Di Gioia ML, Leggio A, Le Pera A, Liguori A, Siciliano C. Optically PureN-Hydroxy-O-triisopropylsilyl-α-l-amino Acid Methyl Esters from AlCl3-Assisted Ring Opening of Chiral Oxaziridines by Nitrogen Containing Nucleophiles.
J Org Chem 2005;
70:10494-501. [PMID:
16323863 DOI:
10.1021/jo051890+]
[Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
[reaction: see text] This article reports a straightforward and unprecedented process of AlCl3-assisted oxaziridine ring opening by nitrogen containing nucleophiles, in a totally anhydrous milieu. Under these conditions, nucleophiles exclusively attack the carbon atom of the three-membered heterocycles, obtained from methyl esters of natural alpha-amino acids, generating N-hydroxy-alpha-L-amino acid methyl esters. No nitrones, amides, or other side products, either from unwanted rearrangements or due to the attack of the nucleophile on the N atom of the oxaziridine systems, are formed. The hydroxylamine compounds are recovered in excellent yields, after their site-specific conversion into the corresponding O-triisopropylsilyl derivatives, by exposure to triisopropylsilyl triflate in the presence of 1H-imidazole. Derivatization, performed immediately after the recovery of the N-hydroxylated precursors, allows the chiral integrity of the asymmetric alpha-carbon atoms in the amino acid methyl esters to be retained. It also protects the obtained compounds from frame degradation by disproportionation. N-Hydroxy-O-triisopropylsilyl-alpha-L-amino acid methyl esters are important intermediates in the study of natural alpha-L-amino acid metabolic pathways and are ideal candidates as starting materials in the synthesis of biologically, pharmacologically, and nutritionally important N-hydroxy peptides.
Collapse