Development of GlcNAc-inspired iminocyclitiols as potent and selective N-acetyl-beta-hexosaminidase inhibitors

Glycosphingolipids in Osteoarthritis and Cartilage-Regeneration Therapy: Mechanisms and Therapeutic Prospects Based on a Narrative Review of the Literature

Glycosphingolipids (GSLs), a subtype of glycolipids containing sphingosine, are critical components of vertebrate plasma membranes, playing a pivotal role in cellular signaling and interactions. In human articular cartilage in osteoarthritis (OA), GSL expression is known notably to decrease. This review focuses on the roles of gangliosides, a specific type of GSL, in cartilage degeneration and regeneration, emphasizing their regulatory function in signal transduction. The expression of gangliosides, whether endogenous or augmented exogenously, is regulated at the enzymatic level, targeting specific glycosyltransferases. This regulation has significant implications for the composition of cell-surface gangliosides and their impact on signal transduction in chondrocytes and progenitor cells. Different levels of ganglioside expression can influence signaling pathways in various ways, potentially affecting cell properties, including malignancy. Moreover, gene manipulations against gangliosides have been shown to regulate cartilage metabolisms and chondrocyte differentiation in vivo and in vitro. This review highlights the potential of targeting gangliosides in the development of therapeutic strategies for osteoarthritis and cartilage injury and addresses promising directions for future research and treatment.

Stereoselective Access to Iminosugar C,C-Glycosides from 6-Azidoketopyranoses

We report the synthesis of iminosugar C,C-glycosides starting from 6-azidoketopyranoses. Their Staudinger-azaWittig-mediated cyclization provided bicyclic N,O-acetals, which were stereoselectively opened with AllMgBr to afford β-hydroxyazepanes with a quaternary carbon α to the nitrogen. Their ring contraction via a β-aminoalcohol rearrangement produced the six-membered l-iminosugars with two functional handles at the pseudoanomeric position. Inversion of the free OH at the azepane level furnished the d-iminosugars.

sp2-Iminosugars targeting human lysosomal β-hexosaminidase as pharmacological chaperone candidates for late-onset Tay-Sachs disease

The late-onset form of Tay-Sachs disease displays when the activity levels of human β-hexosaminidase A (HexA) fall below 10% of normal, due to mutations that destabilise the native folded form of the enzyme and impair its trafficking to the lysosome. Competitive inhibitors of HexA can rescue disease-causative mutant HexA, bearing potential as pharmacological chaperones, but often also inhibit the enzyme O-glucosaminidase (GlcNAcase; OGA), a serious drawback for translation into the clinic. We have designed sp²-iminosugar glycomimetics related to GalNAc that feature a neutral piperidine-derived thiourea or a basic piperidine-thiazolidine bicyclic core and behave as selective nanomolar competitive inhibitors of human Hex A at pH 7 with a ten-fold lower inhibitory potency at pH 5, a good indication for pharmacological chaperoning. They increased the levels of lysosomal HexA activity in Tay-Sachs patient fibroblasts having the G269S mutation, the highest prevalent in late-onset Tay-Sachs disease.

Computational Studies on the Potency and Selectivity of PUGNAc Derivatives Against GH3, GH20, and GH84 β-N-acetyl-D-hexosaminidases

β-N-acetyl-D-hexosaminidases have attracted significant attention due to their crucial role in diverse physiological functions including antibacterial synergists, pathogen defense, virus infection, lysosomal storage, and protein glycosylation. In particular, the GH3 β-N-acetyl-D-hexosaminidase of V. cholerae (VcNagZ), human GH20 β-N-acetyl-D-hexosaminidase B (HsHexB), and human GH84 β-N-acetyl-D-hexosaminidase (hOGA) are three important representative glycosidases. These have been found to be implicated in β-lactam resistance (VcNagZ), lysosomal storage disorders (HsHexB) and Alzheimer's disease (hOGA). Considering the profound effects of these three enzymes, many small molecule inhibitors with good potency and selectivity have been reported to regulate the corresponding physiological functions. In this paper, the best-known inhibitors PUGNAc and two of its derivatives (N-valeryl-PUGNAc and EtBuPUG) were selected as model compounds and docked into the active pockets of VcNagZ, HsHexB, and hOGA, respectively. Subsequently, molecular dynamics simulations of the nine systems were performed to systematically compare their binding modes from active pocket architecture and individual interactions. Furthermore, the binding free energy and free energy decomposition are calculated using the MM/GBSA methods to predict the binding affinities of enzyme-inhibitor systems and to quantitatively analyze the contribution of each residue. The results show that PUGNAc is deeply-buried in the active pockets of all three enzymes, which indicates its potency (but not selectivity) against VcNagZ, HsHexB, and hOGA. However, EtBuPUG, bearing branched 2-isobutamido, adopted strained conformations and was only located in the active pocket of VcNagZ. It has completely moved out of the pocket of HsHexB and lacks interactions with HsHexB. This indicates why the selectivity of EtBuPUG to VcNagZ/HsHexB is the largest, reaching 968-fold. In addition, the contributions of the catalytic residue Asp253 (VcNagZ), Asp254 (VcNagZ), Asp175 (hOGA), and Asp354 (HsHexB) are important to distinguish the activity and selectivity of these inhibitors. The results of this study provide a helpful structural guideline to promote the development of novel and selective inhibitors against specific β-N-acetyl-D-hexosaminidases.

