Sir:As a result of the clinical efficacy of 3'-azido-3'-deoxythymidine (AZT, retrovir) in the treatment of AIDS (acquired immunodeficiency syndrome) ,1-3 a large number of nucleoside including acyclonucleosides,1"20 (1) Yarchoan, R.; Weinhold, K. J.; Lyerly, H. K.; Gelmann, E.; Blum, R. M.; Shearer, G. M.; Mitsuya, H.; Collins, J. M.; Myers, C. E.; Klecker, R. W.; Markham, P. D.; Durack, D. T.; Lehrman, S. N.; Barry, D. W.; Fischl, M. A.; Gallo, R. C.; Bolognesi, D. P.; Broder, S. Lancet 1986, i, 575-580. (2) Fischl, M. A.; Richman, D. D.; Grieco, M. H.; Gottieb, M. S.; Volberding, P. A.; Laskin, 0. L.; Leedom, J. M.; Groopman, J. E.; Mildvan, D.; Schooley, R. T.; Jackson, G. G.; Durack, D. T.; King, D.; the AZT Collaborative Working Group N. Engl. (36) Pauwels, R.; De Clercq, E.; Desmyter, J.; Balzarini, J.; Goubau, P.; Herdewijn, P.; Vanderhaeghe, H.; Vandeputte, M.

A series of 3,5-bis(arylidene)-4-piperidones 1 and related N-acryloyl analogues 2 were prepared as candidate cytotoxic agents with a view to discerning those structural features which contributed to bioactivity. A number of the compounds were markedly cytotoxic toward murine P388 and L1210 leukemic cells and also to human Molt 4/C8 and CEM neoplasms. Approximately 40% of the IC50 values generated were lower than the figures obtained for melphalan. In virtually all cases, the N-acyl compounds were significantly more bioactive than the analogues 1. In general, structure-activity relationships revealed that the cytotoxicity of series 1 was correlated positively with the size of the aryl substituents, while in series 2, a -sigma relationship was established. In particular, various angles and interatomic distances were obtained by molecular modeling, and the presence of an acryloyl group on the piperidyl nitrogen atom in series 2 affected the relative locations of the two aryl rings. This observation, along with some differences in distances between various atoms in series 1 and 2, may have contributed to the disparity in cytotoxicity between 1 and 2. The results obtained by X-ray crystallography of representative compounds were mainly in accordance with the observations noted by molecular modeling. Selected compounds interfered with the biosynthesis of DNA, RNA, and protein in murine L1210 cells, while others were shown to cause apoptosis in the human Jurkat leukemic cell line. This study has revealed the potential of these molecules for development as cytotoxic and anticancer agents.