e (7b) compounds. Treatment with diluted acid followed by potassium cyanide treatment and acid hydrolysis afforded 6-substituted 3-(purin-9-yl)- and 3-(2-aminopurin-9-yl)-2-hydroxypropanoic acids (8-10). Reaction of compounds 3 with malonicacid in aqueous solution gave exclusively the product of isomerisation, 6-substituted 4-(purin-9-yl)-3-butenoic acids (15).