A Suzuki cross-coupling and intramolecular aza-Michael addition reaction sequence towards the synthesis of 1,10b-epi-7-deoxypancratistatins and their cytotoxicity studies

Article abstract of DOI:10.1002/ejoc.200800830

The development of an efficient approach to the construction of a phenanthridone is described. The convergent strategy commences with the preparation of Suzuki cross-coupling reaction precursors, arylboronic acid 12 and α-iodo enone 19, from piperonylamine (9) and (-)-D-quinic acid (10), respectively. The coupling of 12 and 19 followed by a key intramolecular aza-Michael addition produced phenanthridone 21 featuring a cis-fused B-C ring junction. The syntheses of compounds 25 and 26, both of which are C-1 and C-10b epimers of the naturally occurring potent antitumor agent 7-deoxypancratistatin (2), from 21 are elaborated in detail in this paper. The cytotoxicities of 25 and 26 were evaluated against three different cancer cell lines. Compound 26 served as a moderate growth inhibitor of THP-1 monocytic cells (GI₅₀ = 14.5 μg/mL). Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejoc.200800830

FULL PAPER
DOI: 10.1002/ejoc.200800830
A Suzuki Cross-Coupling and Intramolecular Aza-Michael Addition Reaction
Sequence Towards the Synthesis of 1,10b-epi-7-Deoxypancratistatins and Their
Cytotoxicity Studies
Ganesh Pandey,*[a] Madhesan Balakrishnan,[a] and Pandrangi Siva Swaroop[a]
Keywords: Antitumor agents / Chiral pool / Cross-coupling / Intramolecular aza-Michael addition / Pancratistatin
The development of an efficient approach to the construction
of a phenanthridone is described. The convergent strategy
commences with the preparation of Suzuki cross-coupling re-
action precursors, arylboronic acid 12 and α-iodo enone 19,
mers of the naturally occurring potent antitumor agent 7-de-
oxypancratistatin (2), from 21 are elaborated in detail in this
paper. The cytotoxicities of 25 and 26 were evaluated against
three different cancer cell lines. Compound 26 served as a
from piperonylamine (9) and (–)-D-quinic acid (10), respec- moderate growth inhibitor of THP-1 monocytic cells (GI50 =
tively. The coupling of 12 and 19 followed by a key intra-
molecular aza-Michael addition produced phenanthridone
21 featuring a cis-fused B–C ring junction. The syntheses of
compounds 25 and 26, both of which are C-1 and C-10b epi-
14.5 µg/mL).
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
yielding syntheses of the naturally occurring pancratistatins.
This task promoted the screening and development of a
great number of existing and new methodologies[8–11] for
their capabilities. The other dimension is looking for poten-
tial and more bio-available derivatives of pancratistatin.
This particular search has resulted in the syntheses of vari-
ous truncated and unnatural derivatives,[12–14] through
which the scientific community has been enlightened with
a substantial amount of structure-activity information. The
milestones crossed in this area have been extensively re-
viewed at many different occasions.[15]
The synthetic study of these natural products has been
enriched with the successful demonstration of several retro-
synthetic disconnections to date. However, the interesting
molecular framework still continues to fuel innovative ideas
for its efficient construction. A literature survey of synthetic
reports revealed that a practical approach emphasized the
cyclization of the B ring with preconstructed A and C rings
in a convergent fashion. The different modes of cyclization
reported for the formation of the B ring include (i) C-6–N
Introduction
The highly oxygenated phenanthridones, namely pancra-
tistatin (1)[1] and 7-deoxypancratistain (2)[2] along with their
congeners[3] narciclasine (3) and lycoricidine (4) (Figure 1),
isolated from plants of the Amaryllidaceae species, are
known for their broad spectrum of pharmacological pro-
files such as cytotoxicity, insect antifeedent activity and
antiviral properties.[4–6] The low natural abundance[7] cou-
pled with structural complexity of these compounds have
triggered considerable research activities in the synthetic
arena.
Figure 1. A few representatives of oxygenated phenanthridones.
The problems in using these molecules as therapeutic
agents (low abundance) have been addressed by various re-
search groups in two different dimensions over two decades.
One of the dimensions has been the quest for short, high-
[a] Division of Organic Chemistry, National Chemical Laboratory,
Pune 411008, India
Fax: +91-20-25902628
E-mail: gp.pandey@ncl.res.in
Supporting information for this article is available on the
WWW under http://www.eurjoc.org or from the author.
Figure 2. Various cyclization strategies for B-ring closure.
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 5839
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G. Pandey, M. Balakrishnan, P. S. Swaroop
FULL PAPER
bond formation by lactamization[8b] and transamida- present in the C ring of the alkaloid, (ii) the ability of the
tion[8d,10b] reactions, (ii) C-6–C-6a bond formation with C-3 and C-4 stereocenters to direct the installation of the
Banwell’s modified Bischler–Napieralski[9a,9c,10d] reaction, required functionalities at C-2 and C-4 stereoselectively and
(iii) C-10a–C-10b bond formation through either photo- (iii) its natural abundance. We describe herein the detailed
cyclizations like PET-,[10f] aryl-enamide-[10a] or Lewis- results of our studies towards the synthesis of the phen-
acid-mediated coupling reactions of an arene with an allyl anthridone class of alkaloids.
triflate[9b] or epoxide[10e] and (iv) C-4a–C-10b bond forma-
tion by radical cyclization of an oxime ether[8d] and Diels–
Alder cycloadditions[11d] (Figure 2).
Results and Discussion
Synthesis of Arylboronic Acid 12
Background Concept
The aromatic bromination of the hydrochloride salt of
the piperonylamine (9·HCl) by applying a procedure analo-
On careful scrutiny of these catalogued strategies of B-
gous to that of Tietze et al.[18] gave the corresponding 6-
ring closure, we noticed that cyclization through C-4a–N
bromo derivative, which, upon basification followed by ben-
bond formation has not been explored, even though it may
zyl carbamate protection of the resultant free amine, pro-
offer an attractive, practical and general strategy for the
duced 11 in 93% yield. Lithium exchange of the bromide
synthesis of Amaryllidaceae constituents. In this context, we
with nBuLi/THF at –78 °C followed by quenching with ex-
envisioned a retrosynthetic approach as shown in Figure 3.
cess trimethyl borate gave one of the Suzuki cross-coupling
precursors (12) in 69% yield (Scheme 1).
Scheme 1. Synthesis of 12.
