Total synthesis of calyculin C

Article abstract of DOI:10.1021/ja980836q

The study of phosphatases continues to flourish given their prominence in signal transduction pathways and the regulation of cell function. Our research efforts in this area focus on the potent inhibition of serine/threonine phosphatases, PP1 and PP2A, by

Full text of DOI:10.1021/ja980836q

J. Am. Chem. Soc. 1998, 120, 12435-12442
12435
Total Synthesis of Calyculin C
Anthony K. Ogawa1 and Robert W. Armstrong*,2
Contribution from the Department of Chemistry and Biochemistry, UniVersity of California,
Los Angeles, California 90095
ReceiVed March 13, 1998
Abstract: The study of phosphatases continues to flourish given their prominence in signal transduction pathways
and the regulation of cell function. Our research efforts in this area focus on the potent inhibition of serine/
threonine phosphatases, PP1 and PP2A, by a structurally diverse class of natural products. We herein report
the completed total synthesis of the serine/threonine phosphatase inhibitor calyculin C (1) as part of an ongoing
effort to elucidate key structural requirements for phosphatase inhibition by the aforementioned diverse class
of natural products. Synthetic issues addressed include (1) the remote protecting group effect on Brown
crotylboration diastereoselectivity during the introduction of the C10-C11 stereocenters and (2) the formation
of the C25-C26 double bond using a fully deprotected C26-C37 phosphonium salt (3). In addition, the concurrent
synthesis of 34R-calyculin C (29) clarified our previous C34-stereochemical assignment of C26-C37 phosphonium
salts (3 and 27) (Ogawa, A. K.; DeMattei, J. A.; Scarlato, G. R.; Tellew, J. E.; Chong, L. S.; Armstrong, R.
W. J. Org. Chem. 1996, 61, 6153).
The study of phosphatases continues to flourish given their
prominence in signal transduction pathways and the regulation
of cell function.3 Our research efforts in this area focus on the
potent inhibition of serine/threonine phosphatases, PP1 and
PP2A, by a structurally diverse class of natural products.4 In a
previous paper, we proposed a computationally derived enzyme-
inhibitor model that identified structural motifs common to all
PP1 and PP2A natural product inhibitors.5 (See Figure 2)
Within this class of inhibitors, the calyculins6 have attracted
extensive synthetic interest due to their diverse functionality7-9
(see Figure 1). We herein report the completed total synthesis
of the serine/threonine phosphatase inhibitor calyculin C (1) as
part of an ongoing effort to elucidate key structural requirements
for phosphatase inhibition by the aforementioned diverse class
of natural products.
Retrosynthetic analysis yielded an initial disconnection at the
C25-C26 double bond that subdivided calyculin into two
fragments of approximately equal functional complexity (2 and
3)10 (see Scheme 1). Previous synthetic papers outlined a
strategy for C25-C26 double bond construction via Wittig
olefination with a fully deprotected C26-C37 phosphonium salt.7a
Model studies affirmed the viability of this approach which
circumvented downstream protecting group manipulations with
respect to the C26-C37 fragment synthesis. Finally, elaboration
(1) Taken in part from the Ph.D. Thesis of Anthony K. Ogawa, University
of California, Los Angeles, 1997. Present address: The Scripps Research
Institute, La Jolla, CA.
(2) Present address: Amgen Inc., Thousand Oaks, CA.
(3) Wera, S.; Hemmings, B. A. Biochem. J. 1995, 311, 17, and references
therein.
(4) (a) Ishihara, H.; Martin, B. L.; Brautigan, D. L.; Karaki, H.; Ozaki,
H.; Kato, Y.; Fusetani, N.; Watabe, S.; Hashimoto, K.; Uemura, D. Biochem.
Biophys. Res. Commun. 1989, 159, 871. (b) MacKintosh, C.; Klumpp, S.
FEBS Lett. 1990, 277, 137. (c) Honkanen, R. E.; Dukelow, M.; Zwiller, J.;
Moore, R. E.; Khatra, B. S.; Boynton, A. L. Mol. Pharm. 1991, 40, 577.
(d) Honkanen, R. E.; Zwiller, J.; Moore, R. E.; Daily, S. L.; Khatra, B. S.;
Dukelow, M.; Boynton, A. L. J. Biol. Chem. 1990, 265, 19401. (e) Dilip
de Silva, E.; Williams, D. E.; Andersen, R. J.; Klix, H.; Holmes, C. F. B.;
Allen, T. M. Tetrahedron Lett. 1992, 33, 1561.
(9) For other synthetic efforts toward the calyculins: (a) Evans, D. A.;
Gage, J. R.; Leighton, J. L. J. Org. Chem. 1992, 57, 1964. (b) Evans, D.
A.; Gage, J. R.; Leighton, J. L.; Kim, A. S. J. Org. Chem. 1992, 57, 1961.
(c) Evans, D. A.; Gage, J. R. J. Org. Chem. 1992, 57, 1958. (d) Evans, D.
A.; Gage, J. R.; Tetrahedron Lett. 1990, 31, 6129. (e) Vaccaro, H. A.; Levy,
D. E.; Sawabe, A.; Jaetsch, T.; Masamune, S. Tetrahedron Lett. 1992, 33,
1937. (f) Duplanter, A. J.; Nantz, M. H.; Roberts, J. C.; Short, R. P.; Somfai,
P.; Masamune, S. Tetrahedron Lett. 1989, 30, 7357. (g) Kabeya, M.;
Hamada, Y.; Shioiri, T. Tetrahedron 1997, 53, 9777. (h) Kabeya, M.;
Hamada, Y.; Shioiri, T. Tetrahedron 1997, 53, 9769. (i) Yokokawa, F.;
Hamada, Y.; Shioiri, T. Chem. Commun. 1996, 871. (j) Yokokawa, F.;
Hamada, Y.; Shioiri, T. Tetrahedron Lett. 1993, 34, 6559. (k) Yokokawa,
F.; Hamada, Y.; Shioiri, T. Synlett. 1992, 149. (l) Hara, O.; Hamada, Y.;
Shioiri, T. Synlett. 1991, 283. (m) Smith, A. B., III; Iwashima, M.
Tetrahedron Lett. 1994, 35, 6051. (n) Salvatore, B. A.; Smith, A. B., III.
Tetrahderon Lett. 1994, 35, 1329. (o) Smith, A. B., III; Salvatore, B. A.;
Hull, K. G.; Duan, J. J.-W. Tetrahedron Lett. 1991, 32, 4859. (p) Smith,
A. B., III; Duan, J. J.-W.; Hull, K. G.; Salvatore, B. A. Tetrahedron Lett.
1991, 32, 4855. (q) Barrett, A. G. M.; Edmunds, J. J.; Hendrix, J. A.;
Malecha, J. W.; Parkinson, C. J. J. Chem. Soc., Chem. Commun. 1992,
1240. (r) Barrett, A. G. M.; Edmunds, J. J.; Hendrix, J. A.; Horita, K.;
Parkinson, C. J. J. Chem. Soc., Chem. Commun. 1992, 1238. (s) Barrett,
A. G. M.; Edmunds, J. J.; Horita, K.; Parkinson, C. J. J. Chem. Soc., Chem.
Commun. 1992, 1236. (t) Barrett, A. G. M.; Malecha, J. W. J. Org. Chem.
1991, 56, 5243. (u) Koskinen, A. M. P.; Pihko, P. M. Tetrahedron Lett.
1994, 35, 7417. (v) Koskinen, A. M. P.; Chen, J. Tetrahedron Lett. 1991,
32, 6977. (w) Trost, B. M.; Flygare, J. A. Tetrahedron Lett. 1994, 35, 4059.
(10) The structure of 3 was previously assigned in ref 7a as its C34-
epimer.
(5) Gupta, V.; Ogawa, A. K.; Du, X.; Houk, K. N.; Armstrong, R. W. J.
Med. Chem. 1997, 40, 3199.
(6) (a) Kato, Y.; Fusetani, N.; Matsunaga, S.; Hashimoto, K.; Fujita, S.;
Furuya, T. J. Am. Chem. Soc. 1986, 108, 2780. (b) Kato, Y.; Fusetani, N.;
Matsunaga, S.; Hashimoto, K.; Koseki, K. J. Org. Chem. 1988, 53, 3930.
(c) Matsunaga, S.; Fujiki, H.; Sakata, D. Tetrahedron 1991, 47, 2999. (d)
Matsunaga, S.; Wakimoto, T.; Fusetani, N. J. Org. Chem. 1997, 62, 2640.
(e) Matsunaga, S.; Wakimoto, T.; Fusetani, N.; Suganuma, M. Tetrahedron
Lett. 1997, 38, 3763.
(7) Preliminary work from this laboratory: (a) Ogawa, A. K.; DeMattei,
J. A.; Scarlato, G. R.; Tellew, J. E.; Chong, L. S.; Armstrong, R. W. J.
Org. Chem. 1996, 61, 6153. (b) Scarlato, G. R.; DeMattei, J. A.; Chong, L.
