A chemoenzymatic total synthesis of the undecenolide (-)-cladospolide B via a mid-stage ring-closing metathesis and a late-stage photo-rearrangement of the E-isomer

Article abstract of DOI:10.1039/b417685e

A sixteen-step synthesis of the twelve-membered macrolide (-)-cladospolide B (2) from the microbially-derived cis-1,2-dihydrocatechol 5 is described. Pivotal steps include the ring-closing metathesis (RCM) of diene 12 to give the ten-membered lactone 13 t

Full text of DOI:10.1039/b417685e

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A R T I C L E
A chemoenzymatic total synthesis of the undecenolide
−)-cladospolide B via a mid-stage ring-closing metathesis and a
late-stage photo-rearrangement of the E-isomer
(
Kerrie A. B. Austin, Martin G. Banwell,* David T. J. Loong, A. David Rae and
Anthony C. Willis
Research School of Chemistry, Institute of Advanced Studies, The Australian National
University, Canberra, ACT 0200, Australia. E-mail: mgb@rsc.anu.edu.au
Received 23rd November 2004, Accepted 21st January 2005
First published as an Advance Article on the web 15th February 2005
A sixteen-step synthesis of the twelve-membered macrolide (−)-cladospolide B (2) from the microbially-derived
cis-1,2-dihydrocatechol 5 is described. Pivotal steps include the ring-closing metathesis (RCM) of diene 12 to give the
ten-membered lactone 13 together with small amounts of the head-to-tail and head-to-head dimers 14 and 15,
respectively. The saturated lactol 19 derived from compounds 13 and 14 readily participates in a Wadsworth–Horner–
Emmons reaction to give the E-configured a,b-unsaturated ester 20. This last compound is then converted, through
application of a Yamaguchi lactonisation reaction on the derived acid 22, into the macrolide 23 which, upon removal
of the bis-acetal protecting group, affords compound 24, the E-isomer of target 2. Irradiation of a benzene solution
of compound 24 results in its partial photoisomerisation to (−)-cladospolide B (2).
Introduction
Hitherto, no total synthesis of any of the remaining members
of the cladospolide family has been published, although it has
been noted that the absolute configuration of cladospolide
B has been determined by such means and is as illustrated.
Given the dramatic difference in effect that compounds 1 and
Cladospolides A–D (1–4, respectively) represent the currently
known members of a class of undecenolides isolated from
various Cladosporium species of fungi. Cladospolide B (2),
together with an isomer (isocladospolide B), has also been
isolated from the sponge-derived fungus Cladosporium herbarum
by Ireland and co-workers. Congeners A–C have been shown
to inhibit shoot elongation in rice seedlings, and isomer 3
does so without causing signs of necrosis, thus suggesting
that this compound, at least, inhibits gibberellin biosynthesis.
3
1–5
2
exert on the growth of lettuce seedlings, the development
of a synthesis of the latter would seem worthwhile since such
work might offer the capacity to determine which structural
features are responsible for the divergent biological properties
of these systems. To such ends, we have pursued and now detail
a synthesis of (−)-cladospolide B involving preparation of the
E-isomer and photoisomerisation of this system, in the final step
of the reaction sequence, to deliver target 2. The benefit of this
approach is that the E-isomer could also be subject to biological
evaluation as part of a program to establish a detailed SAR
profile for the cladospolides and related systems.
6
3
Fascinatingly, cladospolide A also inhibits root elongation in
lettuce seedlings whilst cladospolide B, which only varies in the
configuration about the D -double bond and (apparently – see
2
,3
end of Results and discussion section) at C4, has the opposite
2
effect. Cladospolide D (4), the structure of which remains to
be fully defined, exhibits antimicrobial activity against Mucor
racemosus and Pyricularia oryzae with IC50 values of 0.15 and
−
1
4
Results and discussion
2
9 lg ml , respectively. Compounds 1 and 2 have also been
7
patented as inhibitors of allergy and inflammation.
The early stages of the reaction sequence employed in es-
tablishing the present synthesis of (−)-cladospolide B are
shown in Scheme 1. This starts with the same enantiomerically
pure cis-1,2-dihydrocatechol, 5, used in our total synthesis of
cladospolide A, but of necessity, inversion of configuration
at C2 is required at some point. In the event, and as part
of a more general program to extend the synthetic utility of
metabolites such as compound 5, we have recently reported
10
simple methods for the conversion of this compound into
congener 6. This involves initial and selective hydrogenation
of the non-chlorinated double-bond within compound 5 then
selective inversion at the centre bearing the allylic hydroxyl group
using a Mitsunobu reaction and involving p-nitrobenzoic acid as
nucleophile. Hydrolysis of the resulting mono-p-nitrobenzoate
ester then delivered the required trans-diol 6 in 59% yield over
the three steps just described.
8
Recently we disclosed an eleven-step total synthesis of (−)-
Trans-diol 6 was protected as the corresponding bis-acetal 7
11
12
cladospolide A (1) from the cis-1,2-dihydrocatechol 5, a starting
material available in large quantity and enantiomerically pure
form through microbial dihydroxylation of chlorobenzene. This
work represents the shortest of the three distinct total syntheses
of compound 1 reported thus far and incorporates a pivotal ring-
closing metathesis (RCM) step, a process that has found increas-
(92%) using protocols developed by Frost and Ley. This last
compound was obtained in a single diastereoisomeric form and
with the illustrated configurations at the anomeric centres as
determined by single-crystal X-ray analysis of a derivative (vide
infra). Chloroalkene 7 was subject to ozonolytic cleavage in the
presence of methanol and after reductive work-up with dimethyl
sulfide the aldehydic ester 8 was obtained. Wittig methylenation
9
ing application in the synthesis of macrolides in recent years.
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8
1 0 8 1

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Scheme 1
of aldehyde 8 gave the corresponding unsaturated ester 9 (67%
overall yield from diol 6), which was saponified under the usual
conditions to give, after acidic work-up, the corresponding free
acid 10 (quantitative). Esterification of the last compound under
Mitsunobu conditions with the enantiomerically pure secondary
alcohol 11, available in multi-gram quantities through lipase-
afforded the doubly-unsaturated ester 12 in 91% overall yield
from ester 9.
Following the strategy used in our recently reported synthesis
8
of cladospolide A, diene 12 was subjected (Scheme 2) to a
13
RCM reaction using Grubbs’ second-generation catalyst in
dichloromethane at room temperature. In this manner the Z-
isomer of target lactone 13 was obtained as the sole monomeric
8
mediated resolution of the corresponding racemic material,
Scheme 2
1
0 8 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8

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product of reaction (18%), and the structure of this compound
was established in an unequivocal manner through single-crystal
X-ray analysis (see Fig. 1 and the Experimental section).
However, the major products of reaction were the chromato-
graphically inseparable head-to-tail and head-to-head “dimers”
of substrate 12, namely bis-lactones 14 and 15, respectively,
which were obtained in 62% combined yield. The structures of
these products follow from the chemical studies detailed below.
