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R Nyfeler

Publications and source records attributed to R Nyfeler.

12 recordsLinked to original sources
PubMed1995

Peptide synthesis using novel S-sulfocysteine derivatives.

New cysteine S-sulfonate derivatives, Boc-Cys(SO3Na)-ONa 2 and Fmoc-Cys(SO3Na)-ONa 3, were prepared and their utility for peptide synthesis examined. The Fmoc derivative 3 was used in the solid-phase peptide synthesis of Arg8-vasopressin 9 via the Bunte salt 7. Satisfactory S-sulfonate stability was observed when p-cresol scavenged the cleavage from the resin. The intermediate 7 was purified by ion-exchange chromatography prior to S-sulfonate cleavage with tributylphosphine.

Amino Acid Sequence↗
PubMed1985

[Immunodetermination of peptide factors. I. Synthesis of N-alpha-maleoyl-peptide derivatives].

A new synthesis of N-maleoyl-omega-amino acids, their use for the introduction of the maleimido group into peptide factors as well as the stability of this group under standard conditions of conventional peptide synthesis are described. The relatively high stability of N-maleoyl-peptide derivatives in aqueous solutions at neutral or slightly acidic pH values as well as the fast addition of thiol compounds to the maleimido group indicate that these peptide derivatives are well suited for the preparation of tracers of peptide factors and of peptide-protein conjugates.

Amino Acid Sequence↗
PubMed1984

Peptide sweeteners. 6. Structural studies on the C-terminal amino acid of L-aspartyl dipeptide sweeteners.

Stereochemical and structural aspects of the variations in the C-terminal residue of L-aspartyl-L-phenylalanine methyl ester have been investigated. Novel configurational analogues such as L-aspartyl-D-alanine benzyl ester and L-aspartyl-D-alpha-aminobutyric acid benzyl ester were found to be sweet. In addition, chiral and achiral alpha, alpha-dialkylglycine and alpha-aminocycloalkanecarboxylic acids were incorporated into the dipeptides. The L-aspartic acid based dipeptide derivatives of alpha-aminoisobutyric acid methyl ester, alpha-aminocyclopropanecarboxylic acid methyl ester, alpha-aminocyclobutanecarboxylic acid methyl ester, and alpha-aminocyclopentanecarboxylic acid methyl ester are sweet. Dipeptides with alpha-aminocyclohexanecarboxylic acid methyl ester and alpha-aminocycloheptanecarboxylic acid methyl ester are bitter, whereas the analogues with alpha-aminocyclooctanecarboxylic acid methyl ester, alpha, alpha-diethylglycine methyl ester, and alpha-aminoisobutyric acid benzyl ester are tasteless. Aspects on chirality and effective volume of the C-terminal residue are discussed and correlated with taste.

Aspartame↗
PubMed1983

[Syntheses of human little gastrin-I and its leucine-15, norleucine-15 and methoxinine-15 analogs].

Human little gastrin-I is known to exhibit a high tendency to air-oxidation of its methionine-15 residue to the corresponding S-oxide derivative, with concomitant loss of biological activity. Since its leucine-15 analog, even if fully biologically active, differs significantly from the parent hormone in the immunological properties, the norleucine-15 and methoxinine-15 analogues were synthetized. For the required comparative analyses new syntheses of human little gastrin-I and of its leucine-15 analog were additionally elaborated. Upon an optimized condensation of the fragments, followed by the deprotection step, partition chromatography as well as preparative high-performance liquid chromatography led to the desired gastrins in satisfactory yields and high degree of purity as judged by the expected and known side products.

Amino Acid Sequence↗
PubMed1982

Peptide sweeteners. 5. Side-chain homologues relating zwitterionic and trifluoroacetylated amino acid anilide and dipeptide sweeteners.

Side-chain homologues of sweet trifluoroacetyl-alpha-L-aspartyl-p-cyanoanilide have been synthesized and tasted. Removal of the trifluoroacetyl group only changes the potency of sweet taste, not the taste property. These results have been compared with the structure-taste relationships of dipeptide sweeteners. An informative discontinuity of taste effects was found to exist with novel aminomalonyl dipeptide derivatives. The results are explained on topochemical grounds.

Anilides↗
PubMed1982

(Alkyldithio)carbonyl groups for protection of amino functions in peptide synthesis.

(Alkyldithio)carbonyl groups were examined for their usefulness as amino-protecting groups in peptide chemistry. Among the derivatives studied, the (cyclohexyldithio)carbonyl function was found to be the most suitable for practical application. The related amino acid derivatives are obtained by relatively simple procedures and are sufficiently stable under normal conditions of peptide synthesis. Reductive cleavage with thiols or phosphines results in quantitative removal of this new amino protecting group.U

Acylation↗