Gold(I,III) Complexes Designed for Selective Targeting and Inhibition of Zinc Finger Proteins

184 Pages·2018·9.39 MB·English

by  Raphael Enoque Ferraz de Paiva

Springer Theses
Recognizing Outstanding Ph.D. Research
Raphael Enoque Ferraz de Paiva

Gold(I,III) Complexes
Designed for
Selective Targeting
and Inhibition of
Zinc Finger Proteins
Springer Theses
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Raphael Enoque Ferraz de Paiva
Gold(I,III) Complexes
Designed for Selective
Targeting and Inhibition
of Zinc Finger Proteins
Doctoral Thesis accepted by
the University of Campinas, Campinas, Brazil
123
Author Supervisor
Dr. Raphael EnoqueFerraz dePaiva Prof. PedroPauloCorbi
Institute of Chemistry Institute of Chemistry
University of Campinas University of Campinas
Campinas, Brazil Campinas, Brazil
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-3-030-00852-9 ISBN978-3-030-00853-6 (eBook)
https://doi.org/10.1007/978-3-030-00853-6
LibraryofCongressControlNumber:2018955155
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The most exciting phrase to hear in science,
the one that heralds the most discoveries, is
not “Eureka!” (I found it!) but “That’s
funny…”
—Isaac Asimov
The mediocre teacher tells. The good teacher
explains. The superior teacher demonstrates.
The great teacher inspires
—William Arthur Ward
I dedicate this thesis to every teacher (in the
most fundamental sense of the word) I had
during my life. Luckily, I’ve had many great
teachers.
’
Supervisor s Foreword
Raphaeljoinedmygroup asanundergraduatestudentattheInstituteofChemistry
of the Campinas State University (UNICAMP), Brazil, in 2010. He obtained his
master’s degree working in the synthesis and biological evaluation of silver and
platinum complexes with anti-inflammatory agents. Raphael developed his Ph.D.
project focusing on the development of gold(I,III) compounds for the inhibition of
zinc finger proteins. This project was developed at UNICAMP with a one year
exchange at VCU under the supervision of Prof. Nicholas Farrell.
The zinc finger family of proteins was explored as target in this work, in par-
ticular, the nucleocapsid protein (NCp7) from the human immunodeficiency virus
(HIV-1).OneofthemostremarkablestructuralandfunctionalcharacteristicsNCp7
is the presence of two -Cys-X2-Cys-X4-His-X4-Cys- zinc finger (ZnF) domains.
Inhibitionofthisproteinsleadstothelossofviralinfectivity,suggestingthatNCp7
inhibitors could be developed as alternatives to the typical anti-retroviral therapies
available today.
The broad contribution of this thesis was on the development of gold-based com-
pounds for the inhibition of zinc finger proteins. Gold(I) compounds were developed
using phosphine ligands as “carriers” and labile pyridine derivatives or chloride as
co-ligands. Innovative approaches were used for evaluating the interaction of gold(I)
compounds with zinc fingers. Travelling-wave ion mobility mass spectrometry
(TWIM-MS)coupledwithtandemMSprovedtobeanextremelypowerfultechnique
fordetectingmetallationsitesinzinc fingers,aswellasforidentifyingandseparating
conformers.X-rayabsorptionspectroscopy(XAS)wasusedforidentifyingchangesin
the coordination sphere and geometry of gold. In addition, gold(III) compounds were
alsodeveloped.Stabilizinggold(III)representsaninterestingchallenge,asitisproneto
reduction in the biological media. The organometallic compounds [Au(2-benzylpy-
ridine)Cl ] isparticularlynoteworthy.It wasabletoinhibitNCp7throughasuigeneris
2
mechanism based on a gold-catalyzed C-S bond formation.
ix
x Supervisor’sForeword
Finally,thededicationandmotivationofDr.RaphaeldePaivaarenoteworthy.He
was always willing to help his colleagues and ready for new challenges. His
published works and conferences awards confirm his wonderful work and his
dedicationtoscience.ItwasagreathonortometowriteaboutDr.RaphaelEnoque
Ferraz de Paiva and I wish him success in his career.
Campinas, Brazil Prof. Pedro Paulo Corbi
July 2018
Abstract
ManycomplementaryapproacheshavebeenusedtoinactivatetheHIV-1nucleocapsid
protein(NCp7)zincfingerfortherapeuticuse.ThecysteineresiduesofNCp7aresome
of the most nucleophilic of all zinc-bound thiolates found in proteins. Although it is
considered anoblemetal,goldhasaveryrichchemistry undertherightconditions.Itis
capableofformingcoordinationcompoundsinbothofitstypicaloxidationstates(1+
and3+).Gold(I)formslinearcompounds,withcoordinationnumber2,whilegold(III)
formssquareplanarcompounds withcoordinationnumber 4.Electron-richmetalssuch
asgoldareparticularlysuitablefordesigningmetal-basedzincejectorsbecause,assoft
Lewis acid electrophiles, they have high affinity for Cys residues. Without the proper
tridimensionalfolding granted by Zn coordination, NCp7 is inactivated and unable to
furtherrecognizespecificnucleicacidsequences.
AseriesofAu(I)complexeswiththegeneralstructure[Au(L)(PR )](R=EtorCy)
3
wasdesigned.ThetwoaromaticresiduesinthestructureofNCp7(Phe16andTrp37)
areresponsibleforp-stackingwithpurineandpyrimidinebasesfoundonRNAand
DNA.Thepresenceoftheseresiduescanbeusedforintroducinganextraselectivity
componentinthedesignedcompounds,asanaromaticLligandcanbeused.Wealso
examinedforcomparisonthe“standard”gold-phosphinecompoundauranofinwhich
containsathiosugarligandcoordinatedto{Au(Et P)}.Thenatureofthephosphine
3
andthenatureofLaffectboththereactivitywiththeC-terminalNCp7ZnF2andthe
“full”NCp7aswellasthefinalcoordinationsphereofAuonceincorporatedintothe
protein.Inthisreaction,thefirststepistheelectrophilicattackoftheAu(I)-phosphine
compounds on the Zn-coordinated residues, forming a heterobimetallic {R PAu}-
3
ZnF species. Two alternative pathways open up from here on. In the most typical
pathway,afterZndisplacement,the{R PAu}moietycanremaincoordinatedtoaCys
3
residue. Afterwards, the phosphine is lost and a Cys-Au-Cys gold finger (AuF) is
obtained.Inthismechanism,compoundswithslowerreactivitysuchas[Au(dmap)
(Et P)]allowustoprobetheinitial auration steps,withspeciessuchas{Et PAu}-
3 3
apoNCp7stillbeingpresent.Longerincubationtimesormorereactivecompounds
suchasthechlorideprecursorsprovideinformationonthefinalspecies,thegoldfinger
itself. In an alternative pathway, observed for the model compound auranofin, the
{R PAu}moietycoordinatestoaHisresidue,andthefinalhypotheticalAuFobtained
3
xi