S.; Ogawa, A. K.; Lin, M. R.; Armstrong, R. W. J. Org. Chem. 1996, 61,
6139. (c) Zhao, Z.; Scarlato, G. R.; Armstrong, R. W. Tetrahedron Lett.
1992, 33, 1609. (d) Armstrong, R. W.; DeMattei, J. A. Tetrahedron Lett.
1992, 33, 5749.
(8) Previous total syntheses of calyculin A: (a) Evans, D. A.; Gage, J.
R.; Leighton, J. L. J. Am. Chem. Soc. 1992, 114, 9434. (b) Tanimoto, N.;
Gerritz, S. W.; Sawabe, A.; Noda, T.; Filla, S. A.; Masamune, S. Angew.
Chem. 1994, 106, 674.
10.1021/ja980836q CCC: $15.00 © 1998 American Chemical Society
Published on Web 11/20/1998

12436 J. Am. Chem. Soc., Vol. 120, No. 48, 1998
Ogawa and Armstrong
Scheme 2
Figure 1.
Scheme 3
Scheme 1
submission to an asymmetric Brown crotylboration reaction,11
afforded olefin 7 as the sole reaction product. This result was
consistent with the Brown algorithm that predicted an anti-
stereochemical relationship for the C12-methyl and C13-hydroxyl
given trans-2-butene as the carbon input. Confirmation of this
assignment arose later through comparison with previously
characterized intermediates7b (see Scheme 2).
The C13-hydroxyl of olefin 7 was readily protected as either
a silyl ether (8) or benzoate ester (9). Ozonolysis of olefin 8,
again followed by Brown crotylboration,11 yielded a single
alkylated reaction product (10). The drastic change in diaste-
reoselectivity from previous results on this section of calyculin
raised suspicion regarding the identity of the newly generated
C10,C11 stereocenters (see Scheme 3).
of the C17-hydroxyl late in the C1-C25 fragment synthesis, as
precedented by Evans and co-workers,8a imparted the requisite
flexibility to explore alternate functional groups at this position.
Modification at this specific location appealed due to the
potential significance of the phosphate toward tertiary structure
organization and/or direct active site interactions. Of interest
was the apparently conflicting evidence regarding the role of
the aforementioned phosphoryl moiety. Examination of the
calyculin A crystal structure suggested a significant role in
molecular folding, which should logically enhance activity by
limiting the entropic cost upon binding. However, Fusetani
recently reported that C17-desphosphoryl calyculin A was
approximately as equipotent as phosphorylated calyculins,6e thus
raising an interesting issue regarding the natural selection for
such an unusual functionalization.
To assign the newly generated stereocenters, acetonide
formation on the C11,C13-diol was effected to utilize the
Rychnovsky correlation for deducing 1,3-diol stereochemical
relationships.12 The determination of stereochemistry followed
from the comparison of the 13C chemical shifts for the 1,3-O-
acetonide methyl groups of the 1,3-dioxane system, which has
been shown to be generally independent of C2-substitution. To
this end, olefin 10 was fully desilylated to afford tetrol 11. The
reaction of tetrol 11 in 2,2-dimethoxypropane in the presence
of catalytic acid afforded acetonides 12 and 13, the latter of
which could be readily converted to the desired mono-ketal
product via mild acid hydrolysis. Analysis of the 13C spectrum
for 12 confirmed an anti-stereochemical relationship based on
the observed resonances, 23.7 and 24.5 ppm. Evidently, the
â-hydroxyl protecting group played a significant role in the
asymmetric induction at C11 that completely overrode the
induction predicted for the Brown crotylboration!11 Indeed, the
overwhelming preference for the anti-syn-anti relationship
Prefacing the completion of the total synthesis were efforts
to improve our synthesis of the C1-C25 fragment (2). Targets
of refinement included (1) an upstream conversion to a global
silyl protecting group strategy that reduced the number of linear
synthetic steps and (2) improving the selectivity during the
introduction of the C10,C11-propionate unit. The switch to a
global silyl protecting group strategy proceeded from spiroketal
4 with the deprotection of both the TPS and benzoate protecting
groups to afford diol 5. Silylation yielded core structure 6 in
high yield, thereby completing the protecting group exchange.
Ozonolysis afforded an aldehyde intermediate that, upon
(11) Representative references: (a) Brown, H. C.; Bhat, K. S. J. Am.
Chem. Soc. 1986, 108, 293. (b) Brown, H. C.; Jadhav, P. K.; Bhat, K. S. J.
Am. Chem. Soc. 1988, 110, 1535.
(12) Rychnovsky, S. D.; Rogers, B.; Yang, G. J. Org. Chem. 1993, 58,
3511.

Total Synthesis of Calyculin C
J. Am. Chem. Soc., Vol. 120, No. 48, 1998 12437
Figure 2.
Scheme 5
Figure 3.
Scheme 4
stereomer to their corresponding tetra-TBS derivatives (21 and
22) and comparison to previously reported compound7b (see
Scheme 7).
Despite the obvious effect of the â-alkoxy protecting group
on stereoselectivity, the discrepancy between the diastereomeric
ratios of 14a:14b and 20a:20b suggested that the remote
protecting groups at C21 and C25 also impacted the crotylboration
diastereoselectivity. This subtle steric effect arose from the
R-stereochemistry at C16, which projected the reaction site (C11)
toward the aforementioned alkoxy groups (protected C21 and
C25). Illustration of this point derived from the effect of a C25-
hydroxyl TBS for TPS exchange on diastereoselectivity at
C10,C11. Spiroketal 4 was converted to its C25-TBS protected
derivative (16) in excellent yield. An initial ozonolysis-Brown
crotylboration sequence yielded, as expected, a single reaction
product (17), the C13-hydroxyl of which was benzoyl-protected
(18). The subsequent ozonolysis-Brown crotylboration sequence
led to a modest reversal of distereoselectivity to yield homo-
allylic alcohols 19a and 19b in a 35:39 ratio, respectively.
Clearly, a definite and remarkable trend exists in which variation
observed for C10-C13 in 10 was consistent with the closed
transition state model of Roush13 (see Scheme 4).
This result represented a drastic departure from our previously
reported synthesis of the C1-C25 fragment, in which the anti-
anti-anti isomer was preferentially generated by a 40:30
diastereomeric ratio (20a:20b, respectively)7b (see Figure 3).
The aldehyde used in that Brown crotylboration was benzoyl-
protected at C13, which prompted the submission of olefin 9 to
a similar ozonolysis-Brown crotylboration sequence. This
yielded the desired anti-anti-anti diastereomer 14a, but as the
minor component in a 22:31 diastereomeric mixture (14a and
14b) favoring the anti-syn-anti isomer. Positive structural
assignments were made through the conversion of each dia-
(13) Roush, W. R. J. Org. Chem. 1991, 56, 4151.

12438 J. Am. Chem. Soc., Vol. 120, No. 48, 1998
Ogawa and Armstrong
Table 1
Scheme 7
R1
R2
R3
yield of A/B
10
14
19
20
TBS
Bz
Bz
TBS
TBS
Bz
TBS
TBS
TBS
TPS
0/48
22/31
35/39
40/30
Bz
Bz
Scheme 8
Scheme 6
fragment. Condensation of the deprotected phosphonium salt
derived from the major amide stereoisomer with aldehyde 26
proceeded in good yield. Submission of the corresponding
Wittig adduct to HF-deprotection afforded a TLC spot that failed
to coelute with an authentic sample of calyculin C. 1H NMR
and HRMS analysis of the resultant product confirmed its
identity as a fully deprotected system. This evidence supported
our structural assignment of 29 as C34-epi-calyculin C and the
major Weinreb amidation product as stereoisomer 27 (see
Scheme 9).
Condensation of the phosphonium salt from the minor
amidation product (3) with aldehyde 26 proceeded in acceptable
yield to protected calyculin 30. Deprotection of 30 under the
previously employed reaction conditions generated a TLC spot
that co-spotted with an authentic sample in multiple solvent
systems.17 1H NMR18 and HRMS data were consistent with
the aforementioned authentic calyculin C sample, which cor-
roborated our structural assignments of compounds 27-30 and
represented the completed total synthesis of calyculin C (1) (see
Scheme 10).
of proximal and remote protecting groups affected the crotyl-
boration diastereoselectivity! (see Table 1)
The conversion of anti-anti-anti olefin isomers (14a and 19a)
to a common tetra-TBS protected compound (21) enabled the
conclusive assignment of stereochemistry at C10-C13 and
established the desired global silyl protection scheme. Elabora-
tion to tetraene 23 over four steps followed a previously
established route.7b,8a Phosphorylation afforded 24 in good yield
using the Evans procedure8a (see Scheme 2). Selective depro-
tection of the C25-TBS group (25), followed by Dess-Martin
oxidation of the corresponding primary hydroxyl14 provided
aldehyde 26 and completed the C1-C25 fragment synthesis
(see Scheme 8).
