Synthesis of a transition-state analog for the hydrolysis of the zearalenone lactone

Article abstract of DOI:10.1016/j.tet.2007.07.042

The development of a catalytic antibody for the hydrolysis of the lactone functionality in zearalenone (1) is viewed as a potential solution to animal fertility problems associated with the estrogenic mycotoxin. A phosphonomacrolactone is proposed as a ha

Full text of DOI:10.1016/j.tet.2007.07.042

Tetrahedron 63 (2007) 10077–10082
Synthesis of a transition-state analog for the hydrolysis
of the zearalenone lactone
*
Krishanthi P. Jayasundera, Samuel J. Brodie and Carol M. Taylor
Institute of Fundamental Sciences, Massey University, Private Bag 11-222, Palmerston North, New Zealand
Received 22 January 2007; revised 28 June 2007; accepted 12 July 2007
Available online 19 July 2007
Abstract—The development of a catalytic antibody for the hydrolysis of the lactone functionality in zearalenone (1) is viewed as a potential
solution to animal fertility problems associated with the estrogenic mycotoxin. A phosphonomacrolactone is proposed as a hapten for the
generation of such antibodies. A suitably functionalized aryl phosphonic acid 4 was condensed with the racemic aliphatic fragment 5
via a Mitsunobu reaction. Macrocyclic formation was achieved via RCM to give advanced intermediate 23, a phosphonate analog of zearal-
enone, ready for deprotection and conjugation to a carrier protein.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
HO
HO
O
OH
O
O
O
P
O
Zearalenone (1) is a mycotoxin, first isolated by Stob and co-
workers in 1962,1 which is produced by various species of
Fusarium.2 Zearalenone is estrogenic and affects a variety
of animals. In New Zealand, sheep ingests zearalenone
when grazing on fungi-infested pastures.3 Levels of the toxin
peak in the warm, dry conditions of late summer, and early
autumn and unfortunately coincide with the sheep mating
season. This results in reduced fertility: more barren ewes,
fewer twins, later lambs, and associated productivity losses.
HO
linkage to
carrier
HO
protein
O
phosphonate analog
transition state
Figure 1. A transition-state analog.
hydrolysis by catalytic antibodies is well established.6 While
lactone hydrolysis has not been reported, the reverse reac-
tion—lactone formation—has been demonstrated.7
This toxin represents a considerable problem to the global
agricultural and horticultural industries. It is not surprising
that a number of methods have been considered to counter
its effects. Degradation of the toxin to harmless byproducts
has been demonstrated by microorganisms.4 AndrovaxÒ is
a steroid-based vaccine that stimulates ovulation and thereby
counteracts the detrimental effects of toxins such as zearal-
enone.5 A novel approach would be the use of catalytic anti-
bodies to degrade the toxin in vivo—either by inoculation
with an antibody preparation or by stimulating the animals
to produce their own therapeutic antibodies.
OH
1
O
10'
O
H2O
1'
HO
6
O
1
OH
non-estrogenic
products
COOH
arising from further
degradation
HO
O
OH
We proposed that a transition-state analog for hydrolysis
of the macrolactone would be a suitable hapten for the pro-
duction of such antibodies (Fig. 1). The byproducts of the
seco-acid (2) are known to be harmless (Scheme 1). Ester
2
Scheme 1. Hydrolysis of zearalenone (1).
Retrosynthetic analysis of the hapten, a phosphonomacro-
lactone,8 is illustrated in Scheme 2. We decided to pursue
a racemic synthesis, since the geometry in the lactone region
of the molecule was already significantly perturbed by the
phosphonate. We felt that fidelity to the 100S configuration
Keywords: Zearalenone; Lactone hydrolysis; Catalytic antibody.
* Corresponding author at present address: Department of Chemistry,
Louisiana State University, Baton Rouge, LA 70803, USA. Tel.:
+1 2255784751; fax: +1 2255783458; e-mail: cmtaylor@lsu.edu
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.07.042

10078
K. P. Jayasundera et al. / Tetrahedron 63 (2007) 10077–10082
i
in zearalenone would serve little purpose. Indeed, the use
of both enantiomers, in antibody generation, would
double our chances of inducing an effective complementary
binding site.
OH
PrO
1. 5 equiv. Me2CHBr
K2CO3, KI, DMF
50 °C, 3 d
O
P(OEt)2
i
2. HP(=O)(OEt)2
CCl4, MeCN
HO
OH
PrO
O
9
phloroglucinol(8)
(28%)
HO
LDA
THF
O
OH
O
(92%)
P
-78 °C
HO
i
linkage to
carrier
PrO
O
P
i
1. NaH, 12-crown-4
THF; TfNPh2
OEt
OR
PrO
O
protein
P(OEt)2
n
2. Bu3SnCH=CH2
i
PrO
i
PrO
OH
Pd(PPh3)2Cl2
LiCl, DMF
i
10
PrO
NaOH
EtOH
O
11 R = Et
R = H
OEt
O
P
(60%)
H2O, Δ
(90%)
4
i
PrO
S
Scheme 3. Synthesis of the aromatic fragment.
