Synthesis of monodeoxy and mono- O-methyl congeners of methyl β- d-mannopyranosyl-(1→2)-β- d-mannopyranoside for epitope mapping of anti- Candida albicans antibodies (original) (raw)
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The Journal of Organic Chemistry, 2006
The synthesis of 4,6-O-benzylidene protected 2-deoxy-arabino, 3-deoxy-arabino-, and 3-deoxy-ribothioglycosides is described and their glycosylation reactions, with activation by either 1benzenesulfinyl piperidine/trifluoromethansulfonic anhydride or diphenyl sulfoxide/ trifluoromethanesulfonic anhydride, studied. In contrast to the corresponding 4,6-O-benzylidene protected glucosyl and mannosyl donors, which are αand β-selective, respectively, poor diastereoselectivity is observed in all cases. The reasons for this poor selectivity are discussed in terms of the interaction between the C2-O2 and C3-O3 bonds in the glucosyl and mannosyl donors and of the influence of this interaction on the ease of formation of the intermediate glycosyl oxacarbenium ions.
Carbohydr. Res, 1989
Four different oligosaccharides containing the 2-acetamido-2-deoxy-@Dglucopyranosyl-(1+2)-aD -mannopyranosyl sequence as a terminal disaccharide unit were synthesized, namely: 4-nitrophenyl O-(2-acetamido-2-deoxy$-D-glucopyranosyl)-(1~2)-O-rw-D-mannopyranosyl-(l~6)-~-D-mannopyranoside (27), 4nitrophenyl 0-(2-acetamido-2-deoxy-~-D-glucopyranosyl)-(l~2)-O-~-D-mannopyranosyl-(1+6)-P-D-glucopyranoside (29)) ally1 O-(2-acetamido-Zdeoxy-P-Dglucopyranosyl-(1~2)-aD -mannopyranosyl-(l~6)-~-D-glucopyranoside (31), and ally1 0-(2-acetamido-2-deoxy-P-D-glucopyranosyI)-(1~2)-0-cy-D-mannopyranosyl-(1~6)-O-P-D-glucopyranosyl-(l~4)-p-D-glucopyranoside (33). A common glycosyl donor, namely, 2-0-(2-acetamido-3,4,6-triO -acetyl-2-deoxy-P-D-glucopyranosyl)-3,4,6-triO -acetyl-cuD -mannopyranosyl bromide was employed for the synthesis of 27, 29, 31, and 33, the structures of which were all established by 13Cn.m.r. spectroscopy.
Organic Letters, 2008
2,3-Di-O-benzyl-4,6-O-benzylidene-thiohexopyranosides, on activation with 1-benzenesulfinyl piperidine and triflic anhydride, react with allyl silanes and stannanes, and with silyl enolethers to give C-glycosides. In mannose the β-isomers are formed selectively whereas the glucose series provides the α-anomers. This selectivity pattern parallels that of O-glycoside formation and eliminates the need to consider donor-acceptor hydrogen bonding in the formation of the Oglycosides. 4,6-O-Benzylidene protected mannopyranosyl triflates carrying ether-type blocking groups on O2 and O3 are highly β-selective in their reactions with alcohols. 1,2 This selectivity is independent of the nature of the triflate precursor, thioglycoside or sulfoxide, and extends to other classes of glycosyl donor including the imidates, 3 the 2-hydroxycarbonylbenzyl glycosides, 4 and the phosphites. 5 The selectivity, however, is highly dependent on the presence of the benzylidene acetal or related group, as the corresponding tetra-O-benzyl or alkyl donors are unselective under comparable conditions. 1 In terms of reaction mechanism, the covalent triflate 6 is understood to serve as a resevoir for a transient contact ion pair (CIP) and, thereafter, for a solvent separated ion pair (SSIP). The CIP, in which the triflate shields the α-face of the oxacarbenium ion, is β-selective whereas the SSIP is α-selective in agreement with the dictates of the anomeric effect (Scheme 1). 7 As established by Bols, 8 the benzylidene effect is due to the locking of the C5-C6 bond in the most electron-withdrawing trans-gauche conformation, which destabilizes the oxacarbenium ion and limits the concentration of the undesired, αselective SSIP.
