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Very Effectively and Selectively without Decrease of Bio-activity

For the synthesis of  MPEG-maleimide  only  MPEG with a  polydispersity of < 1.05 is used. The diol assay of MPEG is < 1% for MW ≤ 5000 and < 2% for MW > 5000. The manufacture of MPEG-maleimide requires very selective reactions and high rates of conversion because the (M)PEG starting material is difficult to separate. Remaining reagent and solvents have to be removed carefully. Specific analytical methods have been developed for all produced intermediates, and consequently to control the quality of the different reactions.


MPEG-maleimide is described to “PEGylate” very effectively and selectively sulfhydryl groups without decrease of bio-activity. The conjugation of a therapeutic protein at a Lysine residue by an amine active MPEG-derivative may cause a loss of bio-activity. However, it is not described in literature that PEGylation of a Cysteine residue affects the bio-activity.

On the other hand an amine group of an API can be transferred to a thiol group using an efficient linker, for instance Traut’s reagent. The conversion extends the use of MPEG-maleimide as a PEGylation reagent.

Chemical structure


Product identification

  • w-methoxy-a-[2-(2,5-dihydro-2,5-dioxo-1H-pyrrol-1-yl)-ethyl]poly(oxy-1,2-ethanediyl)
  • Monomethoxy polyethylene glycol-maleimide
  • MPEG-maleimide
  • Mal-MPEG


MPEG-maleimide is a white to off white powder

Solubility of MPEG-amines

Soluble in e.g. water, methanol, ethanol, THF, dichloromethane.


The MPEG-maleimides are analyzed by IR, NMR and MALDI TOF MS. The quality of the specific derivative is determined by HPLC which is sensitive to the functionality. Other analysis regarding residual solvent, water and heavy metals are performed. The bio-burden (total viable counts and endotoxin) are determined upon request.

Stability & Storage

MPEG-maleimide can be stored in an inert atmosphere for ca 12 months from the date of manufacture in the unopened original container at -10°C to -20°C. The product has to be re-tested after 1 year.


The material is packed in an amber glass bottle or a polyethylene bag under inert atmosphere. The packaged material is put into an aluminum-polyethylene composite foil to protect it from humidity.


For full safety information, necessary precautions and proper handling, please refer to the respective Material Safety Data Sheet (MSDS).


MPEG-maleimide can be prepared on request with molecular weights of 2000, 3000, and 5000.

MPEG-maleimide 5000
Chemical structure


n = ca. 120
CH3O(C2H4O)n+1-CH2CH2 -C4H2NO2
MW  ca. 5080
Polydispersity <1.05
CAS No.: 99126-64-4
diol content of MPEG starting material < 1%