Frequently Asked Questions

What is a CDMO in the context of peptides and oligonucleotides?

We offer comprehensive support from discovery and preclinical development, through clinical phases (Phase I–III), to commercial manufacturing and supply chain management.

What stages of drug development do you support?

We offer comprehensive support from discovery and preclinical development, through clinical phases (Phase I–III), to commercial manufacturing and supply chain management.

Do you handle both generic and proprietary (NCE) peptides/oligonucleotides?

Yes, we specialize in both generic APIs and novel chemical entities (NCEs), including complex conjugates and modified structures.

How do I start a project?

Please share your sequence (or let us know if you'd prefer to keep it confidential until an NDA is in place), along with your specifications and project stage. We'll promptly prepare a tailored proposal and NDA for your review and discussion.

Has Sinopep been inspected by the US-FDA?

Since 2014, Sinopep’s GMP manufacturing facilities have successfully passed four (4) inspections conducted by the U.S. FDA, demonstrating our strong commitment to global regulatory compliance and product quality. In addition to these FDA audits, Sinopep has also undergone inspections by the Korean MFDS and has successfully completed 20 regulatory audits conducted by the NMPA in China.

Do you offer FTE-based collaborations?

Yes, we provide dedicated Full-Time Equivalent (FTE) teams for long-term projects, delivering flexible and fully integrated R&D support tailored to your needs.
For more information, please visit our FTE services page: www.sinopep.com/discovery/fte-services/

How are peptides synthesized?

With very few exceptions, most peptides at Sinopep are synthesized using chemical methods. The source of each peptide—synthetic or recombinant—is clearly indicated in the product description, with recombinant products explicitly designated as recombinant peptides (rec).

Sinopep’s peptides are produced by chemical peptide synthesis, in which amino acids are assembled stepwise from the C-terminus to the N-terminus. Depending on the sequence and application, peptides are manufactured using solid-phase peptide synthesis (SPPS), liquid-phase (solution-phase) synthesis, or hybrid approaches that combine both methods. These complementary strategies allow efficient production across a wide range of peptide lengths and complexities.

What is the difference between 'research- and GMP-grade' peptides or oligonucleotides?

Research-grade peptides are strictly for laboratory and research use only and are not intended for human or therapeutic applications. GMP-grade APIs, by contrast, undergo rigorous monitoring for chemical and biological contaminants to ensure safety and suitability for human use.

How do you ensure peptide purity and quality?

Our CGMP specifications and testing procedures include the following:

• Appearance: Solid, off-white to white
• Solubility: Clear solution at specified concentration
• Purity (HPLC/UPLC): 95–98% (phase-dependent)
• Molecular Weight (MS) / AAA: Within ±10% of theoretical value
• Peptide Content: ≥70%
• Counter-Ion Content: Report
• Elemental Impurities (ICP-MS): Report Sb, As, Bi, Cd, Cu, Pb, Hg, Mo, Ag, Sn
• Endotoxin: Report LAL (Gel Clot) per USP
• Bioburden: Report aerobic and spore counts per USP
• Residual TFA: ≤0.1%
• Residual Solvents: GC-MS, report
• Moisture (Karl Fischer): ≤10%

What scales do you offer for peptide production?

We offer peptide production across a wide range of scales—from milligrams for research and discovery, to multi-kilogram batches for GMP clinical supply, and up to hundreds of kilograms for commercial manufacturing—with fully flexible batch sizes to meet your specific needs.

What modifications are available for custom peptides?

We offer a wide array of modifications to enhance functionality, stability, and targeting, including cyclization (e.g., disulfide bonds), PEGylation, lipidation, fluorescent labels, incorporation of unnatural amino acids, and conjugations (e.g., to carriers or toxins).

To learn more about our available peptide modifications and customization options, please visit: www.sinopep.com/discovery/peptide-synthesis/

Does Sinopep supply BPC-157, TB-500, Thymosin Alpha-1, Ipamorelin, Selank, Semax, GHK-Cu, CJC-1295, MOTS-c, KPV, Epitalon, Emideltide (DSIP), Melanotan II, PEG-MGF, or similar research peptides?

