Phenothiazine

Use

In the manufacture of monomers, phenothiazine is used as a chemical stabilizer or inhibitor to prolong storage and shelf life of products such as acryloyl chloride.

Former uses

Phenothiazine was formerly used as an insecticide and as a drug to treat infections with parasitic worms (antihelminthic) in livestock and people, but its use for those purposes has been superseded by other chemicals.

Phenothiazine was introduced by DuPont as an insecticide in 1935. About 3,500,000 pounds were sold in the US in 1944. However, because it was degraded by sunlight and air, it was difficult to determine how much to use in the field, and its use waned in the 1940s with the arrival of new pesticides like DDT that were more durable. As of July 2015 it is not registered for pesticide use in the US, nor Europe, nor Australia.

It was introduced as antihelminthic in livestock in 1940 and is considered, with thiabendazole, to be the first modern antihelminthic. The first instances of resistance were noted in 1961. Uses for this purpose in the US are still described but it has "virtually disappeared from the market."

In the 1940s it also was introduced as antihelminthic for humans; since it was often given to children, the drug was often sold in chocolate, leading to the popular name, "worm chocolate." Phenothiazine was superseded by other drugs in the 1950s.

Synthesis

The compound was originally prepared by Bernthsen in 1883 via the reaction of diphenylamine with sulfur, but more recent syntheses rely on the cyclization of 2-substituted diphenyl sulfides. Some of the pharmaceutically significant derivatives of phenothiazine are not prepared directly from phenothiazine, although some of them are.

Derivatives

Phenothiazine itself was a pioneering compound, but its derivatives revolutionized psychiatry and other fields of medicine. Other derivatives have been studied for possible use in advanced batteries and fuel cells.

Phenothiazine-derived drugs

In 1876, Methylene blue, a derivative of phenothiazine, was first synthesized by Heinrich Caro at BASF and the structure was determined in 1885 by Heinrich August Bernthsen. Bernthsen synthesized phenothiazine in 1883. In the mid 1880s, Paul Ehrlich began to use methylene blue in his cell staining experiments that led to pioneering discoveries about different cell types; he won a Nobel Prize based in part on that work. He became particularly interested in its use to stain bacteria and parasites such as Plasmodiidae – the genus which includes the malaria pathogen – and found that it could be stained with methylene blue. He thought methylene blue could possibly be used in the treatment of malaria, tested it clinically, and by the 1890s methylene blue was being used for that purpose.

For the next several decades, research on derivatives lapsed until phenothiazine itself came to market as an insecticide and deworming drug. In the 1940s, chemists working with Paul Charpentier at Rhone-Poulenc Laboratories in Paris (a precursor company to Sanofi, began making derivatives. This work led to promethazine which had no activity against infective organisms, but did have good antihistamine activity, with a strong sedative effect. It went to market as a drug for allergies and for anesthesia. As of 2012 it was still on the market. At the end of the 1940s the same lab produced chlorpromazine which had an even stronger sedative and soothing effect, and Jean Delay and Pierre Deniker attempted to use it on their psychiatric patients, publishing their results in the early 1950s. The strong effects they found opened the door of the modern field of psychiatry and led to a proliferation of work on phenothiazine derivatives. The systematic research conducted by chemists to explore phenothiazine derivatives and their activity was a pioneering example of medicinal chemistry; phenothiazine is often discussed as a prototypical example of a pharmaceutical lead structure.

Today, the term "phenothiazines" describes the largest of the five main classes of antipsychotic drugs. These drugs have antipsychotic and, often, antiemetic properties, although they may also cause severe side effects such as extrapyramidal symptoms (including akathisia and tardive dyskinesia), hyperprolactinaemia, and the rare but potentially fatal neuroleptic malignant syndrome, as well as substantial weight gain. Use of phenothiazines has been associated with antiphospholipid syndrome, but no causal relationship has been established.

Phenothiazine antipsychotics are classified into three groups that differ with respect to the substituent on nitrogen: the aliphatic compounds (bearing acyclic groups), the "piperidines" (bearing piperidine-derived groups), and the piperazine (bearing piperazine-derived substituents).

Nondrug applications

The synthetic dye methylene blue, containing the structure, was described in 1876. Many water-soluble phenothiazine derivatives, such as methylene blue, methylene green, thionine, and others, can be electropolymerized into conductive polymers used as electrocatalysts for NADH oxidation in enzymatic biosensors and biofuel cells.

Trade names

Like many commercially significant compounds, phenothiazine has numerous trade names, including AFI-Tiazin, Agrazine, Antiverm, Biverm, Dibenzothiazine, Orimon, Lethelmin, Souframine, Nemazene, Vermitin, Padophene, Fenoverm, Fentiazine, Contaverm, Fenothiazine, Phenovarm, Ieeno, ENT 38, Helmetina, Helmetine, Penthazine, XL-50, Wurm-thional, Phenegic, Phenovis, Phenoxur, and Reconox.