Multiple hydroxyphenethyl glucosinolate isomers and their tandem mass spectrometric distinction in a geographically structured polymorphism in the crucifer Barbarea vulgaris

Glucosinolate hydrolysis products in the crucifer Barbarea vulgaris include a thiazolidine-2-one from a specific phenolic isomer as well as oxazolidine-2-thiones

“…The suggested para-activation is supported by the fact that the m-hydroxylated 4 gave rise to the usual OAT type of product, compatible with the general lack of activating effect in the benzylic position of an m-hydroxy group. This difference in benzylic activation was also observed in ion trap MS/MS of desulfated derivatives of the same two GSLs (Agerbirk et al, 2014b), and similar differences were reported for meta methoxybenzylic isothiocyanates compared to the ortho and para isomers (De Nicola et al, 2013a). The suggested breaking of a C-O bond followed by nucleophilic attack from either orientation to form a C-S bond would be expected to result in loss of chirality, in agreement with the lack of detectable optical rotation of 3p.…”

“…The described rearrangement specifically caused by p-hydroxylation is an additional argument for careful distinction of isomers in GSL analysis (Agerbirk and Olsen, 2012;Agerbirk et al, 2014b). Furthermore, specific structural effects described here and in the cited references is compelling evidence for the potential of even closely related GSLs to exert widely different biological effects.…”

“…Taking into account the observed chemical diversity (Agerbirk et al, 2014b), the observation of isothiocyanate-derived OAT type products from both B. vulgaris types, and the specific effect of phydroxylation on the type of hydrolysis product, a number of different major hydrolysis products of phenethyl GSLs can be expected in the various chemotypes of B. vulgaris (Fig. 1).…”

“…Two major chemotypes of B. vulgaris are the western G-type dominated by 2S and the eastern P-type dominated by 2R and with variable levels of phenolic derivatives such as 3 and 4 ( Fig. 1) (Agerbirk et al, 2014b). Additional GSLs occur but are not discussed further here.…”

“…They function as precursors of defensive hydrolysis products in cruciferous plants (Agerbirk and Olsen, 2012). By mid-2014, around 136 GSLs were to our knowledge documented from natural sources (including three Se-containing from plants fertilized with high levels of Se) Olsen, 2012, 2013;Matich et al, 2012;Agerbirk et al, 2014b). One further hypothetic and unstable GSL, 4-methoxyindolylGSL, was implied in indole phytoalexin biosynthesis based on extensive tracer studies with the synthetic desulfo derivative (Pedras and Yaya, 2013).…”