Synthesis of Modified Peptidoglycan Precursor Analogues for the Inhibition of Glycosyltransferase.

The peptidoglycan glycosyltransferases (GTs) are essential enzymes that catalyze the polymerization of glycan chains of the bacterial cell wall from lipid II and thus constitute a validated antibacterial target. Their enzymatic cavity is composed of a donor site for the growing glycan chain (where the inhibitor moenomycin binds) and an acceptor site for lipid II substrate. In order to find lead inhibitors able to fill this large active site, we have synthesized a series of substrate analogues of lipid I and lipid II with variations in the lipid, the pyrophosphate, and the peptide moieties and evaluated their biological effect on the GT activity of E. coli PBP1b and their antibacterial potential. We found several compounds able to inhibit the GT activity in vitro and cause growth defect in Bacillus subtilis . The more active was C16-phosphoglycerate-MurNAc-(l-Ala-d-Glu)-GlcNAc, which also showed antibacterial activity. These molecules are promising leads for the design of new antibacterial GT inhibitors

Synthesis of α-l-Threose Nucleoside Phosphonates via Regioselective Sugar Protection

A new synthesis route to α-l-threose nucleoside phosphonates via 2-O and 3-O selectively protected l-threose is developed. The key intermediates 2-O-benzoyl-l-threonolactone and 1-O-acetyl-2-O-benzoyl-3-O-t-butyldiphenylsilyl-l-threofuranose were functionalized to synthesize 2'-deoxy-2'-fluoro- and 3'-C-ethynyl l-threose 3'-O-phosphonate nucleosides. The key intermediates developed are important intermediates for the synthesis of new l-threose-based nucleoside analogues, TNA phosphoramidites, and TNA triphosphates.status: publishe

Synthesis of new acyclic nucleoside phosphonates (ANPs) substituted on the 1 ' and/or 2 ' positions

A series of 2' functionalized acyclic nucleoside phosphonate derivatives of 1-[3'-(phosphonomethoxy)propyl]uracil (1-4) have been synthesized together with the 1' and 2'-ethynyl derivatives of 9/1-[2'-(phosphonomethoxy)ethyl]adenine/thymine (5-7). Key intermediates leading to the latter series are (+/-)-[2-{diethyl(phosphonomethoxy)}-1-hydroxy]-but-3-yne (25) and (+/-)-diisopropyl{[2-hydroxy-4-(trimethylsilyl)but-3-yn-1-yl]oxy}methylphosphonate (30). Compounds 25 and 30 are easily obtained starting from (+/-)-solketal. (C) 2011 Elsevier Ltd. All rights reserved.status: publishe

Synthesis and Conformation of Pentopyranoside Nucleoside Phosphonates

In contrast to natural nucleosides, where the nucleobase is positioned at the anomeric center, we report the synthesis of pentopyranoside nucleosides with a phosphonate functionality at the 1'-anomeric oxygen. Starting from l-arabinose, key functionalized l- glycero- and l- erythro-pentopyranose carbohydrate synthons were prepared and further elaborated into the final six-membered ring nucleosides via nucleobase incorporation and phosphonomethylation reactions. NMR analysis demonstrated that these nucleoside phosphonates exist in solution as conformers predominantly adopting a chair structure in which the base moiety is equatorially positioned. Such conformation prevents unfavorable 1,3-diaxial steric and electronic interactions. Notably, the stereochemical outcome of the Vorbrüggen glycosylation step utilized en route to the thymine analogue clearly suggests the absence of anchimeric assistance, as opposed to what is usually observed during nucleoside synthesis using protected furanose precursors. The finding that the diphosphates of the compounds developed in this study are recognized by DNA polymerases is important in view of the future selection of artificial genetic systems and dedicated polymerases as well as applications in therapy.status: publishe

Convergent approach toward the synthesis of the stereoisomers of C-6 homologues of 1-deoxynojirimycin and their analogues: evaluation as specific glycosidase inhibitors