Fortunately, when the RCM reaction of diene 12 was carried
13
out using Grubbs’ first-generation catalyst, the predominant
product was the unsaturated lactone 13 (66%) although now
obtained as a chromatographically inseparable 1.3 : 1 mixture
of E- and Z-isomers. Under such conditions compounds 14
and 15 were still observed, albeit now in only ca. 5% combined
yield. The outcomes of the RCM processes just described
demonstrate that the bis-acetal moiety involved represents an
effective protecting group for a trans-diol during the course of
constructing unsaturated nonenolides by such means. It is also
worth noting that the reason for employing a RCM reaction at
8
this stage is because in our earlier studies we had not been able
to construct the twelve-membered undecenolide ring of target 1
directly by such means.
Scheme 3
followed from a single-crystal X-ray analysis (see Fig. 2 and
the Experimental section) that served to highlight the successful
acquisition of the target undecenolide framework. Removal of
the bis-acetal protecting group within compound 23 was not
entirely straightforward and amongst the various reagents and
reaction conditions examined for this purpose, those involving
◦
TiCl
4
in dichloromethane at 0 C proved most effective, as
evidenced by the delivery, in 94% yield, of the E-isomer, 24,
of target 2.
Fig. 1 Anisotropic displacement ellipsoid plot of the Z-isomer of
compound 13 with labelling of selected atoms. Ellipsoids show 50%
probability levels. Hydrogen atoms are drawn as circles with small radii.
Continuation of the synthesis of target 2 involved (Scheme 2)
conventional hydrogenation of the mixture of E- and Z-isomers
of lactone 13, thus giving the saturated equivalent 16 in 86%
yield. Similarly, hydrogenation of the mixture of dimers 14 and
Fig. 2 Anisotropic displacement ellipsoid plot of compound 23 with
labelling of selected atoms. Ellipsoids show 50% probability levels.
Hydrogen atoms are drawn as circles with small radii.
15 afforded the now chromatographically separable products
7 (35%) and 18 (57%), respectively. Independent subjection
1
of compounds 16 and 17 to reduction with DIBAL-H in
While little work has been done on the photoisomerisation of
carbonyl-conjugated double-bonds contained within medium-
◦
toluene at −78 C afforded lactol 19, which was immediately
14
committed to a Wadsworth–Horner–Emmons reaction with the
anion generated through deprotonation of trimethyl phospho-
noacetate with sodium hydride. In this way the E-configured
a,b-unsaturated ester 20 was obtained, as a single geometric
isomer, in 79 and 62% overall yield from precursors 16 and
ring macrolides we wondered if this sort of process might be oc-
curring naturally as part of a plant growth regulating process ca-
pable of being influenced by the presence (or absence) of incident
light. To investigate these possibilities, a deoxygenated benzene
solution of compound 24 in a Pyrex vessel was irradiated, in a
Rayonet photo-reactor, with 300 nm light. In this manner, iso-
merisation to target 2 was observed. Under the best conditions
we have identified so far, irradiation of the substrate for 16 h at
1
7, respectively. Subjection of the head-to-head “dimer” 15 to
the same reduction–olefination sequence afforded the bis-ester
1 (52%), thereby confirming the structural assignments of the
2
◦
precursors 14 and 15 as head-to-tail and head-to-head “dimers”,
respectively.
ca. 18 C led to an 4 : 1 mixture of compounds 24 (57% recovery)
and (−)-cladospolide B (2) (31% at 43% conversion) which could
be separated from one another using semi-preparative HPLC
techniques. The NMR, IR, and mass spectral data derived from
the synthetic sample of cladospolide B were in good agreement
The end-game associated with the synthesis of cladospolide
B (2) is shown in Scheme 3. Thus, saponification of ester 20
under the usual conditions followed by acidic work-up gave
the x-hydroxy-acid 22, which was subjected to Yamaguchi
lactonisation in refluxing toluene to afford the macrolide 23 in
2
with those reported in the literature for the natural product. The
1
most diagnostic features observed in the H NMR spectrum of
6
2% yield (from precursor 20) as a white crystalline solid. All the
compound 2 were those resonances due to the olefinic protons
associated with the unsaturated ester moiety, which appeared at
d 6.24 and 5.78, each as a doublets of doublets with a mutual
NMR and mass spectral data obtained for product 23 were fully
consistent with the assigned structure, but final confirmation
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8
1 0 8 3

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coupling of J 12.2, as would be expected for cis-related protons
associated with a common double-bond. This contrasts with a
coupling of J 16.1 observed for the equivalent protons in the
0.2 mm thick silica gel 60 F254 plates (Merck) and the chro-
matograms were visualised under a 254 nm UV lamp and/or by
treatment with an anisaldehyde–sulfuric acid–ethanol (3 mL :
4.5 mL : 200 mL) dip or, occasionally, with a phosphomolybdic
acid–ceric sulfate–sulfuric acid–water (37.5 g : 7.5 g : 37.5 mL :
720 mL) dip, followed by heating. Flash chromatography was
E-isomer 24. Significantly, the [a] of the synthetic sample of
D
compound 2 was −162 (c 0.1, MeOH) which is opposite in
3
sign and of considerably greater magnitude than that recorded
16
for the natural product, viz. [a]
D
+45 (c 0.4, MeOH). We also
conducted according to the method of Still and co-workers
note that the specific rotation of the synthetic material did
not vary a great deal with concentration. Such results clearly
imply that the absolute configuration of (+)-cladospolide B has
been misassigned and is, in fact, opposite to that shown in
structure 2. The distinct difference in the magnitude of these
two values suggests that the natural material may only be
enantiomerically enriched with the 4R,5R,11S-form and is not
an enantiomerically pure material. Alternatively, and perhaps
more likely, the natural product is contaminated with some other
material that has a very large and negative rotation.
using silica gel 60 (mesh size 0.040–0.063 mm) as the stationary
phase and the analytical reagent (AR) grade solvents indicated.
Many starting materials and reagents were available from the
Aldrich Chemical Company or EGA–Chemie and were used
as supplied or, in the case of stable liquids, simply distilled.
Drying agents and other inorganic salts were purchased from
AJAX or BDH Chemicals. Reactions employing air- and/or
moisture-sensitive reagents and intermediates were carried out
under an atmosphere of dry, oxygen-free nitrogen in flame-dried
apparatus. Tetrahydrofuran (THF) and diethyl ether were dried
using sodium metal and then distilled, as required, from sodium
benzophenone ketyl. Methanol was distilled from magnesium
methoxide. Dichloromethane was distilled fromcalcium hydride.
N,N-Dimethylformamide (DMF) was heated at reflux over
Interestingly, exposure of a dichloromethane solution of (−)-
cladospolide B (2) to traces of trifluoroacetic acid (TFA) did not
result in any clean isomerisation to 24; only slow decomposition
was observed.
