X-Amino

X-Amino acids ate ampholytic compounds. The chemical reactions of amino acids can be classified according to their carboxyl, amino, and side-chain groups. Most of the reactions have been well known for a long time the details of these reactions have been reviewed (77). 

Formation of N-Carboxy-(X-Amino AeidAnhydride (NCA) (85), NCAs are important as starting materials for amino acid polymers. They are prepared by the reaction of amino acids with phosgene in an aptotic solvent. 

The intermediate formation of iminium salts is postulated in the reduction of (x-amino ketones by the Clemmensen method, occurring with concomitant ring enlargement or contraction (244-246). Reduction of l,2,2-trimethyl-3-piperidone (154) in this manner gave l-methyl-2-iso-propylpyrrolidine (155). 

Carbohydrate-derived titanium cnolates also provide yvn-x-amino-/l-hydroxy esters of high diastcrcomeric and enantiomeric purity. For this purpose, the lithium enolate derived from ethyl (2,2,5,5-tetramcthyl-2,5-disilapyrrolidin-l-yl)acetate is first transmctalated with chloro(cy-clopentadienyl)bis(1,2 5,6-di-0-isopropylidene-a-D-glucofuranos-3-0-yl)titanium and subsequently reacted with aldehydes.. vj-n-a-Amino-/ -hydroxy esters are almost exclusively obtained via a predominant /te-side attack (synjanti 92 8 to 96 4 87-98% ee for the xvn-adducts)623-b. 

Introduction of an electron-withdrawing carboxy function at the x-carbon produces particularly reactive A-acyliminium ions, the so-called glycine cation equivalents, which are of great utility for the synthesis of x-amino acids. 

Carbonsiiure-nitrile konnen durch Hydride zu Aldehyden bzw. Aldiminen oder prim. Aminen reduziert werden. Bei x-Amino-nitrilen gelingt es, die Cyan-Gruppe hy-drogenolytisch abzuspalten. 

Chiral A-substitutcd benzisothiazole-3-one-1,1-dioxide (saccharin) derivatives 258 are synthesized via the direct ortho-lithiation of 3-A-arylsulfonyloxazolidine-2-ones 257 using LDA and HMPA <06TL6405>. Compounds 257 are readily prepared from (X)-amino acids. 

K. Aoi, K. Tsutsumiuchi, A. Yamamoto, and M. Okada, Globular carbohydrate macromolecule sugar balls 3. Radial-growth polymerization of sugar-substituted x-amino acid N-carboxyanhydrides (glyco-NCAs) with a dendritic initiator, Tetrahedron, 53 (1997) 15415-15427. 

Sarnecka-Keller, M., Joraszowa, E., and Noworytko, J., Aminoaciduria u pacjentow Ieczonych promieniami X. [Amino aciduria in patients treated with X-rays.] Polskie Arch. Med. Wewngtrznej 29, 1521-1528 (1959). 

Table X. Amino Acid Compositions of Acid Hydrolyzed Protein Fractions from DMSO and Aqueous Extracts of Pondweed and Water Spinach3...

Method B The protected amino ester (10 mmol) and a,P-unsaturated ketone (10 mmol) are stirred with K,CO, (0.28 g) and TEBA-C1 (0.23 g, 1 mmol) at room temperature until the mixture solidifies. The mixture is allowed to stand for 10 h, and H20 (100 ml) is then added. The precipitated pyrrolidine is collected, washed with H20, and recrystallized from MeOH. 

Another kind of combinatorial synthesis can be applied to reactions that assemble the product from several components in a single step, a multicomponent reaction. A particularly interesting four-component reaction is the Ugi reaction, which generates dipeptides from an x-amino acid, an isocyanide, an aldehyde, an amine, and a carboxylic acid. Use of 10 different isocyanides and amines, along with 40 different aldehydes and carboxylic acids, has the potential to generate 160,000 different dipeptide products ... 

D-p-Hydroxyphenylglycine is an important component of certain semi-synthetic antibiotics such as the semi-synthetic cephalosporins cefadroxil and cefatrizine and the semi-synthetic penicillin amoxicillin, with a combined world market in excess of 3 x 10 /a. Synthesis was possible from DL-5-monosubstituted hydantoins (cyclic ureides of amino acids) provided that a selective D-hydantoinase could be found, which would be competitive with chemical methods. 

