BOC Sciences provides custom long peptide synthesis services for research teams that need structurally complex, modification-rich, or aggregation-prone sequences beyond routine peptide production. Our scientists integrate sequence feasibility assessment, Fmoc solid-phase peptide synthesis, segment design, chemoselective ligation, folding, purification, and orthogonal analysis to build linear, cyclic, branched, disulfide-rich, helix-stabilized, and conjugated long peptides for drug discovery, immunology, diagnostics, structural biology, and biomaterials research.
Long peptide synthesis is the chemical preparation of extended peptide chains whose length, composition, or structural complexity makes a standard single-chain synthesis route inefficient. As a peptide grows, incomplete coupling, deletion sequences, aspartimide formation, oxidation, resin-bound aggregation, and poor solubility can accumulate. Successful production therefore depends on route selection rather than residue count alone. Direct SPPS may be suitable for an accessible sequence, while difficult targets often require optimized resin loading, backbone-disrupting building blocks, fragment condensation, native chemical ligation, selective cyclization, or controlled oxidative folding.
We assemble long linear peptides using optimized SPPS protocols with extended coupling times, double coupling, and proprietary pseudoproline strategies to maintain chain elongation efficiency.
BOC Sciences prepares cyclic long peptides through head-to-tail cyclization, side-chain to C-terminal bridging, and disulfide-mediated ring closure for improved metabolic stability and binding affinity.
We construct branched long peptides including multiple antigen peptides (MAPs) and dendrimer-like structures for enhanced avidity and multivalent recognition applications.
BOC Sciences specializes in assembling long peptides containing multiple disulfide bonds with controlled oxidation protocols for correct cysteine pairing and native fold.
We prepare alpha-helix stabilized long peptides using hydrocarbon stapling, salt-bridge engineering, and helix-nucleating templates to maintain secondary structure in therapeutic sequences.
Our biomolecule labeling and peptide conjugation services extend to long peptides, incorporating fluorophores, PEG, biotin, lipids, and payload-linker systems.
Share the sequence, desired termini, modification sites, structural constraints, target amount, intended application, and any previous synthesis observations. BOC Sciences will evaluate sequence risk and recommend a direct SPPS, hybrid assembly, or multi-segment ligation strategy supported by purification and analytical planning.
BOC Sciences supports long peptide projects across different sequence lengths, with synthesis strategies tailored to sequence complexity, structural features, modification requirements, and downstream applications.
| Sequence Length | Supported Services |
| 40-60 Residues | Linear, cyclic, and modified peptide synthesis with terminal labeling, noncanonical amino acid incorporation, HPLC purification, and LC-MS confirmation. |
| 61-80 Residues | Support for hydrophobic, disulfide-rich, and helix-forming sequences, including selective modification, folding, structural analysis, and application-specific labeling. |
| 81-100 Residues | Multi-step synthesis and fragment assembly for complex long peptides, with post-translational modifications, disulfide mapping, and orthogonal characterization. |
| 101-150 Residues | Multi-segment assembly of protein-like peptides with site-specific modifications, folding support, chromatographic purification, and sequence-level analysis. |
| Above 150 Residues | Project-specific synthesis of ultra-long peptides and synthetic protein constructs using segment ligation, structural processing, and comprehensive analytical confirmation. |
Provide the amino acid sequence, modification map, preferred termini, disulfide pattern, cyclization design, desired structural state, target amount, and downstream use. Our scientists will evaluate difficult motifs, calculate segment options, compare direct and convergent routes, define purification checkpoints, and recommend an analytical package matched to the molecule.
BOC Sciences reviews the target sequence, length, required modifications, and application context. We assess hydrophobicity profiles, aggregation propensity, difficult coupling positions, and disulfide bond requirements to recommend the most viable assembly strategy.
Our team synthesizes peptide segments using SPPS with optimized coupling reagents, pseudoproline dipeptides, and resin selection. For long sequences, we prepare C-terminal thioester fragments and N-terminal cysteine segments for ligation-based assembly.
