Galabiosyl donors; efficient synthesis from 1,2,3,4,6-penta-O-acetyl-β- -galactopyranose

First Synthesis of the α‐L‐Serine Linked Consensus Disaccharide of Neisseria gonorrhoeae and Neisseria meningitidis

“…Next, the known 2,3,4,6-tetra-O-benzyl-b-1-thio-d-galactopyranoside 3 (obtained in 73 % yield over four steps from d-galactose), [13] was treated with bromine, and the so-formed glycosyl bromide was coupled with the acceptor 4, using AgOTf as the promoter, to obtain the a- Global deprotection of 2 involving conversion of the azido group to NHAc using the Zn/AcOH condition, [19] followed by reduction of benzyl, Cbz, and benzylidene acetal groups using H 2 and Pd(OH) 2 [20] afforded the desired target molecule 10 in very good yields. Target molecule 10 and all the synthetic intermediates were thoroughly characterized by 1 H, 13 C, and 2D NMR, as well as HRMS (see supporting information).…”

“…Target molecule 10 and all the synthetic intermediates were thoroughly characterized by 1 H, 13 C, and 2D NMR, as well as HRMS (see supporting information).…”

“…Target molecule 1 can be obtained from the fully protected derivative 2 upon reduction of azide, followed by N-acetylation and global deprotection of all the protecting groups under hydrogenolytic conditions (Scheme 1). The disaccharide 2 can be obtained by the coupling of the known thioglycoside donor 3 [13] with the 3-OH glycosyl acceptor 4, which can, in turn, be obtained by stereoselective coupling of a suitable d-glucosamine donor with an l-serine derived acceptor. It was anticipated that the C2-azido and C2-benzyl groups on the respective glycosyl donors, being non-participating groups in glycosylation, would assist in achieving a-selectivity.…”

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

“…The synthesis of compound 1 started with the glycosylation of the glycosyl acceptor 10 [24], prepared from D-glucose in three steps, with ethyl thioglycoside donor 4 [18], prepared from D-lactose octaacetate, in the presence of N-iodosuccinimide-methyltrifluoromethanesulfonate (NISTMSOTf) [25] to furnish trisaccharide derivative 11 in 78% yield. The compound 11 was converted to the trisaccharide derivative 12 in 60% over all yield following a sequence of reactions involving deacetylation, 3,4-Oisopropylidenation [26] and benzylation [27].…”

“…acetic acid afforded trisaccharide diol 13 in 90% yield, which was selectively acetylated [29] using triethyl orthoacetate to furnish trisaccharide acceptor 14 in 85% yield. 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).…”