Regioselective syntheses of [13C]4-labelled sodium 1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate and sodium 2-carboxy-1-(2-ethylhexyloxycarbonyl)ethanesulfonate from [13C] 4-maleic anhydride

Article abstract of DOI:10.1002/jlcr.3189

The entitled monohydrolysis products, also known as α-ethylhexyl and β-ethylhexyl sulfosuccinate (EHSS), of the surfactant diisooctyl sulfosuccinate (DOSS) were synthesized in stable isotope-labelled form from [¹³C]₄-maleic anhydride. Sodium [¹³C] ₄-1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate (α-EHSS) was prepared by the method of Larpent by reaction of 2-ethylhexan-1-ol with [¹³C]₄-maleic anhydride followed by regioselective conjugate addition of sodium bisulfite to the resulting monoester (38% overall yield). The regiochemical outcome of bisulfite addition was confirmed by a combination of ¹³C/¹³C (incredible natural abundance double quantum transfer) and ¹H/¹³C (heteronuclear multiple-bond correlation (HMBC)) NMR spectral correlation experiments. Sodium [¹³C]₄-2-carboxy-1-(2-ethylhexyloxycarbonyl) ethanesulfonate (β-EHSS) was prepared in four steps by reaction of 4-methoxybenzyl alcohol with [¹³C]₄-maleic anhydride, regioselective sodium bisulfite addition, N,N′-dicyclohexylcarbodiimide- mediated esterification with 2-ethylhexan-1-ol, and p-methoxybenzyl ester deprotection with trifluoroacetic acid (13% overall yield). The regiochemical outcome of the second synthesis was confirmed by a combination of ¹J_CC scalar coupling constant analysis and ¹H/¹³C (HMBC) NMR spectral correlation. The materials prepared are required as internal standards for the liquid chromatography-mass spectrometry (LC-MS)/MS trace analysis of the degradation products of DOSS, the anionic surfactant found in Corexit, the oil dispersant used during emergency response efforts connected to the Deepwater Horizon oil spill of April 2010. Copyright

Full text of DOI:10.1002/jlcr.3189

Note
Received 12 November 2013,
Revised 17 January 2014,
Accepted 21 January 2014
Published online 12 February 2014 in Wiley Online Library
(wileyonlinelibrary.com) DOI: 10.1002/jlcr.3189
13
Regioselective syntheses of [ C]4-labelled
sodium 1-carboxy-2-(2-ethylhexyloxycarbonyl)
ethanesulfonate and sodium 2-carboxy-1-(2-
ethylhexyloxycarbonyl)ethanesulfonate from
†
13
[ C]4-maleic anhydride
Adam L. Barsamian,a Matt J. Perkins,b Jennifer A. Field,b
a
*
and Paul R. Blakemore
The entitled monohydrolysis products, also known as α-ethylhexyl and β-ethylhexyl sulfosuccinate (EHSS), of the
surfactant diisooctyl sulfosuccinate (DOSS) were synthesized in stable isotope-labelled form from [13C]4-maleic anhydride.
Sodium [13C]4-1-carboxy-2-(2-ethylhexyloxycarbonyl)ethanesulfonate (α-EHSS) was prepared by the method of Larpent by
reaction of 2-ethylhexan-1-ol with [13C]4-maleic anhydride followed by regioselective conjugate addition of sodium
bisulfite to the resulting monoester (38% overall yield). The regiochemical outcome of bisulfite addition was confirmed by
a combination of 13C/13C (incredible natural abundance double quantum transfer) and 1H/13C (heteronuclear multiple-bond
correlation (HMBC)) NMR spectral correlation experiments. Sodium
[
13C]4-2-carboxy-1-(2-ethylhexyloxycarbonyl)
ethanesulfonate (β-EHSS) was prepared in four steps by reaction of 4-methoxybenzyl alcohol with [13C]4-maleic anhydride,
regioselective sodium bisulfite addition, N,N′-dicyclohexylcarbodiimide-mediated esterification with 2-ethylhexan-1-ol, and
p-methoxybenzyl ester deprotection with trifluoroacetic acid (13% overall yield). The regiochemical outcome of the second
1
synthesis was confirmed by a combination of JCC scalar coupling constant analysis and 1H/13C (HMBC) NMR spectral
correlation. The materials prepared are required as internal standards for the liquid chromatography–mass spectrometry
(LC-MS)/MS trace analysis of the degradation products of DOSS, the anionic surfactant found in Corexit, the oil dispersant
used during emergency response efforts connected to the Deepwater Horizon oil spill of April 2010.
