Synthetic routes to a constrained ring analog of didemnin B

Article abstract of DOI:10.1021/jo951693i

The didemnin class of biologically active cyclodepsipeptides, isolated from a marine tunicate, has shown antitumor, antiviral, and immunosuppressive activities. Synthetic studies were undertaken to prepare a modified analog of one of the most potent congeners, didemnin B (1). The side chain of the isostatine unit was tethered into the macrocycle via a cyclohexane ring in order to provide a more rigid conformation and determine the importance of this unit in bioactive compounds. This modification created a new macrocycle core and generated a diastereomeric mixture of a constrained analog of didemnin B (2).

Full text of DOI:10.1021/jo951693i

J . Org. Chem. 1996, 61, 1655-1664
1655
Syn th etic Rou tes to a Con str a in ed Rin g An a log of Did em n in B
Scott C. Mayer, Amy J . Pfizenmayer, and Madeleine M. J oullie´*
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323
Received September 14, 1995X
The didemnin class of biologically active cyclodepsipeptides, isolated from a marine tunicate, has
shown antitumor, antiviral, and immunosuppressive activities. Synthetic studies were undertaken
to prepare a modified analog of one of the most potent congeners, didemnin B (1). The side chain
of the isostatine unit was tethered into the macrocycle via a cyclohexane ring in order to provide
a more rigid conformation and determine the importance of this unit in bioactive compounds. This
modification created a new macrocycle core and generated a diastereomeric mixture of a constrained
analog of didemnin B (2).
In tr od u ction
afforded a compound with approximately twice the activ-
ity of cyclosporin A, the first structural variant with
The didemnin class (1) of biologically active cyclodep-
sipeptides, isolated from a marine tunicate,1 has shown
antitumor, antiviral, and immunosuppressive activities.2-13
To date, the structural features considered essential for
activity (the side chains attached to the amino group of
threonine, the isostatine hydroxyl group, and the tyrosine
unit) were based for the most part on the analysis of the
X-ray structure.14 Although the bioactivity of the most
potent member, didemnin B (1), has been attributed to
its side chain,5 few other structural features have been
examined. Therefore, investigations were undertaken to
synthesize a modified macrocycle which tethered the
isostatine unit to the macrocycle via a cyclohexane ring,
to provide a more rigid and structurally stable conforma-
tion, a fused ring system (2). Such changes should alter
the biological activity of the didemnins and help to
determine binding site conformation as well as the
importance of the isostatine hydroxyl group in active
compounds. By using molecular modeling and data from
a complex between cyclosporin A and its receptor, cyclo-
philin, Schreiber designed a bicyclic replacement for two
residues of cyclosporin A. Incorporation of a thiazole ring
inhibitory properties greater than the parent compound.15
X Abstract published in Advance ACS Abstracts, February 1, 1996.
(1) Rinehart, K. L., J r.; Gloer, J . B.; Cook, J . C., J r.; Mizsak, S. A.;
Scahill, T. A. J . Am. Chem. Soc. 1981, 103, 1857-1859.
(2) Li, W.-R.; J oullie´, M. M. In Studies in Natural Products
Chemistry, Vol. 10, Stereoselective Synthesis (Part F); Atta-ur-Rahman,
Ed.; Elsevier: Amsterdam, 1992; pp 241-302.
(3) Maldonado, E.; Lavergne, J . A.; Kraiselburd, E. P. R. Health Sci.
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Antimicrob. Agents Chemother. 1982, 22, 696-697.
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A.; Meng, H.; Moore, M. L.; Gloer, J . B.; Wilson, G. R.; Gutowsky, R.
E.; Zierath, P. D.; Shield, L. S.; Li, L. H.; Renis, H. E.; McGovren, J .
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(6) Rinehart, K. L., J r. In U.S. Patent 4, 493, 796; U.S., 1985; pp
1-19.
(7) Rinehart, K. L., J r. Didemnin and its Biological Properties;
ESCOM: St. Louis, MO, 1988; pp 626-631.
Resu lts a n d Discu ssion
(8) Rinehart, K. L., J r. In U.S. Patent 5,294,603; U.S., 1994; pp
1-25.
A molecular modeling study16 was conducted for a
series of analogs in which the isostatine moiety was
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1992, 54, 188-189.
(10) Fimiani, V. Oncology 1987, 44, 42-46.
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tion 1987, 43, 133-139.
