Studies On Chemical Constituents Of Carpesium Macrocephalum

The genus Carpesium belonging to the family Asteraceae comprises approximately 21 species worldwide.Most of these plants are distributed in central Asia,particularly in the mountainous areas of Southwest China.In China,Korea and Japan,many Carpesium plants have been used extensively in folk medicines.Based on current pharmacological studies,the constituents and their crude extracts exhibit a wide range of biological activities,particularly in anti-inflammatory,anti-tumour,anti-plasmodial,anti-fungal and anti-bacterial effects.Moreover,phytochemical studies have shown that sesquiterpene lactones formed the majority of Carpesium compounds.Seeing that rich sesquiterpene lactone dimers exist in the family Asteraceae,and their characteristics of diverse skeletons,varied linkages,complex stereochemistry,difficulty against total synthesis and potent cytotoxicity have been attractive.Thus,the SLDs from Carpesium species have stimulated our great interst.C.macrocephalum is mainly distributed in Gansu,Sichuan,northeast China,and also distributed in Korea and Japan.Moreover,phytochemical and pharmacological studies have been less performed on C.macrocephalum.Thus,the chemical constituents of C.macrocephalum and their in vitro antitumor activities are investigated.1.Chemical constituents from C.macrocephalumInvestigations on chemical constituents of the acetone extracts of C.macrocephalum led to the isolation and elucidation of 56 compounds,including 42 sesquiterpene lactones,10 monoterpenoids,1 diterpenoid,2 flavonoids,1 steroid.Among these compounds,there are four new compounds,including three new SLDs and one new chlorinated thymol monoterpenoid.According to the skeleton types of sesquiterpene monomers,three new sesquiterpene lactone dimers were classified into eudesmanoid-guaianoid type.On the biosynthesis pathway,the Diels-Alder [4+2] adducts（1-3）,probably arised from a biosynthetic Diels-Alder [4+2] cycloaddition between two hetero monomers,which were linked via two C-C single bonds,exhibiting the region（2,4-/1,3-linkage）and stereo（11S,exo/endo type）selectivity.In terms of structural identification,through the observed NOESY correlations between two monomers and by monomers self,as well as the spectroscopic features of the downfield chemical shift of Ha-2’ or Ha-3’ and dominant positive or negative CE of the CD spectra,we confirmed the exo-configurations of 1-3;by the observation of the key ¹H-¹H COSY,HSQC and HMBC correlations,we confirmed that compounds 1 and 3 could be classified as 1,3-linked SLDs,and compound 2 was classified as 2,4-linked SLD.For corroboration of the absolute configuration of 1,the single-crystal X-ray diffraction was also performed.2.Biological activities of C.macrocephalumThe isolated dimers were tested for cytotoxic activities against human tumor cell lines A549,HCT116,MDA-MB-231 and BEL7404 using MTT assay.The results exhibited that compound 1 showed potent cytotoxicities against A549,HCT116,MDA-MB-231 and BEL7404 with IC₅₀ values of 2.04,2.27,5.17,3.77 μM,respectively,and compound 2 had IC₅₀ values of 3.30,15.68,11.62 μM for HCT116,MDA-MB-231,BEL7404,respectively,which were better than those of the eudesmane monomers.In addition,we found that 3 had no cytotoxicities,whereas the source precursor of 3 showed potent cytotoxicities against these human tumor cell lines.Subsequently,the inhibitory activity on TNF-α-induced NF-κB of 1-3 were evaluated in bEnd.3 cells by testing the regulation effects of P65,p-P65,IκBα,p-IκB proteins.The results showed that 1 and 2 could suppress TNF-α-induced phosphorylation of the NF-κB p65 subunit and degradation of IκBα in bEnd.3 cells,whereas 3 had no regulation effects.The above results showed that the cytotoxicities of exo SLDs might be attributed to suppressing NF-?B activation.