Antimicrobial volatile glucosinolate autolysis products from Hornungia petraea (L.) Rchb. (Brassicaceae) Niko S. Radulovic ´ a, *, Milan S. Dekic ´ a,b , Zorica Z. Stojanovic ´ -Radic ´ c a Department of Chemistry, Faculty of Science and Mathematics, University of Nisˇ, Visˇegradska 33, 18000 Nisˇ, Serbia b Department of Chemical and Technological Sciences, State University of Novi Pazar, Vuka Karadzˇic ´a bb, 36300 Novi Pazar, Serbia c Department of Biology and Ecology, Faculty of Science and Mathematics, University of Nisˇ, Visˇegradska 33, 18000 Nisˇ, Serbia 1. Introduction Glucosinolates (GLSs), known as mustard oil glucosides, are a class of nitrogen and sulfur-containing natural products distribut- ed in 16 dicotyledonous families of the order Capparales (Al- Shehbaz and Al-Shammary, 1987; Verkerk et al., 2009), but also in the genus Drypetes (family Euphorbiaceae) (Rodman et al., 1996). Mostly, glucosinolate-containing genera are clustered within the Brassicaceae, Capparaceae and Caricaceae families (Fahey et al., 2001). Representatives of the Brassicaceae family are of particular importance as vegetables, seasonings and relishes, and sources of vegetable oil. GLSs are recognized as the active constituents responsible for many of the physiological activities proposed for the Brassica vegetables (Holst and Williamson, 2004; Verkerk et al., 2009). Up to date, approximately 200 GLSs were described (Clarke, 2010; Fahey et al., 2001; Halkier and Gershenzon, 2006). Upon plant damage, thioglucoside glucohydrolase (E.C.3.2.3.1), or also called myrosinase, hydrolyzes the relatively non-reactive GLS to give an array of biologically active compounds, i.e. isothiocyanates, thiocyanates, nitriles, etc. GLS metabolites have been recognized as antimicrobial agents for many decades (Fahey et al., 2001) and this activity has been proposed to be a part of the crucifers defense against pathogen attack (Radulovic ´ et al., 2011). In the past few years isothiocyanates have also been identified as potent cancer- prevention agents (Fahey et al., 2001; Halkier and Gershenzon, 2006; Holland et al., 1995; Zhang and Talalay, 1994). Epidemio- logical studies have shown that they show a protective effect against cancer – particularly in the bladder, colon and lung (Song and Thornalley, 2007). In addition to their diverse biological and physiological properties, GLSs and their breakdown products are receiving considerable attention of scientists due to their known great chemotaxonomical significance. The genus Hornungia Rchb. (Brassicaceae) comprises approxi- mately 10 species, distributed in Europe, North Africa and west Asia; one species of this genus grows in Australia, south and North Africa. In Serbia, the genus is represented by only one species – Hornungia petraea (L.) Rchb. 1837 (syn. Hutchinsia petraea (L.) R. Br. 1812; Lepidium petraeum L. 1753; Gones ˇina or granc ˇika, in Serbian) (Jovanovic ´ -Dunjic ´, 1972). In general, a literature survey revealed that the genus Hornungia has been poorly investigated. In general, only two previous references on the phytochemistry of Hornungia and Hutchinsia taxa can be found regarding the analysis of glucosinolates and their breakdown products in Hutchinsia alpina (Bennett et al., 2004; Kjaer et al., 1953). Although there are many articles in the literature dealing with the identification of GLSs, it is often very difficult to identify any consistent results. The difficulty mainly lies in the lack of reliable, standard methods of GLS analysis, their instability and limited analytical data required for the identification. Analysis of volatile GLS autolysis products performed by gas chromatography/mass Phytochemistry Letters 5 (2012) 351–357 A R T I C L E I N F O Article history: Received 25 December 2011 Received in revised form 28 February 2012 Accepted 29 February 2012 Available online 14 March 2012 Keywords: Brassicaceae Hornungia petraea Glucosinolate Isothiocyanate Antimicrobial activity A B S T R A C T Plant samples of Hornungia petraea were analyzed for glucosinolate (GLS) autolysis metabolites for the first time. GC–MS analysis of the autolysate and the synthesis of a series (12 compounds) of possible glucosinolate breakdown products revealed/corroborated the presence of glucoaubrietin, glucolim- nanthin, glucolepigramin and glucotropaeolin in this species as the most likely ‘‘mustard oil’’ precursors. GLS degradation products identified in the autolysate of H. petraea, benzyl isothiocyanate, 3- and 4- methoxybenzyl isothiocyanate, along with several other structurally related compounds were evaluated for antimicrobial activity in order to possibly pinpoint the role of the latter secondary metabolites in the plant tissues. The assays showed a very high antibacterial activity of the tested isothiocyanates against Sarcina lutea and an antifungal effect against Aspergillus fumigatus and Candida albicans with MIC values in the order of 1 mg/ml value. ß 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +381 18223430; fax: +381 18533014. E-mail address: nikoradulovic@yahoo.com (N.S. Radulovic ´). Contents lists available at SciVerse ScienceDirect Phytochemistry Letters jo u rn al h om ep ag e: ww w.els evier.c o m/lo c ate/p hyt ol 1874-3900/$ – see front matter ß 2012 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved. doi:10.1016/j.phytol.2012.02.017