I would like to add a bit to the excellent response from Russ
Lehrman regarding methionine oxidation products. In the course of our
work with psi-CH2S amide bond replacements, we generated a number of
oxidized versions of these surrogates. In every case, the SO analogs
were more hydrophilic than the sulfides (came earlier in RP-HPLC), and
the SO2 variants appeared between the sulfoxides and sulfides. The same
is true of methionine and its oxidized products as discussed in the
amino acid analysis literature.
Interestingly, the sulfoxides represent a new chiral center (they
are configurationally stable) and again in many cases we were able to
separate the resulting diastereomeric pseudopeptides, even in sequences
as long as decapeptides.
In the case of methionine, the oxidized product should also
represent a pair of isomers although most papers refer to methionine
sulfoxide in the singular form. This is probably due to difficulties in
separating the isomers, presumably because the relevant stereocenters
are farther apart.
In our experience, the sulfoxides are readily formed with dilute
hydrogen peroxide, but the sulfone takes more rigorous conditions,
exactly as discussed by Russ in his comments.
Best regards. Arno
-- Dr. Arno F. Spatola Director IMD3 http://www.imd3.org/ Department of Chemistry, University of Louisville Louisville, KY 40292-0001 USA email: spatola@louisville.edu Phone: 502-852-5979 Fax: 502-852-3899
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