Total synthesis of the calphostins: Application of Fischer carbene complexes and thermodynamic control of atropisomers

Article abstract of DOI:10.1021/jo0014663

The total syntheses of the potent protein kinase C inhibitors calphostins A, B, C, and D as well as a variety of structural analogues are reported. An aminobenzannulation reaction of an enantiopure chromium Fischer carbene complex is utilized to prepare a pentasubstituted naphthylamine. After optimization of side-chain substituents, conversion of the naphthylamine to an o-naphthoquinone was followed by biomimetic oxidative dimerization using trifluoroacetic acid and air yielding a 1:2 P/M mixture of atropisomeric perylenequinones. Thermal equilibration to a 3:1 P:M atropisomeric ratio and separation of the perylenequinones followed by side chain desymmetrization and functionalization led to the total synthesis of enantio- and diastereomerically pure calphostin C in only twelve steps from commercially available starting materials. In addition, calphostins A, B, D, and several structural analogues were prepared to evaluate biological activities.

Full text of DOI:10.1021/jo0014663

J . Org. Chem. 2001, 66, 1297-1309
1297
Tota l Syn th esis of th e Ca lp h ostin s: Ap p lica tion of F isch er
Ca r ben e Com p lexes a n d Th er m od yn a m ic Con tr ol of Atr op isom er s
Craig A. Merlic,* Courtney C. Aldrich, J ennifer Albaneze-Walker, Alan Saghatelian, and
J erome Mammen
Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095-1569
merlic@chem.ucla.edu
Received October 10, 2000
The total syntheses of the potent protein kinase C inhibitors calphostins A, B, C, and D as well as
a variety of structural analogues are reported. An aminobenzannulation reaction of an enantiopure
chromium Fischer carbene complex is utilized to prepare a pentasubstituted naphthylamine. After
optimization of side-chain substituents, conversion of the naphthylamine to an o-naphthoquinone
was followed by biomimetic oxidative dimerization using trifluoroacetic acid and air yielding a 1:2
P/M mixture of atropisomeric perylenequinones. Thermal equilibration to a 3:1 P:M atropisomeric
ratio and separation of the perylenequinones followed by side chain desymmetrization and
functionalization led to the total synthesis of enantio- and diastereomerically pure calphostin C in
only twelve steps from commercially available starting materials. In addition, calphostins A, B, D,
and several structural analogues were prepared to evaluate biological activities.
In tr od u ction
Calphostins A, B, C, and D (1-4) are architecturally
interesting and biologically significant perylenequin-
ones that were isolated by Tamaoki et al. in 1989
from Cladosporium cladosporioides (Figure 1).1,2 The
calphostins, and calphostin C in particular, were found
to be potent and selective inhibitors3 of protein kinase C
(PKC), a phosphorylation enzyme that plays a central
role in signal transduction.4,5 PKC represents one arm
of the intracellular signaling pathway, and its overstimu-
lation is thought to underlie not only developmental and
proliferative diseases such as cancer and psoriasis but
also inflammatory diseases, diabetes, and central nervous
system disorders.6,7 PKC exists as a family of 11 related
isozymes,8 and the differential expression of these across
different cell types has led to the search for isozyme
selective inhibitors.9,10 PKC contains two domains, a
highly conserved C-terminal catalytic domain11 and a
N-terminal regulatory domain.8 The vast majority of PKC
inhibitors which have been investigated bind to the less
desirable catalytic domain; however, the calphostins are
unique in that they bind to the regulatory domain,
F igu r e 1. Structures of the calphostins.
making them potentially more suitable as isozyme selec-
tive inhibitors.12 The calphostins have generated consid-
erable attention as potential agents for anticancer therapy
and have been investigated in a variety of cancers
showing excellent results against bladder,13 brain,14
prostate,15 and leukemia cell lines16 where PKC activity
is high. Calphostin C was ineffective against a colorectal
cell line in accord with the low activity of PKC found in
(9) (a) Hofmann, J . FASEB 1997, 11, 649-669. For examples of
specific PKC isozyme modulation, see: (b) PKCγ as a mediator of
neuropathic pain: Malmberg, A. B.; Chen, C.; Tonegawa, S.; Basbaum,
A. I. Science 1997, 278, 279-283. (c) PKCâ implicated in the vascular
complication of diabetes: Ishii, H.; J irousek, M. R.; Koya, D.; Takagi,
C.; Xia, P.; Clermont, A.; Bursell, S.-E.; Kern, T. S.; Ballas, L. M.;
Heath, W. F.; Stramm, L. E.; Feener, E. P.; King, G. L. Science 1996,
272, 728-731. (c) PKCR as a target for antisense cancer chemo-
therapy: Geiger, T.; Mu¨ller, M.; Dean, N. M.; Fabbro, D. Anti-Cancer
Drug Design 1998, 13, 35-45.
(10) Irie, K.; Oie, K.; Nakahara, A.; Yanai, Y.; Ohigashi, H.; Wender,
P. A.; Fukuda, H.; Konishi, H.; Kikkawa, U. J . Am. Chem. Soc. 1998,
120, 9159-9167.
(11) The Protein Kinase Facts Book; Hardie, G., Hanks, S., Eds.;
Academic Press: San Diego, 1995.
(12) For the rational design of a new type of PKC inhibitor that binds
to the regulatory domain, see: Sodeoka, M.; Arai, M. A.; Adachi, K.;
Uotsu, K.; Shibasaki, M. J . Am. Chem. Soc. 1998, 120, 457-458.
(13) Beck, T. P.; Kirsh, E. J .; Chmura, S. J .; Kovar, D. A.; Chung,
T.; Rinker-Schaefer, C. W.; Stadler, W. M. Urology 1999, 54, 573-
577.
(1) (a) Kobayashi, E.; Ando, K.; Nakano, H.; Tamaoki, T. J . Antibiot.
1989, 42, 153-155. (b) Kobayashi, E.; Ando, K.; Nakano, H.; Iida, T.;
Ohno, H.; Morimoto, M.; Tamaoki, T. J . Antibiot. 1989, 42, 1470-1474.
(c) Iida, T.; Kobayashi, E.; Yoshida, M.; Sano, H. J . Antibiot. 1989, 42,
1475-1481.
(2) For a comprehensive review on perylenequinones, see: Weiss,
U.; Nasini, G. Prog. Chem. Org. Nat. Prod. 1987, 52, 1-71.
(3) Kobayashi, E.; Nakano, H.; Morimoto, M.; Tamaoki, T. Biochem.
Biophys. Res. Commun. 1989, 159, 548-553.
(4) Nishizuka, Y. Cancer 1989, 63, 1892-1903.
(5) For a recent review on biological signal transduction and organic
synthesis, see: Hinterding, K.; Alonso-Dı´az, D.; Waldmann, H. Angew.
Chem., Int. Ed. Engl. 1998, 37, 689-749.
(6) Bradshaw, D.; Hill, C. H.; Nixon, J . S.; Wilkinson, S. E. Agents
Actions 1993, 38, 135-146.
(7) (a) Parker, P. J . Pharmacol. Ther. 1999, 82, 263-267. (b) Fabbro,
D.; Buchdnger, E.; Wood, J .; Mestan, J .; Hofmann, F.; Ferrari, S.; Mett,
H.; O’Reilly, T.; Meyer, T. Pharmacol. Ther. 1999, 82, 293-301. (c)
Cho-Chung, Y. S. Pharmacol. Ther. 1999, 82, 437-449.
(8) (a) Newton, A. C. J . Biol. Chem. 1995, 270, 28495-28498. (b)
Liu, W. S.; Heckman, C. A. Cell Signal 1998, 10, 529-542.
(14) Pollack, I. F.; Kawecki, S. J . Neuro-Oncol. 1997, 31, 255-266.
(15) Dubauskas, Z.; Beck, T. P.; Chmura, S. J .; Kovar, D. A.;
Kadkhodaian, M. M.; Shrivastav, M.; Chung, T.; Stadler, W. M.;
Rinker-Schaefer, C. W. Clin. Can. Res. 1998, 4, 2391-2398.
(16) Zhu, D.-M.; Narla, R.-K.; Fang, W.-H.; Chia, N.-C.; Uckun, F.
M. Clin. Can. Res. 1998, 4, 2967-2976.
10.1021/jo0014663 CCC: $20.00 © 2001 American Chemical Society
Published on Web 01/20/2001

1298 J . Org. Chem., Vol. 66, No. 4, 2001
Merlic et al.
colorectal cells.17 Explorations into the downstream ef-
fects of PKC using calphostin C have uncovered several
interesting physiological activities including inhibi-
tion of angiogenesis,18 multidrug resistance (MDR),19 and
Bcl-2.20 One of the key disadvantages of the calphostins
that has hampered their development as therapeutic
agents is their requirement of light for activity; although
this feature has been exploited in their development as
substrates for photodynamic therapy.21,22
Our interest in the calphostins arises from not only
their remarkable biological activity but also their unique
topological features. The defining characteristic of the
calphostins is their central highly substituted perylene-
quinone core, which is not flat, but canted at an angle of
10° out of planarity due to eclipsing interactions of the
side chains at C1 and C12 as well as the methoxy
substituents at C6 and C7.23 The result is that the central
core is axial chiral and can exist as two atropisomers.24
Atropisomerism has recently emerged as a subject of
great interest in organic synthesis.25 Many beautiful
strategies have been developed to address issues in
atropselective synthesis such as Bringmann’s lactone
concept,26 Uemura’s tricarbonyl(arene) chromium com-
plex template,27 Lipshutz’s chiral tether,28 or Meyer’s
oxazoline auxiliary method;29 however, none offer a
general solution or are readily applicable to the synthesis
of the calphostins.
which all take advantage of the inherent symmetry in
the calphostins. Broka reported the first synthesis of a
naturally occurring perylenequinone; however, his syn-
thesis required 18 steps alone to arrive at an ap-
propriately functionalized naphthalene core. This naph-
thalene was dimerized to a perylenequinone and then
further elaborated to calphostins A and D.30 Coleman and
Grant designed innovative new chemistry for the fabrica-
tion of a naphthalene precursor, but their synthesis
suffered from poor atropselective control in the naphtha-
lene dimerization and required ninteen steps to produce
calphostin A.31 Both of the aforementioned syntheses
built the perylenequinone core stepwise from naphtha-
lene derivatives, constructing each biaryl bond sepa-
rately. Diwu and Lown, who were interested in pery-
lenequinones for their use as singlet oxygen sensitizers
in photodynamic therapy, developed the most efficient
synthesis of the perylenequinone core.32 Building on the
work of Chao and Zhang,33 they found that o-naphtho-
quinones underwent oxidative dimerization to afford
perylenequinones in a single step. This new protocol
greatly simplifies perylenequinone synthesis and was
employed by Hauser in a total synthesis of calphostin D,
the simplest member of the calphostins.34 Hauser’s
synthesis is the most efficient synthesis of the three
reported, requiring only 14 steps, but it suffers from lack
of diastereocontrol in the key dimerization process. We
provide herein a detailed report on our synthetic endeav-
ors toward the calphostins culminating in the concise and
enantioselective total syntheses of calphostins A-D, as
well as the synthesis of a number of structural analogues,
featuring a benzannulation of an enantiopure Fischer
carbene complex and an atropselective thermal isomer-
ization to control axial chirality.35
Three total syntheses of the simplest, and least biologi-
cally active, members of this group have been reported
(17) (a) Hochegger, K.; Partik, G.; Scho¨rkhuber, M.; Marian, B. Int.
J . Cancer 1999, 83, 650-656. PKC has been controversially implicated
in colorectal neoplasms. Support for reduced PKC activity in colorectal
cells, see: (b) Kahl, R. P.; Karner, H. J .; Weiss, W.; Marian, B.
Carcinogenesis 1994, 15, 779-782.
(18) Hu, D. E.; Fan, T.-P. D. Inflammation 1995, 19, 39-54.
(19) MDR inhibition may be due to a PKC dependent pathway as
well as direct binding of calphostin to P-glycoprotein. For support for
a PKC-dependent pathway, see: (a) Castro, A. F.; Horton, J . K.;
Vanoye, C. G.; Altenberg, G. A. Biochem. Pharm. 1999, 58, 1723-1733.
For support for a PKC-independent pathway, see: Gupta, S.; Patel,
K.; Singh, H.; Gollapudi, S. Cancer Lett. 1994, 76, 139-145.
(20) (a) Murata, M.; Nagai, M.; Fujita, M.; Ohmori, M.; Takahara,
J . Cell. Mol. Life Sci. 1997, 53, 737-743. (b) Ikemoto, H.; Tani, E.;
Matsumoto, T.; Nakano, A.; Furuyama, J , -I. J . Neurosurg. 1995, 83,
1008-1016.
Retrosynthetically, we sought to assemble the pery-
lenequinone core through a biomimetic oxidative dimer-
ization of two o-naphthoquinone moieties to provide the
fully functionalized perylenequinone nucleus following
the precedent of Diwu and Lown32 as well as Hauser34
(Scheme 1). In this single step, two new biaryl carbon-
carbon bonds are formed with the simultaneous creation
of the chiral axis. This coupling proceeds through a
binaphthalene intermediate; thus, it was envisioned, at
least as a first approach, that relay of the remote side
chain chirality to the incipient biaryl axis would provide
a mechanism for stereocontrol. Elaboration of the side
chain appendages allows access to all of the naturally
occurring calphostins. The most important target, calphos-
(21) For a review on perylenequinones in photodynamic therapy,
see: Lown, J . Can. J . Chem. 1997, 75, 99-119.
(22) Bruns, R. F.; Miller, F. D.; Merriman, R. L.; Howbert, J . J .;
Heath, W. F.; Kobayashi, E.; Takahashi, I.; Tamaoki, T.; Nakano, H.
Biochem. Biophys. Res. Commun. 1991, 176, 288-293.
(23) Nasini, G.; Merlini, L.; Andreetti, G. D.; Bocelli, G.; Sgarabotto,
P. Tetrahedron 1982, 38, 2787-2796.
(24) Atropisomerism, as strictly defined, results from restricted
rotation about a single bond. However, the interconversion about the
perylenequinone chiral axis involves rotation about two bonds, nev-
ertheless the term will be used here. For the definition of atropisom-
erism, see: Eliel, E. L.; Wilen, S. H. Stereochemistry of Carbon
Compounds; Wiley: New York, 1994; Chapter 14, p 1193. For examples
where the term atropisomerism has been used more liberally to
describe hindered rotation about two bonds, see: (a) Morgan, B.; Zaks,
A.; Dodds, D. R.; Liu, J .; J ain, R.; Megati, S.; Njoroge, F. G.;
Girijavallabhan, V. M. J . Org. Chem. 2000, 65, 5451-5459. (b)
Piwinski, J . J .; Wong, J . K.; Chan, T.-M.; Green, M. J .; Ganguly, A. K.
J . Org. Chem. 1990, 55, 3341-3350.
(25) For general reviews on atropisomerism and axial chirality,
see: (a) Oki, M. Top. Stereochem. 1983, 13, 1-81. (b) Meurer, K. P.;
Vo¨gtle, F. Top. Curr. Chem. 1985, 127, 1-76. For reviews on directed
biaryl synthesis and general strategies for atropselective control, see:
(c) Bringmann, G.; Walter, R.; Weirich, R. Angew. Chem., Int. Ed. Engl.
1990, 29, 977-991. (d) Bringmann, G.; Walter, R.; Weirich, R. In
Houben-Weyl Methoden der Organischen Chemie; Helmchen, G., Hoff-
mann, R. W., Mulzer, J ., Schaumann, E., Eds.; Georg Thieme Verlag:
4. Auflage, Stuttgart, 1995; Bd E21, 567-587.
(26) For a review, see: Bringmann, G.; Breuning, M.; Tasler, S.
Synthesis 1999, 4, 525-558.
(27) Uemura, M.; Daimon, A.; Hayashi, Y. J . Chem. Soc., Chem.
Commun. 1995, 1943-1944.
(28) (a) Lipshutz, B. H.; Kayser, F.; Liu, Z.-P. Angew. Chem., Int.
Ed. Engl. 1994, 33, 1842-1844. (b) For applications in synthesis, see:
Lipshutz, B. H.; Mu¨ller, P.; Leinweber, D. Tetrahedron Lett. 1999, 40,
3677-3680. (c) Spring, D. R.; Krishnan, S.; Schreiber, S. L. J . Am.
Chem. Soc. 2000, 122, 5656-5657.
(29) Meyers, A. I. J . Heterocycl. Chem. 1998, 35, 991-1002. For a
recent example used in synthesis, see: Degnan, A. P.; Meyers, A. I. J .
Am. Chem. Soc. 1999, 121, 2762-2769.
(30) Broka, C. A. Tetrahedron Lett. 1991, 32, 859-862.
(31) (a) Coleman, R. S.; Grant, E. B. J . Am. Chem. Soc. 1995, 117,
10889-10904. (b) Coleman, R. S.; Grant, E. B. J . Am. Chem. Soc. 1994,
116, 8795-8796. (c) Coleman, R. S.; Grant, E. B. Tetrahedron Lett.
1993, 34, 2225. (d) Coleman, R. S.; Grant, E. B. J . Org. Chem. 1991,
56, 1357-1359.
(32) (a) Diwu, Z.; Lown, J . W. Tetrahedron 1992, 48, 45-54. (b) Liu,
J .; Diwu, Z.; Lown, J . W. Synthesis 1995, 914-916.
(33) (a) Zhao, C.; Zhang, X. -s; Zhang, P. Liebigs Ann. Chem. 1993,
35-41. (b) Chao, C.; Zhang, P. Tetrahedron Lett. 1988, 29, 225-226.
(34) Hauser, F. M.; Sengupta, D.; Corlett, S. A. J . Org. Chem. 1994,
59, 1967-1969.
(35) For a preliminary report, see: Merlic, C. A.; Aldrich, C. C.;
Albaneze-Walker, J .; Saghatelian, A. J . Am. Chem. Soc. 2000, 122,
3224-3225.

