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N-Boc/Fmoc/Z-N'-formyl-gem-diaminoalkyl derivatives, intermediates particularly useful in the synthesis of partially modified retro-inverso peptides, have been characterized by both positive and negative ion electrospray ionization (ESI) ion-trap multi-stage mass spectrometry (MS(n)). The MS(2) collision induced dissociation (CID) spectra of the sodium adduct of the formamides derived from the corresponding N-Fmoc/Z-amino acids, dipeptide and tripeptide acids show the [M + Na-NH2CHO](+) ion, arising from the loss of formamide, as the base peak. Differently, the MS(2) CID spectra of [M + Na](+) ion of all the N-Boc derivatives yield the abundant [M + Na-C4H8](+) and [M + Na-Boc + H](+) ions because of the loss of isobutylene and CO2 from the Boc protecting function. Useful information on the type of amino acids and their sequence in the N-protected dipeptidyl and tripeptidyl-N'-formamides is provided by MS(2) and subsequent MS(n) experiments on the respective precursor ions. The negative ion ESI mass spectra of these oligomers show, in addition to [M-H](-), [M + HCOO](-) and [M + Cl](-) ions, the presence of in-source CID fragment ions deriving from the involvement of the N-protecting group. Furthermore, MS(n) spectra of [M + Cl](-) ion of N-protected dipeptide and tripeptide derivatives show characteristic fragmentations that are useful for determining the nature of the C-terminal gem-diamino residue. The present paper represents an initial attempt to study the ESI-MS behavior of these important intermediates and lays the groundwork for structural-based studies on more complex partially modified retro-inverso peptides., (Copyright © 2013 John Wiley & Sons, Ltd.)

[alpha]-Amino acids and [alpha]-amino methyl esters are easily converted to their N-monoalkyl derivatives by a reductive condensation reaction using several carbonyl compounds in the presence of sodium borohydride. This reducing agent has shown a wide versatility with minor but essential procedural variations. The reaction allows the [alpha]-monodeuterium labeling of the new N-substituent by use of sodium borodeuteride. Key words: [alpha]-amino acid, [alpha]-amino methyl esters, sodium borohydride, reductive N-monoalkylation, carbonyl compounds.

A simple, efficient two-step synthesis of N-protected N′-formyl- gem-diaminoalkyl derivatives is reported. The procedure involves the unprecedented reduction of the carbamoyl azide of α- N-Boc/Fmoc/Z-protected amino acids and dipeptides (Boc = tert-butoxycarbonyl, Fmoc = 9-fluorenylmethoxycarbonyl, Z = benzyloxycarbonyl) by treatment with NaBH4 at room temperature. The reaction proceeds rapidly (45 min) without detectable epimerization (by HPLC-ESI-MS analysis) and is not influenced by the nature of the starting carbamoyl azide. The 1H and 13C NMR analyses of the synthesized N-protected N′-formamides were carried out in [D6]DMSO. The spectra exhibited the presence of two rotameric forms in solution as a result of the restricted rotation around the N-CO formyl bond. The integration of the N-CH-N protons of the two isomers showed that the cis isomer (rotamer B) was the more abundant conformer by 60 to 78 %. The reported synthesis represents the potential value of carbamoyl azides as versatile chiral starting materials for many synthetic purposes. [ABSTRACT FROM AUTHOR]

[image omitted] A simple and mild one-pot synthesis of potentially bioactive α-N-protected dipeptidyl ureas is reported. The procedure involves the reaction between the carbamoyl azide of an α-N-protected amino acid and an α-amino acid methyl ester. The reaction is fast (3 h at 45 °C), regardless of the nature of both the reagents, and racemization free. The reported protocol represents a valid alternative to existing methods. [ABSTRACT FROM AUTHOR]

The reaction of formaldehyde with enantiomerically pure α-N-protected amino acid hydrazides is described. The system has been investigated in different solvents, including both aqueous formaldehyde and paraformaldehyde, with the aim of simplifying the final reaction mixture. Aqueous formaldehyde in refluxing THF proved to be the best combination, affording mainly the corresponding monomeric N-methylene and 1,3,5-trisubstituted-1,3,5-hexahydrotriazine derivatives. The monomeric form was the only one present at high temperature, as evidenced by 1H and 13C NMR spectroscopy. [ABSTRACT FROM AUTHOR]

A rapid and efficient method for the synthesis of N-carbamoyl-L-amino acids is reported. The procedure, involving the reaction between urea and α-amino acids sodium salts, was performed under microwave conditions using an unmodified domestic microwave oven. A careful study of the operative conditions indicated proline (1d) as the less reactive substrate and phenylglycine (1e) as the more reactive one among all the α-amino acids tested. Substitution of urea with potassium cyanate produced a low conversion into the corresponding N-carbamoyl derivative, and a possible explanation of this result is reported. [ABSTRACT FROM AUTHOR]