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PeptideSynthetics: Peptide Protein Research Ltd.

Peptide Synthesis Service

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Unnatural amino acids and peptide modifications

Take a look at some examples of recent peptide modifications ordered at PPR Ltd. If the modification you require is not listed here please contact us as these are only examples of modifications we can perform.

N-terminal, C-terminal and side chain modifications

Peptides with N-terminal acylation or C-terminal amidation are supplied at no extra cost.

We also provide a wide variety of other peptide modifications that include the following:

← Select a modification from the list to get started

Acetylation & amidation

Peptides can be acetylated at the N-terminus and amidated at the C-terminus for no extra cost. These modifications mimic a peptide bond at the ends of the peptide, which increases stability to peptidases.

Acetylation & amidation

Biotinylated peptides

Biotin is usually coupled to a peptide via an amide bond to either the N-terminus or a side chain amino group. It is useful for affinity applications where its very strong interaction with avidin can be employed.

Biotinylated peptides


Cyclic peptides can be produced by forming a disulphide bond between two cysteine residues, or by head-to-tail or side chain cyclisation, forming an amide bond. Using special protecting groups, it is possible to cyclise between two specific cysteines in a peptide, thus it is possible to have more than one disulphide in a peptide.

Cyclisation: Cyclic peptides

D-amino acids

D-amino acids can be incorporated in place of the natural L-amino acids, either at a specific position, or throughout the whole peptide. D-amino acids are often used to increase a peptides stability to proteases

L-amino acids, D-amino acids

Fluorescent labelled peptides

A variety of fluorescent dyes, including fluorescein (see diagram), rhodamine, Cyanine dyes and many other commercially available dyes can be attached to the N-terminus or a side chain amino group. Fluorescence-quenched substrates are used for assessing protease specificity and protein-protein interactions. By using special microscopy techniques, the passage of a labelled peptide can also be traced within a cell.

Fluorescent labelled peptides: 5-Carboxy Fluorescein

Phosphorylated serine, threonine and tyrosine

These phosphorylated residues can be inserted in place of serine, thronine or tyrosine in the peptide sequence.

Phosphorylated Serine, Threonine and Tyrosine amino acids

Peptide aldehydes

Peptide aldehydes are a common feature of enzyme inhibitors, for example HIV protease inhibitors, or caspase inhibitors (see diagram). Peptide aldehydes are also used in chemoselective ligation, for example in the production of peptide dendrimers. They are also used in the formation of reduced peptide bonds (pseudo peptide bond peptidomimetics).

Peptide aldehydes: Structure of a caspase inhibitor

N-methyl amino acids

We have great expertise in the synthesis of peptides containing N-methyl amino acids. The methyl group replaces a H-bond donor, so is useful for destabilising secondary structure and peptide aggregation.

N-methyl amino acid


Cysteine residues can be oxidised to disulphides, to produce cyclic peptides or peptide dimers. Thioester peptides can be prepared for use in native chemical ligation.

Thiols: PeptideSynthetics can prepare Thioester peptides for use in native chemical ligation.

Unnatural amino acids

There are a wide variety of different commercially available unnatural amino acids, for example butylglycine, pyroglutamic acid norleucine, hydroxy proline and many others. The resulting peptidomimetics, may increase a peptides in-vivo half life and it's potency. If an amino acid is not available, we may be able to synthesise this for you.

Examples of unnatural amino acids

Urea bond peptides

Urea bonds are often incorporated into peptide based inhibitors, for example in a β-secretase inhibitor (see diagram).

Structure of β-secretase inhibitor

Quotes and advice on peptide modification

Please contact us for more information about any of these modifications, or to discuss any other modifications you may require

Peptides for antibody production

Custom peptides conjugated to a carrier protein ready for immunisation

As an additional service, we can conjugate your chosen peptide to a carrier protein such as Keyhole Limpet Hemocyanin (KLH) or Bovine Serum Albumin (BSA).

Our conjugation method of choice is via a cysteine residue in the peptide, using MBS as a bifunctional linker between the cysteine and free amino groups on the carrier protein. If your sequence does not contain a cysteine then either a cysteine residue can be added to the N or C terminus or your peptide can be conjugated via glutaraldehyde, which does not require a cysteine residue in the peptide sequence.

Peptide sets and peptide libraries

Peptides sets consisting of overlapping sequences or related peptide sequences are available in 1-100mg quantities and a range of purities from crude peptide to >98% purity. We can cater for a wide range of peptide lengths, synthesis scales and peptide purities, so please contact us and we can quote for your requirements.

Our crude peptides are guaranteed at >50% purity and are supplied with mass spec and HPLC data.

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