Enantioselective Synthesis of (+)-Cryptophycin 52 (LY355703), a Potent Antimitotic Antitumor Agent

Article abstract of DOI:10.1021/jo035077v

A highly enantioselective and convergent synthesis of cryptophycin 52 (2), an exceedingly potent cytotoxic agent, is described. Cryptophycin 52, a synthetic variant of the cryptophycin family, is currently undergoing clinical trials. The synthesis is conv

Full text of DOI:10.1021/jo035077v

paclitaxel.7 Thus, it is not surprising that the significant
clinical potential of cryptophycins has generated enor-
mous interest in their synthesis, structural modification,
and biological studies. Several total syntheses and syn-
thetic approaches to cryptophycins have been reported.8
In this context, a number of interesting methodologies,
particularly for the synthesis of the octadienamide frag-
ment of desoxycryptophycins, have been developed.9 We
recently reported the synthesis of cryptophycin B utiliz-
ing an ester-derived titanium enolate aldol reaction as
the key step.8b Subsequently, we explored a nonaldol
strategy for the preparation of the key octadienamide
fragment. Herein we describe a highly enantioselective
and convergent synthesis of cryptophycin 52 utilizing
optically active phenylbutyrolactone. Both stereogenic
centers of the octadienamide unit were created on the
basis of the chirality of 4-phenylbutyrolactone, and the
latter was prepared enantioselectively by CBS reduction.
As depicted in Figure 1, our synthetic strategy for
cryptophycin 52 is convergent and involves assembly of
three fragments, phenyl hexenal 3, D-tyrosine phospho-
nate 4, and protected â-amino acid derivative 5. A
Horner-Emmons olefination between aldehyde 3 and
phosphonate 4 would generate the key tyrosine octadi-
enamide subunit. Esterification with acid 5 would afford
the corresponding protected acyclic precursor for cryp-
tophycin 52. Removal of the appropriate protecting
groups followed by cycloamidation of the resulting amino
acid would construct the 16-membered macrocyclic ring.
We planned to incorporate the sensitive epoxide func-
tionality at the final stage of the synthesis. Both stereo-
genic centers in fragment 3 are planned to be accessed
on the basis of the chirality of optically active 4-phenyl-
butyrolactone 8, which can be prepared on a multigram
scale utilizing an enantioselective CBS reduction as the
key step. To this end, we developed an efficient, scalable,
and highly stereocontrolled synthesis of 3 and, conse-
quently, the corresponding octadienamide fragment.
As shown in Scheme 1, enantioselective CBS reduction
of readily available10 ketoester 6 with 8 mol % oxazaboro-
lidine 7 afforded the corresponding (S)-alcohol as de-
scribed by Corey.11 The resulting γ-hydroxyester was
lactonized by heating with a catalytic amount of acetic
acid in toluene to furnish the key lactone 8 in 84% yield
En a n tioselective Syn th esis of
(+)-Cr yp top h ycin 52 (LY355703), a P oten t
An tim itotic An titu m or Agen t
Arun K. Ghosh* and Lisa Swanson
Department of Chemistry, University of Illinois at Chicago,
845 West Taylor Street, Chicago, Illinois 60607
arunghos@uic.edu
Received J uly 24, 2003
Abstr a ct: A highly enantioselective and convergent syn-
thesis of cryptophycin 52 (2), an exceedingly potent cytotoxic
agent, is described. Cryptophycin 52, a synthetic variant of
the cryptophycin family, is currently undergoing clinical
trials. The synthesis is convergent and involves assembly
of three fragments, phenyl hexenal 3, D-tyrosine phospho-
nate 4, and protected â-amino acid derivative 5. The
synthesis of fragment 3 involves an efficient and stereocon-
trolled construction of both stereogenic centers at C-3 and
C-4 by cleavage of a substituted tetrahydrofuran ring via
an acyloxycarbenium ion intermediate. Both of these ste-
reogenic centers were derived from optically active 4-phe-
nylbutyrolactone, synthesized enantioselectively by Corey-
Bakshi-Shibata reduction.
Cryptophycins are a family of macrocyclic depsipep-
tides isolated from terrestrial blue-green algae Nostoc sp.
