Total synthesis and biological evaluation of novel C2-C6 region analogues of dictyostatin

Article abstract of DOI:10.1016/j.bmc.2008.10.084

By exploiting a Still-Gennari HWE coupling with a common C11-C26 aldehyde, a series of C2-C6 modified analogues of the microtubule-stabilising marine natural product dictyostatin were synthesised and evaluated in vitro for growth inhibition against a rang

Full text of DOI:10.1016/j.bmc.2008.10.084

Bioorganic & Medicinal Chemistry 17 (2009) 2282–2289
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry
journal homepage: www.elsevier.com/locate/bmc
Total synthesis and biological evaluation of novel C2–C6 region
analogues of dictyostatin
a
b
b
Ian Paterson a, , Nicola M. Gardner , Esther Guzmán , Amy E. Wright
*
a University Chemical Laboratory, Lensfield Road, Cambridge CB2 1EW, UK
b Harbor Branch Oceanographic Institute at Florida Atlantic University, 5600 US 1 North, Fort Pierce, FL 34946, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 28 March 2008
Revised 12 June 2008
Accepted 31 October 2008
Available online 5 November 2008
By exploiting a Still–Gennari HWE coupling with a common C11–C26 aldehyde, a series of C2–C6
modified analogues of the microtubule-stabilising marine natural product dictyostatin were synthes-
ised and evaluated in vitro for growth inhibition against a range of human cancer cell lines, including
the (P-glycoprotein efflux-mediated) Taxol-resistant NCI/ADR cell line. Removal of the C6 methyl
substituent in dictyostatin was found to be well tolerated and led to the retention of antiproliferative
activity in the low nanomolar range (IC50 = 43 nM in the NCI/ADR cell line), while partial and full
saturation of the (2Z,4E)-dienoate region led to a progressive reduction in biological potency. The
lactone ring size was found to be critical, as C21 to C19 translactonisation to afford 20-membered
isodictyostatin analogues led to a significant loss of cytotoxicity. In a series of incubatory experiments
performed on the PANC-1 cell line, all three of the 22-membered macrolide analogues acted in an
analogous fashion to dictyostatin, through a mechanism of microtubule stabilization, causing both
an accumulation of cells at the G2/M phase and formation of characteristic dense intracellular
microtubule bundles.
Keywords:
Macrolide
Antitumour
Tubulin
Total synthesis
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
istry.6 Concurrent total synthesis efforts, as reported independently
by the Paterson7a and Curran groups,7b,7c confirmed this structure
The tubulin/microtubule system is an important target in cur-
rent cytotoxic chemotherapy.1 TaxolÒ (1, Fig. 1) and its semi-syn-
thetic derivative TaxotereÒ act by stabilising cellular
microtubules and suppressing microtubule dynamics in cell divi-
sion, and are widely used in the treatment of breast, ovarian and
lung cancers. Despite the clinical utility of the taxane class of
microtubule-stabilising agents, they have limited effectiveness to-
wards multidrug-resistant cancers. Over the past decade, various
structurally diverse natural products that are functionally similar
to Taxol have emerged as important leads for anticancer drug dis-
covery programmes to circumvent resistance in chemotherapy.2
Notably, IxempraÒ (2), a semi-synthetic lactam derivative of the
bacterial natural product epothilone B (3), received approval by
the FDA in 2007 as a new microtubule-stabilising drug for the
treatment of advanced breast cancer.3
and facilitated more extensive biological evaluation of this promis-
ing anticancer agent,8 as well as the initiation of SAR studies.9 Dict-
yostatin displays enhanced antiproliferative activity relative to
Taxol against a range of human cancer cell lines, including multi-
drug-resistant cells, and binds to the taxoid binding site on b-tubu-
lin.8 As a conformationally constrained macrolide, dictyostatin
represents an attractive template for the optimisation of a new
structural class of microtubule-stabilising agent. Following exten-
sive NMR studies and molecular modelling, the bioactive conforma-
tion of dictyostatin bound to microtubules was recently disclosed,10
providing a promising tool for analogue design. Furthermore, the
large body of available SAR data for the structurally related micro-
tubule-stabilising agent discodermolide (5) also offers a useful
starting point for identifying active dictyostatin analogues.11 Nota-
bly, dictyostatin represents a naturally evolved analogue of disco-
dermolide, that has significantly enhanced biological potency.
With the goal of identifying a simplified structure with a cytotoxic-
ity profile comparable to that of the parent natural product, we now
describe in full12 the total synthesis of a novel series of C2–C6 mod-
ified dictyostatin analogues (Fig. 2)—6-desmethyl- (6), 2,3-dihydro-
(7) and 2,3,4,5-tetrahydro-dictyostatin (8)—and evaluate their
growth inhibition against a range of human cancer cell lines, includ-
ing the Taxol-resistant NCI/ADR ovarian cell line.
In a similar manner to Taxol and the epothilones, the antimitotic
marine natural product dictyostatin (4) functions by microtubule
stabilisation and G2/M arrest.4–6 Following its re-isolation from a
Caribbean deep-sea sponge by Wright and co-workers,5 detailed
NMR analysis led in 2004 to the assignment of the full stereochem-
* Corresponding author. Tel.: +44 1223 336407; fax: +44 1223 336362.
E-mail address: ip100@cam.ac.uk (I. Paterson).
0968-0896/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2008.10.084

I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
2283
OH
O
OH
Bz
HO
AcO
HO
O
NH
O
HO
S
OH
Ph
O
O
O
O
O
HO
N
NH2
OH
HO
X
OH
O
O
H
AcO
OH OH
BzO
O
OH
O
O
1: Taxol (paclitaxel)
X = O 3: epothilone B
X = NH 2: Ixempra®
4: dictyostatin
IC50 (PANC-1) = 3.4 nM
5: discodermolide
IC50 (PANC-1) = 59 nM
IC50 (PANC-1) = 7 nM
Figure 1. Structures of representative microtubule-stabilising natural products and IC50 data in the PANC-1 pancreatic cancer cell line.
methyldictyostatin was envisaged to be the preparation of the
novel C4–C10 phosphonate 12, lacking a C6 methyl substituent
and having a PMB ether9a at C7 (rather than the TBS ether used
initially7a).
