Glycosylation studies on conformationally restricted 3,5-O-(di-tert-butylsilylene)-d-galactofuranosyl trichloroacetimidate donors for 1,2-cis α-d-galactofuranosylation

Stereocontrolled Synthesis of α-Xylofuranosides Using a Conformationally Restricted Donor

“…R f 0. (12). To a solution of 11 18 (2.26 g, 4.56 mmol) in DMF (40 mL) were added NaH (400 mg, 10.04 mmol) and α,α′-dibromo-o-xylene (1.32 g, 5.02 mmol) slowly at 0 °C.…”

“…Participating protecting groups at O-2 cannot be employed, and the inherently flexible five-membered ring often further complicates stereocontrol by providing two energetically similar reaction pathways that produce mixtures of products . Consequently, the majority of robust methods for the stereocontrolled synthesis of 1,2- cis -furanosides employ conformationally locking groups resulting in a single energetically favored reaction pathway. , Such methods have previously been applied to the synthesis of β-arabinofuranosides ( 3 , Figure B), − β-fructofuranosides ( 4 ), and α-galactofuranosides ( 5 ). − …”

Conformationally Constrained Glycosyl Donors as Tools to Control Glycosylation Outcomes

“…104 In the glycosylation with furanoside acceptor 133, this donor gave a higher β-selectivity than 132, protected with a five-membered 3,5-O-silyl group, which had previously been reported by the Boons group. 102 Similar approaches using 3,5-O-silyl protecting groups were subsequently reported by the Gallo-Rodriguez group for 1,2-cis-galactofuranosylation using trichloroacetimidate 105 and thioglycoside donors. 106 Investigations by Yang and co-workers into the reactivity of arabinofuranoside donors found that bicyclic donor 127 bearing a cyclic 3,5-O-silyl protecting group was less reactive that monocyclic arabinose donors 136, 128, and 137 (Scheme 22c).…”

Stereodirecting Effect of Cyclic Silyl Protecting Groups in Chemical Glycosylation

“…However, the chemical construction of 1,2-cis -D-Galf linkages is more difficult to achieve than that of 1,2-trans -D-Galf linkages, which are readily obtained through neighboring group participation, and no general method is available for this purpose. Tilve and Gallo-Rodriguez (2011) reported the stereochemical construction of 1,2-cis -D-Galf linkages employing 3,5-O-DTBS-protected D-galactofuranosyl donors, the strategy for which exploited the stereochemical relationship between L-arabinofuranose and D-galactofuranose (Fig. 8).…”