Amino acids optically active

The reaction can be used ia the large-scale production of the optically active amino acid detivatives. The chiraUty of the a-carbon is substantially retained and resolution of the product is avoided. 

Asymmetric synthesis is a method for direct synthesis of optically active amino acids and finding efficient catalysts is a great target for researchers. Many exceUent reviews have been pubHshed (72). Asymmetric syntheses are classified as either enantioselective or diastereoselective reactions. Asymmetric hydrogenation has been appHed for practical manufacturing of l-DOPA and t-phenylalanine, but conventional methods have not been exceeded because of the short life of catalysts. An example of an enantio selective reaction, asymmetric hydrogenation of a-acetamidoacryHc acid derivatives, eg, Z-2-acetamidocinnamic acid [55065-02-6] (6), is shown below and in Table 4 (73). 

A recent report describes the conversion of A-formyl- and N-acetyl-L-leucine into optically active azlactones with dicyclohexyl-carbodiimide (DCC) [Eq. (29)]. Other cyclization reagents, e.g. acetic anhydride, POCI3, SOCI2, and polyphosphoric acid, cause racemiza-tion. These azlactones react with optically active amino acid esters to give esters of dipeptides with retention of activity. 

Reductive alkylation with chiral substrates may afford new chiral centers. The reaction has been of interest for the preparation of optically active amino acids where the chirality of the amine function is induced in the prochiral carbonyl moiety 34,35). The degree of induced asymmetry is influenced by substrate, solvent, and temperature 26,27,28,29,48,51,65). Asymmetry also has been obtained by reduction of prochiral imines, using a chiral catalyst 44). Prediction of the major configurational isomer arising from a reductive alkylation can be made usually by the assumption that amine formation comes via an imine, not the hydroxyamino addition compound, and that the catalyst approaches the least hindered side (57). 

Not only the smallest optically active amino acid (alanine), but also leucine, several (substituted) aromatic amino acids, heterosubstituted amino acids (methionine, homomethionine and thienylglydne) and even an iminoacid, proline, are obtainable in both the L- and D-form. 

Photodriven reactions of Fischer carbenes with alcohols produces esters, the expected product from nucleophilic addition to ketenes. Hydroxycarbene complexes, generated in situ by protonation of the corresponding ate complex, produced a-hydroxyesters in modest yield (Table 15) [103]. Ketals,presumably formed by thermal decomposition of the carbenes, were major by-products. The discovery that amides were readily converted to aminocarbene complexes [104] resulted in an efficient approach to a-amino acids by photodriven reaction of these aminocarbenes with alcohols (Table 16) [105,106]. a-Alkylation of the (methyl)(dibenzylamino)carbene complex followed by photolysis produced a range of racemic alanine derivatives (Eq. 26). With chiral oxazolidine carbene complexes optically active amino acid derivatives were available (Eq. 27). Since both enantiomers of the optically active chromium aminocarbene are equally available, both the natural S and unnatural R amino acid derivatives are equally... 

The exchange of the chiral phenylethyl amine against an optically active amino acid fragment 269 allowed the synthesis of conformationally restrained dipeptidyl lactams 271 and 272 including the so called Freidinger lactams as... 

Moreover, the present data may throw some light on the generation of optically active amino acids on the Earth 50-5I). Photocyclization of 96 proceeds efficiently in... 

When we first contemplated thermochemical products available from Glu, a search of the literature revealed no studies expressly directed at hydrogenation to a specific product. Indeed, the major role that Glu plays in hydrogenation reactions is to act as an enantioselectivity enhancer (17,18). Glu (or a number of other optically active amino acids) is added to solutions containing Raney nickel, supported nickel, palladium, or ruthenium catalysts and forms stereoselective complexes on the catalyst surface, leading to enantioselective hydrogenation of keto-groups to optically active alcohols. Under the reaction conditions used, no hydrogenation of Glu takes place. 

Use of optically active amino acids with Co(CN)53 gave negligible optical induction (310). 

In contrast to the success in the synthesis of optically active amino acids and related compounds, only limited success has been achieved in the asymmetric synthesis of chiral amines or related compounds. One breakthrough is the asymmetric hydrogenation of arylenamides with Rh catalysts containing... 

When incorporating an optically active amino acid derivative, a separate imine-forming step should be avoided. 