GSV 224 that have shown exceedingly potent antitumor
properties.1 Cryptophycin A displayed potent cytotoxicity
against KB and LoVo cell lines with IC50 values of 3 and
5 pg/mL, respectively,2 and has been shown to be very
effective against mammary, colon, and pancreatic ad-
enocarcinomas in mouse xenograft models.3 Cryptophycin
52, a synthetic analogue, is currently undergoing phase
II clinical trials.4 This derivative has shown exceptional
in vivo potency and tumor-selective cytotoxicity. Fur-
thermore, it is effective against drug-sensitive and drug-
resistant tumor cells and is metabolically more stable
than cryptophycin A.5 Cryptophycin 52 stabilizes micro-
tubule dynamics and appears to display a mechanism of
action consistent with mitotic arrest.6 Recent studies also
indicated that cryptophycin 52 promotes hyperphospho-
rylation of Bcl2 and may be involved in a second pathway
to apoptosis, similar to but considerably more potent than
(7) Shih, C.; Al-Awar, R.; Norman, B.; Patel, V.; Toth, J .; Varie, D.;
Fray, A.; Mohar, E.; Martinelli, M.; Corbett, T.; Moore, R. Abstracts of
Papers, 219th National Meeting of the American Chemical Society,
San Francisco, CA; American Chemical Society: Washington, DC,
2000; ORG 291.
(1) (a) Schwarz, 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. (b) Kobayashi, M.;
Aoki, S.; Ohyabu, N.; Kurosu, M.; Wang, W.; Kitagawa, I. Tetrahedron
Lett. 1994, 35, 7969. (c) Koiso, Y.; Morita, K.; Kobayashi, M.; Wang,
W.; Ohyabu, N.; Iwasaki, S. Chem.-Biol. Interact. 1996, 102, 183.
(2) 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.
(3) Golakoti, T.; 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.
(4) Stevenson, J . P.; Sun, W.; Gallagher, M.; J ohnson, R.; Vaughn,
D.; Schchter, L.; Algazy, K.; Hahn, S.; Enas, N.; Ellis, D.; Thornton,
D.; O’Dwyer, P. J . Clin. Cancer Res. 2002, 8, 2524.
(8) (a) Eggen, M.-J .; 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. (b) Ghosh, A. K.; Bischoff, A. Org. Lett. 2000, 2, 1573. (c)
Norman, B. H.; Hemscheidt, T.; Schultz, R. M.; Andis, S. L. J . Org.
Chem. 1998, 63, 5288. (d) White, J . D.; Hong, J .; Robarge, L. A. J .
Org. Chem. 1999, 64, 6206. (e) Gardinier, K. M.; Leahy, J . W. J . Org.
Chem. 1997, 62, 7098. (f) Tius, M. A. Tetrahedron 2002, 58, 4343. (g)
Barrow, R. A.; Hemscheidt, T.; Liang, J .; Paik, S.; Moore, R. E.; Tius,
M. A. J . Am. Chem. Soc. 1995, 117, 2479 and references therein.
(9) (a) Liang, L.; Hoard, D. W.; Khau, V. V.; Martinelli, M. J .; Moher,
E. D.; Moore, R. E.; Tius, M. A. J . Org. Chem. 1999, 64, 1459. (b)
Furuyama, M.; Shimizu, I. Tetrahedron: Asymmetry 1998, 9, 1351.
(c) Ali, S. M.; Georg, G. I. Tetrahedron Lett. 1997, 38, 1703.
(10) Vogel, A. I. Vogel’s Textbook of Practical Organic Chemistry,
5th ed.; Furniss, B. S., Hannaford, A. J ., Smith, P. W. G., Tatchell, A.
R., Eds.; Longman: London, 1989; p 1015.
(5) Liang, J .; Moher, E. D.; Moore, R. E.; Hoard, D. W. J . Org. Chem.
2000, 65, 3143; and references cited therein.
(6) Chen, B. D.-M.; Nakeff, A.; Valeriote, F. Int. J . Cancer 1998,
77, 869.
10.1021/jo035077v CCC: $25.00 © 2003 American Chemical Society
Published on Web 11/14/2003
J . Org. Chem. 2003, 68, 9823-9826
9823

SCHEME 2a
F IGURE 1. Retrosynthetic analysis of cryptophycin 52.
SCHEME 1a
a
(a) (EtO)2P(O)CH2CO2H, DCC, THF, 23 °C, 1 h; (b) KCl,
Oxone, aq. MeCN, 23 °C; (c) NaH, THF, then 3, 0 to 23 °C; (d)
EDCI, DMAP, CH2Cl2; (e) H2, 10% Pd-C; (f) 5, 2,4,6-Cl3C6H2COCl,
Et3N, then 15, 23 °C; (g) CF3CO2H, 23 °C, 2 h; (h) FDPP, DMF,
iPr2NEt, 23 °C; (i) m-CPBA, CH2Cl2, 0 to 23 °C, 12 h (70%, 2:1
mixture).
silica gel chromatography providing 9 in 75% yield.