Stereocontrolled Synthesis of α-Iodo Enone 18
The synthesis of the most significant precursor 19
(Scheme 2) in our synthetic design commenced with the in-
troduction of an oxygen functionality at the C-2 position
to form an appropriately hydroxy-protected quinic acid de-
rivative. Towards this end, the regioselective elimination of
the 1-hydroxy group with Whitehead’s[19] protocol gave 13
in 70% overall yield (over three steps). To avoid unforeseen
Figure 3. Retrosynthetic plan for phenanthridones 1–4.
complications during the advanced stage of the synthesis,
we removed the butane diacetal and silyl protections of 13
While designing the above strategy, we envisioned that and reprotected the free hydroxy groups as their corre-
access to phenanthridones 1–4 could be realized easily from sponding methoxymethyl ethers (14). Subsequently, the
the β-amino carbonyl compound 5, which in turn could be catalytic osmylation of the double bond of 14 and the selec-
obtained through an intramolecular aza-Michael[16] reac- tive monoprotection of the resultant diol gave 16 in 68%
tion of the potential precursor 6. The stereochemical origin yield (over two steps). The reduction of the ester moiety of
at C-4a of compound 5 was believed to be controlled by the 16 by LiAlH4/THF at 50 °C produced the corresponding
adjacent stereocenter at C-4, which might direct the ap- diol, which, upon sodium periodate cleavage, gave 17 in
proach of the amine nucleophile to the opposite face of C- 86% yield. Next, we attempted to eliminate the 5-(meth-
4a of the enone. The crucial trans-B–C ring junction (C- oxymethoxy) group with Cs2CO3, tBuOK and 1,3-diazabi-
4a and C-10b) was expected to arise through the resultant, cyclo[5.4.0]undecane (DBU) to obtain the corresponding
thermodynamically stable, trans-perhydroquinoline-like sys- enone 18. However, these reactions produced a complex
tem. The key precursor 6 could be obtained by a Suzuki mixture. Luckily, the reaction of 17 with 0.1  aqueous
cross-coupling reaction[17] between subunits 7 and 8, which NaOH in the presence of catalytic amounts of tetrabu-
were proposed to be obtained easily from commercially tylammonium hydrogen sulfate (TBAHS) in DCM cleanly
available piperonylamine (9) and (–)--quinic acid (10). The produced 18 in 79% yield. Compound 18 was converted
selection of (–)--quinic acid was made considering (i) its into the target precursor 19 quantitatively by applying
syn-3,4-dihydroxy stereochemistry, akin to the stereocenters Johnson’s iodination protocol.[20]
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1,10b-epi-7-Deoxypancratistatins and Their Cytotoxicities
The relative stereochemistry of the newly formed C-4a
and C-10b centers (B–C ring junction) was deduced by
carefully examining the coupling constants between the at-
tached protons (4a-H and 10b-H) in the 1H NMR spectrum
of 21. For example, 10b-H appeared as a doublet (J =
6.8 Hz) at δ = 4.02 ppm, coupling only with 4a-H [signal at
δ = 3.97 (dd, J = 6.8, 9.3 Hz) ppm]. Generally, for the trans-
B–C ring junction, the coupling constant observed for 10b-
H is more than 10 Hz.[10a,10f] However, the lower value
(6.8 Hz) observed indicated a cis relationship between 4a-H
and 10b-H. The additional coupling constant (J = 9.3 Hz)
of 4a-H was accounted for by the coupling of 4a-H with 4-
H. The higher J value observed between 4-H and 4a-H
clearly confirmed a trans-diaxial coupling, establishing the
trans relationship for 4a-H and 4-H. These particular coup-
ling constants (J = 6.8, 9.3 Hz) indicated that the amine
nucleophile approached C-4a on the opposite face from the
4-alkoxy group, producing the C-4a–N bond with the re-
quired configuration at C-4a. The unexpected emergence of
the cis-fused B–C ring junction during cyclization was quite
disappointing to us. The most probable explanation for this
observation is that the protonation of the lithium enolate
intermediate, formed during the aza-Michael reaction, was
governed by the C-4a–N bond stereochemistry.
Scheme 2. Synthesis of 19.
Suzuki Cross-Coupling/Intramolecular Aza-Michael
Addition
We also attempted to invert the stereochemistry at C-10b
of 21 through epimerization with several bases but unsuc-
cessfully. It was surprising to note that our effort to epimer-
ize C-10b with DBU in boiling benzene led to a retro-
Michael reaction and the aromatization of the C-ring by β-
elimination of the methoxymethoxy group at C-3. The re-
sults from the above studies support the thermodynamic
stability of the cis-fused ring junction in these phenanth-
ridones.[10a,13d,21]
The easy accessibility of both of the coupling partners
12 and 19 guided us to carry out a Suzuki cross-coupling
to obtain the aza-Michael precursor 20. In this context, re-
fluxing (20 min) of an equimolar mixture of 12 and 19 with
5 mol-% of Pd(PPh3)4 in benzene/ethanol (2:1) produced 20
in 84% yield (Scheme 3). The characteristic doublet at δ =
1
6.81 (J = 3.7 Hz) ppm in the H NMR spectrum and the
signal of an olefinic CH group at δ = 145.1 ppm in the 13C
NMR spectrum of 20 confirmed its structure.
1,10b-epi-7-Deoxypancratistatin and the Corresponding
Amine Hydrochloride
Although the approach based on an intramolecular aza-
Michael addition produced the cis-fused phenanthridone,
we proceeded with our planned synthetic sequence and
achieved the cis analogues of 7-deoxypancratistatin
(Scheme 4). The sodium borohydride reduction of 21 in
MeOH at 0 °C afforded the corresponding 1-hydroxylated
molecule. This reaction sequence completed the installation
of all the hydroxy functionalities at the periphery of the
C-ring. However, the stereochemistry of this newly created
center could not be established, as the coupling constants
were not well defined, probably due to the bent conforma-
tion of the cis-fused ring. In order to complete the total
Scheme 3. Suzuki cross-coupling/intramolecular aza-Michael ad-
dition sequence.
The crucial intramolecular aza-Michael addition to 20 synthesis of 25 and with the hope that 6-benzylic oxidation
was carried out with nBuLi in hexamethylphosphoramide might result in a crystalline solid for X-ray analysis to con-
(HMPA)/THF (10:1) at –78 °C to provide cyclized product firm all the newly generated stereocenters, we proceeded
21 as a single diastereomer in 83% yield. The role of HMPA with benzylic oxidation. However, this step required a prior
was very crucial in this key reaction, as without HMPA, the protection of the 1-hydroxy group, and thus, it was pro-
reaction failed to bring about the required reorganization. tected as the methoxymethyl ether (22, 82% combined
Compound 21 was fully characterized by 1H and 13C NMR yield). Stirring of 22 with RuCl3/NaIO4 (in situ generation
spectroscopy and mass spectrometry (Scheme 3).
of RuO4)[22] in CCl4/CH3CN/H2O (1:1:2) at room tempera-
Eur. J. Org. Chem. 2008, 5839–5847
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G. Pandey, M. Balakrishnan, P. S. Swaroop
FULL PAPER
ture produced a very complex reaction mixture, possibly
due to the interference of the more activated benzyl group
of the Cbz protecting group. Therefore, we replaced the
benzyl carbamate with the corresponding tert-butyl carba-
mate and subjected it to oxidation as described above. We
were pleased that it underwent smooth oxidation resulting
in 24 in 62% yield (over two steps). Since the global depro-
tection of 24 gave a mixture of partially deprotected prod-
ucts in variable yields, we adopted a two-step deprotection
strategy to complete the synthesis. Initially, the removal of
the tert-butoxycarbonyl group of imide 24 selectively by
Mg(ClO4)2/CH3CN[23] followed by refluxing of the result-
ant amide in HCl/MeOH afforded 1,10b-epi-7-deoxy-
pancratistatin (25) {m.p. 298–304 °C. [α]2D7 = +88.3 (c = 0.35
in DMSO)} in 80% overall yield. The X-ray analysis of the
crystalline solid confirmed the structure of 25 as shown in
Figure 4.