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Y.; Andrus, M.; Alberg, D. G.; Schultz, L. W.; Clardy, J .; Schreiber, S.
L. Synlett 1994, 381-392.
(16) Mohamadi, F.; Richards, N. G. J .; Guida, W. C.; Liskamp, R.;
Lipton, M.; Caufield, C.; Chang, G.; Hendrickson, T.; Still, W. C. J .
Comput. Chem. 1990, 11, 440-467. Still, W. C.; Mohamadi, F.;
Richards, N. G. J .; Guida, W. C.; Lipton, M.; Liskamp, R.; Chang, G.;
Hendrickson, T.; DeGunst, F.; Hasel, W. MacroModel; Department of
Chemistry, Columbia University, New York, NY 10027.
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S. K. Lymphokine Res. 1988, 7, 21-29.
(13) Sakai, R.; Stroh, J . G.; Sullins, D. W.; Rinehart, K. L. J . Am.
Chem. Soc. 1995, 117, 3734-3748.
(14) Hossain, M. B.; van der Helm, D.; Antel, J .; Sheldrick, G. M.;
Sanduja, S. K.; Weinheimer, A. J . Proc. Natl. Acad. Sci. U.S.A. 1988,
85, 4118-4122.
0022-3263/96/1961-1655$12.00/0 © 1996 American Chemical Society

1656 J . Org. Chem., Vol. 61, No. 5, 1996
Mayer et al.
Sch em e 1
replaced by a cyclohexane â-hydroxy-γ-amino acid. All
possible diastereomeric structures were compared to that
of didemnin B in order to generate the correct stereo-
chemistry needed for the ring subunit. The minimized
molecular modeling structure of 1 was generated from
the X-ray coordinates provided by van der Helm and co-
workers.14 The best overlay was obtained for a cyclo-
hexane in which all three contiguous stereogenic centers
had the S configuration. The stereogenic center to which
the nitrogen function is attached had the R configuration
in didemnin B. However, molecular modeling results
showed that an axial amino group with the S configura-
tion afforded the closest superimposed overlay as well
as being the lowest energy-minimized conformation. A
retrosynthetic analysis (Scheme 1) similar to our syn-
thetic approach to the macrocycle17 was undertaken so
that the same methodology could be employed once the
cyclohexane amino acid (5) was synthesized. This unit
would then be esterified with the R-(R-hydroxyisovalery)-
propionyl unit (HIP alcohol, 4) and then coupled with the
tetrapeptide 3.17
diene 6 was obtained in 57% yield from crotonaldehyde
in refluxing Ac2O under basic conditions (68:32 E:Z ratio).
Sch em e 2
In devising a stereoselective route to 5, many different
synthetic strategies were examined for what appeared
to be a trivial project. This deceptively simple substi-
tuted cyclohexane amino acid containing three contiguous
stereogenic centers proved to be a challenge. The initial
stereochemistry for this substructure was obtained by an
asymmetric Diels-Alder reaction using the Oppolzer
camphorsultam directing group (Scheme 2).18-23 The
Only the E isomer reacts in the Diels-Alder reaction.24
Oppolzer’s camphorsultam was coupled with acryloyl
chloride to generate the dienophile 7 in 70% yield. The
(17) Li, W.-R.; Ewing, W. R.; Harris, B. D.; J oullie´, M. M. J . Am.
Chem. Soc. 1990, 112, 7659-7672.
(21) Thom, C.; Kocienski, P. Synthesis 1992, 582-586.
(22) Kim, B. H.; Curran, D. P. Tetrahedron 1993, 49, 293-318.
(23) Towson, J . C.; Weismiller, M. C.; Lal, G. S.; Sheppard, A. C.;
Kumar, A.; Davis, F. A. (+)-(2R, 8aS)-10-(Camphorylsulfonyl)Oxaziri-
dine. Organic Syntheses; J ohn Wiley and Sons: New York, 1993;
Collect. Vol. VIII, pp 104-110.
(18) Mayer, S. C.; Pfizenmayer, A. J .; Cordova, R.; Li, W.-R.; J oullie´,
M. M. Tetrahedron: Asymmetry 1994, 5, 519-522.
(19) Oppolzer, W.; Chapuis, C.; Bernardinelli, G. Helv. Chim. Acta
1984, 67, 1397-1401.
