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Demethylation

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Title: Demethylation  
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Demethylation

Demethylation is the chemical process resulting in the removal of a methyl group (CH3) from a molecule.[1][3] 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.


The counterpart of demethylation is methylation.

Contents

  • In biochemistry 1
  • In Organic chemistry 2
    • O-Desmethylation 2.1
  • History 3
    • N-Demethylation 3.1
  • References 4
  • See also 5

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[6] Alpha-ketoglutarate-dependent nonheme enzymes are active for demethylation of DNA, operating by similar pathway.

In Organic chemistry

O-Desmethylation

Desmethylation, typically refers to cleavage of ethers, especially aryl ethers, although there is some exceptions, for instance cf. "desipramine".

Apparently, aryl ethers are pervasive in lignin-derived compounds.nav_box_header

The reaction typically requires harsh conditions or harsh reagents. For example, the methyl ether in

See also

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References

N-demethylation of 3° amines, is by the Von Braun reaction, which uses BrCN as the reagent to give the corresponding nor derivatives. The etymological meaning of the word nor is ″N ohne R″. A modern variation of the Von Braun rxn has been developed where BrCN has been superseded by ethyl chloroformate, respectively. Paxil prepared from arecoline is a good example of where this rxn has been applied, as well as GSK-372,475, for example.

N-Demethylation

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

ROR + BBr3 → RO+(BBr3)R
RO+(BBr3)R → ROBBr2 + RBr
ROBBr2 + 3 H2O → ROH + B(OH)3 + 2 HBr


hydrolysis to give the alcohol or phenol, boric acid, and hydrogen bromide as products.[14]

[13]

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