Quinones are a class of compounds that include quinones or are easily converted to quinones, and are closely related to quinones in biosynthesis. Quinones are often found in nature as pigments in animals, plants and microorganisms. Quinones are the main active ingredients of many important Chinese medicines, such as rhubarb, cassia seed, Senna leaf, shikong, Polygonum cuspidatum, Polygonum multiflorum, aloe and so on. Some of these quinones play an electron transfer role in redox reactions in organisms, while others have antimicrobial or antineoplastic activities, such as walnut quinone, orchid quinone, lappaquinone and so on. Some of them are also the main active ingredients in Chinese herbal medicine, such as shikonin and isoshikonin, which have hemostatic, anti-inflammatory, anti-viral and anti-tumor activities, are the main active ingredients of shikonin.
According to the different chemical structures, quinones can be classified into benzoquinones, naphthoquinones, anthraquinones and phenanthrenequinones. Benzoquinones can be divided into o-benzoquinones and p-benzoquinones. The structure of o-benzoquinones is unstable, so most of the natural benzoquinones are derivatives of p-benzoquinones. Naphthoquinones are classified into three types: α(1,4), β(1,2) and amphi(2,6). However, most of the naturally occurring α-naphthoquinone derivatives are mostly orange or orange-red crystals, and a few are purple. Anthraquinones can be divided into two categories according to the structure of their mother nuclei: single anthracene nucleus and double anthracene nucleus. Natural phenanthraquinone can be divided into two types: o-quinone and p-quinone. For example, a variety of phenanthraquinone derivatives obtained from the root of Salvia miltiorrhiza belong to o-phenanthraquinone and p-phenanthraquinone compounds.
Quinones have anti-tumor effects, and their mechanisms are mainly manifested in inducing apoptosis of cancer cells, reversing multidrug resistance of cancer cells, enzyme inhibitors, affecting the proliferation and cell cycle of cancer cells, inhibiting the metabolism of cancer cells, killing and mutagenesis of cancer cells, etc. Free anthraquinone substances bind enzymes related to essential sulfhydryl groups in organisms (microorganisms, cancer cells, etc.), blocking the electron transfer in the respiratory chain of organisms, affecting the energy supply required by cells, inhibiting the oxidation and dehydrogenation of substrates such as sugar and amino acids, interfering with cell wall formation and cell membrane permeability. Anthraquinone covalently embedded in DNA plane interferes with DNA template function and inhibits the biosynthesis of DNA, RNA and protein. The antimicrobial mechanism of anthraquinones is mainly to inhibit the oxidation and dehydrogenation of carbohydrate and carbohydrate metabolic intermediates, and to bind to DNA, interfere with its template function, and inhibit the synthesis of protein and nucleic acid.
Mitoxantrone is an antitumor drug used in the treatment of leukemia. Because it has no amino sugar structure, does not produce free radicals, and inhibits lipid peroxidation, it is less toxic to heart. Its anti-tumor activity is comparable or slightly higher than that of doxorubicin, and its anti-tumor spectrum is broad. The main anthraquinone compounds in the active ingredients of aloe are hydroxyanthraquinone derivatives, including more than 20 kinds of aloe emodin glycosides (also known as aloin or aloin), aloe chrysophanol and anthraquinone. Anthraquinones are the main antibacterial substances, as well as anti-inflammatory and detoxification, healing wounds, etc., and have a broad spectrum. Clinical treatment of primary liver cancer with aloin has significantly improved patient survival and quality of life.