Deracemisation of α-amino acids - (R)- and (S)-phenylalanine from the same enantiomer of a homochiral auxiliary

Tetrahedron Asymmetry

Volumn 9, Issue 16, 1998, Pages 2795-2798

  Bull, Steven D ^a   Davies, Stephen G ^a   Epstein, Simon W ^a   Ouzman, Jacqueline V A ^a  

^a UNIVERSITY OF OXFORD   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

ALPHA AMINO ACID; PHENYLALANINE;

AMINO ACID ANALYSIS; AMINO ACID SYNTHESIS; CHIRALITY; ENANTIOMER; MOLECULAR MODEL; PRIORITY JOURNAL; PROTON TRANSPORT; REVIEW; STRUCTURE ANALYSIS; SYNTHESIS;

EID: 0032555634     PISSN: 09574166     EISSN: None     Source Type: Journal    
DOI: 10.1016/S0957-4166(98)00304-8     Document Type: Article

References (20)

1. R. M. Williams, Synthesis of Optically Active α-Amino Acids, Pergamon Press, Oxford, 1989; R. O. Duthaler, Tetrahedron, 1994, 50, 1540.
2. R. M. Williams, Synthesis of Optically Active α-Amino Acids, Pergamon Press, Oxford, 1989; R. O. Duthaler, Tetrahedron, 1994, 50, 1540.
3. Some of the more popular methods are: (a) Seebach's imidazolidinone - D. Seebach, A. R. Sting, M. Hoffmann, Angew. Chem. Int. Ed. Engl., 1996, 35, 2708; (b) Williams' oxazinone - R. M. Williams, M. N. Im, J. Am. Chem. Soc., 1991, 113, 9276; (c) Evans' oxazolidinone - D. A. Evans, A. E. Weber, J. Am. Chem. Soc., 1986, 108, 6757; (d) Oppolzers' sultam - W. Oppolzer, R. Moretti, S. Thomi, Tetrahedron Lett., 1989, 30, 6009; (e) Myers' pseudoephedrine auxiliary - A. G. Myers, J. L. Gleason, T. Yoon, J. Am. Chem. Soc., 1995, 117, 8488.
4. Some of the more popular methods are: (a) Seebach's imidazolidinone - D. Seebach, A. R. Sting, M. Hoffmann, Angew. Chem. Int. Ed. Engl., 1996, 35, 2708; (b) Williams' oxazinone - R. M. Williams, M. N. Im, J. Am. Chem. Soc., 1991, 113, 9276; (c) Evans' oxazolidinone - D. A. Evans, A. E. Weber, J. Am. Chem. Soc., 1986, 108, 6757; (d) Oppolzers' sultam - W. Oppolzer, R. Moretti, S. Thomi, Tetrahedron Lett., 1989, 30, 6009; (e) Myers' pseudoephedrine auxiliary - A. G. Myers, J. L. Gleason, T. Yoon, J. Am. Chem. Soc., 1995, 117, 8488.
5. Some of the more popular methods are: (a) Seebach's imidazolidinone - D. Seebach, A. R. Sting, M. Hoffmann, Angew. Chem. Int. Ed. Engl., 1996, 35, 2708; (b) Williams' oxazinone - R. M. Williams, M. N. Im, J. Am. Chem. Soc., 1991, 113, 9276; (c) Evans' oxazolidinone - D. A. Evans, A. E. Weber, J. Am. Chem. Soc., 1986, 108, 6757; (d) Oppolzers' sultam - W. Oppolzer, R. Moretti, S. Thomi, Tetrahedron Lett., 1989, 30, 6009; (e) Myers' pseudoephedrine auxiliary - A. G. Myers, J. L. Gleason, T. Yoon, J. Am. Chem. Soc., 1995, 117, 8488.
6. Some of the more popular methods are: (a) Seebach's imidazolidinone - D. Seebach, A. R. Sting, M. Hoffmann, Angew. Chem. Int. Ed. Engl., 1996, 35, 2708; (b) Williams' oxazinone - R. M. Williams, M. N. Im, J. Am. Chem. Soc., 1991, 113, 9276; (c) Evans' oxazolidinone - D. A. Evans, A. E. Weber, J. Am. Chem. Soc., 1986, 108, 6757; (d) Oppolzers' sultam - W. Oppolzer, R. Moretti, S. Thomi, Tetrahedron Lett., 1989, 30, 6009; (e) Myers' pseudoephedrine auxiliary - A. G. Myers, J. L. Gleason, T. Yoon, J. Am. Chem. Soc., 1995, 117, 8488.
7. Some of the more popular methods are: (a) Seebach's imidazolidinone - D. Seebach, A. R. Sting, M. Hoffmann, Angew. Chem. Int. Ed. Engl., 1996, 35, 2708; (b) Williams' oxazinone - R. M. Williams, M. N. Im, J. Am. Chem. Soc., 1991, 113, 9276; (c) Evans' oxazolidinone - D. A. Evans, A. E. Weber, J. Am. Chem. Soc., 1986, 108, 6757; (d) Oppolzers' sultam - W. Oppolzer, R. Moretti, S. Thomi, Tetrahedron Lett., 1989, 30, 6009; (e) Myers' pseudoephedrine auxiliary - A. G. Myers, J. L. Gleason, T. Yoon, J. Am. Chem. Soc., 1995, 117, 8488.
