Explorations into New Reaction Chemistry

Mukaiyama, Teruaki

doi:10.1002/anie.200300641

Cited by 189 publications

(76 citation statements)

References 322 publications

(115 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Hence, adding 1 equivalent of TBAI gave rise to b-selectivity (entry 4), while adding 0.5 or even 0.1 equivalent of TBAI afforded a-selectivity (entries 5 and 6). Dimethyl sulfide showed similar effects (entries [11][12][13][14]. In addition, the amount of TBAI and TBAB should not be more than 1 equivalent, because an excess of them resulted in a lower yield, and only trace amount of products were obtained when 2 equivalents of additives were used (entries 3 and 7).…”

mentioning

confidence: 70%

Additive-Controlled Stereoselective Glycosylations of Oxazolidinone-Protected Glucosamine and Galactosamine Thioglycoside Donors Based on Preactivation Protocol

Geng¹,

Ye²

2010

Synlett

View full text Add to dashboard Cite

Based on a pre-activation protocol, the stereoselectivity of oxazolidinone-protected amino sugar thioglycoside donors towards glycosylations can be controlled by additives. Either a-or bselectivity could be obtained by changing additives. 2,4,6-Tri-tertbutylpyrimidine (TTBP) was the best b-directing additive, while thiophene worked as the best a-directing additive. The bifunctional additives such as tetrabutyl ammonium iodide (TBAI) afforded either a-or b-selectivity depending on the amount added. Poor aselectivity of some glycosylations without any additives was greatly improved by adding TBAI or thiophene.Anomeric control in glycosylations is one of the major challenges in the synthesis of complex oligosaccharides and glycoconjugates with biological importance. 1,2 Generally, the 1,2-trans-linked glycosides are constructed by means of a participating neighboring group at the C-2 position of a glycosyl donor, while the formation of 1,2-cislinked glycosides remains a difficult task. 3 Introduction of a nonparticipating neighboring group at C-2 is insufficient to guarantee stereoselective cis-glycosylation reactions and often leads to mixtures of anomers. Recently, 2,3-trans-oxazolidinone developed first by Kerns as a special nonparticipating group for glucosamine donors attract particular attention. 4 It is a good stereodirecting group for the formation of either a-or b-glycosidic linkages. In our own work, 4d the hindered base 2,4,6-tri-tert-butylpyrimidine (TTBP) 5 was found to be a crucial factor in the stereoselectivity-controllable glycosylations of 4,6-di-Oacetyl-N-acetyl oxazolidinone protected donor 1 (Scheme 1). Based on a pre-activation protocol, 6,7 either excellent a-or b-stereoselectivity was obtained by means of the addition of TTBP or the absence of it.These results open a new avenue to modulate the stereoselectivity by changing additives in glycosylation reactions. To investigate the effect of other additives on the stereochemistry outcomes of glucosamine donor 1 and to further extend the stereoselectivity-controllable pattern to the galactosamine case, our attention was paid to exploring additives in glycosylations of amino sugar donors 1 and 2 (Figure 1) under pre-activation conditions, and our findings are reported herein.Enlightened by the mechanistic studies done by Kerns, 8a Oscarson, 8b and Ito, 8c a reasonable explanation for the controllable stereoselectivity is as follows: after pre-activation by the combination of benzenesulfinyl morpholine (BSM) and triflic anhydride (Tf 2 O) 9 donor 1 is converted into a-triflate intermediate, 10 and the glycosyl acceptor attacks in a S N 2-like fashion to form the b-glycoside; in situ anomerization of the b-glycoside under acidic conditions leads to formation of the a-glycoside. TTBP functions as an acid scavenger to hinder the anomerization and make the stereoselectivity controllable. According to this postulation, based on the pre-activation protocol, the good banomeric selectivity seems to arise from the triflate anion. To testify it and find othe...

show abstract

mentioning

confidence: 70%

Additive-Controlled Stereoselective Glycosylations of Oxazolidinone-Protected Glucosamine and Galactosamine Thioglycoside Donors Based on Preactivation Protocol

Geng¹,

Ye²

2010

Synlett

View full text Add to dashboard Cite

show abstract

“…Analytical data for α-28 were essentially the same as reported previously. 9 (29) was obtained using Method C from 5 and 20 in toluene -dioxane (1/3, v/v, 1 mL) in 67% (α/β = 3/1) or in 1,2-DCE in 41% (α/β = 1.5/1) yield. Analytical data for 29 were essentially the same as reported previously.…”

Section: Discussionmentioning

confidence: 99%

S-Benzoxazolyl as a Stable Protecting Moiety and a Potent Anomeric Leaving Group in Oligosaccharide Synthesis

2007

View full text Add to dashboard Cite

As a part of a program for developing new versatile building blocks for stereoselective glycosylation and convergent oligosaccharide synthesis, we demonstrated that S-benzoxazolyl (SBox) glycosides are stable toward major protecting group manipulations employed in carbohydrate chemistry. On the other hand, they can be glycosidated under relatively mild reaction conditions to afford either 1,2-trans or 1,2-cis-linked disaccharides. Selective and chemoselective activations of the SBox moiety were also proved to be feasible, which was demonstrated by synthesizing a number of oligosaccharide sequences.

show abstract

“…Many glycosyl donors introduced during that period gave rise to excellent complimentary glycosylation methodologies. Arguably, trichloroacetimidates [29,30], thioglycosides [31][32][33] and fluorides [34,35] have become the most common glycosyl donors nowadays.…”

Section: Major Types Of O-glycosidic Linkagesmentioning

confidence: 99%

General Aspects of the Glycosidic Bond Formation

Demchenko

2008

Handbook of Chemical Glycosylation

View full text Add to dashboard Cite

Explorations into New Reaction Chemistry

Cited by 189 publications

References 322 publications

Additive-Controlled Stereoselective Glycosylations of Oxazolidinone-Protected Glucosamine and Galactosamine Thioglycoside Donors Based on Preactivation Protocol

Additive-Controlled Stereoselective Glycosylations of Oxazolidinone-Protected Glucosamine and Galactosamine Thioglycoside Donors Based on Preactivation Protocol

S-Benzoxazolyl as a Stable Protecting Moiety and a Potent Anomeric Leaving Group in Oligosaccharide Synthesis

General Aspects of the Glycosidic Bond Formation

Contact Info

Product

Resources

About