Phenylalanine ethyl ester

MP 191° to 192,5°C, Two recrystallizations from aqueous ethanol gave the cinchonidine salt of the L-acid, MP 192,5° to 194°C. To the salt (2.9 g) in warm ethanol (50 ml) was added water (50 ml) and a slight excess (ca 10 ml) of N aqueous sodium hydroxide. The mixture was diluted with water, cooled, filtered from the precipitated base and the filtrate acidified with hydrochloric acid. Refluxing with 2 N ethanolic hydrogen chloride yielded p-nitro-N-phthaloyl-L-phenylalanine ethyl ester, according to U.S. Patent 3,032,585. 

The protease a-chymotrypsin has been used for transesterification reactions by two groups (Entries 7 and 8) [35, 36]. N-Acetyl-l-phenylalanine ethyl ester and N-acetyl-l-tyrosine ethyl ester were transformed into the corresponding propyl esters (Scheme 8.3-2). 

C,H, N204 949-99-5) see Melphalan Zolmitriptan 4-nitro-L-phenylalanine ethyl ester monohydrochloride (C, H 5C1N204 58816-66-3) see Melphalan... 

Some of the pancreatic enzymes in the lumen include pancreatic amylase, pancreatic lipase, elastase, trypsin, a-chymotrypsin, and carboxypeptidase A. For example, the aspirin derivatives aspirin phenylalanine ethyl ester, aspirin phenyllactic ethyl ester, and aspirin phenylalanine amide have been studied as substrates for carboxypeptidase A [67,68], with the phenylalanine ethyl ester derivative proving to be the best substrate. This study indicated that the carboxypeptidase A may serve as a reconversion site for many drug derivatives. 

Table 8 shows a list of compounds29 which have been resolved by liquid chromatography on polv( X-acryloy[phenylalanine ethyl ester) (Chiraspher) on a 150-mg scale. 

Based on a suggestion by Odell and Earlam [119] that crown ethers and cryptands can cause proteins to dissolve in methanol, Broos and coworkers [120] investigated the effects of crown ethers on the enzymatic activity of a-chymotrypsin in the transesterification reaction of N-acetyl-L-phenylalanine ethyl ester with n-propanol in organic solvents. They observed a 30-fold rate acceleration when 18-crown-6 was used in octane. At that time, it was proposed that the water- and cation-complexing... 

Immobilization of enzymes to solid supports can increase activity over a wide range of solvents [78]. As seen in Table 3.2, the transesterification of N-acetyl-L-phenylalanine ethyl ester (APEE) with 1-propanol by a-chymotrypsin (Scheme 3.2) immobilized to glass is 1-2 orders of magnitude higher than that of the free, lyophilized enzyme. 

N-acetyl-L-phenylalanine ethyl ester N-acetyl-L-phenylalanine propyl ester... 

Figure 3.7 Catalytic activity of subtilisin in anhydrous organic solvents ( n-hexane, diisopropyl ether, T THF) as a function of the KCI content in the dry catalyst. The activity is expressed in terms of kat/Km of the transesterification reaction between N-acetyl-L-phenylalanine ethyl ester and n-propanol, used in concentrations of lOmM and 0.85 M, respectively [88].

Scheme 3.4 Trans, of N-acetyl-L-phenylalanine ethyl ester with 1-PrOH by subtilisin Carlsberg to form N-acetyl-L-phenylalanine propyl ester.

Subtilisin generally shows poor transesterification activity in water-free ionic liquids, but Shah and Gupta [73] studied various approaches to maintaining its activity. The best results-up to 10000 times increase in the initial rate N-acetyl-phenylalanine ethyl ester in [BMIm] [PF6]-were obtained by precipitating and washing with 1-propanol. 

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. 

TV-Acetyl-L-phenylalanine ethyl ester [2361-96-8] M 235.3. Crystd from water. l-AcetyI-2-phenyIhydrazine [ 114-83-0] M 150.2, m 128.5". Crystd from aqueous EtOH. 

When an ester such as acetyl-L-phenylalanine ethyl ester is mixed with a solution of chymotrypsin and proflavin, the following events occur. There is a rapid displacement of some of the proflavin from the active site as the substrate combines with the enzyme, leading to a decrease in A465. (This is complete in the dead time of the apparatus.) Then, as the acylenzyme is formed, the binding equilibrium between the ester and the dye is displaced, leading to the displacement of all the proflavin. The absorbance remains constant until the ester is depleted and the acylenzyme disappears. The dissociation constant of the enzyme-substrate complex may be calculated from the magnitude of the initial rapid displacement, whereas the rate constant for acylation may be obtained from the exponential second phase. 

