Michel Wakselman

1-Cyano-4-dimethylamino-pyridinium salts: new water-soluble reagents for the cyanylation of protein sulphydryl groups

1-Cyano-4-dimethylaminopyridinium perchloroate or fluoroborate rapidly react with thiols in neutral or acidic medium: in 11 min at pH 3·6, 98% of the catalytic activity of papain is inhibited; cysteine residues nos. 7 and 19 of the reduced B-chain of bovine insulin are quantitatively cyanylated at pH 3·5, then the N-peptide bonds are selectively cleaved at pH 9·5.

Functionalized N-aryl azetidinones as novel mechanism-based inhibitors of neutrophil elastase

A functionalized N‐aryl azetidinone has been shown to inactive human leukocyte elastase (HLE) and porcine pancreatic elastase (PPE) by an enzyme‐mediated process. The inactivation is characterized by the following kinetic constants at pH 8.0 and 37°C: k max=0.035 s−1, K 1=1.2 × 10 −4 M for HLE, 0.08 s−1 and 2.7 × 10−4 M for PPE, respectively. Two parent molecules devoid of the latent leaving group failed to inactive HLE and PPE and behaved as substrates of these enzymes. A suicide mechanism involving the formation of an acyl‐enzyme and the simultaneous unmasking of a latent quinonimmonium methide ion which irreversibly reacts with an active site nucleophile. Moreover, the inhibitor is still effective at inhibiting elastase preabsorbed onto elastin.

The synthesis and evaluation of benzofuranones as β-lactamase substrates

Abstract 6- and 7-Carboxy-3-phenylacetamido-3 H -1-benzofuran-2-one have been synthesized as potential β-lactamase substrates and/or inhibitors. These compounds were prepared by lactonization of the corresponding, appropriately substituted phenylglycines. The latter compounds were prepared by either the Strecker or the Bucherer–Berg method. The benzofuran-2-ones were less stable in aqueous solution than the analogous acyclic phenaceturate esters but comparably stable to analogous benzopyran-2-ones. They differed from the latter compounds however in that the C-3 hydrogen of the furan-2-ones, adjacent to the lactone carbonyl group, was distinctly acidic; 7-carboxy-3-phenylacetamido-3 H -1-benzofuran-2-one exists largely as an enolate at pH 7.5. The furan-2-ones were β-lactamase substrates with reactivity very similar to the analogous acyclic phenaceturates. They were not, however, dd -peptidase inhibitors and are thus unlikely to have antibiotic activity. The structural basis for these observations is discussed.

Activation of N,N-bis(alkoxycarbonyl) amino acids. Synthesis of N-alkoxycarbonyl amino acid N-carboxyanhydrides and N,N-dialkoxycarbonyl amino acid fluorides, and the behavior of these amino acid derivatives.

Abstract Series of Boc- and Cbz-NCAs ( 2 ), and of N,N- bis (alkoxycarbonyl) amino acid fluorides U 2 AAFs ( 3 ) have been prepared by activation of N,N- bis -Boc- and N-Cbz,N-Boc-α-amino acids ( 1 ) with the Vilsmeier reagent or cyanuric fluoride. The absence of epimerization of 2 and 3 during both their formation and their coupling under standard conditions of peptide synthesis had been demonstrated by optical purity Youngs tests. In other activated derivatives of bis -urethane protected activated amino acids, the exchangeability of the α-H is shown by the considerable racemization of Boc 2 Phe-OSu ( 8 ) in the presence of base, and by the formation of a Dakin-West type product 11 from the dipeptide Boc 2 Phe-Leu-OBn.

Novel α,α-disubstituted α-aminoacids with axial dissymmetry and their N- or C-protected derivatives

Abstract Racemic as well as enantiomerically pure 1,1′-binaphthyl-substituted α-aminoisobutyric acid (Bin), a new chiral atropoisomeric α,α-disubstituted glycine, and its biphenyl analogue (Bip), have been prepared with good yields by bis-alkylation of a glycine tert-butyl ester Schiff base with 2,2′-bis(bromomethyl)-1,1′-binaphthyl and 2,2′-bis(bromomethyl)-1,1′-biphenyl, respectively, under phase transfer conditions. The free aminoacids Bin and Bip, as well as their N-protected (Z, Boc, Fmoc) and/or C-protected (ethyl or tert-butyl esters) derivatives, useful for the incorporation of these new aminoacids into peptides, have been obtained. A slow interconversion between the two enantiomers of the Bip derivatives is generally observed in 1H NMR at room temperature, with a rotational energy barrier of 59 kJ mol−1.

