- Synthesis of β-amino acids: 2-(1H-benzotriazol-1-yl)-1,1,3,3-tetramethyl-uronium tetrafluoroborate (TBTU) for activation of Fmoc-/Boc-/Z-α-amino acids
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A new and efficient method for the homologation of urethane protected α-amino acids to its β-homomers by the Arndt-Eistert method using TBTU as a coupling agent is described. Several Fmoc-/Boc-/Z-protected α-amino diazoketone derivatives have been obtaine
- Patil, Basanagoud S.,Vasanthakumar, Ganga-Ramu,Suresh Babu
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p. 3089 - 3096
(2007/10/03)
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- Synthesis of Fmoc-β-homoamino acids by ultrasound-promoted wolff rearrangement
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A highly efficient protocol for Amdt-Eistert chain elongation of the base-labile fluorenylmethoxycarbonyl (Fmoc) protected α-amino acids by Ag+- catalyzed, ultrasound-promoted Wolff rearrangement of the corresponding α- diazo ketones at room temperature is described. The enantiomeric purity of the products was examined by capillary zone electrophoresis with chiral buffer systems.
- Müller, Annett,Vogt, Carla,Sewald, Norbert
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p. 837 - 841
(2007/10/03)
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- Preparation of N-Fmoc-Protected β2- and β3-Amino Acids and Their Use as Building Blocks for the Solid-Phase Synthesis of β-Peptides
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N-Fmoc-Protected (Fmoc = (9H-fluoren-9-ylmethoxy)carbonyl) β-amino acids are required for an efficient synthesis of β-oligopeptides on solid support. Enantiomerically pure Fmoc-β3-amino acids (β3: side chain and NH2 at C(3)(=C(β))) were prepared from Fmoc-protected (S)- and (R)-α-amino acids with aliphatic, aromatic, and functionalized side chains, using the standard or an optimized Arndt-Eistert reaction sequence. Fmoc-β2-Amino acids (β2 side chain at C(2), NH2 at C(3)(=C(β))) configuration bearing the side chain of Ala, Val, Leu, and Phe were synthesized via the Evans' chiral auxiliary methodology. The target β3-heptapeptides 5-8, a β3- pentadecapeptide 9 and a β2-heptapeptide 10 were synthesized on a manual solid-phase synthesis apparatus using conventional solid-phase peptide synthesis procedures (Scheme 3). In the case of β3-peptides, two methods were used to anchor the first β-amino acid: esterification of the ortho-chlorotrityl chloride resin with the first Fmoc-β-amino acid 2 (Method I, Scheme 2) or acylation of the 4-(benzyloxy)benzyl alcohol resin (Wang resin) with the ketene intermediates from the Wolff rearrangement of amino-acid-derived diazo ketone 1 (Method II, Scheme 2). The former technique provided better results, as exemplified by the synthesis of the heptapeptides 5 and 6 (Table 2). The intermediate from the Wolff rearrangement of diazo ketones 1 was also used for sequential peptide-bond formation on solid support (synthesis of the tetrapeptides 11 and 12). The CD spectra of the β2- and β3-peptides 5, 9. and 10 show the typical pattern previously assigned to an (M) 31 helical secondary structure (Fig.). The most intense CD absorption was observed with the pentadecapeptide 9 (strong broad negative Cotton effect at ca. 213 nm); compared to the analogous heptapeptide 5, this corresponds to a 2.5 fold increase in the molar ellipticity per residue!
- Guichard, Gilles,Abele, Stefan,Seebach, Dieter
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p. 187 - 206
(2007/10/03)
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