The compound of claim 2, whereinR1 is alkanoyloxy or alkenoyloxy, R2 is alkyl or alkenyl, R3 is hydroxy(lower)alkyl, R5 is carboxy(lower)alkyl or esterified carboxy(lower)alkyl, R6 is carboxy or esterifed carboxy, A1 and A2 are each bond or lower alkylene, m is an integer of 1 and n is an integer of 0. 4.