Substrate-dependent chemoselective aldose-aldose and aldose-ketose isomerizations of carbohydrates promoted by a combination of calcium ion and monoamines.
Epimerization of aldoses at C-2 has been extensively investigated by using various metal ions in conjunction with diamines, monoamines, and aminoalcohols. Aldoses are epimerized at C-2 by a combination of alkaline-earth or rare-earth metal ions (Ca(2+), Sr(2+), Pr(3+), or Ce(3+)) and such monoamines as triethylamine. In particular, the Ca(2+)-triethylamine system proved effective in promoting aldose-ketose isomerization as well as C-2 epimerization of aldoses. 13C NMR studies using D-(1-(13)C)glucose and D-(1-(13)C)galactose with the CaCl(2) system in CD(3)OD revealed that the C-2 epimerization proceeds via stereospecific rearrangement of the carbon skeleton, or 1,2-carbon shift, and ketose formation proceeds partially through an intramolecular hydrogen migration or 1,2-hydride shift and, in part, via an enediol intermediate. These simultaneous aldose-aldose and aldose-ketose isomerizations showed interesting substrate-dependent chemoselectivity. Whereas the mannose-type aldoses having 2,3-erythro configuration (D-mannose, D-lyxose, and D-ribose) showed considerable resistance to both the C-2 epimerization and the aldose-ketose isomerization, the glucose-type sugars having 2,3-threo and 3,4-threo configurations, D-glucose and D-xylose, are mainly epimerized at C-2 and those having the 2,3-threo and 3,4-erythro configurations, D-galactose and D-arabinose, were mostly isomerized into 2-ketoses. These features are of potential interest in relevance to biomimic sugar transformations by metal ions.
Tanase
T
T
Department of Chemistry, Faculty of Science, Nara Women's University, Kitauoya-higashi-machi, 630-8285, Nara, Japan. tanase@cc.nara-wu.ac.jp
Takei
T
T
Hidai
M
M
Yano
S
S
D019747:Aldose-Ketose Isomerases / Q000737:chemistry*; D000588:Amines / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D002241:Carbohydrates / Q000737:chemistry*; D005021:Ethylamines / Q000494:pharmacology; D007536:Isomerism; D019216:Metals, Heavy / Q000494:pharmacology; D018716:Molecular Mimicry; D015394:Molecular Structure; D019906:Nuclear Magnetic Resonance, Biomolecular; D009942:Organometallic Compounds / Q000494:pharmacology; D013379:Substrate Specificity
D000588:Amines; D002241:Carbohydrates; D005021:Ethylamines; D019216:Metals, Heavy; D009942:Organometallic Compounds; D019747:Aldose-Ketose Isomerases; D002118:Calcium; C016162:triethylamine