2. Results and discussion
2.1. Synthesis of 6-desmethyldictyostatin
Preparation of the b-ketophosphonate 12 required for the Still–
Gennari fragment coupling started out from the racemic epoxide
13 (Scheme 2).13 Using the (S,S)-Co-Salen catalyst 14,14 a Jacobsen
hydrolytic kinetic resolution reaction afforded the (S)-epoxide,
which was subjected to CuCl-catalysed ring opening with vinyl mag-
nesium bromide to give the secondary alcohol 15 in 99% ee.15 Fol-
lowing PMB ether formation, a sequence of oxidative olefin
In previous SAR work on dictyostatin, the importance of the C16
methyl substituent was probed through the synthesis of 16-des-
methyldictyostatin (9, Fig. 2).9a,9b Our biological results9a for 9
(IC50 = 130 nM in PANC-1, 1500 nM in NCI/ADR) led us to conclude
that the C16 methyl group was both important in contributing to
the low nanomolar levels of cytotoxicity of dictyostatin and per-
mitting its circumvention of P-glycoprotein-mediated drug resis-
tance. These conclusions are consistent with results from docking
the bioactive conformation of dictyostatin into its b-tubulin bind-
ing site (Fig. 3),10 where the C16 methyl group is predicted to oc-
cupy a small localised binding pocket. Looking towards achieving
further structural simplifications on dictyostatin, the docking stud-
ies indicated that the C6 methyl substituent appears to be in a less
important region for binding relative to that of the C16 methyl
group. Hence, it was proposed to explore the contribution of the
C2–C6 region to the pharmacophore by first synthesising 6-des-
methyldictyostatin (6) to evaluate its overall cytotoxicity in a panel
of Taxol-sensitive and resistant cell lines.
Access to the targeted 6-desmethyl analogue 6 was planned by
adapting our existing synthetic strategy for dictyostatin7a and that
followed for preparing an initial set of analogues9a (Scheme 1). This
relies on a pivotal Still–Gennari HWE fragment coupling with the
fully elaborated C11–C26 aldehyde 10, followed in turn by intro-
duction of the (2Z,4E)-dienoate by a Stille coupling with stannane
11 and Yamaguchi macrolactonisation. By pursuing a similar strat-
egy, the primary modification required to assemble 6-des-
Figure 3. Dictyostatin docked into the taxoid binding site on b-tubulin.
26
OH
26
HO
OH
OH
Yamaguchi
macrolactonisation
O
O
HO
HO
11
1
4
6
O
O
O
O
Still-Gennari10
olefination
1
3
6
OH OH
Stille coupling
2
3
6: 6-desmethyldictyostatin
OH OH
OH OH
6: 6-desmethyldictyostatin
7: 2,3-dihydrodictyostatin
TBS
O
26
TBSO
16
OH
OH
11
H
OH
HO
HO
10
O
O
O
O
O
+
1
epoxide opening
CF3CH2O
1
2
CO2TIPS
4
10
5
Bu3Sn
CF3CH2O
+
OH OH
OH OH
P
I
3
O
O
OPMB
9: 16-desmethyldictyostatin
IC50 (PANC-1) = 130 nM
8: 2,3,4,5-tetrahydrodictyostatin
11
12
Figure 2. Structures of dictyostatin analogues 6–9.
Scheme 1. Retrosynthetic analysis of 6-desmethyldictyostatin (6).

2284
I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
10 + 12
14
K2CO3, 18-crown-6
H
H
(72%, 3:1 Z:E)
N
N
PhMe/HMPA
Co
TBS
O
t-Bu
O
O
t-Bu
t-Bu t-Bu
TBSO
1. cat. 14, AcOH/H2O
(33%, 99% ee)
OH
I
TBSO
TBSO
O
2.
MgBr
OH
I
13
O
OPMB
18
15
CuCl, THF (99%)
1. PMBTCA, cat. Sc(OTf)3,
THF (90%)
2. cat. OsO4, NMO, THF/H2O
1. DDQ, CH2Cl2
2a. NaBH(OAc)3, AcOH, THF
or 2b. (R)-CBS, BH3•THF, THF
(2a. 78% over 2 steps,
80:20 dr)
TBSO
(2b. 76%, 89:11 dr)
TBS
O
OPMB
3. NaIO4, THF/pH 7 buffer
(80% over 2 steps)
4. CHI3, CrCl2, THF/1,4-dioxane
16
TBSO
(74%, 5:1 E:Z)
OH
1. TBAF, AcOH, THF (90%)
2. Dess-Martin, CH2Cl2 (91%)
O
I
I
OH OPMB
3. NaClO2, NaH2PO4,
t-BuOH/H2O (99%)
OR OR
17
19: R = H
20: R–R = CMe
(MeO)2CMe2,
PPTS (92%)
2
NMe2
CF3CH2O
CF3CH2O
4
10
2. Cl3(C6H2)COCl, Et3N,
DMAP, PhMe
TBS
1. 11, CuTC, NMP;
1.
Cl , CH2Cl2
KF, THF/MeOH
P
I
2. LiHMDS, (CF3CH2O)2P(O)CH3,
THF (74% over 2 steps)
O
O
OPMB
O
12
TBSO
Scheme 2. Synthesis of the C4–C10 b-ketophosphonate 12.
O
O
cleavage (OsO4, NMO; NaIO4) and Takai olefination16 of the resulting
aldehyde afforded the (E)-vinyl iodide 16 (53% from 15). After TBS
ether cleavage (TBAF, AcOH), the resulting alcohol was converted
via the carboxylic acid 17 into the acid chloride using the Ghosez
chloroenamine reagent,17 followed by the addition of (CF3CH2O)2-
P(O)CH2Li to provide the b-ketophosphonate 12 (60% from 16).
As deployed in our dictyostatin total synthesis, we were now
ready to perform the Still–Gennari HWE coupling18 with the
C11–C26 aldehyde 10 (Scheme 3).7a Following treatment of a mix-
ture of phosphonate 12 and aldehyde 10 with K2CO3 (18-crown-6,
PhMe, HMPA), the required (Z)-enone 18 was obtained in an iso-
lated yield of 54% (3:1 Z:E). Oxidative cleavage (DDQ, pH 7 buffer)
of the PMB ether in 18 then released the b-hydroxyketone in read-
iness for a hydroxyl-directed reduction. Reduction with NaB-
O
O
21
(35% over 4 steps)
HF•pyridine, THF
OH
HO
O
O
OH OH
6: 6-desmethyldictyostatin
Scheme 3. Completion of the synthesis of 6-desmethyldictyostatin (6).
19
H(OAc)3 afforded the expected 1,3-anti diol 19 with moderate
selectivity (78%, 80:20 dr). Interestingly, a switch to the Corey–
Bakshi–Shibata (R)-oxazoborolidine-mediated reduction9f,20 gave
the 1,3-anti diol 19 (76%, 89:11 dr) with improved levels of diaste-
reoselectivity. After formation of the acetonide 20 (Me2C(OMe)2,
PPTS), a CuTC-mediated Liebeskind–Stille coupling21 with the vinyl
stannane 117a installed the (2Z,4E)-dienoate and a Yamaguchi
macrolactonisation22 then gave the 22-membered macrolide 21.
Following global deprotection of 21 with HFꢀpyridine and HPLC
purification, 6-desmethyldictyostatin (6) was isolated in 53% yield
in readiness for biological testing.