Modification of the Thioglycosyl-Naphthalimides as Potent and Selective Human O-GlcNAcase Inhibitors

β-N-Acetylhexosaminidases are widely distributed exoglycosidases and have attracted significant attention due to their important roles in the field of pesticide and drug discovery. Remarkably, human O-GlcNAcase (hOGA) and human β-N-acetylhexosaminidase (HsHex) possess the same catalytic mechanism but play different physiological actions in vivo. In this Letter, we aim to improve the inhibitory potency and selectivity of previously reported thioglycosyl-naphthalimides against hOGA. The rational compound design led to the synthesis of 13r bearing a 4-piperidylnaphthalimide moiety as a highly potent hOGA inhibitor (K _i = 0.6 μM against hOGA) with good selectivity (K _i > 100 μM against HsHexB). Furthermore, to investigate the basis for the potency and selectivity of 13r against hOGA, the possible inhibitory mechanisms of selected inhibitors (15b, 13b, and 13r) against hOGA and HsHexB were studied using molecular docking and MD simulations. These 4-substituted naphthalimide thioglycosides may potentially serve as useful tools for the further study of the function of hOGA.

Selective trihydroxylated azepane inhibitors of NagZ, a glycosidase involved in Pseudomonas aeruginosa resistance to β-lactam antibiotics

The synthesis of a series of d-gluco-like configured 4,5,6-trihydroxyazepanes bearing a triazole, a sulfonamide or a fluorinated acetamide moiety at C-3 is described. These synthetic derivatives have been tested for their ability to selectively inhibit the muropeptide recycling glucosaminidase NagZ and to thereby increase sensitivity of Pseudomonas aeruginosa to β-lactams, a pathway with substantial therapeutic potential. While introduction of triazole and sulfamide groups failed to lead to glucosaminidase inhibitors, the NHCOCF₃ analog proved to be a selective inhibitor of NagZ over other glucosaminidases including human O-GlcNAcase and lysosomal hexosaminidases HexA and B.

Design and synthesis of naphthalimide group-bearing thioglycosides as novel β-N-acetylhexosaminidases inhibitors

GH20 human β-N-acetylhexosaminidases (hsHex) and GH84 human O-GlcNAcase (hOGA) are involved in numerous pathological processes and emerged as promising targets for drug discovery. Based on the catalytic mechanism and structure of the catalytic domains of these β-N-acetylhexosaminidases, a series of novel naphthalimide moiety-bearing thioglycosides with different flexible linkers were designed, and their inhibitory potency against hsHexB and hOGA was evaluated. The strongest potency was found for compound 15j (K_i = 0.91 µM against hsHexB; K_i > 100 µM against hOGA) and compound 15b (K_i = 3.76 µM against hOGA; K_i = 30.42 µM against hsHexB), which also exhibited significant selectivity between these two enzymes. Besides, inhibitors 15j and 15b exhibited an inverse binding patterns in docking studies. The determined structure–activity relationship as well as the established binding models provide the direction for further structure optimizations and the development of specific β-N-acetylhexosaminidase inhibitors.

