Physiologically, saccharides, including sugar molecules hence the Sweet in the rubric, are involved in extremely specific cellular events including cellular acknowledgment ( such as host-pathogen interactions ) , adhesion, cell growing ordinance, mounting of immune response, malignant neoplastic disease cell metastasis, fertilization and redness. By working one or more of these mechanisms, chemists have assembled a broad scope of structurally diverse polymeric unreal saccharide polymers ( glycopolymers ) as effecters or inhibitors of cellular procedures and analytical tools for look intoing carbohydrate-protein binding events. Man-made glycopolymers fundamentally function as mimics of of course happening polyoses, thereby exposing anti-inflammatory, anti-coagulant and anti-tumour belongingss.
Multiple coincident interactions ( polyvalence ) are normally found in nature and exhibit belongingss that are qualitatively different from belongingss than that of monovalent interactions. The construct of ‘multivalency ‘ , the coincident binding of multiple ligands on one entity to multiple receptors on another can ensue in a significantly increased affinity as compared to that for the binding of a individual ligand. These interactions have several mechanistic and functional advantages over their monovalent opposite numbers. Among these are the ability to make conformal contact between big biological surfaces, the ability to bring forth ranked responses with a individual type of interaction, and the ability to increase the specificity of an interaction.
Multivalent interactions can function as the strategic footing for the design of pharmaceutical agents, including agents that could perchance present polyvalent antigens to promote/boost immune cells in order to cut down the incidence of malignant neoplastic disease development.
Figure 1: Illustration of a monovalent and multivalent interaction between ligands and receptors.
Multivalent interactions are able to modulate the strength of an interaction through the figure of ligand-receptor contacts for such as carbohydrate-binding proteins known as lectins. Modification ( barricading or sweetening ) of protein-carbohydrate interaction provides a powerful curative scheme for the intervention of many human diseases. Surveies have shown that saccharide ligands inherently exhibit low affinity for their protein receptors, lectins. Lectins typically exist in multimeric assemblies, a assortment of polyvalent carbohydrate ligands have been prepared in the hunt for high affinity. Although the mechanism by which multivalent ligands act is still ill-defined it is progressively accepted that the bunch glycoside consequence relies on collection [ ref ] .The bunch glycoside consequence, represents the best scheme for get the better ofing the “ weak binding ” job. The overall consequence is the addition in adhering affinity to an extent which exceeds the amount of the component adhering events in sufficient strength to consequence or suppress a cellular or physiological response. ( ref ) . Lectins serve as a utile investigation in analyzing saccharides of cell surfaces, particularly the lectin Concanavalin A ( Con A ) which is widely researched. Surveies have revealed that the physiological responses of multivalent saccharide interactions with lectins include programmed cell death of T cells, ordinance of the T-cell receptors and cell cycling dynamicss and activities of cytokine receptors. ( ref ) .
Victimize A binds specifically to I±-Mannose, I±-Galactose constructions found in sugars, glycoproteins and glycolipids. The lectin has been utilized in endocrine receptor surveies, mitogenic checks and for qualifying normal and malignant cells as malignant neoplastic disease cells are readily aggregated by Con A while normal cells are non. Victimize A can besides originate cell division chiefly by moving on T-lymphocytes.
Polymeric systems, where a aggregation of similar or different ligands can be covalently linked together in polymer ironss, provides for a scaffold to lucubrate the construct of multivalent interactions. Con A has shown increased affinity for a man-made polymer of multiple mannose residues compared to its monosaccharide opposite number. Biessen and co workers showed that the affinity of human mannose receptor increased with a series of lysine-based bunch mannosides when the figure of mannose residues per molecules was increased from two to six ( ref ) , farther foregrounding the importance of multivalent interactions with lectins. Both Con A and galactins ( galactose-binding lectin ) cross-link cell surface receptors have been implicated in induction of signal transduction.
Figure 2: Conventional representation of Con A bunch by multivalent ligand ( glycopolymer ) F: Supriya LABDissertationcon A cluster.jpg
Man-made glycopolymers with biocompatible and biodegradable belongingss are used in tissue technology and controlled drug release devices. Carbohydrate-based vaccinums, such as tumour-associated saccharide antigens ( e.g. , sTn ) , are an active country of research.
