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Abstract
The preparation of a variety of novel aziridine-γ-lactones (3) from carbohydrates is described. In contrast to aziridine-2-carboxylates, the lactones react regiospecifically at C-2 with soft nucleophiles to provide optically pure substituted β-amino acid precursors. Hard nucleophiles react exclusively at the C-3 position to provide α-amino acid precursors. The utility of this methodology was demonstrated by the preparation of (3S,4S)-dihydroxy-L-glutamic acid (DHGA) from the appropriate aziridine-γ-lactone. DHGA was subsequently shown to be a selective partial agonist of mGluR1 receptors. A more concise preparation of aziridine-γ-lactones was achieved by 1,4-Michael addition of benzylamine to 2-O-triflylbutenolides. Use of a 2-O-mesylbutenolide led, under the same conditions, to the corresponding aziridine-2-carboxamides or 2-carboxylates. Finally, a new Evanstype aziridinating agent, Ses-iminoiodinane, was developed and shown to react efficiently with unsaturated substrates to give the corresponding aziridines, whose N-Ses protecting groups can be removed under mild conditions.
Highlights
NH EWGThe preparation of chiral 1 can pose problems, complete stereoselectivity of the ring opening reaction is not always achieved and β-amino acid derivatives are generally not accessible by this process, at best mixtures of α- and β-amino acids being obtained
Introduction α- and β-Amino acids, both natural and unnatural, are important synthetic targets in organic chemistry
To bypass some of these problems, we describe the use of aziridine-γ-lactones 3 for the enantiospecific synthesis of α- or β-amino acid derivatives
Summary
The preparation of chiral 1 can pose problems, complete stereoselectivity of the ring opening reaction is not always achieved and β-amino acid derivatives are generally not accessible by this process, at best mixtures of α- and β-amino acids being obtained. To bypass some of these problems, we describe the use of aziridine-γ-lactones 3 for the enantiospecific synthesis of α- or β-amino acid derivatives. The reaction of aziridine-γ-lactones with a variety of nucleophiles led to different regioselectivities of aziridine ring opening depending on the nature of the nucleophiles [5,6]. Soft nucleophiles gave exclusively the product of C-2 attack, in contrast to reaction of these nucleophiles with aziridine2-carboxylates (1), which attack only at the C-3 position (to give α-amino acids 2). This unexpected regioselectivity in the case of aziridine-γ-lactones gives access to substituted β-amino acids (e.g., 9) in an enantiospecific fashion
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