1093383-67-5Relevant academic research and scientific papers
The impact of oxacarbenium ion conformers on the stereochemical outcome of glycosylations
Walvoort, Marthe T.C.,Dinkelaar, Jasper,Van Den Bos, Leendert J.,Lodder, Gerrit,Overkleeft, Herman S.,Codee, Jeroen D.C.,Van Der Marel, Gijsbert A.
scheme or table, p. 1252 - 1263 (2010/10/02)
The search for stereoselective glycosylation reactions has occupied synthetic carbohydrate chemists for decades. Traditionally, most attention has been focused on controlling the SN2-like substitution of anomeric leaving groups as highlighted by Lemieux's in situ anomerization protocol and by the discovery of anomeric triflates as reactive intermediates in the stereoselective formation of β-mannosides. Recently, it has become clear that also SN1-like reaction pathways can lead to highly selective glycosylation reactions. This review describes some recent examples of stereoselective glycosylations in which oxacarbenium ions are believed to be at the basis of the selectivity. Special attention is paid to the tereodirecting effect of substituents on a pyranosyl ring with an emphasis on the role of the C-5 carboxylate ester in the condensations of mannuronate ester donors.
The stereodirecting effect of the glycosyl C5-carboxylate ester: Stereoselective synthesis of β-mannuronic acid alginates
Codée, Jeroen D. C.,Van Den Bos, Leendert J.,De Jong, Ana-Rae,Dinkelaar, Jasper,Lodder, Gerrit,Overkleeft, Herman S.,Van Der Marel, Gijsbert A.
experimental part, p. 38 - 47 (2009/04/07)
(Chemical Equation Presented) Glycosylations of mannuronate ester donors proceed highly selectively to produce the 1,2-cis-linked products. We here forward a mechanistic rationale for mis counterintuitive selectivity, based on the remote stereodirecting e
Stereoselectivity of glycosylations of conformationally restricted mannuronate esters
Codée, Jeroen D.C.,de Jong, Ana R.,Dinkelaar, Jasper,Overkleeft, Herman S.,van der Marel, Gijsbert A.
experimental part, p. 3780 - 3788 (2009/09/08)
Glycosidation of conformationally unrestricted mannuronate ester donors proceeds in a highly β-selective fashion, whereas condensations of mannuronate ester donors, which are conformationally constrained by a 3,4-butanedimethylacetal or a 2,3-isopropylidene function, provide α-selective products. We hypothesize that the difference in stereochemical outcome of these condensations results from the different conformations of the product forming oxacarbenium intermediate. The formation of the β-linked products from the flexible mannuronates is thought to originate from the most favorable 3H4 oxacarbenium ion, which is not accessible from the conformationally restrained donors. Although an α-triflate intermediate is formed upon activation of the 3,4-butanedimethylacetal protected mannuronate ester thio donor, this is not the product forming intermediate. The anomeric triflate serves as a reservoir for the 4H3 oxacarbenium ion, which is glycosidated to provide the α-linked mannuronates.