DIBAL reduction of 9 followed by Wittig olefination of
the resulting lactol furnished R,â-unsaturated ester 10
in 89% yield with E/ Z selectivity >55:1. Treatment of
10 with KHMDS in THF at -78 °C afforded tetrahydro-
furan derivative 11 diastereoselectively in 90% yield. A
diastereomeric ratio of 22:1 was determined on the basis
of 1H NMR integration of the benzylic proton. The
mixture was inseparable by silica gel chromatography;
therefore, it was used for the subsequent reaction. With
the installation of the corresponding C-3 and C-4 stereo-
genic centers of 3, our synthetic strategy was to unravel
the cyclic stereochemistry of 11 to acyclic intermediate
13 with the appropriate styryl olefin geometry. It is
known that 2-phenyltetrahydrofuran can be selectively
cleaved by acetic anhydride in the presence of a catalytic
amount of acid or metal halides to form 4-acetoxy-1-
phenylbut-1-ene.13 We therefore envisioned an acyloxy-
carbenium ion mediated ring opening of 11 that would
provide 13 through formation of a stable benzylic car-
bonium ion and subsequent loss of a proton. Indeed,
reaction of 11 in acetic anhydride in the presence of a
catalytic amount of ZnCl2 (6 mol %) at 120 °C for 8 h
a
(a) (R)-Oxazaborolidine 7 (8 mol %), BH3‚THF, then AcOH,
toluene, reflux; (b) LiHMDS, MeI, -78 °C; (c) DIBAL-H, CH2Cl2,
-78 °C; (d) Ph3PdCHCO2Et, CH2Cl2, 40 °C; (e) KHMDS, THF,
-78 °C; (f) Ac2O, ZnCl2 (catalytic, 6 mol %), 120 °C.
and optical purity >97% ee.12 For introduction of the
methyl substiutent at C-6, alkylation of 8 was carried
out with LiHMDS and MeI in THF at -78 °C to provide
alkylated lactone 9 as the major diastereomer along with
about 3% cis-alkylation product, which was separated by
(11) Corey, E. J .; Bakshi, R. K.; Shibata, S.; Chen, C.; Singh, V. K.
J . Am. Chem. Soc. 1987, 109, 7925.
1
(12) Optical purity of the alcohol was 95% ee, which was determined
provided 13 in 91% yield as a single isomer by H and
by 1H NMR analysis of the corresponding MTPA ester. Optical purity
of lactone 8 ([R]23 -31.4 (c CHCl3) was >97% ee; lit. [R]D -31 (c 4.3,
D
CHCl3). See: Manzocchi, A.; Casati, R.; Fiecchi, A.; Santaniello, E. J .
Chem. Soc., Perkin Trans. 1 1987, 2753.
(13) Ispiryan, R. M., Belen’kii, L. I.; Gol’dfarb, Y. L. Bull. Acad. Sci.
USSR, Div. Chem. Sci. 1967, 2391.
9824 J . Org. Chem., Vol. 68, No. 25, 2003

13C NMR analysis. Subsequently, DIBAL reduction pro-
vided the requisite aldehyde for Horner-Emmons reac-
tion.
lective chlorination of the tyrosine aromatic ring in the
presence of multiple functionalities is also noteworthy.
The present synthetic route is scalable and easily ame-
nable to the synthesis of other members of the crypto-
phycin family.
The synthesis of phosphonate derivative 4 was carried
out in two steps as shown in Scheme 2. Diethoxyphos-
phenyl acetic acid14 was coupled with tyrosine derivative
148b in the presence of DCC to provide the corresponding
amide in 96% yield. Electrophilic chlorination15 with KCl
and oxone provided chlorotyrosine derivative 4 in 75%
yield after silica gel chromatography. This method mildly
chlorinates the D-tyrosine derivative in the presence of
the acid-sensitive tert-butyl ester. Our initial synthetic
plan for 4 was to carry out electrophilic chlorination of
the corresponding Cbz-tyrosine derivative of 14, remove
the Cbz group, and then couple with diethoxyphosphinyl
acetic acid. Although the above chlorination reaction
conditions provided the corresponding meta-chloroty-
rosine in excellent yield (70%), our attempt to remove
the Cbz group by a catalytic hydrogenation under a
variety of conditions resulted in a substantial dechlori-
nation (25-40%). Horner-Emmons reaction of 4 and
aldehyde 3 furnished the R,â-unsaturated amide deriva-
tive 15 in 52% yield over two steps (from 13). The
synthesis of â-amino acid derivative 5 was carried out
by esterification of known N-Boc-3-amino-2,2-dimethyl-
propionic acid 1616 and benzyl (S)-2-hydroxyisocaproate
178b with EDC and DMAP in CH2Cl2. Catalytic hydro-
genation of the resulting diester over 10% Pd/C in ethyl
acetate under a hydrogen-filled balloon for 1.5 h fur-
nished acid 5 in quantitative yield. Acid 5 was subjected
to esterification by reaction with 2,4,6-trichlorobenzoyl
chloride, triethylamine, and alcohol 15 in the presence
of DMAP under Yamaguchi conditions17 to afford diester
18 in 77% yield after silica gel chromatography. Diester
18 was converted to desoxycryptophycin 52 in two steps
involving the removal of both the tert-butyl ester and Boc-
protecting group by exposure of 18 to trifluoroacetic acid
and subjection of the resulting amino acid to cycloami-
dation with pentafluorophenyl diphenylphosphinate
(FDPP) and iPr2NEt as described by Tius et al.8g to
Exp er im en ta l Section
Gen er a l. 1H and 13C NMR spectra were obtained in CDCl3
at 400 MHz for 1H and 100 MHz for 13C. Chemical shifts are
reported in ppm and coupling constants (J ) are reported in Hertz.
