Novel Synthesis of monosulphated methyl α-D-galactopyranosides

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Abstract
The syntheses of the methyl α-D-galactopyranoside 2-, 3-, 4-, and 6-sulphates (11, 12, 16, and 21 respectively) have been achieved using trimethylamine – sulphur trioxide as the sulphating agent. The procedure used is high yielding and requires shorter reaction times than reported previously. Each compound was obtained in a crystalline form as the potassium salt. Improved syntheses are described of the 3,4-isopropylidene acetal 2 of the methyl α-D-galactopyranoside and methyl. 2-O-acetyl 4,6-O-benzylidene α-D-galactopyranoside 8, which are starting materials in the preparation of the 2- and 3-sulphates (11 and 12 respectively). An efficient route has been devised for the synthesis of methyl 2,3,6-tri-O-acetyl-α-D-galactopyranoside 14 using a base-catalysed transesterification (C4-OH → C6-OH). Keywords: synthesis, methyl α-D-galactopyranoside, monosulphates.