At present, for the purification of proteins adsorbents with ligands giving large protein losses at the eluation of the protein are used.
Even after washing of the adsorbent with 1M caustic solution, protein remains on the adsorbent and alters its characteristics. Re-use thereof may thus cause risks of contamination of further test mixtures with the proteins that remain on the adsorbent. As an alternative to these adsorbents more specific adsorbents have been developed for the isolation of a.o. IgG. These adsorbents are characterized by that a protein is covalently bound to the adsorbent and binds specifically to IgG. The disadvantages are that the covalently bound protein is released and leaks out and can cause medical complications thereby.
As an alternative to such biospecific adsorbents (Protein A and Protein G, resp.) so called tiophilic adsorbents have been developed (Porath, Belew--SE-PS 8405431-1). The tiophilic adsorbents of the kind having been developed hitherto, however, are not alkali stable, wherefore purification and washing with 1M caustic solution can not be performed without risk of the undesirable effect, which is a condition for preventing bacterial and virus infections and risk for pyrogens, when the adsorbent is re-used in large scale processes.
An adsorbent with the structure ##STR1## is previously described in EP-A-0 180 563 and SE-B-462 165 (Porath and Oscarsson). The disadvantage with this adsorbent is that it is not alkali stable, because of the unfavourable electron density distribution within the molecule, which is determined by the positions therein of the sulphur and nitrogen, respectively.
The electron density distribution within the pyridyl sulphide molecule in formula I is shown in formula II below ##STR2##
When the electron density distribution within the molecule is calculated carbon atom C.sub.1 is shown to have an electron deficit in its position, which means that the nucleophilic hydroxyl group can react at position C.sub.1 and result in elimination of hydroxipyridin. If the sulphur is moved from the pyridine ring within the above describe molecule by the introduction of a methylene group between the sulphur and the pyridine ring the undesired effect of an electron deficit on C.sub.1 does not occur. This has also been verified experimentally. The adsorbent will thereby remain stable against alkali, and has a high desorption effectivity towards proteins having been into contact with the adsorbent, and further very low protein residues.