TCEP还原二硫键

2648J.Org.Chem.1991,56,2648-2650SelectiveReductionofDisulfidesbyTris(2-carboxyethy1)phosphineJohnA.Burns,JamesC.Butler,JohnMoran,andGeorgeM.Whitesides*DepartmentofChemistry,HarvardUniversity,Cambridge,Massachusetts02138ReceivedOctober15,1990Tris(2-carboxyethy1)phosphine(TCEP)reducesdisulfidesrapidlyandcompletelyinwateratpH4.5.Itpreferentiallyreducesmorestraineddisulfides,inaccordancewiththeusualmechanismpostulatedforreductionofdisulfidesbyphosphinesinwater.Thereagentcanbesynthesizedconvenientlyinlargequantitiesbyacidichydrolysisofthecommerciallyavailabletris(2-cyanoethy1)phosphine.IntroductionTrialkylphosphinesreduceorganicdisulfidestothiolssmoothlyandquantitativelyinwater(eql).lThestrengthRbP+RSSR+H20-R’,P=O+2RSH(1)ofthephosphorus-oxygenbondrendersreductionirre-versible.Becausetrialkylphosphinesarekineticallystableinaqueoussolution,selectiveforthereductionofthedi-sulfidelinkage,andunreactivetowardmanyotherfunc-tionalgroups,theyareattractiveasreducingagentsinbiochemicalsystems.Theirutilityhasbeenlimitedbythelowsolubilityofmostsimpletrialkylphosphinesinwater,andtheiracceptabilityasreagents(especiallyinbiochem-istry)bytheodorandeaseofautoxidationofmanyspecieswithlowmolecularweights.Water-solublephosphineshavebeenusedasreducingagents,aschelatingagenta,andasligands.Sulfonylatedtriphenylphosphineshavebeenusedextensivelyasligandsforwater-solublemetalcatalysts.2Theyarethesubjectofseveral~atents.~Acommerciallyavailablewater-sol-ubletriarylphosphine,tris(4-carboxyphenyl)phosphine,isrelativelyexpen~ive.~Otherwater-solublephosphineshavebeenmade.S*6Tris(hydroxymethyl)phosphine,aliquidwithanunpleasantodor,cangenerateformaldehydeandotherbyproductsderivedfromitinreductionsofproteins.’Thesecharacteristicshavepreventedthegen-eraluseofphosphinesasreducingagentsforwater-solubledisulfides.Herewedescribeaconvenientpreparationoftris(2-carboxyethy1)phosphinehydrochloride(TCEP.HC1,l.HCl)byacidichydrolysisofthecommerciallyavailabletris(2-cyanoethy1)phosphine(2)(eq2)anddemonstratetheaqHC1reflux(NCCHpCH&P-(HOpCCHCH2)3PH+C1-(2)l.HC!l(88%)2(1)Schhberg,A.Chem.Ber.1935,68,163-164.(2)Sinou,D.Bull.SOC.Chim.Fr.1987,4J30-486.Joo,F.;Toth,Z.J.Mol.Catal.1980,8,369-383.(3)Varre,C.;Desbois,M.;Nouvel,J.FrenchPatent2,561,650,1985.Sabot,J.L.FrenchPatent2,532,318,1984.Kuntz,E.WestGermanPatent2,627,364,1976.(4)Tria(4-carboxypheny1)phosphinecostamorethan$15000/mol;tria(2-cyanoethyl)phosphine,lessthan$350/mol.PricesarefromStrem.(5)Forexample,P(CH2CH2CONHJ3:Jahn,W.2.Naturforsch.1989,44B,79-82.P(pCJ34CH2N(Ac)CH2CH20H)3:Jahn,W.2.Naturforsch.1989,44B,1313-1322.Ph2PCH2(o-C6H4S03K):Paetzold,E.;Oehme,G.;Costisella,B.2.Chem.1989,29,447-448.P(CH2(CHzCH20).Me)3~Okano,T.;Morimoto,K.;Konishi,H.;Kiji,J.NipponKagakuKaishr1985,486-493.RCON(CH2CH2PPhz)2:Nuzzo,R.G.;Haynie,S.L.;Wilson,M.E.;Whitesides,G.M.J.Org.Chem.1981,46,2861-2867.P(p-C6H4CH2NH2)$Bartlett,P.A.;Bauer,B.;Singer,S.J.J.Am.Chem.SOC.1978,100,5085-5089.(6)Rauhut,M.M.;Hechenbleikner,I.;Currier,H.A.;Schaefer,F.C.;Wystrach,V.P.J.Am.Chem.SOC.1959,81,1103-1107.(7)Sweetman,B.J.;Maclaren,J.A.Aust.J.Chem.1966,19,2347-2354.utilityofTCEPasaselectivereducingagentforrepre-sentativedialkyldisulfidesinaqueoussolutions.TCEP-HC1isanonvolatile,water-solublesolidthatiseasilymanipdatedinair.Itisastrongreducingagentthathaspreviouslybeenreportedtocleavedisulfides:8itrapidlyreducesevenverystablealkyldisulfidessuchastruns-4,5-dihydroxy-l,2-dithiane(DTT’”)atroomtem-peratureandpH5.QualitativestudiesoftherelativereactivitiesofTCEPwithseveraldisulfidesalsoestablishthepotentiallyusefulfactthatthesereductionsareki-netically,notthermodynamically,controlled.Forexample,1reducesthedisulfidegroupoflipoicacid(Lipox)tothecorrespondingdithiol(Lipd)morerapidlythanitreducesthatof2-hydroxyethyldisulfide(MEox),althoughLipditselfreducesMEoxalmostquantitativelyatthermody-namicequilibrium.ResultsSynthesisofTCEP.TCEP.HC1wasmadeconven-ientlyin50-gquantitiesbyhydrolysisoftris(2-cyano-ethy1)phosphineinrefluxingaqueousHC1(eq2).TCEPoxidizesrapidlyinaqueousbase(seebelow),makingbasichydrolysismorecumbersomeandlesscleanthanacidichydrolysis:separationofTCEPandTCEPoxideisdif-fi~ult.6*~J~TCEPhasalsobeenmadebyreactionofalu-minumphosphidewithacrylicacid.”Previousprepara-tionsaremuchlessconvenientthantheonereportedhere.PropertiesofTCEP.TCEPaHClisawater-soluble(310g/L),odorless,whitecrystallinesolidthatisstableinairforseveralmonths.ThepKaofthephosphoniumcenterhasbeenestimatedbytitrimetrytobe7.66.9DilutesolutionsofTCEPoxidizeonlyslowlyinairwhenthepHislessthanthatpKa(Figure1).ReductionofStructurallySimpleDisulfidesinWater:CompetitionExperiments.ThereactionofTCEPwithdisulfidesissofastatpH4.5thatitisdifficulttomeasureaccurately.Wehave,instead,measuredrela-tivereactivitiesofrepresentativedisulfidestowardTCEPbycompetitionexperiments.Thecompetitivereductionswerecarriedoutbyallowing0.8equivofTCEPtoreactwith1.0equivofeachoftwodisulfidesinD20atpH4.5.Attheconcentrationsweused(0.2-1.0mM),thereactionwascompletewithin5minforalldisulfides.TheNMRspectraplacelowerboundariesonthese-lec