Aspartic acid stereochemistry

In the case of thienamycin (Fig. lb) the absolute stereochemistry at C-5 was unambiguously deterrnined from the ene-lactam (16). The resultant (R)-aspartic acid (17) demonstrated that the absolute stereochemistry at C-5 of thienamycin is (R), corresponding to that found in the C-5 position of both penicillins and cephalosporins. Confirmation of the stereochemical assignments in both thienamycin (2) and the olivanic acid MM 13902 (3, n = 0) has been confirmed by x-ray crystallography (19,21,22). The stmctural determination of the nonsulfated derivatives from S. olivaceus (23), PS-5 (5) (5), the carpetimycins (6), and the asparenomycins (7) followed a similar pattern. 

Aspartame is a dipeptide, made up of aspartic acid and phenylalanine. Identify all the chiral atoms in aspartame and assign R/S stereochemistry to each. Is the stereochemistry the same as in the natural forms of aspartic acid andphenylalaninel... 

Aspartic acid at 20°C rotates the plane of polarization to the right, [a] D20 = + 4.36° but with the increase in temperature, the plane of polarization is rotated to the left, [a] D90 = -1.86° although the configuration of the antipode remains unchanged. Therefore, determination of the configuration of the isomers is a specific area of stereochemistry. The reader at this state must understand the logic to tackle this problems, the experimental techniques employed have been given later. 

In RmL the nucleophilic triad consists of Ser-144, Asp-203, and His-257, whereas in hPL the analogous amino acids are Ser-153, Asp-177, and His-264. All hydrogen bonds identified in this system are analogous to those observed in serine proteinases Ne2 of the histidine is bonded to the serine hydroxyl, and N31 is H-bonded to the aspartic acid (Fig. 4). Further details of the H-bonding stereochemistry are given in Table II. 

A simple heterocyclic acid needed for an anti-HIV drug A chiral pool synthesis from aspartic acid Choosing a new reaction to solve the stereochemistry problem Making the new reaction asymmetric Part III - Grandisol and Some Bicyclo[3.2.0]Heptan-2-Ols A bicyclic insect attractant used in agriculture Chiral Pool Syntheses from Other Terpenes An attempt from linalool... 

The enzyme aspartase (EC 4.3.1.1.) has long been known to catalyze stereospecific addition of ammonia across the double bond of fumaric acid (216-218), and after the original assignment of stereochemistry to this reaction was corrected, it was realized that addition of ammonia was anti (82). Since the enzyme is commercially available, reaction of fumaric acid 72 in H20/N H3 readily affords (2S, 3R)-[3- Hi]aspartic acid 21a, Hg = H, whereas addition of ammonia to [ Hj] fumaric acid 72, Ha = H, yields (2S, 3S)-[2,3- H2] aspartic acid 21a, H = H (218-221). Recently, aspartase in immobilized... 

The two structures starting from L-aspartic acid are shown in Scheme 10. Pathway A is the acid-catalyzed thermal condensation, and B is the noncatalyzed thermal condensation. The polysuccinimide intermediates hydrolyze at the points indicated to give mixtures of a, p poly (d,l- aspartic acid) salts. Regardless of the stereochemistry of the starting aspartic acid, d or l, the final polymeric product is always the dl racemate. 

Quinazolinone annelation of the 0-protected chiral pyrolidinone 74 (derived from L-aspartic acid) forms pyrrolo[2,l-fc]quinazohn-9(lH)-one 75 subsequent desilylation affords (S)-(-)-vasicinone 10, which is identical with the natural /-product (Scheme 16) [212,213]. Asymmetric oxidation of de-oxyvasicinone 11 (via the imine enolate) with either (R)- or (S)-Davis ox-aziridine reagent (lO-camphorsulfonyloxaziridine) [214,215] provides a convenient route to both enantiomers, thus confirming the recently revised stereochemistry of natural vasicinone (Scheme 16) [212,213]. Recently another approaches to optically active pyrrolo[2,l-fo]quinazolinones 10 have been reported by Kamal et al. (lipase-catalyzed resolution) [56], and Argade et aL (asymmetric synthesis from (S)-acetoxysuccinic anhydride) [216]. One-pot synthesis of 11, and related alkaloids has been also developed by utilizing microwave irradiation by Liu et al. [217]. Biogenetically patterned short-step synthesis of pyrroloquinazolinone alkaloids is well established by On-aka [218], and for many other synthesis, see the references cited in these papers. 

Patel, J., Pelloux-Leon, N., Minassian, F and Vallee, Y. (2005) Synthesis of S-enantiomers of hanishin, longamide B, and longamide B methyl ester from L-aspartic acid P-methyl ester establishment of absolute stereochemistry. J. Org. Chem.. 70, 9081-9084. 

Hydrolysis of aspartame hydrolyzes both the amide group and the ester group in the molecule. Hydrolysis of the ester group produces methanol and the carboxylic acid group in phenylalanine, shown below. Hydrolysis of the amide group converts this group to an amine (shown below on phenylalanine) and a carboxylic acid (on the left side of aspartic acid below). Note that the stereochemistry at both chirality centers is retained because none of the bonds to the chirality centers are broken in this transformation. 

The reaction mechanism of a-amylases is referred to as retaining, which means that the stereochemistry at the cleaved bond of the carbohydrate is retained. Hydrolysis of the glycosidic bond is mediated by an acid hydrolysis mechanism, which is in turn mediated by Aspl97 and Glu233 in pig pancreatic amylase. These interactions have been identified from X-ray crystallography. The aspartate residue has been shown to form a covalent bond with the Cl position of the substrate in X-ray structure of a complex formed by a structurally related glucosyltransferase. " The glutamate residue is located in vicinity to the chloride ion and acts as the acidic catalyst in the reaction. The catalytic site of a-amylases is located in a V-shaped depression on the surface of the enzyme. 

Aminotransferases are useful enzymes for the synthesis and manipulation of amino acids. Young et al. investigated the ability of PLP-dependent aminotransferases to catalyze 3-subshtuhon of L- and D-P-chloroalanine 51 using P-mercap-toethanol (Scheme 2.22). L-Aspartate aminotransferase and D-aminotransferase catalyzed the substitution of l-51 and d-51, respechvely, to 52 with retention of stereochemistry [24]. 

As shown in Fig. 3, Lewis acids (i.e., metal ions and hydrogen bond donors) display syn or anti stereochemistry as they interact with the carboxylate anion. However, in a study of enzyme active sites. Candour (1981) first noticed that hydrogen bond donors to the carboxylates of aspartate and glutamate residues preferentially occur with syn stereochemistry. As a carboxylate-hydrogen bond donor interaction COg-H... 

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