Immune response to saccharides
It has been shown that antibodies that target tumour-related saccharide and glycopeptide antigens have the ability to extinguish go arounding tumour cells. These antibodies can be acquired by inactive immunisation ( i.e. immunisation with the antibody itself ) , or by active immunisation with a vaccinum that contains the saccharide antigenic determinant. The antibodies can besides be acquired of course.
Antibodies against tumour-associated saccharides can intercede riddance of tumor cells by complement-dependent cytotoxicity ( CDC ) and/or by antibody-dependent cellular cytotoxicity ( ADCC ) performed by natural slayer ( NK ) cells and macrophages. The antibodies have besides been shown to interfere with receptor-mediated signalling, adhesion, and metastasis.
Antibodies are produced by B-cells that have been activated with their blood relation antigen. The B-lymphocytes carry membrane-bound Ig proteins that can acknowledge a broad assortment of compounds. Carbohydrates can adhere to receptors of B-lymphocytes and bring on cross-linking of the Ig proteins, which will take to activation of the B-cell and production of low affinity IgM antibodies.
Development of man-made carbohydrate-based malignant neoplastic disease vaccinums
The biggest challenge of developing carbohydrate-based malignant neoplastic disease vaccinums by insulating saccharides from natural beginnings is that they are largely conjugated to a protein bearer by reductive amination through the aldehyde group of the cut downing terminal sugar. This can ensue in devastation of critical acknowledgment elements ensuing in a lessening or perchance complete loss of immunogenicity.
Man-made saccharides offer an advantage in that they can be designed to integrate a linker incorporating a functional group with alone responsiveness for selective junction to a polymer anchor, in a mode that does non interfere with the antigenic antigenic determinant.
Technology of man-made glycopolymers
Man-made glycopolymers incorporating pendent sugar medieties have been shown to interact multivalently with lectins in a similar mode to that of natural glycoproteins. This apery has caused important involvement in the Fieldss of saccharide chemical science and glycobiology, and a figure of different schemes have been employed to obtain the needed multivalent saccharide ligands. Mantovani and colleagues reported the usage of a fresh chink chemistry/living extremist polymerization scheme in order to fix a additive glycopolymer library incorporating saccharides attached pendantly. ( ref )
Extremist polymerization: General constructs
Extremist polymerization ( RP ) is a comparatively simple polymerization procedure and can be used to polymerize a broad scope of monomers. Conventional RP is histories for the production of over 50 % of all commercial polymers including Low denseness polythene, poly ( vinyl chloride ) , polystyrene and its copolymers ( with propenonitrile, butadiene, etc. ) , polyacrylates, polyacrylamides, poly ( vinyl ethanoate ) , poly ( vinyl intoxicant ) and fluorinated polymers. Extremist polymerization is used widely commercially particularly in industrial and personal attention sectors.
The active species, free groups, of extremist polymerization are typically sp2 hybridised and exhibit hapless stereoselectivity. However these free groups can be stabilized via resonance and consequence in polymers of good regioselectivity and chemoselectivity as evidenced by the general high grade of head-to-tail constructions in the concatenation and the formation of high MW polymers.
However, free extremist polymerizations are debatable in that they offer low uniformity of the polymer concatenation, ensuing in a high polymer polydispersity index with heterologic polymer ironss with changing molecular weights i.e. polymers do non exhibit architecture and hence no pure block copolymers can be formed. These unwanted belongingss are attributed to the general dynamicss of conventional extremist polymerization where high concentration of extremist species favours the rate of expiration over the rate of extension.
Recently, new methods have been developed that allow control over extremist polymerisation to understate monomer content and bring forth really unvarying molecules. This control can be achieved by a assortment of techniques including the usage of atom transportation extremist polymerisation ( ATRP ) , reversible addition-fragmentation concatenation transportation ( RAFT ) polymerisation and nitroxide-mediated polymerization ( NMP ) – jointly termed as ‘controlled extremist polymerization ‘ .
Controlled Extremist Polymerisation ( CRP )
CRP systems are reasonably similar to conventional extremist polymerizations in that polymeric groups grow and terminate with similar rate invariables. The chief difference lies in the manner in which the groups ( active species ) are generated. Precise formation of different polymer architecture is attributed to the minimisation of concatenation breakages and coincident growing of all ironss which is the consequence of about instantaneous induction. CRP incorporates a combination of fast induction and absence of irreversible expiration which serve to contrast with free RP, where polymerization returns via slow induction ensuing in many short and unequal turning polymer ironss.
