A Comparative Study of the Influence of Protecting Groups on the Reactivity of<i>chiro</i>-Inositol Glycosyl Acceptors

Cid, M. B.; Alfonso, Francisco; Martín‐Lomas, Manuel

doi:10.1055/s-2005-871945

Cited by 6 publications

(2 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…probably due to the higher reactivity of the benzylated acceptors [56]. Compared to the results described above for 142D, the yield and the regioselectivity for the glycosylation of 172D were similar when using donor 153 affording the α(1 !…”

Section: Superarmed Glycosyl Donors In Glycosylation Reactionssupporting

confidence: 49%

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Miljković

2013

Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry

View full text Add to dashboard Cite

-Reid et al. reported [1] that n-pentenyl glycosides undergo chemospecific cleavage 1 ! 2 ! 3, with N-bromosuccinimide under conditions that leave a wide variety of other protecting groups unaffected ( Fig. 5.1).According to the proposed mechanism ( Fig. 5.1), the addition of water to the reaction mixture will lead to hydrolysis but the addition of alcohol or another sugar having a free hydroxyl group will lead to the formation of glycoside or a disaccharide. In the course of these studies, Fraser-Reid et al. [1] observed that sugar molecules having an acyloxy group at the C2 carbon (6 in Fig. 5.2) hydrolyzed much more slowly than if they had an alkoxy group (7 in Fig. 5.2). This observation suggested that the n-pentenyl glycoside could be made more or less reactive (it could be armed or disarmed) by the type of protecting group placed on the C2 oxygen.The ability of the C2 acyloxy group to disarm the n-pentenyl glycoside was rationalized as shown in Fig. 5.3. Thus, it can be assumed that the cyclic halonium ions 8 and 9 are formed reversibly [2] and that the electron density on the glycosidic oxygen is depleted in 2-O-acyl derivatives so that nucleophilic attack of this oxygen on the halonium ion is less favored than in the 2-O-alkyl counterpart 9. The reason for this is that the electron-withdrawing group at the C2 carbon makes the C2 carbon slightly positively charged so that the formation of another positive charge at the C1 carbon is not a favorable process [there cannot exist two positive charges on two neighboring carbons (C1 and C2) (Fig. 5.3).].Consequently, the armed glycosyl donors react with electrophiles faster than the disarmed ones, and therefore in a solution containing both an armed and disarmed glycosyl donor molecules, whereby disarmed glycosyl donor molecules have one free hydroxyl group, the reaction with an electrophile will result in crosscoupling and not self-coupling, i.e., an armed glycosyl donor will react with the disarmed one, whereas a disarmed donor will not react with itself [3] as illustrated in Fig. 5.5. The promoters for the activation of n-pentenyl group [4,5] are iodonium dicollidine perchlorate (IDCP) and N-iodosuccinimide/triethylsilyl triflate (NIS/Et 3 SiOTf).M. Miljkovic, Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry,

show abstract

Section: Superarmed Glycosyl Donors In Glycosylation Reactionssupporting

confidence: 49%

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Miljković

2013

Electrostatic and Stereoelectronic Effects in Carbohydrate Chemistry

View full text Add to dashboard Cite

show abstract

“…Substituting benzoyl for benzyl groups resulted in an increase of the proportions of the β anomers and small amounts of uncharacterized pseudotrisaccharides, probably due to the higher reactivity of the benzylated acceptors 10e. Compared to the results described above for 1 D , the yield and the regioselectivity for the glycosylation of 24 D were similar when using donor 2 affording the α(1→2) 28 and β(1→2) 29 pseudodisaccharides in a slightly higher proportion than the α(1→3) 30 and β(1→3) 31 compounds (C3/C2 = 1:1.5).…”

Section: Resultsmentioning

confidence: 99%

Simultaneous Regio‐ and Enantiodifferentiation in Carbohydrate Coupling

et al. 2006

Self Cite

View full text Add to dashboard Cite

The glycosylation of 1,2‐trans‐diequatorial diols derived from tetrabenzoylated and tetrabenzylated D‐ and L‐chiro‐inositol with several glycosyl donors has been investigated. An unprecedented dependence of the regioselectivity on the absolute configuration of the acceptor has been found. However this trend is also modulated by the nature of the protecting groups on both the donor and acceptor, with benzoylated acceptors affording higher levels of regioselectivity. Most of the results have been rationalized by DFT calculations which indicate that stereoelectronic factors and hydrogen bonding between the donor and acceptor govern their relative orientation and determine the regiochemical outcome of the process. These studies also highlight the role of the acyl group adjacent to the OH to be glycosylated in facilitating the glycosylation reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

show abstract

Quantifying the Electronic Effects of Carbohydrate Hydroxy Groups by Using Aminosugar Models

Pedersen¹,

Olsen²,

Brka³

et al. 2011

Chemistry A European J

View full text Add to dashboard Cite

Methyl amino-deoxy-glycosides with α- and β-gluco, α-galacto, or α-manno stereochemistry with the amino functionality in each of the four possible non-anomeric positions have been synthesized and their pK(a) values determined by titration. These model compounds were chosen because they are the amino derivatives of the most common glycosyl acceptors. From this study it was possible to evaluate the electron density at each of the given positions in the carbohydrate and compare them. Some general trends were observed: The basicity of the amino groups decreases in the order 6-NH(2)>3-NH(2)>2-NH(2)>4-NH(2) (referring to the position). The basicity of a of an amino-deoxy-sugar generally increases when one or more substituents on the sugar ring are axial. The basicity decreases when the amine is antiperiplanar to an oxygen atom. These findings are in agreement with the observations obtained from glycosylation chemistry and the regioselective protection of sugars.

show abstract

A Comparative Study of the Influence of Protecting Groups on the Reactivity ofchiro-Inositol Glycosyl Acceptors

Cited by 6 publications

References 3 publications

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Armed-Disarmed Concept in the Synthesis of Glycosidic Bond

Simultaneous Regio‐ and Enantiodifferentiation in Carbohydrate Coupling

Quantifying the Electronic Effects of Carbohydrate Hydroxy Groups by Using Aminosugar Models

Contact Info

Product

Resources

About