Studies On The Novel Chemical Constituents From Isodon Scoparius At Unique Habitat

Previous phytochemical studies on Isodon scoparius(C.Y.Wu et H.W.Li)H.Hara,a medicinal plant grown up in a special habitat(alkaline calcium carbonate layer soil in Shangrila County,Yunnan Province),have resulted in the discovery of several novel meroditerpenoids with significant immunosuppressive activity.These findings had aroused our great interests on the meroditerpenoids in I.scoparius.In order to explore more novel meroditerpenoids and carry out the relevant synthetic work,we continued our systematical investigations on the aerial parts of this special specie.As a result of chemical investigation,41 new diterpenoids(including 6 novel dimeric skeletons and 5 novel meroditerpenoid skeletons)were isolated from this plant.All the compounds were tested for their biological activities.This study substantially provided the fundermental for comprehensive discovery of novel dimeric diterpenoids and meroditerpenoids and their immunosuppressive activity from this herb.The dimeric diterpenoids and meroditerpenoids were the trace components of I.scoparius.Their structures were extremely complex.In addition,there were several chiral carbons in the conflexible side chain,therefore,it is almost impossible to determine their configurations only based on ther regular NOE effects.While,the biomimetic synthesis as an efficient method could help us to determine the absolute configurations by the means of analyzing the hypothetical biogenetic pathway and the chemical relationships of the relative constituents from the same plant.This method could help us to resolve the problem of the confirmation of absolute configurations in dimeric diterpenoids and meroditerpenoids.Moreover,biomimetic synthesis could also resolve the problem of synthesizing chiral carbons,which was intractable for the conventional total synthesis.It was not only the chiral controls could be realized unexpectedly,but also the synthetic steps could be skillfully cut down.In this dissertation,biomimetic synthesis method was successfully employed to determine the absolute configurations of the dimeric diterpenoids,and resolve the problem of sample shortage for further studies on biological activities and mechanism of actions by providing a high efficient synthetic way for the preparation of a large amount of target molecules.By carrying out the study on the structure-activity relationship of target molecules to obtain a lead compound with stronger activity is one of the most important strategy to enhance the application values of chemical constituents.In our previous study,despite of the descovery of the merodiperpenoids with immunosuppresive activity,other type of the merodiperpenoids with proor activity were also obtained from I.scoparius.However,their limited amount confined the further studies on biological activities and mechanism of actions.Therefore,under the guidance of the aforemention stragtegy,26 analogs of scopariusicide A were synthesized,and,among them,some ones with stronger immunosuppresive activity were obtained.This study established the basis for further developing of lead compound from the merodiperpenoids.Chapter 1.Novel Chemical and Bioactive Constituents from Isodon scopariusPhytochemical studies on I.scoparius collected on the alkaline calcium carbonate layer soil have resulted in the discovery of several novel meroditerpenoids with immunosuppresive activity.These finding prompted us to continue our systematical investigations on the aerial parts of this special species.As a result,48 diterpenoids were isolated,including 41 new ones.These new ones including 8 new dimeric diterpenoids with six new skeletons,and 21 new meroditerpenoids with five new skeletons:(i)Scopariusicdiacids A and B,two novel dimeric diterpenoids with a complex 6/6/5/6/6 dispiro pentacyclic core;(ii)Scopariusicdiacid C,a novel dimeric diterpenoid with a complex 6/5/6/5/6/6 hexacyclic core;(iii)Scopariusicdiacid D,a novel dimeric diterpenoid with a 6/10/6/6 spiro lactone with