The use of 2-deoxy-2-trichloroacetamido-D-glucopyranose derivatives in syntheses of oligosaccharides

Glycosyl oxazolines serve as active donors for iterative synthesis of type I oligosaccharides

Synthesis of Galβ1 → 3GlcNAc-repeating saccharides is limited mainly by the formation of less-reactive oxazolines. We herein report an expeditious approach that requires trichloroacetyloxazolines as reactive glycosyl donors. Using only two disaccharide building blocks, the iterative oxazoline formation and glycosylation synthesized hexa- and octasaccharides with overall yields of 47% and 26% in four and six steps, respectively.

Diacetyl strategy for synthesis of NHAc containing glycans: enhancing glycosylation reactivity via diacetyl imide protection

The presence of NHAc groups in the substrates (both glycosyl donors and acceptors) significantly reduced the reactivity of glycosylation. This decrease was attributed to the NHAc groups forming intermolecular hydrogen bonds by the NHAc groups, thereby reducing molecular mobility. Hence, a diacetyl strategy involving the temporary conversion of NHAc to diacetyl imide (NAc2) was developed for the synthesis of NHAc-containing glycans. This strategy has two significant advantages for oligosaccharide synthesis. The NAc2 protection of NHAc substantially enhances the rate of glycosylation reactions, resulting in improved yields. Moreover, NAc2 can be readily reverted to NHAc by the simple removal of one acetyl group under mild basic conditions, obviating the necessity for treating the polar amino group. We have achieved the efficient synthesis of oligosaccharides containing GlcNHAc and N-glycans containing sialic acid using the diacetyl strategy.

Synthesis of Dimeric Lewis A and Lewis B-Lewis A Tumor-Associated Carbohydrate Antigen Oligosaccharide Fragments

Despite the interesting potential of tumor-associated carbohydrate antigens (TACAs) dimLe^a and Le^bLe^a to develop anticancer immunotherapies, little research has been conducted on these antigens. In our quest to discover fragments of these TACAs that could be targeted for the development of anticancer therapeutics, we report the synthesis of eight tri- to pentasaccharide fragments of these oligosaccharides. Unforeseen synthetic challenges are reported such as the incompatibility of a bromoalkyl glycoside in the reduction conditions needed to reduce a trichloroacetamide, the mismatched reactivities in a 2 + 1 synthetic strategy, and the surprising greater reactivity of a C-4 GlcNAc hydroxyl group versus that of the galactosyl OH-3 in the selective glycosylation of a trisaccharide diol. The desired final compounds were eventually obtained following a stepwise approach as nonyl or 9-aminononyl glycosides after one-step deprotection reactions in dissolving metal conditions. The 9-aminononyl glycosides will be conjugated to carrier proteins and the nonyl pentasaccharide glycoside will be used as a soluble inhibitor in binding experiments. In contrast, the nonyl tetrasaccharide glycosides are poorly soluble in water and their use in biochemical experiments will be limited.

Research progress on hydroxyl protection of iridoid glycosides

Iridoids, an important active ingredient, are widely distributed in varieties of Chinese herbal medicines and have varieties of pharmacological activities, such as anti-tumor, hypoglycemic, anti-inflammatory and so on, most of which exist in the form of glycosides in nature. However, its clinical application is limited by poor lipid solubility, low bioavailability and short half-life. It is necessary to optimize the structure of iridoids. It is hard to modify the hydroxyl groups at specific sites because iridoid glycosides are polyhydroxy compounds and very complex. In this paper, the words of ‘Iridoid glycosides’ and ‘Hydroxyl protection’ were used as the keywords, more than 200 articles from 1965 to 2021 were obtained from databases, such as CNKI, PubMed, Scifinder and so on. Finally, 60 articles were selected to summarize the hydroxyl protection of iridoid glycosides, which will provide a theoretical basis for their structural modification and stimulate their application potential in the field of drug research and development.

