Glycine anion

Glycine anion (230) is decarboxylated when exposed to hydroxyl radicals. The major initial product is an amino radical cation (231), which suffers rapid 100 ns) fragmentation into CO2 and a carbon-centred radical (232). Oxidative decarboxylation... 

In biological chemistry, the reaction of the glycine anion H2NCH2C02 with HO has been investigated by pulse radiolysis. The major pathway was found to be loss of... 

Monofluoroalanine is accessible, as a racemate, by means of either classical methods or fluoromethylation of a masked glycinate anion by a monofluorohalo-genomethane (CH2C1F). ... 

Trifluoroalamne cannot be prepared by alkylation of a glycine anion with tri-fluoromethyl halides, since these electrophiles are not able to alkylate enolates. Other approaches have been reported using various substrates, but none is really satisfying. The three main ones are ... 

The numerous preparations of mono-, di-, tri-, and hexafluoro derivatives of valine, norvaline, leucine, norleucine, and isoleucine, using classical methods of amino acid chemistry (e.g., amination of an a-bromoacid, " azalactone, Strecker reaction, amidocarbonylation of a trifluoromethyl aldehyde, alkylation of a glycinate anion are not considered here. Pure enantiomers are generally obtained by enzymatic resolution of the racemate, chemical resolution, or asymmetric Strecker reaction. ... 

Trifluorothreonine is one of the rare fluorinated compounds found in nature (cf. Chapter 4). The best method for the synthesis of fluorothreonines is the acylation of an equivalent of glycinate anion by a fluoroacetic derivative. The four stereoisomers of monofluorothreonine have been prepared. A completely stereoselective chiral approach involves the alkylation of the Seebach imidazolidinone by fluoroacetyl chloride (Figure 5.16). ... 

Reduction of a S-aminoketone resulting from the addition of an equivalent of a glycinate anion on ethyl difluoro- or trifluoroacetate is stereoselective and leads to ethyl di- or trifluorothreoninate threo (syn). Release of the acid, performed by saponification, is accompanied by a partial epimerization into an alio compound. However, the amino acids are obtained in enantiopure forms by using a lipase. . It s important to note that (25, 35)-difluorothreonine exhibits activity toward the growth of leukemia cell hnes comparable to 5-fluorouracil. ... 

Fluoral has been condensed with an equivalent of chiral glycinate anion. The chirality stems from a chiral nickel complex with a chiral Schiff base derived from proline as hgand (Figure 5.17). (25, 35)-Difluorothreonine has thus been obtained with an excellent selectivity (de > 95%). This method also allows preparation of numerous fluoroalkyl and fluoroaryl analogues of threonine. Enantiopure difluorothreonine could also be prepared from ascorbic acid. ... 

Husson and co-workers (47-50) have made extensive application of their chiral azomethine ylide precursor. The synthon 177, prepared in one step in essentially quantitative yield on a multi-gram scale, had previously been used in a wide range of asymmetric processes as a chiral glycine anion equivalent. However, low-temperature treatment with TMS triflate (yet another example of the use of... 

Die aus optisch-aktiven 2,5-Dioxo-piperazinen [cyclo-Dipeptiden wie cyclo(-L-Val-Gly-)] zu erhaltenden 3,6-Dimethoxy-2,5-dihydro-pyrazine4 5 liefern mit Butyl-lithium in THF ein chirales, nicht-racemisches Glycin-Anion-Aquivalent (optisch-aktives Aminosaure-Enolat)6, das der elektrophilen Substitution durch Alkylierung oder Michael-Addition zuganglich ist z.B. ... 

Die elektrophile Substitution von Glycin-Anion-Aquivalenten aus weiteren acyclischen Derivaten von a-Amino-carbonsauren hat auBer in cinigen Sonderfallen7-0 fur die Syn-these hoherer a-Aminosaurcn oder deren a-Alkyl-Homologen keine Bedeutung gewonnen. Tab. 71 (S. 509) gibt Hinweise auf die verwendeten Edukte und das berichtete Synthese-Potential. 

Tab.71 Elektrophile Alkylierung von verschiedenen Glycin-Anion-Aquivalenten...

The glycinate anion, gly- = NH2CH2C02-, bonds to metal ions through the N atom and one of the O atoms. Using N O to represent gly-, sketch the structures of the four stereoisomers of Co(gly)3. 

Sprinz H, Adhikari S, Brede O (2001) Transformation of phospholipid membranes by thiyl radicals via ds-tmns isomerization in fatty acid residues. Adv Colloid Interface Sci 89/90 313-325 Stefanic I, Bonifacic M, Asmus K-D, Armstrong DA (2001) Absolute rate constants and yields of transients from hydroxyl radical and H atom attack on glycine and methyl-substituted glycine anions. J Phys Chem A 105 8681-8690... 

Figure 10.1 Chelation of Cu2+ by glycinate anion ligands to form the glycinate chelate. Each electron donor group on the glycinate anion chelating agents is designated with an asterisk. In the chelate, the central copper(ll) metal ion is bonded in four places and the chelate has two rings composed of the five-atom sequence Cu-O-C-C-N.

Specific solute-solvent interactions, which are not explicitly taken into account in continuum models, can play a significant role especially for charged species. A typical cluster formed by the glycine anion radical with four water molecules is shown in figure 16. The analogous supermolecule obtained for the neutral form is quite similar, except for the much weaker interaction energies involved in the neutral species. The number and the position of the solvent molecules are determined by molecular dynamics simulations performed by the AMBER force field [141]. 

Casiraghi, G, Rassu, G, Spanu, P, Pinna, L, A-rerr-Butoxycarbonyl-2-(fert-butyldimethyl-silyloxy)pyrrole as a glycine anion equivalent a flexible enantioselective access to polyhydroxy-a-amino acids. Tetrahedron Lett., 35, 2423-2426, 1994. 

Figure 4.2 The glycinate anion (gly ) at pH 11.5, and the methionine zwitterion, pH 8-9, treated as a neutral molecule.

In 1978, O Donnell and coworkers developed the benzophenone imines of glycine alkyl esters 4 as glycine anion equivalents, which have been found to be perfed to use in the phase-transfer catalysis [10]. An essential feature of this reaction system lies in the selective mono substitution of the starting Schiff base, the O Donnell substrate 4. This can be possible because of the significant difference in acidity of a-hydrogen between starting substrate 4 p/C,(DMSO) 18.7 (R=Et)] and a-monosubstituted produd S p/C,(DMSO) 22.8 (R=Et, E = Me), 23.2 (R=Et, E = CH2Ph)] [11]. This dramatic acidity difference makes it possible for selective formation of only monoalkylated product without concomitant production of undesired dialkylated produd or racemization. 

---