Large-scale preparation of the phytoalexin elicitor glucohexatose and its application as a green pesticide.
Large-scale preparation of the phytoalexin elicitor was achieved through a highly regio- and sterereoselective synthesis using 2,3,4,6-tetra-O-benzoyl-d-glucopyranosyl trichloroacetimidate (1), 1,2:5,6-di-O-isopropylidene-alpha-d-glucofuranose (2), and 6-O-acetyl-2,3,4-tri-O-benzoyl-alpha-d-glucopyranosyl trichloroacetimidate (3) as the synthons. Coupling of 1 with 2 gave the 1-->3-linked disaccharide; subsequent selective removal of 5,6-O-isopropylidene to give 5 followed by selective 6-O-glycosylation with 1 afforded the trisaccharide 6. Hydrolysis to remove the 1,2-O-isopropylidene was accompanied by ring expansion, giving 3,6-branched pyranosyl trisaccharide. Acetylation, selective 1-O-deacetylation, and activation with trichloroacetonitrile gave the trisaccharide donor 7. The trisaccharide acceptor 9 was prepared from condensation of the disaccharide 5 with 3 and subsequent 6-O-deacetylation. Coupling of the trisaccharide donor 7 with the trisaccharide acceptor 9 and subsequent deprotection afforded the glucohexatose elicitor. The cost of the produced glucohexatose should be low enough to allow its applications in agriculture as a green pesticide. At a concentration of 5-10 mg/L, the resultant elicitor was used to treat growing orange trees and harvested oranges, giving very encouraging results, comparable with those obtained using commercial pesticides at a concentration of 1400 mg/L (Topsin-M) for growing trees and 900 mg/L (Tecto) for harvested oranges, respectively. Treatment of tomato leaves against Botrytis cinerea with the synthetic elicitor at a concentration of 10 mg/L gave 82% inhibition, comparable with the inhibition of 84% by Wanmeiling at a concentration of 1000 mg/L. Treatment of tea leaves also showed promising results.
Ning
Jun
J
Research Center for Eco-Environmental Sciences, Academia Sinica, P.O. Box 281, Beijing 100085, China.
Kong
Fanzuo
F
Lin
Bangmao
B
Lei
Huide
H
D020171:Botrytis / Q000187:drug effects; D002957:Citrus / Q000382:microbiology; D020231:Colletotrichum / Q000187:drug effects; D005638:Fruit / Q000382:microbiology; D005659:Fungicides, Industrial / Q000008:administration & dosage / Q000138:chemical synthesis*; D018551:Solanum lycopersicum / Q000382:microbiology; D009844:Oligosaccharides / Q000008:administration & dosage / Q000138:chemical synthesis*; D010936:Plant Extracts / Q000096:biosynthesis*; D018515:Plant Leaves / Q000382:microbiology; D012717:Sesquiterpenes; D013662:Tea / Q000382:microbiology; D013729:Terpenes; D014197:Trees; D000094162:Phytoalexins
D005659:Fungicides, Industrial; D009844:Oligosaccharides; D010936:Plant Extracts; D012717:Sesquiterpenes; D013662:Tea; D013729:Terpenes; C472249:glucohexatose; D000094162:Phytoalexins