Synthesis of Cryptophycins via an N-Acyl-β-lactam Macrolactonization

Article abstract of DOI:10.1021/jo0302197

An efficient and concise approach to the synthesis of the macrolide core of the cryptophycins has been developed. A novel macrolactonization utilizing a reactive acyl-β-lactam intermediate incorporates the β-amino acid moiety within the 16-membered macrol

Full text of DOI:10.1021/jo0302197

Syn th esis of Cr yp top h ycin s via a n N-Acyl-â-la cta m
Ma cr ola cton iza tion
Ramdas Vidya,† MariJ ean Eggen,† Sajiv K. Nair,† Gunda I. Georg,*,† and Richard H. Himes‡
Department of Medicinal Chemistry and Department of Molecular Biosciences, University of Kansas,
Lawrence, Kansas 66045
georg@ku.edu
Received J uly 8, 2003
An efficient and concise approach to the synthesis of the macrolide core of the cryptophycins has
been developed. A novel macrolactonization utilizing a reactive acyl-â-lactam intermediate
incorporates the â-amino acid moiety within the 16-membered macrolide core. This modular
approach, involving a cyanide-initiated acyl-â-lactam ring opening followed by cyclization, was
successfully applied to the total synthesis of cryptophycin-24. The strategy was also used in an
efficient synthesis of the 6,6-dimethyl-substituted dechlorocryptophycin-52. In this case, the cyanide-
initiated ring opening of the bis-substituted 2-azetidinone followed by macrolactonization was
achieved through a catalytic process.
Cryptophycins are potent, tumor-selective tubulin-
binding antimitotic agents1 with excellent activity against
multidrug-resistant (MDR) cancer cells.2-7 Cryptophy-
cin-1 (1, Figure 1), initially isolated from the blue green
algae Nostoc sp. ATCC 537898 and later from GSV 224,9,10
is the major cytotoxic metabolite. Cryptophycin-1 is an
effective inhibitor of tubulin polymerization at substo-
ichiometric concentrations,11 and inhibits vinblastine
binding to tubulin.11-15 Additional studies with tubulin
suggest that upon binding cryptophycin-1 induces the
† Department of Medicinal Chemistry.
‡ Department of Molecular Biosciences.
(1) For review: J ordan, M. A. Curr. Med. Chem. Anti-Cancer Agents
F IGURE 1. Structures of cryptophycins.
2002, 2, 1-17.
formation of ring structures, possibly resulting from
(2) For review: Eggen, M.; Georg, G. I. Med. Res. Rev. 2002, 22,
curvature at two points per heterodimer, with local
85-101.
changes in the â-subunit and long-range changes affect-
(3) For review: Shih, C.; Al-Awar, R. S.; Fray, A. H.; Martinelli, M.
J .; Moher, E. D.; Norman, B. H.; Patel, V. F.; Shultz, R. M.; Toth, J .
E.; Varie, D. L.; Corbett, T. H.; Moore, R. E. In Anticancer Agents:
Frontiers in Cancer Chemotherapy; Ojima, I., Vite, G. D., Altmann,
ing the R-subunit.16,17 A structurally related compound,
arenastatin A, also called cryptophycin-24 (2, Figure 1),
was isolated from the Okinawan marine sponge Dysidea
arenaria18,19 and from Nostoc sp. GSV 224.20 It is a potent
inhibitor of tubulin polymerization21 and possesses excel-
lent cytotoxicity against KB cells in vitro.18,19 In addition
to their action against tubulin and microtubules, the
K., Eds.; American Chemical Society: Washington, DC, 2001; Vol. 796,
pp 171-189.
(4) For review: Tius, M. A. Tetrahedron 2002, 58 4343-4367.
(5) Corbett, T. H.; Valeriote, F. A.; Demchik, L.; Lowichik, N.; Polin,
L.; Panchapor, C.; Pugh, S.; White, K.; Kushner, J .; Rake, J .; Wentland,
M.; Golakoti, T.; Hetzel, C.; Ogino, J .; Patterson, G.; Moore, R. Invest.
New Drugs 1997, 15, 207-218.
(6) Moore, R. E.; Corbett, T. H.; Patterson, G. M. L.; Valeriote, F.
A. Curr. Pharm. Des. 1996, 2, 317-330.
(14) Bai, R.; Schwartz, R. E.; Kepler, J . A.; Pettit, G. R.; Hamel, E.
Cancer Res. 1996, 56, 4398-4406.
(7) Polin, L.; Valeriote, F.; White, K.; Panchapor, C.; Pugh, S.;
Knight, J .; LoRusso, P.; Hussain, M.; Liversidge, E.; Peltier, N.;
Golakoti, T.; Patterson, G.; Moore, R.; Corbett, T. H. Invest. New Drugs
1997, 15, 99-108.
(15) Panda, D.; Himes, R. H.; Moore, R. E.; Wilson, L.; J ordan, M.
A. Biochemistry 1997, 36, 12948-12953.
(16) Watts, N. R.; Cheng, N.; West, W.; Steven, A. C.; Sackett, D.
L. Biochemistry 2002, 41, 12662-12669.
(8) Schwartz, R. E.; Hirsch, C. F.; Sesin, D. F.; Flor, J . E.; Chartrain,
M.; Fromtling, R. E.; Harris, G. H.; Salvatore, M. J .; Liesch, J . M.;
Yudin, K. J . Ind. Microbiol. 1990, 5, 113-124.
(17) Barbier, P.; Gregoire, C.; Devred, F.; Sarrazin, M.; Peyrot, V.
Biochemistry 2001, 40, 13510-13519.
(9) Trimurtulu, G.; Ohtani, I.; Patterson, G. M. L.; Moore, R. E.;
Corbett, T. H.; Valeriote, F. A.; Demchik, L. J . Am. Chem. Soc. 1994,
116, 4729-4737.
(18) Kobayashi, M.; Aoki, S.; Ohyabu, N.; Kuroso, M.; Wang, W.;
Kitagawa, I. Tetrahedron Lett. 1994, 35, 7969-7972.
(19) Kobayashi, M.; Kuroso, M.; Ohyabu, N.; Wang, W.; Fujii, S.;
Kitagawa, I. Chem. Pharm. Bull. 1994, 42, 2196-2198.
(20) Trimurtulu, G.; Ogino, J .; Heltzel, C. E.; Husebo, T. L.; J ensen,
C. M.; Larsen, L. K.; Patterson, G. M. L.; Moore, R. E.; Mooberry, S.
L.; Corbett, T. H.; Valeriote, F. A. J . Am. Chem. Soc. 1995, 117, 12030-
12049.
(10) Subbaraju, G. V.; Golakoti, T.; Patterson, G. M. L.; Moore, R.
E. J . Nat. Prod. 1997, 60, 302-305.
(11) Kerksiek, K.; Mejillano, M.; Schwartz, R. E.; Georg, G. I.; Himes,
R. FEBS Lett. 1995, 377, 59-61.
(12) Mooberry, S. L.; Taoka, C. R.; Busquets, L. Cancer Lett. 1996,
107, 53-57.
(21) Koiso, Y.; Morita, K.; Kobayashi, M.; Wang, W.; Ohyabu, N.;
Iwasaki, S. Chem.-Biol. Interact. 1996, 102, 183-191.
(13) Smith, C. D.; Zhang, X. J . Biol. Chem. 1996, 271, 6192-6198.
10.1021/jo0302197 CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/19/2003
J . Org. Chem. 2003, 68, 9687-9693
9687

Vidya et al.
cryptophycins also inhibit DNA and RNA synthesis22 and
induce apoptosis.23,24 Cryptophycin-induced apoptosis is
accompanied by phosphorylation of c-raf1, bcl-2, bcl-xL,
and c-J un NH2-terminal kinase.23 Cryptophycin-24 is
completely devoid of activity in vivo as it has a half-life
of only 10 min in mouse serum25 due to rapid hydrolysis
of the C5 ester.
