Studies of the chemical selectivity of hapten, reactivity, and skin sensitization potency. 1. Synthesis and studies on the reactivity toward model nucleophiles of the 13c-labeled skin sensitizers hex-1-ene- and hexane-1,3-sultones

Article abstract of DOI:10.1021/tx000225n

The potent skin sensitizers hex-1-ene- and hexane-1,3-sultone have been synthesized isotopically labeled with ¹³C at reactive sites. The reactivity of 2-[¹³C]- and 3-[¹³C]hex-1-ene-1,3-sultones and of 3-[¹³C]hexane-1,3-sultone toward a series of model nucleophiles for protein amino acid residues, i.e., butylamine, diethylamine, imidazole, propanethiol, and phenol, was followed by ¹³C NMR spectroscopy. The reactivity in water of hex-1-ene-1,3-sultone toward model nucleophiles follows the hard and soft acid and base theory with the hard nucleophiles (primary and secondary amine and phenate) mainly reacting at position 3 by S_N substitution, and the soft nucleophiles (thiolate and imidazole) mainly reacting at position 2 by a Michael addition reaction. Hexane-1,3-sultone reacts with model nucleophiles at position 3 by S_N substitution. Both saturated and unsaturated sultones are sensitive to hydrolysis when reacted in water.

Full text of DOI:10.1021/tx000225n

1
10
Chem. Res. Toxicol. 2001, 14, 110-117
Stu d ies of th e Ch em ica l Selectivity of Ha p ten ,
Rea ctivity, a n d Sk in Sen sitiza tion P oten cy. 1. Syn th esis
a n d Stu d ies on th e Rea ctivity tow a r d Mod el
1
3
Nu cleop h iles of th e C-La beled Sk in Sen sitizer s
Hex-1-en e- a n d Hexa n e-1,3-su lton es
Emmanuel Meschkat, Martin D. Barratt, and J ean-Pierre Lepoittevin*,†
†
‡,§
Laboratoire de Dermatochimie associ e´ au CNRS, Universit e´ Louis Pasteur,
Clinique Dermatologique, CHU, F-67091 Strasbourg Cedex, France, and SEAC-Toxicology Unit,
Unilever Research Colworth, Sharnbrook, Bedford, U.K.
Received October 25, 2000
The potent skin sensitizers hex-1-ene- and hexane-1,3-sultone have been synthesized
1
3
13
13
isotopically labeled with C at reactive sites. The reactivity of 2-[ C]- and 3-[ C]hex-1-ene-
1
1
3
,3-sultones and of 3-[ C]hexane-1,3-sultone toward a series of model nucleophiles for protein
amino acid residues, i.e., butylamine, diethylamine, imidazole, propanethiol, and phenol, was
followed by 13C NMR spectroscopy. The reactivity in water of hex-1-ene-1,3-sultone toward
model nucleophiles follows the hard and soft acid and base theory with the hard nucleophiles
(
primary and secondary amine and phenate) mainly reacting at position 3 by S
and the soft nucleophiles (thiolate and imidazole) mainly reacting at position 2 by a Michael
addition reaction. Hexane-1,3-sultone reacts with model nucleophiles at position 3 by S
N
substitution,
N
substitution. Both saturated and unsaturated sultones are sensitive to hydrolysis when reacted
in water.
In tr od u ction
Ch a r t 1
1
Allergic contact dermatitis (ACD) is a common disease
produced by the modification of skin proteins by haptens
1). These low-molecular weight chemicals, usually rather
(
lipophilic, are able to penetrate the skin where, either
directly or after metabolism, they react with nucleophilic
residues of amino acids through an electrophile-nucleo-
phile mechanism or a radical mechanism (2). Subsequent
processing of these modified proteins by Langerhans
cells, the main antigen-presenting cell of the epidermis,
leads to the selection and activation of T-lymphocytes
with receptors able to selectively bind antigenic hapten-
modified peptides (3). In the past few years, quantitative
structure-activity relationships (QSAR) have been de-
veloped to explain the sensitizing potential of several
haptens, and key parameters, such as lipophilicity and
reaction rate, have been identified (4, 5). Furthermore,
it has been shown that, in most cases, haptens exhibit
chemical selectivity for nucleophilic amino acids (6, 7),
although the effect of such selectivity on sensitization
potential is not understood. This paper is intended to be
the first of a series of studies aimed at investigating the
relationship between the chemical selectivity of haptens
with the potency of their skin sensitization potential. The
first two papers in the series concern hex-1-ene-1,3-
sultone and hexane-1,3-sultone.
Alk-1-ene-γ-sultones (Chart 1) have been shown, in
several animal models, to be particularly strong skin
sensitizers (8, 9), exhibiting sensitization potential down
to levels of approximately 1 ppm, while alkane-γ-sultones
were found to be moderate sensitizers. Attention was
focused on these chemicals in the mid-1970s, when the
cause of a 1968 outbreak of contact dermatitis in Scan-
dinavia was traced to 2-chloro-γ-sultones and R,â-
unsaturated γ-sultones, formed as contaminants in a
batch of ether sulfate used to formulate dishwashing
liquids (10). The high sensitizing ability of alkene versus
alkane sultones has been attributed to Michael acceptor
properties of the electron-deficient double bond (8). In
fact, alkenesultones exhibit two potential reactive elec-
trophilic centers that are able to react with nucleophilic
amino acids via two different mechanisms (“Michael type”
*
To whom correspondence should be addressed. Phone: +33 388
3
50 664. Fax: +33 388 140 447. E-mail: jplepoit@chimie.u-strasbg.fr.
†
Universit e´ Louis Pasteur.
Unilever Research Colworth.
Present address: Marlin Consultancy, 10 Beeby Way, Carlton,
N
addition at position 2 and S reaction at position 3), while
alkanesultones have only one reactive electrophilic center
at position 3, which is able to react with nucleophilic
‡
§
Bedford MK43 7LW, U.K.
1
Abbreviations: ACD, allergic contact dermatitis; DIBA-H, diisobu-
amino acids via an S
N
reaction. A comparison of the
tylaluminum hydride; HSA, human serum albumin; HSAB, hard and
soft acid and base; NOE, nuclear Overhauser effect; QSAR, quantita-
tive structure-activity relationships; RAI, relative alkylation index.
chemical behavior of these two molecules could be valu-
able for obtaining new insights into the relationship
1
0.1021/tx000225n CCC: $20.00 © 2001 American Chemical Society
Published on Web 12/15/2000

Labeled Sultones
Chem. Res. Toxicol., Vol. 14, No. 1, 2001 111
between sensitization potential and mechanisms of pro-
tein modification.
(10 mL) and then with water (10 mL) and dried over MgSO
Solvent evaporation under reduced pressure gave 6 (779 mg,
4
.
1
1
3
4.64 mmol, 67% yield): H NMR (200 MHz, CDCl
3
) δ 1.29 (t,
), 3.82 (d, 2H, J H-C ) 153.1 Hz, CH Br),
.23 (q, 2H, J ) 7.1 Hz, CH ) δ
O); 13C NMR (50 MHz, CDCl
4.0, 25.9, 62.3, 167.3 (d, J C-C ) 63.9 Hz); IR (CHCl ) ν 1285
In this paper, we report the synthesis of 3-[ C]- and
3
4
1
H, J ) 7.0 Hz, CH
3
2
1
3
2
-[ C]hex-1-ene-1,3-sultones 1a and 1b, respectively, and
2
3
1
3
of 3-[ C]hexane-1,3-sultone 2a (Chart 1) and their
3
reactivity toward model nucleophiles studied using 13
C
(C-O), 1738 (CdO).
