Total synthesis and evaluation of phostriecin and key structural analogues

Article abstract of DOI:10.1021/jo1010203

Full details of the total synthesis of phostriecin (2), the assignment of its relative and absolute stereochemistry, and the resultant structural reassignment of the natural product previously represented as sultriecin (1), a phosphate versus sulfate mono

Full text of DOI:10.1021/jo1010203

pubs.acs.org/joc
Total Synthesis and Evaluation of Phostriecin and
Key Structural Analogues
Christopher P. Burke,† Mark R. Swingle,‡ Richard E. Honkanen,‡ and Dale L. Boger*,†
†Department of Chemistry and the Skaggs Institute for Chemical Biology, The Scripps Research Institute,
10550 North Torrey Pines Road, La Jolla, California 92037, and ‡Department of Biochemistry and
Molecular Biology, University of South Alabama College of Medicine, Mobile, Alabama 36688
boger@scripps.edu
Received May 24, 2010
Full details of the total synthesis of phostriecin (2), the assignment of its relative and absolute
stereochemistry, and the resultant structural reassignment of the natural product previously
represented as sultriecin (1), a phosphate versus sulfate monoester, are detailed. Studies with
authentic material confirmed that phostriecin, but not sultriecin, is an effective and selective inhibitor
of protein phosphatase 2A (PP2A) defining a mechanism of action responsible for its antitumor
activity. The extension of the studies to the synthesis and evaluation of a series of key synthetic
analogues is disclosed that highlights the importance of the natural product phosphate monoester (vs
sulfate or free alcohol, both inactive and >250-fold), the R,β-unsaturated lactone (12-fold), and the
hydrophobic Z,Z,E-triene tail (C12-C22, ca. 200-fold) including the unique importance of its
unsaturation (50-fold, and no longer PP2A selective).
Introduction
was an early member of a family of natural products3 that
now include fostriecin (3),4-6 cytostatin (4),7 phospholine (5,
phoslactomycin B),8 the leustroducsins (6),9 and the phos-
lactomycins (7) (Figure 1).10 Common structural features
include an electrophilic R,β-unsaturated lactone and hydrophobic
Protein phosphatases are key enzymes in the regulation of
many biological processes. Their function is to catalyze the
dephosphorylation of hydroxyl-containing amino acid side
chains of proteins. Protein phosphatase 2A (PP2A) is a major
serine/threonine phosphatase and plays an important role in
many cell functions including cell growth, replication, mobi-
lity, and signal transduction. Because of the importance of
these processes in human diseases and to further understand
the pathways by which protein phosphorylation affects cells,
there is a need for the development of compounds that
selectively inhibit protein phosphatases including PP2A.1
Sultriecin (1)2 was identified as an antitumor antibiotic
isolated from Streptomyces roseiscleroticus no. L827-7 and
(4) Isolation: (a) Tunac, J. B.; Graham, B. D.; Dobson, W. E. J. Antibiot.
1983, 36, 1595. (b) Stampwala, S. S.; Bunge, R. H.; Hurley, T. R.; Willmer, N. E.;
Brankiewicz, A. J.;Steinman, C. E.;Smitka, T. A.;French, J. C.J. Antibiot. 1983,
36, 1601. Total syntheses: (c) Boger, D. L.; Ichikawa, S.; Zhong, W. J. Am.
Chem. Soc. 2001, 123, 4161. (d) Chavez, D. E.; Jacobsen, E. N. Angew. Chem.,
Int. Ed. 2001, 40, 3667. (e) Reddy, Y. K.; Falck, J. R. Org. Lett. 2002, 4, 969. (f)
Miyashita, K.; Ikejiri, M.; Kawasaki, H.; Maemura, S.; Imanishi, T. Chem.
Commun. 2002, 742. (g) Miyashita, K.; Ikejiri, M.; Kawasaki, H.; Maemura, S.;
Imanishi, T. J. Am. Chem. Soc. 2003, 125, 8238. (h) Esumi, T.; Okamoto, N.;
Hatakeyama, S. Chem. Commun. 2002, 3042. (i) Fujii, K.; Maki, K.; Kanai, M.;
Shibasaki, M. Org. Lett. 2003, 5, 733. (j) Trost, B. M.; Frederiksen, M. U.;
Papillon, J. P.; Harrington, P. E.; Shin, S.; Shireman, B. T. J. Am. Chem. Soc.
2005, 127, 3666. (k) Maki, K.; Motoki, R.; Fujii, K.; Kanai, M.; Kobayashi, T.;
Tamura, S.; Shibasaki, M. J. Am. Chem. Soc. 2005, 127, 17111. (l) Yadav, J. S.;
Prathap, I.; Tadi, B. P. Tetrahedron Lett. 2006, 47, 3773. (m) Hayashi, Y.;
Yamaguchi, H.; Toyoshima, M.; Okado, K.; Toyo, T.; Shoji, M. Org. Lett. 2008,
10, 1405. (n) Sarkar, S. M.; Wanzala, E. N.; Shibahara, S.; Takahashi, K.;
Ishihara, J.; Hatakeyama, S. Chem. Commun. 2009, 5907. (o) Robles, O.;
McDonald, F. E. Org. Lett. 2009, 11, 5498.
(1) (a) Swingle, M.; Ni, L.; Honkanen, R. E. Methods Mol. Biol. 2007,
365, 23. (b) Virshup, D. M.; Shenolikar, S. Mol. Cell 2009, 33, 537. (c)
McConnell, J. L; Wadzinski, B. E. Mol. Pharmacol. 2009, 75, 1249.
(2) Ohkuma, H.; Naruse, N.; Nishiyama, Y.; Tsuno, T.; Hoshino, Y.;
Sawada, Y.; Konishi, M.; Oki, T. J. Antibiot. 1992, 45, 1239.
(3) Lewy, D. S.; Gauss, C.-M.; Soenen, D. R.; Boger, D. L. Curr. Med.
Chem. 2002, 9, 2005.
(5) (a) Boger, D. L.; Hikota, M.; Lewis, B. M. J. Org. Chem. 1997, 62,
1748. (b) Hokanson, G. C.; French, J. C. J. Org. Chem. 1985, 50, 462.
DOI: 10.1021/jo1010203
r
Published on Web 07/29/2010
J. Org. Chem. 2010, 75, 7505–7513 7505
2010 American Chemical Society

Burke et al.
