## 4 Conclusions  
Previously, a family of esters functionalised with monoterpene and adamantine moieties was found to be good inhibitors of Tdp1. Esters are known to be labile (i.e., hydrolyse relatively easily at physiological conditions, rendering compounds containing esters potentially problematic as drug candidates). We; therefore, substituted the ester bridge with amide and thioamide groups and tested them against Tdp1. Derivative **46a** stood out as the most promising candidate as it synergised with topotecan, a Top1 poison in clinical use against cancer, only at 5 uM, which is a fully non-toxic dose. The reported IC50 value is 3.3 uM, which is not the lowest of the series synthesised, but interestingly on **46a** showed synergy with topotecan in the cancer cell line used (A-549 lung adenocarcinoma. According to molecular modelling, a good fit is predicted for **46a** into the substrate pocket of Tdp1, inhibiting its activity. **Supplementary Materials:** The following are available online at [[http://www.mdpi.com/2076-3417/9/13/2767/s1](http://www.mdpi.com/2076-3417/9/13/2767/s1)]([http://www.mdpi.com/2076-3417/9/13/2767/s1](http://www.mdpi.com/2076-3417/9/13/2767/s1)), Table S1: Results of the scoring function for the ligands with and without two water molecules present; Table S2: The calculated molecular descriptors for the ligands; Table S3: Definition of lead-like, drug-like and known drug space (KDS) in terms of molecular descriptors. The values given are the maxima for each descriptor for the volumes of chemical space used; Figure S1: Intrinsic fluorescence spectroscopy of Tdp1 in the presence of compounds **45**, **45a 46a**, **47a** and **51**. Samples contained 10 uM Tdp1 and 1 mM compound (if applicable) dissolved in a buffer containing 20 mM Tris (pH 8.0) and 250 mM NaCl. Control experiments were conducted with DMSO, which is the solvent that the compounds were dissolved in. Excitation wavelength was 280 nm and intrinsic fluorescence was measured between 300 and 450 nm. Maximum fluorescence intensity was reported. Other compounds were not tested because they are not soluble at the required concentration in aqueous buffer; Figure S2: Protein melt curves showing the denaturing temperature of Tdp1 (10 uM, red) and Tdp1 (10 uM) in the presence of compound **44b** (100 uM, blue) as monitored by thermal shift assay. Buffer was 20 mM Tris (pH 8.0) and 250 mM NaCl. Changes in denaturing temperature were found to be \(-\)0.27 \({}^{\circ}\)C; Figure S3: Protein melt curves showing the denaturing temperature of Tdp1 (10 uM, red) and Tdp1 (10 uM) in the presence of compound **45a** (100 uM, blue) as monitored by thermal shift assay. Buffer was 20 mM Tris (pH 8.0) and 250 mM NaCl. Changes in denaturing  
Figure 4: The docked configuration of **46a** in the binding site of Tdp1 as predicted using the ChemScore scoring function. (**A**) The protein surface is rendered. The ligand occupies the binding pocket. Blue depicts a hydrophilic region on the surface; brown depicts hydrophobic region and whites shows neutral areas. (**B**) H-bonds are shown as dotted green lines between the sulphur atom and HOH631. The water molecules also form H-bonds with Thr261 and Asn516. temperature were found to be 0.04 \({}^{\circ}\)C; Figure S4: Protein melt curves showing the denaturing temperature of Tdp1 (10 uM, red) and Tdp1 (10 uM) in the presence of compound **46a** (100 uM, blue) as monitored by thermal shift assay. Buffer was 20 mM Tris (pH 8.0) and 250 mM NaCl. Changes in denaturing temperature were found to be \(-\)0.1 \({}^{\circ}\)C; Figure S5: Protein melt curves showing the denaturing temperature of Tdp1 (10 uM, red) and Tdp1 (10 uM) in the presence of compound **47a** (100 uM, blue) as monitored by thermal shift assay. Buffer was 20 mM Tris (pH 8.0) and 250 mM NaCl.