Compounds of the formula
1
wherein X
1
is C(O), —S(O)—, or —S(O)
2
—;
X
2
is CR
3
or N; X
3
is —NH—, —O—, or —S—;
X
4
is CR
4
or N; X
5
is CR
5
or N; and X
6
is CR
6
or N are useful as inhibitors of IMPDH enzyme. Thus, these compounds can be used as therapeutic agents for IMPDH-associated disorders.