Abstract: While the use of small organic molecules as therapeutic agents (drugs) goes back to antiquity, the therapeutic use of peptide drugs is a very recent phenomenon. Approximately 60 peptides have been introduced for clinical use in the past 25 years. 85% of these peptides contain at least one non-proteinogenic amino acid—those outside of the naturally encoded and translated amino acids—to confer metabolic stability, receptor potency and/or receptor selectivity to the peptide. Finding the optimal residue involves trial and error, each variant peptide being made as the unique product of a long, tedious, and chemically inefficient Solid Phase Peptide Synthesis (SPPS) procedure. We introduce a radically new approach to greatly accelerate the discovery process. Our approach takes advantage of a naturally encoded ‘pro-amino acid’, dehydroalanine, as a chemical lynchpin. Implanted into ordinary peptides, dehydroalanine can become one of any number of non-proteinogenic residues by reaction with one- or two- electron nucleophiles. Applied in parallel formats, entirely new libraires of peptides that address new therapeutic targets can be made, purified, quantified, and biochemically tested.