˚
calcium hydride for 16 h then distilled and stored over 4 A
molecular sieves. Organic solutions obtained from work-up of
reaction mixtures were dried with anhydrous magnesium sulfate
Conclusions
The present work, when considered together our earlier syn-
(MgSO ) then filtered and concentrated under reduced pressure
4
8
15
theses of (−)-cladospolide A and (+)-aspicillin, serves to
demonstrate the utility of cis-1,2-dihydrocatechols as building
blocks in the assembly of various macrolides. This utility follows
from a capacity to “stitch” such building blocks into larger
ring systems through the sequential application of ozonolysis,
methylenation and RCM reactions. As such, simple extensions
of the work detailed herein should enable access to the remaining
members of the cladospolide family as well as related systems
likely to be of interest in a biological sense. Work directed
towards such ends is now underway in these laboratories.
on a rotary evaporator with the water bath temperature generally
◦
not exceeding 40 C. Semi-preparative HPLC separations were
performed on a system comprising two Waters 510 pumps linked
in series and the first of these was fitted with a Rheodyne 7125
injector incorporating a 1 mL loop. A Waters 7.8 × 300 mm
l-Porasil column (irregular particle size) was used and eluting
materials were detected using a Waters 481 UV/Vis detector set
−
1
at 250 nm. A solvent flow rate of 2 mL min was used and the
detector was interfaced with a computer supporting V3.3 of the
Waters Maxima Software.
(
2R,3R,4aS,8aR)-8-chloro-2,3,4a,5,6,8a-hexahydro-2,3-
Experimental
dimethoxy-2,3-dimethylbenzo[b]-[1,4]dioxine (7)
1
13
Unless otherwise specified, proton ( H) and carbon ( C) NMR
spectra were recorded on a Varian Gemini 300 or Varian
Mercury 300 spectrometer operating at 300 MHz for proton
and 75 MHz for carbon nuclei. Chemical shifts were recorded
10
A magnetically stirred solution of trans-diol 6 (153 mg,
.03 mmol), CH(OMe) (450 lL, 4.16 mmol) and [CH C-
1
3
3
(OMe)
2
]
2
(221 mg, 1.24 mmol) in MeOH (5 mL) maintained
◦
under a nitrogen atmosphere at 18 C was treated with (+)-
camphorsulfonic acid (14 mg, 0.06 mmol) and the resulting
mixture heated at reflux for 16 h. The cooled reaction mixture
was treated with solid NaHCO
concentrated under reduced pressure to give a light-yellow
oil. Subjection of this material to flash chromatography (1 :
as d values in parts per million (ppm). Spectra were acquired in
◦
deuterochloroform (CDCl
3
) at 20 C unless otherwise stated.
1
For H NMR spectra recorded in CDCl
residual CHCl (d 7.26) was used as the internal reference
while the central peak (d 77.0) of the CDCl “triplet” was used
3
, the peak due to
3
(∼2 g) then filtered and
3
3
1
3
1
as the reference for proton-decoupled C NMR spectra. H
NMR spectral data are recorded as follows: chemical shift (d)
9
v/v ethyl acetate–hexane elution) and concentration of the
relevant fractions (R 0.4) gave the title compound 7 (248 mg,
2%) as a white crystalline solid. Recrystallisation (CHCl ) of
f
[
relative integral, multiplicity, coupling constant(s) J (Hz)] where
9
3
multiplet or combinations of the above. Infrared spectra (mmax
were recorded on either a Perkin–Elmer 1800 Fourier Transform
Infrared Spectrophotometer or a Perkin–Elmer Spectrum One
instrument. Samples were analysed as KBr discs (for solids)
or as thin films on KBr plates (for liquids/oils). Low- and
high-resolution MS spectra were recorded on an AUTOSPEC
spectrometer or a Kratos Analytical Concept ISQ instrument,
the latter being located at the University of Tasmania. Optical
rotations were determined on a Perkin–Elmer 241 polarimeter
at the sodium D line (598 nm) using spectroscopic grade
multiplicity is defined as: s = singlet; d = doublet; t = triplet; m =)
◦
a sample of this compound gave analytically pure material as
white needles, mp 78–81 C, [a]
CH
D
−276 (c 0.5) [Found: (M −
+
35
3
O·) , 231.0788. C, 55.02; H, 7.10; Cl, 13.57. C12
H
19 ClO
4
+
requires (M − CH
max/cm 2956, 2880, 2834, 1460, 1379, 1120, 1044, 1025, 941,
16, 873, 838, 778; d (CDCl , 300 MHz) 5.78 (1 H, m), 4.20
3
O·) , 231.0788. C, 54.86; H, 7.29; Cl, 13.49%].
−
1
m
9
(
(
H
3
1 H, m), 3.85 (1 H, ddd, J 3.8, 8.7 and 12.4), 3.29 (3 H, s), 3.25
3 H, s), 2.22 (2 H, m), 1.87–1.65 (2 H, complex m), 1.35 (3 H, m),
1
(
.31 (3 H, m); d
C), 99.9 (C), 70.1 (CH), 69.2 (CH), 47.9 (CH
(CH ), 24.6 (CH ), 17.7 (CH ), 17.6 (CH ); m/z (EI, 70 eV) 249
and 247 [(M − CH ) , 2 and 5%], 233 and 231 (11 and 24), 117
10), 116 (35), 114 (87), 101 (62), 79 (100).
C
(CDCl
3
, 75 MHz) 128.8 (C), 126.5 (CH), 100.7
3
), 47.8 (CH ), 25.3
3
◦
2
2
3
3
chloroform (unless otherwise specified) at 20 C and at the
•
+
3
concentrations (c) (g per 100 mL) indicated. Measurements
were carried out in a cell with a path length of 1 dm. Melting
points (mp) were recorded on a Reichert hot-stage apparatus
and are uncorrected. Elemental analyses were performed by the
Australian National University Microanalytical Services Unit
based in the Research School of Chemistry, The Australian
National University, Canberra, Australia. Analytical thin layer
chromatography (TLC) was conducted on aluminium-backed
(
Methyl (2R,3S,5R,6R)-3-(but-3-enyl)-5,6-
dimethoxy-5,6-dimethyl-1,4-dioxane-2-carboxylate (9)
A magnetically stirred solution of alkene 7 (1.12 g, 4.27 mmol)
◦
in MeOH (85 mL) was cooled to −78 C then treated with a
stream of ozone until a blue colour persisted and TLC analysis
1
0 8 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8

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indicated the absence of starting material (ca. 20 min). The excess
ozone was then removed by purging the reaction mixture with a
stream of nitrogen (10 min) and the resulting colourless solution
(R)-Pent-4-en-2-yl (2R,3S,5R,6R)-3-(but-3-enyl)-5,6-
dimethoxy-5,6-dimethyl-1,4-dioxane-2-carboxylate (12)
A magnetically stirred solution of the acid 10 (1.46 g, 5.33 mmol)
was placed in an ice-bath and treated with Me
2
S (313 lL,
◦
◦
in toluene (20 mL) maintained at 0 C under a nitrogen at-
4
.26 mmol). After 1 h the reaction mixture was warmed to 18 C
8
mosphere was treated sequentially with (S)-pent-4-en-2-ol (11)
whereupon TLC analysis indicated the disappearance of the
ozonolysis product. The reaction mixture was diluted with water
(
789 lL, 7.98 mmol) and triphenylphosphine (2.10 g, 7.99 mmol)
◦
then cooled to 0 C and diethyl diazodicarboxylate (1.26 mL,
(
50 mL) and then extracted with ethyl acetate (4 × 100 mL).