Optical rotations were measured using a polarimeter using a
sodium lamp (589 nm) in chloroform unless otherwise stated.
Infrared spectra were measured in chloroform as thin films using
sodium chloride plates. Thin-layer chromatography (TLC) was
performed on silica gel 60-F-254 plates. Mass spectra were
recorded on
a mass spectrometer as the value m/z. Flash
chromatography was performed using 230-400 mesh silica gel.
Tetrahydrofuran was distilled from sodium/benzophenone, and
benzene, methylene chloride, N,N-dimethylformamide, and tolu-
ene were distilled from CaH2 under N2.
Eth yl (3S,4R)-3-Acetoxy-4-m eth yl-6-p h en yl-h exa n -(5E)-
oa te (13). A solution of 1.84 g (7.43 mmol) of cyclic ether 11
and 60 mg (0.44 mmol) of ZnCl2 in 20 mL of Ac2O was heated at
120 °C for 8.5 h. Ethyl acetate (80 mL) was added, and the
solution was washed 8 × 50 mL with 5% NaHCO3 solution. The
organic layer was then dried over Na2SO4, filtered, and concen-
trated. Flash silica gel chromatography (6% to 10% ethyl acetate/
hexanes) provided product 13 as a yellow oil in 91% yield (1.97
1
g). [R]23 + 20.8 (c 0.49, CHCl3); H NMR (400 MHz, CDCl3) δ
D
7.2-7.36 (m, 5H), 6.42 (d, 1H, J ) 15.9), 6.1 (dd, 1H, J ) 8.3,
15.9), 5.33 (td, 1H, J ) 5.2, 7.4), 4.11 (m, 2H), 2.66 (m, 1H),
2.56 (m, 2H), 2.04 (s, 3H), 1.23 (t, 3H, J ) 7.1), 1.12 (d, 3H, J )
6.9); 13C NMR (100 MHz, CDCl3) δ 170.1, 170, 137, 131.5, 130.1,
128.5, 127.3, 126.1, 73.0, 60.6, 40.9, 36.9, 20.9, 16.0, 14.1; IR
(neat) 1741 cm-1; MS (ESI, m/z) 313.1 (M + Na)+; HRMS (ESI,
m/z) calcd for C17H22O4Na (M + Na)+ 313.1416, found 313.1418.
3-(3-Ch lor o-4-m eth oxy-ph en yl)-(2R)-2-((5S,6R)-5-h ydr oxy-
6-m eth yl-8-p h en yl-octa -2(E),7(E)-d ien oyla m in o)-p r op ion -
ic Acid ter t-Bu tyl Ester (15). To a stirring solution of 117 mg
(0.41 mmol) of alkene 13 in 10 mL of CH2Cl2 at -78 °C was
added 1 mL of DIBAL-H (1 M in hexanes) followed by 0.4 mL
over a period of about 30 min, and the reaction was monitored
to ensure all starting material was consumed. After 40 min, 7
mL of 2-propanol was added, the dry ice-acetone bath was
removed, and the reaction was allowed to warm to 23 °C. After
30 min an aqueous solution of potassium sodium tartrate
tetrahydrate (10 g in 60 mL of water) was added, and the
mixture was stirred at 23 °C for 1 h. The layers were separated,
and the organic layer was washed with 5 mL of brine and dried
over Na2SO4. The solution was filtered and concentrated with
dry benzene, and the crude aldehyde 3 was used in the next
reaction without further purification.
