Hydroxyl and Methoxyl Derivatives of Benzylglucosinolate in Lepidium densiflorum with Hydrolysis to Isothiocyanates and non-Isothiocyanate Products: Substitution Governs Product Type and Mass Spectral Fragmentation.
A system of benzylic glucosinolates was found and characterized in common pepperweed, Lepidium densiflorum Schrad. The major glucosinolate was the novel 4-hydroxy-3,5-dimethoxybenzylglucosinolate (3,5-dimethoxysinalbin), present at high levels in seeds, leaves, and roots. Medium-level glucosinolates were 3,4-dimethoxybenzylglucosinolate and 3,4,5-trimethoxybenzylglucosinolate. Minor glucosinolates included benzylglucosinolate, 3-hydroxy- and 3-methoxybenzylglucosinolate, 4-hydroxybenzylglucosinolate (sinalbin), the novel 4-hydroxy-3-methoxybenzylglucosinolate (3-methoxysinalbin), and indole-type glucosinolates. A biosynthetic connection is suggested. NMR, UV, and ion trap MS/MS spectral data are reported, showing contrasting MS fragmentation of p-hydroxyls and p-methoxyls. Additional investigations by GC-MS focused on glucosinolate hydrolysis products. Whereas glucosinolates generally yielded isothiocyanates, the dominating 3,5-dimethoxysinalbin with a free p-hydroxyl group produced the corresponding alcohol and syringaldehyde (4-hydroxy-3,5-dimethoxybenzaldehyde). After thermal deactivation of the endogenous myrosinase enzyme, massive accumulation of the corresponding nitrile was detected. This case study points out how non-isothiocyanate glucosinolate hydrolysis products are prevalent in nature and of interest in both plant-pathogen interactions and human health.
Council for Agricultural Research and Economics, Research Centre for Industrial Crops, CREA-CIN , via di Corticella 133, 40128 Bologna, Italy.
Eleonora
http://orcid.org/0000-0002-9477-1724
E
Pagnotta
Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen , Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
Niels
http://orcid.org/0000-0003-4670-8330
N
Agerbirk
Copenhagen Plant Science Center, Department of Plant and Environmental Sciences, University of Copenhagen , Thorvaldsensvej 40, 1871 Frederiksberg C, Denmark.
Carl E
CE
Olsen
Council for Agricultural Research and Economics, Research Centre for Industrial Crops, CREA-CIN , via di Corticella 133, 40128 Bologna, Italy.
Luisa
L
Ugolini
Council for Agricultural Research and Economics, Research Centre for Industrial Crops, CREA-CIN , via di Corticella 133, 40128 Bologna, Italy.
Susanna
S
Cinti
Council for Agricultural Research and Economics, Research Centre for Industrial Crops, CREA-CIN , via di Corticella 133, 40128 Bologna, Italy.
Luca
L
Lazzeri
D006868:Hydrolysis; D017879:Isothiocyanates / Q000737:chemistry*; D029686:Lepidium / Q000737:chemistry*; D015394:Molecular Structure; D010936:Plant Extracts / Q000737:chemistry*; D018515:Plant Leaves / Q000737:chemistry; D012639:Seeds / Q000737:chemistry; D053719:Tandem Mass Spectrometry; D013861:Thiocyanates / Q000737:chemistry*; D013863:Thioglucosides / Q000737:chemistry*
D017879:Isothiocyanates; D010936:Plant Extracts; D013861:Thiocyanates; D013863:Thioglucosides; C408882:benzylglucosinolic acid; C037152:isothiocyanic acid
Brassicaceae; hydroxylation; methoxylation; novel glucosinolate; phenolics; syringaldehyde