Keywords: sulfosuccinate surfactants; DOSS; EHSS; INADEQUATE
sulfosuccinate (EHSS) monoesters are likewise obtained from
Introduction
the branched sulfosuccinate diester DOSS (1) during its
To mitigate the environmental impact of the massive oil spill
biodegradation by oil-degrading microorganisms found in
the Gulf of Mexico.5
that resulted from a high-pressure methane explosion aboard
the Deepwater Horizon drilling platform on 20 April 2010,
As part of an ongoing effort to develop a trace analysis for
exceptionally large quantities of Corexit 9500 and 9527 oil
surfactants and their degradation products associated with
dispersants were applied to the Gulf of Mexico (4.1 million litres
Corexit oil dispersants in Gulf of Mexico seawater field and
to surface and 2.9 million litres subsurface).1 Details of the
composition of these proprietary formulations were later
released by the US Environmental Protection Agency (EPA) to
facilitate the development of analytical tools to track the fate
of the oil dispersants.2 Accordingly, it is now known that Corexit
9500 and Corexit 9527 contain diisooctyl sulfosuccinate (DOSS,
1) among three other surfactant ingredients (Figure 1). DOSS is
of widespread use in a variety of consumer products3; however,
comparatively, little is known about its biodegradation in aquatic
environments, a critical consideration when one contemplates
the ultimate environmental legacy of the Deepwater Horizon
oil spill to the Gulf of Mexico. Using model microorganisms,
Hales discovered that biodegradative ester hydrolysis of di-
n-alkyl sulfosuccinates occurs under aerobic or anaerobic
conditions to yield both possible monoester regioisomers.4
More recently, an EPA group established that ethylhexyl
laboratory microcosm samples,6 we required access to
stable isotope mass spectrometric standards of α-EHSS (2) and
β-EHSS (3) for quantification of liquid chromatography–mass
spectrometry (LC-MS)/MS experiments. Herein, we report
regioselective syntheses of quadruply labelled stable isotope
aDepartment of Chemistry, Oregon State University, Corvallis, OR 97331, USA
bDepartment of Environmental and Molecular Toxicology, Oregon State
University, Corvallis, OR 97331, USA
*Correspondence to: Paul R. Blakemore, Department of Chemistry, Oregon State
University, 153 Gilbert Hall, Corvallis, OR 97331, USA.
E-mail: paul.blakemore@science.oregonstate.edu
†Additional supporting information may be found in the online version of this
article at the publisher’s web-site.
J. Label Compd. Radiopharm 2014, 57 397–401
Copyright © 2014 John Wiley & Sons, Ltd.

A. L. Barsamian et al.
2-3 bond heteronuclear multiple-bond correlation (HMBC)
1H/13C correlation experiment10 (Figure 2A). The first technique
enabled differentiation of the close proximity in frequency C1
(directly bonded to sulfonate bearing methine) and C4 (distal
from sulfonate bearing methine) carboxyl atom resonances,
while the second method served to indicate the close proximity
of C4 to the ester alkyl chain. This determination complements
and lies in agreement with the less secure regiochemical
assignment for 2 made by Larpent et al. using an argument
based on 1H/13C scalar couplings and the strong dependence
of a free acid carboxyl 13C-atom chemical shift value on changes
to pH.7
Attention was next focused on the synthesis of the second
target, [13C]4-β-EHSS (3). The β-type of sulfosuccinate monoester
has previously been obtained by saponification of DOSS;
however, this procedure leads to β-EHSS in low purity.11 To
improve on the DOSS-based approach, we elected to access
[13C]4-3 in a controlled manner by selective deprotection of a
regiodefined mixed sulfosuccinic diester [13C]4-8 (Scheme 2).
