An Efficient One-Pot Catalyzed Synthesis of 2,4-Disubstituted 5-Nitroimidazoles Displaying

21 Pages·2017·1.88 MB·English

molecules
Article
An Efficient One-Pot Catalyzed Synthesis of
2,4-Disubstituted 5-Nitroimidazoles Displaying
Antiparasitic and Antibacterial Activities
FannyMathias1,YoussefKabri1,LilianeOkdah2,CaroleDiGiorgio3,Jean-MarcRolain2,
CédricSpitz1,MaximeD.Crozet1andPatriceVanelle1,*
1 AixMarseilleUniversity,InstitutdeChimieRadicalaireICR,UMRCNRS7273,Laboratoirede
Pharmaco-ChimieRadicalaire,FacultédePharmacie,27BoulevardJeanMoulin—CS30064,
13385MarseilleCEDEX05,France;[email protected](F.M.);[email protected](Y.K.);
[email protected](C.S.);[email protected](M.D.C.)
2 IHUMéditerranéeInfection,AixMarseilleUniversity,UnitédeRecherchesurlesMaladiesInfectieuseset
TropicalesEmergentes,URMITEUMR63,CNRS7278,IRD198,Inserm1095,FacultédeMédecinedela
Timone,19-21BoulevardJeanMoulin,13005Marseille,France;[email protected](L.O.);
[email protected](J.-M.R.)
3 AixMarseilleUniversity,CNRS,IRD,AvignonUniversité,IMBEUMR7263,LaboratoiredeMutagénèse
Environnementale,13385Marseille,France;[email protected]
* Correspondence:[email protected];Tel.:[phone]
Received:20July2017;Accepted:29July2017;Published:3August2017
Abstract: A one-pot regioselective bis-Suzuki-Miyaura or Suzuki-Miyaura/Sonogashira reaction
on 2,4-dibromo-1-methyl-5-nitro-1H-imidazole under microwave heating was developed. This
methodisapplicabletoawiderangeof(hetero)arylboronicacidsandterminalalkynes. Additionally,
thisapproachprovidesasimpleandefficientwaytosynthesize2,4-disubstituted5-nitroimidazole
derivativeswithantibacterialandantiparasiticproperties.
Keywords: 5-nitroimidazole;Suzuki-Miyaura/Sonogashira;regioselectivity;microwave;antiparasitic;
antibacterial
1. Introduction
Nitroimidazoledrugsshowawiderangeofactivitiesagainstparasitesandanaerobicbacteria.
Theseactivitiesvaryaccordingtothenatureofthesubstituentsandthepositionofthenitrogroup[1–7].
Metronidazole(mtz)appearsontheWHOModelListofEssentialMedicinesandistodaythemost
commonlyused5-nitroimidazolecompoundworldwide.
5-Nitroimidazoles are prodrugs which need to be activated by reduction of their nitro group.
ReducedmetronidazoleformscovalentbondstoDNAmacromolecules,leadingtothelossofhelical
structureandirreversiblebreaking[8]. Thereductionofthesecompoundsinvolvesseveralanaerobic
enzymatic pathways such as ferredoxin oxidoreductase [9], nitroreductase [10] and thioredoxin
reductase[11].
Resistancetometronidazolehasemerged,butdespitestudiesonTrichomonasvaginalis[9,12–15],
Giardiaintestinalis[16–18],andanaerobicbacteria[19–23],themechanismisnotyetfullyunderstood.
Suchresistanceleadsphysicianstousehigherdosesofmetronidazoleandlongercoursesoftreatment
toimproveactivity[24].
However,higherdosesandlongerregimensmaypromotesideeffectsanddecreasecompliance.
Although the most common side effects of metronidazole treatment are mild (headache, vertigo,
nausea,ametallictasteinthemouthandanAntabuse-likeeffectwithalcohol)[25],othermoreserious
adverseeffectshavebeendocumented,suchasmutagenicityonbacteria[26–31]andcarcinogenicityon
Molecules2017,22,1278;doi:10.3390/molecules22081278 www.mdpi.com/journal/molecules
Molecules 2017, 22, 1278 2 of 21
carcinogenicity on mice and rats [32]. Moreover, in recent decades, an increasing number of anaerobic
Molecules2017,22,1278 2of21
bacterial pathogens have been observed to cause severe diarrhea and enterocolitis [33–36].
Therefore, there is an ongoing search for alternative 5-nitroimidazoles effective on anaerobic-
rmesiicsetaanntd srtaratsin[3s 2w].iMthoorueto vseerr,ioinusre acdenvtedrseec aedffeesc,tasn [i3n7c–r4e8as].i nFgonlluomwbinegr othfaen waeorrokb iocfb Wacatelsrhia lept aatlh. oinge 1n9s87
[4h9a]v, ewbeee nfoocbusseervde doutor caruesseeasrecvhe reond iaprhrhaeramaancdomenotderuolcaotiloitnis [o3f3 –t3h6e] . 2- and 4-positions of the 5-
nitroimThideraezfoolree ,scathffeorled [i5s0].a n ongoing search for alternative 5-nitroimidazoles effective on
anaePraolbliacd-rieusmis-tcaanttaslytrzaeinds rweaitchtioountss, epraiorutiscualdavrelyrs Seuezffuekcit-sM[3i7y–a4u8r]a. Fcroollsosw-cionugptlhinegw, oarrke owfiWdeallys hapetpalile.d
inin th1e9 8s7yn[4th9e],siws oeff boicouascetdiveo ucromrepseleaxr cmhoolencuplheasr, mofafceorimngo dmuilladti roenacotfiotnh eco2n-daintidon4s- panosdi tcioonmspoaftibthileity
w5i-tnhi trao ibmroidaadz oralensgcea fofof lfdu[n5c0t]i.onal groups [51,52]. Moreover, some Suzuki-Miyaura cross-coupling
condiPtiaolnlasd aiullmow-c artaelgyizoesdelreecatcivtieo ncsr,opsasr-ctiocuuplalrilnygS uoznu pkio-lMyhiyaaluorgaencraotsesd-c ohuetpelrinogcy,acrleesw [i5d3e,l5y4a],p lpelaievdining a
htahleogsyenntahteesdis αo fpboisoiaticotinv eucnocmhapnlegxedm oalnedcu alebsl,eo tfofe rreinagctm inil da rseeaccotinodn sctoenpd. iTtiohniss eannadbcloesm ap awtiibdieli tryawngiteh of
caombrpooadunradnsg weiotfhf tuhnec tsiaomnael sgtraorutipnsg[ 5m1,a5t2e]r.iaMl.o reover,someSuzuki-Miyauracross-couplingconditions
allowThree grieogsieolescetlievceticvriotyss i-nco tuhpel iSnugzounkip-Molyiyhaaulorgae rneaatcetdiohne tiesr docryivcelens b[5y3 ,t5h4e] ,elleeacvtrinogphailhiac lopgroenpaetretdiesα of
thpeo sihtaiolonguenncahtaendg ecadrabnodn.a bDleurtoinrge atchtein oaxsidecaotinvde satedpd.iTtihoins esnteapbl, etshaew pidalelardaniugmeo cfactoamlypsot uwndhsicwh itihs a
ntuhcelesaompheislitca rstpinegcimesa, tseprieacli.fically links the most electrophilic halogenated carbon [53–55]. The nitro
groupT, heessreengtioiasle fleocrt imvietdyiicninthale pSruozpuekrit-iMesi,y caaunra arlseoac aticot nasis ad crhiveemnibcyalt dheireelcetcintrgo pghroiluicpp droupreinrtgie ssyonftthheesis
halogenatedcarbon. Duringtheoxidativeadditionstep,thepalladiumcatalystwhichisanucleophilic
[56]. Thus, the nitro group in position 5 can significantly increase the electrophilic properties of the
species,specificallylinksthemostelectrophilichalogenatedcarbon[53–55]. Thenitrogroup,essential
C-4, making this position the most reactive toward cross-coupling reactions, although on the naked
formedicinalproperties,canalsoactasachemicaldirectinggroupduringsynthesis[56]. Thus,the
imidazole ring, the C-2 position was described as the most reactive [57,58].
nitrogroupinposition5cansignificantlyincreasetheelectrophilicpropertiesoftheC-4,makingthis
As part of our research program centered on the design and synthesis of novel 5-nitroimidazole
positionthemostreactivetowardcross-couplingreactions,althoughonthenakedimidazolering,the
compounds [40,43,48,50,59,60], we decided to exploit this particular reactivity of the 5-nitroimidazole
C-2positionwasdescribedasthemostreactive[57,58].
series toward cross-coupling reactions, seeking a rapid and versatile pathway for the synthesis of 2,4-
Aspartofourresearchprogramcenteredonthedesignandsynthesisofnovel5-nitroimidazole
disubstitued 5-nitroimidazole derivatives. Therefore, we report herein a regioselective Suzuki-
compounds[40,43,48,50,59,60],wedecidedtoexploitthisparticularreactivityofthe5-nitroimidazole
Miyaura cross-coupling between 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2) and aryl or
series toward cross-coupling reactions, seeking a rapid and versatile pathway for the synthesis
heteroarylboronic acids resulting in the formation of 2-bromo-4-substituted-1-methyl-5-
of 2,4-disubstitued 5-nitroimidazole derivatives. Therefore, we report herein a regioselective
nitroimidazoles which can then undergo a second (Suzuki-Miyaura or Sonogashira) cross-coupling
Suzuki-Miyauracross-couplingbetween2,4-dibromo-1-methyl-5-nitro-1H-imidazole(2)andarylor
reaction to obtain 2,4-disubstituted 5-nitroimidazoles during a sequential one-pot process.
heteroarylboronicacidsresultingintheformationof2-bromo-4-substituted-1-methyl-5-nitroimidazoles
Finally, the antiparasitic activity of the obtained 5-nitroimidazole derivatives was assessed
whichcanthenundergoasecond(Suzuki-MiyauraorSonogashira)cross-couplingreactiontoobtain
against T. vaginalis and anaerobic bacteria of the genus Clostridium and Bacillus.
2,4-disubstituted5-nitroimidazolesduringasequentialone-potprocess.
Finally,theantiparasiticactivityoftheobtained5-nitroimidazolederivativeswasassessedagainst
2. Results
T.vaginalisandanaerobicbacteriaofthegenusClostridiumandBacillus.
2.1. Chemistry
2. Results
The synthesis of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2) was realized from the
2.1. Chemistry
commercial product 4(5)-nitroimidazole in two sequential steps, as shown in Scheme 1. The first step
consisTthede soyfn bthroesmisinoaft2i,o4n-d wibirtohm eole-1m-menettahly bl-r5o-nmitirnoe- 1iHn -wimaitdear zaonled (i2n) wthaes preraelsieznedcef roofm sothdeiucmom hmyderrcoiaglen
cparrobdonuactte4,( a5c)-cnoirtdroinimg itdoa Pzoeldeaidnat weto asl.e [q6u1e]n. Ttihales 2te,4p(s5,)-adsisbhroowmno-i5n(4S)c-hneitmroeim1.idTahzeofiler smtsitxetpurceo nwsaisst ethden
aolkfyblraotmedin bayti odnimweitthhyell esmuelpnhtaalteb r(oDmMinSe) ininw DaMterFa lnedadinintgh etop rtewseon ciseoomfesroidc iupmrodhuydctrso g1e anncda r2b oinna 7te1,%
oavcecroarldl iynigeltdo. Pedadaetal.[61]. The2,4(5)-dibromo-5(4)-nitroimidazolemixturewasthenalkylatedby
dimethylsulphate(DMS)inDMFleadingtotwoisomericproducts1and2in71%overallyield.

