What is Solid-Phase Peptide Synthesis? (Peptide Glossary)

Solid-phase peptide synthesis (SPPS), invented by Bruce Merrifield in 1963 (earning the Nobel Prize), is how virtually every research peptide is manufactured. The first amino acid is anchored to a solid resin bead, then additional amino acids are coupled one at a time in cycles of deprotection, coupling, and washing. When the chain is complete, it is cleaved from the resin and purified.

SPPS explains both the strengths and the failure modes of peptide manufacturing. Each coupling cycle succeeds perhaps 99%+ of the time - excellent for a 5-amino-acid peptide, but for a 39-amino-acid peptide like tirzepatide, even small per-step failure rates compound into significant deletion-sequence contamination that must be purified away. This is why long peptides cost more and why purity varies more between suppliers for complex compounds.

After synthesis, the crude peptide is purified - typically by preparative HPLC - and lyophilized. The quality of a vendor's supply chain is largely the quality of their synthesis lab's SPPS execution and purification rigor. Vendors who name their manufacturing standards (GMP-adjacent facilities, ISO-certified labs) and back them with third-party testing are demonstrating supply chain quality.