Scheme 5. Synthesis of amine hydrochloride 26.
Evaluation of the Cytotoxicity of 25 and 26
Although the cytotoxicities of the 10b-epimer of 7-de-
oxypancratistatin have been studied[10g,10h] against human
cancer cell lines, the 1,10b-epimers (25 and 26) were new,
and no biological activity data were available. Therefore, we
screened them against murine P388 lymphocytic leukemia
and two other human cancerous cell lines, MCF-7 (breast
adenocarcinoma) and THP-1 (promonocytic leukemia).
Compound 25 exhibited 100-fold less activity (GI50
=
44.5 µg/mL) than natural 2 (GI50 = 0.44 µg/mL) against
murine P388. The analogue 26 also showed a similar ac-
tivity (GI50 = 50.0 µg/mL) in the murine P388 cell line.
However, the GI50 of THP-1 monocytic cells with 26 was
14.5 µg/mL in comparison to that of 25 (GI50 Ͼ 100 µg/
mL). In the breast cancer MCF-7 cell line, the analogues
25 and 26 displayed a similar range of activity of 74.6 and
85.3 µg/mL, respectively.
Conclusions
A new synthetic strategy has been developed for the syn-
thesis of the phenanthridone class of alkaloids by em-
ploying a Suzuki cross-coupling/aza-Michael reaction se-
quence. This approach also highlighted the use of cheaply
available (–)--quinic acid as a starting material for the
most difficult C-ring construction in the synthesis of this
class of alkaloids. Although the intramolecular aza-Michael
reaction for the B-ring closure of the present synthesis pro-
duced an incorrect cis-fused phenanthridone, the potential
of this stereoselective reaction could be more appropriately
exploited in the total synthesis of other members of this
family like γ-lycorane, fortucine and siculinine, which fea-
ture cis-B–C ring junctions.[15a,24] Compound 25 was less
cytotoxicity against the studied cancer cell lines, but 26
showed some activity against THP-1 monocytic cells, rais-
ing the hope that subtle variations in its structure may en-
hance the possibility of developing this molecule as a thera-
peutic agent.
Scheme 4. Synthesis of 1,10b-epi-7-deoxypancratistatin (25).
Figure 4. ORTEP diagram of 1,10b-epi-7-deoxypancratistatin (25).
Experimental Section
For the purpose of evaluating its biological profile, com-
General: Unless mentioned, all reactions were performed under ar-
gon. All commercially available reagents were used without further
purification. Thin-layer chromatography was performed with alu-
minum plates precoated with silica gel 60. Compounds were visual-
ized by heating after dipping in a solution of Ce(SO4)2 (2.5 g) and
(NH4)6Mo7O24 (6.25 g) in 10% aqueous H2SO4 (250 mL). Column
pound 26 {m.p. 214–218 °C (with decomposition), [α]D27
=
+40.8 (c = 0.5 in H2O)} was also synthesized (Scheme 5) by
refluxing 22 with an equal amount of DOWEX H+ resin in
MeOH, followed by hydrogenating the resulting tetrol in
acidic MeOH (80% yield).
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1,10b-epi-7-Deoxypancratistatins and Their Cytotoxicities
chromatography was performed with silica gel (100–200 and 230–
400 mesh). Melting points were recorded with a Büchi B-540 melt-
ing point apparatus and reported uncorrected. Optical rotations
were measured with a Jasco P-1030 polarimeter. IR spectra were
recorded with a Shimadzu Infrared Fourier Transform spectrome-
ter. NMR spectra were recorded with Bruker ACF 200, MSL 300,
AV400 and DRX 500 MHz spectrometers. Mass spectrometry was
carried out with a PE SCIEX API QSTAR pulser (LC-MS). Micro-
analyses were conducted with a Carlo–Erba CHNS-O EA 1108
elemental analyzer. CCDC-691503 (for 25) contains the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Methyl (3R,4S,5R)-3,4,5-Tris(methoxymethoxy)cyclohex-1-enecar-
boxylate (14): A solution of 13 (12 g, 28.85 mmol) in 80% aqueous
acetic acid was immersed in an oil bath at 80 °C and stirred over-
night. The resultant yellow solution was distilled at 50 °C under
high vacuum to remove the volatile materials. The brown pasty
residue was triturated with hexanes to facilitate the precipitation,
and the solvent was decanted after settling. The process of tritura-
tion was repeated (approximately four times) to afford the triol as
a chalky powder (4.95 g, 95%) after drying under vacuum. The
triol obtained was subjected to the next step without further purifi-
cation. To a stirred solution of the above intermediate (4.95 g,
26.33 mmol) in dry DCM (80 mL) was successively added DIPEA
(16.51 mL, 94.79 mmol) and MOMCl (10 mL, 131.65 mmol) drop-
wise at 0 °C. The yellow solution was warmed to room temperature
and stirred for 14 h before water (100 mL) was added. The aqueous
layer was extracted with DCM (2ϫ70 mL), and the organic layers
were combined, dried (Na2SO4), filtered and concentrated to pro-
duce a yellow oil. The oil was then purified by column chromatog-
raphy (silica gel, elution with 20% EtOAc/hexanes) to yield 14
(7.60 g, 95%) as a colorless oil. Rf = 0.50 (hexanes/EtOAc, 4:1).
[α]2D7 = –82.8 (c = 1.12 in CHCl3). 1H NMR (200 MHz, CDCl3,
25 °C): δ = 6.85 (br. s, 1 H), 4.77 (d, J = 2.9 Hz, 2 H), 4.74 (s, 2
H), 4.69 (s, 2 H), 4.50 (m, 1 H), 4.11 (m, 1 H), 3.95 (dd, J = 6.4,
3.8 Hz, 1 H), 3.73 (s, 3 H), 3.40 (s, 3 H), 3.38 (s, 3 H), 3.36 (s, 3
H), 2.65–2.81 (tdd, J = 18.6, 4.7, 2.3 Hz, 1 H), 2.33–2.48 (tdd, J =
18.6, 4.1, 1.5 Hz, 1 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ
= 166.6, 136.3, 129.2, 96.8, 96.0, 95.6, 74.2, 72.5, 70.8, 55.6, 55.5,
Benzyl (6-bromo-1,3-benzodioxol-5-yl)methylcarbamate (11): To a
suspension of piperonylamine salt (9·HCl, 5 g, 26.65 mmol) in gla-
cial acetic acid (25 mL) was added bromine (2.73 mL, 53.30 mmol).
