Biocatalytic Synthesis of Non-Natural Monoterpene O-Glycosides Exhibiting Superior Antibacterial and Antinematodal Properties

Abstract

A promiscuous Bacillus glycosyltransferase (YjiC) was explored for the enzymatic synthesis of monoterpene O-glycosides in vitro and in vivo. YjiC converted seven monoterpenes into 41 different sugar-conjugated novel glycoside derivatives. The whole-cell biotransformation of the same set of monoterpenes exhibited robust enzyme activity to synthesize O-glucosyl derivatives from Escherichia coli. These newly synthesized selected monoterpene-O-glucosyl derivatives exhibited enhanced antibacterial activities against human pathogenic bacteria and antinematodal activities against pine wood nematode Bursaphelenchus xylophilus.

Scheme 1. YjiC Mediated In Vitro Glycodiversification of Monoterpene Alcohols

Figure 1

Catalytic promiscuity of YjiC toward selected monoterpenols and diverse NDP-d/l-sugars. (A) Structures of the monoterpenols and glycosides generated (2b, 3b, 4b, 5b, 5f, 5g, 6f, and 7b were not detected). (B) Percent conversion of glycodiversified monoterpenol derivatives catalyzed by YjiC. (C) Structures of different sugar moieties conjugated to monoterpenols. Asterisk (*) represents the glucosylated products that are identified by ¹H and ¹³C NMR analyses. ND indicates no detection of the product.

Figure 2

Transglycosylation by YjiC. (A) Scheme of trans-glycosylation via p-nitrophenyl β-d-galactoside (8) and p-nitrophenyl β-d-xyloside (9) using the enzyme YjiC and eugenol as the substrate in the presence of five different nucleotide diphosphates (UDP, TDP, ADP, GDP, and CDP). (B) Conversion percentage of 1 to eugenol β-d-galactoside (1e) and (C) eugenol β-d-xyloside (1h) at different time intervals in the presence of different nucleotides.

Figure 3

(A) Schematic representation of the whole-cell biotransformation of monoterpenes into glucosides using recombinant E. coli cells. (B) In vivo conversion percentage of monoterpenes into respective glucosides using whole cells of E. coli BL21 (DE3) harboring pET28-YjiC at different time intervals. The conversion of all monoterpenes was checked at a 0.5 mM final concentration. A 5% final concentration of sterile glucose was also supplemented at 0, 12, and 24 h.