Mild and efficient method for the cleavage of benzylidene acetals using HClO4–SiO2 and direct conversion of acetals to acetates

Concise synthesis of the pentasaccharide O-antigen of Escherichia coli O83:K24:H31 present in the Colinfant vaccine

“…Formation of compound 9 was confirmed from its spectral data [δ 5.47 (s, PhCH), 4.90 (d, J=8.5 Hz, H-1 B ), 4.69 (d, J=7.5 Hz, H-1 A ) in 1 H NMR and at δ 103.7 (C-1 A ), 101.9 (C-1 B ), 101.4 (PhCH) in 13 C NMR spectra]. Removal of benzylidene acetal from compound 9 using silica supported perchloric acid (HClO 4 -SiO 2 ) [27,28] (10). Compound 10 was treated with tert-butyldiphenylchloro silane in pyridine [29] to furnish 4-methoxyphenyl (2,3- (11).…”

Convergent synthesis of the pentasaccharide repeating unit of the O-antigenic polysaccharide of enterohaemorrhagic Escherichia coli O113

“…In a one-pot de-benzylidenation and O-acetylation reaction condition [24], compound 10 was treated with acetic anhydride in the presence HClO 4 -SiO 2 to give compound 11 in 80 % yield. Oxidative removal of p-methoxyphenyl group in compound 11 using ceric ammonium (IV) nitrate (CAN) [25] followed by the reaction of the resulting hemiacetal with trichloroacetonitrile in the presence of DBU [26] led to the formation of a α/β mixture of trisaccharide trichloroacetimidate derivate 12 in 74 % yield, which was immediately used in the next step (Scheme 2).…”

Synthesis of oligosaccharide fragments corresponding to the exopolysaccharide released by Streptococcus macedonicus Sc 136

“…Glycosylation of compound 14 with ethyl thioglycoside donor 6 [20], prepared from D-glucosamine hydrochloride in six steps, in the presence of NIS-TMSOTf [25] furnished tetrasaccharide derivative 15 in 82% yield. Removal of the benzylidene acetal [30] from the compound 15 using HClO 4 -SiO 2 afforded tetrasaccharide diol 16 in 90% yield (Scheme 1). Selective glycosylation of tetrasaccharide diol acceptor 16 with ethyl thioglycoside donor 8 [22], prepared from D-glucose in five steps, in the presence of NISTMSOTf [25] furnished pentasaccharide derivative 17 in 78% yield.…”

“…Selective glycosylation of tetrasaccharide diol acceptor 16 with ethyl thioglycoside donor 8 [22], prepared from D-glucose in five steps, in the presence of NISTMSOTf [25] furnished pentasaccharide derivative 17 in 78% yield. Conventional acetylation followed by removal of benzylidene acetal [30] from the compound 17 using HClO 4 -SiO 2 afforded pentasaccharide acceptor 18 in 95% yield, which was selectively glycosylated with ethyl thioglycoside donor 9 [23], prepared from D-galactose, in the presence of NIS-TMSOTf [25] to give hexasaccharide derivative 19 in 81% yield. Conversion of N-phthalimido group to N-acetyl group of compound 19 was achieved in two steps involving the treatment with hydrazine hydrate, followed by N-acetylation [31].…”