Comparison of the crystal structures of the potent anticancer and anti-angiogenic agent regorafenib and its monohydrate

Regorafenib {systematic name: 4‐[4‐({[4‐chloro‐3‐(trifluoromethy)phenyl]carbamoyl}amino)‐3‐fluorophenoxy]‐1‐methylpyridine‐2‐carboxamide}, C21H15ClF4N4O3, is a potent anticancer and anti‐angiogenic agent that possesses various activities on the VEGFR, PDGFR, raf and/or flt‐3 kinase signaling molecules. The compound has been crystallized as polymorphic form I and as the monohydrate, C21H15ClF4N4O3·H2O. The regorafenib molecule consists of biarylurea and pyridine‐2‐carboxamide units linked by an ether group. A comparison of both forms shows that they differ in the relative orientation of the biarylurea and pyridine‐2‐carboxamide units, due to different rotations around the ether group, as measured by the C—O—C bond angles [119.5 (3)° in regorafenib and 116.10 (15)° in the monohydrate]. Meanwhile, the conformational differences are reflected in different hydrogen‐bond networks. Polymorphic form I contains two intermolecular N—H…O hydrogen bonds, which link the regorafenib molecules into an infinite molecular chain along the b axis. In the monohydrate, the presence of the solvent water molecule results in more abundant hydrogen bonds. The water molecules act as donors and acceptors, forming N—H…O and O—H…O hydrogen‐bond interactions. Thus, R42(28) ring motifs are formed, which are fused to form continuous spiral ring motifs along the a axis. The (trifluoromethyl)phenyl rings protrude on the outside of these motifs and interdigitate with those of adjacent ring motifs, thereby forming columns populated by halogen atoms. Regorafenib is a potent anticancer and anti‐angiogenic agent and has been crystallized as polymorphic form I and as the monohydrate. A comparison of both forms shows that they differ in the relative orientation of the biarylurea and pyridine‐2‐carboxamide units. Conformational differences are reflected in different hydrogen‐bond networks.