Dear Wilhelm,
1. Iodine oxidation should leave any pre-formed S-S 'undisturbed'.
Nevertheless there is a lot of side chain functions to care about,
since they are known to suffer from this treatment. Almost "classical"
side reactions like
3-iodination, acetamidomethylation of Tyr and
2-thioether formation from Trp
were further supplemented during last decade with Acm-group transfer to
HO-groups of Ser/Thr and amido functions of Asn/Gln.
At least some of these Acm migrations are sequence-dependent and
highly regioselective (high position preference).
2. We prefer to quench iodine with small portions of powdered ascorbic
acid until colorless solution is obtained (some authors recommend
dropwise addition of 1M ascorbic acid solution in 0.5 M aqueous citric
acid).
In case of using popular thiosulphate there is always a chance of
getting colloidal sulfur solution on acidification or even in the course
of chromatographic process. Probably this will not interfere with HPLC,
but one should expect a variable number of 'major' phantom peaks in
Sephadex GPC profile... (:-)).
Regards,
Igor Rodionov
Laboratory of Peptide Chemistry
Branch of Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry
6 Science Avenue, Pushchino, Moscow Region
142292, Russian Federation
rodionov@fibkh.serpukhov.su
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