Herstellung der 1-Thio-D-chinovose

Synthesis of deoxygalactose-containing sialyl Le(X) ganglioside analogues to elucidate the structure necessary for selectin recognition

Sialyl Lewis X ganglioside analogues containing 4-deoxy-, 6-deoxy-, and 4,6-dideoxy-D-galactopyranose in place of D-galactopyranose have been synthesized. Glycosylations of 2-(trimethylsilyl)ethyl 2,6-di-O-benzyl-beta-D-galactopyranoside and 2-(trimethylsilyl)ethyl beta-D-fucopyranoside with the phenyl 2-thioglycoside derivative of sialic acid, using N-iodosuccinimide (NIS)-trifluoromethanesulfonic acid (TfOH) as the promoter in acetonitrile, gave the desired 2-(trimethylsilyl)ethyl sialyl-alpha-2-->3)-beta-D-galactopyranoside and -beta-D-fucopyranoside, respectively. The sialylgalactose derivative obtained was then modified to 4-deoxy and 4,6-dideoxy derivatives. These were converted, by O-benzoylation, transformation of the 2-(trimethylsilyl)ethyl group to trichloroacetimidates, and introduction of the methylthio group with methylthiomethylsilane, into the corresponding glycosyl donors, which were then coupled with 2-(trimethylsilyl)ethyl O-(2,3,4-tri-O-benzyl-alpha-L-fucopyranosyl)-(1->3)-O-(2-acetamido-6-O- benzyl-2-deoxy-beta-D-glucopyranosyl)-(1->3)-2,4,6-tri-O-benzyl-beta-D- galactopyranoside in the presence of dimethyl(methylthio)sulfonium triflate (DMTST). The resulting pentasaccharides were each converted to the corresponding alpha-trichloroacetimidates, which, on coupling with (2S, 3R, 4E)-2-azido-3-O-benzoyl-4-octadecene-1,3-diol, gave the desired sphingosine derivatives. Selective reduction of the azide group, N-acylation with octadecanoic acid, O-deacylation, and saponification of the methyl ester afforded the target compounds.

Preparation of 4,6-cyclo-hexopyranoses by palladium-mediated intramolecular cyclodehalogenation

4,6-Cyclo-4,6-dideoxy-hexapyronoses were obtained by palladium-mediated intramolecular cyclodehalogenation. Thus, methyl 2,3-di-O-acetyl-4,6-dideoxy-4,6-diiodo-beta-D-galactopyranoside (3) afforded methyl 2,3-di-O-acetyl-4,5-cyclo-4,6-dideoxy-beta-D-galactopyranoside (5) in 56% yield upon treatment with hydrogen in the presence of palladium-on-charcoal and diethylamine. The structure of 5 was proven by MS, NMR including NOE measurements, and by independent conversion of 4 to 5 by zinc-mediated Wurtz synthesis. Similarly, methyl 2,3-di-O-acetyl-4,6-cyclo-4,6-dideoxy-alpha-D-galactopyranoside (6) and O-(2,3,-di-O-acetyl-4,6-cyclo-4,6-dideoxy-alpha-D-galactopyranosyl)-(1-- >4)-1,2,3,6-tetra-O-acetyl-beta-D-glucopyranose (17) were obtained along with the respective 4,6-dideoxy analogues. Also methyl 2,3-di-O-acetyl-4,6-dideoxy-4,6-diiodo-beta-D-glucopyranoside (19) gave galacto-configured 5 stereoselectively.

Syntheses of trisaccharide C-D-E and tetrasaccharide B-C-D-E fragments found in orthosomycins

1,5-Anhydro-3-O-benzyl-2,6-dideoxy-4-O-(3,4-di-O-benzyl-2,6-dideoxy-beta -D- arabino-hexopyranosyl)-D-arabino-hex-1-enitol (17), which corresponds to the B-C fragment of various orthosomycins, was prepared from phenyl 2,3-di-O-benzyl-6-deoxy-4-O-(3,4-di-O-benzyl-2,6-dideoxy- beta-D-arabino-hexopyranosyl)-1-thio-beta-D-glucopyranoside (16) by reductive lithiation. The synthesis of 16 involved a stereoselective coupling of phenyl 2,3-di-O-benzyl-6-deoxy-1-thio-beta-D-glucopyranoside (9) and 1,2-di-O-acetyl-3,4-di-O-benzyl-6-deoxy-beta-D-glucopyranose (14) followed by deoxygenation at C-2'. Glycosylation of methyl 2-O-benzyl-6- deoxy-4-O-methyl-beta-D-galactopyranoside (25) with 3,4,6-tri-O-acetyl-2-deoxy- 2-phthalimido-beta-D-glucopyranosyl trichloroacetimidate, followed by deamination at C-2', led stereospecifically to methyl 2-O-benzyl-6-deoxy-4-O-methyl-3-O-(3,4,6-tri-O-acetyl-2-deoxy-beta-D-ara bino- hexopyranosyl)-beta-D-galactopyranoside (26). The 2-deoxy unit of 26 was then modified by consecutive axial introduction of a C-Me group at position 3', protection of HO-3', and deoxygenation at C-6', in order to obtain methyl 3-O-(3-O-benzoyl-2,6-dideoxy-3-C-methyl-beta-D-arabino-hexopyranosyl)-2- O- benzyl-6-deoxy-4-O-methyl-beta-D-galactopyranoside (39), which corresponds to the D-E fragment of orthosomycins. A glycosyloxyselenation-oxidation-elimination sequence was performed on 39 and either 1,5-anhydro-3,4-di-O-benzyl-2,6- dideoxy-D-arabino-hex-1-enitol (40) or 1,5-anhydro-3-O-benzyl-2,6-dideoxy-4-O-(3,4-di-O-benzyl-2,6- dideoxy-beta-D-arabino-hexopyranosyl)-D-arabino-hex-1-enitol (17) to give the C-D-E tri-and B-C-D-E tetrasaccharide fragments, respectively. Each fragment contained the spiro-ortholactone junction with an (R) configuration at the anomeric carbon atom of the C-unit.

Purin-6-yl 6-deoxy-1-thio-beta-D-glucopyranoside. Enzymology, chemistry, and cytotoxicity

Purin-6-yl 6-deoxy-1-thio-beta-D-glucopyranoside (4) is a substrate for almond beta-glucosidase and a weak competitive inhibitor of bovine liver beta-D-glucuronidase (Ki approximately 20mM). Both 4 and purine-protonated 4 undergo hydrolysis catalyzed by dilute acid in the pH range 0.17-2.59. These results are compared with those previously obtained with ammonium (purin-6-yl 1-thio-beta-D-glucopyranosid)uronate, (purin-6-yl 1-thio-beta-D-glucopyranosid)uronamide, purin-6-yl 1-thio-beta-D-glucopyranoside, and purin-6-yl 2-deoxy-1-thio-beta-D-glucopyranoside, and it is concluded that the data support an involvement of substituents at C-5 in producing productive Michaelis-complex conformers. The 6-deoxyglucoside is more active than the D-glucosiduronic acid in an L1210 mouse screen.