Design and Synthesis of novel analogues of Hipposudoric Acid for therapeutic use

Research into novel antimicrobial agents has never been more pressing with the ever-increasing resistance towards traditional medications. The natural world is a rich source of medicines, with a many drugs on the market originating from natural sources. As evolution progressed, these compounds developed to protect the organism against pathogens in the environment. Now, scientists are exploring the natural environment with renewed vigour in the hope of identifying new antibiotics.

Throughout sub-Saharan Africa, Hippopotamus amphibius inhabits environments such as rivers, lakes, and swamps, which provides shelter and cooling from the scorching hot sun. To adapt to these environments rife with microorganisms, the hippopotamus produces compounds (such as hipposudoric acid) that are secreted through its skin to protect itself from invading pathogens. The secretions are red in colour and change overtime to a brown colour and serve to protect the animals from their harsh environments. The molecular structure of the secretions has been elucidated & the colour change attributed to be the polymerisation of hipposudoric and norhipposudoric acids. These natural products exhibit absorbent properties towards dangerous UV rays and demonstrate antimicrobial activities. This discovery provides a chemophore with potential utility as therapeutic agents.

Yoko Saikawa et al. reported the synthesis of the natural products; however, their procedure featured many steps which causes the procedure to be time-intensive, expensive, & inefficient. This provides a clear opportunity to establish a novel synthetic route to produce the tricyclic scaffold of the natural product. This research is of great importance as it will enable the discovery of a new generation of antimicrobials.

Research Questions

• Can a concise synthetic route be established for construction of a series of novel hipposudoric acid analogues?
• Which structural features are responsible for biological activity? Data will help prioritise efforts towards the discovery of novel antimicrobial agents (&/or sun-blocking materials).
• Can computational chemistry help to unlock potential modes of actions i.e., identify pharmacophores for antimicrobial activity?

Aims and Objectives

To successfully develop a novel series of pharmacologically active natural products based on those from Hippopotamus amphibius for medical and commercial benefit. The proposed project is highly multi-disciplinary in nature.

1. Develop and optimise a concise synthetic route to prepare the Hippopotamus amphibius-based natural products and their derivatives.
2. Determine the activity of the compounds with particular attention to the differences generated by structural variations in the compounds on UV absorbance (for sun screening) and antimicrobial activity. Study the natural skin microbiome of the animals and compare the profiles of the natural compounds with synthetic derivatives.
3. In silico studies to predict drug-likeness and investigate potential modes of actions.

Project strategy and time plan

Month 1: Thorough literature review.

Months 2-30: The student will establish a novel route for the synthesis of the natural product via a substituted 2-nitrobenzophenone and a subsequent Pschorr ring closure reaction to form the fluorene skeleton (Figure 1). Alternative ring closure reactions will also be explored.

Months 13-30: Test synthetic analogues for antibiotic activity (including vs. resistant strains). Work be conducted by Dr Sarah Fouch (Portsmouth). We hope to swab hippos at a UK zoo to study the natural skin microbiome. This would provide (over time) a greater understanding of how the microbial community fluctuates in response to different environmental challenges and specifically in response to increased exposure to antimicrobial pigments. It will also allow to identify commonalities between the species that can withstand exposure. These insights will help gain a greater understanding of underlying mechanisms of action of these antimicrobial compounds. In addition, Dr Sam Robson (Portsmouth) plans to help model the animals’ transcriptome which may assist our mode of action studies.

Months 2-34: Build on exciting preliminary work by the Wren research group to probe potential modes of actions of the synthetic compounds using computational modelling.^[6] These studies will also facilitate the optimisation of our medicinal chemistry and predicted drug-likeness of the structures.

Months 26-34: Selected compounds to be profiled externally (CRO) to gain a preliminary understanding of their in vitro ADME properties, e.g., solubility, metabolism, CYP inhibition & plasma protein binding.

Months 36 onwards: Write-up thesis. We anticipate that this PhD would lead to several Q1 publications during the project.