Cryptophycin-52 (3, Figure 1), a synthetic analogue2,3
that carries a gem-dimethyl group at the C6 position,
displays increased hydrolytic stability and improved in
vivo antitumor efficacy compared to cryptophycin-1.3
Cryptophycin-52 displays high cytotoxicity against nu-
merous cancer cell lines, including MDR cancer cell lines,
and is the most potent suppressor of microtubule dynam-
ics found to date.26,27 Because of these attributes, cryp-
tophycin-52 (3) was selected for clinical development3 and
has been under evaluation.28 Recently, a patent has
described cryptophycin-308, the glycine ester of the
chlorohydrin of cryptophycin-1 (1, Figure 1), as possess-
ing better aqueous solubility, superior microtubule dis-
ruption, and lower toxicities than derivatives previously
disclosed.29
logues derived from modifications of the epoxide20,46 and
synthetic analogues which differ in the tyrosine frag-
ment,47 â-amino acid moiety,48 or octadienoate ester
fragment49 or contain an isosteric replacement of the C5
ester with an amide.50
Our previous experience with the use of chiral â-lactam
precursors prompted us to examine the idea of deriving
the â-amino acid within the cryptophycin core from such
a synthon. N-Acyl-â-lactams were shown to be excellent
sources for the incorporation of the phenylisoserine side
chain of paclitaxel, and readily reacted with the alkoxide
of baccatin III.51 A similar approach involving the in-
tramolecular reaction52-54 of the â-hydroxy group of the
leucic acid ester with the activated acyl â-lactam inter-
mediate (5a , 5b) could represent a novel, concise ap-
proach toward the synthesis of the macrolide core of the
cryptophycins and did provide the basis for our retrosyn-
thetic strategy (Figure 2).
The retrosynthetic analysis for cryptophycins reveals
that the molecule can be assembled from three basic
building blocks, octadienoate esters 6, L-leucic acid
derivative 7, and N-acylazetidinones 8 (Figure 2). The
introduction of the 3′-phenyl group of the cryptophycins
can be accomplished by a Heck reaction, either at an
early stage in the synthesis by attaching the phenyl
group to octadienoate 6a , or later in the synthetic scheme.
This approach makes the synthesis flexible for incorpora-
tion of various aryl substituents at the C3′ position.
The synthesis of cryptophycin-24 (2) started with
secondary alcohol 9,31 which was coupled with acid
chloride 7, derived from bis-silylated L-leucic acid,55 to
provide ester 10 in 75% yield (Scheme 1). Oxidation of
the primary alcohol, obtained after deprotection of the
p-methoxybenzyl group of 10, was found to be problem-
atic as basic oxidation conditions led to significant
decomposition and byproduct formation. However, the
Dess-Martin oxidation cleanly provided the required
aldehyde in 81% yield. The next step in the synthesis,
the Horner-Emmons homologation of the aldehyde, was
also problematic under basic reaction conditions, includ-
ing Masamune and Roush conditions (LiCl/DBU).56 Neu-
tral reaction conditions and the use of phosphorane 11
produced the desired ester 12 in 94% yield (Scheme 1).
The potent bioactivity of the cryptophycins attracted
several research groups, including ours, leading to a large
number of reported formal30-35 and total syntheses.2,36-45
Significant structure-activity relationship studies have
also been carried out involving both semisynthetic ana-
(22) Subramanian, B.; Nakeff, A.; Media, J . E.; Wiegand, R. A.;
Valeriote, F. A. Anti-Cancer Drugs 2002, 13, 1061-1068.
(23) Drew, L.; Fine, R. L.; Do, T. N.; Douglas, G. P.; Petrylak, D. P.
Clin. Cancer Res. 2002, 8, 3922-3932.
(24) Lu, K.; Dempsey, J .; Schultz, R. M.; Shih, C.; Teicher, B. A.
Cancer Chemother. Pharmacol. 2001, 47, 170-178.
(25) Morita, K.; Koiso, Y.; Hashimoto, Y.; Kobayashi, M.; Wang, W.;
Ohyabu, N.; Iwasaki, S. Biol. Pharm. Bull. 1997, 20, 171-174.
(26) Panda, D.; DeLuca, K.; Williams, D.; J ordan, M. A.; Wilson, L.
Proc. Natl. Acad. Sci. U.S.A. 1998, 95, 9313-9318.
(27) Panda, D.; Ananthnarayan, V.; Larson, G.; Shih, C.; J ordan,
M. A.; Wilson, L. Biochemistry 2000, 39, 14121-14127.
(28) Sessa, C.; Weigang-Kohler, K.; Pagani, O.; Greim, G.; Mora,
O.; De Pas, T.; Burgess, M.; Weimer, I.; J ohnson, R. Eur. J . Cancer
2002, 38, 2388-2396.
(29) Corbett, T. H.; Moore, R. E.; Liang, J . US patent 2002/0065261
A1, May 30, 2002.
(30) Ali, S. M.; Georg, G. I. Tetrahedron Lett. 1997, 38, 1703-1706.
(31) Eggen, M.; Georg, G. I. Bioorg. Med. Chem. Lett. 1998, 8, 3177-
3180.
(32) Furuyama, M.; Shimizu, I. Tetrahedron: Asymmetry 1998, 9,
1351-1357.
(33) Varie, D. L.; Brennan, J .; Briggs, B.; Cronin, J . S.; Hay, D. A.;
Rieck, J . A. I.; Zmijewski, M. J . Tetrahedron Lett. 1998, 39, 8405-
8408.
(46) Georg, G. I.; Ali, S. M.; Stella, V. J .; Waugh, W. N.; Himes, R.
H. Bioorg. Med. Chem. Lett. 1998, 8, 1959-1962.
(47) Patel, V. F.; Andis, S. L.; Kennedy, J . H.; Ray, J . E.; Schultz,
R. M. J . Med. Chem. 1999, 42, 2588-2603.
(34) Liang, J .; Hoard, D. W.; Khau, V. V.; Martinelli, M. J .; Moher,
E. D.; Moore, R. E.; Tius, M. A. J . Org. Chem. 1999, 64, 1459-1463.
(35) Fray, A. H. Tetrahedron: Asymmetry 1998, 9, 2777-2781.
(36) Barrow, R. A.; Hemscheidt, T.; Liang, J .; Paik, S.; Moore, R.
E.; Tius, M. A. J . Am. Chem. Soc. 1995, 117, 2479-2490.
(37) de Muys, J .-M.; Rej, R.; Nguyen, D.; Go, B.; Fortin, S.; Lavallee,
J .-F. Bioorg. Med. Chem. Lett. 1996, 6, 1111-1116.
(38) Dhokte, U. P.; Khau, V. V.; Hutchison, D. R.; Martinelli, M. J .
Tetrahedron Lett. 1998, 39, 8771-8774.
(48) Varie, D. L.; Shih, C.; Hay, D. A.; Andis, S. L.; Corbett, T. H.;
Gossett, L. S.; J anisse, S. K.; Martinelli, M. J .; Moher, E. D.; Schultz,
R. M.; Toth, J . E. Bioorg. Med. Chem. Lett. 1999, 9, 369-374.
(49) Al-awar, R. S.; Ray, J . E.; Schultz, R. M.; Andis, S. L.; Kennedy,
J . H.; Moore, R. E.; Liang, J .; Golakoti, T.; Subbaraju, G. V.; Corbett,
T. H. J . Med. Chem. 2003, 46, 2985-3007.
(50) Norman, B. H.; Hemscheidt, T.; Schultz, R. M.; Andis, S. L. J .
Org. Chem. 1998, 63, 5288-5294.
(51) Holton, R. A.; Biedinger, R. J .; Boatman, P. D. In Semisynthesis
of Taxol and Taxotere. Taxol Science and Applications; CRC: Boca
Raton: FL, 1995; pp 97-121.
(39) Kobayashi, M.; Wang, W.; Ohyabu, N.; Kurosu, M.; Kitagawa,
I. Chem. Pharm. Bull. 1995, 43, 1598-1600.
(40) White, J . D.; Hong, J .; Robarge, L. A. J . Org. Chem. 1999, 64,
6206-6216.
(52) Romo, D.; Rzasa, R. M.; Shea, H. A.; Park, K.; Langenhan, J .
M.; Sun, L.; Akhiezer, A.; Liu, J . O. J . Am. Chem. Soc. 1998, 120,
12237-12254.
(41) Eggen, M.; Mossman, C. J .; Buck, S. B.; Nair, S. K.; Bhat, L.;
Ali, S. M.; Reiff, E. A.; Boge, T. C.; Georg, G. I. J . Org. Chem. 2000,
65, 7792-7799.
(53) Gardner, B.; Nakanishi, H.; Kahn, M. Tetrahedron 1993, 49,
3433-3448.
(42) Eggen, M.; Nair, S. K.; Georg, G. I. Org. Lett. 2001, 3, 1813-
(54) Saragovi, H. U.; Fitzpatrick, D.; Raktabutr, A.; Nakanishi, H.;
Kahn, M.; Greene, M. I. Science 1991, 253, 792-795.
(55) Wissner, A.; Grudzinskas, C. V. J . Org. Chem. 1978, 43, 3972-
3974.