7
.99 mmol) added dropwise. The resulting mixture was allowed
The combined organic fractions were washed with CuSO
5
4
(1 ×
◦
to warm to 18 C over 16 h then treated with NaHCO
3
(20 mL of
0 mL of a saturated aqueous solution), water (1 × 50 mL)
4
a saturated aqueous solution) and the separated aqueous layer
extracted with ethyl acetate (3 × 30 mL). The combined organic
fractions were washed with water (1 × 10 mL) then brine (1 ×
and brine (1 × 50 ml) before being dried (MgSO
), filtered and
concentrated under reduced pressure to give aldehyde 8 as an
unstable, yellow oil. This material was used immediately in the
next step of the reaction sequence.
5
mL) before being dried (MgSO ), filtered and concentrated
4
under reduced pressure to give a yellow oil. Subjection of this
material to flash chromatography (1 : 9 v/v diethyl ether–hexane
elution) and concentration of the relevant fractions (R 0.4) gave
A magnetically stirred solution of methyltriphenylphospho-
nium bromide (2.23 g, 6.40 mmol) in THF (45 mL) maintained
◦
f
at 0 C under an atmosphere of nitrogen was treated with
the title compound 12 (1.67 g, 91%) as a clear, colourless oil,
potassium bis(trimethylsilyl)amide (12.8 mL of a 0.5 M solution
in toluene, 6.4 mmol). The resulting yellow mixture was allowed
+
[
a]
D
−162 (c 0.7) [Found: (M − CH
3
O·) , 311.1863. C18
H
30
O
6
+
−1
◦
◦
requires (M − CH
3
O·) , 311.1858]. mmax/cm 2951, 2858, 1744,
to warm to 18 C over 0.5 h then re-cooled to 0 C and
1
120; d
H
(CDCl , 300 MHz) 5.82–5.63 (2 H, complex m), 5.08–
3
treated, via cannula, with a solution of aldehyde 8 (obtained
4.90 (5 H, complex m), 4.04 (1 H, d, J 9.8), 3.83 (1 H, m), 3.25 (3
as described immediately above) in THF (20 mL). After 1 h
◦
H, s), 3.21 (3 H, s), 2.38–2.21 (3 H, complex m), 2.12–2.00 (1 H,
complex m), 1.56–1.50 (2 H, complex m), 1.30 (3 H, s), 1.26
at 18 C the reaction mixture was treated with NH
4
Cl (10 mL
of a saturated aqueous solution) then extracted with diethyl
ether (3 × 40 mL). The combined organic phases were washed
with water (1 × 10 mL) and brine (1 × 10 mL) before
(
1
(
4
3 H, s), 1.23 (3 H, d, J 6.3); d
37.9 (CH), 133.3 (CH), 118.0 (CH
C), 72.5 (CH), 71.2 (CH), 67.8 (CH), 48.1 (CH
C
(CDCl
3
, 75 MHz) 168.5 (C),
), 98.7 (C), 98.5
), 47.8 (CH ),
), 17.3
2
), 114.8 (CH
2
3
3
being dried (MgSO ), filtered and concentrated under reduced
4
0.0 (CH
2
), 29.7 (CH
2
), 28.9 (CH
2
), 19.3 (CH
3
), 17.6 (CH
3
pressure to give a yellow oil. Subjection of this material to
flash chromatography (5 : 95 v/v ethyl acetate–hexane elution)
+
(
(
CH
3
); m/z (EI, 70 eV) 312 (14%), 311 [(M − CH
3
O·) , 31], 257
20), 243 (14), 194 (20), 153 (17), 126 (46), 109 (100).
and concentration of the relevant fractions (R
f
0.4 in 1 : 4 v/v
ethyl acetate–hexane) gave the title compound 9 (823 mg, 67%
(
E/Z,2R,3R,4aR,7R,12aS)-2,3,7,8,12,12a-Hexahydro-2,3-
from diol 6) as a clear, colourless oil, [a]
D
−168 (c 0.8) [Found:
dimethoxy-2,3,7-trimethyl-4aH-[1,4]dioxino[2,3-c]oxecin-
(11H)-one (13)
+
+
(
2
M − CH
3
O·) , 257.1381. C14
H
24
O
6
requires (M − CH
3
O·) ,
5
−
1
57.1389]. mmax/cm 2951, 1749, 1440, 1378, 1121, 1038, 889; d
H
(
CDCl , 300 MHz) 5.75 (1 H, m), 5.03–4.89 (2 H, complex m),
.13 (1 H, d, J 9.9), 3.85 (1 H, td, J 3.8 and 9.9), 3.73 (3 H, s),
.26 (3 H, s), 3.22 (3 H, s), 2.32 (1 H, m), 2.06 (1 H, m), 1.60–
3
Method A: Grubbs’ second-generation catalyst (226 mg,
0.23 mmol) was added to a magnetically stirred solution of
compound 12 (613 mg, 1.79 mmol) in degassed dichloromethane
4
3
1
7
7
◦
.47 (2 H, complex m), 1.32 (3 H, s), 1.27 (3 H, s); d
5 MHz) 169.3 (C), 137.8 (CH), 114.9 (CH ), 98.8 (C), 98.5 (C),
2.7 (CH), 67.7 (CH), 52.2 (CH ), 48.2 (CH ), 47.9 (CH ), 29.7
), 28.9 (CH ), 17.6 (CH ), 17.3 (CH
3%) 271 (17), 258 (54), 257 [(M − CH
C
(CDCl
3
,
(1.80 L) maintained under a nitrogen atmosphere at 18 C. The
2
reaction mixture was stirred at this temperature for 18 h
whereupon TLC analysis indicated the absence of starting
material. DMSO (610 lL) was added to the reaction mixture,
3
3
3
(
CH
2
2
3
3
); m/z (EI, 70 eV) 272
O·) , 100].
+
◦
(
3
which was stirred at 18 C for a further 16 h then filtered through
a pad of TLC-grade silica gel. The pad was then eluted with 1 :
4
v/v ethyl acetate–hexane to give two fractions, A and B.
