Preparation of carboxythiolactones and their active derivatives

Article abstract of DOI:10.1055/s-1999-3377

The design of peptidyl immunogens requires that a number of elements be covalently linked to enable the appropriate immune response to occur. Two of these elements are: (a) T-cell sequences which after processing, bind to major histocompatibility complex (MHC) molecules and T-cell receptors and (b) B-cell sequences which embody the constellation of atoms which will ultimately be recognized by the desired antibody. Our concept, designed to effectuate this, involved a single molecule which could conjugate three peptides, potentially in discrete steps, in one pot. Activated carboxythiolactones, hitherto unknown entities, provide such a system: two acyl sites susceptible to nucleophilic attack at disparate rates and a liberated thiol susceptible to electrophilic alkylation. Such a set of thiolactones and their derivatives have been synthesized from inexpensive starting materials and their reactivities are under investigation. If successful, the system will not only obviate the difficult syntheses of longer linear peptides, but will also allow a rapid structural permutation of the various elements.

Full text of DOI:10.1055/s-1999-3377

270
PAPER
Preparation of Carboxythiolactones and Their Active Derivatives
Bonnie J. Garbiras,* Stephen Marburg
Department of Medicinal Chemistry, Merck and Co., Inc., P.O. Box 2000, Rahway, NJ 07065, USA
Received 14 April 1998; revised 19 May 1998
successful and anion generation via sodium hydride also
failed. Carboxylation of the lithium diisopropylamide
generated anion with gaseous carbon dioxide was suc-
cessful, but required acid workup at 0¡C in order to avoid
Abstract: The design of peptidyl immunogens requires that a num-
ber of elements be covalently linked to enable the appropriate im-
mune response to occur. Two of these elements are: (a) T-cell
sequences which after processing, bind to major histocompatibility
complex (MHC) molecules and T-cell receptors and (b) B-cell se- decarboxylation. Activation of the carboxy moiety to
quences which embody the constellation of atoms which will ulti-
mately be recognized by the desired antibody. Our concept,
give 2 was achieved using perfluorophenol in the pres-
ence of 3-[3-(dimethylamino)propyl]-1-ethylcarbodiim-
designed to effectuate this, involved a single molecule which could
ide (EDAC).
conjugate three peptides, potentially in discrete steps, in one pot.
Activated carboxythiolactones, hitherto unknown entities, provide
such a system: two acyl sites susceptible to nucleophilic attack at
disparate rates and a liberated thiol susceptible to electrophilic alky-
lation. Such a set of thiolactones and their derivatives have been
synthesized from inexpensive starting materials and their reactivi-
ties are under investigation. If successful, the system will not only
obviate the difficult syntheses of longer linear peptides, but will
also allow a rapid structural permutation of the various elements.
Key words: activated carboxythiolactones, peptidyl immunogen
constructs, oxotetrahydrothiophenecarboxylic acids, oxotetrahy-
drothianecarboxylic acids
The design of peptidyl immunogen constructs requires the
incorporation of several entities, to form an ensemble that
generates antibodies. Ladd and co-workers1 have shown
that three peptide elements can be linearly fused together
to elicit an immune response: (1) a T-cell helper epitope,
(2) a B-cell hapten and (3) an optional invasin domain
which acts as a general immune stimulator. Our concept
involves a single molecule which is capable of conjugat-
ing three such peptide elements in one pot or in well-de-
fined stages. Carboxythiolactones afford three different
chemistries: the exocyclic carboxy group can be activated
and reacted with an amine on a peptide or other nucleo-
phile to form an amide bond, an amine function on a sec-
ond peptide or nucleophile can be introduced at the
thiolactone2Ð4 opening the ring to liberate a thiol, and this
thiol is then susceptible to attack by a thiophile such as a
maleimide residing on a third peptide or molecule. This
type of construct would circumvent the complex synthe-
ses of long, linear peptides that Ladd describes as well as
offer some flexibility in its design. Thus, two different
T-cell helper peptides could be included to make the con-
struct more suitable for outbred populations. Conversely,
two B-cell peptides might be incorporated to afford differ-
ent hapten orientations to achieve maximum antigenic ef-
ficacy. Herein we describe the methods to prepare the
aforementioned carboxythiolactones and their activated
derivatives.
a: LDA, THF, Ð78¡C; b: CO2 (g); c: 2 M HCl, 0¡C; d: perfluoro-
phenol, EDAC, CH2Cl2, 0¡C.
