Online NMR for monitoring biocatalysed reactions—the use of lipases in organic solvents

The lipase-catalysed acetylation of 2-hydroxymethylpiperidine was carried out in the NMR tube and monitored by 1H NMR spectroscopy for defined periods of time. Two different acylating agents were used: ethyl acetate in C6D6 and vinyl acetate in C6D6. The lipase employed was porcine pancreatic lipase (PPL). Ethyl acetate in C6D6 was hydrolysed by the enzyme but no formation of acylated product could be detected in these dilute solutions. In case of vinyl acetate as the acyl donor, the reaction did not give the desired N-acylated compound but the corresponding oxazolidine-derivative, which was formed by the reaction of the aminoalcohol and the acetaldehyde. This compound was assigned unambiguously without isolation from the reaction medium by total correlation spectroscopy (TOCSY) and gHSQC experiments.