<P> The first is sometimes referred to as random collection and screening of material, but in fact the collection is often far from random in that biological (often botanical) knowledge is used about which families show promise, based on a number of factors, including past screening . This approach is based on the fact that only a small part of earth's biodiversity has ever been tested for pharmaceutical activity . It is also based on the fact that organisms living in a species - rich environment need to evolve defensive and competitive mechanisms to survive, mechanisms which might usefully be exploited in the development of drugs that can cure diseases affecting humans . A collection of plant, animal and microbial samples from rich ecosystems can potentially give rise to novel biological activities worth exploiting in the drug development process . One example of a successful use of this strategy is the screening for antitumour agents by the National Cancer Institute, started in the 1960s . Paclitaxel was identified from Pacific yew tree Taxus brevifolia . Paclitaxel showed anti-tumour activity by a previously undescribed mechanism (stabilization of microtubules) and is now approved for clinical use for the treatment of lung, breast and ovarian cancer, as well as for Kaposi's sarcoma . Early in the 21st century, Cabazitaxel (made by Sanofi, a French firm), another relative of taxol has been shown effective against prostate cancer, also because it works by preventing the formation of microtubules, which pull the chromosomes apart in dividing cells (such as cancer cells). Other examples are: 1 . Camptotheca (Camptothecin Topotecan Irinotecan Rubitecan Belotecan); 2 . Podophyllum (Etoposide Teniposide); 3a . Anthracyclines (Aclarubicin Daunorubicin Doxorubicin Epirubicin Idarubicin Amrubicin Pirarubicin Valrubicin Zorubicin); 3b . Anthracenediones (Mitoxantrone Pixantrone). </P> <P> The second main approach involves ethnobotany, the study of the general use of plants in society, and ethnopharmacology, an area inside ethnobotany, which is focused specifically on medicinal uses . </P> <P> Both of these two main approaches can be used in selecting starting materials for future drugs . Artemisinin, an antimalarial agent from sweet wormtree Artemisia annua, used in Chinese medicine since 200BC is one drug used as part of combination therapy for multiresistant Plasmodium falciparum . </P> <P> The elucidation of the chemical structure is critical to avoid the re-discovery of a chemical agent that is already known for its structure and chemical activity . Mass spectrometry is a method in which individual compounds are identified based on their mass / charge ratio, after ionization . Chemical compounds exist in nature as mixtures, so the combination of liquid chromatography and mass spectrometry (LC - MS) is often used to separate the individual chemicals . Databases of mass spectras for known compounds are available, and can be used to assign a structure to an unknown mass spectrum . Nuclear magnetic resonance spectroscopy is the primary technique for determining chemical structures of natural products . NMR yields information about individual hydrogen and carbon atoms in the structure, allowing detailed reconstruction of the molecule's architecture . </P>

Name used to describe the molecular structure of a drug