L- Tryptophan

C11H12N2O2. M.p. 289°C. L-Tryptophan is an essential amino-acid, its presence in the food of animals is necessary for proper growth. It is present in small quantities in the hydrolysis products of most proteins, although absent in certain vegetable proteins. 

Figure 3.2. Crystal structures of (upper left) Cu(L-tryptophan)(2,2 bipyridine) CIO 4 (upper right) Cu(L-Tryptophan)(1, l()-phenanthroline)ClO4 . 5H2O and (lower) Cu(L-...

Crystal stmctures of complexes of copper(II) with aromatic amine ligands and -amino acids " " and dipeptides" have been published. The stmctures of mixed ligand-copper complexes of L-tryptophan in combination with 1,10-phenanthroline and 2,2 -bipyridine and L-tyrosine in combination with 2,2 -bipyridine are shown in Figure 3.2. Note the subtle difference between the orientation of the indole ring in the two 1,10-phenanthroline complexes. The distance between the two... 

In contrast, investigation of the effect of ligands on the endo-exo selectivity of the Diels-Alder reaction of 3.8c with 3.9 demonstrated that this selectivity is not significantly influenced by the presence of ligands. The effects of ethylenediamine, 2,2 -bipyridine, 1,10-phenanthroline, glycine, L-tryptophan and L-abrine have been studied. The endo-exo ratio observed for the copper(II)-catalysed reaction in the presence of these ligands never deviated more than 2% from the endo-exo ratio of 93-7 obtained for catalysis by copper aquo ion. 

First, the pH-dependence of the enantioselectivity of the reaction between 3.8c and 3.9 catalysed by the copper(L-tryptophan) complex has been studied. Above pH 5 the enantioselectivity reaches a plateau value (Figure 3.3). The diminished enantioselectivities observed at lower pH most likely... 

Table 3.3. Influence of temperature and ethanol content on the enantiomeric excess of the Diels-Alder reaction between 3.8c and 3.9 catalysed by [Cu(L-tryptophan)] in aqueous...

Likewise, the influence of the ligand catalyst ratio has been investigated. Increase of this ratio up to 1.75 1 resulted in a slight improvement of the enantioselectivity of the copper(L-tryptophan)-catalysed Diels-Alder reaction. Interestingly, reducing the ligand catalyst ratio from 1 1 to 0.5 1 resulted in a drop of the enantiomeric excess from 25 to 18 % instead of the expected 12.5 %. Hence, as anticipated, ligand accelerated catalysis is operative. 

An equilibrium constant for binding of 3.8c to the nickel(II)(L-tryptophan) complex of 805 M has been obtained, compared to 530 M in the presence of glycine... 

The influence of a large number of oc-amino acids on the values of and k at have been determined. These a-amino acids included glycine, L-valine, L-leucine, L-phenylalanine, L-tyrosine, L-tryptophan, NOrmethyl-L-tryptophan (L-abrine), N-methyl-L-tyrosine, N,N-dimethyl-L-tyrosine and p -me thoxy-N-me thyl -L -phenyl al anine. 

Pish protein concentrate and soy protein concentrate have been used to prepare a low phenylalanine, high tyrosine peptide for use with phenylketonuria patients (150). The process includes pepsin hydrolysis at pH 1.5 ptonase hydrolysis at pH 6.5 to Hberate aromatic amino acids gel filtration on Sephadex G-15 to remove aromatic amino acids incubation with papain and ethyl esters of L-tyrosine and L-tryptophan, ie, plastein synthesis and ultrafiltration (qv). The plastein has a bland taste and odor and does not contain free amino acids. Yields of 69.3 and 60.9% from PPG and soy protein concentrate, respectively, have been attained. 

L-tryptophan by hydroxylation to 5-hydroxy-L-tryptophan by the enzyme, ttyptophan-5-hydroxylase. 5-Hydroxy-L-tryptophan is then rapidly decarboxylated by aromatic-L-amino acid deacarboxylase to 5-HT. The actions of 5-HT as a neurottansmitter ate terminated by neuronal reuptake and metabobsm. 

The amino acids L-leucine, T-phenylalanine, L-tyrosine, and L-tryptophan all taste bitter, whereas their D-enantiomers taste sweet (5) (see Amino ACIDS). D-Penicillamine [52-67-5] a chelating agent used to remove heavy metals from the body, is a relatively nontoxic dmg effective in the treatment of rheumatoid arthritis, but T.-penicillamine [1113-41 -3] produces optic atrophy and subsequent blindness (6). T.-Penicillamine is roughly eight times more mutagenic than its enantiomer. Such enantioselective mutagenicity is likely due to differences in renal metaboHsm (7). (R)-ThaHdomide (3) is a sedative—hypnotic (3)-thaHdomide (4) is a teratogen (8). 

The nutritional value of a proteia can be improved by the addition of amino acids of low abundance ia that proteia. Thus the fortification of plant proteias such as wheat, com, and soybean with L-lysiae, DL-methionine, or other essential amino acids (L-tryptophan and L-threonine) is expected to alleviate some food problems (11). Such fortification has been widespread ia the feedstuff of domestic animals. 

The deterruination of amino acids in proteins requires pretreatment by either acid or alkaline hydrolysis. However, L-tryptophan is decomposed by acid, and the racemi2ation of several amino acids takes place during alkaline hydrolysis. Moreover, it is very difficult to confirm the presence of cysteine in either case. The use of methanesulfonic acid (18) and mercaptoethanesulfonic acid (19) as the protein hydroly2ing reagent to prevent decomposition of L-tryptophan and L-cysteine is recommended. En2ymatic hydrolysis of proteins has been studied (20). 

In the case of hyperphenylalaninaemia, which occurs ia phenylketonuria because of a congenital absence of phenylalanine hydroxylase, the observed phenylalanine inhibition of proteia synthesis may result from competition between T.-phenylalanine and L-methionine for methionyl-/RNA. Patients sufferiag from maple symp urine disease, an inborn lack of branched chain oxo acid decarboxylase, are mentally retarded unless the condition is treated early enough. It is possible that the high level of branched-chain amino acids inhibits uptake of L-tryptophan and L-tyrosiae iato the brain. Brain iajury of mice within ten days after thek bkth was reported as a result of hypodermic kijections of monosodium glutamate (MSG) (0.5—4 g/kg). However, the FDA concluded that MSG is a safe kigredient, because mice are bom with underdeveloped brains regardless of MSG kijections (106). 

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