provide 19 ([R]23 +26.2, c 0.5, CHCl3) in 61% yield over
D
two steps. To complete the synthesis of cryptophycin 52,
epoxidation of 19 was carried out with m-CPBA to
furnish cryptophycin 52 and its diastereomer as a 2:1
mixture in 70% yield. The epoxide mixture was separated
by reverse phase HPLC (eluent, 45% aqueous CH3CN)
to provide synthetic cryptophycin 52 (2, [R]23D +20, c 0.08,
CHCl3; lit.16 [R]D 19.9, c 0.5, CHCl3). Spectral data (400
To a stirring solution of 190 mg (0.41 mmol) of phosphonamide
4 in 10 mL of THF at 0 °C was added 40 mg (1 mmol) of NaH
(60% dispersion in mineral oil). After stirring for 1 h, the crude
aldehyde 3 was added in 10 mL of THF, and the ice bath was
removed. After 1.5 h, 4 mL of saturated NH4Cl solution was
added along with 8 mL of water. Ethyl acetate (20 mL) was
added, and the layers were separated. The organic layer was
washed with 6 mL of brine, dried over Na2SO4, filtered, and
concentrated. Purification by flash silica gel chromatography
gave the product 15 as a white solid (109 mg) in 52% yield. Mp
45-48 °C; [R]23D -48 (c 0.76, CHCl3); 1H NMR (400 MHz, CDCl3)
δ 7.37 (d, 2H J ) 7.4), 7.30 (m, 2H), 7.22 (m, 1H), 7.15 (d, 1H,
J ) 2.1), 7.00 (dd, 1H, J ) 2.1, 8.4), 6.90 (ddd, 1H, J ) 7.4, 7.5,
14.9), 6.82 (d, 1H, J ) 8.4), 6.45 (d, 1H, J ) 15.9), 6.15 (dd, 1H,
J ) 8.7, 15.9), 6.11 (d, 1H, J ) 7.5), 5.89 (d, 1H, J ) 15.3), 4.79
(ddd, 1H, J ) 4.4, 5.7, 7.5 Hz), 3.87 (s, 3H), 3.66 (ddd, 1H, J )
4.2, 5.4, 8.2 Hz), 3.05 (d, 2H, J ) 5.7), 2.44 (m, 2H), 2.34 (m,
1H), 1.9 (s, 1H), 1.43 (s, 9H), 1.15 (d, 3H, J ) 7.03); 13C NMR
(100 MHz, CDCl3) δ 170.5, 164.9, 153.9, 141.6, 137.0, 131.7,
131.2, 131.0, 129.2, 128.7, 128.5, 127.3, 126.1, 125.6, 122.0, 111.8,
1
MHz H and 13C NMR) of our synthetic cryptophycin 52
are in full agreement with the reported values for
cryptophycin 52.16
In conclusion, an efficient synthesis of cryptophycin 52
was achieved. The synthesis of the octadienamide frag-
ment highlighted efficient construction of two stereogenic
centers by selective cleavage of the tetrahydrofuran ring
derived from optically active 4-phenylbutyrolactone. Se-
(14) White, J . D.; Hanselmann, R.; J ackson, R. W.; Porter, W. J .;
Ohba, Y.; Tiller, T.; Wang, S. J . Org. Chem. 2001, 66, 5217.
(15) Tamhankar, B. V.; Desai, U. V.; Mane, R. B.; Wadgaonkar, P.
P.; Bedekar, A. V. Synth. Commun. 2001, 31, 2021-2027.
(16) Moore, R. E.; Tius, M. A.; Barrow, R. A.; Liang, J .; Corbett, T.
H.; Valeriote, F. A.; Hemscheidt, T. K. PCT Int. Appl. WO 9640184
A1 19961219, 1996.
(17) Inanaga J .; Hirata K.; Saeki H.; Katsuki T.; Yamaguchi M. Bull.
Chem. Soc. J pn. 1979, 52, 1989.
J . Org. Chem, Vol. 68, No. 25, 2003 9825

82.7, 73.7, 56.0, 53.5, 43.1, 37.2, 36.8, 27.9, 16.8; IR (neat) 3405,
1729, 1670, 1634, 1503, 1368, 1258 cm-1; MS (ESI, m/z) 536.1
(M + Na)+; HRMS (ESI, m/z) calcd for C29H36NO5NaCl (M +
Na)+ 536.2180, found 536.2200.
ing to room temperature. After 2 h, the solution was concen-
trated and then reconcentrated with dry toluene to give a white
solid. The crude solid was dissolved in 15 mL of DMF, and to
this solution was added 68 mg (0.2 mmol) of FDPP in 10 mL of
DMF followed by 74 µL (0.43 mmol) of diisopropylethylamine.
