Lenalidomide, an antineoplastic drug, and its hemihydrate.

The crystal structures of lenalidomide [systematic name: (RS)-3-(4-amino-1-oxoisoindolin-2-yl)piperidine-2,6-dione], C13H13N3O3, (I), an antineoplastic drug, and its hemihydrate, C13H13N3O3.0.5H2O, (II), have been determined by single-crystal X-ray diffraction analysis. The overall conformation of the molecule defined by the orientation of the two ring portions, viz. pyridinedione and isoindolinone, is twisted in both structures. The influence of the self-complementary pyridinedione ring is seen in the crystal packing of both structures through its involvement in forming hydrogen-bonded dimers, although alternate dione O atoms are utilized. An extensive series of N-H...O hydrogen bonds link the dimers into two-dimensional supramolecular arrays built up from infinite chains. The water molecule in (II) has a cohesive function, connecting three lenalidomide molecules by hydrogen bonds. The significance of this study lies in the analysis of the interactions in these structures and the aggregations occurring via hydrogen bonds in the hydrated and dehydrated crystalline forms of the title compound.