Synthesen und Reaktionen von 1,2-Didesoxy-Hexopyrano-[2,1-d]-Oxazolinen und -Oxazoliniumsalzen1,2

Synthesis and study of the glycosyl-donor properties of 2-(2,2,2-trichloroethoxy)-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-galactopyrano)-[2,1-d]-2-oxazoline

A synthesis of 2-(2,2,2-trichloroethoxy)-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-d-galactopyrano)-[2,1-d]-2-oxazoline - a previously unknown 2-alkoxy glyco-[2,1-d]-2-oxazoline derivative with d-galacto configuration was carried out. Glycosylating activity of the obtained galactooxazoline has been studied and it has been shown that in the presence of a weak protic acid, such as sym-collidinium triflate, this substance exhibits properties of a reactive and 1,2-trans-stereoselective glycosyl donor. The homopolymerization reaction of oxazoline derivatives of sugars has been found to proceed under the same conditions, leading to the formation of pseudo-oligosaccharide products. It has been found that this undesirable side reaction could be suppressed by changing the acid catalyst concentration, resulting in the development of efficient methods for the synthesis of glycoside and oligosaccharide derivatives of β-d-galactosamine using the synthesized 2-(2,2,2-trichloroethoxy)-2-oxazoline glycosyl donor under very mild conditions.

New methods for the synthesis of 2-(2,2,2-trichloroethoxy)-(3,4,6-tri-O-acetyl-1,2-dideoxy-α-D-glucopyrano)-[2,1-d]-2-oxazoline and its use for stereo-, chemo- and regioselective glycosylation

New methods for the synthesis of the title oxazoline 2 from the corresponding 2-deoxy-2-(2,2,2- trichloroethoxycarbonylamino)glucosyl bromide were developed. The target 2-(2,2,2-trichloroethoxy) gluco-[2,1-d]-2-oxazoline 2 can be synthesized under conditions of halide ion catalysis, using triethylamine as a base. The synthesized 2-(2,2,2-trichloroethoxy)-2-oxazoline glycosyl donor was used for stereo-, regio-, and chemoselective glycosylation reactions under extremely mild conditions. The undesirable side reaction of intermolecular aglycone transfer between an ethyl thioglycoside glycosyl acceptor and the 2-(2,2,2-trichloroethoxy)-2-oxazoline glycosyl donor occurred to a relatively small extent. Regio-, and chemoselectivity of the disaccharide synthesis with the oxazoline glycosyl donor depended on the reaction conditions.

The study of the acid-catalyzed reaction between 2-methyl and 2-(2,2,2-trichloroethoxy) gluco-[2,1-d]-2-oxazolines. Synthesis of macrocyclic pseudo-tetrasaccharide derivative of d-glucosamine

The formation of macrocyclic pseudo-tetrasaccharide derivative of d-glucosamine as a result of the acid-catalyzed reaction between 2-methyl- and 2-(2,2,2-trichloroethoxy)-substituted oxazoline derivatives of sugars was discovered. The structure of the obtained product was determined using NMR spectroscopy and mass spectrometry. An explanation of the obtained results based on the mechanism of the reaction of electrophilic polymerization of 2-substituted glyco-[2,1-d]-2-oxazolines and the principle of hard and soft acids and bases (HSAB) was proposed.

A Synthetic MUC1 Glycopeptide Bearing βGalNAc-Thr as a Tn Antigen Isomer Induces the Production of Antibodies against Tumor Cells

This study presents the synthesis of the novel protected O-glycosylated amino acid derivatives 1 and 2, containing βGalNAc-SerOBn and βGalNAc-ThrOBn units, respectively, as mimetics of the natural Tn antigen (αGalNAc-Ser/Thr), along with the solid-phase assembly of the glycopeptides NHAcSer-Ala-Pro-Asp-Thr[αGalNAc]-Arg-Pro-Ala-Pro-Gly-BSA (3-BSA) and NHAcSer-Ala-Pro-Asp-Thr[βGalNAc]-Arg-Pro-Ala-Pro-Gly-BSA (4-BSA), bearing αGalNAc-Thr or βGalNAc-Thr units, respectively, as mimetics of MUC1 tumor mucin glycoproteins. According to ELISA tests, immunizations of mice with βGalNAc-glycopeptide 4-BSA induced higher sera titers (1:320 000) than immunizations with αGalNAc-glycopeptide 3-BSA (1:40 000). Likewise, flow cytometry assays showed higher capacity of the obtained anti-glycopeptide 4-BSA antibodies to recognize MCF-7 tumor cells. Cross-recognition between immunopurified anti-βGalNAc antibodies and αGalNAc-glycopeptide and vice versa was also verified. Lastly, molecular dynamics simulations and surface plasmon resonance (SPR) showed that βGalNAc-glycopeptide 4 can interact with a model antitumor monoclonal antibody (SM3). Taken together, these data highlight the improved immunogenicity of the unnatural glycopeptide 4-BSA, bearing βGalNAc-Thr as Tn antigen isomer.

