Natural products have proven to be an excellent resource for discovering new potential drug candidates. For example, a recent study has shown that 64% of anti-cancer drugs and 76% of anti-bacterial drugs are natural products or derivatives. 1. Within a program aimed at the exploration of the biological activities of semisynthetic libraries based on natural product scaffolds – one of which was harmane 1 – 6-aryl-β-carbolines 2. Were identified as potent cytotoxic agents with an in vivo anti-tumour activity. The underlying mechanism was found to be microtubulin depolymerization by interaction with the colchicine binding site.