Synthesis and cytotoxic evaluation of some cribrostatin-ecteinascidin analogues

Article abstract of DOI:10.1021/np800022x

Analogues of cribrostatin IV (1) and the potent antineoplastic agent ecteinascidin 743 (2) have been synthesized. The cytotoxic activity of these compounds (5, 14, 20) has been determined, and the cyanoamine-cribrostatin analogue (14) exhibits a 20-fold improvement with regard to the natural product 1.

Full text of DOI:10.1021/np800022x

J. Nat. Prod. 2008, 71, 409–414
409
Synthesis and Cytotoxic Evaluation of Some Cribrostatin–Ecteinascidin Analogues
Benjamin J. D. Wright,† Collin Chan,† and Samuel J. Danishefsky*,†,‡
Department of Chemistry, Columbia UniVersity, HaVemeyer Hall, 3000 Broadway, New York, New York 10027, and Laboratory for Bioorganic
Chemistry, Sloan-Kettering Institute for Cancer Research, 1275 York AVenue, New York, New York 10065
ReceiVed October 27, 2007
Analogues of cribrostatin IV (1) and the potent antineoplastic agent ecteinascidin 743 (2) have been synthesized. The
cytotoxic activity of these compounds (5, 14, 20) has been determined, and the cyanoamine-cribrostatin analogue (14)
exhibits a 20-fold improvement with regard to the natural product 1.
Since the isolation of naphthyridinomycin in 1974, the tetrahy-
droisoquinoline antitumor antibiotics have elicited significant
excitement both for their complex, intriguing structural features and
for their highly potent cytotoxic properties.1 Most notably,
syntheses2–5 and pharmaceutical evaluation6–9 of ecteinascidin 743
(Et 743, 2) have confirmed the low nanomolar cytotoxic activity
of this benchmark compound (also called Yondelis) and have
propelled it to the brink of FDA approval for the treatment of
ovarian and other forms of cancer.
In 2000, George R. Pettit and co-workers first reported in this
Figure 1. Structures of cribrostatin IV (1) and ecteinascidin 743
(2).
journal the isolation and structure of a new member of this family,
which they termed cribrostatin IV (1, Figure 1).10 Subsequently,
Kubo and colleagues reported a reassignment of the previously
reported structure of renieramycin H as also corresponding to 1.11
Our interest in 1 stemmed from its highly functionalized
pentacyclic core, in which every skeletal carbon appears in an
oxidized form. Additionally, the low-micromolar cytotoxicity of
cribrostatin IV in the absence of the characteristic N-2/C-21
cyanomethinyl or hydroxymethinyl (preiminium ion) functionalities
in Et 770 and 743 suggests that the highly oxygenated core of
cribrostatin IV and/or the idiosyncratic C-3/C-4 olefin allows it to
overcome this ostensible prerequisite for activity.1
Hypothetically, the replacement of the C-21 lactam of 1 with a
labile, preiminium functionality should yield a more active con-
gener. In our longstanding synthesis efforts toward Et 743,12 and
upon completion of the cribrostatin IV odyssey,13 our laboratory
has established access to a wide range of functionalized pentacyclic
scaffolds, many of which include the intriguing C-3/C-4 double
bond of cribrostatin. This report serves to detail the synthesis of
several analogues of this type and to reveal the preliminary
connections we have observed between structure and cytotoxic
activity.
Figure 2. Originally proposed targets for derivatization of the
natural products.
our studies commenced with hydrogenolysis of the known ene-
pentacycle 813 to afford diol 9, which upon sequential treatment
with the ate complex14 derived from a 1:1 admixture of DIBAL-H
and n-BuLi followed by KCN yielded C-21 cyanoamine 10, but in
low yield (<15%). The major product was the over-reduced,
undesired amine 11 (Scheme 1). Unfortunately, attempted optimiza-
tion of this sequence utilizing a variety of reducing agents (borane
complexes, Red-Al, DIBAL-H, or LAH) and cyanation agents
(KCN or TMSCN) uniformly led to this same dead end in the form
Results and Discussion
Chemistry. Arguably, the most intriguing general scaffold for
the purpose of this study is one in which the C-3/C-4 double bond
exists alongside a C-21 preiminium species (Vide infra). Beyond
that, we were also eager to compare some of the other features of
the Et 743 manifold in this context, especially the A/E-ring aromatic
portions, which differ significantly from those found in 1 and which
also have been previously deemed important for potent biological
activity.6 With these two parameters in mind, our initial analogue
goals became those shown in Figure 2.
of 11.
These results are attributed to the presence of the C-3/C-4 double
bond, which reduces a degree of torsional freedom in the B-ring.
As such, upon half-reduction of the C-21 lactam, the lack of
flexibility in the B-ring hinders the formation of an oxazolidine
intermediate, leaving a highly reactive carbinolamine functionality
easily reduced to the undesired amine, 11. In addition, the
conjugation between the electron rich A-ring and N-2 also may
contribute to the relative ease of reduction observed in this system
by stabilizing a transient iminium cation.
With regard to C-21, we hoped to use the reductive-cyanation
conditions optimized in our formal Et 743 synthesis.12 To this end,
Indeed, the only successful cyanoamine syntheses of this type
in the literature are reported on pre-pentacyclic intermediates or
on substrates saturated at C-3.1 Taking these data into account, the
key to our eventual success was found in combining the highly
efficient reductive-cyanation sequence reported in 2005 by Williams
and co-workers15 with a C-3-saturated variant of our own (Scheme
Dedicated to Dr. G. Robert Pettit of Arizona State University for his
pioneering work on bioactive natural products.
* To whom correspondence should be addressed. Tel: (212) 639-5502.
Fax: (212) 772-8691. E-mail: s-danishefsky@ski.mskcc.org.
† Columbia University.
‡ Sloan-Kettering Institute for Cancer Research.
10.1021/np800022x CCC: $40.75
2008 American Chemical Society and American Society of Pharmacognosy
Published on Web 02/16/2008

410 Journal of Natural Products, 2008, Vol. 71, No. 3
Wright et al.
Scheme 3. Synthetic Route toward Hybrid Analogue 20a
Scheme 1. Failed Reductive Cyanation of Unsaturated
Pentacyclic Diol
a Key: (a) LAH, THF; (b) KCN, AcOH, H2O; (c) (Ph3P)2PdCl2, Bu3SnH,
AcOH, CH2Cl2, 62% (over three steps); (d) p-TsOH, MgSO4, benzene; (e) Ac2O,
TEA, CH2Cl2, 90% (over two steps), (f) 10% Pd/C, H2 (1 atm), MeOH, 33%;
(g) salcomine, O2 (5 bar), THF, 82%; (h) SeO2, 1,4-dioxane; (i) DMP, CH2Cl2;
(j) Zn, AcOH, 82% (over three steps).
Scheme 2. Synthetic Route toward Cyano-cribrostatin IV
Analogue 14a
in the short term. However, we believed intermediate 14 could be
an initial analogue to work from, as it had two key structural
features: a C-3/C-4 double bond and a cyanoamine functionality
at C-21. At this time, the focus shifted to the synthesis of cyano-
and hydroxy-hybrid analogues (cf. 6 and 7).