(20) Davis, F. A.; Towson, J . C.; Weismiller, M. C.; Lal, S.; Carroll,
P. J . J . Am. Chem. Soc. 1988, 110, 8477-8482.
(24) Georgieff, K. K.; Dupre´, A. Can. J . Chem. 1960, 38, 1070-1075.

Constrained Ring Analog of Didemnin B
J . Org. Chem., Vol. 61, No. 5, 1996 1657
Sch em e 3
Sch em e 4
best conditions for the Diels-Alder reaction required
lithium perchlorate as reported by Grieco.25,26 This
reaction afforded an 83% yield of the major diastereomer
8 and 5% of another diastereomer which could be
chromatographically separated (based upon 25% recov-
ered dienophile starting material). These conditions
yielded a 5-fold increase in selectivity (3:1 to 17:1) over
initial methods.18 The relative and absolute stereochem-
istries of this Diels-Alder product were confirmed by
single crystal X-ray analysis.18 At this point, two of the
three stereogenic centers were set.
The most practical method for introduction of the third
stereogenic center was an iodolactonization of the meth-
oxy acid 10.18,27 This compound was prepared by removal
of the camphorsultam auxiliary from the Diels-Alder
product 8 with aqueous LiOH, followed by protection of
the intermediate secondary alcohol (9) as its methyl ether
10 (Scheme 3). Originally, several common silyl-protect-
ing groups were investigated, and their steric bulk proved
to be a major problem in the subsequent lactonization
reaction. Therefore, a methyl group protection was
chosen because of its less demanding steric environment
even though we realized the difficulty of removing such
a group at a later stage in the synthesis. A successful
iodolactonization afforded compound 11 in 85% yield. The
iodine was removed with Bu3SnH, and the resulting
lactone 12 was opened with methoxide. A 70% yield of
compound 13 was obtained with ∼25% of a â-ester epimer
(determined by NMR) resulting from the basic conditions.
At that time, it was found that deprotection of the methyl
ether in 12 could be accomplished in 67% yield to provide
alcohol 14.28 This transformation was to be investigated
later in the synthesis because of the need to differentiate
between two secondary hydroxyl groups.
After the third stereogenic center had been introduced,
an appropriate transformation was needed to incorporate
the amino functionality into the ring. Amine formation
via azide displacement of a mesylate intermediate proved
to be an inefficient synthetic pathway.27 Varying condi-
tions and the use of different azides (sodium, lithium,
and trimethylsilyl azides) did not provide the desired
transformation. Mitsunobu conditions using diphe-
nylphosphoryl azide and diisopropyl azodicarboxylate
also failed.29,30 Parr bomb reactions with ammonia or
benzylamine at 100 °C for 24 h afforded very poor yields
of product.31-35 Amine formation via a displacement was
inefficient because, regardless of the mechanism (SN2 or
neighboring group assisted SN1), attack by the nucleo-
phile would be blocked either by steric hindrance or
diaxial interactions with the ring hydrogens.27
At this stage, it was essential to incorporate the amine
function even at the price of destroying previous selectiv-
ity. An alternative route via reductive amination was
employed for amine formation.27 The alcohol 13 was oxi-
dized to 15 under Swern conditions (Scheme 4).36 The
keto group was then subjected to reductive amination
(28) Rice, K. C. J . Med. Chem. 1977, 20, 164-165.
(29) Lal, B.; Pramanik, B. N.; Manhas, M. S.; Bose, A. K. Tetrahe-
dron Lett. 1977, 23, 1977-1980.
(30) Takano, S.; Sugihara, T.; Satoh, S.; Ogasawara, K. J . Am. Chem.
Soc. 1988, 110, 6467-6471.
(31) Pinkus, J . L.; Pinkus, G.; Cohen, T. J . Org. Chem. 1962, 27,
4356-4360.
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J . Org. Chem. 1986, 51, 3215-3217.
(33) Chhen, A.; Vaultier, M.; Carrie´, R. Tetrahedron Lett. 1989, 30,
4953-4956.
(25) Grieco, P. A.; Nunes, J . J .; Gaul, M. D. J . Am. Chem. Soc. 1990,
112, 4595-4596.
(34) Corey, E. J .; Lee, D.-H.; Choi, S. Tetrahedron Lett. 1992, 33,
6735-6738.
(26) Grieco, P. A.; Beck, J . P. Tetrahedron Lett. 1993, 34, 7367-
7370.
(35) Han, S.-Y., Ph.D. Dissertation, University of Pennsylvania,
1992.
