Asymmetric Transfer Hydrogenation of Imines.

Many molecules have the potential to exist in one of two mirror image forms, known as 'enantiomers' (like your hands). Most significantly, a large proportion of the molecules from which biological organisms (cells, animals, plants, us) are made, including carbohydrates, protein and DNA, exist predominantly in a single enantiomeric form, i.e. as a single mirror image.This creates a challenging problem for the pharmaceutical, agrochemical and fine chemicals industries. If a new chemical is made, e.g. a potential drug, pesticide, intermediate etc., then this may also have to potential to exist as a mixture of enantiomers as well, depending on its structure. Although these molecules will be identical in many ways (as your hands are), they are likely to interact very differently with a biological system (i.e. if we swallow them), because they will be seen as two totally different compounds (try shaking hands with a friend's right hand and then with their left hand). The difference in biological effects, however, can be so great that now it is a legal requirement for chemical companies to make all new 'enantiomeric' compounds separately in each 'handedness' and to test each of these for safety and activity (sometimes only one enantiomer works as a drug, sometimes one is dangerous and one is beneficial). Furthermore, it is also often necessary for 'enantiomeric' compounds to be marketed in the single (i.e. most beneficial) handedness.The problem is that this (seemingly easy) task is in fact often quite difficult, because most of the most common and simple routes to new compounds form a 50:50 mixture of both 'enantiomers'. This is analogous to flipping a coin - as each molecule is made (each flip of the coin) then there is a 50:50 chance of making either handedness. To get a product of one 'handedness' it is necessary to make every single molecule the same way round (flip a head every time, or a tail every time). In our research at Warwick, we have developed a series of catalysts which generate 'enantiomeric' molecules through a single step process in which hydrogen is selectively added to a substrate to give a product in which one handedness significantly predominates over the other (i.e. it flips more heads than tails, or vice versa). As well as being active, and selective, the catalyst can be used at low loadings, typically below 0.5 % relative to substrate. This reduces waste, energy use and side products.In previous work, we have applied our catalysts to the synthesis of enantiomerically-pure (i.e. one handedness of) alcohols, which are a pivotal class of molecules represented in many pharmaceutical targets and intermediates. In this project, the catalysts will be adapted to be able to make a further pivotal class of molecules, amines, by adding hydrogen to a simple precursor molecule. If successful, this will provide an effective route to large numbers of valuable synthetic intermediates, target molecules, and complex products which would otherwise be very difficult to prepare.