JOCFeatured Article
FIGURE 2. Assignment of relative and absolute stereochemistry.
functional biological activity and structural similarity to
fostriecin (3) and cytostatin (4), we anticipated that sultriecin
(1) would also be a selective PP2A inhibitor, albeit with a
sulfate versus phosphate interaction with the enzymatic bime-
tallic catalytic core. Pertinent to the work detailed herein and
because of the sultriecin disclosure, we had previously exam-
ined and shown that the corresponding sulfate ester of cytos-
tatin (sulfocytostatin) was unexpectedly inactive as a PP2A
inhibitor.7c Herein, we report a full account of the first total
synthesis and stereochemical determination of sultriecin (1),
the unanticipated structural reassignment of the natural pro-
duct as phosphate monoester 2 (renamed phostriecin), estab-
lishment of its biological activity as an inhibitor of PP2A, and
the synthesis and biological evaluation of key analogues.11
Stereochemical Assignment. The structure of sultriecin was
disclosed without definition of its relative or absolute stereo-
chemistry.2 Based on its biological and structural similarity to
fostriecin and cytostatin as well as its reported spectral data, we
assigned 4S,5S,9S,10S,11S stereochemistry to sultriecin. The
syn C4-C5 stereochemistry assignment was supported by the
observed H4-H5 coupling constant in the reported 1HNMRof
1(J= 2.9 Hz). This coupling constant is similar to that observed
for cytostatin (J = 2.7 Hz), and a similar known lactone
displays a syn H4-H5 coupling constant (J = 3.1 Hz) distinct
from that of the corresponding anti-4,5-disubstituted lactone
(J = 8.7 Hz).12 The H10-H11 coupling constant (J = 10.2 Hz)
reported for sultriecin is indicative of an anti relationship. It is in
particularly good agreement with coupling constants observed
for fostriecin (J= 9.6 vs 3.7 Hz) and cytostatin (J=9.4Hz) and
supports the existence of an intramolecular H-bond between the
C11-OH and putative C9 sulfate resulting in a rigid twist-boat
cyclic structure as found in 3 and 4 (Figure 2).
FIGURE 1. Natural product structures.
Z,Z,E-triene capping the ends of an extended structure that
contains a central functionalized 1,3-diol. Unique to 1 and in
contrast to the more recent members of the family that contain
phosphate monoesters, sultriecin was assigned as a C9 sulfate
ester at the time of its early disclosure. Sultriecin displayed
moderate broad spectrum antifungal activity in vitro, moder-
ate in vitro cytotoxic activity against human and murine tumor
cell lines, and potent in vivo antitumor activity against P388
leukemia and B16 melanoma.2
In efforts on the synthesis and evaluation of members of
this class of antitumor agents that have since been shown to
act as PP2A inhibitors, we reported total syntheses of 34c and
4,7c the establishment of their relative and absolute con-
figuration,5,7 and the preparation of a series of analogues
used to define structural features that are key to their potent
and unusually selective inhibition of PP2A.6,7 Based on its
(6) (a) Buck, S. B.; Hardouin, C.; Ichikawa, S.; Soenen, D. R.; Gauss,
C.-M.; Hwang, I.; Swingle, M. R.; Bonness, K. M.; Honkanen, R. E.; Boger,
D. L. J. Am. Chem. Soc. 2003, 125, 15694. (b) Swingle, M. B.; Amable, L.;
Lawhorn, B. G.; Buck, S. B.; Burke, C. P.; Ratti, P.; Fisher, K. L.; Boger,
D. L.; Honkanen, R. E. J. Pharmacol. Exp. Ther. 2009, 331, 45. (c) Takeuchi,
T.; Takahashi, N.; Ishi, K.; Kusayanagi, T.; Kuramochi, K.; Sugawara, F.
Bioorg. Med. Chem. 2009, 17, 8113.
(7) Isolation: (a) Amemiya, M.; Someno, T.; Sawa, R.; Naganawa, H.;
Ishizuka, M.; Takeuchi, T. J. Antibiot. 1994, 47, 541. (b) Amemiya, M.;
Ueno, M.; Osono, M.; Masuda, T.; Kinoshita, N.; Nishida, C.; Hamada, M.;
Ishizuka, M.; Takeuchi, T. J. Antibiot. 1994, 47, 536. Total syntheses: (c)
Lawhorn, B. G.; Boga, S. B.; Wolkenberg, S. E.; Colby, D. A.; Gauss, C.-M.;
Swingle, M. R.; Amable, L.; Honkanen, R. E.; Boger, D. L. J. Am. Chem.
Soc. 2006, 128, 16720. (d) Lawhorn, B. G.; Boga, S. B.; Wolkenberg, S. E.;
Boger, D. L. Heterocycles 2006, 70, 65. (e) Bialy, L.; Waldmann, H. Chem.;
Eur. J. 2004, 10, 2759. (f ) Bialy, L.; Waldmann, H. Angew. Chem., Int. Ed.
2002, 41, 1748. (g) Jung, W.-H.; Guyenne, S; Riesco-Fagundo, C.; Mancuso,
J.; Nakamura, S.; Curran, D. P. Angew. Chem., Int. Ed. 2008, 47, 1130.
(8) Isolation: (a) Ozasa, T.; Tanaka, K.; Sasamata, M.; Kaniwa, H.;
Shimizu, M.; Matsumoto, H.; Iwanami, M. J. Antibiot. 1989, 42, 1339. Total
syntheses: (b) Wang, Y.-G.; Takeyama, R.; Kobayashi, Y. Angew. Chem.,
Int. Ed. 2006, 45, 3320. (c) Shibahara, S.; Fujino, M.; Tashiro, Y.; Takahashi,
K.; Ishihara, J.; Hatakeyama, S. Org. Lett. 2008, 10, 2139.
Synthetic Approach. A convergent route to sultriecin was
designed that incorporated the flexibility to provide access to
analogues and to allow preparation of any diastereomer in
the event that the initial stereochemical assignment proved
incorrect. The approach relies on a late-stage one-step
installation of the Z,Z,E-triene via chelation-controlled
addition of the cuprate derived from 9 to aldehyde 8. We
envisioned the protected lactol 8 arising from an oxidative
ring expansion of an R-hydroxyfuran that would be accessed
from the coupling of alkyne 10 with 2-furoyl chloride
(9) Isolation: (a) Kohama, T.; Enokita, R.; Okazaki, T.; Miyaoka, H.;
Torikata, A.; Inukai, M.; Kaneko, I.; Kagasaki, T.; Sakaida, Y.; Satoh, A.;
Shiraishi, A. J. Antibiot. 1993, 46, 1503. (b) Kohama, T.; Nakamura, T.;
Kinoshita, T.; Kaneko, I.; Shiraishi, A. J. Antibiot. 1993, 46, 1512. Total
syntheses: (c) Matsuhashi, H.; Shimada, K. Tetrahedron 2002, 58, 5619. (d)
Shimada, K.; Kaburagi, Y.; Fukuyama, T. J. Am. Chem. Soc. 2003, 125,
4048. (e) Miyashita, K.; Tsunemi, T.; Hosokawa, T.; Ikejiri, M.; Imanishi, T.
