The present invention provides compounds of Formula (I): wherein the substituents are as defined in the specification, and compositions comprising any of such novel compounds. These compounds are myeloperoxidase (MPO) inhibitors and/or eosinophil peroxidase (EPX) inhibitors, and may be useful for for the treatment and/or prophylaxis of atherosclerosis, heart failure, chronic obstructive pulmonary disease (COPD), and related diseases.