Peptide Modifications

Fig 5. (a) Mass spectra of synthetic metal binding phytochelatins plant peptides.

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Fig 5. (b) Mass spectrum and HPLC trace of modified peptide with serine-octanoyl and aminohexanoic acid spacer.

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Our company has gained extensive experience in manufacturing research scale difficult and sophisticated peptides. Our synthetic peptides have proven to be generally very stable and to exhibit high biological activity in a wide range of research areas.

Cyclic peptides

Fig 6. (a) Mass spectra of A linear protected precursor and B final cyclized peptide.

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Fig 6. (b) N-terminal amine to internal glutamic acid cyclization of a 27 aa peptide containing 21 hydrophobic residue (theoretical molar mass 2894) was prepared (100 mg) with purity level >95% and a sample analyzed by MALDI-TOF MS. MS shows loss of H2O (-18 amu) by condensation to yield desired product with molecular ion at m/z 2895.0.

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Cyclic peptides have drawn considerable interest because of their improved chemical stability and significantly enhanced resistance to in situ enzymatic clearance. The conformation is more rigid then the open-chain analog and may explain in part some of the observed improved biological activities. We routinely prepare cyclic peptides with head to tail ring closure. Directed cys-cys disulfide cyclization is also frequently achieved, and careful monitoring of the reaction ensures 100% cyclization.

Labels and spacers

Fig 7. (a) Mass spectrum of fluorescent peptide containing a PEG spacer.

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Fig 7. (b) Mass spectrum and HPLC trace of a dimeric cyclic peptide linked with aminohexanoic acid spacer.

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Depending upon your application we may prepare biotinylated or fluorescent peptides with various spacers. Aliphatic C3, C6, C12, C18 or hydrophilic polyethylene glycol (PEG)-derived spacers are available.

Peptide ends

Our peptides are normally synthesized with unblocked termini i.e. amine and carboxylic acid groups. 

However in some instances, one might consider using blocking moieties, or modified ends. 

N-acetyl and C-amide closely mimic internal sequences as they have uncharged ends. In addition, these blocking groups improve resistance to enzymatic degradation. It should be noted that solubility is decreased.

Fig 8. Mass spectrum of a 20 aa peptide with an acetylated lysine and thioester blocked C-end.

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N-terminal (default NH2) C-terminal (default COOH)
acetyl, formyl amide
myristoyl, palmitoyl hydroxyl
carboxyl thioester
2-furoyl (…)

Many modifications available

Genosphere Biotechnologies provides a wide range of established peptide modification as exemplified below. Many more are available, please don’t hesitate to contact us.

Fig 9. (a) MALDI-TOF MS analysis of two 20-aa peptides with two threonine residues: (a) Unmodified peptide, theoretical molar mass of 2404 and (b) Peptide with phosphorylated threonines; theoretical molar mass 2564.

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Fig 9. (b) Mass spectrum of dual labeled peptide: 7-methoxycoumarin (MCA) and 2,4-dinitrophenyl (DNP) linked through the ε-amine of lysine residues.

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Unusual Amino acids Chemical Modifications
D-form Phosphorylation: Tyr, Ser, Thr
Hydroxyproline Biotin, DNP
Pyroglutamine Anilide C-terminal
Methyl-, acetyl-lysine Benzyloxycarbonylation
4-Bromo-, 4-Nitro-phe Nitrosation
beta-alanine N-Methylation
Fluorescent labeling Macromolecular Conjugation
Coumarin Fatty acids
Fluorescein Proteins: KLH, BSA, OVA
Rhodamine Cyclization
DANSYL cys-cys disulfide bridge
NBD Head to tail cycle
DABCYL Internal lactam, lactone