Quantitative conversion of the starting sequence to cyclised product, with negligible formation of the linear desulfurised byproduct, is a gratifying initial result that allows high-yielding and very rapid (10 min) access to macrocyclic peptides. However, the formation of diastereomers is not ideal. Peptide 4 carries an allyl group as the radical trap; while this moiety would generate a less stable secondary radical upon addition of the alanyl radical, intramolecular trapping should still out-compete Hatom abstraction. Under the conditions described above, the starting peptide (4) was consumed within 60 min leading to the production of a major product (72% conversion to product by analytical HPLC, Entry 2). Prior to scaling the reaction up for isolation, a brief optimisation study was undertaken. It was observed that a reduction in the equivalents of TCEP led to a dramatic decrease in conversion to the product (Entry 3; 38% conversion to product 6), as did decreasing the mol% loading of the PC from 5 to 1 mol% (Entry 4). When scaling up to an isolable yield it was observed that the conditions detailed in Entry 2 were not optimal; an increase in the equivalents of TCEP to 50 (25 mM) was necessary to maintain high conversion to product. Using these adjusted conditions (Entry 5) the desired product (6) was isolated in 78% yield and characterized via MS and NMR spectroscopy. The remaining mass balance for these reactions was the linear desulfurised by-product (i.e. the competing Hatom abstraction pathway).