TITLE:
Discovery of Unusual Highly Branched Galactomannan from Seeds of Desmanthus illinoensis
AUTHORS:
Masakuni Tako, Yukihiro Tamaki, Takeshi Teruya
KEYWORDS:
Unusual Highly Branched Galactomannan, Desmanthus illinoensis, NMR Analysis, Methylation Analysis, Chemical Structure
JOURNAL NAME:
Journal of Biomaterials and Nanobiotechnology,
Vol.9 No.2,
April
20,
2018
ABSTRACT:
A galactomannan was isolated from seeds of a leguminous
plant, Desmanthus illinoensis, which is grown in Okinawa,
Japan. D-Galactose (molar ratio, 1.0) and D-mannose
(0.82) were identified via High-performance Anion Exchange Chromatography Coupled
with a Pulse Amperometric Detector. The molecular mass and specific rotation
were estimated to be 1000 kDa and +53.8°, respectively. The infrared spectrum indicated that the galactomannan was
involved in both α- and β-linkages, and two types of α-linkages were detected at 814 and 830
cm-1. The 1H- and 13C-NMR spectra indicated
that the majority of the β-D-mannan
main chain was substituted with mono α-D-galactose
or α-D-galacto-disaccharide-side
chains. Methylation analysis was used to identify 2,3,4,6-tetra-O-methyl-D-galactose
(molar ratio, 3.3), 2,3,4-tri-O-methyl- D-galactose (1.0) and 2,3-di-O-methyl-D-mannose
(3.1). Specifically, unique 2,3,4-tri-O-methyl D-galactose residue was identified from mass spectrum. The results suggested
that the galactomannan was 1,4-linked-β-D-mannan
substituted with α-D-galactose
or 1,6-linked-α-D-galacto-disaccharide
side chains at C-6 on the main chain. The galactomannan isolated from D. illinoensis was an unusual highly
branched polysaccharide, and its chemical structure was proposed. This work is
the first to report on the galactomannan involving 1,6-linked α-D-galacto-disaccharide
side chains in addition to α-D-galactose
mono side chains.