PubMed:16098494 JSONTXT

{"project":"sentences","denotations":[{"id":"TextSentencer_T1","span":{"begin":0,"end":121},"obj":"Sentence"},{"id":"TextSentencer_T2","span":{"begin":122,"end":303},"obj":"Sentence"},{"id":"TextSentencer_T3","span":{"begin":304,"end":520},"obj":"Sentence"},{"id":"TextSentencer_T4","span":{"begin":521,"end":624},"obj":"Sentence"},{"id":"TextSentencer_T5","span":{"begin":625,"end":855},"obj":"Sentence"},{"id":"TextSentencer_T6","span":{"begin":856,"end":1065},"obj":"Sentence"},{"id":"TextSentencer_T7","span":{"begin":1066,"end":1256},"obj":"Sentence"},{"id":"T1","span":{"begin":0,"end":121},"obj":"Sentence"},{"id":"T2","span":{"begin":122,"end":303},"obj":"Sentence"},{"id":"T3","span":{"begin":304,"end":520},"obj":"Sentence"},{"id":"T4","span":{"begin":521,"end":624},"obj":"Sentence"},{"id":"T5","span":{"begin":625,"end":855},"obj":"Sentence"},{"id":"T6","span":{"begin":856,"end":1065},"obj":"Sentence"},{"id":"T7","span":{"begin":1066,"end":1256},"obj":"Sentence"}],"namespaces":[{"prefix":"_base","uri":"http://pubannotation.org/ontology/tao.owl#"}],"text":"One-pot alpha-glycosylation pathway via the generation in situ of alpha-glycopyranosyl imidates in N,N-dimethylformamide.\nDivergent pathways are disclosed in the activation of 2-O-benzyl-1-hydroxy sugars by a reagent combination of CBr4 and Ph3P, all of which afford one-pot alpha-glycosylation methods. When this reagent is used in CH2Cl2, the 1-hydroxy sugar is converted to the alpha-glycosyl bromide in a conventional way and leads to the one-pot alpha-glycosylation method based on a halide ion-catalytic mechanism. In either DMF or a mixture of DMF and CHCl3, however, alternative alpha-glycosyl species are generated. From the 1H and 13C NMR study of the products, as well as the reactions using Vilsmeier reagents [(CH3)2N+=CHX]X- (X=Br and Cl), these were identified as cationic alpha-glycopyranosyl imidates having either Br- or Cl- counter ion. The cationic alpha-glycosyl imidate (Br-), derived specifically in the presence of DMF, is more reactive than the alpha-glycosyl bromide and thus is responsible for the accelerated one-pot alpha-glycosylation. The one-pot alpha-glycosylation methodology performed in DMF was assessed also with different types of acceptor substrates including tertiary alcohols and an anomeric mixture of 1-OH sugars."}