A method of claim 1 wherein the thiazolidine derivative is further selected from compounds where X is methylene; and R1 is of formula IV ##STR57## wherein X is an oxygen or sulfur atom, R41 and R42 are each independently hydrogen or a hydrocarbon residue which may optionally be substituted and R41 and R42 may jointly, together with the oxazole or thiazole ring, form a condensed ring and A is a low