nicotinamide adenine dinucleotide biosynthetic pathway NAD biosynthetic pathway NAD biosynthetic process PW:0000219 Those metabolic reactions involved in the synthesis of nicotinamide adenine dinucleotide (NAD). NAD can be synthesized de novo downstream of kynurenine metabolism of tryptophan degradation, or from precursors such as nicotinamide, nicotinic acid or nicotinamide riboside, collectively known as vitamin B3 or niacin. pathway nicotinamide adenine dinucleotide metabolic pathway