Scheme 1
The synthesis of 5-oxotetrahydrothiophene-3-carboxylic
acid 45 (Scheme 2) began with a Michael addition to com-
mercially available itaconic acid. Sulfur deprotection and
cyclization was accomplished in aqueous hydrochloric
The synthesis of 2-oxotetrahydrothiophene-3-carboxylic
acid 1 (Scheme 1) involved functionalization of g-thiobu-
tyrolactone. Attempts to carboxylate g-thiobutyrolactone
with methoxymagnesium carbonate (MMC) proved un-
a: AcSH, H2O, reflux; b: 6 M HCl, reflux; c: TFA, reflux; d: per-
fluorophenol, DCC, EtOAc, 0¡C.
Scheme 2
Synthesis 1999, No. 2, 270–274 ISSN 0039-7881 © Thieme Stuttgart á New York

PAPER
Preparation of Carboxythiolactones and Their Active Derivatives
271
acid. The aqueous environment, however, prevented com-
plete cyclization to the thiolactone. Therefore, refluxing
in trifluoroacetic acid (TFA) was required to drive the cy-
clization to completion. Activation of the carboxy moiety
to afford 5 was accomplished with perfluorophenol in the
presence of dicyclohexylcarbodiimide in good yield
(91%).
The synthesis of 5-oxotetrahydrothiophene-2-carboxylic
acid 8 (Scheme 3) began with a photobromination of
commercially available glutaryl dichloride.6 Bromide dis-
placement by thiolacetic acid anion gave 7 which can be
purified by activated charcoal with >90% recovery.
Deprotection and cyclization were achieved in one step
with the same conditions as 4 to give crystalline 8 after pu-
rification. NMR indicated cyclization with a shift of the
C2 protons downfield from d = 3.17 to d = 4.47. Transform-
ation of the carboxy moiety to the perfluorophenyl ester
also afforded crystalline material. The synthesis of ring
homolog, 6-oxothiane-6-carboxylic acid 13, (Scheme 4),
paralleled the synthesis of 8. However, deprotection and
cyclization could not be attained in one pot. 2-Thioadipic
acid (12),7 a compound previously synthesized in 1947 by
Danielli and co-workers, was isolated after hydrolysis of
11 with aqueous hydrochloric acid. The cyclization step
required more stringent conditions utilizing trifluoroace-
tic anhydride, which presumably produced a trifluoro-
acetic mixed anhydride (TFAA) side product 14 that was
a: SOCl2, reflux; b:Br2; c: EtOH, 0¡C; d: NaOEt, AcSH, EtOH,
0¡C; e: 6 M HCl, reflux; f: TFA, reflux; g: TFAA, TFA, 0¡C; h: 4-
nitrophenol, EDAC, CH2Cl2, 0¡C.
Scheme 4
removed during purification and never isolated. Another
distinction was that the perfluorophenyl derivative of 13
created a very unstable species that could not be isolated
in appreciable yield. Therefore, the less reactive 4-nitro-
phenyl ester 15 was prepared.
The activated ester derivatives are under investigation to
study their ability to conjugate three different peptides in
one pot or in well-defined stages. Preliminary results sug-
gest that this concept is a viable method for constructing
tripartite products. Efforts will continue toward generat-
ing such compounds.
