合成路线1

A slightly modified method of Houlihan et al. is used in making the intermediate 1-amino-3-hydroxyguanidine tosylate. Thiosemicarbazide (I) (0.5 mol) and methyl p-toluenesulfonate (II) (0.5 mol) are refluxed with stirring for 18 h. The reaction mixture is then evaporated to about 250 ml in vacua, and 500 ml of ether is added. The white precipitate formed is filtered and washed with ether. The resultant S-methylisothiosemicarbazide tosylate (III) (135g) gives a melting point of 144-6 C. Cold methanolic KOH solution (0.5 mol in 250 mI) is added to a cold hydroxyamine hydrochloride solution 10.5 mol). The mixture is stirred for 1 h in a salt-ice bath. The KCl precipitate formed is removed by filtration. S-Methyl-isothiosemicarbazide tosylate (III) (0.4 mol) is added to the filtrate. The reaction mixture is stirred at room temperature for 48 h, then evaporated to dryness in vacua at 40 C. The residue is dissolved in hot ethanol (800 mI) and cooled to room temperature. A small amount of insoluble precipitate is filtered off, then the filtrate is concentrated to about 200 ml in vacuo. Ether (400 ml) is added and mixed thoroughly to precipitate out the desired intermediate. This is filtered and washed with a mixture of ether and ethanol (2:1). White crystalline product of 1-amino-3-hydroxyguanidine tosylate (IV) (50 g) is obtained with an m.p. of 136-7 C, and it decomposes at 150-5 C. To prepare title compound 0.04 mol of freshly distilled 2-formylpyridine (V) is added dropwise to a solution of 0.04 mol of 1-amino-3-hydroxyguanidine tosylate (IV) in 25 ml methanol. The reaction mixture is stirred overnight at room temperature. The solvent is evaporated in vacuo. The final resultant Schiff's base is recrystallized with a mixture of ethanol-ether (1:1). The yield of the final product is 6.48 g (46.1%).