Physicochemical and Pharmacological Characterization of Permanently Charged Opioids

The main aim of synthesizing permanently charged opioids is to ensure that they do not enter the central nervous system. Such drugs can provide analgesic activity with reduced sedation and other side effects on the central nervous system.

We undertook a search of bibliographic databases for peer-reviewed research literature and also summarized our published results in this field.

The present review focuses on the characterization of permanently charged opioids by various physicochemical methods, and in vitro as well as in vivo tests. The basicity and lipophilicity of opioid alkaloids are discussed at the microscopic, speciesspecific level. Glucuronide conjugates of opioids are also reviewed. Whereas the primary metabolite morphine-3-glucuronide does not bind to opioid receptors with high affinity, morphine-6-glucuronide is a potent analgesic, at least, partly due to its unexpectedly high lipophilicity. We discuss the quaternary ammonium opioid derivatives of a permanent positive charge, detailing their antinociceptive activity and effects on gastrointestinal motility in various in vivo animal tests and in vitro studies. Compounds with antagonistic activity are also reviewed. The last part of our study concentrates on sulfate conjugates of morphine derivatives that display unique pharmacological properties because they carry a negative charge at any pH value in the human body.

In conclusion, the findings of this review confirm the importance of permanently charged opioids in the investigated fields of pharmacology.