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Preparation of (S,S)-Fmoc-β2hIle-OH, (S)-Fmoc-β2hMet-OH, and (S)-Fmoc-β2hTyr(tBu)-OH for Solid-Phase Syntheses of β2- and β2/β3-Peptides

✍ Scribed by Radovan Sebesta; Dieter Seebach

Publisher
John Wiley and Sons
Year
2003
Tongue
German
Weight
218 KB
Volume
86
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The preparation of three new N‐Fmoc‐protected (Fmoc=[(9__H__‐fluoren‐9‐yl)methoxy]carbonyl) β^2^‐homoamino acids with proteinogenic side chains (from Ile, Tyr, and Met) is described, the key step being a diastereoselective amidomethylation of the corresponding Ti‐enolates of 3‐acyl‐4‐isopropyl‐5,5‐diphenyloxazolidin‐2‐ones with CbzNHCH~2~OMe/TiCl~4~ (Cbz=(benzyloxy)carbonyl) in yields of 60–70% and with diastereoselectivities of >90%. Removal of the chiral auxiliary with LiOH or NaOH gives the N‐Cbz‐protected β‐amino acids, which were subjected to an N‐Cbz/N‐Fmoc (Fmoc=[(9__H__‐fluoren‐9‐yl)methoxy]carbonyl) protective‐group exchange. The method is suitable for large‐scale preparation of Fmoc‐β^2^hXaa‐OH for solid‐phase syntheses of β‐peptides. The Fmoc‐amino acids and all compounds leading to them have been fully characterized by melting points, optical rotations, IR, ^1^H‐ and ^13^C‐NMR, and mass spectra, as well as by elemental analyses.

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