All reagents were of commercial quality: reagent grade solvents
were used without further purification. 3-[3-(dimethylamino)pro-
pyl]-1-ethylcarbodiimide hydrochloride (EDAC) was purchased
from Sigma. Perfluorophenol was purchased from Fluka. DCC was
purchased from Advanced Chemtech. g-Thiobutyrolactone, LDA,
itaconic acid, AcSH, TFA, Br2, glutaryl dichloride, NaOEt, adipic
acid monoethyl ester, SOCl2, TFAA, and 4-nitrophenol were pur-
chased from Aldrich Chemical Co. Mps were determined on a
ThomasÐHoover capillary apparatus and are uncorrected. NMR
spectra were measured on a Varian XL 400 spectrometer. Elemental
analyses were performed by Robertson Microlit Laboratories (Mad-
a: Br2, hn, 60¡C; b: EtOH, 0¡C; c: NaOEt, AcSH, EtOH, 0¡C; d:
6 M HCl, reflux; e: TFA, reflux; f: perfluorophenol, DCC, EtOAc,
0¡C.
Scheme 3
Synthesis 1999, No. 2, 270–274 ISSN 0039-7881 © Thieme Stuttgart · New York

272
B. J. Garbiras, S. Marburg
PAPER
ison, NJ). Electrospray ionization (ESI) MS were recorded on a
Finnigan TSQ700 (82% CH3CN/17% 1.3 mM trifluoroacetateÐam-
monium formate). These conditions sometimes result in an ammo-
was allowed to stir for 6 h. The reaction was cooled to r.t. and con-
centrated under reduced pressure to afford a solid mixture of uncyc-
lized diacid and product. This mixture was dissolved in TFA (10
mL) and brought to reflux for 1 h. The TFA was removed under re-
duced pressure to give 4 as a white, crystalline solid; yield: 2.61 g
(100%); mp 105Ð106¡C (Lit.5 mp 100Ð106¡C).
+
nium ion (NH4 ) being complexed to the parent ion and will be
noted in spectral data. Electron Ionization (EI) and chemical ioniza-
tion (CI) spectra are run on a Finnigan SSQ710, either by probe
(50Ð300¡C over 5 min) or particle beam (80% MeOH/20% CH2Cl2)
introduction as noted.
C5H6O3S
calcd
C
41.09
H
4.14
S
21.93
(146.2)
found
40.89
4.16
21.75
1H NMR (CD3CN): d = 2.73 (dd, 1H, J = 17.0 and 7.4 Hz, 4-CH2),
2.79 (dd, 1H, J = 17.0 and 7.4 Hz, 4-CH2), 3.40Ð3.48 (m, 1H, CH),
3.60 (dd, 1H, J = 11.4 and 6.5 Hz, 2-CH2), 3.62 (dd, 1H, J = 11.4
and 6.8 Hz, 2-CH2).
2-Oxotetrahydrothiophene-3-carboxylic Acid (1)
A suspension of 10 wt% LDA in hexanes (13 mL, 1.3 g, 12.1 mmol)
was dissolved in anhyd THF (10 mL) and cooled to Ð78¡C (dry ice/
acetone) under N2. To the cooled solution was added a solution of
dihydrothiophen-2(3H)-one (424 µL, 4.9 mmol) in anhyd THF
(5 mL). The golden-brown mixture was allowed to stir at Ð78¡C for
1 h and was then treated with CO2 gas for 15 min. The resulting
creamy yellow suspension was quenched with 6 M HCl (8 mL) and
H2O (8 mL), warmed to r.t. and extracted with Et2O (3 × 25 mL).
The Et2O layers were combined and extracted with sat. aq NaHCO3
(2 × 40 mL). The basic phase was acidified at 0¡C (ice/H2O) with
2 M HCl and then extracted with Et2O (2 × 75 mL). The combined
Et2O extracts were dried (Na2SO4), filtered and concentrated under
reduced pressure to afford 1 as an off-white, crystalline solid; yield:
488 mg (68%); mp 92Ð93¡C.
MS (Probe-EI): m/z (%) = 146 (M+, 100).
Perfluorophenyl 5-Oxotetrahydrothiophene-3-carboxylate (5)
To a solution of 4 (2.73 g, 18.7 mmol) in EtOAc (30 mL) chilled to
0¡C (ice/H2O) was added a solution of perfluorophenol (3.45 g,
18.7 mmol) in EtOAc (5 mL) followed by a solution of DCC
(3.86 g, 18.7 mmol) in EtOAc (2 mL). The reaction was allowed to
slowly warm to r.t. and stir for 1.5 h. The resulting dicyclohexylurea
(DCU) was filtered and the filtrate was concentrated to a white solid
which was redissolved in CHCl3 (125 mL) and extracted with 5%
NaHCO3 (50 mL) and brine (50 mL). The organic layer was dried
(Na2SO4), filtered and concentrated under reduced pressure to af-
ford 5 as a white, crystalline solid; yield: 5.29 g (91%); mp 79Ð
80¡C.