SScchheemmee 11.. SSyynntthheessiiss ooff 22,,44--ddiibbrroommoo--11--mmeeththyyl-l5-5-n-nitirtoro-1-H1H-i-mimidiadzaozloel(e2 ()2.).
Molecules2017,22,1278 3of21
Molecules 2017, 22, 1278 3 of 21
Our particular aim in exploring the reactivity of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2)
Our particular aim in exploring the reactivity of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole
in Suzuki-Miyaura reactions was to test the regioselectivity of this type of reaction toward the
(2) in Suzuki-Miyaura reactions was to test the regioselectivity of this type of reaction toward the
halogenated positions C-2 and C-4.
halogenatedpositionsC-2andC-4.
We began our study by optimizing the regioselective coupling reaction of compound 2 with
We began our study by optimizing the regioselective coupling reaction of compound 2 with
pphheennyyllbboorroonniicc aacciidd ((11..11 eeqquuiivv.).) iinn tthhee pprreesseennccee ooff PPdd((PPPPhh3))4 ((00..0044 eeqquuiivv..)) aass ccaattaallyysstt,, NNaa2CCOO3 ((33 eeqquuiivv..))
3 4 2 3
aass bbaassee,, iinn aa mmiixxttuurree oof fDDMMEE/E/tEOtOHH/H/2HO (O3/1(3/1/)1 a/s1 s)oalsvesnotl.v Feinrts.t,F tihres tr,etahcetiroena cwtiaosn pwerafsorpmerefdo ramt reodomat
2
temperature, and after 1.5 h, no conversion of compound 2 was observed (Table 1, entry 1). When the
roomtemperature,andafter1.5h,noconversionofcompound2wasobserved(Table1,entry1).When
ttehmepteemraptuerraet uwraesw inacsrienacsreeda steod 6t0o °6C0, ◦aCft,ear f4te8r h4 8ofh roefacretiaocnti, oan ,maixmtuixretu oref coofmcopmoupnodusn d2/s32a//43/a5/ w4/a5s
observed with both low conversion and selectivity (LC/MS ratio 25/28/26/21%, respectively) (Table 1,
wasobservedwithbothlowconversionandselectivity(LC/MSratio25/28/26/21%,respectively)
entry 2). In these conditions, the reactivity of positions C-2 and C-4 was similar. The use of microwave
(Table1,entry2). Intheseconditions,thereactivityofpositionsC-2andC-4wassimilar. Theuseof
imrriacdroiawtiaovne aitr r8a0d °iaCt ifoonr 1a th8 (0T◦aCblfeo 1r,1 ehnt(rTya 4b)l eal1l,oewnetdry b4e)ttaelrlo cwonevdebresitotenr ocfo cnovmerpsoiounnodf 2c oinm tphoeu Snudzu2kiin-
Miyaura reaction, with lower selectivity and improved yield of the dicoupled compound 5. Next, we
theSuzuki-Miyaurareaction,withlowerselectivityandimprovedyieldofthedicoupledcompound5.
eNxeaxmt,iwneede txhaem ininfleudetnhcee ionffl outehnecr epoaflloadthiuermp saolluardcieusm suscohu racse PsdsuCclh2(PaPshP3d)2C, Pld(P(DPhPP)F,)CPld2 (aDnPdP PFd)C(OlAacn)d2.
2 3 2 2
WPdi(tOh APdc)C.l2(WPPithh3)P2 adnCdl P(PdP(DhP)PFa)nCdl2,P ldo(wD PcoPnFv)Cerlsi,olno wwacos novbesresrivoend wanasd othbesererv wedasa nnod itmheprreovweamsennot
2 2 3 2 2
in terms of selectivity (Table 1, entries 5 and 6). To our satisfaction, good conversion and selectivity
improvementintermsofselectivity(Table1,entries5and6). Tooursatisfaction,goodconversionand
wseelercet iovbitsyerwveerde wobitshe rPvded(OwAitch)2 Padn(dO cAocm) paonudncdo m3ap wouans dob3atawinaesdo ibnt a6i0n%ed yiinel6d0 %(Tyaibelled 1(,T eanbtlery1 ,7e).n Mtryor7e).
2
importantly, the use of 1.3 equiv. of phenylboronic acid for a longer time afforded compound 3a in
Moreimportantly,theuseof1.3equiv. ofphenylboronicacidforalongertimeaffordedcompound3a
better yield (64%, Table 1, entry 12). No yield improvement for compound 3a was observed when we
inbetteryield(64%,Table1,entry12). Noyieldimprovementforcompound3awasobservedwhen
carried out the reaction in presence of Xantphos (Table 1, entry 8) or increased the temperature (Table 1,
wecarriedoutthereactioninpresenceofXantphos(Table1,entry8)orincreasedthetemperature
(eTnatbrilees1 1,0e natnrdie s111)0. aMnodd1e1r)a.tMe soedleecratitveistye lwecatisv oitbytawinasedo bwtahienne dPPwhh3e wnaPsP ahddweads (aTdadbeled 1(,T eanbtlrey1 9,)e.n Ttrhyes9e).
3
Ttrhiaelsse wtritihal dsiwffeitrhendti cffaetraelynsttcsa rteavlyeastlesdr ethveaat lreedgitohsaetlercetgivioitsye ldeecptievnitdys donep tehned csatoanlytthice sycasttaemly:t iPcds(yOsAtecm)2:
performed best, both on conversion and selectivity, in our reaction conditions.
Pd(OAc) performedbest,bothonconversionandselectivity,inourreactionconditions.
2
TTaabbllee 11.. OOppttiimmiizzaattiioonn ooff tthhee rreeggiioosseelleeccttiivvee SSuuzzuukkii--MMiiyyaauurraa rreeaaccttiioonn..