Protecting group free glycosylation: one-pot stereocontrolled access to 1,2-trans glycosides and (1→6)-linked disaccharides of 2-acetamido sugars

Unprotected 2-acetamido sugars may be directly converted into their oxazolines using 2-chloro-1,3-dimethylimidazolinium chloride (DMC), and a suitable base, in aqueous solution. Freeze drying and acid catalysed reaction with an alcohol as solvent produces the corresponding 1,2-trans-glycosides in good yield. Alternatively, dissolution in an aprotic solvent system and acidic activation in the presence of an excess of an unprotected glycoside as a glycosyl acceptor, results in the stereoselective formation of the corresponding 1,2-trans linked disaccharides without any protecting group manipulations. Reactions using aryl glycosides as acceptors are completely regioselective, producing only the (1→6)-linked disaccharides.

Selective Acetylation of Non-anomeric Groups of per-O-Trimethylsilylated Sugars

Selective modification of the hydroxyl groups of sugars has been a long-standing challenge due to their proximate relative reactivity. Herein, we report a TMSOTf-catalyzed selective acetylation of the non-anomeric hydroxyl groups of several per-O-TMS-protected sugar substrates while leaving their anomeric group unaffected. In addition to standing versatile by itself, the anomeric O-TMS group left intact can be functionalized to afford key sugar precursors such as imidate donors, which could otherwise be synthesized via a stepwise anomeric deprotection-functionalization procedure.

Chemical Synthesis of Fucosylated Chondroitin Sulfate Oligosaccharides

Fucosylated chondroitin sulfates (FuCSs) are a unique type of polysaccharides occurring in sea cucumber that show a variety of biological activities. In particular, well-defined FuCS oligosaccharides, consisting of a trisaccharide repeating unit of β-d-GalNAc(4,6-diS)-(1→4)-[α-l-Fuc(2,4-diS)-(1→3)]-β-d-GlcUA, display potent anticoagulant activity via selective inhibition of the intrinsic tenase, which could be developed into anticoagulant drugs without bleeding risk. Herein, we report an effective approach to the synthesis of FuCS oligosaccharides, as demonstrated by the successful elaboration of FuCS tri-, hexa-, and nonasaccharides. The syntheses employ an orthogonally protected trisaccharide as a pivotal building block that can be readily converted into the donor and acceptor for glycosidic coupling. In addition, the internal patterns of protecting groups, involving N-trichloroacetyl for N-acetyl group, benzylidene and benzyl groups for sulfonated hydroxyl groups, and benzoyl and methyl esters for free hydroxyl and carboxylic acid, respectively, ensure stereoselective formation of the glycosidic linkages and sequential transformation into the desired FuCS oligosaccharides.

Total Synthesis of Tri-, Hexa- and Heptasaccharidic Substructures of the O-Polysaccharide of Providencia rustigianii O34

A general and efficient strategy for synthesis of tri-, hexa- and heptasaccharidic substructures of the lipopolysaccharide of Providencia rustigianii O34 is described. For the heptasaccharide seven different building blocks were employed. Special features of the structures are an α-linked galactosamine and the two embedded α-fucose units, which are either branched at positions-3 and -4 or further linked at their 2-position. Convergent strategies focused on [4+3], [3+4], and [4+2+1] couplings. Whereas the [4+3] and [3+4] coupling strategies failed the [4+2+1] strategy was successful. As monosaccharidic building blocks trichloroacetimidates and phosphates were employed. Global deprotection of the fully protected structures was achieved by Birch reaction.

Synthesis of a meso-Oxa-Diaminopimelic Acid Containing Peptidoglycan Pentapeptide and Coupling to the GlcNAc-anhydro-MurNAc Disaccharide

The syntheses of peptidoglycan (PG)-derived peptides containing meso-diaminopimelic acid (meso-Dap) are typically quite lengthy due to the need to prepare orthogonally protected meso-Dap. In this work, the preparation of the PG pentapeptide containing the isosteric analog meso-oxa-Dap is described. The synthesis relies on the ring opening of a peptide embedded aziridine via the attack of a serine residue. The pentapeptide was attached to a GlcNAc-anhydro-MurNAc disaccharide, to produce a putative substrate for the AmpG pore protein.