Concentration of fraction A (R
Z-13 (102 mg, 18%) as colourless plates, mp 147 C, [a]
f
0.2) afforded the lactone
(
2R,3S,5R,6R)-3-(But-3-enyl)-5,6-dimethoxy-5,6-dimethyl-1,4-
◦
D
dioxane-2-carboxylic acid (10)
+
−
134 (c 0.6) [Found: (M − CH
3
O·) , 283.1539. C, 61.29; H,
+
A magnetically stirred solution of ester 9 (2.48 g, 8.6 mmol)
in ethanol (170 mL) maintained at 18 C was treated with
8.05. C16
H
26
O
6
requires (M − CH
3
O·) , 283.1545. C, 61.13; H,
◦
−1
8.34%]. mmax/cm 2947, 1750, 1463, 1379, 1122, 1039; d
H
(CDCl ,
3
NaOH (29 mL of a 1.5 M aqueous solution, 10.5 mmol). The
resulting mixture was kept at 18 C for 1 h then acidified
with HCl (50 mL of a 1 M aqueous solution) and extracted
300 MHz) 5.61 (1 H, m), 5.46 (1 H, m), 5.11 (1 H, m), 4.09
(1 H, d, J 9.3), 3.68 (1 H, m), 3.22 (3 H, s), 3.21 (3 H, s), 2.56
(1 H, m), 2.32–1.94 (2 H, complex m), 1.90–1.82 (1 H, complex
m), 1.80–1.72 (1 H, complex m), 1.68–1.54 (1 H, complex m),
◦
with dichloromethane (3 × 50 mL). The combined organic
fractions were dried (MgSO
4
), filtered and concentrated under
1.32 (3 H, s), 1.27 (3 H, d, J 6.3), 1.24 (3 H, s); d
125 MHz) 168.5 (C), 133.3 (CH), 126.6 (CH), 98.9 (C), 98.7 (C),
), 47.8 (CH
C
(CDCl ,
3
reduced pressure to give the crude acid 10 (2.36 g, 100%) as
a light-yellow solid. Recrystallisation (CHCl
3
) of a sample of
73.5 (2 × CH), 71.3 (CH), 48.2 (CH
3
3
), 30.5 (2 ×
◦
this material gave analytically pure material, mp 109–110 C,
CH
2
), 22.9 (CH
2
), 17.6 (2 × CH
3
), 17.2 (CH
3
); m/z (EI, 70 eV)
+
+•
+
[
a]
D
−147 (c 0.4) [Found: (M − CH
3
O·) , 243.1238. C, 56.92;
313 [(M − H) , <1%], 283 [(M − CH
3
O·) , 72], 225 (12), 211
+
H, 8.23. C13
H
22
O
6
requires (M − CH
3
O·) , 243.1232. C, 56.92;
(10), 166 (62), 123 (67), 122 (78), 101 (78), 95 (73), 81 (80), 68
(86), 55 (84), 43 (100).
−
1
H, 8.08%]. mmax/cm 3200, 2931, 1737, 1375, 1119, 1034; d
H
(CDCl
3
, 300 MHz) 5.79 (1 H, dm, J 17.2), 5.03 (1 H, dm, J
Concentration of fraction B (R 0.1) afforded an inseparable
f
1
7.2), 4.96 (1 H, dm, J 10.3), 4.18 (1 H, d, J 10.3), 3.77 (1 H,
and ca. 3 : 5 mixture of compound 14 and compound 15 (348 mg,
+
td, J 2.5 and 10.3), 3.29 (3 H, s), 3.24 (3 H, s), 2.42–2.28 (1
H, complex m), 2.19–2.04 (1 H, complex m), 1.99–1.84 (1 H,
complex m), 1.72–1.56 (1 H, complex m), 1.37 (3 H, s), 1.30 (3
62%) as a clear, colourless oil [Found: (M − CH
3
O·) , 597.3276.
+
−1
C
32
H
52
O
12 requires (M − CH
3
O·) , 597.3275]. mmax/cm 2945,
+
1746, 1379, 1121, 1042; m/z (EI, 70 eV) 597 [(M − CH
3
O·) ,
H, s); d
C
(CDCl
9.3 (C), 98.5 (C), 72.1 (CH), 67.6 (CH), 48.5 (CH
9.7 (CH ), 28.9 (CH ), 17.6 (CH ), 17.3 (CH
O·) , 27%], 126 (31), 116 (46), 101 (64), 81 (49),
3
, 75 MHz) 171.3 (C), 137.8 (CH), 115.1 (CH
2
),
7%], 565 (23), 416 (18), 332 (29), 283 (12), 207 (15) 194 (33), 189
(19), 166 (29), 149 (37), 148 (46), 121 (48), 116 (85), 101 (86), 81
(87), 68 (71), 67 (70), 55 (53) 43 (100).
9
2
2
7
3
), 48.1 (CH
3
),
2
2
3
3
); m/z (EI, 70 eV)
+
43 [(M − CH
3
Method B: Grubbs’ first-generation catalyst (46 mg,
0.06 mmol) was added to a magnetically stirred solution of
5 (100).
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8
1 0 8 5

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compound 12 (317 mg, 0.92 mmol) in degassed dichloromethane
1.57 (2 H, m), 1.47 (2 H, m), 1.43–1.52 (14 H, complex m), 1.34
◦
(
920 mL) maintained under a nitrogen atmosphere at 18 C. The
(6 H, s), 1.28 (6 H, s), 1.25 (6 H, d, J 6.3); d
168.9 (C), 98.9 (C), 98.6 (C), 73.1 (CH), 72.0 (CH), 69.1 (CH),
48.2 (CH ), 47.8 (CH ), 36.1 (CH ), 30.4 (CH ), 29.2 (CH ), 26.0
(CH ), 25.1 (CH ), 17.7 (CH ), 17.4 (CH ); m/z (EI,
C
(CDCl
3
, 125 MHz)
reaction mixture was stirred at this temperature for 18 h after
which time TLC analysis indicated the absence of starting
material. DMSO (215 lL) was added to the reaction mixture,
3
3
2
2
2
2
3
), 19.9 (CH
2
3
3
◦
+
which was then stirred at 18 C for a further 16 h before being
70 eV) 601 [(M − CH
3
O·) , 3%], 569 (14), 452 (10), 420 (43),
concentrated under reduced pressure. Subjection of the residue
to flash chromatography (1 : 4 v/v ethyl acetate–hexane elution)
gave two fractions, A and B.
336 (15), 208 (100), 116 (75), 101 (99), 69 (85).
Methyl (E)-3-{(2S,3S,5R,6R)-3-[(R)-6-hydroxyheptyl]-5,6-
dimethoxy-5,6-dimethyl-1,4-dioxan-2-yl}acrylate (20)
Method A: DIBAL-H (408 lL of a 1 M solution in hexane,
Concentration of fraction A (R
191 mg, 66%) as an inseparable and ca. 1.3 : 1 mixture of E-
f
0.2) afforded compound 13
(
and Z-isomers.
0
.41 mmol) was added, in portions over 1 h, to a magnetically
Concentration of fraction B (R 0.1) afforded an inseparable
f
stirred solution of the lactone 16 (89 mg, 0.28 mmol) in toluene
and ca. 2 : 3 mixture of compounds 14 and 15 (14 mg, 5%).
◦
(
3 mL) maintained at −78 C under a nitrogen atmosphere.
Stirring was continued for 0.5 h, the reaction then quenched by
adding NaK tartrate (5 mL of a 1 M aqueous solution), the
resulting mixture warmed to 0 C over an additional 10 min and
(
2R,3R,4aR,7R,12aS)-Octahydro-2,3-dimethoxy-2,3,7-
trimethyl-4aH-[1,4]dioxino[2,3-c]-oxecin-5(7H)-one (16)
◦
1
0% Palladium on carbon (9 mg, 10 wt%) was added to a
then extracted with ethyl acetate (3 × 10 mL). A few drops of
1 M aqueous HCl were added to disperse the emulsion formed
during extraction. The combined organic fractions were washed
magnetically stirred solution of alkene 13 (89 mg, 0.28 mmol)
in absolute ethanol (3 mL). A balloon of dihydrogen was
attached and the reaction vessel evacuated and flushed twice
with dihydrogen. The resulting black suspension was stirred
under an atmosphere of dihydrogen at 18 C for 14 h, then
filtered through a pad of Celite . Concentration of the filtrate
with brine (1 × 5 mL) before being dried (MgSO
4
), filtered
and concentrated under reduced pressure to give lactol 19 as an
unstable, yellow oil which was used immediately in the next step
of the reaction sequence.
