title: Leloir Glycosyltransferases and Natural Product Glycosylation: Biocatalytic Synthesis of theC-Glucoside Nothofagin, a Major Antioxidant of Redbush Herbal Tea.
abstract: Nothofagin is a major antioxidant of redbush herbal tea and represents a class of bioactive flavonoid-likeC-glycosidic natural products. We developed an efficient enzymatic synthesis of nothofagin based on a one-pot coupled glycosyltransferase-catalyzed transformation that involves perfectly selective 3'-C-β-d-glucosylation of naturally abundant phloretin and applies sucrose as expedient glucosyl donor.C-Glucosyltransferase fromOryza sativa(rice) was used for phloretinC-glucosylation from uridine 5'-diphosphate (UDP)-glucose, which was supplied continuouslyin situthrough conversion of sucrose and UDP catalyzed by sucrose synthase fromGlycine max(soybean). In an evaluation of thermodynamic, kinetic, and stability parameters of the coupled enzymatic reactions, poor water solubility of the phloretin acceptor substrate was revealed as a major bottleneck of conversion efficiency. Using periodic feed of phloretin controlled by reaction progress, nothofagin concentrations (45 mM; 20 g l-1) were obtained that vastly exceed the phloretin solubility limit (5-10 mM). The intermediate UDP-glucose was produced from catalytic amounts of UDP (1.0 mM) and was thus recycled 45 times in the process. Benchmarked against comparable glycosyltransferase-catalyzed transformations (e.g., on quercetin), the synthesis of nothofagin has achieved intensification in glycosidic product formation by up to three orders of magnitude (μM→mM range). It thus makes a strong case for the application of Leloir glycosyltransferases in biocatalytic syntheses of glycosylated natural products as fine chemicals.
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12, 8010 Graz, Austria, ; phone:(+43)-316-873-8400.
authors.forename: Linda
authors.initials: L
authors.lastname: Bungaruang
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12, 8010 Graz, Austria, ; phone:(+43)-316-873-8400.
authors.forename: Alexander
authors.initials: A
authors.lastname: Gutmann
authors.affiliation: Institute of Biotechnology and Biochemical Engineering, Graz University of Technology, Petersgasse 12, 8010 Graz, Austria, ; phone:(+43)-316-873-8400.
authors.forename: Bernd
authors.initials: B
authors.lastname: Nidetzky
keywords: C-glycosides; UDP-glucose recycling; carbohydrates; glycosyltransferases; natural products