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Medicinal chemistry and drug research require diverse chemical components to meet strict requirements not only in terms of physical and chemical properties but also in terms of chemical reactivity.
The chemists use the 'build–couple–pair' strategy of organic synthesis, which entails preparing molecular building blocks that contain several chemical groups.
The chemical building block (CBB) is a molecule which can be converted to various secondary chemicals and intermediates, and, in turn, into a broad range of different downstream uses.
Oxazolines and oxazolidines comprise an important type of heterocyclic compounds with a five-membered structure, which consists of three carbon atoms, one nitrogen atom and another oxygen atom. They can be produced by hydrogenation reaction from oxazole, Oxazolines are obtained by partial hydrogenation and oxazolidines are produced by totally hydrogenation without any residual double bond (Fig 1). Numerous biologically active compounds have been demonstrated that the oxazoline or oxazolidine moiety is the major structural framework offering potential application in pharmacological synthesis. It is noteworthy that oxazolines and oxazolidines are flammable, toxic smoke such as NO, CO will be generated through combustion. Therefore, their use and storage should be very careful.
Fig.1. Oxazole and thiazole compounds
Different from the poor water solubility of oxazole, oxazolines and oxazolidines are water-soluble, because the former conjugated structure of oxazoles limits their dissolution. besides, the oxygen and nitrogen atoms in oxazolines and oxazolidines can form hydrogen bond with water molecule which effectively promote the solubility with their polar structure. oxazolines and oxazolidines possess relative low boiling point and melting point thus they are commonly presented as colorless liquid. After a long period of research, oxazolines and oxazolidines are the key active functional groups of natural products, advancing the fabrication of various modern medicine and bioactive molecules.
Oxazoline compounds can participate in ring-opening polymerization to produce polymers with nitrogen atom in main chain. isomerization is the major driving force of this polymerization, which can be classified into two type, including ionic type and covalent type (mechanisms are depicted in Fig 2 respectively).
Fig.2. Types of polymerization mechanisms for 2-oxazolines. (Prog. Polym. Sci. 1996, 21, 151-208.)
Inspired by the reactivity of the oxazoline polymers, plasma-assisted deposition is utilized to form oxazoline-containing films on specific surfaces. With the help of plasma technology, the obtained plasma polymer film can play an important role as cell guidance substrate, cancer cell sensing and implant coating, offering potential application in biological monitoring (Fig 3).
Fig.3. Plasma film (top) and its applications (bottom) (Materials 2019, 12. 191, 1-18.)
It is well known that ligand designation is a key point in catalyst synthesis, oxazoline-containing ligands have been reported in numerous chiral ligands (Fig 4), which are utilized in the further correlative catalyst characterization for promoting the efficiency of chemical reaction.
Fig.4. The development of chiral ligands containing an oxazoline moiety (Chem. Soc. Rev. 2018, 47, 1783-1810.)