Thus, known keto-pentacycle 17 of the Et 743 series12 was
treated in the same fashion as previously described for the
conversion of 12 into 14. These results are depicted in Scheme 3.
Having achieved intermediate 18 without issue, the difficult task
of deprotecting the benzyl groups in the presence of the sensitive
C-21 cyanoamine function (cf. 14 to 15) was again at hand. In the
event, treatment of 18 under catalytic hydrogenation conditions did
afford the partially debenzylated compound 19, albeit in low yield
(33%), along with the undesired amine saturated at C-21 (not
shown). The limited amount of material that was obtained was thus
advanced through a series of efficient oxidation state adjustments.
Oxidation of the phenol gave the E-ring benzoquinone,13,17 allylic
oxidation of the quinone yielded the C-14 alcohol,18 Dess–Martin
periodinane19 oxidation afforded the corresponding keto-quinone
intermediate, and, finally, quinone reduction with zinc gave the
desired keto-hydroquinone 20.20,21 Not surprisingly, an extensive
search for conditions to debenzylate the C-22 benzyloxy function
led to undesired reduction of the C-21 cyanoamine.16 Despite our
unsuccessful attempts to install the C-22 angelate ester in either
reduced-lactam series, keto-hydroquinone 20 couldslike 14sbe
used as an initial hybrid-analogue for biological testing, as it had
several key structural features worth examining.
In addition to our work toward the cyanoamine-type cribrostatin
IV analogues, we also synthesized a lactam variant (5) containing
all of the features held in the natural B-E-ring scaffold of
cribrostatin IV, but substituting the A-ring of the more potent Et
743. This synthesis followed a modified, though analogous, route
to that which we reported for the natural product (Scheme 4).13
In summary, attempts to synthesize cyano- and hydroxy-
cribrostatin IV analogues 3 and 4 and cyano- and hydroxy-hybrid
analogues 6 and 7 were interrupted due to difficulties in benzyl
ether deprotection in the presence of the C-21 cyanoamine.
Nevertheless, a simplified cyano-cribrostatin IV analogue (14) has
been synthesized, which will allow us to evaluate the significance
of both the C-3/C-4 double bond and the key C-21 cyanoamine
function in the context of the cribrostatin IV scaffold. In addition,
des-angelate-cyano-hybrid analogue 20 was synthesized. Important
structural features of this analogue include (1) the Et 743 methyl-
a Key: (a) LAH, THF; (b) KCN, AcOH, H2O; (c) (Ph3P)2PdCl2, Bu3SnH,
AcOH, CH2Cl2, 69% (over three steps); (d) p-TsOH, MgSO4, benzene; (e) Ac2O,
TEA, CH2Cl2, 90% (over two steps).
2). In the event, treatment of known keto-pentacycle 1213 under
the Williams protocol installed the desired C-21 cyanoamine
function. The stereochemistry at C-4 was not rigorously assigned
since installation of the double bond would follow. Accordingly,
removal of the phenolic allyl ether, dehydration of the C-4 benzylic
alcohol under acidic conditions, and protection of the A-ring phenol
led to desired cyano-ene pentacyclic analogue 14 (Scheme 2). It
should be noted that attempted dehydration prior to phenol
deprotection failed in this case.
In the forward progression, what remained was introduction of
the C-22 angelate ester and oxidation state adjustments of the A-,
D-, and E-rings. To that end, a screening of various hydrogenolysis
(palladium, platinum, Raney nickel catalysts), Lewis acidic (BCl3,
BBr3), and nucleophilic (TMSI, thiolates) conditions typically
employed for deprotection of benzyl ethers16 led to either recovered
starting material, decomposition, or the undesired amine 16.
The difficulties accompanied with installing the C-21 cyanoamine
coupled with our inability to find debenzylation conditions had
significantly depleted the supply of advanced material. It soon
became apparent that reaching the C-21 cyano-cribrostatin IV
analogue (3) through our current route was not an achievable goal

Cribrostatin–Ecteinascidin Analogues
Journal of Natural Products, 2008, Vol. 71, No. 3 411
Scheme 4. Successful Synthesis of Et 743–Cribrostatin IV
Hybrid Analogue 5a
the highest dose, without net cell killing. The assay performed with
synthetic cribrostatin IV (1) corroborated the results obtained by
Pettit and co-workers, which indicated 1 to exhibit low micromolar
cytotoxicity (GI50 ∼ 5 µM).10 It should be noted that the cyano-
hybrid analogue (20) presented some cytotoxic activity in HT-29
colon cells (LC50 ∼ 14.5 µ M). The total hybrid analogue (5) is
the least active in terms of potency, showing only minor cytostatic
activity at the highest concentration used. Excitingly, the cyano-
cribrostatin IV analogue (14) exhibits concentration-dependent
cytotoxic activity in all three cell lines studied, with LC50 values
in the high nanomolar range (∼400 nM).
Lending further support to the well-documented mechanism of
action for this family of alkaloids, the overarching trend observed
in this study is that the ability for C21 to accept a nucleophile is
paramount when predicting cytotoxicity.7 Indeed, the cyano-
cribrostatin IV analogue (14) (GI50 ∼ 250 nM) displayed a 20-fold
increase in cytotoxicity as compared to isolated cribrostatin IV (1),
despite its relative structural simplicity. Unfortunately, from this
preliminary study the actual effect of the C-3/C-4 double bond is
inconclusive. In addition, the oxidation states of the A-, D-, and
E-rings showed no definitive influence on cytotoxicity in the case
of cyano-analogues.15 However, the positive effect on cytotoxicity
of the vinylogous imide13 framework resulting from the quinone
in natural cribrostatin IV is supported by the lack of activity
observed in hybrid 5. Armed with these preliminary observations
and with confirmation that a simpler structural analogue bearing
the cyanoamine (e.g., 14) can exhibit significant improvements in
potency, we have embarked on a more general SAR study to gain
a finer understanding of this intriguing system, the results of which
will appear in a later publication.
a Key: (a) TBAF, then Ac2O, CH2Cl2, 0 °C, quant; (b) 10% Pd/C, H2, EtOAc,
2 h, 85%; (c) Co(salen)2, 5 atm O2, THF, 76%; (d) SeO2, 1,4-dioxane, 100°C,
quant; (e) DMP, CH2Cl2, rt, 2 h; (f) Zn, HOAc, 83%, 2 steps; (g) 10% Pd/C,
H2, EtOAc, 54% (28% of C14 alcohol); (h) 24, toluene, 70 °C, 2–3 days, 55%.22
Table 1.a
synthetic compound
cell line
GI50
TGI
nd
11.60
7.43
nd
nd
nd
0.35
0.30
0.26
nd
LC50
cribrostatin IV (1)
breast
lung
colon
breast
lung
colon
breast
lung
colon
breast
lung
4.49
7.09
6.74
14.00
7.73
11.10
0.26
0.24
0.20
5.63
6.57
4.06
nd
nd
nd
nd
nd
nd
0.48
0.41
0.36
nd
Experimental Section
hybrid (5)
General Experimental Procedures. All nonaqueous reactions were
carried out in oven-dried glassware under a slight positive pressure of
argon unless otherwise noted. All reagents were commercially available
and used without further purification from Sigma-Aldrich and TCI
America, unless indicated otherwise. Solvents were reagent grade and
purified by standard techniques: THF was distilled from Na-benzophe-
none or filtered through a dry-solvent system; CH2Cl2 was distilled
from CaH2 or filtered through a dry-solvent system; all other solvents
were Aldrich “anhydrous” grade solvents, unless indicated otherwise.