Segments are ligated or condensed using native chemical ligation or convergent coupling. The assembled long peptide undergoes preparative RP-HPLC purification, followed by intact mass analysis, purity assessment, and structural confirmation by LC-MS/MS and CD spectroscopy.
Clients receive the purified long peptide with a comprehensive analytical package including HPLC chromatograms, mass spectra, peptide mapping data, net peptide content, and complete synthesis and purification records for downstream research use.
Every coupling and deprotection step creates an opportunity for incomplete conversion, so small inefficiencies become significant across an extended sequence. Deletion products may differ from the target by only one residue and can coelute during purification. BOC Sciences maps difficult motifs, adjusts activation chemistry and reaction time, applies selective double coupling or capping, and uses pseudoproline or backbone-protected building blocks where appropriate. Analytical checkpoints help distinguish coupling failure from cleavage-related or purification-related losses.
Long hydrophobic stretches, beta-sheet-forming motifs, and repeated residues can promote secondary structure while the chain remains attached to the resin. Restricted reagent diffusion then leads to incomplete acylation and broad crude profiles. We address this problem by comparing resin chemistry and loading, introducing backbone-disrupting elements, modifying solvent and temperature conditions, and repositioning segment boundaries. For highly persistent aggregation, a convergent route can isolate the difficult region in a shorter, more manageable fragment.
A long peptide may precipitate during cleavage, ligation, concentration, buffer exchange, or chromatography, especially when it contains extended hydrophobic or charge-neutral regions. Closely related deletion and oxidation products may also show minimal retention differences. BOC Sciences screens compatible co-solvents, pH conditions, ion-pairing systems, sample loading levels, and stationary phases. Orthogonal chromatography and fraction-by-fraction mass analysis are used when a single reverse-phase method cannot resolve the target reliably.
Native chemical ligation can be limited by an unfavorable junction, steric congestion, poorly soluble fragments, thioester hydrolysis, oxidation, or competing thiol chemistry. BOC Sciences evaluates alternative segment boundaries, ligation additives, concentration, pH, reducing conditions, and reaction order. Temporary solubilizing groups or desulfurization-compatible residues can expand the available junctions. Reaction monitoring tracks unreacted fragments, hydrolyzed intermediates, full-length product, and post-ligation transformations so that losses are addressed at the correct stage.
Work with BOC Sciences to combine sequence analysis, advanced SPPS, multi-segment ligation, selective folding, application-specific modification, chromatographic separation, and orthogonal characterization in one coordinated long peptide synthesis workflow.
BOC Sciences treats long peptide synthesis as a route-development problem rather than a routine extension of short-peptide SPPS. Sequence risk, resin behavior, segment length, ligation junctions, modification stability, purification selectivity, and final structure are evaluated together. This integrated planning reduces the likelihood that an apparently convenient early step will create an insoluble intermediate, an unsuitable junction, or an analytically inseparable final mixture.
Our scientists can compare direct Fmoc-SPPS, optimized stepwise assembly, protected-fragment condensation, native chemical ligation, sequential ligation, cyclization, and oxidative folding. The route is adapted when the data indicate a bottleneck. This flexibility is particularly valuable for hydrophobic, modification-rich, cysteine-dense, branched, or conformationally constrained sequences that cannot be addressed effectively with a single standardized protocol.
Long peptides often need more than the correct primary sequence. BOC Sciences supports position-specific phosphorylation, acetylation, methylation, glycosylation, lipidation, labeling, isotope incorporation, crosslink installation, cyclization, and disulfide formation. Through our broader biomolecule labeling capabilities, modifications can be planned around assay readout, structural analysis, surface immobilization, quantitative detection, or target-binding requirements.
Long peptide products frequently contain truncations, oxidation variants, misfolded forms, residual segments, and linkage isomers that cannot be understood with one analytical method. We combine chromatographic separation with mass-based and structure-focused analysis, then use the combined evidence to select fractions and refine the route. This approach provides clients with decision-ready information about identity, sequence coverage, modification placement, folding, and sample behavior.
