Small molecule

In pharmacology, a small molecule is a small organic compound that is biologically active (biomolecule) but is not a polymer. This term is very loosely used and it may or may not include monomers or primary metabolites, in fact it is generally used to denote molecules that are not protein which play a endogenous or exogenous biological role, such as cell signalling, are used as a tool in molecular biology or are a drug in medicine.

These compounds can be natural (such as secondary metabolites) or artificial (such as antiviral drugs); they may have a beneficial effect against a disease (such as FDA approved drugs) or may be detrimental (such as teratogens and carcinogens).

Drugs

Most drugs are small molecules, although some drugs can be proteins, e.g. insulin. Many proteins are degraded if administered orally and most often cannot cross the cell membrane. This is often not the case for small molecules, some though of which are orally available as a Prodrug. Many dietary supplements are small molecules (but not herb extracts, such as ginkgo).

econdary metabolites

For organisms to produce small molecules they need one or more specialized enzymes (to create and destroy), which as a result are not that abundant in vertebrates (recent and small + slow population size), but very common in soil bacteria (such as streptomyces) and fungi, which in particular secrete antibiotics.

Plants also have several secondary metabolites, which play a role in cell signalling, pigmentation or in defence, several of which have also been used as drugs (medical and recreational).

*Alkaloids
*Glycosides
*Lipids
*Flavonoids
*Nonribosomal peptides, such as actinomycin-D
*Phenazines
*Phenols
*Polyketide
*Terpenes, including steroids
*Tetrapyrroles

Investigative tools

Enzymes and receptors are often activated or inhibited by endogenous protein, but can be also inhibited by endogenous or exogenous small molecule inhibitors or activators with can bind to the active site or on allosteric site.

An example is the teratogen and carcinogen phorbol 12-myristate 13-acetate which is a plant terpene which activates protein kinase C resulting in cancer, making it a very useful investigative tool. Voet and Voet (1995) Biochemistry, 2nd ed., John Wiley & Sons, Inc., New York, NY] There is also interest in creating small molecule artificial transcription factors to regulate gene expression, examples include wrenchnol (a wrench shaped molecule). [cite journal |author=Koh JT, Zheng J |title=The new biomimetic chemistry: artificial transcription factors |journal=ACS Chem. Biol. |volume=2 |issue=9 |pages=599–601 |year=2007 |month=September |pmid=17894442 |doi=10.1021/cb700183s |url=]

ee also

* Chemical compound microarray
* Chemogenomics
* Peptidomimetic

References