S
3
We prepared iodide 6, and the corresponding bromide 15, in
racemic form, according to Scheme 4. Hydrolysis of the lac-
tone in g-valerolactone (12) and protection of the sodium
salt gave the bis-TBDMS derivative 13. The ester was re-
duced to the primary alcohol 14 by analogy to a procedure
reported by Amino et al.15 The bromide 15 had been pre-
pared and utilized previously,16 but in our hands it was unsta-
ble and difficult to purify. Fortunately, iodide 6 was readily
obtained; although it was best to prepare this compound
immediately prior to coupling.
i
TBDMSO
PrO
OEt
O
I
P
6
OH HO
+
+
i
PrO
S
S
S
4
S
5
7
Scheme 2. Retrosynthetic analaysis.
1. NaOH
OTBDMS
COOTBDMS
13
O
Compound 3 represents an advanced intermediate that re-
quires deprotection, followed by conjugation of the ketone
to a carrier protein.9 Compound 3 is conveniently broken
down into an aromatic fragment 4 and a aliphatic fragment
5. It was envisaged that formation of a phosphonate ester
would precede formation of the 14-membered ring via an
H2O, dioxane
O
2. TBDMSCl
valerolactone
imidazole, DMF
(12)
(quant.)
OTBDMS
LiAlH4, THF
(52%)
X
RCM reaction. The latter has precedent in a recent synthesis
€
10
14 X = OH
X = I
15 X = Br
I2, PPh3
of zearalenone itself by Furstner et al. We considered
imidazole
a number of approaches to the synthesis of the aliphatic frag-
ment 5. A key building block was an alkyl halide typified by
iodide 6. Displacement of the halide in 6, with the anion
derived from dithiane 7,11 could be expected to assemble
the carbon skeleton of the aliphatic fragment. The aryl phos-
phonate presented two significant challenges: formation of
the Ar–P bond and formation of the phosphonomacrolac-
tone. We have recently reported the trials and tribulations
associated with the synthesis of 4.12 In this paper, we de-
scribe our synthesis of 5 and the amalgamation of the two
fragments.
6
(94%)
Scheme 4.
Dithiane 7 has been prepared previously by reaction of
the anion of 1,3-dithiane (16) with 5-bromopent-1-ene
(Scheme 5).17 Careful optimization of reaction conditions
led to the formation of 7 inw70% yield, but it was incredibly
difficult to separate 7 from residual 16 and byproducts of
the butyllithium. An alternative synthesis, via hex-5-
enal,18 gave a lower yield of dithiane 7, but it could be
produced on gram scale in high purity. Condensation of
the anion of 7 with iodide 6 gave compound 1819 in excellent
yield. The secondary alcohol was liberated under standard
conditions to give 5, ready for coupling to the aromatic
fragment.
2. Results and discussion
The synthesis of diethyl phosphonate 11 was reported else-
where12 and is summarized in Scheme 3. The only low-yield-
ing step was the conversion of C3-symmetric phloroglucinol
(8) to its diisopropyl ether derivative. Phosphorylation of the
remaining phenol was conducted under Atherton–Todd con-
ditions.13 An anionic phospho-Fries rearrangement14 led to
compound 10. The phenol in compound 10 was converted
to the corresponding triflate and then to the styrene 11, under
Stille conditions. Partial hydrolysis of the phosphonate ester
gave compound 4.
Prior to committing our valuable intermediates 4 and 5, we
investigated the assembly of a phosphonomacrolactone in
a model system (Scheme 6). There are many methods for
phosphonate ester formation, but recent reports encouraged
us to use Mitsunobu conditions.8b Thus, condensation of the
simplified phosphonate 1912 and dec-9-en-1-ol via a Mitsu-
nobu reaction20 gave 20 in moderate yield. Closure of the

K. P. Jayasundera et al. / Tetrahedron 63 (2007) 10077–10082
10079
i
PrO
S
S
O
O
i
PrO
O
P
P
OEt
OH
16
O
1. DMAD, THF
n
1. BuLi, THF
2. CH2=CH(CH2)3Br
2. alcohol 5, PPh3
THF, RT, 4 h
(26%)
i
PrO
(~70%)
i
S
PrO
22
4
S
S
S
Grubbs II
toluene
(48%)
7
1. PCC
(30%)
2. HS(CH2)3SH
i
PrO
O
O
P
OH
RO
O
17
i
PrO
S
n
1. BuLi, -20 °C
THF
23
S
7
2. compound 6
Scheme 7. Formation of the hapten macrocycle.
S
(93%)
S
TBAF
THF
(72%)
18 R = TBDMS
R = H
3. Conclusion
5
We have prepared compound 23, an advanced intermediate
en route to a transition-state analog for the hydrolysis of
the lactone functionality in zearalenone. The phosphonic
acid was introduced onto the aromatic ring via an anionic
phospho-Fries rearrangement. Phosphonate ester formation,
via a Mitsunobu reaction, gave a disappointing yield in the
formation of model system 20 and this deteriorated in the
real system 22. Ring closing metathesis was an effective
means of forming the macrocycle in zearalenone itself10
and the model system 21 (Scheme 6). The yield was low
in the real system. Nevertheless, sufficient material can be
produced in a convergent manner, to investigate the genera-
tion of antibodies that might catalyze the degradation of
zearalenone.
Scheme 5. Assembly of the aliphatic fragment.
O
OEt
O
OEt
OH
P
1. DMAD, THF
P
O
2.
OH
THF, rt,74 h
19
20
(48%)
Grubbs II
toluene
(90%)
O
OEt
O
P
4. Experimental
21
Scheme 6. Model system for macrocycle formation.
