The present invention provides a compound represented by the following formula (1): wherein X1 and X2 each independently represent a hydrogen atom or a hydroxyl-protecting group; Y represents a C7-20 aralkyl group which may optionally have one or more substituents selected from a halogen atom, a lower alkyl group or a lower alkoxy group; and Z represents a halogen atom, a C1-4 alkylthio, or an arylthio group, or its corresponding sulfoxide group.