DL-/3-Phenylalanine

DL-Phenylalanin anhydride (171), readily available by heating DL-phenylalanine (170) in ethylene glycol, was treated with a mixture of... 

Diethyl-p-nitrobenzyl-phthalimidomalonate (70 g) and sodium carbonate (70 g) in water (700 ml) were refluxed overnight with mechanical stirring (to avoid bumping). The clear brown solution was acidified with hydrochloric acid and refluxing and stirring were continued for a further 40 minutes. The mixture was cooled and the colorless precipitate (31 g) collected. A second crop (18.5 g) was obtained on evaporation of the mother liquors. Crystallization from aqueous ethanol gave the compound N-carboxybenzoyl-p-nitro-DL-phenylalanine as small needles, MP 198° to 200°C. 

A solution of p-nitro-N-phthaloyl-DL-phenylalanine (1.0 g) in methanol (25 ml) and a solution of cinchonidine (0.865 g) in methanol (30 ml) were mixed. Crystallization soon set in. The mixture was left overnight, and the colorless needles (0,97 g), MP 209° to 210°C, collected. After two recrystallizations from methanol the cinchonidine salt of the D-acid had MP 211°C,... 

Selection of these regulatory mutants is often done by using toxic analogues of amino adds for example p-fluoro-DL-phenylalanine is an analogue of phenylalanine. Mutants that have no feedback inhibition or repression to the amino add are also resistant to the analogue amino add. They are therefore selected for and can be used to overproduce the amino add. Some amino add analogues function as false co-repressors, false feedback inhibitors or inhibit the incorporation of foe amino acid into foe protein. 

To achieve overproduction of phenylalanine, the micro-organism should be derepressed at the pheA level and free of inhibition at the arcG level. Both genes are located on the chromosomal DNA of the micro-organism and, by means of amino add analogues such as p-fluoro-DL-phenylalanine, it is possible to make (phenylalanine) feedback resistant mutants of E.cdi (pheA and oroF mutants). The following procedure can be used ... 

The optical resolution of the chemically synthesised N-acetyl-DL-phenylalanine by an acylase enzyme is given in reaction 4 (Figure 8.6). A selective hydrolysis of N-acetyl-L-phenylalanine is performed. 

According to a hypothesis launched by Larionov et al in the 1960s, some new nitrogen mustard derivatives were developed. They contain metabolites and heterocyclic structures as carriers of the cytotoxic chloroethylamine groups. By this way the synthesis of aliylating metabolites started melphalan (sarcolysine) as L- or DL-phenylalanine derivative prospidine with a tricyclic piperazine moiety and chlorambucil as butyric acid derivative. It was proven that each alkylating metabolite has its own spectrum of selective antitumor activity. 

Aus dem gemischten Anhydrid des N-Benzoyl-DL-phenylalanins wird in ahnlicher Weise 2-Benzoylamino-3-phenyl-propanol erhalten. Das mildere Reduktionsmittel Na-triumboranat wird z.B. zur Herstellung des amorphen 6-Phenylacetamino-penicillanyl-al-kohols3 eingesetzt. 

Another approach for the synthesis of enantiopure amino acids or amino alcohols is the enantioselective enzyme-catalyzed hydrolysis of hydantoins. As discussed above, hydantoins are very easily racemized in weak alkaline solutions via keto enol tautomerism. Sugai et al. have reported the DKR of the hydantoin prepared from DL-phenylalanine. DKR took place smoothly by the use of D-hydantoinase at a pH of 9 employing a borate buffer (Figure 4.17) [42]. 

Novozymes, a subtilisin produced by Bacillus licheniformis, was used by Chen et al ° to carry out a dynamic kinetic resolution of benzyl, butyl, or propyl esters of DL-phenylalanine, tyrosine, and leucine. The hydrolysis was performed at pH 8.5 in 2-methyl-2-propanol/water (19 1) and the freed L-amino acids precipitated. The key feature bringing about continual racemization of the remaining D-amino acid esters was the inclusion of 20 mmol 1 pyridoxal phosphate. 