J. Org. Chem. 2008, 73, 5360.
(11) Burke, C. P.; Haq, N.; Boger, D. L. J. Am. Chem. Soc. 2010, 132,
(10) Isolation: (a) Fushimi, S.; Nishikawa, S.; Shimazu, A.; Seto, H.
€
J. Antibiot. 1989, 42, 1019. Total synthesis: (b) Konig, C. M.; Gebhardt, B.;
Schleth, C.; Dauber, M.; Koert, U. Org. Lett. 2009, 11, 2728.
2157.
(12) Yang, Z.-C.; Jiang, X.-B.; Wang, Z.-M.; Zhou, W.-S. J. Chem. Soc.,
Perkin Trans. 1 1997, 317.
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SCHEME 1
SCHEME 2
FIGURE 3. Retrosynthetic plan for sultriecin (1).
followed by asymmetric (R)-CBS ketone reduction to set the
C5 stereochemistry and subsequent stereoselective alkyne
reduction (Figure 3).
Results and Discussion
Synthesis of C1-C11. The synthesis began with protection
of methyl (S)-3-hydroxy-2-methylpropionate (11) as a PMB
ether followed by its reduction to alcohol 12 (PMBOC(dNH)-
CCl3, camphorsulfonic acid, CH2Cl2, 25 °C, 12 h; LiAlH4,
Et2O, 0 to 25 °C, 12 h, 91%, two steps) (Scheme 1). After
oxidation of 12 to the corresponding aldehyde (DMSO, oxalyl
chloride, Et3N, CH2Cl2, -78 to 0 °C, 2 h), asymmetric allyl-
boration (allyldiisopinocampheylborane, -100 °C, 4 h; NaOH,
H2O2, 25 °C, 16 h, 14:1 dr)13 gave alcohol 13 that was protected
as the ethoxyethyl acetal (14) (ethyl vinyl ether, PPTS, CH2Cl2,
25 °C, 2 h). The ethoxyethyl acetal (EE) protecting group was
chosen due to its ability to direct a subsequent chelation-
controlled cuprate addition as well as its unique ability to be
removed under mildly acidic conditions in the presence of the
labile triene and sensitive allylic alcohol despite the complicating
diastereomeric mixture it introduces. Oxidative cleavage of the
double bond in 14 (OsO4, NaIO4, NMO, THF, H2O, 25 °C,
18 h, 73%, four steps) provided aldehyde 15.
In the course of our efforts, several routes to the furyl
alcohol 19 were investigated. Initially and although not pur-
sued in depth, hydroboration of model alkynes 16 followed by
transmetalation to zinc and asymmetric addition to furfural
with (-)-MIB[(-)-MIB=(2S)-3-exo-(morpholino)isoborneol]
as a chiral ligand14 were examined but failed to provide the
desired addition products. Similarly, preliminary efforts
on diastereoselective alkyne addition of 16 to furfural fol-
lowing established procedures15-17 were also unsuccessful
(Scheme 2).
We also examined methods of diastereoselective reduction
of ketone 18, synthesized by Horner-Wadsworth-Emmons
reaction of phosphonate 17 with aldehyde 15. However,
hydrogenation in the presence of ketone-selective chiral
catalysts (e.g., (S)-BINAP-RuCl2)18 as well as attempted
reduction with chiral aluminum hydride reagents (e.g., (S)-
BINAL-H)19 reduced the olefin in preference to or along
with the ketone. Reduction of 18 with (R)-Me-CBS (1.5
equiv) and BH3-Me2S (4 equiv) gave exclusive ketone
reduction in good yield (80%), but with only 2:1 diastereos-
electivity (Scheme 3).
With a recognition that higher diastereoselectivity could
be obtained by replacing the alkene in 18 with an alkyne
providing a smaller substituent and affording a better stereo-
differentiation with respect to the furan, aldehyde 15 was
subjected to the Corey-Fuchs homologation (CBr4, PPh3,
CH2Cl2, 0 °C, 10 min, 71%; n-BuLi, THF, -78 to 25 °C,
16 h, 93%)20 giving alkyne 10 (Scheme 4). Coupling of 10
with 2-furoyl chloride (Pd(PPh3)2Cl2, CuI, Et3N, 25 °C, 24 h,
85%)21 gave ketone 21 that was subjected to asymmetric
reduction (methyl-(R)-CBS-oxazaborolidine, BH3-Me2S,
THF, -40 °C, 3 h) giving the desired alcohol diastereomer 22
(13) (a) Racherla, U. S.; Brown, H. C. J. Org. Chem. 1991, 56, 401. (b)
Nicolaou, K. C.; Patron, A. P.; Ajito, K.; Richter, P. K.; Khatuya, H.;
Bertinato, P.; Miller, R. A.; Tomaszewski, M. J. Chem.;Eur. J. 1996, 2, 847.
(14) Oppolzer, W.; Radinov, R. N. Helv. Chim. Acta 1992, 75, 170.
(15) Trost, B. M.; Weiss, A. H.; von Wangelin, A. J. J. Am. Chem. Soc.
2006, 128, 8.
(16) Takita, R.; Yakura, K.; Oshima, T.; Shibasaki, M. J. Am. Chem. Soc.
2005, 127, 13760.
€
(17) Frantz, D. E.; Fassler, R.; Carreira, E. M. J. Am. Chem. Soc. 2000,
(18) (a) Noyori, R.; Ohta, M.; Hsiao, Y.; Kitamura, M.; Ohta, T.;
Takaya, H. J. Am. Chem. Soc. 1986, 108, 7117. (b) Noyori, R.; Ohkuma,
T.; Kitamura, H.; Takaya, H.; Sayo, H.; Kumobayashi, S.; Akutagawa, S.
J. Am. Chem. Soc. 1987, 109, 5856.
(19) (a) Noyori, R.; Tomino, I.; Tanimoto, Y.; Nishizawa, M. J. Am.
Chem. Soc. 1984, 106, 6709. (b) Noyori, R.; Tomino, I.; Yamada, M.;
Nishizawa, M. J. Am. Chem. Soc. 1984, 106, 6717.
(20) (a) Corey, E. J.; Fuchs, P. L. Tetrahedron Lett. 1972, 13, 3769. (b)
Ramirez, F.; Desai, N. B.; McKelvie, N. J. Am. Chem. Soc. 1962, 84, 1745.
(21) Tohda, Y.; Sonogashira, K.; Hagihara, N. Synthesis 1977, 777.
122, 1806.