CIDEP Effects of Intramolecular Quenching of Singlet and Triplet Excited States by Nitroxide Radicals in Oligopeptides: A Potentially Useful New Method for Investigating Peptide Secondary Structures in Solution

Two hexapeptides, each bearing one photoactive alpha-amino acid (Bin or Bpa) and one nitroxide-containing TOAC residue, have been synthesized and fully characterized. FT-IR absorption measurements indicate that a 3(10)-helical conformation is adopted by these peptides in solution. As two amino acid units separate the photoactive residue from TOAC in the peptide sequences, the two moieties face each other at a distance of about 6 A after one complete turn of the ternary helix. Irradiation by a light pulse from an excimer laser populates the excited states localized on the chromophores. An intramolecular interaction between the singlet (Bin) or triplet (Bin and Bpa) excited states and the doublet state of the TOAC nitroxide makes a spin-selective decay pathway possible, that produces transient spin polarization. In addition, in order to determine whether the intramolecular exchange interaction occurs through-bond or through-space, we have prepared linear and cyclic TOAC-Bin dipeptide units. A CIDEP study revealed that a through-space intramolecular interaction is operative. The observation of spin polarization makes the two helical hexapeptides suitable models to test the possibility of application of this novel technique to conformational studies of peptides in solution.

A new chiral α-aminoacid with only axial dissymmetry: Synthesis and X-ray analysis of a 1,1′-binaphthyl-substituted α-aminoisobutyric acid (Bin) and of its biphenyl analogue (Bip)

Abstract Racemic as well as optically pure 1,1′-binaphthyl-substituted α-aminoisobutyric acid (Bin), a new chiral atropoisomeric α,α-disubstituted glycine, and its biphenyl analogue (Bip), have been prepared by bis-alkylation of a glycine tert-butyl ester Schiff base. The free aminoacids Bin and Bip, as well as their C-and/or N-protected derivatives have been obtained. X-ray analysis of H-Bip-OtBu and H-(S)Bin-OH is presented.

4-Amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylic acid (β-TOAC), the first spin-labelled, cyclic, chiral β-amino acid resolved in an enantiomerically pure state

Abstract Amination of 3-carboxymethyl-1-oxyl-2,2,6,6-tetramethyl-4-piperidone with (R)-α-methylbenzylamine, NaBH3CN reduction of the resulting enamine and removal of the chiral auxiliary from the separated diastereoisomers, led to enantiomerically pure (3S,4S) and (3R,4R) methyl 4-amino-1-oxyl-2,2,6,6-tetramethylpiperidine-3-carboxylates.

Synthesis of α,α-disubstituted-β-aminoacids with axial chirality

6-aminomethyl-6,7-dihydro-5H-dibenzo[a,c]cycloheptene-6-carboxylic acid ethyl ester H-β2-Bip-OEt1a and its 1,1′-binaphthyl optically pure analog (R) H-β2-Bin-OEt2a, have been readily synthesized by bis-alkylation of ethyl cyanoacetate with 2,2′-bis-(bromomethyl)-1,1′-diphenyl or optically pure (+)-(R)-2,2′-bis-(bromomethyl)-1,1′-binaphthyl, followed by NaBH4CoCl2 selective reduction of the cyano group. The N-Boc protected derivatives and short peptides of these novel aminoacids have also been prepared.

Bip: a Cα-Tetrasubstituted, Axially Chiral α-Amino Acid. Synthesis and Conformational Preference of Model Peptides

Abstract By using the recently proposed biphenyl-based, Cα-tetrasubstituted, cyclic, axially chiral α-amino acid Bip we synthesised by solution methods a large set of model peptides, including the homo-oligomer series, to the pentamer level. All of the peptides were fully characterised and their preferred conformation was assessed in solution by means of a FT-IR absorption and 1H NMR study. Results of X-ray diffraction analyses of two Bip derivatives and a terminally protected tripeptide with the sequence –Gly–Bip–Gly– are also presented. Our findings indicate that Bip tends to support β-turn and 310-helical structures, although in short peptides the fully-extended (C5) conformation would also be populated to some extent.