Reactive extraction of N-acetylneuraminic acid—A new method to recover neuraminic acid from reaction solutions

A new method for the purification of N-acetylneuraminic acid (Neu5Ac) is presented. A mixture of phenylboronic acid (PBA) and trioctylmethylammonium chloride (TOMAC) efficiently extracts the compound, which usually needs to be purified by elaborate chromatographic procedures or precipitation with glacial acetic acid. The presented extraction method is suitable to enrich Neu5Ac referring to pyruvate and the other compounds and facilitate further purification via classical crystallisation or chromatography, thus facilitating the established production process which utilises a large excess of pyruvate. The extraction system was characterised in detail by equilibrium studies for various solvents, pH values and carrier and substrate concentrations. The equilibrium constants determined for the two reaction steps (reaction with phenylboronic acid and reactive extraction) show that the equilibrium of extraction is more important than the extent of reaction with phenylboronic acid. The results obtained for pure compounds could be assigned to mixtures and reaction solutions without difficulty. Furthermore an efficient recovery of the carbohydrates from the organic phase is presented. The treatment of reactions mixtures showed that this system is not only feasible at lab scale and concentrations typical for scientific studies, but also for high substrate concentrations as used in industrial processes. The extraction step was shown to be the limiting factor in the extraction/recovery process.