Synthesis 2001(11): 1719-1730
DOI: 10.1055/s-2001-16745
SPECIALTOPIC
© Georg Thieme Verlag Stuttgart · New York

Efficient Asymmetric Synthesis of Unnatural β-Amino Acids

Carsten Bolm*, Ingo Schiffers, Christian L. Dinter, Laurent Defrère, Arne Gerlach, Gerhard Raabe
Institut für Organische Chemie der, RWTH Aachen, Professor-Pirlet-Strasse 1, 52056 Aachen, Germany
Fax: +49(241)8888391; e-Mail: Carsten.Bolm@oc.rwth-aachen.de;
Further Information

Publication History

Received 18 April 2001
Publication Date:
28 September 2004 (online)

Abstract

The simple and highly enantioselective methanolysis of cyclic meso-anhydrides mediated by cinchona alkaloids leads to a broad variety of dicarboxylic acid mono-methyl esters with up to 99% ee. From these products, unnatural N-protected β-amino esters can be obtained by means of Curtius degradation of the corresponding acyl azides. Subsequent cleavage of the protecting groups leads to the free β-amino acids in excellent yields. By enantiomer differentiating opening of racemic anhydrides, synthetically highly useful regioisomeric amino acid esters become readily available.

20

(a) See also: Martín-Vilà, M.; Muray, E.; Aguado, G.P.; Alvarez-Larena, A.; Branchadell, V.; Minguillón, C.; Giralt, E.; Ortuño, R.M. Tetrahedron: Asymmetry 2000, 11, 3569.
(b) Such a sequence has also been used for the preparation of acyclic β-amino acids. For a recent summary of citations, see within ref. 12d.

23

X-ray crystal structure analysis of 4: formula C16H19O4N; M = 289.33, colorless crystal 0.3 × 0.3 × 0.3 mm, a = 5.3448(3), b = 15.878(2), c = 17.199(3) Å, V = 1459.6(8) Å3, ρcalcd = 1.317 gcm-1, µ = 7.39 cm-1, Z = 4, orthorhombic, space group P212121 (No. 19), λ = 1.54179 Å, T = 180 K, ω/2θ scans, 3666 reflections collected, 3013 independent and 2371 observed reflections [I ≥ 2 σ(I)], 266 refined parameters, R1 = 0.057, wR2 = 0.052, residual electron density -0.35/0.39 eÅ-3, hydrogens located and refined isotropically.

29

Attempts to hydrolyse the ester moiety of ent-2 under basic conditions led to epimerization.

32

MOZ = 4-MeO-C6H4CH2CO2-; (2-NO2)-Z = 2-NO2-C6H4CH2CO2-; hZ = C6H5CH2CH2CO2-.

37

The failure of this reaction is in agreement with the observations by Gellman, see ref. 21.

45

X-ray crystal structure analysis of 26: formula C17H21O4N; M = 303.35, colorless crystal 0.24 × 0.24 × 1.00 mm, a = 5.242(4), b = 9.344(4), c = 32.12(2) Å, V = 1573.28 Å3, ρcalcd = 1.281 gcm-1, µ = 7.45 cm-1, Z = 4, orthorhombic, space group P212121 (No. 19), λ = 1.54179 Å, T = 150 K, ω/2θ scans, 3884 reflections collected, 3236 independent and 2924 observed reflections [I ≥ 2 σ(I)], 199 refined parameters, R1 = 0.064, wR2 = 0.085, residual electron density -0.57/0.45 eÅ-3, hydrogens located in part. Us fixed at 1.5 times U of the relevant Leavy atoms prion to final refinement of the heavy atoms not refined.