Due to the controlled rate of growing of the polymer ironss, CRP allows for the formation finely tuned polymers of a scope of as shown in figure ___ ?
The bosom of all CRPs lies with the constitution of a dynamic equilibrium between extension groups and assorted hibernating species. Groups are either reversibly trapped in a deactivation/activation procedure or they may be involved in a degenerative exchange ‘reversible transportation ‘ ( figure? )
In an ideal life polymerization, there is no irreversible concatenation transportation for expiration as all ironss are initiated at the start of the reaction ; ironss grow at similar rates and survive polymerization. As compared to conventional extremist polymerization where induction is rapid with regard to extension, the molecular weight distribution is narrow and ironss can be extended by farther adding monomer into the reaction.
Principles of atom transportation extremist polymerisation ( ATRP )
The basic mechanism of ATRP involves a reversible shift between two oxidization provinces of a passage metal composite. The polymerization active species is generated through a reversible oxidation-reduction in a passage metal composite ( Mtn-Y/Ligand ) undergoes a one-electron oxidization with coincident transportation of halogen atom, X, from a hibernating species, R-X ( figure 2 ) . Polymer ironss turn by the add-on of monomer to the intermediate groups in a similar manner to conventional extremist polymerization.
Figure3: Basic mechanism of ATRP
The figure above high spots that the equilibrium is preponderantly shifted to the left or hibernating species in order to understate irreversible expiration and transportation reactions which are favoured in the presence of high concentrations of extremist species. Irreversible expiration ideally is limited to merely a few per centum of the polymer ironss. This little sum of expiration really serves to bring forth oxidized metal composites, X-Mtn+1, as relentless groups to cut down the stationary concentration of turning groups therefore minimising the part of expiration. Polymers formed from a successful ATRP by and large exhibits unvarying growing, guaranting a unvarying distribution of molecular weight which accounts for a low polydispersity index ( pdi ) . This is due to concatenation growing achieved by speedy induction and rapid but reversible inactivation. ( ref )
The chief disadvantage of ATRP is guaranting the complete remotion of the passage metal from the concluding polymer merchandise. Depending on the metal accelerator used, for illustration, utilizing Cu ( I ) bromide can be slippery as it is purely air sensitive and can be converted to Cu ( II ) bromide doing expiration of polymerization, ensuing in short and unequal polymer ironss.
Cobalt catalysed concatenation transportation polymerization ( CCCTP )
In the instance of metal-mediated ( such as Cu ) populating extremist polymerization ( ATRP ) the polymer concatenation carried a terminal halide atom which undergoes several activation-deactivation rhythms and is susceptible to side reactions taking to loss of polymer concatenation terminal unity. Thus it is disputing for polymer chemists to synthesise end functional polymers with high unity. Hence CCCTP is a versatile technique employed to bring forth end functional polymers whilst keep its fidelity and besides exhibit controlled molecular weight. This is because CCCTP employs Bi ( boron difluorodimethylglyoximate ) Co ( II ) ( CoBF ) which is accelerator in impersonal aqeous media that allows for polymerization of acidic monomers unsuitable for anionic polymerization and besides provides stableness.
Reversible Addition-Fragmentation concatenation Transfer ( RAFT ) polymerization
RAFT polymerisation is a reversible inactivation extremist polymerisation and one of the more robust and various methods for supplying populating features to extremist polymerization.1-7
In recent old ages RAFT polymerisation has emerged as a really attractive method for bring forthing polymers whilst supplying for control of molecular weight and molecular weight distributions with polydispersity indexes typically in the scope of 1.03-1.25. Its chief possible prevarications in its versatility towards the types of monomers it can polymerise, including styrenic, ( Methedrine ) acrylamides, ( Methedrine ) acrylates, acrylonitrile, vinyl ethanoates, vinyl formamide, vinyl chlorides every bit good as a scope of other vinyl monomers. ( ref )
This type of CRP is tolerant of unprotected functionality in monomer and dissolver, therefore polymerizations can be carried out in aqueous or protic media. RAFT polymerization is compatible with huge reaction conditions such as majority, organic/aqueous, emulsions and suspensions. It is one of the most easy to implement and besides cheap as compared to other CRP methods.
In RAFT polymerization, reagents that are capable of reversibly deactivating propagating groups are used so that the bulk of life ironss are maintained in a hibernating signifier. The reaction conditions support a rapid equilibrium between the active and hibernating species.
