Synthesis of Novel Homoserine Analogues - Towards t he Development of Substrate-based Peptide Inhibitors of cAMP-dependent Protein Kinase
Sammanfattning: Protein kinases are enzymes that via phosphorylation of proteins/peptides regulate most aspects of cell functions and physiology. The enzymes transfer a ?-phosphoryl group from ATP to hydroxyl groups of Ser, Thr and Tyr residues in their substrates. Abnormal phosphorylations due to overactive, mutated or malfunctioning protein kinases are associated with common disease states, including cancers and inflammatory disorders. By targeting the substrate-binding site of a certain protein kinase, it might be possible to develop inhibitors that are both potent and selective. This thesis illustrates an approach to generate specific inhibitors that are based on a peptide substrate. Such inhibitors are referred to as substrate-based kinase inhibitors. In order to convert short peptide substrates into peptide-based inhibitors, non-natural amino acids need to be introduced into the peptide sequence to create tight interactions with naturally existing pockets of the protein kinase. The enzyme targeted in this case is cAMP-dependent protein kinase (PKA). The peptide substrate chosen is the heptapeptide LRRASLG (kemptide). The inhibitor design strategy is based on the replacement of the phosphorylatable Ser residue with a non-phosphorylatable and nonproteinogenic homoserine ?-amino acid analogue. The major part of this thesis deals with the synthetic efforts to prepare enantiomerically pure homoserine derivatives using Schöllkopf’s methodology. The synthetic strategy applied is mainly based on the generation of a bislactim ether epoxide, and its subsequent nucleophilic opening with different nucleophiles, followed by mild acidic hydrolysis to cleave the chiral bislactim ether auxiliary to obtain the desired free amino acid ester (and the D-Val ester). A mixture of 1:1 diastereomeric bislactim ether epoxides were successfully prepared via diastereoselective allylation of Schöllkopf’s chiral bislactim ether followed by epoxidation of the terminal alkene. Single diastereomeric epoxides were generated in low to moderate yields from alkylation of Schöllkopf’s chiral bislactim ether with enantiomerically pure (S)- and (R)-epichlorohydrin, respectively. Unfortunately, subsequent nucleophilic opening of the epoxides generated, with azide, primary or secondary amines acting as nucleophiles, resulted in the formation of bicyclic bislactim ether derivatives, which upon mild acidic hydrolysis were partially hydrolysed to their corresponding dipeptide esters. As amide bonds require harsh conditions to be cleaved, the route chosen for preparation of enantiomerically pure homoserine analogues proved to be unsuccessful. All results presented indicate that the synthetic strategy employed, and the use of Schöllkopf’s chiral auxiliaries for asymmetric amino acid synthesis, are not useful for preparation of the enantiomerically pure homoserine analogues desired. This thesis also describes a new route for the preparation of Schöllkopf’s chiral auxiliaries in a relatively large scale. In this new synthetic pathway microwave-assisted heating is used in one key step.
Denna avhandling är EVENTUELLT nedladdningsbar som PDF. Kolla denna länk för att se om den går att ladda ner.