2.2. Synthesis of 2,3-dihydro- and 2,3,4,5-tetrahydrodictyo-
statin
The remarkable structural and stereochemical homology be-
tween the C8–C26 region of dictyostatin and the corresponding
C6–C24 region of discodermolide has previously been exploited
in the design of novel dictyostatin analogues9 and hybrid mole-
cules.9d,9f In contrast, the discodermolide structure features a d-lac-
tone in the C1–C5 region, whereas the dictyostatin macrolide
differs in having a (2Z,4E)-dienoate moiety. Examination of these
Figure 4. Dictyostatin (blue) and discodermolide (green) docked into the taxoid
binding site on b-tubulin.
two natural products docked10 into their putative common binding
site on b-tubulin (Fig. 4) reveals the dictyostatin dienoate domain
occupies a space that appears to be vacant for discodermolide.
Hence, it was proposed to further probe the SAR associated with

I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
2285
the unique C1–C5 region of dictyostatin through the total synthesis
TBSO
of two novel reduced analogues, 2,3-dihydro- (7) and 2,3,4,5-tetra-
hydrodictyostatin (8).23
OPMB
26
In designing a synthetic route to analogues 7 and 8, it was
apparent that removal of the dienoate negated the requirement
for the Stille coupling step and hence the presence of a vinyl iodide
in the b-ketophosphonate fragment. By retaining the Yamaguchi
macrolactonisation and Still–Gennari HWE olefination with the
pivotal aldehyde 10, a unified route was planned to the phospho-
nates 22 and 23, which differed only in the presence or absence
CrO3, H2SO4,
Me2CO (88%)
O
OH OPMB
27
of a
D
4,5-olefin, as required for the construction of analogues 7
1. (COCl)2, CH2Cl2
2. (CF3CH2O)2P(O)CH3,
LiHMDS
(65% over 2 steps)
and 8, respectively (Scheme 4). It was envisaged that the key C1–
C10 building block 22 might arise from a cross-metathesis reaction
between b-ketophosphonate 24 and the simple olefin 25. This se-
quence was viewed as particularly attractive due to its enhanced
convergence and versatility.
CF3CH2O
CF3CH2O
P
O
O
OPMB
24
Starting from the previously reported PMB ether 269a obtained
using a Brown crotylation sequence, treatment with Jones re-
agent24 (CrO3, H2SO4) led to cleavage of the TBS ether and subse-
quent oxidation of the resulting alcohol to provide the acid 27 in
88% yield (Scheme 5). Conversion to the acid chloride was now
possible using oxalyl chloride, and addition of (CF3CH2O)2P(O)-
CH2Li provided the b-ketophosphonate 24 (65% from 27) in readi-
ness for the planned cross-metathesis reaction25 with the terminal
olefin 25. Only when the Grubbs second-generation Ru catalyst
(10 mol%) was used in the presence of AcOH26 (10 mol%) did this
afford the desired unsaturated phosphonate 22 in high yield
(81%, 10:1 E:Z).27 Raney nickel catalysed hydrogenation of alkene
22 then gave the corresponding saturated phosphonate 23 (89%),
as required for the construction of 2,3,4,5-tetrahydrodictyostatin.
OPMB
10 mol% Grubbs II,
10 mol% AcOH,
40 oC, CH2Cl2
25
(81% 10:1 E:Z)
OPMB
CF3CH2O
CF3CH2O
P
O
O
O
OPMB
22
Ra Ni, H2, EtOH
(89%)
OPMB
CF3CH2O
CF3CH2O
P
O
OPMB
23
Scheme 5. Synthesis of phosphonates 22 and 23.
OH
HO
Yamaguchi
macrolactonisation
O
O
With the two b-ketophosphonates 22 and 23 in hand, the tar-
geted analogues 7 and 8 were then completed in a parallel synthe-
sis sequence (Scheme 6). First the phosphonates were each coupled
with the fully elaborated C11–C26 aldehyde 10 under modified
Still–Gennari HWE olefination conditions,18 providing the corre-
sponding (Z)-enones, 22 ? 28 (65%) and 23 ? 29 (54%). DDQ-med-
iated oxidative cleavage of the C1 and C7 PMB ethers then gave the
corresponding triols, 28 ? 30 and 29 ? 31. In this situation, the
Evans-Saksena hydroxyl-directed reduction proceeded with little
or no stereocontrol. As previously observed, a switch to the Cor-
ey–Bakshi–Shibata (R)-oxazoborolidine-mediated reduction9f,20
afforded the desired 1,3-anti diols, 30 ? 32 (95%, 88:12 dr) and
31 ? 33 (85%, 89:11 dr), with high diastereoselectivity. The 1,3-
diols were then transformed into their acetonides,28 followed by
chemoselective oxidation of the primary alcohol (TEMPO/BAIB;
NaClO2) to afford the seco-acids, 32 ? 34 and 33 ? 35. Finally,
macrolactonisation under Yamaguchi conditions proceeded in high
yield, and subsequent global deprotection and HPLC purification
afforded 2,3-dihydrodictyostatin (7, 39%) and 2,3,4,5-tetra-
hydrodictyostatin (8, 45%) in readiness for biological evaluation.
Irrespective of the chosen deprotection conditions (HFꢀpyridine
or HCl/MeOH), some translactonisation to the C19 hydroxyl oc-
curred to generate the isodictyostatins29 (36, 28% and 37, 23%)
which were also isolated in the aforementioned HPLC purification.
Sufficient material was obtained to allow the additional biological
evaluation of these novel 20-membered macrolides.
2
Still-Gennari
olefination
5
3
OH OH
7: Δ4,5, 2,3-dihydrodictyostatin
8: 2,3,4,5-tetrahydrodictyostatin
TBS
O
TBSO
H
OH
10
O
+
OPMB
OPMB
1
CF3CH2O
CF3CH2O
10
4
P
5
O
O
O
OPMB
23 (for 8)
1
CF3CH2O
CF3CH2O
10
P
O
OPMB
cross-metathesis
22 (for 7)
OPMB
1
CF3CH2O
10
CF3CH2O
P
+
3. Biological evaluation
25
O
O
OPMB
24
The cell growth inhibitory activities of the five novel dictyosta-
tin analogues 6, 7, 8, 36 and 37 were evaluated in vitro relative to
Scheme 4. Retrosynthetic analysis of dictyostatin analogues 7 and 8.