C5H6O3S
calcd
C
41.09
40.91
H
4.14
4.00
S
21.93
21.63
(146.2)
found
1H NMR (CD3CN): d = 2.43Ð2.59 (m, 2H, 4-CH2), 3.35Ð3.47 (m,
2H, 5-CH2), 3.54 (dd, 1H, J = 7.4 and 7.4 Hz, CH).
C11H5F5O3S calcd
C
42.32 H 1.61
F
30.43 S 10.27
(312.2) found
42.36 1.76
30.23 10.36
MS (Probe-EI): m/z (%) = 146 (M+, 25), 102 (MH+ Ð CO2, 100).
1H NMR (CD3CN): d = 2.95 (dd, 1H, J = 17.0 and 7.4 Hz, 4-CH2),
2.97 (dd, 1H, J = 16.8 and 7.2 Hz, 4-CH2), 3.77 (dd, 1H, J = 11.6
and 6.4 Hz, 2-CH2), 3.81 (dd, 1H, J = 11.6 and 6.9 Hz, 2-CH2),
3.89Ð3.97 (m, 1H, CH).
Perfluorophenyl 2-Oxotetrahydrothiophene-3-carboxylate (2)
To a chilled (0¡C, ice/H2O) solution of 1 (112 mg, 0.77 mmol) in
CH2Cl2 (5 mL) was added a solution of perfluorophenol (141 mg,
0.77 mmol) in CH2Cl2 (1 mL) followed by a solution of EDAC
(147 mg, 0.77 mmol) in CH2Cl2 (2 mL). The reaction was allowed
to slowly warm to r.t. and stir for 3 h. The reaction was diluted with
CH2Cl2 (50 mL). The organic layer was extracted with H2O (2 ×
25 mL), 5% NaHCO3 (2 × 25 mL) and brine (25 mL) and concen-
trated under reduced pressure to afford 2 as a clear oil which crys-
tallized under vacuum; yield: 117 mg (49%); mp 57Ð58¡C.
MS (Probe-EI): m/z (%) = 312 (M+, 55), 129 (M+ Ð OC6F5, 100).
Diethyl 2-Bromoglutarate (6)
At r.t. under a drying tube containing Drierite, Br2 (7.5 mL,
146 mmol) was added dropwise to glutaryl dichloride (22.4 g,
129 mmol). The reaction was warmed to 60¡C and irradiated with
a 450W Hanovia (Model 679A36) lamp for 2 h. The reddish-brown
solution was allowed to stir at 60¡C for 3 h and was cooled to r.t. to
stir for 1 h. The solution was slowly poured into EtOH (75 mL)
which had been cooled to 0¡C and stirred for 1.5 h. The excess bro-
mine was reduced with sat. sodium bisulfite (20 mL) and Et2O
(100 mL) was added. The organic layer was extracted with H2O
(2 × 50 mL), dried (Na2SO4), filtered and concentrated under re-
duced pressure to afford a magenta liquid. Purification of the crude
product by distillation afforded 6 as a clear liquid; yield: 11.95 g
(35%); bp 79Ð85¡C/0.15 Torr (Lit.6 bp 136Ð144¡C/11 Torr).
C11H5F5O3S calcd
C
42.32 H 1.61
F
30.43 S 10.27
(312.2) found
42.34 1.73
30.27 10.38
1H NMR (CD3CN): d = 2.43Ð2.60 (m, 1H, 4-CH2), 2.62Ð2.80 (m,
1H, 4-CH2), 3.35Ð3.47 (m, 1H, 5-CH2), 3.49Ð3.56 (m, 1H, 5-CH2),
4.04 (dd, 1H, J = 7.2 and 7.2 Hz, CH).