The solid dissolved to form a clear red solution, which was stirred
at room temperature for an additional 3 h. Saturated aqueous
Na2SO3 was added until decolorization was achieved. The reaction
mixture was cooled in an ice bath and made strongly basic by add-
ing 20% aqueous NaOH. To this mixture, DCM (100 mL) and ben-
zyl chloroformate (4.2 mL, 29.31 mmol) were added, and the tem-
perature was maintained at 0 °C. The biphasic solution was
warmed to room temperature and stirred for a further 6 h. The
aqueous layer was extracted with DCM (2ϫ50 mL). The combined
organic extracts were washed with water (2ϫ75 mL) and brine
(1ϫ75 mL) and dried with Na2SO4. The solution was filtered and
concentrated under reduced pressure. The crude solid was recrys-
tallized from EtOAc/hexanes (1:9) to afford 11 (9 g, 93%) as white
55.4, 51.7, 28.5 ppm. IR (neat): ν = 2953, 1717, 1439, 1036 cm–1.
˜
MS (ESI): m/z (%) = 323 (100), 320 (7), 318 (43), 271 (17).
C14H24O8 (320.15): calcd. C 52.49, H 7.55; found C 52.42, H 7.41.
1
crystals, m.p. 96–97 °C. Rf = 0.30 (hexanes/EtOAc, 9:1). H NMR
Methyl (1S,2R,3R,4S,5R)-1,2-Dihydroxy-3,4,5-tris(methoxymethoxy)-
cyclohexanecarboxylate (15): Trimethylamine N-oxide dihydrate
(3.57 g, 32.12 mmol) was added to a solution of 14 (7.34 g,
22.94 mmol) in a mixture of tBuOH (62 mL), pyridine (3.5 mL)
and water (3.5 mL). The solution was stirred until all solids were
dissolved, and a crystal of OsO4 was added at room temperature.
The resulting stirred yellow solution was immersed in an oil bath
at 80 °C and heated for 15 h. The reaction mixture was cooled,
solid Na2SO3 (1 g) was added, and the mixture was stirred for
30 min. The solvent was removed by rotary evaporation, the residue
was redissolved in EtOAc (150 mL) and partitioned with a mini-
mum amount of water (50 mL). The aqueous layer was extracted
with EtOAc (2ϫ75 mL). The organic layers were combined, dried
(Na2SO4) and purified by column chromatography (silica gel, elu-
tion with 60% EtOAc/hexanes) to give 15 (6.66 g, 82%) as white
(200 MHz, CDCl3, 25 °C): δ = 7.34 (s, 5 H), 6.98 (s, 1 H), 6.90 (s,
1 H), 5.95 (s, 2 H), 5.27 (br. s, 1 H), 5.10 (s, 2 H), 4.33 (d, J =
6.2 Hz, 2 H) ppm. 13C NMR (75 MHz, CDCl3, 25 °C): δ = 156.2,
147.7, 147.4, 136.3, 130.7, 128.4, 128.0, 113.8, 112.6, 109.8, 101.7,
66.8, 45.2 ppm. IR (CHCl ): ν = 3446, 3018, 1718, 1506, 1215 cm–1.
˜
3
MS (ESI): m/z (%) = 388 (27) [M + 2 + Na]+, 386 (27) [M +
Na]+, 343 (9), 301 (18), 264 (100). C16H14BrNO4 (363.01): calcd. C
52.77, H 3.87, N 3.85; found C 52.69, H 3.82, N 3.71.
6-[(Benzyloxycarbonylamino)methyl]-1,3-benzodioxol-5-ylboronic Acid
(12): To a solution of carbamate 11 (5 g, 13.74 mmol) in dry THF
(70 mL) was added nBuLi (2  hexane, 17.5 mL, 34.92 mmol) at
–78 °C over a period of 10 min. The resultant dark yellow solution
was stirred at the same temperature for 20 min, and trimethyl bo-
rate (18.0 mL, 158.73 mmol) was added rapidly in one portion. The
solution became colorless, and the reaction mixture was stirred at
–78 °C for a further 30 min. The reaction mixture was warmed to
room temperature over 2 h before it was quenched with a large
excess of saturated aqueous NH4Cl (50 mL). The heterogeneous
mixture was stirred for 1 h and extracted with EtOAc (3ϫ60 mL).
The combined organic layers were dried (Na2SO4), filtered and
concentrated by rotary evaporation. The residue was purified by
column chromatography (silica gel, elution with 45% EtOAc/hex-
anes) to provide 12 (3.12 g, 69%) as a white amorphous solid, m.p.
crystals, m.p. 83–84 °C. Rf = 0.30 (hexanes/EtOAc, 2:3). [α]2D7
=
–8.7 (c = 1.62 in CHCl3). 1H NMR (200 MHz, CDCl3, 25 °C): δ =
4.83–4.62 (m, 6 H), 4.20 (d, J = 10.0 Hz, 1 H), 4.08 (m, 1 H), 4.01
(dd, J = 6.2, 3.4 Hz, 1 H), 3.92 (dd, J = 10, 2.8 Hz, 1 H), 3.79 (s,
3 H), 3.41 (s, 3 H), 3.39 (s, 3 H), 3.38 (s, 3 H), 3.12 (br. s, 1 H),
2.38–2.26 (dd, J = 15.0, 3.5 Hz, 1 H), 2.09–1.96 (ddd, J = 15.0, 2.3,
1.5 Hz, 1 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 173.8,
96.9, 95.9, 76.3, 74.4, 71.4, 55.6, 55.5, 52.7, 32.2 ppm. IR (CHCl3):
ν = 3471, 2893, 1730, 1255, 1151 cm–1. MS (ESI): m/z (%) = 377
˜
(17) [M + Na]+, 372 (13) [M + NH4]+, 355 (3) [M + H]+, 279 (44),
246 (24), 218 (100), 190 (35), 156 (24). C14H26O10 (354.15): calcd.
C 47.45, H 7.40; found C 47.32, H 7.33.
1
152–153 °C. Rf = 0.30 (hexanes/EtOAc, 3:2). H NMR (200 MHz,
[D6]DMSO, 25 °C): δ = 8.15 (s, 2 H), 7.67 (br. s, 1 H), 7.34 (s, 5
H), 7.00 (s, 1 H), 6.80 (s, 1 H), 5.96 (s, 2 H), 5.02 (s, 2 H), 4.28 (d,
J = 6.1 Hz, 2 H) ppm. 13C NMR (50 MHz, [D6]DMSO, 25 °C): δ Methyl (1S,2R,3S,4S,5R)-1-Hydroxy-2,3,4,5-tetrakis(methoxymeth-
= 157.1, 148.8, 145.9, 139.0, 137.4, 128.8, 128.2, 113.4, 108.4, 101.1,
oxy)cyclohexanecarboxylate (16):
(3.49 mL,45.90 mmol) in dry DCM (35 mL) was added to the pre-
A
solution of MOMCl
66.0, 44.1 ppm. IR (CHCl ): ν = 2926, 1693, 1462, 1250 cm–1. MS
˜
3
(ESI): m/z (%) = 380 (50) [M + 2 MeOH – 2 H2O + Na]+, 326 dissolved solution of 15 (6.5 g, 18.36 mmol) in dry DCM (60 mL)
(22), 188 (15), 156 (100). C16H16BNO6 (329.11): calcd. C 58.39, H and DIPEA (6.40 mL, 36.72 mmol) by utilizing a syringe pump at
4.90, N 4.26; found C 58.45, H 4.72, N 4.09.