2286
I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
Table 1
22 or 23 + 10
(5:1 Z:E)
Growth inhibitory concentrations of analogues 6, 7, 8, 36 and 37 relative to Taxol (1),
dictyostatin (4) and discodermolide (5)9a against four cultured human cancer cell
K2CO3, 18-crown-6,
lines, as determined by MTT metabolism following 72 h exposure to the test agent
PhMe/HMPA
TBS
O
Compound
IC50/nMa
AsPC-1
(pancreatic)
DLD-1
(colon)
PANC-1
(pancreatic)
NCI/ADR (paclitaxel-
resistant)
TBSO
1
89 ( 23)
6.2 ( 1.7)
98 ( 34)
56 ( 25)
94 ( 28)
3100 ( 890)
22 ( 3.5)
2.2 ( 0.9)
29 ( 8)
8.1 ( 3.8)
22 ( 13)
930
9.9 ( 3.6)
4.2 ( 1.7)
59 ( 34)
17 ( 10)
42 ( 7)
1300 ( 345)
6.6 ( 1.0)
160 ( 34)
43 ( 13)
66 ( 11)
1600 ( 490)
HO
OR
4
4
5b
6
5
O
OR
28: R = PMB, Δ4,5 (65%); 29: R = PMB (54%)
30: R = H, Δ4,5 (77%); 31: R = H (84%)
7
36
DDQ, CH2Cl2
1900 ( 330)
( 580)
8
37
120 ( 25)
4900 ( 1100)
55 ( 13)
1500
( 200)
64 ( 33)
3200 ( 170)
130 ( 66)
3100 ( 790)
(R)-CBS, BH3•THF, THF
TBS
O
a
Values are standard deviation (in parentheses) from a minimum of three
TBSO
experiments.
b
Data taken from Ref. 9a
HO
OH
ilar to dictyostatin, and notably superior to discodermolide, in both
the Taxol-sensitive and resistant cell lines. This result is consistent
with the findings of the Curran group,9e where 6-epi-dicyostatin
was found to be essentially equipotent to dictyostatin in its activity
against the Taxol-resistant ovarian 1A9/Ptx22 cell line. Moreover,
both sets of results are consistent with the C6 substituent being
in a relatively open region of the binding site on b-tubulin, where
it forms no strong binding interaction. In both the Taxol-sensitive
and resistant cell lines, 2,3-dihydrodictyostatin (7) and 2,3,4,5-tet-
rahydrodictyostatin (8) showed growth inhibitory activity resem-
bling that of discodermolide, but lower levels relative to
dictyostatin. We attribute this to a decreased entropic component
of the binding energy as a result of the greater rotational freedom
of the C1–C5 region upon partial and complete saturation. As a
nanomolar level of antiproliferative activity was still observed for
both these analogues against the AsPC-1 (pancreatic), DLD-1 (co-
lon), PANC-1 cell lines, the presence of the (2Z)-olefin or (4E)-olefin
does not appear to be critical. With regard to the isodictyostatin
analogues 36 and 37, a large decrease in cell growth inhibition to
micromolar levels was observed upon translactonisation to the
20-membered macrolactone. Presumably, this drastically alters
the conformation and reduces the binding energy relative to that
of dictyostatin, leading to the dramatic attenuation of antiprolifer-
ative activity. In a separate series of incubatory experiments per-
formed on the PANC-1 cell line, the most active analogues, 6-
desmethyl- (6) and 2,3-dihydrodictyostatin (7), were shown to
act in an analogous fashion to dictyostatin, through a mechanism
of microtubule stabilisation, causing both an accumulation of cells
at the G2/M phase (Table 2) and formation of characteristic dense
intracellular microtubule bundles (Fig. 5).
OH OH
32: Δ4,5 (95%, 88:12 dr); 33 (85%, 89:11 dr))
1. PPTS, (MeO)2CMe2; PPTS,
CH2Cl2/MeOH
2. TEMPO, BAIB, CH2Cl2
3. NaClO2, NaH2PO4, t-BuOH/H2O
TBS
O
TBSO
HO
CO2H
O
O
34: Δ4,5 (59%); 35 (97%)
1. Cl3(C6H2)COCl, Et3N,
DMAP, PhMe
2. HCl, MeOH
OH
HO
O
O
OH OH
7: Δ4,5, 2,3-dihydrodictyostatin (38%)
8: 2,3,4,5-tetrahydrodictyostatin (45%)
+
HO
19
HO
O
O
OH OH
4. Conclusions
36: Δ4,5, 2,3-dihydro-isodictyostatin (27%)
37: 2,3,4,5-tetrahydro-isodictyostatin (23%)
By adapting our total synthesis, a series of novel C2–C6 modi-
fied analogues of the microtubule-stabilising marine natural prod-
uct dictyostatin were prepared and evaluated in vitro for growth
inhibition against a range of human cancer cell lines, including
the (P-glycoprotein efflux-mediated) Taxol-resistant NCI/ADR cell
line. Removal of the C6 methyl substituent, as in 6-des-
methyldictyostatin (6), was found to be well tolerated and led to
the retention of low nanomolar antiproliferative activity
(IC50 = 43 nM in the Taxol-resistant NCI/ADR cell line), while par-
tial and full saturation of the (2Z,4E)-dienoate region in analogues
7 and 8, respectively, led to a progressive reduction in potency. In
contrast, the isomeric 20-membered macrolides 36 and 37 were
essentially inactive (micromolar IC50). Notably, 6-des-
Scheme 6. Completion of the synthesis of 2,3-dihydro- (7) and 2,3,4,5-tetra-
hydrodictyostatin (8).
Taxol (1), dictyostatin (4) and discodermolide (5)9a against four hu-
man cancer cell lines: AsPC-1 (pancreatic), DLD-1 (colon), PANC-1
(pancreatic) and NCI/ADR (Taxol-resistant ovarian) (Table 1).
Drug resistance is mediated in the NCI/ADR cell line by the
overexpression of a P-glycoprotein in the cell membrane, facilitat-
ing the removal of the drug agent from the cell. A broad spectrum
of activities against all four cancer cell lines were shown by our
synthetic dictyostatin analogues. As anticipated, 6-des-
methyldictyostatin (6) displayed low nanomolar cytotoxicity sim-

I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
2287
Table 2
cence imaging of PANC-1 cells were conducted as per protocols de-
scribed previously.5
Cell cycle analysis by flow cytometry of PANC-1 cells incubated for 24 h with ethanol
(vehicle control) and 100 nM concentrations of analogues 6, 7, 8 and dictyostatin. All
three analogues and dictyostatin show an accumulation of cells at the G2/M phase
5.2. General experimental procedures
Compound
% of cells in cell cycle phase
Observations
1H and 13C NMR spectra were recorded in CDCl3, C6D6 or CD3OD
on a Bruker Avance BB-ATM, TCI-ATM and DRX-400. IR spectra were
measured on a Perkin Elmer Spectrum One (FT-IR) spectrophotome-
ter. HRMS were obtained from the EPSRC Mass Spectrometry Service
(Swansea, UK) using a Micromass 0-+-Q-TOF or Bruker Bioapex FT-
ICR spectrometer. Optical rotations were recorded on a Perkin Elmer
G1
S
G2
Ethanol control
46
33
14
17
17
9.0
21
82
76
75
84
Normal
4
6
7
8
4.2
8.0
9.0
6.0
G2/M arrest
G2/M arrest
G2/M arrest
G2/M arrest
241 polarimeter and [
centration, c (g/100 mL). Preparative HPLC on a Varian silica HPLC
column (250 mm, 5 m, flow 1 mL/min) used IPA/hexane (gradi-
a]
D values given in 10ꢁ1 deg cm2 gꢁ1 at a con-
methyldictyostatin (6) was the most potent analogue studied, with
a cytotoxicity in both Taxol-sensitive and resistant cell lines only
slightly less than the parent dictyostatin, and superior to that dis-
played by discodermolide. The next most active analogue was 2,3-
dihydrodictyostatin (7), which had an activity resembling that of
discodermolide. These new SAR results and that reported for other
analogues,9 combined with consideration of the bioactive confor-
mation of dictyostatin and docking studies,10 should facilitate the
design and synthesis of further simplified dictyostatin analogues
that retain a low nanomolar cytotoxicity profile comparable to
the natural product.
