# Synthesis and Biological Activity of 1,3,4-Oxadiazoles Used in Medicine and Agriculture
## 4 1,3,4-Oxadiazoles Used Commercially in Agriculture and Medicine  
Due to their insecticidal, fungicidal and herbicidal properties, 1,3,4-Oxadiazoles are widely used in agriculture. For example, an effective herbicide may be obtained by combining 1,3,4-oxadiazole with 3,5-dihalophenoxypyridines (**5**) (Figure 5). These compounds show the expected activity against _Ethinochloa cruss-galli_, _Avena fattu_ and _Sorghum halepense_[78]. Many compounds based on the 1,3,4-oxadiazole ring have already been authorized and commercialized. Among others, we can distinguish derivatives of metoxadiazome, which is an insecticide, or oxadiazone (**6**) derivatives, showing herbicidal activity [79; 80; 81]. The compounds exhibiting insecticidal activity also include symmetrical 2,5-bis(2,4-dichlorophenyl)-1,3,4-oxadiazole derivatives (DCPO) (**7**) (Figure 5). Such compounds show strong activity against house flies, flies and leaf rollers [82]. Analogs based on the DCPO structure, unlike traditional agents of this type, are able to control the process of growth and development of insects by interfering with their chitin biosynthesis process. The process of inhibiting the structure of the external shell of insects is based on the interference with the incorporation of carbon-labeled \(N\)-acetylglucosamine, which is active in the synthesis of chitin. Additionally, DCPO and its analogs are able to inhibit the synthesis of both DNA and insect proteins. Unfortunately, due to their poor solubility in polar solvents, their use is limited. Research is ongoing to improve their solubility and increase their biological effectiveness [83]. Compounds having a 1,3\(\mathcal{A}\)-oxadiazole ring with antibacterial activity can be used successfully in agriculture. The bacteria _Xanthomonas oryzae_ and _Ralstonia solanacearum_ cause bacterial blight on rice leaves and contribute to bacterial wilt in tobacco. This causes enormous damage and loss to farmers around the world [84]. Indole derivatives containing a double 1,3,4-oxadiazole unit (**8**) may be be effective against _Xanthomonas oryzae_ and _Ralstonia solanacearum_. Biological studies have shown that the antimicrobial activity against these two pathogens was greater than that of the reference sample with _Bismerthiazol_ (BMT). The efficacy of the agents in question was already high at very low concentrations, i.e., around 100 ug/mL [85]. Molecules containing the 1,3,4-oxadiazole core and exhibiting biological activity are used in medicine as effective antiviral, antibacterial, antifungal, anti-inflammatory, analgesic, blood pressure-lowering and anticancer agents (Figure 6) [88,89]. _Raltegravir_ (**10**) is one of the most recognized chemical compounds approved for therapy that contains a 1,3,4-oxadiazole moiety. This substance has a strong antiviral effect. It is currently used as the primary drug in the treatment of HIV infection. Its activity is based on the inhibition of integrase--an enzyme that can integrate viral genetic material with human chromosomes. This stage is considered crucial in the entire pathogenesis of AIDS [90]. The use of _Raltegravir_ in medicine made it possible to significantly reduce the dynamics of the virus and accelerate its decomposition in the human body. Clinical studies have shown that the viral load in one ml of blood was below 50 copies after taking _Raltegravir_. This result turned out to be superior to the use of other drugs capable of blocking reverse transcriptase. Currently, _Raltegravir_ is being tested for its effects on hidden viral reservoirs [91]. _Nesapidil_ **(11)** is also included among the substances authorized as medicinal products. It is a compound belonging to the IV class of antiarrhythmic drugs. Its principle of operation is to block the calcium channel by directly inhibiting the influx of calcium ions to the cells of the heart muscle and the smooth muscles of the blood vessels. This increases blood flow and relieves coronary vasoconstriction. Additionally, _Nesapidil_ helps to slow AV conduction and sinus rhythm [92].