QSC Peptide Manufacturing Process

QSC (Qingdao Sigma Chemical) produces research-grade peptides using solid-phase peptide synthesis (SPPS) — the established standard for producing defined-sequence peptides at research purity. This page documents each stage of the QSC synthesis pipeline from amino acid assembly through to the lyophilised product shipped to customers.

1. Solid-Phase Peptide Synthesis (SPPS)

SPPS was first described by Robert Bruce Merrifield in 1963 and has since become the universal method for producing research peptides. The defining feature is that synthesis takes place on a solid resin support, allowing unreacted reagents to be washed away between coupling steps — a critical advantage over solution-phase methods for longer sequences.

QSC employs the Fmoc (9-fluorenylmethoxycarbonyl) protection scheme, which is now the dominant method in research peptide production. Fmoc offers several advantages over the alternative Boc scheme: base-labile Fmoc groups are removed by mild piperidine treatment rather than the harsh HF deprotection required by Boc chemistry, reducing side reactions and enabling synthesis of acid-sensitive sequences.

Resin Selection

The C-terminal amino acid is loaded onto an appropriate resin depending on the desired C-terminus of the final peptide. Common choices include:

• Wang resin — for peptides requiring a free carboxylic acid (–COOH) C-terminus. Standard for most research peptides.
• Rink amide resin — for peptides requiring a C-terminal amide (–CONH₂), which provides improved metabolic stability. Used for many GH secretagogues and GLP-1 analogues.
• 2-Chlorotrityl chloride resin — for particularly acid-sensitive sequences, allowing mild cleavage conditions.

Amino Acid Coupling Chemistry

Each amino acid is activated immediately before coupling using reagents that suppress racemisation and maximise coupling efficiency. QSC uses HATU (hexafluorophosphate azabenzotriazole tetramethyl uronium) with DIPEA (N,N-diisopropylethylamine) as base — the current best-practice combination for Fmoc SPPS.

Coupling efficiency is monitored for critical positions using colorimetric tests (Kaiser test for primary amines; chloranil test for secondary amines/proline). Incomplete couplings are double-coupled before proceeding to prevent truncated sequences that would reduce final purity.

Fmoc Deprotection

After each coupling step, the Fmoc group on the newly added residue is removed by treatment with 20% piperidine in DMF. This exposes the free amine for the subsequent coupling cycle. The dibenzofulvene byproduct is UV-active and can be quantified to monitor deprotection completeness.

2. Cleavage and Global Deprotection

After all amino acids have been assembled, the completed peptide chain is cleaved from the resin and the side-chain protecting groups are removed simultaneously. QSC uses a standard TFA (trifluoroacetic acid) cleavage cocktail with a scavenger mixture appropriate to the amino acid composition — typically including water, triisopropylsilane (TIS), and/or ethanedithiol (EDT) for cysteine-containing sequences.

The cleavage reaction is performed at room temperature for 2–3 hours. The resin is filtered off, the crude peptide is precipitated in cold diethyl ether, and the solid is collected by centrifugation. The crude peptide at this stage typically has 60–85% purity by HPLC — it contains truncated sequences, oxidation products, and other synthesis by-products that must be removed by purification.

3. Reverse-Phase HPLC Purification

Crude peptide is purified by preparative reverse-phase HPLC to achieve the ≥99% purity specification. This is the critical quality step that distinguishes research-grade peptides from crude synthesis products.

Column and Mobile Phase

QSC uses C18 stationary phase (octadecylsilane bonded silica) for most peptides. The mobile phase is a gradient of:

• Solvent A: 0.1% TFA in water
• Solvent B: 0.1% TFA in acetonitrile

Gradient conditions are optimised per compound. UV detection at 220nm monitors peptide bond absorbance. The target fraction is collected based on peak identity (confirmed by analytical HPLC and MS of collected fractions).

Purity Confirmation

Collected fractions are analysed by analytical HPLC before pooling. Only fractions meeting the ≥99% purity threshold are pooled. Fractions below threshold are either re-purified or discarded. This conservative approach ensures the final product consistently meets specification.

4. Lyophilisation

Purified peptide in aqueous acetonitrile is first diluted with water to reduce the organic content, then frozen rapidly (typically at –80°C or in liquid nitrogen). The frozen material is placed on a lyophiliser (freeze dryer) and sublimed under vacuum to remove water while maintaining the peptide in its solid state.

The resulting lyophilised powder is the finished form. Compared to liquid solutions, lyophilised peptides offer significantly improved stability — they can be stored for months to years at 2–8°C or longer at –20°C without degradation. This is why all QSC compounds ship as lyophilised powder rather than pre-dissolved solutions.

5. Final QC and COA Issuance

Before any batch is released, it undergoes final quality control testing:

Upon passing all tests, an independent Certificate of Analysis is issued by Janoshik Analytical Laboratories. The Janoshik COA includes the HPLC chromatogram, MS spectrum, batch number, and testing date. Customers can verify the COA authenticity directly on the Janoshik website using the batch identifier.

In-House vs Partner Synthesis

QSC's 75+ compound catalogue spans a wide range of peptide types — from small 5-residue fragments to complex 39-residue GLP-1 analogues. For compounds requiring specialist equipment (e.g., very long sequences requiring microwave-assisted SPPS, or compounds with unusual post-translational modifications), QSC partners with validated contract synthesis organisations. All partner-produced compounds are subject to the same QC standards and Janoshik COA requirement before acceptance.