published the third in their series of analyses of the sources of drugs, covering the period
from 01/1981 to the middle of 2006 and showing the sourcesof the listed 974 small molecule drugs. The analysis demonstrated the continuing and valuable contributions of Nature as a source not only of potential chemotherapeutic agents but also of lead compounds that have provided the
basis and inspiration for the semisynthesis or total synthesis of effective new drugs. In this analysis, the drugs were classified as N (an unmodified natural product); ND (a modified natural product); S (a synthetic compound with no natural product conception); S/NM (a synthetic ompound
showing competitive inhibition of the natural product substrate); S* (a synthetic compound with a natural product pharmacophore); and S*/NM (a synthetic compound with a natural product pharmacophore showing competitive inhibition of the natural product substrate).