room temperature over a period of 2 h. The mixture was stirred for
Eur. J. Org. Chem. 2008, 5839–5847
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5843

G. Pandey, M. Balakrishnan, P. S. Swaroop
FULL PAPER
a further 6 h before water (80 mL) was added to it. The aqueous
layer was extracted with DCM (2ϫ75 mL). The combined organic
extracts were dried (Na2SO4) and filtered. Removal of the solvent
by rotary evaporation gave a dark brown paste, which was purified
by column chromatography (silica gel, elution with 45% EtAOc/
EtOAc, 3:1). [α]2D7 = +113.1 (c = 1.62 in CHCl3). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 6.90 (dd, J = 10.2, 4.5 Hz, 1 H),
6.05 (d, J = 10.2 Hz, 1 H), 4.86–4.71 (m, 6 H), 4.53 (dd, J = 4.2,
4.0 Hz, 1 H), 4.46 (d, J = 8.7 Hz, 1 H), 4.10 (dd, J = 8.6, 3.4 Hz,
1 H), 3.42 (s, 3 H), 3.38 (s, 6 H) ppm. 13C NMR (50 MHz, CDCl3,
hexanes) to give 16 (6.07 g, 83%) as a pale yellow paste. Rf = 0.30 25 °C): δ = 196.1, 145.7, 129.2, 96.9, 96.7, 76.9, 71.5, 55.9, 55.7,
(hexanes/EtOAc, 1:1). [α]2D7 = –51.0 (c = 1.13 in CHCl3). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 4.89–4.56 (m, 8 H), 4.19 (s, 1 H),
55.6 ppm. IR (neat): ν = 2951, 1703, 1441, 1113 cm–1. MS (ESI):
˜
m/z (%) = 299 (100) [M + Na]+. C12H20O7 (276.12): calcd. C 52.17,
4.17 (d, J = 2.2 Hz, 1 H), 4.10 (m, 1 H), 3.98 (dd, J = 6.7, 3.5 Hz, H 7.30; found C 52.06, H 7.27.
1 H), 3.78 (s, 3 H), 3.67 (br. s, 1 H), 3.39 (s, 3 H), 3.38 (s, 6 H),
(4S,5S,6R)-2-Iodo-4,5,6-tris(methoxymethoxy)cyclohex-2-enone (19):
3.28 (s, 3 H), 2.43–2.30 (dd, J = 14.9, 3.7 Hz, 1 H), 2.03–1.90 (ddd,
J = 14.9, 2.7. 1.3 Hz, 1 H) ppm. 13C NMR (50 MHz, CDCl3,
25 °C): δ = 173.9, 98.3, 96.9, 96.5, 96.2, 78.6, 77.8, 76.8, 74.5, 74.4,
Iodine (4.05 g, 15.94 mmol), dissolved in CCl4/pyridine (1:1,
20 mL), was added dropwise under argon to a solution of 18
(1.76 g, 6.38 mmol) in CCl4/pyridine (1:1, 20 mL) at 0 °C. The mix-
ture was stirred for 1 h, during which time the mixture was warmed
to room temperature. The mixture was diluted with EtOAc
(100 mL) and washed successively with HCl (1 , 5ϫ20 mL), satu-
rated aqueous NaHCO3 (1ϫ30 mL), aqueous Na2S2O3 (20%,
40 mL) and dried (Na2SO4). After filtration and concentration of
the organic layers under reduced pressure, the residue was subjected
to column chromatography (silica gel, elution with 25% EtOAc/
hexanes) to afford 19 (2.56 g, quantitative) as a pale yellow oil. Rf
= 0.30 (hexanes/EtOAc, 4:1). [α]2D7 = +85.9 (c = 1.32 in CHCl3). 1H
NMR (200 MHz, CDCl3, 25 °C): δ = 7.67 (d, J = 4.6 Hz, 1 H),
4.85–4.71 (m, 6 H), 4.56 (d, J = 8.0 Hz, 1 H), 4.51 (d, J = 4.4 Hz,
1 H), 4.15 (dd, J = 8.0, 3.3 Hz, 1 H), 3.41 (s, 3 H), 3.39 (s, 3 H),
3.36 (s, 3 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ = 190.0,
154.4, 103.8, 96.9, 96.7, 96.5, 76.7, 75.7, 73.4, 56.0, 55.7, 55.6 ppm.
56.2, 55.7, 55.6, 55.5, 52.7, 33.1 ppm. IR (neat): ν = 3460, 2895,
˜
1745, 1443, 1244, 1150 cm–1. MS (ESI): m/z (%) = 421 (30) [M +
Na]+, 416 (13) [M + NH4]+, 259 (100), 229 (19), 199 (28).
C16H30O11 (398.18): calcd. C 48.24, H 7.59; found C 48.22, H 7.80.
(2R,3S,4S,5R)-2,3,4,5-Tetrakis(methoxymethoxy)cyclohexanone (17):
To a suspension of LAH (0.86 g, 22.61 mmol) in dry THF (25 mL)
at 0 °C was cannulated dropwise
a solution of 16 (4.5 g,
11.30 mmol), dissolved in dry THF (40 mL), over a period of
30 min. The reaction mixture was warmed to room temperature
and then stirred at 50 °C in an oil bath for 18 h. The suspension
was cooled to room temperature and poured cautiously (by washing
the flask with EtOAc) into Na2SO4 (approximately 50 g). The mix-
ture was mixed thoroughly and put aside for 2 h. The milky white
suspension was filtered through a Büchner funnel, and the inor-
ganic material was washed with EtOAc (150 mL). The filtrate was
dried (Na2SO4) and concentrated under reduced pressure to obtain
the crude diol (4.0 g), which was carried forward to the next step
without further purification. The crude diol (4.0 g) was dissolved
in phosphate buffer (pH = 7, 35 mL) and cooled to 0 °C. Solid
NaIO4 (3.65 g, 17.04 mmol) was added in portions over a period
of 10 min, while the temperature was maintained at 0–5 °C. The
reaction mixture was stirred at the same temperature for additional
20 min and extracted with EtOAc (3ϫ50 mL). The combined or-
ganic layers were dried (Na2SO4), filtered and concentrated by ro-
tary evaporation. The residue was subjected to column chromatog-
raphy (silica gel, elution with 30% EtOAc/hexanes) to produce 17
(3.29 g, 86% over two steps) as a colorless paste. Rf = 0.30 (hex-
anes/EtOAc, 3:1). [α]2D7 = –10.2 (c = 1.02 in CHCl3). 1H NMR
(200 MHz, CDCl3, 25 °C): δ = 4.90–4.59 (m, 8 H), 4.52 (d, J =
10.1 Hz, 1 H), 4.20–4.04 (m, 3 H), 3.41 (s, 3 H), 3.40 (s, 3 H), 3.39
(s, 3 H), 3.32 (s, 3 H), 2.91–2.80 (dd, J = 14.3, 3.5 Hz, 1 H), 2.64–
2.52 (ddd, J = 14.3, 3.3, 1.1 Hz, 1 H) ppm. 13C NMR (50 MHz,
CDCl3, 25 °C): δ = 204.4, 97.2, 96.8, 96.5, 96.2, 80.1, 77.0, 76.2,
IR (neat): ν = 2895, 1693, 1443, 1034 cm–1. MS (ESI): m/z (%) =
˜
441 (7) [M + K]+, 425 (100) [M + Na]+, 403 (Յ1) [M + H]+, 327
(5). C12H19IO7 (402.02): calcd. C 35.84, H 4.76; found C 35.90, H
4.86.