l
ents) as solvent, with UV absorption detection at 254 nm and
205 nm. Analytical TLC was carried out on Merck Kieselgel 60 F254
plates with visualization using UV (254 nm), potassium permanga-
nate and/or PMA/Ce(SO4)2 dip. Flash column chromatography was
carried out on Merck Kieselgel 60 (230–440 mesh) under a positive
pressure. Solvents were redistilled prior to use. Reagents were used
as received unless stated otherwise.
5.2.1. 6-Desmethyldictyostatin (6)
To a solution of macrolactone 21 (13 mg, 16
lmol, 1.0 equiv) in
THF (1600
l
L) was added dropwise HFꢀpyridine (400
l
L) at 0 °C.
5. Experimental
After warming to room temperature the reaction mixture was stir-
red for 48 h. The reaction was quenched after cooling to 0 °C by the
careful addition of NaHCO3 (1 mL) and the phases separated. The
aqueous phase was extracted with EtOAc (3 ꢂ 2 mL) and the com-
bined organic extracts dried (Na2SO4) and concentrated in vacuo.
Flash column chromatography (50% EtOAc/hexane ? 100% EtOAc)
5.1. Biological assays
Cytotoxicity assays were conducted using a standard MTT based
protocol as described previously.30 Cell cycle and immunofluores-
Figure 5. Immunofluorescence images of PANC-1 cells stained with anti-a-tubulin (green) and propidium iodide (red) and observed by confocal microscopy. Cells were
exposed to ethanol (vehicle control) or 100 nM concentrations of 6-desmethyldictyostatin, 2,3-dihydrodictyostatin or dictyostatin. All three of these compounds show dense
microtubule bundles characteristic of microtubule polymerising and stabilising agents.

2288
I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
and HPLC (10% IPA/hexane) afforded 6-desmethyldictyostatin 6
5.2.3. 2,3-Dihydro-isodictyostatin (36)
(4.4 mg, 53%) as a colourless solid.
½
a 2D0
ꢃ
ꢁ1.3 (c 0.11, CHCl3); IR (liquid film)/cmꢁ1 3360, 2957,
½
a 2D0
ꢃ
+45.1 (c 0.18, CHCl3); IR (liquid film)/cmꢁ1 3384, 2959,
2923, 2853, 1715, 1660, 1633, 1467; 1H NMR (500 MHz, C6D6) dH
6.75 (1H, app dtd, J = 1.0, 10.6, 16.6 Hz, H25), 6.06 (1H, app t,
J = 11.0 Hz, H24), 5.63 (1H, dd, J = 9.5, 10.6 Hz, H10), 5.52–5.48
(1H, m, OH), 5.38–5.34 (1H, m, H19), 5.33–5.25 (3H, m,
H4 + H5 + H23), 5.20 (1H, app t, J = 10.8 Hz, H11), 5.13 (1H, dd,
J = 2.0, 16.8 Hz, H26a), 5.06 (1H, br d, J = 10.3 Hz, H26b), 4.77–
4.72 (1H, m, H9), 3.75 (1H, ddd, J = 2.6, 4.8, 10.3 Hz, H7), 3.36
(1H, dd, J = 4.2, 6.6 Hz, H21), 3.13 (1H, dd, J = 3.9, 7.2 Hz, H13),
2.93–2.84 (1H, m, H22), 2.64–2.55 (1H, m, H12), 2.37–2.30 (1H,
m, H3a), 2.27 (1H, app d, J = 6.2 Hz, H2a), 2.26 (1H, app d,
J = 7.1 Hz, H2b), 2.18–2.06 (2H, m, H3b + OH), 2.06–2.00 (1H, m,
2927, 2855, 1697, 1640, 1600, 1458; 1H NMR (500 MHz, C6D6) dH
7.77 (1H, dd, J = 11.6, 15.3 Hz, H4), 6.62 (1H, app td, J = 10.9,
17.1 Hz, H25), 6.22 (1H, app t, J = 11.4 Hz, H3), 5.95 (1H, app t,
J = 11.0 Hz, H24), 5.70 (1H, ddd, J = 7.7, 8.0, 12.8 Hz, H5), 5.55–
5.48 (2H, m, H2 + H10), 5.29 (1H, app t, J = 10.3 Hz, H23), 5.27
(1H, app t, J = 10.9 Hz, H11), 5.10–5.05 (2H, m, H21 + H26a), 5.01
(1H, br d, J = 10.2 Hz, H26b), 4.74 (1H, app q, J = 8.4 Hz, H9), 4.00–
3.94 (1H, m, H7), 3.68–3.61 (1H, m, OH), 3.32–3.26 (1H, m, H19),
3.25–3.21 (1H, m, H13), 3.06–3.01 (1H, m, OH), 2.98–2.90 (1H,
m, H22), 2.74–2.66 (1H, m, H12), 2.29–2.20 (1H, m, H6a), 2.20–
2.11 (1H, m, H6b), 2.02–1.96 (1H, m, H15a), 1.81–1.66 (4H, m,
H8a + H8b + H14 + H20), 1.63–1.55 (1H, m, H18a), 1.54–1.47 (1H,
m, H18b), 1.45–1.16 (3H, m, H16 + H17a + H17b), 1.08 (3H, d,
J = 6.7 Hz, CH3-20), 0.98 (3H, d, J = 6.9 Hz, CH3-14), 0.93–0.86 (1H,
m, H15b), 0.89 (3H, d, J = 6.7 Hz, CH3-16), 0.83 (3H, d, J = 6.7 Hz,
CH3-22), 0.82 (3H, d, J = 6.5 Hz, CH3-12); 13C NMR (125 MHz,
C6D6) dC 166.5 (C1), 146.3 (C3), 142.0 (C5), 134.7 (C23), 134.4
(C11), 133.8 (C10), 132.6 (C25), 130.4 (C24), 129.3 (C4), 117.9
(C26), 115.8 (C2), 76.1 (C21), 75.3 (C13), 73.0 (C19), 67.7 (C7),
66.3 (C9), 44.3 (C8), 40.7 (C6), 40.3 (C15), 39.6 (C14), 35.8 (C22),
35.6 (C12), 32.2 (C20), 32.01 (C17 or C18), 31.96 (C17 or C18),
29.3 (C16), 21.4 (Me16), 17.4 (Me22), 17.3 (Me12), 14.2 (Me14),
10.3 (Me20); HRMS (ESI+) Calcd for C31H50O6Na [M+Na]+
541.3479, found 541.3500; Rf 0.80 (80% EtOAc/hexane); Rt
21.2 min (10% IPA/hexane).
