The analysis of agarose by the reductive cleavage method

Agarose was structurally characterised by permethylation and subsequent reductive cleavage. Treatment of the fully methylated polysaccharide with triethylsilane and a mixture of trimethylsilyl methanesulfonate and boron trifluoride etherate followed by a newly developed, acid-catalysed, in situ acetylation yielded two main products: the expected 4-O-acetyl-1,5:3,6-dianhydro-2-O-methyl-L-galactitol and 3-O-acetyl-1,5-anhydro-2,4,6-tri-O-methyl-D-galactitol in the molar ratio 1:1, and traces of 1,5-anhydro-2,3,4,6-tetra-O-methyl-D-galactitol. Reductive cleavage using triethylsilane and trimethylsilyl trifluoromethanesulfonate as the catalyst yielded the same anhydroalditols as well as a smaller amount of 1,4,5-tri-O-acetyl-3,6-anhydro-2-O-methyl-L-galactitol due to ring-opening of 3,6-anhydrogalactopyranosyl residues during reductive cleavage. In this paper, results from reductive cleavage are compared with results using standard methylation analysis.