Application Of Guanosine-based Supramolecular Hydrogels In Asymmetric Reactions

In recent years,supramolecular gels have been widely used in biomedical,tissue engineering,controlled drug release and photoelectric materials.The gelation factors have received extensive attention as the basic structural unit of the supramolecular gels.The majority of low molecular weight gelators are derived from natural products,such as nucleobases,fatty acids,sugars,cholesterol,amino acids and peptides.Guanine of nucleobases can form hydrogen bonds with other molecules in three directions,due to additional hydrogen bond receptors and donor groups.Guanosine and its derivatives have excellent self-assembly ability,as its unique characteristics.Recently,the guanosine-based supramolecular gels have become a research hotspot.Guanosine-based supramolecular gels have been widely applyed in chiral separation,separation of charged substances,tissue engineering,drug delivery,and ion channels.However,few applications about asymmetric catalysis have been reported.In this paper,the guanosine-based supermolecule hydrogels were applyed to asymmetric catalysis.GBG hydrogels based on guanosine were prepared according to literature procedures.We analyzed its structural and morphology by 'H-NMR,VT-NMR,XRD,CD,FTIR,TEM,SEM and AFM.Then we prepared a new hybrid catalyst containing GBG hydrogel and Cu2+to catalyze Friedel-Crafts reaction and the result showed that GBG-Cu2+can effectively catalyze the asymmetric catalytic reaction.We explored the ratio of GBG/Cu2+,reaction temperature and reaction time to optimize the reaction conditions,where the highest ee value was up to 55.95.%.At the same time,we explored the repeatability of the catalyst.We found that the repeatability of GBG-Cu2+ was significant,which could be reused 4 times.In order to further explore the structure of GBG hydrogel and its possible catalytic mechanism.In this paper,molecular simulation was carried out.The results of molecular simulation showed that the distance between the adjacent G-quartet was 3.4 A and the rotation angle was 30°.G-quartet forms a columnar G-quadruplex with a pronounced helix structure by ?-? stacking interaction.The O of boric acid ester and ?,?-unsaturated-2-acetyl imidazole coordinated with Cu2+.The substrate molecule was placed in the G-quadruplex resulting space steric hindrance on the Re surface of the substrate,so the indole derivatives attacked from Si surface and achieved asymmetric catalysis.