(2R,3R,4S,5S)-2,3,4,5-tetrahydroxyhexanal → D-Arabinose

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The teachings also provide a method of preparing the extracts. The methods comprise isolating a crude extract from Astragalus membranaceus and mildly treating the crude extract with an acid. The mildly treating includes applying the acid to the crude extract at a concentration ranging from about 0.05M to about 0.5M, at a temperature ranging from about 15° C. to 25° C., and for a time ranging from about 1 hour to about 24 hours. The temperature and time for applying the acid are selected to obtain an arabinose:galactose ratio greater than about 3.5:1; from about 5% to about 10% rhamnose; from about 15% to about 20% galactose; from about 10% to about 20% galacturonic acid; from about 10% to about 15% glucose; and a high yield. The high yield is substantially higher than a yield of an extract of the Astragalus membranaceus produced using a second process that includes applying the acid to the crude extract at a temperature and time selected to obtain an arabinose:galactose ratio of less than 3.5:1, 20%-35% galactose, and less than about 10% glucose. In some embodiments, the arabinose:galactose ratio can reduced to within a range of about 4.0:1 to about 4.5:1, about 3.75:1 to about 4.5:1, about 3.8:1 to about 4.25:1, or any range therein.

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