Pteridine studies. Part XXXIX. Pteridines unsubstituted in the 4-position; a new synthesis from pyrazines, via 3,4-dihydropteridines

Abstract

3-Aminopyrazine-2-carboxamide (IIa), warmed in phosphoryl chloride and dimethylformamide, gave 3-aminopyrazine-2-carbonitrile (IV), which was hydrogenated to give 2-amino-3-aminomethylpyrazine (I). This diamine was cyclised to 3,4-dihydropteridine and its 2-methyl-, 2-hydroxy-, and 2-amino-derivatives by treatment with ethyl orthoformate, ethyl orthoacetate, ethyl chloroformate, and S-methylisothiouronium hydrochloride, respectively. Similarly 2-amino-3-aminomethyl-5-methylpyrazine, obtained from 3-amino-6-methylpyrazine-2-carbonitrile by hydrogenation, furnished 3,4-dihydro-6-methylpteridine. All these 3,4-dihydropteridines were selectively oxidised (e.g. by manganese dioxide) to the corresponding pteridines, including the long-sought 6-methylpteridine.