molecules Review Synthetic Strategies for Dinucleotides Synthesis Lucie Appy, Crystalle Chardet, Suzanne Peyrottes andand Béatrice Béatrice Roy Roy * * Nucleosides & Phosphorylated EEffectors,ffectors, Institut desdes BiomolBiomoléculesécules MaxMax MousseronMousseron (IBMM),(IBMM), UMRUMR 52475247CNRS, CNRS,Universit Universitéé de Montpellier, de Montpellier, ENSCM, ENSCM, Campus Camp Triolet,us Triolet, cc 1705, cc Place 1705, Eug Placeène Eugène Bataillon, Bataillon, CEDEX 34095 5, Montpellier,34095 Montpellier, CEDEX France; 5, France; [email protected] [email protected] (L.A.);m (L.A.); [email protected] [email protected] (C.C.); (C.C.); [email protected]@umontpellier.fr (S.P.) * Correspondence: [email protected]; Tel.: ++33-4-6714387933-4-6714-3879 Academic Editor: György Keglevich Academic Editor: György Keglevich Received: 7 November 2019; Accepted: 25 November 2019; Published: 27 November 2019 Received: 7 November 2019; Accepted: 25 November 2019; Published: 27 November 2019 Abstract: DinucleosideDinucleoside 5′,5′ 5-polyphosphates0,50-polyphosphates (DNPs) (DNPs) are endogenous are endogenous substances substances that play important that play intra-important and extracellular intra- and extracellular roles in various roles biological in various processes, biological such processes, as cell proliferation, such as cell proliferation,regulation of enzymes,regulation neurotransmissio of enzymes, neurotransmission,n, platelet disaggregation platelet disaggregation and modulation and modulation of vascular of tone. vascular Various tone. methodologiesVarious methodologies have been have developed been developed over the past over fifty the years past fifty to access years these to access compounds, these compounds, involving enzymaticinvolving enzymaticprocesses or processes chemical orprocedures chemical based procedures either on based P(III) either or P(V) on chemistry. P(III) or P(V) Both chemistry. solution- phaseBoth solution-phaseand solid-support and strategies solid-support have strategiesbeen developed have beenand are developed reported and here. are Recently, reported green here. chemistryRecently, greenapproaches chemistry have approaches emerged, offering have emerged, attracting o ffalternatives.ering attracting This alternatives.review outlines This the review main syntheticoutlines thepathways main synthetic for the pathways preparation for theof preparationdinucleoside of 5 dinucleoside′,5′-polyphosphates, 50,50-polyphosphates, focusing on pharmacologicallyfocusing on pharmacologically relevant compounds, relevant compounds,and highlighting and highlighting recent advances. recent advances. Keywords: phosphorylation;phosphorylation; dinucleoti dinucleotides;des; organophosphorus organophosphorus chemis chemistry;try; mechanochemistry; mechanochemistry; dry dry eye syndrome; diquafosol; denufosol 1. Introduction Introduction Dinucleoside 5 ′0,5,5′0-polyphosphates-polyphosphates (DNPs), (DNPs), commonly commonly abbreviated abbreviated as as Np NpnnNs,Ns, are are essential to human biological systems [1,2]. [1,2]. They They contain contain two two ribonucleosi ribonucleosides,des, which are linked at the 5 ′0-position-position of their sugar moiety through n phosphate groups (Figure1 1).). O O B' B O P O P O O O O n O HO OH HO OH B, B' = Ade, Gua, Ura n = 1-6 PURINES PYRIMIDINES NH2 O NH2 O O 7 6 4 N 5 1 N 3 N NH 5 N NH NH 8 2 6 9N 4 N 2 N N NH O H H 2 N 1 N O N O 3 H H H Adenine (Ade) Cytosine (Cyt) Nucleobases BH Nucleobases Guanine (Gua) Uracil (Ura) Thymine (Thy) Figure 1. GeneralGeneral structure structure of natural dinucleoside 5 ′0,5-polyphosphates,5-polyphosphates and and canonical canonical nucleobases. nucleobases. Molecules 2019,, 24,, x; 4334; doi: doi: 10.3390/molecules24234334 www.mdpi.comwww.mdpi.com/journal/molecules/journal/molecules Molecules 2019, 24, 4334 2 of 27 Molecules 2019, 24, x 2 of 27 Historically,Historically, dinucleoside 5 5′0,5,5′-polyphosphates0-polyphosphates (i.e., (i.e., Ap Ap2A2 Aand and Up Up2U)2 U)were were first first isolated isolated by bychemists chemists [3]. [In3]. 