Entry EnPtrdy (0.04 ePqdu(i0v.0.)4 equivT.)empT (e°mCp)(◦C) TiTmime e(h(h)) 22( %(%) ) 3a3(a% ()%) 4(%4 )(%) 5(%5 )(%)
1 a 1a Pd(PPh3)P4 d(PPh3)4 25 25 1.15. 5 101000 - - - - - -
2 a 2a Pd(PPh3)P4 d(PPh3)4 60 60 484 8 2525 2828 2626 2121
3 a 43aa Pd(PPh3)PP4 dd((PPPPhh33))44 60 MW6800 MMWW 1.110.. 00 219229 222422 223723 236726
4 a 5a Pd(PPhP3)d4C l2(PPh3)2 80 MW60 MW 1.10. 0 4812 2724 1627 9 37
5 a 6aPdCl2(PPPhd3()D2 PPF)Cl2 60 MW60 MW 1.10. 0 4248 3727 1416 7 9
6 a 87acPd(DPPPdF(O)CPAdlc2() O2/AXca)n2tph6os0 MW6600 MMWW 1.110.. 00 210842 650837 tra9ce1s4 185 7
7 c 9c Pd(OAPcd)(2O Ac)2/PPh360 MW60 MW 1.10. 0 1620 3060 2t4races 14 8
8 a P1d0(cOAc)2/XanPtpd(hOoAsc )2 60 MW80 MW 1.10. 0 518 3658 traces9 2615
9 c 1121Pbc,dc(OAc)2/PPPPddh((3OO AAcc))22 60 MW7600 MMWW 1.120.. 00 110316 461430 ttrraaccee2ss4 19914
10 c Pd(OAc)2 80 MW 1.0 5 36 traces 26
11 c Pd(OAca)L2 C/MSratio;7b01 .M3eWqu iv.ofphenylb1o.0ro nicacid;cIso1l0a tedyields4.1 traces 19
12 b,c Pd(OAc)2 60 MW 2.0 13 64 traces 9
So,thebestreactionconditionswere1equivalentofimidazole2,1.3equivalentsofphenyl-boronic
a LC/MS ratio; b 1.3 equiv. of phenylboronic acid; c Isolated yields.
acid,0.04equivalentsofpalladiumacetateand3equivalentsofsodiumcarbonateinDME/EtOH/H O
2
(3/1/S1o), fthore 2behst artea6c0ti◦oCn uconnddeirtiomnisc rwoweraev 1e eirqruaidviaalteionnt .ofW imithidathzoeleo p2t,i m1.3iz eedqurievaaclteinotns coof npdhietinoynls-
boronic acid, 0.04 equivalents of palladium acetate and 3 equivalents of sodium carbonate in
in hand, we assessed the scope and limitations of the regioselective Suzuki-Miyaura reaction of
D2,4M-dEi/bErtoOmHo/-H1-2mOe (t3h/y1l/-15)- nfoitrr o2- 1hH a-ti m60id °aCz oulned(2e)r. mAivcraorwietayveo firsruabdsitaittuiotned. Wariythlb tohreo noipctaimcidizse(dw riethacbtoiotnh
conditions in hand, we assessed the scope and limitations of the regioselective Suzuki-Miyaura
electron-donatingorelectron-withdrawinggroups)wereusedtogivethecorrespondingcoupling
reaction of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2). A variety of substituted arylboronic acids
products3a–iinmoderatetogoodyields(55–65%). However,theuseofhydroxymethylphenylboronic
(with both electron-donating or electron-withdrawing groups) were used to give the corresponding
acid (3i) and boronic acids substituted by withdrawing groups such as NO or CF required
2 3
caotuepmlipnegr atpurroediuncctrse as3ea–tio 6in5 ◦Cmo(Tdaebralete2 ,tCo omgopoodu ndysie3ldcs, 3d(5)5.–6O5n%)t.h eHoothweervhera,n dt,heth euuses e ooff
hydroxymethylphenylboronic acid (3i) and boronic acids substituted by withdrawing groups such
as NO2 or CF3 required a temperature increase to 65 °C (Table 2, Compounds 3c, 3d). On the other
Molecules2017,22,1278 4of21
Molecules 2017, 22, 1278 4 of 21
hand, the use of heteroarylboronic acids (pyridine-3-ylboronic acid, 5-methylthiophen-2-ylboronic
heteroarylboronicacids(pyridine-3-ylboronicacid,5-methylthiophen-2-ylboronicacid)ledtovery
acid) led to very low conversion under our optimal conditions. Increasing the temperature in these
lowconversionunderouroptimalconditions. Increasingthetemperatureinthesecasesimprovedthe
cases imMoplercuolevs e2d01 7t,h 2e2, y12i7e8l d of the corresponding dicoupled product. 4 of 21
yieldofthecorrespondingdicoupledproduct.
hand, the use of heteroarylboronic acids (pyridine-3-ylboronic acid, 5-methylthiophen-2-ylboronic
Table 2. Scope of the regioselective Suzuki-Miyaura reaction.
Table2.ScopeoftheregioselectiveSuzuki-Miyaurareaction.
acid) led to very low conversion under our optimal conditions. Increasing the temperature in these
cases im proved the yield of the corresponding dicoupled product.
Table 2. Scope of the regioselective Suzuki-Miyaura reaction.

CompoCuonmdpound R1 R1 Yield (%) Yield(%)
3a 3a C6HC5 H 64 64
6 5
3b 3b p-(OpC-(OHC3)H-C)6-HC4H 65 65
3 6 4
3ca 3Cco ma pound p-(CpF-(3C)R-FC136)H-C46H4 Yiel6d2 (%) 62
3da 3d a 3a m-(Nm-O(CN2)6O-HC25)6-HC46H4 6641 61
3e 3e 3b pp-(-C(OpN-C(C)H-NC3))6--HCC646HH44 6654 64
3f 3f 3c a pp-(-F(pC)--F(CF3))6--HCC646HH44 6622 62
3g 3g 3d a m, mm, ,mpm--((,ONp-CO(OH2)C-3C)H-6CH3)64-HC26H2 6515 55
3h 3e pp-(-C(CNH)-C)-6CH4H 64 63
3ia 3h 3f p-p(C-(pCH-(HF3))--OCC36H6HH)4-46C H4 6623 58
3i a 3g pm-(,C mH, p2O-(OH2C)-HC36)-HC466H24 5558
ReRaecatcitoionn ccoonndidtiiotniosn:sb:o robnoircoanciidcs 3(a1hc.3 ideqs ui(v1.).,3P de(Oqp-uA(iCcv)H2.)(,30 ).-0CP4d6eH(qO4uAiv.c),)2N a(20C.0O43 (63e3qequuiviv..)),, DNMaE2/CEOtO3 H(/3H 2eOq(u3i/v1./),1 ),
DMMWE,/E60tO◦CH,/2Hh2.Oa M(3W/1,/16)5, ◦MC,W2,h 36.i0 a °C, 2 h. a Mp-W(C,H 625O °HC),- 2C 6hH. 4 58
Reaction conditions: boronic acids (1.3 equiv.), Pd(OAc)2 (0.04 equiv.), Na2CO3 (3 equiv.),
The X-ray crystal structure (Figure 1) was determined for compound 3c to confirm the regioselective
The DXM-rEa/EytOHcr/yHs2tOa l(3/1s/t1r)u, MctWur, e60 °(CF,i g2 uh.r ae M1W), 6w5 °aCs, 2 dhe. termined for compound 3c to confirm
Suzuki-Miyaura reaction on 4-position of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2).
the regioTsheele Xc-triavye crSyustzalu sktriu-Mctuiyrea (uFrigaurree 1a)c wtiaosn deotenrm4in-pedo sfoitri coonmpoofun2d,4 3-cd tiob croonmfiorm-1 t-hme eretghiyols-e5le-cntiitvreo -1H-
imidaSzuozluek(i-2M).iyaura reaction on 4-position of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2).

