Synthesis and X-ray structures of sulfate esters of fructose and its isopropylidene derivatives. Part 1: 2,3:4,5-di-O-isopropylidene-β-d-fructopyranose 1-sulfate and 4,5-O-isopropylidene-β-d-fructopyranose 1-sulfate Original Research Article

2,3:4,5-Di-O-isopropylidene-β-d-fructopyranose 1-sulfate have been synthesized by treatment of 2,3:4,5-di-O-isopropylidene-β-d-fructopyranose with pyridine–sulfur trioxide complex. Direct hydrolysis of the isopropylidene group at C-4, C-5 gave 2,3-O-isopropylidene-β-d-fructopyranose 1-sulfate. The crystal and molecular structures of ammonium (1a) and potassium (1b) salts of diisopropylidene derivative and ammonium (2) salt of monoisopropylidene derivative were determined by X-ray crystallography. Data for 1a and 1b were collected in 120 K and in 150 K for 2. All salts crystallized in P212121 space group. There are three independent anions in asymmetric unit in 1b. Pyranose rings in the diisopropylidene derivative salts studied adopt 2S0 twist boat conformation, whereas in the monoisopropylidene exists in a slightly distorted chair conformation (4C1). A staggered conformation is preferred by the sulfate group as indicated by values of CO(ester)SO(terminal) torsion angles: −173.2(4)° in 1a, 175.1(6)° in anion A of 1b, 170.8(6)° in anion C of 1b and 177.9(2)° in 2. However, strong interactions such as potassium–oxygen and H-bonds may affect the geometry: in anion B of 1b the value of the torsion angle is 139.4(6)°.