Dissecting PUGNAc-mediated inhibition of the pro-survival action of insulin

Previous studies utilizing PUGNAc, the most widely used β-N-acetylglucosaminidase (OGA) inhibitor to increase global O-N-acetylglucosamine (GlcNAc) levels, have reported a variety of effects including insulin resistance as a direct result of elevated O-GlcNAc levels. The notion of OGA inhibition causing insulin resistance was not replicated in studies in which elevated global O-GlcNAc levels were achieved using two other OGA inhibitors. Related to insulin action, work by others has suggested that O-GlcNAc elevation may inhibit the anti-apoptotic action of insulin. Thus, we examined the pro-survival action of insulin upon serum deprivation in the presence of PUGNAc as well as two selective OGA inhibitors (GlcNAcstatin-g and Thiamet-G), and a selective lysosomal hexosaminidase inhibitor (INJ2). We established that PUGNAc inhibits the pro-survival action of insulin but this effect is not recapitulated by the selective OGA inhibitors suggesting that elevation in O-GlcNAc levels alone is not responsible for PUGNAc's effect on the anti-apoptotic action of insulin. Further, we demonstrate that a selective hexosaminidase A/B (HexA/B) inhibitor does not impact insulin action suggesting that PUGNAc's effect is not due to inhibition of lysosomal hexosaminidase. Finally, we tested a combination of selective OGA and lysosomal hexosaminidase inhibitors but were not able to recapitulate the inhibition of insulin action generated by PUGNAc alone. These results strongly suggest that the defect in insulin action upon PUGNAc treatment does not derive from its inhibition of OGA or HexA/B, and that there is an unknown target of PUGNAc that is the likely culprit in inhibiting the protective effect of insulin from apoptosis.

Amino-functionalized iminocyclitols: synthetic glycomimetics of medicinal interest

A review on the syntheses and biological activities of unnatural glycomimetics highlighting the effect of replacement of hydroxyl groups of natural iminosugars by amino functionalities is presented.

Aglycone mimics for tuning of glycosidase inhibition: design, synthesis and biological evaluation of bicyclic pyrrolidotriazole iminosugars

Various fuco-configured bicyclic pyrrolidotriazole aglycone mimics were synthesised using copper-catalysed coupling of allyl bromides with terminal alkynes and Sonogashira–Hagihara reaction followed by intramolecular azide-alkyne ‘click’ reaction.

Efficient stereoselective synthesis of 2-acetamido-1,2-dideoxyallonojirimycin (DAJNAc) and sp(2)-iminosugar conjugates: Novel hexosaminidase inhibitors with discrimination capabilities between the mature and precursor forms of the enzyme

Due to their capacity to inhibit hexosaminidases, 2-acetamido-1,2-dideoxy-iminosugars have been widely studied as potential therapeutic agents for various diseases. An efficient stereoselective synthesis of 2-acetamido-1,2-dideoxyallonojirimycin (DAJNAc), the most potent inhibitor of human placenta β-N-acetylglucosaminidase (β-hexosaminidase) among the epimeric series, is here described. This novel procedure can be easily scaled up, providing enough material for structural modifications and further biological tests. Thus, two series of sp(2)-iminosugar conjugates derived from DAJNAc have been prepared, namely monocyclic DAJNAc-thioureas and bicyclic 2-iminothiazolidines, and their glycosidase inhibitory activity evaluated. The data evidence the utmost importance of developing diversity-oriented synthetic strategies allowing optimization of electrostatic and hydrophobic interactions to achieve high inhibitory potencies and selectivities among isoenzymes. Notably, strong differences in the inhibition potency of the compounds towards β-hexosaminidase from human placenta (mature) or cultured fibroblasts (precursor form) were encountered. The ensemble of data suggests that the ratio between them, and not the inhibition potency towards the placenta enzyme, is a good indication of the chaperoning potential of TaySachs disease-associated mutant hexosaminidase.

Stereoselective synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc) and ureido-DNJNAc derivatives as new hexosaminidase inhibitors

A novel approach to the synthesis of 2-acetamido-1,2-dideoxynojirimycin (DNJNAc) and ureido-DNJNAc derivatives as potent hexosaminidase inhibitors is reported.

Exploring NAG-thiazoline and its derivatives as inhibitors of chitinolytic β-acetylglucosaminidases

NAG-thiazoline (NGT) and its derivatives are well-known inhibitors against most β-acetylglucosaminidases (β-GlcNAcases) except for insect and bacterial chitinolytic β-GlcNAcases, including the molting-indispensable OfHex1 from the insect Ostrinia furnacalis. Here, we report the co-crystal structure of OfHex1 in complex with NGT. This structure reveals a large active pocket in OfHex1 that may account for the poor inhibitory activity of NGT. To test this hypothesis, a bulky substituent was designed and synthesized on the thiazoline ring of NGT. The resulting compound (NMAGT) was determined to be a submicromolar inhibitor of OfHex1 with a Ki value of 0.13 μM, which is 600-fold lower than Ki value of NGT. Molecular dynamics simulation analysis supported the good fit of NMAGT to the active pocket.