1815.
(43) Li, L.-H.; Tius, M. A. Org. Lett. 2002, 4, 1637-1640.
(44) Hoard, D. W.; Moher, E. D.; Martinelli, M. J .; Norman, B. H.
Org. Lett. 2002, 4, 1813-1815.
(45) Vidya, R.; Eggen, M. J .; Georg, G. I.; Himes, R. H. Bioorg. Med.
Chem. Lett. 2003, 13, 757-760.
(56) Blanchette, M. A.; Choy, W.; Davis, J . T.; Essenfeld, A. P.;
Masamune, S.; Roush, W. R.; Sakai, T. Tetrahedron Lett. 1984, 25,
2183-2186.
9688 J . Org. Chem., Vol. 68, No. 25, 2003

Synthesis of Cryptophycins
SCHEME 1
F IGURE 2. Retrosynthetic analysis.
Ester cleavage with TFA, followed by coupling with
aminoacylazetidinone 8a using HBTU/DIEA, provided
acyl-â-lactam intermediate 5a in 88% yield. Attempts to
cyclize this intermediate with NaH and NaHMDS (pa-
clitaxel conditions) were incompatible with this substrate,
presumably as a result of its sensitivity to basic condi-
tions. The reactions provided no isolable product and led
to the formation of baseline material. The key macrolac-
tonization was achieved with use of CH2Cl2-soluble Bu4-
NCN52 to furnish the 16-membered macrolide 14 in 68%
yield (Scheme 1). Introduction of the C3′-phenyl group
under Heck conditions produced the desepoxy analogue
1541 in only 31% yield. The final epoxidation utilizing
dimethyldioxirane (DMD)40,57 provided a diastereomeric
mixture of cryptophycin-24 (2, â:R ) 2:1) in 76% yield,
which was separated by reverse-phase HPLC.58
As an extension of this methodology, we were inter-
ested in the synthesis of the macrolide core of crypto-
phycin-52, the C6 gem-dimethyl-substituted derivative,
which is under clinical development. Cryptophycin-52
was first prepared by Barrow et al. utilizing an asym-
metric Sharpless epoxidation as a key step.36 Later, the
synthesis was modified by the group at Eli Lilly to
produce a synthesis that involved more than 30 discrete
synthetic operations.3,38,59 Herein we describe a concise
total synthesis of dechlorocryptophycin-52 (4) using dim-
ethyl-2-azetidinone as a building block.
Since the late-stage Heck coupling provided a poor
yield, octadienoate ester 6b was synthesized from 1,3-
propanediol by using a nine-step sequence reported
earlier from our laboratory (17% overall yield).41 Frag-
ment 6b was coupled with acid chloride 755 with use of
triethylamine and DMAP to afford the diester 16 in 92%
yield (Scheme 2). The TBS and tert-butyl ester groups in
compound 16 were deprotected simultaneously with
excess TFA to provide hydroxy acid 17 in 90% yield.
The key N-acylazetidinone 8b was prepared as shown
in Scheme 3. â-Lactam 19, prepared from ethyl cyanoac-
etate in three steps in 42% overall yield,60-62 was coupled
with tyrosine derivative 1836 with use of HBTU and DIEA
to furnish 20 in 91% yield. The Boc group of amine 20
was cleaved in quantitative yield with 4 M HCl in 1,4-
dioxane to afford 8b.
(57) Adam, W.; Bialas, J .; Hadjiarapoglou, L. Chem. Ber. 1991, 124,
2377.
(58) For separation of epoxides by RP-HPLC, see ref 40. Alterna-
tively, for separation of epoxides with a halohydrin approach see ref
48.
(60) Fotouhi, N.; J oshi, P.; Fry, D.; Cook, C.; Tilley, J . W.; Kaplan,
G.; Hanglow, A.; Rowan, K.; Schwinge, V.; Wolitzky, B. Bioorg. Med.
Chem. Lett. 2000, 10, 1171-1173.
(61) Testa, E.; Fontanella, L. Liebigs Ann. Chem. 1959, 625, 95-
98.
(59) Liang, J .; Moher, E. D.; Moore, R. E.; Hoard, D. W. J . Org.
Chem. 2000, 65, 3143-3147.
(62) Testa, E.; Fontanella, L.; Cristiani, G. F.; Fava, F. Liebigs Ann.
Chem. 1958, 614, 158-166.
J . Org. Chem, Vol. 68, No. 25, 2003 9689

Vidya et al.
SCHEME 2
SCHEME 4
assays [IC50 ) 32 µM in the tubulin assembly assay; IC50
) 1.7 nM in the MCF-7 cell line].
SCHEME 3
In summary, a novel macrolactonization approach
utilizing a reactive acyl-â-lactam for the incorporation
of the â-amino acid moiety has been developed for a
unique and convergent synthesis of cryptophycin-24 (2).
This approach also allowed an efficient and convergent
synthesis of dechlorocryptophycin-52 (4). The modular
approach allows for multiple alterations throughout the
structure by modification of the amino acyl â-lactam,
hydroxy acid, and C3′-aromatic group. The acyl-â-lactam
macrolactonization strategy provides a concise and ef-
ficient entry into the macrocyclic core of this promising
family of antitumor macrolides.
Coupling of hydroxy compound 17 and â-lactam 8b
with HBTU and DIEA furnished the macrolide precursor
5b, which possessed all of the elements necessary for the
formation of the macrocycle (Scheme 4). Initially, the
simultaneous ring opening of the acyl-â-lactam followed
by cyclization was tried with excess tetrabutylammonium
cyanide as reported earlier.42,52,63,64 Interestingly, we later
found that the key macrolactonization can be achieved
using a “catalytic” amount of tetrabutylammonium cya-
nide or potassium cyanide to produce the 16-membered
macrolide 21 in 65% yield. The final epoxidation of 21
utilizing dimethyldioxirane (DMD)57 provided a diaster-
eomeric mixture of dechlorocryptophycin-52 (4) in a 2:1
(â:R) ratio and in 75% yield.40,48 The mixture was sepa-
rated by reverse-phase HPLC. The preliminary biological
testing of the dechlorocryptophycin-52 analogue showed
Exp er im en ta l Section
(1S,2R)-1-{2-[(4-Meth oxyp h en yl)m eth oxy]eth yl}-2-m e-
th ylbu t-3-en yl-(2S)-4-m eth yl-2-(1,1,2,2-tetr a m eth yl-1-si-
la p r op oxy)p en ta n oa te (10). To bis-TBS protected L-leucic
acid (6.5 g, 18 mmol) in CH2Cl2 (30 mL) was added 15 drops
of DMF.55 The solution was cooled to 0 °C and oxalyl chloride
(3.2 mL, 36 mmol) was added dropwise with an addition
funnel. Vigorous bubbling was observed, which gradually
subsided. After addition was complete, the mixture was
warmed to room temperature and stirred at room temperature
for 4.5 h. The mixture was concentrated in vacuo and used in
the next step. The crude acid chloride 7 was added dropwise
to a solution of alcohol 941 (1.5 g, 6 mmol), DMAP (2.2 g, 18
mmol), and TEA (1.7 mL, 12 mmol) in CH2Cl2 (15 mL) at 0
°C. The reaction was stirred at 0 °C for 45 min at which time
TLC indicated the disappearance of alcohol 9. The reaction
was quenched with saturated aqueous NaHCO3 and Et2O. The
aqueous layer was extracted with Et2O. The combined organic
layers were dried (MgSO4) and concentrated. Flash chroma-
tography (hexanes to 95:5 hexanes:EtOAc) provided ester 10
as an oil (2.22 g, 78%). [R]D -42 (c 1.5, CHCl3); IR (film) 2920,
good activity in both the tubulin assembly assay [IC50
)
3 µM; for Cr-1, IC50 ) 2.5 µM] and the cytotoxicity assay
[MCF-7 cell line, IC50 ) 0.3 nM; for Cr-1, IC50 ) 0.007
nM].65,66 The R-isomer was found to be less active in both
2820, 1730, 1625 cm-1 1H NMR δ 7.25-7.23 (d, J ) 8 Hz,
;
2H), 6.87-6.85 (d, J ) 8 Hz, 2H), 5.77-5.68 (m, 1H), 5.08-
(63) Rzasa, R. M.; Shea, H. A.; Romo, D. J . Am. Chem. Soc. 1998,
120, 591-592.