Total Synthesis of the Calphostins
J . Org. Chem., Vol. 66, No. 4, 2001 1299
Sch em e 1. Retr osyn th etic Discon n ection s for th e
Ca lp h ostin s
Sch em e 2. P h otoch em ica l a n d Th er m a l
Ben za n n u la tion Rea ction s of a n Ar yl-Alk en yl
Ca r ben e Com p lex
Sch em e 3. P r ep a r a tion of Mod el
o-Na p h th oqu in on e 11
tin C, has different side-chain substituents, so we planned
on effecting a desymmetrization of a symmetric pery-
lenequinone rather than the cross-coupling of two naph-
thalene subunits as initially proposed by Coleman and
Grant.31
This analysis targets a highly functionalized o-naph-
thoquinone as a critical intermediate. The requisite
o-naphthoquinone precursors can be prepared by either
of two benzannulation strategies developed in these
laboratories utilizing chromium carbene complexes. In
the first, photolysis of a formally dienyl chromium
carbene complex leads, via electrocyclization of a chro-
mium complexed ketene intermediate, to an o-alkoxy
phenol product (path A, Scheme 2).36 The second annu-
lation method involves an isonitrile thermal addition
reaction forming a chromium complexed ketenimine
intermediate, which undergoes an electrocyclization lead-
ing to an o-alkoxy aromatic amine product (path B,
Scheme 2).37 Oxidation of either of these products yields
the same o-naphthoquinone required for perylenequinone
synthesis. The carbene complexes are prepared from the
corresponding aryl bromides which are in turn accessible
by a variety of procedures. Moreover, our antithetic
disconnections allow us to easily introduce different side-
chain appendages to prepare a variety of modified side-
chain analogues, which is important for our mapping of
structure-activity relationships.
of chromium hexacarbonyl, and methylation employing
methyl triflate afforded the methoxy carbene complex 8.
Attempts to achieve the desired photocyclization36 to the
o-alkoxynaphthol derivative 9 were impeded by the very
electron-rich aryl ring, which may inhibit carbonyl inser-
tion in the carbene moiety. Fortunately, the alternative
thermal isonitrile reaction37 proved more productive.
Addition of tert-butyl isonitrile to carbene complex 8 at
room temperature provided the chromium complexed
ketenimine. This step was conveniently monitored by
observing loss of the deep red color of the carbene
complex. Subsequent heating at reflux in THF effected
electrocyclization to give the o-alkoxynaphthylamine
derivative 10 which could be isolated, but was more
conveniently oxidized in situ with ceric ammonium
nitrate (CAN) to afford the desired o-naphthoquinone 11.
With the key o-naphthoquinone in hand, we began to
explore dimerization conditions. Following the work of
Diwu and Lown, we found that, through the agency of
iron(III) chloride in acetonitrile, dimerization proceeded
smoothly to afford 91% of the perylenequinone 12 (eq
1)!32a Interestingly, if this oxidative dimerization was not
Resu lts a n d Discu ssion
Mod el System . Our initial foray into the synthesis of
the calphostins involved preparation of a model system
that retained the essential features of the real system.
To this end, we chose to prepare the n-propyl side chain
derivative, which lacked the alcohol functionality of the
natural products, thus simplifying the structure and
making the issue of atropselectivity moot. Regioselective
monobromination of 3,5-dimethoxybenzaldehyde with
bromine in cold acetic acid provided bromoaldehyde 638
(Scheme 3). Wittig olefination with n-butyltriphenylphos-
phonium bromide furnished an approximately 1:1 mix-
ture of isomeric olefins 7. Treatment of the aryl bromide
with n-BuLi to effect metal-halogen exchange, addition
(36) (a) Merlic, C. A.; Xu, D. Q. J . Am. Chem. Soc. 1991, 113, 7418-
7420. (b) Merlic, C. A.; Roberts, W. M. Tetrahedron Lett. 1993, 34,
7379-7382.
(37) (a) Merlic, C. A.; Burns, E. E.; Xu, D. Q.; Chen, S. Y. J . Am.
Chem. Soc. 1992, 114, 8722-8724. (b) Merlic, C. A.; Burns, E. E.
Tetrahedron Lett. 1993, 34, 5401-5404.
conducted under strictly anaerobic conditions, varying
amounts (5-10%) of the novel anhydride byproduct 13

1300 J . Org. Chem., Vol. 66, No. 4, 2001
Merlic et al.
Sch em e 5. Attem p ted F or m a tion of Ca r ben e
Sch em e 4. Meth yla tion -Dem eth yla tion Sequ en ce
Com p lex 23
Sch em e 6. Syn th esis of Su bstitu ted
were isolated. This impressive transformation bears close
resemblance to that carried out by a class of enzymes
known as the catechol dioxygenases. These are non-heme
iron enzymes that catalyze oxidation of catechols to the
corresponding bis-carboxylic acids via intermediate an-
hydrides.39
o-Na p h th oqu in on e 29
Adjustment of the methylation pattern to reflect the
natural methylation pattern found in the calphostins was
readily accomplished (Scheme 4). Treatment of pery-
lenequinone 12 with methyl iodide using tetrabutylam-
monium fluoride (TBAF) as base provided hexamethoxy-
perylenequinone 14 in quantitative yield.40 Regioselective
demethylation was achieved using 9-bromo-9-borabicyclo-
[3.3.1]nonane (9-Br-BBN), which afforded the chromato-
graphically isolable bis-cyclic borane adduct 15. Subse-
quent exposure to trifluoroacetic acid (TFA) liberated the
product perylenequinone 16.41 This route to dideoxy-
calphostin D proved to be extremely efficient, highlighted
by an innovative o-naphthoquinone synthesis, an out-
standing oxidative dimerization process, and new condi-
tions for regioselective demethylation.
Tow a r d th e Ca lp h ostin s. With an efficient route to
the perylenequinone core established, we set out to
explore the real system, which differed from the model
solely by the alcohol functionality at the 2′ positions of
the side chains. With the resulting introduction of ste-
reocenters, the issue of atropselectivity became central
and guided many of the modifications to the model route.
The synthesis of aryl bromide 22 followed a similar
synthetic sequence outlined for the model system except
that the umpolung coupling arrangement of aldehyde 21
and phosphonium salt 20 proved more successful (Scheme
5). Unfortunately, only low yields of the desired carbene
complex 23 were obtained with attendant formation of
diene 24. Generation of this side product is reconciled
by E2 elimination of the lithiated cis-alkene, which
positions the allylic hydrogens in close proximity to the
aryl anion.
in the benzannulation reaction; however, we now needed
an olefination approach that exclusively delivered the
trans-olefin.42 This was easily achieved employing benzyl
phosphonate 25 and (R)-3-triisopropylsiloxybutyralde-
hyde 26 to provide solely the desired E-bromoarylalkene
27 (Scheme 6). The triisopropylsilyl protecting group was
required to avoid silyl migration in the intermediate
alkoxide of the olefination reaction.43 Carbene formation
from E-olefin 27 now proceeded without incident to
furnish 28 in 88% yield. Conversion of the pivotal carbene
complex to the o-naphthoquinone using the isonitrile
method37 proceeded smoothly to afford 29 in 82% yield.
However, small amounts of an indenone side product 30
were isolated, presumably arising from direct electrocy-
clization of the carbene complex.44 This side reaction was
overridden by conducting the reaction at high concentra-
tions (∼1 M) to favor reaction with the isonitrile. Sur-
prisingly, photocyclization of carbene complex 28 fur-
Previously, we were satisfied with a nonstereoselective
olefin synthesis since the geometry of the olefin is lost
(42) Alkene 22 could be isomerized to a 6:1 E/ Z mixture of isomers
employing iodine; however, the moderate selectivity coupled with the
additional synthetic step favored the Horner-Wadsworth-Emmons
olefination.
(43) The bulkier TIPS group has a reduced propensity to migrate
as compared to the smaller TBS group. For an encyclopedic review of
the TIPS protecting group, see: Ru¨cker, C. Chem. Rev. 1995, 95, 1009-
1064.
(38) Lock, G.; Nottes, G. Monatsh. Chem. 1936, 68, 51-67.
(39) (a) Que, L., J r.; Ho, R. Y. N. Chem. Rev. 1996, 96, 2607-2624.
(b) For a simple model system employing only FeCl3 and H2O, see:
Funabiki, T.; Yoneda, I.; Ishikawa, M.; Ujiie, M.; Nagai, Y.; Yoshida,
S. J . Chem. Soc., Chem. Commun. 1994, 1453-1454.
(40) Miller, J . M.; So, K. H.; Clark, J . H. Can. J . Chem. 1979, 57,
1887-1889.
(44) Barluenga, J .; Lopez, L. A.; Martinez, S.; Tomas, M. Tetrahe-
dron 2000, 56, 4967-4975.
(41) Bhatt, M. V. J . Organomet. Chem. 1978, 156, 221-226.

