In our most recent deprotection, there was a great deal of white precipitate that sat on top of the silica column, but we have not finished evaluating the experiment; therefore, I cannot say whether or not the precipitate is associated with a good or bad result. The price of polystyrene-piperazine is moderately high, but not prohibitive. I like the idea of resin-supported piperazine in some respects, but possibly a cheaper alternative would be to use centrifugation in Corex glass centrifugation tubes if the precipitate forms and if
one is certain that all of the desired product is in solution. Corex tubes can be spun more quickly than simple glass test tubes.
Here are the four references within the Chapter written by Fields, from my previous message:
10. Carpino, L. A., Sadat-Aalaee, D., and Beyermann, M. (1990) Tris(2-ammoethyl) amine as a substitute for 4-(aminomethyl)piperidine in the FMOC/polyamine approach to rapid peptide synthesis. J. Org. Chem. 55, 1673-1675. https://pubs.acs.org/doi/10.1021/jo00292a050
44. Beyermann, M, Bienert, M., Niedrich, H., Carpino, L. A., and Sadat-Aalaee, D (1990) Rapid continuous peptide synthesis via FMOC amino acid chloride coupling and 4-(aminomethyl)piperidine deblocking. J. Org. Chem. 55,721-728. https://pubs.acs.org/doi/abs/10.1021/jo00289a056
45. Carpino, L. A. and Williams, J. R. (1978) Polymeric de-blocking agents for the
fluoren-9-ylmethoxycarbonyl (FMOC) amino-protecting group. J. Chem Soc, Chem. Communications 450, 451. DOI https://doi.org/10.1039/C39780000450
46 Arshady, R., Atherton, E., and Sheppard, R. C. (1979) Basic polymers for the cleavage
of fluorenylmethoxycarbonyl ammo-protecting groups n peptide synthesis Tetrahedron Lett., 1521-1524.
Supra Sciences makes a couple of solid phase versions of piperazine. http://suprasciences.com/wp-content/uploads/2014/07/Piperazine1.pdf