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The Elusive Indigo Precursors in Woad ( Isatis tinctoria L.) – Identification of the Major Indigo Precursor, Isatan A, and a Structure Revision of Isatan B
Author(s) -
Oberthür Christine,
Schneider Bernd,
Graf Heidemarie,
Hamburger Matthias
Publication year - 2004
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200490009
Subject(s) - indigo , chemistry , glycoside , herb , hydrolysis , chromatography , botany , stereochemistry , organic chemistry , medicinal herbs , traditional medicine , biology , art , visual arts , medicine
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 1 H ‐indol‐3‐yl β ‐ D ‐ribohex‐3‐ulopyranoside. Isatan A ( 4 ) was identified as 1 H ‐indol‐3‐yl 6′‐ O ‐(carboxyacetyl)‐ β ‐ 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.