Aspartic amide

Alitame (trade name Adame) is a water-soluble, crystalline powder of high sweetness potency (2000X, 10% sucrose solution sweetness equivalence). The sweet taste is clean, and the time—intensity profile is similar to that of aspartame. Because it is a stericaHy hindered amide rather than an ester, ahtame is expected to be more stable than aspartame. At pH 2 to 4, the half-life of aUtame in solution is reported to be twice that of aspartame. The main decomposition pathways (Fig. 6) include conversion to the unsweet P-aspartic isomer (17) and hydrolysis to aspartic acid and alanine amide (96). No cyclization to diketopiperazine or hydrolysis of the alanine amide bond has been reported. AUtame-sweetened beverages, particularly colas, that have a pH below 4.0 can develop an off-flavor which can be avoided or minimized by the addition of edetic acid (EDTA) [60-00-4] (97). 

Breakdown of the amide dihydrate occurs by a mechanism similar to its formation. The ionized aspartate carboxyl (Asp in Figure 16.27) acts as a general base to accept a proton from one of the hydroxyl groups of the amide dihydrate, while the protonated carboxyl of the other asparate (Asp in this case) simultaneously acts as a general acid to donate a proton to the nitrogen atom of one of the departing peptide products. 

The carboxamidomethyl ester was prepared for use in peptide synthesis. It is formed from the cesium salt of an A-protected amino acid and o -chloroacet-amide (60-85% yield). It is cleaved with 0.5 M NaOH or NaHC03 in DMF/H2O. It is stable to the conditions required to remove BOC, Cbz, Fmoc, and t-butyl esters. It cannot be selectively cleaved in the presence of a benzyl ester of aspartic acid. ... 

A more general method for preparation ofa-amino acids is the amidotnalmatesynthesis, a straightforward extension of the malonic ester synthesis (Section 22.7). The reaction begins with conversion of diethyl acetamidomalonate into an eno-late ion by treatment with base, followed by S 2 alkylation with a primary alkyl halide. Hydrolysis of both the amide protecting group and the esters occurs when the alkylated product is warmed with aqueous acid, and decarboxylation then takes place to vield an a-amino acid. For example aspartic acid can be prepared from, ethyl bromoacetate, BrCh CCHEt ... 

The mechanism for the lipase-catalyzed reaction of an acid derivative with a nucleophile (alcohol, amine, or thiol) is known as a serine hydrolase mechanism (Scheme 7.2). The active site of the enzyme is constituted by a catalytic triad (serine, aspartic, and histidine residues). The serine residue accepts the acyl group of the ester, leading to an acyl-enzyme activated intermediate. This acyl-enzyme intermediate reacts with the nucleophile, an amine or ammonia in this case, to yield the final amide product and leading to the free biocatalyst, which can enter again into the catalytic cycle. A histidine residue, activated by an aspartate side chain, is responsible for the proton transference necessary for the catalysis. Another important factor is that the oxyanion hole, formed by different residues, is able to stabilize the negatively charged oxygen present in both the transition state and the tetrahedral intermediate. 

NH3, GOj, and the amide nitrogen of aspartate provide the atoms of urea. 

In an attempt to design the p-turn-peptide-mimics, aspartic acid (an amino acid also known as aspartate) and lysine (an amino acid especially found in gelatin and casein) were attached to each amine group of 1,3-diaminoada-mantane in the form of amide bonds. The term p-turn refers to a peptide chain that forms a tight loop such that the carbonyl oxygen of one residue is hydrogen... 

Diethyl ether, methyl n-propyl ether, diethylamine, N-methyl-1 -propanamine, acetone, allyl alcohol, dimethylformamide, propanamide, 2-methylpropan-amide, 2,2-dimethylpropanamide, benzamide, dichloromethane, toluene, ethyl N-acetyl-glycinate, -alaninate, -methioninate, and -aspartate, ethyl acetate, tetrahydrofuran... 

Many enzymes have absolute specificity for a substrate and will not attack the molecules with common structural features. The enzyme aspartase, found in many plants and bacteria, is such an enzyme [57], It catalyzes the formation of L-aspartate by reversible addition of ammonia to the double bond of fumaric acid. Aspartase, however, does not take part in the addition of ammonia to any other unsaturated acid requiring specific optical and geometrical characteristics. At the other end of the spectrum are enzymes which do not have specificity for a given substrate and act on many molecules with similar structural characteristics. A good example is the enzyme chymotrypsin, which catalyzes hydrolysis of many different peptides or polypeptides as well as amides and esters. 

The NPN content has been demonstrated to range from 15 to 37% at harvest (6, 7). The only published report of the composition showed the NPN fraction to be nutritionally unbalanced, containing mostly amino acids and amides (6). The major components were asparagine, 61% aspartic acid, 11% glutamic acid, 4% serine,... 

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