Glucosinolates: Novel Sources and Biological Potential

Mini Review

Austin J Bioorg & Org Chem. 2014;1(1): 4.

Glucosinolates: Novel Sources and Biological Potential

Ivica Blaževic*

Department of Organic Chemistry, University of Split, Croatia

*Corresponding author: Ivica Blaževic, Department of Organic Chemistry, University of Split, Teslina 10, 21000 Split, Croatia, Europe.

Received: August 08, 2014; Accepted: September 10, 2014; Published: September 11, 2014


Glucosinolates investigation is an ongoing research activity and new structures are documented. Extraction and purification of fair amounts of glucosinolates from suitable plant species that contain high concentrations of a single or a small number of glucosinolates represent one of the most used sources of these compounds. In some cases, for obtaining enough amounts several synthesis paths are available. Occurrence in nature of some glucosinolates, such as long-chain olefinic ones, during the years of investigation are reported only by their breakdown products and not confirmed with spectroscopic data, and as such have to be re-evaluated. Despite the generally adopted scheme of glucosinolate degradation, there is further evidence that some isothiocyanates degrade further into various compound classes. As precursors of biologically active compounds, glucosinolates represent compounds with wide possible implementation and thus the novel sources by the isolation and synthesis are reviewed.

Keywords: Brassicaceae; Glucosinolates; Isolation; Synthesis; Isothiocyanates; Biological activity


GL: Glucosinolate; ITC: Isothiocyanate; GC-MS: Gas Chromatography-mass Spectrometry; HPLC: High-performance Liquid Chromatography; NMR: Nuclear Magnetic Resonance; AChE: Acetylcholinesterase


Glycosides are very large and diverse group of secondary metabolites, which usually occur in higher plants, but are also found in some lower species. They consist of a sugar part-carbohydrate moiety and non-sugar part-aglycone components, together connected by glycosidic bonds. Given the type of atoms through which realizes glycosidic bond, glycosides are divided into four groups: O-, S-, N-and C-glycosides.

Glucosinolates (GLs) are natural S-glucosides, and are abundant in sixteen families Capparales order in which the family Brassicaceae, which encompasses many of our daily vegetables (cabbages, radishes, mustards, cauliflower, broccoli, horseradish, mustard, turnip, oilseed rape, etc.), is by far the most important. All known GLs display a remarkable structural homogeneity based on a hydrophilic β-D-glucopyrano unit, a NO-sulfated anomeric (Z)-thiohydroximate function connected to aglucone part with different R-groups. The variation of R-groups, whose constitution include mostly aliphatic, arylaliphatic and indole side chain, is responsible for the variation in biological activities of these plant compounds. GL investigation is an ongoing research activity and new structures, after Fahey's review [1], have been documented by Agerbirk and Olsen [2], now including more than 130 compounds.

Glucosinolate sources

The lack of commercially available desulfo-GL standards represents one of the major troubles in investigations of GLs. This major drawback is overcomed through the purification of fair amounts of GLs and their desulfo-counterparts starting from suitable species that contain high concentrations of a single or a small number of GLs. The content of GLs in plants varies between cultivars, plant individuals and part of the plants, due to factors such as genetics, environment and plant nutrients. GLs can be found in the roots, seeds, leaf and stem of the plant, while youngest tissues contain the highest amount [3]. The sound seed-screening reported by Bennett et al. has brought to light clear subdivisions based on GL content: (i) only short- to medium chain-length aliphatic (C-3, or C-3 and C-4 with traces of C-5); (ii) only long-chain-length aliphatic; (iii) only simple arylaliphatic (such as benzyl, 4-hydroxybenzyl, 2-phenylethyl GL); and (iv) highly substituted arylaliphatic (such as 3,4-dihydroxybenzyl, 3,4dimethoxybenzyl, 3,4,5-trimethoxybenzyl GLs) [4,5]. C3-C5 aliphatic glucosinolates are a common characteristic of most Brassica species [4]. Recent reports of the plants included in tribe Alysseae (Aurinia species, Degenia velebitica and Fibigia triquetra) showed high GL contents ranging from 9.9 to 135.4 μmol/g of dried material in different plant parts - especially in the seeds (over 4.0% w/w with the highest, 6.1% w/w in F. triquetra). Those Alysseae are found to represent appropriate sources for GLs bearing a C-4 and/or C-5 olefinic aglycon chain (gluconapin, glucoberteroin) and/or a thiofunctionalized chain (glucoerucin, glucoberteroin, glucoraphanin, glucoalyssin) [5-7]. Long-chain-length aliphatic glucosinolates (C7-C10) are generally restricted to a few species within the Brassicaceae such as Arabis, Nasturtium and certain wild Lepidium species [4]. Seeds of Arabis, Barbarea, Lepidium, Moringa, and Sinapis species were good sources of aromatic glucosinolates [4].

Most of the research has aimed at identifying GLs by GC-MS of their breakdown products (mostly isothiocyanates) and HPLC analysis of the enzymatically desulfated GLs. Characterization and quantification of GLs based on the HPLC analysis of desulfo-GLs is described in the ISO 9167-1 official method [8]. However, some GL breakdown products are unstable in the conditions applied for determination and in the case of desulfated GLs there are difficulties in interpreting results of the individual GLs, due to concerns over the effect of pH value, time, and enzyme sulfatase (EC concentration on desulfation products. Some GLs in nature, were reported only through their breakdown products, such as the presence of long chain C8-C10 unsaturated isothiocyanates in autolyzates of Nasturtium montanum [9]. Their existence were not compared with authentic standards or literature spectra of such, the interpretation of mass spectra was not discussed, NMR data were not provided, and the origin from GLs was not tested [2]. Therefore, the direct analysis of intact GLs by LC-MS and nuclear magnetic resonance (NMR) spectrometry is needed for more specific and accurate determination and for better interpretation of analytical results. In other respects, the NMR spectral data are indispensable for structure elucidation of novel GLs [2].

Dedicated extractive methods allow one to isolate a number of GLs from adequate plant material, but in many cases, organic synthesis is an alternative neccesary to obtain necessary quantities of natural GLs [10]. In other respects, synthesis is the only way to elaborate a diversified range of artificial GL analogues. From a chemical synthetic point of view, two major approaches (Figure 1) for the elaboration of GLs structures have been developed by a limited number of groups over the past 50years and are summerized in the recent review [10]. These are based on a retrosynthetic scheme where a single specific bond formation affords the GL skeleton: two types of disconnection have been considered, either on the anomeric center (A) or on to the hydroximoyl moiety (B) (Figure 1).

Citation: Blaževic I. Glucosinolates: Novel Sources and Biological Potential. Austin J Bioorg & Org Chem. 2014;1(1): 4.