(27) Mayer, S. C.; J oullie´, M. M. Synth. Commun. 1994, 24, 2351-
2365.
(36) Mancuso, A. J .; Swern, D. Synthesis 1981, 165.

1658 J . Org. Chem., Vol. 61, No. 5, 1996
Mayer et al.
Sch em e 5
Sch em e 6
with benzylamine and sodium triacetoxyborohydride to
afford the secondary amine product (16a : ∼1:1 ratio by
NMR analysis).37,38 Amine formation through oxime 17
was less effective, giving poorer selectivity (16d : ∼1:3
ratio by NMR analysis). Although this strategy de-
stroyed the third stereogenic center, if a diastereomeric
mixture of amines could be obtained, separation could
be accomplished at a later stage such as after esterifica-
tion with the R-(R-hydroxyisovaleryl)propionyl unit (HIP
alcohol, 4). Both diastereomers could then be used to
make two new analogs. In addition, the major diastereo-
mer might be obtainable through equilibrating condi-
tions.
Much time was spent investigating suitable conditions
for the esterification of the HIP alcohol 4 with the
cyclohexane amino acid 16d (diastereomeric mix-
turessdetermined by NMR analysis).39 The best condi-
tions were obtained using Carpino’s acid fluoride activa-
tion.40,41 Initially, the alkoxide of the HIP alcohol was
added to the acid fluoride 20 of 2-methoxy-3-cyclohex-
enecarboxylic acid (10) to obtain the ester 18 in 75% yield
(Scheme 5). To convert the alcohol to its corrresponding
alkoxide, several bases were used, but sodium hexam-
ethyldisilazane proved to be the best.
Next, investigations into the coupling of the new
synthetic intermediates were undertaken. Lactone 12
could be cleaved with the use of hydroxide instead of
methoxide to afford hydroxy acid 21 in quantitative yield
as a single diastereomer (Scheme 6). The hydroxyl
function in 21 was oxidized to a ketone (22), in the
presence of the acid group, employing J ones’ oxidation
conditions.42 Using Carpino’s activation protocol,40,41 the
acid fluoride 23 was added to the alkoxide of 4, generated
from either sodium hexamethylsilazane or n-butyllithi-
um, to afford the ester 24 in 70% yield. Introduction of
the ester functionality before amine incorporation was
chosen with the expectation that the bulkier substituent
would induce some selectivity in the reductive amination.
Ketone 24 was subjected to reductive amination condi-
tions incorporating benzylamine and sodium triacetoxy-
borohydride (Scheme 6).37,38 The benzyl group of the
resulting secondary amine (25) was removed by catalytic
hydrogenation to afford amine 26 in 99% of a 1:1
diastereomeric mixture. Unfortunately, the bulkier sub-
stituent did not induce the selectivity we had hoped for.
The inseparable mixture of diastereomers was therefore
utilized in the remaining synthetic scheme with the
intent of separating the diastereomers at a later stage
to obtain two drug candidates for biological testing.
The coupling of the two halves of the macrocycle (26
+ 3) to give 27 was investigated using our previous
methodology as shown in Scheme 7.17,43 Originally, this
transformation was accomplished with isopropenyl chlo-
roformate activation44,45 to prepare the linear precursor
of the constrained ring analog 27 in 55% yield. The yield
was increased to 65% by the use of (1H-1,3-benzotriazol-
1-yloxy)tris(dimethylamino)phosphonium hexafluoro-
phosphate (BOP) activation46 and a catalytic amount of
DMAP.
As was the case with our original linear precursor,
intermediate 27 had to be functionalized at both ends to
(37) Abdel-Magid, A. F.; Maryanoff, C. A.; Carson, K. G. Tetrahedron
Lett. 1990, 31, 5595-5598.
(38) Abdel-Magid, A. F.; Maryanoff, C. A. Synlett 1990, 537-539.
(39) Mayer, S. C.; J oullie´, M. M. Synth. Commun. 1994, 24, 2367-
2377.
(43) Mayer, S. C.; Ramanjulu, J .; Vera, M. D.; Pfizenmayer, A. J .;
J oullie´, M. M. J . Org. Chem. 1994, 59, 5192-5205.
(44) J ouin, P.; Castro, B.; Zeggaf, C.; Pantaloni, A.; Senet, J . P.;
Lecolier, S.; Sennyey, G. Tetrahedron Lett. 1987, 28, 1661-1664.