◦
TM
under reduced pressure gave a grey-yellow oil that was subjected
to flash chromatography (1 : 9 v/v diethyl ether–hexane elution).
A magnetically stirred suspension of NaH (23 mg of a 60%
dispersion in mineral oil, 0.57 mmol) in THF (3 mL) maintained
at 0 C under a nitrogen atmosphere was treated dropwise with
◦
Concentration of the relevant fractions (R
f
0.3 in 1 : 4 v/v
ethyl acetate–hexane) then gave the title compound 16 (77 mg,
trimethyl phosphonoacetate (91 lL, 0.56 mmol). The resulting
mixture was warmed to 18 C over 0.5 h and a solution of
◦
8
6%) as a clear, colourless oil, [a]
D
−160 (c 0.2) [Found:
+
+
(
2
M − CH
3
O·) , 285.1706. C16
H
28
O
6
requires (M − CH
3
O·) ,
the lactol 19 (obtained as described immediately above) in THF
−
1
◦
◦
85.1702]. mmax/cm 2944, 1752, 1456, 1378, 1183, 1123, 1038;
(CDCl , 500 MHz) 5.51 (1 H, m), 4.19 (1 H, d, J 8.8), 3.63
(3 mL) was added via cannula at 0 C. After re-warming to 18 C
d
H
3
over a period of 1 h the reaction mixture was diluted with ethyl
(
1 H, tm, J 9.8), 3.24 (3 H, s), 3.20 (3 H, s), 1.74–1.54 (8 H,
complex m), 1.44–1.34 (2 H, complex m), 1.33 (3 H, s), 1.27
3 H, d, J 6.3), 1.26 (3 H, s); d (CDCl , 125 MHz) 168.9 (C),
9.1(7) (C), 99.1(1) (C), 73.5 (CH), 71.8 (CH), 70.5 (CH), 48.3
acetate (10 mL) and quenched with NH Cl (10 mL of a saturated
4
aqueous solution). The separated aqueous fraction was ex-
tracted with ethyl acetate (3 × 15 mL) and the combined organic
fractions washed with water (1 × 10 ml) and brine (1 × 10 mL)
(
9
C
3
(
(
CH
CH
3
), 47.8 (CH
3
), 31.9 (CH
2
), 28.4 (CH
2
), 26.9 (CH
2
), 22.7
before being dried (MgSO ), filtered and concentrated under
4
2
), 20.4 (CH ), 19.4 (CH
3
2
), 17.7 (CH
3
), 17.3 (CH
3
); m/z (EI,
reduced pressure to give a light-yellow oil. Subjection of this
material to flash chromatography (3 : 7 v/v ethyl acetate–hexane
7
8
0 eV) 285 (41%), 271 (10), 168 (32), 139 (22), 116 (68), 101 (69),
1 (72), 68 (68), 55 (59), 43 (100).
elution) and concentration of the relevant fractions (R
f
0.1
in 1 : 4 v/v ethyl acetate–hexane) gave the title compound 20
Compounds 17 and 18
(82 mg, 79% from lactone 16) as a clear, colourless oil, [a]
D
−163
+
(
(
c 0.5) [Found: (M − CH
3
O·) , 343.2119. C19
H
34
O
7
requires
Hydrogenation of compounds 14 and 15 under the same
conditions as employed in the conversion 13 → 16 afforded
a grey-yellow oil on work-up. Subjection of this material to flash
chromatography (1 : 4 v/v diethyl ether–hexane to 3 : 7 v/v
ethyl acetate–hexane gradient elution) afforded two fractions, A
and B.
+
−1
M − CH
3
O·) , 343.2121]. mmax/cm 3399, 2938, 1727, 1660,
1437, 1376, 1307, 1124, 1038; d
H
(CDCl , 300 MHz) 6.85 (1 H,
3
dd, J 5.6 and 15.6), 6.19 (1 H, dd, J 1.6 and 15.6), 4.14 (1 H,
ddd, J 1.6, 5.6 and 9.5), 3.74 (3 H, s), 3.52 (1 H, m), 3.24 (1 H,
m), 3.23 (6 H, s), 1.68–1.20 (10 H, complex m), 1.54 (1 H, br s),
1
7
7
.31 (3 H, s), 1.30 (3 H, s), 1.17 (3 H, d, J 6.2); d
5 MHz) 166.7 (C), 143.0 (CH), 123.1 (CH), 98.7 (C), 98.6 (C),
1.7 (CH), 70.7 (CH), 68.1 (CH), 51.7 (CH ), 48.0 (CH ), 47.9
), 25.7 (CH ), 25.0
); m/z (EI, 70 eV) 343
C
(CDCl
3
,
Concentration of fraction A (R 0.4 in 3 : 7 v/v ethyl acetate–
hexane) gave compound 17 (161 mg, 35%) as a clear, colourless
f
+
3
3
oil, [a]
D
−96 (c 0.4), [Found: (M − CH
3
O·) , 601.3593. C32
H
56
O
12
(
(
CH
CH
3
2
), 39.2 (CH
2
), 30.5 (CH
2
), 29.5 (CH
2
2
+
−1
requires (M − CH
3
O·) , 601.3588]. mmax/cm 2940, 2860, 1746,
), 23.5 (CH
3
), 17.7 (CH ), 17.5 (CH
3
3
1458, 1379, 1120, 1041; d
H
(CDCl , 500 MHz) 5.02 (2 H, m), 4.06
3
+
[
(
(
(M − CH
3
O·) , 20%], 327 (15), 311 (31), 225 (20), 208 (18), 194
(
(
2 H, d, J 9.3), 3.81 (2 H, dt, J 1.0 and 8.8), 3.27 (6 H, s), 3.21
6 H, s), 1.62–1.40 (8 H, complex m), 1.37–1.24 (12 H, complex
40), 138 (52), 117 (76), 116 (78), 101 (77), 96 (69), 73 (79), 55
74), 43 (100).
m), 1.32 (6 H, s), 1.26 (6 H, s), 1.22 (6 H, d, J 5.9); d
C
(CDCl
25 MHz) 168.8 (C), 98.7 (C), 98.5 (C), 72.4 (CH), 71.9 (CH),
8.8 (CH), 48.2 (CH ), 47.8 (CH ), 35.6 (CH ), 30.3 (CH ), 29.6
), 24.4 (CH ), 19.8 (CH ), 17.7 (CH ), 17.3
); m/z (EI, 70 eV) 601 [(M − CH O·) , 5%], 569 (26), 452
3
,
Method B: Reaction of bis-lactone 17 with DIBAL-H in the
1
6
same manner as described above but using 4 (rather than 1.5)
mole equivalents of the reducing agent gave the lactol 19. This
material was immediately subjected to reaction with the anion
derived from trimethyl phosphonoacetate (see Method A) and
in this way the title compound 20 (62% from lactone 17) was
obtained as a clear, colourless oil. This material proved identical,
3
3
2
2
(
(
(
CH
CH
2
3
), 24.7 (CH
2
3
2
3
+
3
29), 420 (94), 336 (43), 285 (21), 168 (46), 150 (91), 116 (85),
1
01 (100).
