A. U. De

QSAR With Electrotopological State Atom Index: Human Factor Xa Inhibitor N 2 -Aroylanthranilamides

Recently, N2-aroylanthranilamides have been reported as novel series of possible anticoagulant drug candidates and the two aryl rings (A and B) have been suggested to interact with S1 and S4 regions, respectively, of human factor Xa (hfXa). In the present effort, quantitative structure-activity relationship (QSAR) of the hfXa binding affinity of 32 N2-aroylanthranilamides have been attempted, in continuation of our previous report on the QSAR analysis of the data set using linear free energy related (LFER) model, with electrotopological state atom (ETSA) index (Kier and Hall, 1991, Adv. Drug Design., 22, 1-38), to explore the atoms/regions of the compounds that modulate the activity comparatively to the greater extent. The univariate and bivariate relations involving the ETSA values of different common atoms of the compounds show importance of the atom nos. 12, 3 and 17 (arbitrary numbering): B ring carbon bearing meta R2 substituents, C ring carbon bearing R4 substituent, and carbonyl oxygen of A ring amide linkage. The importance of atom 12 is suggested to be due to detrimental effects of meta R2 substituents (B ring) on the hfXa binding affinity, which may be owing to interference in the attainment of the proper orientation of the phenyl ring in the S4 site. Atom 3 signifies the impact of R4 substituents (central C ring) on the binding affinity. Again, atom 17 (carbonyl oxygen of A ring amide linkage) has been suggested to form hydrogen bonding with the NH group of the other amide linkage, producing a pseudo ring and thus stabilizing the structure. The relations were improved further using indicator and physicochemical variables and the present results are in good agreement with the previous findings of the Hansch analysis.

QSAR of human factor Xa inhibitor N2-aroylanthranilamides using principal component factor analysis.

Quantitative structure-activity relationship (QSAR) study of human factor Xa inhibitor N2-aroylanthranilamides, recently reported by Yee et al. (J. Med. Chem., 43, 873-882), has been performed using principal component factor analysis as the preprocessing step. The study reveals that presence of electron-donating R2 substituent at the para position (with respect to the amide linkage) is conducive to the binding affinity, whereas a meta R2 substituent decreases the affinity. Again, electron-donating R1 substituents with less bulk and optimum hydrophilic-lipophilic balance (particularly, methyl and methoxy groups) favor the activity. The study further suggests that electron-withdrawing R3 substituents are detrimental for the activity, whereas bulkier R4 substituents (particularly NHSO2Me group) increase the activity.

QSAR of Antimalarial Cyclic Peroxy Ketals II: Exploration of Pharmacophoric Site Using AM1 Calculations

A series of antimalarial cyclic peroxy ketals (n=20) have been subjected to energy minimization using AM1 method, and Wang–Ford charges of the non-hydrogen common atoms (Figure 1), obtained from molecular electrostatic potential surface of the energy minimized geometries, have been used to model the antimalarial activity against P. falciparum. It is found that the difference in charges between the peroxy oxygens contribute positively to the activity, and this is in good agreement with the mode of antimalarial action of the peroxy compounds involving breakage of the peroxy bridge by the haem-iron within the parasite. It is hypothesized that difference in charges between two peroxy oxygens may facilitate the bond breakage. It is further found that the activity increases with increase in negative charge of the methoxy carbon of the common fragment of the molecule. This is related with possible secondary electronic interaction with the positively charged side chains of the histidine rich protein of P. falciparum. Attempt was made to incorporate steric and indicator parameters which emerged as important contributors from previous Hansch analysis. The present results support the previous observations that bulky phenyl ring substituents and a seven-member carbocylic ring attached to the peroxy bridge-containing ring are conducive to the activity.