H6),
1.88–1.82
(1H,
m,
H20),
1.79–1.56
1.42–1.15
(6H,
(4H,
m,
m,
H8a + H8b + H14 + H16 + H18a + H18b),
H15a + H15b + H17a + H17b), 1.07 (3H, d, J = 7.0 Hz, CH3-20), 0.98
(3H, d, J = 7.0 Hz, CH3-6), 0.91 (3H, d, J = 6.6 Hz, CH3-16), 0.89
(6H, app d, J = 6.7 Hz, CH3-14 + CH3-22), 0.85 (3H, d, J = 6.6 Hz,
CH3-12); 13C NMR (125 MHz, C6D6) dC 173.1, 135.0, 134.5, 133.5,
133.1, 132.8, 131.1, 130.2, 118.2, 76.6, 76.5, 75.5, 72.2, 66.0, 43.7,
41.8, 38.1, 36.41, 36.38, 34.0, 33.4, 30.4, 30.17, 30.16, 28.3, 20.4,
17.7, 17.6, 15.9, 15.1, 8.4; HRMS (ESI+) Calcd for C32H54O6Na
[M+Na]+ 557.3818, found 557.3840; Rf 0.45 (80% EtOAc/hexane);
Rt 25.6 min (5% IPA/hexane).
5.2.4. 2,3,4,5-Tetrahydrodictyostatin (8)
To a solution of the protected macrolactone precursor in
Scheme 6 (6.6 mg, 8.2
lmol, 1.0 equiv) in MeOH (1 mL) at 0 °C
was added a premixed solution of 3 N HCl (500
lL) and MeOH
5.2.2. 2,3-Dihydrodictyostatin (7)
(2.2 mL). After slowly warming to room temperature the reaction
was stirred for 18 h, before dilution with water (2 mL) and EtOAc
(2 mL). The phases were separated, the aqueous phase extracted
with EtOAc (3 ꢂ 2 mL) and the combined organic extracts dried
(Na2SO4) and concentrated in vacuo. Flash column chromatogra-
phy (60% EtOAc/hexane) afforded a mixture of 2,3,4,5-tetra-
To a solution of the protected macrolactone precursor in
Scheme 6 (6.9 mg, 8.6
was added a premixed solution of 3N HCl (300
(900 L). After warming slowly to room temperature, the reaction
l
mol, 1.0 equiv) in MeOH (600
lL) at 0 °C
L) and MeOH
l
l
was stirred for 16 h, before being diluted with H2O (2 mL) and
EtOAc (2 mL). The phases were separated, the organic phase ex-
tracted with EtOAc (3 ꢂ 2 mL) and the combined organic extracts
dried (Na2SO4) and concentrated in vacuo. The crude material
was purified using HPLC (5% IPA/hexane) to yield 2,3-
dihydrodictyostatin 7 (1.8 mg, 39%) and 2,3-dihydro-isodictyosta-
tin 36 (1.3 mg, 28%) as colourless solids.
hydrodictyostatin
8 and 2,3,4,5-tetrahydro-isodictyostatin 37
(3.0 mg, 1.5:1 8:37, 75%) which were subsequently separated using
HPLC (5% IPA/hexane) affording 8 (1.9 mg, 45%) and 37 (1.0 mg,
23%) as colourless solids.
½
a 2D0 +17.6 (c 0.13, CHCl3); IR (liquid film)/cmꢁ1 3385, 2961,
ꢃ
2925, 2856, 1715, 1668, 1460; 1H NMR (500 MHz, C6D6) dH
6.66 (1H, app dtd, J = 1.0, 10.5, 17.0 Hz, H25), 6.00 (1H, app t,
J = 11.0 Hz, H24), 5.65 (1H, dd, J = 8.0, 11.1 Hz, H10), 5.33 (1H,
app t, J = 11.0 Hz, H23), 5.19 (1H, dd, J = 1.8, 8.9 Hz, H21), 5.12
(1H, dd, J = 2.0, 16.9 Hz, H26a), 5.10 (1H, app dt, J = 1.1,
11.1 Hz, H11), 5.02 (1H, br d, J = 10.0 Hz, H26b), 4.70–4.64 (1H,
m, H9), 3.80 (1H, br d, J = 10.5 Hz, H7), 3.44–3.38 (1H, m, H19),
3.07 (1H, dd, J = 2.1, 8.1 Hz, H13), 2.95–2.86 (1H, m, H22),
2.54–2.46 (1H, m, H12), 2.32 (1H, ddd, J = 6.2, 9.5, 15.7 Hz,
H2a), 2.23 (1H, ddd, J = 7.0, 13.1, 16.6 Hz, H2b), 2.16–1.93 (1H,
br s, OH), 1.79–1.65 (5H, m, H3a + H8a + H14 + H15a + H20),
1.64–1.50 (4H, m, H3b + H8b + H16 + H18a), 1.45–1.30 (7H, m,
H4a + H5a + H5b + H6 + H17a + H17b + H18b), 1.26–1.19 (1H, m,
H4b), 1.02 (3H, d, J = 7.1 Hz, CH3-20), 0.90 (3H, d, J = 6.6 Hz,
CH3-16), 0.87 (6H, app d, J = 6.9 Hz, CH3-6 + CH3-14), 0.82 (3H,
d, J = 6.7 Hz, CH3-22), 0.79 (3H, d, J = 6.7 Hz, CH3-12), 0.84 (1H,
app t, J = 9.1 Hz, H15b); 13C NMR (125 MHz, C6D6) dC 173.6
(C1), 135.5 (C10), 135.2 (C23), 133.1 (C11), 132.8 (C25), 130.0
(C24), 117.7 (C26), 75.5 (C21), 75.0 (C13), 74.4 (C19), 71.9
C(7), 67.4 (C9), 40.7 (C20), 39.9 (C6), 39.2 (C15), 38.9 (C8),
36.4 (C12), 35.6 (C22), 35.2 (17), 34.4 (C2), 32.1 (C4), 31.7
(C14), 31.1 (C18), 29.3 (C16), 26.8 (C5), 25.4 (C3), 21.2 (Me16),
17.4 (Me22), 17.3 (Me12), 15.2 (Me6), 14.4 (Me14), 10.0
(Me20); HRMS (ESI+) Calcd for C32H56O6Na [M+Na]+ 559.3975,
found 559.3948; Rf 0.37 (80% EtOAc/hexane); Rt 22.4 (5% IPA/
hexane).
