Every peptide drug, from a nine-residue hormone analog to a 39-residue molecule like tirzepatide, is built the same fundamental way chemist Bruce Merrifield worked out in 1963: one amino acid at a time, anchored to a solid resin bead. How solid-phase peptide synthesis actually works, why protecting groups exist, what goes wrong during a coupling cycle, why purification is the real cost center, and why scaling this 60-year-old chemistry to blockbuster-drug volumes is a genuine engineering problem.
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How Peptide Drugs Are Made