(64) Palomo, C.; Aizpurua, J . M.; Cuevas, C.; Mielgo, A.; Galarza,
R. Tetrahedron Lett. 1995, 36, 9027-9030.
(66) IC50 value for cryptophycin-52 in the MCF-7 cell line is 37 ( 2
pM. See ref 26 and: Wagner, M. M.; Paul, D. C.; Shih, C.; J ordan, M.
A.; Wilson, L.; Williams, D. C. Cancer Chemother. Pharmacol. 1999,
43, 115-125.
(65) Liu, Y.; Ali, S. M.; Boge, T. C.; Georg, G. I.; Victory, S.; Zygmunt,
J .; Marquez, R. T.; Himes, R. H. Comb. Chem., High Throughput
Screening 2002, 5, 39-48.
9690 J . Org. Chem., Vol. 68, No. 25, 2003

Synthesis of Cryptophycins
5.05 (m, 2H), 5.02-5.01 (d, 5 Hz, 1H), 4.43-4.40 (d, J ) 11
Hz, 1H), 4.37-4.34 (d, J ) 11 Hz, 1H), 4.20-4.17 (dd, J ) 9,
4 Hz, 1H), 3.79 (s, 3H), 3.48-3.36 (m, 2H), 2.43-2.38 (m, 1H),
1.85-1.83 (d, J ) 7 Hz, 1H), 1.82-1.80 (d, J ) 7 Hz, 1H), 1.75
(m buried, 1H), 1.64-1.57 (ddd, J ) 5, 9, 14 Hz, 1H), 1.50-
1.44 (ddd, J ) 4, 9, 14 Hz, 1H), 1.00-0.99 (d, J ) 7 Hz, 3H),
0.92-0.91 (d, J ) 7 Hz, 3H), 0.91 (buried, 3H), 0.90 (s, 9H),
0.07 (s, 3H), 0.04 (s, 3H); 13C NMR δ 173.8, 159.1, 139.0, 130.4,
129.2 (2C), 115.8, 113.7 (2C), 74.3, 72.7, 70.7, 66.5, 55.2, 44.3,
41.6, 31.6, 25.7 (3C), 24.1, 23.4, 21.7, 18.2, 15.7, -4.6, -5.3;
MS (EI) m/z 477 (M - 1).
J ) 6 Hz, 1H), 4.19-4.16 (dd, J ) 4, 9 Hz, 1H), 2.45-2.38 (m,
3H), 1.81-1.74 (m, 1H), 1.63-1.57 (ddd, J ) 5, 9, 13 Hz, 1H),
1.48-1.42 (buried, 1H), 1.45 (s, 9H), 1.02-1.00 (d, J ) 7 Hz,
3H), 0.92-0.89 (buried, 6H), 0.89 (s, 9H), 0.06 (s, 3H), 0.02 (s,
3H); 13C NMR δ 173.8, 165.3, 142.3, 138.6, 125.9, 116.3, 80.2,
75.3, 70.7, 44.3, 41.2, 34.1, 28.1 (3C), 25.7 (3C), 24.1, 23.4, 21.7,
18.2, 16.0, -4.6, -5.4; MS (EI) m/z 399 (9), 341 (9), 267 (20),
201 (100), 189 (100); HRMS (FAB, m/z) calcd for C25H47O5Si
(M+ + H) 455.3193, found 455.3171.
Tw o-Step Syn th esis of 13 fr om 12. 1. Dep r otection of
Ester 12 to In ter m ed ia te Acid : (2E)-5-[(2S)-4-Meth yl-2-
(1,1,2,2-tetr am eth yl-1-silapr opoxy)pen tan oyloxy]-(5S,6R)-
6-m eth ylocta -2,7-d ien oic Acid . The tert-butyl ester 12 (40
mg, 0.088 mmol) was dissolved in CH2Cl2 (0.1 mL) and cooled
to 0 °C. A TFA solution (1 M in CH2Cl2, 1.1 mL) was added
via syringe. The ice bath was removed after 2 h and the
reaction was continued with vigorous stirring. After 6 h, the
reaction was found to be complete by TLC. Toluene (0.10 mL)
was added and the reaction was concentrated under vacuum
to provide the acid as a colorless oil (29 mg, 83%). IR (film)
Th r ee-Step Syn th esis of 12 fr om 10. 1. DDQ Dep r o-
tection of 10 To F or m In ter m ed ia te Alcoh ol: 1-[(1R)-1-
Meth ylp r op -2-en yl]-(1S)-3-h yd r oxyp r op yl-(2S)-4-m eth yl-
2-(1,1,2,2-tetr a m eth yl-1-sila p r op oxy)p en ta n oa te. Ester 10
(276 mg, 0.577 mmol) was dissolved in CH2Cl2 (2 mL) and H2O
(0.1 mL). The mixture was cooled to 0 °C and DDQ (144 mg,
0.635 mmol) was added. After 30 min at 0 °C, the bath was
removed and the mixture was stirred an additional 90 min at
room temperature. Additional CH2Cl2 was added and the
organic layer was washed with saturated aqueous NaHCO3
solution. The combined organic layers were dried (MgSO4),
filtered, and concentrated. Flash chromatography (hexanes to
85:15 hexanes:EtOAc) provided the desired alcohol (176 mg,
85%) as an oil (often a mixture of alcohol and aldehyde
byproduct were utilized in the next reaction). IR (film) 3420,
1
3060, 3000, 2930, 1740, 1715 cm-1; H NMR δ 6.99-6.92 (dt,
J ) 8, 15 Hz, 1H), 5.88-5.84 (br d, J ) 15 Hz, 1H), 5.74-5.65
(ddd, J ) 8, 10, 17 Hz, 1H), 5.09-4.99 (m, 3H), 4.19-4.16 (dd,
J ) 4, 9 Hz, 1H), 2.49-2.38 (m, 3H), 1.79-1.74 (m, 1H), 1.63-
1.56 (ddd, J ) 4, 9, 13 Hz, 1H), 1.45-1.38 (ddd, J ) 4, 9, 13
Hz, 1H), 1.02-1.00 (d, J ) 7 Hz, 3H), 0.91-0.90 (d, J ) 4 Hz,
3H), 0.89-0.88 (d, J ) 4 Hz, 3H), 0.88 (s, 9H), 0.06 (s, 3H),
0.02 (s, 3H); 13C NMR δ 173.8, 146.7, 138.5, 123.3, 116.5, 75.0,
70.7, 44.4, 41.3, 34.5, 25.7 (3C), 24.1, 23.4, 21.7, 18.2, 16.1,
-4.7, -5.4; MS (EI) m/z 399 (M+ + H); HRMS (FAB, m/z) calcd
for C21H39O5Si (M+ + H) 399.2576, found 399.2559.
1
2920, 2890, 1730 cm-1; H NMR δ 5.76-5.68 (ddd, J ) 8, 10,
18 Hz, 1H), 5.08-4.99 (m, 3H), 4.25-4.22 (dd, J ) 4, 9 Hz,
1H), 3.65-3.60 (m, 1H), 3.51-3.45 (ddd, J ) 4, 10, 11 Hz, 1H),
2.42-2.37 (m, 2H), 1.84-1.75 (m, 2H), 1.71-1.58 (m, 2H),
1.54-1.47 (ddd, J ) 4, 9, 13 Hz, 1H), 1.03-1.01 (d, J ) 7 Hz,
1H), 0.92-0.91 (d, J ) 7 Hz, 3H), 0.92-0.90 (d, J ) 7 Hz, 3H),
0.89 (s, 9H), 0.07 (s, 3H), 0.04 (s, 3H); 13C NMR δ 175.2, 139.0,
116.1, 74.5, 70.7, 58.5, 44.4, 41.9, 34.7, 25.7 (3C), 24.2, 23.4,
21.7, 18.2, 16.2, -4.7, -5.3.
2. F or m a t ion of Am id e 13 fr om Acid a n d Sa lt 8a :
(3E)-4-(N-{(1R)-2-(3,3-Dim et h yl-2-oxoa zet id in yl)-1-[(4-
m eth oxyp h en yl)m eth yl]-2-oxoeth yl}ca r ba m oyl)-1-((1R)-
1-m eth ylpr op-2-en yl)-(1S)-bu t-3-en yl-(2S)-4-m eth yl-2-(1,1,2-
tr im eth yl-1-sila p r op oxy)p en ta n oa te (13). The N-Boc pro-
tected (D)-tyrosine derivative36 (120 mg, 0.41 mmol) was
dissolved in CH3CN (4 mL) and cooled to 0 °C. 2-Azetidinone
(50 mg, 0.69 mmol), DIEA (142 µL, 0.81 mmol), and HBTU
(262 mg, 0.69 mmol) were added consecutively. After 20 min,
the ice bath was removed and the mixture was stirred for 1 h.