Journal of Organic Chemistry, 2007
A series of 4,6-O-benzylidene protected 2-O-benzyl-3-deoxy-3-fluoro-and 3-O-benzyl-2-deoxy-2fluoro-gluco-and mannopyranosyl thioglycosides were synthesized and their coupling reactions with a series of alcohols, on preactivation with 1-benzenesulfinylpiperidine and trifluoromethanesulfonic anhydride, investigated. In all cases the selectivities were lower than observed with the corresponding simple 4,6-O-benzylidene 2,3-O-benzyl gluco-and mannopyranosyl thioglycosides. This leads to the conclusion that the high β-selectivity observed with 4,6-O-benzylidene 2,3-Obenzylmannopyranosyl donors under the same conditions is in large part derived from the compression of the O2-C2-C3-O3 torsion angle on going from the intermediate covalent glycosyl triflate to the oxacarbenium ion, as compared to the relaxation of this torsion angle in the glucoseries.
Liebigs Annalen der Chemie, 1985
P-D-Galp-( 1 -+4)-@-~-ManpNAc-(l-+6)-~-Gd (ll), and @-D-Galp-( 1 -+4)-a-~-GlcpNAc-(1 -+6)-~-Gal(l2) is achieved utilizing the readily accessible lactose-derived building blocks hexa-0-benzoyl-a-D-lactosulosyl bromide (4) and its 2-(benzoyloxy)imino analogue 5 as glycosyl donors and 1,2: 3,4-di-O-isopropylidene-~-gdactose (6) as the acceptor. Stereocontrolled a-(silver triflate) and @-glycosidations (silver carbonate) were as smoothly effected as the subsequent, essentially stereospecific reductions of 0x0 (NaBH4) and (benzoy1oxy)imino functions (diborane). The overall yields of 55-60% attainable for 4 -+ 8 and 5 -+ 11/ 12 render this disaccharide-derived building block approach highly effective for the construction of oligosaccharides with interior @-D-Man, @-D-ManNAc, and a-D-GlcNAc units.
A convenient synthesis of short-chain α-(1 → 2) mannopyranosyl oligosaccharides
Carbohydrate Research, 2020
Sugar 1,2-orthoesters are by-products of chemical glycosylation reactions that can be subsequently rearranged in situ to give trans glycosides. They have been used as donors in the synthesis of the latter glycosides with good regio- and stereo-selectivity. Alkyl α-(1 → 2) linked mannopyranosyl disaccharides have been reported as the major products from the rearrangement of mannopyranosyl orthoesters. Recent studies in this laboratory have shown that α-(1 → 2) linked mannopyranosyl di-, tri- and tetrasaccharides can be obtained in one step from mannopyranosyl allyl orthoester under optimized reaction conditions. In addition to the expected mono- and disaccharides (56%), allyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl-(1 → 2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl-(1 → 2)-tri-O-acetyl-α-D-mannopyranoside and allyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranosyl-(1 → 2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl-(1 → 2)-3,4,6-tri-O-acetyl-α-D-mannopyranosyl-(1 → 2)-3,4,6-tri-Oacetyl-α-D-mannopyranoside were obtained in 23% and 6% isolated yields, respectively, from the oligomerization of a β-D-mannopyranosyl allyl 1,2-orthoester, along with small amounts of higher DP oligomers. Possible mechanisms for the oligomerization and side reactions are proposed based on NMR and mass spectrometric data.
Synthesis of some disaccharide derivatives containing a β-l-rhamnopyranosidic bond
Carbohydrate Research, 1982
We have reportedrV2 a practical, stereoselective synthesis of P-D-mannopyranosides and /I-r_-rhamnopyranosides. The @-stereoselectivity of these glycosidations is the result' of the interaction of opposing dipoles of a strongly electronegative, nonparticipating substituent on C-2, and a highly reactive, electronegative leaving-group on C-l. A systematic study of the synthesis of oligosaccharides containing P-Lrhamnosyl residues is needed because this structural unit occurs in bacterial antigens3.". Recently, Kochetkov and his co-workers5 and Iversen and Bundle6 reported syntheses of @-L-rhamnopyranosides that involve approaches that have been used previously for the preparation of j%D-mannopyranosides7-10.
Molecules
Regioselective deprotection of acetylated mannose-based mono- and disaccharides differently functionalized in anomeric position was achieved by enzymatic hydrolysis. Candida rugosa lipase (CRL) and Bacillus pumilus acetyl xylan esterase (AXE) were immobilized on octyl-Sepharose and glyoxyl-agarose, respectively. The regioselectivity of the biocatalysts was affected by the sugar structure and functionalization in anomeric position. Generally, CRL was able to catalyze regioselective deprotection of acetylated monosaccharides in C6 position. When acetylated disaccharides were used as substrates, AXE exhibited a marked preference for the C2, or C6 position when C2 was involved in the glycosidic bond. By selecting the best enzyme for each substrate in terms of activity and regioselectivity, we prepared a small library of differently monohydroxylated building blocks that could be used as intermediates for the synthesis of mannosylated glycoconjugate vaccines targeting mannose receptors of...