Glucobrassicin

Glucobrassicin is a type of glucosinolate that can be found in almost all cruciferous plants, such as cabbages, broccoli, mustards, and woad. As for other glucosinolates, degradation by the enzyme myrosinase is expected to produce an isothiocyanate, indol-3-ylmethylisothiocyanate. However, this specific isothiocyanate is expected to be highly unstable, and has indeed never been detected. The observed hydrolysis products when isolated glucobrassicin is degraded by myrosinase are indole-3-carbinol and thiocyanate ion (plus glucose, sulfate, and hydrogen ion), which are envisioned to result from a rapid reaction of the unstable isothiocyanate with water. However, a large number of other reaction products are known, and indole-3-carbinol is not the dominant degradation product when glucosinolate degradation takes place in crushed plant tissue[1] or in intact plants.[2][3]

Glucobrassicin
Names
IUPAC name
1-S-[(1Z)-2-(1H-Indol-3-yl)-N-(sulfooxy)ethanimidoyl]-1-thio-β-D-glucopyranose
Other names
Indol-3-ylmethylglucosinolate
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.231.968
UNII
  • InChI=1S/C16H20N2O9S2/c19-7-11-13(20)14(21)15(22)16(26-11)28-12(18-27-29(23,24)25)5-8-6-17-10-4-2-1-3-9(8)10/h1-4,6,11,13-17,19-22H,5,7H2,(H,23,24,25)/b18-12-/t11-,13-,14+,15-,16+/m1/s1 ☒N
    Key: DNDNWOWHUWNBCK-PIAXYHQTSA-N ☒N
  • c1ccc2c(c1)c(c[nH]2)C/C(=N/OS(=O)(=O)O)/S[C@H]3[C@@H]([C@H]([C@@H]([C@H](O3)CO)O)O)O
Properties
C16H20N2O9S2
Molar mass 448.46 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Glucobrassicin is also known to be a highly active egg-laying stimulant of cabbage white butterflies such as the small white (Pieris rapae) and the large white (Pieris brassicae).

Several derivatives of glucobrassicin are known. The compound itself was first isolated from Brassica plants, hence the ending of the name. When a second, similar natural product was discovered, it was named neoglucobrassicin. When further derivatives were discovered, a more systematic nomenclature was used. Currently, the following six derivatives are known from plants:

  • 1-Methoxyglucobrassicin (neoglucobrassicin)
  • 4-Hydroxyglucobrassicin
  • 4-Methoxyglucobrassicin
  • 1,4-Dimethoxyglucobrassicin
  • 1-Sulfoglucobrassicin
  • 6′-Isoferuloylglucobrassicin

The three first mentioned derivatives are as frequent in crucifers as glucobrassicin itself. The additional three derivatives appear to be rare in nature. 4-methoxyglucobrassicin was recently reported to be a signal molecule involved in plant defence against bacteria and fungi.[2][3]

Biosynthesis from tryptophan

The biosynthesis of glucobrassicin begins with tryptophan produced through several steps from the shikimic acid pathway compound, chorismic acid.[4] Tryptophan is converted to indole-3-acetaldoxime (IAOx) by cytochrome p450 enzymes (the redundant CYP92B3 and CYP79B3 in Arabidopsis thaliana) using NADPH and molecular Oxygen.[5] A separate p450 enzyme (CYP83B1 in Arabidopsis) catalyzes a second subsequent monooxygenase reaction to create a proposed the intermediate 1-aci-nitro-2-indolyl-ethane.[5] A cysteine is utilized by glutathione S-transferase (GST) in a conjugation process to produce an S-alkylthiohydroximate derivative, which is then cleaved off by a carbon–sulfur lyase (like the SUR1 enzyme found in Arabidopsis) to create a free thiol.[6] A single glucosylation occurs attaching a glucose molecule to the indole hydroximate through a thioether linkage. Finally, the hydroximate itself is sulfated creating glucobrassicin.[5]

Biosynthesis of glucobrassicin

See also

References
  1. Agerbirk, Niels; Vos, Martin; Kim, Jae Hak; Jander, Georg (2008). "Indole glucosinolate breakdown and its biological effects". Phytochemistry Reviews. 8: 101. doi:10.1007/s11101-008-9098-0.
  2. Clay, N. K.; Adio, A. M.; Denoux, C.; Jander, G.; Ausubel, F. M. (2009). "Glucosinolate Metabolites Required for an Arabidopsis Innate Immune Response". Science. 323 (5910): 95–101. Bibcode:2009Sci...323...95C. doi:10.1126/science.1164627. PMC 2630859. PMID 19095898.
  3. Bednarek, P.; Pislewska-Bednarek, M.; Svatos, A.; Schneider, B.; Doubsky, J.; Mansurova, M.; Humphry, M.; Consonni, C.; Panstruga, R.; Sanchez-Vallet, A.; Molina, A.; Schulze-Lefert, P. (2009). "A Glucosinolate Metabolism Pathway in Living Plant Cells Mediates Broad-Spectrum Antifungal Defense". Science. 323 (5910): 101–106. Bibcode:2009Sci...323..101B. doi:10.1126/science.1163732. PMID 19095900.
  4. Herrman, Klaus M.; Weaver, Lisa M. (1999). "The Shikimate Pathway". Annu. Rev. Plant Physiol. Plant Mol. Biol. 50: 473–503. doi:10.1146/annurev.arplant.50.1.473. PMID 15012217.
  5. Bender, Judith; Celenza, John L. (2008). "Indolic Glucosinolates at the Crossroads of Tryptophan Metabolism". Phytochem. Rev. 8: 25–37. doi:10.1007/s11101-008-9111-7.
  6. Mikkelsen, Michael; Naur, Peter; Halkier, Barbara (March 2004). "Arabidopsis Mutants in the C–S Lyase of Glucosinolate Biosynthesis Establish a Critical Role for Indole-3-acetaldoxime in Auxin Homeostasis". The Plant Journal. 37 (5): 770–777. doi:10.1111/j.1365-313x.2004.02002.x. PMID 14871316.

Further reading
  • Galletti, Stefania; Barillari, Jessica; Iori, Renato; Venturi, Gianpietro (2006). "Glucobrassicin enhancement in woad (Isatis tinctoria) leaves by chemical and physical treatments". Journal of the Science of Food and Agriculture. 86 (12): 1833. doi:10.1002/jsfa.2571.
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