The reaction was quenched with saturated aqueous NH4Cl
solution and extracted with EtOAc. The combined organic
layers were dried (MgSO4), filtered, and concentrated. Flash
chromatography (80:20 to 50:50 hexanes:EtOAc) provided (2R)-
(tert-butoxy)-N-((4-methoxyphenyl)methyl)-2-oxo-2-((2-oxoaze-
tidinyl)ethyl)formamide as a cream colored solid (85 mg, 60%).
Mp 107-109°; [R]D -56 (c 1.0, CHCl3); IR (film) 3390, 1790,
1705, 1690 cm-1; 1H NMR δ 7.12-7.10 (d, J ) 9 Hz, 2H), 6.82-
6.80 (d, J ) 9 Hz, 2H), 5.05 (br s, 2H), 3.76 (s, 3H), 3.64-3.59
(m, 1H), 3.51-3.46 (m, 1H), 3.08-2.98 (m, 3H), 2.82-2.78 (m,
1H), 1.35 (s, 9H); 13C NMR δ 170.7, 164.7, 159.4, 155.7, 130.8
(2C), 128.1, 114.3 (2C), 80.4, 56.2, 55.7, 37.5, 36.9, 36.4, 28.7
(3C); MS(FAB+, NBA) m/z 349 (M+ + H), 121 (100); HRMS
(FAB, m/z) calcd for C18H25N2O5 (M+ + H) 349.1763, found
349.1782.
This compound (150 mg, 0.431 mmol) was dissolved in 4 N
HCl in dioxane (4 mL) and stirred for 1.5 h. A precipitate
formed and the reaction was concentrated to provide a light
tan salt 8a . The acid (40 mg, 0.10 mmol) and salt 8a (40 mg,
0.140 mmol) were placed in a flask and CH3CN (1 mL) was
added. The solution was cooled to 0 °C and DIEA (52 µL, 0.30
mmol) was added. When the solution was clear, HBTU (57
mg, 0.15 mmol) was added and the reaction stirred for 30 min
at 0 °C and room temperature for 90 min. Saturated NaHCO3
solution and CH2Cl2 were added. The aqueous layer was
further extracted with CH2Cl2. The combined organic layers
were dried (MgSO4), filtered, and concentrated. Flash chro-
matography (70:30 to 40:60 hexane/EtOAc) provided the
product 13 as a viscous oil (40 mg, 64%). IR (film) 3280, 3060,
2920, 2900, 2825, 1770, 1730, 1690, 1660, 1620 cm-1; 1H NMR
δ 7.10-7.07 (d, J ) 9 Hz, 2H), 6.82-6.80 (d, J ) 9 Hz, 2H),
2. Oxid a tion of DDQ Dep r otected Alcoh ol to In ter m e-
d ia te Ald eh yd e: 1-[(1R)-1-Meth ylp r op -2-en yl]-(1S)-3-oxo-
pr opyl-(2S)-4-m eth yl-2-(1,1,2,2-tetr am eth yl-1-silapr opoxy)-
p en ta n oa te. The alcohol (95 mg, 0.265 mmol) was dissolved
in CH2Cl2 (2.7 mL) and Dess-Martin periodinane (169 mg,
0.397 mmol) was added. After 2 h, a 1:1 mixture of saturated
aqueous Na2S2O3 and NH4Cl solutions was added. After 10
min of vigorous stirring, the mixture was diluted with CH2-
Cl2 and H2O. The aqueous phase was extracted with CH2Cl2.
The combined extracts were washed with saturated aqueous
NaHCO3 solution, dried (MgSO4), filtered, and concentrated.
The product was a colorless oil (76 mg, 81%). IR (film) 3750,
1
2940, 2910, 2840, 1740, 1715 cm-1; H NMR δ 9.70 (dd, J )
2.5, 1.4 Hz, 1H), 5.76-5.67 (ddd, J ) 17, 10, 8 Hz, 1H), 5.39-
5.34 (dt, J ) 8, 5 Hz, 1H), 5.11-5.09 (m, 1H), 5.10-5.06 (m,
1H), 4.19-4.16 (dd, J ) 4, 9 Hz, 1H), 2.68-2.62 (ddd, J ) 17,
8, 2.5 Hz, 1H), 2.62-2.56 (ddd, J ) 17, 5, 1.4 Hz, 1H), 2.53-
2.48 (m, 1H), 1.80-1.74 (m, 1H), 1.63-1.56 (ddd, J ) 14, 9, 5
Hz, 1H), 1.48-1.42 (ddd, J ) 14, 9, 4 Hz, 1H), 1.04-1.03 (d, J
) 7 Hz, 3H), 0.92-0.89 (buried, 6H), 0.89 (s, 9H), 0.07 (s, 3H),
0.03 (s, 3H); 13C NMR δ 199.2, 173.7, 138.2, 116.9, 71.7, 70.7,
45.5, 44.2, 41.3, 25.7 (3C), 24.1, 23.4, 21.7, 18.2, 15.5, -4.7,
-5.4; MS (EI) m/z 357 (M+ + H), 316; HRMS (FAB, m/z) calcd
for C19H37O4Si (M+ + H) 357.2461, found 357.2463.
3. Wittig Rea ction of In ter m ed ia te Ald eh yd e To F or m
12. ter t-Bu tyl-(2E)-5-[(2S)-4-m eth yl-2-(1,1,2,2-tetr a m eth yl-
1-sila p r op oxy)p en t a n oyloxy]-(5S,6R)-6-m et h yloct a -2,7-
d ien oa te (12). The aldehyde (80 mg, 0.22 mmol) was dissolved
in CH2Cl2 (2.2 mL) and cooled to 0 °C. (tert-Butoxycarbonyl-
methylene)triphenylphosphorane 11 (101 mg, 0.27 mmol) was
added. After 30 min at 0 °C and 90 min at room temperature,
the reaction was concentrated and purified by flash chroma-
tography (95:5 hexane:EtOAc) to provide 12 as a colorless oil
(96 mg, 94%). [R]D -25 (c 0.50, CHCl3); IR (film) 3070, 2935,
1
2910, 2840, 1740, 1700, 1645 cm-1; H NMR δ 6.77-6.69 (dt,
J ) 7, 15 Hz, 1H), 5.79-5.75 (d, J ) 15 Hz, 1H), 5.75-5.66
(m, 1H), 5.08 (br s, 1H), 5.07-5.03 (m, 1H), 4.99-4.95 (app q,
J . Org. Chem, Vol. 68, No. 25, 2003 9691

Vidya et al.
6.75-6.68 (dt, J ) 7, 15 Hz, 1H), 5.98-5.96 (br d, J ) 7 Hz,
1H), 5.82-5.78 (d, J ) 15 Hz, 1H), 5.73-5.65 (m, 1H), 5.39-
5.34 (app q, J ) 7 Hz, 1H), 5.06-5.01 (m, 2H), 4.94-4.89 (app
q, J ) 6 Hz, 1H), 4.18-4.15 (dd, J ) 4, 9 Hz, 1H), 3.77 (s, 3H),
3.64-3.59 (m, 1H), 3.53-3.48 (m, 1H), 3.15-3.10 (dd, J ) 6,
14 Hz, 1H), 3.08-2.99 (m, 2H), 2.97-2.91 (dd, J ) 7, 14 Hz,
1H), 2.43-2.39 (m, J ) 7 Hz, 3H), 1.80-1.73 (m, 1H), 1.62-
1.55 (ddd, J ) 5, 9, 13 Hz, 1H), 1.47-1.41 (ddd, J ) 4, 9, 13
Hz, 1H), 0.99-0.98 (d, J ) 7 Hz, 3H), 0.91-0.89 (d, J ) 7 Hz,
3H), 0.90-0.88 (d, J ) 7 Hz, 3H), 0.88 (s, 9H), 0.04 (s, 3H),
0.01 (s, 3H); 13C NMR δ 173.8, 169.5, 164.7, 164.2, 158.8, 140.1,
138.6, 130.3 (2C), 127.2, 125.6, 116.3, 114.0 (2C), 75.4, 70.7,
55.2, 54.5, 44.3, 40.8, 36.7, 36.6, 36.0, 34.0, 25.7 (3C), 24.1,
23.4, 21.7, 18.2, 16.3, -4.7, -5.4; MS (EI) m/z 629 (M+); HRMS
(FAB, m/z) calcd for C34H52N2O7Si 629.3622, found 629.3622.
