Hydroxamic acid derivative

A compound represented by the following formula (II):

• ##STR31## each character in this formula means as follows;
• R.sup.1 :
• a lower alkyl group which may be substituted by a substituent group selected from the class consisting of a mercapto group, a lower alkylthio group, an arylthio group and a lower acylthio group,
• R.sup.2, R.sup.3 and R.sup.4 :
• the same or different from one another and each represents a lower alkyl group,
• X:
• an oxygen atom or a sulfur atom,
• Y:
• a single bond or a lower alkylene group, a salt thereof or a stereoisomer thereof.