Figure 1. X-ray crystal structure of compound 3c.
FigFuigruer1e. 1X. X-r-arayyc crryyssttaall ssttrruuccttuurree oof fcocommpopuonudn 3dc.3 c.
Following optimization of the regioselective Suzuki-Miyaura reaction, we investigated the one-
Following optimization of the regioselective Suzuki-Miyaura reaction, we investigated the one-
FollowingoptimizationoftheregioselectiveSuzuki-Miyaurareaction,weinvestigatedtheone-pot
pot regpioots reelegciotisvelee cbtiisv-eS buizs-uSkuiz-uMkiiy-Mauiyraau rreaa rcetaicotniosn os fo 2f ,24,-4d-dibibrroommoo--11--mmeetthhyyl-l5-5-n-nitirtor-o1-H1-Him-iimdaizdoalze o(2le). (2).
regioselectivebis-Suzuki-Miyaurareactionsof2,4-dibromo-1-methyl-5-nitro-1H-imidazole(2).
The seTqhuee snetqiaule onntiael- ponoet -tpwoto t-wstoe-ps tbepis b-Sisu-Szuuzkui-kMi-Miyiayuaurara r reeaaccttiioonnss ooff ccoommppoouundn d2 w2 ewree rsetu sdtuieddi uedsi nugs ing
Thesequentialone-pottwo-stepbis-Suzuki-Miyaurareactionsofcompound2werestudiedusing
phenylpbhoernoynlbico raocniidc aacnidd a4n-md e4t-hmoexthyopxhyepnhyelnbyolbroornoinc ica caicdid u unnddeerr mmiiccrroowwaavvee i rirrardaidaitaiotnio. nP.h Penhyelnbyolrboonirco nic
acpihde ncayanclib dbo erco anenx icbpeea ccetixedpdae cnttode d4r e-toma crete tahsceotl xesycetplievhceteilnvyey lalybt oattrh otenh eiCc C-a4-c 4ip dpouossnititdiiooennr,, mwwiicittrhho wtthhaee v seusubirsbresaqeduqieuanteti noatnd .adPdithdioeintni oyonlfb 4oo-rf o4n-ic
acid mcaenthobxeypehxepneyclbteodrontoic arceiadc lteasdeilnegc ttiov reelayctiaotn taht etheC C-4-2 ppoossiittiioonn o,f wcoimthpotuhned s2u (bTsaebqleu 3e)n. t addition of
methoxyphenylboronic acid leading to reaction at the C-2 position of compound 2 (Table 3).
4-mTehtheo fxiryTsphte hs eftienrpsyt l wsbtoeaprso wpneiacrsf aopcreimrdfoelredma idendi n tihgne tt hoperr eepsareecsnteiconenc eoa fot fpt phhheeenCny-yl2lbbpoororoosnnitiiicco anaccioiddf ( c1(o1.3m. 3e pqeouquiuvni.)vd, .P)2,d P((TOdaA(bOcle)A2 3(c0))..20 (40 .04
Teqhueivfi.)r, sNtas2tCeOp3 w(3 aesqupive.r)f ionr DmMedE/EintOtHh/eHp2Ore (s3e/1n/c1e) aot f60p °hCe unnydlbeor rmoincricowaacvide ir(r1a.3diaetqiouni vf.o)r, 2P hd. (IOn Ac)
equiv.), Na2CO3 (3 equiv.) in DME/EtOH/H2O (3/1/1) at 60 °C under microwave irradiation for 2 h. In 2
(0.04tehqeu sievc.)o,nNda steCpO, th(e3 reeaqcutiiovn.) winasD cMarrEi/edE otOutH w/iHthoOut (a3d/d1i/tio1n) aotf 6a0 p◦aCllaudniudme rcamtailcyrsotw anadv eini rprraedseiantcieo nfor
the second step, th2e re3action was carried out withou2t addition of a palladium catalyst and in presence
2h. Ionf t4h-meseethcooxnydphsetenpy,lbtohreonreica acctiiodn (1w.3 aesquciavr.r),i eNda2oCuOt3w (3i tehqouuivt.)a adtd 6i0t i°oCn uonfdaerp mailclarodwiuamve cirartaadliyastitoann din
of 4-mefothr o1 xhy, gpihveinngy tlhbeo eroxpneicc taecdi ddi (s1u.b3s etiqtuutievd. )i,m Nidaa2CzoOle3 6( 3in e mquoidve.r)a atte 6y0ie °ldC ( u22n%d,e Tr ambliec r3o, ewnatrvye 1 i)r. rTahdeisaet ion
presenceof4-methoxyphenylboronicacid(1.3equiv.),Na CO (3equiv.) at60◦Cundermicrowave
for 1 h,c ognivdiintigo ntsh de iedx npoetc atleldow d ais cuobmstpilteuttee cdo nimveirdsaiozno olef t6h ien i nmteordm2eerdait3aet ey cioemldp (o2u2n%d, 3Taa, bwlhe i3ch, e rnemtryai n1s). t Theh ese
irradiation for 1 h, giving the expected disubstituted imidazole 6 in moderate yield (22%, Table 3,
conditimonajso rditiyd pnrootd aulclto wwi tah cao ymiepldle otfe 4 c7o%n.v Aedrsdiionng oPfd t(hOeA icn)2t e(0rm.04e edqiautive .c) oinm thpeo suencodn 3da s, tweph iincchr eraesmeda itnhse the
meanjotrryityy1ie )pl.drT oohdf eucoscemt wcpoointuhdn diat iy6o itneols d3d0 o%idf 4(nT7ao%bt.la eA l3ldo, edwnintargyc P2o)dm. (POpelrAefotcer)m2c (io0nn.g0v 4teh eresq riuoeainvct.o)io finnt h ateht 1ei1 ns0te e°crCom nindecd rsietaeatspee dicn otchmree payosieeulddn dth3ea ,
yiwelhdi cohoff r cecoommmappinoosuuntnhdde 66m t otao j4 o30r%0i%t y(T (paTrbaolbed lu3e,c 3etn,w terniytth 3ry)a. I2yn)it.e ePlrdeesrotfifon4rgm7ly%i, n.ugAs itndhgde iP nrdeg(aPPcPtdhio(3O)n4 A (a0ct. 0)1241 (e00q .°u0C4iv ei.)nq ocurri evaa.d)sdeiindn gtth hoeen slyyei ceoldn d
ofs tceopmiPnpPcohrue3 na(d0se. 16d ettoqhu e4i0vy%.)i e il(ndT atohbfel ceso e3mc, oepnnodtu rsynt ed3p)6 . lIetnodt 3etro0e %sctoi(mnTgapbllyelte,e u 3cs,oiennngvte rPrysdi2o(P)n.P Pohfe3 )rt4hf o(e0r m.i0n4tien regmqtuehdiveia.r)te eo ar3c ata idoandndian tgth1 eo1 n0ly◦C
increacsoerrdesthpoenydieinldg porfocdoumctp 6o uisnodlat6edto r4es0p%ec(tTivaebllye i3n, 6e0n tarnyd3 6).4%In tyeireeldstsi n(Tgalyb,leu 3si, negntPrides(P 4P ahnd) 5()0. .N04oteeq uiv.)
PPh3 (0.1 equiv.) in the second step led to complete conversion of the intermediate3 43a and the
oradtdhiant,g wohnelny thPeP rheac(t0io.1n eteqmupive.r)atiunrteh weasse rceodnudcesdt etop 9l0e °dCt, oinccoommpplleetete cocnovnevresirosnio onf tohfe tihneterinmteedrimateed iate
corresponding produ3ct 6 isolated respectively in 60 and 64% yields (Table 3, entries 4 and 5). Note
3a was observed (according to LC/MS analysis).
3a and the corresponding product 6 isolated respectively in 60 and 64% yields (Table 3, entries 4
that, when the reaction temperature was reduced to 90 °C, incomplete conversion of the intermediate

3a was observed (according to LC/MS analysis).
Molecules2017,22,1278 5of21
Molecules 2017, 22, 1278 5 of 21
and5). NToatbelteh 3a. tO,pwtihmeiznattihoen roef athcet isoencotnedm stpeepr oaft uthree ownea-psorte rdeguicoesedletcotiv9e0 b◦isC-S,uinzuckoim-Mpiyleatuerac roenavcteiorns.i onofthe
Molecules 2017, 22, 1278 5 of 21
intermediate3awasobserved(accordingtoLC/MSanalysis).

Table 3. Optimization of the second step of the one-pot regioselective bis-Suzuki-Miyaura reaction.
Table3.Optimizationofthesecondstepoftheone-potregioselectivebis-Suzuki-Miyaurareaction.

