Abstract
Glucosinolates (GSLs) are secondary plant metabolites abundantly found in plant order Brassicales. GSLs are constituted by an S-β-d-glucopyrano unit anomerically connected to O-sulfated (Z)-thiohydroximate moiety. The side-chain of the O-sulfate thiohydroximate moiety, which is derived from a different amino acid, contributes to the diversity of natural GSL, with more than 130 structures identified and validated to this day. Both the structural diversity of GSL and their biological implication in plants have been biochemically studied. Although chemical syntheses of GSL have been devised to give access to these secondary metabolites, direct extraction from biomass remains the conventional method to isolate natural GSL. While intact GSLs are biologically inactive, various products, including isothiocyanates, nitriles, epithionitriles, and cyanides obtained through their hydrolysis of GSLs, exhibit many different biological activities, among which several therapeutic benefits have been suggested. This article reviews natural occurrence, accessibility via chemical, synthetic biochemical pathways of GSL, and the current methodology of extraction, purification, and characterization. Structural information, including the most recent classification of GSL, and their stability and storage conditions will also be discussed. The biological perspective will also be explored to demonstrate the importance of these prominent metabolites.
Highlights
Amino acid-derived glucosinolates (GSLs), which are secondary plant metabolites constituted of a sulfate and thioglucose moiety, play important biological roles in the Brassicaceae family defense system, crops of great relevance to agriculture [1]
In an early study of GSL biosynthesis in the 1960s, Chrisholm and Wetter used radio-labeled methionine as an aglucone precursor to provide the first evidence for the side-chain elongation phase [128]
Further investigation should be conducted to examine the biosynthesis of GSL, which can lead to a deeper understanding of the biological role of GSLs under environmental stresses as the regulation of these metabolites is tightly related to the survival of the plants
Summary
Amino acid-derived glucosinolates (GSLs), which are secondary plant metabolites constituted of a sulfate and thioglucose moiety, play important biological roles in the Brassicaceae family defense system, crops of great relevance to agriculture [1]. In a study on Arabidopsis thaliana under abiotic stress (e.g., high salt), the overproduction of short-chain aliphatic GSL and underproduction of indolic GSL in leaves occurred [3], suggesting the adaptation of the plant in response to environmental stresses, and demonstrating the biological importance of GSLs in the Brassicaceae survival system, besides their prominent role involved in defense mechanism. The isolation of natural GSL from biomass is the method of choice to complement the limitation of synthetical approaches. The effect of the extraction process onto their biological activities, the stability, and the concentration of extracted GSLs are critical factors for determining the adequation of the isolation method. The current extraction strategy, along with the purification and characterization methods of GSLs will be explored to complement the limitations of chemical syntheses. The detailed mechanism of MYR-mediated hydrolysis, the fate of the GSL aglucone, and its health benefits will be developed in Section 7 of this review
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