Chirality of Central Nervous System (CNS) Acting Drugs: A Formidable Therapeutic Hurdle Against CNS Diseases

Background: Over fifty percent of drugs being used clinically are chiral and 90% of them are racemates. Unfortunately, they have both adverse and beneficial effects on body systems. Methods: Because of the erratic effects of chiral compounds on body functional systems, literature search was carried out with a view to identify CNS chiral drugs, their clinical advantages and disadvantages, unique physicochemical properties and structural modifications into safer drugs. Results: Findings have shown that majority of CNS and non-CNS acting drugs have chiral functional groups that may occur as either dextrorotatory (clockwise) or levorotatory (anticlockwise) or racemates which are inert. Sometimes, the enantiomers (optical isomers) could undergo keto-enol tautomerism, appearing in either acidic or basic or inert form. Chiral CNS acting drugs have agonistic and antagonistic effects, clinical advantages, disadvantages, and special clinical applications, possible modifications for better therapeutic effects and possible synthesis of more potent drugs from racemates. Clockwise chirality may be more effective and safer than the drugs with anticlockwise chirality. When chiral drugs are in racemate state they become inert and may be safer than when they are single. Also, diastereoisomers may be more dangerous than stereoisomers. Conclusion: Therefore, chiral compounds should be adequately studied in lab rodents and primates, and their mechanisms of actions should be comprehensively understood before being used in clinical setting. Since many of them are toxic, their use should be based on principle of individualized medicine. Their molecular weights, functional groups, metabolites, polymers and stereoisomers could be valuable tools for their modifications.