The pharmacophore generation and prediction of the tested qu

The pharmacophore generation and prediction of the tested quinazolines as xanthine oxidase inhibitors was obtained adopting literature methodologies [25–27]. Compound 16 (Fig. 2) served as the reference to which all conformations of each analogue were aligned. All structures were built de novo using 2D/3-D editor sketcher in MOE [28]. Conformational models were calculated using a 15 Kcal energy cut off (minimization convergence criteria during conformational analysis: energy convergence = 0.01 kcal/mol, gradient convergence = 0.01 kcal/mol). The number of conformers generated for each substrate was limited to a maximum of 100. All molecules with their associated conformations were regrouped including the biological data, lipophilic and steric parameters. Hypothesis generation was performed using low energy conformers of the molecules. After assignment of possible pharmacophore elements for each analogue, the calculation and analysis were carried out using the MOE program [28] and a superposition of the molecules, including the assigned elements, was attempted (Fig. 2). Several runs of calculation were repeated, for each run a distinct number of specified pharmacophore elements were adapted. All adapted models showed that the acceptors are 4-carbonyl oxygen atom, and 6-NO2, while the donor atoms are NH2 and amide moiety at position 6- of the quinazoline, all considered as hydrophilic elements, while the aromatic rings or small alkyl group are considered as hydrophobic elements. All were well superimposed within the set distance tolerance. This confirms the important role of the hydrophilic and hydrophobic moieties for xanthine oxidase inhibitory activity. Models for Tedizolid HCl manufacturer 16 and the other active analogues (Fig. 2; lower left panel) possess pharmacophore elements in hydrophobic aromatic and aliphatic fragments, the 4-carbonyl oxygen of both quinazoline core and amide moiety at position 6- (hydrogen bond acceptor region) as well as 6-NH or 6-NO2 groups as a region for hydrogen bonding. In the contrary, model for compound 9 (Fig. 2; lower right panel) showed common elements only in Hydrogen bonding area as described above and a deviation in hydrophobic area and hydrogen bond acceptor area. Since the hydrophobic and hydrogen bond acceptor parts of compound 16 plays an important role in activity, models for compound 9 was excluded from further considerations. Therefore, models for compound 16 were considered as the representative pharmacophore map of the xanthine oxidase inhibitory activity. According to the pharmacophore generated by MOE [28], the minimal structural requirements for xanthine oxidase inhibitory activity (Fig. 2; upper right panel) consist of four hydrophobic areas which are distance 5.04, 7.07, 7.31 and 8.98 Å apart from each other, two H-bonding acceptor groups represented by 6-amidic oxygen and 4-carbonyl oxygen with a distance 4.78 Å apart, a H-bonding acceptor/donor group (NH or NO2) directly attached to quinazoline core. For all of the active molecules, reasonable non-bonded distances among the H-bonding acceptors, and the H-donor group as well as non-bonded distances among four hydrophobic fragments align on the predicted pharmacophore maps were found (Fig. 2; upper right panel). This pharmacophoric assumption was in consistence with experimental results for xanthine oxidase inhibitory activity. The pharmacophore generation and prediction of the tested quinazolines as aldehyde oxidase was also obtained. Compound 3 (Fig. 3) served as the reference to which all conformations of each analogue were aligned. The developed pharmacophore was constructed by the same methodology described above taking into account the importance of steric and hydrophobic parameters. All adapted models showed that the acceptors are the oxygen and the nitrogen atoms of the quinazoline\'s NH2 or NO2 groups at position 6-, as acceptor/donor atoms (hydrophilic element), also the aromatic rings as hydrophobic element were well superimposed within the set distance tolerance. This confirms the important role of the hydrophilic residue as a main cause for activity with a minor importance of the hydrophobic residue for aldehyde oxidase inhibitory activity. This model is opposite to the model developed for xanthine oxidase inhibiting activity which depends mainly on both hydrophilic and hydrophobic interaction (Figs. 2 and 3). It is obvious that the most active molecule 3 was well fitted with the pharmacophore elements while the least active molecule 7 was deviated from this mapping. Models for compound 3 were considered as the representative pharmacophore map for aldehyde oxidase inhibitors. Accordingly the minimal structural requirements for aldehyde oxidase inhibitory activity (Fig. 3; upper right panel) consist of two hydrophobic areas which are distant 6.99 Å apart from each other, two H-bonding acceptor group represented by the 4-carbonyl oxygen and nitrogen atom of the quinazoline core with a distance of 4.01 Å apart, and the H-bonding acceptor/donor group (6-NH or 6-NO2).