Zwitterionic Phosphodiester-Substituted Neoglycoconjugates as Ligands for Antibodies and Acute Phase Proteins

Zwitterionic modifications of glycans, such as phosphorylcholine and phosphoethanolamine, are known from a range of prokaryotic and eukaryotic species and are recognized by mammalian antibodies and pentraxins; however, defined saccharide ligands modified with these zwitterionic moieties for high-throughput studies are lacking. In this study, we prepared and tested example mono- and disaccharides 6-substituted with either phosphorylcholine or phosphoethanolamine as bovine serum albumin neoglycoconjugates or printed in a microarray format for subsequent assessment of their binding to lectins, pentraxins, and antibodies. C-Reactive protein and anti-phosphorylcholine antibodies bound specifically to ligands with phosphorylcholine, but recognition by concanavalin A was abolished or decreased as compared with that to the corresponding nonzwitterionic compounds. Furthermore, in array format, the phosphorylcholine-modified ligands were recognized by IgG and IgM in sera of either non-infected or nematode-infected dogs and pigs. Thereby, these new compounds are defined ligands which allow the assessment of glycan-bound phosphorylcholine as a target of both the innate and adaptive immune systems in mammals.

4,6- O-Pyruvyl Ketal Modified N-Acetylmannosamine of the Secondary Cell Wall Polysaccharide of Bacillus anthracis Is the Anchoring Residue for Its Surface Layer Proteins

The secondary cell wall polysaccharide (SCWP) of Bacillus anthracis plays a key role in the organization of the cell envelope of vegetative cells and is intimately involved in host-guest interactions. Genetic studies have indicated that it anchors S-layer and S-layer-associated proteins, which are involved in multiple vital biological functions, to the cell surface of B. anthracis. Phenotypic observations indicate that specific functional groups of the terminal unit of SCWP, including 4,6- O-pyruvyl ketal and acetyl esters, are important for binding of these proteins. These observations are based on genetic manipulations and have not been corroborated by direct binding studies. To address this issue, a synthetic strategy was developed that could provide a range of pyruvylated oligosaccharides derived from B. anthracis SCWP bearing base-labile acetyl esters and free amino groups. The resulting oligosaccharides were used in binding studies with a panel of S-layer and S-layer-associated proteins, which identified structural features of SCWP important for binding. A single pyruvylated ManNAc monosaccharide exhibited strong binding to all proteins, making it a promising structure for S-layer protein manipulation. The acetyl esters and free amine of SCWP did not significantly impact binding, and this observation is contrary to a proposed model in which SCWP acetylation is a prerequisite for association of some but not all S-layer and S-layer-associated proteins.

Metabolic engineering for the production of chitooligosaccharides: advances and perspectives

Chitin oligosaccharides (CTOs) and its related compounds chitosan oligosaccharides (CSOs), collectively known as chitooligosaccharides (COs), exhibit numerous biological activities in applications in the nutraceutical, cosmetics, agriculture, and pharmaceutical industries. COs are currently produced by acid hydrolysis of chitin or chitosan, or enzymatic techniques with uncontrollable polymerization. Microbial fermentation by recombinant Escherichia coli, as an alternative method for the production of COs, shows new potential because it can produce a well-defined COs mixture and is an environmentally friendly process. In addition, Bacillus subtilis, a nonpathogenic, endotoxin-free, GRAS status bacterium, presents a new opportunity as a platform to produce COs. Here, we review the applications of COs and differences between CTOs and CSOs, summarize the current preparation approaches of COs, and discuss the future research potentials and challenges in the production of well-defined COs in B. subtilis by metabolic engineering.

