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1、CHAPTER1ProcedurestoImproveDifficultCouplingsMichaeZW.PenningtonandMichaelE.Byrnes1.IntroductionThesuccessfulcouplingofaminoacidderivativesduringthesynthe-sisofapeptidebyeithersolutionorsolid-phaseproceduresdependsonboththereactivityofthecarboxylgroupoft
2、heN-protectedaminoacidandthestericaccessibilityofthereactivenucleophile(eitheraprimaryorsecondaryamine).Activationofthecarboxylgroupisarequisiteforthesynthesisofanamidebond.Manyactivationprocedureshavebeendevelopedtoaccomplishthis,andultimately,thereacti
3、vityoftheacti-vatedspeciesiscrucialindeterminingthecouplingyield.Improvementsinsolid-phaseassemblytechniquesnowpermittherou-tinesynthesisoflong(>40residues)complexpeptides.However,astheabilitytoassembletheselongermoleculesonasolid-phasematriximproved,new
4、problemswereencountered.Successfulsynthesiswashamperedbystericfactorsofthebulkyprotectedderivatives(I),inter-molecularaggregationoftheprotectedpeptidechain(2,3),formationofhydrogenbondingstructures,suchasP-sheet(4-7),prematuretermina-tion,orcyclizationon
5、theresin(a-10).Ourlaboratoryroutinelysynthesizeslargequantitiesofmanypeptides.Weemployasemiautomatedprocedurewhereeachindividualcouplingismonitoredforcompletenesspriortothenextdeblocking/elongationstep.Asaresultofthistypeofstrategy,weencountermanycouplin
6、gsFrom:MethodsmMolecularB!olagy,Vol.35:PeptldeSynthewsProtocolsEditedby:M.W.PennmgtonandBM.DunnCopyright01994HumanaPressInc.,Totowa,NJ12PenningtonandByrnesthatdonotproceedtocompletenessusingeitherasinglecarbodiimide/HOBTcoupling(II)ordoublecouplingemploy
7、ingthesamecarbo-diimide/HOBTstrategy.Duringthepastseveralyears,wehaveevalu-atedmanyofthemethodsdescribedintheliteraturetoimprovethecouplingyield.Itisimportanttopointoutthateverypeptidepresentsitsownuniquesetofcomplications.Thus,itisimpossibletogiveaunive
8、r-salprocedurethatwillworkforeverypeptide.Itisthepurposeofthischaptertopresentseveraloftheseprotocols,whichwehavefoundtobeveryuseful.2.Materials1.Allmaterialsandreagentsarepurchasedfromcommercialsourcesandusedassuch.2.Synt
