Non-injured maize contains several 1,4-benzoxazin-3-one related compounds but only as glucoconjugates

DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) and its derivatives are known to participate in the resistance of the Poaceae to several pests. A more efficient analytical method for the determination of these compounds is reported, employing high performance liquid chromatography coupled with UV and atmospheric pressure chemical ionisation–tandem mass spectrometric detection. The results showed that in non-injured 5 or 15-day-old plants only the glucosylated forms of DIMBOA and related compounds were present: aglycones were only detected when enzymatic deglucosylation occurred during sample work-up. Maize plants contain seven glucosides related to DIMBOA belonging to three classes: hydroxamates, lactams and N-O-methylated hydroxamate derivatives. Rarely reported dimethoxylated compounds and 8-methoxy-N-O-methylated DIMBOA are now reported in the Poaceae, the latter for the first time. Their presence and relative concentrations in 5 and 15-day-old maize roots and aerial parts are discussed. The non-hydroxamic N-O-methylated DIMBOA is present in the plant in significant quantities which exceed all others in 15-day-old maize roots. After enzymatic degradation, deglucosylation products from hydroxamates and lactams are observed. The N-O-methylated deglucosylated compounds are not observed as they are chemically degraded, most probably to benzoxazolinone derivatives. The results reported here provide a new view on the DIMBOA-related compounds present in maize plants, and the implications of these findings are discussed.