Analysis of pyruvylated beta-carrageenan by 2D NMR spectroscopy and reductive partial hydrolysis

A polysaccharide rich in 4',6'-O-(1-carboxyethylidene)-substituted (i.e., pyruvylated) beta-carrageenan has been prepared by solvolytic desulfation of a polysaccharide containing predominantly pyruvylated alpha-carrageenan, which was extracted from the red seaweed, Callophycus tridentifer. The 13C and 1H NMR chemical shifts of pyruvylated beta-carrageenan have been fully assigned using 2D NMR spectroscopic techniques. The 4',6'-O-(1-methoxycarbonylethylidene) group, generated during chemical methylation of the polysaccharide, has been shown to survive under the conditions of acidic hydrolysis that cleave the 3,6-anhydro-alpha-D-galactosidic bonds in permethylated samples of both pyruvylated beta- and pyruvylated alpha-carrageenans. As a result, two novel pyruvylated carrabiitol derivatives have been prepared.