Practical synthesis of a tetrasaccharide derivative corresponding to ristomycin A and ristocetin A

Abstract

A practical synthesis of fully benzoylated tetrasaccharide, whose free form is indispensable to the antibiotic ristomycin A for the process of dimerization and binding to the cell wall, was achieved via sequential assembly of the building blocks, allyl 3,4-di-O-benzoyl-a-D-glucopyranoside, 2,3,4-tri-O-benzoyl-a-L-rhamnopyranosyl trichloroacetimidate, 2-O-acetyl-3,4,6-tri-O-benzoyl-a-D-mannopyranosyl trichloroacetimidate, and 2,3,5-tri-O-benzoyl-a-D-arabinofuranosyl trichloroacetimidate. A one-pot preparation of allyl 3,4-di-O-benzoyl-2-O-tertbutyldimethylsilyl-6-O-triphenylmethyl-a-D-glucopyranoside is described, and regioselective glycosylation is carried out using perbenzoylated sugar trichloroacetimidates as glycosyl donors in the presence of a catalytic amount of trimethylsilyl trifluoromethanesulfonate (TMSOTf).

Probing myo-inositol 1-phosphate synthase with multisubstrate adducts

“…The protection of the anomeric hemiacetal with an allyl group under Fisher conditions was followed by the protection of the C6-position with trityl chloride affording allyl 6- O -trityl-D-glucopyranoside intermediate in 52% overall yields. 17 The remaining free hydroxyl groups were then benzylated giving allyl-2,3,4-tri- O -benzyl-6- O -trityl-D-glucopyranoside ( 3 ) in excellent 92% yields. 18 After the removal of the allyl group, the reduction of the pyranose ring yielded 2,3,4-tri- O -benzyl-6- O -trityl-D-glucytol ( 4 ) almost quantitatively.…”

“…The trityl protected MAs ( 16) and (17) were deprotected via a two-step process consisting in the use of sodium methoxide in methanol followed by hydrogenolysis (Table 2, Method B). While the trityl moiety could be deprotected under mild acidic conditions in (16), 19 these conditions also yielded the removal of the phosphate tri-ester group at the C1 position in the protected MA (17).…”

“…The trityl protected MAs ( 16) and (17) were deprotected via a two-step process consisting in the use of sodium methoxide in methanol followed by hydrogenolysis (Table 2, Method B). While the trityl moiety could be deprotected under mild acidic conditions in (16), 19 these conditions also yielded the removal of the phosphate tri-ester group at the C1 position in the protected MA (17). This phosphate hydrolysis was assumed to occur via an intramolecular nucleophilic substitution initiated by the initial release of C6-OH group and acid catalysed activation of the PvO bond.…”

Synthesis of oleanolic acid saponins mimicking components of Chinese folk medicine Di Wu

“…To prepare compound 4, trisaccharide 10 was first synthesized via one-pot glycosylation technology (Scheme 3). Thus, 2,3,4-tri-O-benzoyl-a-L-rhamnopyranosyl trichloroacetimidate (8, 1.4 equiv) 24 was slowly added into ethyl 2,3-di-O-acetyl-6-O-benzoyl-1-thio-b-Dglucopyranoside 25 N-iodosuccinimide (NIS) in dry CH 2 Cl 2 , respectively, were added at À15°C, obtaining 4-methoxyphenyl 2,3, …”

HClO4–SiO2 catalyzed glycosylation using sugar trichloroacetimidates as glycosyl donors

“…Moreover, no workup was required beyond the mere filtration of the catalyst, followed by chromatographic purification. A variety of hydroxyl protecting groups such as isopropylidene (5), benzylidene (7), TBS (13), Bz (16), All (17), Tr (19), Bn (22, 28), Ac (31), and other functional groups as lactone (2, 26), aldehyde (29, 32), azide (25) and thioglycoside (11) were found to be compatible under these glycosylation conditions. More impressively, the yields for trityl-containing product 21 (85%), fucosyl 30 (89%), 33 (80%), and lactosyl 36 (84%) were significantly improved using HClO 4 -SiO 2 .…”