1976, In 1976,E. Rapaport E. Rapaport and P.C. and Zamecnik P.C. Zamecnik brought brought to light to the light presence the presence of P1,P of4- 1 4 Pdiadenosine-5,P -diadenosine-5′-tetraphosphate0-tetraphosphate (Ap4A) (Apin mammals4A) in mammals [4]. The authors [4]. The assumed authors that assumed this dinucleotide that this dinucleotidecould have acould role in have cellular a role communication in cellular communication as a “signal asnucleotide”. a “signal nucleotide”.Later, Up4A was Later, the Up first4A wasendogenous the first endogenous dinucleotide, dinucleotide, possessing possessingboth purine both and purine pyrimidine and pyrimidine moieties, moieties,to be identified to be identified in living inorganisms living organisms [5,6]. Currently, [5,6]. Currently, 17 symmetrical 17 symmetrical or mixed or Np mixednNs have NpnNs been have isolated been isolated from human from humantissues tissuesand characterized and characterized [2]. DNPs [2]. are DNPs released are released into the intoextracellular the extracellular space from space different from di typesfferent of typescells, ofsuch cells, as platelets such asplatelets and endothelial and endothelial cells, where cells, they where stimulate they stimulateseveral cell-surface several cell-surface purinergic purinergic receptors. receptors.They have Theya strong have physiological a strong physiological and pathophysiological and pathophysiological impact on the impact cardiovascular on the cardiovascular system [2,7], systemand may [2, 7also], and interact may also with interact enzymes, with acting enzymes, as inhi actingbitors as inhibitors (e.g., kinases) (e.g., kinases)or substrates or substrates [8–11]. [Three8–11]. Threeclasses classes of enzymes of enzymes are known are known to catalyze to catalyze the the de degradationgradation of of dinucleotides dinucleotides [10–12]: [10–12]: symmetrically cleavingcleaving dinucleosidedinucleoside polyphosphate polyphosphate hydrolases, hydrolas asymmetricallyes, asymmetrically cleaving dinucleoside cleaving polyphosphatedinucleoside hydrolases,polyphosphate and hydrolases, dinucleoside and polyphosphate dinucleoside polyphosphate phosphorylases. phosphor Over theylases. years, Over DNPs the haveyears, gained DNPs increasedhave gained attention increased and theirattention therapeutic and their potential ther hasapeutic been potential revealed. has Likewise, been structuralrevealed. analoguesLikewise, havestructural been analogues developed have and somebeen ofdeveloped them are and drug some candidates. of them are drug candidates. Herein,Herein, wewe firstfirst describedescribe purinergicpurinergic signalling,signalling, i.e.,i.e., thethe rolerole ofof nucleotidesnucleotides asas extracellularextracellular signalsignal molecules,molecules, withwith a a focus focus on on the the P2Y P2Y receptor receptor subtypes subtypes that interactthat interact with dinucleotides. with dinucleotides. Then, we Then, present we thepresent synthetic the synthetic strategies strategies to obtain dinucleotides.to obtain dinucl Pyrophosphateeotides. Pyrophosphate bond formation bond has formation been addressed has been in someaddressed recent in reviews some andrecent book reviews chapters and [1, 13book–15 ].chap Theters current [1,13–15]. review The focuses current on methods review reportedfocuses foron themethods synthesis reported of dinucleoside for the 5synthesis0,50-polyphosphates, of dinucleoside especially 5′,5 those′-polyphosphates, of biological andespecially pharmacological those of interest.biological We and also pharmacological highlight recent interest. advances We in also the field,highlight such recent as green advances chemistry in the approaches. field, such It as should green bechemistry noted that approaches. methods It for should preparing be noted cyclic that dinucleotides methods for [16 preparing] are beyond cyclic the dinucleotides scope of this [16] review. are Furthermore,beyond the scope the synthesis of this review. of nicotinamide Furthermore, adenine the dinucleotidessynthesis of nicotinamide [17] and mRNA adenine cap analogues dinucleotides such 7 m[17]Gp andnN mRNA (see reviews cap analogues [18–20]) are such not m presented.7GpnN (see reviews [18–20]) are not presented. 2.2. Interaction of DNPs with Purine and Pyrimidine ReceptorsReceptors PurinergicPurinergic receptorsreceptors areare extracellularextracellular receptors, currently consisting of four subtypes of P1P1 (or(or adenosine)adenosine) receptors,receptors, seven seven subtypes subtypes of P2Xof P2X ion channelion channel receptors, receptors, and eight and subtypes eight subtypes of P2Y receptors of P2Y (Figurereceptors2). (Figure Specifically, 2). Specifically, P2Y receptors P2Y (P2YRs) receptors are G-protein-coupled(P2YRs) are G-protein-coupled receptors (GPCRs) receptors activated (GPCRs) by extracellularactivated by nucleotides,extracellular which nucleo aretides, divided which into are two divided groups into on two the basisgroups of on sequence the basis homology of sequence and thehomology type of and G protein the type they of areG protein primarily they coupled are primarily to [21– 23coupled]. to [21–23]. FigureFigure 2. The 2. classificationThe classification of purine of purine and pyrimidineand pyrimidi receptorsne receptors and theirand their main main physiological physiological agonists. agonists. Molecules 2019, 24, 4334