Gerald O. Aspinall

Rapeseed hull pectin

A pectin isolated from rapeseed, hulls by extraction with aqueous ammonium oxalate, had a degree of esterification of 83% and contained residues of hexuronic (mainly D-galacturonic) acid (76%), D-galactose (2–3%), L-arabinose (8–9%), D-xylose (2%), L-rhamnose (2–3%), and L-fucose (1%). Partial acid hydrolysis of the derived pectic acid furnished 2-O-(α-D-galactopyranosyluronic acid)-L-rhamnose, 4-O-(α-D-galactopyranosyluronic acid)-D-galacturonic acid and the polymer-homologous tri- and tetrasaccharides, and 4-O-(glucopyranosyluronic acid)-L-fucose. The cleavage products from the methylated pectin were examined by g.l.c. and the partially methylated alditol acetates from the methylated carboxyl-reduced polysaccharide by g.l.c.-mass spectrometry. Parallel methylation studies on lemon-peel pectin have established a close similarity between the two pectins.

The synthesis of 3,4-dideoxyhex-3-enitols

Abstract Syntheses of ( E )-3,4-dideoxy- erythro -, ( Z )-3,4-dideoxy- D - threo - and ( E )-3,4-dideoxy- D - threo -hex-3-enitols are described. The action of potassium selenocyanate on 1,2:5,6-di- O -isopropylidene- D -mannitol 3,4-di- p -toluenesulfonate has been reexamined. Epoxidation of (E)-3,4-dideoxy-1,2:5,6-di- O -isopropylidene- D - threo -hex-3-enitol affords 3,4-anhydro-1,2:5,6-di- O -isopropylidene- D -mannitol and - D -iditol in the approximate proportions of 3:1. The configurations of the two epoxides were assigned on the basis of the reaction of the latter compound with sodium methoxide to give 1,2:5,6-di- O -isopropylidene-4- O -methyl- D -altritol.

Characterization of alkaline-degradation products of some 3,4-di- and 3,4,6-tri-methyl ethers of hexoses by G.L.C.-mass spectrometry of O-trimethylsilyl derivatives

Abstract G.l.c.-mass spectrometry has been used to provide information on the O -trimethylsilyl derivatives of the products of alkaline degradation of 3,4-di- and 3,4,6-tri- O -methyl- D -glucose, and 3,4,6-tri- O -methyl- D -galactose. During reaction with sodium hydroxide-sodium borohydride mixtures, reduction occurs more rapidly than β-elimination and the only detectable products were the corresponding alditols and the epimeric 3-deoxyalditols. Extended reaction with sodium hydroxide alone, followed by treatment with sodium borohydride, gives mixtures of aldonic acids including the epimeric 3-deoxy-4- O -methylaldonic acids (metasaccharinic acids), 3-deoxyaldonic acids (with loss of the 4- O -methyl substituent), and 3,4-dideoxy-aldonic acids. Possible reaction-pathways are discussed.