Research in the Anderson Group for Non-Chemists
WHAT IS AN 'ORGANIC' CHEMIST?
Organic chemists have little to do with organic food – other than the eating part. To a chemist, the term "organic” refers to molecules which contain (by definition) the elements carbon and hydrogen; also often other elements such as oxygen, nitrogen, chlorine, and so on. This includes molecules such as petrol, ethanol, paracetamol (beneficial) and strychnine (poisonous!). In fact, “organic” chemists often typify the opposite end of the spectrum to “organic” farming and produce, as they are at the heart of the agrochemicals industry, which produces many selective herbicides and fungicides. Nevertheless, modern organic chemistry has a real interest in being “green” – we aim to minimise the amount of waste and toxic reagents that are involved in our reactions.
WHAT IS THE DIFFERENCE BETWEEN AN ORGANIC PRODUCT AND A SYNTHETIC PRODUCT?
In short – nothing! At the molecular level, a molecule harvested from nature and the same molecule prepared in the laboratory are identical. They have identical properties, and will be treated in the same way by our bodies if it is a molecule that we ingest. They degrade the same way in the environment. In fact, it may be that the synthetic molecule is actually of higher purity than that produced by Nature, due to trace contaminants that are difficult or impossible to separate. In fact, without organic chemists and the ability to prepare molecules in the laboratory, we would have no plastics, pharmaceuticals, nylon and polyester, or baked beans (no preservatives!!).
WHAT DO WE DO?
Our research in organic chemistry – the chemistry of molecules containing carbon and hydrogen, and often oxygen, nitrogen, and other elements – is centred in natural products, molecules that are produced by plants, bacteria, and marine organisms. These natural products are produced in Nature for a variety of reasons – for example signalling or defence – but often also exhibit activity against human diseases, which means they can offer a lead for the development of new drugs.
However, for our group this is just the beginning, as devising a chemical synthesis of complex natural products can take years – mainly as we are looking for a route (synthetic sequence) which is short, can easily be scaled up, and can enable the synthesis of analogues – synthetic molecules which look like the natural product but have slightly different structures with potentially improved biological properties. So, we also aim to develop new chemical reactions alongside the synthetic endeavour – reactions we intend to use in our natural product synthesis, but which we also hope can be used by chemists worldwide to facilitate their own work, by applying these techniques on totally different molecules.
This is known as “synthetic methodology” and is the largest field within organic chemistry. We are particularly interested in two branches of methodology – reactions involving silicon in organic chemistry, and reactions catalysed by “transition metals” (metals which lie at the centre of the periodic table, such as palladium, ruthenium, rhodium, iridium and platinum).
In both of these areas, we are very much interested in the chemistry of molecules containing carbon-carbon double bonds (i.e. C=C, like ethylene / ethene) and triple bonds (i.e. C≡C, like acetylene).
Silicon is a wonderful element for the organic chemist. It forms strong bonds to carbon and oxygen, so is quite stable within an organic molecule, but can also be activated when required by the chemist to perform chemical reactions, through the action of hydroxide ions (OH-), or fluoride ions (F-). It is also non-toxic, and in many of its applications promises to displace previously-used toxic reagents.
We are interested in the ability of silicon to form new carbon-oxygen bonds, and carbon-carbon bonds. In both of these contexts we would actually like to avoid the use of fluoride as an activating agent, as this provides selectivity – in other words, we can react one silicon group within a molecule in the presence of another.
TRANSITION METAL-CATALYSED REACTIONS
Transition metals offer unique methods to form carbon-carbon bonds – the glue that organic chemists use to put molecules together. Several members of the group use palladium catalysts to effect these bond formations, where we form at least one ring in the course of the catalytic process. In one case, this involves a “cascade” reaction, where multiple carbon-carbon bonds are formed in one reaction. This is an appealing type of reaction to organic chemists, as it generally involves the preparation of a significantly more complicated molecule in a single step. In another case, we are using palladium to control the chirality of ring systems containing oxygen or nitrogen (i.e. one mirror image form of a molecule being formed in preference to another).
We are also using other transition metals in ring-forming reactions which create no waste – so-called “isomerisations”. These reactions are very appealing as they rely solely on the transition metal to mediate bond formation in a selective and mild manner.