J. Org. Chem. Vol. 75, No. 22, 2010 7507

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SCHEME 3
mixture of inseparable anomers. Due to its instability to
silica gel chromatography, diastereoselective 1,2-reduction
of the enone was performed on crude 24 (LiAlH4,Et2O, -60 °C,
2.5 h, dr >30:1, 51-64% for three steps) (Scheme 4). Alter-
native reducing agents including NaBH4-CeCl3 and DIBAL
produced varying amounts of the syn isomer as a minor
product, and we were not successful in identifying a reducing
agent that would selectively or exclusively provide this syn
isomer. Consequently, the stereochemistry of the C4 alcohol in
25 was necessarily inverted and directly protected as its pivalate
ester using the Mitsunobu reaction (DIAD/PPh3, pivalic acid,
THF, 0-25 °C, 75%).26 Aldehyde 8 was obtained following
PMB removal (DDQ, CH2Cl2/H2O, 25 °C, 1 h, 74%) and
oxidation of alcohol 27 (DMP, CH2Cl2, 25 °C, 1 h, 92%).27
Synthesis of C12-C22. With aldehyde 8 in hand, focus
turned toward synthesis of the sensitive triene portion of the
molecule. Following an approach adopted in our total synth-
esis of cytostatin7c and originally introduced by Taylor,28
treatment of pyrilium tetrafluoroborate with n-pentyllithium
(THF, -78 °C, 4 h) gave, after room temperature electrocyclic
ring-opening of the adduct, aldehyde 28 as a single isomer
(eq 1). Because of its instability to storage and its volatility,
aldehyde 28 was immediately converted by dibromoolefination
(CBr4, PPh3, Et3N, CH2Cl2, 0 °C, 15 min, 85% for two steps)20
to 29 which could be stored as a solution in Et2O at 4 °C for
several weeks. Unstable Z,Z,E-bromotriene 9 was produced
immediately before use by selective E-bromide reduction
(Bu3SnH, Pd(PPh3)4, Et2O, 0 °C, 45 min, 78%).29
SCHEME 4
Total Synthesis of Sultriecin and Phostriecin. Incorpora-
tion of the sensitive Z,Z,E-triene required conversion of 9 to
the corresponding cuprate (t-BuLi, Et2O, -78 °C, 1 h;
CuI-PBu3, Et2O, -78 °C, 15 min) followed by slow addition
of aldehyde 8 (Et2O, -78 °C, 1 h, 85%, >5:1 dr),7c,30
providing 30 derived from a chelation-controlled addition
to the aldehyde (Scheme 5). Removal of the pivalate ester
(DIBAL, CH2Cl2, -78 °C, 2 h) followed by silylation of the
secondary alcohols of 31 (TBDPSCl, AgNO3, pyr/CH2Cl2,
25 °C, 16 h, 80%, two steps) afforded 32 that was treated with
dilute HCl (THF/H2O, 25 °C, 12 h, 71%) to simultaneously
and selectively remove the EE and TBS protecting groups.
The resulting lactol was selectively oxidized to give lactone
33 (Ag2CO3-Celite, benzene, 80 °C, 1.5 h, 91%). Sulfate
ester introduction (SO3-pyr, THF, 25 °C, 10 min, 80%)
followed by desilylation (HF-pyr, pyr/THF, 25 °C, 60%)
with 12.5:1 selectivity and setting the C5 stereochemistry.22
Olefin 19 was subsequently obtained by stereoselective reduc-
tion of the alkyne (LiAlH4, THF, 0-25 °C, 24 h, 84%, two
steps) (Scheme 4).23
Lactol 23 was obtained as a mixture of anomers following
oxidative ring expansion of 19 (NBS, NaHCO3, NaOAc,
THF/H2O, 0 °C, 1 h).24 Installation of a range of lactol
protecting groups was examined including Boc, Piv, Bz, and
Me groups. However, 23 and its corresponding protected
products proved to be especially sensitive to both acidic and
basic conditions, and attempts at installation of these pro-
tecting groups largely failed. TBS protection of the lactol
under mild conditions (TBSCl, AgNO3, pyr, CH2Cl2, 25 °C,
15 min) was most effective,25 providing an inconsequential
gave 1, which did not match the spectroscopic (1H NMR, 13
C
(22) Corey, E. J.; Bakshi, R. K.; Shibata, S. J. Am. Chem. Soc. 1987, 109,
5551.
(23) Corey, E. J.; Katzenellenbogen, J. A.; Posner, G. H. J. Am. Chem.
Soc. 1967, 89, 4245.
(26) Mitsunobu, O. Synthesis 1981, 1.
(27) Dess, D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277.
(24) (a) Georgiadis, M. P.; Couladouros, E. A. J. Org. Chem. 1986, 51,
2725. (b) Babu, R. S.; Zhou, M.; O’Doherty, G. A. J. Am. Chem. Soc. 2004,
126, 3428.
(25) Hakimelahi, G. H.; Proba, Z. A.; Ogilvie, K. K. Tetrahedron Lett.
1981, 22, 4775.
(28) Belosludtsev, Y. Y.; Borer, B. C.; Taylor, R. J. K. Synthesis 1991,
320.
(29) Uenishi, J.; Kawahama, R.; Yonemitsu, O.; Tsuji, J. J. Org. Chem.
1998, 63, 8965.
(30) Still, W. C.; Schneider, J. A. Tetrahedron Lett. 1980, 21, 1035.
7508 J. Org. Chem. Vol. 75, No. 22, 2010

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SCHEME 5. Synthesis of Sultriecin (1)
FIGURE 4. Diagnostic region of 1H NMR of 1 and 2.
SCHEME 6. Synthesis of Phostriecin (2)
NMR, IR) or physical characteristics (TLC, [R]D, solubility,
stability to silica gel) of the natural product.
Several possibilities for this noncorrelation with the nat-
ural product were envisioned including the accuracy of our
stereochemical assignment as well as spectroscopic perturba-
tions derived from the protonation state or salt form of the
sulfate. To confirm the C9/C11 anti relationship of synthetic
1, 33 was deprotected (HF-pyr, pyr/THF, 25 °C, 12 h,
90%),31 and the resultant 1,3-diol 35 was converted to
acetonide 36 (2,2-dimethoxypropane, TsOH, THF, 25 °C,
45 min, 52%) (eq 2). The 13C NMR chemical shifts observed
for the acetonide carbons of 36 (CD3CN, δ 24.6, 25.0, 101.3)
were found to be indicative of the anti-1,3-diol acetonide as
desired and anticipated.32
1.8 Hz vs dddd, J = 9.6, 7.8, 7.2, 1.8 Hz) of C9-H adjacent to
the putative sulfate ester (Figure 4). Careful examination of
1
the H NMR spectra of synthetic 1 and natural sultriecin
revealed that the natural product H9 signal exhibited an
additional long-range coupling (JP-H9 = 7.8 Hz) that would
be characteristic of a phosphate (monoisotopic mass =
492.1889) versus sulfate ester (monoisotopic mass = 492.1794).
