Efficient one-pot per-O-acetylation–thioglycosidation of native sugars, 4,6-O-arylidenation and one-pot 4,6-O-benzylidenation–acetylation of S-/O-glycosides catalyzed by Mg(OTf)₂

Abstract

Sequential one-pot per-O-acetylation–S-/O-glycosidation under neat condition, regioselective 4,6-O-arylidenation and sequential one-pot benzylidenation–acetylation of Mg(OTf)2as non-hygroscopic, recyclable catalyst are reported.

Synthetic avenues towards a tetrasaccharide related to Streptococcus pneumonia of serotype 6A

“…The galactosyl trichloroacetimidate donor 2 was prepared following literature procedures [ 26 ]. On the other hand the D-glucosyl thioglycoside 8 was converted to the known benzylidene derivative 9 [ 29 – 30 ] according to our previously reported procedure. Benzylation of 9 under phase-transfer conditions led to 10 [ 31 ] in 49% yield ( Scheme 1 ).…”

“…The L-rhamnosyl thioglycoside 14 [ 29 – 30 ], prepared from L-rhamnose ( 13 ), was deacetylated quantitatively in the presence of Et 3 N/MeOH/H 2 O [ 35 ], and then stannylene-mediated selective naphthylmethylation at the O-3 position was carried out to give the known derivative 15 in 82% yield [ 36 ]. This was next benzoylated almost quantitatively to give 16 .…”

Synthesis of Structurally Defined Nitroxide Spin-Labeled Glycolipids as Useful Probes for Electron Paramagnetic Resonance (EPR) Spectroscopy Studies of Cell Surface Glycans

“…26,27 After all of the acetyl groups in 6b and 6c were removed by using NaOMe, the 4,6-O-positions were selectively protected with a benzylidene group by a reaction with benzaldehyde dimethyl acetal under the influence of p-toluenesulfonic acid (p-TsOH); this was followed by O-acetylation to give 16 and 17. [28][29][30] Next, the azido groups in 16 and 17 were reduced and the resultant free amines were coupled with lipid 7 according to the above-described protocols; this was followed by removal of the benzylidene group in methanol by using p-TsOH as the catalyst to afford diols 18 and 19 in good overall yields. Then, the primary 6-hydroxyl group in 18 and 19 was selectively tosylated with 1-tosylimidazole to provide 20 and 21.…”

One-pot construction of carbohydrate scaffolds mediated by metal catalysts

“…In a broader case study for this tandem sequence Mukherjee et al used 0.5 mol% of Mg(OTf) 2 as recyclable and robust catalyst for per-O-acetylation of unprotected mono and disaccharides, and subsequent one-pot transformation to the corresponding O-/S-glycosides, in reaction with various thiols and pmethoxyphenol, in the presence of 1.2 equivalents of BF 3 $Et 2 O ((C) in Scheme 1). 11 The corresponding S-/O-glycosides were isolated in excellent yields and exclusive 1,2-trans selectivity Scheme 1 One-pot per-O-acetylation-thioglycosidation reaction.…”

“…15 Later the same group used 0.1 equivalent of Mg(OTf) 2 as a single catalyst for 4,6-or 4 0 ,6 0 -Obenzylidene formation of mono and disaccharide glycosides followed by acetylation of the remaining free hydroxy groups in the same pot ((B) in Scheme 4) in comparable overall yield, 73-84%. 11 Galan and co-workers employed Cu(OTf) 2 as catalyst for onepot synthesis of diverse sugar derivatives. The one-pot procedure involving 4,6-O-benzylidene ring formation was extended to traditional acetylation and nally in situ reductive benzylidene ring opening.…”