Chemical Constituents Of Four Liverworts And Their Biological Activities

Bryophytes as sporophytes,which release spores and reproduce alternately from generation to generation after the sporophyte matures,are placed taxonomically between algae and pteridophyte.There are approximately 23,000 species in the world,and divided into mosses(14,000 species),liverworts(6,000 species),and homworts(300 species).The secondary metabolites,isolated from liverworts,are more novel in species and structures than other two bryophytes,which may be morphologically related to the appealing and characteristic cell organelles,possessing a cellular oil body.Great progress has been made in the chemical and biological study of liverworts since the 1970s,and it has been found that there are two kinds of characteristic compounds of bibenzyl and terpenoids in liverworts.In addition,the dimers with various binding modes and special skeleton are also the characteristic of liverworts.Apart from the novel skeleton,the compounds from liverworts show a wide range of biological activities,such as cytotoxic,antifungal,anti-inflammatory,antioxidant,plant growth regulation,anti-alzheimer’s disease and others.In this research,four Chinese liverworts,including Radula apiculata Sande Lac.ex Stephani,Pallavicinia ambigua(Mitt.)Stephani,Mylia nuda Inoue&Yang,and Lepidozia reptans(L.)Dumort,were phytochemically investigated.Using column chromatography and semi-prepared liquid phase,based on nuclear magnetic resonance,mass spectrometry,circular dichroism,infrared,ultraviolet,single crystal diffraction,nuclear magnetic calculation and time-dependent density functional theory ECD calculation,a total of 87 compounds,including 53 new ones,were isolated and identified from these four liverworts.Most of these compounds are bibenzyls,terpenes and their dimers,of which prenylated bibenzyls and their dimers,7,8-seco-labdane and their dimeric compounds,1,10-seco-aromadendrane and their dimers with phenylether,as well as 9,10-seco-cycloartanes.The biological activity of the isolated compounds was studied,and it was found that prenylated bibenzyls and the terpenoids which contain α,β-unsaturated ketones showed better cytotoxic activity.In the doctoral stage,continuing the master’s work,we carried on the inverstigation of the remaining components of the Radula apiculata that collected from Jiulongshan National Nature Reserve in Lishui,Zhejiang Province,and obtained 12 derivatives of isopentenyl bibenzyl and seven new compounds(1-7),including four dimers of isopentene bibenzyl[(±)-radulapins L-O(1-4)].Combined with 14 compounds obtained during the master’s degree,we screened the cytotoxic activity of 26 isopentenyl bibenzyl that purified from Radula apiculata.It was found that dimer showed significant cytotoxic effect.Further studies found that it increased the level of ROS and decreased the mitochondrial membrane potential to induce apoptosis of PC-3 cells.The biogenic sources of nine isopentene dibenzyl dimers were speculated.It was found that these dimers with special structure were the result of Diels-Alder cycloaddition and free radical coupling.Based on the investigation of the chemical constituents of Pallavicinia ambigua,which were collected from Zhangjiajie,25 compounds were obtained,of which 17 were new compounds,including 10 highly oxidized labdanes[pallaviambins I-R(21-29)]and four dimeric compounds of 7,8-seco-labdanes[pallaviambins E-H(17-20)].These dimers were formed by Diels-Alder reaction under the action of oxidase.In addition,two cis-trans isomers[pallaviambins A(13)and B(14)],with a new skeleton of tetracyclic[5.2.1.02,5.04,10]decane,were also obtained from the p.ambigua.The photoinduced rearrangement of compound 33,indicated that compounds 13 and 14 are formed by[2+2]cycloaddition of compound 33 under photocatalysis.It has been reported that the anti-tumor mechanism of compounds with α,β-unsaturated ketones is related to reactive oxygen species(ROS).ROS induction usually is an effective mechanism to kill cancer cells in treatments.Drug-induced "redox reset" will lead to chemotherapy resistance,breaking the "redox reset" will provide a new way to overcome drug resistance.Compound 33 with two α,β-unsaturated ketone structural fragments was found that showed a selective inhibitory effect on PC-3 after cytotoxic activity screening,and the inhibition of tumor proliferation occurred in G2/M phase.Subsequent activity studies found that it’s resulted in an increase in the level of ROS and apoptosis of PC-3 cells.32 compounds including 18 new ones were isolated and identified from Mylia nuda,which was collected from Ya’an,Sichuan Province,including four phenylethers,five rare sesquiterpenes and eight new skeletons of dimers[mylnudones A-H(42-49)]formed by phenylether and aromadendrane-type sesquiterpenes,of which compounds 42-48 were formed by Diels-Alder reaction while compound 49 via free radical coupling.14 known compounds were also obtained.The antifungal activities of these compounds were studied,except that compound 68 showed certain antifungal toxicity,the other activities were weak.Twelve new compounds including nine 9,10-seco-cycloartanes(70-78),along with six known compounds(81-87),were isolated from the Chinese liverwort Lepidozia reptans.In the cytotoxic activity screening,it was found that compounds 70,75,and 76 showed significant cytotoxic inhibitory effect on a series of cell lines.The representative compound 76 containing α,β-unsaturated ketone structure was further explored,and it was found that this triterpenoid could induce apoptosis of PC-3 cells by increasing ROS-mediated mitochondrial damage.On the basis of previous studies,we have obtained some compounds with novel structure and special skeleton,especially dimers,most of which are the products of Diels-Alder cycloaddition and free radical coupling under the action of plant somatic oxidase.With the development of separation and identification technology,more trace components have been found,which has greatly enriched the library of natural product compounds.The biological activity screening of these compounds also showed satisfactory biological activity,which provided a number of potential small molecular compounds for the development of new drugs.The results of the study on the chemical composition of liverworts show a certain species-genus specificity,which also has a certain reference value for the chemical classification of liverworts.