4.1. General details
All reactions were conducted under a dry nitrogen atmo-
sphere unless otherwise noted. Reagents were obtained
from commercial suppliers and used directly with the
following exceptions. Tetrahydrofuran was dried over
sodium/benzophenone and distilled prior to use. Diisopropyl-
ethylamine, triethylamine, and pyridine were dried and
distilled from CaH2 and stored over KOH pellets. Flash
chromatography was performed using Scharlau 60 silica
gel (230–400 mesh) with the indicated solvents. Thin layer
chromatography (TLC) was carried out on precoated silica
plates (Merck Kieselgel 60 F254) and compounds were visu-
alized by UV fluorescence or by staining with anisaldehyde
14-membered ring to give 21 was accomplished in excellent
yield via standard RCM conditions.
Turning our attention to the more complex system, we en-
countered considerable difficulties (Scheme 7). The best
yield obtained for the Mitsunobu reaction was 26% and
this required the use of 2 equiv of the acid (so-called alco-
hol-limiting conditions). Previous experience21 encouraged
us to prepare the acid chloride of 4, but this failed to con-
dense at all with alcohol 5, even in the presence of silver
cyanide.
1
or phosphomolybdic acid. H and 13C NMR spectra were
obtained using either a JEOL JNM-GX270W or a Bruker
Avance 400 spectrometer. Chemical shifts for spectra in
CDCl3 are given in parts per million (ppm) downfield from
tetramethylsilane as internal standard (1H) or relative to
residual solvent (13C). High resolution mass spectra were
recorded using a VG7070 mass spectrometer operating at
nominal accelerating voltage of 70 eV.
The RCM step was also much lower yielding than in the
model system. We suspected that the dithiane functionality
may be the cause of problems in one or both of these crucial
steps. We therefore removed the dithiane from alcohol 5
(HCl, DMSO) and performed the esterification and RCM
reactions with no improvements in yields.

10080
K. P. Jayasundera et al. / Tetrahedron 63 (2007) 10077–10082
4.1.1. (2,4-Diisopropoxy-6-vinyl-phenyl)phosphonic acid
monoethyl ester (4). A solution of diester derivative 11
(100 mg, 0.8 mmol, 1 equiv) in EtOH (2 mL) and 2 M
NaOH (2 mL) was heated at reflux for 3 h. The mixture
was concentrated to remove the ethanol, diluted with water
(8 mL), neutralized with concd HCl, and extracted with
EtOAc (2ꢀ15 mL). The combined organic extracts were
washed with water (20 mL), dried over MgSO4, filtered,
and concentrated to give 4 as a colorless oil (191 mg,
90%). This crude product was used without further purifica-
tion. Rf 0.25 (10:1 CH2Cl2–MeOH). 1H NMR (CDCl3,
400 MHz) d 1.28 (3H, t, J 7.0 Hz, OCH2CH3), 1.35 (6H,
d, J 6.0 Hz, CHMe2), 1.39 (6H, d, J 6.0 Hz, CHMe2), 4.04
(2H, app.p, J 7.0 Hz, POCH2CH3), 4.62 (2H, hept., J
6.0 Hz, 2ꢀCHMe2ꢀ2), 5.29 (1H, d, J 10.8 Hz, CH]CH2
cis), 5.51 (1H, dd, J 17.2, 1.4 Hz, CH]CH2 trans), 6.39
(1H, dd, J 5.5, 2.3 Hz, ArH), 6.66 (1H, dd, J 5.5, 2.3 Hz,
ArH), 7.68 (1H, dd, J 17.2, 10.8 Hz, CH]CH2); 13C
NMR (CDCl3, 100 MHz) d 16.2 (d, J 7 Hz), 21.8, 22.0,
61.2 (d, J 6 Hz), 69.9, 71.6, 101.2 (d, J 10 Hz), 106.6 (d, J
15 Hz), 107.7 (d, J 193 Hz), 116.0, 137.7 (d, J 4 Hz),
146.2 (d, J 10 Hz), 161.7, 161.7 (d, J 6 Hz); HRMS (EI+):
M+, found 328.14442. C16H25O5P requires 328.14396.
hexanes–EtOAc to give 14 (620 mg, 52%). Rf 0.33 (3:1 hex-
anes–EtOAc). H NMR (CDCl3, 270 MHz) d 0.07 (6H, s,
1
SiMe2), 0.89 (9H, s, SitBu), 1.16 (3H, d, J 6.2 Hz, Me-
CHOTBDMS), 1.5–1.7 (4H, m, CH2CH2CH2OH), 3.63
(2H, m, CH2OH), 3.89 (1H, m, CHOTBDMS); 13C NMR
(CDCl3, 100 MHz) d ꢂ4.8, ꢂ4.5, 18.1, 23.2, 25.8, 28.5,
36.0, 63.0, 68.4; HRMS (FAB+): MH+, found 219.1777.
C11H27O2Si requires 219.1780.
4.1.4. ( )-2-tert-Butyldimethylsilyloxy-5-iodopentane (6).