In our previously reported synthesis of the C26-C37 fragment,7a
Weinreb amidation15 to generate the C33-N3 amide bond
resulted in a C34-epimeric mixture of products,16 which we were
unable to definitively assign. Consequently, both diastereomers
were carried on into coupling reactions with the C1-C25
In summary, our pursuit of an improved synthesis for the
C1-C25 fragment exposed a remarkable, remote protecting group
effect on the diastereoselectivity that was observed during the
(17) The solvent systems sampled were (a) 10% acetone:ethyl acetate
(Rf ) 0.7), (b) 30% acetone:hexane (double elution; Rf ) 0.3), (c) 20%
acetonitrile:methylene chloride (double elution; Rf ) 0.6), and (d) 5%
methanol:methylene chloride (double elution; Rf ) 0.4).
(18) 1H NMR data for authentic and synthetic calyculin C were obtained
in both CDCl3 and C6D6.
(14) Meyer, S. D.; Schreiber, S. L. J. Org. Chem. 1994, 59, 7549.
(15) Basha, A.; Lipton, M.; Weinreb, S. M. Tetrahedron Lett. 1977, 4171.
(16) Noteworthy is our ability to recycle recovered ester from the Weinreb
amidation. The diastereoselectivity of the amidation is not affected by the
corresponding epimeric mixture present in the ester starting material.

Total Synthesis of Calyculin C
J. Am. Chem. Soc., Vol. 120, No. 48, 1998 12439
Dichloromethane was distilled from phosphorus pentoxide. Methanol
was distilled from magnesium turnings. Dimethylformamide, dimethyl
sulfoxide, and in some cases diisopropylamine were distilled from
barium oxide and stored over 4 Å molecular sieves. All reactions
involving moisture-sensitive reagents were performed under either a
nitrogen or an argon atmosphere.
Scheme 9
(2R,3R,5R,7S,8R,9R)-9-Hydroxy-7-(2-hydroxyethyl)-2-[(1S)-meth-
oxy-but-3ene]-3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-1,6-
dioxaspiro[4.5]decane (5). To a solution of benzoate 4 (1.60 g, 2.06
mmol, 1.0 equiv) in CH2Cl2 (45 mL) at -78 °C was added allylmag-
nesium bromide (1.0 M in diethyl ether, 15 mL, 7.25 equiv) rapidly
dropwise. The cloudy white reaction mixture was warmed to room
temperature over 30 min. The reaction was quenched via addition of
H2O (10 mL), and the resulting suspension was filtered. The solid
residue was washed with CH2Cl2 (3 × 40 mL), and the filtrate was
partitioned between CH2Cl2 (20 mL) and brine (60 mL). The layers
were separated, and the aqueous layer was extracted with CH2Cl2 (3
× 40 mL). The combined organic layers were dried over Na2SO4,
filtered, and concentrated.
The resulting crude, yellow oil was eluted in THF (50 mL), and
TBAF (1.0 M in THF, 2.5 mL, 1.2 equiv) was added. After 16 h, the
reaction mixture was concentrated, and column chromatography on
silica gel (70-100% ethyl acetate-hexane) afforded diol 5 (804 mg,
90%). [R]D ) -64.5 (c 5.0, CHCl3). IR (thin film) 3501, 2924, 1472,
1419 cm-1 1H NMR (500 MHz, CDCl3) δ 5.87 (1H, m), 5.10 (1H,
.
Scheme 10
dd, J ) 17.2, 1.2 Hz), 5.06 (1H, m), 4.71 (2H, s), 4.47 (1H, dt, J )
11.2, 2.0 Hz), 4.16 (1H, dd, J ) 9.1, 4.9 Hz), 4.06 (1H, dd, J ) 11.1,
1.1 Hz), 3.80 (2H, m), 3.71 (4H, m), 3.52, (3H, s), 3.48 (2H, m), 3.33
(3H, s), 2.47 (1H, m), 2.17 (1H, m), 1.91 (1H, m), 1.78 (1H, d, J )
13.7 Hz), 1.63 (1H, m), 1.57 (1H, m, J ) 14.2 Hz), 1.38 (1H, m), 1.06
(3H, s), 0.90 (3H, s), 0.84 (3H, d, J ) 7.1 Hz). 13C NMR (125 MHz,
CDCl3) δ 134.1, 117.3, 108.2, 97.3, 86.7, 83.4, 80.0, 71.5, 70.5, 69.9,
68.5, 63.5, 59.0, 58.9, 50.5, 38.1, 34.8, 34.4, 28.8, 22.9, 17.5, 10.8.
HRFABMS calcd for (M + H) C22H41O8: 433.2801, found: 433.2807.
(2R,3R,5R,7S,8R,9R)-9-tert-Butyldimethylsiloxy-7-(2-tert-butyl-
dimethylsiloxyethyl)-2-[(1S)-methoxy-but-3ene]-3-(2-methoxyethoxy-
methyl)oxy-4,4,8-trimethyl-1,6-dioxaspiro[4.5]decane (6). To a so-
lution of diol 5 (50 mg, 0.116 mmol, 1.0 equiv) in CH2Cl2 (5 mL) at
0 °C was added 2,6-lutidene (81 µL, 0.693 mmol, 6 equiv). TBSOTf
(80 µL, 0.347 mmol, 3 equiv) was added dropwise, and the clear
reaction mixture was stirred at 0 °C for 15 min. Saturated aqueous
NaHCO3 (2 mL) was added, and the resulting mixture was partitioned
between CH2Cl2 (20 mL) and brine (15 mL). The layers were separated,
and the aqueous layer was extracted with CH2Cl2 (2 × 30 mL). The
combined organics were dried over Na2SO4, filtered, and concentrated.
Purification via column chromatography on silica gel (10% ethyl
acetate-hexane) afforded silyl ether 6 (70 mg, 92%). [R]D ) -75.8
(c 3.6, CHCl3). IR (thin film) 2928, 1471, cm-1 1H NMR (400 MHz,
.
CDCl3) δ 5.87 (1H, m), 5.07 (1H, dd, J ) 17.2, 1.7 Hz), 5.00 (1H, m),
4.70 (1H, d, J ) 13.1 Hz), 4.67 (1H, d, J ) 13.1 Hz), 4.34 (1H, dt, J
) 10.6, 2.3 Hz), 4.02 (1H, dd, J ) 9.2, 5.2 Hz), 3.90 (1H, ddd, J )
15.5, 10.4, 5.1 Hz), 3.78 (1H, m), 3.62-3.70 (4H, m), 3.59 (3H, s),
3.49 (2H, m), 3.38 (1H, dd, J ) 9.3, 2.3 Hz), 3.35 (3H, s), 2.34 (1H,
m), 2.04 (1H, m), 1.72 (1H, m), 1.60 (1H, dd, J ) 14.3, 3.8 Hz), 1.36-
1.44 (3H, m), 1.00 (3H, s), 0.88 (9H, s), 0.85 (9H, s), 0.78 (3H, d, J
generation of the C10,C11-propionate stereocenters. In addition,
we were able to unequivocally assign the stereochemistry at
C34. We, therefore, report the total synthesis of calyculin C, a
member of a family of structurally diverse serine/threonine
phosphatase inhibitors.
) 7.1 Hz), 0.04 (3H, s), 0.03 (3H, s), 0.02 (3H, s), -0.02 (3H, s). 13
C
NMR (125 MHz, CDCl3) δ 135.6, 116.1, 106.8, 97.6, 87.7, 84.1, 81.0,
71.6, 71.2, 68.1, 63.5, 62.1, 60.4, 59.0, 50.5, 38.7, 36.5, 35.7, 30.6,
26.1, 25.8, 23.0, 18.4, 18.1, 17.7, 10.5, -4.7, -5.1, -5.2 (2 carbons).
HRFABMS calcd for (M + H) C34H69O8Si2: 661.4531, found:
661.4529.
(2R,2(1S,3S,4S),3R,5R,7S,8R,9R)-9-tert-Butyldimethylsiloxy-7-(2-
tert-butyldimethylsiloxyethyl)-2-(3-hydroxy-1-methoxy-4-methyl-5-
hexenyl)-3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-1,6-dioxa-
spiro[4.5]decane (7). Ozone was bubbled through a solution of olefin
6 (993 mg, 1.51 mmol, 1.0 equiv) in CH2Cl2 (15 mL) at -78 °C until
a light blue endpoint was achieved. The excess ozone was purged via
a stream of argon (until colorless). Tributylphosphine (350 µL, 1.47
mmol, 0.97 equiv) was added dropwise, and the clear colorless reaction
mixture was warmed slowly to room temperature. After 12.5 h, the
reaction mixture was concentrated to afford a crude aldehyde which
Experimental Section
General Methods. NMR spectra were obtained from Bruker
AM360, ARX400, and ARX500 spectrometers. IR data was collected
on a Nicolet PCIR. Optical rotations were taken at 22 °C on a Perkin-
Elmer model 241MC. High-resolution FAB mass spectra were obtained
by the Mass Spectroscopy Facilities at UCLA or UC-Riverside. For
FAB mass spectra, 2σ ) 4 ppm.
