Glucosinolates, reactions

Biosynthesis of glucosinolates (reaction 17.10) starts from the corresponding amino acids, and proceeds via an oxime (I) and thiohydroximic acid (III). The intermediate reactions between... 

Lazzeri L, Tacconi R and Palmieri S (1993), In vitro activity of some glucosinolates and their reaction products toward a population of the nematode Heterodera schachtii , J Agric Food Chem, 41, 825-829. 

These reactions to 4-methylthiobutyl glucosinolate, the precursor for sulforaphane formation, have been extensively studied in Eruca sativa (arugula, rocket).64 A gene controlling variation in the glucosinolates of Arabidopsis is part of the methionine elongation pathway just described.65... 

S-Nucleophiles are very reactive in 1,3-addition reactions with nitrile oxides. A series of a-glucosinolates 27 (R = CR1=NOH R1 =Ph, CH2PI1, CH2CH2PI1, ( )-CH=CHPh, 3-indolylmethyl) was prepared by addition reactions of thiol 27 (R = H) with nitrile oxides (123). The indolyl-substituted glucosinolate was then converted to a-glucobrassicin 28. 

Figure 13.2 Biosynthetic pathways of (A) cyanogenic glucosides and (B) glucosinolates. The CYP79s are assumed to catalyze the same reaction in both pathways. It is not known whether the oxime is oxidized to an aci-nitro compound or a nitrile oxide in the glucosinolate pathway.

Skutlarek D, Faerber H, lippert F, Ulbrich A, Wawrzun A, Buening-Pfaue H (2004) Determination of glucosinolate profiles in Chinese vegetables by precursor ion scan and multiple reaction monitoring scan mode (LC-MS/MS). Eur Food Res Technol 219 643-649... 

Trimethylsilylation normally proceeds without any change in the carbohydrate, but glucosinolates have been found126 to undergo desulfation during the reaction it was also observed that, even though trimethylsilylation was conducted overnight at 105°, only 80% reaction was obtained. 

Volatile compounds formed by anabolic or catabolic pathways include fatty acid derivatives, terpenes and phenolics. In contrast, volatile compounds formed during tissue damage are typically formed through enzymatic degradation and/ or autoxidation reactions of primary and/or secondary metabolites and includes lipids, amino acids, glucosinolates, terpenoids and phenolics. 

Indolic glucosinolates have been reported in Balis marilinta, but a test of this species did not give a reaction with DragendorfT s reagent. 

A major proportion of the glucosinolate hydrolysis products formed upon myrosinase cleavage in some plants are nitriles. In vitro, nitrile formation associated with myrosinase-catalyzed hydrolysis is enhanced at low pH (pH<3) and in the presence of ferrous ions. In vivo, protein factors in addition to myrosinase may be responsible for nitrile formation. If the glucosinolate side chain has a terminal double bond, the sulfur released from the thioglucosidic bond may be captured by the double bond and an epithionitrile is formed.9 This reaction takes place only in plants that possess a protein factor known as epithiospecifier protein (ESP). ESP activities have been identified in several species of the Brassicaceae and shown to influence the outcome of the myrosinase-catalvzed hydrolysis reaction although they have no hydrolytic activity by themselves.10 12 The mechanism by which ESPs promote epithionitrile formation is not known. 

The reaction products depend on pH and other factors such as the presence of ferrous ions, epithiospecifier protein, and the nature of the glucosinolate side chain. Epithiospecifier protein has recently been independently purified and characterized7,8 and appears to require ferrous ions indicating the formation of an organometallic (FeN - aglycone) intermediate that leads to die formation of a thiirane ring. 

Figure 3.15 Mustard oil formation. After hydrolysis of glucosinolates, the unstable intermediates rearrange. In general, the main reaction products are isothiocyanates, but nitriles and thiocyanates are also produced.

Figure 2. Enzymatic and nonenzymatic reactions of glucosinolates Enzymatic Cleavage of Glucosinolates to Isothiocyanates...

Another goitrogenic compound in cabbage is thiocyanate ion (107) which results from breakdown of indolylmethyl isothiocyanate produced from the corresponding glucosinolate, glucobrassicin (97,106,108) (reaction G). The 5-hydroxymethylindole thus produced can dimerize to 3,3 -diindolylmethane or form a complex (ascorbigen) with ascorbic acid (perhaps a novel type of feedback inhibition of ascorbate-dependent... 

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