Transfer alkyl group

5-Adenosylmethionine (SAM) is the main agent for the transfer of methyl groups, although in some cells chgline, betaine, and related compounds also play such a role. Some methyltransferases are very specific with respect to the acceptor substrate while others are unspecific. In all, a very wide variety of acceptors have been identified. The nucleotide product of methylation is S-adenosylhomocysteine (SAH). (See reference H-) T3rpes and reactions include  

Unsaturated fatty acids + SAM — SAH - - cyclopropane fatty acids 

Coenzyme B12 is involved in wframolecular alkyl group transfer in the methylmalonyl-CoA isomerase and glutamate mutase reactions. (see reference I4), both of which may be schematically represented as  

The actual mechanism is uncertain. The methylation of homocysteine and certain other coenzyme Bia-requiring reactions appear to involve inter-molecular alkyl transfer, but the details of these reactions are still obscure. 

Those reactions of coenzyme A in which the a-methylene group of acetyl-CoA is added to an acceptor molecule may also be considered a type of alkyl group transfer. Although this position is activated by being in a CoA ester, the ester group itself is not primarily involved in the new carbon-carbon bond formation. 

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Mixed-Metal Systems. Mixed-metal systems, where a zirconium alkyl is formed and the alkyl group transferred to another metal, are a new apphcation of the hydrozirconation reaction. These systems offer the advantages of the easy formation of the Zr—alkyl as well as the versatiUty of alkyl—metal reagents. For example, Cp2ZrRCl (R = alkyl or alkenyl) reacts with AICI3 to give an Al—alkyl species which may then be acylated with... 

There has been much recent interest in the role of zinc in activating cysteine residues to nucleophilic attack.542-545 Alkyl group transfer to coordinated cysteine residues occurs in a number of zinc proteins, such as Ada (the E. coli DNA repair protein) and the cobala-... 

The presence of Cu(i) or Cu(n) salts in the aforementioned reactions is critical. It is believed that organozinc reagents undergo transmetallation with copper species to yield more reactive complexes.301 A proposed301 catalytic cycle (Scheme 118) suggests that the alkyl group transferred to the enone from the copper metal in a bimetallic intermediate 207. 

Many organoarsenic compounds are prepared by reactions of AsC13 with alkyl group transfer agents such as Grignard reagents, lithium alkyls, or aluminum alkyls. Typical reactions include... 

This process is the result of the stability of trimethylboron. Alkyl group transfer also occurs in the reaction... 

Cobalt, Co2+ d1) 4, tetrahedral S-Thiolate, thioether, V-i midazole Alkyl group transfer, oxidases... 

Cobalt, Co3+ 6, octahedral O-Carboxylate, Alkyl group transfer in... 

Consequently, this reaction could be identified with a process where an alkyl fragment is transferred from one alkane molecule to another. The methyl group is the smallest alkyl fragment and the easiest to be transferred. However, crossmetathesis shows that ethyl and propyl groups can also be transferred. Indeed, heavier homolog alkanes can result from successive reactions or from heavier alkyl group transfer. Consequently, because of the successive reactions, the real product distribution corresponds to the following equation ... 

An intramolecular alkyl group transfer occurs upon warming up solutions of the ate-complex 180 generated by transmetalation of 1-lithio-l-methoxyethene 56 (equation 76)405,406 Tungsten and chromium carbene complexes 181 and 182, respectively, have been isolated from l-lithio-l,2-dimethoxyethene (equation 11... 

For instance, if the metal is lost by Sn2 attack on coordinated carbon, this constitutes R loss, and alkyl migration to an electrophilic centre such as coordinated CO may resemble R loss. R- loss may take place by simple homolysis, or by alkyl group transfer. Moreover, as Yamamoto has pointed out an electroneutral metal-carbon bond lengthening may be a prelude to more complex processes such as 0-elimination, or may lead to internal hydrogen abstraction rather than to actual free ligand release. 

In an earlier study,60 the alkyl group transfer was observed between Craq2 + and a macrocyclic cobalt complex, Co(dmgBF2)2. 

It is anticipated that all of the complex reactions observed in the boron system and in the studies on indium and gallium derivatives to be discussed below will be found in alkylaluminum systems. There also will be some additional complications which arise from the fact that the A1R3 moiety often occurs in a dimeric form which will alter the energetics of the reaction and may in some instances govern the mechanism of exchange as observed for alkyl group transfer. 

In addition to the magnesium compounds, lithium alkyls are versatile reagents that also function as alkyl group transfer agents. Lithium alkyls are prepared by the reaction of lithium with an alkyl halide using benzene or petroleum ether as a solvent ... 

Alkyl group transfer. When metal alkyls react with compounds of a different metal, the products frequently are those in which one product forms a stable crystal lattice. For example, in the reaction... 

These compounds function as alkyl group transfer agents, particularly when the other compound is a somewhat covalent halide. Some typical reactions that illustrate alkyl... 

The oxidation of the two boron-sp- carbon bonds with trimethylamine A-oxide before the coupling (Scheme 2-28) solves the difficulty arising from protonolysis of the B-C bond and avoids contamination of the coupling product by side products resulting from alkyl group transfer [69, 70]. 

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