Solvents and reagents were used as supplied from commercial
sources with the following exceptions. All moisture sensitive reagents
not packaged in Aldrich sure seal bottles were distilled prior to use
and stored in a desiccated environment. Particularly sensitive reagents,
such as dimethyl phosphite and phosphorus trichloride, were freshly
distilled prior to each usage. Tetrahydrofuran and diethyl ether were
distilled from sodium benzophenone ketyl immediately prior to use.

12440 J. Am. Chem. Soc., Vol. 120, No. 48, 1998
Ogawa and Armstrong
was carried on without purification. It should be noted that, although
the aldehyde generally withstood column chromatography, purification
did not improve the yields of the subsequent crotylboration reactions.
To a cloudy solution of KOtBu (676 mg, 6.02 mmol, 4.0 equiv)
and trans-2-butene (∼1 mL, excess) in THF (9 mL) at -78 °C was
added dropwise 2.14 M nBuLi (2.4 mL, 5.13 mmol, 3.4 equiv). Upon
initial addition of nBuLi, the reaction mixture became yellow. After,
15 min, a solution of (+)-B-Methoxydiisopinocampheylborane (2.18
g, 6.89 mmol, 4.6 equiv) in THF (2.5 mL) was added dropwise.
Addition of the borane solution resulted in a clear colorless reaction
mixture. After 30 min, BF3-Et2O (820 µL, 6.66 mmol, 4.4 equiv) was
added rapidly, followed immediately by a solution of the crude aldehyde
in THF (2 mL + 0.7 mL rinse). The resulting cloudy, colorless reaction
mixture was stirred at -78 °C for 4 h. Then 3 N NaOH (3 mL) and
30% H2O2 (1.5 mL) were added, and the cold bath was removed. After
3 h, the mixture was diluted with ethyl acetate (20 mL), poured into
brine (20 mL), and the layers were separated. The aqueous layer was
extracted with ethyl acetate (3 × 40 mL), and the combined organics
were dried over Na2SO4, filtered and concentrated. Purification via
column chromatography on silica gel (5% ethyl acetate-hexane)
afforded olefin 7 (714 mg, 66%). [R]D ) -61.7 (c 7.7, CHCl3). IR
initial addition of nBuLi, the reaction mixture became yellow. After,
15 min, a solution of (+)-B-Methoxydiisopinocampheylborane (1.03
g, 3.26 mmol, 5.4 equiv) in THF (1.2 mL) was added dropwise.
Addition of the borane solution resulted in a clear colorless reaction
mixture. After 30 min, BF3-Et2O (350 µL, 2.85 mmol, 4.7 equiv) was
added rapidly, followed immediately by a solution of the crude aldehyde
from above in THF (1.2 mL + 0.5 mL rinse). The resulting cloudy,
colorless reaction mixture was stirred at -78 °C for 4 h. Then 3 N
NaOH (4 mL) and 30% H2O2 (2 mL) were added, and the cold bath
was removed. After 13 h, the mixture was diluted with ethyl acetate
(20 mL) and poured into brine (20 mL), and the layers were separated.
The aqueous layer was extracted with ethyl acetate (3 × 25 mL), and
the combined organics were dried over Na2SO4, filtered, and concen-
trated. The resultant crude was eluted in THF (8 mL), 3 N NaOH (2
mL), and 30% H2O2 (1 mL) to complete oxidation of the borane
intermediate. After 2 h, the mixture was worked-up as previously
mentioned. The excess isopinocamphol was removed via Kugelrohr
distillation (high vacuum pressure at 80 °C). Purification via column
chromatography on silica gel (5-20% ethyl acetate-hexane) afforded
olefins 14a (118 mg, 22%) and 14b (163 mg, 31%) (53% overall for
both steps). For 14a: [R]D ) -59.1 (c 2.4, CHCl3). IR (thin film)
3443, 2928, 1719, 1377 cm-1 1H NMR (500 MHz, CDCl3) δ 8.04
.
(thin film) 3503, 2928, 1472, cm-1 1H NMR (500 MHz, CDCl3) δ
.
(2H, m), 7.54 (1H, m), 7.42 (2H, m), 5.87 (1H, ddd, J ) 17.1, 8.6, 6.6
Hz), 5.64 (1H, m), 5.06 (2H, m), 4.70 (1H, d, J ) 6.8 Hz), 4.65 (1H,
d, J ) 6.8 Hz), 4.34 (1H, m), 4.05 (1H, dd, J ) 9.0, 4.9 Hz), 3.80 (1H,
m), 3.69 (3H, s), 3.35-3.75 (9H, m), 3.33 (3H, s), 2.96 (1H, br d, J )
5.1 Hz), 4.41 (1H, m), 2.12 (1H, ddd, J ) 9.0, 6.9, 3.4 Hz), 1.77 (2H,
m), 1.62 (1H, m), 1.42 (3H, m), 1.16 (3H, d, J ) 6.9 Hz), 1.04 (3H,
s), 0.95 (3H, d, J ) 6.9 Hz), 0.89 (3H, s), 0.88 (3H, s), 0.86 (9H, s),
0.80 (9H, s), 0.79 (3H, d, J ) 5.1 Hz), 0.03 (3H, s), -0.01 (3H, s),
-0.09 (6H, s). 13C NMR (125 MHz, CDCl3) δ 165.8, 139.3, 132.7,
130.9, 129.6, 128.3, 115.8, 107.0, 98.1, 88.1, 84.9, 79.2, 76.6, 73.3,
71.7, 71.2, 68.0, 63.8, 61.3, 60.9, 59.0, 50.4, 40.6, 39.6, 38.3, 36.3,
32.2, 30.8, 29.7, 26.1, 25.9 (two carbons), 23.2, 18.2, 18.2, 18.0, 17.8,
11.6, 10.5, -4.6, -5.1, -5.3 (two carbons). HRFABMS calcd for (M
+ Na) C47H84O11Si2Na: 903.5450, found: 903.5459.
5.83 (1H, ddd, J ) 18.6, 10.7, 7.8 Hz), 5.05 (1H, s), 5.03 (1H, m),
4.70 (1H, d, J ) 6.4 Hz), 4.63 (1H, d, J ) 6.4 Hz), 4.36 (1H, m), 4.12
(1H, dd, J ) 9.4, 5.1 Hz), 3.88 (1H, m), 3.77-3.80 (2H, m), 3.62-
3.72 (6H, m), 3.51 (3H, m), 3.36 (3H, s), 2.82 (1H, d, J ) 5.0 Hz),
2.18 (1H, m), 1.70 (1H, m), 1.57-1.64 (2H, m), 1.38-1.48 (4H, m),
1.02 (3H, d, J ) 7.0 Hz), 1.01 (3H, s), 0.89 (9H, s), 0.88 (9H, s), 0.80
(3H, d, J ) 7.2 Hz), 0.04 (3H, s), 0.03 (3H, s), 0.03 (3H, s), -0.01
(3H, s). 13C NMR (125 MHz, CDCl3) δ 141.0. 115.0, 106.9, 98.1,
88.3, 84.3, 79.4, 71.8, 71.6, 71.2, 68.0, 63.5, 61.8, 60.6, 59.0, 50.5,
44.4, 38.6, 36.5, 35.4, 30.6, 26.0, 25.8, 23.0, 18.3, 18.2, 17.6, 16.0,
10.5, -4.7, -5.1, -5.2, -5.2. HRFABMS calcd for (M + H)
C37H75O9Si2: 719.4949, found: 719.4953.
(2R,2(1S,3S,4S),3R,5R,7S,8R,9R)-9-tert-Butyldimethylsiloxy-7-(2-
tert-butyldimethylsiloxyethyl)-2-(1-methoxy-4-methyl-3-(benzoyl)oxy-
5-hexenyl)-3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-1,6-di-
oxaspiro[4.5]decane (9). To a solution of alcohol 7 (99 mg, 0.138
mmol, 1 equiv) in pyridine (2 mL) was added benzoyl chloride (32
µL, 0.276 mmol, 2.0 equiv). The clear yellow mixture was heated to
50 °C for 24 h. Concentration in vacuo, followed by purification via
column chromatography on silica gel (0-5% ethyl acetate/(1:1)
(2R,2(1S,3S,4S,5S,6S),3R,5R,7S,8R,9R)-9-tert-Butyldimethylsiloxy-
7-(2-tert-butyldimethylsiloxyethyl)-2-(5-hydroxy-1-methoxy-4,6-di-
methyl-3-benzoyloxy-8-nonenyl)-3-(2-methoxyethoxymethyl)oxy-
4,4,8-trimethyl-1,6-dioxaspiro[4.5]decane (14b). [R]D ) -57.7 (c
3.4, CHCl3). IR (thin film) 3492, 2928, 1717, 1472 cm-1 1H NMR
.
