PyOxim

Technical Specifications

Product Description & Scientific Applications

PyOxim ([ethyl cyano(hydroxyimino)acetato-O²]tri-1-pyrrolidinylphosphonium hexafluorophosphate) is a phosphonium-type peptide coupling reagent that pairs the Oxyma leaving group (ethyl 2-cyano-2-(hydroxyimino)acetate) with a tripyrrolidinophosphonium cation and a hexafluorophosphate counterion. It belongs to the non-benzotriazole, Oxyma-based family of coupling reagents. In the presence of a tertiary-amine base such as DIPEA it activates a carboxylic acid as the corresponding Oxyma-based active ester, which then acylates the amine to form the amide bond. Its coupling efficiency is comparable to COMU; in demanding model couplings it outperformed the benzotriazole-based phosphonium reagents PyBOP, PyAOP and PyClock, with low racemisation. Because it carries a phosphonium rather than an aminium centre, PyOxim cannot guanidinylate the free amine of the growing chain — a chain-terminating side reaction associated with aminium reagents such as HATU and HBTU. It dissolves readily in DMF and is used in solid- and solution-phase peptide synthesis.

Common Scientific Applications

Solid- and solution-phase peptide synthesis: PyOxim is a phosphonium coupling reagent for solid- and solution-phase peptide-bond formation, activating protected amino acids with high coupling efficiency and low racemisation across short to demanding sequences.

Cyclic peptide synthesis and fragment condensation: Because it forms no guanidinated by-products, PyOxim preserves the free N-terminus during convergent fragment (segment) condensation and peptide cyclisation. In cyclisation models it delivered a higher proportion of cyclic product than other established phosphonium salts, supporting its use in cyclic-peptide work.

Sterically hindered and configurationally labile couplings: The Oxyma-based activation couples demanding residues — including consecutive α-aminoisobutyric acid (Aib) and other hindered amino acids — with low epimerisation, in model couplings where benzotriazole-based phosphonium reagents give lower conversion.

Stable reagent solutions: PyOxim combines high solubility in DMF with good stability in solution, so activator solutions prepared in advance remain usable longer than those of less stable reagents — useful wherever reagent solutions stand before use, including automated multi-cycle synthesis.

Further Reading

For guidance on selecting between carbodiimides, aminium/uronium salts, phosphonium salts, and other reagent classes for amide and peptide bond formation, see NorrChemica's Lab Journal guide: Choosing a Coupling Reagent for Amide and Peptide Bond Formation.

Shipping Destinations

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• Worldwide: 7–14 business days, selected locations.