Towards the Total Synthesis of the Polyketide Natural Product DEM30355/A and Associated Crystallisation Studies

PhD ThesisDue to the continuing rise in drug resistant pathogenic bacteria, there is an urgent need for new Mode of Action antibiotics. We have identified the polyketide natural product DEM30355/A as a potential new Mode of Action antibiotic versus Methicillin-resistant Staphylococcus aureus. This project aims to develop a synthetic route to DEM30355/A and its synthetic analogues to support new antibiotic development. We have shown that the ABC anthracene-like core of DEM30355/A can be constructed by employing a key tandem, Michael-Dieckmann reaction. The functionalised C-ring was synthesised via a stereoselective Michael-Wittig reaction introducing the desired C-4a/C-10a C=C double bond, C-2 methyl and C-3 ethyl ester, followed by a stereoselective Rubottom oxidation to introduce the required hydroxyl group at C-3. A Michael-Dieckmann reaction between the A-ring and C-ring precursors allowed access to the ABC fused ring carbon skeleton of our target DEM30355/A, with a significant number of the required functional groups in place. Future work will focus on lactone ring formation, oxidation of the C-ring and installation of the B-ring C=C double bond between C-10/C-10a (Scheme 1.00). Scheme 1.00: Synthesis of the ABC fused ring core of DEM30355/A via a key Michael-Dieckmann cyclisation. Our synthetic work was supported by crystallographic studies including an investigation into the propensity of shikimate esters to form high Z’ structures and the crystallisation of biologically active small molecules. Our results serve to further confirm the tandem Michael-Dieckmann reaction as a robust method of coupling functionalised aromatic rings for the construction of natural product scaffolds

High-Throughput Oil-Encapsulated Nanodroplet Crystallisation for Organic-Soluble Small Molecule Structure Elucidation and Polymorph Screening (ENaCt)

Single crystal X-ray diffraction analysis (SCXRD) constitutes a universal approach for the elucidation of molecular structure and for the study of crystalline forms. However, the discovery of viable crystallisation conditions remains both experimentally challenging and resource intensive, in time and quantity of analyte(s). We report a robot-assisted, high-throughput method for the crystallisation of organic-soluble small molecules, employing only micrograms of analyte per experiment. This allows hundreds of crystallisation conditions to be screened in parallel, with minimal overall sample requirements. Crystals suitable for SCXRD analysis are grown from nanolitre droplets of a solution of analyte in organic solvent(s), each of which is encapsulated within an inert oil to control the rate of solvent loss. This encapsulated nanodroplet crystallisation methodology can also be used in the search for new crystal forms, as exemplified through both our discovery of a new (thirteenth) polymorph of the olanzapine precursor ROY and the SCXRD analysis of the “uncrystallisable” agrochemical dithianon

Encapsulated Nanodroplet Crystallization of Organic-Soluble Small Molecules

Small molecules can form crystalline solids, in which individual molecules pack together into ordered three-dimensional arrays. Once a suitable crystal is grown, the packing and atomic connectivity of the constituent molecules can be studied by X-ray diffraction. However, the discovery of experimental conditions for successful crystal growth is often challenging. We have developed a nanoscale crystallization technique for organic-soluble small molecules by using high-throughput liquid-handling robotics to undertake multiple crystallization experiments simultaneously with minimal sample requirements and high success rates. We showcase our methodology through the crystallization of a diverse set of small molecules, including “uncrystallizables,” combined with structural analysis by X-ray diffraction. We anticipate that this rapid and reliable method for small-molecule crystallization will have far-reaching impact, facilitating academic and industrial research in the molecular sciences