Tetrahydrophthalic esters of prednisolone

Abstract

The two biologically active isomers of prednisolone tetrahydrophthalate have been studied by X-ray diffraction methods. The compounds crystallize in the orthorhombic system in the space groupP2₁2₁2₁, with similar lattice parameters. The isomers differ both in configuration [(1′S),(6′R) isomerA and (1′R),(6′S) isomerB] and conformation of the thetetrahydrophthalic part of the molecules. Cell parameters of isomerA:a=9.595(2),b=14.465(2),c=18.988(3) Å andB:a=9.114(2),b=14.283(6),c=20.398(5) Å. The O(3) carbonyl oxygen atom interactsvia hydrogen bonds with three neighboring molecules accepting hydrogen bonds from two hydroxyl groups and one carboxylic group. Additional short intermolecular C−H…O type contacts occur in the structure of theB isomer, which has a somewhat larger unit cell and significantly higher melting point.