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First discrimination of enantiomeric cyclic hemiacetals and methyl acetals derived from hydroxamic acids and lactams of Gramineae by means of 1 H NMR using various chiral solvating agents
Author(s) -
Klein Jens,
Hartenstein Holger,
Sicker Dieter
Publication year - 1994
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260321205
Subject(s) - chemistry , enantiomer , stereochemistry , atropisomer , tautomer , hydroxamic acid , benzaldehyde , organic chemistry , catalysis
The discrimination of enantiomeric cyclic hemiacetals and methyl acetals derived from hydroxamic acids and lactams with the 2 H ‐1,4‐benzoxazin‐3(4 H )‐one and 2 H ‐1,4‐benzothiazin‐3(4 H )‐one skeleton was investigated using ( S )‐(−)‐phenylethylamine, (−)‐quinine, β‐cyclodextrin and, for the first time, (5 R ,11 R )‐(+)‐2,8‐dimethyl‐6 H ,12 H ‐5,11‐ methanodibezo [ b,f ] [1,5]diazocine, a Troeger's base enantiomer, as chiral solvating agents (CSA). Conditions for the enantiomeric discrimination of six configurationally stable methyl acetals are reported. 2,4‐Dihydroxy‐2 H ‐1,4‐benzoxazin‐3(4 H )‐one and its 7‐methoxy derivative, bioactive aglucones from Gramineae species, are the first cyclic hemiacetals that could be differentiated into enantiomers by means of 1 H NMR, despite their oxo–cyclo tautomerization that prevented enantioseparation by chromatography or capillary electrophoresis. However, 2‐hydroxy‐2 H ‐1,4‐benzothiazin‐3(4 H )‐ones (thiohemiacetals) could not be differentiated by the use of these CSA. The influence of the structure of the enantiomers, CSA, temperature and concentration on the size of the chemical shift anisochrony is discussed.