Study On Some Theoretical Issues In The Synthesis,Hydrolysis And Biological Activity Of Cantharimides

Cantharidin?CAN?derived from Chinese blister beetles and is in fact the principle active ingredient of this traditional Chinese medicine.As the protein phosphatase inhibitors,cantharidin expresses strong antitumor properties and has been used worldwide as an anticancer agent since 1264.However,cantharidin also possesses cytotoxicity to a series of normal cells,such as gastrointestinal tract,urethra and kidney.As a result,this agent is restricted in clinical applications.Therefore,it is important to design and synthesize cantharidin derivatives with high anticancer activity and low cytotoxicity.Among various cantharidin derivatives,norcantharidin has the similar anticancer activity with cantharidin and lower cytotoxicity,as well as easier preparation,which make it become the focus of new derivatives.Norcantharimide is one of the important norcantharidin derivatives due to the possibility to incorporate any kinds of substituent in the nitrogen,as well as essentially equipotent inhibitory activity of the serine/threonine protein phosphatases 1 and 2A?PP1 and PP2A?with cantharin.We have investigated the design and synthesis of different norcantharidine derivatives.Their structures are confirmed by elemental analysis and NMR.Moreover,in vitro cytotoxic activities of these novel compounds have been evaluated with MTT[3-?4,5-dimethylthiazol-2-yl?-2,5-diphenyltetrazolium bromide]assays.When considering the crystal structure of norcantharidin?DNCA?derivatives,the structure of DNCA-A and DNCA-NA attracted our attention,After analyzing the single crystal structure of these two compounds.We found that they are isomorphous,yet another series of more similar and simpler compounds?DNCA and NCA?can form very different crystal structures,which is an illustration of conditional isomorphism.To gain insight into the similarities and differences of these weak interactions in these two series of structures,we made detailed comparisons on the point of structural analysis and quantum calculations.The analysis results show that intermolecular Non-Covenlent Interactions?NCIs?are the results as well as causes of different crystal structures.Previously,our lab had obtained most of the intermediates in the hydrolysis of maleimide during the synthesis of unsaturated norcantharimide dimers.To the best of our knowledge,no high level theoretical studies have been reported for the hydrolysis ofN-alkylmaleimidessofar.Twosymmetricalbismaleimides N,N'-ethylenedimaleimide?EDM?and N,N'-propylenedimaleimide?PDM?were chosen as the models to explain how these hydrolytic degradations occur.For the hydrolysis of the above two N-alkylmaleimide dimmers,only concerted hydrolysis mechanism is considered in this work.In this paper,we present our theoretical studies on the hydrolytic degradation of these two model dimers with the participation of one,two and three water molecules or one ethanol molecule.These computational results indicate that all four steps of EDM and PDM hydrolysis reaction should proceeds through a concerted mechanism,instead of previously reported stepwise mechanism.That is to say,the nucleophilic attack of H₂O to carbonyl C,the cleavage of C-N bond and proton transfer steps are concurrent and not consecutive steps.In addition,the catalytic efficiency associated with extra H₂O is due to the decreased ring strain in TSsIn the study of the biological activity of norcantharimide dimers?NCDs?,we found that the activity of different NCDs is quite different.In order to elucidate the reasons for the differences in the activity of different NCDs,we investigated the interaction between different NCDs and protein phosphatase PP2A through molecular docking.By analyzing the binding pattern of NCDs to PP2A,we found that the growing of linking carbon chain helps the molecule to penetrate into the hydrophobic pockets formed by Gln122,Ile123,His191,and Trp200,which in turn can produce a hydrophobic interaction with PP2A,making it more comparable to PP2A.Therefore,the combination is more stable.