Phosphorylated sugars. Part 27. Synthesis and reactions, in acid medium, of 5-O-substituted methyl 3-deoxy-α-D-manno-oct-2-ulopyranosidonic acid 4-phosphates

Abstract

Synthesis of the α-methyl glycosides of 5-O-methyl-, 5-O-benzyl-8-O-methyl-, and 5,7,8-tri-O-methyl-3-deoxy-D-manno-oct-2-ulosonic acid 4-phosphates are described. The corresponding ‘reducing’ glycose, formed upon hydrolysis at pH 4 and 100 °C, immediately eliminates the phosphate group. The olefinic acids thus produced from 5-O-methyl-, and from 5-O-benzyl-8-O-methyl 4-phosphates are not stable under these conditions: they are transformed into 4,7- and 4,8 -anhydro-derivatives which have no ethylenic protons and show negligible absorption in the region 220–300 nm. The olefinic acid produced from the 5,7,8-tri-O-methyl derivative is unable to form such an anhydro-derivative: two ethylenic protons are present in its ¹H NMR spectrum and, like other conjugated olefinic α-keto acids, it has a strong UV absorption band (λ_max 235 nm, ε 8000).