title: Glucosinolate hydrolysis products in the crucifer Barbarea vulgaris include a thiazolidine-2-one from a specific phenolic isomer as well as oxazolidine-2-thiones.
abstract: Two isomeric phenolic glucosinolates, m- and p-hydroxyl derivatives of epiglucobarbarin [(R)-2-hydroxy-2-phenylethylglucosinolate], co-occur in an eastern chemotype (P-type) of the crucifer Barbarea vulgaris along with epiglucobarbarin itself. Levels of the phenolic derivatives in B. vulgaris were low in summer but higher during fall and winter, allowing isolation of all three glucosinolates. Hydrolysis in vitro, catalyzed by Sinapis alba myrosinase at near neutral pH, resulted in expectable oxazolidine-2-thione type hydrolysis products of epiglucobarbarin and its m-hydroxyl derivative. In contrast, a thiazolidine-2-one type product was formed in vitro from p-hydroxy epiglucobarbarin and characterized by UV, IR, MS/MS and 2D NMR. Maceration of leaf material resulted in disappearance of the glucosinolates and formation of the same oxazolidine-2-thione and thiazolidine-2-one products as found in vitro. The detected amounts were comparable to initial amounts of precursor glucosinolates. The corresponding oxazolidine-2-thione type product was also detected quantitatively from glucobarbarin in foliage of a western genotype (G-type). We suggest that p-hydroxy epiglucobarbarin is initially converted into the conventional oxazolidine-2-thione, which would further rearrange to a thiazolidine-2-one due to the activating effect of the p-hydroxyl group. We conclude that a subtle difference between isomeric phenolic glucosinolates results in significantly different natural hydrolysis products.
authors.affiliation: Copenhagen Plant Science Center and Plant Biochemistry Laboratory, Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark. Electronic address: nia@plen.ku.dk.
authors.forename: Niels
authors.initials: N
authors.lastname: Agerbirk
authors.affiliation: Copenhagen Plant Science Center and Plant Biochemistry Laboratory, Department of Plant and Environmental Sciences, University of Copenhagen, Thorvaldsensvej 40, DK-1871 Frederiksberg C, Denmark.
authors.forename: Carl Erik
authors.initials: CE
authors.lastname: Olsen
mesh_terms: D031216:Barbarea / Q000737:chemistry*; D002384:Catalysis; D005961:Glucosinolates / Q000737:chemistry*; D006868:Hydrolysis; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D010080:Oxazoles / Q000737:chemistry / Q000302:isolation & purification*; D018515:Plant Leaves; D013237:Stereoisomerism; D053778:Thiazolidines / Q000737:chemistry* / Q000302:isolation & purification*; D013871:Thiones / Q000737:chemistry*
chemical_list: D005961:Glucosinolates; D010080:Oxazoles; D053778:Thiazolidines; D013871:Thiones; C064210:oxazolidine
keywords: 2-Oxazolidinethione; 2-Thiazolidinone; Glucosinolate hydrolysis; Oxazolidine-2-thione; Polymorphism; Thiazolidine-2-one; para-Activation