Synthesis, crystal structure and local anti-inflammatory activity of the L-phenylalanine methyl ester derivative of dexamethasone-derived cortienic acid

The L-phenylalanine methyl ester derivative of dexamethasone-derived cortienic acid (DF) was synthesized and its crystal structure characterized by the X-ray diffraction method. The crystal system is orthorhombic with space group P2(1)2(1)2(1) and cell constants a = 8.2969(3) angstrom, b = 18.9358(8) angstrom, c = 20.0904(6) angstrom, V = 3156.4(2) angstrom(3) and Z = 4. Ring A of the steroid nucleus and phenyl ring in the 17 beta-side chain are almost planar. Rings B and C have a slightly distorted chair conformation, whereas ring D has an envelope conformation. The packing of DF is characterized by a network of intermolecular hydrogen bonds involving the O4 atom from one side of the steroid nucleus and O1 and F1 atoms from the other side as hydrogen bond acceptors. Apart from the intermolecular hydrogen bonds in the crystal packing, there are also numerous intramolecular hydrogen bonds of the N-H center dot center dot center dot O, C-H center dot center dot center dot O and C-H center dot center dot center dot F type. The local anti-inflammatory activity of DF was evaluated using the croton oil-induced ear oedema test. This derivative achieved maximal inhibition of ear oedema at significantly lower concentration in comparison with dexamethasone.