Benzyl {6-[(3S,4S,5R)-3,4,5-Tris(methoxymethoxy)-6-oxocyclohex-
1-enyl]-1,3-benzodioxol-5-yl}methylcarbamate (20): To a solution of
19 (1 g, 2.49 mmol) in distilled benzene (20 mL) was added a solu-
tion of 12 (0.82 g, 2.49 mmol) in ethanol (14 mL), aqueous Na2CO3
(2 , 8 mL) and
a catalytic amount of Pd(PPh3)4 (0.14 g,
0.12 mmol). The vigorously stirring yellow solution was heated in
an oil bath at 65 °C under argon for 20 min, producing a dark
brown mixture. The mixture was cooled and diluted with water
(20 mL) and extracted with EtOAc (3ϫ75 mL). The combined or-
ganic extracts were dried (Na2SO4), filtered and concentrated under
reduced pressure. The residue was purified by column chromatog-
raphy (silica gel, elution with 30% EtOAc/hexanes) to yield 20
(1.17 g, 84%) as a dark orange paste. Rf = 0.30 (hexanes/EtOAc,
2:1). [α]2D7 = +69.5 (c = 1.16 in CHCl3). 1H NMR (200 MHz,
CDCl3, 25 °C): δ = 7.32 (s, 5 H), 6.90 (s, 1 H), 6.81 (d, J = 3.7 Hz,
1 H), 6.51 (s, 1 H), 5.93 (s, 2 H), 5.39 (br. s, 1 H), 5.07 (s, 2 H),
4.86 (d, J = 7.0 Hz, 1 H), 4.81–4.70 (m, 6 H), 4.50 (d, J = 7.6 Hz,
1 H), 4.27 (dd, J = 7.5, 2.9 Hz, 1 H), 4.02 (br. s, 2 H), 3.41 (s, 3
H), 3.40 (s, 3 H), 3.37 (s, 3 H) ppm. 13C NMR (75 MHz, CDCl3,
25 °C): δ = 194.8, 156.2, 147.9, 146.8, 145.1, 139.3, 136.6, 131.1,
128.2, 127.8, 127.5, 109.6, 109.3, 101.2, 96.9, 96.8, 96.4, 77.2, 76.9,
74.4, 55.7, 55.6, 55.4, 41.4 ppm. IR (CHCl ): ν = 2895, 2359, 1732,
˜
3
1030 cm–1. MS (ESI): m/z (%) = 377 (14) [M + K]+, 361 (100) [M
+ Na]+, 123 (10). C14H26O9 (338.16): calcd. C 49.70, H 7.75; found
C 49.54, H 7.67.
(4S,5S,6R)-4,5,6-Tris(methoxymethoxy)cyclohex-2-enone (18): To a
solution of 17 (3.00 g, 8.88 mmol) in distilled DCM (260 mL) was
added aqueous NaOH (0.1 , 65 mL) at 0 °C. To the vigorously
stirred biphasic solution was added a catalytic amount of tetrabu-
tylammonium hydrogen sulfate (0.15 g, 0.44 mmol), and the mix-
ture was stirred at the same temperature until the starting material
was completely consumed (GC monitoring). The reaction mixture
was separated in a separatory funnel, and the aqueous layer was
extracted with DCM (2ϫ50 mL). The combined organic extracts
were dried (Na2SO4) and filtered, and the solvent was distilled off
under reduced pressure. The crude material was purified by column
chromatography (silica gel, elution with 30% EtOAc/ hexanes) to
produce 18 (1.94 g, 79%) as a colorless oil. Rf = 0.30 (hexanes/
71.4, 66.5, 55.9, 55.6, 55.5, 42.7 ppm. IR (neat): ν = 2895, 1730,
˜
1713, 1693, 1504, 1485, 1371, 1240, 1042 cm–1. MS (ESI): m/z (%)
= 583 (29) [M + H + Na]+, 582 (100) [M + Na]+, 577 (12) [M +
NH4]+, 560 (13). C28H33NO11 (559.21): calcd. C 60.10, H 5.94, N
2.50; found C 60.24, H 5.76, N 2.43.
Benzyl
(2R,3S,4S,4aR,11bS)-2,3,4-Tris(methoxymethoxy)-1-oxo-
2,3,4,4a,6,11b-hexahydro-[1,3]dioxolo[4,5-j]phenanthridine-5(1H)-
carboxylate (21): To a stirred solution of 20 (0.7 g, 1.25 mmol) in
dry THF (12 mL) was added HMPA (1.20 mL) at room tempera-
ture. The solution temperature was decreased to –78 °C, and nBuLi
5844
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2008, 5839–5847

1,10b-epi-7-Deoxypancratistatins and Their Cytotoxicities
(1.62  in hexane, 1 mL, 1.62 mmol) was added over a period of
10 min. The resultant clear solution was stirred at the same tem-
perature for 30 min. A solution of p-toluenesulfonic acid (TSA,
0.36 g, 1.88 mmol) in THF (3 mL) was added dropwise, and the
The residue was purified by column chromatography (silica gel,
elution with 25% EtOAc/hexanes) to afford 23 (0.36 g, 96%) as a
colorless gum. Rf = 0.30 (hexanes/EtOAc, 3:1). [α]2D7 = –18.5 (c =
1
0.80 in CHCl3). H NMR (200 MHz, CDCl3, 25 °C): δ = 7.71 (br.
