Electrotopological state indices (E K ) of atom types is used to describe the structures of 19 conjugates (LHCc) of levofloxacin-thiadiazole HDAC inhibitor (HDACi) and related to the inhibitory activity (pW i , i=1, 6) of LHCc against histone deacetylases(HDACs, HDAC1 and HDAC6). The optimal two-parameter(E 17 , E 18 ) quantitative structure-activity relationships(QSAR) models are established by using leaps-and-bounds regression analysis for the inhibitory activities(pW i ) of 19 above

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... to HDAC1 and HDAC6 along with the E K . The correlation coefficients (R 2 ) and the leave-one-out (LOO) cross validation R cv 2 for the pW 1 and pW 6 models were 0.942 and 0.918, 0.943 and 0.919, respectively. The QSAR models have favorable correlation, as well as robustness and good prediction capability by R 2 , F, R cv 2 , A IC , F IT , V IF tests. The results indicate that the molecular structural units: -NH 2 , -NH-are main factors which can affect the inhibitory activity(pW i )bioactivities of these compounds directly. Accordingly, it is suggested that the main interactions between HDACs inhibitor and HDACs are hydrophobic, hydrogen bond, and coordination compounds with Zn 2+ . This is consistent with the molecular docking results of document.