The invention described herein is based in part on the discovery of a protein/peptide crosslink, which introduces fluorescent properties, and which has been applied to synthesize analogues of melanocortin and amanitin as choice peptides to be explored in the context of isoindole peptides. Without limitation, it is expected that those trained in the art of peptide synthesis and stapling would appreciate the consequences of this invention such that other peptides of varied length can be similarly constrained by isoindole staples as featured herein.