mixture was stirred for a further 10 min. Saturated aqueous s, 1 H), 6.49 (s, 1 H), 5.86 (dd, J = 5.2, 1.4 Hz, 2 H), 4.90–4.60 (m,
NaHCO3 (10 mL) was added after warming the reaction mixture
to room temperature, and the mixture was extracted with EtOAc
(3ϫ25 mL). The combined organic extracts were dried (Na2SO4),
filtered and concentrated under reduced pressure. The residue was
subjected to column chromatography (silica gel, elution with 25%
EtOAc/hexanes) to give 21 (0.57 g, 83%) as a pale yellow paste. Rf
= 0.40 (hexanes/EtOAc, 2:1). [α]2D7 = +56.9 (c = 0.64 in CHCl3). 1H
NMR (200 MHz, CDCl3, 25 °C): δ = 7.34 (m, 5 H), 6.65 (s, 1 H),
6.61 (s, 1 H), 5.93 (dd, J = 4.6, 1.5 Hz, 2 H), 5.24–5.03 (m, 3 H),
5.98–4.80 (m, 2 H), 4.80–4.61 (m, 6 H), 4.59 (d, J = 3.3 Hz, 1 H),
4.48 (dd, J = 6.7, 5.3 Hz, 1 H), 4.02 (d, J = 6.8 Hz, 1 H), 3.97 (dd,
J = 9.3, 6.8 Hz, 1 H), 3.65 (d, J = 15.8 Hz, 1 H), 3.40 (d, J =
15.8 Hz, 1 H), 3.35–3.32 (m, 7 H) ppm. 13C NMR (100 MHz,
CDCl3, 25 °C): δ = 205.3, 155.9, 147.0, 136.1, 128.5, 128.4, 128.2,
128.1, 128.0, 124.9, 108.5, 107.0, 101.1, 96.6, 96.5, 79.4, 75.5, 73.7,
8 H), 4.52 (br. s, 1 H), 4.42–4.28 (m, 2 H), 4.28–4.00 (m, 2 H),
3.95–3.75 (m, 2 H), 3.55 (br. s, 1 H), 3.40 (s, 2ϫ3 H), 3.36 (s, 3
H), 3.21 (s, 3 H) ppm. 13C NMR (50 MHz, CDCl3, 25 °C): δ =
145.5, 127.5, 125.0, 109.7, 105.2, 100.4, 96.3, 95.2, 79.7, 77.2, 76.8,
75.6, 74.2, 71.1, 55.6, 55.4, 50.4, 42.9, 39.0, 28.3 ppm. IR (CHCl3):
ν = 2891, 1695, 1485, 1365, 1151, 1037 cm–1. MS (ESI): m/z (%) =
˜
594 (100) [M + Na]+. C27H41NO12 (571.26): calcd. C 56.73, H 7.23,
N 2.45; found C 56.56, H 7.16, N 2.56.
tert-Butyl (1S,2S,3S,4S,4aR,11bS)-1,2,3,4-Tetrakis(methoxymeth-
oxy)-6-oxo-2,3,4,4a,6,11b-hexahydro[1,3]dioxolo[4,5-j]phenanthridine-
5(1H)-carboxylate (24): To a vigorously stirred solution of 23 (0.24 g,
0.42 mmol) in distilled CH3CN/CCl4 (1:1, 20 mL) was added aque-
ous NaIO4 (0.27 g in 15 mL of H2O) and RuCl3 (24 mg). After being
stirred for 3 h, the reaction mixture was diluted with DCM (30 mL),
and the aqueous phase was extracted with DCM (3ϫ15 mL) and
EtOAc (3ϫ15 mL). The combined organic extracts were dried
(Na2SO4) and concentrated. The residue was diluted with diethyl
ether (20 mL), filtered through a pad of Celite and concentrated.
The residue was purified by column chromatography (silica gel, elu-
tion with 40% EtOAc/hexanes) to give 24 (0.16 g, 65%) as a colorless
paste. Rf = 0.30 (hexanes/EtOAc, 1:1). [α]D27 = +27.2 (c = 1.25 in
67.7, 55.9, 55.8, 55.6, 54.8, 50.0, 44.4 ppm. IR (neat): ν = 2954,
˜
1730, 1713, 1693, 1487, 1217, 1039 cm–1. MS (ESI): m/z (%) = 598
(23) [M + K]+, 582 (39) [M + Na]+, 560 (2) [M + H]+, 361 (86),
331 (100). C28H33NO11 (559.21): calcd. C 60.10, H 5.94, N 2.50;
found C 60.02, H 5.87, N 2.64.
Benzyl (1S,2S,3S,4S,4aR,11bS)-1,2,3,4-Tetrakis(methoxymethoxy)-
2,3,4,4a,6,10b-hexahydro[1,3]dioxolo[4,5-j]phenanthridine-5(1H)-car- CHCl3). 1H NMR (400 MHz, CDCl3, 25 °C): δ = 7.74 (s, 1 H), 7.57
boxylate (22): Sodium borohydride (0.1 g, 2.68 mmol) was added
to a solution of 21 (0.5 g, 0.89 mmol) in dry MeOH (10 mL). The
resulting mixture was stirred for 12 h and then quenched by the
addition of excess saturated aqueous NaCl. The brownish suspen-
sion was stirred overnight and extracted with EtOAc (3ϫ15 mL).
The combined organic extracts were dried (Na2SO4), and the sol-
vent was distilled off. The residue (0.44 g) was concentrated to dry-
ness and used for the next step without purification. To a solution
of the above crude alcohol (0.44 g, 0.78 mmol) in dry DCM (8 mL)
were successively added DIPEA (0.68 mL, 3.92 mmol) and
MOMCl (0.6 mL, 7.84 mmol) dropwise at 0 °C. The yellow solu-
tion was warmed to room temperature and stirred for 12 h before
water (10 mL) was added. The aqueous layer was extracted with
DCM (2 ϫ 7 mL), and the organic layers were combined, dried
(Na2SO4), filtered and concentrated to produce an orange paste,
which was purified by column chromatography (silica gel, elution
with 30% EtOAc/hexanes) to yield 22 (0.44 g, 82% over two steps)
as a colorless paste. Rf = 0.30 (hexanes/EtOAc, 7:3). [α]2D7 = –17.1
(c = 1.24 in CHCl3). 1H NMR (200 MHz, CDCl3, 25 °C): δ = 7.72
(br. s, 1 H), 6.50 (br. s, 1 H), 5.87 (dd, J = 5.2, 1.4 Hz, 2 H), 5.35–
5.02 (m, 2 H), 4.90–4.60 (m, 8 H), 4.53–4.20 (m, 4 H), 4.09 (appar-
ent s, 1 H), 4.00–3.81 (m, 2 H), 3.58 (br. s, 1 H), 3.39 (s, 2ϫ3 H),
3.29 (s, 3 H), 3.22 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3,
25 °C): δ = 156.0, 145.6, 137.0, 136.6, 128.4, 128.2, 128.0, 127.5,
124.7, 109.7, 105.2, 100.5, 97.6, 97.1, 96.4, 95.4, 75.62, 74.5, 71.3,
71.2, 67.2, 66.8, 55.9, 55.7, 55.6, 55.4, 50.5, 42.9, 39.2 ppm. IR
(s, 1 H), 5.98 (d, J = 12.1 Hz, 2 H), 5.01 (dd, J = 11.1, 4.8 Hz, 1 H),
4.81 (s, 2 H), 4.78 (d, J = 7.1 Hz, 1 H), 4.72 (d, J = 7.1 Hz, 1 H),
4.68 (d, J = 6.8 Hz, 1 H), 4.58 (d, J = 7.1 Hz, 1 H), 4.46 (dd, J =
7.6, 7.1 Hz, 2 H), 4.38 (dd, J = 5.1, 3 Hz, 1 H), 4.10 (apparent s, 1
H), 3.94 (s, 1 H), 3.92 (apparent s, 1 H), 3.89 (t, J = 5.1 Hz, 1 H),
3.42 (s, 3 H), 3.40 (s, 3 H), 3.30 (s, 3 H), 3.24 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3, 25 °C): δ = 162.2, 152.4, 150.8, 146.5,
135.3, 123.2, 109.4, 108.3, 101.4, 97.5, 96.6, 95.7, 82.8, 77.2, 77.1,
75.3, 74.9, 72.0, 55.9, 55.8, 55.7, 53.1, 39.4, 28.0 ppm. IR (CHCl3):
ν = 2895, 1764, 1693, 1483, 1242, 1151, 1038 cm–1. MS (ESI): m/z
˜
(%) = 609 (100) [M + H + Na]+, 586 (7) [M + H]+, 508 (19), 486
(15). C27H39NO13 (585.24): calcd. C 55.38, H 6.71, N 2.39; found C
55.23, H 6.91, N 2.18.
