The invention discloses a method for the manuf. of a peptidic folding precursor (switch-peptide) stable and sol. at physiol. conditions, derived from a peptide having a potential for self-assembling and fibrillogenesis. Another object of the invention is to provide a tool for the quant., controlled in vitro study of fibrillogenesis and its inhibition of peptides involved in degenerative diseases. Prepn. of peptides is described.