The present invention provides a compound represented by formula (1) (wherein each of X1 and X2 independently represents -OR1, -NR2R3 or -CR4R5R6 or the like, each of R1, R2, R3, R4, R5 and R6 independently represents an unsubstituted or substituent-bearing glycosyl group or an unsubstituted or substituent-bearing C1 to C30 alkyl group or the like, and A represents an unsubstituted or substituent-bearing C1 to C30 alkyl group or the like) or a salt thereof.