icosahydro-2'H-spiro[benzo[e]oxecine-5,1'-naphthalene] core;(iv)Scopariusicdiacids E and F,two novel dimeric diterpenoids with a 6/6/6/6/6 spiro pantacyclic core with icosahydro-2'H-spiro[benzo[f]chromene-3,1'-naphthalene];(v)Scopariusicdiacids G and H,two novel dimeric diterpenoid including 1-[2-(octahydro-1Hinden-2-yl)ethyl]decahydronaphthalene unit;(vi)Scopariusicide G,a novel ent-clerodanebased meroditerpenoid with a 4/6/6 spiro tricyclic core;(vii)Scopariusicide H,a novel entclerodane-based meroditerpenoid with a 4/6/6 tricyclic core;(viii)Scopariusicide I,a novel ent-clerodane-based meroditerpenoid;(ix)Scopariusicides J and K,a novel ent-labdanebased meroditerpenoid with a unique cyclobutane ring;(x)Scopariusicides L and M,a novel ent-halimane-based meroditerpenoid with a unique cyclobutane ring.The unique cyclobutane ring of meroditerpenoids was biosynthetically formed via an intermolecular [2+2] cycloaddition between the double bonds of phenylpropanoid and diterpenoid.On the basis of anlayzing the hypothetical biogenetic pathway,five factors which responsible for the configurations of meroditerpenoids were found:(i)the types of diterpenoids;(ii)the biosynthetical chemoselectivity of diterpenoid;(iii)the Z/E configuration of bonds of diterpenoid;(iv)the Z/E configuration of bonds of phenylpropanoid;(v)the different mode of cycloaddition(head to tail and head to head between two units);(vi)the different orientation of bonding(front side and back side).The configurations and connection modes of the meroditerpenoids could be deduced by analyzing the afromentioned factors.Morever,merodipenoids 21,22,26 and 28 showed moderate immunosuppressive activities.Compound 26 also showed significant inhibitory activity against acetylcholinesterase(ACh E)with IC50 values of 3.55 ?M.Compound 31 showed significant inhibitory activity against butylcholinesterase(Bu Ch E)with IC50 values of 3.85 ?M.Chapter 2.Structure modification of meroditerpenoid scopariusicide APrevious phytochemical studies on this herb have resulted in the discovery of several novel meroditerpenoids with significant immunosuppressive activity.In order to discover meroditerpenoids with stronger immunosupresive activity and explore their structure-activity relationship.The structure modification research of scopariusicide A was conducted.As a result,26 analogs of scopariusicide A were prepared by intramolecular condensation,[2+2] photocycloaddition and C-H arylation(Scheme 1).Five of them showed moderate immunosuppressive activities.The activity of a compound(2-8d)was five times stronger than that of scopariusicide A.Chapter 3.Biomimetic Synthesis of Novel Dimeric DiterpenoidsEight novel dimeric diterpenoids with six unprecedent skeletons were discovered from I.scoparius.Unfortunately,there were only two compounds have comfirmed their absolute configurations by single-crystal X-ray diffraction.For those undetermined ones,they shared same biogenetic precursor with a rational biosynthetic pathway.According to this assumption,a biomimetic synthesis of dimeric diterpenoids were conducted.As a result,dilactone of scopariusicdiacid E was synthesized by oxidation,[4+2] heter-Diels-Alder cycloaddition and electrochemical oxidation,using the precursor isoscoparin P as startmaterial.Its absolute configuration at position of C-4 and C-11(C-11')were assigned as R and S,respectively,by single crystal X-ray diffraction of the intermediate.The dimers dilactone and dimethyl 11,11'-O-diacetyl ester of scopariusicdiacid D were also prepared with the same methods.The synthesis study of other diterpenoid dimers were in progress(Scheme 2).Chapter 4.Advances in Natural Meroterpenoids from Plants and Their BioactivitiesThis review summarized the research advances of natural meroterpenoids with monoterpenoid,sesquiterpenoid,diterpenoid and triterpenoid units,from plants by 76 references from 2008 to 2018.Accoding to literature reviewing the source,structures,hypothetical biosythesis pathway,biological activities and synthesis of meroterpenoids,it will be helpful for further understanding of the diversifiacation and utilization of meroterpenoids.