(500 MHz, CDCl3) δ 8.05 (2H, m), 7.56 (1H, m), 7.43 (2H, m), 5.85
(1H, ddd, J ) 17.6, 10.3, 7.9 Hz), 5.47 (1H, ddd, J ) 9.5, 6.9, 2.2
Hz), 5.08 (2H, m), 4.76 (1H, d, J ) 6.9 Hz), 4.72 (1H, d, J ) 6.9 Hz),
4.31 (1H, ddd, J ) 7.9, 5.2, 2.0 Hz), 4.06 (1H, dd, J ) 9.0, 5.0 Hz),
3.79 (1H, d, J ) 2.8 Hz), 3.74 (2H, m), 3.55 (3H, s), 3.37 (3H, s),
3.35-3.65 (7H, m), 2.64 (1H, d, J ) 3.7 Hz), 2.32 (1H, m), 1.95 (2H,
m), 1.76 (1H, m), 1.63 (1H, dd, J ) 14.3, 3.9 Hz), 1.51 (1H, m), 1.41
(3H, m), 1.04 (3H, s), 0.98 (3H, d, J ) 6.9 Hz), 0.94 (3H, d, J ) 6.8
Hz), 0.87 (3H, s), 0.82 (9H, s), 0.79 (9H, s), 0.78 (3H, d, J ) 7.2 Hz),
0.02 (3H, s), -0.02 (3H, s), -0.11 (3H, s), -0.12 (3H, s). 13C NMR
(125 MHz, CDCl3) δ 166.9, 141.9, 132.9, 130.4, 129.7, 128.4, 115.1,
106.9, 98.0, 87.7, 84.9, 78.2, 74.4, 73.8, 71.8, 71.2, 68.1, 64.0, 61.1,
60.9, 59.0, 50.5, 41.0, 39.4, 38.0, 36.0, 33.9, 30.7, 26.1, 25.9, 25.9,
23.2, 18.2, 18.1, 17.8, 16.5, 10.4, 8.7, -4.7, -5.1, -5.3, -5.3.
HRFABMS calcd for (M + H) C47H85O11Si2: 881.5630, found:
881.5630.
1
methylene chloride/hexane) afforded spirocycle 9 (101 mg, 89%). H
NMR (500 MHz, CDCl3) δ 8.02 (2H, d, J ) 7.4 Hz), 7.52 (1H, m),
7.41 (2H, m), 5.84 (1H, ddd, J ) 17.6, 9.7, 7.4 Hz), 5.48 (1H, m),
5.03 (2H, m), 4.70 (1H, d, J ) 6.9 Hz), 4.65 (1H, d, J ) 6.9 Hz), 4.31
(1H, m), 4.01 (1H, dd, J ) 8.9, 4.9 Hz), 3.78 (1H, d, J ) 2.3 Hz), 3.70
(1H, m), 3.55-3.65 (6H, m), 3.43-3.50 (3H, m), 3.36 (4H, m), 2.52
(1H, m), 1.78 (1H, dd, J ) 13.1, 10.8 Hz), 1.60 (1H, dd, J ) 14.2, 3.7
Hz), 1.45-1.56 (2H, m), 1.30-1.42 (3H, m), 1.05 (3H, d, J ) 8.6
Hz), 1.02 (3H, s), 0.84 (12H, m), 0.76 (12H, m), 0.02 (3H, s), -0.03
(3H, s), -0.15 (3H, s), -0.16 (3H, s). 13CNMR (125 MHz, CDCl3) δ
166.1, 139.3, 132.6, 130.8, 129.6, 128.2, 115.6, 106.8, 98.0, 88.1, 84.9,
77.9, 74.0, 71.7, 71.1, 67.9, 63.8, 61.1, 60.9, 59.0, 50.4, 42.5, 38.1,
34.1, 30.7, 25.8, 25.8, 23.2, 18.1, 18.0, 17.8, 15.8, 10.4, -4.7, -5.2,
-5.4, -5.4, -5.4.
(2R,2(1S,3S,4S,5R,6R),3R,5R,7S,8R,9R)-9-tert-Butyldimethylsiloxy-
7-(2-tert-butyldimethylsiloxyethyl)-2-(5-hydroxy-1-methoxy-4,6-di-
methyl-3-benzoyloxy-8-nonenyl)-3-(2-methoxyethoxymethyl)oxy-
4,4,8-trimethyl-1,6-dioxaspiro[4.5]decane (14a). Ozone was bubbled
through a solution of olefin 9 (500 mg, 0.609 mmol, 1 equiv) in CH2Cl2
(25 mL) at -78 °C until a light blue color persisted. The excess ozone
was purged via a stream of argon (until colorless), at which time DMS
(2.3 mL, >50 equiv) was added. The reaction mixture was warmed
to room temperature slowly. After 14 h, triphenylphosphine (84 mg
total, ∼0.6 equiv) was added in three portions over 3 h. The reaction
mixture was concentrated after 19 h, and the resulting crude aldehyde
was carried on without purification.
(2R,3R,5R,7S,8R,9R)-9-Benzoyloxy-7-(2-hydroxyethyl)-2-[(1S)-
methoxy-but-3ene]-3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-
1,6-dioxaspiro[4.5]decane (15). To a solution of silyl ether 4 (1.100
g, 1.42 mmol, 1 equiv) in THF (15 mL) was added 1.0 M TBAF (3.5
mL, 3.55 mmol, 2.5 equiv). After 2.5 h, the reaction mixture was
concentrated. Purification via column chromatography on silica gel
(30-50% ethyl acetate-hexane) afforded alcohol 15 (736 mg, 97%).
[R]D ) -52.0 (c 28.0, CHCl3). IR (thin film) 3497, 2924, 1713, 1453
cm-1 1H NMR (500 MHz, CDCl3) δ 8.13 (2H, m), 7.49 (1H, m),
.
7.37 (2H, m), 5.87 (1H, m), 5.11 (1H, m), 5.07 (1H, dd, J ) 17.2, 1.0
Hz), 5.02 (1H, d, 10.0 Hz), 4.71 (2H, s), 4.58 (1H, m), 4.19 (1H, m),
4.14 (1H, dd, J ) 9.1, 4.8 Hz), 3.83 (1H, m), 3.65-3.74 (4H, m), 3.53
(4H, m), 3.46 (2H, m), 3.30 (3H, s), 2.43 (1H, m), 2.15 (1H, m), 1.89
(1H, m), 1.84 (1H, dd, J ) 15.0, 4.1 Hz), 1.74 (2H, m), 1.35 (1H, dd,
To a cloudy solution of KOtBu (352 mg, 3.14 mmol, 5.1 equiv)
and trans-2-butene (∼1 mL, excess) in THF (4 mL) at -78 °C was
added dropwise 2.02 M nBuLi (1.35 mL, 2.74 mmol, 4.5 equiv). Upon

Total Synthesis of Calyculin C
J. Am. Chem. Soc., Vol. 120, No. 48, 1998 12441
J ) 14.5, 4.0 Hz), 1.08 (3H, s), 0.97 (3H, d, J ) 7.1 Hz), 0.88 (3H, s).
13C NMR (125 MHz, CDCl3) δ 165.9, 134.6, 132.7, 130.6, 129.8, 128.1,
116.7, 106.6, 97.2, 87.2, 83.1, 80.3, 73.4, 71,4, 69.9, 68.3, 63.0, 59.1,
58.8, 50.6, 35.2, 34.8, 34.7, 27.3, 22.7, 17.4, 10.2. HRFABMS calcd
for (M + H) C29H45O9: 537.3064, found: 537.3066.
(2R,3R,5R,7S,8R,9R)-9-Benzoyloxy-7-(2-tert-butyldimethylsiloxy-
ethyl)-2-[(1S)-methoxy-but-3ene]-3-(2-methoxyethoxy methyl)oxy-
4,4,8-trimethyl-1,6-dioxaspiro[4.5]decane (16). To a solution of
alcohol 15 (736 mg, 1.37 mmol, 1 equiv) in CH2Cl2 (15 mL) at 0 °C
was added 2,6-lutidine (390 µL, 3.34 mmol, 2.4 equiv), followed by
TBSOTf (380 µL, 1.65 mmol, 1.2 equiv). After 10 min, the reaction
mixture was partitioned between CH2Cl2 (30 mL) and saturated aqueous
NaHCO3 (20 mL). The layers were separated, and the aqueous layer
was extracted with CH2Cl2 (3 × 30 mL). The combined organics were
dried over Na2SO4, filtered, and concentrated. Purification via column
chromatography on silica gel (5-15% ethyl acetate-hexane) afforded
79.3, 73.1, 71.8, 71.4, 68.0, 64.0, 61.3, 60.1, 58.9, 50.6, 44.4, 36.1,
35.0, 34.8, 27.8, 25.9, 22.8, 18.2, 17.6, 15.9, 10.1, -5.3, -5.4.
HRFABMS calcd for (M + Na) C38H64O10SiNa: 731.4166, found:
731.4205.
