Aspartate ester complex

Not only is OH- a potent nucleophile in this context but so is NH2- bound to the metal ion. The pentaammine maleatoester complexes of the type Co(NHa)s00CCH=CHC00R2+ readily react in basic aqueous solution to give the chelated aspartate ester complex (11). 

Selectivity studies with DTU indicated marked discrimination in the clathrate formation 23,45). As in other types of clathrates, the steric factor is important in differentiation between compounds of similar functionality but different shape. For example, DTU forms crystalline complexes with some alcohols (methanol, ethanol, propanol, 1-butanol) but not with others (2-butanol). It complexes the ethyl esters of N-acetyl derivatives of glycine, alanine, methionine and aspartic acid, but not of proline, serine, phenylalanine and glutamic acid. 

BINAP-Ru is effective for the diastereoselective hydrogenation of some chiral yS-keto esters (Fig. 32.13). Reaction of N-Boc-protected (S)-y-amino / -keto esters 13A catalyzed by the (R)-BINAP-Ru complex results in the syn alcohols 13B exclusively [52]. The stereocenter at the / -position is controlled by the chirality of the catalyst therefore, use of the S catalyst affords the anti isomer, as predicted. Derivatives of statine, a key component of the aspartic proteinase inhibitor pep-... 

More detailed studies of reactions of this type have been reported.96,97 Nickel(II) complexes of histidine and tryptophan provide stereoselectivity in the hydrolysis of histidine methyl ester, but stereoselectivity is not observed with nickel(Il) complexes of aspartic acid or methionine. Only tridentate ligands with a minimum steric bulk appear to be capable of exhibiting stereoselectivity in reactions of this type. 

Fast-atom-bombardment mass spectrometry of a proteinase-truncated glucosyl-enzyme complex showed that the glucose was covalently linked as a /3-acetal ester to the carboxyl group of the aspartic acid located at the sixth residue from the N-terminal of the peptide ... 

In addition to this we have several examples of which the polymer conformation of the polymeric complex leads the asymmetrical selectivity Hydrogenation reactions of 1-methylcinnamic acid and 1-acetamidocinnamic acid by several poly(L-amino acid)-Pd complexes are observed (142-144). Poly(L-valine) (/3-form) and poly(/3-benzyl-L-aspartate) (a-helix, sinistral) give dextrorotative products, and poly(L-leucine) and poly( 3-benzyl-L-aspartate) (a-helix, dextral) do levo-rotatory products. Also, optical active poly-/3-hydroxyl esters-Raney Ni catalyst (145) and Ion-exchange resin modified by optical active amino acid-metal complex (146,147) are observed in asymmetrically selective hydrogenations. 

The earliest, and most complex, protocol is presented by Burgess and cowoikers [66]. Starting from aspartic acid dimethylester, the amino group is acylated by adamantyl carboxylic acid chloride (see Figure 6.26). Reduction of the two ester groups, but not the amide function, with NaBH in ethanol followed by ring closure yields an oxazolineto-sylate that is transformed into the iodide. 

A complex procedure for determining the content of asparagine and glutamine separately in proteins has been described (see Chibnall et al. 1958). This procedure makes use of esterification of the protein, reduction of the resulting esters of aspartic acid and glutamic acid with lithium borohydride and hydrolysis of asparagine and glutamine to the acids in which form they are analyzed. Despite the side reactions for which corrections must be made, this method, in conjunction with total enzymic hydrolysis, may be useful to those who must quantitatively estimate these 4 amino acids. 

Proposed mechanism for the catalytic hydrolysis of the sulfate ester bond by the active form of aryl sulfatase-B (AS-B), and the structure (right) of the active centre of the vanadate AS-B complex, otherwise containing the substrate sulfate. The active centre also accommodates a seven-coordinated calcium ion, ligated to three aspartates (one of which is in the Y-mode), an asparagine and two 0X0 anions of the sulfate/vanadate. Structure modified from that provided in ref. 95. 

The biosynthesis of threonine from aspartate involves formation of the four metabolic intermediates illustrated in Fig. 2. The /3-carboxyl group of aspartate is first activated by formation of an acylphosphate, and this reaction is followed by two reductive steps resulting in the synthesis of homoserine. After formation of a C4 phosphate ester of homoserine, threonine is synthesized by a complex rearrangement which entails formation of the terminal methyl group and transfer of the oxygen atom from C-4 to form a hydroxyl group at C-3. 

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