7.09 (d, J ) 8.6 Hz, 2H), 7.05-7.02 (t, J ) 5.5 Hz, 1H), 6.81-
6.78 (d, J ) 8.6 Hz, 2H), 6.73-6.66 (ddd, J ) 4.7, 10, 15 Hz,
1H), 6.41-6.37 (d, J ) 16 Hz, 1H), 6.03-5.96 (dd, J ) 8.8, 16
Hz, 1H), 5.77-5.75 (d, J ) 7.9 Hz, 1H), 5.75-5.71 (d, J ) 15
Hz, 1H), 5.06-5.01 (ddd, J ) 2, 6.6, 11 Hz, 1H), 4.91-4.88
(dd, J ) 3.6, 10 Hz, 1H), 4.73-4.67 (m, 1H), 3.76 (s, 3H), 3.54-
3.48 (m, 1H), 3.46-3.39 (m, 1H), 3.15-3.11 (dd, J ) 6, 14 Hz,
1H), 3.04-2.98 (dd, J ) 7.5, 14 Hz, 1H), 2.57-2.52 (m, 3H),
2.39-2.30 (m, 1H), 1.78-1.57 (m, 3H), 1.35-1.27 (m, 1H),
1.13-1.11 (d, J ) 6.8 Hz, 3H), 0.73-0.72 (d, J ) 6.4 Hz, 3H),
0.70-0.69 (d, J ) 6.4 Hz, 3H); 13C NMR δ 172.8, 170.9, 170.8,
165.6, 158.5, 141.7, 136.7, 131.8, 130.2 (2C), 128.6 (2C), 128.5,
127.5, 126.1 (2C), 125.0, 114.1 (2C), 76.6, 71.5, 55.2, 54.3, 42.2,
39.7, 36.4, 35.2, 34.2, 32.4, 24.3, 22.6, 21.2, 17.2; MS (FAB)
m/z 591.3 (M+ + H); HRMS (FAB, m/z) calcd for C34H43N2O4
(M+ + H) 591.3070, found 591.3069.
(3E)-4-(N-{(1R)-2-(3,3-Dim eth yl-2-oxoa zetid in yl)-1-[(4-
m eth oxyp h en yl)m eth yl]-2-oxoeth yl}ca r ba m oyl)-1-((1R)-
1-m et h ylp r op -2-en yl)-(1S)-b u t -3-en yl-(2S)-2-h yd r oxy-4-
m eth ylp en ta n oa te (5a ). The silyl ether 13 (6.0 mg, 9.5 µmol)
was dissolved in CHCl3 (1 mL, dried over activated 4 Å
molecular sieves). BF3‚Et2O (10 µL, 76.3 µmol) was added via
syringe. After 1 h, CHCl3 (5 mL) and saturated aqueous
NaHCO3 (2 mL) were added. The organic layers were dried
(MgSO4), filtered, and concentrated to provide clean 5a as an
oil (4.4 mg, 88%). 1H NMR δ 7.10-7.08 (d, J ) 9 Hz, 2H), 6.83-
6.81 (d, J ) 9 Hz, 2H), 6.71-6.63 (dt, J ) 7, 15 Hz, 1H), 6.07-
6.05 (br d, J ) 7 Hz, 1H), 5.81-5.77 (d, J ) 15 Hz, 1H), 5.71-
5.62 (ddd, J ) 8, 10, 17 Hz, 1H), 5.36-5.33 (app q, J ) 6 Hz,
1H), 5.08-5.02 (m, 2H), 4.97-4.93 (app q, J ) 6 Hz, 1H), 4.14-
4.12 (br s, 1H), 3.77 (s, 3H), 3.64-3.61 (m, 1H), 3.54-3.49 (m,
1H), 3.16-3.11 (dd, J ) 6, 14 Hz, 1H), 3.08-3.03 (m, 2H),
2.95-2.90 (dd, J ) 8, 14 Hz, 1H), 2.45-2.40 (m, 3H), 1.91-
1.84 (m, 1H), 1.52-1.48 (m, 2H), 1.00-0.99 (d, J ) 6.9 Hz,
3H), 0.95-0.93 (d, J ) 7 Hz, 3H), 0.94-0.92 (d, J ) 7 Hz, 3H);
13C NMR δ 175.4, 169.6, 164.9, 164.3, 158.8, 139.7, 138.4, 130.3
(2C), 127.2, 125.8, 116.6, 114.0 (2C), 76.4, 69.0, 55.2, 54.6, 43.5,
41.1, 36.6 (2C), 36.0, 34.1, 24.5, 23.3, 21.4, 16.2.
Ar en a sta tin A (2). Olefin 15 (5.0 mg, 8.5 µmol) was reacted
as previously reported40 with dimethyldioxirane57 to obtain a
2:1 mixture (de was determined by HPLC Phenomenex Hy-
persil 5µ, C18, 150 × 3.2 mm, 254 nm, 3:2 CH3CN:H2O, 0.5
mL/min, retention time â ) 7.2 min, R ) 7.9 min) of epoxide
diastereomers (3.9 mg, 76%). [R]D +37 (c 0.10, CHCl3).40
ter t-Bu tyl (2E,7E)-5-[(2S)-4-Meth yl-2-(1,1,2,2-tetr a m e-
th yl-1-silapr opoxy)pen tan oyloxy]-(5S,6R)-6-m eth yl-8-ph e-
n yloct a -2,7-d ien oa t e (16). To alcohol 6b 41 (181 mg, 0.599
mmol) in CH2Cl2 (3 mL) at 0 °C under a nitrogen atmosphere
were added DMAP (370 mg, 3.028 mmol) and triethylamine
(0.43 mL, 3.052 mmol). To the above solution was added acid
chloride 7 (5 equiv), obtained from bis-TBS protected L-leucic
acid,55 in CH2Cl2 (6 mL) dropwise at 0 °C. After 10 min the
solution was brought to room temperature and stirred for 2
h. The reaction mixture was diluted with excess CH2Cl2 and
washed with water, saturated bicarbonate solution, and brine,
dried over sodium sulfate, filtered, and concentrated. The
residue was purified by flash column chromatography (5%
ethyl acetate-hexanes) to provide 16 (292 mg, 92%) as a
colorless oil. [R]D +19 (c 2.4, CHCl3); IR (film) 2957, 2857, 1751,
1
Dep h en yld esep oxya r en a sta tin A (14). Alcohol 5a (4.4
mg, 8.6 µmol) was dissolved in CH2Cl2 (2 mL). Bu4NCN (21
mg, 77.0 µmol) was dissolved in CH2Cl2 (2 mL) and both were
stirred with flame-activated crushed 4 Å molecular sieves for
1 h. The Bu4NCN solution was transferred via syringe drop-
wise to the solution of 5a . After 16 h, the reaction was filtered
through Celite and concentrated. Column chromatography (50:
50 to 75:25 EtOAc:hexanes) provided clean product 14 (3.0 mg,
1715, 1151 cm-1; H NMR δ 7.37-7.23 (m, 5H), 6.80 (dt, 1H,
J ) 7.4, 15 Hz), 6.43 (d, 1H, J ) 16 Hz), 6.08 (dd, 1H, J ) 8.5,
16 Hz), 5.82 (d, 1H, J ) 14 Hz), 5.10-5.05 (m, 1H), 4.21 (dd,
1H, J ) 4.0, 9.2 Hz), 2.66-2.60 (m, 1H), 2.51-2.47 (m, 2H),
1.82-1.71 (m, 1H), 1.57 (ddd, 1H, J ) 4.6, 9.2, 14 Hz), 1.49 (s,
9H), 1.44 (ddd, 1H, J ) 5.2, 9.4, 14 Hz), 1.13 (d, 3H, J ) 6.8
Hz), 0.92 (s, 9H), 0.88 (d, 3H, J ) 6.5 Hz), 0.82 (d, 3H, J ) 6.7
Hz), 0.09 (s, 3H), 0.05 (s, 3H); 13C NMR δ 174.4, 165.8, 142.6,
137.4, 132.0, 130.7, 128.9 (2C), 127.8, 126.6 (2C), 126.4, 80.7,
75.9, 71.0, 44.8, 41.3, 34.8, 28.5 (3C), 26.1 (3C), 24.4, 23.7, 21.9,
18.6, 17.2, -4.2, -4.9; MS (FAB+, NBA) m/z 531.4 (M+ + H);
1
68%). IR (film) 3420, 3300, 2990, 1740, 1675, 1525 cm-1; H
NMR δ 7.11-7.09 (d, J ) 8.6 Hz, 2H), 7.05-7.02 (t, J ) 5.7
Hz, 1H), 6.81-6.79 (d, J ) 8.6 Hz, 2H), 6.71-6.63 (ddd, J )
5, 10, 15 Hz, 1H), 5.84-5.82 (d, J ) 8 Hz, 1H), 5.75-5.71 (d,
J ) 14 Hz, 1H), 5.69-5.65 (m, 1H), 5.08 (br s, 1H), 5.05-5.04
(d, J ) 6 Hz, 1H), 5.02-4.97 (ddd, J ) 2, 5, 11 Hz, 1H), 4.94-
4.91 (dd, J ) 4, 9.5 Hz, 1H), 4.72-4.66 (m, 1H), 3.76 (s, 3H),
3.54-3.47 (m, 1H), 3.47-3.40 (m, 1H), 3.16-3.11 (dd, J ) 6,
14 Hz, 1H), 3.03-2.97 (dd, J ) 7.6, 14 Hz, 1H), 2.44-2.28 (m,
2H), 1.76-1.66 (m, 1H), 1.48-1.40 (m, 1H), 1.04-1.02 (d, J )
7 Hz, 3H), 0.92-0.90 (d, J ) 6.4 Hz, 3H), 0.88-0.87 (d, J )
6.4 Hz, 3H); 13C NMR δ 172.8, 170.82, 170.76, 165.7, 158.5,
141.8, 138.6, 130.2 (2C), 128.5, 124.9, 116.5, 114.1 (2C), 76.8,
71.4, 55.2, 54.3, 42.4, 39.8, 36.1, 35.2, 34.2, 32.5, 24.5, 22.9,
21.5, 16.6; MS (FAB) m/z 515.3 (M+ + H); HRMS (FAB, m/z)
calcd for C28H39O7N2 (M+ + H) 515.2757, found 515.2775.