NMR. The results of these experiments are used in the
following paper (11) to analyze the reaction of these
chemicals in water with human serum albumin (HSA),
used as a model protein.
-[13C ](E t h o x y c a r b o n y lm e t h y l)t r ip h e n y lp h o s p h o -
n iu m Br om id e (7). Ethyl 2-[ C]-2-bromoacetate 6 (779 mg,
2
13
4
.64 mmol) in ethyl acetate (2.5 mL) was slowly added to a
solution of triphenylphosphine (1.22 g, 4.64 mmol) in ethyl
acetate (2.5 mL). The reaction mixture was then stirred at room
temperature for 12 h and the white precipitate filtered off,
Ma ter ia ls a n d Meth od s
washed with ether (3 × 10 mL), and dried under vacuum at 40
1
°
C for 5 h to give 7 (1.73 g, 4.03 mmol, 87% yield): H NMR
Ca u tion : Skin contact with sultone derivatives must be
avoided. Since these are sensitizing substances, they must be
handled with care.
Ch em istr y. 1H and 13C NMR spectra were recorded on a
(
200 MHz, CDCl
3
) δ 0.99 (t, 3H, J ) 7.1 Hz, CH
3
), 3.97 (q, 2H,
J ) 7.1 Hz, CH
Hz, CH
δ 13.6, 33.0 (d,
2
O), 5.39 (dd, 2H, J H-C ) 134.6 Hz, J H-P ) 13.8
1
3
2
3
P), 7.58-7.88 (m, 15H, ArH); C NMR (50 MHz, CDCl )
1
1
J
C-P ) 56.1 Hz), 62.8, 117.8 (d,
J
C-P ) 87.4
Bruker AC 200 MHz spectrometer in CDCl
specified. Chemical shifts are reported in parts per million (δ)
with respect to TMS, and CHCl was used as an internal
standard (δ ) 7.26 ppm). Multiplicities are indicated by s
singlet), d (doublet), t (triplet), and m (multiplet). Infrared
3
unless otherwise
3
2
Hz), 130.2 (d, J C-P ) 13.2 Hz), 133.8 (d, J C-P ) 11.5 Hz), 135.1
4
(
(
d, J C-P ) 3.3 Hz), 164.2 (d, J C-C ) 59.4 Hz); IR (CHCl
CdO).
3
) ν 1733
3
2-[1 3 C ](E t h o x y c a r b o n y lm e t h y le n e )t r ip h e n y lp h o s -
(
spectra were recorded on a Perkin-Elmer FT-IR 1600 spectrom-
eter, the peaks being reported in reciprocal centimeters. Melting
points were determined on a Buchi Tottoli 510 apparatus and
are uncorrected. Dried solvents were freshly distilled before use.
Tetrahydrofuran and ethyl ether were distilled from sodium
benzophenone. Triethylamine was distilled from powdered
p h or a n e (8). A solution of sodium hydroxide (1.0 M, 15 mL)
1
3
was added to a solution of 2-[ C](ethoxycarbonylmethyl)-
triphenylphosphonium 7 (1.73 g, 4.03 mmol) in dichloromethane
(15 mL) and the reaction mixture stirred vigorously for 15 min.
The organic layer was removed and the aqueous layer extracted
with dichloromethane (2 × 5 mL). The combined organic layers
calcium hydride. Methylene chloride was dried over P
2
O
5
before
4
were dried over MgSO and concentrated under vacuum to give
1.38 g (3.96 mmol, 98% yield) of phosphorane 8: 1 C NMR (50
MHz, CDCl ) δ 14.8, 30.1 (d, J C-P ) 125.3 Hz), 57.8, 128.0 (d,
C-P ) 90.6 Hz), 128.7 (d, 3
C-P ) 11.9 Hz), 131.9, 133.0 (d,
) ν 1610 (CdO).
Eth yl (E)-2-[13C]Hex-2-en oa te (4b). To a solution of bu-
tyraldehyde (434 µL, 4.77 mmol) in dichloromethane (15 mL)
3
distillation. All air- or moisture-sensitive reactions were con-
ducted in flame-dried glassware under an atmosphere of dry
argon. Chromatographic purifications were performed on silica
gel columns according to the flash chromatography technique.
3
1
J
J
J
2
C-P ) 9.9 Hz); IR (CHCl
3
Eth yl (E)-3-[13C]Hex-2-en oa te (4a ). To a solution of Na13
-
CN (328 mg, 6.43 mmol) in water (1 mL) were added tributy-
lamine (23 mg) and 1-bromopropane (807 mg, 6.43 mmol). The
reaction mixture was stirred and heated under reflux for 12 h,
and then extracted with dichloromethane (2 × 20 mL). The
1
3
was added 2-[ C](ethoxycarbonylmethylene)triphenylphos-
phorane 8 (1.38 g, 3.96 mmol) in dichloromethane (15 mL) and
the reaction mixture stirred for 1.5 h. The solvent was evapo-
rated under reduced pressure and the crude product purified
4
combined organic layers were dried over MgSO and filtered
under an atmosphere of argon, and then a solution of DIBA-H
in dichloromethane (7.69 mL, 7.69 mmol, 1.0 M) was added at
by column chromatography over silica (pentane, 6% Et
give 465 mg (3.25 mmol, 82% yield) of 4b: 1H NMR (200 MHz,
CDCl ) δ 0.92 [t, 3H, J ) 7.4 Hz, CH (CH ], 1.27 (t, 3H, J )
7.1 Hz, CH CH O), 1.47 (tq, 2H, J ) 7.3 Hz, CH CH CH ), 2.09-
2.23 (m, 2H, CH CH CH ), 4.17 (q, 2H, J ) 7.1 Hz, O-CH ),
5.80 (ddt, 1H, J H-C ) 161.7 Hz, J ) 15.7 Hz, J ) 1.5 Hz,
2
O) to
-78 °C. After 1 h, the reaction mixture was hydrolyzed at 0 °C
3
3
2 2
)
and for 1.5 h with a tartaric buffer [26 mL, prepared from
tartaric acid (54 g), sodium hydroxide (4.5 g), and water (360
mL)] in the presence of dichloromethane (12 mL). The aqueous
layer was again extracted with dichloromethane (2 × 15 mL),
and the combined organic layers were washed successively with
3
2
3
2
2
3
2
2
2
1
3
CHd CH), 6.94 (ddt, 1H, J ) 15.7 Hz, J ) 6.9 Hz, J H-C ) 1.7
1
3
13
Hz, CHd CH); C NMR (50 MHz, CDCl
3
) δ 13.6, 14.3, 21.3 (d,
saturated solutions of NaHCO
over MgSO , and filtered in a reaction flask. A solution of
ethoxycarbonylmethylene)triphenylphosphorane (2.35 g, 6.4
3
(15 mL) and NaCl (15 mL), dried
J C-C ) 3.3 Hz), 34.2, 60.1, 121.4, 149.1 (d, J C-C ) 70.9 Hz), 166.8
(d, J C-C ) 74.2 Hz).
