The present invention relates to compounds having a structure according to Formula I wherein n, m, z, R, R<;SUB>;2<;/SUB>;, R<;SUB>;3<;/SUB>;, R<;SUB>;4<;/SUB>;, R<;SUB>;5<;/SUB>;, R<;SUB>;6<;/SUB>;, A, E, X, Y, a and b are as defined above; or an optical isomer, diastereomer or enantiomer thereof; a pharmaceutically acceptable salt, hydrate, or prodrug thereof.