Structure–activity relationships for ferriprotoporphyrin IX association and β-hematin inhibition by 4-aminoquinolines using experimental and ab initio methods
作者:Samkele Nsumiwa、David Kuter、Sergio Wittlin、Kelly Chibale、Timothy J. Egan
DOI:10.1016/j.bmc.2013.04.040
日期:2013.7
In order to probe structure-activity relationships of association with ferriprotoporphyrin IX (logK) and inhibition of beta-hematin formation, a series of 4-aminoquinolines with varying substituents at the 7-position (X) have been synthesized. These have been further elaborated by introduction of two different R groups on the 4-amino nitrogen atom in the form of methyl (R = Me) and ethylamine (R = EtNH2) side chains. Data for a previously investigated series containing an N,N-diethyl-ethylamine side chain were also compared with the findings of this study. Experimentally, logK values for the simple 4-aminoquinoline series (R = H) were found to correlate with the hydrophobicity constant (pi) of the group X. The logK values for the series with R = Me and EtNH2 were found to correlate with those of the series with R = H. The log of the 50% beta-hematin inhibitory activity (log BHIA(50)) was found to correlate with logK and either meta (sigma(m)) or para (sigma(p)) Hammett constants for the series with R = Me and EtNH2, but not the simple series with R = H. To further improve predictability, correlations with ab initio electrostatic parameters, namely Mulliken and CHelpG charges were investigated. The best correlations were found with CHelpG charges which indicated that logK values can be predicted from the charges on atom H-8 and the group X in the quinolinium species computed in vacuum, while log BHIA50 values can be predicted from the CHelpG charges on C-7, C-8 and N-1 for the neutral species in vacuum. These correlations indicate that association and inhibition of beta-hematin formation are separately determined. They also suggest that electron withdrawing groups at the 7-position, but not necessarily hydrophobic groups are required for hemozoin inhibition. The upshot is that the correlations imply that considerably more hydrophilic hemozoin inhibitors are feasible. (C) 2013 Elsevier Ltd. All rights reserved.