Discovery of a new drug candidate is a long iterative process, where properties of molecules are improved systematically. The number of theoretically possible structures to be synthesized is unlimited - but what is actually synthesized depends on careful selection and structural design.

In the beginning of a new project, scientists are searching for compounds suitable for chemical optimization of desired properties. In silico virtual screening methods are utilized in the search of so-called Hit structures. Creation of Structure Activity Relationships (SAR) will be possible after suitable experimental data related to structures have been obtained. SARs guide structural design of the new structures to be synthesized.

Many properties are already acceptable for a lead compound, but they still need to be optimized. During the optimization, scientists have to improve many important properties of the compounds in addition to the biological activity, e.g. absorption, distribution, metabolism, excretion and safety parameters. With further optimization it is ensured that efficacy, kinetics and safety of a new chemical entity fulfil requirements of a drug candidate.

As a final outcome of the optimization process usually only one drug candidate will be selected for further development and clinical studies, where the final proof of concept as well as feasibility will be tested.