This invention provides caspase inhibitors of formula I:
wherein Z is oxygen or sulfur; R
1
is hydrogen, —CHN
2
, R, CH
2
OR, CH
2
SR, or —CH
2
Y;
between R
3
and R
4
represents a single or double bond; Y is an electronegative leaving group; R
2
is CO
2
H, CH
2
CO
2
H, or esters, amides or isosteres thereof; R
3
is a group capable of fitting into the S2 subsite of a caspase enzyme; R
4
is a hydrogen or C
1-6
alkyl or R
3
and R
4
taken together form a ring; Ring A and Ring B are each heterocyclic rings, and R and R
5
are as described in the specification. The compounds are effective inhibitors of apoptosis and IL-1β secretion.