Solvent Engineering for Nonpolar Substrate Glycosylation Catalyzed by the UDP-Glucose-Dependent Glycosyltransferase UGT71E5: Intensification of the Synthesis of 15-Hydroxy Cinmethylin β-d-Glucoside

Abstract

Sugar nucleotide-dependent glycosyltransferases are powerful catalysts of the glycosylation of natural products and xenobiotics. The low solubility of the aglycone substrate often limits the synthetic efficiency of the transformation catalyzed. Here, we explored different approaches of solvent engineering for reaction intensification of β-glycosylation of 15HCM (a C15hydroxylated, plant detoxification metabolite of the herbicide cinmethylin) catalyzed by safflower UGT71E5 using UDP-glucose as the donor substrate. Use of a cosolvent (DMSO, ethanol, and acetonitrile; ≤50 vol %) or a water-immiscible solvent (n-dodecane, nheptane, n-hexane, and 1-hexene) was ineffective due to enzyme activity and stability, both impaired ≥10-fold compared to a pure aqueous solvent. Complexation in 2-hydroxypropyl-β-cyclodextrin enabled dissolution of 50 mM 15HCM while retaining the UGT71E5 activity (∼0.32 U/mg) and stability. Using UDP-glucose recycling, 15HCM was converted completely, and 15HCM β-Dglucoside was isolated in 90% yield (∼150 mg). Collectively, this study highlights the requirement for a mild, enzyme-compatible strategy for aglycone solubility enhancement in glycosyltransferase catalysis applied to glycoside synthesis.

Highly Promiscuous Flavonoid Di-O-glycosyltransferases from Carthamus tinctorius L.

“…Furthermore, the expression pattern of the CsUGT75L12 gene was consistent with the accumulation pattern of 7-O-glucosides and 7-O-neohesperidoside in tea plants, indicating its involvement in the biosynthesis of bitter flavonoid 7-O-neohesperidoside [35]. In addition, genes such as NpUGT6, UGT73CD1, TwUGT3, and UGT71E5 have been found to exhibit catalytic activity in the O-glycosylation of various flavonoid compounds [36][37][38][39]. However, there is currently a relatively limited amount of research on glycosyltransferases in safflower.…”