4
(
(E)-3-[13C]Hex-2-en -1-ol (9a ). A solution of DIBA-H in
mmol) in dichloromethane (10 mL) was added, and the reaction
mixture was stirred at room temperature for 2 h. Solvents were
removed under vacuum, and the crude product was purified by
dichloromethane (6.60 mL, 6.60 mmol, 1.0 M) was added at -78
°C to a solution of ethyl 3-[13C]-2-bromoacetate (433 mg, 3.0
mmol) 4a in dichloromethane (8 mL). After 1 h at 0 °C, the
reaction mixture was hydrolyzed, at 0 °C for 1.5 h, with vigorous
stirring with a tartaric buffer [13 mL, made from tartaric acid
(54 g), sodium hydroxide (4.5 g), and water (360 mL)] and
dichloromethane (6.5 mL). The aqueous phase was again
extracted with ether (3 × 30 mL), and the combined organic
chromatography over silica (pentane, 6% Et
2
O) to give 433 mg
3.02 mmol, 47% yield) of 4a : 1H NMR (200 MHz, CDCl
) δ 0.91
t, 3H, J ) 7.3 Hz, CH (CH ], 1.26 (t, 3H, J ) 7.1 Hz, CH
O), 1.36-1.57 (m, 2H, CH CH CH ), 2.08-2.22 (m, 2H, CH
CH ), 4.16 (q, 2H, J ) 7.1 Hz, O-CH
(
[
3
3
2
)
2
3
3
-
-
CH
CH
2
2
3
2
2
2
2
), 5.78 (dt, 1H, J )
1
3
1
5.7 Hz, J ) 1.5 Hz, CHdCH), 6.93 (ddt, 1H, J H-C ) 153.9
layers were washed with saturated solutions of NaHCO (10
3
1
3
13
Hz, J ) 15.7 Hz, J ) 6.9 Hz, CHdCH); C NMR (50 MHz,
CDCl ) δ 13.6 (d, J C-C ) 3.3 Hz), 14.3, 21.3, 34.2 (d, J C-C
1.2 Hz), 60.1, 121.4 (d, J C-C ) 69.3 Hz), 149.1, 166.8.
Eth yl 2-[13C]-2-Br om oa ceta te (6). Bromine (0.82 mL, 15.9
mL) and NaCl (15 mL), dried over MgSO , and concentrated
4
3
)
under reduced pressure. The crude product was purified by
4
column chromatography over silica (pentane, 30% Et O) to give
2
1
242 mg (2.39 mmol, 79% yield) of 9a : H NMR (200 MHz,
1
3
mmol) was slowly added to CH
3
COOH (431 mg, 6.92 mmol)
CDCl
CH CH
4.07 (m, 2H, CH
J ) 1.5 Hz, J H-C ) 1.5 Hz, 13CHdCH), 5.67 (ddtt, 1H, J H-C
3
) δ 0.89 (t, 3H, J ) 7.4 Hz, CH
), 1.56 (s, 1H, OH), 1.94-2.08 (m, 2H, CH
OH), 5.62 (dttd, 1H, J ) 15.3 Hz, J ) 6.0 Hz,
3
), 1.29-1.49 (m, 2H,
and PBr (1.93 g, 6.92 mmol) and the reaction mixture stirred
3
3
2
3
CH CH ),
2
2
at room temperature for 15 min and then heated under reflux
for 3 h. Ethanol (0.8 mL) was slowly added at room temperature
and the mixture stirred for 12 h, and then more ethanol (2 mL)
was added before extraction with water (10 mL) and ether (20
mL). The combined organic layers were successively washed
2
)
150.9 Hz, J ) 15.3 Hz, J ) 6.7 Hz, J ) 1.4 Hz, CHdCH); 13
13
C
NMR (50 MHz, CDCl
3
) δ 13.6 (d, J C-C ) 3.3 Hz), 22.3, 34.3 (d,
C-C ) 41.2 Hz), 63.8, 128.9 (d, J C-C ) 72.6 Hz), 133.2; IR
J
with saturated solutions of NaHCO
3
(2 × 10 mL) and Na
2
S
2
O
3
3
(CHCl ) ν 1671 (CdC), 3608 (OH).

1
12 Chem. Res. Toxicol., Vol. 14, No. 1, 2001
E)-2-[13C]Hex-2-en -1-ol (9b). The same procedure that was
Meschkat et al.
), 3.83-3.97 (m, 1H, CH S),
(
13.5 Hz, J AX ) 9.8 Hz, 1H, SCH
2
2
1
3
used for 9a was used for 9b, starting from ethyl 2-[ C]-2-
bromoacetate (465 mg, 3.25 mmol) 4b, to give 258 mg (2.55
mmol, 78% yield) of 9b: H NMR (200 MHz, CDCl
4.20-4.38 (m, 1H, CHBr), 4.65 (dedoubled part A of an ABX
system, 1H, J H-C ) 157.9 Hz, J ) 8.9 Hz, J AX ) 8.8 Hz, J BX
)
)
1
3.1 Hz, CHO); 13C NMR (50 MHz, CDCl
13
3
) δ 0.89 (t,
CH ), 1.59
), 4.07 (m, 2H,
3
) δ 13.5 (d, J C-C
3
(
H, J ) 7.2 Hz, CH
s, 1H, OH), 1.94-2.08 (m, 2H, CH
CH OH), 5.62 (ddtt, 1H, J H-C ) 153.8 Hz, J ) 15.3 Hz, J ) 6.0
Hz, J ) 1.5 Hz, CHd CH), 5.67 (dttd, J ) 15.3 Hz, J ) 6.8 Hz,
3
), 1.39 (tq, 2H, J ) 7.3 Hz, CH
3
2
4.9 Hz), 18.7, 33.8 (d, J C-C ) 39.6 Hz), 40.3 (d, J C-C ) 36.3 Hz),
3
CH CH
2
2
54.4, 88.0; IR (CHCl
symmetric).
3 2 2
) ν 1170 (SO asymmetric), 1371 (SO
2
1
3
2-[13C]-2-Br om oh exa n e-1,3-su lton e (11b). The same pro-
1
3
13
J ) 1.5 Hz, J H-C ) 1.5 Hz, 1H, CHd CH); C NMR (50 MHz,
CDCl ) δ 13.6, 22.2 (d, J C-C ) 3.3 Hz), 34.3, 63.7 (d, J C-C
6.2 Hz), 129.0, 133.3 (d, J C-C ) 72.6 Hz); IR (CHCl ) ν 1671
CdC), 3608 (OH).
E)-3-[13C]-1-Br om oh ex-2-en e (10a ). PBr
cedure that was used for 11 was used for 11b, starting from
)
(E)-2-[13C]-1-bromohex-2-ene (313 mg, 1.91 mmol), to give 234
3
4
(
3
mg (0.96 mmol, 50% yield) of 11b: H NMR (200 MHz, CDCl3)
1
δ 0.99 (t, 3H, J ) 7.3 Hz, CH ), 1.35-2.08 (m, 4H, CH CH CH
3
3
2
2
(
3
(117 µL, 1.19
and CH
CH
CH-O); 13C NMR (50 MHz, CDCl
Hz), 33.8, 40.3, 54.4 (d, J C-C ) 36.3 Hz), 88.0 (d, J C-C ) 34.6
Hz); IR (CHCl ) ν 1170 (SO asymmetric), 1371 (SO symmetric).
