Synthesis of imidazo[1,2-a]pyrazine derivatives with uterine-relaxing, antibronchospastic, and cardiac-stimulating properties.

A series of imidazo[1,2-alpha]pyrazine derivatives was synthesized by condensation of alpha-halogenocarbonyl compounds and aminopyrazines. Various compounds resulted from competitive reactions or reagent isomerization and demonstrated in vitro uterine-relaxing and in vivo antibronchospastic activities. On isolated atria, 5-bromoimidazo-[1,2-alpha]pyrazine showed positive chronotropic and inotropic properties; the latter was associated with an increase in the cyclic AMP tissue concentration. Potentiation of the isoproterenol positive inotropic effect of 5-bromoimidazo[1,2-alpha]pyrazine and the lack of blockade of the 5-bromoimidazo[1,2-alpha]pyrazine positive inotropic effect by propranolol suggested phosphodiesterase-inhibiting properties.