Total Synthesis of the Calphostins
J . Org. Chem., Vol. 66, No. 4, 2001 1301
Sch em e 7. P h otocycliza tion of Ca r ben e Com p lex
28
nished naphthol 31 in 36% yield in contrast to the model
system, which never provided more than a few percent
of the benzannulated product (Scheme 7). The bulky
triisopropylsiloxy group may contribute to the improved
photocyclization by not allowing the carbene to remain
in coplanar conjugation with the electron-rich aromatic
core. Nevertheless, the photocyclization efficiency could
not be further improved, as a result the isonitrile route
continued to be employed.
We were now ready to explore dimerization of the
o-naphthoquinone 29 employing iron(III) chloride in
acetonitrile. Dimerization, with concomitant deprotection
of the TIPS groups, afforded 70% of the desired pery-
lenequinone 32 as an approximately 1.1:1 P/M mixture
of atropisomers along with small amounts of the dihy-
drofuranyl fused tricycle 33 (eq 2). The interesting
F igu r e 2. Tether design.
temperature of all the side-chain hydrogens, suggestive
of hindered rotation of the side chains. Although we had
gained rapid entry into a functionalized perylenequinone,
the dimerization was rather discouraging since the
process was not atropselective and the recalcitrant
perylenequinone could not be coerced into any useful
reaction manifold, despite great efforts.
Atr op selective Syn th esis. Provision for control of
atropselectivty was not properly addressed in the original
synthetic design, a most crucial issue for synthesis of the
calphostins. At this point in the synthesis, much effort
had already been expended, so an approach that main-
tained as much continuity in our synthetic scheme was
desired. Employing a tether would be synthetically
minimally disruptive and potentially favor the formation
of a single diastereomer in addition to facilitating the
dimerization process by bringing the two quinone moi-
eties in close proximity.46 The tether could be achiral and
utilize the side-chain chirality to control atropisomer
formation or the tether could be chiral with the resultant
possibility of double diastereoselection for control of
atropisomerism. Attachment could be achieved at several
positions on the quinone precursor, clearly the most
synthetically accessible position was the side-chain al-
cohol (Figure 2).
Before proceeding synthetically, several achiral tethers
were first examined computationally by a molecular
mechanics conformational search of perylenequinone
products with tethers linking the side-chain alcohols
using Spartan.47 The product geometries were minimized
for each atropisomer and all tethers uniformly favored
the undesired M atropisomer. To verify the computational
results, several tethered bis-naphthoquinones were pre-
pared, but only the o-phthaloyl-tethered bis-naphtho-
quinone 35 underwent dimerization to afford a single
diastereomeric product 36 (Scheme 8). Bis-naphtho-
quinone 35 was prepared from carbene complex 28 in the
sequence outlined in Scheme 8. Conversion of 36 to
derivative 38M by methylation of the enols and cleavage
of the tether with NaOMe (Scheme 9) secured the
absolute configuration by comparison to the CD spectra
of 38P (prepared independently), which indicated that
36 was the M atropisomer as predicted by computations.
tricyclic o-quinone 33 side product was always isolated
in 5-10% yields and resulted from Michael addition of
the side chain alcohol into the quinone followed by
oxidation. Product 32 only varies from calphostin D in
the methylation pattern; consequently, we attempted to
convert this inseparable mixture of atropisomers to
calphostin D by a methylation-demethylation sequence.
Regrettably, the obstinate side-chain alcohols or the enols
evaded all attempts at methylation or further function-
alization. Mild conditions failed to induce reaction, while
more forcing conditions led to demethylation and decom-
position of 32.45 Some of this difficulty may be attributed
to an extended hydrogen-bonding network that is formed
between the carbonyl, enol, and side-chain alcohol func-
tions. Evidence for this is provided in the 1H NMR
spectrum, which shows very broad signals at room
(45) A brief list of some methylation conditions surveyed: (a)
CH2N2: see ref 32b. (b) K2CO3, MeI: Adams, S. P.; Whitlock, H. W.,
J r. J . Org. Chem. 1981, 46, 3474-3478. (c) Ag2O, MeI: Arnone, A.;
Camarda, L.; Nasini, G. J . Chem. Soc., Perkin Trans. 1 1985, 1387.
(d) AgOTf, MeI: Burk, R. M.; Gac, T. S.; Roof, M. B. Tetrahedron Lett.
1994, 8111-8112. (e) CsF, MeI: Dijkstra, G.; Kruizinga, W. H.;
Kellogg, R. M. J . Org. Chem. 1987, 52, 4230-4234. (f) Bu2Sn(OMe)2,
MeI: Boons, G.-J .; Castle, G. H.; Clase, J . A.; Grice, P.; Ley, S. V.;
Pinel, C. Synlett 1993, 913-914. (g) Me2SO4, EtOH, NaOH: Organic
Syntheses; Wiley: New York, 1973; Collect. Vol. VI, pp 800-803. (h)
For H-bonded alcohols: TBAF, DMF, MeI: see, ref 40. (i) For a recent
paper with excellent references for the chemoselective O-methylation
of phenols under nonaqueous conditions, see: Basak, A.; Nayak, M.
K.; Chakraborti, A. K. Tetrahedron Lett. 1998, 39, 4883-4886.
While our synthetic options had been severely limited,
we realized that a simple protecting group change might
(46) Several tethering strategies have been developed using a chiral
auxiliary to control the sense of atropselection. (a) Feldman, K. S.;
Ensel, S. M. J . Am. Chem. Soc. 1994, 116, 3357-3366. For an
application in synthesis, see: Feldman, K. S.; Smith, R. S. J . Org.
Chem. 1996, 61, 2606-2612. (c) Miyano, S.; Fukushima, H.; Handa,
S.; Ito, H.; Hashimoto, H. Bull. Chem. Soc. J pn. 1988, 61, 3249-3254.
(d) See ref 28.
(47) Spartan, SGI Version 5.0; Wavefunction Inc., 18401 Von
Karman Ave., Suite 370, Irvine, CA 92612. http://www.wavefun.com/.

1302 J . Org. Chem., Vol. 66, No. 4, 2001
Merlic et al.
Sch em e 8. P r ep a r a tion of a Teth er ed
P er ylen equ in on e
employing trifluoroacetic acid (TFA) and air as the
oxidant to provide perylenequinone 40 in 71% yield with
the benzoate intact (Scheme 10).32b,50 Disappointingly, a
2:1 mixture of atropisomers favoring the undesired M
isomer was obtained.51 We were aware that the chiral
axis was not configurationally stable at high tempera-
tures as the isomerization barrier was measured for a
related perylenequinone to be 21 kcal/mol, and we had
accordingly taken precautions to avoid reactions at
elevated temperatures.23 Now, we considered turning this
apparent limitation to our advantage. After carefully
sparging with argon, the perylenequinone was found to
smoothly epimerize in refluxing toluene over 36 h. We
were elated to discover that the 1:2 P/M ratio of atrop-
isomers thermally equilibrated to a 3:1 separable mixture
favoring the desired P atropisomer! Recycling 40M led
to an overall yield of 56% for 40P from 39. From
molecular modeling, as well as NMR data, the observed
selectivity can be explained as arising from a stabilizing
π interaction52 of the side chain benzoate with the
perylenequinone core, which is favorable for the P isomer,
but conformationally inaccessible for the M isomer.53 The
1H NMR beautifully illustrates this, as the ortho protons
of the side chain benzoate groups of the P isomer are
shielded by 0.7 ppm relative to the M isomer.
Sch em e 9. Secu r in g th e Ster eoch em istr y of 36 by
Con ver sion to Der iva tive 38M
The binaphthoquinone 41 could also be isolated as a
1:1 mixture of atropisomers, if the reaction was stopped
prematurely (Scheme 11).54 Since the biaryl bond that is
remote from the side chain stereogenic centers is gener-
ated first, the lack of significant stereoinduction is
understandable. Formation of the remote bond is the
stereodefining step as the biaryl axis is configurationally
stable at room temperature. To verify that the binaph-
thoquinone chirality was preserved in conversion to the
perylenequinone, atropisomerically pure binaphthoquin-
one 41M was oxidatively closed to perylenequinone 40M
with retention of configuration in accord with a related
binaphthalene system observed by Broka (eq 3).30
Sch em e 10. P r ep a r a tion of Ben zoyla ted
P er ylen equ in on e
greatly alleviate our difficulties.48 Since the TIPS protect-
ing group was incompatible under the dimerization
conditions, it was anticipated that the benzoate protect-
ing group, which also happens to conveniently be the
side-chain functional group in some of the calphostins,
should be stable.49 Deprotection of o-naphthoquinone 29
proved to be problematic, due to the propensity for the
side-chain alcohol to undergo an internal Michael addi-
tion into the quinone; however, installation of the ben-
zoate at an earlier stage was readily accomplished.
Protection of naphthalene 34 as the benzoate ester and
oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone
(DDQ) provided the benzoylated naphthoquinone 39
(Scheme 10).
Hauser proposed a very tenable mechanism for acid-
catalyzed dimerization of o-naphthoquinones via inter-
mediates such as 42 (Scheme 11).34 Two mechanistic
(50) Conditions employing FeCl3/CH3CN also provided useful yields
of the product perylenequinone, typically 40-50%; however, the
experimentally simpler conditions utilizing TFA and oxygen were
cleaner and afforded higher overall yields.
(51) The stereochemistry was confirmed by elaborating the minor
diastereomer to Calphostin A by a methylation/demethylation sequence
which indicated that this was indeed the P atropisomer by comparison
to the literature data in ref 1b. Similarly, the major diastereomer was
elaborated to the M-atropisomer of Calphostin A as determined by
comparison of its CD spectra to that of Calphostin A.
(52) Cozzi, F.; Cinquini, M.; Annuziata, R.; Siegel, J . S. J . Am. Chem.
Soc. 1993, 115, 5330-5331.
We were delighted to find that dimerization proceeded
smoothly using modified conditions of Diwu and Lown
(53) The hexamethoxyperylenquinone 44 with only side chain
alcohols isomerized to a 1:1 mixture of atropisomers demonstrating
the importance of the benzoate function. See ref 23 for a similar finding
with cercosporin.
(54) A related binaphthoquinone was isolated by Hauser; see ref 34.
Diwu and Lown also isolated a regioisomeric binaphthoquinone; see
ref 32a.
(48) For an excellent review on the importance of protecting group
strategies, see: Schelhaas, M.; Waldmann, H. Angew. Chem., Int. Ed.
1996, 35, 2056-2083.
(49) The acetate protecting group was stable to TFA in Hauser’s
synthesis (ref 34) of Calphostin D and the more stable benzoate was
anticipated to also be stable under the reaction conditions.