Reactions were magnetically stirred and monitored by thin-layer
chromatography (TLC) on Merck silica gel 60-F254 coated 0.25 mm
plates. Compounds were visualized by dipping the plates in a cerium
sulfate–molybdate solution followed by heating. Concentrations were
performed under reduced pressure using a Büchi rotary evaporator.
Flash chromatography was performed using Silicycle silica gel
(0.040–0.063 mesh) unless otherwise indicated. Preparative thin-layer
chromatography (pTLC) was performed with Merck silica gel 60-F254
coated 0.50 mm plates. Yields reported are for isolated, spectroscopi-
cally pure compounds. Melting points are uncorrected. CDCl3 was
allowed to stand over K2CO3 and 4 Å molecular sieves to neutralize
cyano-cribrostatin (14)
cyano-hybrid (20)
nd
6.72
nd
14.50
colon
a Cytotoxicities reported in µM (nd ) not determined).
enedioxybenzene A-ring, (2) the C-3/C-4 double bond, D- and
E-rings of cribrostatin IV (1), and (3) the C-21 cyanoamine function.
Lastly, a formal Et 743-cribrostatin IV hybrid was also synthesized
for the purpose of analyzing the effect of substituting both oxidation
state and substitution pattern on the A-ring, while otherwise
maintaining the entirety of the cribrostatin IV framework. These
analogues (14, 20, and 5) along with synthetic cribrostatin IV (1)
were submitted to our collaborators at PharmaMar for biological
testing, the results and preliminary analyses of which are described
below.
Biology. In collaboration with PharmaMar, a biopharmaceutical
company based in Spain, the cytotoxicities of synthetic cribrostatin
IV (1) as well as cribrostatin IV analogues were studied. The
methods used by PharmaMar are described in the Experimental
Section.
Synthetic cribrostatin IV (1), cyano-cribrostatin IV analogue 14,
cyano-hybrid analogue 20, and total hybrid analogue 5 were tested
for cytotoxicity against representative human tumor cell lines,
including breast (MDA-MB-231), lung (A-549), and colon (HT-
29) in the dosing range of 10 to 0.0026 µg/mL. Dose–response
curves for each of the test compounds were generated using the
National Cancer Institute (NCI) algorithm.23 From the generated
curves, values of GI50, TGI, and LC50 were interpolated, as
summarized in Table 1.
1
and dry prior to NMR sample preparation. H and 13C NMR spectra
were measured at 300, 400, or 500 and 75, 100, or 125 MHz,
respectively, with either a Bruker AMX-300, AMX-400, or DRX-500
FT NMR spectrometer. Chemical shifts are reported as δ values in
ppm referenced to CDCl3 (1H NMR ) δ 7.26 and 13C NMR ) δ 77.16).
Multiplicity is indicated as follows: s (singlet); d (doublet); t (triplet);
q (quartet); dd (doublet of doublets); m (multiplet); bs (broad singlet).
Infrared spectra (IR) were obtained as thin films on a Perkin–Elmer
Paragon 1000 FTIR spectrometer and are reported in wavenumbers
(cm-1). Mass spectra and high-resolution mass spectra (HRMS) were
obtained on a JEOL JMS-DMX-303 and a NERMAG R10-10 spec-
trometer. Optical rotations were measured on a JASCO DIP-1000
spectrometer.
The cytotoxicity assay performed by PharmaMar consisted of three
representative human tumor cell lines: non-small cell lung cancer (A-
549), colon cancer (HT-29), and breast cancer (MDA-MB-231). These
cells were plated in 96-well microtiter plates and incubated 24 h before
treatment with vehicle alone (control) or varying concentrations of
synthetic cribrostatin IV (1), cyano-cribrostatin IV analogue (14), cyano-
The results suggest that synthetic cribrostatin IV (1) and the
cyano-hybrid analog (20) behave in a similar manner, acting as
cytostatic compounds, reaching a total growth inhibition (TGI) at

412 Journal of Natural Products, 2008, Vol. 71, No. 3
Wright et al.
hybrid analogue (20), and total hybrid analogue (5) ranging from 10
to 0.0026 µg/mL (10 dilutions). The sulforhodamine B (SRB) method
was used to measure the cellular protein content of adherent and
suspension cell cultures. This method consists of the following steps:
(1) the cells in the 96-well microtiter plates were washed twice with a
phosphate buffer solution (PBS), then (2) fixed for 15 min with a 1%
glutaraldehyde solution, then (3) rinsed twice more with PBS, (4) then
stained with 0.4% (wt/vol) SRB dissolved in 1% acetic acid for 30
min at room temperature, (5) the cells were then rinsed several times
in 1% acetic acid solution and air-dried, (6) the protein-bound SRB
dye was then extracted with 10 mM unbuffered tris(hydroxymethy-
l)aminomethane (Tris) base solution, and finally (7) the absorbance of
this solution was determined at 490 nm. Data points were collected
in the following way: (1) before treatment, one plate from each of the
three cell lines was analyzed using the SRB method and used for the
time zero (Tz) point references, (2) treated cells were further incubated
for 72 h and analyzed with the SRB method. With these data points
dose–response curves were generated using the National Cancer Institute
(NCI) algorithm.
Synthesis of Dimethoxybenzene-cyanoamine (13). To a solution
of keto-pentacycle 12 (67.0 mg, 0.0933 mmol) in 15 mL of THF, at
–78 °C, was added, dropwise, a 1.0 M THF solution of LiAlH4 (2.80
mL, 2.80 mmol, 30 equiv). The solution was aged for 12 h to room
temperature. The reaction was then cooled to –78 °C, which was
followed by careful addition of KCN (69.0 mg, 1.41 mmol, 15 equiv)
in 3.0 mL of H2O. The cooling bath was removed, followed by addition
of AcOH (0.11 mL, 1.77 mmol, 20 equiv) and 1.5 mL of THF. The
resultant slurry was aged for 12 h to room temperature. The reaction
was then quenched by a saturated solution of NaHCO3 and extracted
with CH2Cl2 (3×). The organic layers were combined, dried with
MgSO4, and concentrated by rotary evaporation. The crude foam was
dissolved in 5 mL of CH2Cl2. To this solution, at room temperature,
was added Bu3SnH (38 µL, 0.121 mmol, 1.5 equiv), AcOH (53 µL,
0.936 mmol, 10 equiv), and (Ph3P)2PdCl2 (13.0 mg, 0.185 mmol, 0.2
equiv). The solution was aged 15 min and then the reaction concentrated
by rotary evaporation. The residue was purified by column chroma-
1453, 1350, 1205, 1064, 1007 cm-1; HRMS (FAB) calcd for
C43H45N3O7 [M + H] 715.33; found 716.3328.
