A cyclic sulfur amino acid derivative with potential antineoplastic and antioxidant activities. Acting on cellular membranes of malignant cells through an unknown mechanism, timonacic may induce malignant cells to revert back to an untransformed state. This agent may also restore contact inhibition, a phenomenon characterized by the paracrine inhibition of mitosis following the formation of a critical cell mass, presumably the result of cell-to-cell signal transfer. Timonacic may also produce antioxidant effects secondary to its release of cysteine and restoration of glutathione concentrations.