(2R,2(1S,3S,4S),3R,5R,7S,8R,9R)-9-Benzoyloxy-7-(2-tert-butyldi-
methylsiloxyethyl)-2-(3-benzoyloxy-1-methoxy-4-methyl-5-hexenyl)-
3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-1,6-dioxaspiro[4.5]-
decane (18). To a solution of alcohol 17 (712 mg, 1.00 mmol, 1 equiv)
in pyridine (10 mL) was added DMAP (32 mg, 0.26 mmol, 0.26 equiv),
followed by benzoyl chloride (190 µL, 1.64 mmol, 1.6 equiv). The
clear yellow-brown reaction mixture was heated at 58 °C for 14.5 h, at
which time concentration afforded a brown slurry. Purification via
column chromatography on silica gel (10-20% ethyl acetate-hexane)
afforded dibenzoate 18 (578 mg, 71%), as well as a tribenzoate
byproduct (101 mg, 13%). [R]D ) -76.0 (c 12.0, CHCl3). IR (thin
film) 2930, 1719 cm-1 1H NMR (500 MHz, CDCl3) δ 8.09 (2H, m),
.
silyl ether 16 (924 mg, 103%, contaminated with TBS-OH). [R]D
)
8.02 (2H, m), 7.51 (1H, m), 7.47 (1H, m), 7.39 (2H, m), 7.35 (2H, m),
5.82 (1H, ddd, J ) 17.4, 9.7, 7.1 Hz), 5.48 (1H, m), 5.11 (1H, m),
5.04 (2H, m), 4.71 (1H, d, J ) 6.9 Hz), 4.67 (1H, d, J ) 6.9 Hz), 4.41
(1H, m), 4.06 (1H, dd, J ) 9.1, 4.9 Hz), 3.72 (1H, ddd, J ) 9.0, 5.3,
3.4 Hz), 3.63 (1H, ddd, J ) 10.1, 6.2, 4.2 Hz), 3.60 (1H, d, J ) 4.9
Hz), 3.53 (3H, s), 3.40-3.50 (4H, m), 3.35 (3H, s), 2.53 (1H, m), 1.81
(2H, m), 1.75 (2H, m), 1.60 (1H, m), 1.52 (1H, ddd, J ) 12.5, 10.3,
2.2 Hz), 1.41 (1H, m), 1.07 (3H, s), 1.04 (3H, d, J ) 6.9 Hz), 0.92
(3H, d, J ) 7.2 Hz), 0.89 (3H, s), 0.71 (9H, s), -0.18 (3H, s), -0.19
(3H, s). 13C NMR (125 MHz, CDCl3) δ 166.1, 166.0, 139.2, 132.6,
130.7, 130.6, 129.8, 129.5, 128.2, 128.0, 115.7, 106.5, 97.9, 87.6, 84.5,
77.8, 73.8, 73.1, 71.6, 67.9, 64.2, 60.6, 60.5, 58.9, 50.4, 42.5, 35.7,
34.4, 33.8, 27.8, 25.7, 23.0, 17.9, 17.7, 15.7, 10.0, -5.5, -5.6.
(2R,2(1S,3S,4S,5R,6R),3R,5R,7S,8R,9R)-9-benzoyloxy-7-(2-tert-
butyldimethylsiloxyethyl)-2-(5-hydroxy-1-methoxy-4,6-dimethyl-3-
benzoyloxy-8-nonenyl)-3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-
1,6-dioxaspiro [4.5]decane (19a). Ozone was bubbled through a
solution of olefin 18 (841 mg, 1.03 mmol, 1 equiv) in CH2Cl2 (15 mL)
at -78 °C until a light blue color persisted. The excess ozone was
purged via a stream of argon (until colorless), at which time DMS (3.6
mL, ∼50 equiv) was added. The reaction mixture was warmed to room
temperature slowly. After 11 h, triphenylphosphine (105 mg total, ∼0.4
equiv) was added in two portions over 3 h. The reaction mixture was
concentrated after 16 h (total reaction time), and the resulting crude
aldehyde was carried on without purification.
-77.7 (c 20.2, CHCl3). IR (thin film) 2928, 1715, 1453 cm-1
.
1H
NMR (500 MHz, CDCl3) δ 8.14 (2H, m), 7.48 (1H, m), 7.38 (2H, m),
5.88 (1H, dddd, J ) 17.7, 7.8, 4.3, 2.1 Hz), 5.13 (1H, m), 5.07 (1H,
dd, J ) 17.1, 1.2 Hz), 5.01 (1H, d, J ) 10.2 Hz), 4.69 (2H, m), 4.42
(1H, m), 4.07 (1H, dd, J ) 9.3, 5.2 Hz), 3.90 (1H, m), 3.68 (3H, m),
3.62 (1H, d, J ) 5.2 Hz), 3.51 (3H, s), 3.49 (5H, m), 3.33 (3H, s),
2.40 (1H, m), 2.11 (1H, m), 1.81 (1H, dd, J ) 11.1, 4.0 Hz), 1.68-
1.78 (3H, m), 1.46 (1H, m), 1.07 (3H, s), 0.94 (3H, d, J ) 7.1 Hz),
0.86 (3H, s), 0.84 (9H, s), 0.01 (3H, s), 0.00 (3H, s). 13C NMR (125
MHz, CDCl3) δ 165.9, 135.1, 132.5, 130.7, 129.8, 128.0, 116.2, 106.3,
97.5, 87.2, 83.1, 80.6, 72.9, 71.5, 68.0, 63.8, 61.4, 59.2, 58.8, 50.5,
36.0, 34.9, 34.8, 27.5, 25.9, 22.8, 18.2, 17.5, 10.0, -5.4, -5.4.
HRFABMS calcd for (M + Na) C35H58O9SiNa: 673.3748, found:
673.3775.
(2R,2(1S,3S,4S),3R,5R,7S,8R,9R)-9-Benzoyloxy-7-(2-tert-butyldi-
methylsiloxyethyl)-2-(3-hydroxy-1-methoxy-4-methyl-5-hexenyl)-3-
(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-1,6-dioxaspiro[4.5]-
decane (17). Ozone was bubbled through a solution of olefin 16 (653
mg, 1.00 mmol, 1.0 equiv) in CH2Cl2 (12 mL) at -78 °C until a light
blue endpoint was achieved. The excess ozone was purged via a stream
of argon (until colorless). Tributylphosphine (250 µL, 1.05 mmol, 1.05
equiv) was added dropwise, and the clear, colorless reaction mixture
was warmed slowly to room temperature. After 10 h, the reaction
mixture was concentrated to afford a crude aldehyde that was carried
on without purification.
To a cloudy solution of KOtBu (600 mg, 5.35 mmol, 5.2 equiv)
and trans-2-butene (∼2 mL, excess) in THF (6 mL) at -78 °C was
added dropwise 2.02 M nBuLi (2.30 mL, 4.65 mmol, 4.5 equiv). Upon
initial addition of nBuLi, the reaction mixture became yellow. After,
15 min, a solution of (+)-B-Methoxydiisopinocampheylborane (1.74
g, 5.49 mmol, 5.3 equiv) in THF (2 mL) was added dropwise. Addition
of the borane solution resulted in a clear, colorless reaction mixture.
After 30 min, BF3-Et2O (600 µL, 4.86 mmol, 4.7 equiv) was added
rapidly, followed immediately by a solution of the crude aldehyde in
THF (2.2 mL + 1.2 mL rinse). The resulting cloudy, colorless reaction
mixture was stirred at -78 °C for 3.5 h. Then 3 N NaOH (4 mL) and
30% H2O2 (2 mL) were added, and the cold bath was removed. After
1 h, the mixture was diluted with ethyl acetate (20 mL) and poured
into brine (20 mL), and the layers were separated. The aqueous layer
was extracted with ethyl acetate (5 × 30 mL), and the combined
organics were dried over Na2SO4, filtered, and concentrated. The
resultant crude was eluted in THF (10 mL), 3 N NaOH (3 mL), and
30% H2O2 (1.5 mL) to complete oxidation of the borane intermediate.
After 1 h, the mixture was worked-up as previously mentioned. The
excess isopinecamphol was removed via Kugelrohr distillation (high
vacuum pressure at 65 °C). Purification via column chromatography
on silica gel (5-20% ethyl acetate-hexane) afforded olefins 19a (315
mg, 35%) and 19b (351 mg, 39%) (74% overall for both steps). For
19a: [R]D ) 71.9 (c 10.5, CHCl3). IR (thin film) 3500 (br), 2930,
To a cloudy solution of KOtBu (560 mg, 4.99 mmol, 5.0 equiv)
and trans-2-butene (∼1.5 mL, excess) in THF (6 mL) at -78 °C was
added dropwise 2.02 M nBuLi (2.3 mL, 4.65 mmol, 4.6 equiv). Upon
initial addition of nBuLi, the reaction mixture became yellow. After,
15 min, a solution of (+)-B-Methoxydiisopinocampheylborane (1.72
g, 5.42 mmol, 5.4 equiv) in THF (2 mL) was added dropwise. Addition
of the borane solution resulted in a clear, colorless reaction mixture.