Synthesis of 2-Amino-2-deoxy-β-D-galactopyranosyl-(1→4)-2-amino-2-deoxy-β-D-galactopyranosides: Using Various 2-Deoxy-2-phthalimido-D-galactopyranosyl Donors and Acceptors

A systematic study is presented of the efficiency of the most common glycosylation methods using standard 2-deoxy-2-phthalimidogalactopyranosyl donors ethyl 4-O-acetyl-3,6-di-O- benzyl-2-deoxy-2-phthalimido-1-thio-β-D-galactopyranoside (3a), 4-O-Acetyl-3,6-di-O-benzyl- 2-deoxy-2-phthalimido-β-D-galactopyranosyl bromide (4), 4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl fluoride (5b), O-(4-O-acetyl-3,6-di-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranosyl) trichloroacetimidate (7) and ethyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-1-thio-β-D-galactopyranoside (8), pent-4-enyl 3,6-di-O-benzyl- and 3-O-allyl-6-O-benzyl-2-deoxy-2-phthalimido-β-D-galactopyranoside (10a) and (10b) and pent-4-enyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-4-O-(trimethylsilyl)-β-D-galactopyranoside (11) as glycosyl acceptors in the synthesis of 2-amino-2-deoxy-β-D-galactopyranosyl-(1→4)-2-amino-2-deoxy-β-D-galactopyranosides 12, 16a and 17a. It was found that due to a low reactivity of the axial OH(4) group of glycosyl acceptors, disaccharides 16b and 17b with α(1→4) bond were also formed. The unexpected intermolecular migration of ethylsufanyl group from the reducing end of glycosyl acceptor 8 the reducing end of the activated form of glycosyl donor 4 in the glycosylation step to give ethylsulfanyl derivative 3a was proved. For preparation of the glycosyl donors and glycosyl acceptors with galacto configuration an approach based on epimerization of 4-O-mesyl derivatives of appropriate synthons with gluco configuration 2a and 2b was employed.

Improved Synthesis of 1,2-trans-Acetates and 1,2-trans Ethyl 1-Thioglycosides Derived from 3,4,6-Tri-O-acetyl-2-deoxy-2-phthalimido-D-hexopyranosides

Effective one-pot synthesis of 1,2-trans-acetates 4b, 5b and 6a derived from N-phthaloyl-protected D-glucosamine, D-galactosamine and D-mannosamine, respectively, is presented. Anomerisation of the corresponding 1,2-cis-acetates 4a, 5a and 6b and direct conversion of all of them to 1,2-trans ethyl 1-thioglycosides 7, 8 and 9 are also described and discussed.

An efficient synthesis of two monosulfated trisaccharides with the Galbeta1,3GlcNacbeta1,3Galbeta-O-allyl backbone

The GlcNAcbeta(1-->3) Gal linked disaccharide 7 was synthesized as key building blocks for the construction of target monosulfated trisaccharides 1 and 2 using oxazoline 3 as glycosyl donor promoted by BF3 x Et2O.

1,3,4,6-Tetra-O-acetyl-2-chloroacetamido-2-deoxy-beta-D-glucopyranose as a glycosyl donor in syntheses of oligosaccharides

1,3,4,6-Tetra-O-acetyl-2-chloroacetamido-2-deoxy-beta-D-glucopyran ose was tested as a glycosyl donor for oligosaccharide synthesis via a ferric chloride-catalyzed coupling reaction. Glycosyl acceptors tried (6 in all) were O-benzyl-protected D-galactosides having free OH groups at positions 3 and 4, respectively, and similarly protected glycosides of D-glucose and 2-acetamido-2-deoxy-D-glucose unsubstituted on O-4. Existing syntheses of all the acceptors were improved, in four instances by exploitation of Garegg and Hultberg's cyanoborohydride procedure for the conversion 4,6-O-benzylidene----6- O-benzyl [Carbohydr. Res., 93 (1981) c10-c11; 108 (1982) 97-101]. Good to excellent yields of beta-linked disaccharides were obtained from the galactoside and glucoside acceptors, but with allyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-alpha-D-glucopyranoside, stereoselectivity was lost (alpha:beta-ratio 1:2). Allyl and benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-beta-D-glucopyranosides gave, respectively, the allyl and benzyl beta-glycosides of the donor as major products. A mechanism is proposed for this transglycosidation reaction. The N-chloroacetyl groups in the disaccharide products were readily converted into N-acetyl by reduction with zinc-acetic acid.