Mechanism of stigmasterol dealkylation in insect

Deuterated stigmasterols (10, 11 and 12) were chemically synthesized and fed to silk-worm larvae. GC-MS analysis of the metabolites, cholesterol (4) and desmosterol (6), indicates the migration of 25-hydrogen to C-24 position during stigmasterol dealkylation. 22,24(28)-Dienes(8a and 8b) were shown to be converted to 22,24-diene (5), desmosterol and cholesterol.     

Selective demethylation of phosphorus esters

The selective cleavage of methyl phosphorus esters by t-butylamine is described.     

Enzymic demethylation of lignin model polymers

We have studied the demethylation of [O¹⁴CH₃]-polyguaiacol byPhanerochaete chrysosporium as a model for the fungal demethylation of lignin. Demethylating activity of whole-cell ligninolytic cultures was compared to demethylating activities of various oxygen-activating systems. Some of these systems demethylated polyguaiacol (e.g., Fenton’s reagent, rose bengal sensitized photolysis, and horseradish peroxidase + H₂O₂). Other systems did not (e.g., xanthine/xanthine oxidase). Even where oxygen-activating systems did demethylate polyguaiacol, we found no convincing evidence that these systems are used byPhanerochaete. We have detected in concentrated extracellular culture filtrates of ligninolyticPhanerochaete cultures an enzymatic activity that demethylates [O¹⁴CH₃]-polyguaiacol. The activity was stabilized greatly by concentrating culture filtrates by pressure dialysis (20,000 MW cutoff membrane). Concentrated enzyme preparations could be filter sterilized and stored at 4‡C for several days without extensive loss of activity. The methoxyl label released by our enzyme preparation was nongaseous (e.g., not¹⁴CO₂,¹⁴CO, or¹⁴CH₄), but volatile (e.g., CH₃OH or CH₂O). The amount of labeled methoxyl released by the enzyme preparation was about the same as that released by intact cultures. The enzyme preparation contained ∼50 Μg/mL of protein and had laccase activity against catechol or hydroquinone. Unsupplemented preparations lacked activity againsto-dianisidine, a dye used to assay peroxidase. However, when H₂O₂ was provided (0.8 mM),o-dianisidine was oxidized rapidly. This indicates that the preparation contained peroxidase, but lacked substrate levels of H₂O₂. Demethylation of polyguaiacol by the enzyme preparation was not stimulated by NADH, NADPH, FAD, or FMN. Demethylation was stimulated by >50% upon addition of H₂O₂ (0.5 mM). Concentrated culture filtrates ofPhanerochaete produced ethylene from methional, a reaction that has been used as an indicator of hydroxyl radical generating systems. However, the ethylene-generating activity and the demethylase activity in such preparations showed different purification and stability characteristics. Pure horseradish peroxidase and H₂O₂ demethylated polyguaiacol and produced ethylene from methional.Phanerochaete does produce H₂O₂, so our demethylase activity appears to be similar to a peroxidase, although we have not yet determined the identity of the methyl product of either enzyme preparation. We suspect that the demethylase operates by a freeradical mechanism, and that the methyl product released is likely to be methanol. Confirmation of these hypotheses provides the basis for our future work with this novel fungal enzyme system.     

甲基醚的选择性去甲基试剂

本文综述了甲基醚的选择性去甲基反应所采用的试剂,并按甲基醚在化合物中所处的环境及试剂所适用的范围进行分类。参考文献37篇。     

Oxidative demethylation of some methylnitropyridine 1-oxides

3-Nitropyridine 1-oxide and 5-methyl-3-nitropyridine 1-oxide are produced readily by oxidative demethylation using SeO₂ of 2-methyl- and 2,5-dimethyl-3-nitropyridine 1-oxides.     

Iron catalyzed demethylation of acetic acid*

Abstract

The iron(IV)-oxo catalyzed cleavage of acetic acid is reported. Iron(II) complexes are used as catalyst precursors and H₂O₂ as oxidant in reactions in aqueous solution with an excess of chloride and, in some experiments, with ascorbic acid added as an OH^. radical scavenger. It is shown that the acetic acid is cleaved into CO₂ and a methyl radical. In the presence of O₂ and OH^. radicals, the initially generated methyl radicals produce methanol and formate. Halogenated alkanes are also formed and, in the absence of O₂ and OH^. radicals, methane is obtained as the major product. A mechanism for the formation of various environmentally important volatile C₁ compounds is deduced from the present results and published studies, and its relevance as an additional source for these compounds in the atmosphere is discussed.     

