Sequence Analysis of Chitooligosaccharides by Matrix-Assisted Laser Desorption Ionization Postsource Decay Mass Spectrometry

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Abstract
Chitin/chitosan oligosaccharides composed of 2-acetamido-2-deoxy-d-glucopyranose (GlcNAc) and/or 2-amino-2-deoxy-d-glucopyranose (GlcN) were prepared by chemical degradation of chitin or chitosan and separated by gel permeation chromatography. Oligosaccharides obtained after enzymatic hydrolysis of chitosan [FA 0.19] with a fungal chitinase were derivatized by reductive amination with 2-aminoacridone and sequenced by matrix-assisted laser desorption ionization time-of-flight postsource decay (PSD) mass spectrometry (MS). The sequence of a trimer, D1A2, was established as D−A−A. The composition of a hexamer D3A3 was ca. 65% D−A−D−D−A−A and 35% D−D−A−D−A−A. The PSD MS of a nonamer D5A4-amac revealed four isobaric species D−X−Y−D−X−Y−D−A−A, where A is GlcNAc, D is GlcN, and X and Y (X ≠ Y) are mutually either D or A. This structure motif was also observed in a dodecamer D7A5 which was composed of eight isobaric sequences of the general formula (D−X−Y)3−D−A−A.

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