½
a 2D0 +10.6 (c 0.15, CHCl3); IR (liquid film)/cmꢁ1 3364, 2957,
ꢃ
2924, 2854, 1715, 1660, 1633, 1457; 1H NMR (500 MHz, C6D6) dH
6.65 (1H, app td, J = 10.4, 16.6 Hz, H25), 6.00 (1H, app t,
J = 11.0 Hz, H24), 5.61 (1H, dd, J = 8.1, 10.9 Hz, H10), 5.35–5.28
(3H, m, H4 + H5 + H23), 5.18 (1H, dd, J = 1.7, 9.1 Hz, H21), 5.09
(1H, dd, J = 2.0, 16.6 Hz, H26a), 5.04 (1H, app t, J = 10.9 Hz, H11),
5.00 (1H, br d, J = 10.3 Hz, H26b), 4.75–4.70 (1H, m, H9), 3.71
(1H, br dd, J = 2.6, 10.5 Hz, H7), 3.52–3.47 (1H, m, H19), 3.07 (1H,
dd, J = 2.7, 7.7 Hz, H13), 2.95–2.86 (1H, m, H22), 2.61 (1H, m,
H12), 2.45–2.29 (3H, m, H2a + H2b + H3a), 2.25–2.13 (2H, m,
H3b + OH), 2.13–2.06 (1H, m, OH), 2.05–1.97 (1H, m, H6), 1.79–
1.63 (5H, m, H8a + H14 + H15a + H18a + H20), 1.62–1.56 (1H, m,
H16), 1.52 (1H, ddd, J = 1.7, 7.6, 14.2 Hz, H8b), 1.47–1.17 (3H, m,
H17a + H17b + H18b), 1.05 (3H, d, J = 6.8 Hz, CH3-20), 0.98 (3H, d,
J = 6.9 Hz, CH3-6), 0.90 (6H, app d, J = 6.5 Hz, CH3-14 + CH3-16),
0.82 (3H, d, J = 6.6 Hz, CH3-22), 0.80 (3H, d, J = 6.5 Hz, CH3-12),
0.76–0.70 (1H, m, H15b); 13C NMR (125 MHz, C6D6) dC 173.0
(C1), 136.1 (C10), 135.3 (C23), 133.0 (C11), 132.8 (C25), 132.5
(C5), 130.2 (C4), 130.0 (C24), 117.7 (C26), 76.0 (C21), 74.9 (C13),
74.1 (C19), 71.9 (C7), 66.3 (C9), 43.5 (C6), 41.8 (C8), 40.3 (C20),
40.1 (C15), 36.6 (C12), 35.6 (C16 + C22), 34.6 (C17), 34.0 (C2),
31.7 (C14), 31.1 (C18), 28.1 (C3), 21.2 (Me16), 17.4 (Me22), 17.3
(Me12), 16.1 (Me6), 14.5 (Me14), 9.6 (Me20); HRMS (ESI+) Calcd
for C32H54O6Na [M+Na]+ 557.3818, found 557.3835; Rf 0.57 (80%
EtOAc/hexane); Rt 16.3 min (5% IPA/hexane).

I. Paterson et al. / Bioorg. Med. Chem. 17 (2009) 2282–2289
2289
7. (a) Paterson, I.; Britton, R.; Delgado, O.; Meyer, A.; Poullennec, K. G. Angew.
Chem. Int. Ed. 2004, 43, 4629; (b) Shin, Y.; Fournier, J. H.; Fukui, Y.; Bruckner, A.
M.; Curran, D. P. Angew. Chem. Int. Ed. 2004, 43, 4634; (c) Shin, Y.; Fournier, J.
H.; Bruckner, A.; Madiraju, C.; Balachandran, R.; Raccor, B. S.; Edler, M. C.;
Hamel, E.; Sikorski, R. P.; Vogt, A.; Day, B. W.; Curran, D. P. Tetrahedron 2007, 63,
8537.
8. (a) Madiraju, C.; Edler, M. C.; Hamel, E.; Raccor, B. S.; Balachandran, R.; Zhu, G.;
Giuliano, K. A.; Vogt, A.; Shin, Y.; Fournier, J. H.; Fukui, Y.; Brückner, A. M.;
Curran, D. P.; Day, B. W. Biochemistry 2005, 44, 15053; (b) Buey, R. M.;
Barasoain, I.; Jackson, E.; Meyer, A.; Giannakakou, P.; Paterson, I.; Mooberry, S.;
Andreu, J. M.; Diaz, J. F. Chem. Biol. 2005, 12, 1269.
9. (a) Paterson, I.; Gardner, N. M.; Poullennec, K. G.; Wright, A. E. Bioorg. Med.
Chem. Lett. 2007, 17, 2443; (b) Shin, Y.; Fournier, J. H.; Balachandran, R.;
Madiraju, C.; Raccor, B. S.; Zhu, G.; Edler, M. C.; Hamel, E.; Day, B. W.; Curran, D.
P. Org. Lett. 2005, 7, 2873; (c) Paterson, I.; Gardner, N. M.; Poullennec, K. G.;
Wright, A. E. J. Nat. Prod. 2008, 71, 364; (d) Shin, Y.; Choy, N.; Balachandran, R.;
Madiraju, C.; Day, B. W.; Curran, D. P. Org. Lett. 2002, 4, 4443; (e) Fukui, Y.;
Bruckner, A. M.; Shin, Y.; Balachandran, R.; Day, B. W.; Curran, D. P. Org. Lett.
2006, 8, 301; (f) Paterson, I.; Gardner, N. M. Chem. Commun. 2007, 49; (g) Jung,
W. H.; Harrison, C.; Shin, Y.; Fournier, J. H.; Balachandran, R.; Raccor, B. S.;
Sikorski, R. P.; Vogt, A.; Curran, D. P.; Day, B. W. J. Med. Chem. 2007, 50, 2951;
(h) Raccors, B. S.; Vogt, A.; Sikorski, R. P.; Madiraju, C.; Balachandran, R.;
Montgomery, K.; Shin, Y.; Fukui, Y.; Jung, W. H.; Curran, D. P.; Day, B. W. Mol.