Concentration of fraction A [R 0.3(5) in 3 : 7 v/v ethyl
f
1
3
1
as judged by C and H NMR analysis, with that obtained by
Method A.
acetate–hexane)] gave compound 18 (258 mg, 57%) as white
◦
+
needles, mp 160 C, [a]
D
−187 (c 0.2) [Found: (M − CH
3
O·) ,
+
6
6
1
01.3573. C, 60.84; H, 8.71. C32
01.3588. C, 60.74; H, 8.92%]. mmax/cm 2936, 2858, 1747, 1457,
H
56
O
12 requires (M − CH
3
O·) ,
Compound 21
−
1
379, 1121, 1039; d
H
(CDCl
3
, 500 MHz) 4.99 (2 H, m), 4.08 (2 H,
Reaction of bis-lactone 18 with DIBAL-H in the same manner
as described above for the conversion 16 → 19 but using 4
d, J 9.8), 3.79 (2 H, m), 3.26 (6 H, s), 3.22 (6 H, s), 1.70 (2 H, m),
1
0 8 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8

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(
rather than 1.5) mole equivalents of the reducing agent gave
and treated with distilled TiCl
resulting orange solution was maintained at 0 C for 1.5 h,
4
(23 lL, 0.21 mmol). The
◦
the corresponding bis-aldehyde on work-up. This material was
immediately treated with the anion derived from trimethyl
phosphonoacetate in the same manner as described above for the
conversion 19 → 20 but using 4 (rather than 2) mole equivalents
of the anion. In this way a yellow oil was obtained on work-up.
Subjection of this material to flash chromatography (3 : 7 v/v
ethyl acetate–hexane elution) and concentration of the relevant
quenched with NaHCO (1 ml of a saturated aqueous so-
3
lution) and extracted with ethyl acetate (3 × 10 ml). The
combined organic fractions were washed with water (1 × 2 ml)
and brine (1 × 2 ml) before being dried (MgSO
4
), filtered
and concentrated under reduced pressure to give a yellow
residue. Subjection of this material to flash chromatography
(7 : 3 v/v ethyl acetate–hexane elution) followed by con-
fractions (R 0.6 in 1 : 4 v/v ethyl acetate–hexane) gave compound
f
2
1 (52% from lactone 18) as a clear, colourless oil, [a]
D
+11 (c 0.4)
centration of the relevant fractions (R 0.3) gave compound
f
+
[
Found: (M − CH
3
O·) , 571.3122. C30
H
50
O
12 requires (M −
24 (37 mg, 94%) as a clear, colourless oil, [a]
D
−20 (c 0.2)
+
−1
+•
CH
3
O·) , 571.3118]. mmax/cm 2947, 2857, 1728, 1662, 1436,
[Found: (M − H
2
O) , 210.1256. C12
H
20
O
4
requires (M −
+
•
−1
1
6
4
3
376, 1307, 1125, 1039, 978, 889, 853; d
H
(CDCl
3
, 300 MHz)
H
2
O) , 210.1256]. mmax/cm 3394, 2937, 2863, 1712, 1647, 1464,
.84 (2 H, dd, J 5.8 and 15.7), 6.19 (2 H, dd, J 1.4 and 15.7),
.13 (2 H, ddd, J 1.4, 5.8 and 9.5), 3.74 (6 H, s), 3.51 (2 H, m),
.22 (12 H, s), 1.72–1.20 (12 H, complex m), 1.31 (6 H, s), 1.30
1259, 1165, 1116, 1049, 1029; d
H
(CDCl , 600 MHz) 6.94 (1 H,
3
dd, J 5.9 and 16.1), 6.12 (1 H, dd, J 1.5 and 16.1), 5.12 (1 H,
m), 4.12 (1 H, ddd, J 1.5, 5.9 and 7.3), 3.32 (1 H, m), 2.25 (2 H,
br s), 1.76–1.60 (3 H, complex m), 1.52–1.32 (5 H, complex m),
(
6 H, s); d
C
(CDCl
3
, 75 MHz) 166.6 (C), 143.0 (CH), 123.2 (CH),
), 48.0 (CH ),
), 17.7 (CH ), 17.5
9
4
8.7 (C), 98.6 (C), 71.8 (CH), 70.7 (CH), 51.7 (CH
3
3
1.29 (3 H, d, J 6.8), 1.22 (1 H, m), 1.02 (1 H, m); d
150 MHz) 166.9 (C), 146.6 (CH), 122.4 (CH), 77.8 (CH), 77.6
(CH), 72.8 (CH), 33.0 (CH ), 32.4 (CH ), 28.1 (CH ), 24.8 (CH ),
22.6 (CH ), 18.8 (CH ); m/z (EI, 70 eV) 228 (M , <1%), 210
[(M − H O) , 7], 199 (39), 184 (28), 171 (100).
C
(CDCl
3
,
7.9 (CH
3
), 30.6 (CH
); m/z (EI, 70 eV) 571 [(M − CH
2
), 29.6 (CH
2
), 25.1 (CH
2
3
+
(
CH
3
3
O·) , 11%], 539 (46), 507
2
2
2
+
2
•
(
2
29), 439 (21), 390 (72), 274 (47), 249 (45), 220 (55), 219 (100),
05 (60), 166 (55), 149 (68).
2
3
+
•
2
Compound 23
(
−)-Cladospolide B (2)
A magnetically stirred solution of compound 24 (37 mg,
.16 mmol) in degassed benzene was irradiated for 16 h at
A magnetically stirred solution of methyl ester 20 (129 mg,
0
.34 mmol) in ethanol (7 mL) was treated with NaOH (1.1 mL
0
of a 1.5 M aqueous solution, 1.65 mmol). The resulting mixture
was allowed to stir at 18 C for 3 h, diluted with water (10 ml),
acidified to pH 3 (with 1 M aqueous HCl) and extracted with
◦
300 nm in a Rayonet photoreactor. Evaporation of the solvent
and subjection of the resulting clear, colourless oil to semi-
preparative HPLC purification (7 : 3 v/v ethyl acetate–hexane
elution) provided two fractions, A and B.
dichloromethane (3 × 10 mL). The combined organic phases
were dried (MgSO ), filtered and concentrated under reduced
4
Concentration of fraction A (R
21 mg, 57% recovery) identical, in all respects, with authentic
material.
Concentration of fraction B (R
compound 2 (5 mg, 31% at 43% conversion) as a white solid,
t
12.3 min) gave compound 24
pressure to give the carboxylic acid 22 as a light-yellow oil.