A crystal structure-guided rational design switching non-carbohydrate inhibitors' specificity between two β-GlcNAcase homologs

Selective inhibition of function-specific β-GlcNAcase has great potential in terms of drug design and biological research. The symmetrical bis-naphthalimide M-31850 was previously obtained by screening for specificity against human glycoconjugate-lytic β-GlcNAcase. Using protein-ligand co-crystallization and molecular docking, we designed an unsymmetrical dyad of naphthalimide and thiadiazole, Q2, that changes naphthalimide specificity from against a human glycoconjugate-lytic β-GlcNAcase to against insect and bacterial chitinolytic β-GlcNAcases. The crystallographic and in silico studies reveal that the naphthalimide ring can be utilized to bind different parts of these enzyme homologs, providing a new starting point to design specific inhibitors. Moreover, Q2-induced closure of the substrate binding pocket is the structural basis for its 13-fold increment in inhibitory potency. Q2 is the first non-carbohydrate inhibitor against chitinolytic β-GlcNAcases. This study provides a useful example of structure-based rationally designed inhibitors as potential pharmaceuticals or pesticides.

Selective trihydroxyazepane NagZ inhibitors increase sensitivity of Pseudomonas aeruginosa to β-lactams

AmpC β-lactamase confers resistance to β-lactam antibiotics in many Gram negative bacteria. Inducible expression of AmpC requires an N-acetylglucosaminidase termed NagZ. Here we describe the synthesis and characterization of hydroxyazepane inhibitors of NagZ. We find that these inhibitors enhance the susceptibility of clinically relevant Pseudomonas aeruginosa to β-lactams.

The development of selective inhibitors of NagZ: increased susceptibility of Gram-negative bacteria to β-lactams

The increasing incidence of inducible chromosomal AmpC β-lactamases within the clinic is a growing concern because these enzymes deactivate a broad range of even the most recently developed β-lactam antibiotics. As a result, new strategies are needed to block the action of this antibiotic resistance enzyme. Presented here is a strategy to combat the action of inducible AmpC by inhibiting the β-glucosaminidase NagZ, which is an enzyme involved in regulating the induction of AmpC expression. A divergent route facilitating the rapid synthesis of a series of N-acyl analogues of 2-acetamido-2-deoxynojirimycin is reported here. Among these compounds are potent NagZ inhibitors that are selective against functionally related human enzymes. These compounds reduce minimum inhibitory concentration values for β-lactams against a clinically relevant Gram-negative bacterium bearing inducible chromosomal AmpC β-lactamase, Pseudomonas aeruginosa. The structure of a NagZ–inhibitor complex provides insight into the molecular basis for inhibition by these compounds.

Development of Unsymmetrical Dyads As Potent Noncarbohydrate-Based Inhibitors against Human β-N-Acetyl-d-hexosaminidase

Human β-N-acetyl-d-hexosaminidase has gained much attention due to its roles in several pathological processes and been considered as potential targets for disease therapy. A novel and efficient skeleton, which was an unsymmetrical dyad containing naphthalimide and methoxyphenyl moieties with an alkylamine spacer linkage as a noncarbohydrate-based inhibitor, was synthesized, and the activities were valuated against human β-N-acetyl-d-hexosaminidase. The most potent inhibitor exhibits high inhibitory activity with K i values of 0.63 μM. The straightforward synthetic manners of these unsymmetrical dyads and understanding of the binding model could be advantageous for further structure optimization and development of new therapeutic agents for Hex-related diseases.

