(3-Oxo-3,4-dihydro-2H-benzo[1,4]oxazin-2-yl)-acetic acid2-(3-oxo-3,4-dihydro-2H-benzo[b][1,4]oxazin-2-yl)acetic acid3,4-Dihydro-3-oxo-2H-(1,4)-benzoxazin-2-yl-acetic acid3,4-二氢-3-氧代-2H-(1,4)-苯并噁嗪-2-基-乙酸(3-oxo-3,4-dihydro-2H-1,4-benzoxazin-2-yl)acetic acid