Merrifield's resin, coupling and deprotection cycles — and why it shapes the whole market
The problem SPPS solved
A peptide is a precise, ordered chain of amino acids. Building one by classic solution chemistry — making and purifying after every single bond — is brutally slow. In 1963 Bruce Merrifield introduced solid-phase peptide synthesis (SPPS), which won him the 1984 Nobel Prize in Chemistry and made modern peptide drugs possible.1
The cycle
The trick is to anchor the growing chain to an insoluble resin bead, so excess reagents and byproducts can simply be washed away between steps. Each amino acid is added by repeating a cycle:
Solid-phase peptide synthesis: build the chain one amino acid at a time on an anchored resin — couple, deprotect, repeat — then cleave the finished peptide off.
Couple the next (protected) amino acid to the chain's free end.
Deprotect — remove the temporary protecting group to expose the next reaction site.
Wash & repeat — until the full sequence is built.
Cleave the finished peptide off the resin and remove side-chain protections.
Boc vs Fmoc
Two protecting-group strategies dominate: Boc (older, uses strong acid) and Fmoc (milder base-removable chemistry, now the workhorse). The choice affects which sequences and modifications are practical.1
Why purity is everything: because the chain is built stepwise, any missed coupling creates a slightly-wrong "deletion" peptide. That's exactly why the Certificate of Analysis (HPLC purity + mass spec) matters so much for research material.
Why this shapes the whole market
A short, naturally-occurring sequence is hard to patent. No patent means no company will fund the expensive human trials — which is precisely why compounds like BPC-157 have striking animal data but almost no human trials, and end up sold "research use only." The chemistry that makes peptides cheap to make is the same reason many never become approved drugs.
Further reading — primary sources
Mitchell — Bruce Merrifield and solid-phase peptide synthesis: a historical assessment. Peptide Science (Wiley)
For educational and research purposes only. This content is not medical advice. Compounds referenced are research use only unless noted as approved drugs, and nothing here is an instruction to use, prepare, or administer anything. Free Peptide University does not sell compounds.