Synthesis and characterization of tyramine-derivatized (1-->4)-linked alpha-D-oligogalacturonides

The reducing end C-1 of (1-->4)-linked alpha-D-oligogalacturonides (oligogalacturonides), with degrees of polymerization (dp) 3 and 13, was coupled to tyramine via reductive amination in the presence of sodium cyanoborohydride. These derivatives were purified in milligram quantities and structurally characterized. Tyramination of trigalacturonic acid proceeded to completion. The yield of apparently homogeneous tyraminated trigalacturonic acid after desalting was 35%. Derivatization of tridecagalacturonide with tyramine was incomplete. The tyraminated tridecagalacturonide was purified to apparent homogeneity using semipreparative high-performance anion-exchange chromatography (HPAEC) with a yield of 30%. The structures of the derivatized oligogalacturonides were established by 1H NMR spectroscopy and electrospray mass spectrometry.