Synthesis of Hybrid Cyanoamine Acetate (18). To a solution of
keto-pentacycle 17 (84.0 mg, 0.119 mmol) in 12 mL of THF, at –78
°C, was added, dropwise, a 1.0 M THF solution of LiAlH4 (3.00 mL,
2.99 mmol, 25 equiv). The solution was aged for 12 h to room
temperature. The reaction was then cooled to –78 °C followed by careful
addition of KCN (87.0 mg, 1.78 mmol, 15 equiv) in 3.8 mL of H2O.
The cooling bath was removed, followed by addition of AcOH (0.13
mL, 2.38 mmol, 20 equiv) and 3 mL of THF. The resultant slurry was
aged for 12 h to room temperature. The reaction was then quenched
by a saturated solution of NaHCO3 and extracted with CH2Cl2 (3×).
The organic layers were combined, dried with MgSO4, and concentrated
by rotary evaporation. The crude foam was dissolved in 5 mL of
CH2Cl2. To this solution, at room temperature, was added Bu3SnH (48
µL, 0.179 mmol, 1.5 equiv), AcOH (67 µL, 1.19 mmol, 10 equiv),
and (Ph3P)2PdCl2 (16.7 mg, 0.0238 mmol, 0.2 equiv). The solution was
aged 15 min and then the reaction concentrated by rotary evaporation.
The residue was purified by column chromatography with 35% EtOAc/
hexanes to provide 50.0 mg (62%) of hybrid cyanoamine alcohol as
an off-white foam: [R]17D +4.37 (c 1.0 CHCl3); 1H NMR (CDCl3, 400
MHz) δ 7.94 (1H, s), 7.41–7.30 (5H, m), 7.26 (3H, m), 6.96 (2H, m),
6.57 (1H, s), 5.83 (2H, d, J ) 1.98 Hz), 5.58 (1H, t, J ) 10.10 Hz),
5.09 (1H, d, J ) 10.92 Hz), 5.02 (1H, d, J ) 10.92 Hz), 4.28 (1H, s),
3.92 (1H, d, J ) 12.10 Hz), 3.88 (1H, d, J ) 2.48 Hz), 3.82 (1H, d, J
) 12.07 Hz), 3.79 (1H, d, J ) 1.57 Hz), 3.77 (3H, s), 3.62 (1H, dd, J
) 2.83 Hz, 11.25 Hz), 3.30–3.08 (3H, m), 2.93 (1H, d, J ) 9.96 Hz),
2.50 (1H, d, J ) 17.86 Hz), 2.27 (3H, s), 2.16 (3H, s), 2.09 (3H, s),
1.39 (1H, d, J ) 10.35 Hz); 13C NMR (CDCl3, 100 MHz) δ 150.2,
148.7, 148.3, 145.5, 138.3, 137.1, 135.8, 130.5, 129.6, 128.8, 128.6,
128.4, 127.9, 127.1, 126.7, 125.8, 124.7, 120.1, 113.3, 111.1, 107.4,
100.0, 75.1, 73.7, 70.4, 62.9, 60.7, 60.1, 59.3, 58.2, 55.7, 51.0, 41.9,
25.3, 15.9, 8.80; IR (NaCl) 3436, 2918, 2357, 1455, 1385, 1325, 1237,
1109, 1072 cm-1; HRMS (FAB) calcd for C40H41N3O7 [M + H] 675.29;
found 675.2941.
To a solution of hybrid cyanoamine alcohol (14.0 mg, 0.0207 mmol)
and MgSO4 (10.0 mg, 0.0839 mmol, 4 equiv) in 1.5 mL of benzene, at
25 °C, was added p-TsOH (59.0 mg, 0.311 mmol, 15 equiv). The
solution was aged for 1 h at room temperature. The reaction was then
diluted with H2O and extracted with CH2Cl2 (3×). The organic layers
were combined, dried with MgSO4, and concentrated by rotary
evaporation. The crude ene-pentacyclic film was dissolved in 1.5 mL
of CH2Cl2. To this solution, at room temperature, were added Ac2O
(19.6 µL, 0.207 mmol, 10 equiv) and TEA (28.9 µL, 0.207 mmol, 10
equiv). The solution was aged 5 h at room temperature. The reaction
was then quenched with an aqueous solution of NaHCO3 and extracted
with CH2Cl2 (3×). The residue was purified by pTLC with 35% EtOAc/
hexanes to provide 13.0 mg (90%) of acetate as a yellowish foam:
[R]17D +80.21 (c 1.0 CHCl3); 1H NMR (CDCl3, 400 MHz) δ 7.50 (2H,
d, J ) 7.24 Hz), 7.43 (2H, t, J ) 7.28 Hz), 7.37- 7.26 (4H, m), 7.14
(2H, d, J ) 7.04 Hz), 6.46 (1H, s), 5.92 (1H, s), 5.88 (1H, s), 5.65
(1H, s), 5.12 (1H, d, J ) 11.24 Hz), 5.03 (1H, d, J ) 11.24 Hz), 4.61
(1H, dd, J ) 2.52 Hz, 9.76 Hz), 4.54 (1H, s), 4.19 (1H, s), 4.02 (1H,
d, J ) 11.96 Hz), 3.99 (1H, d, J ) 11.96 Hz), 3.80 (3H, s), 3.41 (1H,
d, J ) 7.08 Hz), 3.18 (1H, dd, J ) 2.68 Hz, 9.36 Hz), 3.11–2.98 (2H,
m), 2.62 (1H, d, J ) 17.84 Hz), 2.35 (3H, s), 2.21 (3H, s), 1.97 (3H,
s), 1.92 (3H, s); 13C NMR (CDCl3, 100 MHz) δ 168.7, 148.9, 148.6,
140.1, 138.1, 137.8, 130.4, 128.4, 128.0, 127.6, 127.3, 126.7, 126.4,
124.8, 118.9, 118.0, 112.3, 105.6, 101.2, 96.7, 74.1, 73.2, 72.8, 60.4,
58.3, 56.8, 56.6, 56.3, 41.7, 26.6, 20.1, 16.0, 9.8; IR (NaCl) 2929, 1762,
1455, 1368, 1317, 1202, 1120, 1074, 1028 cm-1; HRMS (FAB) calcd
for C42H41N3O7 [M + H] 699.29; found 700.3031.
