ABSTRACT
Recent investigations have clearly established that enantiomers of racemic pharmaceutical drug mixtures can present different pharmacokinetic properties. These can be attributed to the capacity of the desired enantiomer to exhibit higher binding affinity with its intended receptor or enzyme, to display a better bioavailability, or to present a more advantageous side-effect profile. A well-known example is ibuprofen, which has been manufactured as a racemate for several decades. Post-market-introduction studies, which were permitted by improved analytical technology, revealed that the (S) enantiomer was the active form of the drug [1]. Similarly, the bronchodilatory effects of the antiasthma agent albuterol were found to be associated with its (R) enantiomer, whereas (S) albuterol generally provides no therapeutic benefit [2]. Because of these vast differences in the therapeutic potential of enantiomers, it is not surprising that pharmaceutical development increasingly targets single enantiomer products. Consequently, the manufacture of only the active enantiomeric form of a drug has become a norm in the industry [3-6]. Most chiral syntheses are traditionally achieved through chemical methods employing an ever-expanding range of chiral catalysts and reagents [5]. Despite chirotechnology’s swift technical advances, some chiral syntheses, especially those requiring both regioselectivity and stereoselectivity, remain difficult and can be extremely costly. This has substantial economic implications. In 2000, for instance, about 40% of all marketed pharmaceuticals were single enantiomers and accounted for about $130 billions in sales, representing a nearly 100% increase since 1996 [6,7].
