Solvents for Solid Phase Peptide Synthesis HEADING_TITLE

Efficient solvation of the peptide resin is essential for successful solid phase peptide synthesis.  Achieving satisfactory solvation of peptide resin during synthesis may not be straight forward for the physicochemical properties of the peptide resin may change greatly as the peptide chain is elongated.  Methylene chloride (DCM), N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) are the commonly utilized solvents in solid phase peptide synthesis.  Mixtures containing DMSO1, TFE2 or HFIP3 have be employed when aggregation of the resin peptide hinders reactions.


Methylene chloride (DCM) is often used in Boc chemistry protocols because it readily dissolves most Boc-protected amino acids, it produces good swelling of polystyrene-based resins, and it is unreactive to TFA.  It is seldom used in Fmoc chemistry, however, because it slowly reacts with piperdine forming insoluble crystals.  DCM may not solvate peptide chains efficiently and difficult couplings in DCM have been attributed to this.4

 
N-methylpyrrolidone (NMP) is the solvent of choice for many peptide chemists. NMP is more polar than DCM; it efficiently solvates the resin and in many cases improves coupling yield.5  Most common peptide reagents are very soluble in NMP, however it has been reported that Fmoc-amino acids exhibit greater decomposition over extended time when dissolved in NMP as opposed to DMF.6

 
Dimethylformamide (DMF) tends to spontaneously break down over time, releasing dimethylamine impurities. Dimethylamine is reactive toward the Fmoc protecting group and may remove it. This could result in excess couplings, and accordingly impure products.

 
DMF is cheaper than NMP, so many peptide chemists use it in spite of its tendency to release reactive amines. These impurities can be removed by degassing DMF just prior to use.  Use of DMF in microwave heated synthesis has been reported to result in N-fomylation;7 a mixture of DCM and DMF on the other hand has been reported as superior to DMF or NMP.8 

 
Acetonitrile and tetrahydrofuran (THF) have been reported to be excellent solvents when used with PEG-based resins, especially for coupling hindered amino acids.9


Footnotes

  Hoeprich, P. D., Jr.; Hugh, T. E., Biochemistry, 1986, 25, 1945-1950; Ho, S. P.; DeGrado, W. F., J. Am. Chem. Soc., 1987, 109, 6761-6758; Hyde, C.; Johnson, T; Sheppard, R. C., J. Chem. Soc., Chem. Commun., 1992, 1573-1575.
  Yamashiro, D.; Blake, J.; Li, C. H., Tetrahedron Lett., 1976, 1469-1472; Narita, M.; Umeyama, H.; Yoshida, T., Bull. Chem. Soc. Jpn., 1989, 62, 3582-3586; Fields, G. B.; Fields, C. G., J. Am. Chem. Soc., 1991, 113, 4202-4207.
  Milton, S. C. F.; Miltom, R. C. de L., Int. J. Peptide Protein Res., 1990, 15, 25-32.
  Hancock, W. S.; Prescott, D. J.; Vagelos, P. R.; Marshall, G. R., J. Org. Chem., 1973, 38, 774-781; Westall, F. C.; Robinson, A. B., J. Org. Chem., 1970, 35, 2842-2844; Kent, S. B. H.; Merrifield, R. B., Peptides 1980 (K. Brunfeldt Ed), Pierce Chemical Company, Rockford, IL, pp 328-333.
  Bagley, C. J.; Otteson, K. M.; May, B. L.; McCurdy, S. N.; Pierce, L.; Ballard, F. J.; Wallace, J. C., Int. J. Pept. Protein Res., 1990, 36, 356-361; Nilsson, M. R.; Nguyen, L. L.; Raleigh, D. P., Anal Biochem., 2001, 288, 76-82.
  Atherton, E.; Bury, C.; Sheppard, R. C.; Williams, P.J., Tetrahedron Lett., 1979, 32, 3041-3042.
  El-Faham, A.; Albericio, F., J. Pept. Sci., 2010, 16, 6–9.
  Vigil-Cruz, S. C.; Peck, A. M.; Aldrich, J. V., “Understanding Biology Using Peptides: Proceedings of the 19th American Peptide Symposim” (S. E. Blondelle, Ed.), Volume 9, Springer, 2006, pp 162-163.
  Acosta, G. A.; del Fresno, M.; Paradis-Bas, M.; Rigau-DeLlobet, M.; Côté, S.; Royo, M.; Albericio, F., J. Pept. Sci., 2009, 15, 629-633.

1 Hoeprich, P. D., Jr.; Hugh, T. E., Biochemistry, 1986, 25, 1945-1950; Ho, S. P.; DeGrado, W. F., J. Am. Chem. Soc., 1987, 109, 6761-6758; Hyde, C.; Johnson, T; Sheppard, R. C., J. Chem. Soc., Chem. Commun., 1992, 1573-1575. 

2 Yamashiro, D.; Blake, J.; Li, C. H., Tetrahedron Lett., 1976, 1469-1472; Narita, M.; Umeyama, H.; Yoshida, T., Bull. Chem. Soc. Jpn., 1989, 62, 3582-3586; Fields, G. B.; Fields, C. G., J. Am. Chem. Soc., 1991, 113, 4202-4207.

3 Milton, S. C. F.; Miltom, R. C. de L., Int. J. Peptide Protein Res., 1990, 15, 25-32.

4 Hancock, W. S.; Prescott, D. J.; Vagelos, P. R.; Marshall, G. R., J. Org. Chem., 1973, 38, 774-781; Westall, F. C.; Robinson, A. B., J. Org. Chem., 1970, 35, 2842-2844; Kent, S. B. H.; Merrifield, R. B., Peptides 1980 (K. Brunfeldt Ed), Pierce Chemical Company, Rockford, IL, pp 328-333.

5 Bagley, C. J.; Otteson, K. M.; May, B. L.; McCurdy, S. N.; Pierce, L.; Ballard, F. J.; Wallace, J. C., Int. J. Pept. Protein Res., 1990, 36, 356-361; Nilsson, M. R.; Nguyen, L. L.; Raleigh, D. P., Anal Biochem., 2001, 288, 76-82.

6 Atherton, E.; Bury, C.; Sheppard, R. C.; Williams, P.J., Tetrahedron Lett., 1979, 32, 3041-3042.

7 El-Faham, A.; Albericio, F., J. Pept. Sci., 2010, 16, 6–9.

8 Vigil-Cruz, S. C.; Peck, A. M.; Aldrich, J. V., “Understanding Biology Using Peptides: Proceedings of the 19th American Peptide Symposim” (S. E. Blondelle, Ed.), Volume 9, Springer, 2006, pp 162-163.

9 Acosta, G. A.; del Fresno, M.; Paradis-Bas, M.; Rigau-DeLlobet, M.; Côté, S.; Royo, M.; Albericio, F., J. Pept. Sci., 2009, 15, 629-633; Jad, Y. E.; Acosta, G. A.; Khattab, S. N.; de la Torre, B.; Govender, T.; Kruger, H. G.; El-Faham, A.; Albericio, F., Org. Biomol. Chem., 2015, 13, 2393-2398.