Developing inhibitors of glycan processing enzymes as tools for enabling glycobiology

Glycoconjugates are ubiquitous biomolecules found in all kingdoms of life. These diverse structures are metabolically responsive and occur in a cell line- and protein-specific manner, conferring tissue type-specific properties. Glycans have essential roles in diverse processes, including, for example, intercellular signaling, inflammation, protein quality control, glucohomeostasis and cellular adhesion as well as cell differentiation and proliferation. Many mysteries remain in the field, however, and uncovering the physiological roles of various glycans remains a key pursuit. Realizing this aim necessitates the ability to subtly and selectively manipulate the series of different glycoconjugates both in cells and in vivo. Selective small-molecule inhibitors of glycan processing enzymes hold great potential for such manipulation as well as for determining the function of 'orphan' carbohydrate-processing enzymes. In this review, we discuss recent advances and existing inhibitors, the prospects for small-molecule inhibitors and the challenges associated with generating high-quality chemical probes for these families of enzymes. The coordinated efforts of chemists, biochemists and biologists will be crucial for creating and characterizing inhibitors that are useful tools both for advancing a basic understanding of glycobiology in mammals as well as for validating new potential therapeutic targets within this burgeoning field.

Scalable syntheses of both enantiomers of DNJNAc and DGJNAc from glucuronolactone: the effect of N-alkylation on hexosaminidase inhibition

The efficient scalable syntheses of 2-acetamido-1,2-dideoxy-D-galacto-nojirimycin (DGJNAc) and 2-acetamido-1,2-dideoxy-D-gluco-nojirimycin (DNJNAc) from D-glucuronolactone, as well as of their enantiomers from L-glucuronolactone, are reported. The evaluation of both enantiomers of DNJNAc and DGJNAc, along with their N-alkyl derivatives, as glycosidase inhibitors showed that DGJNAc and its N-alkyl derivatives were all inhibitors of α-GalNAcase but that none of the epimeric DNJNAc derivatives inhibited this enzyme. In contrast, both DGJNAc and DNJNAc, as well as their alkyl derivatives, were potent inhibitors of β-GlcNAcases and β-GalNAcases. Neither of the L-enantiomers showed any significant inhibition of any of the enzymes tested. Correlation of the in vitro inhibition with the cellular data, by using a free oligosaccharide analysis of the lysosomal enzyme inhibition, revealed the following structure-property relationship: hydrophobic side-chains preferentially promoted the intracellular access of iminosugars to those inhibitors with more-hydrophilic side-chain characteristics.

Inhibitors for Bacterial Cell-Wall Recycling

Gram-negative bacteria have evolved an elaborate process for the recycling of their cell wall, which is initiated in the periplasmic space by the action of lytic transglycosylases. The product of this reaction, β-D-N-acetylglucosamine-(1→4)-1,6-anhydro-β-D-N-acetylmuramyl-L-Ala-γ-D-Glu-meso-DAP-D-Ala-D-Ala (compound 1), is internalized to begin the recycling events within the cytoplasm. The first step in the cytoplasmic recycling is catalyzed by the NagZ glycosylase, which cleaves in a hydrolytic reaction the N-acetylglucosamine glycosidic bond of metabolite 1. The reactions catalyzed by both the lytic glycosylases and NagZ are believed to involve oxocarbenium transition species. We describe herein the synthesis and evaluation of four iminosaccharides as possible mimetics of the oxocarbenium species, and disclose one as a potent (compound 3, K(i) = 300 ± 15 nM) competitive inhibitor of NagZ.

Gaining insight into the inhibition of glycoside hydrolase family 20 exo-β-N-acetylhexosaminidases using a structural approach

One useful methodology that has been used to give insight into how chemically synthesized inhibitors bind to enzymes and the reasons underlying their potency is crystallographic studies of inhibitor-enzyme complexes. Presented here is the X-ray structural analysis of a representative family 20 exo-β-N-acetylhexosaminidase in complex with various known classes of inhibitor of these types of enzymes, which highlights how different inhibitor classes can inhibit the same enzyme. This study will aid in the future development of inhibitors of not only exo-β-N-acetylhexosaminidases but also other types of glycoside hydrolases.

Inhibition of O-GlcNAcase using a potent and cell-permeable inhibitor does not induce insulin resistance in 3T3-L1 adipocytes

To probe increased O-GlcNAc levels as an independent mechanism governing insulin resistance in 3T3-L1 adipocytes, a new class of O-GlcNAcase (OGA) inhibitor was studied. 6-Acetamido-6-deoxy-castanospermine (6-Ac-Cas) is a potent inhibitor of OGA. The structure of 6-Ac-Cas bound in the active site of an OGA homolog reveals structural features contributing to its potency. Treatment of 3T3-L1 adipocytes with 6-Ac-Cas increases O-GlcNAc levels in a dose-dependent manner. These increases in O-GlcNAc levels do not induce insulin resistance functionally, measured using a 2-deoxyglucose (2-DOG) uptake assay, or at the molecular level, determined by evaluating levels of phosphorylated IRS-1 and Akt. These results, and others described, provide a structural blueprint for improved inhibitors and collectively suggest that increased O-GlcNAc levels, brought about by inhibition of OGA, does not by itself cause insulin resistance in 3T3-L1 adipocytes.

