Imidazopteridines. i. synthesis of imidazo(1,2-c)pteridine and its alkyl derivatives

The synthesis of imidazo[1,2-c]pteridine and its alkyl derivatives is described. The reaction of 4-aminopteridine with chloroacetaldehyde gave the ring-opened 2-formamido-3-(2-imidazolyl)pyrazine and the isomeric 2-amino-3-(1-formyl-2-imidazolyl)pyrazine but no imidazopteridine. 4-Amino-2-methylpteridine and chloroacetaldehyde similarly gave 2-acetamino-3-(2-imidazolyl)pyrazine in high yield. Hydrolysis of these compounds gave 2-amino-3-(2-imidazolyl)pyrazine, which was used as the key intermediate for the synthesis of the title compounds. Thus it reacted with triethyl orthoformate and homologues to give respectively the parent imidazo-[1,2-c]pteridine and its 6-methyl and 6-ethyl homologues. Their 2,3-dimethyl derivatives were prepared likewise from 2-amino-3-(2-imidazolyl)-5,6-dimethylpyrazine, which in turn was prepared from 4-amino-6,7-dimethyl- or 4-amino-2,6,7-trimethylpteridine.