3
CH
2
CH
2
), 3.46-3.63 (m, 1H, CH
2
S), 3.83-3.97 (m, 1H,
1
3
13
mmol) was added at -10 °C to (E)-3-[ C]hex-2-en-1-ol 9a (242
mg, 2.39 mmol) in diethyl ether (1.5 mL). The reaction mixture
was stirred for 20 min at -10 °C and for 14 h at room
temperature, and then hydrolyzed slowly, at 0 °C, with water
2
S), 4.30 (dm, J H-C ) 159.4 Hz, 1H, CH), 4.65 (m, 1H,
3
) δ 13.5, 18.7 (d, J C-C ) 3.3
3
2
2
(
1.5 mL); the aqueous phase was then extracted with pentane
Hex-1-en e-1,3-su lton e (1). To a solution of triethylamine
(3.2 mL) was added at 0 °C a solution of 2-bromohexane-1,3-
sultone 11 (316 mg, 1.30 mmol) in ether (8 mL). The reaction
mixture was stirred at room temperature for 2 h, and the white
precipitate that formed was filtered and washed with ethyl
acetate. The organic solvents were concentrated under reduced
pressure, and the residue was taken up in ethyl acetate (30 mL)
and washed with water (7 mL). The organic layer was dried
(
3 × 5 mL). The combined organic layers were washed with a
saturated solution of NaCl (2 × 5 mL), dried over MgSO
4
,
filtered, and concentrated under vacuum. The crude product was
purified by silica gel column chromatography (100% pentane)
1
to give 298 mg (1.82 mmol, 76% yield) of 10a : H NMR (200
MHz, CDCl
m, 2H, CH
CH Br), 5.69 (dttd, 1H, J ) 15.0 Hz, J ) 7.6 Hz, J ) 1.4 Hz,
H-C ) 1.4 Hz, CHdCH), 5.77 (ddtt, 1H, J H-C ) 151.9 Hz, J
15.0 Hz, J ) 6.9 Hz, J ) 1.0 Hz, 13CHdCH); 13C NMR (50
MHz, CDCl ) δ 13.6 (d, J C-C ) 3.3 Hz), 22.0, 33.6, 34.1 (d, J C-C
46.2 Hz), 126.4 (d, J C-C ) 70.9 Hz), 136.5; IR (CHCl ) ν 1656
CdC).
E)-2-[13C]-1-Br om oh ex-2-en e (10b). The same procedure
that was used for 10a was used for 10b, starting from (E)-2-
3
) δ 0.90 (t, 3H, J ) 7.2 Hz, CH
3
CH
2
), 1.32-1.50
(
3
CH ), 1.97-2.11 (m, 2H, CH CH CH
2
3
2
2
), 3.95 (m, 2H,
2
over MgSO , filtered, and evaporated under vacuum to give a
4
1
3
J
)
crude product which was purified by column chromatography
over silica (hexane, 40% AcOEt) to give 197 mg (1.21 mmol, 93%
1
3
yield) of hex-1-ene-1,3-sultone as a pale yellow liquid:
H NMR
)
(
3
(200 MHz, CDCl ) δ 0.97 (t, 3H, J ) 7.1 Hz, CH ), 1.50 (tq, 2H,
3
3
J ) 7.1 Hz, CH CH ), 1.75-1.87 (m, 2H, CH CHO), 5.28 (part
3
2
2
(
X of an ABX system, 1H, CH-O), 6.73 (part A of an ABX system,
1H, J AB ) 6.4 Hz, J AX ) 2.2 Hz, CHdCH-S), 6.87 (part B of an
1
3
13
[
C]hex-2-en-1-ol 9b (258 mg, 2.55 mmol), to give 313 mg (1.91
ABX system, 1H, J AB ) 6.4 Hz, J BX ) 1.6 Hz, CHdCH-S);
C
1
mmol, 75% yield) of 10b: H NMR (200 MHz, CDCl
3
) δ 0.90 (t,
), 1.41 (tq, 2H, J ) 7.3 Hz, CH CH ),
CH CH ), 3.95 (dd, 2H, J ) 7.6 Hz, J H-C
Br), 5.69 (ddtt, 1H, J H-C ) 152.1 Hz, J ) 15.1
NMR (50 MHz, CDCl
3
) δ 13.5, 17.9, 35.8, 85.2, 124.6, 140.4; IR
3
1
)
H, J ) 7.3 Hz, CH
.97-2.11 (m, 2H, CH
4.2 Hz, CH
Hz, J ) 7.6 Hz, J ) 1.5 Hz, CHd CH), 5.77 (dt, 1H, J ) 15.3,
3
CH
2
3
2
(CHCl ) ν 1183 (SO
3
2
2
asymmetric), 1343 (SO symmetric); EIMS
163 (M + 1), 145, 134, 120, 102, 81, 71, 56. Anal. Calcd for
6 10 3
C H O S: C, 44.43; H, 6.22. Found: C, 44.54; H, 6.30.
3
2
2
2
1
3
3-[13C]Hex-1-en e-1,3-su lton e (1a ). The same procedure that
1
3
13
13
J ) 6.7 Hz, CHd CH); C NMR (50 MHz, CDCl
3
) δ 13.6, 22.0
d, J C-C ) 4.9 Hz), 33.6 (d, J C-C ) 49.5 Hz), 34.1, 126.5, 136.5
d, J C-C ) 70.9 Hz); IR (CHCl ) ν 1656 (CdC).
-Br om oh exa n e-1,3-su lton e (11). (E)-1-Bromohex-2-ene
400 mg, 2.45 mmol) was added to a solution of Na SO (620
PBr (3.7 mg) in water (1
was used for 1 was used for 1a , starting from [3- C]-2-
(
(
bromohexane-1,3-sultone (227 mg, 0.93 mmol), to give 142 mg
(0.87 mmol, 94% yield) of 1a : 1H NMR (200 MHz, CDCl ) δ 0.98
3
3
2
(t, 3H, J ) 7.3 Hz, CH
3
), 1.42-1.62 (m, 2H, CH
3 2
CH ), 1.75-
(
2
3
1.88 (m, 2H, CH CHO), 5.27 (dedoubled part X of an ABX
2
system, J H-C ) 155.9 Hz, 1H, 13CH-O), 6.73 (part A of an ABX
system, 1H, J H-C ) 9.6 Hz, J AB ) 6.6 Hz, J AX ) 2.2 Hz,
CHdCH-S), 6.86 (part B of an ABX system, 1H, J H-C ) 9.3
Hz, J AB ) 6.6 Hz, J BX ) 1.7 Hz, CHdCH-S); 13C NMR (50 MHz,
mg, 4.9 mmol), NaI (1.6 mg), and Bu
4
mL). The reaction mixture was stirred at 40 °C for 16 h, then
washed with ether (3 × 5 mL), and hydrolyzed with a solution
of HCl (2 mL, 6 M) to give (E)-hex-2-ene sulfonic acid, and then
bromine (200 mL, 3.92 mmol) was added at 0 °C. The reaction
mixture was stirred at room temperature for 1 h and then
extracted with ether (3 × 25 mL). The combined organic layers
CDCl ) δ 13.5 (d, J C-C ) 4.9 Hz), 18.0, 35.8 (d, J C-C ) 37.9 Hz),
3
85.1, 124.9, 140.1 (d, J C-C ) 37.9 Hz); EIMS 164 (M + 1), 146,
135, 121, 103, 82, 72, 57.