Elevation of Global O-GlcNAc in rodents using a selective O-GlcNAcase inhibitor does not cause insulin resistance or perturb glucohomeostasis

The O-GlcNAc modification is proposed to be a nutrient sensor with studies suggesting that global increases in O-GlcNAc levels cause insulin resistance and impaired glucohomeostasis. We address this hypothesis by using a potent and selective inhibitor of O-GlcNAcase, known as NButGT, in a series of in vivo studies. Treatment of rats and mice with NButGT, for various time regimens and doses, dramatically increases O-GlcNAc levels throughout all tissues but does not perturb insulin sensitivity or alter glucohomeostasis. NButGT also does not affect the severity or onset of insulin resistance induced by a high-fat diet. These results suggest that pharmacological increases in global O-GlcNAc levels do not cause insulin resistance nor do they appear to disrupt glucohomeostasis. Therefore, the protective benefits of elevated O-GlcNAc levels may be achieved without deleteriously affecting glucohomeostasis.

4-C-Me-DAB and 4-C-Me-LAB - enantiomeric alkyl-branched pyrrolidine iminosugars - are specific and potent α-glucosidase inhibitors; acetone as the sole protecting group

The syntheses of 4-C-Me-DAB [1,4-dideoxy-1,4-imino-4-C-methyl-d-arabinitol] from l-erythronolactone and of 4-C-Me-LAB [from d-erythronolactone] require only a single acetonide protecting group. The effect of pH on the NMR spectra of 4-C-Me-DAB [pK(a) of the salt around 8.4] is discussed and illustrates the need for care in analysis of both coupling constants and chemical shift. 4-C-Me-DAB (for rat intestinal sucrase K(i) 0.89 μM, IC(50) 0.41 μM) is a competitive - whereas 4-C-Me-LAB (for rat intestinal sucrase K(i) 0.95 μM, IC(50) 0.66 μM) is a non-competitive - specific and potent α-glucosidase inhibitor. A rationale for the α-glucosidase inhibition by DAB, LAB, 4-C-Me-DAB, 4-C-Me-LAB, and isoDAB - but not isoLAB - is provided. Both are inhibitors of endoplasmic reticulum (ER) resident α-glucosidase I and II.

A high-throughput matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry-based assay of chitinase activity

A high-throughput matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) assay is described for determination of chitolytic enzyme activity. The assay uses unmodified chitin oligosaccharide substrates and is readily achievable on a microliter scale (2μl of total volume containing 2μg of substrate and 1ng of protein). The speed and sensitivity of the assay make it potentially well suited for the high-throughput screening of chitinase inhibitors. The mass spectrum is acquired in approximately 2min, as opposed to typically 30-40min for a single run with a high-performance liquid chromatography (HPLC)-based assay. By using the multiple-place MALDI MS targets, we estimate that 100 assays could be run in approximately 2-3h without needing to remove the target from the instrument. In addition, because the substrate and product chitomers are visualized simultaneously in the TOF spectrum, this gives immediate information about the cleavage site and mechanism of the enzyme under study. The assay was used to monitor the purification and transgenic expression of plant class IV chitinases. By performing the assay with chitomer substrates and C-glycoside chitomer analogs, the enzyme mechanism of the class IV chitinases is described for the first time.

2-Acetamido-N-benzyl-1,4-imino-1,2,4-trideoxy-L-xylitol (N-benzyl-L-XYLNAc)

X-ray crystallography defines the relative configuration at the three-stereogenic centres in the title compound N-benzyl-l-XYLNAc, C₁₄H₂₀N₂O₃. The five-membered pyrrolidine ring adopts an envelope conformation with the N atom lying out of the plane of the other four atoms. In the crystal structure, inter­molecular O—H⋯O, N—H⋯O and O—H⋯N hydrogen bonds link the mol­ecules into chains along [100]. The carbonyl group O atom acts as an acceptor for a bifurcated hydrogen bond. The absolute configuration is determined by the use of l-glucuronolactone as the starting material for the synthesis.