The sequence of addition-fragmentation equilibria is a cardinal characteristic of RAFT polymerization. Initiation and radical-radical expiration occur as in conventional extremist polymerization. Addition of propagating extremist ( PnI‡ ) to a concatenation transportation agent followed by atomization of the intermediate extremist gives rise of to a polymeric concatenation transportation agent and a new extremist – all occur during the early phases of polymerisation.The key to the RAFT polymerisation procedure is the concatenation transportation agent or besides known as RAFT agent.
Z-group controls the responsiveness of the
C-S dual bond ; influences the rate
of extremist add-on and atomization
RAFT agent – general construction
Free extremist go forthing group, R
( must be able to reinitiate polymerisation )
Chemical reaction of the extremist ( RI‡ ) with monomer signifiers a new propagating extremist ( PmI‡ ) . A rapid equilibrium between the active propagating groups ( PnI‡ and PmI‡ ) and the hibernating polymeric RAFT agent allows for equal chance for all ironss to turn and production of narrow dispersity polymers. Groups are neither formed nor destroyed in the concatenation equilibration procedure, hence one time the equilibria are established ; the rates of polymerization should be similar to that of conventional extremist polymerization. Surveies have shown that with some RAFT agents, RAFT polymerization is half order in instigator and zero order in the RAFT agent over a broad scope of instigator and RAFT agent concentrations.
Figure 3: The RAFT mechanismF: Supriya LABDissertationRAFT MECHANISM SCHEME.jpg
Nitroxide Mediated Polymerisation ( NMP )
Prior to the development of NMP, nitroxides were good known as inhibitors of polymerization. Nitroxides are able to expeditiously scavenge carbon-centred groups by uniting with them at near diffusion-controlled rates to organize alkoxyamines. These alone belongingss of nitroxides lead to its use as a pin downing agents to specify induction mechanisms. The development of alkoxyamines as polymerization instigators, NMP has grown in popularity for bring forthing block and end-functional polymers as first described in by Solomon et Al. With suited choice of alkoxyamine and control of reaction conditions, NMP resulted in synthesis of narrow dispersity polymers.
The implicit in rule behind nitroxides-mediated polymerization is the use of the nitroxides group to expeditiously crest the terminal of the turning polymer ironss by a reversible expiration reaction, guaranting equal growing of all polymer ironss and stamp downing unwanted expiration reactions. Alkoxyamines serves a double map in NMP reactions as an instigator and end-capping group. This gives full control over the concentration of originating groups in the reaction mixture. ( ref )
Figure 4: NMP mechanismF: Supriya LABDissertationPicture1.jpg
Figure 4 illustrates the NMP mechanism. The reaction begins with the hemolytic cleavage of the alkoxyamine upon heating to bring forth the originating extremist R3 I? and the stabilised I?ONR1R2 that is present long plenty for a monomer unit M to respond with R3 I? before recombination occurs. NMP reactions were really carried out at temperatures over 100aµ’C but late have besides been carried out at temperatures below this in aqueous media.
The alkoxyamine group can defy reaction conditions of other controlled-polymerisations such as RAFT and ATRP which allows for the synthesis of block co-polymers by uniting NMP with other techniques ( ref )
Ringing opening polymerization ( ROP )
ROP is non a portion of controlled life polymerization but is a concatenation polymerization technique that offers entree to a wider scope of cyclic monomers which could non be polymerised by other techniques. It is possible to command the molecular weight of polymers made via pealing opening polymerization due to its dependance on transition and the ratio of monomer to initiator concentration. It is of import to advert ROP as a polymerization technique as it can be used to fix polymers to later signifier biodegradable glycopolymers.
However, compared to command life polymerization this technique requires clip and attempt to bring forth a well defined polymer. Due to the sensitiveness of reactions it is necessary to guarantee that the reactants are non in any contact with H2O or air to avoid inactivation of ionic instigators, long reactions times and low temperatures. Hence this is non a popular method of polymerization to finally take to glycopolymer formation.
