Serge David

Preparation of disaccharides having a β-d-mannopyranosyl group from N-phthaloyllactosamine derivatives by double or triple SN2 substitution

Condensation of 1,2,3,4,6-penta-O-acetyl-beta-D-galactopyranose with methyl 3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranoside, followed by alkaline methanolysis, gave a derivative of lactosamine that has an unsubstituted beta-D-galactopyranosyl group. Tributyltin oxide-mediated allylation gave a good yield of the 3-O-allyl (9) and a poor yield of the 3,6-di-O-allyl ether (8). Protection of 9 at O-6 was achieved by reductive opening of the 4,6-O-anisylidene derivative, to give the 6-O-(4-methoxybenzyl) ether 15. Conversion of 8 and 15 to their 2,4-bis(trifluoromethanesulfonates), followed by SN2 reaction with benzoate, gave the corresponding beta-D-mannopyranosyl disaccharides. However, the model methyl 3-O-allyl-beta-D-galactopyranoside and 9 were converted into beta-D-mannopyranosyl derivatives in better yield (52-55%) by a one-pot, triple SN2 substitution of the tris(trifluoromethanesulfonates).

119Sn Nuclear magnetic resonance and mass spectrometric studies of the stannylenes of chiral and achiral diols: an interpretation of their regiospecific activation.

Resume 119 Sn n.m.r., and (in some cases) mass spectrometric studies of carbohydrate-derived chiral diols, and other ones, suggested that they are dimer with C-2 symmetry in all physical states (except, may be, in polar solvents), and this may be the origin of the unique nucleophilic enhancement of one oxygen atom to the parent diols.

The synthesis of 3,6-di-O-(2-acetamido-2-deoxy-β-D-glucopyranosyl)-D-galactose, a branched trisaccharide reported as a hydrolysis product of blood-group substances☆

Protected disaccharides were the only products that could be isolated after condensation of 3, 4, 6-tri-O-acetyl-2-deoxy-2-diphenoxyphosphoramido-alpha-D-glucopyranosyl bromide or 2-acetamido-3, 4, 6-tri-O-acetyl-2-deoxy-alpha-D-glucopyranosyl chloride with benzyl 2, 4-di-O-benzyl-beta-D-galactopyranoside. On the other hand, reaction of 2-methyl-(3, 4, 6-tri-O-acetyl-1, 2-dideoxy-alpha-D-glucopyrano)-[2, 1: 4, 5]-2-oxazoline (6 moles) with the same galactopyranoside (1 mole) gave benzyl 3, 6-di-O-(2-acetamido-3, 4, 6-tri-O-acetyl-beta-D-glucopyranosyl)-2, 4-di-O-benzyl-beta-D-galactopyranoside, which was converted, by alkaline methanolysis followed by hydrogenolysis, to the title compound. This appears identical with an oligosaccharide previously obtained through degredation of a blood-group A glycoprotein from hog gastric mucin.

Synthesis with immobilized enzymes of two trisaccharides, one of them active as the determinant of a stage antigen.

Abstract Glycosidation of disaccharides I and III with a system of five immobilized enzymes gave excellent yields of trisaccharides β-D -Gal-(1→4)- β-D -GlcNAc-(1→6)- D -Gal ¦ the I(Ma) determinant ¦ and β-D -Gal-(1→4)- β-D -Glc-NAc-(1→3)- D -Gal, on the milimole scale.

A simple, stereoselective, room-temperature synthesis of cis vinyloxiranes and trans 1-phenyl-1,3-butadiene

Abstract The organotin reagent from 1-chloro-3-iodoprop-1-ene and SnCl 2 in dimethylformamide reacted with aldehydes by ite chlorine-substituted carbon atom. Treatment with NaOMe then gave cis vinyloxiranes with good stereo-selectivity. benzaldehyde and 1-bromo-3-iodoprop-1-ene in the presence of two equivalents of SnCl 2 gave exclusively trans -1-phenyl-1,3-butadiene.