Total Synthesis of the Calphostins
J . Org. Chem., Vol. 66, No. 4, 2001 1303
Sch em e 11. Dim er iza tion Mech a n ism
Sch em e 12. Com p letion of Ca lp h ostin C
Syn th esis
niently followed colorimetrically as the blood-red pery-
lenequinone solution turned dark green upon addition
of TBAF indicating formation of the anion and the
sanguine color returned within minutes upon completion
of methylation. Desymmetrization of the calphostin side
chains was performed by a carefully controlled metha-
nolysis of 44, which provided an astonishing 84% yield
of the monobenzoate 45 based on a 58% conversion. This
was indeed noteworthy since we expected a statistical
mixture of products. One rationale is a steric activation
for loss of the first benzoyl group. A second, and more
intriguing explanation, would be mono debenzoylation
followed by hemiortho ester formation under the basic
conditions that protects the second benzoate.
The final task remaining was installation of the mixed
carbonate linkage, which was fashioned by reacting the
secondary alcohol on 45 with phosgene to afford the
chloroformate ester that was not isolated, but reacted in
situ with 4-acetoxyphenol providing the mixed carbonate
46.55 A monoprotected hydroquinone had to be employed
due to the preference of dihydroquinone to react on both
hydroxy groups. Careful choice of the protecting group
was made such that it could be removed under extremely
mild conditions, provide favorable solubility properties
to the hydroquinone, and enhance the reactivity of the
p-hydroxyl group. Illustrating this final point, the mono-
TBS protected dihydroquinone failed to react, but the
monoacetate-protected dihydroquinone reacted rapidly.
manifolds diverge from this common intermediate. The
first involves closure to dihydroperylenequinone 43 where
subsequent oxidation leads to perylenequinone 40. The
second, less fruitful, pathway for 42 is direct oxidation
to binaphthoquinone 41. Hauser found that this second
pathway was unproductive as the binaphthoquinone did
not undergo closure to the perylenequinone; conse-
quently, he attempted to avoid this pathway by slow
addition of an oxidant. In contrast, we found that
binaphthoquinone 41 closed to perylenequinone 40, albeit
much more slowly. Thus, 50% yields of perylenequinone
40 could be isolated from 39 after only a few hours
reaction along with 20-30% of binaphthoquinone 41.
Since the binaphthoquinone closed slowly, the naphtho-
quinone dimerization reaction was routinely run for 24-
36 h until complete consumption of intermediate binaph-
thoquinone was observed by TLC. The reluctance to
closure of the binaphthoquinone can be readily under-
stood by examining the reaction mechanism. Reduction
to intermediate 42 would formally allow a pathway
whereby binaphthoquinone could reenter a productive
pathway to perylenequinone; however, considering the
reaction conditions (TFA, O2), this seems unlikely, but
would account for the sluggishness of the reaction. One
possible reducing agent is of course dihydroperylene-
quinone 43.
Regioselective demethylation using freshly prepared
34,56
MgI2
followed by chemoselective methanolysis of the
acetate in the presence of the benzoate and carbonate
linkages provided calphostin C (3). While our 9-Br-BBN/
TFA protocol developed in the model system for the
regioselective demethylation proved satisfactory, the
simple one-step procedure used initially by Hauser
employing MgI2 provided higher overall yields on the
more highly functionalized calphostin C. Analogously, the
other calphostins were efficiently prepared from the
common hexamethoxyperylenequinone intermediate 44
(Scheme 13). Regioselective demethylation of 44 with
MgI2 yielded calphostin A (1). Initial attempts to prepare
calphostin D by hydrolysis of the benzoates followed by
Com p letion of th e Syn th esis. With a successful
route to enantiomerically and atropisomerically pure
perylenequinone 40P , completion of the calphostin C
synthesis was undertaken (Scheme 12). Methylation of
40P provided hexamethoxyperylenequinone 44 which
was utilized as a common intermediate for the synthesis
of all four calphostin targets. This reaction was conve-
(55) Petersen, U. In Houben-Weyl Methoden der Organischen Che-
mie; Hagemann, H., Ed.; Georg Thieme Verlag: 4. Auflage, Stuttgart,
1983; Bd E4, 66-77.
(56) Yamaguchi, S.; Nedachi, M.; Yokoyama, H.; Hirai, Y. Tetrahe-
dron Lett. 1999, 40, 7363-7365.

1304 J . Org. Chem., Vol. 66, No. 4, 2001
Merlic et al.
Sch em e 13. Syn th esis of Ca lp h ostin s A, B, a n d D
F igu r e 3. SAR analysis.
photodynamic therapy.57 Moreover, the change in hydro-
gen-bonding capabilites would be expected to modulate
calphostin binding. We planned at the outset to explore
most extensively modifications on the side chains as
slight structural perturbations within the natural series
have significant effects on the bioactivity.1b
It will be interesting investigating the activity of model
perylenequinone 16 since it will provide insight into
whether side chain oxygenation is required. The trun-
cated des-methyl analogue 47 reduces the stereochemical
elements present in the calphostins by removing the
stereogenic center of the side chain (Figure 4). In
analogue 48, the appendage oxygenation has been shifted
to the terminal position of the side chain, which probes
the positional requirements of the side-chain oxygen-
ation. The methylation patterns of all three series of
compounds will also be examined to determine how
alteration of these important functionalities affects the
biological activity. The interesting cyclized perylene-
quinone 50 was isolated during the synthesis of analogue
48. The novel structure will be investigated as the side
chains are now completely folded back onto the pery-
lenequinone core and the resulting drastic conformational
change should affect the biological profile. The phthaloyl-
tethered perylenequinone 49 will be investigated because
the side-chain sector is also fairly restricted as in 50, but
has an aromatic residue which appears to be important
for activity. Additionally, 49 possesses the opposite M
axial chirality. To more appropriately address the axial
chirality issue, we prepared analogue 51 from 40M which
is the M-axial diastereomer of calphostin A. Last, we
hypothesize that the calphostins bind edge-on in the
binding pocket, whereby only half of the molecule strongly
interacts, while the other half resides outside the bind-
ing pocket. Thus, the greater activity of calphostin C
versus calphostin A may be due to the presence of the
p-hydroxyphenyl carbonate moiety versus the benzoate
function. Therefore, the C2 symmetric analogue 52 was
prepared from 44 via a route analogous to that for
calphostin C. Future studies may explore replacement
of the carbonate moiety with a more stable isostere since
a pilot pharmokinetics study has shown that calphostin
C is hydrolyzed to the less active calphostin B by loss of
the carbonate moiety.58
demethylation of the peri-methoxy groups were unre-
warding, providing only trace amounts of product. How-
ever, the reversed sequence of demethylation followed by
methanolysis was more productive. Thus, methanolysis
of calphostin A provided calphostin D (4). Calphostin B
(2) was in turn prepared by demethylation of 45. Syn-
thetic calphostins A, B, C, and D were identical to natural
1
samples by comparison of H NMR, 13C NMR, CD, UV,
IR, and HRMS spectral data.1c
Syn th esis of An a logu es. Our flexible and efficient
synthetic route allowed us to prepare a number of
calphostin analogues that kept the central perylene-
quinone pharmacophore intact while varying the func-
tionality around the periphery of this core. Additionally,
we explored structures of key intermediates and side
products that we obtained during the total synthesis of
the calphostins. Together, these approaches afforded
more than twenty structurally unique compounds that
will provide a preliminary examination of the SAR of the
calphostins. The structural features that we addressed
were as follows: (1) the axial chirality of the perylene-
quinone; (2) the methylation pattern; (3) the appendage
length; and (4) the appendage oxygenation pattern
(Figure 3). Although much effort was spent in controlling
the axial chirality, we were also interested in the bioac-
tivity of the unnatural M-atropisomer. Adjustments to
the methylation pattern are worth investigating since the
methylation of the C-2 and C-11 enols leads to compounds
that possess a significant red-shift in the UV spectrum
making these derivatives more suitable as agents for
(57) Henderson, B. W.; Dougherty, T. J . Photochem. Photobiol. 1992,
55, 145-157.
(58) Chen, C.-L.; Tai, H.-L.; Zhu, D.-M.; Uckun, F. M. Pharm. Res.
1999, 16, 1003-1009.

Total Synthesis of the Calphostins
J . Org. Chem., Vol. 66, No. 4, 2001 1305
F igu r e 4. Analogue structures.
magnetic resonance (NMR) spectra were obtained with a
Bruker AM 360 instrument or ARX 400 instrument in deu-
teriochloroform and/or deuteriobenzene solutions, unless oth-
erwise specified. Chemical shifts are reported in parts per
million downfield from tetramethylsilane, and coupling con-
stants are reported in Hertz. EI mass spectra were recorded
on a Micromass Autospec instrument. FAB mass spectra were
recorded on a (VG) ZAB-SE instrument. Specific rotations
[R]22D were determined on a Perkin-Elmer 241MC polarimeter
at the sodium D line at 22 °C. Precoated silica gel plates
(Macherey-Nagel) were used for analytical thin-layer chroma-
tography (TLC). ICN Silitech silica gel 60 (230-400 mesh) was
employed for column chromatography. Tetrahydrofuran (THF)
and diethyl ether were distilled from sodium-benzophenone
ketyl; dichloromethane, acetonitrile, and hexanes were dis-
tilled from calcium hydride. Reagents were obtained com-
mercially and used as received unless otherwise specified. All
moisture- or air-sensitive reactions were carried out under a
static argon atmosphere.
2-Br om o-3,5-d im eth oxyben zyl a lcoh ol (18). NBS (21.8
g, 122 mmol) was added in one portion to a solution of 3,5-
dimethoxybenzyl alcohol (20.5 g, 122 mmol) in DMF (100 mL)
at room temperature in the dark and then stirred for 60 h.
The reaction was poured onto H2O (500 mL), and the white
precipitate was collected by vacuum filtration and air-dried.
The crude product was recrystallized from 2:1 CH2Cl2/hexanes
(120 mL) to afford 23.8 g (79%) of the product as white needles:
Rf ) 0.18 (70:30 hexanes/EtOAc); 1H NMR (360 MHz, CDCl3)
δ 2.03 (t, J ) 6.5 Hz, 1H), 3.83 (s, 3H), 3.88 (s, 3H), 4.74 (d, J
) 6.5 Hz, 2H), 6.44 (d, J ) 2.7 Hz, 1H), 6.70 (d, J ) 2.7 Hz,
1H); 13C NMR (90 MHz, CDCl3) δ 55.6, 56.3, 65.3, 98.9, 102.2,
104.7, 141.7, 156.5, 160.0; IR (film) 3283, 3005, 2934, 2841,
1586, 1491, 1421, 1329, 1290, 1201, 1041, 1020 cm-1; HRMS
(EI) calcd M+ (C9H1179BrO3) 247.9871, found 247.9867; LRMS
(EI) 248 (85), 246 (100), 215 (10), 137 (27), 124 (25).
Con clu sion
The final route to calphostin C proceeded in only 12
steps from commercially available starting materials. The
synthesis hinged on a rapid and efficient construction of
an o-naphthoquinone using benzannulation of a chro-
mium carbene complex. The atropselectivity was in turn
controlled by thermal epimerization of the chiral axis to
provide the desired P-atropisomer. The use of a tether
to provide stereochemical induction followed by removal
represents a general strategy for challenging stereochem-
ical issues found in the calphostins, albeit with poor atom
economy. Nevertheless, for stereochemically complex and
rare situations, as found with axial chirality, case by case
studies need to be done.59 Calphostin C likely represents
the most complex natural product yet prepared using
Fischer carbene complexes.60 Furthermore, the brevity
and versatility of our synthetic route allowed preparation
of analogues which will provide a mapping of the struc-
tural requirements for the biological activity of the
calphostins. Biological testing of these analogues will be
reported in due course and the results will provide the
first SAR for the calphostins. The calphostins are fasci-
nating structures and their unparalleled potent and
selective inhibition of PKC warrants further exploration.
Exp er im en ta l Section
Ap p a r a tu s a n d Rea gen ts. Infrared (IR) spectra were
recorded on a Nicolet 510P FT-IR spectrophotometer and
selected absorption maxima are reported in cm-1. Nuclear
(59) For examples where substrate control has been successfully
applied to direct the sense of atropselection, see: (a) Evans, D. A.;
Wood, M. R.; Trotter, B. W.; Richardson, T. I.; Barrow, J . C.; Katz, J .
L. Angew. Chem., Int. Ed. 1998, 37, 2700-2704. (b) Evans, D. A.;
Dinsmore, C. J .; Watson, P. S.; Wood, M. R.; Richardson, T. I.; Trotter,
B. W.; Katz, J . L. Angew. Chem., Int. Ed. 1998, 37, 2704-2708. (c)
Boger, D. L.; Miyazaki, S.; Kim, S. H.; Wu, J . H.; Loiseleur, O.; Castle,
S. L. J . Am. Chem. Soc. 1999, 121, 3226-3227. (d) Boger, D. L.; Castle,
S. L.; Miyazaki, S.; Wu, J . H.; Beresis, R. T.; Loiseleur, O. J . Org. Chem.
1999, 64, 70-80. (e) Yoshimura, F.; Kawata, S.; Hirama, M. Tetrahe-
dron Lett. 1999, 40, 8281-8285. (f) Lipshutz, B. H.; Keith, J . M. Angew.
Chem., Int. Ed. Engl. 1999, 38, 3530-3533. (g) Landais, Y.; Robin,
J .-P. Tetrahedron Lett. 1986, 27, 1785-1788.
(60) For a review of syntheses employing benzannulation of Fischer
carbene complexes in natural product synthesis, see: (a) Wulff, W. D.
In Comprehensive Organometallic Chemistry II; Abel, E. W., Stone, F.
G. A., Wilkinson, G., Eds.; Pergamon Press: 1995; Vol. 12, pp 491-
497. (b) For the synthesis of amino acids and peptides utilizing
chromium complex photochemistry, see: Hegedus, L. S. Tetrahedron
1997, 53, 4105-4128.
2-Br om o-3,5-d im eth oxyben zyl Iod id e (19). Iodine (41.1
g, 162 mmol) was added in portions to a solution of triphen-
ylphosphine (42.5 g, 162 mmol) in CH2Cl2 (300 mL) at 0 °C
and allowed stir for 5 min. To the resulting yellow slurry was
added dropwise via an addition funnel over 10 min a solution
of 18 (26.7 g, 108 mmol) and imidazole (22.0 g, 324 mmol) in
CH2Cl2 (200 mL). After being stirred for 1 h at 0 °C, the
reaction mixture was diluted with CH2Cl2 (300 mL) and
washed successively with 5% NaHSO3 (300 mL), H2O (300
mL), and brine (300 mL), dried with MgSO4, and filtered
through a 1 in. plug of silica gel, washing with an additional
500 mL of CH2Cl2. The filtrate was concentrated to a white
solid and recrystallized from 1:1 CH2Cl2/hexanes (500 mL) to
provide 22.4 g of white needles from the first crop and an
additional 9.0 g from the second crop for a total yield of 31.4
g (81%): Rf ) 0.35 (90:10 hexanes/EtOAc); 1H NMR (360 MHz,
CDCl3) δ 3.81 (s, 3H), 3.86 (s, 3 H), 4.53 (s, 2 H), 6.39 (d, J )

