D-6-Deoxy-ntyo-inositol 1,3,4,5-tetrakisphosphate [D-6-deoxy-Ins(l,3,4,5)P-4] 3 is a novel deoxygenated analogue of D-myo-inositol 1,3,4,5-tetrakisphosphate [Ins(1,3,4,5)P-4] 2, a central and enigmatic molecule in the polyphosphomositicle pathway of cellular signalling. D-6-Deoxy-Ins(1,3,4,5)P-4 is a moderate inhibitor of Ins(1,4,5)P-3 5-phosphatase [1.8 muM] compared to Ins(1,3,4,5)P-4 [0.15 muM] and similar to that of L-Ins(1,3,4,5)P-4 [1.8 muM]. In displacement of [H-3] Ins(1,4,5)P-3 from the rat cerebellar Ins(1,4,5)P-3 receptor, while slightly weaker [IC50 = 800 nM] than that of D-Ins(1,3,4,5)P-4 [IC50 = 220 nM], 3 is less markedly different and again similar to that of L-Ins(1,3,4,5)P-4 [IC50 = 660 nM]. 3 is an activator of I-CRAC when inward currents are measured in RBL-2H3-M1 cells using patch-clamp electrophysiological techniques with a facilitation curve different to that of Ins(1,3,4,5)P-4. Physicochemical properties were studied by potentiometric P-31 and H-1 NMR titrations and were similar to those of Ins(1,3,4,5)P-4 apart from the observation of a biphasic titration curve for the P1 phosphate group. A novel vicinal phosphate charge-induced conformational change of the inositol ring above pH 10 was observed for D-6-deoxy-Tns(1,3,4,5)P4 that would normally be hindered because of the central stabilising role played by the 6-OH group in Ins(1,3,4,5)P-4. We conclude that the 6-OH group in Ins(1,3,4,5)P-4 is crucial for its physicochemical behaviour and biological properties of this key inositol phosphate. (C) 2004 Elsevier Inc. All rights reserved.