What are the facts of life One of the most striking is that all known living systems involve the same types of polymers, i.e., three varieties of homochiral biopolymers. That is, each variety is composed of unique molecular building blocks having the same three-dimensional handedness. Thus, with rare exceptions, the proteins found in cells are composed exclusively of the 1-enantiomers of 19 optically active amino acids (Fig. 11.1). Similarly, only D-ribose and 2-deoxy-D-ribose sugars are found in the nucleic acid polymers that make up the RNAs and DNAs, which are essential for protein synthesis in the cell and for the transmission of genetic information from one generation to the next. 

A new route to optically active amino-acids has been achieved by treatment of halogen compounds with Fe° or Ni° diastereoisomeric complexes of a-methylbenzyliminoglyoxylic acid ethyl ester. ... 

Enantiomer separation on optically active amino acid, dipeptide, diamide and amide phases by association via hydrogen bonding. " ... 

The third method of separating optically active substances by combining them with optically active bases or acids had not been employed with any success until E. Fischer took up this question, the study of the optically active amino acids being his first work upon the chemical constitution of the proteins. The non-success of this method was in all probability due to the small affinity which the simple amino acids themselves have for combining with acids and bases even the attempts to separate the monoaminodicarboxylic acids, which are fairly strong acids, were not successful. 

E. Fischer und K. Raske. See under optically active amino acids. 

R. M. Williams in Synthesis of Optically Active. Amino Acids, Pergamon. Oxford 1989. 

R.M. Williams u. J.E. Baldwin, Synthesis of Optically Active Amino-Acids, S. 113, Pergamoil Press, Oxford New York Beijing Frankfurt Sao Paulo Sydney Tokio Toronto 1989 (Organic Chemistry Series, Vol. 7). 

K. Yonaha u. K. Soda, Ad v. Biochem. Eng./Biotcchnol. 33,95 -130 (1986) . .Applications of Stereoselectivity of Enzymes Synthesis of Optically Active Amino Acids and a-Hydroxy Adds and Stereospecific Isotope Labeling of Amino Acids, Amines, and Coenzymes". 

The co-polymerization of D-alanine-derived A-propargylamide 22, L-valine-derived 23, and pyrene-based monomer 24 gives helical poly(22 -< o-23-c -24) carrying pyrene. The secondary structure of the co-polymer is tunable by the composition of the optically active amino acid units and solvent, which makes it possible to control the direction of the pyrene groups in the side chain. The interaction between the pyrene groups is small when the co-polymer takes a helical structure. The pyrene groups are regularly positioned in the polymer side chain. The co-polymer emits weak... 

In 1976, Achiwa 40) synthesized the first functionalized chiral hiphosphanes starting with an optically active amino acid, namely 4-hydroxy-(S)-proline (12). 

Miller and his co-workers60) reported surprisingly high optical yields, close to 50 %, in the reduction of 2-acetylpyridine in the presence of strychnine. They also prepared chemically modified electrodes with optically active amino acids and attempted asymmetric induction in both reduction and oxidation61 . The best optical yield, only 14.5 %, seemed to be obtained in the reduction of 4-acetyl-pyridine on a graphite cathode modified with (S)-phenylalanine methyl ester. 

Nonaka et al. 62) examined the asymmetric reduction of open-chain olefins in the presence of optically active amino acids. In the best case (R)-methylsuccinic acid (23) was formed in 2.4 % and 53 % optical and chemical yields, respectively, from citraconic acid (24) in the presence of (R)-cysteine. 

The protoberberine alkaloid, xylopinine, has been synthesized in an optically active form by Kametani et al.22 ). A key reaction in this synthesis was the photochemical cyclization of the optically active amino acid derivative 1,2,3,4-tetrahydro-6,7-dimethoxy-3-methoxycarbonyl-1 -methylene-2-veratroylisoquinoline with 1,3... 

For instance, RNi modified with an optically active amino acid or hydroxy acid hydrogenates methyl acetoacetate (MAA) to produce optically active methyl 3-hydroxybutyrate (MHB) as shown in Fig. 1. 

Independently, Isoda el al. in 1958 reported strange results from hydrogenations in the presence of RNi (60a) and RNis treated with optically active amino acids (60b). Table I shows examples of some of the results of their experiments. 

Nickel, cobalt, copper, ruthenium, and copper-ruthenium catalysts modified with optically active amino acid or hydroxy acid have been extensively investigated by Klabunovskii s group since 1964 (82). However, those catalysts have been reported to have lower EDA than that of MRNi. 

Since enzymes are proteins made up of optically active amino acids, enzymes are themselves optically active and therefore react with only one enantiomer of a chiral substrate. 

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