Xylose

D-Xylose
IUPAC name D-Xylose
Other names (+)-Xylose Wood sugar
Identifiers
CAS number	58-86-6 Y, 609-06-3 (L-isomer) Y[ESIS], 41247-05-6 (racemate) Y[ESIS]
PubChem	6027
UNII	A1TA934AKO Y
EC-number	200-400-7
ChEMBL	CHEMBL502135 N
Properties[1][2]
Molecular formula	C5H10O5
Molar mass	150.13 g/mol
Appearance	monoclinic needles or prisms, colourless
Density	1.525 g/cm3 (20 °C)
Melting point	144-145 °C
Chiral rotation [α]D	+22.5º (CHCl3)
Related compounds
Related aldopentoses	Arabinose Ribose Lyxose
Related compounds	Xylulose
N (verify) (what is: Y/N?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Xylose (cf. Greek ξυλος, xylos, "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 an aldehyde functional group. It is the precursor to 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.

Occurrence

Xylose is the main building block for hemicellulose, which comprises about 30% of plant matter. Xylose is otherwise pervasive, being found in the embryos of most edible plants. It was first isolated from wood by Koch in 1881.

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.^[3]

Use

The acid-catalysed degradation of hemicellulose gives furfural,^[4] a specialty solvent in industry and a precursor to synthetic polymers.^[5]Xylose is not metabolised by humans. It is completely absorbed and secreted from the kidneys.

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.^[6] Reduction of xylose by catalytic hydrogenation produces the non-cariogenic sugar substitute xylitol.

See also

• Xylose metabolism
• Xylonic acid
• Saccharophagus degradans

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. ^ 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 .
4. ^ Roger Adams and V. Voorhees (1921), "Furfural", Org. Synth. 1: 49, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1p0280 ; Coll. Vol. 1: 280 
5. ^ 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
6. ^ "D-xylose absorption", MedlinePlus (U.S. National Library of Medicine), July 2008, http://www.nlm.nih.gov/medlineplus/ency/article/003606.htm, retrieved 2009-09-06 .