Triphenylphosphine (528 mg, 2 mmol, 2 equiv), imidazole
(204 mg, 3 mmol, 3 equiv), and iodine (764 mg, 3 mmol,
3 equiv) were added sequentially to a solution of primary al-
cohol 14 (218 mg, 1 mmol, 1 equiv) in THF (10 mL) at 0 ꢁC
under nitrogen. The mixture was warmed to rt and stirred for
3 h. The mixture was filtered through a pad of silica gel and
the filtrate was concentrated. The residue was purified by
flash chromatography, eluting with 10:1 hexanes–EtOAc to
give the iodide derivative 6 as a colorless oil (308 mg,
94%). Rf 0.60 (10:1 Hex–EtOAc). 1H NMR (CDCl3,
400 MHz) d 0.03 (6H, s, SiMe2), 0.87 (9H, s, SitBu), 1.11
(3H, d, J 6.0 Hz, MeCHOTBDMS), 1.46–1.50 (2H, m,
CH2CH2CH2I), 1.79–1.93 (2H, m, CH2CH2I), 3.17 (2H, t,
J 7.0 Hz, CH2I), 3.80 (1H, sext., J 6.0 Hz, CHOTBDMS);
13C NMR (CDCl3, 100 MHz) d ꢂ4.8, ꢂ4.4, 7.3, 18.0,
23.8, 25.8, 29.8, 40.3, 67.6; HRMS (EI+): MH+, found
329.07945. C11H26IOSi requires 329.07977.
4.1.2. ( )-4-tert-Butyldimethylsilyloxypentanoic acid tert-
butyldimethylsilyl ester (13). g-Valerolactone (12) (2.60 g,
26 mmol, 1.0 equiv) was dissolved in a mixture of water
(15 mL) and dioxane (15 mL). Sodium hydroxide (1.038 g,
26 mmol, 1.0 equiv) was added and the solution stirred at rt
for 30 min. The mixture was concentrated and dried over
P2O5 to give the sodium salt of 4-hydroxypentanoic acid as
a colorless solid. This was suspended in DMF (60 mL). tert-
Butyldimethylsilylchloride (11.75 g, 78 mmol, 3.0 equiv),
imidazole (7.08 g, 104 mmol, 4.0 equiv), and DMAP
(1.59 g, 13 mmol, 0.50 equiv) were added. The mixture was
stirred at rt overnight and then at 50 ꢁC for 1 h. Water
(60 mL) was added and the mixture extracted with diethyl
ether (3ꢀ35 mL). The combined organic layers were washed
with 10% citric acid (20 mL) and brine (20 mL), dried over
MgSO4, filtered, and concentrated. The residue was purified
by distillation to give 13 as a colorless oil (6.84 g, 91%).
Rf 0.72 (3:1 hexanes–EtOAc); bp 110 ꢁC (0.1 mmHg).
1H NMR (CDCl3, 270 MHz) d 0.04 (6H, s, SiMe2),
0.26 (6H, s, SiMe2), 0.88 (9H, s, SitBu), 0.93 (9H, s,
SitBu), 1.13 (3H, d, J 6.2 Hz, MeCHOTBDMS), 1.68
(2H, m, CH2CH2COOTBDMS), 2.38 (2H, t, J 7.5 Hz,
CH2COOTBDMS), 3.86 (1H, m, CHOTBDMS); 13C NMR
(CDCl3, 67.5 MHz) d ꢂ4.8, ꢂ4.4, 17.6, 18.1, 23.8, 25.6,
25.9, 32.0, 34.6, 67.4, 174.1; HRMS (FAB+): MH+, found
347.2428451. C17H39O3Si2 requires 347.243777.
4.1.5. Hex-5-enal.22 Molecular sieves (2.5 g, 4 A) were
˚
added to a solution of 5-hexen-1-ol (1.00 g, 10 mmol,
1.0 equiv) in CH2Cl2 (100 mL) at 0 ꢁC. The mixture was
stirred for 5 min. Pyridinium chlorochromate (3.23 g,
15 mmol, 1.5 equiv) was added in portions over a period
of 5 min, and the mixture was stirred at rt for 4 h. The reac-
tion mixture was diluted with diethyl ether (100 mL) and fil-
tered through a mixture of silica gel, CeliteÔ, and activated
charcoal. The dark brown residue was washed with diethyl
ether (40 mL). The greenish yellow solution was concen-
trated tow10 mL and transferred to a round bottomed flask.
Short-path distillation led to the isolation of hex-5-enal as
1
a colorless liquid (325 mg, 32%). Bp 38 ꢁC (1 atm). H
NMR (CDCl3, 400 MHz) d 1.72 (2H, pent., J 7.3 Hz,
CH2CH2CH2), 2.07 (2H, q, J 7.3 Hz, CH2CH]CH2), 2.45
(2H, td, J 7.3, 1.6 Hz, CH2CH]O), 4.90–5.09 (2H, m,
CH]CH2), 5.74 (1H, ddt,
J 17.0, 10.7, 7.3 Hz,
CH]CH2), 9.74 (1H, d, J 1.6 Hz, CH]O); 13C NMR
(CDCl3, 100 MHz) d 21.1, 32.9, 43.0, 115.5, 137.5, 202.5.
4.1.6. 2-(4-Pentenyl)-1,3-dithiane (7). Propane-1,3-dithiol
(101 mL, 108 mg, 1 mmol, 1 equiv) was added to a solution
of hex-5-en-al (100 mg, 1 mmol, 1 equiv) in CHCl3 (2 mL)
at rt, stirred for 1 h, and then cooled to ꢂ10 ꢁC. BF3$OEt2
(128 mL, 144 mg, 1 mmol, 1 equiv) was added dropwise
and the resulting solution was allowed to warm to rt and
stirred for 17 h. The mixture was washed with water
(3ꢀ5 mL), 10% aqueous NaOH (5 mL), and water (5 mL),
dried over MgSO4, filtered, and concentrated. The residue
was purified by flash chromatography, eluting with 10:1 hex-
anes–EtOAc to give the dithiane derivative 7 as a colorless oil
(177 mg, 94%). Rf 0.43 (10:1 Hex–EtOAc). 1H NMR
(CDCl3, 400 MHz) d 1.55–1.63 (2H, m, CH2CH2CH]CH2),
1.71–1.79 (2H, m, CH2CH2S), 1.80–1.88 (2H, m, CH2CHS),
2.03–2.12 (2H, m, CH2CH]CH2), 2.77–2.90 (4H, m,
4.1.3. ( )-4-tert-Butyldimethylsilyloxy-pentan-1-ol (14).