Because of the potential ambiguity introduced by the closely
related molecular weights, the original natural product assign-
ment was additionally based on a negative Hanes test used to
characterize a phosphate (vs sulfate) monoester, and exposure
of the natural product to a sulfatase resulted in putative sulfate
monoester hydrolysis.2 Since these are also not unambiguous,
phosphate monoester 2 was targeted for synthesis (Scheme 6).
Alcohol 33 was phosphorylated (i-Pr2NP(OFm)2, tetrazole,
CH2Cl2/CH3CN, 25 °C, 1 h; H2O2, 15 min, 96%)7 to give 37
that was desilylated (HF-pyr, pyr/THF, 25 °C, 4 d). Removal
of the fluorenylmethyl groups (Fm) in 38 (Et3N, CH3CN,
25 °C, 16 h; Dowex Naþ, 63% for two steps) unmasked the
phosphate giving 2 (renamed phostriecin), which proved
identical to the reported properties of 1 as well as a sample
of the natural product (1H NMR, 31P NMR, [R]D, TLC,
HPLC, HRMS), the latter of which also displayed a 31P
NMR signal like that found with synthetic 2 (δ 3.4, CD3OD).
Thus, the total synthesis of 2 and its correlation with authentic
natural material requires a structural reassignment of the
natural product formerly known as sultriecin.
To address potential issues of the protonation state and
sulfate counterion identity, naturally derived sultriecin33 was
subjected to the conditions of the last step of the synthesis of
1 (HF-pyr, pyr/THF, aq NaHCO3 quench, silica gel
chromatography). This action, however, resulted only in
decomposition of the natural material indicating that there
was a more fundamental distinction in the synthetic (stable)
and natural (unstable) materials.
The most apparent difference observed in the 1H NMR of
synthetic 1 and the natural product was the chemical shift
(CD3OD, δ 4.82 vs 4.64) and multiplicity (ddd, J = 8.4, 6.0,
(31) 1H NMR data for “desulfated” 1 were reported; however, these data
alone were not sufficient to confirm that it and triol 35 share the same
structure. See ref 2.
(32) (a) Rychnovsky, S. D.; Skalitzky, D. J. Tetrahedron Lett. 1990, 31,
945. (b) Evans, D. A.; Rieger, D. L.; Gage, J. R. Tetrahedron Lett. 1990, 31,
7099.
Synthesis of Key Analogues. With a synthesis and structur-
al reassignment of the natural product in hand, we extended
the efforts to the preparation of a series of analogues
(33) Commercially available from Bioaustralis.
J. Org. Chem. Vol. 75, No. 22, 2010 7509

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SCHEME 7. Synthesis of Analogues 45 and 48
SCHEME 8. Synthesis of Analogues 55 and 58
designed to probe and identify key features necessary for
potent and selective PP2A inhibition. To address the im-
portance of the R,β-unsaturated lactone and the presence of
a phosphate rather than sulfate ester for PP2A inhibition,
truncated analogues 45 and 48 were targeted (Scheme 7).
Deprotection of PMB ether 14 (DDQ, CH2Cl2/H2O,
25 °C, 1 h, 58%) gave alcohol 39 that was oxidized to aldehyde
40 (DMP, CH2Cl2, 1 h, 80%) (Scheme 7). Addition of the
cuprate derived from 9 (Et2O, -78 °C, 1 h, 78%, >10:1 dr) to
40 provided alcohol 41 that was subsequently protected (TBSCl,
AgNO3, pyr/CH2Cl2, 25 °C, 30 min, 78%). The EE acetal of 42
was selectively removed with dilute HCl (THF/H2O, 25 °C,
2.5 h, 82%) to yield alcohol 43. Sulfate installation (SO3-pyr,
THF, 25 °C, 10 min, 98%) and desilylation (HF-pyr, pyr/
THF, 25 °C, 3 h, 80%) provided sulfate 45, whereas phosphor-
ylation of 43 (i-Pr2NP(OFm)2, tetrazole, CH2Cl2/CH3CN,
25 °C, 1 h; H2O2, 15 min, 75%) followed by desilylation
(HF-pyr, pyr/THF, 25 °C, 18 h, 73%) and fluorenylmethyl
removal (Et3N, CH3CN, 25 °C, 16 h; Dowex Naþ, 81%)
provided the corresponding phosphate monoester 48 lacking
the unsaturated lactone unit.
The importance of the Z,Z,E-triene tail as well as the C11
hydroxyl group was investigated with the synthesis of 55
and 58 (Scheme 8). Replacement of the pivalate ester of 26
with a TBDPS protecting group (LiAlH4, THF, 0 °C, 2 h;
TBDPSCl, AgNO3, pyr/CH2Cl2, 16 h) followed by EE and
TBS deprotection (aq HCl, THF, 12 h, 52% for three steps)
gave lactol 51 that was oxidized to lactone 52 (Ag2CO3-
Celite, benzene, 80 °C, 1.5 h, 59%). Compound 52 was
phosphorylated (i-Pr2NP(OFm)2, tetrazole, CH2Cl2/CH3CN,
25 °C, 1 h; H2O2, 15 min, 95%) to give protected phosphate 53.
In the course of these studies, we found that reversing the final
deprotection steps, conducting first the fluorenylmethyl re-
moval followed by desilylation of the crude phosphate with
TAS-F,34 often gave higher yields and cleaner reactions than
the order and final HF-pyridine conditions typically employed.
By using this method, 55 wassynthesized(Et3N, CH3CN, 25 °C,
16 h; TAS-F, CH3CN, 25 °C, 16 h, 67% for two steps). The
PMB group of 53 was removed (DDQ, CH2Cl2/H2O, 25 °C,
1.5 h, 70%), and 56 was fully deprotected under the same
conditions (Et3N, CH3CN, 25 °C, 16 h; TAS-F, CH3CN,
25 °C, 16 h, 84% for two steps) to give 58.
The storage instability of fostriecin led to a premature
discontinuation of its clinical trials,35 and a possible source
of this instability is the sensitive Z,Z,E-triene. Thus, analo-
gues that replace the triene with more stable hydrophobic
groups are of special interest. The synthesis of one such key
analogue 65, bearing a fully saturated variant of the Z,Z,E-
triene, began with chelation-controlled addition of the cup-
rate derived from 1-bromoundecane to aldehyde 8 (Et2O,
-78 °C, 1 h, 71%, >19:1 dr) (Scheme 9). Notably, the
diastereoselectivity of the addition and the remarkable over-
all clean conversion with this substrate are the best we have
observed among the substrates that we have examined.