The yellow solution was stirred at 23 °C under argon. After 12
h, 40 mL of ethyl acetate was added. The organic layer was
washed with 40 mL of 1 N HCl, 40 mL of H2O, and 40 mL of
brine and finally dried over Na2SO4. After filtration and
concentration the crude product was purified by flash silica gel
chromatography (45% to 60% ethyl acetate/hexanes) to give 57
(2S)-2-[3′(ter t-Bu t yloxyca r b on yl)a m in o-2′,2′-d im et h yl-
p r op a n oyloxy]-4-m eth ylp en ta n oic Acid (5). To a stirring
solution of 143 mg (0.76 mmol) of BOC-protected amino acid 16
and 116 mg (0.52 mmol) of benzyl ester 17 in 12 mL of CH2Cl2
at 0 °C were added 148 mg (0.77 mmol) of EDCI and 95 mg (0.77
mmol) of DMAP. Stirring was continued at 23 °C for 17 h. After
this period, 10 mL of water and 10 mL of CH2Cl2 were added.
The layers were separated, and the organic layer was washed
with 10% aqueous HCl, saturated NaHCO3 solution, and brine.
The solution was dried over Na2SO4, filtered, and concentrated.
The residue was purified by flash silica gel chromatography (8%
mg (61% yield) of macrolactam as a white amorphous solid. [R]23
D
+26.2 (c 0.5); [lit.16 [R]23 +26.4 (c 0.25, CHCl3)]; H NMR (400
1
D
MHz, CDCl3) δ 7.21-7.33 (m, 6H), 7.2 (d, 1H, J ) 1.9), 7.05 (dd,
1H, J ) 2.0, 8.4), 6.84 (d, 1H, J ) 8.4), 6.77 (ddd, 1H, J ) 4.4,
10.8, 15.1), 6.4 (d, 1H, J ) 15.8), 6.01 (dd, 1H, J ) 8.8, 15.8),
5.75 (d, 1H, J ) 15.2), 5.56 (d, 1H, J ) 7.8), 5.05 (m, 1H), 4.84
(dd, 1H, J ) 3.4, 10.1), 4.74 (dd, 1H, J ) 6.6, 13.3 Hz), 3.87 (s,
3H), 3.41 (dd, 1H, J ) 8.6, 13.5), 3.12 (d, 1H, J ) 3.3 Hz), 3.07-
3.09 (m, 2H), 2.55 (m, 2H), 2.38 (ddd, 1H, J ) 11, 11.3, 14.3),
1.66 (m, 1H), 1.61 (m, 1H), 1.32 (ddd, 1H, J ) 3.5, 8.4, 13.2),
1.22 (s, 3H), 1.15 (s, 3H), 1.13 (d, 3H, J ) 6.9), 0.73 (d, 3H, J )
6.9), 0.72 (d, 3H, J ) 6.9); 13C NMR (100 MHz, CDCl3) δ 178,
170.5, 170.2, 165, 154, 142.2, 136.5, 131.7, 130.8, 130.1, 129.5,
128.5, 128.2, 127.5, 126.1, 124.4, 122.5, 112.2, 77, 71.4, 56.1, 54.2,
46.4, 42.6, 42.2, 39.4, 36.5, 35.2, 24.5, 22.8, 22.7, 22.6, 21.1, 17.3;
EtOAc/hexanes) to give 172 mg (78%) of ester product as a yellow
1
oil. [R]23 -40.5 (c 0.64, CHCl3); H NMR (400 MHz, CDCl3) δ
D
7.36 (m, 5H), 5.41 (t, 1H, J ) 6.3), 5.18 (dd, 2H, J ) 12.2, 24),
5.09 (dd, 1H, J ) 3.6, 9.8), 3.28 (m, 2H), 1.81 (m, 1H), 1.76-
1.62 (m, 2H), 1.43 (s, 9H), 1.20 (s, 6H), 0.92 (dd, 6H, J ) 6.3,
10.0); 13C NMR (100 MHz, CDCl3) δ 176.4, 170.8, 156.3, 135.0,
128.5, 128.4, 128.3, 78.9, 70.8, 67.1, 48.5, 43.9, 39.3, 28.3, 24.7,
23.0, 22.9, 22.2, 21.4; IR (neat) 3392, 1737, 1721, 1510 cm-1
.
