Unusual methionine-derived glucosinolates in Turritis glabra (Brassicaceae) include previously missing side chain lengths as well as 3-oxo and 3-hydroxy derivatives, characterized by NMR and tandem mass spectrometry

Several previously unreported glucosinolates (GSLs) were detected in rosette leaves of the Brassicaceous plant Turritis glabra . Four of them were isolated as desulfated derivatives. From MS/MS, NMR and UV of desulfoGSLs, four major T. glabra leaf GSLs were identified as 6-(methylsulfonyl)hexylGSL ( 78 ), 7-(methylsulfonyl)heptylGSL ( 160 ), 3-hydroxy-7-(methylsulfonyl)heptylGSL ( 161 ), and 6-(methylsulfonyl)-3-oxohexylGSL ( 162 ). The existence of intact 78 , 160 , 161 and 162 were supported by MS and demonstration of loss of hydrogen sulfate in MS/MS as well as sensitivity to Sinapis alba myrosinase. The identification of the position of the keto-group in 162 was challenging but confirmed by extensive 2D-NMR and MS of desulfo 162 . Attention was paid to equilibrium between a ring-closed and an open form of desulfo 162 due to the oxo group, an atypical UV spectrum, and observed semi-stable exchange of side chain hydrogens with deuterium from D 2 O in the alpha-position relative to the oxo group, which were all in agreement with the structural conclusion. Tentative interpretation of the remaining GSL profile (investigated by LC-MS/MS of desulfated derivatives) suggests that T. glabra contains further yet undescribed but minor GSLs including 5-(methylsulfonyl)pentylGSL ( [81] ) as well as some previously known, structurally related GSLs. A reference seed accession of T. glabra allowing easy, permanent access to plants with this atypical GSL content, was characterized including DNA barcode confirmation of identity. • Four glucosinolates discovered in the wild Brassicaceous plant Turritis glabra . • Extensive spectroscopic characterization established 3-hydroxy and 3-oxo groups. • Tandem MS to facilitate future recognition of these glucosinolates. • UHPLC-MS screening for similar predicted glucosinolates. • Permanent access to reference accession of the plant material investigated.