Mass spectrometry of N-(Pyrimidin-2-yl)amino acids and their methyl esters

N(Pyrimidin-2-yl)-glycine, -alanine and -phenylalanine (1-3) and their methyl esters (4-6) were investigated using electron impact (EI) mass Spectrometry. The results showed that EI-induced decomposition occurs on the carboxylic group or involves the loss of R₂OH. In contrast to earlier investigations on N-(pyrimidin-4-yl)amino acids, elimination of water (in 1-3) or methanol (in 4-6) was found to be of EI-induced nature. The loss of 'COOH from M⁺ of ester 4 suggests the occurrence of a skeletal rearrangement leading to the isomeric N-methylamino acid.     

Syntheses of amino alkyl sulphonic acids and their peptide analogues

New amino alkyl sulphonic acids have been synthesized, including some substituted derivatives and several peptide analogues containing the ---CO·NH--- group formed from amino acid and amino alkyl sulphonic acid components. Peptide-like compounds containing the ---SO₂·NH--- group were prepared from N-substituted taurine and esters of amino acids. Theoretical aspects underlying the reactions involved are discussed.     

Resonant electron capture by some amino acids and their methyl esters

Resonant electron capture mass spectra of aliphatic and aromatic amino acids and their methyl esters show intense [M-H](-) negative ions in the low-energy range. Ion formation results from a predissociation mechanism mediated by the low-energy pi*oo resonant state. Methylation in general has little influence on the electronic structure according to quantum chemical calculations, but the corresponding ions from the methyl esters, [M-Me](-), could be ascertained to arise only at higher resonance energies. Aromatic amino acids are characterized by an additional low-energy fragmentation channel associated with the generation of negative ions with loss of the side chain. The complementary negative ions of the side chains are more efficiently produced at higher energies. The results have significant implications in biological systems as they suggest that amino acids can serve as radiation protectors since they have been found to efficiently thermalize electrons.     

Enzymatic C-terminal amidation of amino acids and peptides

Herein, we describe two versatile and high yielding enzymatic approaches for the conversion of semi-protected amino acid and peptidyl C-terminal α-carboxylic acids into their corresponding amides. In the first approach, the lipase Candida antarctica lipase-B (Cal-B), and in the second approach, the protease Subtilisin A, are used, respectively. We found that by using the ammonium salt of the α-carboxylic acid instead of separate ammonia sources, the enzymatic amidation reactions proceeded much faster without side reactions and gave near to quantitative yields of products.     

Synthesis and reduction of esters of N-(4-amino-5-nitro-6-pyrimidyl)amino acids

The reaction of esters of amino acids with 4-amino-6-chloro-5-nitropyrimidine has yielded esters of (4-amino-5-nitro-6-pyrimidyl)amino acids. The reduction of the esters of -(4-amino-5-nitro-6-pyrimidylamino) acids has yielded 4-amino-6-hydroxy-7,8-dihydropteridines. -(4-Amino-5-nitro-6-pyrimidylamino) acids and the ester of N-(4-amino-5-nitro-6-pyrimidyl)--alanine do not cyclize and on reduction give the corresponding diaminopyrimidine derivatives.     

The microscopy of the amino acids and their compounds

Summary Of 27 amino acids studied all yielded definite crystalline salts with picrolonic acid. The predominant crystal habit of the picrolonates is acicular, the needles usually being arranged in rosettes. While the appearance of the crystals is thus often insufficiently characteristic, it was found that in nearly all instances the refractive indices can serve for identification of the amino acid.

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Zusammenfassung Die Eignung der Pikrolonsäure für die Erkennung von Aminosäuren wurde einer systematischen Untersuchung unterzogen. Von 27 Säuren gaben alle deutlich kristalline Pikrolonate, welche allerdings meist als Nadeln, die oft zu Rosetten vereinigt sind, abgeschieden werden. Obschon das mikroskopische Bild häufig eine Unterscheidung der Aminosäuren nicht gestattet, wurde festgestellt, daß die Bestimmung der Brechungsexponenten in fast allen Fällen die Erkennung der vorliegenden Aminosäure ermöglicht.

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Résumé (W) Pour identifier l'acide picrolonique, employé souvent pour la détermination des amino acides, on a soumis celui-ci à une étude systématique.On a étudié 27 acides qui tous donnèrent nettement des picrolonates bien cristallisés formant des aiguilles s'assemblant souvent en rosettes. Bien qu'en général on ne pouvait pas distinguer les sels amino au microscope, il fut établi que la détermination de l'indice de réfraction rend possible, presque dans tous les cas, l'identification de l'amino acide présent.

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Aided by a grant from the Research Board of the University of California. We are indebted to the Cyrus M. Warren Fund of the American Academy of Arts and Sciences for the loan of a petrographic microscope.     

Non-protein amino acids in peptide design

An overview of the use of non-protein amino acids in the design of conformationally well-defined peptides, based on work from the author’s laboratory, is discussed. The crystal structures of several designed oligopeptides illustrate the useα-aminoisobutyric acid (Aib) in the construction of helices, D-amino acids in the design of helix termination segments and^DPro-Xxx segments for nucleating ofβ-hairpin structures.β- andγ-amino acid residues have been used to expand the range of designed polypeptide structures. Dedicated to Professor C N R Rao on his 70th birthday     

Oxathiaphospholane approach to N- and O-phosphorothioylation of amino acids

A method of highly efficient synthesis of N- and O-phosphorothioylated amino acids was developed. N- and O-(2-Thiono-1,3,2-oxathiaphospholanyl)amino acid methyl esters (3) were prepared in high yields in reaction of amino acid methyl esters with 2-chloro-1,3,2-oxathiaphospholane in pyridine in the presence of elemental sulfur. Compounds 3 were converted in high yield into the corresponding methyl or benzyl phosphorothioamides 6 and 7 by DBU-assisted treatment with methanol or benzyl alcohol. When 3-hydroxypropionitrile was used instead of methanol or benzyl alcohol, the corresponding 2-cyanoethylphosphorothioamidates 4 were obtained in high yield, from which the 2-cyanoethyl group was removed with concentrated ammonium hydroxide. The oxathiaphospholane methodology was also applied for the phosphorylation of amino acids. Thus, 2-oxo-1,3,2-oxathiaphospholane derivatives 10 were prepared by oxidation of compounds 3 with SeO(2.) Compounds 10 were transformed into the corresponding phosphate diesters or amidoesters upon treatment with 3-hydroxypropionitrile in the presence of DBU. The DBU-assisted oxathiaphospholane ring-opening process in 3 and 10 did not cause any measurable C-racemization of phosphorothioylated/phosphorylated amino acids.