In vitro bioactivation of a selective estrogen receptor modulator (2S,3R)-(+)-3-(3-hydroxyphenyl)-2-[4-(2-pyrrolidin-1-ylethoxy)phenyl]-2,3-dihydro-1,4-benzoxathiin-6-ol (I) in liver microsomes: formation of adenine adducts

The Importance of Tracking "Missing" Metabolites: How and Why?

Technologies currently employed to find and identify drug metabolites in complex biological matrices generally yield results that offer a comprehensive picture of the drug metabolite profile. However, drug metabolites can be missed or are captured only late in the drug development process. This could be due to a variety of factors, such as metabolism that results in partial loss of the molecule, covalent bonding to macromolecules, the drug being metabolized in specific human tissues, or poor ionization in a mass spectrometer. These scenarios often draw a great deal of attention from chemistry, safety assessment, and pharmacology. This review will summarize scenarios of missing metabolites, why they are missing, and associated uncovering strategies from deeper investigations. Uncovering previously missed metabolites can have ramifications in drug development with toxicological and pharmacological consequences, and knowledge of these can help in the design of new drugs.

Drug metabolism in drug discovery and development

Drug metabolism as a discipline plays an important role in drug discovery and development and the effects of drug metabolism on pharmacokinetics (PK), pharmacodynamics (PD), and safety should be carefully considered. This communication provides an overview of common strategies in the area of drug metabolism for improving PK/PD and safety profiles of drug candidates; these include, but are not limited to, collaboration with medicinal chemists on structure–activity relationships (SAR) to overcome high clearance, using deuterium replacement to further optimize a lead, prodrug approaches to circumvent formulation and delivery difficulties, and addressing issues such as species differences in metabolism, drug–drug interactions (DDI) and formation of reactive metabolites.

Synthesis of Sulfur Perfluorophenyl Compounds Using a Pentafluorobenzenesulfonyl Hypervalent Iodonium Ylide

A novel pentafluorobenzenesulfonyl hypervalent iodonium ylide 3 was designed and synthesized as a useful tool for the preparation of sulfur pentafluorophenyl compounds containing a C₆F₅S or C₆F₅SO₂ unit. Electrophilic pentafluorophenylthiolation of enamines, formal [3+2] cycloaddition reaction of nitriles and alkynes, and intramolecular S_NAr cyclization were achieved using iodonium ylide 3. The fluoro-click reaction was also demonstrated using one of the products via an intermolecular S_NAr reaction with heterocentered nucleophiles.

Detecting reactive drug metabolites for reducing the potential for drug toxicity

INTRODUCTION

A number of withdrawn drugs are known to undergo bioactivation by a range of drug metabolizing enzymes to chemically reactive metabolites that bind covalently to protein and DNA resulting in organ toxicity and carcinogenesis, respectively. An important goal in drug discovery is to identify structural sites of bioactivation within discovery molecules for providing strategic modifications that eliminate or minimize reactive metabolite formation, while maintaining target potency, selectivity and desired pharmacokinetic properties leading to the development of efficacious and nontoxic drugs.

AREAS COVERED

This review covers experimental techniques currently used to detect reactive drug metabolites and provides recent examples where information from mechanistic in vitro studies was successfully used to redesign candidate drugs leading to blocked or minimized bioactivation. Reviewed techniques include in vitro radiolabeled drug covalent binding to protein and reactive metabolite trapping with reagents such as glutathione, cyanide, semicarbazide and DNA bases. Case studies regarding reactive metabolite detection using a combination of varied techniques, including liquid chromatography-tandem mass spectrometry and NMR analyses and subsequent structural modification are discussed.

EXPERT OPINION

Information derived from state-of-art mechanistic drug metabolism studies can be used successfully to direct medicinal chemistry towards the synthesis of candidate drugs devoid of bioactivation liabilities, while maintaining desired pharmacology and pharmacokinetic properties.