Pivalate removal (LiAlH4, THF, 0 °C, 3 h) was followed
by silylation of the secondary alcohols of 60 (TBDPSCl,
AgNO3, pyr/CH2Cl2, 25 °C, 16 h) to give 61. Selective TBS
and EE removal (aq HCl, THF, 25 °C, 12 h, 48% for three
steps) resulted in lactol 62 that was oxidized to lactone 63
(Ag2CO3-Celite, benzene, 80 °C, 1.5 h, 84%). The alcohol of
63 was phosphorylated as before (i-Pr2NP(OFm)2, tetrazole,
CH2Cl2/CH3CN, 25 °C, 1 h; H2O2, 15 min, 90%). At this
time, we also found that TAS-F is sufficiently basic to
(35) De Jong, R. S.; Mulder, N. H.; Uges, D. R. A.; Sleijfer, D. Th.;
Hoppener, F. J. P.; Groen, H. J. M.; Willemse, P. H. B.; Van der Graf,
W. T. A.; De Vries, E. G. E. Br. J. Cancer 1999, 79, 882.
(34) Sheidt, K. A.; Chen, H.; Follows, B. C.; Chemler, S. R.; Coffey, D. S.;
Roush, W. R. J. Org. Chem. 1998, 63, 6436.
7510 J. Org. Chem. Vol. 75, No. 22, 2010

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SCHEME 9. Synthesis of Analogue 65
TABLE 1. Protein Phosphatase Activity (IC50, μM)
remove the fluorenylmethyl groups on the phosphate and
that 64 could be fully deprotected in one step using this
reagent (TAS-F, CH3CN, 25 °C, 3 d, 73%).
Biological Evaluation. The natural products and their key
analogues were examined for phosphatase inhibition against
native PP2Ac (Crassostrea virginica), rhPP1cR, and rhPP5c
using phosphohistone1 as substrate (Table 1). Sultriecin (1)
was devoid of PP2A inhibitory activity indicating that a
sulfate is a poor phosphate substitute for coordination to the
bimetallic core of the enzyme. This is in good agreement with
our prior observation that the sulfate derivative of cytostatin
(sulfocytostatin) showed no activity against all three phos-
phatases as well.7c Although this latter observation was
viewed as unexpected and unusual at the time it was made,
the result now is in full agreement with the sultriecin ob-
servations. The actual natural product, phostriecin (2), ex-
hibited PP2A inhibitory activity as anticipated, albeit at a
level that is less potent and selective than either fostriecin (3,
170-fold) or cytostatin (4, 15-fold). Dephosphophostriecin
(35) was inactive against all three phosphatases, confirming
the importance of the phosphate for inhibitory activity.
Compound 48, lacking the R,β-unsaturated lactone, was
significantly less potent than the natural product but still
showed moderate inhibition of PP2A (4.5 μM) and good
selectivity. Notably, this compound lacking the electrophile
responsible for reversible conjugate addition of the PP2A
active site Cys2696 proved to be only 12-fold less active than
phostriecin itself and still selective for PP2A. Although its
potency is 1000-fold lower than fostriecin and 100-fold lower
than cytostatin, it maintains PP2A selectivity indicating that
this portion of the natural products productively contributes
to their properties. This is consistent with a prior observation
made with fostriecin and a related set of key analogues6
reinforcing a generality to this observation. Compound 45,
identical to 48 lacking the unsaturated lactone, but bearing a
sulfate versus phosphate monoester was inactive, providing a
aAssays were conducted with native PP2A, rhPP1R, and rhPP5 catalytic
subunits as detailed.1 bPhosphohistone used as substrate.
result also in line with present expectations. Also consistent
with the importance of this portion of the molecule, remov-
ing the Z,Z,E-triene tail (C12-C22) providing 58 led to a
200-fold loss in activity, and its replacement with a PMB
ether (55), albeit with removal of the important C11 second-
ary alcohol,7c resulted in a 100-fold loss in activity. Impor-
tant in these comparisons is the observation that 48 is 15-fold
more potent than 58 emphasizing the key role the C12-C22
tail plays in contributing to the properties of 2. Most
surprising and most interesting, simply replacing the Z,Z,
E-triene tail (C12-C22) with its saturated counterpart
providing 65 lacking only the π-unsaturation not only
lost potency (50-fold), but also lost selectivity for PP2A.
Although the activity is modest, potentially masking more
subtle distinctions, 65 was essentially equally active against
PP2A, PP1, and PP5 indicating that the unsaturation in the
C12-C22 tail contributes in a significant manner to the
PP2A selectivity of this class of natural products.
Conclusion
Total syntheses of 1 and 2 unequivocally established the
structural composition and stereochemical configuration of
the natural product previously known as sultriecin (renamed
phostriecin). Key steps include a CBS reduction to establish
the lactone stereochemistry, oxidative ring expansion of
an R-hydroxyfuran to access a pyran lactol precursor, and
J. Org. Chem. Vol. 75, No. 22, 2010 7511

Burke et al.
JOCFeatured Article
one-step installation of the sensitive Z,Z,E-triene unit using
a chelation-controlled cuprate addition to an intermediate
aldehyde. Studies with authentic material established that
phostriecin, but not sultriecin, is an effective and selective
inhibitor of protein phosphatase 2A (PP2A) defining a
mechanism of action responsible for its antitumor activity.
Examination of a series of synthetic analogues prepared by
extending the route developed for 1 and 2 defined key
structural features of the natural product contributing to
the potency and selectivity of the PP2A inhibition.
