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Title: Studies on modified peptides and related compounds
Author: Ibrahim, M. N.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1978
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This thesis includes in its introductory Chapters a discussion on the chemistry, natural occurrence, synthesis, and properties of the didehydro peptide residues. Later Chapters include a discussion of the work undertaken by the author in the synthesis of model didehydro valyl peptide derivatives and the results obtained from hydrogenation studies carried out under a variety of conditions. Synthesis of the model compounds involved mainly the coupling of an unsaturated azlactone with the appropriate amino acid ester. Hydrogenation usually required Raney nickel as catalyst. Estimation of the diastereoisomers formed on hydrogenation of the unsaturated peptides depends on the observation that different chemical shifts are obtained for the ester methyl protons in the H - n.m.r. spectra of diastereoisomeric N-benzoyl dipeptide methyl esters. The integration of these ester peaks is an assessment of the amount of each diastereoisomer present. The results clearly showed that the presence of a neighbouring chiral aromatic amino acid greatly influences the stereochemistry of addition of hydrogen to the double bond of the didehydro amino acid residue. A chiral preference of up to 80% of the D - L diastereoisomer was achieved in some cases. In the investigation of the hydrogenation reaction of N-trifluoro acetyl didehydro peptide derivatives, g.l.c. was used for detection and determination of the amount of each diastereoisomer formed. The results showed very good agreement with the chiral ratios obtained from the N-benzoyl analogous, thus suggesting that the hydrogenation is independent of the nature of the Nl protecting group. Other additional reactions to didehydro valyl peptide derivatives revealed that selective cleavage of terminal N-benzoyl didehydro valyl residue occurs in preference to the addition across the double bond. The last Chapter describes attempts which have been made to prepare didehydro alanyl derivatives by using different procedures and different starting material. These approaches met with very limited success. Ideally, the didehydro alanyl residues would have contributed valuable information on the asymmetric hydrogenation studies of didehydro peptides using homogeneous chiral catalysts, which are currently very popular. However, a synthetic route to produce the model system was not found in the time available, and a continuation of these studies would obviously be desirable.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available