Pharmacol. 2008, 73, 718.
5.2.5. 2,3,4,5-Tetrahydro-isodictyostatin (37)
+8.5 (c 0.06, CHCl3); IR (liquid film)/cmꢁ1 3361, 2961, 2924,
½ ꢃ
a 2D0
2854, 1715, 1663, 1634, 1460; 1H NMR (500 MHz, C6D6) dH 6.72
(1H, app dtd, J = 0.9, 10.5, 16.8 Hz, H25), 6.03 (1H, app t,
J = 10.8 Hz, H24), 5.62 (1H, dd, J = 9.1, 11.1 Hz, H10), 5.52–5.48
(1H, m, OH), 5.33 (1H, app td, J = 5.3, 7.9 Hz, H19), 5.24 (1H, app
t, J = 10.8 Hz, H11), 5.21 (1H, app t, J = 10.2 Hz, H23), 5.12 (1H,
dd, J = 1.8, 16.6 Hz, H26a), 5.04 (1H, br d, J = 10.3 Hz, H26b),
4.69–4.63 (1H, m, H9), 3.85 (1H, br dd, J = 3.8, 9.7 Hz, H7), 3.29
(1H, app td, J = 3.9, 7.1 Hz, H21), 3.02 (1H, dd, J = 4.4, 6.6 Hz,
H13), 2.92–2.84 (1H, m, H22), 2.53–2.46 (1H, m, H12), 2.30 (1H,
app td, J = 8.0, 15.4 Hz, H2a), 2.23 (1H, ddd, J = 6.5, 8.0, 15.3 Hz,
H2b), 2.13–2.06 (2H, m, 2 ꢂ OH), 1.88–1.82 (1H, m, H20), 1.80–
1.70 (2H, m, H8a + H18a), 1.67–1.42 (9H, m, H3a + H3b +
H6 + H8b + H14 + H15a + H15b + H16 + H18b), 1.40–1.10 (6H, m,
H4a + H4b + H5a + H5b + H17a + H17b), 1.06 (3H, d, J = 6.7 Hz,
CH3-20), 0.89 (3H, d, J = 7.0 Hz, CH3-16), 0.86 (3H, d, J = 7.1 Hz,
CH3-14), 0.85 (6H, app d, J = 6.9 Hz, CH3-6 + CH3-22), 0.83 (3H, d,
J = 6.7 Hz, CH3-12); 13C NMR (125 MHz, C6D6) dC 173.3, 134.6,
134.3, 132.8, 132.7, 131.0, 118.4, 76.5, 76.1, 75.7, 71.8, 66.9, 41.5,
38.7, 38.5, 36.2, 34.2, 32.9, 31.9, 30.7, 30.2, 29.7, 29.6, 29.5, 27.7,
26.1, 25.3, 20.3, 17.7, 17.5, 14.7, 9.1; HRMS (ESI+) Calcd for
C32H56O6Na [M+Na]+ 559.3975, found 559.3948; Rf 0.18 (50%
EtOAc/hexane); Rt 31.7 min (5% IPA/hexane).
10. Canales, A.; Matesanz, R.; Gardner, N. M.; Andreu, J. M.; Paterson, I.; Díaz, F.;
Jiménez-Barbero, J. Chem. Eur. J. 2008, 14, 7557.
11. (a) Florence, G. J.; Gardner, N. M.; Paterson, I. Nat. Prod. Rep. 2008, 25, 342; (b)
Paterson, I.; Florence, G. J. Eur. J. Org. Chem. 2003, 2193; (c) Smith, A. B., III.;
Freeze, S. B. Tetrahedron 2008, 64, 261.
12. For a preliminary account of this work, See: Paterson, I.; Gardner, N. M.;
Guzman, E.; Wright, A. E. Biorg. Med. Chem. Lett. 2008, 18. doi:10.1016/
j.bmcl.2008.09.109.
13. Ficini, J.; Claude, B.; Desmaele, D.; Ouerfelli, O. Heterocycles 1987, 25, 329.
14. Schlaus, S. E.; Brandes, B. D.; Larrow, J. F.; Tokunaga, M.; Hansen, K. B.; Gould, A.
E.; Furrow, M. E.; Jacobsen, E. N. J. Am. Chem. Soc. 2002, 124, 1307.
15. The enantiomeric excess was determined by 1H NMR analysis of the Mosher
ester derivatives of alcohol 15.
16. Takai, K.; Nitta, K.; Utimoto, K. J. Am. Chem. Soc. 1986, 108, 7408.
17. Devos, A.; Remion, J.; Frisque-Hesbain, A. M.; Colens, A.; Ghosez, L. J. Chem. Soc.,
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Acknowledgements
NIH Grant No. CA-93455 provided financial support for the bio-
logical assays and general project support was provided by the
EPSRC and AstraZeneca (CASE studentship to N.M.G.). We thank
Professor John Leonard (AstraZeneca) for helpful discussions, Dr.
J. Fernando Diaz (CSIC, Madrid) for providing AutoDock 3D struc-
tures, Ms. Tara Pitts (HBOI) and Ms. Pat Linley (HBOI) for assistance
in our biological evaluation, Samantha Cheung (Cambridge) for
some preliminary synthetic studies and Dr. Stuart Mickel (Novar-
tis) for the gift of chemicals.
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Org. Lett. 2004, 6, 4933.
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complicated by the increased degree of rotational freedom associated with the
C2–C5 carbon chain.
Supplementary data
24. Bowden, K.; Heilbron, I. M.; Jones, E. R. H. J. Chem. Soc. 1946, 39.
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27. Without the AcOH additive, the cross-metathesis reaction proceeded only in
low yield (ca. 10%). It is proposed that the in situ generation of ruthenium
hydride facilitates olefin isomerisation, preventing the metathesis proceeding.
See: Hong, S. H.; Wenzel, A. G.; Salguero, T. T.; Day, M. W.; Grubbs, R. H. J. Am.
Chem. Soc. 2007, 129, 7961.
28. During the course of acetonide protection, the primary C1 alcohol formed a
mixed acetal which was cleaved selectively (PPTS, CH2Cl2 and MeOH) before
the oxidation sequence.
29. Translactonisation has been avoided previously by employing anhydrous
deprotection conditions using HFꢀpyridine. The increased reactivity of the
saturated lactones to transacylation may be responsible for the reappearance
of these isodictyostatin by-products.
30. Gunasekera, S. P.; Zuleta, I. A.; Longley, R. E.; Wright, A. E.; Pomponi, S. A. J. Nat.
Prod. 2003, 66, 1615.
Supplementary data associated with this article, including full
experimental details for intermediates and copies of NMR spectra
of analogues prepared can be found, in the online version, at
doi:10.1016/j.bmc.2008.10.084.
References and notes
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