Synthesis of UDP-activated oligosaccharides with commercial β-galactosidase from Bacillus circulans under microwave irradiation

We report here on the synthesis of nucleotide activated oligosaccharides by transglycosylation with β-galactosidase from Bacillus circulans applying microwave irradiation (MWI) and conventional heating. The presented products could serve as novel inhibitors or donor substrates of Leloir-glycosyltransferases. Some of them have been isolated from human milk but the biological role remains unclear due to limited access to the nucleotide oligosaccharides. The synthesis with β-galactosidases is challenging, because of competing hydrolysis of the product by the same enzyme. Effects of MWI and thermal heating on the hydrolytic and synthetic performance of the enzyme were systematically analysed and described here. We demonstrate that under both conditions similar product yields are obtained, however, the enzymatic hydrolysis of the product is significantly decreased under MWI leading to stable product formation. The obtained product yields and absence of product hydrolysis under MWI can be rationalized by time-dependent activation and inactivation of the β-galactosidase.