Here, the N-terminal amine at position-1 (12) reacts with bis(4-nitrophenyl)carbonate to provide a carbamate en route to a semicarbazide intermediate (13a) (see the Supplementary Information). Treatment of the semicarbazide intermediate (13a) on solid support with 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) promotes cyclization to form the desired urazole-peptide ( ) following acid-promoted cleavage and global deprotection. Unfortunately, we found this method limited to sequences bearing proline (Pro) or a pseudoproline residue at position 2, as deviations from this led to undesirable hydantoin-peptide (15) formation during the cyclization step.