Open Collections

Hagar, Mostafa

University of British Columbia

Natural products continue to serve as a rich source of bioactive molecules and interesting chemistry. However, contemporary endeavours are often frustrated by the re-isolation of known compounds. A variety of approaches emerged for targeting novel natural products for isolation. Rapid advancements in genomics have enabled ‘genome-mining’ techniques, frequently deployed when studying microbes, using bioinformatics-based predictions of genes encoding biosynthetic enzymes. This work describes the application of a hybrid ‘genome-mining’ and spectroscopic screening approach leading to isolation of the biologically potent and chemically novel caveamides. The dynamic structures of caveamides presented a challenging structure elucidation, requiring detailed interpretations of spectroscopic data and chemical degradation experiments. Chapter 1 gives a brief overview of the field, and explains the hybrid genome-mining/spectroscopy approach previously described by our groups. The method targets the isolation of compounds containing piperazate residues, cyclic hydrazine amino acids that frequently coincide with bioactivity and structural novelty. Genes encoding piperazate biosynthesis can be identified, and piperazate residues give a distinct NMR spectroscopic signature. Chapters 2 and 3 describe piperazate-targeting isolation of caveamides A (1) and B (2) from Streptomyces sp. strain BE230, a soil microbe collected from New Rankin Cave (Missouri). These chapters describe detailed structure elucidation, as well as the results of in vitro bioassays. In addition to piperazate residues, caveamides exhibit a rare cyclohexenylalanine moiety, not previously seen as a free peptide residue. This residue is hydrolytically unstable, and assigning its configuration necessitated a novel use of dibromination to preserve stereochemical information, as described in Chapter 3. Chapter 4 describes the identification of caveamide congeners by taking advantage of diagnostic mass spectrometry fragmentation. It also explores the generalizability of this screen using public data, setting the stage for further research. Chapter 5 describes the biogenetic considerations of caveamides, placing their structures in the context of known biosynthetic pathways. Notably, the isolation of caveamides along with their putative biosynthetic gene cluster enables some inferences about cyclohexenylalanine biosynthesis, which is poorly understood. This chapter provides an interpretation of previously reported experimental findings in light of new insights afforded by caveamides. Chapter 6 concludes by proposing future avenues for investigation.

Text

2024-10-28

Attribution-NonCommercial-ShareAlike 4.0 International

http://hdl.handle.net/2429/89553

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-sa/4.0/