## 4 Antiviral Activity of the Styrylquinoline Integrase Inhibitor Class  
All compounds were evaluated for their antiviral activities against HIV-1 replication in either Hela or CEM cells. They were tested for their ability to lower the viral charge in culture supernatants and for their eventual cytotoxicity. The results are summarized in Tables 10-12. Figure 5: View of one SQ-IN complex typical conformation belonging to each cluster: a, cluster 1; b, cluster 2. The protein is shown in magenta, Mg\({}^{2+}\) in green, water in white; drug in red, the catalytic triad (Asp64-Asp116-Glu152) in cyan (sticks and balls) and contacting residues are in yellow. Influence of the quinoline substitution of the (3',4'-dihydroxyphenyl)-substituted styrylquinoline scaffold on the antiviral activity  
Simple quinoline derivatives such as compound **3b** or **7** were found completely inactive (Table 10). These result markedly contrast with the high antiviral potency of the ketone **14** developed by the Merck Laboratories devoid of any substituent at the C-2 carbon center. Introduction of the (3',4'-dihydroxyphenyl)ethenyl motive (as in **22**) provided some biological activity, although burdened by cytotoxicity. Several compounds in Table 10 displayed moderate antiviral properties while completely devoid of integrase inhibition potency (See for example compounds **26**, **28**, **29**, **30**), it may thus be concluded that the styrylquinoline scaffold interacted with other targets within HIV-1. For example the diacid **30** was found to inhibit the HIV-1 RT with IC\({}_{50}\) = 10 \(\upmu\)M. Such activity may account for the apparent discrepancy observed. The observation that an additional carboxyl group at the C-7 position of the quinoline nucleus produced efficient antiviral agent was a crucial breakthrough in the design of styrylquinoline class. Indeed, styrylquinoline **35** gave rise to a strong antiviral effect as measured by \(\beta\)-gal assay, whereas no toxicity on either infected or noninfected cells was observed. By contrast either a nitrile group (**34**) or a carbomethoxy group (**54**) induced strong cytotoxicity masking the antiviral effect. These results confirmed that the 8-hydroxy-quinoline-7-carboxylic acid system is required for both good anti-integrase inhibition and antiviral activity. Since the pKa of the carboxyl group is below 4, it may be assumed that the 7-carboxyl group is ionized under physiological conditions. Accordingly, it appeared that a carboxylate ion at C-7 is required for efficient antiviral activity. Complexation of the magnesium ion within the active site of integrase could tentatively be invoked to explain this result. The favourable influence of an acid group on the activity is evident, however, when the acid is in a position C-5 (compound **32**) this effect is less marked. On the other hand, whatever the position of the acid group the cytotoxicity was deeply reduced. Compounds **43** and **46** (Table 10) bearing at the C-7 position isosters of the carboxyl group were found completely inactive, whereas the acid **42** in which the carboxyl group is bound at C-7 through an ethylenic linker preserved some activity [30]. The \(\alpha\)-ketoacid **47** displayed a moderate antiviral activity although devoid of integrase inhibition potency. Finally, the styrylquinoline derivative **53** bearing two similar dihydroxyphenylethhenyl subunits was found inactive. This result revealed that contrary to the integrase inhibition structure-activity relationship criteria, _ex vivo_ the available space for the substituent at C-7 is limited. The dichloro and dibromo derivatives **60** and **61** displayed high cytotoxicity masking the antiviral activity. Curiously, the introduction of a large bromine atom at C-5 (**62**) induced a dramatic decline of the antiviral potency with respect to the parent compound **35**. Similarly, styrylquinolines **64** which displayed an unsaturated acid at C-5 was poorly active.