tography with 35% EtOAc/hexanes to provide 44.0 mg (69%) of an
1
off-white foam: [R]17 +11.21 (c 1.0 CHCl3); H NMR (CDCl3, 400
D
MHz) δ 7.94 (1H, s), 7.43–7.32 (5H, m), 7.26 (3H, m), 6.98 (2H, m),
6.58 (1H, s), 5.58 (1H, t, J ) 9.77 Hz), 5.09 (1H, d, J ) 11.02 Hz),
5.05 (1H, d, J ) 11.02 Hz), 4.15 (1H, s), 3.99 (1H, dd, J ) 2.54 Hz,
8.50 Hz), 3.85 (3H, m), 3.77 (3H, s), 3.76 (3H, s), 3.62 (1H, dd, J )
2.76 Hz, 11.25 Hz), 3.31–3.05 (4H, m), 2.54 (1H, d, J ) 17.92 Hz),
2.27 (3H, s), 2.14 (3H, s), 2.13 (3H, s), 1.44 (1H, d, J ) 10.00 Hz);
13C NMR (CDCl3, 100 MHz) δ 151.1, 148.8, 148.2, 142.1, 138.5, 137.1,
130.5, 129.6, 128.7, 128.6, 128.4, 128.0, 127.1, 126.9, 125.9, 124.8,
123.6, 119.9, 118.6, 117.2, 75.1, 73.7, 71.6, 63.1, 61.4, 60.5, 60.1, 60.0,
58.8, 58.2, 55.8, 41.8, 25.3, 15.9, 8.9; IR (NaCl) 3373, 2931, 2360,
1455, 1414, 1121, 1066, 1013 cm-1; HRMS (FAB) calcd for
C41H45N3O7 [M + H] 691.33; found 692.3310.
Synthesis of Dimethoxybenzene-cyanoamine Analogue (14). To
a solution of cyanoamine 13 (15.0 mg, 0.0217 mmol) and MgSO4 (11.0
mg, 0.0868 mmol, 4 equiv) in 1.5 mL of benzene, at 25 °C, was added
p-TsOH (61.8 mg, 0.325 mmol, 15 equiv). The solution was aged for
4 h at room temperature. The reaction was then diluted with H2O and
extracted with CH2Cl2 (3×). The organic layers were combined, dried
with MgSO4, and concentrated by rotary evaporation. The crude film
was dissolved in 1.5 mL of CH2Cl2. To this solution, at room
temperature, was added Ac2O (20 µL, 0.217 mmol, 10 equiv) and TEA
(30 µL, 0.217 mmol, 10 equiv). The solution was aged 5 h at room
temperature. The reaction was then quenched with an aqueous solution
of NaHCO3 and extracted with CH2Cl2 (3×). The residue was purified
by pTLC with 35% EtOAc/hexanes to provide 13.8 mg (90%) of a
Synthesis of Hybrid Phenol (19). To solution of acetate 18 (28.0
mg, 0.0400 mmol) in 3 mL of MeOH, at 25 °C, was added 30% Pd/C
(5.6 mg, 20% w/w), and the mixture was purged and pressurized under
1 atm of H2. The solution was aged for 6 h at room temperature. The
reaction was then filtered through cotton and concentrated. The residue
was purified by pTLC with 50% EtOAc/hexanes to provide 8 mg
1
yellowish foam: [R]17 +95.92 (c 1.0 CHCl3); H NMR (CDCl3, 400
D
MHz) δ 7.50 (2H, d, J ) 7.51 Hz), 7.42 (2H, t, J ) 7.37 Hz), 7.37-
7.26 (4H, m), 7.13 (2H, d, J ) 7.33 Hz), 6.43 (1H, s), 5.62 (1H, s),
5.11 (1H, d, J ) 11.27 Hz), 5.05 (1H, d, J ) 11.27 Hz), 4.73 (1H, d,
J ) 7.47 Hz), 4.56 (1H, s), 4.21 (1H, s), 3.98 (2H, dd, J ) 12.18 Hz,
15.65 Hz), 3.83 (3H, s), 3.79 (3H, s), 3.74 (3H, s), 3.45 (1H, d, J )
7.75 Hz), 3.25–2.95 (3H, m), 2.66 (1H, d, J ) 17.80 Hz), 2.40 (3H, s),
2.20 (3H, s), 1.98 (3H, s), 1.95 (3H, s); 13C NMR (CDCl3, 100 MHz)
δ 168.4, 148.9, 148.5, 146.2, 139.0, 138.2, 137.9, 130.5, 128.4, 128.1,
127.7, 127.6, 127.5, 127.2, 126.7, 125.0, 124.5, 121.1, 119.1, 117.1,
96.1, 74.1, 73.0, 72.7, 60.7, 60.5, 60.2, 57.6, 57.2, 56.6, 56.0, 41.6,
29.8, 27.6, 20.2, 16.0, 9.9; IR (NaCl) 2929, 2852, 2360, 1762, 1685,
1
(32.8%) of a yellow film: H NMR (CDCl3, 400 MHz) δ 7.34 (3H,
m), 7.15 (2H, d, J ) 7.60 Hz), 6.23 (1H, s), 5.93 (1H, s), 5.87 (1H, s),
5.72 (1H, s), 5.68, (1H, s), 4.63 (1H, dd, J ) 2.40 Hz, 9.60 Hz), 4.50
(1H, s), 4.25 (1H, s), 4.11 (1H, d, J ) 12.00 Hz), 3.98 (1H, d, J )
12.00 Hz), 3.78 (3H, s), 3.43 (1H, d, J ) 7.60 Hz), 3.18 (1H, dd, J )
2.80 Hz, 9.20 Hz), 3.11–2.98 (2H, m), 2.59 (1H, d, J ) 17.60 Hz),
2.48 (3H, s), 2.38 (3H, s), 2.21 (3H, s), 1.97 (3H, s); 13C NMR (CDCl3,

Cribrostatin–Ecteinascidin Analogues
Journal of Natural Products, 2008, Vol. 71, No. 3 413
100 MHz) δ 169.3, 145.8, 144.5, 143.1, 140.4, 138.3, 137.8, 136.1,
128.4, 128.1, 127.4, 127.0, 121.0, 119.5, 119.3, 118.4, 112.3, 105.8,
101.3, 95.8, 73.1, 73.0, 60.8, 57.5, 56.6, 55.8, 41.5, 29.7, 26.9, 20.4,
15.8, 9.5; IR (NaCl) 3441, 2918, 2363, 1769, 1638, 1462, 1434, 1374,
1198, 1121, 1083 cm-1; HRMS (FAB) calcd for C35H35N3O7 [M + H]
3.66–3.62 (4H, m), 3.47 (1H, s), 3.30–3.06 (3H, m), 2.96 (2H, d, J )
16.44 Hz), 2.53 (3H, s), 2.41 (3H, s), 2.10 (3H, s), 2.00 (3H, s); 13C
NMR (CDCl3, 75 MHz) δ 169.6, 168.5, 145.7, 143.7, 138.9, 132.7,
129.7, 128.7, 128.4, 127.4, 127.1, 122.5, 119.6, 112.7, 119.1, 102.1,
102.0, 72.9, 70.4, 61.3, 56.9, 46.9, 42.0, 33.4, 21.0, 16.1, 9.9; HRMS
(FAB) calcd for C34H34N2O8 [M + H] 598.23; found 599.2393.
To a solution of ene-pentacyclic phenol (14 mg, 30.1 µmol) in 2
mL of THF, in a Parr-type bomb apparatus, at 25 °C, was added N,N′-
bis(salicylidene)ethylenediaminocobalt(II) (salcomine, 4 mg, 40 mol
%). The reaction was purged and pressurized under 5–10 atm of O2.
