*Review* **Leloir Glycosyltransferases in Applied Biocatalysis: A Multidisciplinary Approach**

**Luuk Mestrom 1, Marta Przypis 2,3, Daria Kowalczykiewicz 2,3, André Pollender 4, Antje Kumpf 4,5, Stefan R. Marsden 1, Isabel Bento 6, Andrzej B. Jarz ˛ebski 7, Katarzyna Szyma ´nska 8, Arkadiusz Chru´sciel 9, Dirk Tischler 4,5, Rob Schoevaart 10, Ulf Hanefeld <sup>1</sup> and Peter-Leon Hagedoorn 1,\***


Received: 2 October 2019; Accepted: 18 October 2019; Published: 23 October 2019

**Abstract:** Enzymes are nature's catalyst of choice for the highly selective and efficient coupling of carbohydrates. Enzymatic sugar coupling is a competitive technology for industrial glycosylation reactions, since chemical synthetic routes require extensive use of laborious protection group manipulations and often lack regio- and stereoselectivity. The application of Leloir glycosyltransferases has received considerable attention in recent years and offers excellent control over the reactivity and selectivity of glycosylation reactions with unprotected carbohydrates, paving the way for previously inaccessible synthetic routes. The development of nucleotide recycling cascades has allowed for the efficient production and reuse of nucleotide sugar donors in robust one-pot multi-enzyme glycosylation cascades. In this way, large glycans and glycoconjugates with complex stereochemistry can be constructed. With recent advances, LeLoir glycosyltransferases are close to being applied industrially in multi-enzyme, programmable cascade glycosylations.

**Keywords:** glycosyltransferase; applied biocatalysis; enzyme cascades; chemoenzymatic synthesis; sugar chemistry; carbohydrate; Leloir; nucleotide