1306 J . Org. Chem., Vol. 66, No. 4, 2001
Merlic et al.
2.7 Hz, 1H), 6.59 (d, J ) 2.7 Hz, 1H); 13C NMR (90 MHz,
CDCl3) δ 6.3, 55.5, 56.3, 99.4, 104.5, 106.2, 139.8, 157.1, 159.5;
IR (film) 2977, 2940, 2840, 1591, 1458, 1427, 1329, 1205, 1155,
1078, 1020, 936, 820, 650 cm-1; HRMS (EI) calcd M+
(C9H1079BrIO2) 355.8909, found 355.8916; LRMS (EI) 357 (25),
355 (25), 229 (100), 135 (45).
6,8-Dim et h oxy-3-(2′(R)-(t r iisop r op ylsilyloxyp r op yl)-
1,2-n a p h th oqu in on e (29). Neat tert-butylisonitrile (50 µL,
0.44 mmol) was added to a stirring orange solution of carbene
complex 28 (120 mg, 0.20 mmol) in THF (0.5 mL) and the
mixture allowed to stir for 10 h at room temperature. The
reaction was diluted with an additional 10 mL of THF, and
the resulting yellow solution was heated at gentle reflux for
16 h before becoming transparent green. After cooling, a
solution of CAN (548 mg, 1.0 mmol) in H2O (2 mL) was added,
and the resulting deep orange solution was stirred for 15 min.
The reaction was poured into aqueous saturated NaHCO3 and
extracted with chloroform. The combined organic extracts were
washed with brine, dried with MgSO4, filtered, and concen-
trated to an orange oil. Chromatography with chloroform
afforded 94 mg (82% yield) of the o-naphthoquinone 29 as an
orange oil. When the initial reaction was run more dilute (0.1
M) then the indenone 30 was isolated in 20-25% yields with
Dieth yl 2-Br om o-3,5-d im eth oxyben zyl P h osp h on a te
(25). A slurry of 19 (11.6 g, 32.5 mmol) in neat triethyl
phosphite (20 mL) was heated until all the solids went into
solution and a gentle reflux began (∼60-70 °C evolution of
ethyl iodide). Heating was stopped when reflux was noted to
stop (2 h). Excess triethyl phosphite was removed by vacuum
distillation, and the oily residue was recrystallized from 2:3
Et2O/hexanes (125 mL) to afford 11.2 g (93%) of white needles:
1H NMR (360 MHz, CDCl3) δ 1.24 (t, J ) 7.1 Hz, 6H), 3.40 (d,
J ) 22.1 Hz, 2H), 3.77 (s, 3H), 3.83 (s, 3H), 4.03 (pent, J ) 7.2
Hz, 4H), 6.37 (t, J ) 2.4 Hz, 1H), 6.63 (t, J ) 2.7 Hz, 1H); 13
C
NMR (90 MHz, CDCl3) δ 16.3 (d, J ) 6.1 Hz), 33.7 (d, J ) 139
Hz), 55.5, 56.2, 62.2 (d, J ) 6.5 Hz), 98.7 (d, J ) 3.3 Hz), 105.6
(d, J ) 9.1 Hz), 107.3 (d, J ) 4.8 Hz), 133.5 (d, J ) 8.7 Hz),
156.8 (d, J ) 2.8 Hz), 159.2 (d, J ) 3.4 Hz); IR (film) 2930,
2857, 1612, 1514, 1464, 1250, 1096, 835 cm-1; HRMS (EI) calcd
M+ (C13H2079BrO5P) 368.0211, found 368.0218; LRMS (EI) 368
(50), 366 (50), 287 (100), 259 (30).
a corresponding decrease in the yield of the desired o-
naphthoquinone 29.
Da ta for 29: Rf ) 0.33 (98:2 CH2Cl2/MeOH); 1H NMR (360
MHz, CDCl3) δ 1.03 (d, J ) 6.4 Hz, 18H), 1.00-1.10 (m, 6H),
2.52 (dd, J ) 13.2, 5.7 Hz, 1H), 2.58 (dd, J ) 13.3, 6.3 Hz,
1H), 3.91 (s, 3H), 3.96 (s, 3H), 4.20 (sext, J ) 6.0 Hz, 1H),
6.38 (d, J ) 2.2, 1H), 6.41 (d, J ) 2.2 Hz, 1H), 7.12 (s, 1H); 13
C
(E)-2-Br om o-3,5-d im eth oxy-1-(4′(R)-(tr iisop r op ylsilyl-
oxy)p en t-1′-en yl)ben zen e (27). A 2.0 M solution of n-
butyllithium (1.35 mL, 2.71 mmol) was added to a solution of
hexamethyldisilazane (574 µL, 2.72 mmol) in THF (5 mL) at
0 °C, turning the solution pale yellow over 15 min. A solution
of phosphonate 25 (903 mg, 2.46 mmol) in THF (10 mL) was
slowly added and the reaction allowed to stir for 30 min until
it became orange-yellow. A solution of aldehyde 26 (680 mg,
2.96 mmol) in THF (5 mL) was added and the reaction mixture
allowed to warm slowly to room temperature with stirring for
16 h. The reaction mixture was diluted with water and
extracted with ether, dried with MgSO4, filtered, and concen-
trated to a yellow oil. Chromatography with 97:3 hexanes/
EtOAc afforded 966 mg (92%) of a colorless oil: Rf ) 0.28 (95:5
NMR (90 MHz, CDCl3) δ 12.4, 18.1, 23.8, 40.0, 55.8, 56.3, 67.1,
98.4, 109.1, 112.9, 137.8, 138.8, 143.3, 165.4, 166.4, 176.1,
181.8; IR (film) 2944, 2867, 1655, 1565, 1462, 1354, 1235, 1121
cm-1; HRMS (EI) calcd M+ (C24H36O5Si) 432.2332, found
432.2324; LRMS (EI) 434 (53), 433 (37), 432 (38), 389 (100),
361 (70), 343 (43), 260 (58), 157 (25); [R]22 ) 1.3 (c ) 0.0020,
D
Et2O).
Da ta for 30: Rf ) 0.6 (70:30 hexanes/EtOAc); 1H NMR (200
MHz, CDCl3) δ 1.01-1.11 (m, 21H), 1.12 (d, J ) 6.0 Hz, 3H),
2.32 (dd, J ) 13.9, 7.5 Hz, 1H), 2.54 (dd, J ) 14.0, 4.8 Hz,
1H), 3.82 (s, 3H), 3.89 (s, 3H), 4.16 (sext, J ) 6.0 Hz, 1H),
6.11 (d, J ) 1.7 Hz, 1H), 6.20 (d, J ) 1.8 Hz, 1H), 6.92 (s, 1H).
13C NMR (90 MHz, CDCl3) δ 12.3, 18.0 (2C), 23.3, 35.3, 55.6,
55.8, 67.2, 96.1, 103.5, 108.6, 139.0, 140.3, 149.2, 158.1, 166.7,
194.8; IR (film) 2961, 2866, 1698, 1624, 1601, 1464, 1377, 1209,
1159, 1122, 1096, 1003 cm-1; HRMS (FAB) calcd (M + H)+
(C23H37O4Si) 405.2461, found 405.2455; [R]22D ) 83.6 (c ) 1.74,
CH2Cl2).
1
hexanes/EtOAc); H NMR 360 MHz (CDCl3) δ 1.03-1.09 (m,
21H), 1.22 (d, J ) 6.1 Hz, 3H), 2.37-2.51 (m, 2H), 3.81 (s,
3H), 3.86 (s, 3H), 4.09 (sext, J ) 5.9 Hz, 1H), 6.22 (dt, J )
15.7, 7.3 Hz, 1H), 6.39 (d, J ) 2.7 Hz, 1H), 6.65 (d, J ) 2.7 Hz,
1H), 6.80 (d, J ) 15.7, 1 H); 13C NMR 90 MHz (CDCl3) δ 12.4,
18.1, 23.6, 43.5, 55.4, 56.3, 68.4, 98.6, 102.6, 104.1, 130.7, 131.0,
139.2, 156.7, 159.4; IR (film) 2942, 2866, 1734, 1581, 1464,
1415, 1204, 1163, 1134, 1088, 883, 679 cm-1; HRMS (EI) calcd
M+ (C22H3779BrO3Si) 456.1695, found 456.1687; LRMS (EI) 458
(8), 456 (7), 413 (20), 371 (27), 201 (100), 157 (35), 131 (29),
2-H yd r oxy-3-(2′(R)-t r iisop r op ylsilyloxyp r op yl)-1,6,8-
tr im eth oxyn a p h th a len e (31). A solution of freshly prepared
carbene 28 (308 mg, 0.50 mmol) in THF (18 mL) was degassed
by sparging with argon for 20 min and then pressurized to 40
psi with CO in a Pyrex pressure tube. The red carbene solution
was irradiated using a 450 W medium-pressure mercury lamp
fitted with a quartz filter. The color of the solution faded and
turned yellow after 1 h. The contents were concentrated to a
yellow-green film and chromatographed with 90:10 hexanes/
EtOAc to provide 80 mg (36%) of a colorless oil: Rf ) 0.1 (95:5
hexanes/EtOAc); 1H NMR (360 MHz, CDCl3) δ 1.03-1.10 (m,
21H), 1.15 (d, J ) 6.0 Hz, 3H), 2.87 (dd, J ) 13.2, 6.6 Hz, 1H),
3.04 (dd, J ) 13.2, 5.7 Hz, 1H), 3.86 (s, 3H), 3.87 (s, 3H), 3.96
(s, 3H), 4.38 (sext, J ) 6.0 Hz, 1H), 6.47-6.49 (m, 2H), 6.61
(d, J ) 2.2 Hz, 1H), 7.22 (s, 1H); 13C NMR (90 MHz, CDCl3) δ
12.4, 18.0, 18.1, 23.3, 41.7, 55.2, 56.0, 62.2, 68.5, 98.5, 98.7,
114.7, 125.1, 128.4, 131.0, 140.6, 144.4, 155.7, 156.0; IR (film)
2959, 2943, 2867, 1613, 1585, 1452, 1371, 1348. 1265, 1205,
1159, 1109, 1055 cm-1; HRMS (EI) calcd M+ (C25H40O5Si)
448.2645, found 448.2639; LRMS (EI) 448 (97), 390 (75), 274
103 (22); [R]22 ) 0.050 (c ) 0.10, Et2O).
D
[(2,4-Dim eth oxy-6-((E)-4′(R)-(tr iisop r op ylsilyloxyp en t-
1′-e n yl)p h e n yl)(m e t h oxy)m e t h yle n e ]p e n t a ca r b on yl-
ch r om iu m (28). A 1.5 M solution of t-BuLi (5.3 mL, 7.92
mmol) was added to a stirred slurry of Cr(CO)6 (924 mg, 4.20
mmol) and aryl bromide 27 (1.70 g, 3.96 mmol) in ether (40
mL) at 0 °C. The reaction turned yellow then orange-brown
over 10 min when all solids were noted to go into solution.
Neat methyl triflate (1.34 mL, 11.88 mmol) was added and
the reaction stirred for 30 min before becoming orange-red.
The reaction was quenched at 0 °C with 500 µL of saturated
aqueous NaHCO3 solution, followed by dilution with ether (50
mL) and addition of MgSO4. The reaction mixture was passed
through a pad of silica gel (1/4 in.), and the filtrate was
concentrated to a red oil. Chromatography with 95:5 hexanes/
EtOAc afforded 2.12 g (88%) of a dark orange-red oil. The
product is unstable and was used immediately in the subse-
quent cyclization reaction: Rf ) 0.20 (95:5 hexanes/EtOAc); 1H
NMR (360 MHz, C6D6) δ 1.16 (br s, 24H), 2.45 (br s, 2H), 3.23
(br s, 3H), 3.40 (br s, 3H), 3.54 (br s, 3H), 4.05 (br s, 1H), 6.25
(br s, 1H), 6.35 (br s, 1H), 6.74 (br s, 1H), 7.20 (br s, 1H); 13C
NMR (100 MHz, C6D6) δ 12.8, 18.4, 23.7, 44.0, 54.9 (2C), 64.6,
68.7, 97.9, 101.3, 130.3, 131.1, 131.4, 132.0, 150.9, 161.3, 217.0,
225.5, 360.0; IR (film) 2946, 2868, 2062, 1935, 1599, 1570,
1462, 1254, 1134, 937, 881, 650 cm-1; HRMS (CI) calcd M+
(C29H4052CrO9Si) 612.1847, found 612.1814; LRMS (CI) 612
(0.2), 556 (13), 472 (19), 470 (15), 420 (65), 363 (42), 219 (100).
(100), 259 (25), 157 (23); [R]22 ) -12 (c ) 0.93, CH2Cl2).
D
(2′R)-2,11-Dih yd r oxy-4,6,7,9-tetr a m eth oxy-1,12-bis(2′-
h yd r oxyp r op yl)-3,10-p er ylen eq u in on e (32). Solid iron
trichloride (54 mg, 0.34 mmol) was added to a degassed
solution (freeze-pump-thaw) of quinone 29 (58 mg, 0.134
mmol) in acetonitrile (2 mL) to provide a deep red solution
that was stirred 16 h at room temperature before turning
brown. After 48 h, the solution was dark blue. The reaction
was diluted with chloroform, washed with an aqueous 0.5 N
HCl, and dried with CaCl2. Charcoal was added to the solution,
which was then filtered and concentrated to a red oil. Chro-
matography with CHCl3 f 98:2 CHCl3/MeOH afforded 26 mg
(70%) of perylenequinone 32 as a red oil as a 0.55 P/0.45 M

