7248-88-6Relevant articles and documents
Structure-activity relationships for ferriprotoporphyrin IX association and β-hematin inhibition by 4-aminoquinolines using experimental and ab initio methods
Nsumiwa, Samkele,Kuter, David,Wittlin, Sergio,Chibale, Kelly,Egan, Timothy J.
, p. 3738 - 3748 (2013/07/19)
In order to probe structure-activity relationships of association with ferriprotoporphyrin IX (log K) and inhibition of β-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, log K values for the simple 4-aminoquinoline series (R = H) were found to correlate with the hydrophobicity constant (π) of the group X. The log K 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% β-hematin inhibitory activity (log BHIA50) was found to correlate with log K and either meta (σm) or para (σp) 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 log K 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 β-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.
Structural specificity of chloroquine-hematin binding related to inhibition of hematin polymerization and parasite growth
Vippagunta, Sudha Rani,Dorn, Arnulf,Matile, Hugues,Bhattacharjee, Apurba K.,Karle, Jean M.,Ellis, William Y.,Ridley, Robert G.,Vennerstrom, Jonathan L.
, p. 4630 - 4639 (2007/10/03)
Considerable data now support the hypothesis that chloroquine (CQ)- hematin binding in the parasite food vacuole leads to inhibition of hematin polymerization and parasite death by hematin poisoning. To better understand the structural specificity of CQ-hematin binding, 13 CQ analogues were chosen and their hematin binding affinity, inhibition of hematin polymerization, and inhibition of parasite growth were measured. As determined by isothermal titration calorimetry (ITC), the stoichiometry data and exothermic binding enthalpies indicated that, like CQ, these analogues bind to two or more hematin μ-oxo dimers in a cofacial π-π sandwich-type complex. Association constants (K(a)'s) ranged from 0.46 to 2.9 x 105 M-1 compared to 4.0 x 105 M-1 for CQ. Remarkably, we were not able to measure any significant interaction between hematin μ-oxo dimer and 11, the 6-chloro analogue of CQ. This result indicates that the 7-chloro substituent in CQ is a critical structural determinant in its binding affinity to hematin μ-oxo dimer. Molecular modeling experiments reinforce the view that the enthalpically favorable π-π interaction observed in the CQ-hematin μ-oxo dimer complex derives from a favorable alignment of the out-of-plane π-electron density in CQ and hematin μ-oxo dimer at the points of intermolecular contact. For 4- aminoquinolines related to CQ, our data suggest that electron-withdrawing functional groups at the 7-position of the quinoline ring are required for activity against both hematin polymerization and parasite growth and that chlorine substitution at position 7 is optimal. Our results also confirm that the CQ diaminoalkyl side chain, especially the aliphatic tertiary nitrogen atom, is an important structural determinant in CQ drug resistance. For CQ analogues 1-13, the lack of correlation between K(a) and hematin polymerization IC50 values suggests that other properties of the CQ-hematin μ-oxo dimer complex, rather than its association constant alone, play a role in the inhibition of hematin polymerization. However, there was a modest correlation between inhibition of hematin polymerization and inhibition of parasite growth when hematin polymerization IC50 values were normalized for hematin μ-oxo dimer binding affinities, adding further evidence that antimalarial 4-aminoquinolines act by this mechanism.
