2′-Deoxy Cyclic Adenosine 5′-Diphosphate Ribose Derivatives: Importance of the 2′-Hydroxyl Motif for the Antagonistic Activity of 8-Substituted cADPR Derivatives

The structural features needed for antagonism at the cyclic ADP-ribose (cADPR) receptor are unclear. Chemoenzymatic syntheses of novel 8-substituted 2′-deoxy-cADPR analogues, including 8-bromo-2′-deoxy-cADPR <b>7</b>, 8-amino-2′-deoxy-cADPR <b>8</b>, 8-<i>O</i>-methyl-2′-deoxy-cADPR <b>9</b>, 8-phenyl-2′-deoxy-cADPR <b>10</b> and its ribose counterpart 8-phenyl-cADPR <b>5</b> are reported, including improved syntheses of established antagonists 8-amino-cADPR <b>2</b> and 8-bromo-cADPR <b>3</b>. Aplysia californica ADP-ribosyl cyclase tolerates even the bulky 8-phenyl-nicotinamide adenine 5′-dinucleotide as a substrate. Structure−activity relationships of 8-substituted cADPR analogues in both Jurkat T-lymphocytes and sea urchin egg homogenate (SUH) were investigated. 2′-OH Deletion decreased antagonistic activity (at least for the 8-amino series), showing it to be an important motif. Some 8-substituted 2′-deoxy analogues showed agonist activity at higher concentrations, among which 8-bromo-2′-deoxy-cADPR <b>7</b> was, unexpectedly, a weak but almost full agonist in SUH and was membrane-permeant in whole eggs. Classical antagonists <b>2</b> and <b>3</b> also showed previously unobserved agonist activity at higher concentrations in both systems. The 2′-OH group, without effect on the Ca²⁺-mobilizing ability of cADPR itself, is an important motif for the antagonistic activities of 8-substituted cADPR analogues