DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is an algicide and

herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

of the aryl

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

class that inhibits

photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

. It was introduced by

Bayer Bayer AG (English: , commonly pronounced ; ) is a German multinational pharmaceutical and biotechnology company and is one of the largest pharmaceutical companies and biomedical companies in the world. Headquartered in Leverkusen, Bayer' ...

in 1954 under the trade name of Diuron.

History

In 1952, chemists at E. I. du Pont de Nemours and Company patented a series of

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

derivatives as

herbicides Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

. Several compounds covered by this patent were commercialized as herbicides: chlortoluron (3-chloro-4-methylphenyl) and DCMU, the (3,4-dichlorophenyl) example. Subsequently, over thirty related urea analogs with the same mechanism of action reached the market worldwide.

Synthesis

As described in the du Pont patent, the starting material is 3,4-dichloro

aniline Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...

, which is treated with

phosgene Phosgene is an organic chemical compound with the formula . It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. It can be thought of chemically as the double acyl chloride analog of ...

to form a

isocyanate In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...

derivative. This is subsequently reacted with

dimethylamine Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to around ...

to give the final product. :Aryl-NH₂ + COCl₂ → Aryl-NCO :Aryl-NCO + NH(CH₃)₂ → Aryl-NHCON(CH₃)₂

Mechanism of action

DCMU is a very specific and sensitive inhibitor of photosynthesis. It blocks the Q_B

plastoquinone Plastoquinone (PQ) is a terpenoid-quinone ( meroterpenoid) molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4- ...

binding site of

photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem ...

, disallowing the electron flow from photosystem II to plastoquinone. This interrupts the photosynthetic

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

in photosynthesis and thus reduces the ability of the plant to turn light energy into chemical energy ( ATP and reductant potential). DCMU only blocks electron flow from photosystem II, it has no effect on photosystem I or other reactions in photosynthesis, such as light absorption or carbon fixation in the

Calvin cycle The Calvin cycle, light-independent reactions, bio synthetic phase, dark reactions, or photosynthetic carbon reduction (PCR) cycle of photosynthesis is a series of chemical reactions that convert carbon dioxide and hydrogen-carrier compounds into ...

. However, because it blocks electrons produced from water oxidation in PS II from entering the plastoquinone pool, "linear" photosynthesis is effectively shut down, as there are no available electrons to exit the photosynthetic electron flow cycle for reduction of NADP⁺ to NADPH. In fact, it was found that DCMU not only does not inhibit the cyclic photosynthetic pathway, but, under certain circumstances, actually stimulates it. Because of these effects, DCMU is often used to study energy flow in

Toxicity

DCMU (Diuron) has been characterized as a known/likely human carcinogen based on animal testing.

References

{{phenylurea herbicides Herbicides Ureas Anilines Chlorobenzene derivatives Suspected carcinogens Group 5 herbicides