(SiO2, 10-30% EtOAc/hexanes gradient) to give 0.055 g (48%
overall for three steps) of 62 as a mixture of anomers as a colorless
oil that was immediately taken to the next step without further
characterization. Ag2CO3 (50% on Celite, 2.52 g, 4.6 mmol) was
added in four portions over the course of 1 h to a solution of 62
(0.055 g, 0.063 mmol) in 6.3 mL of benzene at reflux. After the final
addition, the mixture was stirred for 30 min, cooled to room
temperature, and filtered through a plug of Celite while washing
with EtOAc. The filtrate was concentrated, and the residue was
purified by flash chromatography (SiO2, 10% EtOAc/hexanes) to
give 0.046 g (84%) of 63 as a colorless oil: [R]25 þ44 (c 0.75,
CHCl3); 1H NMR (C6D6, 600 MHz) δ 7.85-D7.77 (m, 4H),
7.27-7.15 (m, 12H), 5.98 (dd, J = 15.0, 6.6 Hz, 1H), 5.90 (dt,
J = 15.0, 7.2 Hz, 1H), 5.86 (dd, J = 9.6, 4.8 Hz, 1H), 5.66 (d, J =
9.6Hz, 1H), 4.29(t, J= 6.6 Hz, 1H), 4.26 (dd, J=7.2, 3.0Hz, 1H),
3.86 (dd, J = 4.8, 3.6 Hz, 1H), 3.86-3.82 (m, 1H), 3.34 (brs, 1H),
2.51-2.43 (m, 1H), 2.18-2.10 (m, 1H), 1.80-1.72 (m, 1H),
1.64-1.55 (m, 2H), 1.39-0.94 (m, 18H), 1.17 (s, 9H), 1.15 (d,
J = 6.6 Hz, 3H), 1.08 (s, 9H), 0.91 (t, J = 7.2 Hz, 3H); 13C NMR
(C6D6, 150MHz) δ162.3, 144.2, 136.5, 136.4, 136.22, 136.18, 134.5,
133.8, 133.5, 133.23, 133.17, 130.4, 130.32, 130.31, 130.1, 128.0,
127.1, 122.5, 81.2, 80.0, 70.1, 65.2, 39.5, 38.8, 35.1, 32.3, 30.09,
30.05, 30.0, 29.9, 29.81, 29.78, 27.3, 27.0, 25.8, 23.1, 19.7, 19.5, 14.4,
11.3 ; IR (film) νmax 3504, 1731, 1106, 701 cm-1; HRMS (ESI-
TOF) calcd for C55H76O5Si2 þ Hþ 873.5304, found 873.5302.
Bis((9H-fluoren-9-yl)methyl) ((4S,5S,6S,E)-6-((tert-Buty-
ldiphenylsilyl)oxy)-1-((2S,3S)-3-((tert-butyldiphenylsilyl)oxy)-
6-oxo-3,6-dihydro-2H-pyran-2-yl)-5-methylheptadec-1-en-4-yl)
Phosphate (64). i-Pr2NP(OFm)2 (0.044 g, 0.084 mmol) in CH2Cl2
(0.64 mL) was added at room temperature to a stirred solution of
63 (0.020 g, 0.023 mmol)andtetrazole(0.45MinMeCN, 0.14mL,
0.064 mmol) in anhydrous MeCN (0.33 mL) under N2. After 1 h,
aqueous H2O2 (35%, 0.12 mL) was added, and the mixture
was stirred vigorously for 15 min. Saturated aqueous NaHCO3
(4.6 mL) was added, and the mixture was extracted with CH2Cl2.
The combined organic extracts were dried (Na2SO4) and concen-
trated, and the residue was purified by flash chromatography
(SiO2, 20-25% EtOAc/hexanes gradient) to give 0.027 g (90%) of
64 as a colorless oil: [R]25D þ34 (c 0.20, CHCl3); 1H NMR (C6D6,
600 MHz) δ 7.86-7.77 (m, 3H), 7.67-7.57 (m, 4H), 7.55-7.45
(m, 6H), 7.39-7.35 (m, 1H), 7.34-7.07 (m, 22H), 5.92 (dd, J =
10.2, 4.8 Hz, 1H), 5.79 (dd, J = 15.6, 6.6 Hz, 1H), 5.71 (d, 10.2 Hz,
1H), 5.67 (dt, J = 15.6, 7.8 Hz, 1H), 4.49 (p, 6.0 Hz, 1H),
4.30-4.23 (m, 2H), 4.23-4.17 (m, 2H), 4.14 (dd, J = 6.6, 3.0
Hz, 1H), 4.00-3.96 (m, 1H), 3.95 (t, J = 6.6 Hz, 1H), 3.88 (t, J =
6.6 Hz, 1H), 3.82 (dd, J = 4.8, 3.0 Hz, 1H), 2.48-2.40 (m, 1H),
2.11-2.04 (m, 1H), 1.71-1.44 (m, 3H), 1.42-1.07 (m, 18H), 1.21
(s, 9H), 1.10 (d, J = 3H), 1.03 (s, 9H), 0.92 (t, J = 7.2 Hz, 1H); 13C
NMR (C6D6, 150 MHz) δ 162.2, 144.0, 143.84, 143.82, 143.81,
143.76, 141.80, 141.79, 141.77, 136.54, 136.47, 136.2, 134.9, 134.5,
133.7, 133.1, 130.5, 130.4, 130.3, 130.0, 129.9, 128.5, 127.5, 127.40,
127.39, 127.3, 125.65, 125.57, 125.5, 122.7, 120.23, 120.21, 120.16,
80.7, 80.6, 80.5, 75.0, 69.14, 69.10, 69.07, 65.0, 48.44, 48.42, 48.39,
48.37, 43.24, 43.21, 37.2, 33.1, 32.4, 30.3, 30.26, 30.19, 30.15, 30.1,
29.8, 27.4, 27.0, 26.6, 23.1, 22.5, 19.7, 19.5, 14.4, 10.0; 31P NMR
Experimental Section
(2S,3S)-6-((tert-Butyldimethylsilyl)oxy)-2-((4S,5S,6S,E)-4-(1-
ethoxyethoxy)-6-hydroxy-5-methylheptadec-1-en-1-yl)-3,6-dihydro-
2H-pyran-3-yl Pivalate (59). t-BuLi (1.7 M in pentane, 0.97 mL,
1.7 mmol) was slowly added to a degassed solution of 1-bromoun-
decane (0.22 g, 0.92 mmol) in Et2O (6.3 mL) under Ar with stirring
at -78 °C. After 1.5 h, a solution of CuI-PBu3 (0.14 g, 0.37 mmol)
in 2.2 mL of Et2O was added at -78 °C, and the mixture was stirred
for 15 min. A solution of 8 (0.095 g, 0.19 mmol) in 5.3 mL
of anhydrous Et2O was added slowly to the mixture down the
side of the flask over 15 min at -78 °C. After 1 h, the reaction
was quenched by addition of saturated aqueous NH4Cl/NH4OH
(pH 8, 2 mL) and warmed to room temperature. The mixture
was extracted with Et2O, and the combined organic phases
were washed with H2O and saturated aqueous NaCl, dried
(Na2SO4), and concentrated. The residue was purified by flash
chromatography (SiO2 pretreated with 2% Et3N/hexanes,
10-20% EtOAc/hexanes gradient) to give 0.088 g (71%) of 59
D
1
as a yellow oil: [R]25 þ65 (c 0.47, CHCl3); H NMR (C6D6,
400 MHz) δ 5.87 (dd, J = 9.6, 5.6 Hz, 1H), 5.85-5.65 (m, 3H),
5.35 (d, J = 2.8 Hz, 1H), 5.02 (dd, J = 5.6, 2.4 Hz, 1H), 4.81 (q,
J = 5.2 Hz, 1H), 4.64 (dd, J = 5.6, 2.4 Hz, 1H), 3.97 (td, J = 7.6,
2.8 Hz, 1H), 3.66-3.57 (m, 1H), 3.57-3.48 (m, 1H), 3.42-3.32
(m, 1H), 2.85 (d, J = 5.6 Hz, 1H), 2.60-2.50 (m, 1H), 2.42-2.32
(m, 1H), 1.80-1.66 (m, 2H), 1.67-1.57 (m, 1H), 1.50-1.24 (m,
18H), 1.27 (d, J = 5.2 Hz, 3H), 1.21 (s, 9H), 1.13 (t, J = 7.2 Hz,
3H), 0.96 (s, 9H), 0.90 (d, J = 6.8 Hz, 3H), 0.90 (t, J = 6.8 Hz,
3H), 0.17 (s, 3H), 0.11 (s, 3H); 13C NMR (C6D6, 150 MHz) δ
177.7, 133.0, 130.4, 128.9, 124.1, 100.0, 89.4, 77.6, 73.0, 70.4, 65.2,
62.7, 60.1, 41.2, 39.1, 35.8, 35.5, 33.3, 32.3, 30.5, 30.3, 30.21, 30.19,
30.1, 29.8, 27.3, 26.2, 26.00, 25.9, 23.1, 20.4, 18.2, 15.6, 14.4, 11.3,
-4.0, -5.3; IR (film) νmax 35.07, 1727, 1024 cm-1; HRMS (ESI-
TOF) calcd for C38H72O7Si þ Naþ 691.4939, found 691.4938.
