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An Intermediate in the Synthesis of Glucobrassicins from 3-Indoleacetaldoxime by Woad Leaves ¹

^a Department of Biology, Kline Biology Tower, Yale University, New Haven, Connecticut 06520

Leaves of woad (Isatis tinctoria L.) were found to incorporate efficiently tritiated indoleacetaldoxime and ³⁵S from ³⁵S-L-cystine into glucobrassicin and sulfoglucobrassicin. Time course of incorporation of ³⁵S from ³⁵S-cystine into the glucosinolates indicated that glucobrassicin was formed first and then sulfoglucobrassicin. Simultaneous administration of tritiated indoleacetaldoxime and ³⁵S-cystine gave doubly labeled glucobrassicin and sulfoglucobrassicin. About twice as much ³⁵S was present in sulfoglucobrassicin as compared to glucobrassicin per unit of ³H incorporated, indicating that a second, probably oxidized, atom of ³⁵S was later introduced into sulfoglucobrassicin. However, the ³⁵S incorporated from cystine into both glucosinolates during the first 8 hours of metabolism was almost exclusively in the divalent sulfur moiety. The incorporation patterns of ³⁵S and titritated indoleacetaldoxime into the glucosinolates suggested a fast turnover of glucobrassicin in the metabolizing leaves.

A new indolic, sulfur-containing neutral compound X was found to accumulate in woad leaves when administered ³H-3-indoleacetaldoxime and cold cystine or ³⁵S-cystine and cold 3-indoleacetaldoxime. This accumulation was enhanced about 2- to 2.5-fold by the simultaneous administration of postassium selenate, an inhibitor of biological sulfation processes. Selenate also appeared to inhibit the conversion of glucobrassicin to 1-sulfoglucobrassicin. Partially purified compound X was efficiently converted (56-60%) to glucobrassicin and 1-sulfoglucobrassicin on readministration to woad leaves, indicating it to be a precursor of the glucosinolates. Compound X, on treatment with myrosinase, slowly yielded a less polar, indolic, sulfur containing compound Y and glucose. Compound Y decomposed with time into indoleacetonitrile suggesting that it may be indoleacetothiohydroximate. Compound X has been tentatively assigned the structure of desthioglucobrassicin, the nonsulfated form of glucobrassicin.

¹ This work was supported by United State Public Health Service Research Grant GM-06921 from the National Institutes of Health to B. B. Stowe.