The α-type sulfosuccinate monoester [13C]4-7 was first prepared
by analogy to [13C]4-2 via opening of [13C]4-maleic anhydride
with p-methoxybenzyl (PMB) alcohol followed by regioselective
addition of sodium bisulfite as before. Extensive hydrolysis
of the sensitive PMB ester occurred during the sulfonation
step, and [13C]4-7 was obtained as a ca. 1:1 mixture with
[13C]4-sulfosuccinic acid (refer to the Experimental section for
details). The mixture of monoester [13C]4-7 and [13C]4-sulfosuccinic
Figure 1. Sodium diisooctyl sulfosuccinate (DOSS, 1), a significant component of
Corexit oil dispersants 9500 and 9527, and its monoester derivatives α-ethylhexyl
sulfosuccinate (α-EHSS, 2) and β-ethylhexyl sulfosuccinate (β-EHSS, 3).
mass spectrometric standards for α-EHSS ([13C]4-2) and β-EHSS acid was further converted to a chromatographically inseparable
([13C]4-3) from [13C]4-maleic anhydride (4) and prove the mixture of diesters [13C]4-8 and [13C]4-DOSS (1) by N,N′-
regiochemistry of both compounds by 13C/13C and H/13C NMR dicyclohexylcarbodiimide (DCC)-mediated coupling with 2-
1
spectral correlation experiments.
ethylhexan-1-ol (5).7 Treatment of the mixture of diesters with
trifluoroacetic acid resulted in selective removal of only the PMB
moiety from [13C]4-8 leaving [13C]4-DOSS (1) intact. The lipophilic
component ([13C]4-1) was then easily removed from the desired
Results and discussion
Larpent and co-workers have described the regioselective polar target molecule by a simple trituration with Et2O that left
synthesis of α-type alkyl sulfosuccinate monoesters (e.g. 2) by behind β-EHSS [13C]4-3 as a colourless amorphous powder in a
addition of sodium bisulfite to maleic acid monoesters obtained 13% overall yield from [13C]4-maleic anhydride.8 In this case, the
by alcoholysis of maleic anhydride (4).7 Given the commercial 13C NMR signals arising from the 13C-atom-enriched sulfosuccinate
availability of [13C]4-maleic anhydride, we elected to apply this moiety showed fully resolved multiplets, and pairwise mapping of
1
straightforward approach to access our first target [13C]4-2. The the well-differentiated individual JCC scalar coupling constants
Larpent procedure was modified slightly to function on the small enabled an unambiguous assignment of C1 and C4 carboxyl atom
scale necessitated by the expense of [13C]4-4 and gave [13C]4-2 resonances without recourse to an INADEQUATE experiment
as indicated in a 38% overall yield (Scheme 1).8 The high level (Figure 2B). As before, an HMBC experiment then served to locate
of 13C-atom enrichment in [13C]4-2 afforded us the opportunity the point of attachment of the ester side chain to the
to unambiguously establish the location of the sulfonate sulfosuccinate region, and in this manner, the compound prepared
group in relation to the ester side chain by a combined use was confirmed to possess the desired β-type regiochemistry in line
of two 2D NMR spectral correlation experiments: the rarely with expectation.
used incredible natural abundance double quantum transfer
(INADEQUATE) 13C/13C correlation experiment9 and a standard
Experimental
All commercially available reagents were used as received unless
otherwise noted. Preparative chromatographic separations were
performed on silica gel 60 (35–75 μm), and reactions were followed by
thin layer chromatography analysis using silica gel 60 plates (2–25 μm)
with fluorescent indicator (254 nm) and visualized with UV or
phosphomolybdic acid. Infrared (IR) spectra were recorded in Fourier
transform mode using KBr discs for solids, while oils were supported
between NaCl plates (neat). 1H and 13C NMR spectra were recorded in
Fourier transform mode at the field strength specified and from the
indicated deuterated solvents in standard 5-mm diameter tubes. Chemical
shift in ppm is quoted relative to residual solvent signals calibrated as
follows: CDCl3 δH (CHCl3) = 7.26ppm, δC = 77.2 ppm; (CD3)2SO δH
Scheme 1. Synthesis of sodium
ethanesulfonate ([13C]4-2).
[
13C]4-1-carboxy-2-(2-ethylhexyloxycarbonyl)
(CD3SOCHD2) = 2.50 ppm, δC = 39.5ppm; CD3OD δH (CHD2OD) = 3.31 ppm,
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Copyright © 2014 John Wiley & Sons, Ltd.
