omethylated

O-methylated, often written as O-methylated, describes a molecule in which a methyl group is attached to an oxygen atom, forming an ether linkage such as a methoxy (-O-CH3) group. The term is used to distinguish this specific type of methylation from N-, C-, or other methylation patterns. In this sense, omethylated compounds have undergone O-methylation.

In organic chemistry, O-methylation is a functional group transformation that converts alcohols or phenols into their methyl ethers. It is typically achieved with electrophilic methylating agents, resulting in the replacement of a hydrogen on an oxygen with a methyl group. In biological systems, O-methylation is carried out by O-methyltransferases, which transfer a methyl group from S-adenosyl-L-methionine (SAM) to an oxygen atom on the substrate, producing S-adenosylhomocysteine as a byproduct. This enzymatic route is selective for oxygen sites and is common in the modification of phenolic, flavonoid, and lignin-related compounds.

Common examples of omethylated substances include simple aryl ethers such as anisole (methoxybenzene) and guaiacol, as well as numerous naturally occurring compounds like methoxylated flavonoids and lignin precursors. In pharmacology and toxicology, O-methylation can alter a compound’s polarity, solubility, and metabolic fate. For example, catecholamines can be inactivated by catechol-O-methyltransferase (COMT), producing O-methylated metabolites that influence pharmacokinetics and therapeutic effects.

In research and databases, omethylated describes molecules bearing methoxy groups at oxygen sites, highlighting a specific type of methylation relevant to structure, metabolism, and function.