The elusive indigo precursors in woad (Isatis tinctoria L.)--identification of the major indigo precursor, isatan A, and a structure revision of isatan B.

Abstract

A metabolite-profiling study of shock-frozen leaves of Isatis tinctoria L., an old indigo dye plant and medicinal herb, revealed a complex pattern of indigo-forming compounds with higher polarities than the known indigo precursors isatan B and indican. These highly unstable compounds underwent rapid post-harvest transformation and were not detected in air-dried leaves. The major indigo precursor, named isatan A (4), was isolated by rapid normal-phase and gel chromatography, along with isatan B (3). A full spectral data set of 3 showed that the previous structure assignment as 'indoxyl-5-ketogluconate' has to be revised to 1H-indol-3-yl beta-D-ribohex-3-ulopyranoside. Isatan A (4) was identified as 1H-indol-3-yl 6'-O-(carboxyacetyl)-beta-D-ribohex-3'-ulopyranoside. In aqueous solution, glycosides 3 and 4 occur as hydrates and undergo rapid hydrolysis under very mild acidic or basic conditions.

• Authors: Christine Oberthür, Bernd Schneider, Heidemarie Graf, Matthias Hamburger
• Journal: Chemistry & biodiversity (Chem Biodivers) Vol. 1 Issue 1 Pg. 174-82 (Jan 2004) ISSN: 1612-1880 [Electronic] Switzerland
• PMID: 17191785 (Publication Type: Comparative Study, Journal Article)

Chemical References

• Glycosides
• Indoles
• Plant Extracts
• indoxyl-3-O-(6'-O-malonyl-beta-D-ribohexo-3-ulopyranoside)
• isatan B
• Indigo Carmine

Topics

• Glycosides (chemistry, isolation & purification)
• Indigo Carmine
• Indoles (chemistry, isolation & purification)
• Isatis
• Plant Extracts (chemistry, isolation & purification)
• Plant Leaves