This invention provides compounds defined by Formula I or a pharmaceutically acceptable salt thereof,wherein R1, Q, Y2, Y3, Y4, U5, U6, U8, and R2 are as defined in the specification. The invention also provides pharmaceutical compositions comprising a compound of Formula I, or a pharmaceutically acceptable salt thereof, as defined in the specification, together with a pharmaceutically acceptable carrier, 
diluent, or 
excipient. The invention also provides methods of inhibiting an MMP-13 
enzyme in an animal, comprising administering to the animal a compound of Formula I, or a pharmaceutically acceptable salt thereof. The invention also provides methods of treating a 
disease mediated by an MMP-13 
enzyme in a patient, comprising administering to the patient a compound of Formula I, or a pharmaceutically acceptable salt thereof, either alone or in a pharmaceutical composition. The invention also provides methods of treating diseases such as 
heart disease, 
multiple sclerosis, osteo- and 
rheumatoid arthritis, 
arthritis other than osteo- or 
rheumatoid arthritis, cardiac insufficiency, 
inflammatory bowel disease, 
heart failure, age-related 
macular degeneration, chronic obstructive 
pulmonary disease, 
asthma, periodontal diseases, 
psoriasis, atherosclerosis, and 
osteoporosis in a patient, comprising administering to the patient a compound of Formula I, or a pharmaceutically acceptable salt thereof, either alone or in a pharmaceutical composition. The invention also provides combinations, comprising a compound of Formula I, or a pharmaceutically acceptable salt thereof, together with another pharmaceutically 
active component as described in the specification.