Enantiomerically pure, 3-methyl- or 3-ethoxycarbonyl-substituted (5S)- and (5R)-5-acetyl-2-isoxazolines were obtained from the corresponding racemic mixtures by means of an enzymatic reduction with baker's yeast, followed by the separation of the enantiopure syn- and anti-alcohols and oxidation of the alcohol group. The reaction between these ketones and (2R)-Schöllkopf's bislactim ether azaenolate was studied: using (5S)- and (5R)-3-methyl derivatives, two diastereoisomeric adducts were obtained in good yield and stereoselectivity, whereas reaction with the (5S)- and (5R)-3-ethoxycarbonyl derivatives led to a complex mixture of products. Subsequent controlled hydrolysis of the pyrazine ring led to β-(3-methyl-4,5-dihydro-isoxazol-5- yl)-l-threonines methyl ester together with the corresponding (R)-valine dipeptides.
Stereoselective synthesis of β-substituted-l-threonines from enantiopure 5-acetyl-2-isoxazolines / G. Cremonesi, P. Dalla Croce, A. Forni, M. Gallanti, C. La Rosa. - In: TETRAHEDRON. - ISSN 0040-4020. - 67:16(2011), pp. 2925-2933.
|Titolo:||Stereoselective synthesis of β-substituted-l-threonines from enantiopure 5-acetyl-2-isoxazolines|
CREMONESI, GIUSEPPE (Primo)
DALLA CROCE, PIERO (Secondo)
GALLANTI, MADDALENA (Penultimo)
LA ROSA, CONCETTA (Ultimo)
|Parole Chiave:||β-Hydroxy-α-amino acids; 2-Isoxazolines; Aldol addition on prochiral ketones; l-Threonines; Schöllkopf's bislactim ether|
|Settore Scientifico Disciplinare:||Settore CHIM/06 - Chimica Organica|
|Data di pubblicazione:||2011|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1016/j.tet.2011.02.055|
|Appare nelle tipologie:||01 - Articolo su periodico|