Chemo-enzymatic synthesis of isotopically labeled nicotinamide riboside

As a cofactor for numerous reactions, NAD(+) is found widely dispersed across many maps of cellular metabolism. This core redox role alone makes the biosynthesis of NAD(+) of great interest. Recent studies have revealed new biological roles for NAD(+) as a substrate for diverse enzymes that regulate a broad spectrum of key cellular tasks. These NAD(+)-consuming enzymes further highlight the importance of understanding NAD(+) biosynthetic pathways. In this study, we developed a chemo-enzymatic synthesis of isotopically labeled NAD(+) precursor, nicotinamide riboside (NR). The synthesis of NR isotopomers allowed us to unambiguously determine that NR is efficiently converted to NAD(+) in the cellular environment independent of degradation to nicotinamide, and it is incorporated into NAD(+) in its intact form. The versatile synthetic method along with the isotopically labeled NRs will provide powerful tools to further decipher the important yet complicated NAD(+) metabolism.