A solution of 13 (910 mg, 2.6 mmol, 1.0 equiv) in diethyl
ether (3 mL) was added dropwise over 10 min to a suspen-
sion of LiAlH4 (220 mg, 5.8 mmol, 2.2 equiv) in diethyl
ether (7.4 mL) at 0 ꢁC. The mixture was stirred at 0 ꢁC for
1 h 45 min and then at rt for 10 min. The reaction was
quenched by the addition of a few drops of methanol. The
mixture was diluted with EtOAc (70 mL) and washed with
brine (35 mL). The combined aqueous layers were extracted
with EtOAc (20 mL). The combined organic extracts were
dried over MgSO4, filtered, and concentrated. The residue
was purified by flash chromatography, eluting with 10:1

K. P. Jayasundera et al. / Tetrahedron 63 (2007) 10077–10082
10081
CH2Sꢀ2), 4.02 (1H, t, J 7.0 Hz, SCHS), 4.93–5.03 (2H, m,
CH]CH2), 5.72–5.82 (1H, m, CH]CH2); 13C NMR
(CDCl3, 100 MHz) d 25.7, 26.0, 30.4 (2C), 33.2, 34.8,
47.4, 114.9, 138.0; HRMS (EI): M+, found 188.06936.
C9H16S2 requires 188.06934.
gradient from 10:1 to 5:1 to give the ester derivative 20 as
a colorless oil (135 mg, 48%). Rf 0.25 (2:1 Hex–EtOAc).
1H NMR (CDCl3, 400 MHz) d 1.18–1.36 (13H, m, CH2ꢀ5
and OCH2CH3), 1.58–1.66 (2H, m, POCH2CH2), 1.96–
2.06 (2H, m, CH2CH]CH2), 3.92–4.16 (4H, m,
POCH2ꢀ2), 4.86–5.02 (2H, m, CH2CH]CH2), 5.35 (1H,
d, J 10.8 Hz, ArCH]CH2 cis), 5.70 (1H, d, J 17.4 Hz,
ArCH]CH2 trans), 5.74–5.82 (1H, m, CH2CH]CH2),
7.29–7.44 (2H, m, ArH), 7.49 (1H, t, J 7.0 Hz, ArH), 7.63
(1H, t, J 7.0 Hz, ArH), 7.3 (1H, dd, J 17.4, 10.8 Hz,
ArCH]CH2); 13C NMR (CDCl3, 100 MHz) d 16.2 (d, J
7 Hz), 25.4, 28.8, 28.9, 29.0, 29.2, 30.3 (d, J 7 Hz), 33.7,
62.0 (d, J 5 Hz), 66.0 (d, J 5 Hz), 114.0, 116.7, 125.6 (d, J
181 Hz), 126.1 (d, J 15 Hz), 127.1 (d, J 15 Hz), 134.0 (d, J
3 Hz), 134.1 (d, J 10 Hz), 135.3 (d, J 5 Hz), 139.1, 141.2
4.1.7. 2-tert-Butyldimethylsilyloxy-10-undecen-6-1,3-di-
thiane (18).19 nBuLi (350 mL of 1.5 M solution in hexane,
33.6 mg, 0.525 mmol, 1.05 equiv) was added dropwise to
a stirred solution of dithiane 7 (94 mg, 0.5 mmol,
1.00 equiv) in THF (3 mL) at ꢂ20 ꢁC under nitrogen. The
mixture was stirred at ꢂ20 ꢁC for 2 h. The temperature
was decreased to ꢂ78 ꢁC and a solution of freshly prepared
iodide 6 (180 mg, 0.55 mmol, 1.10 equiv) in THF (2 mL)
was added dropwise. The temperature was gradually
warmed to ꢂ20 ꢁC and stirred for 3 h. The reaction was
quenched with aq NaHCO3 (2 mL) and extracted with di-
ethyl ether (2ꢀ15 mL). The combined organic layers were
washed with water (15 mL) and brine (15 mL), dried over
MgSO4, filtered, and concentrated. The residue was purified
by flash chromatography, eluting with 20:1 hexanes–EtOAc
to give dithiane derivative 18 as a colorless oil (181 mg,
93%). Rf 0.48 (10:1 Hex–EtOAc). 1H NMR (CDCl3,
400 MHz) d 0.06 (3H, s, SiMe), 0.07 (3H, s, SiMe), 0.90
(9H, s, SitBu), 1.14 (3H, d, J 6.1 Hz, MeCHOTBDMS),
1.22–1.52 (6H, m), 1.83–1.99 (6H, m), 2.08 (2H, q, J
7.0 Hz, CH2CH]CH2), 2.79–2.82 (4H, m, CH2Sꢀ2), 3.81
(1H, app. sext., J 6.1 Hz, CHOTBDMS), 4.97–5.07 (2H,
m, CH]CH2), 5.80 (1H, ddt, J 17.2, 10.2, 7.0 Hz,
CH]CH2); 13C NMR (CDCl3, 100 MHz) d ꢂ4.7, ꢂ4.4,
18.1, 20.4, 23.4, 23.8, 25.6, 25.9, 33.7, 37.4, 38.4, 39.8,
53.2, 68.5, 115.0, 138.3; HRMS (EI): M+, found
388.23008. C20H40OS2Si requires 388.22899.
(d,
J
10 Hz); HRMS (EI): M+, found 350.20067.
C20H31O3P requires 350.20108.
