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Description
Natural products have been the source of valuable lead structures in the development of new therapeutics, providing novel structures that target unique biological pathways. Sansalvamide A (SanA) and Urukthapelstatin A (UstatA) are two such natural products. Both are peptide macrocycles isolated from marine organisms that display anticancer activity over a broad spectrum of cancer cell lines. Though peptides are sometimes considered poor drugs due to poor solubility and rapid degradation inside the cell, cyclic peptides have proven to be quite effective in minimizing these factors. Several peptide macrocycles are currently used as antibacterial (Vancomycin), antifungal (Caspofungin), anticancer (Aplidine), and immunosuppressant (Cyclosporine A) agents. Cyclic peptides require only a few amino acids to generate an overall 3D structure, thus minimizing molecular weights and improving solubility. Cyclic peptides have also shown to be more stable inside the cell relative to linear peptides due to the lack of terminal amino acids being exposed to proteases. With this in mind we have endeavored to synthesize both Sansalvamide A and Urukthapelstatin A as well as a library of derivatives in order to investigate the SAR of these macrocycles. We also will synthesize additional derivatives in order to investigate the compounds' mechanism of action in inhibiting cancer cell growth. The SanA project is well established with a library of over 100 derivatives synthesized to investigate its SAR. A decapeptide side product was also discovered to have anticancer activity and was also investigated. The pentapeptide and decapeptide derivatives I made were synthesized using a convergent solution phase approach. Boc-protected and OMe protected commercially available amino acids were coupled using standard peptide coupling conditions. Intermediates and the final products were purified via flash-column chromatography and HPLC and were characterized via ¹H-NMR and LC-MS. Inhibition has been to shown to occur via binding to Heat Shock Protein 90 (Hsp90). Current work includes synthesis of additional derivatives and multiple assays to ascertain the client proteins affected by our compounds' binding to Hsp90. Urukthapelstatin A is a heterocyclic macrocycle containing two oxazole, two thiazole, and one phenyloxazole moieties, which demonstrated growth inhibition against cancer cells in the low nanomolar range. Merchercharmycin, telomestatin, muscoride A and hennoxazoles are a few examples of pharmacologically active compounds recently synthesized and studied that contain similar poly-azole motifs. Upon thorough review of literature regarding the synthesis of some of these compounds and the various techniques employed in the synthesis of oxazoles and thiazoles, we have developed an efficient solution phase synthetic strategy for this molecule. We have employed standard peptide coupling conditions on commercially available Boc-protected and OMe protected amino acids to generate di and tripeptides as our precursors. We used Dieythylaminosulfurtrifluoride (DAST) and Diaza(1,3)bicycle[5.4.0]undecane (DBU) to perform a cyclodehydration/oxidation on Serine containing peptides to generate the oxazole and phenyloxazole moieties. The Hantzsch thiazole synthesis conditions were used to generate the first thiazole and were expected to generate the second thiazole in the final macrocyclization. Precursor compounds and the final product will be characterized by ¹HNMR and LC-MS. They were purified via flash-column chromatography and/or HPLC when necessary. Once the natural product is synthesized and the structure is confirmed and tested for cytotoxicity, we will proceed to synthesize derivatives to begin investigating SAR. Shortly thereafter, a derivative containing a biotinylated tag will be made to determine the mechanism of action. Considering the low nanomolar cytotoxicity of the natural product, Urukthapelstatin A could be a very promising scaffold for development of a cancer therapeutic.
