Piperidones comprise a significant analogue of heterocyclic compounds, which consist of a six membered nitrogen-containing ring with a secondary amine group and carbonyl group. α, β and γ-piperidine are nominated when secondary amine group is located in ortho, meta and para-position (Fig 1). Piperidones exhibit high boiling point and high melting point, thus they are commonly presented as white crystal. They offer major scaffolds in numerous biologically and pharmacological compounds, offering potential application in medicinal synthesis. It is noteworthy that piperidone compounds are flammable, toxic smoke such as NO, CO will be generated through combustion. Therefore, their use and storage should be very cautious.
Fig.1. Piperidone compounds
Most piperidones are water-soluble, because the existence of the nitrogen and oxygen atoms can form stable hydrogen bond with water molecule which coordinatively facilitates its solubility in water. All the piperidone compounds possess secondary amine group as a major reaction site and carbonyl group. Their chemical properties are similar to that of aliphatic secondary amines and carbonyl compounds, which the amine group can react with inorganic acids to produce corelative salts or participate in N-methylation to produce tertiary amines while carbonyl group is able to react with nucleophile reagents. Besides, piperidone compounds exist in every aspect of our lives, they are widely distributed in natural products and play a key role in medical application, pesticide-manufacture and pharmacological research.
Because of the existence of ring tension and reactive groups like amine or carbonyl groups, piperidones can be converted to a series of chemical products via oxidation reaction. Various complex compounds are produced from piperidone analogs and have been utilized for further application (Fig 2).
Fig.2. Chemical structure of products from piperidone derivatives. (Tetrahedron Lett. 2013, 54, 573-575.)
Piperidone compounds have been detected in various natural medicinal molecules, motivating the synthesis of artificial derivatives to fabricate biologic precursors, which possess excellent pharmacological and physiological activities, such as antibacterial, antidiabetic, anti-tumor and anti-inflammatory behavior, etc. For example, the antimicrobial activity of the piperidone analogues can be optimized by adjusting different functional groups (Fig 3).
Fig.3. Representative antimicrobial compounds with piperidone motif (J. Serb. Chem. Soc. 2016, 81, 859-870.)
Owing to the antibacterial activity in above medicinal precursors, piperidone derivatives can be also applied as fungicides, insecticide, herbicide and so on. a variety of piperidone analogues are designed and their antibacterial activities are characterized for further potential fabrication (Fig 4).
Fig.4. Representative antibacterial compounds with piperidone framework (Appl. Biochem. Biotechnol. 2014, 172, 3363-3373.)