P-Aminophenylalanine

The free base was obtained from the hydrochloride by adding a slight excess of dilute ammonium hydroxide to the aqueous solution, and crystallizing the product from aqueous methanol. A further recrystallization with charcoal treatment gaye almost colorless needles, MP 110° to 112°C of ethyl N-phthaloyl p-aminophenylalaninate. 

Ethyl N-phthaloyl p-aminophenylalaninate (3.15 g) (unrecrystallized) was suspended in water (50 g) and glacial acetic acid (30 g) added. To the clear solution, ethylene oxide (8.0 g) was added, the mixture allowed to stand for 17 hours, and then poured into water (350 g). The solution was neutralized with sodium hydrogen carbonate and the liberated gum extracted with ether. The ethereal solution was dried (magnesium sulfate) and eyapo-rated. The residual gum (3.95 g) was dissolved in benzene (50 g) and the solution dried azeotropically by distilling off some of the solvent. Freshly distilled phosphorus oxychloride (8 g) was added and the mixture heated under reflux for 30 minutes. 

Chloramphenicol is produced by S. venezuelae via the following pathway chorismic acid — p-aminophenylalanine — p-aminophenylserine — dichloroacetyl — p-aminophenylserine — chloramphenicol. 

A completely autonomous bacterium with a 21 amino acid genetic code was engineered. The bacterium can generate p-aminophenylalanine from basic carbon sources and incorporate this amino acid into proteins in response to the amber nonsense codon [132]. 

L-N-Phthalimido-p-aminophenylalanine ethyl ester when reacted with ethylene oxide yields an intermediate which on treatment with phosphorus oxychloride gives rise to 4-5/5-(2-chloroethyl)-amino-L-phenylalanine ethyl ester. This on hydrolysis with hydrochloric acid offers the desired compound. 

Moradian, A. Mosbach, K. Preparation of a functional, highly selective polymer by molecular imprinting. A demonstration with L-p-aminophenylalanine anilide as a template molecule allowing multiple points of attachment. J. Mol. Recognit. 1989, 2, 167-169. 

But even AT-t-butoxycarbonyl-p-aminophenylalanine can be converted to the aryl azide by this method in 2 HCl without loss of the protecting group."... 

Chloramphenicol Analogs - From studies on the biosynthesis of chloramphenicol using l c-iabeled compounds it was concluded that p-aminophenylalanine is a specific precursor. Oxidaticm of the amino function gives rise to the nitro group in chloramphenicol. 69... 

Recently, Fridkin et al. reported on the synthesis of gonadotropin-releasing hormone (GnRH) analogs containing a p-aminophenylalanine residue in their sequence [130]. Azo-cycUzation has been performed in solution by di-azotization of the p-aminophenylalanine residue foUowed by intramolecular coupUng of the formed diazo salt with either tyrosine or histidine side chains... 

Fig. 15.5 Bioconjugation methods for VNPs. (A) An overview of the three most common bioconjugation chemistries, Lys-NHS, Cys-maleimide, and carbodiimide. (B) Diazonium coupling chemistry. (C) Oxidative coupling to the unnatural amino acid p-aminophenylalanine. (D) Condensation reactions to form oximes and hydrazones, two strategies for the introduction of aldehydes into proteins and bioorthogonal condensation reaction.

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