The Aims of Isolating Active Principles

Analysis of the biological effects (pharmacodynamics) of individual ingredients and of their fate in the body (pharmacokinetics). 

Ensuring a precise and constant dosage in the therapeutic use of chemically pure constituents. 

The possibility of chemical synthesis, which would afford independence from limited natural supplies and create conditions for the analysis of structure-activity relationships. 

Finally, derivatives of the original constituent may be synthesized in an effort to optimize pharmacological properties. Thus, derivatives of the original constituent with improved therapeutic usefulness may be developed. 

Modification of the chemical structure of natural substances has frequently led to pharmaceuticals with enhanced potency. An illustrative example is fentanyl, which acts like morphine but requires a dose only 0.1-0.05 times that of the parent substance. Derivatives of fentanyl such as carfentanyl (employed in veterinary anesthesia of large animals) are actually 5000 times more potent than morphine. 

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