Pivalates in the selective protection and activation of maltose for the synthesis of sulfated 3-deoxy-maltosyl-(1-->4)-alpha, alpha-trehalose.

Pivaloylation of maltose gave, in satisfactory yield, 1,2,6,2',3',4',6'-hepta-O-pivaloyl-beta-maltose which was converted to the 3-deoxygenated analogue in a Barton-McCombie reaction. This compound was used directly in a trimethylsilyl triflate-mediated glycosylation reaction with 2,3,6-tri-O-benzyl-alpha-D-glucopyranosyl 2,3-di-O-benzyl-4,6-O-benzylidene-alpha-D-glucopyranoside to give the corresponding maltosyl-(1-->4)-alpha, alpha-trehalose derivative. After deprotection, the monodeoxygenated tetrasaccharide was sulfated; in the reaction product, one compound fully sulfated at the outer pyranose rings predominated.

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.