J. Label Compd. Radiopharm 2014, 57 397–401

A. L. Barsamian et al.
Figure 2. Assignment of the sulfosuccinate-related 13C NMR signals (175 MHz, d6-DMSO) for [13C]4-2 and [13C]4-3 by one bond 13C/13C correlation (INADEQUATE or 1JCC
scalar coupling) and identification of ester side-chain attachment point by three bond 1H/13C correlation (HMBC). Numbers in parentheses following 13C NMR chemical shift
values indicate the number of attached hydrogen atoms.
(6 × 5 mL) to remove less polar contaminants; this time, the triturant
being the discard and the residual powder the retained material. The
powder was further purified by column chromatography (SiO2, eluting
with 0.5% CF3CO2H/19.5% MeOH in EtOAc) followed by a final trituration
with EtOAc (4 × 1 mL) to afford pure [13C]4-2 (64 mg, 0.190 mmol, 38%
yield from [13C]4-4) as a colourless residual amorphous solid. Data for
[
13C]4-2: IR (KBr) 3528, 2959, 2931, 1677, 1557, 1372, 1224, 1154, 1035,
859, and 643 cmÀ1
;
1H NMR (700 MHz, d6-DMSO) δ 12.11 (1H, br s),
1
1
3.93–3.87 (2H, m), 3.61 (1H, dm, JCH = 138.4 Hz), 2.84 (1H, dm, JCH
=
1
128.4 Hz), 2.73 (1H, dm, JCH = 130.0 Hz), 1.50 (1H, septet, J = 5.9 Hz),
1.33–1.21 (8H, m), 0.86 (3H, t, J = 6.9 Hz), and 0.83 (3H, td, J = 7.4, 1.1 Hz)
ppm; 13C NMR (175 MHz, d6-DMSO) δ 171.3 (0, d, JCC = 58.4 Hz), 169.5
1
1
1
(0, d, JCC = 56.4 Hz), 65.9 (2), 61.4 (1, dd, JCC = 56.3, 38.2 Hz), 38.1 (1),
1
34.0 (2, dd, JCC = 58.4, 38.2 Hz), 29.7 (2), 28.3 (2), 23.2 (2), 22.4 (2), 13.9
(3), and 10.8 (3) ppm; MS (ES+) m/z 359 (M + Na)+; and HRMS (ES+) m/z
359.0943 (calcd. for 12C813C4H21Na2O7S: 359.0938).
*Data for intermediate compound [13C]4-6: IR (KBr) 3043, 2960, 2931,
Scheme 2. Synthesis of sodium
[
13C]4-2-carboxy-1-(2-ethylhexyloxycarbonyl)
ethanesulfonate ([13C]4-3). PMB = p-methoxybenzyl.
1690, 1668, 1463, 1396, 1380, 1200, 1160, and 803 cmÀ1 1H NMR
;
(700 MHz, CDCl3) δ 6.44 (1H, dtm, J= 166.8, 14.0 Hz), 6.37 (1H, dt, J = 167.5,
13.0 Hz), 4.22–4.16 (2H, m), 1.65 (1H, septet, J= 6.1Hz), 1.40–1.35 (2H, m),
1.34–1.24 (6H, m), 0.90 (3H, t, J = 7.5Hz), and 0.89 (3H, t, J = 7.0Hz) ppm;
δC = 49.0ppm; and (CD3)2CO δH (CD3COCHD2) = 2.05ppm, δC = 29.8ppm.
Multiplicities in the 1H NMR spectra are described as follows: s= singlet,
d = doublet, t = triplet, q = quartet, m = multiplet, and br = broad. Numbers
in parentheses following carbon atom chemical shifts refer to the number
of attached hydrogen atoms as revealed by distortionless enhancement
of polarization transfer or heteronuclear single quantum correlation
techniques. Low (MS) and high resolution mass spectra (HRMS) were
obtained using either electron impact (EI) or electrospray (ES) ionization
techniques. Ion mass/charge (m/z) ratios are reported as values in atomic
mass units.
1
1
13C NMR (175 MHz, CDCl3) δ 168.1 (0, d, JCC = 72.1Hz), 165.1 (0, d, JCC
=
1
1
67.4 Hz), 136.4 (1, t, JCC = 67.6 Hz), 129.6 (1, t, JCC = 69.8 Hz), 69.6 (2),
38.7 (1), 30.4 (2), 29.0 (2), 23.8 (2), 23.1 (2), 14.2 (3), and 11.1 (3) ppm; MS
(EI+) m/z 233 (39%, M + H)+, 121 (100), 112 (22), 104 (52), 83 (22), 70 (57);
and HRMS (EI+) m/z 233.1570 (calcd. for 12C813C4H21O4: 233.1574).
