Amino Acid: Threonine

Threonine

Threonine is an amino acid represented by Thr and T. It's molecular weight is 119 grams. It is a neutral and polar molecule. This amino acid has a hydroxyl group, a methyl group, an amino group, and a carboxylic acid group. It is one of two common amino acids that contains a chiral side chain. Threonine has two pKa values: 2.63 and 9.10 for the carboxylic acid and amino group. The isoelectric point for this amino acid is 5.64.  There are three peaks that appear on the proton NMR spectrum of threonine. The first peak is a multiplet at 4.10 to 4.15 ppm. The second peak is a doublet at 3.5 ppm. The third peak is a doublet at 1.20 to 1.25 ppm.

A small polypeptide that contains threonine is N-acetylgalactosamine. N-acetylgalactosamine is needed for communication between cells. It also has a role in the disease processes of cancer, inflammation, and immunity in the human body. It is present in the colon, intestines, retinas, sweat glands, blood vessels, ducts of kidneys, hair follicles, testes, and skin. The hydroxy side chain can undergo O-linked glycosylation. O-glycosylation is an enzymatic process that attaches gyclans (polysaccharides) to proteins, lipids, or other organic molecules. This occurs in the Golgi apparatus of eukaryotic cells.  As an essential amino acid, threonine is not synthesized in humans. Therefore, we must ingest threonine in the form of threonine-containing proteins. Foods high in threonine include cottage cheese, poultry, fish, meat, lentils, and sesame seeds.

Sources:

http://en.wikipedia.org/wiki/Threonine

http://www.ncbi.nlm.nih.gov/pubmed/8254121
http://www.online-vitamins-guide.com/images/threonine.gif

Synthesis with Electrophilic Aromatic Substitution

I found a synthesis in an article called Synthesis, Electrophilic Substitution and Structure-Activity Relationship Studies of Polycyclic Aromatic Compounds Towards the Development of Anticancer Agents, which was published in the Current Medicinal Chemistry journal in 2001. The article is about polycyclic aromatic hydrocarbons (PAH) which are considered potentially carcinogenic. Substituted PAH derivatives may serve as anticancer agents, and as chemotherapeutics. This article presents a review of their use. Electrophlic substituation reactions are used during the synthesis of these new compounds. Here is a picture of one of the two of the steps which use electrophilic aromatic substitution:

This depicts a halogenation by replacing a hydrogen atom on the benzene ring with a bromine in each reactant. These compounds underwent bromination regioselectively in a single site. There was another step of this synthesis to make anitcancer agents from substituted  polycyclic aromatic hydrocarbons which involved an electrophilic aromatic substitution.

This step is a nitration of one of the benzene rings of the reactant. During the study, it was shown that benz[a]aceanthrylene (62) and indeno[1,2,3-cd]pyrene (63) produced single mononitro derivatives 64 and 65. The conformation of the nitro derivatives was important in determining the mutagenic activities. It is proposed that suitably substituted polycyclic aromatic compounds can inhibit cancer cellgrowth even though there was a concept that these are only carcinogenic in nature. The hope is to see potent antitumor drugs with novel mechanisms of action based on the chemistry described above.

Reference: Banik B, Becker F. Synthesis, electrophilic substitution and structure-activity relationship studies of polycyclic aromatic compounds towards the development of anticancer agents. Current Medicinal Chemistry [serial online]. October 2001;8(12):1513-1533. Available from: MEDLINE, Ipswich, MA. Accessed March 6, 2011.