The chemical libraries contain distinct types of compounds that, depending on their primary source and/or obtention method, can be classified as synthetic or semi-synthetic compounds, natural products, and virtual compounds. The properties of these several types of compounds differ significantly. In general, naturally occurring substances, with a larger number of stereocenters, are more complex than synthetic ones. This complexity can lead to the development of more selective pharmaceuticals. In fact, in some pharmacological groups, such as anti-tumor drugs, many of the pharmaceuticals are of natural origin or based on them.