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1、Phyrocknristry,Vol.32,No.4,pp.1073-1075,19930031-9422/93$6.00+0.00PrintedinGreatB&m.PergamonPressLtdREASSIGNMENTOFSTRUCTURESOFTHENEOLIGNANS,MAGNOSALINANDANDAMANICINR.N.MAHINDRU,S.C.TANFJA,K.L.DHAR*andR.T.BROWN?NaturalProductsChemistryDivision,RegionalResearchLaboratory,CanalRoad,JammuTawi
2、180001,India;TDepartmentofChemistry,UniversityofManchester,ManchesterMl3PLU.K.(Receivedinrevisedform21July1992)KeyWordIndex-Piperclusii;P.sumatranum;Piperaceae;neolignans;revisedstructures;magnosalin;andamanicin;X-raycrystallography.AIrstract-OnthebasisofsinglecrystalX-raycrystallographyt
3、hestructureofmagnosalinnowisolatedfromPiperclusiihasbeenrevisedto1~,2a,3~,4~-1,2-dimethyl-3,4-bis~2,4,5-trimethoxyphenyl)-cyclobutane.Byanalogy,anotherneolignanandamanicin,isolatedfromP.sumatranumvarandamanicaisalsorevisedtolcr,2fl,3j?,4a,1,2-dimethyl-3,4-his-(2,4,5-trimethoxyphenyl)-cycl
4、obutane.INTRODUCTIONHNMRassignmentsremainedunexplainedonthebasisInanearliercommunication[l]wereportedtheisola-oftheirstructures.tionandstructuralassignmentofanewneolignan,namely,la,2B,3a,4/?-or1/?,2q3~,4a-1,2-dimethyl-3,4-bis-(2,4,5-trimethoxyphenyl)-cyclobutane(A)fromPiperRESULTSANDDISCU
5、SSIONsumatranumvarandamanica.ThestructuralassignmentTheHNMRsignalsformethineaswellasbenzylicofAwassolelybasedonitsspectraldataandbyanalogyprotonsinstructureAarelocatedmuchmoredownfieldwiththereportedspectraldataoftwootherisomericthantheircounterpartsinthestructureofmagnosalin(C).neolignan
6、sofsimilarconstitution,i.e.heterotropan(B)Themodels,however,suggestotherwise,i.e.thesignalsofandmagnosalin(C)[2,31.theseprotonsinstructureA(1)shouldappearmoreRecently,wehavebeenabletoisolatefromthepetrolupfieldthaninstructureC(2)duetotheshieldingcausedextractofP.clusiiaminorconstituent,Pc
7、Qmp96-97,byaromaticringwhichisbisectingthecyclobutaneringwhichwaslateridentifiedasmagnosalin(C)aftercom-insuchamannerthattheseprotonsfallintoitsshieldingparisonofitsreportedphysicalandspectraldata.Asthezone.InstructureC,however,thearomaticringadoptsastructuresofther