4.1.10. 2-Ethoxy-(2,3-benzo-1-oxa-2-phosphacyclotetra-
dec-5-ene) 2-oxide (21). Grubbs’ second generation catalyst
(12 mg, 0.014 mmol, 5 mol %) was added to a solution of es-
ter 20 (100 mg, 0.28 mmol, 1 equiv) in toluene (70 mL). The
mixture was stirred at 80 ꢁC under nitrogen for 23 h, concen-
trated, and the resulting residue purified by flash chromato-
graphy, eluting with 2:1 hexanes–EtOAc to give 21 as
a colorless oil (82 mg, 90%). Rf 0.13 (2:1 Hex–EtOAc). 1H
NMR (CDCl3, 400 MHz) d 1.23–1.63 (12H, m, CH2ꢀ6),
1.25 (3H, t, J 6.8 Hz, POCH2CH3), 2.24 (2H, q, J 6.5 Hz,
CH]CHCH2), 3.91–4.16 (4H, m, POCHꢀ2), 6.12 (1H,
dt, J 15.7, 6.5 Hz, ArCH]CH), 7.03 (1H, d, J 15.7 Hz,
ArCH]CH), 7.18–7.23 (1H, m, ArH), 7.40 (1H, t, J
7.3 Hz, ArH), 7.56 (1H, t, J 7.3 Hz, ArH), 7.91 (1H, dd, J
14.8, 7.3 Hz, ArH); 13C NMR (CDCl3, 100 MHz) d 16.3
(d, J 6 Hz), 22.9, 24.5, 25.7, 26.1, 26.2, 29.1 (d, J 7 Hz),
31.0, 62.3 (d, J 5 Hz), 64.9 (d, J 7 Hz), 124.8 (d, J
185 Hz), 125.8 (d, J 14 Hz), 126.1 (d, J 14 Hz), 128.4 (d, J
5 Hz), 132.5 (d, J 3 Hz), 133.7, 134.2 (d, J 10 Hz), 141.3
(d, J 9 Hz); HRMS (EI): M+, found 322.16973. C18H27O3P
requires 322.16978.
4.1.8. 2-(4-Hydroxypentyl)-2-(4-pentenyl)-1,3-dithiane
(5). TBAF (220 mL, 1 M solution in THF, 0.22 mmol,
1.1 equiv) was added to a solution of silyl ether 18 (78 mg,
0.2 mmol, 1.0 equiv) in THF (1 mL) at rt under nitrogen.
The mixture was stirred overnight, and then filtered through
a pad of silica gel. The filtrate was concentrated and the resi-
due purified by flash column chromatography, eluting with
5:1 hexanes–EtOAc to give alcohol 5 as a colorless oil
(40 mg, 72%). Rf 0.13 (5:1 Hex–EtOAc). 1H NMR
(CDCl3, 400 MHz) d 1.16 (3H, d, J 6.2 Hz, MeCHOH),
1.39–1.53 (6H, m), 1.83–1.92 (6H, m), 2.06 (2H, q, J
7.0 Hz, CH2CH]CH2), 2.77–2.78 (4H, m, CH2Sꢀ2), 3.78
(1H, sext., J 6.2 Hz, CHOH), 4.96 (1H, dd, J 10.2, 2.0 Hz,
CH]CH2 cis), 5.00 (1H, dd, J 17.2, 2.0 Hz, CH]CH2
trans), 5.78 (1H, ddt, J 17.2, 10.2, 7.0 Hz, CH]CH2); 13C
NMR (CDCl3, 100 MHz) d 20.4, 23.3, 23.5, 25.4, 25.9
(2C), 33.6, 37.5, 38.1, 39.2, 53.1, 67.8, 115.0, 138.2;
HRMS (EI): M+, found 274.14275. C14H26OS2 requires
274.14251.
4.1.11. Ethyl 2-[6-(1,3-dithiane)undec-10-enyl] (4,6-diiso-
propoxy-2-vinylphenyl)phosphonate (22).
A solution
of alcohol 5 (60 mg, 0.22 mmol, 1.0 equiv) and triphenyl-
phosphine (58 mg, 0.22 mmol, 1.0 equiv) in THF (2 mL)
was added dropwise to a solution of acid 4 (144 mg,
0.44 mmol, 2.0 equiv) and dimethylazodicarboxylate (32 mg,
0.22 mmol, 1.0 equiv) in THF (3 mL) at rt. The mixture was
stirred under an atmosphere of nitrogen for 3 h, concentrated,
and the residue purified by flash chromatography, eluting
with hexanes–EtOAc with a gradient from 10:1 to 5:1 to
give the ester derivative 22 as a colorless oil (33 mg, 26%).
