4H-pyrimido [1, 6-a]-1, 3, 5-triazin-4-ylidene) guanidine (4) and (6, 7-dihydro-6-oxo-4H- pyrimido [1, 6-a]-1, 3, 5-triazin-4-y1idene) guanidine (5), respectively. The interrelationship between the two compounds was established by deribosidation of 4. The reaction of 1 with isocytosine gave two isomeric products (6-oxo-6H-pyrimido-[1, 2-~]-1, 3, 5-triazin-4-yl) guanidine (9) and (8-0~ 0-8H-pyzimido [l, 2-a]-1, 3, 5-triazin-4-yl) guanidine (10). The two ...