This book aims to guide and inspire drug researchers as they enter the 21st century. Stereochemistry is an essential dimension in pharmacology and should be understood as such by all drug researchers whatever their background. When used as probes or medicines, stereoisomeric drugs offer invaluable insights or innovative therapeutic strategies. The book spans the subject from the molecular to the clinical. The first section on chemical aspects contains chapters on chemical synthesis, analysis, natural products, chiral stability (racemezation) and physical properties. The second section is on experimental pharmacology, with chapters on drug-receptor interactions, chiral recognition, ion channels, and molecular toxicology. The third section focuses on drug disposition, with chapters on absorption, distribution, protein binding, metabolism and elimination. The final section is dedicated to regulatory and clinical aspects.

State-of-the-Art Chirality Stereochemistry in general and chirality in particular have long been recog- nized as major structural factors influencing pharmacological activity and pharmacokinetic behavior. For more than a century, relevant information in these fields has been accumulating at an accelerating pace, leading to rationalizations, concepts and theories of increasing breadth and depth. Frequently, fundamental advances in stereochemical aspects of molecular pharmacology, drug disposition and pharmacochemistry have been translated into corresponding progress in clinical pharmacology and pharmacotherapy. There have been exceptions, however, since some extrapolations from the biochemical and in vitro situations to the in vivo human situation have proven premature. This notion resulted in the now appeased, but far from closed, debate regarding racemic versus enantiopure drugs, which saw some pro- ponents state that "in many cases, only one isomer contributes to the thera- peutic action while the other, the 'isomeric ballast', only contributes to the side effects and toxicity" (ARIENS 1986,1989,1992). Other authors, in contrast, have cautioned against hasty generalizations and advocated a more pragmatic, case- by-case and evidence-based view (CALDWELL 1995; DE CAMP 1989; SZELENYI et al. 1998; TESTA 1991; TESTA and TRAGER 1990; TESTA et al. 1993).