Antimicrobial resistance poses an escalating threat to global health, necessitating the pursuit of innovative therapeutic solutions. Many antibiotic compounds are produced by non-ribosomal peptide synthesis (NRPS), a complex and versatile pathway that allows for the generation of diverse and potent bioactive compounds, often with unique structures not typically found in ribosomally synthesised peptides. TE domains are integral to the NRPS assembly line, catalysing peptide release through either hydrolysis or cyclisation. TE domains demonstrate remarkable substrate versatility, and often have high tolerance for altered peptide structures, including non-proteogenic amino acids. These inherent characteristics of TE domains offer novel opportunities for drug modification and therapeutic enhancements. The ability to accommodate and process a plethora of peptide structures can be leveraged to cyclise diverse linear antibiotic precursors. The chemical synthesis of such precursor peptides using solid phase peptide synthesis allows us to bypass modification within the NRPS system, increasing the biosynthetic scalability of the cyclic product. The activity of TEs from the NRPS of ramoplanin and tyrocidine has been assessed towards a range of peptide substrates using an in vitro assay, with the resultant compounds analysed using LC-MS. These antibiotic peptide precursors can then be tuned and modified to hopefully develop drugs with properties that are better suited to combat resistant strains or to deliver enhanced therapeutic effects.