(5S,6S)-5-((tert-Butyldiphenylsilyl)oxy)-6-((4S,5R,6S,E)-6-((tert-
butyldiphenylsilyl)oxy)-4-hydroxy-5-methylheptadec-1-en-1-yl)-5,6-
dihydro-2H-pyran-2-one (63). LiAlH4 (1.0 M in THF, 0.26 mL,
0.26 mmol) was added to a solution of 59 in 1.8 mL of anhydrous
THF at 0 °C under N2 with stirring. After 3 h, the reaction was
quenched at 0 °C by careful addition of H2O, and the mixture was
extracted with EtOAc. The combined organic extracts were dried
(Na2SO4) and concentrated. The crude 60 was dissolved in CH2Cl2/
pyridine (1:1, 2.6 mL). AgNO3 (0.21 g, 1.2 mmol) was added
followed by TBDPSCl (0.36 g, 1.3 mmol), and the mixture was
stirred at room temperature for 24 h in the dark. The mixture was
diluted with Et2O and filtered through Celite. The filtrate was
concentrated and the residue purified by flash chromatography
(SiO2 pretreated with 2% Et3N/hexanes, 3% EtOAc/hexanes) to
give 61 as a colorless oil which was taken to the next step without
further characterization. A solution of 0.5 M aqueous HCl (2.6 mL)
was added to a solution of 61 in THF (54 mL) at room temperature,
and the mixture was stirred overnight. The reaction was quenched
by addition of saturated aqueous NaHCO3, and the aqueous phase
was extracted with EtOAc. The combined organic phases were
washed with saturated aqueous NaCl, dried (Na2SO4), con-
centrated, and the residue was purified by flash chromatography
(CD3OD 160 MHz) δ -0.6; IR (film) νmax 1733, 1106, 988 cm-1
;
HRMS (ESI-TOF) calcd for C83H97O8PSi2 þ Hþ 1309.6532, found
1309.6513.
Sodium (4S,5S,6S,E)-6-Hydroxy-1-((2S,3S)-3-hydroxy-6-oxo-
3,6-dihydro-2H-pyran-2-yl)-5-methylheptadec-1-en-4-yl Hydrogen
Phosphate (65). TAS-F (1.0 M in DMF, 0.037 mL, 0.037 mmol)
was added to a solution of 64 (4.8 mg, 0.0037 mmol) in MeCN
(0.23 mL), and the mixture was stirred for 72 h at room tempera-
ture after which time it was concentrated. The residue was
dissolved in 0.1 M sodium phosphate buffer (pH 7) and was
purified by flash chromatography (C18 reversed-phase SiO2,
0-50% MeCN/H2O gradient) giving 1.4 mg (73%) of 65 as a
white solid: [R]25D þ38 (c 0.03, MeOH); 1H NMR (CD3OD, 600
7512 J. Org. Chem. Vol. 75, No. 22, 2010

Burke et al.
JOCFeatured Article
MHz) δ 7.04 (dd, J = 9.6, 5.4 Hz, 1H), 6.06 (d, J = 9.6 Hz, 1H),
5.92 (dt, J= 15.3, 7.2 Hz, 1H), 5.81 (dd, J= 15.3, 7.8 Hz, 1H), 4.85
(dd, J = 8.4, 2.7 Hz, 1H), 4.61 (m, 1H), 4.20 (dd, J = 5.4, 2.7 Hz,
1H), 3.53 (t, J = 8.4 Hz, 1H), 2.66-2.59 (m, 1H), 2.39-2.32 (m,
1H), 1.66-1.41 (m, 3H), 1.41-1.24 (m, 18H), 0.90 (t, J = 7.2 Hz,
3H), 0.89 (d, J = 7.2 Hz, 3H); 13C NMR (CD3OD, 150 MHz) δ
166.3, 147.4, 133.9, 127.8, 122.7, 83.4, 74.65, 74.61, 73.3, 63.7,
44.01, 43.98, 38.2, 35.5, 33.1, 30.97, 30.93, 30.89, 30.86, 30.84, 30.5,
27.2, 23.8, 14.5, 9.8; 31P NMR (CD3OD 160 MHz) δ 3.4; IR (film)
νmax 3386, 1720, 1084, 945 cm-1; HRMS (ESI-TOF) calcd for
C23H41O8P þ Hþ 477.2612, found 477.2593.
CA042056, (R.E.H.) CA060750), and the studies in
Alabama were conducted in a facility constructed with
support from the Research Facilities Improvement Pro-
gram (Grant No. CD6-RR11174) from the NIH National
Center for Research Resources. We thank Nadia Haq and
Danielle Soenen for early studies targeting sultriecin in
which many of the strategic elements of the total synthesis
were explored.
Supporting Information Available: Full experimental details
and 1H, 13C, and 31P NMR spectra for 1, 2, 35, 36, and 39-58.
This material is available free of charge via the Internet at http://
pubs.acs.org.
Acknowledgment. We gratefully acknowledge the finan-
cial support of the National Institutes of Health ((D.L.B.)
J. Org. Chem. Vol. 75, No. 22, 2010 7513