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

Abstract

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 P2 12 12 1 space group. There are three independent anions in asymmetric unit in 1b. Pyranose rings in the diisopropylidene derivative salts studied adopt 2 S 0 twist boat conformation, whereas in the monoisopropylidene exists in a slightly distorted chair conformation ( 4 C 1). 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)°.