Reverse hydroxamic acid derivatives having specific structure represented by a general formula (Ia):
1
(wherein A is a hydrogen atom or the like; Ar
1
is an arylene or the like; Ar
2
is an optionally substituted aryl, a heteroaryl or the like; R
1
is a hydrogen atom, an alkyl or the like; R
2a
is a substituted cycloaryl, a heterocycloaryl or the like) and a general formula (I):
2
(wherein A, Ar
1
, Ar
2
, and R
1
are the same as defined above and R
2
is an hydrogen atom, R
2a
or the like) and salts thereof, which have TNF-&agr; converting enzyme (TACE) inhibitory activity.