(45) Chen, F. M. F.; Lee, Y.; Steinauer, R.; Benoiton, N. L. Can. J .
Chem. 1987, 65, 613-618.
(40) Carpino, L. A.; Mansour, E.-S. M. E. J . Org. Chem. 1992, 57,
6371-6373.
(41) Carpino, L. A.; Mansour, E.-S. M. E.; El-Faham, A. J . Org.
Chem. 1993, 58, 4162-4164.
(42) Bowers, A.; Halsall, T. G.; J ones, E. R. H.; Lemin, A. J . J . Chem.
Soc. 1953, 2548-2560.
(46) Castro, B.; Dormoy, J . R.; Evin, G.; Selve, C. Tetrahedron Lett.
1975, 14, 1219-1222.

Constrained Ring Analog of Didemnin B
J . Org. Chem., Vol. 61, No. 5, 1996 1659
Sch em e 7
achieve cyclization (Scheme 7). First, the TBDMS pro-
tecting group was removed under acid conditions to afford
primary alcohol 28. This alcohol was then subjected to
a two-stage oxidation protocol first to the aldehyde using
the Dess-Martin periodinane reagent [1,1,1-triacetoxy-
1,1-dihydro-1,2-benziodoxol-3(1H)-one]47 and then by
Masamune conditions48 to the acid (29) needed for
cyclization. Finally, the amino protecting group was
removed by catalytic hydrogenation to generate the
unprotected linear precursor 30.
Macrocyclization was originally conducted with pen-
tafluorophenyl diphenylphosphinate (FDPP).49 However,
in contrast with the excellent results obtained in our
previous macrocyclizations, yields for this transformation
could not be raised above 30%. Using a new derivative
of the BOP reagent, O-benzotriazol-1-yl-N,N,N′,N′-tet-
ramethyluronium hexafluorophosphate (HBTU),50 the
cyclization yields of 31 were increased to a modest 50%
(Scheme 8). The yields of the remaining steps of the
synthesis were on the average slightly lower than with
the original macrocycle salt. The MOM protecting group
of compound 31 was removed with dimethylboron bro-
mide in 77% yield,51,52 and the subsequent oxidation with
periodinane afforded a modest 70% of compound 33. In
the last step of Scheme 8, the protected macrocycle 33
was quantitatively converted to the macrocycle salt of the
constrained ring analog 34 when treated with hydrogen
chloride in ethyl acetate.17
macrocycle salt 34 was coupled to the didemnin B side
chain17 (35, Scheme 8). Once again, the BOP reagent was
used to activate the acid for addition. It was determined
by NMR that the reaction was successful in producing a
1:1 diastereomeric mixture of the coupled products;
however, thus far yields of this reaction have not been
optimized and separation of the diastereomers is cur-
rently being pursued using reversed-phase HPLC tech-
niques. The mixture has been submitted for initial
biological screening to determine if further investigations
are applicable; these results should help clarify the effect
of a constrained ring system as well as that of the
isostatine hydroxyl protection as no activity was found
in other didemnins in which this functionality was not
free.8,13 Currently, we are continuing these investigations
with two main goals: to achieve a totally stereocontrolled
synthesis of the cyclohexane amino acid 5 and to isolate
the optically pure constrained ring analog 2.
Con clu sion s
An asymmetric Diels-Alder reaction incorporating an
oxygenated diene in the presence of 3.0 M lithium
perchlorate-diethyl ether was used to generate the
initial stereochemistry for the cyclohexane amino acid,
a key intermediate in the preparation of the fused ring
didemnin analog 2.18 After introduction of the third
stereogenic center, some difficult steps were encountered.
The deceptively simple transformation of an alcohol to
an amino group was finally achieved using the reductive
amination of ketones 15 or 24 with sodium triacetoxy-
borohydride or the hydrogenation of oxime 17 under
acidic conditions.27 Nucleophilic displacement proved to
be an impossible synthetic route to the amine function.
Incorporation of the amine at a later stage such as from
ketone 24 was not as selective as expected. However,
the diastereomeric mixture did not present a problem in
the latter part of the synthesis and will provide both
diastereomers for biological testing.
To complete the synthesis of the constrained ring
didemnin B analog (2b, 1:1 diastereomeric mixture), the
(47) Dess, D. B.; Martin, J . C. J . Am. Chem. Soc. 1991, 113, 7277-
7287.
(48) Abiko, A.; Roberts, J . C.; Takemasa, T.; Masamune, S. Tetra-
hedron Lett. 1986, 27, 4537-4540.