Reaction of D-phenylalanine ethyl ester with cinnamaldehyde has been reported to give a chiral Schiff base, that underwent an asymmetric Staudinger [2+2] cycloaddition reaction with phthalimidoacetyl chloride to give the monocyclic... 

Scheme 29 Synthesis of mono- and bicyclic P-lactams starting from D-phenylalanine ethyl ester...

Phenylalanine ethyl ester hydrochloride.124 To a stirred, ice-cold suspension of (S)-phenylalanine (30 g, 0.182 mol) in absolute ethanol (800 ml), thio-nyl chloride (32.5 g, 0.273 mol) is added dropwise, and the reaction mixture is then heated under reflux for 3.5 hours. The pale yellow solution is allowed to stand at room temperature overnight, and then the ethanol is evaporated in vacuo to leave colourless crystals of the hydrochloride which are stirred with dry ether, filtered off and dried in vacuo. 

S)-2-Amino-3-phenylpropan-1 -ol [(S)-phenylalaninol. 124 To a solution of sodium borohydride (3.5 g, 0.092 mol) in 50 per cent aqueous ethanol (50 ml) is added dropwise a solution of (S)-phenylalanine ethyl ester hydrochloride (5.0 g, 0.022 mol) in 50 per cent aqueous ethanol (50 ml). After the resulting mixture is refluxed for 4.5 hours, ethanol is evaporated in vacuo. The aqueous solution thus obtained is then extracted with ethyl acetate and the extract washed with saturated sodium chloride solution and dried over anhydrous sodium sulphate. Evaporation of the ethyl acetate under reduced pressure affords (S)-phenylalaninol (2.8 g, 84%) as a pale yellow solid m.p. 85-92 °C. Recrystallisation from ether gives colourless crystals of m.p. 91-93 °C, [oc] 5 - 25.6° (c. 1.037 in EtOH). 

Blaschke et al. [54—56] synthesized polyacrylamide and polymethacrylamide containing chiral side chains. In order to make CSPs, these polymers were bonded to silica gel chemically [54-56]. The CSP obtained by /V-acrylol-(.S)-phenylalanine ethyl ester was commercialized by Merck Chemical Company by the trade name ChiraSpher. The racemic compounds resolved are those capable of forming hydrogen-bondings (i.e., amides, imides, carboxylic acids, and alcohols). It has been reported that nonpolar solvents like benzene and toluene individually or their mixtures were the best mobile phases. In addition to these CSPs, other amide CSPs were prepared and tested for the chiral resolution [57,58]. 

Immobilization in a sol-gel matrix accelerated the propanolysis of N-acetyl-i-phenylalanine ethyl ester in cyclohexane for several serine proteases compared to the non-immobilized lyophilized enzymes 31-fold for Subtilisin Carlsberg, 43-fold for a-chymotrypsin, and 437-fold for trypsin (van Unen, 2001). The activity yield upon immobilization was 90% (a-chymotrypsin). The rate enhancement effect of immobilization on the enzyme activity is highest in hydrophobic solvents. 

When switching from water to an organic solvent, or switching between organic solvents, the substrate specificity can change. In the example of the standard reaction, transesterification of N-acetyl-i-phenylalanine ethyl ester with n-propanol by Subtilisin Carlsberg, which has been mentioned several times in this chapter already, the relative specificity between the rather hydrophobic phenylalanine compound and its more hydrophilic analog N-acetyl-L-serine ethyl ester varies with the solvent (Table 12.8) (Wescott, 1993). 

Fontes et al. (1998a) Batch Transesterification of IV-acetyl-L-phenylalanine ethyl ester with 1-propanol Subtilisin Carlsberg... 

Polyphosphazenes are a relatively new class of biodegradable polymers. Their hydrolytic stability or instability is determined not by changes in the backbone structure but by changes in the side groups attached to an unconventional macromolecular backbone. Synthetic flexibility and versatile adaptability of polyphosphazenes make them unique for drug delivery applications. For example, Veronese et al.18 prepared polyphos-phazene microspheres with phenylalanine ethyl ester as a phosphorous substituent and loaded it with succinylsulphathiazole or naproxen. The kinetics of release from these matrices were very convenient in yielding local concentrations of the two drugs that are useful per se or when mixed with hydroxyapatite for better bone formation. Polyphosphazene matrices are also considered as potential vehicles for the delivery of proteins and vaccines.19... 

The heterocycle 43 was needed as an intermediate in a cytochalasan synthesis.10 Disconnection of the 1,3-diCO relationship between the two ketones reveals the amide 44 that is the acetoacetyl derivative of phenylalanine ethyl ester 45. 

---