Nucleoside synthesis from thioglycosides

A general method for N-glycosylation of nucleobases promoted by (p-Tol)2SO/Tf2O with thioglycoside as donor

35 nucleosides were synthesized by coupling thioglycosides with pyrimidines and purines under the preactivation of (p-Tol)₂SO/Tf₂O in high yields and with β-stereoselectivities.

Highly efficient O-glycosylations with p-tolyl thioribosides and p-TolSOTf

A wide variety of p-tolyl thioriboside donors are examined for O-ribosylations of primary and secondary alcohols. p-Tolylsulfenyl trifluoromethanesulfonate (p-TolSOTf) is very effective in promoting O-ribosylations with p-tolyl thioriboside; all reactions are completed within 1-15 min to provide the desired products in good yield with reliable alpha/beta selectivity. A wide range of functional groups are tolerated under these conditions. The described O-ribosylation conditions are very useful for the generation of ribosaminouridine library molecules in solution or on polymer support.

Ring-Modified Analogues and Molecular Dynamics Studies To Probe the Requirements for Fungicidal Activities of Malayamycin A and Its N-Nucleoside Variants

The importance of functional group orientations and the integrity of the bicyclic perhydrofuran core of malayamycin A and two equally active N-nucleoside analogues as fungicides were investigated. Two analogues 10 and 11, representing a THP-truncated and a bicyclic aza-variant, were synthesized and found to be inactive. Molecular dynamics studies on malayamycin A and analogues were performed to highlight the importance of properly orientating the urea and methyl ether groups.

Investigation of the regioselectivity for the staudinger reaction and its application for the synthesis of aminoglycosides with N-1 modification

The criteria for controlling the regioselectivity of Staudinger reduction of azides have been investigated. These findings enable a convenient direct N-1 modification of the perazidoneamine and perazidoribostamycin resulting in the synthesis of aminoglycoside antibiotics with activity against drug-resistant bacteria.

Structure-Based Organic Synthesis of a Tricyclic N-Malayamycin Analogue

The solid-state structure of crystalline malayamycin A reveals a urea substituent that bisects the plane of the chairlike tetrahydropyran subunit. On the basis of this topological feature, we synthesized a tricyclic N-nucleoside analogue in which an ethano bridge linked the urea NH group with the ring junction of the bicyclic tetrahydrofuropyran unit.

Short Synthesis of Octosyl Nucleosides

[reaction: see text] Commercial 1,2:5,6-di-O-isopropylidene-alpha-d-allofuranose was converted to a protected bicyclic octosyl acid thioglycoside donor by a 10-step sequence that features an intramolecular ester enolate alkylation. Glycosylation of N-benzoyladenine and methyl uridine-5-carboxylate followed by deprotection gave the respective nucleosides "octosyl adenine" and octosyl acid A.

Total Synthesis of N-Malayamycin A and Related Bicyclic Purine and Pyrimidine Nucleosides

Methods are described for the total synthesis of bicyclic perhydrofuropyran nucleosides as N-analogues of the naturally occurring malayamycin A. Formation of the N-nucleosides relied on the activation of thioglycosides, proceeding via sulfonium intermediates. Ring closure metathesis was used in two approaches to build the bicyclic dioxa heterocycle. Another approach relied on the use of a sugar precursor and cyclization to the bicyclic thioglycoside.

Synthesis of the ezomycin nucleoside disaccharide

[equation--see text] A protected ezomycin octosyl nucleoside was glycosylated at O-6' with a protected ezoaminuroic acid donor to afford, following several functional group modifications, the title compound 1 ( identical with 4-desamino-4-oxoezomycin A(2)).

Carbohydrate natural products as a scaffolding for the preparation of potential neuraminidase inhibitors

Compound 10b, 6-acetamido-6,8-dideoxy-D-erythro-beta-D- galacto-octopyranosyl-1-oxyacetic acid sodium salt, was synthesised by hydrazinolysis of Lincomycin, acetylation of methylthiolincosaminide (MTL) 9a, and by subsequent glycosylation of acetate 9b with methyl glycolate under mild conditions (NIS/TfOH). The methyl ester 10a was hydrolysed by treatment with Amberlite Ira-4OO (OH-) resin and aqueous sodium hydroxide, followed by neutralisation with Dowex-50 W x 8 (H+) resin and lyophilisation to give 10b. This carboxylate may represent the first derivative in a novel series of sialidase inhibitors utilising carbohydrate natural products. The phosphonate 11c, prepared under the same experimental conditions with dibenzyl(hydroxymethyl)phosphonate as acceptor, also displays an inhibitory activity towards Clostridium perfringens sialidase (Ki in mM range as with Neu5Ac).