The invention is directed to substituted benzothiadiazine derivatives. Specifically, the invention is directed to compounds according to Formula (I):wherein R, R1, R2, R3, R4 and R5 are as defined herein. The compounds of the invention are inhibitors of CD73 and can be useful in the treatment of cancer, pre-cancerous syndromes and diseases associated with CD73 inhibition, such as AIDS, autoimmune diseases, infections, atherosclerosis, and ischemia-reperfusion injury. Accordingly, the invention is further directed to pharmaceutical compositions comprising a compound of the invention. The invention is still further directed to methods of inhibiting CD73 activity and treatment of disorders associated therewith using a compound of the invention or a pharmaceutical composition comprising a compound of the invention.