Tuberculosis remains one of the top 10 causes of death worldwide, and the leading cause from a single infectious agent – Mycobacterium tuberculosis (Mtb), having once again surpassed HIV/AIDS. The gene encoding the Mtb enzyme CYP121 is essential for mycobacterial viability. CYP121 generates the natural product, mycocyclosin, an oxidatively modified cyclic dipeptide. It is therefore postulated that mycocyclosin has a crucial role in Mtb viability – yet the biological role of this compound remains unknown. 

The aim of this collaborative project is to elucidate the molecular target of mycocyclosin using a photoaffinity labelling (PAL) strategy, which will ultimately lead to new targets for the development of anti-TB drugs. To identify and characterise protein binding, additional chemical functionality can be incorporated onto the affinity-binding small molecule to generate a probe that will ‘capture’ that interaction so it can be isolated and elucidated. In this work we present efforts towards the synthesis of initial peptide-based photo-affinity probe designs. The PAL probe has a modular design, consisting of the essential components for the labelling process: the affinity unit, which will bind to its native target; the photoactive group, which when activated by photolysis should form an irreversible covalent bond with the corresponding substrate; the reporter tag, to identify and purify the complex that has formed; and linker groups. These segments are synthesised in fragments and appended together via peptide chemistry and biorthogonal click chemistry. Once synthesis of a library of probes is complete biological testing and photoaffinity labelling will proceed.