2-phosphorylation of D-erythorbic acid using phosphoryl chlorid

A stabilized form of D-erythorbic acid, D-erythorbate 2-O-phosphate (3) was prepared by phosphorylation of 5,6-O-isopropylidene-D-erythorbate (6) with phosphoryl chloride at high pH in the presence of pyridine.;Reverse-phase LC-UV analysis and ion-exchange column chromatography indicated that a mixture of four phosphoric esters were produced in the phosphorylation reaction. Two of the products were found to be the 2-monophosphate ester (3) and bis-(D-erythorbyl) 2,2$spprime$-phosphate (5). The third product was tentatively identified as 2-pyrophosphate (7) of D-erythorbic acid (1) while the fourth was not identified.;After hydrolytic cleavage of the 5,6-acetal group and removal of inorganic phosphate and chloride, compound (3) was isolated in 67% yield as its crystalline magnesium salt. Compounds 5 and 7 accounted for over 13% of the phosphorylated products. The magnesium salt was purified by ion exchange chromatography to give pure 3 isolated as its tricyclohexylammonium salt. The structures of the phosphoric esters were established by UV and NMR spectroscopy ($sp{31}$P and $sp1$H), and in the case of the monophosphate (3) and phosphodiester (5), by elemental analysis.;When D-erythorbic acid (1) was reacted with phosphoryl chloride (1.5 equivalents) at pH 9.5-10.5 (by addition of barium hydroxide) without the presence of pyridine, it was possible to remove solid barium phosphate and then to crystallize barium bis-(D-erythorbyl) 2,2$spprime$-phosphate from the cold aqueous solution of the reaction mixture. Preliminary data showed D-erythorbate 2-phosphate inhibited browning of freshly cut apples and potatoes.