Cyclopentanes (also known as pentamethylene) comprise a significant family of five-membered carbocyclic compounds. They are widely prevalent in natural products, cyclopentane moiety have been detected as structural framework in numerous biological compounds. Cyclopentanes possess two kind of foldable conformations (envelope conformation and half-chair conformation) that can change through reversible interchange of the carbon ring (ball-and-stick model is depicted in Fig 1). Most cyclopentanes are produced by reduction reaction of relative alkene, ketone and carboxylic acid.
Fig.1. Ball-and-stick model of cyclopentane compounds
Cyclopentanes are almost not water-soluble, because the five-membered rings do not possess polar groups to support the solubility in water but promote their solubility in organic solvent. Besides, the light carbocyclic ring gives cyclopentanes a low boiling point and melting point, thus they are commonly presented as white liquid. It is noteworthy that cyclopentanes are flammable and slightly toxic. The stability of cyclopentane is stronger than cyclopropane or cyclobutene and approximate with cyclohexane. After a long period of research, cyclopentanes are the key active functional groups of natural products, advancing the fabrication of various modern medicine and bioactive molecules.
Biology: As the genetic material of an organism, DNA (DeoxyriboNucleic Acid) is responsible for guiding protein synthesis and controlling metabolic process, thus DNA play a particularly important role in sustaining the growth of organisms. Cyclopentane group has been reported to incorporate into specific positions of DNA, promoting the higher binding affinity in DNA diagnostics and treatment (Fig 2).
Fig.2. Representative DNA with incorporated cyclopentane (DNA Microarrays Part A. Vol. 410, 2006, pp. 189-200.)
Lipid Membranes: Researchers have discovered that cyclopentane structure existed in the lipid membrane of ancient bacteria (Fig 3), which a higher temperature brings an incremental number of cyclopentane rings and tightens the membrane packing. On the whole, the presence of cyclopentane rings is of great concern to the growth of ancient bacteria and the adaptation of ambient environment.
Fig.3. molecular structure of the lipid membrane on ancient bacteria (Archaea-an International Microbiological Journal 2012. 19, 126-134.)
Organic synthesis: Five-membered carbocyclic ring has also been utilized in the fabrication of fascinating compounds. For example, cyclopentanes are utilized as the building block of the substance in Fig 4. This process is just like LEGO toys and brings chemical beauty, which motivates chemists to synthesize more complex and symmetrical compounds.
Fig.4. Some organic compounds with cyclopentane motif (Chem. Rev. 2006, 106, 4885-4925.)