Entry Catalyst Temp (°C) 3a (%) 5 (%) 6 (%) 7 (%)

1 - 60 47 6 22 13
Entry Catalyst Temp(◦C) 3a(%) 5(%) 6(%) 7(%)
Entry2 Pd(OCAatca)2l y0s.0t4 equiv. Temp6 0(° C) 3a 3(%5 ) 5 (6% ) 6 3(0% ) 71 (6% )
1 - 60 47 6 22 13
2 1 3 Pd(OPdA(Oc)A2c0)-.2 0 04.0e4q ueqivu.iv. 616010 0 4271 35 66 6 4202 11353 0 16
3 Pd(OAc) 0.04equiv. 110 21 6 40 15
2
4 2 4 PdP(dPP(PdOh(AP3P)c4)h203 )0.40. 0044.0 ee4qq euuqiiuvv.i.v . 611011 00 35- - 68 8 6300 11686 0 18
5 PPh 0.1equiv. 110 - 12 64 10
3
3 5 Pd(OPAPch)23 00..01 4e qeuquivi.v . 111100 21- 162 6440 1105
InaIdnd aidtidoint4i, otnh,e thuPesd eu(PsoPef ho43f)- 44m 0-.me0t4eh teohqoxuxyivyp.p hheennyyllbb1oo1rr0oo nniicc aacciidd ini-n ththe efifirsrts8 st tsetpe pana6dn0 p dhpenhyel1nb8yo lrboonrico nacicida icni din
thestehceo snedcosntde ps5tge pa vgeavthe etPhcPeoh cr3 or0er.1rse pesqopunoidnvi.d ninggp prorodduu1cc1tt0 66 aa iinn bbeetttteer-r yyieieldld (7(1712%1 %, S,cShceh6m4e me 2e).2 )1.0
In addition, the use of 4-methoxyphenylboronic acid in the first step and phenylboronic acid in
the second step gave the corresponding product 6a in better yield (71%, Scheme 2).