No. Sinopep-Allsino does not manufacture, sell, or distribute these compounds as consumer products, supplements, or "research chemicals" for individual or retail use.
These peptides are not approved drugs in the United States and are not lawful dietary supplement ingredients. Their regulatory status is governed by FDA compounding rules (503A/503B bulk substance lists) and, in many cases, by anti-doping regulations such as the WADA Prohibited List. Distribution for human consumption outside these frameworks carries legal and safety risks, and Sinopep does not participate in that market.
Beyond regulatory status, none of these compounds has completed the clinical trial process required to establish safety and efficacy in humans. Approved drugs undergo Phase 1 through Phase 3 trials to characterize dosing, pharmacokinetics, adverse events, and long-term risk before reaching the market. For the compounds below, that evidence base does not exist at the level required for approval; most human data comes from small studies, preclinical models, or anecdotal use.
Given this gap in clinical evidence, along with the unresolved regulatory status of these substances, Sinopep-Allsino does not offer them as finished products for human use.
Sinopep-Allsino also does not permit these compounds to be labeled, marketed, or sold as "research-grade" or "for research use only" as a workaround to reach end consumers. This labeling practice is frequently used to sidestep regulatory oversight while the product is, in practice, intended for human use. We do not manufacture products for this purpose, and we do not authorize distributors or partners to represent our materials in this way.
Sinopep-Allsino is a GMP-certified CDMO. Our business is the development and manufacture of peptide, oligonucleotide, conjugate, and small molecule APIs for licensed pharmaceutical and biotechnology companies operating under proper regulatory pathways, not the sale of finished compounds to individuals or unlicensed distributors.
If your organization has a legitimate development or manufacturing need involving peptide APIs, including any of the compounds listed above, within a compliant regulatory framework, we welcome the inquiry through our standard business development channels.

How to dissolve peptides effectively

Peptide solubility depends primarily on its amino acid composition (polarity) and conformation. For guidance, download our Technical Note “Solubilization of Peptides” from the Sinopep website.

Key Strategies by Peptide Type

• Highly polar peptides (rich in charged residues like Arg, Lys, His, Asp, Glu, or polar ones like Asn, Gln, Ser, Thr, Gly): These generally dissolve well in water. For acidic peptides (Asp/Glu), add dilute ammonia to form ammonium salts and improve solubility.
• Non-polar or hydrophobic peptides (high in Ile, Leu, Met, Phe, Pro, Trp, Val, or fluorophoric/chromophoric labels): Use DMSO (dimethyl sulfoxide) as the primary solvent—it excels at dissolving these and disrupting aggregates. Alternatives: DMF, acetonitrile, or other polar, water-miscible organic solvents. Caution: Avoid mixing DMSO with strong acids (e.g., trifluoroacetic acid).
• General tips for most peptides: Acetic acid (dilute) dissolves the majority of peptides effectively. For Cys- or Met-containing peptides, minimize exposure to air/oxygen to prevent oxidation.

Practical Tips

• Peptides are typically supplied as trifluoroacetate salts; protonation of basic groups enhances aqueous solubility.
• Dissolution can be slow for long peptides or zwitterionic forms—use gentle warming or brief sonication to speed it up.
• Avoid dissolving directly in assay buffer unless the peptide is highly water-soluble.
• Always consider the intended downstream application when selecting solvents.

These steps help achieve clear, stable solutions quickly and reliably. Contact us for custom advice!

How to dissolve peptides containing free cysteines

Peptides with free cysteine residues (thiol groups) are prone to oxidation, which can lead to unwanted dimerization or complex mixtures. Proper solvent selection and conditions are essential to minimize this risk.

Key Considerations

• A single free cysteine can oxidize to form reversible dimers at pH >7.
• Peptides with two or more cysteines often produce intramolecular disulfides or polymeric mixtures upon oxidation.
• Optimal pH for controlled disulfide formation is 7.5–8, but for initial dissolution, avoid this range to prevent uncontrolled oxidation.

Recommended Solvents and Conditions

• Use degassed solvents to remove dissolved oxygen and slow oxidation.
• Preferred options:
  • Buffers at pH <7 (e.g., slightly acidic phosphate or acetate buffers).
  • Dilute acetic acid (e.g., 5–10%).
  • 0.1% trifluoroacetic acid (TFA) in aqueous acetonitrile.

These acidic, low-oxygen conditions help maintain free thiols during dissolution.

