Structural study and NMDA activity of an enantiopure dihydroxazole derivative

The enantiopure 5-(2-amino-2-carboxethyl)-4,5-dihydroisoxazole-3-carboxylic acid (-)-1b and its racemic tert-butoxycarbonylamino (Boc) precursor (±)-11 were structural characterized by the single crystal X-ray diffraction technique. The geometrical features and the intermolecular interaction of the pure (3S,5S)-aminoacid are compared with the racemic derivative. This analysis has evidenced a different conformation of the dihydroisoxazole ring: in (±)-11 adopts an envelope shape, while in (-)-1b is almost planar. The intermolecular assembly is characterized by hydrogen bonds of NH…O type in (±)-11 with the formation of polymeric chains, whereas in (-)-1b the hydrogen bonds determine a three dimensional network. The tight intermolecular interactions of (-)-1b could be responsible of the short distances between ionizable groups, which are important as pharmacophoric parameters for the NMDA activity