Scheme2.One-potregioselectivebis-Suzuki-Miyaurareaction.
Scheme 2. One-pot regioselective bis-Suzuki-Miyaura reaction.
WithWoitpht imopitziemdizceodn dciotniodnitsioenstsa beslitsahbelidsh,ethde, sthcoe psecoopfeth oefo nthee- poonter-epgoito sreelgeicotsievleecbtiivs-eS ubzisu-Skui-zM ukiyi-aura
Miyaura reaction was explored using a variety of (hetero)arylboronic acids. We chose 4-methoxy-
reactionwasexploredusingavarietyof(hetero)arylboronicacids. Wechose4-methoxy-phenylboronic
phenylboronic acid for the first step and different boronic acids for the second step (Table 4). This
acidforthefirststepaSncdhedmifefe 2r.e Onnteb-poorot rneigcioasceildecstifvoer btihse-Ssuezcuokni-dMsiyteaupra(T raebacletio4n).. Thisapproachenabled
approach enabled a broad range of (hetero)arylboronic acids bearing an electron-donating or
a broad range of (hetero)arylboronic acids bearing an electron-donating or withdrawing group to
wiWthidthra wopintigm girzoeudp ctoo nbde iutisoends u nesdtearb slitsahnedda,r dt hceo nsdciotipoen so, af ntdh ep roonveid-pedo tt hree gdiiosuseblsetcittuivteed b imis-iSduazzoulkei -
be used under standard conditions, and provided the disubstituted imidazole derivatives 6a–j in
derivatives 6a–j in moderate to good yields (Table 4, 50–71%).
Miyaura reaction was explored using a variety of (hetero)arylboronic acids. We chose 4-methoxy-
moderatetogoodyields(Table4,50–71%).
In view of these encouraging results, we then turned our attention to the sequential one-pot
phenylboronic acid for the first step and different boronic acids for the second step (Table 4). This
rIengiovsieelwectoivfet hSeuszeukein-Mcoiuyaraugrain/Sgonroesguaslthsi,raw reeatchteionn toufr n2,e4d-doiburromatot-e1n-mtioenthytol-5t-hneitrsoe-q1uHe-nimtiiadlaozonlee- pot
approach enabled a broad range of (hetero)arylboronic acids bearing an electron-donating or
regio(2s)e. leHcativviengS uozputikmi-iMzeidy aruearact/ioSno ncoognadsihtioirnas refoarc ttihoen orefg2i,o4s-edleibctriovme oS-u1z-umkei-tMhyiyl-a5u-rnai trcoo-u1pHli-nigm, iwdaez ole
withdrawing group to be used under standard conditions, and provided the disubstituted imidazole
(2). Hdeacvidinegd otop dtiemviezloedp trheea cotnioen-pcoot nSduiztuiokni-sMfioyratuhrea/rSeognioogsealsehcitriav seeSquuzenuckei.- Miyauracoupling,wedecided
derivatives 6a–j in moderate to good yields (Table 4, 50–71%).
todeveloTphuths,e boanseed-p oont Sthuez uaklrie-aMdyiy oaputriam/iSzoedn orgegaisohsierlaecsteivqeu eSnuczeu.ki-Miyaura reaction conditions and
In view of these encouraging results, we then turned our attention to the sequential one-pot
thTeh uclsa,sbsiacsael dcoonnditthioenas lfroera dSyonoopgtaismhiirzae drearectgioions, ewleec tpivreepSaurezdu kthie-M diiysuabusrtaitureteadc t5io-nnitcrooinmdiidtiaoznolse and
regioselective Suzuki-Miyaura/Sonogashira reaction of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole
the cdlearsivsiactaivlec 8oan fdroitmio n4-smfeotrhoSxoynpohgeansyhlbiroarorneiacc atcioidn a,nwde etphryenpyalbreednztehnee (dSicshuebmstei t4u).t eTdhe5 f-inrsitt rsoteimp widaasz ole
(2). Having optimized reaction conditions for the regioselective Suzuki-Miyaura coupling, we
deripveartfiovrem8eadf rionm pr4e-smenecteh ooxf y4p-mheetnhyolxbyoprhoennicylabcoirdonaincd aceitdh y(1n.y3 lebqeunizve.)n, eN(aS2cChOe3m (e3 3e)q.uTivh.e), fiPrds(tOsAtecp)2 was
decided to develop the one-pot Suzuki-Miyaura/Sonogashira sequence.
perf(o0r.m04e edquinivp.) riens ean mceixotufr4e -omf eDthMoEx/yEptOhHen/Hyl2bOo (r3o/n1/i1c) aucnidde(r1 .m3iecrqouwiva.v),e NirraadCiaOtion(3 foerq u2 ihv .)a,t P60d (°OCA. c)
Thus, based on the already optimized regioselective Suzuki-Miyaura2 reac3tion conditions and 2
(0.04Aefqteur icvo.)oliinnga, methixytnuyrlebeonfzDenMe E(1/.3E etOquHiv/.)H, PPOh(3 3(0/.11 /e1q)uuivn.)d, CerumI (0ic.1ro ewquaivve.) iarnrdad Eita3Ntio (n2 efqouri2v.h) water6e0 ◦C.
the classical conditions for Sonogashira rea2ction, we prepared the disubstituted 5-nitroimidazole
added and the mixture was heated again under microwave irradiation for 1 h at 70 °C. This sequence
Adfteerlrievdcao ttooivl itenh 8eg a,d efertsohirmyend 4y c-lmobmeentphzooeuxnnyedp( h81a.e3 niney qlgbuooiorvdo.) n,yiPiceP ladhc i3(d6(7 0a%.n1)d ea eqntudhi ycvon.)my,lCpbuoeunInz(0ed.ns1 e7e (qaSnucdhiv e9.m) inaen 14d1).% ET tah3nNed f i(1r20st%e qs tyueiipevl .dw)swa, se re
adpdererfedosrpamencedtdivt hienely mp (Sriecxshteuenmrceeew 3o)af. s 4h-meaettehdoaxgypaihnenuynldbeorromniiccr oawcida v(e1.i3r reaqduiaivti.o),n Nfoa2rC1Oh3 a(3t 7e0qu◦Civ..)T, hPisd(sOeqAuce)2n ce
le(d0.0to4 tehqeTuhdivee. )ss iicrnoe pdae c mooimfx tptuhoriesu noSdfu Dz8uaMkiiEn-M/gEiotyOoadHur/yaH/iSe2oOldn o((36g/7a1s%/h1)i)r aaun nsddeeqcrou memnpicceor ouwwnadasvs et7h iaernrna ddini9avitenisotn1ig1 fa%oter ad2n udhs 1aint0 g%6 0t yh°ieCe l. ds,
reAspftoeepcr ttciimvooeillzyiend(gS ,p cehrtohecymendeyu3lrb)e.e. nWzeen ew (e1r.e3 epqleuaisve.d), PtoP ho3b (s0e.r1v eeq uthiev .)f,o CrmuaI t(i0o.n1 eoqfu tihve.) dainsdu bEstt3iNtu t(e2d e qimuiivd.a) zwoeler e
adddTeedhri evaanstdicv otehpse e8 mao–ifjx ittnuh rmies owSdauesrza huteek atiot-eM gdoi ayogadau yirniae u/ldnSsdo wenrho megnai c4srh-omiwreatahvsoeex qiyrupreahndeicnaeytilbowonar fosonrti hc1 e ahnc iadti nw7v0a e°ssC uti.s gTeadht ieisnd s tehuqesu fieinrnsgct et he
olpetdi m toi ztehde dpersoicreedd ucorem.pWouendw 8eare inp gleoaosde dyietold o(6b7s%er)v aentdh ceofmorpmouantidosn 7o afntdh 9e idni 1su1%bs atintudt 1e0d%i myiiedldasz,o le
dreersivpaetcitviveesly8a (–Sjchinemmeo 3d)e. ratetogoodyieldswhen4-methoxyphenylboronicacidwasusedinthefirst
The scope of this Suzuki-Miyaura/Sonogashira sequence was then investigated using the
optimized procedure. We were pleased to observe the formation of the disubstituted imidazole
derivatives 8a–j in moderate to good yields when 4-methoxyphenylboronic acid was used in the first
Molecules 2017, 22, 1278 6 of 21
Molecules 2017, 22, 1278 6 of 21
step and various terminal alkynes in the second step (Table 5). Both electron-poor (compounds 8c, 8h
anstde p8 ia) nadn dva erlieocutrso tner-mricinha (lc aolmkypnoeusn ind st h8eb s, e8cdo nadn dst 8epf) (sTuabbsltei t5u).e Bnotst ho nel eacrtyrlo anl-kpyonoers ( caorem wpoeulln tdosle 8rca,t 8edh .
Molecules2017,22,1278 6of21
MIonlaetcneudrlee s8s 2ti0i)1n a7g,n l2dy2,, e1tl2he7ci8s t rsotnra-rtiecghy ( cwoamsp aoluson dtos l8ebra, n8td t aon cdy 8clfo) aslukbyslt iatlukeynntse so n(c oarmypl aoluknydnse s8 aer ae nwde l8lj t)o a6l enorfd a2 t1te od .a
Interestingly, this strategy was also tolerant to cycloalkyl alkynes (compounds 8e and 8j) and to a
hydroxyl moiety (compound 8g).
stespteahpny dadnvrdoa xvryiaolr uimosuotsiee rttemyr mi(ncioanmlaalp lakoluyknnyndese 8sig ni)n.t hthees seeccoonndd sstteepp ((TTaabbllee 55)).. BBootthh eelelecctrtoronn-p-poooor r(c(ocmompopuonudnsd 8sc8, 8c,h8 h
and 8i) and electron-rich (compounds 8b, 8d and 8f) substituents on aryl alkynes are well tolerated.
and8i)andelectron-rTicahbl(ec o4.m Scpoopue nodf osn8eb-p,o8td reagniodse8lfe)ctsivueb bsitsi-tSuueznutksi-oMniyaaruyrlaa rlekaycntioens. aa rewelltolerated.
Interestingly, this strTataebgley 4w. Sacso pales oof toonlee-rpaontt r etog iocsyeclleocatilvkey bl ias-lSkuyznueksi -(Mcoiymauproau rneadcst io8ne. aa nd 8j) and to a
Interestingly, thisstrategywasalsotoleranttocycloalkylalkynes(compounds8eand8j)andtoa
h ydroxyl moiety (compound 8g). H3CO
hydro xylmoiety(compound8g). H3CO
Br
TaTbalebl4e. 4S.c SocpoepeoB forof noNne-ep-poottr 1er)eg4gi-CoioHs3seOelPelehcBct(tiOivvHee)2 bb(1ii.ss3--eSSquuuizzv)uukkii--MMiiyyaauurraa Nrreeaacctitoionn. .a a
OBO2rN2N22 CNCNHHN33BBrr 221)))RR42-B2CB(HO(O3HOH)2P)2h(1(B1.(3.O3eHeqq)u2uivi(v1)).3equiHv)3CO 66OaOa--22jjNN NCNCHHN33 RR22
CCoommppoouunNndd 1)4-CH3OPhB(OHRR)222(1.3equiv) YYNiieelldd ((%%))
O2N66626baba CNH3 Br 2)R2B(OH)p2p-(-1((.FC3FC)e6)-q6H-CHuCiv56)56 H H44 6Oa-2jN NCH3 R777721010
ComCpooumndpo66ucc n d pp--(R(CC2Rll))2--CC66HH44 Yield (66%00Y )ield(%)
6a 6a6 6dd mm--C((NN6CHO6OH52 2)5)--CC66HH44 71 6655 71
6b 6b6 6ee mm, ,m pm-,( ,pFp -p(-)-F-((CO)O-C6CHC6HHH4 433))--CC66HH22 70 5500 70
666dec 66dc666 6h6gfg f mm,np-mma-mp(mp(N,pp--C--p((--h((NOC(-l(CCC()tCOOH2-hlHF)C)FC2-a-33CC)336))Hl-))H--eC6--6CC3nHHCC64) 66-H-6644HHC2HH 4-644y44H l2 6605 5565586186 665050
6f 6e 6h m, m,n pma--p((OChCFth3H)a-lC3e)6-nHC-246H-y2l 50 61 58
6g 6f6 6i i 55--mmme-ept(th-Ch(yCFylH3lt)th3-hC)ii-ooC6pHp6hHh4 ee4nn--22--yyll 58 5522 56
6h 6g6 6j j p-n(aC3p3H-h-ptp3hy)y-arCrlieid6dnHi-in2n4-e ey l 56 6699 61
6i 5-methylthiophen-2-yl 52
a Ra Reaecatciotino nc ocnodnidtiitoi6nojns:s S: St6ethepp 1 1: :4 4-m-meeththooxxyypnphahepenhnyt3ylh-lbpbaoyolrerroiondnn-ii2nicc- e ayaccli idd ((11..33 eeqquuiivv..)),, PP6dd1(( OOAAcc))622 9((00..0044 eeqquuiivv..)),, NNaa22CCOO33
(3( 3e qeuqiuvi.v),. )D, DMMEE/E/EtOtOHH6/Hi/ H2O2O ( 3(3/1/1/1/1)5,) ,M- MmWWet, h,6 6y00 l° t°ChC,i ,o2 2p hhh;; e SSnttee-p2p - 22y:: l b boorroonniicc aacciidd5 2((11 ..33 eeqquuiivv..)),, PPPPhh33 ((00..11 eeqquuiivv..)),,
aDRMeEaNc/tNiEao2tnaCO2cCOHonO3/ d(H3i3 t(i2 3oeO nqesuq(:3uiS/vit1v.e)/p.,) 1M,1 )M,:WM46W-jm,W ,1 e,11t610h00 o° ◦xC°CCy,,p ,1 2h1 heh hn.; .yS ltbeopr32o:-npbicoyrarociniddiicn(1ae.c3 ideq(1u.i3v.e),qPudiv(.O),APcP)h236(0(90.0 .14eeqquuiivv..)),,NNaa22CCOO33((33eeqquuiivv..)),,
MWa ,R1e1a0ct◦iCon, 1cohn.ditions: Step 1: 4-methoxyphenylboronic acid (1.3 equiv.), Pd(OAc)2 (0.04 equiv.), Na2CO3
(3 equiv.), DME/EtOH/H2O (3/1/1), MW, 60 °C, 2 h; Step 2: boronic acid (1.3 equiv.), PPh3 (0.1 equiv.),

Na2CO3 (3 equiv.), MW, 110 °C, 1 h.

SSchchememee 3 3. .O Onnee-p-poot tr reeggioiosseeleleccttiivvee SSuuzzuukkii--MMiiyyaauurraa//SSoonnooggaasshhiirraa rreeaaccttiioonn..
Scheme3.One-potregioselectiveSuzuki-Miyaura/Sonogashirareaction.
TTabablele 5 5. .S Sccooppee o of ft hthee o onnee--ppoott S Suuzzuukkii--MMiiyyaauurraa//SSoonnooggaasshhiirraa rreeaaccttiioonn.. aa
Table5.Scopeoftheone-potSuzuki-Miyaura/Sonogashirareaction.a
Scheme 3. One-pot regioselective Suzuki-Miyaura/Sonogashira reaction.

