Depolymerization and de-N-acetylation of glycosaminoglycuronans by the action of alkali in the presence of sodium borohydride.

Abstract

Depolymerization of Ch-4-S, Ch-6-S, HA and HP was observed by gel filtration after treatment with 2-10 N NaOH or Ba(OH)2 in the presence of NaBH4 at 80-83 degrees for 1-5 hr. Depolymerized products were isolated after these treatments. 4-Deoxy-alpha-L-threo-4-enohexopyranosyluronic acid residue as the nonreducing end group was demonstrated by the H-1 and H-4 proton signals in the NMR spectra and by the absorption at 225-230 nm. L-Gulonic acid, which was produced from D-glucuronic acid by the action of NaBH4, was detected as the reducing end group in the depolymerized products of Ch-6-S, but no hexosaminitol was detected. De-N-acetylation to the extent of 34-50% occurred after treatment with 2.5 N NaOH in the presence of NaBH4, and almost complete de-N-acetylation accompanied by considerable destruction was observed with Ch-4-S and Ch-6-S after treatment with 5.5-10.0 N NaOH. A reaction mechanism is proposed for the depolymerization of glycosaminoglycuronans by the action of alkali.