2-[13C]Hex-1-en e-1,3-su lton e (1b). The same procedure that
were washed successively with saturated solutions of NaHCO
3
1
3
(
2 × 10 mL), Na
2
S
2
O
3
(10 mL), and NaCl (2 × 10 mL), dried
was used for 1 was used for 1b, starting from 2-[ C]-2-
over MgSO
(
4
, and concentrated under vacuum to give 316 mg
bromohexane-1,3-sultone (234 mg, 0.96 mmol), to give 146 mg
(0.90 mmol, 94% yield) of 1b: 1H NMR (200 MHz, CDCl
) δ 0.99
), 1.50 (tq, 2H, J ) 7.4 Hz, CH CH ),
CHO), 5.28 (part X of an ABX system,
1H, CH-O), 6.74 (part A of an ABX system, 1H, J AB ) 6.6 Hz,
H-C ) 2.5 Hz, J AX ) 2.5 Hz, 13CHdCH-S), 6.87 (part B of an
ABX system, 1H, J H-C ) 176.0 Hz, J AB ) 6.6 Hz, J BX ) 1.7 Hz,
1.30 mmol, 53% yield) of 2-bromohexane-1,3-sultone 11 as a
3
1
pale yellow liquid: H NMR (200 MHz, CDCl
7.2 Hz, CH ), 1.35-2.08 (m, 4H, CH CH CH
an ABX system, CH CH CH ), 3.54 (part A of an ABX system,
H, J AB ) 13.5 Hz, J AX ) 9.9 Hz, SCH ), 3.90 (part B of an ABX
system, 1H, J AB ) 13.5 Hz, J BX ) 8.1 Hz, SCH ), 4.30 (dedoubled
3
) δ 0.99 (t, 3H, J
(t, 3H, J ) 7.3 Hz, CH
1.76-1.89 (m, 2H, CH
3
3
2
)
3
3
2
2
and part AB of
2
3
2
2
1
2
J
2
1
3
13
part X of an ABX system, 1H, J AX ) 9.9 Hz, J BX ) 8.1 Hz, J )
8
3
CHdCH-S); C NMR (50 MHz, CDCl ) δ 13.5, 18.0, 35.9, 85.0
.9 Hz, CHBr), 4.65 (dedoubled part X of an ABX system, 1H,
(d, J C-C ) 37.9 Hz), 124.9 (d, J C-C ) 72.6 Hz), 140.1; EIMS 164
(M + 1), 146, 135, 121, 103, 82, 71, 57.
Hexa n e-1,3-su lton e (2). To a suspension of Pd/C (5%, 15
mg) in ethyl ether (10 mL) under hydrogen was added the
sultone 1 (60 mg, 0.37 mmol) in ethyl ether (5 mL). The reaction
mixture was stirred at room temperature for 30 min, degassed
under vacuum, and filtered on Celite. The organic layer was
1
3
J
AX ) 8.9 Hz, J BX ) 3.2 Hz, J ) 8.9 Hz, CH-O); C NMR (50
) δ 13.5, 18.7, 33.7, 40.3, 54.4, 88.0; IR (CHCl ) ν
asymmetric), 1371 (SO symmetric). Anal. Calcd for
S: C, 29.64; H, 4.56. Found: C, 29.70; H, 4.60.
-[13C]-2-Br om oh exa n e-1,3-su lton e (11a ). The same pro-
cedure that was used for 11 was used for 11a , starting from
MHz, CDCl
170 (SO
3
3
1
2
2
6 3
C H11BrO
3
1
3
(
E)-3-[ C]-1-bromohex-2-ene (298 mg, 1.82 mmol), to give 227
dried over MgSO
give 60.9 mg (0.37 mmol, 100% yield) of 2 as a colorless oil:
NMR (200 MHz, CDCl ) δ 0.95 (t, J ) 7.3 Hz, 3H, CH ), 1.36-
1.94 (m, 4H, CH CH CH ), 2.17-2.38 (m, 1H, CH CH S), 2.51-
4
, filtered, and evaporated under vacuum to
1
1
mg (0.93 mmol, 51% yield) of 11a : H NMR (200 MHz, CDCl
δ 0.99 (t, 3H, J ) 7.3 Hz, CH ), 1.38-2.10 (m, 4H, CH CH CH
and CH CH CH ), 3.54 (part A of an ABX system, 1H, J AB
3
)
H
3
3
2
2
3
3
3
2
2
)
3
2
2
2
2

Labeled Sultones
Chem. Res. Toxicol., Vol. 14, No. 1, 2001 113
signal-to-noise ratio. The measured 13C chemical shifts of the
different adducts were compared with those calculated using
the additivity principle and to NMR data of analogous com-
pounds reported in the literature.
Sch em e 1. Syn th etic P a th w a y to Syn th on 4a
These assignments were further confirmed by 1H chemical
shifts obtained by heteronuclear correlations (11) and are
in accordance with the sequence of adduct formation and
hydrolysis.
2
.67 (m, 1H, CH
2
CH
CHO); C NMR (50 MHz, CDCl
2.6; IR (CHCl ) ν 1163 (SO
metric); EIMS 165 (M + 1), 121, 82, 71, 65, 55. Anal. Calcd for
S: C, 43.88; H, 7.37. Found: C, 43.96; H, 7.48.
-[13C]Hexa n e-1,3-su lton e (2a ). The same procedure that
2
S), 3.16-3.39 (m, 2H, CH
) δ 13.6, 18.5, 29.5, 37.1, 45.7,
asymmetric), 1346 (SO sym-
2
S), 4.63 (m, 1H,
1
3
3
8
3
2
2
Resu lts a n d Discu ssion
C
6
H
12
O
3
13
13
Syn th esis. 3- C- and 2- C-labeled sultones (1a and
3
13
1
b, respectively) were synthesized from 3-[ C]-(E)-ethyl
was used for 2 was used for 2a , starting from 1a (59.9 mg, 0.37
mmol), to give 60.3 mg (0.37 mmol, 100% yield) of 2a as a
1
3
hex-2-enoate 4a and 2-[ C]-(E)-ethyl hex-2-enoate 4b,
respectively, according to Scheme 3. Intermediate 4a was
directly prepared (Scheme 1) from propyl bromide 3 via
a substitution reaction with Na CN (12), followed by
reduction of the intermediate cyanate to an aldehyde
function with DIBAH (13) and its subsequent reaction
with (ethoxycarbonylmethylene)triphenylphosphorane.
These steps were carried out without purification due to
the very low boiling point of intermediate compounds,
1
colorless oil: H NMR (200 MHz, CDCl
3
) δ 0.96 (t, J ) 7.3 Hz,
CH ), 2.17-2.00 (m, 1H,
CH S), 3.16-3.41 (m, 2H,
S), 4.63 (dm, J H-C ) 153.5 Hz, 1H, CHO); C NMR (50
) δ 13.6 (d, J C-C ) 4.9 Hz), 18.5, 29.5 (d, J C-C
1.3 Hz), 37.2 (d, J C-C ) 39.6 Hz), 45.6, 82.5; EIMS 166 (M +
), 122, 83, 72, 65, 56.
Rea ction s of 1a , 1b, a n d 2a w ith n -Bu tyla m in e a n d
Dieth yla m in e in Ch lor ofor m . n-Butylamine or diethylamine
13.5 mg, 0.18 mmol, 30 equiv) in CDCl (0.4 mL) was added to
3
CH
CH
H, CH
3
), 1.36-1.97 (m, 4H, CH
3
CH
2
2
1
3
2
CH
2
S), 2.51-2.68 (m, 1H, CH
2
2
1
3
2
MHz, CDCl
3
)
3
1
13
and 4a was obtained in an overall yield of 47%. 2-[ C]-
(
3
Acetic acid 5, after bromination (PBr
was transformed into its phosphonium salt 7 by reaction
with PPh (14) in quite good yield. The phosphonium salt
3
) and esterification,
compound 1a , 1b, or 2a (1 mg, 6 µmol), and the solution was
filtered into an NMR tube and the reaction followed by 13C NMR.
Rea ction s of 1a , 1b, a n d 2a w ith n -Bu tyla m in e a n d
Dieth yla m in e in Wa ter . n-Butylamine or diethylamine (13.5
3
was then treated with NaOH to give, in 98% yield,
phosphorane 8, which was condensed with butyralde-
hyde, giving the 13C-labeled intermediate 4b in 82% yield
(Scheme 2).
Intermediates 4a and 4b were reduced with an excess
of DIBAH to give alcohols 9a and 9b, respectively, which
mg, 0.18 mmol, 30 equiv) in a mixture of H
and 0.05 mL, respectively) was added to compound 1a , 1b, or
a (1 mg, 6 µmol), and then the solution was filtered into an
2 2
O and D O (0.35
2
NMR tube, a trace of acetonitrile added as an internal reference,
and the reaction followed by 13C NMR.