Synthetic and semi-synthetic approaches to unprotected N-glycan oxazolines

N-Glycan oxazolines have found widespread use as activated donor substrates for endo-β-N-acetylglucosaminidase (ENGase) enzymes, an important application that has correspondingly stimulated interest in their production, both by total synthesis and by semi-synthesis using oligosaccharides isolated from natural sources. Amongst the many synthetic approaches reported, the majority rely on the fabrication (either by total synthesis, or semi-synthesis from locust bean gum) of a key Manβ(1-4)GlcNAc disaccharide, which can then be elaborated at the 3- and 6-positions of the mannose unit using standard glycosylation chemistry. Early approaches subsequently relied on the Lewis acid catalysed conversion of peracetylated N-glycan oligosaccharides produced in this manner into their corresponding oxazolines, followed by global deprotection. However, a key breakthrough in the field has been the development by Shoda of 2-chloro-1,3-dimethylimidazolinium chloride (DMC), and related reagents, which can direct convert an oligosaccharide with a 2-acetamido sugar at the reducing terminus directly into the corresponding oxazoline in water. Therefore, oxazoline formation can now be achieved in water as the final step of any synthetic sequence, obviating the need for any further protecting group manipulations, and simplifying synthetic strategies. As an alternative to total synthesis, significant quantities of several structurally complicated N-glycans can be isolated from natural sources, such as egg yolks and soy bean flour. Enzymatic transformations of these materials, in concert with DMC-mediated oxazoline formation as a final step, allow access to a selection of N-glycan oxazoline structures both in larger quantities and in a more expedient fashion than is achievable by total synthesis.

Synthesis of Chondroitin Sulfate A Bearing Syndecan-1 Glycopeptide

Syndecan-1 chondroitin sulfate glycopeptide was synthesized for the first time using the cassette approach. The sequence of glycosylation to form the octasaccharide serine cassette was critical. The glycopeptide was successfully assembled via a 2+ (3 + 3) glycosylation strategy followed by peptide chain elongation.

Biosynthetic and synthetic access to amino sugars

Amino sugars are important constituents of a number of biomacromolecules and products of microbial secondary metabolism, including antibiotics. For most of them, the amino group is located at the positions C1, C2 or C3 of the hexose or pentose ring. In biological systems, amino sugars are formed due to the catalytic activity of specific aminotransferases or amidotransferases by introducing an amino functionality derived from L-glutamate or L-glutamine to the keto forms of sugar phosphates or sugar nucleotides. The synthetic introduction of amino functionalities in a regio- and stereoselective manner onto sugar scaffolds represents a substantial challenge. Most of the modern methods of for the preparation of 1-, 2- and 3-amino sugars are those starting from "an active ester" of carbohydrate derivatives, glycals, alcohols, carbonyl compounds and amino acids. A substantial progress in the development of region- and stereoselective methods of amino sugar synthesis has been made in the recent years, due to the application of metal-based catalysts and tethered approaches. A comprehensive review on the current state of knowledge on biosynthesis and chemical synthesis of amino sugars is presented.

Efficient and stereocontrolled synthesis of chondroitin mono- and disaccharide linked to variously sulfated biotinylated trisaccharides of the linkage region of proteoglycans

Efficient and stereocontrolled preparation of a library of variously sulfated biotinylated tetra- and pentasaccharides possessing the backbone of the partial linkage region plus the first chondroitin sulfate mono- or disaccharide unit (d-GlcA)n-β-d-(1,3)-GalNAc-β-d-(1,4)-GlcA-β-d-(1,3)-Gal-β-d-(1,3)-Gal (n = 0 or 1) is reported herein for the first time. The synthesis of these compounds was achieved using common key intermediates and a disaccharide building block obtained by semisynthesis. Stereoselective glycosylation, selective protection/deprotection steps, efficient reduction of the N-trichloroacetyl group into the corresponding N-acetyl group, efficient sulfation strategy, deprotection and biotinylation afforded target oligomers in good yield with high purity.

