Polymorph II of hydroxyurea 150 years after its first synthesis

A new polymorph of hydroxyurea (HU) was crystallized 150 years after its first synthesis. Due to its medicinal use in neoplastic diseases and sickle cell anemia, a high throughput screen of HU binary cocrystals was attempted. Instead of a cocrystal, an isoenergetic form II crystallized concomitantly with urea in methanol. Form II of hydroxyurea (HU) has been crystallized in the presence of urea in methanol solvent. The isoenergetic novel form II is isolated 150 years after its first synthesis (form I).