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The Cyanopivaloyl Ester: A Protecting Group in the Assembly of Oligorhamnans
Author(s) -
Geert Volbeda Anne,
Reintjens Niels R. M.,
Overkleeft Herman S.,
van der Marel Gijsbert A.,
Codée Jeroen D. C.
Publication year - 2016
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201600956
Subject(s) - chemistry , protecting group , moiety , orthoester , rhamnose , glycosylation , enterococcus faecium , group (periodic table) , carbohydrate chemistry , polysaccharide , functional group , stereochemistry , combinatorial chemistry , organic chemistry , biochemistry , polymer , alkyl , antibiotics
Protecting groups play a vital role in the assembly of oligosaccharides. The pivaloyl (Piv) ester is commonly used to ensure 1,2‐ trans ‐selective glycosylation reactions. A significant drawback of the Piv ester is its stability, necessitating strong alkaline conditions for its removal. We here present the cyanopivaloyl (CNPiv) group, a modified pivaloyl group having a cyano group appended to the tert ‐butyl moiety. The CNPiv group benefits from the profitable features of the Piv group (stability and effective neighboring‐group participation with minimal orthoester formation during glycosylation reactions), but can be removed under mild conditions (reduction of the cyano function followed by mild base treatment). The applicability of the CNPiv group is demonstrated in the assembly of two rhamnose oligosaccharides, a hexarhamnan that represents a fragment of the capsular polysaccharide of Enterococcus faecium and a tetrarhamnan that is part of the polyrhamnose backbone of the Lancefield Group A carbohydrate (GAC).