Total Synthesis of the Calphostins
J . Org. Chem., Vol. 66, No. 4, 2001 1307
mixture of diastereomers and 4 mg (10%) of tricyclic o-
naphthoquinone 33 as a yellow oil.
1263, 1205, 1159, 1113, 1055 cm-1; HRMS (FAB) calcd (M +
H)+ (C48H61N2O10) 825.4326, found 825.4307; [R]22 ) -21 (c
D
Da ta for 32: Rf ) 0.16 (95:5 CH2Cl2/MeOH); 1H NMR (400
MHz, CD2Cl2, 235 K) δ 1.31 (d, J ) 6.1 Hz, 3H), 1.63 (d, J )
6.2 Hz, 3H), 2.68 (dd, J ) 15.9, 10.5 Hz, 1H), 3.09 (dd, J )
15.3, 8.2 Hz, 1H), 3.28 (dd, J ) 15.2, 9.5 Hz, 1H), 3.65 (dd, J
) 16.0, 8.4 Hz, 1H), 4.07 (s, 3H), 4.10 (s, 3H), 4.13 (s, 3H),
4.14 (s, 3H), 4.75-4.85 (m, 1H), 5.02-5.12 (m, 1H), 6.74 (s,
) 0.40, CH2Cl2).
P r ep a r a tion of P h th a loyl-Teth er ed Bis-o-n a p h th o-
qu in on e (35). CAN (46 mg, 0.08 mmol) in H2O (0.3 mL) was
added to a solution of phthaloyl-tethered naphthylamine (15.8
mg, 0.019 mmol) in THF (2 mL) at room temperature. TLC
showed completion after 30 min. The reaction mixture was
diluted with CHCl3 (5 mL) and washed successively with H2O
and brine. The organic layer was dried with Na2SO4 and
concentrated to an orange oil. Chromatrography with 98:2 CH2-
Cl2/MeOH afforded 12.2 mg (80%) of the title compound as an
orange oil: Rf ) 0.24 (95:5 CH2Cl2/MeOH); 1H NMR (400 MHz,
CDCl3) δ 1.35 (d, J ) 6.3 Hz, 6H), 2.67 (dd, J ) 14.7, 8.0 Hz,
2H), 2.77 (dd, J ) 14.7, 4.6 Hz, 2H), 3.91 (s, 12H), 5.25-5.30
(m, 2H), 6.39 (d, J ) 2.0 Hz, 2H), 6.48 (d, J ) 2.0 Hz, 2H),
7.16 (s, 2H), 7.47 (dd, J ) 5.6, 3.3 Hz, 2H), 7.59 (dd, J ) 5.7,
3.3 Hz, 2H); 13C NMR (100 MHz, CDCl3) δ 20.1, 34.9, 55.9,
56.2, 70.9, 98.8, 109.6, 113.0, 128.7, 130.9, 132.3, 136.3, 138.7,
143.0, 165.3, 166.5, 166.8, 175.9, 181.6; IR (film) 2936, 1716,
1653, 1591, 1456, 1327, 1263, 1165 cm-1; HRMS (EI) calcd (M
+ H)+ (C38H35O12) 683.2129, found 683.2105; LRMS (EI) 683
1
1H), 6.75 (s, 1H); H NMR (200 MHz, DMSO-d6, 298 K) new
signals appear at δ 5.75 (s, 2H, OH) and δ 8.31 (s, 2H, OH);
13C NMR (100 MHz, CD2Cl2, 235 K) δ 20.4, 20.5, 41.0, 41.5,
56.4, 56.6, 81.1, 81.2, 94.0 (2C), 108.4, 108.5, 111.0, 111.1,
121.4, 122.3, 126.8, 127.0, 130.7, 131.3, 154.3, 154.7, 163.1,
163.2, 164.1, 164.2, 174.0, 174.3, (2 OCH3 peaks under CD2-
Cl2 signal); IR (film) 3443, 2925, 1618, 1541, 1209 cm-1
;
FABMS 551.1 M + H (weak), 515.3 (strong) (loss of 2 H2O from
M + H); UV-vis (MeOH) λmax nm (ꢀ) 437 (5300), 510 (7400);
CD (MeOH) nm (∆ꢀ) 307 (+3.9), 348 (-1.1), 440 (+1.9), 571
(-1.3).
Da ta for 33: Rf ) 0.27 (95:5 CH2Cl2/MeOH); 1H NMR (400
MHz, CDCl3) δ 1.54 (d, J ) 6.3 Hz, 3 H), 2.74 (dd, J ) 16.3,
7.6 Hz, 1 H), 3.28 (dd, J ) 16.3, 10.1 Hz, 1 H), 3.94 (s, 3 H),
3.95 (s, 3 H), 5.15 (ddq, J ) 16.5, 7.5, 6.4 Hz, 1 H), 6.64 (d, J
) 2.4 Hz, 1 H), 7.28 (d, J ) 2.5 Hz, 1 H); 13C NMR (100 MHz,
CDCl3) δ 21.9, 34.1, 56.0, 56.4, 83.0, 102.8, 104.1, 113.5, 120.5,
137.8, 161.4, 162.5, 165.2, 175.9, 181.7; IR (film) 2925, 2851,
1653, 1631, 1589, 1456, 1370, 1316, 1224, 1157 cm-1; HRMS
(EI) calcd M+ (C15H14O5) 274.0841, found 274.0835; LRMS (EI)
275 (49), 274 (100), 259 (28), 257 (26), 227 (15).
(3), 279 (76), 246 (100), 204 (75), 148 (82); [R]22 ) -75 (c )
D
0.42, CH2Cl2).
P r ep a r a tion of P h th a loyl-Teth er ed P er ylen equ in on e
(36). A solution of bis-o-naphthoquinone 35 (31.6 mg, 0.046
mmol) in CH2Cl2 (10 mL) was added via syringe pump over 7
h to neat trifluoroacetic acid (10 mL) at room temperature
under an oxygen atmosphere and then stirred for an additional
15 h. The dark blue reaction was diluted with CHCl3 (20 mL)
and then quenched by the slow addition of an aqueous
saturated NaHCO3 solution. The deep red organic layer was
washed with brine, dried over Na2SO4, and concentrated to a
red oil. Chromatography with 95:5 EtOAc/MeOH affored 16.2
mg (51%) of a single diastereomeric product as a red oil: Rf )
2-ter t-Bu t yla m in o-3-(2′(R)-h yd r oxyp r op yl)-1,6,8-t r i-
m eth oxyn a p h th a len e (34). tert-Butylisonitrile (0.38 mL, 3.3
mmol) was added to carbene 28 (929 mg, 1.51 mmol) in THF
(2 mL) at room temperature and the mixture allowed to stir
for 20 h. The solution faded from a deep red to a light brown
with formation of a white precipitate (Cr(CO)5CN-t-Bu). The
solution of ketenimine was then diluted with THF (15 mL)
and heated at reflux for 24 h. The reaction was allowed to cool
to room temperature, and then a 1.0 M solution of tetrabutyl-
ammonium fluoride in THF (4.8 mL, 4.8 mmol) was added.
After 4 h, the resulting green solution was diluted with Et2O
(50 mL), washed with brine, dried over MgSO4, and concen-
trated to a yellow-brown oil. Chromatography with 60:40
hexanes/EtOAc afforded 317 mg (60%) of a yellow oil: Rf )
0.2 (60:40 hexanes/EtOAc); 1H NMR (360 MHz, CDCl3) δ 1.15
(d, J ) 6.2 Hz, 3H), 1.25 (s, 9H), 2.99 (dd, J ) 14, 1.9 Hz, 1H),
3.17 (dd, J ) 14, 7.4 Hz, 1H), 3.80 (s, 3H), 3.86 (s, 3H), 3.95
(s, 3H), 3.95-4.05 (m, 1H), 6.48 (d, J ) 2.2 Hz, 1H), 6.62 (d, J
) 2.2 Hz, 1H), 7.19 (s, 1H); 13C NMR (90 MHz, CDCl3) δ 24.0,
30.4, 44.2, 55.2, 56.1 (2C), 61.9, 69.9, 98.3, 98.7, 114.7, 124.8,
132.4, 135.2, 138.8, 152.2, 156.4, 157.6; IR (film) 3360 (br),
2965, 2930, 1624, 1578, 1450, 1391, 1338, 1261, 1205, 1157,
1111, 1057, 910, 733 cm-1; HRMS (EI) calcd M+ (C20H29NO4)
347.2097, found 347.2095; LRMS (EI) 347.2 (100), 332.2 (16),
1
0.28 (95:5 CH2Cl2/MeOH); H NMR (360 MHz, CDCl3) δ 1.15
(d, J ) 6.3 Hz, 6H), 2.93 (dd, J ) 15.7, 7.0 Hz, 2H), 3.79 (dd,
J ) 15.7, 9.2 Hz, 2H), 4.12 (s, 6H), 4.20 (s, 6H), 6.05-6.10 (m,
2H), 6.74 (s, 2H), 7.49 (dd, J ) 5.7, 3.3 Hz, 2H), 7.73 (dd, J )
5.8, 3.3 Hz, 2H), 8.08 (br s, 2H); 13C NMR (90 MHz, CDCl3) δ
19.0, 38.5, 56.2, 56.6, 71.6, 93.9, 105.2, 106.0, 111.4, 117.6,
128.8, 130.6, 131.4, 131.8, 149.7, 164.2, 164.9, 167.6, 175.7;
IR (film) 3279 (br), 2934, 2851, 1714, 1591, 1296, 1217 cm-1
;
HRMS (FAB) calcd (M + H)+ (C38H33O12) 681.1972, found
681.1986; UV-vis (MeOH) λmax nm (ꢀ) 229 (32 000), 273
(22 300), 344 (13 900), 520 (3300); [R]22 ) 2.3 × 103 (c )
D
0.0032, MeOH).
3-(2′(R)-(Ben zoyloxy)p r op yl)-6,8-d im eth oxy-1,2-n a p h -
th oqu in on e (39). Pyridine (19 µL, 0.19 mmol), benzoyl
chloride (19 µL, 0.16 mmol), and catalytic 4-(dimethylamino)-
pyridine were added consecutively to a stirring solution of
naphthylamine 34 (43 mg, 0.125 mmol) in CH2Cl2 (6 mL) at
room temperature. The reaction was stirred for 3 h, and then
DDQ (86 mg, 0.38 mmol) was added in one portion. The
solution immediately turned deep brown. After 1 h, the
solution was diluted with CH2Cl2, washed with brine, dried
with MgSO4, and concentrated to an orange oil. Chromatog-
raphy with 99:1 CH2Cl2/MeOH afforded 41 mg (87%) of an
orange solid: Rf ) 0.40 (95:5 CH2Cl2/MeOH); 1H NMR (360
MHz, CDCl3) δ 1.39 (d, J ) 6.2 Hz, 3H), 2.70-2.85 (m, 2H),
3.86 (s, 3H), 3.92 (s, 3H), 5.33 (sext, J ) 6.2 Hz, 1H), 6.29 (d,
J ) 1.9 Hz, 1H), 6.38 (d, J ) 1.9 Hz, 1H), 7.10 (s, 1H), 7.40 (t,
J ) 7.7 Hz, 2H), 7.52 (t, J ) 7.4 Hz, 1H), 7.97 (d, J ) 7.4 Hz,
2H); 13C NMR (90 MHz, CDCl3) δ 20.3, 35.3, 56.0, 56.5, 70.4,
98.9, 109.5, 113.1, 128.5, 129.7, 130.5, 133.1, 136.8, 138.5,
143.0, 165.6, 166.1, 166.6, 175.9, 181.6; IR (film) 3065, 2980,
2939, 1713, 1657, 1591, 1562, 1327, 1273, 1165, 1113, 713
cm-1; HRMS (EI) calcd M+ (C22H20O6) 380.1260, found 380.1263;
LRMS (EI) 380.1 (23), 336.1 (5), 259.1 (15), 230.1 (42), 105.0
291.1 (12), 276.1 (10), 259.1 (36), 219.1 (10), 213.1 (6); [R]22
) -87.3 (c ) 1.28, CH2Cl2).
D
P r ep a r a tion of P h th a loyl-Teth er ed Na p h th yla m in e.
Sodium hydride (55 mg, 1.50 mmol, 65% dispersion in oil,
hexanes-washed) was added to a stirring solution of alcohol
34 (175 mg, 0.50 mmol) (azeotroped 3 × 5 mL, benzene) in
THF (5 mL) at room temperature and the mixture allowed to
stir 1 h. Phthaloyl chloride (36 µL, 0.25 mmol) was added to
the sodium alkoxide and the reaction stirred for 12 h when
TLC showed completion. The reaction was diluted with Et2O
(30 mL), washed with brine, dried with MgSO4, and concen-
trated to a brown oil. Chromatrography with 80:20 hexanes/
EtOAc afforded 136 mg (66%) of a colorless oil: TLC Rf ) 0.47
(80:20 hexanes/EtOAc); 1H NMR (400 MHz, CDCl3) δ 1.21 (s,
18H), 1.30 (d, J ) 6.2 Hz, 6H), 3.17 (dd, J ) 13.1, 7.0 Hz, 2H),
3.30 (dd, J ) 13.3, 6.1 Hz, 2H), 3.76 (s, 6H), 3.86 (s, 6H), 3.96
(s, 6H), 5.46 (hext, J ) 6.6 Hz, 2H), 6.47 (d, J ) 2.2 Hz, 2H),
6.62 (d, J ) 2.2 Hz, 2H), 7.34 (s, 2H), 7.41 (dd, J ) 5.7, 3.3
Hz, 2H), 7.52 (dd, J ) 5.7, 3.3 Hz, 2H); 13C NMR (100 MHz,
CDCl3) δ 19.4, 30.8, 38.9, 55.1, 55.2, 56.2, 61.2, 73.0, 98.2, 98.6,
115.3, 123.9, 128.7, 130.6, 132.6, 133.9, 134.8, 136.0, 151.4,
156.5, 157.0, 167.0; IR (film) 2963, 1720, 1624, 1577, 1339,
(100); [R]22 ) -154 (c ) 1.28, CH2Cl2).
D
(2′R)-1,12-Bis(2′-b en zoyloxyp r op yl)-2,11-d ih yd r oxy-
4,6,7,9-tetr a m eth oxy-3,10-p er ylen equ in on e (40). Neat tri-
fluoroacetic acid (4 mL) was added to o-naphthoquinone 39
(248 mg, 0.65 mmol) at 0 °C. The solution instantly turned
green and then dark blue over a few minutes. A stream of

