Cyclic ADP Ribose, frequently abbreviated as cADPR, is a cyclic adenine nucleotide (like cAMP) with two phosphate groups present on 5' OH of the adenosine (like ADP), further connected to another ribose at the 5' position, which, in turn, closes the cycle by glycosidic bonding to the nitrogen 1 (N) of the same adenine base (whose position N has the glycosidic bond to the other ribose). The N-glycosidic bond to adenine is what distinguishes cADPR from ADP-ribose (ADPR), the non-cyclic analog. cADPR is produced from nicotinamide adenine dinucleotide (NAD) by ADP-ribosyl cyclases (EC 3.2.2.5) as part of a second messenger system.