The present invention provides a compound having the structure of formula I: ##STR00001## wherein R.sup.1 is hydrogen, (C.sub.1 C.sub.6) alkyl, unconjugated (C.sub.3 C.sub.6) alkenyl, benzyl, YC(.dbd.O)(C.sub.1 C.sub.6) alkyl or --CH.sub.2CH.sub.2--O--(C.sub.1 C.sub.4) alkyl; X is CH.sub.2 or CH.sub.2CH.sub.2; Y is (C.sub.2 C.sub.6) alkylene; Z is (CH.sub.2).sub.m, CF.sub.2, or C(.dbd.O), where m is 0, 1 or 2; R.sup.2 and R.sup.3 are selected independently from hydrogen, halogen, --(C.sub.1 C.sub.6) alkyl optionally substituted with from 1 to 7 halogen atoms, and --O(C.sub.1 C.sub.6) alkyl optionally substituted with from 1 to 7 halogen atoms, or R.sup.2 and R.sup.3 each together with the atom to which it is connected independently form C(.dbd.O), S.fwdarw.O, S(.dbd.O).sub.2, or N.fwdarw.O; and ##STR00002## is a 5- to 7-membered monocyclic heteroaryl group selected from pyridinyl, pyridone, pyridazinyl, imidazolyl, pyrimidinyl, pyrazolyl, triazolyl, pyrazinyl, furyl, thienyl, isoxazolyl, thiazolyl, oxazolyl, isothiazolyl, pyrrolyl, cinnolinyl, triazinyl, oxadiazolyl, thiadiazolyl and furazanyl groups.