(49) Chen, S.; Xu, J . Tetrahedron Lett. 1991, 32, 6711-6714.
(50) Knorr, R.; Trzeciak, A.; Bannwarth, W.; Gillessen, D. Tetrahe-
dron Lett. 1989, 30, 1927-1930.
(51) Guindon, Y.; Yoakim, C.; Morton, H. E. Tetrahedron Lett. 1983,
24, 2969-2972.
(52) Guindon, Y.; Morton, H. E.; Yoakim, C. Tetrahedron Lett. 1983,
24, 3969-3972.

1660 J . Org. Chem., Vol. 61, No. 5, 1996
Mayer et al.
Sch em e 8
solution of LiOH (35 mL) dropwise over a 10 min period. After
being stirred at 0 °C for 30 min and rt for 16 h, the solution
was concentrated to one-half volume. The resulting aqueous
mixture was washed with diethyl ether (Et2O, 2 × 5 mL). The
Et2O layers were extracted with saturated aqueous NaHCO3
(5 mL). The aqueous layers were combined, acidified to pH 4
with 1 N aqueous KHSO4, and then extracted with ethyl
acetate (EtOAc, 3 × 40 mL). The resulting organic layers were
combined, dried (MgSO4), filtered, and concentrated to afford
the product 21 as a white solid (0.594 g, 99% yield): mp 83-
85 °C; Rf 0.29 (10:90 MeOH:CHCl3); 1H NMR (500 MHz,
CDCl3) δ 1.22-1.26 (m, 1H), 1.61 (dq, J ) 3.8, 11.4 Hz, 1H),
1.68-1.75 (m, 3H), 1.78 (ddd, J ) 4.2, 8.6, 17.4 Hz, 1H), 2.48
(ddd, J ) 2.8, 4.3, 10.8 Hz, 1H), 3.53 (s, 3H), 3.66-3.69 (m,
1H), 3.94 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 21.5, 21.7,
29.4, 45.5, 60.3, 71.6, 80.4, 178.4; IR (neat) 2760-3620 (br),
2940 (s), 2860 (m), 1705 (s), 1455 (w), 1445 (w), 1370-1420
(m), 1300 (m), 1260 (m), 1215 (m), 1180 (m), 1145 (m), 1105
(m), 1075 (s), 980 (w) cm-1; HRMS m/ z calcd for C8H15O4 (M
Esterification of a hindered alcohol (HIP unit, 4) was
accomplished using the acid fluoride coupling method of
Carpino.40,41 Standard coupling procedures were unsuc-
cessful because of the steric bulk and weak nucleophi-
licity of the secondary alcohol. This recently described
strategy40,41 was superior to all reported esterification
procedures and was applied to the coupling of 4 and 22.
The new methodology offers great potential as an alter-
native to typical activation protocols.39
The constrained ring analog 2b was synthesized, and
the separation of the two diastereomers is being inves-
tigated via HPLC and traditional column chromatogra-
phy. For the cyclization, HBTU proved to be a better
activating agent than FDPP. We are still examining a
more stereoselective synthetic route to the ring analog,
but before the additional investment of time is made, we
would like to see if the final product(s) have any bioac-
tivity and warrant further investigation.
+ H+) 175.0970, found 175.0973; [R]20 +1.98° (c ) 1.42,
D
CHCl3).
