Characterization of cyclic ADP-ribose and 2′-phospho-cyclic-ADP-ribose by 31P NMR spectroscopy

Aberrant cyclization affords a C-6 modified cyclic adenosine 5'-diphosphoribose analogue with biological activity in Jurkat T cells

Two nicotinamide adenine dinucleotide (NAD(+)) analogues modified at the 6 position of the purine ring were synthesized, and their substrate properties toward Aplysia californica ADP-ribosyl cyclase were investigated. 6-N-Methyl NAD(+) (6-N-methyl nicotinamide adenosine 5'-dinucleotide 10) hydrolyzes to give the linear 6-N-methyl ADPR (adenosine 5'-diphosphoribose, 11), whereas 6-thio NHD(+) (nicotinamide 6-mercaptopurine 5'-dinucleotide, 17) generates a cyclic dinucleotide. Surprisingly, NMR correlation spectra confirm this compound to be the N1 cyclic product 6-thio N1-cIDPR (6-thio cyclic inosine 5'-diphosphoribose, 3), although the corresponding 6-oxo analogue is well-known to cyclize at N7. In Jurkat T cells, unlike the parent cyclic inosine 5'-diphosphoribose N1-cIDPR 2, 6-thio N1-cIDPR antagonizes both cADPR- and N1-cIDPR-induced Ca(2+) release but possesses weak agonist activity at higher concentration. 3 is thus identified as the first C-6 modified cADPR (cyclic adenosine 5'-diphosphoribose) analogue antagonist; it represents the first example of a fluorescent N1-cyclized cADPR analogue and is a new pharmacological tool for intervention in the cADPR pathway of cellular signaling.

Rapid synthetic route toward structurally modified derivatives of cyclic adenosine 5'-diphosphate ribose

A concise synthesis of five new analogues of the second messenger cADPR (cyclic adenosine 5'-diphosphate ribose) is presented. The synthetic plan centered around the key derivative 8-Br-N1-cIDPR (cyclic 8-Br-inosine 5'-diphosphate ribose, 2), which was prepared in only three steps from IMP (inosine 5'-monophosphate) via an unusual enzymatic cyclization reaction. The enhanced stability of 2 allowed for the direct modification of this cyclic dinucleotide at the 8 position, providing the unsubstituted parent N1-cIDPR (4) as well as the 8-phenyl (5), 8-azido (6), and 8-amino (7) N1-cIDPR analogues. In Jurkat T-lymphocytes, N1-cIDPR 4 induced Ca2+ release with an almost identical profile as the natural agonist cADPR, illustrating the value of this approach.

NMR studies and semi-empirical energy calculations for cyclic ADP-ribose

A possible pH-dependent conformational switch was investigated for cyclic ADP-ribose. NMR signals for the exchangeable protons were observed in H2O at low temperature, but there was no direct evidence for the protonation of N-3 at neutral pH that has previously been postulated. MNDO calculations indicated that pH dependent 31P chemical shift changes are attributable to protonation of the phosphate adjacent to the N-1 of adenine, and not due to trans-annular hydrogen bonding with a protonated N-3.

Bioorganic chemistry of cyclic ADP-ribose (cADPR)

The objective of this brief review is to present an overview of the bioorganic chemistry of cyclic-ADP-ribose (cADPR) with special emphasis on the methodology used for the synthesis of analogues of cADPR. New structural analogues of cADPR can be prepared using either the biomimetic method or ADP-ribosyl cyclase from Aplysia californica. For the most part, both procedures give similar product profiles, but higher yields are generally obtained with the enzymatic method. These synthetic methodologies have allowed the transformation of a variety of structurally modified analogues of NAD+ into their corresponding cyclic nucleotides. Several of these novel analogues are more potent than cADPR in inducing calcium release and are also more stable towards degradative enzymes. They could serve as valuable affinity probes for the isolation of cADPR-binding proteins.