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A practical synthesis of Nalpha-Fmoc protected L-threo-beta-hydroxyaspartic acid derivatives for coupling via alpha- or beta-carboxylic group

A simple and practical general synthetic protocol towards orthogonally protected tHyAsp derivatives fully compatible with Fmoc solid-phase peptide synthetic methodology is reported. Our approach includes enantioresolution of commercially available D, L-tHyAsp racemic mixture by co-crystallization with L-Lys, followed by ion exchange chromatography yielding enantiomerically pure L-tHyAsp and D-tHyAsp, and their selective orthogonal protection. In this way Na-Fmoc protected tHyAsp derivatives were prepared ready for couplings via either a- or b-carboxylic group onto the resins or the growing peptide chain. In addition, coupling of tHyAsp via b-carboxylic group onto amino resins allows preparation of peptides containing tHyAsn sequences, further increasing the synthetic utility of prepared tHyAsp derivatives.

hydroxyaspartic acid; enantioresolution; orthogonal protection; Fmoc solid-phase peptide synthesis

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