Rea ction s of 1a , 1b, a n d 2a w ith Im id a zole. Imidazole
were brominated with PBr
3
(15). Compounds 10a and
SO (16) in water under
(
(
1
12.6 mg, 0.18 mmol, 30 equiv) in a mixture of H
0.35 and 0.05 mL, respectively) was added to compound 1a ,
b, or 2a (1 mg, 6 µmol) in 1 drop of acetone, and then the
2 2
O and D O
1
0b were sulfonated with Na
2
3
phase transfer conditions and in the presence of a
catalytic amount of NaI. Cyclization of the crude sul-
fonates was achieved via a bromation reaction (Br in
2
solution was filtered into an NMR tube, a trace of acetonitrile
added as an internal reference, and the reaction followed by 13
NMR.
C
water) to give the 2-bromosultones, 11a and 11b, in an
overall yield of approximately 50% (17); this rather poor
yield is due to the formation, in 30% yield, of a byproduct
resulting from the hydrolysis of the intermediate bromo-
nium which competes with the cyclization reaction. The
stereochemistry of compounds 11a and 11b was found
to be trans as shown by NOE interactions observed
between the H-2 (4.3 ppm) and both H-4 (2.0 ppm) and
H-4′ (1.8 ppm) protons. The 2-bromosultones were finally
R ea ct ion s of 1a , 1b, a n d 2a w it h Sod iu m P h en a t e.
PhONa‚3H O (10.5 mg, 0.06 mmol, 10 equiv) in a mixture of
O and D O (0.35 and 0.05 mL, respectively) was added to
2
H
2
2
compound 1a , 1b, or 2a (1 mg, 6 µmol), and then the solution
was filtered into an NMR tube, a trace of acetonitrile added as
an internal reference, and the reaction followed by 13C NMR.
Rea ction s of 1a , 1b, a n d 2a w ith Sod iu m P r op a n eth i-
ola te. A solution of propanethiolate (0.35 mL, 10 equiv)
[
prepared from sodium hydroxide (70 mg, 1.75 mmol), pro-
panethiol (138 mg, 164 mL, 1.76 mmol), and water (10 mL)]
and D O (0.05 mL) were added to compound 1a , 1b, or 2a (1
1
3
13
transformed, in 94% yield, into labeled 3-[ C]- and 2-[ C]-
2
sultones (1a and 1b, respectively) by simple treatment
mg, 6 µmol). The solution was filtered into an NMR tube, a trace
of acetonitrile added as an internal reference, and the reaction
followed by C NMR.
13
3
with Et N in ethyl ether (Scheme 3). 3-[ C]Hexane-1,3-
sultone 2a was quantitatively prepared by catalytic
1
3
13
hydrogenation of 3-[ C]sultone 1a . The NMR data of the
Str u ctu r e Assign m en t. Structures of the different adducts
sultones were in accordance with those of previously
reported unlabeled sultones (17).
Rea ction of 1a a n d 1b w ith Bu tyla m in e (Sch em e
4). Both labeled unsaturated sultones 1a and 1b were
reacted with butylamine, often considered a model for
1
13
were assigned using a combination of { H}-decoupled C NMR
and C DEPT 135 sequences. In DEPT 13C{ H} sequences with
a Θ angle of 135°, up peaks correspond to methyl (CH ) or
methine (CH) signals while down peaks correspond to methylene
CH ) signals. Moreover, this sequence allows us to increase the
1
3
1
3
(
2
Sch em e 2. Syn th etic P a th w a y to Syn th on 4b

1
14 Chem. Res. Toxicol., Vol. 14, No. 1, 2001
Meschkat et al.
Sch em e 3. Syn th etic P a th w a y to Un sa tu r a ted
Su lton es 1, 1a , a n d 1b a n d Sa tu r a ted Su lton es 2
a n d 2a
Sch em e 4. Rea ction of 1a a n d 1b w ith Bu tyla m in e
F igu r e 1. (A) DEPT 135 NMR spectrum of 1a incubated with
n-butylamine (30 equiv) in CDCl after 4 days. (B) DEPT 135
3
NMR spectrum of 1a incubated with n-butylamine (30 equiv)
in CDCl after 30 days.
3
the reactivity of lysine. This amine has, for example, been
successfully used during the development of the relative
alkylation index (RAI) to determine the relative reaction
rate of different haptens (18, 19). Reactions with 30 equiv
of butylamine, to work under quasi-first-order conditions
supposed to reflect an excess of protein over hapten, were
followed by 13C NMR in either CDCl
or water. The
3
structures of the adducts that formed were assigned by
comparison of the measured 13C chemical shifts with
those calculated using the additivity principle. In CDCl ,
3
the reaction was found to be rather slow, with most of
the starting material remaining after 30 days, allowing
the formation and/or disappearance of intermediates and/
or products to be followed. Thus, after 5 h, aziridines 12a
and 12b were already present, together with the trans
“
Michael” adduct 12c. After 4 days (Figures 1A and 2A),
the amount of 12a (42.4 and 38.3 ppm), 12b (45.7 and
1.1 ppm), and 12c (78.2 and 57.2 ppm) increased, with
the appearance of a tiny trace of cis Michael adduct 12d
77.3 and 55.2 ppm) and of the diadduct, 12e (57.8 and
6.5 ppm). After 30 days (Figures 1B and 2B), the main
change was an increase in the content of the diadduct,
2e, and aziridines 12a and 12b were present as a 1/1
4
(
5
F igu r e 2. (A) DEPT 135 NMR spectrum of 1b incubated with
1
n-butylamine (30 equiv) in CDCl after 4 days. (B) DEPT 135
3
mixture of cis and trans isomers.
The formation of the two minor Michael type adducts,
NMR spectrum of 1b incubated with n-butylamine (30 equiv)
in CDCl after 30 days.
3
1
2b and 12d , was confirmed by reaction of 1a and 1b
with pure butylamine for 40 min, evaporation of the
amine under vacuum, and analysis of the products by
C NMR in water (Figure 3). Under these reaction
conditions, formation of these Michael adducts seemed
to be favored, allowing us to obtain unambiguous chemi-
cal shifts. This experiment also confirmed that the anti
addition, leading to the formation of the trans adduct 12c,
was highly favored for steric hindrance reasons (20).
1
3

Labeled Sultones
Chem. Res. Toxicol., Vol. 14, No. 1, 2001 115
Sch em e 5. Rea ction of 1a a n d 1b w ith
Dieth yla m in e
3
the Michael monoadducts observed in CDCl , or formed
in pure butylamine and then observed in water, seemed
to be rather stable for several days.
Reaction of 1a an d 1b with Dieth ylam in e (Sch em e
5
). The same kind of experiment was carried out with
3
0 equiv of diethylamine as a model for secondary
amines. As for n-butylamine, the reaction with 1a and
b was found to be very slow in CDCl , most of the
1
3
starting material still being present after 30 days, while
that in water was rapid with no starting material left
after 1 h. In CDCl
3
, only one monoadduct (14a ), resulting
from an S reaction at position 3, was formed (the
N
intermediate monoadduct is not able to react intramo-
lecularly), but a second Michael type addition can occur
on the intermediate sulfonate leading to the diadduct
F igu r e 3. (A) 13C NMR spectrum in water of n-butylamine
adducts on 1a . (B) C NMR spectrum in water of n-butylamine
adducts on 1b.
1
4b. A rearrangement product 15, resulting from the
1
3
abstraction of proton H-3 by diethylamine, was also seen.