Magnesium-assisted intramolecular demethylation utilizing carborane C-H geometry

A novel type of demethylation reaction was designed in the Pd-catalyzed coupling reaction of iodocarboranes with several Grignard reagents, CH₃OPhMgBr. 3-Iodo-o-carborane 1 reacted with 2-CH₃OPhMgBr to afford the corresponding phenol compound 4b in 78% yield. However, when compound 1 was reacted with the other Grignard reagents, the corresponding methoxyl compounds 5a and 6a were obtained in excellent yields. 2-Iodo-p-carborane 3 reacted with 2-CH₃OPhMgBr to afford the corresponding phenol 8b in 50% yield and the methoxyl compound 8a in 41% yield. The carborane C-H geometry, which can form an intramolecular C-H?O hydrogen bonding, seems to be an important factor in the demethylation process. To examine the mechanism of the demethylation, compounds 1 and 4a were treated with CH₃MgBr and quenched with D₂O. While the two C-Hs of compound 1 were completely deuterated, compound 4a showed a replacement of one C-H with C-D. Therefore, we propose a mechanism involving intramolecular C-Mg?O interaction instead of intramolecular C-H?O interaction, via the generation of 3-iodo-o-carboranyl(MgBr)₂, 11. Since it is also possible to replace the C-Hs with various metals other than Mg, new applications of carboranes in coordination and metal catalyst chemistry can be expected.     

The demethylation chemistry of 3-substituted 2-methoxypyridines

Upon acylation of 3-amino-2-methoxypyridines, two side products were discovered, a pyridone, 5,6 , and 8 , and a pyridyloxazine, 4 and 9. The ratios of these products can be affected by changes in the reaction parameters. When oxalyl chloride was the acylating agent a pyridone 13 was isolated.     

Folding-promoted TBAX-mediated selective demethylation of methoxybenzene-based macrocyclic aromatic pentamers

Described in this study is the ability of tetrabutylammonium salts (TBAX) to mediate an efficient mono- or di-demethylation removing one or two out of five aromatic methoxy methyl groups situated in similar chemical microenvironments in a H-bonded macrocyclic aromatic pentamer. These demethylations are found to be both chemo- and regioselective, and promoted by the H-bonding directed folding of the macrocyclic backbone.     

An efficient method for demethylation of aryl methyl ethers

A new efficient method for demethylation of aryl methyl ethers using iodocyclohexane in DMF under reflux condition is described.     

LSD1: more than demethylation of histone lysine residues

Lysine-specific histone demethylase 1 (LSD1) represents the first example of an identified nuclear protein with histone demethylase activity. In particular, it plays a special role in the epigenetic regulation of gene expression, as it removes methyl groups from mono- and dimethylated lysine 4 and/or lysine 9 on histone H3 (H3K4me1/2 and H3K9me1/2), behaving as a repressor or activator of gene expression, respectively. Moreover, it has been recently found to demethylate monomethylated and dimethylated lysine 20 in histone H4 and to contribute to the balance of several other methylated lysine residues in histone H3 (i.e., H3K27, H3K36, and H3K79). Furthermore, in recent years, a plethora of nonhistone proteins have been detected as targets of LSD1 activity, suggesting that this demethylase is a fundamental player in the regulation of multiple pathways triggered in several cellular processes, including cancer progression. In this review, we analyze the molecular mechanism by which LSD1 displays its dual effect on gene expression (related to the specific lysine target), placing final emphasis on the use of pharmacological inhibitors of its activity in future clinical studies to fight cancer.Subject terms: Epigenetics, Histone post-translational modifications     

Competitive disproportionation and demethylation of toluene on Mg-containing Y zeolites

On Mg-containing Y zeolites toluene undergoes disproportionation and demethylation. The relative importance of the two processes is discussed.

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Mg- Y . .