2 using 10 N sodium hydroxide and 6N sulfuric acid. After 7.5 hours at reflux, the reaction was diluted with 3.8 L of isopropanol then filtered hot. The filtrate was diluted again with 6 L of isopropanol (40-430) and stirred for 16 hours as it cooled. Cooling to 5-80 gives 1528 g (79%) of 2-[(2-furylmethyl)thio]ethylguanidine hemisulfate. A mixture of 992 g of the guanidine sulfate, 6 L of n-propanol and 880 ml of 25% sodium methoxide in 0 methanol was heated to 50 . Ethyl 2-formyl-3- (6-methyl-3-pyridinyl)propionate (91 g) was added and the mixture heated to reflux at which time five 157 g portions of the formyl compound were added at half hour time intervals [total 880 g (4.0 m)]. After 3 hours, about 2 L of solvent was removed by distillation. Water (14 L) was added to the hot solution. The resulting slurry was allowed to stir for 12 hours cooling to room temprature 0 then was cooled to 5-8 . The solid product was separated, dried, slurried in boiling anhydrous ethyl acetate and dried again to give 897 g (63%) 2-[[2-[(2-furylmethyl)thio]ethylaminol-5-1(6-methyl-3- pyridinyl)methyl]-4(1H)-pyrimidinone (III). The ethyl acetate slurry process effectively removes the isomeric byproducts. Other organic solvents such as acetone may also be used in this purification procedure.

Claims: Claims 1. The method of preparing a furyl pyrimidinone compound of the formula: EMI6.1 which comprises reacting in substantially equimolar quantities a guanidine compound of the formula: EMI6.2 and a 2-formyl-3-pyridinylpropionate compound of the formula: EMI6.3 in which alk is lower alkyl of 1-6 carbon atoms, in the presence of a base in an organic solvent toward which the reactants are chemically inert and in which the reactants are soluble enough to react. 2. The process of claim 1 in which alk is methyl or ethyl, the solvent for reaction is n-propanol or toluene -and the base is sodium or potassium methoxide, ethoxide, n-propoxide or isopropoxide. 3. The process of claims 1 or 2 in which the furyl pyrimidinone is purified by slurrying in ethyl acetate, acetone or a similar organic solvent.

Inventors: LABAW, CLIFFORD STEVEN, MENDELSON, WILFORD LEE, TREMPER, ALAN WILLIAM
Applicants: SMITHKLINE BECKMAN CORPORATION
Application year: 1982
Main classification: C07D405
IPC codes: C07B61, C07D405