Sodium [13C]4-1-carboxy-2-(4-methoxybenzyloxycarbonyl)
ethanesulfonate ([13C]4-7)
A solution of [13C]4-maleic anhydride ([13C]4-4, 51 mg, 0.50 mmol) and p-
methoxybenzyl alcohol (PMBOH, 62 μL, d = 1.113, 69 mg, 0.50 mmol) in
PhH (2.0 mL) was stirred at a gentle reflux for 21 h under Ar and then
concentrated in vacuo. 1H NMR (700 MHz, d6-acetone) spectral analysis
confirmed predominant conversion of the anhydride to the desired
monoester (diester : monoester : maleic anhydride : maleic acid = 6:85:6:3).
Sodium [13C]4-1-carboxy-2-(2-ethylhexyloxycarbonyl)
ethanesulfonate ([13C]4-2)
A 3.0-mL glass vial was charged with 2-ethylhexan-1-ol (5, 86 μL,
d = 0.833, 71.5 mg, 0.55 mmol) and [13C]4-maleic anhydride (4, 51 mg,
0.50 mmol) then heated to 80–90 °C (oil bath) and sealed with a screw
cap. After heating for 24 h, 1H NMR (700 MHz, d6-acetone) spectral The residue was dissolved in i-PrOH (3.0 mL) and transferred to a 20-mL
analysis indicated a molar ratio of monoester* [13C]4-6 : diester : alcohol thick-walled glass reaction vessel (a ’sealed-tube’ apparatus) equipped
5 of 14:1:1. The mixture was allowed to cool to room temperature (rt),
dissolved in i-PrOH (3.0 mL) and transferred to a 50-mL round-bottomed
with a magnetic stir bar. The vessel was flushed with Ar, and the contents
were treated dropwise with a freshly prepared solution of aq. NaHSO3
(RB) flask provided with a magnetic stir bar. The flask was flushed with Ar (2.3 mL, 0.44 M, 1.01 mmol; sparged with Ar for 30 min before use). The
and the contents treated dropwise with a freshly prepared solution of
aqueous NaHSO3 (2.3 mL, 0.44 M, 1.01 mmol; sparged with Ar for 30 min
before use). The resulting mixture was stirred for 48 h at 60°C (oil bath)
under Ar. After this time, the reaction mixture was allowed to cool and
concentrated in vacuo. The residue was triturated with MeOH–H2O (4:1,
5 × 5 mL) to leave behind inorganic matter. The methanolic triturant
was concentrated in vacuo, and the residue was triturated with Et2O
reaction vessel was then partially submerged in a 60°C oil bath, sealed
with a Teflon screw stopper, and the contents stirred vigorously for
48 h. After this time, the reaction mixture was allowed to cool, and the
stopper was removed cautiously. The mixture was concentrated in vacuo,
and the residue was triturated with MeOH–H2O (4:1, 5 × 5 mL) to leave
behind inorganic matter. The methanolic triturant was concentrated in
vacuo, and the residue was dried azeotropically by repeated addition of
J. Label Compd. Radiopharm 2014, 57 397–401
Copyright © 2014 John Wiley & Sons, Ltd.
www.jlcr.org

