The structural formula of isothiourea is NH=C(SH)NH. Isothiourea has tautomerism under certain conditions and can form a thiourea structure. A chiral isothiourea can be obtained by introducing different substituents on the isothiourea group to obtain a chiral center. A chiral isothiourea compound contains three elements of nitrogen, carbon, and sulfur, and is a compound formed by substituting an oxygen atom in a urea molecule with a sulfur atom. Due to the particularity of the structure, chiral isothiourea derivatives have important applications in organic synthesis and biomedicine.
Figure 1. Chiral isothioureas
Chiral isothiourea has a wide range of applications in organic synthesis, biomedicine, agriculture, and metal extraction.
- Biology and Medicine: The isosulfur group is a biologically active group, and the chiral isothiourea compound has various biological activities such as insecticidal, antibacterial, and inhibition of nitric oxide synthase activity, etc. Nitric oxide (NO) is a cellular messenger with multiple functions and plays a very important role in the cardiovascular system, nervous system and immune system. Therefore, nitric oxide synthase (NOS) is indispensable for most organisms. However, inducible nitric oxide synthase (iNOS) induces a large amount of NO production, accompanied by the occurrence of diseases such as inflammation and septic shock. Different chiral isothiourea compounds (eg, isothiourea compounds of tetrahydroisoquinolines, monosubstituted or disubstituted isothioureas, S-benzylisothioureas, etc.) have varying degrees of iNOS inhibitory activity, and different such compounds are also specific and selective for iNOS. Therefore, chiral isothiourea compounds can be used as effective iNOS inhibitors to control the production of nitric oxide in living organisms. The chiral aryl isosulfide compound is hydrolyzed under acidic conditions, and the resulting thiol compound may form an enzyme-inhibitor complex with the enzyme in the form of a disulfide bond, thereby inhibiting the H+/K+-ATPase activity and then producing acid suppression. Therefore, chiral aryl isosulfide compounds can be used for the treatment of peptic ulcers. In addition, chiral isothiazepine compounds can enhance the neuroprotective and sensory capabilities of the glutamate receptor channel, thereby enabling effects on neuronal signaling, memory consolidation, and synaptic plasticity of the cranial nerve.
- Agriculture: In agriculture, chiral isothiourea also has certain applications. Certain chiral isothioureas can be used to promote plant germination, increase crop yield and oil content, and therefore can be used as plant growth regulators. Some chiral isothiourea compounds can destroy the bacterial actin cytoskeleton, causing morphological and chromosome separation defects, and thus have an antibacterial effect and can be used as a bactericide. The chiral isothiourea compound can reduce the activity of catalase and peroxidase in the pericarp, thereby reducing the browning index and fruit decay rate of fruit peel, delaying fruit senescence, increasing fruit commodity rate and prolonging storage and shelf life. Therefore, chiral isothiourea can be used as a fruit preservative. In addition, some chiral isothioureas can break the seed dormancy period (such as mustard and rape in the dormant period), which can be beneficial to the off-season cultivation, thus achieving the long-term supply of fresh green vegetables.
- Organic Synthesis: Chiral isothiourea also has certain applications in organic synthesis. First, a chiral isothiourea can be used as a reaction raw material for the synthesis of a specific compound.
- Extracting Agent: The hydrochloride salt of some chiral isothioureas has an extraction function and can be used as a stationary phase for reversed phase paper chromatography for the separation of precious metals such as Ag, Os, and Ru.
- Merad, Jeremy. (2016). "Enantioselective Catalysis by Chiral Isothioureas." European Journal of Organic Chemistry 2016(34), 5589-5610.
- Woods, Philip A.. (2011). "Isothiourea-Catalysed Asymmetric C-Acylation of Silyl Ketene Acetals." Chemistry - A European Journal 17(39), 11060-11067.
- Merad, Jeremy. (2015), "Highly Enantioselective Acylation of Acyclic Meso 1,3-Diols through Synergistic Isothiourea-Catalyzed Desymmetrization/Chiroablative Kinetic Resolution." Organic Lettersl 17(9), 2118-2121.
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