Glycoside carbamates from benzoxazolin-2(3H)-one detoxification in extracts and exudates of corn roots

Zea mays was incubated with the natural phytotoxin benzoxazolin-2(3H)-one ( BOA) to investigate the detoxification process. A hitherto unknown detoxifi cation product, 1-(2-hydroxyphenylamino)-1-deoxy-beta -gentiobioside 1,2-ca rbamate (3), was isolated and identified. A reinvestigation of known BOA de toxification products by NMR methods led to the finding that the structure of benzoxazolin-2(3H)-one-N-beta -glucoside (1) first reported from Avena s ativa has to be revised. In fact, the correct structure is that of the isom eric 1-(2-hydroxyphenylamino)-1-deoxy-beta -glucoside 1,2-carbamate 2, whic h is structurally related to 3. It was now shown with a synthetic mixture o f I and 2 that I underwent spontaneous isomerization to form 2 in solution. Thus, N-glucosylation of BOA in the plant led finally to the carbamate 2. In contrast to BOA-6-O-glucosylation, BOA-induced N-glucosylation appears f irst after 6-8 h of incubation. As soon as N-glucosylation is possible, BOA -6-O-glucoside is not further accumulated, whereas the amount of glucoside carbamate increases continuously during the next 40 h. Synthesis of gentiob ioside carbamate seems to be a late event in BOA detoxification. All detoxi fication products are released into the environment via root exudation. (C) 2001 Elsevier Science Ltd. All rights reserved.