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.