What to Avoid

• DMSO: Strongly discouraged, especially with peptide trifluoroacetates, as it can promote unwanted oxidation or side reactions.
• High pH (>7) solvents or buffers during initial reconstitution.

Practical Tips

• Dissolve under inert atmosphere (e.g., nitrogen or argon) if possible for maximum protection.
• For downstream applications requiring disulfides, perform controlled oxidation separately after dissolution.
• Gentle sonication or warming can aid solubility without promoting oxidation if done briefly.

Following these guidelines ensures stable, monomer-rich solutions of cysteine-containing peptides. For more details, refer to our Technical Note “Solubilization of Peptides” available on the Sinopep website. Contact us for tailored recommendations!

Can peptide solubility in aqueous buffers be predicted?

Predicting the aqueous solubility of a peptide solely from its sequence or structure is challenging—there is no fully reliable rule or algorithm that guarantees accurate forecasts. However, the amino acid composition provides valuable insights that can guide expectations and dissolution strategies.
Basic peptides rich in lysine (Lys) and arginine (Arg) are typically highly soluble in neutral or slightly acidic aqueous buffers. This is because peptides are commonly supplied as trifluoroacetate (TFA) salts, where the strongly basic guanidino group of Arg and the moderately basic ε-amino group of Lys remain protonated, conferring significant positive charge and promoting water interaction.
In contrast, acidic peptides with a high proportion of aspartic acid (Asp) and glutamic acid (Glu) often exhibit poor solubility in pure water due to the deprotonated carboxylate forms at neutral pH. These can be effectively dissolved by adding dilute ammonia (to form ammonium salts) or by using mildly basic buffers that keep the side-chain carboxylates ionized.
For peptides containing free cysteines or methionine, special care is required: always use degassed buffers to minimize unwanted oxidation. Thiol oxidation to disulfides is strongly pH-dependent and accelerates at higher pH, so dissolve cysteine-containing peptides in acidic buffers (pH <7) to preserve the reduced state. Methionine is less sensitive but can still form sulfoxides upon prolonged air exposure.
While these guidelines are helpful, empirical testing remains the gold standard—small-scale solubility trials with different buffers and pH values are recommended for critical applications. Contact our technical team for sequence-specific advice or to discuss optimal reconstitution protocols.

How should non-GMP peptides be stored?

To maintain stability and integrity of non-GMP (research-grade) peptides over time, proper storage conditions are essential.
Long-term storage
Store peptides in lyophilized (dry, solid) form at -20 °C or below (preferably in a deep freezer at ≤ -15 °C). This minimizes degradation and preserves activity for years.
Short-term storage
A standard refrigerator at +4 °C is sufficient for periods of weeks to a few months, especially if the peptide will be used frequently.

General best practices:

• Keep vials tightly sealed and desiccated (include silica gel packets if possible) to prevent moisture absorption.
• Protect from direct or intense sunlight and excessive light exposure.
• Peptides containing fluorophores, chromophores, or light-sensitive modifications should be stored in the dark (e.g., wrapped in aluminum foil or in opaque containers).
• Avoid repeated freeze-thaw cycles—aliquot peptides into single-use portions when practical.

Following these guidelines will help ensure optimal performance and reproducibility in your experiments.

What degradation reactions may occur during peptide storage?

Even under optimal conditions, peptides can undergo gradual chemical degradation over time, particularly if exposed to moisture, oxygen, light, or elevated temperatures. The most common instability pathways include:

• Oxidation: Sensitive residues such as methionine (forming methionine sulfoxide), tryptophan, tyrosine, and cysteine (potentially progressing to cysteic acid) are prone to oxidative damage, especially in the presence of air or trace metal ions.
• Deamidation: Asparagine (Asn) and glutamine (Gln) residues, as well as C-terminal amides, can lose an ammonia molecule, resulting in aspartic/glutamic acid or carboxylic acid formation—this is one of the most frequent degradation routes.
• Aspartimide formation: Particularly common in sequences containing Asp-Gly or Asp-Asn motifs, leading to cyclic intermediates that can further hydrolyze into iso-aspartic acid products.
• Peptide bond cleavage: Notably at Asn-Pro sites, which are unusually labile under acidic or neutral conditions.
• Pyroglutamate formation: N-terminal glutamine (Gln) readily cyclizes to pyroglutamic acid (pGlu), with N-terminal glutamic acid (Glu) showing similar but much rarer cyclization.
• Dimerization and aggregation: Tryptophan and tyrosine residues can form intermolecular cross-links, leading to dimers or higher-order aggregates.
• Racemization: Slow epimerization of chiral amino acids, particularly under basic conditions or prolonged storage, resulting in D-amino acid impurities.

