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Biomedical subjects

F M Chen

Publications and source records attributed to F M Chen.

117 records · Page 7Linked to original sources
PubMed1980

Racemization in peptide synthesis. A laboratory experiment for senior undergraduates.

A laboratory experiment involving the coupling of N-benzoylamino acids with methyl N epsilon-benzyloxycarbonyl-L-lysinate using various methods is described. The extents of racemization are determined by analysis for the protected diastereomeric dipeptide ester products by quantitation of the separated ester methyl proton peaks of their nuclear magnetic resonance (60 MHz) spectra. Synthesis of the starting materials and additional exercises are included as options.

Benzyl Compounds↗
PubMed1979

A series of lysyldipeptide derivatives for racemization studies in peptide synthesis.

The series of diastereomeric peptide derivatives N-benzoyl-D,L-X-N epsilon-benzyloxycarbonyl-L-lysine methyl ester where X = alanyl, valyl, leucyl, phenylalanyl and isoleucyl are submitted as model systems for studying racemization in peptide synthesis. The diastereomers can be analyzed by quantitation of the separated ester methyl proton peaks of their nuclear magnetic resonance spectra. Data on the tendency to racemize of the different residues are presented. In polar solvents, valyl and isoleucyl residues racemize more readily than the other residues.

Amino Acids↗
PubMed1979

Lysyl dipeptide and tripeptide model systems for racemization studies in amino acid and peptide chemistry.

Four series of diastereomeric peptide pairs (X-Lys, Lys-Y, Gly-X-Lys, and Gly-Lys-Y; where X and Y = Ala, Leu, Val, Ile, Phe, and Pro) have been synthesized by conventional procedures using benzyl-based protecting groups. Chromatographic separation of each pair, except Gly-Lys-Pro, has been achieved by elution from a 15-cm Aminex A-5 resin column using pH 5.5 buffer for tripeptides, pH 6.5 buffer for dipeptides, and pH 7.5 buffer for phenylalanyl peptides. The isomers have been identified by chromatography of the L-L isomers. Examples of the use of the model peptides for optical purity determinations and as tests for racemization are presented. The series Gly-X-Lys allows comparison of the tendencies to racemize of residues X during couplings. The separations of other peptides where Y = MeVal and X = N- and O-methylhydroxyamino acids are also described.

Amino Acids↗
PubMed1978

Studies on the use of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline for the synthesis of acylamino acid anilides and p-nitroanilides.

The use of N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) for coupling acyl-L-amino acids with aniline and p-nitroaniline has been investigated. Optically pure anlides are obtained in good yield but partial racemization occurred in one case. p-Nitroanlides cannot be obtained under similar conditions but if the reaction solvent is removed and the residue left for several days, coupling occurs giving a racemic product in moderate yields. Reaction mechanisms are proposed on the basis of isolated and characterized intermediates. It has been found that N-benzoylamino acid anilides and p-nitroanilides are cleaved within a few minutes by hydrogen bromide in acetic acid to give the N-benzoylamino acid and the amine.

Amino Acids↗
PubMed1978

Reductive N,N-dimethylation of amino acid and peptide derivatives using methanol as the carbonyl source.

Formaldehyde is readily formed from methanol in the presence of palladium-on-charcoal and air. The use of this methanolic formaldehyde solution for the reductive methylation of amino groups in amino acid and peptide derivatives by catalytic hydrogenation has been studied and found to be superior to the use of aqueous formaldehyde because no contaminating paraformaldehyde is present. Some data on N-isopropylation are given.

Amino Acids↗