1308 J . Org. Chem., Vol. 66, No. 4, 2001
Merlic et al.
oxygen was passed through the solution for 3 h at 0 °C, and
then the reaction was stirred for another 30 h at room
temperature under a static oxygen atmosphere until TLC
indicated completion. The reaction was quenched at 0 °C with
saturated aqueous NaHCO3 (30 mL), and then the aqueous
solution was extracted with CH2Cl2. The combined organic
extracts were dried with Na2SO4 and concentrated to a deep
red oil. Chromatography with 95:5 EtOAc/MeOH provided 175
mg (71%) of a deep red oil as an approximately 1:2 (40P /40M)
mixture of diastereomers.
vided three fractions. Recovered starting material 44 was
isolated from the first fraction 49 mg (42%). The desired
product 45 eluted next affording 50 mg (49%) of a deep red
oil. Finally, the bis-debenzoylated product 38P (see charac-
terization and independent preparation of 38P in supporting
info) was isolated as the third fraction 3.8 mg (4%).
Da ta for 45: Rf ) 0.15 (95:5, CH2Cl2/MeOH); 1H NMR (360
MHz, CDCl3) δ 0.90 (d, J ) 6.2 Hz, 3H), 1.24 (d, J ) 6.2 Hz,
3H), 2.69 (dd, J ) 13.2, 7.7 Hz, 1H), 2.95 (dd, J ) 13.4, 9.9
Hz, 1H), 3.30-3.40 (m, 2H), 3.65-3.75 (m, 1H) 3.94 (s, 3H),
4.01 (s, 3H), 4.02 (s, 3H), 4.14 (s, 3H), 4.16 (s, 3H), 4.18 (s,
3H), 5.02-5.12 (m, 1H), 6.54 (s, 1H), 6.62 (s, 1H), 6.92 (t, J )
7.8 Hz, 2H), 7.00 (d, J ) 7.4 Hz, 2H), 7.22 (t, J ) 7.2 Hz, 1H);
13C NMR (90 MHz, CDCl3) δ 21.0, 23.2, 37.7, 40.6, 55.7, 56.0,
56.3, 56.4, 60.4, 60.5, 68.9, 72.4, 94.6, 94.8, 108.8, 110.8, 127.5,
128.7, 129.6, 130.2, 130.7, 131.0, 131.5, 131.7, 132.4, 153.7,
153.9, 162.6, 162.7, 163.6 (2C), 165.0, 178.1, 178.4 (3 aryl C’s
not observed); IR (film) 3426, 3000, 2975, 2938, 2883, 2845,
1715, 1614, 1576, 1543, 1464, 1367, 1287, 1214, 1154, 983, 752,
711 cm-1; HRMS (FAB) calcd (M + H)+ (C39H39O11) 683.2493,
found 683.2489; [R]22D ) -3.3 × 103 (c ) 0.0038, MeOH); UV-
vis (MeOH) λmax nm (ꢀ) 221 (42 000), 268 (27 000), 338 (4800),
471 (21 000), 657 sh (6200).
(2′R,2′′R,P )-1-(2′-(Ben zoyloxyp r op yl)-2,4,6,7,9,11-h exa -
m et h oxy-12-(2′′-(4′′′-a cet oxy)p h en oxyca r b on yloxyp r o-
p yl)-3,10-p er ylen equ in on e (46). Triethylamine (20 µL, 0.13
mmol) and phosgene (78 µL, 0.13 mmol, 1.9 M/toluene) were
added consecutively to a solution of 45 (29.7 mg, 0.0435 mmol)
in THF (5 mL) at 0 °C. After 15 min of stirring, when TLC
indicated complete conversion to the chloroformate ester, the
solvent and excess phosgene were removed in vacuo. The
residue was redissolved in THF (5 mL), then triethylamine
(60 µL, 0.39 mmol), p-acetoxyphenol (66 mg, 0.435 mmol), and
catalytic 4-(dimethylamino)pyridine were added. After 1.5 h,
the reaction was diluted with chloroform (30 mL), washed with
aqueous 1 N HCl and brine, dried with Na2SO4, and concen-
trated to a red oil. Chromatography with 99:1 f 98:2 CH2Cl2/
MeOH afforded 34.1 mg (91%) of a deep red oil.
Da ta for 40P : Rf ) 0.13 (98:2 CHCl3/MeOH); 1H NMR (360
MHz, CDCl3) δ 1.24 (d, J ) 6.2 Hz, 6H), 3.15 (dd, J ) 13.7,
9.7 Hz, 2H), 3.46 (dd, J ) 13.8, 2.4 Hz, 2H), 3.92 (s, 6H), 4.16
(s, 6H), 5.15-5.25 (m, 2H), 6.48 (s, 2H), 6.88 (t, J ) 7.5 Hz,
4H), 6.99 (d, J ) 7.1 Hz, 4H), 7.19 (t, J ) 7.4 Hz, 2H), 8.11 (br
s, 2H); 13C NMR (90 MHz, CDCl3) δ 21.0, 37.5, 55.9, 56.6, 71.8,
94.0, 106.3, 111.2, 119.8, 127.6, 128.9, 130.0, 130.9, 131.1,
131.7, 149.8, 164.1, 164.8, 165.2, 176.3; IR (film) 2934, 1717,
1593, 1547, 1435, 1368, 1273, 1215, 1053, 711 cm-1; HRMS
(FAB) calcd (M + H)+ (C44H39O12) 759.2442, found 759.2454;
[R]22D ) -2.1 × 103 (c ) 0.0030, MeOH); UV-vis (MeOH) λmax
nm (ꢀ) 271 (29 000), 344 (4100), 517 (22 000).
Da ta for 40M: Rf ) 0.17 (98:2 CHCl3/MeOH); 1H NMR (360
MHz, CDCl3) δ 0.76 (d, J ) 6.3 Hz, 6H), 3.19 (dd, J ) 13.4,
7.4 Hz, 2H), 3.62 (dd, J ) 13.4, 4.8 Hz, 2H), 4.10 (s, 6H), 4.16
(s, 6H), 5.05 (sext, J ) 6.7 Hz, 2H), 6.60 (s, 2H), 7.26 (t, J )
8.2 Hz, 4H), 7.42 (t, J ) 7.4 Hz, 2H), 7.69 (d, J ) 7.2 Hz, 4H),
8.14 (br s, 2H); 13C NMR (90 MHz, CDCl3) δ 19.3, 36.2, 56.3,
56.6, 70.9, 94.3, 106.2, 111.4, 117.8, 128.2, 129.5, 130.5, 131.0,
131.1, 132.5, 150.5, 164.4, 164.9, 165.7, 176.1; IR (film) 2938,
1711, 1593, 1547, 1466, 1435, 1367, 1298, 1273, 1215, 1178,
1161, 1053, 819, 754, 711 cm-1; HRMS (FAB) calcd (M + H)+
(C44H39O12) 759.2442, found 759.2447; [R]22 ) +8.0 × 102 (c
D
) 0.0042, MeOH); UV-vis (MeOH) λmax nm (ꢀ) 226 (54 000),
273 (31 000), 345 (4200), 511 (23 000).
Isom er iza tion to 40P . A solution of 40 (1:2, 40P /40M, 726
mg, 0.96 mmol) in toluene (100 mL) was sparged with argon
for 20 min and then heated at reflux for 36 h. The solvent was
removed and the red oil chromatographed with 99:1 CHCl3/
MeOH. The diastereomers were difficult to separate, but after
repeated chromatography of the overlap region 472 mg (65%)
of 40P and 153 mg (21%) of 40M were isolated as a red solids.
Thermal equilibration of 40M provided another 100 mg (14%)
of 40P .
Da ta for in ter m ed ia te ch lor ofor m a te ester : Rf ) 0.29
(95:5 CH2Cl2/MeOH).
Da ta for 46: Rf ) 0.29 (95:5 CH2Cl2/MeOH); 1H NMR (360
MHz, CDCl3) δ 1.17 (d, J ) 6.3 Hz, 3H), 1.25 (d, J ) 6.2 Hz,
3H), 2.26 (s, 3H), 2.83 (dd, J ) 13.5, 9.6 Hz, 1H), 2.92 (dd, J
) 13.4, 10.0 Hz, 1H), 3.32-3.42 (m, 2H), 3.69 (s, 3H), 3.91 (s,
3H), 4.04 (s, 3H), 4.16 (s, 3H), 4.18 (s, 3H), 4.19 (s, 3H), 4.72-
4.80 (m, 1H), 5.05-5.15 (m, 1H), 6.23-6.30 (m, 2H), 6.47 (s,
1H), 6.54 (s, 1H), 6.72-6.79 (m, 2H), 6.91 (t, J ) 8.0 Hz, 2H),
6.98 (dd, J ) 8.2, 1.2 Hz, 2H), 7.20 (tt, J ) 7.4, 1.2 Hz, 1H);
13C NMR (90 MHz, CDCl3) δ 20.5, 21.0 (2C), 37.1, 37.4, 55.6,
55.7, 56.3, 56.4, 60.3, 60.4, 72.4, 76.6, 94.4, 94.7, 108.9 (2C),
110.8 (2C), 121.3, 121.6, 127.5, 128.7, 129.0, 129.6, 129.8,
130.6, 131.1, 131.2, 131.5, 132.4, 147.5, 147.9, 152.3, 154.0
(2C), 162.6, 162.9, 163.5, 163.8, 165.0, 169.3, 178.2 (1 aryl C
not observed); IR (film) 3000, 2980, 2937, 1753, 1716, 1618,
1576, 1541, 1458, 1369, 1284, 1213, 1180, 1161, 983, 752, 713
cm-1; HRMS (FAB) calcd (M + H)+ (C48H45O15) 861.2758, found
(2′R,P )-1,12-Bis(2′-ben zoyloxyp r op yl)-2,4,6,7,9,11-h exa -
m eth oxy-3,10-p er ylen equ in on e (44). Tetrabutylammonium
fluoride (0.32 mL, 1.0 M THF) was added to a stirring solution
of 40P (55 mg, 0.073 mmol) in THF (10 mL) and MeI (3 mL)
to provide a dark green solution, which turned deep red within
3 min. The solution was allowed to stir for an additional 20
min and then diluted with chloroform (20 mL) and poured onto
H2O (20 mL). The organic layer was separated and dried with
Na2SO4. Chromatography with 99:1 CHCl3/MeOH afforded 53
mg (92%) of a deep red oil: Rf ) 0.26 (95:5, CH2Cl2/MeOH); 1H
NMR (360 MHz, CDCl3) δ 1.24 (d, J ) 6.2 Hz, 6H), 2.93 (dd,
J ) 13.4, 10.0 Hz, 2H), 3.40 (dd, J ) 13.4, 1.9 Hz, 2H), 3.85 (s,
6H), 4.10 (s, 6H), 4.20 (s, 6H), 5.05-5.15 (m, 2H), 6.44 (s, 2H),
6.87 (t, J ) 8.1 Hz, 4H), 6.95 (d, J ) 7.0 Hz, 4H), 7.18 (t, J )
7.2 Hz, 2H); 13C NMR (90 MHz, CDCl3) δ 21.0, 37.5, 55.5, 56.3,
60.3, 72.4, 94.5, 108.7, 110.5, 127.4, 128.6, 129.4, 130.3, 130.6,
131.4, 131.7, 153.8, 162.4, 163.4, 165.0, 178.1; IR (film) 3000,
2978, 2940, 2883, 2847, 1715, 1618, 1576, 1543, 1367, 1285,
1213, 1159, 983, 711 cm-1; HRMS (FAB) calcd (M + H)+
861.2767; [R]22 ) -2.1 × 103 (c ) 0.0070, MeOH); UV-vis
D
(MeOH) λmax nm (ꢀ) 220 (43 000), 269 (27 000), 334 (4600), 473
(21 000), 570 sh (6200).
Ca lp h ostin C (3). A freshly prepared MgI2 solution61 (0.64
mL, 0.064 mmol, 0.10 M/Et2O) was added to a solution of 46
(22 mg, 0.026 mmol) in THF (10 mL) at room temperature.
The solution gradually changed from deep red to green over
30 min. After 2 h, the reaction was diluted with chloroform
(20 mL), washed successively with aqueous 1 N HCl and brine,
dried with Na2SO4, treated with EDTA to remove any residual
magnesium, and concentrated to a purple oil. The intermediate
acetyl calphostin C was chromatographed on a short column
of silica gel eluting with CH2Cl2 f 99:1 CH2Cl2/MeOH to afford
a red oil that was treated with methanol (5 mL) and solid
NaHCO3 (40 mg). The solution was stirred for 2 h under argon
and then diluted with CHCl3 (20 mL), washed with aqueous 1
(C46H43O12) 787.2754, found 787.2769; [R]22 ) -2.9 × 103 (c
D
) 0.0032, MeOH); UV-vis (MeOH) λmax nm (ꢀ) 340 (4200), 472
(20 000), 572 (6200).
(2′R,2′′R,P )-1-(2′-Ben zoyloxyp r op yl)-2,4,6,7,9,11-h exa -
m et h oxy-12-(2′′-h yd r oxyp r op yl)-3,10-p er ylen eq u in on e
(45). A solution of NaOMe (30 mL, 13 mmol, 0.43 M NaOMe/
MeOH) was added to a stirring solution 44 (117 mg, 0.15
mmol) in MeOH (20 mL) at room temperature. The progress
of the reaction was monitored by TLC. After 3.15 h, the
reaction was diluted with chloroform (50 mL), washed succes-
sively with aqueous saturated NaHCO3, brine, and dried with
Na2SO4. Chromatography with 98:2f96:4 CH2Cl2/MeOH pro-
(61) See the Supporting Information.

