Chemistry Reference
In-Depth Information
RCH
2
SH
R = CH(NH
2
)CO
2
H
+ HOCl
-Cl
•
/Cl
-
+R
'
NH
2
RCH
2
S
•
RCH
2
SCl
RCH
2
S(O)
2
-NHR'
Sulfonamide
+ HOCl
+ H
2
O
2×
+ Cys
Cystine
RCH
2
S-SCH
2
R
RCH
2
SO
3
H
Cysteic acid
+ HOCl
+ H
2
O
+
RCH
2
S-SCH
2
R
+ H
2
O
RCH
2
S-SCH
2
R
Cl
O
Figure 3.6.
Mechanisms and products of chlorination of Cys and cystine (adapted from
Hawkins et al. [33] with the permission of Springer America).
HOCl-induced oxidation of thiols [51]. Formation of sulfenyl chloride has also
been proposed in the reactions of aryl sulfinates with HOCl (
k
∼ 10
9
/M/s) [53].
The sulfenyl chloride intermediates may also react with other Cys molecules
to yield cystine (Fig. 3.6). A recent study showed the formation of CySSCy,
CySO
2
H, and CySO
3
H in the reaction of a 1 : 1 molar ratio of CySH with HOCl
at pH 11.4 [52]. Production of the cysteine thiosulfonate ester has also been
suggested through the reaction of Cys with HOCl under alkaline media [52].
Further reaction of the cysteine thiosulfinate ester with Cys produces cysteine
sulfenic acid [52].
N
,
N
′-Dichlorocystine has been shown to form in the reaction
of CySSCy with HOCl [57]. The oxidation of cystine by HOCl may also take
place via a sulfenyl chloride intermediate RS
+
(Cl)SR, which, upon hydrolysis,
forms cysteic acid. Significantly, these intermediates can react with nitrogen
centers to form additional products [54, 58-61]. For example, sulfenamide
(RSN-) cross-links were formed in the reaction of sulfenyl chlorides with the
side-chain amines of lys. The reactions of sulfenamides with oxygen resulted
in sulfinamides (RS(O)N-) and sulfonamides (RS(O)
2
N-) [61].
Studies on the oxidation of gSH by HOCl showed the formation of three
products, glutathione disulfide (gSSg), glutathione thiosulfonate, and gluta-
thione sulfonamide [54, 59]. The treatment of human umbilical vein endothelial
cells (HUVEC) with HOCl formed glutathione sulfonamide as the major
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