Purification of 2,5-anhydro-d-hexitol bis(phosphates) and identification of a major 1,4,6-tris(phosphate) contaminant by 31P-, 13C-, and 1H-N.M.R. spectroscopy

The reaction of two equivalents of diphenylchlorophosphate in cold pyridine with 2,5-anhydrohexitols has been assumed to result in only 1,6-bis(diphenylphosphate) products. However, by thin-layer, silica gel dry-column, and DEAE-Sephadex A-25 column chromatography, the products of this reaction have been shown to contain three major components; monophosphates (32 or 30%, by weight), 1,6-bis(phosphates) (40 or 56%), and 1,4,6-tris(phosphates) (28 or 14%): the former percentages for the product from 2,5-anhydro-d-mannitol (1) and the latter for the product from 2,5-anhydro-d-glucitol (10). The identity of each bis- and tris-(phosphate) of 1 or 10 was established by ³¹P- and ¹³C-n.m.r. spectroscopy. Acetylated bis- and tris-(diphenylphosphates) of 1 were also examined by ¹H-n.m.r. The significance of these findings on the interpretation of studies of the anomeric specificity of enzymes and on the specificity of the reagent diphenylchlorophosphate are discussed. The formation of only a 1,4,6-tris(phosphate) of 10 suggests that the 1,6-bis(diphenylphosphate) of 10 may undergo formation of a 1,3-cyclic phosphate triester by transesterification with elimination of phenol. A method for the determination of the number of cyclohexylammonium groups crystallizing with a sugar phosphate is proposed that simplifies the elemental analysis of this type of salt.