Detailed Investigation of the Immunodominant Role of O-Antigen Stoichiometric O-Acetylation as Revealed by Chemical Synthesis, Immunochemistry, Solution Conformation and STD-NMR Spectroscopy for Shigella flexneri 3a

Shigella flexneri 3a causes bacillary dysentery. Its O-antigen has the {2)-[α-d-Glcp-(1→3)]-α-l-Rhap-(1→2)-α-l-Rhap-(1→3)-[Ac→2]-α-l-Rhap-(1→3)-[Ac→6]≈40 % -β-d-GlcpNAc-(1→} ([(E)ABAc CAc D]) repeating unit, and the non-O-acetylated equivalent defines S. flexneri X. Propyl hepta-, octa-, and decasaccharides sharing the (E')A'BAc CD(E)A sequence, and their non-O-acetylated analogues were synthesized from a fully protected BAc CD(E)A allyl glycoside. The stepwise introduction of orthogonally protected mono- and disaccharide imidate donors was followed by a two-step deprotection process. Monoclonal antibody binding to twenty-six S. flexneri types 3a and X di- to decasaccharides was studied by an inhibition enzyme-linked immunosorbent assay (ELISA) and STD-NMR spectroscopy. Epitope mapping revealed that the 2C -acetate dominated the recognition by monoclonal IgG and IgM antibodies and that the BAc CD segment was essential for binding. The glucosyl side chain contributed to a lesser extent, albeit increasingly with the chain length. Moreover, tr-NOESY analysis also showed interaction but did not reveal any meaningful conformational change upon antibody binding.

Non-stoichiometric O-acetylation of Shigella flexneri 2a O-specific polysaccharide: synthesis and antigenicity

Synthetic functional mimics of the O-antigen from Shigella flexneri 2a are seen as promising vaccine components against endemic shigellosis. Herein, the influence of the polysaccharide non-stoichiometric di-O-acetylation on antigenicity is addressed for the first time. Three decasaccharides, representing relevant internal mono- and di-O-acetylation profiles of the O-antigen, were synthesized from a pivotal protected decasaccharide designed to tailor late stage site-selective O-acetylation. The latter was obtained via a convergent route involving the imidate glycosylation chemistry. Binding studies to five protective mIgGs showed that none of the acetates adds significantly to broad antibody recognition. Yet, one of the five antibodies had a unique pattern of binding. With IC50 in the micromolar to submicromolar range mIgG F22-4 exemplifies a remarkable tight binding antibody against diversely O-acetylated and non-O-acetylated fragments of a neutral polysaccharide of medical importance.

Orthoesters formation leading to mismatched Helferich glycosylations at O-3 of N-trichloroacetylated glucosamine residues

Using trisaccharide diol acceptors displaying two glucosamine residues free at O-3, we observed that α-l-fucosylation with α armed donor proceeded smoothly at the most accessible N-trichloroacetyl nonreducing end glucosamine residue. In contrast, glycosylations with peracetylated glycosyl bromide donors activated under Helferich conditions seemed to proceed preferentially or exclusively at the more sterically hindered N-acetylated reducing end unit. Thus, we concluded that disarmed donors were mismatched at O-3 of the N-trichloroacetylated glucosamine residue regardless of α or β configuration of the glycosidic bond formed and d or l configuration of the donor. Interestingly orthoester formation occurred in some cases at this position while they were not observed at the reducing end unit. Conversion of the nonreducing end trichloroacetamido to an acetamido allowed the Helferich catalyzed galactosylation to occur at both positions and revealed the impact of the N-trichloroacetamido on the mismatched glycosylations. Changing the activation conditions from the mild Lewis acid Hg(CN)2 to the stronger acid AgOTf revealed that in fact β-d-galactosylation at the less hindered N-trichloroacetylated residue was kinetically favored over that at the reducing end residue. Isolation of equal amounts of orthoester at this position suggested that it was formed first but that the strong AgOTf Lewis acid was able to promote rearrangement to the β-d-galactosidic bond. These results shed additional light on the apparent mismatch of disarmed glycosyl donors with hydroxyl groups deemed more accessible. Depending on electronic factors imposed by the acceptor and activation conditions, transient unstable orthoester formation may explain in some cases why these donors appear mismatched with the most accessible hydroxyl groups which are otherwise glycosylated by armed donors.

