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.

We have shown that whole Escherichia coli cells overexpressing NADPH‐dependent cyclohexanone monooxygenase carry out a model Baeyer‐Villiger oxidation with high volumetric productivity (0.79 g ϵ‐caprolactone/L·h ) under nongrowing conditions (Walton, A. Z.; Stewart, J. D. Biotechnol. Prog. 2002, , 262–268). This is approximately 20‐fold higher than the space‐time yield for reactions that used growing cells of the same strain. Here, we show that the intracellular stability of cyclohexanone monooxygenase and the rate of substrate transport across the cell membrane were the key limitations on the overall reaction duration and rate, respectively. Directly measuring the levels of intracellular nicotinamide cofactors under bioprocess conditions suggested that E. coli cells could support even more efficient NADPH‐dependent bioconversions if a more suitable enzyme‐substrate pair were identified. This was demonstrated by reducing ethyl acetoacetate with whole cells of an E. coli strain that overexpressed an NADPH‐dependent, short‐chain dehydrogenase from bakerapos;s yeast ( Saccharomyces cerevisiae). Under glucose‐fed, nongrowing conditions, this reduction proceeded with a space‐time yield of 2.0 g/L·h and a final product titer of 15.8 g/L using a biocatalyst:substrate ratio (g/g) of only 0.37. These values are significantly higher than those obtained previously. Moreover, the stoichiometry linking ketone reduction and glucose consumption (2.3 ± 0.1) suggested that the citric acid cycle supplied the bulk of the intracellular NADPH under our process conditions. This information can be used to improve the efficiency of glucose utilization even further by metabolic engineering strategies that increase carbon flux through the pentose phosphate pathway.

Economical methods of supplying NADPH must be developed before biotransformations involving this cofactor can be considered for large‐scale applications. We have studied the enzymatic Baeyer–Villiger oxidation of cyclohexanone as a model for this class of reactions and developed a simple approach that uses whole, non‐growing Escherichia coli cells to provide high productivity (0.79 g ϵ‐caprolactone/L/h ≡ 18 μmol ϵ‐caprolactone/min/g dcw) and an 88% yield. Glucose supplied the reducing equivalents for this process, and no exogenous cofactor was required. The volumetric productivity of non‐growing cells was an order of magnitude greater than that achieved with growing cells of the same strain. Cells of an engineered E. coli strain that overexpresses Acinetobacter sp. cyclohexanone monooxygenase were grown under inducing conditions in rich medium until the entry to stationary phase; the subsequent cyclohexanone oxidation was carried out in minimal salts medium lacking a nitrogen source. After the biotransformation was complete, the lactone product was adsorbed to a solid support and recovered by washing with an organic solvent.