The Crystal Structure of Cinmetacin ($C_{21}H_{19}NO_4$), A Non-steroidal Antiinflammatory Agent

The structure of cinmetacin was determined by single crystal X-ray diffraction analysis. The compound was recrystallized from a mixture of acetone and water in orthorhombic, space group $P2_12_12_1$, with Z=4, a=35.681(8), b=9.482(2), c:5.071(1) ${\AA}$, $D_x=1.352 g/cm^3$, and $D_m=1.35g/cm^3$. The structure was solved by direct method and refined by least-squares procedure to the final R value of 0.036 for 1441 observed reflections ($F{\geq}3{\sigma}(F)$). The carboxyl group of the molecule is nearly perpendicular to the indole ring. The dihedral angle between indole ring and phenyl group is $64.5^{\circ}$. The molecules are linked together via O(1)-H ----O(3) hydrogen bonds, and arranged along 2-fold screw axis in the crystal. The intermolecular contacts are the normal van der Waals' forces.