Alpha-eliminations

ALPHA-ELIMINATION (a-ELIMINATION) ALPHA EXPULSION ALPHA PARTICLE Alternant,... 

Y Ji, A Marra, M Rosenberg, G Woodnutt. Regulated antisense RNA eliminates alpha-toxin virulence in Staphylococcus aureus infection. J Bacteriol 181 6585— 6590, 1999. 

Alpha Particles. Alpha particles are high energy particles that are emitted from various radioactive elements. These particles have the capability to change the state of the memory cell. As the size and functionality of the DRAHs has increased, the active cell size has decreased and the DRAHs have become more susceptible to alpha particle damage. This damage became critical with the 16R DRAM and, since that time, action has been taken to eliminate alpha particle damage (7). 

Possibly the measurement of the chlorine isotope effect for a series of suitably substituted substrates may help to decide whether or not greater stereospecificity is associated with decreased carbanion character of the transition state for elimination from alkenes. Of course, such studies must be accompanied by labelling experiments to exclude the possibility that alkynes arise by an apparent alpha-elimination (Section 5.1) involving formation of a carbanion at the alpha carbon, which subsequently eliminates alpha halogen simultaneously with migration of a substituent from the beta carbon. Results with alcoholic media, however, tend to indicate this alternative mechanism is unimportant if a normal beta-elimination is possible. 

FRITSCH BUTTENBERG - WIECHELL Acetylene Synthesis Alpha elimination from haloethylenes leading via carbene rearrangement to acetylenes... 

The biologically active form of vitamin Bg is pyridoxal-5-phosphate (PEP), a coenzyme that exists under physiological conditions in two tautomeric forms (Figure 18.25). PLP participates in the catalysis of a wide variety of reactions involving amino acids, including transaminations, a- and /3-decarboxylations, /3- and ") eliminations, racemizations, and aldol reactions (Figure 18.26). Note that these reactions include cleavage of any of the bonds to the amino acid alpha carbon, as well as several bonds in the side chain. The remarkably versatile chemistry of PLP is due to its ability to... 

The soiution was treated with 0.01 mol of formaldehyde in aqueous solution, with agitation. The solution was then filtered to eliminate traces of insoluble product and the filtrate was lyophilized. Sodium 6-[ D(-)-alpha-(methylene-amino-phenylacetamido)] -penicillanate was obtained. 

Half-life is the time taken to decrease the concentration of a drug to one-half its original value. There may be several phases in the elimination, and the most common is the so-called beta-phase. Alpha-phase is a distribution phase and gamma-phase is the terminal phase when the drug is finally leaving the tissues. 

CYP27A1 catalyzes the side chain oxidation (27-hydroxylation) in bile acid biosynthesis. Because bile acid synthesis is the only elimination pathway for cholesterol, mutations in the CYP27A1 gene lead to abnormal deposition of cholesterol and cholestanol in various tissues. This sterol storage disorder is known as cerebrotendinous xanthomatosis. CYP27B1 is the 1-alpha hydroxylase of vitamin D3 that converts it to the active vitamin form. The function of CYP27C1 is not yet known. 

The use of this direct oxide reduction process is replacing fluoride reduction as it eliminates neutron exposure to operating personnel (alpha particles from plutonium decay have sufficient energy to eject neutrons from fluorine by the a,n reaction) and eliminates reduction residues which require subsequent recovery. 

Rossol I, A Ptihler (1992) The Corynebacterium glutamicum aecD gene encodes a C-S lyase with alpha-beta-elimination activity that degrades aminoethylcysteine. J Bacteriol 174 2968-2977. 

This experiment eliminated the plum pudding model as a possible structure of the atom. But what did an atom look like Rutherford figured that the only way to make alpha particles bounce backward... 

The tetraols were found to be highly sensitive toward acidic and basic conditions. Under Bronsted acidic conditions, the hemiaminals readily eliminated to generate a tetraene, while under basic conditions, the tetraol either decomposed or epimerized to generate a mixture of diastereomers. It is speculated that the base-mediated epimerization proceeds through ring-chain tautomerization involving a putative alpha-keto amide derivative. It is also of note that simple dissolution of tetraol (+)-95 in methanol also leads to its degradation to a complex mixture of products. 

The silicon analogue of carbene is now called silylene and it was discovered by the thermally-induced alpha elimination of methoxydisilanes. The most common method of silylene generation is ... 

The first evidence that an elimination-addition mechanism could be important in nucleophilic substitution reactions of alkanesulfonyl derivatives was provided by the observation (Truce et al., 1964 Truce and Campbell, 1966 King and Durst, 1964, 1965) that when alkanesulfonyl chlorides RCH2S02C1 were treated in the presence of an alcohol R OD with a tertiary amine (usually Et3N) the product was a sulfonate ester RCHDS020R with exactly one atom of deuterium on the carbon alpha to the sulfonyl group. Had the ester been formed by a base-catalysed direct substitution reaction of R OD with the sulfonyl chloride there would have been no deuterium at the er-position. Had the deuterium been incorporated by a separate exchange reaction, either of the sulfonyl chloride before its reaction to form the ester, or of the ester subsequent to its formation, then the amount of deuterium incorporated would not have been uniformly one atom of D per molecule. The observed results are only consistent with the elimination-addition mechanism involving a sulfene intermediate shown in (201). Subsequent kinetic studies... 

Gotti C, Moretti M, Clementi F, Riganti L, McIntosh JM, Collins AC (2005) Expression of ni-grostriatal alpha 6-containing nicotinic acetylchohne receptors is selectively reduced, but not eliminated, by beta 3 subunit gene deletion. Mol Pharmacol 67 2007-2015 Gotti C, Zoli M, Clementi F (2006a) Brain nicotinic acetylcholine receptors native subtypes and their relevance. TIPS 27 482 91... 

The plasma protein binding of tacrolimus is approximately 99%. Tacrolimus is bound mainly to albumin and alpha-1-acid glycoprotein and has a high level of association with erythrocytes. It is extensively metabolized by the mixed-function oxidase system, primarily the cytochrome P450 system (CYP3A). The disposition of tacrolimus from whole blood was biphasic with a terminal elimination half-life of 11.7 hours in liver transplant patients. 

When the original methyl D-fructofuranoside sirup was fermented with yeast, the unstable beta isomer was selectively eliminated and the residue yielded a crystalline methyl D-fructoside melting at 81° and with [a] D +93° in water. The ring structure of this new isomer was proved to be furan by methylation to the liquid tetramethyl derivative, of [a] °D +129.4°, and subsequent hydrolysis to 1,3,4,6-tetramethyl-D-fructofuranose (structure IX) with the correct specific rotation of +29.8° in water. Both the methyl D-fructoside and its fully methylated derivative were therefore of the alpha configuration, since the latter was more dextrorotatory than the tetramethyl-D-fructose and also since the former was more dextrorotatory than the isomer, of [a] D —51°, unstable to invertase. Similar work with the benzyl D-fructofuranoside sirup produced the crystalline alpha isomer, melting point 89°, [a] D +45.7° in water, the liquid tetramethyl derivative, [a] D +83.3° in chloroform and, after acid hydrolysis of the latter, 1,3,4,6-tetramethyl-D-fructofuranose. 

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