A. L. Barsamian et al.
PhH (5 × 10 mL) followed each time by concentration. To remove less
polar contaminants, the residue was triterated with Et2O (4 × 5 mL); this
time, the triturant being the discard and the residual powder the
retained material. Analysis of the resulting amorphous powder (115 mg,
the desired labelled β-EHSS (>94 wt.% in [13C]4-3, eff. 15 mg, 0.045 mmol,
83% yield) associated now with only a minor residual amount of [13C]4-1
(<6 wt.%). Data for [13C]4-3: IR (KBr) 2927, 1679, 1463, 1400, 1262, 1219,
1199, 1153, 1054, 898, 789, 729, 669, and 645 cmÀ1
;
1H NMR (700 MHz,
dry weight) by 1H NMR spectroscopy revealed it to be a 1:1 molar mixture d6-DMSO) δ 12.2 (1H, br s, OH), 3.93–3.83 (2H, m), 3.59 (1H, br d, JCH
=
1
of [13C]4-7 and [13C]4-sulfosuccinate (i.e. 61 wt% in [13C]4-7, 70 mg,
0.203 mmol, 41% yield from [13C]4-4) that was used without further
purification in the next step. NMR spectral data for [13C]4-7 (from a
139.0 Hz), 2.85 (1H, br d, JCH = 132.5 Hz), 2.72 (1H, br d, JCH = 131.0 Hz),
1.52–1.48 (1H, m), 1.37–1.20 (8H, m), 0.86 (3H, t, J = 6.4 Hz), and 0.83
(3H, tm, J = 7.2 Hz) ppm; 13C NMR (175 MHz, d6-DMSO) δ 172.7 (0, d,
1
1
mixture with [13C]4-sulfosuccinate): 1H NMR (700 MHz, CD3OD-D2O, 2:1) 1JCC = 55.1 Hz), 168.6 (0, d, JCC = 59.7 Hz), 66.0 (2, d, JCC = 7.2 Hz), 61.6
1
2
1
1
δ 7.32 (2H, d, J = 8.5 Hz), 6.95 (2H, d, J = 8.6 Hz), 5.08 (1H, d, J = 12.5 Hz), (1, dd, JCC = 59.9, 38.0 Hz), 38.1 (1), 34.1 (2, dd, JCC = 54.8, 38.0 Hz),
1
5.06 (1H, d, J = 13.2 Hz), 4.06 (1H, dm, JCH = 136.4 Hz), 3.82 (3H, s), and 29.5 (2), 28.3 (2), 22.9 (2), 22.4 (2), 13.9 (3), and 10.7 (3) ppm; MS (ES
3.35–2.88 (2H, m) ppm; 13C NMR (175 MHz, CD3OD-D2O, 2:1) δ 173.6 (0,
+) m/z 359 (M + Na)+; and HRMS (ES+) m/z 359.0926 (calcd. for
1
d, JCC = 58.3 Hz), 172.5–171.6 (0, m), 131.6 (2C, 1), 115.4 (2C, 1), 66.8 (2),
12C183C4H21Na2O7S: 359.0938).
1
64.4–63.3 (1, m), 56.5 (3), and 35.3 (2, dd, JCC = 58.5, 37.8 Hz) ppm.
Sodium [13C]4-1-(2-ethylhexyloxycarbonyl)-2-(4-methoxy-
Conclusion
benzyloxycarbonyl)-ethanesulfonate ([13C]4-8)
Regioselective syntheses of stable isotope-labelled α-EHSS
([13C]4-2) and β-EHSS ([13C]4-3) have been successfully realized.
The ultimate regiochemical outcome of each synthesis was
unequivocally established by the combined action of 13C/13C
and 1H/13C NMR spectral correlation experiments that were
facilitated by the high level of 13C-atom enrichment. The stable
isotope-labelled materials described herein will prove useful as
LC-MS/MS standards for the trace analysis of DOSS and its
A 100-mL RB flask equipped with a magnetic stir bar was charged with
the mixture of [13C]4-7 and [13C]4-sulfosuccinate obtained previously
(115 mg, 1:1 molar ratio, 0.203 mmol
(5, 86 μL, d = 0.833, 72 mg, 0.551 mmol), 4-(dimethylamino)pyridine
(DMAP, 122 mg, 1.00 mmol), and 4-(dimethylamino)pyridinium chloride
(DMAP•HCl, 119 mg, 0.751 mmol). The flask was flushed with Ar gas
and, then, the contents dissolved in anhydrous dimethylformamide
(DMF) (6.0 mL) with stirring (30 min). DCC (185 mg, 0.898 mmol) in
[
13C]4-7), 2-ethylhexan-1-ol
anhydrous DMF (1.0 mL) was added dropwise, and the resulting mixture degradation products in laboratory microcosms and in Gulf
was allowed to stir for 96 h at rt. After this time, the mixture was diluted
with EtOAc (75 mL), filtered, and the filtrate was concentrated in vacuo.
The residue was triturated with three portions of EtOAc (25 mL then
2 × 7 mL), and the combined triturant was concentrated in vacuo. The
residue (244 mg) was subjected to column chromatography (SiO2, eluting
with 0–5% MeOH in EtOAc) to afford a co-eluting mixture of [13C]4-8,
of Mexico field samples collected as a result of emergency
response efforts connected to the Deepwater Horizon oil spill.