(1S,2S)-2-Met h oxy-3-oxocycloh exa n eca r b oxylic Acid
(22). To a solution of hydroxy acid 21 (0.432 g, 2.48 mmol)
and acetone (15.0 mL) at 0 °C was added a solution of CrO3
(0.497 g, 4.97 mmol) in H2SO4 (0.523 mL) and H2O (2.02 mL)
dropwise over a 20 min period.42 The reaction was stirred at
0 °C for 1 h and then at rt overnight. Ice/H2O (∼20 mL) was
added to dissolve the precipitate that formed, and the resulting
solution was poured into an additional amount of ice/H2O (∼50
mL). The aqueous layer was extracted with Et2O (3 × 150
mL). If the organic layer was light green, it was washed with
additional volumes of H2O (50 mL each). The resulting organic
solution was washed with saturated aqueous NaCl (30 mL),
dried (MgSO4), filtered, and concentrated to afford the product
22 (0.380 g, 89% yield) as a white solid: mp 125-126 °C; Rf
0.36 (10:90 MeOH:CHCl3); 1H NMR (500 MHz, CDCl3) δ 1.66-
1.73 (m, 1H), 1.97 (dt, J ) 4.2, 14.1 Hz, 1H), 2.06-2.20 (m,
3H), 2.25-2.30 (m, 1H), 2.63-2.69 (m, 1H), 2.96-3.00 (m, 1H),
3.39 (s, 3H), 3.86 (d, J ) 3.8 Hz, 1H); 13C NMR (125 MHz,
CDCl3) δ 22.9, 23.8, 38.1, 48.4, 58.2, 83.3, 177.0, 208.5; IR
(neat) 2360-3580 (b), 2950 (s), 1735 (s), 1700 (s), 1460 (w),
1440 (m), 1420 (m), 1275 (m), 1250 (m), 1215 (m), 1180 (s),
1135 (m), 1110 (s), 1065 (m), 1005 (m), 900 (m) cm-1; HRMS
Exp er im en ta l Section
Provided in the supporting information are the analytical
data for the intermediates (6-18, 3, and 35) prepared previ-
ously18,27,39 in our group. All spectroscopic data confirmed the
isolation of these important intermediates.
Gen er a l P r oced u r es. All manipulations were conducted
under an inert atmosphere (argon or nitrogen). All solvents
were reagent grade. Anhydrous ether, tetrahydrofuran (THF),
benzene, and toluene were distilled from sodium and/or
benzophenone ketyl. Dichloromethane (CH2Cl2) and dichlo-
roethane (DCE) were distilled from calcium hydride (CaH2).
N,N-Dimethylformamide (DMF) and acetonitrile were distilled
from phosphorus pentoxide and calcium hydride. Methanol
was distilled from magnesium and iodine. Organic acids and
bases were reagent grade. Triethylamine (Et3N), diisopropyl-
ethylamine (i-Pr2NEt), and N-methylmorpholine (NMM) were
distilled from calcium hydride. All other reagents were
commercial compounds of the highest purity available. Ana-
lytical purification and structure determination techniques
were carried out using previously reported procedures.43
(1S,2S,3R)-3-H yd r oxy-2-m et h oxycycloh exa n eca r b ox-
ylic Acid (21). To a mixture of lactone 12 (0.538 g, 3.44 mmol)
and THF (35 mL) at 0 °C was added a cooled 0.20 M aqueous
m/ z calcd for C8H12O4 (M+) 172.0736, found 172.0735; [R]20
D
-14.6° (c ) 0.445, CHCl3).

Constrained Ring Analog of Didemnin B
J . Org. Chem., Vol. 61, No. 5, 1996 1661
(1S,2S)-2-Met h oxy-3-oxocycloh exa n eca r b on yl F lu o-
r id e (23). To a solution of acid 22 (372 mg, 2.16 mmol) in
CH2Cl2 (10.0 mL) between -20 and -30 °C was added pyridine
(175 µL, 2.16 mmol) followed by cyanuric fluoride (0.584 mL,
6.48 mmol) dropwise.40,41 The reaction was kept at this
temperature for 1 h, followed by addition of crushed ice (20 g)
and additional CH2Cl2 (100 mL). The layers were separated,
and the aqueous layer was extracted with CH2Cl2 (100 mL).
The combined organic layers were washed with ice-cold H2O
(10 mL), dried (MgSO4), filtered, and concentrated to afford
the acid fluoride 23 (376 mg, 99% yield), which was im-
mediately utilized in the next step.
1035 (s), 985 (m), 920 (m) cm-1; HRMS m/ z calcd for C31H56
-
SiNO6 (M + H+) 566.3877, found 566.3866; [R]20 -0.191° (c
D
) 1.70, CHCl3).
(1S,2S,3R)-4-[(ter t-Bu tyldim eth ylsilyl)oxy]-1-isopr opyl-
2-(m eth oxym eth oxy)-3-m eth ylbu tyl (1S,2S)-3-Am in o-2-
m eth oxycycloh exa n eca r boxyla te (26). Under a hydrogen
atmosphere (40 psi), secondary amine 25 (0.683 g, 1.21 mmol)
was combined with MeOH:EtOAc (1:1, 10.0 mL) and 10% Pd/C
(0.444 g, 20.7 mmol) and shaken in a Parr apparatus for 8 h.