After 30 min, BF3-Et2O (590 µL, 4.79 mmol, 4.8 equiv) was added
rapidly, followed immediately by a solution of the crude aldehyde in
THF (2.4 mL + 1 mL rinse). The resulting cloudy colorless reaction
mixture was stirred at -78 °C for 3 h. Then 3 N NaOH (4 mL) and
30% H2O2 (2 mL) were added, and the cold bath was removed. After
5 h, the mixture was diluted with ethyl acetate (50 mL) and poured
into brine (20 mL), and the layers were separated. The aqueous layer
was extracted with ethyl acetate (4 × 50 mL), and the combined
organics were dried over Na2SO4, filtered and concentrated. Purification
via column chromatography on silica gel (5% ethyl acetate-hexane)
afforded olefin 17 (390 mg, 55%). [R]D ) -87.3 (c 12.9, CHCl3). IR
(thin film) 3500 (br), 2930, 1713 cm-1 1H NMR (500 MHz, CDCl3)
.
δ 8.13 (2H, m), 7.50 (1H, m), 7.40 (2H, m), 5.82 (1H, ddd, J ) 17.0,
10.7, 7.8 Hz), 5.14 (1H, m), 5.06 (1H, s), 5.03 (1H, d, J ) 8.1 Hz),
4.73 (1H, d, J ) 6.3 Hz), 4.65 (1H, d, J ) 6.4 Hz), 4.45 (1H, m), 4.18
(1H, dd, J ) 9.5, 5.0 Hz), 3.88 (1H, m), 3.79 (1H, m), 3.65-3.75 (3H,
m), 3.64 (1H, m), 3.58 (3H, s), 3.57 (1H, m), 3.51 (2H, m), 3.37 (3H,
s), 2.82 (1H, s br), 2.18 (1H, m), 1.83 (1H, dd, J ) 15.0, 4.0 Hz),
1.72-1.79 (3H, m), 1.62 (1H, m), 1.45-1.50 (2H, m), 1.07 (3H, s),
1.02 (3H, d, J ) 6.8 Hz), 0.96 (3H, d, J ) 7.1 Hz), 0.89 (3H, s), 0.84
(9H, s), 0.01 (3H, s), 0.00 (3H, s). 13C NMR (125 MHz, CDCl3) δ
166.1, 140.8, 132.7, 130.7, 129.9, 128.1, 115.1, 106.5, 98.1, 87.9, 83.7,
1717, 1453 cm-1 1H NMR (500 MHz, CDCl3) δ 8.03-8.13 (4H, m),
.
7.47-7.55 (2H, m), 7.35-7.42 (4H, m), 5.83 (1H, ddd, J ) 17.0, 10.5,
8.5 Hz), 5.68 (1H, m), 5.12 (1H, m), 5.06 (2H, m), 4.71 (1H, d, J )
6.7 Hz), 4.68 (1H, d, J ) 6.7 Hz), 4.43 (1H, ddd, J ) 6.3, 4.1, 2.1
Hz), 4.10 (1H, dd, J ) 9.1, 4.9 Hz), 3.69 (2H, m), 3.64 (1H, d, J ) 4.8
Hz), 3.60 (3H, s), 3.36-3.58 (6H, m), 3.33 (3H, s), 3.30 (1H, m), 2.60

12442 J. Am. Chem. Soc., Vol. 120, No. 48, 1998
Ogawa and Armstrong
(1H, br), 2.41 (1H, m), 2.11 (1H, m), 1.57-1.90 (6H, m), 1.45 (1H,
m), 1.14 (3H, d, J ) 6.9 Hz), 1.09 (3H, s), 0.96 (3H, d, J ) 7.3 Hz),
1.40-1.85 (8H, m), 1.33 (3H, d, J ) 6.8 Hz), 1.25 (3H, s), 1.19 (3H,
d, J ) 6.5 Hz), 1.16 (3H, s), 1.03 (3H, d, J ) 6.9 Hz), 0.94 (9H, s),
0.88 (3H, d, J ) 9.0 Hz), 0.86 (9H, s), 0.85 (9H, s), 0.82 (3H, d, J )
7.0 Hz), 0.20 (3H, s), 0.08 (3H, s), 0.07 (3H, s), 0.05 (3H, s), 0.04
(3H, s), -0.01 (3H, s).
0.94 (3H, d, J ) 7.4 Hz), 0.91 (3H, s), 0.75 (9H, s), -0.14 (6H, s). 13
C
NMR (125 MHz, CDCl3) δ 166.2, 165.8, 139.2, 132.7, 132.7, 130.8,
130.6, 129.8, 129.5, 128.2, 128.1, 116.0, 106.6, 97.9, 87.5, 84.6, 79.0,
76.6, 73.2, 72.6, 71.7, 68.0, 64.3, 60.8, 60.7, 58.9, 40.6, 39.6, 35.9,
34.6, 31.8, 27.8, 25.7, 23.0, 18.0, 17.8, 17.7, 11.2, 10.0, -5.4, -5.5.
HRFABMS calcd for (M + Na) C48H74O12SiNa: 893.4847, found:
893.4817.
34R-Calyculin C (29). To a Nalgene tube (2 mL) containing
protected calyculin 28 (3 mg, 1.8 µmol) and a magnetic stirbar was
added an HF stock solution (130 µL; composed of 215 µL of CH3CN,
45 µL of H2O, and 23 µL of 48% aqueous HF). After a total reaction
time of 65 h, the entire reaction mixture was chromatographed directly
on silica gel (0-12% CH3OH-CH2Cl2) to afford 34R-calyculin C 29
(1 mg, 52%). 1H NMR (500 MHz, CDCl3) δ 8.34 (1H, m), 7.33 (1H,
s), 6.99 (1H, dd, J ) 14.9, 11.1 Hz), 6.88 (1H, m), 6.81 (1H, d, J )
14.9 Hz), 6.32 (1H, d, J ) 11.5 Hz), 6.13 (1H, d, J ) 16.1 Hz), 6.01
(1H, J ) 9.8 Hz), 5.05 (1H, s), 4.57 (1H, m), 4.45 (1H, s), 4.35 (1H,
m), 4.26 (1H, dd, J ) 10.3, 3.5 Hz), 4.24 (1H, m), 4.05 (1H, m), 3.97
(2H, m), 3.87 (1H, m), 3.78 (1H, dd, J ) 9.7, 9.4 Hz), 3.56 (2H, m),
3.54 (3H, s), 3.39 (3H, s), 3.16 (1H, m), 2.85 (6H, s), 2.73 (1H, m),
2.49 (1H, m), 2.07 (3H, d, J ) 1.0 Hz), 1.97 (3H, s), 1.84 (3H, s),
1.45-2.10 (8H, m), 1.32 (3H, d, J ) 6.6 Hz), 1.29 (3H, d, J ) 6.9
Hz), 1.23 (3H, s), 1.03 (3H, d, J ) 6.9 Hz), 0.95 (3H, s), 0.88 (3H, d,
J ) 7.1 Hz), 0.71 (3H, d, J ) 6.8 Hz). HRFABMS calcd for
C51H84N4O15P (MH+): 1023.5671, found: 1023.5690.
(2S,3S,4S)-N-[(1R,3S)-3-[4-(1E)-3[(2R,3R,5R,7S,8R,9R)-2-[(1S,3S,-
4S,5R,6R,7E,9E,11E,13Z)-3,5-Bis(tert-butyldimethylsiloxy)-14-cyano-
1-methoxy-4,6,8,9,13-pentamethyl-7,9,11,13-tetradecatetraenyl]-9-
(tert-butyldimethylsiloxy)-3-[bis(p-methoxybenzyl)phosphatyl]-4,4,8-
trimethyl-1,6-dioxaspiro[4.5]dec-7-yl]propenyl]-2-oxazolyl]-1-
methylbutyl]-2,3-dihydroxy-4-(dimethylamino)-5-methoxy Valeramide
(30). To a solution of aldehyde 26 (9 mg, 0.007 mmol) and phos-
phonium salt 3 (10 mg, 0.017 mmol) in DMF (120 µL) at 0 °C was
added LDA (37 µL, 0.5M in THF, 1 equiv). Six successive portions
of LDA (6 × 37 µL, 0.5M in THF) were added over 1 h, at which
time the reaction mixture was partitioned between ethyl acetate (10
mL) and saturated aqueous NaHCO3 (10 mL). The layers were
separated, and the aqueous layer was extracted with ethyl acetate (5 ×
10 mL). The combined organics were dried over Na2SO4, filtered, and
concentrated. Purification via column chromatography on silica gel
(2-6% CH3OH-CH2Cl2) afforded aldehyde 26 (4 mg, 44%) and olefin
30 (2.7 mg, 24%, 41% based on recovered starting material, 26).
HRFABMS calcd for C85H142N4O17PSi3 (MH+): 1605.9415, found:
1605.9381.
