A CONFORMATIONALLY RESTRICTED CYCLIC PHOSPHATE ANALOG OF INOSITOL TRISPHOSPHATE - SYNTHESIS AND PHYSICOCHEMICAL PROPERTIES

The design and total synthesis of DL-6-deoxy-6-(hydroxymethyl)-scyllo- inositol 1:7-cyclic 2,4-trisphosphate (4), a conformationally restrict ed cyclic phosphate analogue of the second messenger inositol 1,4,5-tr isphosphate [Ins(1,4,5)P-3], is described. The protected inosose (p-me thoxybenzyl)-2,4,6-O-methylidynecyclohexanone (7) was obtained from my oinositol orthoformate in two steps, and Wittig methylenation and then hydroboration-oxidation using 9-BBN-H/OH-/H2O2 gave the axial hydroxy methyl derivative 9. A series of protection/ deprotection steps provid ed the diol 13, which was converted into two cyclic phosphate esters 1 4a and 14b, epimeric at phosphorus, by reaction with (benzyloxy)bis(N, N-diisopropylamino)phosphine /1H-tetrazole followed by m-CPBA. Two oth er hydroxyl groups were then exposed and phosphorylated, and total dep rotection gave racemic 4. NMR studies confirmed that in 4 the phosphat e group equivalent to the 4-phosphate of Ins(1,4,5)P-3 is held in the positive gauche orientation and that the inositol ring maintains a cha ir conformation from pH 2 to 12. Investigation of the acid-base proper ties of 4 using potentiometric and P-31 NMR techniques showed that, ov er the physiological pH range, 4 behaves as a diprotic acid and that t he ionization of the phosphate group equivalent to the 5-phosphate of Ins(1,4,5)P-3 is enhanced. In biological assays, 4 appears to behave a s a weak full agonist at the platelet Ins(1,4,5)P-3 receptor, and the possible interpretation of this result is discussed.