In water, only monoadduct 14a was detected together
with the hydrolysis compound 13. Reaction with diethy-
lamine confirmed our findings for butylamine with an
Aziridines 12a and 12b were formed in a 1/1 ratio, and
their cis and trans structure was assigned by comparison
with other aziridine derivatives described in the litera-
ture (21).
S
N
reaction being favored.
Rea ction of 1a a n d 1b w ith Im id a zole (Sch em e
In water, the reaction was much faster and found to
be complete after 1 h. Only the two aziridines, 12a and
6). Imidazole was used as a simple model for histidine,
which has been shown to be important in the induction
of allergic contact dermatitis to certain haptens (2, 3).
As imidazole is much less reactive than n-butylamine or
diethylamine, we decided to study its reactivity toward
sultones in water. Even under these conditions, the
reaction of labeled sultones 1a and 1b was much slower
than with n-butylamine or diethylamine and some start-
ing material was still present after 40 days. With
imidazole, we observed the formation of monoadducts
resulting both from Michael addition (16a and 16b), the
1
2b, were formed in a 1/1 mixture of cis and trans
isomers, together with a new compound 13 resulting from
hydrolysis of the starting sultone.
Mech a n istic In ter p r eta tion of Azir id in e F or m a -
tion w ith Bu tyla m in e. In water, the reaction of 1a and
1
1
b with butylamine was found to be rapid, and aziridines,
2a and 12b , were the only detected compounds. The
problem of which mechanism is involved in the formation
of these intermediates remains. Compounds 12a and 12b
could conceivably arise either from a first Michael type
anti addition being favored, and from an S
N
reaction
addition followed by an intramolecular S
N
reaction or
(16e). The slow reaction also allowed the formation of
several hydrolysis products: 13 resulting from the hy-
drolysis of the original sultone and a mixture of products
16c and 16d resulting from the hydrolysis of compounds
16a and 16b. The formation of a diadduct 16f was also
detected, although it is not known if it results from a
second addition on intermediate 16a , 16b, or 16e.
Thus, in contrast to the other two amines, with
imidazole, Michael addition at position 2 predominated
from S reaction followed by an intramolecular Michael
N
type addition on the intermediate R,â-unsaturated sul-
fonate. Instinctively, the first hypothesis would tend to
be favored, but our data support the second. As seen
3
using butylamine in CDCl , pure butylamine, or imida-
zole in water, Michael addition at position 2 of the
sultones is very sensitive to steric hindrance, and anti
addition, leading to the trans adduct, is highly favored.
A subsequent intramolecular S
N
reaction at position 3
N
over S substitution at position 3.
would not change this ratio, and we should therefore
obtain the trans aziridine 12b as the major adduct. On
the other hand, an S reaction at position 3 would lead
N
to the formation of a racemic sulfonate intermediate with
a freely rotating C2-C3 bond, allowing this 1/1 ratio to
be maintained during the subsequent Michael cyclization.
Moreover, the intramolecular aziridine formation seems
to be very rapid, and a further argument in favor of an
R ea ct ion of 1a a n d 1b w it h P r op a n et h iol a n d
P h en ol (Sch em e 7). Propanethiol, a model for cysteine,
and phenol, a model for tyrosine, were found to be
nonreactive toward alkenesultones 1a and 1b in water.
Nevertheless, to obtain 13C NMR reference values for
further studies, we forced the reaction conditions using
sodium salts of the thiol and phenol. Thus, the reaction
of 1a and 1b with 10 equiv of sodium propanethiolate
was rapid and led to the formation of diadducts 17a and
17b, but the major peaks were due to the elimination
S
N
reaction as the initial step is that no intermediate
resulting from an S monoaddition was seen. In contrast,
N

1
16 Chem. Res. Toxicol., Vol. 14, No. 1, 2001
Sch em e 6. Rea ction of 1a a n d 1b w ith Im id a zole
Meschkat et al.
Sch em e 7. Rea ction of 1a a n d 1b w ith
P r op a n eth iol a n d P h en ol
from an S
product 21 was also detected in the reaction mixture. The
structure of 21 was confirmed by the hydrolysis (H O,
00 °C) of sultone 2 which led to a mixture of cis and
N
reaction at position 3. A minor elimination
2
1
trans alcene, the trans isomer (J ) 15.3 Hz) being the
major one.
The reaction of sultone 2a in water with ethylamine
confirmed the low reactivity of this molecule toward
amino groups with mainly the formation of the hydrolysis
product 20. The only adduct formed was 22, resulting of
an S
N
reaction at position 3. Traces of 21 were also
detected.
With imidazole, the low reactivity of sultone 2a was
confirmed. The reaction of 2a in water led mainly to the
formation of 20, the hydrolysis product, together with 23,
an imidazole adduct at position 3.
Interestingly, the reaction of 2a with propanethiolate
was found to be faster than the hydrolysis reaction with
the formation of a monoadduct 24 as the major reaction
product.
Sch em e 8. Rea ction of 2a w ith Mod el Nu cleop h iles
The reaction of 2a with sodium phenate was found to
be competitive with the hydrolysis reaction. Thus, an
almost equimolecular mixture of the monoadduct 25 and
of the hydrolysis product 20 was formed.
Rea ctivity of Su lton es. Electrophiles and nucleo-
philes can be regarded, respectively, as Lewis acids and
bases, and their classification as hard or soft acids and
bases can also be applied to their electrophilicity and
nucleophilicity. Following the HSAB theory, if an elec-
trophile is hard, its reactivity toward hard nucleophiles
will be increased and its reactivity toward soft nucleo-
philes decreased. Conversely, if the electrophile is soft,
its reactivity toward hard nucleophiles will be decreased
and its reactivity toward soft nucleophiles increased.
Hard electrophiles or nucleophiles react through low-
energy vacant or occupied orbitals, respectively, and are
less polarizable. Soft electrophiles and nucleophiles react
through higher-energy orbitals and are more polarizable.
Examples of hard nucleophiles are water, alkoxides, and
primary and secondary amines, while examples of soft
nucleophiles are thiol and thiolate anions, sulfides, or the
thiosulfate anion.
products 17c and 17d . The major product was the trans
derivative 17c, derived by cis dithio elimination of the
intermediate diadduct 17a . For mechanistic reasons, it
therefore seems that the initial step is anti addition of
N
propanethiolate at position 2, followed by an S substitu-
tion at position 3 which may possibly be assisted by the
thio atom through the formation of an intermediate cyclic
sulfonium.
The reaction of 1a and 1b with 10 equiv of sodium
phenate was much slower and resulted in the formation
N
of only one monoadduct (18) resulting from S substitu-
tion at position 3 and of the hydrolysis product 13.
This difference in reactivity between thio and oxo
nucleophiles is in agreement with the hard and soft acid
and base (HSAB) theory (22), the thiolate being consid-
ered a “soft” nucleophile compared to the phenate.
Rea ction of 2a w ith Mod el Nu cleop h iles (Sch em e
On the basis of the above description, it seems clear
that for sultone 1 the soft electrophilic center 2 (R,â-
-
unsaturated system) should be more reactive toward S
groups and the hard electrophilic center 3 (S
N
center)
-
8
). Reaction of the labeled sultone 2a with butylamine
more reactive toward RNH and PhO groups. Interest-
2
was followed using the previously described conditions.
As opposed to sultones 1a and 1b, sultone 2a was found
to be nonreactive toward butylamine in chloroform even
after 14 days. In water, the reaction was slow and the
major product that was observed was the hydrolysis
derivative 20 together with the monoadduct 19 resulting
ingly, imidazole is border-line with a marked reactivity
toward the soft electrophilic center 2, but still reacting
with the hard electrophilic center 3.