MS (Probe-EI): m/z (%) = 312 (M+, 12), 129 (M+ Ð OC6F5, 100).
2-(Acetylthiomethyl)succinic Acid (3)
To a stirred solution of itaconic acid (2.57 g, 19.8 mmol) in anhyd
THF (20 mL) was added AcSH (7 mL, 98 mmol). The golden-yel-
low mixture was heated to reflux and stirred for 4 h. The resulting
clear solution was cooled to r.t. and concentrated under reduced
pressure to afford 3 as a light yellow solid; yield: 3.69 g (91%).
1H NMR (D2O): d = 2.38 (s, 3H, CH3), 2.70 (dd, 1H, J = 17.3 and
5.5 Hz, CH2CO2H), 2.76 (dd, 1H, J = 17.2 and 8.4 Hz, CH2CO2H),
3.07Ð3.13 (m, 1H, CHCO2H), 3.20 (dd, 1H, J = 14.1 and 6.1 Hz,
CH2S), 3.24 (dd, 1H, J = 14.1 and 6.7 Hz, CH2S).
C9H15BrO4 calcd
C
40.47
H
5.66
Br
29.91
(267.1) found
40.71
5.70
30.25
1H NMR (CDCl3): d = 1.27 (t, 3H, J = 7.2 Hz, CH3), 1.31 (t, 3H, J
= 7.2 Hz, CH3), 2.22Ð2.35 (m, 1H, 3-CH2), 2.35Ð2.43 (m, 1H, 3-
CH2), 2.49Ð2.53 (m, 2H, 4-CH2), 4.15 (q, 2H, J = 7.1 Hz, OCH2),
4.24 (q, 2H, J = 7.2 Hz, OCH2), 4.36 (dd, 1H, J = 5.8 and 5.8 Hz,
CHBr).
MS (Probe-EI): m/z (%) = 269, 267 (M+, 5), 223, 221 (M+ Ð OEt,
70), 194, 192 (M+ Ð OEt Ð Et, 47).
MS (Particle Beam-EI): m/z (%) = 146 (M+, 100) due to compound
cyclization under conditions of mass spectrometer.
Diethyl 2-(Acetylthio)glutarate (7)
To a cooled (0¡C, ice bath), stirred solution of 6 (2.22 g, 8.3 mmol)
in EtOH (10 mL) was added AcSH (630 mL, 8.3 mmol) followed by
NaOEt (590 mg, 8.3 mmol). The golden-yellow mixture was al-
5-Oxotetrahydrothiophene-3-carboxylic Acid (4)
Compound 3 (3.69 g, 17.9 mmol) was dissolved in 6 M HCl
(20 mL) and brought to a reflux under N2. The refluxing solution
Synthesis 1999, No. 2, 270–274 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Preparation of Carboxythiolactones and Their Active Derivatives
273
lowed to stir for 2 h. A white precipitate formed (NaBr). The result-
ing yellow slurry was concentrated under reduced pressure and the
residue was diluted with CH2Cl2 (75 mL) and extracted with 5%
NaHCO3 (50 mL) and brine (25 mL). The organic layer was dried
(Na2SO4), filtered and concentrated under reduced pressure to a yel-
low liquid. The crude material was dissolved in 75% CH3CN/H2O
(5 mL). Activated charcoal (418 mg) was added, and the slurry was
allowed to stir for 15 h at r.t. The charcoal was filtered through
Celite, and the filtrate was concentrated under reduced pressure to
give 7; yield: 1.88 g (90%).
1H NMR (CDCl3): d = 1.23 (t, 3H, J = 6.8 Hz, CH3), 1.25 (t, 3H, J
= 7.2 Hz, CH3), 2.00Ð2.10 (m, 1H, 3-CH2), 2.21Ð2.30 (m, 1H, 3-
CH2), 2.34 (s, 3H, COCH3), 2.37Ð2.41 (m, 2H, 4-CH2), 4.12 (q, 2H,
J = 7.1 Hz, OCH2), 4.17 (q, 2H, J = 7.2 Hz, OCH2), 4.21 (dd, 1H, J
= 6.7 and 6.8 Hz, CHS).
solution was extracted with Et2O (300 mL). The organic layer was
extracted with 5% NaHCO3 (4 × 100 mL) and H2O (2 × 100 mL),
dried (Na2SO4), filtered and concentrated under reduced pressure to
afford a brownish-red liquid. Purification of the crude product by
distillation afforded 10 as a clear liquid; yield: 18.2 g (46%); bp 85Ð
90¡C/0.18 Torr; (Lit.8 bp 133Ð135¡C/5 Torr.
