Question

describe the meaning of the term chiral switch strategy

Answer 1

Carbon atom in a molecule wherein all the four substituents are different is termed as chiral and its mirror image is non-superimposable. These non-superimposable mirror image compounds are termed as enantiomers. During synthesis of chiral compounds, a synthetic chemist might not always get an enatiomerically pure compound (or the overall synthesis might not be feasible or economically not viable) but prepared as racemates. In many cases, enantiomerically pure compounds are more beneficial and biologically more active i,e the pharmacological and toxicological activity varies for the enantiomers when present as one pure form or as a racemic mixture. The benefits of a potential drug depends a lot on the risk-benefit ratio and varies on case-to-case basis. It was realised that certain drugs which were initially marketed as racemic mixtures when studied for their biological activity by resolving the racemic mixture into enantiomerically pure components showed different or more beneficial activity for one enantiomer. The chiral switch is the development of a single enantiomer from a previously known/marketed racemate.For example, the use of a racemic Dopa for the treatment of Parkinsons disease was known to cause adverse effects such as nausea, vomitting, anorexia etc. However, the replacement of the racemic Dopa with L-Dopa (which is the single enatiomer) reduced the adverse effects and an increase in number of improved patients was observed.