Synthesis of anti-inflammatory α-and β-linked acetamidopyranosides as inhibitors of toll-like receptor 4 (TLR4)

The low-molecular weight isopropyl 2-acetamido-α-glucoside 16 (C34) inhibits toll-like receptor 4 (TLR4) in enterocytes and macrophages in vitro, and reduces systemic inflammation in mouse models of endotoxemia and necrotizing enterocolitis. We used a copper(II)-mediated solvolysis of anomeric oxazolines and an acid-mediated conversion of β-glucosamine and β-galactosamine pentaacetates to generate analogs of 16 at the anomeric carbon and at C-4 of the pyranose ring. These compounds were evaluated for their influence on TLR4-mediated inflammatory signaling in cultured enterocytes and monocytes. Their efficacy was confirmed using a NF-kB-luciferase reporter mouse, thus establishing the first structure-activity relationship (SAR) study in this series and identifying the more efficacious isopropyl 2-acetamido-α-galactoside 17.

Stereocontrolled preparation of biotinylated chondroitin sulfate E di-, tetra-, and hexasaccharide conjugates

The synthesis of biotinylated conjugates of oligomers of the basic repeating unit of chondroitin sulfate E (CS-E) with the sequence [GlcA-4,6-disulfated GalNAc]n is reported herein for the first time. An efficient and stereocontrolled preparation of di-, tetra-, and hexasaccharide derivatives was achieved using a common key disaccharide intermediate in an iterative way. An unexpected and never reported side reaction on the carbonyl group of the levulinate ester was observed during a coupling reaction. These complex molecules should be useful to study their interactions with various proteins.

Synthesis of the zwitterionic repeating unit of the O-antigen from Shigella sonnei and chain elongation at both ends

Shigella sonnei O-antigen features a zwitterionic disaccharide repeat encompassing two rare monosaccharides. The synthesis of the AB repeat and of trisaccharides ABA' and B'AB, which validates chain elongation at either end, is reported. All targets were synthesized using a postglycosylation oxidation strategy in combination with imidate chemistry. Precursors to residue A were obtained from L-glucose. The AAT (B) donor and acceptor were obtained from D-glucosamine. A one-step Pd(OH)2/C-mediated deprotection provided the propyl glycoside targets.

From chitin to bioactive chitooligosaccharides and conjugates: access to lipochitooligosaccharides and the TMG-chitotriomycin

The direct and chemoselective N-transacylation of peracetylated chitooligosaccharides (COSs), readily obtained from chitin, to give per-N-trifluoroacetyl derivatives offers an attractive route to size-defined COSs and derived glycoconjugates. It involves the use of various acceptor building blocks and trifluoromethyl oxazoline dimer donors prepared with efficiency and highly reactive in 1,2-trans glycosylation reactions. This method was applied to the preparation of the important symbiotic glycolipids which are highly active on plants and to the TMG-chitotriomycin, a potent and specific inhibitor of insect, fungal, and bacterial N-acetylglucosaminidases.

Glycosylation with N-acetyl glycosamine donors using catalytic iron(iii) triflate: from microwave batch chemistry to a scalable continuous-flow process

Efficient glycosylation reactions of peracetylated β-d-N-acetyl glycosamines are described using catalytic iron(iii) triflate under microwave conditions or in a continuous flow process.