C10H17BrO4 calcd
C
42.72
H
6.09
Br
28.42
(281.1) found
42.95
5.95
28.10
1H NMR (CDCl3): d = 1.23 (t, 3H, J = 7.2 Hz, CH3), 1.27 (t, 3H, J
= 7.2 Hz, CH3), 1.60Ð1.72 (m, 1H, 4-CH2), 1.76Ð1.85 (m, 1H, 4-
CH2), 1.94Ð2.04 (m, 1H, 3-CH2), 2.04Ð2.13 (m, 1H, 3-CH2), 2.32
(t, 2H, J = 7.4 Hz, 5-CH2), 4.11 (q, 2H, J = 7.2 Hz, OCH2), 4.20 (q,
2H, J = 7.2 Hz, OCH2), 4.20 (dd, 1H, J = 5.8 and 5.8 Hz, CHBr).
MS (ESI): m/z (%) = 300, 298 (M+ + NH4 , 100), 283, 281 (MH+,
+
42).
MS (Particle Beam-CI): m/z (%) = 263 (MH+, 58), 189 (M+
Ð
CO2Et, 100).
Diethyl 2-(Acetylthio)adipate (11)
To a cooled (0¡C, ice bath), stirred solution of 10 (2.08 g, 7.4 mmol)
in EtOH (10 mL) was added AcSH (582 mL, 8.1 mmol) followed by
NaOEt (529 mg, 7.8 mmol). The golden-yellow mixture was al-
lowed to stir for 4 h. A white precipitate formed (NaBr). The result-
ing yellow slurry was diluted with EtOAc (100 mL) and extracted
with 0.1 M HCl (50 mL), 5% NaHCO3 (50 mL) and brine (50 mL).
The organic layer was dried (Na2SO4), filtered and concentrated un-
der reduced pressure to afford 11 as a yellow liquid; yield: 1.92 g
(94%).
5-Oxotetrahydrothiophene-2-carboxylic Acid (8)
Compound 7 (2.28 g, 8.7 mmol) was covered with 6 M HCl (20 mL)
and brought to reflux under N2. The refluxing, homogeneous solu-
tion was allowed to stir for 17 h. The reaction was cooled to r.t. and
concentrated under reduced pressure to afford an oily mixture of the
open diacid and cyclic product. This mixture was dissolved in TFA
(10 mL) and refluxed for 2 h. The TFA was removed under reduced
pressure to give a golden brown oil. The crude product was purified
by flash chromatography (silica gel, 4% EtOH/1% AcOH/95%
CH2Cl2) to give 8 as a white crystalline solid; yield: 1.21 g (95%);
mp 38Ð40¡C.
C12H20O5S calcd
C
52.16
H
7.29
S
11.60
(276.4) found
51.83
7.13
11.36
C5H6O3S
calcd
C
41.09
H
4.14
S
21.93
1H NMR (CDCl3): d = 1.22 (t, 3H, J = 7.2 Hz, CH3), 1.24 (t, 3H, J
= 7.2 Hz, CH3), 1.61Ð1.80 (m, 3H, 4-CH2, 3-CH2), 1.89Ð1.98 (m,
1H, 3-CH2), 2.29 (t, 2H, J = 7.2 Hz, 5-CH2), 2.33 (s, 3H, COCH3),
4.09 (q, 2H, J = 7.2 Hz, OCH2), 4.16 (q, 2H, J = 7.2 Hz, OCH2), 4.16
(dd, 1H, J = 5.6 and 5.8 Hz, CHS).