HRMS (FAB, m/z) calcd for
548.3771, found 548.3765.
C
31H54N1O5Si1 (M+ + NH4)
N-{(1R)-2-(3,3-Dim eth yl-2-oxoa zetid in yl)-1-[(4-m eth ox-
yp h en yl)m et h yl]-2-oxoet h yl}(ter t-b u t oxy)ca r b oxa m id e
(20). To the tyrosine derivative 1836 (221 mg, 0.748 mmol) in
acetonitrile (4 mL) at 0 °C was added DIEA (0.5 mL, 2.993
mmol) under a nitrogen atmosphere, followed by HBTU (625
mg, 1.646 mmol). To this mixture was added lactam 1960-62
(114 mg, 1.122 mmol) in acetonitrile (6 mL) and the solution
was stirred at room temperature for 5 h. The reaction was
quenched with saturated NH4Cl solution and the compound
was extracted with ethyl acetate (3 × 20 mL). The combined
organic layers were washed with water and brine, dried over
sodium sulfate, filtered, and concentrated. Flash column
chromatography (20% ethyl acetate-hexanes) of the crude
material afforded Boc-protected N-acylazetidinone 20 (256 mg,
91%) as a colorless crystalline solid. Mp 112-113 °C; [R]D
Desep oxya r en a sta tin A (15).40,41 Olefin 14 (17 mg, 33
µmol) was dissolved in CH3CN (0.33 mL) in a dry sealed tube.
The solution was flushed with argon and iodobenzene (4.0 mL,
36 µmol), Pd(OAc)2 (1.1 mg, 5.0 µmol), and TEA (46 mL, 330
µmol) were added. The tube was sealed and placed in a 80-
85 °C oil bath with vigorous stirring overnight. After 20 h,
the solution was filtered and purified by silica gel chromatog-
raphy to obtain product 15 as a solid (3 mg, 31% based on
recovered starting material) and unreacted starting material
14 (6 mg). [R]D +27 (c 0.80, CHCl3); IR (film) 3365, 3260, 2940,
-37.5 (c 1.46, CHCl3); IR (film) 3365, 1789, 1712, 1513 cm-1
;
1H NMR δ 7.11 (d, 2H, J ) 8.2 Hz), 6.79 (d, 2H, J ) 8.5 Hz),
5.22 (br d, 1H, J ) 7.3 Hz), 5.07 (br d, 1H, J ) 4.2 Hz), 3.73
(s, 3H), 3.36 (1/2 ABq, 1H, J ) 7.2 Hz), 3.21 (1/2 ABq, 1H, J )
7.2 Hz), 3.03-2.98 (m, 1H), 2.88-2.82 (m, 1H), 1.36 (s, 9H),
1.30 (s, 3H), 1.22 (s, 3H); 13C NMR δ 171.2, 159.0 (2C), 155.4,
130.9 (2C), 128.0, 114.2 (2C), 80.1, 56.3, 55.6, 51.7, 50.3, 38.1,
1
1725, 1710, 1665 cm-1; H NMR δ 7.33-7.15 (m, 5H), 7.11-
9692 J . Org. Chem., Vol. 68, No. 25, 2003

Synthesis of Cryptophycins
28.7 (2C), 21.8, 21.5 (2C); MS (FAB+, NBA) m/z 377.2 (M+
+
137.1, 132.2, 130.6 (3C), 129.0 (2C), 128.6, 128.0, 126.6 (2C),
124.9, 114.6 (2C), 77.4, 71.9, 55.7, 54.8, 46.8, 43.1, 42.7, 39.9,
37.0, 36.0, 24.9, 23.2, 23.1, 23.0, 21.6, 17.8; MS (FAB+, NBA)
m/z 619.4 (M+ + H); HRMS (FAB, m/z) calcd for C36H47N2O7
(M+ + H) 619.3383, found 619.3381.
H); HRMS (FAB, m/z) calcd for C20H29N2O5 (M+ + H) 377.2076,
found 377.2078.
(3E)-1-[(2E)-3-(N-{(1R)-2-(3,3-Dim eth yl-2-oxoazetidin yl)-
1-[(4-m et h oxyp h en yl)m et h yl]-2-oxoet h yl}ca r b a m oyl)-
p r op -2-en yl]-(1S,2R)-2-m eth yl-4-p h en ylbu t-3-en yl-(2S)-2-
h yd r oxy-4-m eth ylp en ta n oa te (5b). To Boc protected amino-
acylazetidinone 20 (140 mg, 0.372 mmol) was added 4 N HCl
in 1,4-dioxane (3 mL) and the solution was stirred at room
temperature for 4 h. The volatiles were removed under vacuo
and the residue amine hydrochloride salt 8b was taken to the
next step without further purification. To compound 8b in
acetonitrile (2 mL) at 0 °C was added DIEA (0.36 mL, 2.081
mmol) dropwise under a nitrogen atmosphere, followed by
HBTU (316 mg, 0.833 mmol). To this solution was added
hydroxy acid 17 [obtained by the simultaneous deprotection
of the TBS and tert-butyl ester groups of 16 (232 mg, 0.437
mmol), using excess trifluoroacetic acid and CH2Cl2] in aceto-
nitrile (8 mL) and the solution was stirred for 4 h. The reaction
mixture was diluted with ethyl acetate, washed with water,
saturated bicarbonate solution, and brine, dried over sodium
sulfate, filtered, and concentrated. The crude residue was
purified by flash column chromatography (40% ethyl acetate-
hexanes) to afford 5b (148 mg, 58%) as a colorless oil. [R]D
+10 (c 1.1, CHCl3); IR (film) 3346, 1790, 1707, 1513 cm-1; 1H
NMR δ 7.34-7.21 (m, 5H), 7.12 (d, 2H, J ) 8.5 Hz), 6.83 (d,
2H, J ) 8.5 Hz), 6.76 (dt, 1H, J ) 7.7, 15 Hz), 6.40 (d, 1H, J
) 16 Hz), 6.34 (br d, 1H, J ) 6.8 Hz, NH), 6.03 (dd, 1H, J )
8.7, 16 Hz), 5.86 (d, 1H, J ) 15 Hz), 5.42 (br d, 1H, J ) 6.1
Hz), 5.06-5.01 (m, 1H), 4.14 (br s, 1H), 3.77 (s, 3H), 3.40 (br
s, 1H), 3.26 (d, 1H, J ) 7.3 Hz), 3.10 (dd, 1H, J ) 6.5, 14 Hz),
3.00 (dd, 1H, J ) 7.4, 14 Hz), 2.89 (br s, 1H, OH), 2.63-2.43
(m, 3H), 1.87-1.79 (m, 1H), 1.50-1.40 (m, 2H), 1.35 (s, 3H),
1.27 (s, 3H), 1.11 (d, 3H, J ) 6.8 Hz), 0.90 (d, 3H, J ) 6.5 Hz),
0.83 (d, 3H, J ) 6.7 Hz); 13C NMR δ 175.9, 171.3, 170.7, 165.3,
159.2, 140.0, 137.3, 132.2, 130.8 (2C), 130.4, 129.0 (2C), 127.9,
127.7, 126.6 (2C), 126.4, 114.4 (2C), 77.0, 69.4, 55.6, 55.2, 51.9,
50.5, 44.0, 41.2, 37.5, 34.7, 24.8, 23.6, 21.8, 21.7, 21.5, 17.3;
MS (FAB+, NBA) m/z 619.5 (M+ + H); HRMS (FAB, m/z) calcd
for C36H47N2O7 (M+ + H) 619.3383, found 619.3402.