Synthesis and scalable conversion of L-iduronamides to heparin-related di- and tetrasaccharides

A diastereomerically pure cyanohydrin, preparable on kilogram scale, is efficiently converted in one step into a novel L-iduronamide. A new regioselective acylation of this iduronamide and a new mild amide hydrolysis method mediated by amyl nitrite enables short, scalable syntheses of an L-iduronate diacetate C-4 acceptor, and also L-iduronate C-4 acceptor thioglycosides. Efficient conversions of these to a range of heparin-related gluco-ido disaccharide building blocks (various C-4 protection options) including efficient multigram access to key heparin-building block ido-thioglycoside donors are described. A 1-OAc disaccharide is converted into a heparin-related tetrasaccharide, via divergence to both acceptor and donor disaccharides. X-ray and NMR data of the 1,2-diacetyl iduronate methyl ester and the analogous iduronamide show that while both adopt (1)C(4) conformations in solution, the iduronate ester adopts the (4)C(1) conformation in solid state. An X-ray structure is also reported for the novel, (4)C(1)-conformationally locked bicyclic 1,6-anhydro iduronate lactone along with an X-ray structures of a novel distorted (4)C(1) iduronate 4,6-lactone. Deuterium labeling also provides mechanistic insight into the formation of lactone products during the novel amyl nitrite-mediated hydrolysis of iduronamide into the parent iduronic acid functionality.

Synthetic and semi-synthetic chondroitin sulfate oligosaccharides, polysaccharides, and glycomimetics

Chondroitin sulfate (CS) is a sulfated polysaccharide involved in a myriad of biological processes. Due to the variable sulfation pattern of CS polymer chains, the need to study in detail structure-activity relationships regarding CS biomedical features has provoked much interest in obtaining synthetic CS species. This paper reviews two decades of synthetic and semi-synthetic CS oligosaccharides, polysaccharides, and glycomimetics obtained by chemical, chemoenzymatic, enzymatic, and microbiological-chemical strategies.

Water-soluble substrates of the peptidoglycan-modifying enzyme O-acetylpeptidoglycan esterase (Ape1) from Neisseria gonorrheae

Peptidoglycan is the component of the bacterial cell wall that is essential for maintaining the shape and rigidity of the cell. As such, its polymeric structure, consisting of alternating units of N-acetylglucosamine (GlcNAc) and N-acetylmuramic acid (MurNAc), is also a target for the action of host defense enzymes, such as lysozymes. Many bacteria have developed methods of masking their cell wall from these environmental dangers through the addition of aglycon moieties that prevent recognition or sterically hinder the degradative action of exogenous enzymes that would otherwise prove detrimental to the cell. Peptidoglycan acetyl-transferases (Pat's) and O-acetylpeptidoglycan esterases (Ape's) are the enzymes responsible for the controlled addition and removal of acetate onto the C-6 hydroxyl group of MurNAc residues in peptidoglycan. Studies on Ape1, an O-acetylpeptidoglycan esterase found in Neisseria gonorrheae, have suggested that this enzyme is essential for bacterial viability and thus presents an attractive target for antibacterial design. Previous studies on Ape1 have been hindered by the fact that Ape1's natural substrate is an insoluble polymer. In this paper we outline the design, synthesis, and testing of the water-soluble di- and monosaccharide substrate analogues 1 and 2. Both 1 and 2 serve as substrates of Ape1 with k(cat)/K(M) values of (5.1 ± 1.7) × 10(3) M(-1) s(-1) and (3.1 ± 0.8) × 10(3) M(-1) s(-1), respectively. It was determined that the substitution of the GlcNAc residue in compound 1 with an O-benzyl group in compound 2 did not significantly decrease the enzyme's affinity for the monosaccharide. These findings are important as they demonstrate that the catalytic prowess of Ape1 is not dependent on its binding to a polymeric substrate. This ensures that small molecule transition state/intermediate analogues can also capture the transition state binding energy of Ape1 and potentially serve as potent inhibitors. The synthetic route to compounds 1 and 2 could readily be modified to allow for the installation of a wide variety of functional groups at the MurNAc C-6 position in both the mono- and disaccharide scaffolds. This will serve as a general method for the construction of Ape1 substrates and inhibitors.