diene at a carbon-carbon double bond. In Diels-Alder reactions quinones are used as dienophiles. Historically important syntheses include cholesterol, cortisone, morphine, and reserpine. Occurrence and uses Production of hydrogen peroxide A large scale industrial application of quinones is for the production of hydrogen peroxide. 2-Alkylanthraquinones are hydrogenated to the corresponding hydroquinones (quinizarins), which then transfer to oxygen: dihydroanthraquinone + → anthraquinone + in this way, several million metric tons of are produced annually. 1,4-Naphthoquinone, derived by oxidation of naphthalene with chromium trioxide. It is the precursor to anthraquinone. Biochemistry Numerous quinones are significant roles in biology. Vitamin K, which involved in coagulation of blood, is a quinone. Ubiquinone-10 is a naturally occurring 1,4-benzoquinone involved in respiration apparatus. Plastoquinone is a redox relay involved in photosynthesis. Pyrroloquinoline quinone is another biological redox cofactor. Quinones are conjectured to occur in all respiring organisms. Some serve as electron acceptors in electron transport chains such as those in photosynthesis (plastoquinone, phylloquinone), and aerobic respiration (ubiquinone). Phylloquinone is also known as Vitamin K1 as it is used by animals to carboxylate certain proteins, which are involved in blood coagulation, bone formation, and other processes. Conversely, the toxicity of paracetamol is due to its metabolism to a quinone imine, which then reacts with liver proteins to cause liver failure. The auto-oxidation of the neurotransmitter dopamine and its precursor L-Dopa generates the comparatively stable dopamine quinone which inhibits the functioning of dopamine transporter (DAT) and the TH enzyme and leads to low mitochondrial ATP production. The benzoquinone blattellaquinone is a sex pheromone in cockroaches.In the spray of bombardier beetles, hydroquinone reacts with hydrogen peroxide to produce a fiery blast of steam, a deterrent in the animal world. Medical Several quinones are of pharmacological interest. They form a major class of anticancer cytotoxins. One example is daunorubicin, which is antileukemic. Some of them show anti-tumoral activity. They embody some claims in herbal medicine. These applications include purgative (sennosides), antimicrobial and antiparasitic (rhein and saprorthoquinone, atovaquone), anti-tumor (emodin and juglone), inhibition of PGE2 biosynthesis (arnebinone and arnebifuranone) and anti-cardiovascular disease (tanshinone). Malbranchea cinnamomea is a thermophilic fungus, which produces a quinone antibiotic. Another quinone-containing drug is Mecarbinate (dimecarbine), made by the reaction of ethyl N-methyl-β-aminocrotonate with para-benzoquinone. Others include Amendol, Oxyphemedol, Phemedol all in FR5142 (M) ― 1967-06-05. Note: These are all indoles made via the Nenitzescu indole synthesis. The antineoplastic Apaziquone. Benzoquinone compounds are a metabolite of paracetamol.