The suspension was stirred for 12 h at room temperature. Upon
completion (TLC), the red reaction mixture was concentrated and
purified (pTLC, 65% EtOAc/hexane) to provide 14 mg (76%) of
609.25; found 610.2531; [R]17 +69.28 (c 1.0 CHCl3).
D
Synthesis of Hybrid-Cyanoamine Analogue (20). To solution of
phenol 19 (11.2 mg, 0.0184 mmol) in 3 mL of THF, at 25 °C, was
added salcomine (1 mg, 0.00308 mmol, 0.17 equiv), and the mixture
was purged and pressurized under 5 bar of O2. The solution was aged
for 12 h at room temperature. The reaction was then filtered through
cotton and concentrated. The residue was purified by pTLC with 50%
EtOAc/hexanes to provide 9.4 mg (82.2%) of quinone as a purple film:
[R]17D -70.20 (c 1.0 CHCl3); 1H NMR (CDCl3, 400 MHz) δ 7.34 (3H,
m), 7.18 (2H, d, J ) 6.96 Hz), 5.93 (1H, s), 5.87 (1H, s), 5.54, (1H,
s), 4.63 (1H, dd, J ) 2.61 Hz, 9.46 Hz), 4.42 (1H, s), 4.29 (1H, d, J
) 11.64 Hz), 4.19 (1H, d, J ) 11.64 Hz), 4.16 (1H, s), 4.00 (3H, s),
3.42 (1H, d, J ) 7.33 Hz), 3.30 (2H, m), 2.79 (1H, d, J ) 7.53 Hz),
1
quinone as a red residue: H NMR (CDCl3, 400 MHz) δ 7.26–7.21
(3H, m), 7.01–7.00 (2H, m), 6.12 (1H, t, J ) 6 Hz), 5.94 (1H, s), 5.92
(1H, s), 5.9 (1H, s), 4.42 (1H, s), 4.27 (2H, dd, J ) 12.0, 62.6 Hz),
3.86 (3H, s), 3.67–3.6 (1H, m), 3.3309 (2H, d, J ) 5.92 Hz), 2.88–2.86
(2H, m), 2.49 (1H, s), 2.43 (1H, s), 2 (1H, s), 1.8 (1H, s); 13C NMR
(CDCl3, 75 MHz) δ 186.8, 181.0, 169.2, 167.0, 155.5, 146.1, 141.0,
139.8, 139.4, 137.9, 137.1, 129.9, 129.1, 128.4, 127.5, 127.0, 116.6,
112.7, 108.8, 104.3, 102.0, 72.9, 69.7, 61.1, 59.8, 54.9, 46.3, 41.3, 29.8,
29.4, 20.7, 9.6, 8.8; HRMS (FAB) calcd for C34H32N2O9 [M + H]
612.21; found 613.2186.
2.48 (1H, m), 2.42 (3H, s), 2.37 (3H, s), 1.97 (3H, s), 1.96 (3H, s); 13
C
NMR (CDCl3, 100 MHz) δ 186.9, 181.5, 179.1, 155.5, 137.4, 137.1,
136.4, 132.6, 128.5, 127.9, 127.8, 118.6, 117.7, 112.7, 105.6, 101.5,
98.9, 73.6, 72.9, 61.0, 57.3, 56.4, 55.6, 53.8, 41.3, 21.8, 20.4, 9.5, 8.7;
IR (NaCl) 2926, 2852, 1762, 1654, 1457, 1198, 1075 cm-1; HRMS
(FAB) calcd for C35H33N3O8 [M + H] 623.23; found 624.2360.
To a solution of cyanohybrid quinone (13.0 mg, 0.0181 mmol) in 3
mL of dioxane was added selenium(IV) oxide (1 mg, 0.00308 mmol,
0.17 equiv). The solution was aged for 12 h at 100 °C in an oil bath.
The reaction was quenched with NaHCO3 and extracted with CH2Cl2
(3×). The organic layers were combined, dried with MgSO4, and
concentrated in Vacuo. The residue was purified taken up in 2 mL of
CH2Cl2, and DMP was added at room temperature. The mixture was
aged for hours. The reaction was quenched with 10% NaS2O3 in
saturated NaHCO3 and extracted with CH2Cl2 (3×). The residue was
then dissolved in 1 mL of AcOH, and zinc was added at room
temperature. The reaction was aged for 15 min with vigorous stirring
and then filtered through cotton, quenched with NaHCO3, and extracted
with CH2Cl2 (3×). The residue was purified by pTLC with 50% EtOAc/
hexanes to provide 9.4 mg (82.2%) of ketohydroquinone as a purple
To a solution of ene-pentacyclic quinone (14 mg, 22.9 µmol) in 2
mL of 1,4-dioxane, at 25 °C, was added selenium(IV) oxide (7.6 mg,
3 equiv). The reaction was stirred at 100 °C in a sealed vial for 7 h
and monitored by TLC. When complete, the reaction was cooled to rt,
concentrated, and purified (pTLC, 70% EtOAc/hexane) to provide 15
mg (quant) of quinone alcohol as a red residue: 1H NMR (CDCl3, 400
MHz) δ 7.26–7.19 (3H, m), 7.01–6.95 (2H, m), 6.01–6.05 (1H, m),
5.98 (1H, s), 5.92 (1H, s), 5.91 (1H, s), 4.84 (1H, s), 4.43 (1H, s), 4.24
(2H, dd, J ) 11.92, 69.82 Hz), 3.86 (3H, s), 3.66 (1H, s), 3.48 (1H, s),
3.35–3.25 (2H, m), 2.89 (1H, s, br), 2.55 (3H, s), 2.44 (3H, s), 2.01
(3H, s), 1.81 (3H, s); 13C NMR (CDCl3, 75 MHz) δ 186.7, 181.5, 169.2,
163.7, 155.6, 146.3, 141.0, 139.6, 138.3, 137.8, 129.4, 128.4, 127.7,
127.6, 127.1, 116.4, 112.8, 108.9, 105.4, 102.1, 72.9, 69.5, 67.2, 65.2,
61.1, 55.3, 46.3, 41.6, 29.8, 20.7, 9.6, 8.7; HRMS (FAB) calcd for
C34H32N2O10 [M + H] 628.21; found 629.2132.
