Enzymatic synthesis of avermectin B1a glycosides for the effective prevention of the pine wood nematode Bursaphelenchus xylophilus

Avermectin produced by Streptomyces avermitilis is an anti-nematodal agent against the pine wood nematode Bursaphelenchus xylophilus. However, its potential usage is limited by its poor water solubility. For this reason, continuous efforts are underway to produce new derivatives that are more water soluble. Here, the enzymatic glycosylation of avermectin was catalyzed by uridine diphosphate (UDP)-glycosyltransferase from Bacillus licheniformis with various UDP sugars. As a result, the following four avermectin B-1a glycosides were produced: avermectin B-1a 4aEuro(3)-beta-d-glucoside, avermectin B-1a 4aEuro(3)-beta-d-galactoside, avermectin B-1a 4aEuro(3)-beta-l-fucoside, and avermectin B-1a 4aEuro(3)-beta-2-deoxy-d-glucoside. The avermectin B-1a glycosides were structurally analyzed based on HR-ESI MS and 1D and 2D nuclear magnetic resonance spectra, and the anti-nematodal effect of avermectin B-1a 4aEuro(3)-beta-d-glucoside was found to exhibit the highest activity (IC50 = 0.23 mu M), which was approximately 32 times greater than that of avermectin B-1a (IC50 = 7.30 mu M), followed by avermectin B-1a 4aEuro(3)-beta-2-deoxy-d-glucoside (IC50 = 0.69 mu M), avermectin B-1a 4aEuro(3)-beta-l-fucoside (IC50 = 0.89 mu M), and avermectin B-1a 4aEuro(3)-beta-d-galactoside (IC50 = 1.07 mu M). These results show that glycosylation of avermectin B-1a effectively enhances its in vitro anti-nematodal activity and that avermectin glycosides can be further applied for treating infestations of the pine wood nematode B. xylophilus.