A mixture of 778 mg (1.85 mmol) of the above ester and 81
mg of 10% Pd-C in 25 mL of ethyl acetate was stirred at 23 °C
under a H2 balloon for 1.5 h. The mixture was then filtered
through Celite and concentrated. The crude product was sub-
jected to flash silica gel chromatography (10% MeOH/CH2Cl2)
IR (neat) 3413, 3276, 1747, 1721, 1658, 1536, 1504, 1259 cm-1
;
MS (ESI, m/z) 675.3 (M + Na)+; HRMS (ESI, m/z) calcd for
C36H45N2O7NaCl (M + Na)+ 675.2813, found 675.2822.
to give the acid 5 in quantitative yield as a colorless oil. [R]23
D
-32.5 (c 0.55, MeOH); lit.5 [R]23 -29.9 (c 1.1, MeOH); 1H NMR
Cr yp top h ycin 52 (2). To a stirring solution of 53 mg (0.08
mmol) of macrolactam 17 in 5 mL of CH2Cl2 at 0 °C was added
29 mg (0.17 mmol) of m-CPBA. After dissolution, the ice bath
was removed, and stirring was continued with warming to 23
°C for 12 h. The solution was diluted with 25 mL of ethyl acetate,
and the organic layer was washed successively with 10 mL of
5% NaHCO3 solution, 10 mL of water, and 10 mL of brine. After
drying over Na2SO4, filtration, and concentration, the crude
D
(400 MHz, CDCl3) δ 5.4 (m, 1H), 5.08 (dd, 1H, J ) 3.4, 9.7), 3.28
(m, 2H), 1.7-1.9 (m, 3H), 1.42 (s, 9H), 1.22 (s, 3H), 1.20 (s, 3H),
0.97 (d, 3H, J ) 6.3 Hz), 0.93 (d, 3H, J ) 6.1); 13C NMR (100
MHz, CDCl3) δ 176.5, 175.5, 156.5, 79.1, 70.5, 48.5, 43.9, 39.4,
28.3, 24.7, 23.1, 22.1, 21.3; IR (neat) 3349, 1725, 1672, 1524,
1368 cm-1; MS (ESI m/z) 354.2 (M + Na)+.
(2S)-2-(3-ter t-Bu t oxyca r b on yla m in o-2,2-d im et h yl-p r o-
p ion yloxy)-4-m et h yl-p en t a n oic Acid (1S,2R,2E)-1-{3-[1-
ter t-Bu toxyca r bon yl-(2R)-2-(3-ch lor o-4-m eth oxy-p h en yl)-
et h ylca r b a m oyl]-a llyl}-2-m et h yl-4-p h en yl-b u t -(3E)-en yl
Ester (18). To a stirring solution of 117 mg (0.48 mmol) of 2,4,6-
trichlorobenzoyl chloride in 5 mL of THF was added 139 mg (0.42
mmol) of acid 5 in 15 mL of THF followed by 78 µL (0.56 mmol)
of Et3N. The resulting mixture was continued to stir at 23 °C
for 3.5 h and then concentrated.
1
product (a 2:1 mixture of epoxides by H NMR) was purified by
reverse-phase HPLC (YMC ODS-AQ S5 120 Å, 4.6 mm × 250
mm, 45% H2O/CH3CN, λ ) 254 nm, 0.9 mL/min; Cryptophycin
52 (2) retention time ) 53.35 min; Cryptophycin epoxide
diastereomer, retention time ) 58.25 min, in (38 mg) 70% yield.
Cryptophycin 52 (white amorphous solid). [R]23 +20 (c 0.08);
D
[lit.16 [R]23 +19.9 (c 0.5, CHCl3)]; 1H NMR (400 MHz, CDCl3) δ
D
7.33-7.39 (m, 3H), 7.20-7.26 (m, 3H), 7.19 (d, 1H, J ) 2.0),
7.05 (dd, 1H, J ) 1.9, 8.4), 6.84 (d, 1H, J ) 8.4), 6.76 (ddd, 1H,
J ) 4.3, 10.7, 15), 5.71 (d, 1H, J ) 15.2), 5.44 (d, 1H, J ) 7.8
Hz), 5.21 (dd, 1H, J ) 4.7, 9.6 Hz), 4.82 (dd, 1H, J ) 3.4, 10.1),
4.74 (dd, 1H, J ) 6.4, 14 Hz), 3.88 (s, 3H), 3.68 (d, 1H, J ) 1.6),
3.42 (dd, 1H, J ) 8.7, 13.5), 3.11 (d, 1H, J ) 3.3), 3.08 (d, 2H, J
) 5.7), 2.92 (dd, 1H, J ) 1.7, 7.6), 2.58 (m, 1H), 2.45 (ddd, 1H,
J ) 10.9, 11, 14.4), 1.78 (m, 1H), 1.72 (m, 1H), 1.67 (m, 1H),
1.32 (m, 1H), 1.22 (s, 3H), 1.16 (s, 3H), 1.14 (d, 3H, J ) 7.5),
0.85 (d, 3H, J ) 6.6), 0.83 (d, 3H, J ) 6.6); 13C NMR (100 MHz,
CDCl3) δ 178.1, 170.5, 170.2, 164.9, 154.1, 141.9, 136.7, 130.9,
129.3, 128.7, 128.6, 128.3, 125.6, 124.6, 122.6, 112.3, 75.9, 71.2,
63.1, 59.1, 56.1, 54.2, 46.4, 42.7, 40.7, 39.3, 36.9, 35.3, 24.6, 22.9,
22.8, 22.7, 21.2, 13.7; IR (neat) 3409, 3263, 1747, 1719, 1653,
1539, 1505, 1259 cm-1; MS (ESI, m/z) 691.3 (M + Na)+; HRMS
(ESI, m/z) calcd for C36H45N2O8NaCl (M + Na)+ 691.2762, found
691.2767.
