Understanding and Exploring the Diverse Potential of Natural Products

In this thesis, the diverse potential of natural products for their use in consumer products and as therapeutics has been explored. The importance of design of extraction experiments has been highlighted; a well-developed method not only allows targeted extraction of natural products from biological matrices but can also reduces the number of purification steps significantly. This in turn makes processes more environmentally friendly as well as cost and time-effective. During literature research, it was noted that natural product extracts and isolated compounds were often not fully characterised which can lead to error. In this project, all extracts and the isolated compounds were monitored and analysed using a range of analytical techniques to facilitate reliable and reproducible characterisation of the extracts.
In first part of this thesis, blackcurrant extract was fully characterised and a scalable method for extraction of polyphenols and generation of three product streams was developed. Fourteen polyphenols were isolated and fully characterised using mass spectrometry, IR, UV/Vis and NMR spectroscopy. Extinction coefficients were calculated for all compounds. The extract was quantified using HPLC and external standards. Total monomeric anthocyanin content assay (TMAC) was evaluate for its efficiency of estimating percentage of anthocyanins in natural extracts and compared with HPLC. The effect of organic solvents and co-occurring flavonoids on the assay results was studied. The stability of anthocyanins during extraction and purification processes was also studied.
Second part of this thesis was focussed on discovery of antibacterial compounds from microbial extracts. This project was further divided into two areas of research: revisiting previously discarded antibiotic compounds and exploration of novel sources of antibiotic compounds. These projects were done in close collaboration with Dr Alex O’Neill and his PhD students. Previously discarded actinorhodin family of compounds were revisited and extracellular γ-actinorhodin with strong antistaphylococcal activity was identified. Targeted scalable method of extraction and purification was developed. γ-Actinorhodin was isolated in 19 wt./wt.% yield and fully characterised using mass spectrometry, IR, UV/Vis and NMR spectroscopy. A TLC–bioautography assay was developed which allowed efficient screening of active crude extracts. VF48A and P5-25 extracts with strong activity against S. aureus SH1000 and MDR E. coli CMR400 were chosen to take to next stage. Seventeen 2,5-diketopiperazines were isolated from these extracts altogether. These DKPs showed selective activity against targeted organisms. Thirteen DKPs were synthesised to confirm assignments and bioactivity.