To find their potential use in protein research, direct
addition
of a disulfide compound to alkyne (namely disulfide–yne reaction)
and S-arylation with arenediazonium salt (namely disulfide–diazonium
reaction) were investigated in aqueous or protic solutions. The reaction
of dimethyl disulfide with 5-hexynol performed best under 300 nm irradiation
in the presence of sodium acetate to afford 5,6-bis(methylthio)-5-hexenol
in 60% yield. Without the prior reduction of a disulfide bond to thiols,
the disulfide–yne reactions have the advantage of 100% atom
economy. Disulfide–diazonium reaction was triggered by sodium
formate and accelerated by photoirradiation with a 450 nm LED lamp
(5 W). The reaction of 3,4-dihydroxy-1,2-dithiane with 2-(prop-2-yn-1-yloxy)benzene-1-diazonium
tetrafluoroborate (8b) afforded 2-(benzofuran-3-yl)-1,3-dithiepane-5,6-diol
(13), confirming that both S substituents originate from
the same disulfide molecule. The trastuzumab antibody was incubated
with diazonium 8b, followed by α-lytic protease
digestion, LC-ESI-MS/MS analysis, and Mascot search, to verify that
the proximal C229 and C232 residues on the same heavy chain were reconnected
with a (benzofuranyl)methine moiety that originated from 8b, unlike the expected disulfide rebridging across two heavy chains.
Nonetheless, disulfide–diazonium reactions still have potential
for rebridging disulfide bonds if appropriate proteins and diazonium
agents are chosen.