Abstract: During the synthesis of protected tetrasaccharide fragment of the repeating unit of polysaccharide of Azospirillum brasilense sp7 we found that glycosylation with a mixture of protected N-trifluoroacetyl (TFA)-protected glucosamine N-phenyltrifluoroacetimidate and the corresponding 2-trifluoromethyl-oxazoline led to 1,2-cis-linked glycoside along with the expected 1,2-trans-linked isomer. This fact looks quite unusual bearing in mind that both N-TFA-containing glycosyl donor and 2-trifluoromethyl-oxazoline are usually expected to favor the formation of 1,2-trans-glycosides. Formation of 1,2-cis-glycoside was explained by hydrogen-bond mediated complexation of hydrogen atom of NHTFA at C-2 of oxacarbenium ion derived from glycosyl donor and oxygen atom of hydroxy group of the incoming nucleophile. Conversely, glycosylations with N-phthaloyl protected glycosyl donors resulted in exclusive formation of 1,2-trans-isomer presumably due to a significant steric effect and the absence of additional hydrogen-bonding sites of N-phthaloyl group.

Cite: Abronina P.I. , Zinin A.I. , Chizhov A.O. , Kononov L.O.
Unusual Outcome of Glycosylation: Hydrogen‐Bond Mediated Control of Stereoselectivity by N‐Trifluoroacetyl Group?
European Journal of Organic Chemistry. 2020. V.2020. N27. P.4146-4160. DOI: 10.1002/ejoc.202000520 WOS Scopus OpenAlex

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Web of science:	WOS:000546661100001
Scopus:	2-s2.0-85087739958
OpenAlex:	W3033896142

Citing:

DB	Citing
OpenAlex	17
Scopus	17
Web of science	17

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