## 2 Chemistry and Structure-Activity Relationship of Styrylquinolines _in vitro_
### Modulation of the C-8 substituent of the syrylquinoline inhibitors  
In the quest for more potent inhibitors the introduction of an additional metal-chelating system was thus studied. An aryl nucleus possessing various hydroxy substitution patterns linked by means of an appropriate central spacer was chosen for the second chelating subunit, on the basis of the observation that the most potent HIV-integrase inhibitors known to date generally contained an ortho-dihydroxylated (catechol-type) aromatic ring. All compounds were prepared by condensing the given guanidine with 3,4-dihydroxybenzaldehyde (**16**) according to a Perkin-type condensation as depicted in Scheme 2 [14]. Similarly, [PERSON] _et al_. prepared the corresponding styrylquinazoline **20** in 5% overall yield by condensation of 3,4-dihydroxybenzaldehyde with the 2-methylquinazoline **19** which is easily available from anthranilic acid (**18**) [24]. \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Compound** & **3’Processing I** & **Strand** \\  & **C\({}_{\text{50}}\) (\(\underline{\text{uM}}\))** & **Transfer IC\({}_{\text{50}}\)** & **Reference** \\ \hline
**2b** & & \(>\)100.000 & \(>\)100.000 & 14 \\
**3a** & & \(>\)100.000 & \(>\)100.000 & 19 \\
**3b** & & \(>\)100.000 & 114.000 & 14 \\
**4** & & \(77.000\) & untested & 19 \\
**4** & & \(>\)100.000 & untested & 19 \\
**4** & & \(>\)100.000 & untested & 21 \\
**4** & & \(0.033\) & 23 \\
**4** & & \(0.370\) & 22 \\ \end{tabular}
\end{table} 
Table 1: HIV-1 IN inhibitory potency of the quinoline scaffold. **Scheme 2. ** Synthesis of 8-substituted 3',4'-dihydroxyyrylquinolines. The influence of the C-8 substituent on the 3',4'-dihydroxyyrylquinoline scaffold is summarized in Table 2.  
Although the parent compound **21** is devoid of activity, the 8-hydroxystyrylquinoline **19** displayed a modest but encouraging _in vitro_ activity. However, the replacement of the free hydroxyl group by an acetoxy substituent completely abolished the activity (compare **22** with **23**) [14]. Hence, the inhibitory potency is clearly associated with the presence of \"free\" phenolic hydroxyl group at C-8 since a nitro \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Compd.** & & & & & & **3’-Processing** & **References** \\
**Nb** & & & & & & **IC\({}_{\text{50}}\) (\(\upmu\)M)** & \\ \hline  & **R\({}^{\text{s}}\)** & **R\({}^{\text{6}}\)** & **R\({}^{\text{7}}\)** & **R\({}^{\text{8}}\)** & **X** & & \\ \hline
**21** & H & H & H & H & CH & \(>\)100.0 & 14 \\
**22** & H & H & H & OH & CH & 7.4 & 14 \\
**20** & H & H & H & OH & N & 57.0 & 24 \\
**23** & H & H & H & OAc & CH & \(>\)100.0 & 14 \\
**24** & H & H & H & NO\({}_{2}\) & CH & \(>\)100.0 & 14 \\
**25** & H & H & H & NH\({}_{2}\) & CH & \(>\)100.0 & 14 \\
**26** & H & H & H & CO\({}_{2}\)H & CH & \(>\)100.0 & 25 \\
**27** & CO\({}_{2}\)H & H & H & H & CH & \(>\)100.0 & 25 \\
**28** & H & CO\({}_{2}\)H & H & H & CH & \(>\)100.0 & 25 \\
**29** & H & H & CO\({}_{2}\)H & H & CH & \(>\)100.0 & 25 \\
**30** & CO\({}_{2}\)H & H & CO\({}_{2}\)H & H & CH & \(>\)100.0 & 25 \\
**31** & OH & CO\({}_{2}\)H & H & H & CH & \(>\)100.0 & 19 \\
**32** & CO\({}_{2}\)H & H & H & OH & CH & 7.0 & 19 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: HIV-1 IN inhibitory potency of various 3’,4’-dihydroxypyridylquinolines. or a carboxyl groups at C-8 were unable to assure integrase inhibition. SQLs **23-31** proved to be completely devoid of activity, despite the presence of a catechol moiety in all these compounds [14,25]. Unexpectedly, no noticeable integrase inhibition was observed when an amino group was fixed at C-8, indicating that a simple hydrogen bond donor residue is inefficient in promoting inhibition. The influence of the carboxylic residue in the absence of the 8-hydroxy group was also briefly investigated [25]. Acids **26-29** were found to be completely devoid of integrase inhibition potency, a result indicating that IN affinity seems to be strongly connected with the Mg\({}^{2+}\) complexing ability of the oxine moiety.