Tuning Effect of Silyl Protecting Groups on the Glycosylation Reactivity of Arabinofuranosyl Thioglycosides

Abstract

The tuning effect of silyl protecting groups on the glycosylation reactivity of arabinofuranosyl phenyl thioglycoside donors is presented. Silyl ethers on the 3-, 5-, and 3,5-positions of the arabinofuranose ring are found to have an arming effect on the donor reactivity, whereas the cyclic 3,5-acetal type protecting groups reduce the reactivity.

Regioselective Benzoylation of Diols and Carbohydrates by Catalytic Amounts of Organobase

“…The yield of 2 increased with the amount of DBU used up to 0.4 equiv (Entries 12, 13 and 14). [15][16][17][18]. The addition of DMF is not necessary for diols due to their good solubility in acetonitrile.…”

“…More specifically, developing environment-friendly, convenient, efficient and highly regioselective carbohydrate protection methods remains as one of the most prominent challenges [9]. Over the last several decades, many protection methods have been developed, including the use of reagents such as organotin [10][11][12], organoboron [13,14], organosilicon [15][16][17], metal salts [18][19][20][21][22][23], organobase [24][25][26], and enzymes [27][28][29][30]. Although these reagents each have advantages, they also possess troublesome shortcomings including inherent toxicity, high cost and the necessity to pre-protect secondary hydroxyl groups.…”

Silyl-protective groups influencing the reactivity and selectivity in glycosylations

“…Yang and co-workers have extended the concept to the furanoside series [ 29 ]. They showed that the arabinofuranosyl donor 37 and its 2- O -TBS analogue were more reactive than the corresponding benzylated thioglycosides in competition reactions and used the reactivity differences in a one-pot glycosylation reaction between 37 , a disarmed donor/acceptor 38 and an acceptor 39 , which gave the trisaccharide 40 in a remarkable yield of 88% ( Scheme 7 ).…”

A propos of glycosyl cations and the mechanism of chemical glycosylation; the current state of the art

“…48 A series of Wong-type competition glycosylations with arabinofuranosyl thioglycosides revealed the β-directing 3,5- O -di( tert- butyl) silylene acetal introduced earlier by the Boons 50 and Crich 51 laboratories to be strongly disarming consistent with the approximate tg conformation it imposes on the C4-C5 bond. 52 …”