To discover an efficient strategy for the conversion of the antibacterial activity of fluoroquinolones into the antitumor activity, the three series of C-3 s-triazole-based derivatives including sulfide ketones (6a-6g), thiosemicarbazones (7a-7g) and fused heterocyclic thiazolotriazoles (8a-8g) were synthesized from ciprofloxacin (1), respectively. The structures were characterized by elemental analysis and spectral data. The antitumor activity was tested against three tumor cell lines (Hep-3B, Capan-1 and HL60) using the MTT assay. The three types of compounds all exhibited stronger anti-proliferative activities than ciprofloxacin in the test. The order of their activities was in compounds 7>8>6, and the order of selectivity against cancer cell lines was Capan-1, Hep-3B and HL60. Meanwhile, the SAR revealed that some compounds with electron-drawing group substituted such as fluoro- and nitro-phenyl compounds (6f, 7f, 8f) and (6g, 7g, 8g) displayed more significant activity than the control compounds, especially the IC50 values of thiosemicarbazone compounds 7f and 7g against Capan-1 was comparable to doxorubicin. Thus, a five-membered triazole as the C-3 bioisostere modified with the functionalized side-chain of sulfide-ketone thiosemicarbazone warrants special attention and further investigation.

To discover novel antitumor rhodanine unsaturated ketones, a series of fluoroquinolone (rhodanine α, β-unsaturated ketone) amine derivatives (5a-5r) were designed and synthesized with fluoroquinolone amide scaffold as a carrier. The structures of eighteen title compounds were characterized by elemental analysis, 1H NMR and MS. The in vitro anti-proliferative activity against Hep-3B, Capan-1 and HL60 cells was evaluated by MTT assay. The results showed that the title compounds not only had more significant anti-proliferative activity against three tested cancer cell lines than that of the parent ciprofloxacin 1, but also exhibited the highest activity against Capan-1 cells. The SAR revealed that some compounds carrying aromatic heterocyclic rings or phenyl attached to an electron-withdrawing carboxyl or sulfonamide substituent were comparable to or better than comparison doxorubicin against Capan-1 cells. As such, it suggests that fluoroquinolone (rhodanine α, β-unsaturated ketone) amines are promising leads for the development of novel antitumor fluoroquinolones or rhodanine analogues.

To search for fluoroquinolones(FQs)with antitumor activity;the C-3 carboxylic acid group of peflox-acin (1)was replaced by fused heterocyclic core;and twelve novel thiazolo[3;2-b][1;2;4]triazole heterocycles(6a-6l)were designed and synthesized.The structures of target compounds were characterized by elemental anal-ysis and spectral data.The results of the in vitro antiproliferative effect on SMMC-7721;L1210 and HL60 cell lines showed that the title compounds exhibited more significant antitumor activity than both of the pefloxacin and the corresponding opening-ring intermediates(5 a-5 l).Among them;the target compounds which possess a ben-zene ring bearing a hydroxyl group (6e)or a fluorine atom (6j)exhibited more potent antiproliferative effect on SMMC-7721 cells than other compounds.Therefore;the antitumor fluoroquinolones can be designed by replacing the C-3 carboxylic acid group of fluoroquinolones with the thiazolo[3;2-b][1;2;4]triazole moiety.

To discover novel antitumor fluoroquinolone lead compounds from a rational modification for antibacterial fluoroquinolones, a fused heterocyclic ketone corresponding to thiazolo[2,3- b][1,2,4]triazolone used as a bioisosteric replacement of the C-3 carboxylic acid group of ciprofloxacin 1, and further modification by a Claisen condensation reaction with substituted benzaldehydes formed novel fluoroquinolone C-3 fuse heterocyclic α, β-unsaturated ketones as the title compounds (6a-6r), separately. The structures of eighteen title compounds were characterized by elemental analysis, 1H NMR and MS, and the in vitro anti-proliferative activity against human hepatoma Hep-3B cells, pancreatic Capan-1 cells and leukemia HL60 cells was evaluated by a MTT assay. The preliminary results showed that the title compounds not only had more significant anti-proliferative activity against three tested cancer cell lines than that of the parent ciprofloxacin 1, but also exhibited the highest activity against Capan-1 cells. In particular, compounds carrying an electron-withdrawing carboxyl (6k, 6m) or sulfonamide substituent (6q, 6r) attached to benzene ring were comparable to or better than constractive drug doxorubicin against Capan-1 cells. As such, it suggests that it is favorable for a fused heterocyclic α, β-unsaturated ketone scaffold instead of the C-3 carboxylic acid group to improve the antitumor activity of fluoroquinolones.

To improve the antitumor activity of fluoroquinolones for a promising development of druggability, twelve novel fluoroquinolone C-3 s-triazole sulfide-one thiosemicarbazone derivatives(6a-6l)were designed and synthesized with a functionalized sulfide-one thiosemicarbazone as a modified side-chain for the C-3 bioisteric s-triazole ring of pefloxacin(1). The structures were characterized by elemental analysis and spectral data。The in vitro antitumor activity of novel compounds against SMMC-7721, L1210 and HL60 cell lines was evaluated. The preliminary pharmacological results demonstrated that the title compounds exhibited more significantly antiproliferative activity than either the parent 1 or the corresponding sulfide-one intermediates(5a-5l). In particular, compounds bearing a hydroxyl group or a fluorine atom attached to benzene ring were comparable to the control doxorubicin with an IC50 value of micro-molar concentration, respectively. It suggests that an azole ring modified with functional side-chain instead of the C-3 carboxylic group is favorable to the improve ment of antitumor activity.