Acknowledgements
[
13C]4-DOSS (1), and DMAP. To remove the DMAP, the mixture was
The BP Gulf of Mexico Research Initiative (GoMRI) funded
research consortium project ‘Ecosystem Impacts of Oil and Gas
Inputs to the Gulf (ECOGIG)’, led by the University of Mississippi,
is thanked for support of this work. This is ECOGIG manuscript
number 190. Research reported in this publication was
supported in part by the National Institute of Environmental
Health Sciences of the National Institutes of Health under Award
Number T32ES007060. The content is solely the responsibility of
the authors and does not necessarily represent the official views
of the National Institutes of Health. Mr. Rodger Kohnert (OSU) is
thanked for his assistance in obtaining the INADEQUATE NMR
spectrum for [13C]4-2, and Ms. Michelle Romero (OSU) is
gratefully acknowledged for obtaining mass spectra.
dissolved in EtOAc (35 mL), washed with aq. 1.0 M HCl (2 × 1.50 mL),
H2O (1 mL), and brine (3 × 1.0 mL), then dried (Na2SO4) and
concentrated in vacuo. This treatment afforded 94 mg of a pure two
component mixture of [13C]4-8 (36 wt.%, eff. 34 mg, 0.075 mmol, 37%)
and [13C]4-DOSS (1) as a colourless paste that was used directly in
the next transformation. Data for [13C]4-8 (from a mixture with [13C]4-1):
1H NMR (700 MHz, CDCl3) δ 7.24 (2H, d, J = 8.1 Hz), 6.83 (2H, d, J = 8.2 Hz),
1
5.02 (2H, s), 4.40 (1H, br d, JCH = 139.9 Hz), 4.12–3.90 (2H, m), 3.77 (3H,
1
s), 3.18 (2H, br d, JCH = 132.0 Hz), 1.53–1.45 (1H, m), 1.40–1.20 (8H, m),
and 0.90–0.82 (6H, m) ppm; 13C NMR (175 MHz, CDCl3) δ 171.8 (0, d, 1JCC
=
58.7 Hz), 170.0 (0, d, 1JCC = 58.9 Hz), 159.7 (0), 130.2 (2C, 1), 128.0 (0), 114.0
(2C, 1), 69.0 (2), 66.8 (2), 61.2 (1, dd, 1JCC = 59.1, 36.4 Hz), 55.4 (3), 38.5 (1),
1
33.2 (2, dd, JCC = 59.0, 36.7 Hz), 30.1 (2), 28.9 (2), 23.4 (2), 23.1 (2), 14.2
(3), and 10.9 (3) ppm; MS (ES+) m/z 479 (M + Na)+; and HRMS (ES+) m/z
Conflict of interest
479.1524 (calcd. for 12
13
C C4H29Na2O8S: 479.1513).
16
The authors did not report any conflict of interest.
Sodium [13C]4-2-carboxy-1-(2-ethylhexyloxycarbonyl)
ethanesulfonate ([13C]4-3)
References
A stirred solution of a portion of the two component mixture of [13C]4-8
and [13C]4-DOSS (1) obtained previously (68 mg, 36 wt.% in [13C]4-8, eff.
24.5 mg, 0.054 mmol) in CH2Cl2 (1.5 mL) at 0°C was treated dropwise with
trifluoroacetic acid (0.10 mL) during 1 min. The resulting mixture was
allowed to warm to rt during 1 h and then concentrated in vacuo. The
residue was treated with Et2O (5 mL) and H2O (0.1 mL), shaken, and
concentrated. The resulting solids were triturated with excess pentane
(17 mL), the triturant was separated by filtration, and the filter cake was
washed with further pentane (3 mL). The combined pentane filtrate
and washings (containing [13C]4-3 and [13C]4-1 but now free of any minor
inorganic impurities) were concentrated in vacuo. To remove a majority
of [13C]4-1 from [13C]4-3, the residue was now triturated with Et2O
(3 × 5 mL); this time, the triturant being discarded and the residual
powder retained. Analysis of this final colourless amorphous solid
material (16 mg, dry weight) by 1H NMR spectroscopy revealed it to be
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Supporting information
Additional supporting information may be found in the online
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J. Label Compd. Radiopharm 2014, 57 397–401
Copyright © 2014 John Wiley & Sons, Ltd.
www.jlcr.org