8. (S)-Penicillamine, for example, is used for the treatment of heavy metal poisoning while (R)-penicillamine causes atrophy and blindness; G. M. Coppola, K. M. Schuster, Asymmetric Synthesis - Construction of Chiral Molecules using Amino Acids, Wiley, New York, 1987.
9. For an excellent review on the enantiospecific reprotonation of prochiral enolates see: C. Fehr, Angew. Chem. Int. Ed. Engl., 1996, 35, 2566.
10. S. D. Bull, S. G. Davies, S. W. Epstein, J. V. A. Ouzman, Chem. Commun, 1998, 659.
11. The α-amino acids had identical specific rotations to authentic samples of homochiral phenylalanine and valine purchased from Aldrich chemical company.
12. ™) suite of Molecular Mechanics programs using PM3 parameters.
13. Juaristi and Seebach have employed a similar enolate reprotonation strategy to epimerise alanine derived imidazolidinone auxiliaries containing two stereogenic centres, although no d.e. values were reported for these transformations; E. Juaristi, J. L. Anzorena, A. Boog, D. Madrigal, D. Seebach, E. V. García-Baez, O. García-Barradas, B. Gordillo, A. Kramer, I. Steiner, S. Zürcher, J. Org. Chem., 1995, 60, 6408.
14. 3 position of DKP 6 could only be achieved when 5 equiv. of n-BuLi and prolonged reaction times were employed.
15. 3 at δ 5.17 and 5.38: W. H. Pirkle, P. E. Adams, J. Org. Chem., 1980, 45, 4117.
16. An alternative approach to the deracemisation of α-amino acids has been reported involving a stereo specific reprotonation approach using pantolactone as a chiral auxiliary, M. Calmes, J. Daunis, N. Mai, F. Natt, Tetrahedron Lett., 1996, 37, 379; M. Calmes, J. Daunis, N. Mai, Tetrahedron: Asymmetry, 1997, 8, 1641.
17. An alternative approach to the deracemisation of α-amino acids has been reported involving a stereo specific reprotonation approach using pantolactone as a chiral auxiliary, M. Calmes, J. Daunis, N. Mai, F. Natt, Tetrahedron Lett., 1996, 37, 379; M. Calmes, J. Daunis, N. Mai, Tetrahedron: Asymmetry, 1997, 8, 1641.
18. Synthesis of the epimeric mixture of DKPs 2 and 6 from racemic phenylalanine may be achieved viap-methoxybenzylation of the parent DKPs cyclo-(SR)-Phe-(S)-Val which are derived in a similar yield either via condensation of the Leuch's anhydride of (S)-valine with (±)-phenylalanine methyl ester according to the procedure described by S. D. Bull, S. G. Davies, W. O. Moss, Tetrahedron: Asymmetry, 1998, 9, 321; or via DCC coupling of Z-(S)-valine and (±)-phenylalanine methyl ester according to the method described by J. E. Rose, P. D. Leeson, D. Gani, J. Chem. Soc., Perkin. Trans, 1, 1995, 157.
19. Synthesis of the epimeric mixture of DKPs 2 and 6 from racemic phenylalanine may be achieved viap-methoxybenzylation of the parent DKPs cyclo-(SR)-Phe-(S)-Val which are derived in a similar yield either via condensation of the Leuch's anhydride of (S)-valine with (±)-phenylalanine methyl ester according to the procedure described by S. D. Bull, S. G. Davies, W. O. Moss, Tetrahedron: Asymmetry, 1998, 9, 321; or via DCC coupling of Z-(S)-valine and (±)-phenylalanine methyl ester according to the method described by J. E. Rose, P. D. Leeson, D. Gani, J. Chem. Soc., Perkin. Trans, 1, 1995, 157.
20. The high diastereoselectivity observed for reprotonation of enolate 5 is under kinetic control, since thermodynamic equilibration of trans-2 or cis-6 via treatment with sodium methoxide in methanol afforded a 60:40 ratio of trans-2:cis-6.