## 2 Chemistry and Structure-Activity Relationship of Styrylquinolines _in vitro_
### Modulation of the C-7 substituent on the 8,3',4'-trihydroxyyrylquinoline scaffold
In turn, phosphonic acid **46** was prepared in 15% overall yield from **44** through sequential lithium bromine exchange with \(n\)-butyllithium and treatment of the resulting lithio derivative with diethylchlorophosphate, followed with HBr deprotection [30]. Unexpectedly, the tetrazole **43** did not show any improved integrase inhibition activity whereas the phosphonic acid **46** was completely inactive. On the other hand, the \(\alpha\),\(\beta\)-unsaturated acid **42** was found equipotent than the parent compound **35**, suggesting that the geometric constraints for the additional interaction at the C-7 carbon center were not stringent. Structurally, compound **47** only differs from lead inhibitor **35** in the presence of an additional keto group at C-7. The factor that has stimulated interest in synthesizing styrylquinoline **47** has been the striking structural analogy between the HOOC-CO-C=C(OH)- system and the enol form of the \(\alpha\),\(\gamma\)-diketo acid pharmacophore found in the potent Merck inhibitor L 731,988 [31]. The introduction of this critical moiety has taken advantage of the one-carbon elongation of esters using the anion of tris(methylthio)methane **49** according to the Scheme 5. In contrast with parent compound **35**, this keto acid exhibited a complete lack of _in vitro_ inhibitory potency (IC\({}_{50}\)\(>\)100 \(\upmu\)M) [32]. This result confirmed that structural requirements of INBIs strongly differ from those of diketoacid strand transfer inhibitors. The influence of non-acidic functional groups at the C-7 position of the quinoline half was also studied. Thus, 7-(2-furyl)styrylquinoline **56** available in 24% overall yield by Stille coupling of bromide **38** with 2-(tributylstannyl)furan followed by Perkin-type condensation, was found inactive [30]. This result is in line with the hypothesis of the requirement of a Lewis base atom at the C-7 center. On the other hand the quinoline derivative **53** bearing two similar dihydroxyphenylethenyl subunits at C-2 and C-7 was found equally potent that the lead compound **35**[14], indicating that the catechol group might play the same role that the C-7, C-8 hydroxy acid group and that the exact orientation of the molecule in the active site is still in debate (Table 3). Since 7-aroyl-8-hydroxyquinoline derivatives such as **14** (Table 1) were found to be highly efficient strand transfer inhibitors by Merck [22], a series of 7-acyl/aroyl SQLs were prepared and evaluated. All these compounds were obtained in 10-40% overall yield from the fully protected 7-bromo-styrylquinoline **44** through sequential lithium/halogen exchange (PhLi, Et\({}_{2}\)O, -78 \({}^{\circ}\)C), condensation of the resulting 7-lithio derivative with the given aldehyde, MnO\({}_{2}\) oxidation and finally demethylation using either HBr at reflux or BBr\({}_{3}\) at -78 \({}^{\circ}\)C (Scheme 6) [33]. In sharp contrast with SQLs of type **35** displaying a carboxylic acid group at C-7, most of these compounds proved to be inactive in 3'-processing or overall binding assays as shown in Table 4 probably due to the steric bulk of the C-7 substituent. In line with this hypothesis, the acetyl substituted compound **59d** constituted a notable exception. However, this result could not directly be compared since the ancillary half is modified [34]. The acid substituted derivatives **59n-p** constituted another exception, reinforcing the previous finding that carboxylic acid residues improved the anti-IN activity [33]. \begin{table}
\begin{tabular}{c c c c c} \hline
**53** & **X** = HO & 2.3 & Untested & 14 \\
**56** & **X** = HO & 100 & Untested & 30 \\
**55** & **X** = & **H**N & \textgreater{}300 & Untested & 19 \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._