Synthesis of the orthogonally protected amino alcohol Phaol and analogs.

The development of a multigram synthesis of the orthogonally protected amino acid-derived Phaol [2-{[(2S)-2-amino-3-phenylpropyl]amino}ethanol] is described. The goal of this work is to synthesize an orthogonally protected Phaol in a multigram scale up to 10 g (Cbz-Phaol), so it can be used in solution-based peptide synthesis of peptaibols. Two synthetic schemes were proposed and examined. Between the reduction-coupling and the coupling-reduction scheme, the latter gave the best results. A two-step synthesis affords easily purifiable products. Several analogs were synthesized using this methodology. All the molecules were orthogonally protected, so that they can be used in peptide synthesis. Deprotection posed no problems.