Table 1. a-Substituted x-Amino Acetates (Glycine Derivatives) by Alkylation of 3.6-Dialkoxy-2,5-dihy-dropyrazines. Followed by Hydrolysis... 

Edukt1 (Konfig.) Alkylierung mit Produkt (Konfig.) Schmp. [°C] Ausbeute [%] (% ds) Hydrolyse mit x-Alkyl-x-amino- carbonsaure Ausbeute [%] Md Lite- ratur... 

Die nachstehenden, durch Hydrolyse und Hydrogenolyse in (/ )- bzw. (S )-(X-Amino-car-bonsauren IV iiberfiihrbaren N-substituierten Verbindungen II und III wurden u. a. ent-sprechend synthetisiert ... 

B. Ganem, Electrophilic azide transfer to chiral enolates, a general approach to the asymmetric synthesis of x-amino-aeids, Chemtracts Org. Chem. 1, 145 (1988). 

The isolation of the diaquo-nitrate depends on its sparing solubility, on account of which it may be precipitated from a solution in which there is equilibrium between the ju-amino-ol and the /x-amino-diol compounds, by means of nitric acid thus ... 

In 1913 Werner 2 described a new series of optically active cobalt compounds containing two asymmetric cobalt atoms in the molecule, the tetraethylenediamino-/i-amino-nitro-dicobaltic salts. The resolution is effected by treating tetraethylencdiamino - /x - amino - nitro-dicobaltic bromide with silver d-bromo-camphor sulphonate and fractionally crystallising the product. 

Optically active peroxo-salts may be transformed into /x-amino-ol-cobaltic salts. Thus, l-tetraethylenediamino-/x-amino-peroxo-dieobaltic salts yield d-tetraethylenediamino-p.-amino-ol-salts and d-tetraethyl-enediamino-p,-amino-nitro-dicobaltic salts. In each case there is a change in sign from the /x-peroxo-salts to the yx-amino-ol or u-amino-nitro-dieobaltie salts, and a distinct diminution in rotation. 

Soloshonok and co-workers have developed a method for the synthesis of a-(perfluoro-alkyl)amines from perfluoroalkyl carbonyl compounds by a transamination involving an azomethine a/omethine (Schiffbase) isomerization. They call this method a biomimetic, base-catalyzed 1,3-proton shift reaction, and have applied it to perfluoroaldehydes,12-15 perfluoroalkyl ketones,12 18 / -(perfluoroalkyl)-/l-oxo esters,15 16 19 24 and - -( perfluoroalkyl)-a-oxo es-ters2 " -26 to synthesize the corresponding a-(perfluoroalkyl)amincs, / -(perfluoroalkyl )-/i-amino acids, and 3 -(perfluoroalkyl)- x-amino acids. 

Use of benzyl alcohol resulted in formation of the benzyl ether corresponding to allyl ethers 52, but attempted Claisen rearrangement resulted in an 82 % yield of the product of a 1,3-benzyl shift (see Section 5.1.3.).20 To demonstrate the utility of the methodology outlined in Table 14, x-oxoester 53a was converted into the corresponding x-amino acid by hydrolysis and reductive animation.20... 

With an amino ester as nucleophile, the example shown in Equation 8E.5 demonstrates that the catalyst rather than the substrates can dominate in determining the diastereoselectivity. The 3 1 selectivity exhibited in the alkylation with the achiral catalyst was increased to 19 1 with (/ ,/ )-5 whereas the (S,5)-5, under identical conditions, gave a 1 3 ratio. 

Aminodinitrotoluenes, x,x-Dinitro-x-amino-toluenes, x,x-Dmitro-x-methyl anilines or x,x-Dinitro- (o-, m-, p-) -toluidines). CH3.C6H2-NH2(N02)2, C7H7N304 mw 197.17 N 21.32% OB to C02 —109.55%, V sol in acet fairly sol in RT ethanol, eth and acetic acid si sol in coned hydrochloric acid... 

The effects of small amounts of anionic x-amino acids and several small peptides on the kinetics of 5n 1 hydrolysis of 2-(4-nitrophenoxy)tetrahydropyran have been investigated at pH of 11 and 40 °C.124 The retarding effect of 1 molal co-solute was plotted as ln(km=i/km=a) versus the number of CH groups in the amino acid side-chain. Various linear correlations were observed and the results were interpreted in terms of the hydrophobicity of CH. The effects of alcohols as co-solute were also studied. 

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