Client Needs: A structural biology group required an 82-residue linear peptide corresponding to an extended extracellular loop of a G-protein coupled receptor for binding and NMR structural studies. Previous attempts by the client using standard SPPS protocols resulted in heavy resin aggregation at positions 45–58 and a crude purity below 15%.
Challenges: The sequence contained a hydrophobic stretch of 14 consecutive aliphatic residues that promoted beta-sheet aggregation on the resin, combined with two sterically hindered Val-Ile pairs that resisted single coupling. The C-terminal region was also rich in beta-branched amino acids that complicated chain elongation.
Solution: We redesigned the synthesis strategy using three convergent segments with native chemical ligation at strategically placed cysteine positions. The central hydrophobic segment was prepared with pseudoproline dipeptide insertions at two positions to disrupt aggregation. We applied double coupling with COMU activation at all beta-branched residues, used ChemMatrix resin at 0.4 mmol/g loading to minimize inter-chain interactions, and optimized ligation conditions with MPAA thiol additive at pH 7.0. The final product was purified by preparative RP-HPLC with a shallow acetonitrile gradient and characterized by intact LC-MS and CD spectroscopy.
Outcome: The client received 45 mg of purified 82-residue peptide at 94% analytical HPLC purity with confirmed intact mass, enabling successful receptor binding assays and subsequent NMR structural characterization.
Client Needs: A kinase signaling research team needed a 126-residue phosphoprotein mimic containing four site-specific phosphoserine residues distributed across the sequence for phosphorylation-dependent protein interaction studies and pulldown assays.
Challenges: The target length exceeded practical direct SPPS limits, requiring multi-segment assembly. Phosphoserine residues introduced additional synthetic complexity due to phosphate group lability under strong acid conditions, and the four phosphorylation sites were distributed across three separate segments that needed precise ligation.
Solution: We designed a four-segment native chemical ligation strategy with thioester activation at C-terminal positions and N-terminal cysteine residues at each junction. Phosphoserine was incorporated using Fmoc-Ser(PO(OBzl)OH)-OH building blocks with controlled TFA cleavage conditions to minimize phosphate hydrolysis. Segments were synthesized on ChemMatrix resin, purified individually by preparative RP-HPLC, and ligated sequentially using one-pot kinetically controlled ligation with MESNa thiol additive. Final purification employed two-step RP-HPLC with ion-pairing modifier, and the product was verified by intact HRMS and phosphosite mapping using tryptic digest LC-MS/MS.
Outcome: The team obtained 18 mg of full-length 126-residue phosphoprotein mimic at 89% purity with all four phosphoserine sites intact and confirmed, supporting successful kinase-substrate interaction studies and downstream pulldown experiments.
Client Needs: An antimicrobial drug discovery program required a 68-residue cyclic peptide containing three disulfide bonds in a defined pattern for structure-activity relationship studies against Gram-positive pathogens. The client needed the correct cysteine pairing confirmed analytically.
Challenges: The three disulfide bonds required regioselective formation in a specific pairing pattern (C1-C5, C2-C4, C3-C6) rather than random oxidation. Incorrect pairing would yield inactive conformers that would confound biological screening results. The sequence also contained a tryptophan residue sensitive to oxidation conditions.
Solution: We employed an orthogonal protection strategy using Trt for C1/C5, Acm for C2/C4, and tBu for C3/C6. Linear peptide assembly used standard Fmoc-SPPS on Rink amide resin. Stepwise oxidation proceeded first with iodine for Trt-deprotected C1-C5, then palladium-catalyzed Acm removal and oxidation for C2-C4, and final tBu deprotection with air oxidation for C3-C6. Cyclization was completed by head-to-tail amide bond formation. Disulfide bond connectivity was confirmed by partial reduction with DTT, alkylation with iodoacetamide, and LC-MS/MS sequencing of the differentially alkylated fragments.
Outcome: The client received 12 mg of correctly folded 68-residue cyclic peptide with verified disulfide bond mapping, showing potent antimicrobial activity in preliminary assays against Staphylococcus aureus and supporting the planned SAR campaign.
