COMMUNICATION
Disulfide formation via sulfenamideswz
Jia Pan and Ming Xian*
Received 24th June 2010, Accepted 4th August 2010
DOI: 10.1039/c0cc02076a
A
phosphine-mediated one-step disulfide formation from
S-nitrosothiols has been developed. This reaction can convert
unstable S-nitrosothiols to stable disulfides via sulfenamide
intermediates under very mild conditions. It has the potential
to be used for the detection of S-nitrosothiols.
As an important post-translational modification, S-nitrosation
converts protein cysteine residues (SH) to S-nitrosothiols
(SNO). This protein modification leads to modulation of
structure, inhibition of active site cysteines, disruption of
allosteric interactions with other molecules, etc.1 The formation
of S-nitrosothiols in proteins may be directed by peptide
sequences surrounding sensitive cysteine residues, by exogenous
versus endogenous nitric oxide (NO) sources or by compart-
mentalization of nitric oxide synthases. Although the
importance of S-nitrosation has been well recognized, the
detection of S-nitrosation is still a challenge.2 This is primarily
due to the lability of S-nitrosothiols and the lack of reliable
methods for their detection. From a chemistry point-of-view,
SNO is a unique functional group; it might have some distinct
reactivity from other biological functional groups. If specific
reactions which only target SNO can be developed, such
reactions may be very useful for the detection of S-nitrosation.
Our group recently initiated a program to study phosphine-
based reactions of S-nitrosothiols. In 2008, a fast reductive
ligation of SNO was developed (Scheme 1).3 This reaction
selectively converts unstable SNO to stable sulfenamide products
via a Staudinger ligation-like mechanism.3,4 However, we also
noticed that sulfenamides generated from cysteine derivatives
could be over-reduced by the excess of phosphine ligation
reagents. This might be a problem for directly applying
reductive ligation in SNO detection.
Scheme 2 Bis-ligation of SNO.
To solve this problem, we developed a bis-ligation of SNO
in 2009 (Scheme 2).5 This reaction can convert SNO to stable
disulfide-iminophosphorane conjugates in one step. Previous
studies have revealed that disulfides are stable towards excess
triarylphosphines such as the phosphine reagents used in our
reaction.3–5
Given the high reactivity of the sulfenamide intermediates
towards the thiolate observed in bis-ligation, we propose
another one-step reaction to convert unstable SNO to stable
products (Scheme 3). As such, SNO will be treated with
regular reductive ligation reagent 1. As the reductive ligation
is a very fast reaction, sulfenamide products should be formed
in minutes. Then, if a nucleophile is added into the reaction
mixture, it may convert sulfenamide 4 to a stable final product
9 and liberate the phosphine oxide 10. The formation of simple
adducts, without the bulky triarylphosphine-oxide, would be
attractive for applications in protein systems. We realized that
if this one-pot reaction is used in the detection of protein SNO,
one critical concern is that the nucleophile should only react
with sulfenamides, not with protein disulfides.
To test this idea, sulfenamide 11 was prepared and used as a
model compound to test the reactivity of a series of mild
nucleophiles. The reaction was carried out in a mixture of
THF and PBS buffer (pH 7.4) solution. At the same time,
compound 12 was used to examine the reactivity of the
nucleophiles towards disulfides under the same conditions.
As shown in Table 1, two thiol nucleophiles (13a and 13b)
showed good selectivity for the sulfenamide, as no reaction
Scheme 1 Reductive ligation of SNO.
Department of Chemistry, Washington State University, Pullman,
WA 99164, USA. E-mail: mxian@wsu.edu; Fax: 509-335-8867;
Tel: 509-335-6073
w This article is part of the ‘Emerging Investigators’ themed issue for
ChemComm.
Scheme 3 Proposed one-pot reaction to convert SNO to stable
z Electronic supplementary information (ESI) available: Experimental
details. See DOI: 10.1039/c0cc02076a
products.
c
352 Chem. Commun., 2011, 47, 352–354
This journal is The Royal Society of Chemistry 2011
Pan, Jia
