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Demethylation is the chemical process resulting in the removal a of methyl group (CH₃) from a molecule.^[1]^[2] A common way of demethylation is the replacement of a methyl group by a hydrogen atom, resulting in a net loss of one carbon and two hydrogen atoms.

In biochemistry

In biochemical systems, the process of demethylation is catalyzed by demethylases. These enzymes oxidize N-methyl groups, which occur in histones and some forms of DNA.

R₂N-CH₃ + O → R₂N-H + CH₂O

One such oxidative enzyme family is the cytochrome P450^[3] Alpha-ketoglutarate-dependent nonheme enzymes are active for demethylation of DNA, operating by similar pathway.

In organic chemistry

In organic chemistry, demethylation typically refers to the cleavage of ethers, especially aryl ethers, which are pervasive in lignin-derived compounds. The reaction typically requires harsh conditions or harsh reagents. For example, the methyl ether in vanillin can be removed by heating near 250 °C with strong base.^[4] Stronger nucleophiles such as dirganophosphides (LiPPh₂) also cleave aryl ethers under milder conditions.^[5]

Boron tribromide is a classical reagent for the dealkylation of methyl arylethers. The mechanism of ether dealkylation proceeds via the formation of a complex between the boron center and the ether oxygen followed by the elimination of an alkyl bromide to yield a dibromo(organo)borane. The dibromo(organo)borane can then undergo hydrolysis to give the alcohol or phenol, boric acid, and hydrogen bromide as products.^[6]

ROR + BBr₃ → RO⁺(^-BBr₃)R

RO⁺(^-BBr₃)R → ROBBr₂ + RBr

ROBBr₂ + 3 H₂O → ROH + B(OH)₃ + 2 HBr

Methyl esters also are susceptible to demethylation, which is usually achieved by saponification. Highly specialized demethylations are abundant such as the Krapcho decarboxylation:

References

^ Clayden Jonathan, Nick Greeves, Stuart Warren, Peter Wothers (2001). Organic chemistry. Oxford, Oxfordshire: Oxford University Press. ISBN 0-19-850346-6. http://www.organic-chemistry.org/books/reviews/0198503466.shtm.
^ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7, http://books.google.com/books?id=JDR-nZpojeEC&printsec=frontcover
^ Roland Sigel; Sigel, Astrid; Sigel, Helmut (2007). The Ubiquitous Roles of Cytochrome P450 Proteins: Metal Ions in Life Sciences. New York: Wiley. ISBN 0-470-01672-8.
^ Irwin A. Pearl (1949), "Protocatechulic Acid", Org. Synth. 29: 85, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV3P0745; Coll. Vol. 3: 745
^ Robert E. Ireland and David M. Walba (1977), "Demethylation of Methyl Aryl Ethers: 4-Ethoxy-3-hydroxybenzaldehyde", Org. Synth. 56: 44, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV6P0567; Coll. Vol. 3: 745
^ J. F. W. McOmie, D. E. West (1969), "3,3'-Dihydroxybiphenyl", Org. Synth. 49: 13, http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=CV5P0412; Coll. Vol. 5: 412

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English Journal

Evolution of a contagious cancer: epigenetic variation in Devil Facial Tumour Disease.

Ujvari B, Pearse AM, Peck S, Harmsen C, Taylor R, Pyecroft S, Madsen T, Papenfuss AT, Belov K.SourceFaculty of Veterinary Sciences, University of Sydney, , Sydney, New South Wales 2006, Australia, Devil Facial Tumour Project, Diagnostic Services, Animal Health Laboratory, Department of Primary Industries, Water and Environment, , Launceston, Tasmania 7250, Australia, Save the Tasmanian Devil Program, The Department of Primary Industries, Parks, Water and Environment, GPO Box 44, , Hobart, Tasmania 7001, Australia, School of Biological Sciences, University of Wollongong, , Wollongong, New South Wales 2522, Australia, Bioinformatics Division, The Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3050, Australia, Department of Mathematics and Statistics, The University of Melbourne, , Melbourne, Victoria 3010, Australia.
Proceedings. Biological sciences / The Royal Society.Proc Biol Sci.2013 Jan 7;280(1750):20121720. Epub 2012 Nov 7.
The emergence of Devil Facial Tumour Disease (DFTD), a highly contagious cancer, is driving Tasmanian devils (Sarcophilus harrisii) to extinction. The cancer is a genetically and chromosomally stable clonal cell line which is transmitted by biting during social interactions. In the present study, we
PMID 23135679

Embryo manipulation via assisted reproductive technology and epigenetic asymmetry in mammalian early development.

Kohda T, Ishino F.SourceDepartment of Epigenetics, Medical Research Institute, Tokyo Medical and Dental University, , 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.
Philosophical transactions of the Royal Society of London. Series B, Biological sciences.Philos Trans R Soc Lond B Biol Sci.2013 Jan 5;368(1609):20120353. doi: 10.1098/rstb.2012.0353.
The early stage of mammalian development from fertilization to implantation is a period when global and differential changes in the epigenetic landscape occur in paternally and maternally derived genomes, respectively. The sperm and egg DNA methylation profiles are very different from each other, an
PMID 23166403