Each CRP technique has its restriction and advantages and some possibly more suited to polymerize different monomers or exhibit different conditions to optimise the polymerization procedure and is summarized in table ___
Most monomers with activated dual bonds
No vinyl ethanoate
Largely all monomers
Styrenes with 2,2,6,6-tetramethyl-1-piperidinyloxy ( TEMPO )
Large temperature scope ( -30 to 150aµ’C )
Less reactive monomers require elevated temperatures
Elevated temperature & lt ; 120aµ’C for Tempo
Some tolerance to oxygen
Sensitive to oxygen
Sensitive to oxygen
Either SN, E, or extremist chemical science for transmutations
Extremist chemical science for transmutations
Extremist chemical science for transmutations
Transition metal accelerator should be removed
May bring forth many new ironss
NMP possibly accelerated with acyl counpounds
Cheap and available
RAFT polymerizations can be carried out at temperatures which are typical for any extremist polymerization which is around 60-110aµ’C. ATRP is typically performed at temperatures runing from 20-120aµ’C. All three systems RAFT, ATRP and NMR are sensitive to oxygen but in peculiar ATRP as it employs the usage of metal accelerator, normally Copper, and O is quickly scavenged by metals than by turning groups. It is possible to execute ATRP in the presence of Cu ( 0 ) or Fe ( 0 ) even with limited sum of O and inhibitor nowadays in the system which highlights the influence of pick of metal accelerator used on the medium of ATRP to oxygen.
In ATRP a halogen is reversibly transferred to transition metal doing it exchangeable with other halogens which controls the construction and responsiveness of terminal groups and allows for the formation of block copolymers. NMP and ATRP can be initiated by conventional extremist instigators such as AIBN in the presence of nitroxides or metal halides with higher oxidization provinces. Additional additives need to be used in NMP unless reaction rate acceleration is required whereas RAFT depends on a extremist beginning and ATRP on a accelerator. The extremist instigators in RAFT may ensue in the production of excessively many new ironss and cut down concatenation terminal functionality if used in larger sums. In ATRP the metal accelerator should ideally be removed or recycled as even a minute sum of residuary accelerator can consequence polymer stableness and mechanical belongingss.
ATRP works optimally with low molar mass polymers with particular functionalities and besides can be used to fix block copolymers that are non easy synthesized via other techniques. RAFT works expeditiously with less reactive monomers and high molecular weight polymers. NMP works optimally with systems that require absence of metals and other elements such as Sulfur.
Part 2: CLICK chemical science
Click chemical science is a construct that was introduced by K. Barry Sharpless in 2001 which incorporates the coevals of substances both rapidly and faithfully by fall ining little units together via simple chemical science. Click chemical science itself is non a individual reaction but a restricted group of chemical transmutations which should ideally carry through a list of standards as defined by Barry Sharpless. The basic standard is that the reaction is broad in range, easy to execute, uses merely readily available reagents, insensitive to oxygen and H2O and relies on simple and efficient procedures – i.e. distillment or crystallization, for the purification of the concluding merchandises.
Table 1: Ideal ‘Click ‘ chemical science reaction standards
The reactions should ideally:
The procedure should ideally:
give really high chemical outputs
generate merely unoffending byproducts
be physiologically stable
exhibit a big thermodynamic drive force & gt ; 84 kJ/mol to favor a reaction with a individual reaction merchandise.
high atom economic system
have simple reaction conditions
usage readily available get downing stuffs and reagents
usage no dissolver or utilize a dissolver that is benign or easy removed ( sooner H2O )
provide simple merchandise isolation by non-chromatographic methods ( crystallization or distillment )
Several types of reaction have been identified that fulfil these standards, thermodynamically-favoured reactions that lead specifically to one merchandise, such as nucleophilic pealing opening reactions of epoxides and aziridines, non-aldol type carbonyl reactions, i.e. formation of hydrazones and heterocyclic compounds, add-ons to carbon-carbon multiple bonds, such oxidative formation of epoxides and Michael Additions, and cycloaddition reactions.
Given that a figure of reactions could perchance suit the basic chink standards, it is the 1,3-dipolar cycloaddition of acetylenes to azides to organize 1,4-disubsituted-1,2,3-triazoles that serves as the ‘perfect ‘ illustration of a click reaction. This reaction uses Copper ( I ) as a accelerator, does non necessitate protecting groups and in many cases the merchandise formed does non necessitate purification. The azide and alkyne functional groups are mostly inert towards biological molecules and aqueous environments and at ambient temperature merely respond with each other when an appropriate Cu accelerator is introduced. Hence the cycloaddition can be used for mark guided synthesis and activity based protein profiling. ( ref ) The triazole has similarities to the omnipresent amide mediety found in nature, but unlike amides, is non susceptible to cleavage and about impossible to oxidise or cut down.