Rf 0.28 (2:1 Hex–EtOAc). 1H NMR (CDCl3, 400 MHz)
d 1.16 (3H, d, J 6.2 Hz, CH(OR)Me), 1.25 (3H, td, J 7.0,
4.4 Hz, POCH2CH3), 1.31 (12H, d, J 6.0 Hz, OCHMe2ꢀ2),
1.37–2.06 (14H, m), 2.65–2.77 (4H, m, CH2Sꢀ2), 3.90–
4.13 (2H, m, POCH2), 4.48–4.63 (3H, m, CHMe2ꢀ2 and
CH(OR)Me), 4.90–5.05 (2H, m, CH2CH]CH2), 5.23 (1H,
d, J 10.8 Hz, ArCH]CH2 cis), 5.44 (1H, dd, J 17.2,
1.6 Hz, ArCH]CH2 trans), 5.73 (1H, ddt, J 17.2, 10.8,
6.8 Hz, CH2CH]CH2), 6.31 (1H, d, J 4.0 Hz, ArH), 6.52
(1H, dd, J 4.0, 2.4 Hz, ArH), 7.81 (1H, dd, J 17.2, 10.8 Hz,
ArCH]CH2); 13C NMR (CDCl3, 100 MHz) d 16.2, 20.0,
21.5, 22.0 (2C), 22.1 (3C), 23.3, 25.6, 26.0, 33.8, 37.7,
4.1.9. Ethyl non-8-enyl (2-vinylphenyl)phosphonate (20).
A solution of dec-9-en-1-ol (156 mL, 137 mg, 0.88 mmol,
1.1 equiv) and triphenylphosphine (231 mg, 0.88 mmol,
1.1 equiv) in THF (8 mL) was added dropwise to a solution
of acid 19 (170 mg, 0.8 mmol, 1.0 equiv) and dimethylazo-
dicarboxylate (174 mL, 128 mg, 0.88 mmol, 1.1 equiv) in
THF (8 mL) at rt. The mixture was stirred under nitrogen
for 4 h, concentrated, and the residue purified by flash chro-
matography, eluting with hexanes–EtOAc, with solvent

10082
K. P. Jayasundera et al. / Tetrahedron 63 (2007) 10077–10082
Workshop, Munich, June 2–4, 1997; (c) Towers, N. R.;
Sprosen, J. M. NZ Vet. J. 1993, 41, 223–224.
4. (a) El-Sharkaway, S.; Abdul-Hajj, Y. J. Xenobiotica 1988, 18,
365–371; (b) Megharaj, M.; Garthwaite, I.; Thiele, J. H. Lett.
Appl. Microbiol. 1997, 24, 329–333.
38.2, 53.0, 60.9, 61.0, 69.7, 70.4, 73.0, 100.5, 105.7, 107.2 (J
154 Hz), 114.9, 115.5, 138.1, 138.2, 147.0, 161.6, 162.0;
HRMS (EI): M+, found 584.27636. C30H49O5PS2 requires
584.27591.
4.1.12. 2-Ethoxy-2,3-(10,50,-diisopropoxy)benzo-10-(1,3-
dithiane)-14-methyl-1-oxa-2-phosphacyclotetradec-5-
ene 2-oxide (23). Grubbs’ second generation catalyst
(8.5 mg, 0.01 mmol, 10 mol %) was added to a solution of
ester 22 (58.5 mg, 0.1 mmol, 1 equiv) in toluene (50 mL).
The reaction mixture was stirred at 80 ꢁC under nitrogen
for 23 h, concentrated, and the resulting residue purified
by flash chromatography, eluting with 2:1 hexanes–EtOAc
to give macrolactone 23 as a colorless oil (27 mg, 48%).
Rf 0.30 (2:1 Hex–EtOAc). 1H NMR (CDCl3, 400 MHz)
d 1.28–1.36 (18H, m, MeCHO, POCH2CH3, OCHMe2ꢀ2),
1.47–2.37 (14H, m), 2.73–2.83 (4H, m, CH2Sꢀ2), 3.84–
3.99 (1H, POCH2), 4.02–4.15 (1H, m, POCH2), 4.50 (1H,
pent, J 6.0 Hz, OCHMe2), 4.58 (1H, pent, J 6.0 Hz,
OCHMe2), 4.72–4.81 (1H, m, MeCHO), 5.94 (1H, dt, J
15.8, 7.1 Hz, ArCH]CH), 6.28 (1H, dd, J 5.0, 2.2 Hz,
ArH), 6.49 (1H, dd, J 5.0, 2.2 Hz, ArH), 7.56 (1H d, J
15.8 Hz, ArCH]CH); 13C NMR (CDCl3, 100 MHz)
d 12.7, 16.4, 21.9 (2C), 22.0 (4C), 23.9, 25.7, 26.0, 30.2,
35.6, 37.2, 37.5, 53.4, 61.2, 61.3, 69.7, 70.8, 71.3, 100.6,
107.3 (d, J 193 Hz), 115.1, 132.5, 147.5, 161.5, 161.6;
HRMS (EI): M+, found 556.24517. C28H45O5PS2 requires
556.24461.
5. http://www.agvax.com/animal_health/sheep/androvax/index.
htm.
6. For example, antibodies have been developed for the hydrolysis
of cocaine: Landry, D. W.; Zhao, K.; Yang, G. X.-Q.; Glickman,
M.; Georgiadis, T. M. Science 1993, 259, 1899–1901.
7. (a) Formation of a six-membered ring: Napper, A. D.;
Benkovic, S. J.; Tramontano, A.; Lerner, R. A. Science 1987,
237, 1041–1043; (b) Formation of a 14-membered ring:
Pungente, M. D.; Weiler, L.; Ziltener. Can. J. Chem. 2002,
30, 1643–1645.