The unstable acid obtained as described above was im-
mediately dissolved in THF (3 mL) containing triethylamine
(
t
9.9 min) gave the title
(
57 lL, 0.41 mmol) and the resulting and magnetically stirred
◦
solution cooled to 0 C, treated with 2,4,6-trichlorobenzoyl
chloride (54 lL, 0.35 mmol) and warmed to 18 C. After 1 h
TLC analysis indicated that all of the starting material had
been consumed. The reaction mixture was diluted with toluene
◦
3
◦
◦
mp 108–109 C {lit. mp [for (+)-cladospolide B] 109–110 C},
a]
−162 (c 0.1, MeOH). mmax/cm 3409, 2926, 2855, 1707,
633, 1460, 1377, 1279, 1047, 838; d (CDCl , 500 MHz) 6.24
−
1
[
1
D
H
3
(
(
1
1
2
1
1 H, dd, J 8.3 and 12.2), 5.78 (1 H, dd, J 1.5 and 12.2), 5.27
1 H, m), 4.89 (1 H, m), 3.78 (1 H, m), 3.64–3.41 (2 H, br m),
(
30 mL) and added, over ca. 10 minutes and via cannula, to a
solution of DMAP (210 mg, 1.72 mmol) in refluxing toluene
30 mL). The resulting mixture was heated at reflux for 1 h then
cooled, quenched with NaHCO (10 mL of a saturated aqueous
solution) and extracted with ethyl acetate (3 × 10 mL). The
combined organic fractions were washed with CuSO
(1 × 5 mL
of a saturated aqueous solution), water (1 × 5 ml) and brine
), filtered and concentrated
.80–1.27 (10 H, complex m), 1.29 (3 H, d, J 6.3); d
C
(CDCl ,
3
(
50 MHz) 165.8, 148.5, 121.9, 74.4, 73.9, 67.4, 31.9, 30.5, 25.6,
3
•
+
4.1, 21.3, 19.6; m/z (EI, 70 eV) 228 [(M , <<1%), 169 (29),
09 (28), 102 (100), 84 (65), 55 (57).
4
(
1 × 5 mL), and then dried (MgSO
4
Crystallographic studies
under reduced pressure to give a light-yellow oil. Subjection of
this material to flash chromatography (1 : 9 v/v ethyl acetate–
Crystal data for compound Z-13.
C
16
H
26
O
6
, M = 314.378,
T = 200(1) K, trigonal, space group P3
1
, Z = 9, a = 18.6850(2),
hexane elution) and concentration of the relevant fractions (R
.2) gave the macrolactone 23 (73 mg, 62%) as white, crystalline
f
3
˚
˚
b = 18.6850(2), c = 12.2539(1) A, V = 3705.02(6) A , Dx =
0
−
3
◦
1
.268 Mg m , 5629 unique data (2hmax = 55 ), 5022 with I >
3.00r(I); R = 0.038, wR = 0.048, S = 1.292.
solid. Recrystallisation (hexane) of a sample of this material gave
analytically pure material, mp 159–160 C, [a]
◦
D
−152 (c 0.3)
+
[
Found: (M − CH
3
O·) , 311.1862. C18
H
30
O
6
requires (M −
+
−1
Crystal data for compound 23.
00(1) K, orthorhombic, space group P2
C
18
H
30
O
6
, M = 342.43, T =
CH
1
3
O·) , 311.1858]. mmax/cm 2942, 1718, 1462, 1376, 1246,
2
1
2
˚
1
2
1
, Z = 4, a =
122, 1039, 857; d
H
(CDCl , 300 MHz) 6.86 (1 H, dd, J 7.1 and
3
7
.0435(1), b = 16.1734(4), c = 16.3288(4) A, V = 1860.13(7)
1
6.1), 6.16 (1 H, dd, J 1.2 and 16.1), 5.06 (1 H, m), 4.22 (1 H,
3
−3
◦
˚
A , Dx = 1.223 Mg m , 1903 unique data (2hmax = 50 ), 1399
with I > 2.00r(I); R = 0.0276, wR = 0.0297, S = 1.1307.
ddd, J 1.2, 6.8 and 8.3), 3.41 (1 H, m), 3.24 (3 H, s), 3.21 (3 H, s),
.74–1.01 (10 H, complex m), 1.29 (3 H, s), 1.28 (3 H, s), 1.27
3 H, d, J 6.6); d (CDCl , 75 MHz) 167.0 (C), 143.2 (CH),
23.7 (CH), 99.4 (C), 98.7 (C), 73.9 (CH), 72.9 (CH), 72.8 (CH),
8.0 (CH ), 47.8 (CH ), 32.2 (CH ), 30.5 (CH ), 27.5 (CH ), 25.6
), 22.7 (CH ), 19.1 (CH ), 17.8 (CH ); m/z (EI,
0 eV) 342 (M , <1%), 311 [(M − CH
1
(
C
3
Structure determination. Images were measured on a Nonius
KappaCCD diffractometer (MoKa, graphite monochromator,
1
4
3
3
2
2
2
17
˚
k = 0.71073 A) and data extracted using the DENZO package.
(
CH
2
2
3
3
), 17.4 (CH
O·) , 52], 117 (65), 116
3
18
+
•
+
Structure solution was by direct methods (SIR92). The crystals
7
3
of compound Z-13 were twinned so the structure was refined
using RAELS2000. Full details will be reported elsewhere.
The structure of compound 23 was refined using the CRYSTALS
program package. Atomic coordinates, bond lengths and
angles, and displacement parameters have been deposited at
the Cambridge Crystallographic Data Centre (CCDC reference
(
78), 101 (77), 83 (60), 73 (70), 55 (90), 43 (100).
19
20
E-Isomer of (−)-cladospolide B (24)
A magnetically stirred solution of compound 23 (60 mg,
21
◦
0
.17 mmol) in dichloromethane (2 ml) was cooled to 0
C
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8
1 0 8 7

View Article Online
numbers 253914 and 253913 for compounds Z-13 and 23 respec-
tively). See http://www.rsc.org/suppdata/ob/b4/b417685e/
for crystallographic data in .cif or other electronic format.
8 (a) M. G. Banwell, K. A. Jolliffe, D. T. J. Loong, K. J. McRae and
F. Vounatsos, J. Chem. Soc., Perkin Trans. 1, 2002, 22; (b) M. G.
Banwell and D. T. J. Loong, Org. Biomol. Chem., 2004, 2, 2050.
9
(a) M. G. Banwell and D. T. J. Loong, Heterocycles, 2004, 62,
13; (b) A. F u¨ rstner, K. Radkowski, C. Wirtz, R. Goddard, C. W.
7
Lehmann and R. Mynott, J. Am. Chem. Soc., 2002, 124, 7061; (c) E.
Diez, D. J. Dixon, S. V. Ley, A. Polara and F. Rodriguez, Synlett,
2003, 1186 and references cited therein.
Acknowledgements
Dr Gregg Whited (Genencor International Inc., Palo Alto)
and Professor Tomas Hudlicky (Brock University, Ontario) are
warmly thanked for providing us with generous quantities of
compound 5. Financial support from the Australian Research
Council is gratefully acknowledged.
10 M. G. Banwell, A. J. Edwards and D. T. J. Loong, ARKIVOC, 2004,
x, 53.
1
1
1
1 J.-L. Montchamp, F. Tian, M. E. Hart and J. W. Frost, J. Org. Chem.,
996, 61, 3897.
1
2 S. V. Ley, H. M. I. Osborn, H. W. M. Priepke and S. L. Warriner,
Org. Synth., 1998, 75, 170 and references cited therein.
3 (a) M. Scholl, S. Ding, C. W. Lee and R. H. Grubbs, Org. Lett., 1999,
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1
0 8 8
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 1 0 8 1 – 1 0 8 8