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PyOxim® is a novel and highly efficient coupling reagent that mediates coupling reactions with efficiencies superior to HATU and PyBOP® and comparable to COMU®.

CAS: 153433-21-7

Synonym:1-Cyano-2-ethoxy-2-oxoethylideneaminooxy-tris-pyrrolidino-phosphonium hexafluorophosphate; O-[(1-cyano-2-ethoxy-2-oxoethylidene)amino]-oxytri(pyrrolidin-1-yl) phosphonium hexafluorophosphate




Molecular Formula


Molecular Weight

527.38 [gr/mol]


White crystalline powder

Storage Conditions

Store in a cool and dry place (2-8oC)


  • It has excellent solubility in DMF and is stable in solution under an inert atmosphere for two days.
  • PyOxim® shows higher stability in acetone and DMF than all benzotriazole counterparts, consequently standing out as promising choice for cyclization.
  • Furthermore, PyOxim® is safer to handle and less allergenic than HOBt-based coupling reagents, and it is not explosive under normal operating conditions.


  • PyOxP and PyOxB: the Oxyma-based novel family of phosphonium salts
    Ramon Subir´os-Funosas, Ayman El-Faham and Fernando Albericio Org. Biomol. Chem., 2010, 8, 3665–3673.
    Read Article
  • Fast conventional Fmoc solid-phase peptide synthesis: a comparative study of different activators
    Christina Ann Chantell, Michael Abayomi Onaiyekan and Mahendra Menakuru J. Pept. Sci. 2012; 18: 88–91.
    Read Article
  • Kilogram-Scale GMP Manufacture of Tirzepatide Using a Hybrid SPPS/LPPS Approach with Continuous Manufacturing

    Michael O. Frederick, Raymond A. Boyse, Timothy M. Braden, Joel R. Calvin, Bradley M. Campbell, Shujauddin M. Changi, Stephanie R. Coffin, Carmel Condon, Olivia Gowran, Jennifer McClary Groh, Stephen R. Groskreutz, Zachary D. Harms, Ashley A. Humenik, Neil J. Kallman, Nicholas D. Klitzing, Michael E. Kopach, Juliana K. Kretsinger, Gordon R. Lambertus, Jeffrey T. Lampert, Laura M. Maguire, Humphrey A. Moynihan, Nessa S. Mullane, John D. Murphy, Marie E. O’Mahony, Rachel N. Richey, Kevin D. Seibert, Richard D. Spencer, Mark A. Strege, Nil Tandogan, Frank L. Torres Torres, Sergey V. Tsukanov, and Han Xia
    Organic Process Research & Development 2021 25 (7), 1628-1636

Reactivity and Racemization

Solid-Phase Fragment Condensation of  Z-Gly-Gly-Val-OH + H-Pro-Gly-Gly-NH-Resin (1) in 2eq. DIEA

Coupling Reagent DL (%)
PyAOP 33.7
PyBOP 51.0
PyClock 43.1
PyOxim 22.2

Solution Cyclization of H-Ala-Ala-MeAla-Ala-Ala-OH (1)

Coupling Reagent Cyclic(%) Linear (%) Linear Dimer (%)
PyAOP 54 10 36
PyBOP 43 28 29
PyClock 61 15 24
PyOxim 70 10 20

Manufacture of Tirzepatide (GIP/GLP-1 dual agonist).  Fragment coupling. (3)

Fragments coupling reagent solvent Base Coupling time/temp Yield after purification %
AA 22-20 + AA 30-39 PyOxim DMSO:ACN DIEA 1h/200C 75-80
AA22-39 + AA 15-21 PyOxim DMSO: ACN DIEA 3h/200C 68-75
AA 15-39+ AA1-14 HATU DMF:ACN DIEA 3h/00C 95-100


Green chemistry

Pyoxim is a much greener coupling reagent that PyBOP, hazardous and mutagenic HOBt is not used in production. It is also safer for the user than uronium(guanidinium) coupling reagents because it does not produce toxic urea waste and is not a sensitizer.



PyOxim solid is stable at 540C for at least two weeks. Stable for at least 24 months if stored at RT and keep away from light.

Shows superior to PyBOP stability in a solvent.

0.25 M solutions of coupling reagents in DMF 0 days 1 day 2 days


PyOxim 99 82 47


PyBOP 99 73 34



Coupling Reagent DMF DCM
PyAOP 260mg/0.25ml (1.99M) 230mg/0.25ml (1.79M)
PyBOP 200mg/0.25ml (1.54M) 160mg/0.25ml (1.23M)
PyClock 200mg/0.25ml (1.44M) 100mg/0.25ml (0.72M)
PyOxim 340mg/0.25ml (2.58M) 260mg/0.25ml (1.97M)


Flamability and Expolsivity hazard

According to test results, PyOxim should not be regulated as a Class 1 explosive and Class 4.1 flammable.



We are offering several packing options that can be tailored to the customer’s needs.

-Various-sized HDPE stacking containers with Black antistatic PE liner.

-DoverPac® provides a high level of powder containment during loading and offloading operation.


Solid phase peptide synthesis of ‘difficult sequences’ using Pyoxim

Erik Holm Nielsen and Troels Skrydstrup

View Poster

Evaluation of the “ResPep continuous flow synthesizer” with real-time UVmonitoring,
automated feedback & heating in solid phase peptide synthesis

Felix Niethammer, Daniel Maisch, Marcus Rothe
INTAVIS Bioanalytical Instruments AG

View Poster

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