To a stirring mixture of crude mixed anhydride in 5 mL of
toluene was added 185 mg (0.36 mmol) of 15 in 8.5 mL of toluene,
56 µL (0.4 mmol) of Et3N, and finally 5.5 mg (0.04 mmol) of
DMAP. The mixture was stirred at 23 °C under N2 for 30 min.
After this period, 10 mL of 0.1 N HCl followed by 15 mL of ethyl
acetate were added. The layers were separated, and the organic
layer was washed with 5 mL of brine, dried over Na2SO4, and
concentrated. The crude product was purified by flash silica gel
chromatography (25% and 30% ethyl acetate/hexanes) to give
229 mg of 18 as a white solid in 77% yield. Mp 45-47 °C [R]23
D
1
-23 (c ) 1.0, CHCl3); H NMR (400 MHz, CDCl3) δ 7.28-7.33
(m, 4H), 7.22 (m, 1H), 7.15 (d, 1H, J ) 1.9), 7.02 (dd, 1H, J ) 2,
8.5), 6.84 (d, 1H, J ) 8.5), 6.82 (m, 1H), 6.42 (d, 1H, J ) 15.7),
6.41 (d, 1H, J ) 7.7), 6.02 (dd, 1H, J ) 8.6, 15.7), 5.89 (d, 1H, J
) 15.6), 5.44 (t, 1H, J ) 6.5), 5.05 (td, 1H, J ) 5.9, 6.0), 4.93
(dd, 1H, J ) 3.6, 9.6), 4.78 (dd, 1H, J ) 5.8, 13.3), 3.85 (s, 3H),
3.26 (d, 2H, J ) 6.6), 3.04 (m, 2H), 2.63 (m, 1H), 2.54 (m, 2H),
1.64-1.76 (m, 2H), 1.55 (m, 1H), 1.43 (s, 9H), 1.42 (s, 9H), 1.20
(s, 3H), 1.15 (s, 3H), 1.11 (d, 3H, J ) 6.9), 0.86 (d, 3H, J ) 6.4),
0.82 (d, 3H, J ) 6.4); 13C NMR (100 MHz, CDCl3) δ 176, 170.8,
170.3, 165, 156.5, 153.9, 139, 136.9, 131.7, 131.4, 130.1, 129.5,
128.8, 128.6, 127.5, 126.2, 125.8, 121.9, 111.8, 82.5, 79, 76.5, 71.2,
56.1, 53.7, 48.6, 44, 40.9, 39.5, 36.9, 33.5, 28.4, 28, 24.8, 23.0,
22.8, 22.3, 21.4, 16.7; IR (neat) 3378, 1731, 1677, 1503, 1366,
1257 cm-1; MS (ESI, m/z) 849.3; HRMS (ESI, m/z) calcd for
C45H63N2O10ClNa (M + Na)+ 849.4069, found 849.4095.
Ack n ow led gm en t. This research was supported in
part by the National Institutes of Health.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
1
tails for compounds 4, 9-11, H NMR and 13C NMR spectra
for compounds 2, 4, 5, 9-11, 13, 15, and 18-19. This material
is available free of charge via the Internet at http://pubs.acs.org.
Cr yp top h ycin 51 (19). To a stirring solution of 117 mg (0.14
mmol) of 18 in 3 mL of CH2Cl2 at 0 °C was added 1.6 mL (20.8
mmol) of CF3COOH slowly. Stirring was continued with warm-
J O035077V
9826 J . Org. Chem., Vol. 68, No. 25, 2003