Synthesis, cytotoxicity testing, and structure-activity relationships of novel 6-chloro-7-(4-phenylimino-4H-3,1-benzoxazin-2-yl)-3-(substituted)-1,4,2-benzodithiazine 1,1-dioxides.

A new series of 16 6-chloro-1,1-dioxo-7-{4-[(4-R(1)-phenyl)imino]-4H-3,1-benzoxazin-2-yl}-3-(substituted amino)-1,4,2-benzodithiazines 7-22 was prepared in order to evaluate the cytotoxic activity against six human cancer cell lines. The structures of the new compounds were confirmed by IR, (1)H-, and (13)C-NMR, elemental analysis and in the cases of 11 and 31 by X-ray crystal structure analysis. This analysis showed that contrary to our earlier report the structures contain a benzoxazine ring instead of the proposed quinazolinone ring. The bioassay indicated that the benzodithiazine derivatives 7-22 possess cancer cell growth-inhibitory properties. Some compounds showed a high level of selectivity for certain cell lines. The most active compounds 11, 12, 16, 19, 21, and 22 exhibited potency higher or comparable to cisplatin. The compounds were particularly effective in LCLC-103H and MCF-7 cell lines with IC(50) values of 0.49-1.60 µM. Quantitative structure activity relationships (QSAR) revealed that a chloro substituent R(1) in the phenyl ring as well as the shape of the substituted amino group at R(2) (e.g., unsaturation is beneficial) are important for potency.