Today, tuberculosis remains one of the top 10 causes of death worldwide, and the leading cause from a single infectious agent – mycobacterium tuberculosis (Mtb).1 The gene encoding the Mtb enzyme CYP121 is essential for mycobacterial viability. 2 CYP121 catalyses the final step in the biosynthesis of mycocyclosin, a cross-linked cyclic dipeptide. 3 It is therefore postulated that mycocyclosin has a crucial role in Mtb viability – yet the biological role of this compound remains unknown.
We aim 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. 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 the native target; a photoactive group, which when activated by photolysis forms a reactive carbene that results in a covalent bond between the probe and target protein; and a reporter tag to assist separation and purification of the bound protein. 4, 5 These segments are synthesised in fragments and appended via peptide chemistry and biorthogonal click chemistry. Once synthesis of a small library of probes is complete, photoaffinity labelling of a Mycobacterium cell-free extract will be undertaken.