A compound of the formula (I):
##STR1##
- wherein X1 and X2 are the same or different and
each is a bond or a spacer having 1 to 20 atom(s) in the main chain;
- one of R1 and R2 is a cycle group having substituent(s)
selected from 1) an optionally substituted carboxy-C1-6 alkoxy group
and 2) an optionally substituted carboxy-C1-6 aliphatic hydrocarbon
group, wherein the cycle group optionally has additional substituent(s), and the
other is an optionally substituted cycle group or a hydrogen atom; and
- R3, R4 and R5 are the same or different
and each is a hydrogen atom or a substituent, or R4 may link together
with R3 or R5 to form an optionally substituted ring;
- provided that when R3 is a hydrogen atom, R4 is
a hydrogen atom and R5 is methyl, X2-R2 is not
4-cyclohexylphenyl; when R3 is 4-methoxyphenyl, R4 is a hydrogen
atom and R5 is methyl, X2-R2 is not 4-methoxyphenyl;
and when R1 or R2 is a hydrogen atom, the adjacent X1
or X2 is not a C1-7 alkylene;
- or a salt thereof exhibits a protein tyrosine phosphatase inhibitory
action and is useful as a prophylactic or therapeutic agent for diabetes or the like.
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