Identification of rare 6-deoxy-d-altrose from an edible mushroom (Lactarius lividatus)

6-Deoxy-l-altrose is well known as a constituent sugar moiety of lipopolysaccharides in Gram-negative bacteria. However, its isomer, 6-deoxy-d-altrose, is little known. Identification of 6-deoxy-d-altrose isolated from a polysaccharide extracted from an edible mushroom (Lactarius lividatus), its comparison with chemically synthesized 6-deoxy-d-altrose using 1H and 13C NMR including COSY, HMQC spectroscopy, and investigation of its specific optical rotation were all conducted in this study. The 6-deoxy-hexose isolated from acid hydrolysate of the polysaccharide extracted from L. lividatus was involved in four anomeric isomers (α-pyranose and β-pyranose, and α-furanose and β-furanose), as was chemically synthesized 6-deoxy-d-altrose in an aqueous solution because of mutarotation. Almost all signals of 1D (1H NMR and 13C NMR) and 2D (COSY and HMQC)-NMR spectra agreed with those of the authentic 6-deoxy-d-altrose. The specific optical rotation [α]589 of 6-deoxy-sugar showed a value of +18.2°, which was in agreement with that of authentic 6-deoxy-d-altrose. Consequently, 6-deoxy-hexose was identified as the 6-deoxy-d-altrose. This work is the first complete identification of 6-deoxy-d-altrose in a natural environment.

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► 1H NMR, 13C NMR, COSY and HMQC spectra of the unknown sugar were identical with those of synthesized 6-deoxy-d-altrose.
► The specific rotation was +18.2°.
► The unknown sugar was identified as rare 6-deoxy-d-altrose.
► The work was the first complete identification of rare 6-deoxy-d-altrose in nature.