Xylose

D-Xylose

Names
IUPAC name D-Xylose
Other names (+)-Xylose Wood sugar
Identifiers
CAS Number	58-86-6 609-06-3 (L-isomer)^[ESIS] 41247-05-6 (racemate)^[ESIS]
3D model (Jmol)	Interactive image
ChEMBL	ChEMBL502135
ChemSpider	119104
ECHA InfoCard	100.117.085
EC Number	200-400-7
PubChem	135191
UNII	A1TA934AKO
InChI InChI=1S/C5H10O5/c6-2-1-10-5(9)4(8)3(2)7/h2-9H,1H2/t2-,3+,4-,5?/m1/s1 Key: SRBFZHDQGSBBOR-IOVATXLUSA-N InChI=1/C5H10O5/c6-2-1-10-5(9)4(8)3(2)7/h2-9H,1H2/t2-,3+,4-,5?/m1/s1 Key: SRBFZHDQGSBBOR-IOVATXLUBL
SMILES C1[C@H]([C@@H]([C@H](C(O1)O)O)O)O
Properties[1][2]
Chemical formula	C5H10O5
Molar mass	150.13 g/mol
Appearance	monoclinic needles or prisms, colourless
Density	1.525 g/cm^3 (20 °C)
Melting point	144 to 145 °C (291 to 293 °F; 417 to 418 K)
Chiral rotation ([α]D)	+22.5° (CHCl3)
Hazards
NFPA 704	1 1 0
Related compounds
Related aldopentoses	Arabinose Ribose Lyxose
Related compounds	Xylulose
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Xylose (cf. Greek ξύλον, xylon, "wood") is a sugar first isolated from wood, and named for it. Xylose is classified as a monosaccharide of the aldopentose type, which means that it contains five carbon atoms and includes a formyl functional group. It is derived from hemicellulose, one of the main constituents of biomass. Like most sugars, it can adopt several structures depending on conditions. With its free carbonyl group, it is a reducing sugar.

Structure

The acyclic form of xylose has chemical formula HOCH₂(CH(OH))₃CHO. The cyclic hemiacetal isomers are more prevalent in solution and are of two types: the pyranoses, which feature six-membered C₅O rings, and the furanoses, which feature five-membered C₄O rings (with a pendant CH₂OH group). Each of these rings subject to further isomerism, depending on the relative orientation of the anomeric hydroxy group.

The dextrorotary form, D-xylose, is the one that usually occurs endogenously in living things. A levorotary form, L-xylose, can be synthesized.

Occurrence

Xylose is the main building block for the hemicellulose xylan, which comprises about 30% of some plants (birch for example), far less in others (spruce and pine have about 9% xylan). Xylose is otherwise pervasive, being found in the embryos of most edible plants. It was first isolated from wood by Finnish scientist, Koch, in 1881,^[3] but first became commercially viable, with a price close to sucrose, in 1930.^[4]

Xylose is also the first saccharide added to the serine or threonine in the proteoglycan type O-glycosylation, and, so, it is the first saccharide in biosynthetic pathways of most anionic polysaccharides such as heparan sulfate and chondroitin sulfate.^[5]

Applications

Chemicals

The acid-catalysed degradation of hemicellulose gives furfural,^[6] a specialty solvent in industry and a precursor to synthetic polymers.^[7]

Human consumption

Xylose is metabolised by humans, though it is not a major human nutrient and largely excreted by the kidneys.^[8] Humans must obtain xylose from their diet. An oxido-reductase pathway is present in eukaryotic microorganisms. Humans have enzymes called protein xylosyltransferases (XYLT1, XYLT2), which transfers xylose from UDP to a serine in the core protein of proteoglycans.

Xylose contains 0 calories per gram.^[9]

Animal medicine

In animal medicine, xylose is used to test for malabsorption by administration in water to the patient after fasting. If xylose is detected in blood and/or urine within the next few hours, it has been absorbed by the intestines.^[10]

High xylose intake on the order of approximately 100g/kg of animal body weight is relatively well tolerated in pigs, and in a similar manner to results from human studies, a portion of the xylose intake is passed out in urine undigested.^[11]

Hydrogen production

In 2014 a low-temperature 50 °C (122 °F), atmospheric-pressure enzyme-driven process to convert xylose into hydrogen with nearly 100% of the theoretical yield was announced. The process employs 13 enzymes, including a novel polyphosphate xylulokinase (XK).^[12][13]

Derivatives

Reduction of xylose by catalytic hydrogenation produces the sugar substitute xylitol.

See also

• Saccharophagus degradans
• Xylonic acid
• Xylose metabolism

References

1. The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals (11th ed.), Merck, 1989, ISBN 091191028X, 9995.
2. Weast, Robert C., ed. (1981). CRC Handbook of Chemistry and Physics (62nd ed.). Boca Raton, FL: CRC Press. p. C-574. ISBN 0-8493-0462-8..
3. Advances in carbohydrate chemistry, Volume 5, pg 278 Hudson & Cantor 1950
4. Pentose Metabolism 1932
5. Buskas, Therese; Ingale, Sampat; Boons, Geert-Jan (2006), "Glycopeptides as versatile tool for glycobiology", Glycobiology, 16 (8): 113R–36R, doi:10.1093/glycob/cwj125, PMID 16675547
6. Roger Adams and V. Voorhees (1921). "Furfural". Org. Synth. 1: 49.; Coll. Vol., 1, p. 280
7. H. E. Hoydonckx, W. M. Van Rhijn, W. Van Rhijn, D. E. De Vos, P. A. Jacobs "Furfural and Derivatives" in Ullmann's Encyclopedia of Industrial Chemistry 2007, Wiley-VCH, Weinheim. doi:10.1002/14356007.a12_119.pub2
8. Johnson, S. A. (2006). "Thesis" (PDF).
9. GASTRO-INTESTINAL STUDIES. VII. THE EXCRETION OF XYLOSE IN PERNICIOUS ANEMIA, The Journal of Clinical Investigation, retrieved 2016-02-17
10. "D-xylose absorption", MedlinePlus, U.S. National Library of Medicine, July 2008, retrieved 2009-09-06
11. Nutritional implications of D-Xylose in pigs
12. "Virginia Tech team develops process for high-yield production of hydrogen from xylose under mild conditions". Green Car Congress. 2013-04-03. doi:10.1002/anie.201300766. Retrieved 2014-01-22.
13. Martín Del Campo, J. S.; Rollin, J.; Myung, S.; Chun, Y.; Chandrayan, S.; Patiño, R.; Adams, M. W.; Zhang, Y. -H. P. (2013). "High-Yield Production of Dihydrogen from Xylose by Using a Synthetic Enzyme Cascade in a Cell-Free System". Angewandte Chemie International Edition. 52 (17): 4587. doi:10.1002/anie.201300766.