Structural and conformational studies on two diasteromeric dihydroisoxazolyl cyclopropane derivatives

The molecular structures of 2-(3'-bromo-4',5'-dihydroisoxazol-5'-yl)-1-tert-butoxycarbonylaminocyclo propanecarboxylic acid (±)-10a and 1-amino-2-(3'-hydroxy-4',5'-diydroisoxazol-5'-yl)cyclopropanecarboxylic acid (±)-11b were determined by single crystal X-ray diffraction method. The geometrical features and the intermolecular interactions of the two diastereoisomers have been compared evidencing a different conformation of the dihydroisoxazole ring: in (±)-10a is almost planar, while in (±)-11 adopts an envelope shape. Intermolecular hydrogen bonds of OH...O and NH...O type in (±)-10a determine the formation of a three-dimensional network, whereas in (±)-11b polimeric chains due to NH...O interactions are obtained. These compounds are key intermediates of conformationally constrained glutamic acid homologues and the opposite stereochemistry of C(3) leads to different pharmacophoric distances, important for the ligand-receptor interaction. The results of the X-ray molecular structures have been complemented by theoretical calculations.