1
film: H NMR (CDCl3, 400 MHz) δ 7.93 (2H, d, J ) 8.00 Hz), 7.83
To a solution of quinone alcohol (15 mg, 23.9 µmol) in 2 mL of
CH2Cl2, at 25 °C, was added DMP (15 mg, 1.5 equiv). The reaction
was stirred 1–2 h, monitored by TLC before being quenched with
aqueous 10% Na2S2O3 in saturated NaHCO3, and extracted with CH2Cl2
(3 × 5 mL). The organic layer was dried over MgSO4, filtered (cotton),
concentrated, and taken forward as is. To the crude keto-quinone were
added AcOH (0.5 mL) and a small scoop of zinc dust at rt. Within 5
min, the reaction mixture changed from blue to yellow, and TLC
indicated a complete conversion. The AcOH was removed under
reduced pressure and the residue purified by pTLC to give 12.5 mg
(83%, 2 steps, 19.9 µmol) of yellow, hydroquinone residue. Keto-
quinone: 1H NMR (CDCl3, 400 MHz) δ 7.21–7.18 (3H, m), 6.95–6.90
(2H, m), 6.15–6.09 (1H, m), 6.02 (1H, s), 5.91 (2H, s), 4.68 (1H, s),
4.19 (2H, dd, J ) 12.12, 58.78 Hz), 3.98 (1H, s), 3.85 (3H, s), 3.45–3.35
(1H, m), 3.35–3.26 (1H, m), 2.55 (3H, s), 2.45 (3H, s), 2.01 (3H, s),
1.8 (3H, s); 13C NMR (CDCl3, 75 MHz) δ 185.7, 183.7, 182.3, 169.2,
159.7, 155.2, 146.9, 141.0, 139.9, 137.6, 130.3, 129.1, 128.3, 127.7,
126.9, 126.6, 125.1, 116.1, 112.9, 109.0, 107.1, 106.0, 102.2, 73.9,
72.7, 71.7, 69.6, 57.0, 55.9, 47.8, 47.3, 46.8, 41.5, 29.8, 20.7, 9.4, 8.9;
HRMS (FAB) calcd for C34H30N2O10 [M + H] 626.19; found 629.2153.
(2H, m), 7.29 (2H, m), 7.08 (2H, m), 5.93 (1H, s), 5.87 (1H, s), 5.75
(1H, s), 4.63 (1H, dd, J ) 2.61 Hz, 9.46 Hz), 4.60 (1H, s), 4.25 (1H,
d, J ) 11.64 Hz), 3.90 (3H, s), 3.88 (1H, d, J ) 11.64 Hz), 3.56 (1H,
s), 3.11 (2H, d, J ) 7.53 Hz), 2.90 (1H, m), 2.60 (3H, s), 2.37 (3H, s),
2.21 (3H, s), 1.96 (3H, s); HRMS (FAB) calcd for C35H33N3O9 [M +
H] 639.22; found 640.2325.
Synthesis of Acetate 22. To a solution of known ene-pentacycle
21 (34 mg, 44.8 µmol) in 2 mL of CH2Cl2, at 0 °C, was added TBAF
(67µL, 1 M in THF, 1.5 equiv). TLC indicated complete conversion
to phenol in 5 min, at which time acetic anhydride (67 µL, 1 M in
CH2Cl2, 1.5 equiv) was added. After 5 min, TLC indicated a complete
reaction. The reaction mixture was poured into brine and extracted with
CH2Cl2 (3 × 5 mL), dried with MgSO4, and filtered (cotton). pTLC
with 50% EtOAc/hexanes gave 31 mg (quantitative) of the acetate as
a yellow oil: 1H NMR (CDCl3, 400 MHz) δ 7.48–7.37 (5H, m),
7.26–7.19 (3H, m), 6.96 (2H, d, J ) 6.40 Hz), 6.51 (1H, s), 6.14–6.11
(1H, m), 5.92 (1H, s), 5.88 (1H, s), 5.73 (1H, s), 5.06 (2H, dd, J )
10.40, 64.00 Hz), 4.56 (1H, s), 3.94 (2H, dd, J ) 12.0, 36.0 Hz), 3.74
(3H, s), 3.63 (1H, d, J ) 4.00 Hz), 3.27–3.23 (2H, m), 3.15–3.01 (1H,
m), 3.99 (1H, d, J ) 4.00 Hz), 2.46 (3H, s), 2.14 (3H, s), 2.04 (3H, s),
1.98 (3H, s); 13C NMR (CDCl3, 75 MHz) δ 169.1, 168.2, 149.5, 148.6,
145.7, 141.2, 139.0, 138.4, 138.2, 133.2, 131.8, 128.7, 128.2, 127.8,
127.6, 127.2, 126.9, 126.7, 126.3, 116.7, 114.5, 108.9, 102.0, 101.9,
73.9, 72.7, 70.2, 60.9, 60.5, 56.9, 46.6, 41.7, 33.2, 20.3, 15.9, 9.6;
HRMS (FAB) calcd for C41H40N2O8 [M + H] 688.3; found 689.2863.
To a solution of the acetate (60 mg, 87.1 µmol) in 24 mL of EtOAc,
at 25 °C, was added 10% Pd/C (20 mg, 33% w/w), and the mixture
was purged and pressurized under 1 atm of H2. The suspension was
stirred for 2 h at room temperature and monitored by LCMS, which
showed product and starting material. Additional 10% Pd/C (25 mg,
42% w/w) was added, and after stirring for 2 h more the reaction was
filtered through cotton and concentrated. The residue was purified by
pTLC with 60% EtOAc/hexanes to provide 45 mg (85%) of clean
1
Keto-hydroquinone (22): H NMR (CDCl3, 400 MHz) δ 11.33 (1H,
s), 7.26–7.15 (3H, m), 6.90225 (2H, d, J ) 6.68 Hz), 6.19–6.10 (1H,
m), 5.99 (1H, s), 5.93 (1H, s), 5.9 (1H, s), 5.61 (1H, s, br), 4.75 (1H,
s), 4.07 (1H, s), 3.96 (2H, s), 3.74 (3H, s), 3.29–3.15 (2H, m), 2.57
(3H, s), 2.42 (3H, s), 2.09 (3H, s), 2.01 (3H, s); 13C NMR (CDCl3, 75
MHz) δ 193.9, 169.3, 160.9, 156.3, 153.1, 146.1, 141.2, 139.4, 138.0,
137.9, 129.8, 128.3, 127.3, 126.9, 122.2, 118.5, 116.4, 112.7, 109.1,
108.7, 102.8, 102.0, 72.8, 72.7, 70.1, 61.2, 56.9, 47.3, 41.4, 20.7, 9.6,
9.0; HRMS (FAB) calcd for C34H32N2O10 [M + H] 628.21; found
629.2157.
Synthesis of Homobenzylic Alcohol (23). To solution of 22 (12.5
mg, 19.9 µmol) in 7 mL of EtOAc, at 25 °C, was added 10% Pd/C (7 mg,
56% w/w), and the mixture was purged and pressurized under 1 atm of
H2. The suspension was stirred for 24 h at room temperature and monitored
by TLC and LCMS. Upon complete consumption of 21, the mixture was
filtered (cotton), concentrated, and purified (pTLC, 70% EtOAc/hexanes)
to provide 5.8 mg (54%) of desired product along with 3 mg of keto-
1
phenol: H NMR (CDCl3, 400 MHz) δ 7.26–7.18 (3H, m), 6.99 (2H,
d, J ) 6.84 Hz), 6.24 (1H, s), 6.16–6.09 (1H, m), 5.91 (2H, s), 5.88
(1H, s), 5.81 (1H, s), 4.55 (1H, s), 3.86 (2H, dd, J ) 12.16, 32.4 Hz),

414 Journal of Natural Products, 2008, Vol. 71, No. 3
Wright et al.
reduced product (28%, shown in box above): 1H NMR (CDCl3, 400 MHz)
δ 11.39 (1H, s), 6.02–5.97 (3H, m), 5.93 (1H, s), 5.68 (1H, s, br), 4.75
(1H, s), 4.07 (1H, s), 3.85 (3H, s), 3.49–3.40 (1H, m), 3.35–3.25 (1H, m),
2.56 (3H, s), 2.42 (3H, s), 2.19 (3H, s), 2.01 (3H, s); 13C NMR (CDCl3,
75 MHz) δ 193.9, 169.3, 162.0, 156.3, 153.2, 146.2, 141.4, 139.5, 137.9,
129.8, 121.7, 118.9, 116.0, 113.0, 108.9, 108.1, 102.7, 102.1, 72.6, 64.4,
61.4, 56.8, 49.9, 41.4, 20.7, 9.6, 9.1; HRMS (FAB) calcd for C27H27N2O10
[M + H] 538.16; found 539.1658.
