Physicochemical and crystallographic evidence for polymorphism of the racemic ethyl (2-chloromethyl-2,3-dihydro-5H-oxazolo [3,2-a]pyrimidin-5-one)-6-carboxylate

The various crystalline forms of an original bicyclic compound [ethyl (2-ch loromethyl-2,3- dihydro-5H-oxazolo [3,2-a] pyrimidin-5-one)-6-carboxylate); EOC] have been obtained and characterized by powder and single-crystal X-r ay diffraction, differential scanning calorimetry (DSC), and infrared (IR) and Raman spectroscopy. At 4 degreesC in methanol, a monoclinic racemate (f orm II) crystallized from the racemic mixture, whereas at 20 degreesC, an o rthorhombic racemate (form I) was isolated in trichloroethylene By increasi ng the temperature, a solid-solid transition from the stable form II to the stable form I was observed with a Guinier-Simon camera. A I --> II transfo rmation was observed at ambient temperature by DSC. (C) 2000 Wiley-Liss, In c. and the American Pharmaceutical Association.