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A recent Chemical Science article by Filip Teply and colleagues caught my eye because of the name given to an intermediate that the researchers have discovered – saddlequat!
The saddlequat is an intermediate that occurs on the racemisation pathway in which an optically active helicene – a helquat – turns into a racemic one with no optical properties, on heating. It’s finally been captured by the teams from the Academy of Sciences of the Czech Republic in Prague and the Institute of Chemical Research, Tarragona, Spain.
Helicene research has been going on for a long time – over 100 years – and in that time, no one has been able to isolate the saddlequat, despite its existence being predicted. Helicenes are polycyclic aromatic compounds in which benzene rings or other aromatics are angularly annulated to give helically-shaped molecules. They have fascinated scientists with their shape and inherent chirality and this fascination has led to studies into their self-assembly and catalytic, chiroptical and acid–base properties. They have recently been reported to inhibit telomerase activity and interact with DNA, which promises interesting future applications.
Teply’s team found that after isolation, the saddlequat could be transformed into a chiral helquat helix. They also add that helquat is an example of a ‘rubber glove’ molecule. The rubber glove theory was introduced by Kurt Mislow in the 1950s – it describes the process of going from one form to another exclusively via a chiral pathway, like turning a right-handed glove inside out leading to an object that’s superimposable onto a left-handed glove without being symmetric on the journey.