Various compounds comprising a thiazolidine ring are described as well as the use of such compounds to inhibit at least one BCL-2 protein family member. One of the compounds described has the structure the structure A, ##STR00001## wherein each of R.sub.1, and R.sub.2 comprises hydrogen, a substituted or unsubstituted straight-chained aliphatic group, a halogen, an alkoxyl, a halogen-substituted alkyl, a halogen-substituted alkoxyl, hydroxyl, carboxyl, cyano group, an amido group, a substituted or unsubstituted cycloaliphatic group, a substituted or unsubstituted aromatic group, or a substituted or unsubstituted heterocyclic group; X comprises oxygen, sulfur, or imino group; and Z comprises a moiety such as naphthaline or dehydronaphthaline, among others.