A new and stereoselective strategy is developed to synthesize an appropriate template 9 to obtain C-6 homologues of 1-deoxyazasugars such as 1-deoxy-d-galactohomonojirimycin (5), 1-deoxy-4-hydroxymethyl-d-glucohomonojirimycin (6), and their enantiomers. The template 9 is also used to obtain neutral nonbasic pseudo-glyconolactam (8), C-4 amino, and methyl analogues of 1-deoxy-homonojirimycin as new analogues of 1-deoxyhomoazasugars. Compound 5 is found to be a potent and specific inhibitor to α-galactosidase (Ki = 1.7 μ M). Similarly compounds 6 (Ki = 28 μ M), ent-5 (Ki = 129 μ M), and ent-6 (Ki = 12 μ M) exhibited specific inhibition of β -glucosidase

Peptidoglycan glycosyltransferase-ligand binding assay based on tryptophan fluorescence quenching.

Peptidoglycan glycosyltransferases (GTase) of family 51 are essential enzymes for the synthesis of the glycan chains of the bacterial cell wall. They are considered potential antibacterial target, but discovery of inhibitors was hampered so far by the lack of efficient and affordable screening assay. Here we used Staphylococcus aureus MtgA to introduce a single tryptophan reporter residue in selected positions flanking the substrates binding cavity of the protein. We selected a mutant (Y181W) that shows strong fluorescence quenching in the presence of moenomycin A and two lipid II analogs inhibitors. The assay provides a simple method to study GTase-ligand interactions and can be used as primary high throughput screening of GTase inhibitors without the need for lipid II substrate or reporter ligands

Peptidoglycan glycosyltransferase-ligand binding assay based on tryptophan fluorescence quenching

Peptidoglycan glycosyltransferases (GTase) of family 51 are essential enzymes for the synthesis of the glycan chains of the bacterial cell wall. They are considered potential antibacterial target, but discovery of inhibitors was hampered so far by the lack of efficient and affordable screening assay. Here we used Staphylococcus aureus MtgA to introduce a single tryptophan reporter residue in selected positions flanking the substrates binding cavity of the protein. We selected a mutant (Y181W) that shows strong fluorescence quenching in the presence of moenomycin A and two lipid II analogs inhibitors. The assay provides a simple method to study GTase-ligand interactions and can be used as primary high throughput screening of GTase inhibitors without the need for lipid II substrate or reporter ligands.status: publishe

Synthesis of α‑l‑Threose Nucleoside Phosphonates via Regioselective Sugar Protection

A new synthesis route to α-l-threose nucleoside phosphonates via 2-<i>O</i> and 3-<i>O</i> selectively protected l-threose is developed. The key intermediates 2-<i>O</i>-benzoyl-l-threonolactone and 1-<i>O</i>-acetyl-2-<i>O</i>-benzoyl-3-<i>O</i>-<i>t</i>-butyldiphenylsilyl-l-threofuranose were functionalized to synthesize 2′-deoxy-2′-fluoro- and 3′-<i>C</i>-ethynyl l-threose 3′-<i>O</i>-phosphonate nucleosides. The key intermediates developed are important intermediates for the synthesis of new l-threose-based nucleoside analogues, TNA phosphoramidites, and TNA triphosphates

Synthesis and evaluation of 1-deoxy-8-epi-castanospermine, 1-deoxy-8-hydroxymethyl castanospermine, and (6S,7S,8R,8aR)-8-amino-octahydroindolizine-6,7-diol

A short, versatile, and enantioselective synthesis of 1-deoxy-8-epi-castanospermine (5), 1-deoxy-8-hydroxymethyl castanospermine (6), and (6S,7S,8R,8aR)-8-amino-octahydroindolizine-6,7-diol (7) is achieved from a common template 12. The key step utilized is PET provoked amine radical cyclization of 11 to 12 in excellent diastereoselectivity. The exocyclic double bond at C-8 of the template is functionalized to obtain 5-7 as exclusive diastereomers. 1-Deoxy-8-epi-castanospermine exhibited inhibition of α- and β-galactosidase and β-glucosidase. Compounds 6 and 7 were found to be weak inhibitors of β-glucosidase