Study of glycosylation with N-trichloroacetyl-D-glucosamine derivatives in the syntheses of the spacer-armed pentasaccharides sialyl lacto-N-neotetraose and sialyl lacto-N-tetraose, their fragments, and analogues.

The syntheses of 2-aminoethyl glycosides of the pentasaccharides Neu5Ac-alpha(2-->3)-Gal-beta(1-->4)-GlcNAc-beta(1-->3)-Gal-beta(1-->4)-Glc and Neu5Ac-alpha(2-->3)-Gal-beta(1-->3)-GlcNAc-beta(1-->3)-Gal-beta(1-->4)-Glc, their asialo di-, tri-, and tetrasaccharide fragments, and analogues included a systematic study of glycosylation with variously protected mono- and disaccharide donors derived from N-trichloroacetyl-D-glucosamine of galactose, lactose, and lactosamine glycosyl acceptors bearing benzoyl protection around the OH group to be glycosylated. Despite the low reactivity of these acceptors, stereospecificity and good to excellent yields were obtained with NIS-TfOH-activated thioglycoside donors of such type, or with AgOTf-activated glycosyl bromides, while other promotors, as well as a trichloroacetimidate donor, were less effective, and a beta-acetate donor was inactive. In NIS-TfOH-promoted glycosylation with the thioglycosides, the use of TfOH in catalytic amount led to rapid formation of the corresponding oxazoline, but the quantity of TfOH necessary for further efficient coupling with an acceptor depended on the reactivity of the donor, varying from 0.07 equiv for a 3,6-di-O-benzylated monosaccharide derivative to 2.1 equiv for a peracetylated disaccharide one. In the glycosylation products, the N-trichloroacetyl group was easily converted into N-acetyl by alkaline hydrolysis followed by N-acetylation.

Synthesis of propyl and 2-aminoethyl glycosides of alpha-D-galactosyl-(1-->3')-beta-lactoside.

Propyl and 2-aminoethyl alpha-D-galactopyranosyl-(1-->3')-beta-lactosides (1 and 2) were prepared from the corresponding perbenzylated trisaccharide allyl glycoside 6 which, in turn, was obtained by methyl triflate promoted alpha-galactosylation of benzylated allyl lactoside acceptor 4 with thiogalactoside 3. Transformation of the allyl moiety in compound 6 into 2-azidoethyl one was achieved by cleavage of the double bond followed by reduction into alcohol 9, subsequent mesylation, and mesylate-->azide substitution. Alternatively trisaccharide 2 was synthesized using alpha-galactosylation of selectively benzoylated 2-azidoethyl lactoside 19 with 3 as the key step.

Synthesis of Neu5Ac- and Neu5Gc-alpha-(2-->6')-lactosamine 3-aminopropyl glycosides.

In order to prepare 3-aminopropyl glycosides of Neu5Ac-alpha-(2-->6')-lactosamine trisaccharide 1, and its N-glycolyl containing analogue Neu5Gc-alpha-(2-->6')-lactosamine 2, a series of lactosamine acceptors with two, three, and four free OH groups in the galactose residue was studied in glycosylations with a conventional sialyl donor phenyl [methyl 5-acetamido-4,7,8,9-tetra-O-acetyl-3,5-dideoxy-2-thio-D-glycero-alpha- and beta-D-galacto-2-nonulopyranosid]onates (3) and a new donor phenyl [methyl 4,7,8,9-tetra-O-acetyl-5-(N-tert-butoxycarbonylacetamido)-3,5-dideoxy-2-thio-D-glycero-alpha- and beta-D-galacto-2-nonulopyranosid]onates (4), respectively. The lactosamine 4',6'-diol acceptor was found to be the most efficient in glycosylation with both 3 and 4, while imide-type donor 4 gave slightly higher yields with all acceptors, and isolation of the reaction products was more convenient. In the trisaccharides, obtained by glycosylation with donor 4, the 5-(N-tert-butoxycarbonylacetamido) moiety in the neuraminic acid could be efficiently transformed into the desired N-glycolyl fragment, indicating that such protected oligosaccharide derivatives are valuable precursors of sialo-oligosaccharides containing N-modified analogues of Neu5Ac.

Synthesis of 3-O-sulfoglucuronyl lacto-N-neotetraose 2-aminoethyl glycoside and biotinylated neoglycoconjugates thereof.