HH33CCOO
Table 5. Scope of the one-pot Suzuki-Miyaura/Sonogashira reaction. a
BrBr
NN 11))44-M-Meeththooxxyypphheennyylblbrroonnicicaaccidid NN

OBO2rN22N2 CNCNHH33BBrr 22))RR33 HH H3CO O8O8aa22-N-Njj NCNCHH33 RR33
Com88pCObaoC2oNu2omnmd88pCN88bpaHNoba 3 ou uBnrndd 12))4R-3MethoxymmpHmh-e-(-n(C(yCClCbHCHrCRHo6R36nRH63H3)icH33-)3)5C-a-5Cc5 C6i dH66HH444 O8a2-Nj NCHN3 YYRii3eell7676Ydd4747i e ((%l%67d74))(%)
C888odecm8pao88 88ducdc n d ooo---(((CCCHHmHmm33-c-3))-fflCy)--flp-ucpRlu6pu-lHo-o(o3-(Oor(pOr5oOr Ceo-oCnCC-H-tC6HCyH3H6l)63H-3H4)C)--46C4C H66H3H33 Yiel6d7 (5555%3939 )655093
8f 8b8 8ee mp--((tcCecryyHtc-cbl3lou)o-ptCpyele6)nHn-Ctty4y6 lHl 4 74 6600 63
888hgi 888dec88 88gfg f o-(CHmpp-c3--()ymf(ot-ltec-pu-ecrcl-rhootCCh(tC-lOprl-HobHoboHeruCr2u-on2oOC2tO-Ht-OtyCCyHy6Hl3H6Hl6)l))H H-- -4C CC 44666HHH344 655039 65651313 655121
8j cyclopropyl 63
8f p-(tert-butyl)-C6H4 63
aReactionconditions:Step1:84g-m ethoxyphenylboronCicHa2cOidH(1 .3equiv.),Pd(OAc)2(501.0 4equiv.),Na2CO3(3equiv.),
DME/EtOH/H2O(3/1/1),MW,60◦C,2h;Step2: alkyne(1.3equiv.),PPh3 (0.1equiv.),Et3N(2equiv.),CuI
(0.1equiv.),MW,70◦C,1h.
Molecules2017,22,1278 7of21
2.2. AntimicrobialActivity
Theantimicrobialactivityofthenewlysynthesizedproductswasevaluatedagainstanaerobic
Gram positive bacteria of the genus Clostridium and Bacillus. They were also evaluated for their
antiparasiticactivityagainstT.vaginalis. Metronidazole(mtz)wasusedascontroldrugtoevaluatethe
potencyofthetestedcompoundsunderthesameconditions.
2.2.1. AntibacterialActivity
Antibacterial activity was determined by the disc diffusion method, according to European
committeeonAntimicrobialSusceptibilityTesting(EUCAST)recommendations[62]. Wefirstscreened
the 27 molecules synthesized for their antibacterial activity against C. butyricum, C. perfringens,
C. neonatale, C. difficile, B. circulans and E. coli. The observed data on the antibacterial activity of
the3seriesofcompoundsarereportedforcompounds3a–3iinTable6,forcompounds6a–6jinTable7,
andforcompounds8a–8jinTable8. Moleculesareconsideredactivewhentheinhibitiondiameteris
largerthan20mm,andveryactivewhenitislargerthantheinhibitiondiameterofmetronidazole.
Table 6. Antibacterial activity of molecules 3a–3i obtained with the first regioselective
Suzuki-Miyaurareaction.
Compounds
BacterialSpecies
3a 3b 3c 3d 3e 3f 3g 3h 3i mtz
C.butyricumNec0 14 38 0 26 18 14 27 21 0 >30
C.perfringens >20 0 0 0 0 0 0 0 0 <20
C.neonatale 25 29 14 >20 24 28 30 25 22 32
C.difficile >20 31 15 10 25 28 23 29 32 >20
B.circulans 0 0 0 0 0 0 0 0 0 <20
E.coli 0 0 0 0 0 0 0 0 0 0
Inhibitionzonediameter(mm).
Table 7. Antibacterial activity of molecules 6a–j obtained with the one-pot regioselective
bis-Suzuki-Miyaurareaction.
Compounds
BacterialSpecies
6a 6c 6d 6e 6g 6h 6i 6j mtz
C.butyricumNec0 24 20 29 14 0 0 25 >20 >30
C.perfringens 0 0 0 0 0 >20 0 0 <20
C.neonatale 22 >20 >20 >20 14 0 >20 >20 32
C.difficile 23 12 14 14 16 13 0 15 >20
B.circulans 0 0 0 0 0 0 0 0 <20
E.coli 0 0 0 0 0 0 0 0 0
Inhibitionzonediameter(mm).
Table 8. Antibacterial activity of molecules 8a–j obtained with the one-pot Suzuki-Miyaura/
Sonogashirareaction.
Compounds
BacterialSpecies
8a 8b 8c 8d 8e 8g 8h 8i 8j mtz
C.butyricumNec0 0 25 0 0 17 17 8 18 23 >30
C.perfringens 0 0 0 24 0 0 >20 0 0 <20
C.neonatale 11 >20 29 0 15 23 0 13 18 32
C.difficile 0 13 0 0 17 20 0 0 19 >20
B.circulans 0 0 0 0 0 0 0 0 0 <20
E.coli 0 0 0 0 0 0 0 0 0 0
Inhibitionzonediameter(mm).
Molecules2017,22,1278 8of21
Results show that none of the molecules tested, including metronidazole, were active on
facultative anaerobic bacteria (B. circulans) and aerobic bacteria (E. coli). Indeed, to be active,
5-nitro-imidazole compounds must undergo a reduction of their nitro group which can only be
carried out in an anaerobic environment [2]. If the molecules were active on aerobic bacteria, this
wouldsuggestanothermechanismofaction.
Fortheanaerobicbacteria,itwasobservedthatcompounds3b,3e–i(Table6),withabrominein
2-position,possessedanactivityonC.butyricumNec0,C.neonataleandC.difficileequivalentorhigher
thanthestandardmetronidazole. Ontheotherhand,compounds6a–j(Table7)withanarylgroupin
2-positionhadaloweractivitythancompounds3a–j. Onlycompound6awasactiveonC.butyricum
Nec0,C.neonataleandC.difficile. Compounds8a–j,thelastseries,withanalkynein2-position,hada
loweractivitythanthemoleculesofthefirsttwoseries(Table8).
The second step consisted in testing the most active molecules, 3b, 3e–i on other particularly
virulentbacteriasuchasB.cereus,C.beijerenckii,C.tetaniandC.difficile027(Table9). Thefirstresults
showedthatabrominein2-positioncouldimprovetheactivityofourcompounds,so,wedecided
totestthestartingcompound2withtwobromineatomsin2and4-position. Unfortunately,thislast
compounddidnotexhibitanyactivity(Table9). Whateverthenatureofthearylgroupin4-position,
themoleculeswithabrominein2-position(3b,3e–3i)hadpromisingactivityonC.butyricumNec0,
Nec 1, Nec 8 and on C. difficile O27. One of them, compound 3g, with a trimethoxyphenyl group
in4-position, exhibitedhigheractivityagainstC.butyricumNec8thanmetronidazole. Itwasthus
observedfromtheinvestigationonanaerobicbacteriascreeningdatathatthecombinationofabromine
atomin2-positionandanarylgroupin4-positionenhancedthecompounds’antibacterialactivities.
Table9.Antibacterialactivityofthemostpromisingmolecules.
Compounds
BacterialSpecies
2 3b 3e 3f 3g 3h 3i mtz
B.cereus 0 10.9 9.6 9.6 10.9 10.7 11.5 0
B.beijerenckii 0 0 0 9 0 0 0 11
C.butyricumNec0 0 29.4 24.6 26.7 30.4 27.6 30.2 31
C.butyricumNec1 0 32.8 27 29.8 32.2 29.3 34.1 34
C.butyricumNec8 0 31.3 24.8 27.8 34.5 27.8 32 30
C.tetani 0 0 0 0 0 0 0 56
C.perfringens 0 0 20 0 26 0 29 30
C.difficileO27 5.8 32.4 35 30.6 33.7 29.7 32.8 37
Inhibitionzonediameter(mm).
2.2.2. AntiparasiticActivity
Weselectedthesixmolecules3b,3e–3ishowingthemostpromisingactivitiesagainstanaerobic
