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

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Abstract
A series of imidazo[1,2-a]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 rat uterine-relaxing and in vivo antibronchospastic activities. On isolated guinea pig atria, 5-bromoimidazo[1,2-a]pyrazine showed positive chronotropic and inotropic properties; the latter was associated with an increase in the cAMP tissue concentration. Potentiation of the isoproterenol positive inotropic effect of 5-bromoimidazo[1,2-a]pyrazine and the lack of blockade of the 5-bromoimidazo[1,2-a]pyrazine positive inotropic effect by propranolol suggested phosphodiesterase-inhibiting properties.