Abstract: There are provided a novel compound having irreversible inhibitory activity against neuraminidase, a therapeutic agent and a detection agent for a disease involving neuraminidase. A compound represented by the following formula (I) and a salt thereof, a production method thereof, and an application method thereof, wherein: A1 represents an aryl group optionally having a substituent group or a heteroaryl group optionally having a substituent group; A2 represents —CX2R6 or —CHXR6 wherein X represents —F, —Cl, —Br, or —I; R1 represents a hydrogen atom or an alkyl group optionally having a substituent group; R2, R3, R4, and R5 represent each independently —OC(?O)R6, —OR6, —N(R6)2, —N3, —NHC(?NH)NHR6, —NHCOR6, —OSO3R6, —OPO3(R6)2, F, Cl, Br, or I; and R6 represents each independently a hydrogen atom, an alkyl group optionally having a substituent group, an aryl group optionally having a substituent group, or an optionally substituted heteroaryl group.