bacteria,andassessedtheirtherapeuticinterestonT.vaginalisbydeterminingminimuminhibitory
concentration(MIC,Table10). WealsoperformedacytotoxicityevaluationviatheNeutralRedUptake
(NRU)toxicitytest[63]onCHO-K1ChineseHamsterOvarycells(ATCCCCL61)todetectcytotoxic
concentrationsof50%(CC ). Thisprocedureenabledustodeterminetheselectivityindexofthese
50
6compounds(Table10),allofwhichareshowntohaveasignificantlyhigheractivity,withlowerMICs,
thanmetronidazole. Ontheotherhand,theyhaveasignificantandhighertoxicitythanmetronidazole,
especiallyforcompounds3b,3fand3iwithmethoxyphenyl,fluorophenylorhydroxymethylphenyl
groupsinthe4-position.
Molecules2017,22,1278 9of21
Table10.AntiparasiticevaluationonT.vaginalis.
Compounds ActivityT.vaginalisMIC(µM) CytotoxicityCC (µM) SelectivityIndexa
50
3b 4.00 2.58 0.64
3e 4.07 - -
3f 1.04 1.72 1.65
3g 0.84 2.59 3.08
3h 1.05 3.59 3.42
3i 0.99 1.13 1.13
mtz 7.30 557.34 18.65
aSelectivityindexcalculatedaccordingtotheformula:IC50/MIC.
2.2.3. CytotoxicityEvaluation
Themoleculeswithanaryl(6a–j)oralkyne(8a–j)groupat2-positionshowcytotoxicityequivalent
tothatofmoleculeswithabrominein2-position(3a–i)(Table11). Thehomogeneityofthecytotoxicity
ofourmoleculesinthethreedifferentseriesshowstheimportanceofthesubstituentatthe2-position
oftheimidazolenucleus.
Table11.CytotoxicityevaluationonChineseHamsterOvarycells.
Compounds CytotoxicityCC (µM)
50
3a 1.89
3b 2.58
3d 1.87
3f 1.72
3g 2.59
3h 3.59
3i 1.13
6a 3.21
6c 1.41
6d 6.94
6e 0.90
6g 2.97
6h 0.83
6i 1.48
6j 1.24
8a 2.65
8b 1.33
8c 1.35
8d 0.43
8e 2.39
8g 0.27
8h 4.57
8i 2.73
8j 1.17
mtz 557.34
3. ExperimentalSection
3.1. GeneralInformation
MeltingpointsweredeterminedonBüchiB-540(BÜCHILabortechnikAG,Flawil,Switzerland)
and are uncorrected. Elemental analyses and HRMS were carried out at the Spectropole, Faculté
des Sciences et Techniques de Saint-Jérôme, Marseille. Elemental analyses were performed on
a EA1112 instrument (Thermo Finnigan, San Jose, CA, USA). HRMS spectra were recorded on a
Molecules2017,22,1278 10of21
QStarElite(AppliedBiosystemsSCIEX,FosterCity,CA,USA)spectrometer. PEGwasamatrixfor
HRMS.LC/MSanalyseswereperformedattheFacultédePharmaciedeMarseilleonanAccelaHigh
System®chainU-HPLCcoupledwithaThermoMSQPlus®simplequadrupole. AThermoHypersil
Gold® 50×2.1mmchromatographiccolumnwasused(SiO C18)with1.9µmdiameterparticles.
2
Analysisis8minrunning,withanMeOH/H Oeluentgradientfrom50/50to95/05. Both1H-NMR
2
spectra(250MHz,referenceCDCl δ=7.26,[d ]DMSOδ=2.50)and13C-NMRspectra(62.5MHz,
3 6
referenceCDCl δ=77.0,[d ]DMSOδ=39.7)wererecordedat24◦ConanARX250spectrometer
3 6
(Bruker, Wissembourg, France) in CDCl and [d ]DMSO solvents at the Faculté de Pharmacie de
3 6
Marseille. Solvents were dried by conventional methods. The following adsorbent was used for
columnchromatography: silicagel60(Merck, Darmstadt, Germany, particlesize0.063–0.200mm,
70–230meshASTM).TLCwasperformedon5cm×10cmaluminiumplatescoatedwithsilicagel
60F-254 (Merck) in an appropriate eluent. Microwave reactions were performed with an Initiator
microwave oven (Biotage®, Charlotte, NC, USA) using 2–5 mL sealed vials; temperatures were
measuredwithanIR-sensorandreactiontimesaregivenasholdtimes.
3.2. Chemistry
3.2.1. 2,4-Dibromo-1-methyl-5-nitro-1H-imidazole(2)
Firststep: toasolutionof4(5)-nitro-1H-imidazole(20g,177mmol),NaHCO (44.6g,3equiv.,
3
531 mmol) in water (120 mL) was added dropwise at 0 ◦C dibromine (27 mL, 3 equiv., 531 mmol)
and the reaction mixture was heated at 65 ◦C for 6 h. After cooling, the solution was poured into
bathofice. Ayellowprecipitateappearedandwasfiltered, washedwithwater(3 × 100mL)and
dried in vacuum drying oven (dessicator cabinet). The aqueous layer was extracted with ethyle
acetate(3×100mL)andtheorganiclayerwaswashedwithbrine(3×100mL),driedoverNa SO
2 4
and evaporated. Yellow solid was obtained and added to the precipitate to give 36.3 g (80%) of
2,4(5)-dibromo-5(4)-nitroimidazole.
Secondstep;toasolutionof2,4(5)-dibromo-5(4)-nitroimidazole(34g,126mmol)inDMF(80mL)
wasaddeddropwiseat0◦Cdimethylsulfate(13.1mL,1.1equiv.,138mmol)andthereactionmixture
was heated at 100 ◦C for 2 h. After cooling, the solution was treated with a saturated solution of
sodiumhydrogencarbonateat0◦C.Awhiteprecipitateappearedandwasfiltered. Onepartofthe
precipitatewassolubilisedinethylacetateandevaporatedafterfiltration.Theprecipitatenotdissolved
wasthe2,5-dibromo-1-methyl-4-nitro-1H-imidazole(1,38%,14g),M.p. 192◦C(lit.[26]204–205◦C).
1H-NMR (CDCl ): δ = 3.75 (s, 3H, NCH ) ppm. 13C-NMR (CDCl ): δ = 35.0 (NCH ), 106.7 (C ),
3 3 3 3 Ar
120.4(C )ppm(CNO wasnotvisibleundertheseconditions). Theaqueouslayerwasextracted
Ar 2
withethylacetate(3 × 100mL)andtheorganiclayerwaswashedwithbrine(3 × 100mL),dried
overNa SO andevaporated. Thecrudeproductwaspurifiedbycolumnchromatography[silica
2 4
gel,petroleumether/ethylacetate(9/1)andthe2,4-dibromo-1-methyl-5-nitro-1H-imidazole(2)was
obtainedin33%inyield(12.1g). M.p. 167◦C(lit.[42]160–161◦C).1H-NMR(CDCl ): δ=4.02(s,3H,
3
NCH )ppm. 13C-NMR(CDCl ): δ=37.2(NCH ),119.8(C ),126.4(C )ppm(CNO wasnotvisible
3 3 3 Ar Ar 2
undertheseconditions).
3.2.2. GeneralProcedurefortheRegioselectiveSuzuki-MiyauraCouplingReaction
A solution of 2,4-dibromo-1-methyl-5-nitro-1H-imidazole (2, 0.1 g, 0.35 mmol), boronic acid
(0.46mmol,1.3equiv.),Pd(OAc) (3mg,0.014mmol,0.04equiv.),Na CO (0.11g,1.05mmol,3equiv.),
2 2 3
inaDME/EtOH/H Omixture(3/1/1,5mL)washeatedat60◦Cundermicrowaveirradiationfor
2
2h. Aftercooling,60mLofwaterwereaddedandthesolutionwasextractedwithdichloromethane
(3×50mL).Theorganiclayerwaswashedwithwater(3×100mL),driedoverNa SO andevaporated.
2 4
Thecrudeproductwaspurifiedbycolumnchromatography[silicagel,petroleumether/ethylacetate
(9/1),(1/1for3i),cyclohexane/ethylacetate(9/1for3a)]andrecrystallizedfrompropan-2-ol.