Synthesis of Hybrid Analogue 5. A 0.25 M solution of mixed
anhydride 24 was prepared by dissolving angelic acid (5 mg, 50 µmol) in
toluene (0.2 mL) and adding TEA (7µL) and 2,4,6-trichlorobenzoyl
chloride (8 µL). To a solution of 23 (3 mg, 5.6 µmol) in 150 µL of toluene,
at 25 °C, was added 0.25 M 24 solution (33 µL, 1.5 equiv). The reaction
mixture was then stirred in a sealed vial at 70 °C for 72 h before solvent
(3) Cuevas, C.; Perez, M.; Martin, M. J.; Chicharro, J. L.; Fernandez-
Rivas, C.; Flores, M.; Francesch, A.; Gallego, P.; Zarzuelo, M.; de la
Calle, F.; Garcia, J.; Polanco, C.; Rodriguez, I.; Manzanares, I. Org.
Lett. 2000, 2, 2545–2548.
(4) Endo, A.; Yanagisawa, A.; Abe, M.; Tohma, S.; Kan, T.; Fukuyama,
T. J. Am. Chem. Soc. 2002, 124, 6552–6554.
(5) Chen, J. C.; Chen, X. C.; Bois-Choussy, M.; Zhu, J. P. J. Am. Chem.
Soc. 2006, 128, 87–89.
(6) Martinez, E. J.; Owa, T.; Schreiber, S. L.; Corey, E. J. Proc. Natl.
Acad. Sci. U.S.A. 1999, 96, 3496–3501.
(7) Jin, S.; Gorfajn, B.; Faircloth, G.; Scotto, K. W. Proc. Natl. Acad.
Sci. U.S.A. 2000, 97, 6775–6779.
(8) Martinez, E. J.; Corey, E. J.; Owa, T. Chem. Biol. 2001, 8, 1151–
1160.
(9) Marco, E.; David-Cordonnier, M. H.; Bailly, C.; Cuevas, C.; Gago,
F. J. Med. Chem. 2006, 49, 6925–6929.
(10) Pettit, G. R.; Knight, J. C.; Collins, J. C.; Herald, D. L.; Pettit, R. K.;
Boyd, M. R.; Young, V. G. J. N. Prod. 2000, 63, 793–798.
(11) Saito, N.; Sakai, H.; Suwanborirux, K.; Pummangura, S.; Kubo, A.
Heterocycles 2001, 55, 21–28.
removal and purification (pTLC, 50% EtOAc/hexanes) gave 1.9 mg (55%)
1
of a yellow residue: [R]17 +173.82 (c 0.20 CHCl3); H NMR (CDCl3,
D
400 MHz) δ 11.36 (1H, s), 6.25 (1H, m), 6.03 (1H, s), 5.98 (1H, s),
5.95–5.90 (2H, m); 5.54 (1H, s), 4.72 (1H, s), 4.04 (1H, s), 3.93–3.85
(5H, m), 2.55 (3H, s), 2.41 (3H, s), 2.15 (3H, s), 2.02 (3H, s), 1.77 (3H,
d, J ) 6 Hz), 1.51 (3H, s); 13C NMR (CDCl3, 75 MHz) δ 193.7, 169.2,
167.0, 160.9, 156.2, 153.1, 146.2, 141.2, 139.5, 139.1, 138.0, 129.5, 127.0,
121.6, 118.6, 116.2, 113.1, 109.0, 107.5, 102.8, 102.3, 76.7, 72.7, 62.7,
61.4, 56.9, 46.5, 41.4, 29.8, 20.6, 20.0, 15.7, 9.7, 9.1; HRMS (FAB) calcd
for C32H32N2O11 [M + H] 620.20; found 621.2071.
(12) Zheng, S. P.; Chan, C.; Furuuchi, T.; Wright, B. J. D.; Zhou, B.; Guo,
J.; Danishefsky, S. Angew. Chem., Int. Ed. 2006, 45, 1754–1759.
(13) Chan, C.; Heid, R.; Zheng, S. P.; Guo, J. S.; Zhou, B. S.; Furuuchi,
T.; Danishefsky, S. J. J. Am. Chem. Soc. 2005, 127, 4596–4598.
(14) Kim, S.; Ahn, K. H. J. Org. Chem. 1984, 49, 1717–1724.
(15) Lane, J. W.; Chen, Y. Y.; Williams, R. M. J. Am. Chem. Soc. 2005,
127, 12684–12690.
(16) Greene, T. W.; Wuts, P. G. M., ProtectiVe Groups in Organic
Synthesis, 3rd ed.; John Wiley & Sons, Inc.: New York, 1999; pp
76–86..
(17) Martinez, E. J.; Corey, E. J. Org. Lett. 1999, 1, 75–77.
(18) Saito, N.; Ohira, Y.; Wada, N.; Kubo, A. Tetrahedron 1990, 46, 7711–
7728.
(19) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277–7287.
(20) Conant, J. B.; Fieser, L. F. J. Am. Chem. Soc. 1924, 46, 1858–1881.
(21) Saito, N.; Harada, S.; Nishida, M.; Inouye, I.; Kubo, A. Chem. Pharm.
Bull. 1995, 43, 777–782.
Acknowledgment. This work was supported by the National
Institutes of Health (Grant HL25848). We thank PharmaMar Corpora-
tion of Madrid, Spain, for testing our compounds as part of an ongoing
collaborative effort. B.J.D.W. is grateful for an NSF predoctoral
fellowship. We thank Bristol Myers Squibb for a fellowship awarded
to C.C. We also thank Dr. Y. Itagaki (Columbia University) for mass
spectrometric analyses.
(22) Hartmann, B.; Kanazawa, A. M.; Depres, J. P.; Greene, A. E.
Tetrahedron Lett. 1991, 32, 5077–5080.
References and Notes
(1) Scott, J. D.; Williams, R. M. Chem. ReV. 2002, 102, 1669–1730.
(2) Corey, E. J.; Gin, D. Y.; Kania, R. S. J. Am. Chem. Soc. 1996, 118,
9202–9203.
(23) Boyd, M. R.; Paull, K. D. Drug DeV. Res. 1995, 34, 91.
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