To minimize these risks, store peptides lyophilized at –20 °C or below, protected from light and moisture, and consider aliquoting to avoid repeated freeze-thaw cycles. For critical applications, periodic stability testing is recommended. Our technical team can provide sequence-specific stability predictions and customized storage advice.

How are oligonucleotides synthesized?

Solid-phase oligonucleotide synthesis (SPOS), commonly performed using phosphoramidite chemistry, is the gold-standard method for producing synthetic oligonucleotides in both research and therapeutic applications.
In this automated, iterative process, nucleotides are sequentially added to a growing chain anchored to an insoluble solid support (typically controlled-pore glass or polystyrene beads). Each cycle involves four key steps:

Deprotection – removal of the protecting group (usually dimethoxytrityl, DMT) from the 5'-hydroxyl of the terminal nucleotide;
Coupling – reaction of an activated phosphoramidite monomer with the free 5'-hydroxyl to form a phosphite triester linkage;
Capping – acetylation of unreacted 5'-hydroxyl groups to prevent further elongation of failed sequences;
Oxidation – conversion of the unstable phosphite triester to a stable phosphate triester (or phosphorothioate if sulfurization is used instead).

After the desired sequence is assembled, the oligonucleotide is cleaved from the support and fully deprotected, followed by purification (typically HPLC or PAGE) and quality control (e.g., mass spectrometry).
Phosphoramidite-based SPOS offers high coupling efficiency (>98% per step), scalability from nanomoles to multimoles, and compatibility with a wide range of chemical modifications, making it the preferred method for synthesizing antisense oligonucleotides (ASOs), siRNAs, aptamers, primers, probes, and therapeutic conjugates.

What is the difference between 'research- and GMP-grade' peptides or oligonucleotides?

Research-grade peptides are strictly for laboratory and research use only and are not intended for human or therapeutic applications. GMP-grade APIs, by contrast, undergo rigorous monitoring for chemical and biological contaminants to ensure safety and suitability for human use.

What types of oligonucleotides does Sinopep develop?

Sinopep specializes in a wide range of advanced oligonucleotide modalities to support therapeutic and research applications, including:

• Antisense Oligonucleotides (ASOs)
• siRNA (small interfering RNA)
• miRNA (microRNA) mimics and inhibitors
• Morpholino Phosphorodiamidate Oligomers (PMOs) – splice-switching and gene knockdown technologies
• Aptamers – DNA/RNA-based ligands for targeted binding
• CpG Oligos – immunostimulatory sequences
• Decoy Oligonucleotides – transcription factor inhibitors
• Peptide-Oligo Conjugates (POCs and PPMOs) – enhanced delivery and cell-penetrating variants

Our expertise covers custom synthesis, modification, and scale-up of these oligos, with full analytical support and GMP capabilities for clinical and commercial development. Contact us to discuss your specific project needs!

What chemistries and modifications do you offer for oligonucleotides?

We provide a comprehensive range of advanced chemistries and modifications to enhance stability, nuclease resistance, delivery, and therapeutic potency. Key backbone and sugar modifications include phosphorothioate linkages, 2’-O-methyl (2’-OMe), 2’-fluoro (2’-F), 2’-methoxyethyl (2’-MOE), locked nucleic acids (LNA), and constrained ethyl (cEt). We support diverse oligo types such as ASOs, siRNAs, miRNAs, morpholinos (PMOs), aptamers, CpG oligos, and peptide-oligo conjugates. Additional options include 5’/3’ phosphorylation, linkers/spacers (e.g., amino, biotin, thiol, C3, Spacer 18), fluorophores (FAM, Cy3, Cy5, TAMRA) with dark quenchers, click chemistry for efficient labeling, and PEGylation to improve in vivo stability, solubility, and circulation time. These customizations enable optimized performance across research, diagnostic, and therapeutic applications.

What scales are available for oligonucleotide production?

From nmol/mmol (discovery) to grams/kilograms (GMP clinical/commercial), using automated synthesizers and large-scale chromatography.