Chemical synthesis can support peptides across a broad length range, but feasibility depends on sequence complexity rather than residue count alone. Hydrophobicity, charge distribution, repetitive motifs, secondary-structure tendency, cysteine placement, and modification density can all influence assembly. Some long peptides can be produced directly through optimized solid-phase peptide synthesis, while more complex sequences may require fragment condensation or native chemical ligation. BOC Sciences evaluates each sequence individually and recommends a route based on coupling efficiency, fragment solubility, purification behavior, structural requirements, and the intended research application.
Difficult sequences are first assessed for hydrophobic regions, aggregation-prone motifs, repetitive residues, steric hindrance, and potential side reactions. BOC Sciences can optimize resin selection, coupling chemistry, reaction temperature, deprotection conditions, protecting-group design, and temporary solubilizing strategies. When direct solid-phase synthesis is not suitable, the sequence can be divided into shorter segments and assembled through fragment condensation or native chemical ligation. Segment boundaries are selected to improve synthesis performance, fragment handling, ligation efficiency, purification, and recovery of the intended full-length peptide.
Long peptides can incorporate terminal, side-chain, backbone, or site-selective modifications according to the intended application. Common options include acetylation, amidation, phosphorylation, methylation, lipidation, PEG spacers, biotin, fluorescent labels, affinity handles, stable-isotope-labeled residues, noncanonical amino acids, and conjugation-ready functional groups. Disulfide bonds, cyclization sites, and helix-stabilizing elements can also be introduced when compatible with the sequence. BOC Sciences reviews modification placement early to determine whether orthogonal protection, post-assembly modification, specialized ligation planning, folding, or adjusted purification conditions are required.
Long peptides may contain closely related deletion, truncation, oxidation, or misassembled species, so a single analytical method is often insufficient. BOC Sciences develops purification conditions according to peptide hydrophobicity, charge, size, solubility, and structural state. Preparative reversed-phase chromatography can be combined with complementary separation methods when needed. Characterization may include analytical HPLC or UPLC, LC-MS, high-resolution mass spectrometry, peptide mapping, disulfide analysis, free-thiol testing, and circular dichroism spectroscopy. This orthogonal approach supports confirmation of identity, sequence coverage, modification placement, folding status, and relevant product variants.
A useful feasibility assessment begins with the complete amino acid sequence, terminal groups, modification sites, disulfide pattern, intended molecular format, required amount, and downstream application. Clients should also indicate whether sequence substitutions are acceptable, whether a specific salt form or counterion is preferred, and whether the final peptide must be folded, cyclized, labeled, or conjugation-ready. Information about known solubility issues, previous synthesis attempts, assay buffers, sensitive motifs, or storage conditions can further improve route selection. BOC Sciences uses these details to identify risks and design a practical synthesis, purification, and characterization strategy.
Our original sequence was highly hydrophobic and had already failed in a standard synthesis workflow. BOC Sciences explained the risk regions clearly, proposed a two-fragment route, and connected each design choice to the expected analytical outcome. The resulting plan was scientifically practical and easy for our project team to evaluate.
— Nichols, Senior Scientist, Peptide Discovery
The team systematically compared resin loading, backbone protection, cleavage conditions, and chromatographic methods instead of relying on repeated synthesis attempts. Their data identified where material was being lost and led to a substantially more useful recovery of our long, aggregation-prone peptide for downstream biophysical studies.
— Hoffman, Research Project Manager, Structural Biology
The analytical package went beyond an intact mass result. We received chromatographic comparisons, segment and ligation data, modification-site evidence, and a clear discussion of the remaining minor variants. This gave our scientists the information needed to choose the appropriate fraction and plan the next assay series with confidence.
— Riley, Principal Scientist, Protein Chemistry
We submitted several peptides with different challenges, including phosphorylation, disulfide folding, and terminal labeling. BOC Sciences adapted the route for each target while keeping the documentation and analytical presentation consistent. That combination of flexibility and disciplined execution made it easier to compare results across our broader research program.
— Meyer, Director, Translational Research Tools
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