Butyric acid, 2-amino ester

The hydrogenation of 2,4-diketo acid derivatives to the corresponding 2-hydroxy compounds with cinchona-modified Pt catalysts as depicted in Figure 2.4 can be carried out with chemoselectivities more than 99% and enantioselectivities up to 87% (R) and 68% (S), respectively [30a]. Enrichment to more than 98% ee was possible for several substrates by recrystallization, giving rise to an efficient technical synthesis of (R)-2-hydroxy-4-phenyl butyric acid ethyl ester [30b], a building block for several ACE (angiotensin-converting enzyme) inhibitors, as well as some enantio-merically enriched a-hydroxy and a-amino acid esters (see below) [30c]. 

Butyric acid, allyl ester. See Allyl butyrate Butyric acid, 4-amino-. See Aminobutyric acid, Butyric acid anhydride n-Butyric acid anhydride. See Butyric anhydride Butyric acid, benzyl ester. See Benzyl butyrate... 

Butyric acid, butyl ester. See Butyl butyrate Butyric acid, 4-((2-carboxyethyl) amino)-. See Carboxyethyl aminobutyric acid Butyric acid chloride. See Butyryl chloride Butyric acid, 4-((4-chloro-o-tolyl) oxy)-. See MCPB... 

The interaction with both synthetic and naturally occurring amino acids has been studied extensively glycine (138, 173, 219-221), a-(173, 219) and /3-alanine (138, 220), sarcosine (219), serine (222), aspartic acid (138, 173, 222-226), asparagine (222), threonine (222), proline (219), hydroxyproline (219), glutamic acid (138, 222-225), glutamine (222), valine (219, 227), norvaline (219), methionine (222, 226), histidine (228, 229), isoleucine (219), leucine (219, 230), norleu-cine (219), lysine (222), arginine (222), histidine methyl ester (228), phenylalanine (138, 222), tyrosine (222), 2-amino-3-(3,4-dihydroxy-phenyl jpropanoic acid (DOPA) (222), tryptophan (222), aminoiso-butyric acid (219), 2-aminobutyric acid (219,231), citrulline (222), and ornithine (222). 

Amino-4-(ethylmercapto)-butyric acid, S-ethyl-L-homocysteine, homocysteine-S-ethyl ester. 

The first enzymatic reaction investigated in the whole project concerned the introduction of chirality in route B (Fig. 2) by generation of succinic acid mononitrile (R)-12 from its racemic precursor. Since in a broad sense the nitrile ester substrate 10 can be interpreted as an amino acid analogue, proteases recommended themselves as catalysts to be tested. From the literature, 2-substituted succinic and butyric acid esters were known to be resolved by proteases [6, 7]. Proteases are... 

The D-enantiomer of 393 was obtained in an identical sequence of reactions starting frc m 2,3-0-isopropylidene-4-deoxy-D-threitol (395). This compound was prepared from L-threonine (394) in the following way the amino acid was deaminated to 25 3/ -dihydroxy-butyric acid. Esterification of the carboxyl group and protection of both hydroxyl groups with an isopropylidene grouping gave methyl 4-deoxy-2,3-0-isopropylidene-D-threonate. Reduction of the ester group afforded 395 smoothly. 

There is also a later report by the same group regarding the use of a related catalyst 127 in the Michael addition of a-nitro ketones to enones (Scheme 6.19). In this case, a variety of peptides were tested as eatalysts but the best results were obtained with pentapeptide 127, in whieh, among many other different changes, the a-amino iso-butyric acid was employed instead of tert-leucine for the p-turn inducer sequence an additional modified arginine and a phenylalanine methyl ester were incorporated at the NH2 and the CO2H ends respectively. This catalyst furnished the final Michael adducts with moderate enantioselectivities, albeit in good yields in many cases. 

With the exception of a-keto glutaric acid the acids can be identified after total hydrolysis together with the amino acids. A distinction between succinic acid and its amide is possible by reduction with NaBH4 after esterification Only the ester will be reduced to y hydroxy butyric acid which can be identified as r-butyrolactone (ref. 18). 

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