Synthesis with an immobilized enzyme of N-acetyl-9-O-acetyl-neuraminic acid, a sugar reported as a component of embryonic and tumor antigens

Abstract Condensation of 2-acetamido-6- O -acetyl-2-deoxy-D-mannose with pyruvic acid in the presence of immobilized acylneuraminate pyruvate lyase (2.8 units) gave 5-acetamido-9- O -acetyl-3,5-dideoxy-D- glycero -D- galacto -2-nonulopyranos-1-onic acid ( N -acetyl-9- O -acetylneuraminic acid) on the 0.3 mmole scale.

Réactivité des N-imidazolylsulfonates en C-2 D′α-d-manno- et galacto-pyranosides

Abstract The N -imidazolylsulfonyl derivatives of methyl 3- O -benzyl-4,6- O -benzylidene-α- d -mannopyranoside, methyl 3,4,6-tri- O -benzyl-α- d -mannopyranoside, a lactose derivative 10 protected everywhere except at OH-2′, benzyl 6- O -allyl-3,4- O -isopropylidene- α- d -galactopyranoside, and methyl 3,4,6-tri- O -methyl-β- d -galactopyranoside were prepared. Reactions of the manno derivatives with azide in toluene solution gave a moderate yield of the gluco azides 3 and 6 , probably because of the prevalence of trans -elimination. A normal substitution product was obtained with one of the galacto derivatives, namely benzyl 6- O -allyl-2-azido-2-deoxy-3,4- O -isopropylidene- α- d -talopyranoside, a precursor of benzyl 2-acetamido-2-deoxy-α- d -talopyranoside. However, the main reaction was always a ring contraction with C-1 substitution, leading to the epimeric pairs 12, 13 ; 14, 15 ; 26, 27 ; and 32, 33 .

Glycol-cleavage reagents also act on stannylene derivatives.

The well-known cleavage reactions of vicinal diols by such reagents as Pb(OAc)4, NaIO4, PhI(OAc)2 and Ph3BiV-compounds have now been observed for the first time on covalent derivatives of these vicinal diols, their dibutylstannylenes.

Biosynthesis of thiamine: Origin of the methyl carbon atom of the pyrimidine moiety in Salmonella typhimurium

Two biosynthetic, unevenly labeled samples of 5-aminoimidazole riboside were prepared. The incorporation of radioactivity from these labeled samples was studied in a Salmonella typhimurium strain able to use this riboside as precursor of the pyrimidine moiety of thiamine. In one sample, the ribose part was labeled almost equally at C-1 and C-2 and threefold more at C-3 but unlabeled at C-4 and C-5. The pyrimidine moiety of thiamine derived from it was found almost inactive at C-5, C-7; the specific activity of the methyl carbon atom was found close to that of C-1 or C-2 of ribose in the precursor. On the other hand, only a poor incorporation of radioactivity occurred from a sample in which the ribose part was labeled mainly at C-1. We conclude that C-5, C-7 of the pyrimidine moiety of thiamine derive from C-4, C-5 and the methyl carbon atom of the pyrimidine derives from C-2 of the ribose part of 5-aminoimidazole ribotide.

Further definition of the size of the blood group-i antigenic determinant using a chemically synthesised octasaccharide of poly-N-acetyllactosamine type

In earlier studies, the minimum structure which inhibited the binding of anti-i to an i-active glycoprotein was the linear trisaccharide, beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-D-Gal. There was an increasing hierarchy of inhibitory activities in the linear tetrasaccharide, beta-D-Galp-(1----4)-beta-D-GlcpNAc-(1----3)-beta-D-Galp-(1----4)-beta-D -GlcNAc , its methyl beta-glycoside, and in the methyl beta-glycoside of the hexasaccharide. The linear octasaccharide methyl beta-glycoside in this series is approximately only half as active as the hexasaccharide methyl beta-glycoside. Analyses by high resolution 1H-n.m.r. of these two oligosaccharides indicated that they have similar conformations in solution, and there is no evidence for the occurrence of inter-molecular interactions which might partially hinder the binding of anti-i to the octasaccharide methyl beta-glycoside. These results are consistent with the size of the i antigen being in the region of a hexasaccharide. It is proposed that the methyl aglycon group of the hexasaccharide methyl beta-glycoside confers an above normal activity by presenting a hydrophobic area for additional contact in the vicinity of the antibody-combining site.