Aplysia californica mediated cyclisation of novel 3′-modified NAD+ analogues: a role for hydrogen bonding in the recognition of cyclic adenosine 5′-diphosphate ribose Original Research Article

Cyclic ADP-ribose mobilizes intracellular Ca2+ in a variety of cells. To elucidate the nature of the interaction between the C3′ substituent of cADP-ribose and the cADPR receptor, three analogues of NAD+ modified in the adenosine ribase (xyloNAD+ 3′F-xyloNAD+ and 3′F-NAD+ were chemically synthesised from d-xylose and adenine starting materials. 3′F-NAD+ was readily converted to cyclic 3′F-ADP ribose by the action of the cyclase enzyme derived from the mollusc Aplysia californica. XyloNAD+ and 3′F-xyloNAD+ were cyclised only reluctantly and in poor yield to afford unstable cyclic products. Biological evaluation of cyclic 3′F-ADP ribose for calcium release in sea urchin egg homogenate gave an EC50 of 1.5±0.5 μM. This high value suggests that the ability of the C3′ substituent to donate a hydrogen bond is crucial for agonism.