Expedient synthesis of a novel class of pseudoaromatic amino acids: tetrahydroindazol-3-yl- and tetrahydrobenzisoxazol-3-ylalanine derivatives |
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Authors: | Richard J. Middleton Siri Ram Chhabra Weng C. Chan |
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Affiliation: | a School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD, UK b Institute of Infection, Immunity and Inflammation, University of Nottingham, University Park, Nottingham NG7 2RD, UK |
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Abstract: | A concise synthesis of novel homochiral aromatic amino acid surrogates comprising a tetrahydroindazole or a benzisoxazole system was developed via the acylation of a cyclic 1,3-diketone by the side-chain carboxyl functionality of either Boc-Asp-OtBu or Boc-Glu-OtBu followed by regioselective condensation with hydrazine, N-benzylhydrazine and hydroxylamine. The tetrahydroindazole nucleus was also constructed by the condensation of Boc-Asp-OtBu with the enamine, 1-pyrrolidino-1-cyclohexene followed by acid-hydrolytic treatment and reaction with hydrazines. Further functional group transformations gave Nα-Fmoc-protected derivatives as useful building blocks for solid-phase peptide assembly. |
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Keywords: | Unnatural amino acids Pseudoaromatic Tetrahydroindazoles |
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