Chemical Constituents Of Four Liverworts And Their Biological Activities

Bryophytes are land pioneers,placed taxonomically between algae and pteridophyta,which are considered as aquatic to terrestrial transitional plants.There are approximately 23,000 species in the world,divided into mosses(14,000 species),liverworts(6,000 species),and hornworts(300 species).Many liverworts possess characteristic fragrant odors and an intense pungent,sweet,or bitter taste and are not damaged by microorganism or insects.Furthermore,some liverworts cause intense allergic contact dermatitis and allelopathy.These phenomena indicate that there are some active substances in liverworts to participate in chemical defense.The secondary metabolites isolated from liverworts are much more novel in species and structure than other two bryophytes,which may be related to the appealing,characteristic cell organelles they possessed:cellular oil bodies,morphologically.Liverworts contain two characteristic compounds,namely benzyl and terpene,and have a variety of activities,such as cytotoxic,antifungal,anti-inflammatory,antioxidant,plant growth regulation,anti-alzheimer’s disease and other important biological activities.Liverworts can be found in traditional medicines all over the world.However,the study of liverworts as a medicinal resource is insufficient,and the number of species studied in chemical biology is less than 10%.In this research,four Chinese liverworts,Scapania carinthiaca J.B.Jack ex Lindb collected from Jilin Provence,Frullania hamatiloba Stephani and Plagiochila fruticosa Mitt collected from Shanxi Province,and Jungermannia tetragona Lindenb collected from Zhejiang Province,were phytochemically investigated.A total of 70 compounds,including 44 new ones,were isolated and identified on the basis of NMR,MS,single crystal X-ray diffraction analysis,and time-dependent density functional theory(TDDFT)ECD calculations.These compounds are all terpenes,of which,sesquiterpenes include aromadendranes,eudesmanes,and bicyclogermacrane;diterpenes include clerodanes,labdanes,kauranes,fusicoccanes,eunicellanes and gersemians.Among them,clerodane diterpenoids exhibited significant vasorelaxant effects.Labdane diterpenoids displayed moderate antioxidant effects.Bicyclogermacrene sesquiterpenoids showed antifungal virulence bioactivity.ent-Kauranes have anti-tumor effects and shows potential applications for sensitizing CDDP resistance in cancer chemotherapy.Four new diterpenoids scapanacins A-D(1-4)including one kaurane and three clerodane derivatives,along with eleven known compounds(9-15),were isolated from the Chinese liverwort Scapania carinthiaca J.B.Jack ex Lindb.Vasorelaxant activity assays of the clerodane-type diterpenoids 2,and 4-8 revealed that they relaxed 3rd-order rat mesenteric arterioles pre-contracted with norepinephrine(NE).Further assays with scapanacin D(4)confirmed that the vasodilatation was mediated through inhibition of Ca2+influx via voltage-dependent Ca2+channels(VDCs),and this Ca2+channel blocking effect was also confirmed by inhibiting the extracellular Ca2+influx in MOVAS cells.Besides,very little decrease of the relaxant activity caused by 4 on endothelium-denuded mesenteric arterioles with NE also suggested the vasodilatation was mainly produced by inhibiting Ca2+-induced contraction of smooth muscle.In addition,cytotoxicity testing showed that compounds 1 and 9 withα,β-unsaturated ketone exhibited inhibitory activities against several human cancer cell lines.Six previously undescribed labdane diterpenoids,frullanians A-F,along with five known diterpenoids(16-26),were isolated from the Chinese liverwort Frullania hamatiloba Stephani.NAD(P)H:QR(quinone reductase)assay demonstrated that frullanian D(19)and four known compounds displayed antioxidant effect mediated via Nrf2(Nuclear factor-erythroid 2-related factor 2)induction.Further investigation of the most bioactive frullanian D in MOVAS cells revealed that it ameliorated H2O2-induced oxidative insults without toxicity by increasing cell viability,attenuating morphological changes,and reducing intracellular ROS production.In addition,frullanian D promoted the nuclear translocation of Nrf2 and upregulated the expressions of antioxidant proteins NQO1(NAD(P)H quinone oxidoreductase 1)andγ-GCS(γ-glutamyl cysteine synthetase).Docking analysis using MOE software further supported the activation of the Nrf2 pathway by frullanian D.Fourteen new terpenoids plagicosins A-N(27-40),including seven sesquiterpenoids(27-33)consisting of six ent-bicyclogermacranes and one ent-2,3-seco-aromadendrane,as well as seven diterpenoids(34-40)comprising five fusicoccanes,a eunicellane and a rare gersemiane,were isolated from the Chinese liverwort Plagiochila fruticosa Mitt.Plagicosin F(32)displayed potent anti-virulence activity through inhibiting the hyphal morphogenesis,adhesion,and biofilm formation of Candida albicans.The genes related to hyphal formation were accordingly regulated by 32.Thirty ent-kaurane diterpenoids(41-70)are reported in this study,including 20 new samples isolated from the Chinese liverworts Jungermannia tetragona Lindenb,of which,11β-hydroxy-ent-16-kaurene-15-one(63,11-OH-K)was revealed to be the most active in cytotoxic screening.Previous reports have demonstrated that the antitumor mechanisms of kauranes are related to reactive oxygen species(ROS).Reactive oxygen species(ROS)induction is an effective mechanism to kill cancer cells for many therapeutic remedies while resettled redox homeostasis induced by the drugs will lead to chemoresistance.Redox resetting destruction will provide one way to overcome the resistance.As a covalent agent,11-OH-K was found to induce mitochondria-mediated apoptosis in HepG2 cells by elevating the intracellular ROS levels.ROS accumulation induced by 11-OH-K was caused by inhibition of antioxidant systems through targeting peroxiredoxin Ⅰ/Ⅱ(Prdx Ⅰ/Ⅱ)and depletion of glutathione(GSH).Furthermore,combined application of 11-OH-K and CDDP in vitro and in vivo revealed.that 11-OH-K not only enhances the cytotoxic effect of cisplatin but also behaves as a potent chemosensitizer for CDDP-resistant tumors.Moreover,the reaction half-life(t1/2)of approximately 4-6 h from the covalent bond formation reactivity of 11-OH-K with GSH suggests that it accords with the suitable reactivity window of covalent drugs.Accordingly,the ent-kaurane derivative shows potential applications for sensitizing CDDP resistance through perturbation of redox resetting via the dual inhibition of Prdx Ⅰ/Ⅱ and GSH in cancer chemotherapy.As an ongoing research of our groups’ standing on the shoulders of many other predecessors’ phytochemical investigation of liverworts,this study further suggested the abundance and novelty of secondary metabolites from liverworts,which greatly enriched the database of natural products.Some of these compounds also show significant biological activity,which provide several potential small molecules for the development of new drugs.Some genera also produce unique components,which will also be valuable for chemical classification.