Synthesis And Application Of Camphor-based Imidazolium Ionic Liquids

Camphor,as a versatile building block,is a kind of monoterpenoid and has a lot of bio-activities such as anti-bacteria and parasite-expelling.Camphor derivatives have shown great value in pharmaceutical chemistry and material chemistry and have been applied in essential oil manufacture,cosmetic production and traditional medicine,such as antiphlogosis and analgesia.Nowadays,more and more camphor derivatives have been modified to be used in drug manufacture.Camphor-derivatives have been emerging in recent years and can be applied in enantioselective organic reactions due to bulky molecular volume and multiple stereocenters,and they are widely used as the sources of chiral auxiliaries,chiral reagents and asymmetric catalysts.Ionic liquids,made of organic cations and organic anions or inorganic anions,have been one of the most prevalent scientific areas in recent years due to their versatile properties,such as non-volatility,thermal stability and good solvation ability.Moreover,these properties can be changed and modified by changing the substituents of the cation or anion specifically.These advantages of ionic liquids make it beloved by scientists in various fields e.g.,biocatalysis,organic synthesis,electrochemistry,dissolution and polymer materials.Imidazolium ionic liquids have greater potential in catalytic field due to their higher stability.Sixteen new camphor-based imidazolium ionic liquids have been synthesized with renewable camphorsulfonic acid as the starting material.The chemical shifts of the characteristic proton of C2 on the imidazolium ring(N-C=N)were discussed thoroughly and all of these imidazolium salts exhibit good thermal stability.Furthermore,the excellent catalytic performance of the synthesized imidazolium salts were observed in the oxidative esterification between aromatic or aliphatic aldehydes containing electron-withdrawing or electron-donating groups on aromatic ring and primary or secondary alcohol by air as the sole oxidant.The antifungal test against R.solani,F.proliferatum and B.cinerea were evaluated by the method of mycelial growth.The results showed that all these compounds have the inhibition efficacy to the three fungus to some extent.Compared to chlorothalonil,more than half of these compounds have an better inhibition effect towards B.cinerea,especially compound 3d and 5a,whose inhibition rate could reach 100%.Compound 4a and 3b have the most outstanding inhibition rate to F.proliferatum and R.solani respectively.In the in vitro anticancer activity,all the inhibition rates of these coompounds against Hep G2,A549 and MCF-7 have been tested.Compounds 4b,4c,4d and 3a have moderate inhibition rate and have the potential to be the leading compounds due to the remaining carbonyl group in the camphor ring,which can be further modified to obtain improving bioactivities.