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Abstract: Using the cinchonidine-derived phase-transfer catalyst developed by Park and Jew as a lead structure, we have prepared novel chiral ammonium salts and investigated their efficacy for the preparation of β-hydroxy α-amino acids via asymmetric aldol reactions. The modifications were performed at C3 of the cinchonidine nucleus and include dimers as well as catalysts possessing electron-deficient alkyne and alkene moieties. Some of the new catalysts yielded improvements relative to the Park–Jew catalyst in the aldol reaction. [Copyright &y& Elsevier]

Abstract: τ-Histidinoalanine, with an unusual cross-link between His and Ala, is the central component of theonellamides, a family of bioactive peptidic natural products. Previous syntheses of this residue were plagued with low regioselectivity in the alkylation step. Herein, we report two novel routes to τ-histidinoalanine, involving alkylation of Boc-His-OMe with a serine-derived β-lactone and β-bromoalanine, respectively, as the electrophiles. The use of Mg(OTf)2 as a catalyst was found to be essential to ensure high regioselectivity for the τ-isomer, presumably due to the formation of a six-membered ring chelation involving the π-nitrogen atom of histidine. [Copyright &y& Elsevier]