The starting stuffs for the reaction such as monosubstituted acetylenes and organic azides are commercially available and many others can easy be synthesized embracing a broad assortment of functional groups, and their cycloaddition reaction selectively gives 1,2,3-triazoles.
Non CuI Huisgen 1,3-Dipolar Cycloaddition of acetylenes to azides requires elevated temperatures and produces mixtures of the two regioisomers when utilizing asymmetric acetylenes, therefore fails as a true chink reaction. A polish made by Sharpless et al introduced a copper-catalyst which allowed for the reaction to happen even at room temperature. Besides this copper-catalyzed reaction allows the synthesis of the 1,4-disubstituted regioisomers specifically, better following with the definition of click chemical science. The incorporation of the CuAAC procedure allows sugar monomers to be prepared with easiness by the debut of azide functionality. This reaction has now become the focussed chink reaction paradigm.
Figures 5 & A ; 6: Mechanism of the Copper-Catalyzed Azide-Alkyne Cycloaddition ( CuAAC )
F: Supriya LABDissertationhuisgen cycled mechanism.jpg
The Cu ( I ) -catalyzed cycloaddition between the azide and the alkyne returns through a stepwise mechanism as illustrated in figure 6. The mechanism starts by coordination of the acetylene ( B ) to Cu ( I ) ( A ) . This displaces one ligand and re-coordination gives the Cu acetylide ( C ) . This is so followed by the replacing of one of the ligands by the azide ( D ) and the Cu complex binds to the N adjacent to the C, organizing intermediate ( E ) . The terminal N on the composite ( E ) onslaughts on C-2 in the acetylide to organize a 6-membered Copper ( III ) intermediate ( F ) . Finally, rearrangement of the Cu ( III ) intermediate consequences in a 5-membered composite ( G ) which is so proteolysed to give complex ( H ) . ( ref )
Applications of click chemical science
The Huisgen 1,3-cycloaddition reaction catalysed by Cu ( I ) is now extremely recognized as 1 that is really efficient and besides stereoselective tagged with exceeding functional group compatibility. The belongingss of the reaction allow for exactly synthesized complex stuff including bioconjugates, dendrimers, therapeutics, functionalized polymers, affinity chromatogram supports and besides sugar derived functions.
Introduce non-pot path
A decennary ago formation of glycopolymer was disputing with limited efforts at responding a functional polymeric anchor with a saccharide. The ground being the trouble of presenting sufficiently reactive pendent groups onto the polmer anchor to make with saccharide. The alteration of poly ( vinylalchohol ) with 4-nitrophenyl carbonate groups to give a reactive polymer anchor was one successful effort at organizing glycopolymers. The reactive nitrophenyl carbonate groups were transformed with glucosamine into glycopolymers and were so investigated for their interaction with a normally used lectin, Concanavalin A ( Con A ) .
The one pot path to clickable scaffolds ( ref )
The one pot path in synthesising clickable scaffolds is utile in organizing functional polymers which can so be ‘clicked ‘ to saccharides, or more specifically, sugar molecules to organize the coveted glycopolymer. This procedure is the basic construct in possible majority formation of a saccharide -based malignant neoplastic disease vaccinum.
Figure 7: Illustration of a polymeric system with clickable functional unitsThe advantage in utilizing the one-pot path one is that libraries of different stuffs can be generated from one individual polymeric precursor. The functional polymers green goodss will exhibit the same macromolecular features which include the grade of polymerization, polydispersity index and besides polymeric architecture. Another benefit is that some molecules that exhibit functional groups that are incompatible with the conditions used to polymerize them. These conditions can possible toxicant the polymerization accelerator i.e. the accelerator is really be incorporated onto the polymer anchor. F: Supriya LABDissertationpolymer and clicklable scaffold.jpg
One path in synthesizing glycopolymers involves the one measure synthesis of a trimethylsilyl protected ( TMS ) propargyl methacrylate monomer. The monomer is polymerized via ATRP which is so followed by the deprotection which generates a reactive propargyl unit, turn outing a ‘clickable ‘ scaffold onto which a assortment of functional sugar azides can respond. This path of glycopolymer synthesis was optimized to cut down the figure of stairss required to synthesise sugar azides. This reaction makes it possible to bring forth a library of polymers all incorporating the same macromolecular features, the lone discrepancy is that the different sugars possibly chosen to be ‘clicked ‘ onto the polymer scaffold.
