The obtained acid 2 was allowed to condense with the ethyl
ester of glycine using EDCHCl and the potassium salt of Oxyma
as a coupling reagent in a dichloromethane water mixture to afford
the desired product stevia glycine ethyl ester 3 (Scheme 1).
Recently OxymaPure was introduced, by our research group
(Cherkupally et al., 2013), as an additive for peptide bond formation
through a new formulation in which the N-hydroxylamine
group is replaced by a potassium salt. The complete suppression
of its acidity converts K-Oxyma into the most suitable coupling
choice when peptides are assembled in highly acid-labile
solid-supports. The coupling efficiency and epimerisation reduction
ability are conserved with regard to the parent OxymaPure.
In addition, K-Oxyma displays great solubility in water and a
variety of organic solvents and is safer than classical 1-hydroxybenzotriazole
additives.