Detailed kinetic studies revealed that glycine methyl ester and phenylalanine methyl ester in glycine buffer at pH 7.3 undergo a facile hydrolysis catalyzed by cupric ion (11). Under these conditions the reactions closely follow a first-order rate law in the substrate. Using these kinetic data it is possible to compare the rates of hydrolysis of DL-phenylalanine ethyl ester as catalyzed by hydronium, hydroxide, and cupric ion (see Table III). 

Table III. Acidic, Basic, and Cupric Ion—Catalyzed Hydrolysis of DL-Phenylalanine Ethyl Ester at pH 7.3 and 25° C.

The enhanced reactivity in the cupric ion-catalyzed hydrolysis cannot be due solely to the electrostatic effect of an attack of hydroxyl ion on a positively charged a -amino ester, since the introduction of a positive charge, two atoms from the carbonyl group of an ester, increases the rate constant of alkaline hydrolysis by a factor of 103 (10), whereas there is a difference of approximately 106 between the cupric ion-catalyzed and the alkaline hydrolyses of DL-phenylalanine ethyl ester. The effective charge on the cupric ion-glycine (buffer)-ester complex is +1, so that the factor of 106 cannot be explained by an increase in charge over that present in the case of betaine. Furthermore, the reaction cannot be due to attack by a water molecule on a positively charged a-amino acid ester, since the rate constant of the acidic hydrolysis of phenylalanine ethyl ester is very small. It thus seems... 

Carbonyl oxygen exchange was found during the cupric ion-catalyzed hydrolysis of DL-phenylalanine ethyl ester-carbonyl-O18 at pH 7.3 (11). This indicates that an additional intermediate is formed in this reaction. A mechanism (II) consistent with both the kinetic evidence and the oxygen-exchange evidence is given below. 

Complexes with SBs from Hsal and ar-amino acids (glycine, l- and DL-alanine, L-methionine, L-valine, L-leucine, l- and DL-phenylalanine) were prepared and characterized.786 The complexes are bluish-grey and there is no appreciable interaction between V atoms. The compounds were [VO(SB)(H20)] (111), confirmed in an X-ray study of (111 R = Me, L-Ala derivative).787 v(V=0) was at —1000 cm-1 the compounds are not soluble in noncoordinating solvents, but when dissolved in py v(V=0) shifts to —970 cm-1 several orange py adducts (112) were isolated.686 Complexes (111) have electronic spectra that resemble those of... 

Fig. 10. Conversion-time curves for polymerisation of NCA s in 80% nitrobenzene —20% N-inethyi formamide mixture 26° C. [NCA] — 0.109 mol. I"1 Initially in all cases, (a) y-benzyl-L-gtutamate NCA [sodium dl-hydrocinnamate = 4.6 x 10 mol 1-J (b) DL-phenylalanineNCA [sodiumdihydrocinnamate] — 4.6 x 10 moll-1 (c) DL-phenylalanine NCA [sodiumhydantoin 3-acetate] = 9.2 x 10 moll-1. 100% evolution of CO . [Reprinted from paper by D. G. H. Ballard and C. H. Bamford Special Publication of Chem. Soc.

Fig. 21. Polymerization of DL-phenylalanine NCA initiated by sarcosine dimethylamide (o) polysarcosine...

Fig 22. Polymerization of DL-phenylalanine NCA initiated by polysarcosine dimethylamides with different degrees of polymerization. Nitrobenzene solution temperature 15°C [Af]0 = 0.100 moll"1, [XI — 5.4 x... 

FIGURE 16 Effect of temperature on the chiral resolution of DL-phenylalanine on CSP prepared by imprinted L-phenylalanine molecule hy capillary electrochromatography using acetonitrile-acetic acid (95 5, v/v). Imprinted polymers were prepared at ( ) 60°C, ( ) 40°C, and (O) 4°C. (From Ref. 91.)... 

DL-Phenylalanine, dansyl-DL-leucine L-Phenylalanine, Dansyl-Leucine 106... 

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