Synthesis and Evaluation of Azaoxindoles and Pyrrolopyrimidines as Antibacterial Agents
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- Institutt for kjemi 
Antimicrobial resistance is a global problem. Since the end of the golden age of antibiotics in the 1970s, few new antibiotics have been developed and most of these belong to established classes of drugs. As the world’s arsenal of viable drugs is diminishing due to increased resistance, the need for novel classes of antibiotics is dire, as these are less prone to hereditary- and cross-resistance. The main goal of this thesis has been developing inhibitors of E. coli thymidylate monophosphate kinase (TMPK), an essential enzyme for DNA replication and repair. Its inhibition initiates thymineless death, which is lethal to the cell. To achieve this goal, the azaoxindole and pyrrolopyrimidine scaffolds were explored as possible TMPK inhibitors. Inspired by a reported imidazopyridinone inhibitor of P. aeruginosa TMPK, which was also active towards the E. coli variant, we investigated the chemistry of the azaoxindole scaffold. During this work, a key step was the development of a water-free Suzuki crosscoupling on a labile di-Boc protected intermediate, which enabled us to arrive at our target compound. Several other synthetic routes were also investigated which enables structural alterations to be installed across the prototype inhibitor with few steps. From an E. coli TMPK inhibition assay of our local library of fused heterocycles, we found two pyrrolo[2,3-d]pyrimidine hit structures. Based on these, a collection of related structures with C4 or C6 alterations was synthesized for developing a structure-activity relationship towards the enzyme. First, we explored pyrrolopyrimidines with bulky C4 substituents, where 4-naphthyl-6-(4-hydroxyphenyl) substitution was the most potent derivative. Despite the high activity on the enzyme-level, no activity was seen in cell cultures of E. coli or S. aureus. For our second lead, the 4-benzylamine-6-(4-hydroxyphenyl) substituted pyrrolopyrimidine, we assessed our developed compounds directly in culture and found several potent analogues against S. aureus, another highpriority pathogen. Further, all active compounds had a synergistic effect in combination with the antibiotic peptide MDR-26 (assayed at ½ MIC), giving between 2- and 8-fold reduction in MIC. From our SAR study, the highest potency was obtained with a para- or meta-hydroxyphenyl in C6 position, and with a para-bromo or -iodo substituent on the C4 benzylamine.