(2R,2(1S,3S,4S,5S,6S),3R,5R,7S,8R,9R)-9-benzoyloxy-7-(2-tert-bu-
tyldimethylsiloxyethyl)-2-(5-hydroxy-1-methoxy-4,6-dimethyl-3-ben-
zoyloxy-8-nonenyl)-3-(2-methoxyethoxymethyl)oxy-4,4,8-trimethyl-
1,6-dioxaspiro [4.5]decane (19b). [R]D ) -70.3 (c 10.9, CHCl3). IR
(thin film) 3500 (br), 2930, 1713, 1453 cm-1 1H NMR (500 MHz,
.
CDCl3) δ 8.07 (4H, m), 7.32-7.56 (6H, m), 5.83 (1h, ddd, J ) 17.8,
10.3, 7.9 Hz), 5.46 (1H, m), 5.04-5.14 (3H, m), 4.75 (2H, m), 4.40
(1H, ddd, J ) 7.6, 5.1, 1.8 Hz), 4.10 (1h, dd, J ) 9.0, 4.9 Hz), 3.0.39-
3.77 (12H, m), 3.35 (3H, s), 3.34 (1H, m), 2.50 (1H, br), 2.31 (1H,
m), 1.97 (2H, m), 1.83 91H, dd, J ) 15.2, 4.2 Hz), 1.76 (3H, m), 1.57
(1H, m), 1.41 (1H, m), 1.09 (3H, s), 0.97 (3H, d, J ) 6.9 Hz), 0.93
(3H, d, J ) 6.8 Hz), 0.93 (3H, d, J ) 7.1 Hz), 0.91 (3H, s), 0.71 (9H,
s), -0.17 (3H, s), -0.19 (3H, s). 13C NMR (125 MHz, CDCl3) δ 166.7,
166.1, 141.6, 132.9, 132.6, 130.6, 130.3, 129.8, 129.6, 128.3, 128.0,
115.3, 106.6, 97.8, 87.3, 84.5, 78.0, 74.1, 73.8. 71.7, 68.1, 64.2, 60.6,
60.5, 59.0, 50.4, 40.9, 39.4, 35.6, 34.3, 33.6, 27.8, 25.7, 23.0, 17.9,
17.7, 16.4, 10.0, 8.6, -5.5, -5.6. HRFABMS calcd for (M + Na)
C48H74O12SiNa: 893.4847, found: 893.4860.
(2R,2(1S,3S,4S,5R,6R),3R,5R,7S,8R,9R)-9-tert-Butyldimethylsiloxy-
7-(2-tert-butyldimethylsiloxyethyl)-2-(1-methoxy-4,6-dimethyl-3,5-
bis(tert-butyldimethylsiloxy)-8-nonenyl)-3-(2-methoxyethoxymeth-
yl)oxy-4,4,8-trimethyl-1,6-dioxaspiro[4.5]decane (21). [R]D ) -41.9
(c 1.7, CHCl3). IR (thin film) 2928, 1472 cm-1 1H NMR (500 MHz,
.
CDCl3) δ 5.89 (1H, ddd, J ) 17.4, 10.4, 7.1 Hz), 4.98 (2H, m), 4.80
(1H, d, J ) 7.3 Hz), 4.57 (1H, d, J ) 7.3 Hz), 4.38 (1H, m), 4.30 (1H,
m), 3.96 (1H, dd, J ) 9.1, 4,7 Hz), 3.75-3.85 (3H, m), 3.62 (3H, s),
3.47-3.67 (6H, m), 3.38-3.41 (1H, m), 3.38 (3H, m), 2.42 (1H, m),
1.86 (1H, m), 1.71 (1H, m), 1.64 (1H, dd, J ) 14.2, 4.0 Hz), 1.40-
1.53 (3H, m), 1.25 (2H, m), 1.05 (3H, s), 1.04 (3H, d, J ) 6.9 Hz),
0.91 (3H, s), 0.89 (9H, s), 0.88 (9H, s), 0.87 (18H, s), 0.81 (3H, d, J
) 7.1 Hz), 0.74 (3H, d, J ) 7.1 Hz), 0.13 (3H, s), 0.10 (3H, s), 0.07
(3H, s), 0.05 (3H, s), 0.04 (3H, s), 0.03 (6H, s), 0.01 (3H, s). 13C
NMR (125 MHz, CDCl3) δ 141.5, 113.6, 106.8, 98.7, 89.6, 86.4, 77.6,
77.4, 71.8, 71.4, 68.1, 67.8, 64.0, 61.3, 60.3, 59.0, 50.1, 43.7, 42.6,
37.9, 36.1, 33.9, 31.2, 29.7, 26.3, 26.1, 26.0, 25.9, 25.7, 23.3, 18.4,
18.3, 18.2, 18.1, 17.9, 15.4, 10.6, 10.4, -3.0, -3.8, -4.0, -4.0, -4.6,
-5.0 (3 carbons).
(2R,3S,4S)-N-[(1R,3S)-3-[4-(1E)-3[(2R,3R,5R,7S,8R,9R)-2-[(1S,-
3S,4S,5R,6R,7E,9E,11E,13Z)-3,5-Bis(tert-butyldimethylsiloxy)-14-cy-
ano-1-methoxy-4,6,8,9,13-pentamethyl-7,9,11,13-tetradecatetraenyl]-
9-(tert-butyldimethylsiloxy)-3-[bis(p-methoxybenzyl)phosphatyl]-
4,4,8-trimethyl-1,6-dioxaspiro[4.5]dec-7-yl]propenyl]-2-oxazolyl]-1-
methylbutyl]-2,3-dihydroxy-4-(dimethylamino)-5-methoxy Valeramide
(28). To a solution of aldehyde 26 (9.6 mg, 0.015 mmol) and
phosphonium salt 27 (10.4 mg, 0.008 mmol) in DMF (200 µL) at 0 °C
was added LDA (32 µL, 0.5 M in THF, 1 equiv). Four successive
portions of LDA (3 × 32 µL, then 15 µL, 0.5 M in THF) were added
over 30 min, at which time the reaction mixture was partitioned between
ethyl acetate (10 mL) and saturated aqueous NaHCO3 (10 mL). The
layers were separated, and the aqueous layer was extracted with ethyl
acetate (3 × 10 mL). The combined organics were dried over Na2SO4,
filtered, and concentrated. Purification via column chromatography
on silica gel (2-6% CH3OH-CH2Cl2) afforded aldehyde 26 (6 mg,
58%) and olefin 28 (3 mg, 23%, 55% based on recovered starting
material, 26). 1H NMR (500 MHz, CDCl3) δ 7.36 (1H, s), 6.99-7.08
(4H, m), 6.77-6.85 (5H, m), 6.36 (1H, d, J ) 11.1 Hz), 6.16 (2H, m),
6.07 (1H, d, J ) 8.9 Hz), 5.06 (1H, s), 5.01 (1H, dd, J ) 20.9, 11.6
Hz), 4.91 (1H, dd, J ) 25.6, 13.6 Hz), 4.80 (1H, dd, J ) 11.2, 5.3
Hz), 4.67 (1H, dd, J ) 11.0, 5.8 Hz), 4.56 (2H, m), 4.38 (1H, br d),
4.29 (1H, br), 4.09 (3H, m), 3.84 (1H, br), 3.76-3.79 (9H, m), 3.66
(4H, m), 3.58 (1H, m), 3.48 (1H, m), 3.35 (3H, s), 2.99 (1H, m), 2.73
(7H, br m), 2.65 (2H, m), 2.07 (3H, s), 2.01 (3H, s), 1.88 (3H, s),
Calyculin C (1). To a Nalgene tube (2 mL) containing protected
calyculin 30 (2.5 mg, 1.5 µmol) was added an HF stock solution (100
µL; composed of 215 µL of CH3CN, 45 µL of H2O, and 23 µL of 48%
aqueous HF). After a total reaction time of 60 h, the entire reaction
mixture was chromatographed directly on silica gel (0-5% CH3OH-
CH2Cl2) to afford calyculin C (1) (0.4 mg, 30%). Thin-layer chroma-
tography of 1 was performed in multiple solvent systems against an
authentic sample of calyculin C.17 For 1HNMR of 1 and authentic
calyculin C, see Supporting Information. HRFABMS calcd for
C51H84N4O15P (MH+): 1023.5671, found: 1023.5723.
Acknowledgment. This paper is dedicated to Professor
Yoshito Kishi on the occasion of his 60th birthday. This work
was supported by funding from the NIH (Grant No. 51095).
The authors are deeply indebted to past group members, without
whose efforts this work would not be possible. The authors thank
Varsha Gupta for her efforts in providing the C33-C37 fragment.
The authors graciously thank Professor Nobuhiro Fusetani for
his generous gift of authentic calyculin C.
Supporting Information Available: Experimental proce-
dures and/or data for compounds 8, 10-12, and 22, as well as
copies of 1H NMR for compounds 1, 5-19b, 21-22, and 28-
29 are provided. Mass spectral data for compounds 1 and 30
are also provided (36 pages, print/PDF). See any current
masthead page for ordering information and Web access
instructions.
JA980836Q