Total Synthesis of the Calphostins
J . Org. Chem., Vol. 66, No. 4, 2001 1309
N HCl and brine, dried with Na2SO4, and concentrated to a
deep red oil. Chromatography with 198:2 f 197:3 CH2Cl2/
MeOH afforded 15.5 mg (78%) of a deep red solid.
Da ta for in ter m ed ia te a cetyl ca lp h ostin C: Rf ) 0.53
(95:5 CH2Cl2/MeOH).
6.86 (d, J ) 7.1 Hz, 2H), 6.92 (t, J ) 7.4 Hz, 2H), 7.26 (t, J )
7.5 Hz, 1H), 15.75 (br s, 1H), 15.93 (br s, 1H); 13C NMR (90
MHz, CDCl3) δ 21.1, 23.8, 39.0, 42.5, 55.9, 56.1, 61.2 (2C), 69.0,
72.2, 101.2, 101.4, 106.2, 106.4, 117.2, 117.5, 125.3, 125.5,
127.4, 127.5, 128.3, 128.4, 129.1, 132.0, 134.7, 136.5, 151.1,
151.2, 164.5, 166.5, 166.8, 171.1, 171.8, 178.9, 179.2; IR (film)
3387, 2967, 2934, 2852, 1717, 1605, 1540, 1450, 1271, 1214,
1157, 1113, 760, 712 cm-1; HRMS (FAB) calcd (M + H)+
Da ta for ca lp h ostin C: Rf ) 0.31 (95:5 CH2Cl2/MeOH); 1H
NMR (400 MHz, CDCl3) δ 1.19 (d, J ) 6.2 Hz, 3H), 1.29 (d, J
) 6.2 Hz, 3H), 3.10 (dd, J ) 13.3, 10.2 Hz, 1H), 3.17 (dd, J )
13.4, 10.0 Hz, 1H), 3.60-3.67 (m, 2H), 3.67 (s, 3H), 3.85 (s,
3H), 4.30 (s, 6H), 4.67-4.75 (m, 1H), 5.00-5.10 (m, 1H), 5.59
(br s, 1H), 6.13 (d, J ) 8.7 Hz, 2H), 6.28 (s, 1H), 6.30 (s, 1H),
6.49 (d, J ) 8.7 Hz, 2H), 6.88 (d, J ) 7.6 Hz, 2H), 6.94 (t, J )
7.5 Hz, 2H), 7.23-7.25 (m, 1H), 15.81 (br s, 1H), 15.82 (br s,
1H); 13C NMR (100 MHz, CDCl3) δ 20.7, 21.2, 38.7, 38.9, 53.4,
56.0 (2C), 61.2, 72.3, 76.3, 101.2 (2C), 106.4, 106.5, 115.4, 116.8,
117.3, 121.3, 125.3, 125.8, 127.1, 127.5, 127.6, 128.4, 129.1,
132.1, 133.6, 134.3, 143.8, 151.5, 151.6, 152.6, 153.2, 164.6,
166.6, 166.7, 172.1 (2C), 178.2, 178.6; IR (film) 2964, 2936,
(C37H35O11) 655.2179, found 655.2188; [R]22 ) -2.3 × 103 (c
D
) 0.0032, MeOH); UV-vis (MeOH) λmax nm (ꢀ) 225 (45 000),
269 (24 000), 348 (3700), 476 (19 000), 541 (9900), 586 (9700);
CD (MeOH) nm (∆ꢀ) 233 (-68.5), 291 (+43.4), 360 (-14.3),
448 (+19.1), 584 (-13.5).
Ca lp h ostin D (4). A solution of NaOMe (15 mL, 5.6 mmol,
0.37 M/MeOH) was added to 1 (22.0 mg, 0.028 mmol) at room
temperature to provide a green solution. After 72 h, the
reaction was diluted with chloroform (30 mL) and washed
successively with aqueous 1 N HCl and brine, dried with Na2-
SO4, and concentrated to a deep purple oil. Chromatography
with 98:2 CH2Cl2/MeOH afforded 10.1 mg (66%) of a red oil:
1755, 1717, 1605, 1508, 1450, 1269, 1207, 1159, 752, 711 cm-1
;
HRMS (FAB) calcd (M + H)+ (C44H39O14) 791.2340, found
791.2352; [R]22 ) -8.7 × 102 (c ) 0.0062, MeOH); UV-vis
1
D
Rf ) 0.31 (95:5 CH2Cl2/MeOH); H NMR (CDCl3, 400 MHz) δ
(MeOH) λmax nm (ꢀ) 223 (36 000), 271 (18 000), 349 (2900), 477
(15 000), 543 (7400), 587 (7100); CD (MeOH) nm (∆ꢀ) 232
(-64.5), 292 (+52.3), 359 (-14.9), 448 (+22.2), 584 (-12.2).
Ca lp h ostin A (1). A freshly prepared MgI2 solution61 (2.63
mL, 0.095 mmol, 0.036 M/Et2O) was added to a stirring
solution of 44 (29 mg, 0.038 mmol) in THF (40 mL) at room
temperature under argon. The solution gradually changed
from deep red to green. After 6 h, TLC showed complete
reaction. The solution was diluted with chloroform (60 mL),
washed with aqueous 1 N Hcl (20 mL), dried with Na2SO4,
treated with EDTA to remove any residual magnesium, and
concentrated to a deep purple oil. Chromatography with 200:1
CHCl3/MeOH afforded 26 mg (92%) of a deep red solid: Rf )
0.97 (d, J ) 6.1 Hz, 6H), 2.95 (dd, J ) 13.2, 8.7 Hz, 2H), 3.56
(dd, J ) 13.2, 2.8 Hz, 2H), 3.70-3.80 (m, 2H), 3.92 (s, 6H),
4.24 (s, 6H), 6.31 (s, 2H), 15.83 (br s, 2H); 13C NMR (90 MHz,
CDCl3) δ 24.1, 43.8, 57.3, 61.5, 69.7, 101.8, 107.1, 118.2, 127.5,
130.2, 139.0, 152.8, 168.6, 175.3, 178.1; IR (film) 3387, 2968,
2927, 2854, 1604, 1541, 1456, 1277, 1157 cm-1; HRMS (FAB)
calcd (M + H)+ (C30H31O10) 551.1917, found 551.1937; [R]22
D
) -3.6 × 103 (c ) 0.0031, MeOH); UV-vis (MeOH) λmax nm
(ꢀ) 224 (48 000), 268 (32 000), 345 (4700), 476 (24 000), 538
(13 000), 583 (12 000); CD (MeOH) nm (∆ꢀ) 225 (-56.1), 291
(+ 44.4), 358 (-14.2), 442 (+18.7), 586 (-11.5).
Ack n ow led gm en t. We thank the National Insti-
tutes of Health for support of this work. Support from
National Science Foundation Young Investigator (1992-
1997), Camille Dreyfus Teacher-Scholar (1994-1999),
and Alfred P. Sloan Research Fellowship (1995-1997)
awards to C.A.M. is gratefully acknowledged. C.C.A. is
a recipient of National Institutes of Health training
grant support and support from the Rohm and Haas Co.
A.S. is a recipient of the Presidents Undergraduate
Research Fellowship and the J ean Dreyfus Boissevain
Undergraduate Research Scholarship. We thank Merck
and Co. for a generous donation of (R)-methyl 3-hy-
droxybutyrate.
1
0.75 (95:5 CH2Cl2/MeOH); H NMR (CDCl3, 360 MHz) δ 1.28
(d, J ) 6.3 Hz, 6H), 3.16 (dd, J ) 13.2, 10.0 Hz, 2H), 3.67 (dd,
J ) 13.4, 1.2 Hz, 2H), 3.79 (s, 6H), 4.33 (s, 6H), 5.00-5.10 (m,
2H), 6.21 (s, 2H), 6.82 (d, J ) 8.0 Hz, 4H), 6.90 (t, J ) 7.6,
4H), 7.22 (t, J ) 7.2 Hz, 2H), 15.85 (s, 2H); 13C NMR (90 MHz,
CDCl3) δ 21.1, 39.0, 55.8, 61.2, 72.3, 101.2, 106.3, 116.6, 125.5,
127.3, 127.5, 128.4, 129.0, 131.9, 134.6, 151.4, 164.6, 166.2,
172.4, 177.9; IR (film) 3010, 2980, 2940, 2875, 2847, 1717,
1607, 1541, 1456, 1271, 1211, 1159, 1109, 756, 709 cm-1
;
HRMS (FAB) calcd (M + H)+ (C44H39O12) 759.2442, found
759.2422; [R]22 ) -1.4 × 103 (c ) 0.0036, MeOH); UV-vis
D
(MeOH) λmax nm (ꢀ) 225 (53 000), 270 (23 000), 350 (4000), 477
(19 000), 543 (9800), 587 (9400); CD (MeOH) nm (∆ꢀ) 232
(-96.4), 291 (+46.7), 360 (-14.6), 451 (+20.9), 588 (-12.8).
Ca lp h ostin B (2). A freshly prepared MgI2 solution61 (0.90
mL, 0.090 mmol, 0.10 M/Et2O) was added to a solution of 45
(23.5 mg, 0.034 mmol) in THF (30 mL) at room temperature.
The solution gradually changed from deep red to green over 2
h. The reaction was diluted with chloroform (75 mL), washed
successively with aqueous 1 N HCl and brine, dried with Na2-
SO4, treated with EDTA to remove any residual magnesium,
and concentrated to a deep purple oil. Chromatography with
200:1 CH2Cl2/MeOH afforded 16.2 mg (72%) of a deep red solid:
Su p p or tin g In for m a tion Ava ila ble: Description of the
experimentals and characterization data for compounds 6-8,
11-16, 20, 22, 26, 37. Description of the complete syntheses
of analogues 47-52 starting from commercially available
starting materials. 1H NMR and 13C NMR for compounds
1-22, 25-37, 38M, 38P , 39, 40M, 40P , 41M, 41P , 44-46.
Additionally, complete 1H NMR and 13C NMR spectra for
analogues 47-52, including all intermediates in their synthe-
sis. CD spectra for 1-4, 32, 38M, 38P , 41M, and 41P This
material is available free of charge via the Internet at
http://pubs.acs.org.
1
Rf ) 0.42 (95:5 CH2Cl2/MeOH); H NMR (CDCl3, 360 MHz) δ
0.99 (d, J ) 6.1 Hz, 3H), 1.27 (d, J ) 6.3 Hz, 3H), 2.91 (dd, J
) 13.2, 8.8 Hz, 1H), 3.22 (dd, J ) 13.3, 9.7 Hz, 1H), 3.55-3.68
(m, 2H), 3.69-3.77 (m, 1H) 3.80 (s, 3H), 3.84 (s, 3H), 4.26 (s,
3H), 4.31 (s, 3H), 4.95-5.08 (m, 1H), 6.11 (s, 1H), 6.27 (s, 1H),
J O0014663