Rare Case of Polymorphism in the Binary System of Enantiomers of a Praziquantel Derivative
Résumé
A rare caseof a polymorphicracemiccompoundhas beendiscoveredin the binarysystemof enantiomersof thepraziquantelderivative2-(cyclopropanecarbonyl)dodecahydro-4H-pyrazino[2,1-a]isoquinolin-4-one.Solid-statecharacterizationofthe threepolymorphshas beenperformed,includingthe resolutionof theircrystalstructuresand the constructionof a binaryphasediagrambetweenthe enantiomers.Althoughthe threepolymorphsdemonstratehighkineticstabilityat roomtemperature,athoroughexaminationof the binaryphasediagramthroughthermodynamicconsiderationrevealsa complexsituationin whichthethreeracemicformsare foundto be enantiotropicallyrelated.As a resultof majorstructuraldifferencesbetweenthe polymorphs,nosolid−solidpolymorphictransitionwas observed,and the conversionfromone formto the othersystematicallyrequiredmeltingandrecrystallization.Suchenantiotropicbehavioris rarelyobservedand highlightsthe diversityof crystallizationbehaviorsthat can resultfromslightchemicalmodification.