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Quantifying Electronic Effects of Common Carbohydrate Protecting Groups in a Piperidine Model System
Author(s) -
Heuckendorff Mads,
Pedersen Christian M.,
Bols Mikael
Publication year - 2010
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201002313
Subject(s) - epimer , substituent , chemistry , carbohydrate , carbohydrate chemistry , heteroatom , piperidine , stereochemistry , medicinal chemistry , hydroxymethyl , protecting group , ring (chemistry) , organic chemistry , alkyl
A study of the substituent effects of protecting groups in hydroxypiperidines was carried out and compared with the electronic effects in glycosylation chemistry. 1‐Deoxynojirimycin, the aza‐sugar analogue of 1‐deoxy‐ D ‐glucose, was used as a carbohydrate model, and protected with the most common carbohydrate protecting groups. The different stabilization of positive charge on the ring heteroatom was determined by p K a measurements. The protecting groups could be ranked in the following way after their destabilization of the piperidinium ion: benzoyl≥acetyl≫4,6‐ O ‐benzylidine>benzyl≈methyl>H>3,6‐anhydro> tert ‐butyldimethylsilyl. The observed effects of having protecting groups with different electronic characteristics were found to be in agreement with the “armed–disarmed” concept. Comparison of the p K a of benzylated and benzoylated epimers of 3‐hydroxy‐6‐hydroxymethyl piperidines showed increased stabilization of the piperidinium ion in the axial epimer. The difference between axial and equatorial epimers was larger in the benzylated than in the benzoylated piperidines.