1,10b-epi-7-Deoxypancratistatin (25): To a solution of 24 (0.1 g,
0.17 mmol) in dry CH3CN (1 mL) was added a catalytic amount of
solid Mg(ClO4)2 (8 mg, 0.036 mmol) at room temperature. The
stirred mixture was heated in an oil bath at 50 °C for 1.5 h. The
mixture was cooled to room temperature and partitioned between
EtOAc (10 mL) and water (5 mL) in a separating funnel. The aque-
ous layer was extracted with EtOAc (2ϫ5 mL). The organic extracts
were combined, dried (Na2SO4), filtered and subjected to rotary
evaporation to afford the pure amide (75 mg, 90%) as white solid,
which was forwarded to the next step. To a solution of the above
intermediate (75 mg, 0.15 mmol) in MeOH (4 mL) was added HCl
(6 , 2 mL), and the reaction mixture was refluxed for 18 h. The
solvent was evaporated to dryness to afford a brown solid, which
was triturated with distilled MeOH (2 mL), and allowed to settle.
The solvent was decanted. The trituration was repeated once again,
and removal of the solvent afforded 1,10b-epi-7-deoxypancratistatin
(CHCl ): ν = 2891, 1693, 1487, 1217, 1035 cm–1. MS (ESI): m/z
˜
3
(%) = 628 (100) [M + Na]+. C30H39NO12 (605.25): calcd. C 59.50,
H 6.49, N 2.31; found C 59.39, H 6.25, N 2.22.
tert-Butyl (1S,2S,3S,4S,4aR,11bS)-1,2,3,4-Tetrakis(methoxymeth-
(25, 42 mg, 89%) as an off-white solid, m.p. 298–305 °C. Rf = 0.20
1
oxy)-2,3,4,4a,6,11b-hexahydro-[1,3]dioxolo[4,5-j]phenanthridine-5(1H)- (CHCl3/MeOH, 4:1). [α]D27 = +88.3 (c = 0.35 in DMSO). H NMR
carboxylate (23): A mixture of 22 (0.4 g, 0.66 mmol) and (Boc)2O
(0.2 mL, 0.86 mmol) in distilled MeOH (12 mL) was hydrogenated
at atmospheric pressure in the presence of 10% Pd on charcoal
(40 mg) for 7 h. The reaction mixture was passed through a short
pad of Celite, and the solvent was removed by rotary evaporation.
(400 MHz, [D6]DMSO, 25 °C): δ = 7.22 (s, 1 H), 6.89 (s, 1 H), 5.99
(d, J = 5.3 Hz, 2 H), 3.95 (s, 1 H), 3.80–3.62 (m, 4 H), 2.99 (s, 1 H)
ppm. 13C NMR (100 MHz, [D6]DMSO, 25 °C): δ = 164.6, 149.9,
146.3, 135.7, 125.8, 107.4, 106.2, 101.4, 73.8, 70.6, 69.7, 67.0, 55.3,
38.4 ppm. MS (ESI): m/z (%) = 332 (16) [M + Na]+, 310 (20) [M +
Eur. J. Org. Chem. 2008, 5839–5847
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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5845

G. Pandey, M. Balakrishnan, P. S. Swaroop
FULL PAPER
H]+, 301 (21), 295 (100), 253 (98). C14H15NO7 (309.08): calcd. C
54.37, H 4.89, N 4.53; found C 54.31, H 4.76, N 4.58.
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Amine Hydrochloride 26: To a solution of 22 (70 mg, 0.116 mmol)
in MeOH (2 mL) was added pre-activated Dowex 50WX2-400 resin
(90 mg). The heterogeneous mixture was refluxed with stirring for
14 h. The mixture was cooled, filtered through a short pad of Celite,
and the filtrate was concentrated by rotary evaporation to afford a
brown residue, which was purified by column chromatography (silica
gel, elution with 5% MeOH/CHCl3) to produce the corresponding
tetrol (40 mg, 80%) as an amorphous white solid. To a solution of
the above tetrol (40 mg, 0.093 mmol) in distilled MeOH (2 mL) was
added concentrated HCl (2 drops), and the mixture was hydroge-
nated in the presence of 20% Pd(OH)2 on carbon (8 mg) under at-
mospheric pressure for 12 h. After passing the mixture through a
pad of Celite, the solvent was evaporated to dryness to afford 26
(31 mg, ca. 100%) as a pale yellow solid, m.p. 214–216 °C with de-
[9]
[10]
1
composition. [α]2D7 = +40.8 (c = 0.5 in H2O). H NMR (500 MHz,
D2O, 25 °C): δ = 6.73 (s, 1 H), 6.60 (s, 1 H), 5.85 (d, J = 3.0 Hz, 1
H), 4.28 (d, J = 7.5 Hz, 1 H), 4.25 (dd, J = 3.1, 2.8 Hz, 1 H), 4.09
(m, 2 H), 3.93 (dd, J = 10.3, 3.4 Hz, 1 H), 3.88 (dd, J = 10.3, 2.5 Hz,
1 H), 3.62 (m, 1 H), 3.20 (m, 1 H) ppm. 13C NMR (125 MHz, D2O,
25 °C): δ = 147.1, 146.7, 125.0, 121.5, 107.8, 105.6, 101.2, 74.7, 69.6,
68.7, 66.6, 57.4, 45.5, 35.1 ppm. MS (ESI): m/z (%) = 296 (100) [M –
Cl]+. C14H18ClNO6 (331.08): calcd. C 50.69, H 5.47, N 4.22; found
C 50.44, H 5.59, N 4.18.
[11]
Supporting Information (see footnote on the first page of this article):
Copies of 1H and 13C NMR spectra of all new compounds, cytotox-
icity data of 25 and 26.
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Acknowledgments
We thank Dr. V. R. Pedireddi and Mr. P. Sathyanarayana Reddy for
the X-ray structure analysis. The cytotoxic evaluation data from Dr.
Dhiman Sarkar and Ms. Sampa Sarkar are gratefully acknowledged.
M. B. and P. S. S. thank the Council of Scientific and Industrial Re-
search (CSIR), New Delhi for the award of research fellowships.
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Received: August 28, 2008
Published Online: October 20, 2008
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5847