(146.2)
found
41.07
4.23
21.62
1H NMR (CDCl3): d = 2.39Ð2.48 (m, 1H, 3-CH2), 2.50Ð2.63 (m,
2H, 3-CH2, 4-CH2), 2.83Ð2.92 (m, 1H, 4-CH2), 4.47 (dd, 1H, J = 6.5
and 6.6 Hz, CH).
MS (Particle Beam-CI): m/z (%) = 294 (M+ + NH4 , 28), 277 (MH+,
+
MS (Probe-EI): m/z (%) = 146 (M+, 100).
100).
Perfluorophenyl 5-Oxotetrahydrothiophene-2-carboxylate (9)
To a solution of 8 (184 mg, 1.26 mmol) in EtOAc (3 mL) chilled to
0¡C (ice/H2O) was added a solution of perfluorophenol (232 mg,
1.26 mmol) in EtOAc (2 mL) followed by a solution of DCC
(260 mg, 1.26 mmol) in EtOAc (3 mL). The reaction was allowed
to slowly warm to r.t. and stir for 3 h. The resulting DCU was fil-
tered and the filtrate was diluted with EtOAc (25 mL) and extracted
with 5% NaHCO3 (25 mL) and brine (25 mL). The organic layer
was dried (Na2SO4), filtered and concentrated under reduced pres-
sure to afford 9 as a clear oil which crystallized under vacuum;
yield: 333 mg (85%); mp 68Ð69¡C.
2-Thioadipic Acid (12)
A solution of 11 (1.92 g, 6.9 mmol) was covered with 6 M HCl
(20 mL) and brought to a reflux under N2. The refluxing, homoge-
neous solution was allowed to stir for 24 h. The reaction was cooled
to r.t. and concentrated under reduced pressure to afford 12 as an off
white, crystalline solid: yield: 1.2 g (100%); mp 112Ð114¡C (Lit.7
mp 112Ð113¡C).
C6H10O4S calcd
C
40.44
H
5.66
S
17.99
(178.2) found
40.69
5.67
18.27
1H NMR (CD3CN): d = 1.57Ð1.73 (m, 3H, 4-CH2, 3-CH2), 1.84Ð
1.91 (m, 1H, 3-CH2), 2.29 (t, 2H, J = 7.2 Hz, 5-CH2), 3.35 (q, 1H, J
= 7.0 Hz, CH).
C11H5F5O3S calcd
C
42.32 H 1.61
F
30.43 S 10.27
(312.2) found
42.58 1.50
30.27 10.55
1H NMR (CDCl3): d = 2.53Ð2.62 (m, 1H, 3-CH2), 2.65Ð2.74 (m,
2H, 3-CH2, 4-CH2), 2.89Ð2.98 (m, 1H, 4-CH2), 4.78 (dd, 1H, J = 6.8
and 6.8 Hz, CH).
MS (Particle Beam-EI): m/z (%) = 160 (M+, 100) due to compound
cyclization under conditions of mass spectrometer.
MS (Probe-EI): m/z (%) = 312 (M+, 18), 101 (M+ Ð CO2C6F5, 100).
6-Oxothiane-2-carboxylic Acid (13)
Compound 12 (412 mg, 2.31 mmol) was dissolved in TFA (5 mL)
and allowed to reflux for 3 h under N2. The reaction was concentrat-
ed to give a light brown oil. The crude oil was redissolved in fresh
TFA (2 mL) and chilled to 0¡C (ice/water). To the stirred solution
was added TFAA (0.25 equiv, 82 mL, 0.58 mmol). The reaction was
allowed to stir for 1 h in the ice bath. The TFA and TFAA were re-
moved under reduced pressure to give a brown oil. The crude prod-
uct was purified by flash chromatography (silica gel, 4% EtOH/1%
AcOH/95% CH2Cl2) to give 13 as a white crystalline solid; yield:
255 mg (69%); mp 61Ð64¡C.
