Classroom Enters the Courtroom: Stereochemistry of S_N1 and S_N2 Reactions in Enantiomer Patent Litigations of the Antidepressant Escitalopram

The role of elementary stereochemistry is illustrated in the patent litigations of the blockbuster antidepressant drug escitalopram oxalate. An undergraduate student of organic chemistry would recognize the stereochemical courses of the intramolecular S_N2 and S_N1 reactions of the single-enantiomer (S)-diol intermediate in the synthesis of the blockbuster antidepressant drug escitalopram oxalate: retention of configuration of the chiral carbon atom under basic conditions and racemization under acidic conditions, respectively. He/she, in searching for a stereoselective ring-closure reaction of the enantiomeric diol, will think of an S_N2 reaction in a basic medium. From these points of view, the process claim in the enantiomer patents of escitalopram is obvious/lacks an inventive step. An organic chemistry examination problem based on this scenario is offered.