The invention is concerned with the compounds of formula (I):
and pharmaceutically acceptable salts thereof, wherein X, Y, Z, R
1
, R
2
, R
3
and R
3′
are defined in the detailed description and claims. In addition, the present invention relates to methods of manufacturing and using the compounds of formula I as well as pharmaceutical compositions containing such compounds. The compounds of formula I are LMP7 inhibitors and may be useful in treating associated inflammatory diseases and disorders such as, for example, rheumatoid arthritis, lupus and irritable bowel disease.