title: Differentiation of natural and synthetic phenylalanine and tyrosine through natural abundance 2H nuclear magnetic resonance.
abstract: The natural abundance deuterium NMR characterization of samples of the amino acids tyrosine (1) and phenylalanine (2), examined as the acetylated methyl esters 4 and 6, has been performed with the aim to identify by these means the contribution in animals of the hydroxylation of the diet l-phenylalanine (2) to the formation of l-tyrosine (1), a feature previously revealed on the same samples through the determination of the phenolic delta(18)O values. The study, which includes also the NMR examination of benzoic acid (5) from 2 and of tyrosol (7) from 1, substantially fails in providing the required information because the mode of deuterium labeling of tyrosine samples of different origins is quite similar but indicates a dramatic difference in the deuterium labeling pattern of the two amino acids 1 and 2. The most relevant variation is with regard to the deuterium enrichments at the CH(2) and CH positions, which are inverted in the two amino acids of natural derivation. Moreover, whereas the diastereotopic benzylic hydrogen atoms of l-tyrosine (1) appear to be equally deuterium enriched, in l-phenylalanine (2) the (D/H)(3)(R)() > (D/H)(3)(S)(). Similarly, benzoic acid (5) shows separate signals for the aromatic deuterium nuclei, which are quite indicative of the natural or synthetic derivation. The mode of deuterium labeling of the side chain of 1 and 2 is tentatively correlated to the different origins of the two amino acids, natural from animal sources for l-tyrosine and biotechnological probably from genetically modified microorganisms for l-phenylalanine.
authors.affiliation: Dipartimento di Chimica, Materiali e Ingegneria Chimica Giulio Natta, Politecnico di Milano and CNR, Istituto di Chimica del Riconoscimento Molecolare, Sezione A. Quilico, Via Mancinelli 7, 20131 Milano, Italy.
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Brenna
authors.forename: Giovanni
authors.initials: G
authors.lastname: Fronza
authors.forename: Claudio
authors.initials: C
authors.lastname: Fuganti
authors.forename: Matteo
authors.initials: M
authors.lastname: Pinciroli
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D001565:Benzoates / Q000737:chemistry; D003903:Deuterium; D009682:Magnetic Resonance Spectroscopy; D010649:Phenylalanine / Q000032:analysis* / Q000737:chemistry; D010626:Phenylethyl Alcohol / Q000031:analogs & derivatives* / Q000032:analysis; D014443:Tyrosine / Q000032:analysis* / Q000737:chemistry
chemical_list: D001565:Benzoates; C011867:4-hydroxyphenylethanol; D014443:Tyrosine; D010649:Phenylalanine; D003903:Deuterium; D010626:Phenylethyl Alcohol