In vitro cytotoxicity of three (E)-3-(4′-X-benzylidene)-1-indanones (2a-c) displayed lower cytotoxicity towards murine P388 and L1210 leukemic cells as well as human Molt 4/C8 and CEM T-lymphocytes than the respective six- (3a-c) and seven-membered (4a-c) analogs. To study whether thiol reactivity—as a possible basis of their mechanism of action—correlates with the observed cytotoxicities, kinetics of the non-enzyme catalyzed reactions with reduced glutathione (GSH) and N-acetylcysteine (NAC) of 2a-c were investigated. Furthermore, it was also the aim of the work to compare the thiol reactivity of the open-chain chalcones (1) and their carbocyclic analogs (2-4) with different ring sizes (n = 5–7). The reactivity of the compounds and the stereochemical outcome of the reactions were evaluated using high-pressure liquid chromatography–mass spectrometry (HPLC-MS). Molecular modeling calculations were performed to rationalize the high initial rate and low conversion of the 2a indanone in comparison with those of the carbocyclic analog tetralone (3a) and benzosuberone (4a). Thiol reactivity and cancer cell cytotoxicity showed a dependence on both the ring size and the nature of aromatic substituents.

In vitro relative cytotoxicity (IC₅₀ (IIb)/IC₅₀ (IIIb) of (E)-3-(4′-methylbenzylidene)-4-chromanone (IIIb) towards human Molt 4/C8 and CEM T-lymphocytes showed a >50-fold increase in comparison to those of the respective tetralone derivative (IIb). On the other hand, such an increase was not observed in the analogous 4-OCH₃ (IIc and IIIc) derivatives. In order to study whether thiol reactivity—as a possible basis of the mechanism of action—correlates with the observed cytotoxicities, the kinetics of the non-enzyme catalyzed reactions with reduced glutathione (GSH) and N-acetylcysteine (NAC) of IIIb and IIIc were investigated. The reactivity of the compounds and the stereochemical outcome of the reactions were evaluated using high-pressure liquid chromatography-mass spectrometry (HPLC-MS). Molecular modeling calculations were performed to rationalize the unexpectedly higher thiol reactivity of the chromanones (III) compared to the carbocyclic analog tetralones (II). The results indicate the possible role of spontaneous thiol reactivity of compounds III in their recorded biological effects.

In vitro cancer cell cytotoxicity (IC50 values) of (E)-3-(4’-methylbenzylidene)-4-chromanone (IIIb) showed >50.0 decreases in comparison to those of the respective tetralone derivative (IIIc). On the other hand, such a decrease was not observed in the analogous 4-OCH3 (IIc and IIIc) derivatives. Since the compounds can be considered cyclic chalcone analogs, kinetics and diastereoselectivity of non-enzyme catalyzed reactions with reduced glutathione (GSH) and N-acetylcysteine (NAC) of IIIb and IIIc were investigated to assess the possible role of thiol-reactivity in the increased cytotoxicity of IIIb. Reactivity of the compounds and stereochemical outcome of the reactions were evaluated using high-pressure liquid chromatography-mass spectrometry (HPLC-MS). Molecular modeling calculations were performed to rationalize the observed differences in the thiol-reactivities of the chromanones (III) and the previously investigated tetralones (II). The results indicated possible role of spontaneous thiol-reactivity of compounds III in their recorded biological effects.