(3E)-1-[(2E)-3-(N-Meth ylcar bam oyl)pr op-2-en yl]-(1S,2R)-
2-m eth yl-4-p h en ylbu t-3-en yl-(2S)-2-{3-[3-(4-m eth oxyp h e-
n yl)pr opan oylam in o]-2,2-dim eth ylpr opan oyloxy}-4-m eth -
ylp en ta n oa te (21). To hydroxy compound 5b (40 mg, 0.065
mmol) in THF (20 mL) was added tetrabutylammonium
cyanide (1.7 mg, 0.006 mmol) in THF (1 mL) at room temper-
ature under a nitrogen atmosphere. The solution was stirred
for 30 min. The solvent was removed in vacuo and the residue
was subjected to silica gel column chromatography (60% ethyl
acetate-hexanes) to afford macrolide 21 as a colorless solid
(26 mg, 65%). Mp 85-87 °C; [R]D +31 (c 0.55, acetone); IR (film)
3411, 3283 (br), 1747, 1721, 1651 cm-1; 1H NMR δ 7.35-7.23
(m, 6H), 7.11 (d, 2H, J ) 8.5 Hz), 6.83 (d, 2H, J ) 8.5 Hz),
6.80 (ddd, 1H, J ) 4.0, 11, 15 Hz), 6.42 (d, 1H, J ) 16 Hz),
6.03 (dd, 1H, J ) 8.8, 16 Hz), 5.75 (d, 1H, J ) 15 Hz), 5.60 (d,
1H, J ) 7.4 Hz), 5.10-5.05 (m, 1H), 4.87 (dd, 1H, J ) 3.2, 9.9
Hz), 4.78-4.73 (m, 1H), 3.80 (s, 3H), 3.47 (dd, 1H, J ) 9.1, 13
Hz), 3.13-3.04 (m, 3H), 2.61-2.53 (m, 2H), 2.44-2.34 (m, 1H),
1.72-1.57 (m, 2H), 1.34 (ddd, 1H, J ) 3.7, 8.8, 12 Hz), 1.24 (s,
3H), 1.17 (s, 3H), 1.14 (d, 3H, J ) 6.8 Hz), 0.74 (app t, 6H, J
) 6.0 Hz); 13C NMR δ 178.6, 171.1, 171.0, 165.4, 159.1, 142.7,
Dech lor ocr yp top h ycin -52 (4). To macrolide 21 (10 mg,
0.016 mmol) in acetone (2 mL) was added dimethyl dioxirane57
in acetone (2 mL) at room temperature and the solution was
stirred for 2 h. The solvent was removed in vacuo. Silica gel
column chromatography (60% ethyl acetate-hexanes) of the
residue furnished a diastereomeric mixture (â:R ) 2:1) of
dechlorocryptophycin-52 (4; 7 mg, 68%) as a colorless solid.
The mixture was separated by reverse-phase HPLC. 4â: Mp
119-121 °C; [R]D +26.7 (c 0.62, CHCl3); IR (film) 3411, 3271,
2959, 2931, 1747, 1720, 1651, 1514, 1247, 1147 cm-1; 1H NMR
δ 7.41-7.33 (m, 3H), 7.27-7.22 (m, 3H), 7.10 (d, 2H, J ) 8.6
Hz), 6.83 (d, 2H, J ) 8.6 Hz), 6.79 (ddd, 1H, J ) 4.2, 10, 15
Hz), 5.70 (d, 1H, J ) 15 Hz), 5.51 (d, 1H, J ) 7.6 Hz), 5.25-
5.21 (m, 1H), 4.84 (dd, 1H, J ) 3.2, 10 Hz), 4.75 (q, 1H, J )
6.6 Hz), 3.80 (s, 3H), 3.70 (s, 1H), 3.48 (dd, 1H, J ) 9.1, 13
Hz), 3.13-3.03 (m, 3H), 2.94 (d, 1H, J ) 7.6 Hz), 2.62-2.57
(m, 1H), 2.51-2.42 (m, 1H), 1.82-1.69 (m, 3H), 1.32 (ddd, 1H,
J ) 3.6, 8.9, 12 Hz), 1.24 (s, 3H), 1.18 (s, 3H), 1.16 (d, 3H, J )
8.2 Hz), 0.86 (d, 3H, J ) 6.5 Hz), 0.84 (d, 3H, J ) 6.5 Hz); 13
C
NMR δ 178.6, 171.0, 170.9, 165.2, 159.1, 142.2, 137.2, 130.6
(2C), 129.1 (2C), 129.0, 128.5, 126.0 (2C), 125.0, 114.7 (2C),
76.3, 71.6, 63.5, 59.6, 55.7, 54.8, 46.8, 43.2, 41.1, 39.7, 37.3,
35.9, 25.0, 23.3 (2C), 23.1, 21.6, 14.0; MS (FAB+, NBA) m/z
635.6 (M+ + H); HRMS (FAB, m/z) calcd for C36H47N2O8 (M+
+ H) 635.3332, found 635.3351. 4r: Mp 94-96 °C; [R]D +29.6
(c 0.27, CHCl3); IR (film) 3413, 3275, 2958, 2927, 1749, 1721,
1
1659, 1514, 1247, 1148 cm-1; H NMR δ 7.40-7.33 (m, 3H),
7.27-7.25 (m, 3H), 7.13 (d, 2H, J ) 8.6 Hz), 6.86 (d, 2H, J )
8.6 Hz), 6.81 (ddd, 1H, J ) 4.4, 11, 15 Hz), 5.80 (d, 1H, J ) 15
Hz), 5.54 (d, 1H, J ) 7.7 Hz), 5.25-5.20 (m, 1H), 4.94 (dd, 1H,
J ) 3.1, 10 Hz), 4.77 (q, 1H, J ) 6.0 Hz), 3.82 (s, 3H), 3.61 (d,
1H, J ) 2 Hz), 3.49 (dd, 1H, J ) 9.0, 13 Hz), 3.15-3.07 (m,
3H), 2.93 (dd, 1H, J ) 2.0, 7.9 Hz), 2.75-2.57 (m, 2H), 1.84-
1.69 (m, 3H), 1.50 (ddd, 1H, J ) 3.3, 9.0, 12 Hz), 1.26 (s, 3H),
1.20 (s, 3H), 1.07 (d, 3H, J ) 7.1 Hz), 0.92 (d, 3H, J ) 6.5 Hz),
0.89 (d, 3H, J ) 6.5 Hz); 13C NMR δ 178.6, 171.0, 170.9, 165.4,
159.1, 142.6, 137.5, 130.6 (2C), 129.0 (2C), 128.7, 128.5, 125.8
(2C), 125.0, 114.7 (2C), 77.1, 71.8, 63.6, 56.7, 55.7, 54.8, 46.8,
43.2, 41.4, 40.0, 37.2, 36.0, 25.2, 23.5, 23.3, 23.2, 21.8, 13.9;
MS (FAB+, NBA) m/z 635.6 (M+ + H); HRMS (FAB, m/z) calcd
for C36H47N2O8 (M+ + H) 635.3332, found 635.3339.
Ack n ow led gm en t. We thank the National Insti-
tutes of Health (NCI) for financial support (CA 70369).
The Department of the Army is acknowledged for
postdoctoral fellowships from the Breast Cancer Re-
search Program to M.E. and R.V. This work was
supported in part by the Kansas Technology Enterprise
Corporation through the Centers of Excellence Program.
Su p p or tin g In for m a tion Ava ila ble: General experimen-
tal details and 1H NMR and 13C NMR spectra of compounds
4, 5a , 5b, 10, 12, 13, 14, 16, 20, and 21. This material is
available free of charge via the Internet at http://pubs.acs.org.
J O0302197
J . Org. Chem, Vol. 68, No. 25, 2003 9693