Anomeric Thioglycosides Give Different Anomeric Product Distributions under NIS/TfOH Activation

Abstract

The reaction of a series of anomeric thioglycosides with various glycosyl acceptors and N-iodosuccinimide/catalytic triflic acid was investigated with respect to reactivity and anomeric selectivity. In general, β-configured donors were found to give a more β-selective reaction outcome compared to their α-configured counterparts. The relative reactivity of various thioglycosides was measured through competition experiments, and the following order was established: phenyl, tolyl, methyl, ethyl, isopropyl, and 1-adamantyl.

α-Selective Glucosylation Can Be Achieved with 6-O-para-Nitrobenzoyl Protection

“…As mentioned earlier, we have previously observed how β-configured glucosyl donors of the thioglycoside type return a higher proportion of β-configured O -glucoside product than the analogous α-configured donor under NIS/TfOH (cat.) activation . The results of Table further confirm these observations (entries 6, 10, and 12).…”

Solvent free, catalytic and diastereoselective preparation of aryl and alkyl thioglycosides as key components for oligosaccharide synthesis

“…conditions, a competition experiment was conducted, as previously described by us. [21][22][23] Scheme 2 Screening of Lewis acid chlorides for the conversion of 1 to 2. The anomeric ratio is based on 1 H-NMR analysis of the crude reaction mixture.…”

“…This lower reactivity of thioglycosides originating from a primary thiol compared to thioglycosides of a secondary thiol (iPrSH) has previously been reported by us (Scheme 3). 22 After having shown that InCl 3 indeed functions as an active catalyst under solvent-free conditions for the synthesis of various thioglycosides, we decided to explore the practicality of the reaction on a large (multigram) scale. As shown in Table 1, glucose pentaacetate (1) successfully reacted with thiocresol (4) and just 1 mol% InCl 3 to give the expected thioglycoside (5) that could be isolated after precipitation with abs.…”

“…22, HRMS(ES): calcd for C 13 H 18 O 9 K + m/z 357.0582, found m/z 357.0590.1 H NMR (400 MHz, CDCl 3 ) δ H 6.37-6.34 (m, 1H, H1α), 6.17…”

“…This lower reactivity of thioglycosides originating from a primary thiol compared to thioglycosides of a secondary thiol ( i PrSH) has previously been reported by us (Scheme 3). 22…”