Using ATRP and click chemical science as the path for glycopolymer synthesis, Mantovani and colleagues reported a successful junction of glycopolymers to bovine serum albumen ( BSA ) , a glycopolymer mimic. This was shown to bring on immunological behavior via interaction with mannose adhering lectin. Glycopolymers formed via this path have successfully proven to demo biological activity.
Figure 8: Glycopolymer synthesis via clickable sugars ( sugar azide ) path
Adapted from: Slavin Stacy, Burns James, Haddleton David M. Synthesis of glycopolymers via click reactions, European Polymer Journal
Haddleton and colleagues reported that a protected maleimide ( PM ) instigators enables convenient junction to available thiol residues present in proteins after deprotection. Hence glycopolymers formed via the clickable sugar path are suited for inciting interactions with mannose-binding lectin while extinguishing the effects of concatenation length or architecture. Chiseled maleimide terminal functionalized glycopolymers can be formed with the combination of ATRP and CuAAC. This most dramatic characteristic of this combination is that is it simple, efficient and a broad scope of glycopolymers can be synthesized.
Another path to glycopolymer synthesis ( figure 9 ) is the production of a sugar methacrylate monomer via CuAAC click reaction. This is followed by the polymerization of this sugar monomer via ATRP but without the demand to protect the hydroxyl group nowadays on the sugar molecular, typically required in glycopolymer synthesis. The maleimide terminal group is so deprotected in the concluding measure merely carried out in a vacuity oven at 80aµ’C. This eliminates the usage of unneeded organic dissolvers and purification stairss.
Figure 9: Glycopolymer synthesis via a sugar monomer
F: Supriya LABDissertationCLICK SUGAR REACTION 2.jpg
Another path ( figure 10 ) for synthesising glycopolymers investigated was via a one-pot procedure with coincident CuAAC and populating extremist polymerization nevertheless the mechanism is non yet to the full understood. However it was demonstrated that it is possible to both populating polymerization and CuAAC reactions happening in the same reaction mixture. Tweaking reaction conditions such as dissolvers used temperature and dressed ore of accelerator proved to act upon the rate of each procedure. The ability to tweak reaction conditions is of import as any un-clicked acetylene groups may really undergo side reactions in situ and lead to hapless control over polymerization. Besides the one-pot system eliminates the usage of sugar functional methacrylate monomers, cut downing the figure of man-made stairss involved in glycopolymer synthesis.
In the past five old ages thiol based chink reactions have gained more attending due to the commercial handiness of a broad assortment of thiols. Thiol based chink reactions are various and can really be used to orient do macromolecular architectures such as complex dendritic polymers. Thiol reactions with assorted functional groups such as olefines, acetylenes, para-fluoro phenyl and halides are used to do glycopolymers. These reactions are really efficient and render high outputs of glycopolymer under defined conditions.
UV-light and a exposure instigator can be used to supply a extremist beginning for thiol-ene click reactions. Other thiol chink reactions are either catalysed by base or are nucleophilic in natures and continue via ambient conditions. Preparation of thiol-sugars are much more complex than sugar-azides, nevertheless, due to the commercial handiness of thiol-sugars, the figure of man-made stairss to fix glycopolymers is reduced. Polymers with olefine, acetylene, para-fluoro and halide pendent groups can easy be obtained and undergo thiol-click chemical science to bring forth glycopolymers. ( ref page 436 )
There are different combinations of click reactions and polymerization techniques with different sugars ( carbohydrates ) to synthesise glycopolymers and are tabulated below.
Acrylate or Methacrylate
Acrylate or Methacrylate
Acrylate or Methacrylate
The combination of CuAAC and ATRP works peculiarly good as clickable functionality into polymers can be incorporated with easiness to polymers prepared by ATRP. ATRP method of polymerization plants really good with Copper ( I ) chink chemical science. The Cu ( I ) accelerator typically used in ATRP is besides used to catalyze the CuAAC chink reaction and both procedures are typically performed with similar Nitrogen based ligands. This combination to organize trim glycopolymers has allowed for one-pot synthesis and chinks functionalization of polymers ( ref ) and has resulted in a huge assortment of new polymeric stuffs for biological application and macromolecular technology. ( ref )
On the other manus combination of RAFT and CuAAC besides works good sing the broad assortment of monomers RAFT polymerization can suit. RAFT procedure does non necessitate the usage of a metal accelerator which can turn out hard to take to obtain a pure polymer.