## 2 Chemistry and Structure-Activity Relationship of Styrylquinolines _in vitro_
### Modulation of the ancillary ring  
Following the initial finding that a (3,4-dihydroxyphenyl)ethenyl substituent bound to the C-2 position of the 8-hydroxyquinoline scaffold produced good integrase inhibitor a systematic program of modulation of the ancillary ring was engaged. All compounds were prepared by Perkin-type \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Compd.** & \multicolumn{3}{c}{\(\mathbf{R^{5}}\)} & \multicolumn{3}{c}{\(\mathbf{R^{7}}\)} & \multicolumn{2}{c}{**3’-Processing**} & **Strand Transfer** & \\  & & & \(\mathbf{IC_{50}}\) (\(\mathbf{\mu M}\)) & \(\mathbf{IC_{50}}\) (\(\mathbf{\mu M}\)) & \\ \hline
**60** & Cl & Cl & \(>\)100.00 & \(>\)100.00 & 26 \\
**61** & Br & Br & 21.00 & 33.00 & 19 \\
**62** & Br & CO\({}_{2}\)H & 5.00 & Untested & 30 \\
**63\({}^{\mathrm{a}}\)** & CO\({}_{2}\)H & CO\({}_{2}\)H & 0.20 & 0.07 & 34 \\
**64** & CO\({}_{2}\)H & CO\({}_{2}\)H & 1.40 & 1.00 & 34 \\
**65** & CO\({}_{2}\)H & CO\({}_{2}\)H & \(>\)100.00\({}^{\mathrm{c}}\) & Untested & 19 \\
**76\({}^{\mathrm{b}}\)** & Cl & SO\({}_{2}\)NH\(\rho\)CIPh & \(>\)100.00 & Untested & 36 \\ \hline \end{tabular}  
* 3,4-dihydroxy-5-methoxy-5-methoxy-1 instead of the 3,4-dihydroxy-phenyl ancillary ring \({}^{\mathrm{b}}\) 2,4-dihydroxy-phenyl instead of the 3,4-dihydroxy-phenyl ancillary ring; \({}^{\mathrm{c}}\) Overall binding assay.  
\end{table} 
Table 5: HIV-1 IN inhibitory potency of 5,7-disubstituted -8-hydroxystyrylquinoline derivatives. condensations of the given aldehyde with 8-hydroxy-2-methyl-quinoline-7-carboxylic acid (**3b**) according to Scheme 2. More than thirty analogues were synthesized and evaluated against integrase. The results obtained with compounds bearing simple phenyl groups, heteroaromatic and monosubstituted aromatic ancillary groups are depicted in Table 6. Whatever the nature of the ancillary ring, SQLs **77a-i** displayed good level of IN inhibition potency. This result seemed indicate that this part of the molecule interacts at least in part, with IN through hydrophobic or pi-type interactions. However, the chlorobenzamide group in **77k,** and at a lesser extent the thiomethyl group in **77j** were too bulky to fit in the hydrophobic pocket of the enzyme, making these compounds inactive. Results obtained with SQLs di- and trisubstituted on the aromatic ancillary ring are listed in Table 7. Beside the 3,4-dihydroxy pattern, good IN inhibitory activities were also observed with isomers, **77l-n**, with a special mention for compound **77n** in which the phenyl nucleus is 2,3-dihydroxyd. Replacement of the hydroxyl groups with fluorine atoms reduced the activity significantly but did not suppress it totally, in line with our assumption that hydrophobic interaction is the main factor _for in vitro_ integrase inhibition. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{1}{c}{HO\({}_{2}\)C} & \multicolumn{1}{c}{N\({}_{\text{R}}\)} & \multicolumn{1}{c}{_In vitro_ Biological activity} & \multicolumn{1}{c}{**Reference**} \\ OH & & & \\ \hline
**Compd.** & **R** & **3’-Processing** & **Strand Transfer** & \\
**nb.** & & **IC\({}_{\text{80}}\) (\(\upmu\)M)** & **IC\({}_{\text{80}}\) (\(\upmu\)M)** & \\ \hline
**77a** & & 5.3 & 2.1 & 14 \\
**77b** & & 1.9 & 5.1 & 26 \\
**77c** & & 3.4 & 3.0 & 26 \\
**77d** & & 4.0 & 11.0 & 26 \\
**77e** & & 1.6 & untested & 26 \\
**77f** & & 2.2 & 3.5 & 26 \\
**77g** & & 1.2 & 1.7 & 26 \\
**77h** & & 3.4 & 31.0 & 26 \\
**77i** & & 5.0 & untested & 25 \\
**77j** & & 39.0 & 30.0 & 30 \\
**77k** & & \(>\)100.0 & untested & 30 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Influence of the ancillary ring on the HIV-1 IN inhibitory potency of 8-hydroxy-2-styryl-quinoline-7-carboxylic acids. It is noteworthy that compared with the catechol-containing compound **35**, the same level of activity was gained with substrates **77q**,**r**,**s** in which one of the hydroxyl substituents was replaced by a methoxy or carboxyl group [14,26].