Reactions with the alkanesultone are much simpler
with only one reactive site, namely, position 3, which is
N
able to react with nucleophiles through an S reaction.

Labeled Sultones
Chem. Res. Toxicol., Vol. 14, No. 1, 2001 117
Sultone 2 was found to have a very low reactivity toward
amino groups even in water. In three cases (butylamine,
diethylamine, and imidazole), the major product that was
obtained was always the hydrolysis one resulting from a
nucleophilic attack of water at position 3. The only
significant addition reactions were observed with pro-
panethiolate and sodium phenate which can significantly
compete with the hydrolysis reaction.
The very potent skin sensitizing properties of alkyl-1-
ene-1,3-sultones have been attributed to the presence of
an electron-deficient double bond that allows the forma-
tion of protein adducts through Michael type nucleophilic
additions (8). This explanation was mainly supported by
the markedly lower sensitizing potential of saturated
analogues of sultones.
(8) Ritz, H. L., Connor, D. S., and Sauter, E. D. (1975) Contact
sensitization of guinea-pigs with unsaturated and halogenated
sultones. Contact Dermatitis 1, 349-358.
(
9) Goodwin, B. F. J ., Roberts, D. W., Williams, D. L., and J ohnson,
A. W. (1983) Relationships between skin sensitization potential
of saturated and unsaturated sultones. In Immunotoxicology
(
4
Gibson, G. G., Hubbard, R., and Parke, D. V., Eds.) pp 443-
48, Academic Press, London.
(
10) Magnusson, B., and Gilje, O. (1973) Allergic contact dermatitis
from dishwashing liquid containing lauryl ether sulfate. Acta
Derm.-Venereol. 53, 136-140.
(
11) Meschkat, E., Lepoittevin, J . P., and Barratt, M. D. (2001) Studies
of chemical selectivity of hapten, reactivity and skin sensitization
13
potency. 2. NMR studies of the covalent binding of C-labeled
skin sensitizers, 2-[13C]- and 3-[13C]hex-1-ene and 3-[13C]hexane-
1,3-sultones, to human serum albumin. Chem. Res. Toxicol. 14,
1
18-126.
(
12) Reeves, W. P., and White, M. R. (1976) Phase transfer catalysis:
preparation of alkylcyanides. Synth. Commun. 6, 193-197.
13) Adj e´ , N., Vogeleisen, F., and Uguen, D. (1996) Improved conditions
for the Kiliani-Fischer synthesis. Tetrahedron Lett. 37, 5893-
The reactivity of sultones toward model nucleophiles
does not support this hypothesis except in the case of
histidine residues. If it seems obvious that introduction
of a double bond increases the reactivity of sultone toward
amino groups, the major reactive site remains position
(
5
896.
(
14) J ansen, F. J ., Kwestro, M., Schmitt, D., and Lugtenburg, J . (1994)
1
3
Synthesis and characterization of all E (12, 12′-
C
2
)-, (13, 13′-
13
13
13
13
C
2
)-, (14, 14′-
2 2 2
C )-, (15, 15′- C )- and (20, 20′- C ) astaxanthin.
3
and the major reaction a nucleophilic substitution.
Rec. Trav. Chim. Pays-Bas 113, 552-562.
(
15) Villieras, J ., and Rambaud, M. (1982) Wittig-Horner reaction in
heterogeneous media: an easy synthesis of ethyl R-hydromethy-
lacrylate and ethyl R-halomethylacrylates using formaldehyde in
water. Synthesis 17, 924-926.
These results, obtained in water, but with model nucleo-
philes, need to be confirmed under more realistic condi-
tions, i.e., with a large protein, such as human serum
albumin.
(16) Palecek, J ., Svoboda, J ., Lutisanova, M., Mostecky, J ., Hampl,
F., Votava, V., Dlask, J ., Buskova, J ., Vesely, K., and Olysar, K.
(
1987) Chem. Abstr. 106, 198124s.
Ack n ow led gm en t. We thank the Centre National
de la Recherche Scientifique (CNRS-France) and Uni-
lever Research for a fellowship to E.M.
(
17) Roberts, D. W., Sztanko, S., and Williams, D. L. (1981) An
improved route to alk-1-ene 1,3-sultones, involving sulphonation
of R-olefins by means of a sulphur trioxide/dioxan complex.
Tenside Deterg. 18, 113-116.
(
18) Franot, C., Roberts, D. W., Smith, R. G., Basketter, D. A., Benezra,
C., and Lepoittevin, J . P. (1994) Structure-activity relationships
for contact allergenic potential of γ,γ-dimethyl-γ-butyrolactone
derivatives. 1. Synthesis and electrophilic reactivity studies of
R-(ω-substituted-alkyl)-γ,γ-dimethyl-γ-butyrolactones and cor-
relation of skin sensitization potential and cross-sensitization
patterns with structure. Chem. Res. Toxicol. 7, 297-306.
Refer en ces
(
1) Rycroft, R. J . G., Menn e´ , T., and Frosch, P. J ., Eds. (1995)
Textbook of contact dermatitis, Springer-Verlag, Berlin.
2) Lepoittevin, J . P., Basketter, D. A., Goossens, A., and Karlberg,
A. T., Eds. (1997) Allergic contact dermatitis: the molecular basis,
Springer, Berlin.
(
(
3) Lepoittevin, J . P., and Leblond, I. (1997) Hapten-peptide-T cell
receptor interactions: molecular basis for the recognition of
haptens by T lymphocytes. Eur. J . Dermatol. 7, 151-154.
4) Roberts, D. W., and Williams, D. L. (1982) The derivation of
quantitative correlations between skin sensitization and physi-
cochemical parameters for alkylating agents, and their application
to experimental data for sultones. J . Theor. Biol. 99, 807-825.
(19) Franot, C., Roberts, D. W., Basketter, D. A., Benezra, C., and
Lepoittevin, J . P. (1994) Structure-activity relationships for
contact allergenic potential of γ,γ-dimethyl-γ-butyrolactone de-
rivatives. 2. Quantitative structure-skin sensitization relation-
ships for R-substituted-R-methyl-γ,γ-dimethyl-γ-butyrolactones.
Chem. Res. Toxicol. 7, 307-312.
(20) Takahata, H., Uchida, Y., and Momose, T. (1995) Concise
syntheses of natural γ-butyrolactones (+)-trans-whisky lactone,
(+)-trans-cognac lactone, (-)-methylenolactocin, (+)-nephroster-
anic acid and (+)-roccellaric acid using novel chiral butenolide
synthons. J . Org. Chem. 60, 5628-5633.
(
(5) Barratt, M., Basketter, D. A., and Roberts, D. W. (1997) Structure-
activity relationships for contact hypersensitivity. In Allergic
contact dermatitis, the molecular basis (Lepoittevin, J . P., et al.,
Eds.) pp 129-154, Springer, Berlin.
(
6) Lepoittevin, J . P., and Benezra, C. (1992) 13C-enriched methyl
alkanesulfonates: new lipophilic methylating agents for the
identification of nucleophilic amino acids of proteins by NMR.
Tetrahedron Lett. 33, 3875-3878.
(21) M u¨ ller, P., Baud, C., and J acquier, Y. (1996) A method for
rhodium(II)-catalyzed aziridination of olefins. Tetrahedron 52,
1543-1548.
(22) Pearson, R. G. (1963) Hard and soft acids and bases. J . Am. Chem.
(
7) Franot, C., Benezra, C., and Lepoittevin, J . P. (1993) Synthesis
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1
3
and interaction studies of C labeled lactone derivatives with a
1
3
model protein using C NMR. Bioorg. Med. Chem. 1, 389-397.
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