Synthesis and antihypertensive activity of some imidazoindole derivatives

The synthesis of pyridino[1,2-a]imidazo[5,4-b]indole (1) and thiazolo[3,2-a-a]imidazo[5,4-b-a]indole (2) has been achieved by phosphite reduction of 3-nitroso-6-phenylimidazo[1,2-a]pyridine and 5-nitroso-6-phenylimidazo[2,1-bb]thiazole. Compound 1 has shown strong antihypertensive activity in spontaneously hypertensive rats while compound 2 showed similar bioactivity both in spontaneously hypertensive rats and in normotensive dogs. A tricyclic amino derivative, 3-amino-2-phenylimidazo[1,2-a]pyridine, which has structural resemblance to compound 1, showed no hypotensive activity.