Diethyl 2-Bromoadipate (10)8
SOCl2 (41 mL, 560 mmol) was added to adipic acid monoethyl ester
(25.0 g, 143 mmol). The opaque solution was warmed to reflux for
2.75 h under a drying tube containing Drierite. To the resulting
brown solution, Br2 (7.9 mL, 147 mmol) was added dropwise over
a period of 2 h while keeping a gentle reflux. The mixture was
cooled to r.t. then stirred for 17 h. The solution was slowly poured
into EtOH (75 mL) which had been cooled to 0¡C and stirred for 2
h. H2O (200 mL) was added to quench the reaction and the aqueous
Synthesis 1999, No. 2, 270–274 ISSN 0039-7881 © Thieme Stuttgart · New York

274
B. J. Garbiras, S. Marburg
PAPER
C6H8O3S
(160.2)
calcd
C
44.99
45.01
H
5.03
4.99
S
20.01
19.63
Acknowledgement
found
The authors would like to thank Amy Bernick for providing mass
spectral data and Dr. Richard L. Tolman for his counsel and sup-
port.
1H NMR (CDCl3): d = 1.88Ð2.98 (m, 1H, 4-CH2), 2.12Ð2.23 (m,
2H, 4-CH2 and 3-CH2), 2.27Ð2.35 (m, 1H, 3-CH2), 2.61 (dt, 2H, 5-
CH2), 4.24 (dd, 1H, J = 7.8 and 7.8 Hz, CH).
MS (Probe-EI): m/z (%) = 160 (M+, 100).
References
(1) Ladd, A. E.; Wang, C. Y.; Zamb, T. Patent application number
PCT/US94/04832, 1994.
4-Nitrophenyl 6-Oxothiane-2-carboxylate (15)
To a solution of 13 (310 mg, 1.94 mmol) in CH2Cl2 (5 mL) chilled
to 0¡C (ice/H2O) was added a solution of 4-nitrophenol (269 mg,
1.94 mmol) in CH2Cl2 (3 mL) followed by a solution of EDAC
(371 mg, 1.94 mmol) in CH2Cl2 (2 mL). The reaction was allowed
to slowly warm to r.t. and stir for 4 h. The reaction solution was con-
centrated under reduced pressure to afford a brownish-orange oil.
The oil was purified by flash chromatography(silica gel, 1% AcOH/
99% CH2Cl2) to give 15 as a white crystalline solid; yield: 190 mg
(35%); mp 83Ð85¡C.
(2) Brands, K. M. J.; Marchesini, G.; Williams, J. M.; Dolling,
U.-H.; Reider, P.J. Tetrahedron Lett. 1996, 37, 2919.
(3) Marburg, S.; Jorn, D.; Tolman, R. T.; Arison, B.; McCauley,
J.; Kniskern, P. J.; Hagopian, A.; Vella, P. P. J. Am. Chem.
Soc. 1986, 108, 5282.
(4) Matsumura, H.; Bando, T.; Sunagawa, M. Heterocycles 1996,
1, 147.
(5) Holmberg, B.; Schjanberg, E. Ark. Kemi 1940, 14a, 1.
(6) Karrer, P.; Kehrer, F. Helv. Chim. Acta. 1944, 27, 142.
(7) Danielli, J. F.; Danielli, M.; Fraser, J. B.; Mitchell, P. D.;
Owen, L. N.; Shaw, G. Biochem. J. 1947, 41, 325.
(8) Schwenk, E.; Papa, D. J. Am. Chem. Soc. 1948, 70, 3626.
C12H11NO5S calcd
C
51.24 H 3.94 N 4.98
S 11.40
(281.3) found
51.12 3.85 4.82
11.37
1H NMR (CDCl3): d = 1.94Ð2.04 (m, 1H, 4-CH2), 2.20Ð2.30 (m,
1H, 4-CH2), 2.31Ð2.42 (m, 2H, 3-CH2), 2.67 (dd, 2H, J = 7.3 and
7.5 Hz, 5-CH2), 4.45 (dd, 1H, J = 7.4 and 7.4 Hz, CH), 7.29 (dd, 2H,
J = 7.0 and 7.0 Hz, CHC), 8.28 (dd, 2H, J = 7.1 and 7.0 Hz, CHC).
MS (Probe-EI): m/z (%) = 281 (M+, 23), 115 (M+ Ð CO2C6H4NO2,
100).
Synthesis 1999, No. 2, 270–274 ISSN 0039-7881 © Thieme Stuttgart · New York