8. For previous syntheses of phosphonomacrolactones, see: (a)
Smith, W. W.; Bartlett, P. A. J. Am. Chem. Soc. 1998, 120,
4622–4628; (b) Pungente, M. D.; Weiler, L. Org. Lett. 2001,
3, 643–646.
9. Zearalenone has been conjugated to a carrier protein via the
ketone previously, generating antibodies which are used in an
ELISA assay for the toxin: Dixon, D. E.; Warner, R. L.;
Ram, B. P.; Hart, L. P.; Pestka, J. J. J. Agric. Food Chem.
1987, 35, 122–126.
€
10. Furstner, A.; Thiel, O. R.; Kindler, N.; Bartkowska, B. J. Org.
Chem. 2000, 65, 7990–7995.
11. For a review of dithiane couplings: Smith, A. B., III; Adams,
C. M. Acc. Chem. Res. 2004, 37, 365–377.
12. Jayasundera, K. P.; Watson, A. J.; Taylor, C. M. Tetrahedron
Lett. 2005, 46, 4311–4313.
13. (a) Atherton, F. R.; Todd, A. R. J. Chem. Soc. 1947, 674–676;
(b) Silverberg, L. J.; Dillon, J. L.; Vemishetti, P. Tetrahedron
Lett. 1996, 37, 771–774.
14. Taylor, C. M.; Watson, A. J. Curr. Org. Chem. 2004, 8, 623–
636.
Acknowledgements
We thank the Massey University Research Fund (MURF) for
a postdoctoral fellowship to C.M.T and K.P.J. We thank Drs.
Chris Miles, Ian Garthwaite, Mark Dines, and Neale Towers
of AgResearch (Ruakura, NZ) for helpful discussions.
15. Amino, Y.; Eto, H.; Eguchi, C. Chem. Pharm. Bull. 1989, 37,
1481–1487.
16. (a) Kalivretenos, A.; Stille, J. K.; Hegedus, L. S. J. Org. Chem.
1991, 56, 2883–2894; (b) Demeke, D.; Forsyth, C. J.
Tetrahedron 2002, 58, 6531–6544.
17. (a) Chung, S. K.; Dunn, L. B., Jr. J. Org. Chem. 1984, 49, 935–
939; (b) Grig, R.; Markandu, J.; Surendrakuma, S.; Thornton-
Pett, M.; Warnock, W. J. Tetrahedron 1992, 48, 10399–10422;
(c) Suenaga, K.; Araki, K.; Sengoku, T.; Uemura, D. Org. Lett.
2001, 3, 527–529; (d) Araki, K.; Seuenaga, K.; Sesngoku, T.;
Uemura, D. Tetrahedron 2002, 58, 1983–1995.
Supplementary data
1H and 13C NMR spectra for compounds 4, 5, 6, 7, 13, 14,
18, 20, 21, 22, and 23. Supplementary data associated with
this article can be found in the online version, at
doi:10.1016/j.tet.2007.07.042.
References and notes
18. It is implied that material of superior quality was obtained this
way: Yamaguchi, Y.; Yamada, H.; Hayakawa, K.; Kanematsu,
K. J. Org. Chem. 1987, 52, 2040–2046.
19. Compound 18 has been prepared via a different approach:
Bracher, F.; Krauss, J. Monatsh. Chem. 2001, 132, 805–811.
20. For the introduction of the Mitsunobu reaction to phosphonate
ester formation, see: (a) Campbell, D. A. J. Org. Chem. 1992,
57, 6331–6335; (b) Campbell, D. A.; Bermak, J. C. J. Org.
Chem. 1994, 59, 658–660.
21. (a) Smith, A. B., III; Taylor, C. M.; Benkovic, S. J.;
Hirschmann, R. Tetrahedron Lett. 1994, 35, 6853–6856; (b)
Hirschmann, R.; Yager, K. M.; Taylor, C. M.; Witherington, J.;
Sprengeler, P. A.; Phillips, B. W.; Moore, W.; Smith, A. B., III.
J. Am. Chem. Soc. 1997, 119, 8177–8190.
1. (a) Stob, M.; Baldwin, R. S.; Tuite, J.; Andrews, F. N.; Gillette,
K. G. Nature 1962, 196, 1318; (b) Urry, W. H.; Wehrmeister,
H. L.; Hodge, E. B.; Hidy, P. H. Tetrahedron Lett. 1966, 27,
3109–3114.
2. (a) Placinta, C. M.; D’Mello, J. P. F.; Macdonald, A. M. C.
Animal Feed Sci. Technol. 1999, 78, 21–37; (b) Newsome, R.
Food Technol. 2006, 60, 51–58; (c) Bennett, J. W.; Klich, M.
Clin. Microbiol. Rev. 2003, 16, 497–516; (d) Conkova, E.;
ꢀ
Laciakova, A.; Kovac, G.; Seidel, H. Vet. J. 2003, 165,
214–220.
3. (a) De Menna, M. E.; Lauren, D. R.; Poole, P. R.; Mortimer,
P. H.; Hill, R. A.; Agnew, M. P. NZ J. Agr. Res. 1987, 30,
499–504; (b) Towers, N. R. 19th German Mycotoxin
22. Spino, C.; Barriault, N. J. Org. Chem. 1999, 64, 5292–5298.