The 2-aminoethyl glycoside of pentasaccharide 3-O-sulfo-GlcA(beta-1-->3)Gal(beta-1-->4)GlcNAc(beta-1-->3)Gal(beta-1--> 4)Glc(beta (1) and its conjugates with biotin and biotinylated polyacrylic acid were synthesized as molecular probes to investigate the recognition of the HNK-1 epitope containing carbohydrates by proteins. Key steps in the first of two investigated schemes for the preparation of the target compound 1 were (a) assembling of the pentasaccharide backbone (compound 10) by glycosylation of selectively substituted allyl glycoside of the trisaccharide GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta with glucuronyl-galactose glycosyl donor, (b) transformation of the allyl aglycon in 10 into 2-azidoethyl one (to give 11), (c) selective deprotection of the OH group at C-3 of the GlcA residue in 11 via saponification, intramolecular formation of 6,3-lacton (13) and its methanolysis, and (d) subsequent O-sulfation. The alternative scheme with the use of 2-azido-ethyl glycoside of the trisaccharide GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta instead of the allyl glycoside 6 was less effective due to smaller yield at the step of pentasaccharide synthesis. Additionally to 1 the 2-aminoethyl glycosides of the oligosaccharides GlcA(beta-1-->3)Gal(beta-1-->4)GlcNAc(beta-1-->3)Gal(beta-1-->4)Glc(beta, 3-O-sulfo-GlcA(beta-1-->3)Gal(beta, and GlcA(beta-1-->3)Gal(beta were also synthesized.

[Synthesis of oligosaccharides related to HNK-1 antigen. 2. Synthesis of 3'''-O-(3-O-sulfo-beta-D-glucuronopyranosyl)-lacto-N-neotetrao se beta-propylglycoside]. / Sintez oligosakharidov, rodstvennykh antigenu HNK-1. 2. Sintez beta-propilglikozida 3'''-O-sulfo-beta-D-gliukuronopiranozil)-lakto- N-neotetraozy.

A derivative of allyl 3"-O-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-beta-lactoside with a free OH group at C-4GlcNAc was glycosylated with trichloroacetimidate of selectively protected GlcA(beta 1-->3)Gal alpha disaccharide in dichloromethane in the presence of trimethylsilyl triflate resulting in a pentasaccharide product with an 82% yield. This product was converted to monohydroxy derivative with a free OH group at C-3GlcA via the formation and the subsequent opening of the 6,3-lactone ring in the glucuronic acid residue. The 3"'-O-sulfation of the monohydroxy derivative, the removal of the protective groups, and the reduction of the allyl aglycon yielded the pentasaccharide propyl glycoside NaSO3-3GlcA(beta 1-->3)Gal(beta 1-->4)GlcNAc(beta 1-->3)Gal(beta 1-->4)Glc beta-Opr comprising the oligosaccharide chain of the SGGL-1 glycolipid, which is recognized by HNK-1 antibodies. NaSO3-3GlcA(beta 1--> 3)Gal beta OAll, GlcA(beta 1-->3)Gal(beta 1-->4)GlcNAc(beta 1-->3)Gal(beta 1-->4)Glc beta-OPr and GlcA(beta 1-->3)Gal beta OAll were synthesized in a similar way.

[Synthesis and study of NMR spectra and conformations of branched oligosaccharides. 2,3-di-O-glycosylated methyl-alpha-L-rhamnopyranosides with one or two 2-acetamido-2-deoxy-beta-D-glucopyranosyl residues]. / Sintez i issledovanie spektrov IaMR i konformatsii razvetvlennykh oligosakharidov. 2,3-Di-O-glikozilirovannye metil-alpha-L-ramnopiranozidy s odnim ili dvumia 2-atsetamido-2-dezoksi-beta-D-gliukopiranozil'nymi ostatkami.

A series of methyl 2,3-di-O-glycosyl-alpha-L-rhamnopyranosides with 2-acetamido-2-deoxy-beta-D-glucopyranosyl substituents have been synthesized and the deviations from additivity (delta delta) in their 13C-NMR spectra determined. It is shown that the delta delta values for the trisaccharides with the GlcNAc substituent at O-2 of the diglycosylated Rha may markedly differ from the delta delta values in the spectra of the respective trisaccharides with the Glc substituent. These deviations are probably associated with the intramolecular spatial interactions with participation of the NHAc-group.