Pre-activation protocol leading to highly stereoselectivity-controllable glycosylations of oxazolidinone protected glucosamines

Abstract

Under pre-activation glycosylation conditions, the 4,6-di-O-acetyl-N-acetyloxazolidinone protected donor afforded either excellent beta- or alpha-stereoselectivity simply by means of the addition of hindered base TTBP or the absence of base, leading to the controllable stereochemistry of coupling reactions.

Stereocontrolled 1,2-cis glycosylation as the driving force of progress in synthetic carbohydrate chemistry

“…76a,77a These donors showed switchable stereoselectivity in glycosylation that was achieved by tuning the reaction conditions. 79 This interesting finding stimulated further studies. Mechanistically it was suggested that the β-linked product is formed initially, which rapidly anomerizes into the corresponding α-anomer.…”

Methodology Development and Physical Organic Chemistry: A Powerful Combination for the Advancement of Glycochemistry

“…127b Related observations on the kinetic nature of the β-product with subsequent anomerization to the α-anomer were reported by Ye. 128 The use of various oxazolidinone protected glucosamine derivatives as glycosyl donors had been previously investigated by the Kerns with selectivities that depended on the nitrogen protecting group and on the reactivity of the acceptor ( 77 ). 125,129 Ito and coworkers showed the N -benzyloxazolidinone protected glucosamine donor 78 (Fig 8) to be unselective at low temperatures and α-selective at room temperature and, like Oscarson, came to the conclusion that this was the result of an equilibration process involving endocyclic cleavage.…”

Chemoenzymatic Syntheses of Tumor‐Associated Carbohydrate Antigen Globo‐H and Stage‐Specific Embryonic Antigen 4

“…The presence or absence of the base TTBP did not significantly affect either the yield or the stereochemical selectivity of this reaction. [62]…”