The slurry was filtered through Celite followed by thorough
washing with MeOH:EtOAc. The filtrate was concentrated in
vacuo, and the residue was azeotroped with toluene several
times to give the product 26 as an oil (20.7 mg, 99% yield): Rf
0.11 (10:90 MeOH:CHCl3); 1H NMR (500 MHz, CDCl3) δ 0.048
and 0.051 (s, 6H), 0.88-0.94 (m, 9H), 0.89 and 0.90 (s, 9H),
1.43-1.67 (m, 2H), 1.69-1.83 (m, 3H), 1.85-1.98 (m, 2H),
2.28-2.40 (m, 1H), 2.64-2.68 (m, 1H), 2.77-2.84 (m, 1H),
3.335 and 3.339 (s, 3H), 3.355 and 3.363 (s, 3H), 3.42-3.56
(m, 3H), 3.78-3.83 (m, 1H), 4.59-4.68 (m, 2H), 5.02-5.07 (m,
1H); 13C NMR (125 MHz, CDCl3) δ -5.53, -5.47, 10.9, 16.0,
18.2, 19.8, 22.2, 25.8, 28.8, 28.9, 30.7, 37.4, 43.7, 47.8, 56.0,
56.5, 65.0, 78.3, 78.5, 78.6, 98.6, 174.4 (diastereomers present
in NMR); IR (neat) 3280-3400 (w), 2930-2970 (s), 2870 (s),
1730 (s), 1670 (w), 1580 (w), 1565 (w), 1545 (w), 1530 (w), 1460
(m), 1355-1385 (m), 1255 (s), 1125-1170 (s), 1095 (s), 1035
(s), 920 (m) cm-1; HRMS m/ z calcd for C24H50SiNO6 (M + H+)
(1S,2S,3R)-4-[(ter t-Bu tyldim eth ylsilyl)oxy]-1-isopr opyl-
2-(m eth oxym eth oxy)-3-m eth ylbu tyl (1S,2S)-2-Meth oxy-
3-oxocycloh exa n eca r boxyla te (24). A solution of 4 (1.04
g, 3.24 mmol) in THF (32 mL) was prepared and cooled to -78
°C. A solution of either sodium hexamethyldisilazane (NaHM-
SA, 4.32 mL 0.75 M in THF) or n-BuLi (2.03 mL 1.6 M in
hexane) was added dropwise and the mixture stirred at -78
°C for 30 min and then at 0 °C for 10 min. The previously
prepared acid fluoride (23) in THF (2.0 mL) was added at this
temperature and the resulting mixture stirred for 10 min and
then at rt for 4 h. The solution was concentrated to an oily
residue and diluted with EtOAc (200 mL). The organic
solution was washed with 5% aqueous HCl (30 mL), 5%
aqueous NaHCO3 (30 mL), and saturated NaCl (30 mL), dried
(MgSO4), filtered, and concentrated. The crude oil was purified
by flash column chromatography, eluting with EtOAc:petro-
leum ether (5:95) to remove unreacted 4 (2.31 g) and then
eluting with EtOAc:petroleum ether (10:90:15:85) to obtain 24
(0.718 g, 70% yield) as a colorless oil: Rf 0.47 (20:80 EtOAc:
476.3407, found 476.3425; [R]20 -15.0° (c ) 1.26, CHCl3).
D
N-[N-[N-(Ben zyloxyca r bon yl)-L-leu cyl]-L-p r olyl]-3-(p-
m eth oxyp h en yl)-N-m eth yl-L-a la n in e, Ester w ith (1S,2S)-
3-[(2S,3R)-2-[(ter t-Bu toxyca r bon yl)a m in o]-3-h yd r oxybu -
t yr a m id o]-2-m et h oxycycloh exa n eca r b oxylic
Acid ,
1
petroleum ether); H NMR (500 MHz, CDCl3) δ 0.04 (s, 6H),
(1S,2S,3R)-4-[(ter t-Bu tyld im eth ylsilyl)oxy]-1-isop r op yl-
2-(m eth oxym eth oxy)-3-m eth ylbu tyl Ester (27).17,43 Meth od
A. To acid 3 (1.42 g, 1.88 mmol) in THF (30 mL) at -15 °C
was added dropwise NMM (1.88 mL of a 1.0 M solution in
THF, 1.88 mmol). To this solution was added isopropenyl
chloroformate (IPCF, 1.88 mL of a 1.0 M solution in THF, 1.88
mmol) dropwise.44,45 The mixture was stirred for 3 min, and
then amine 26 (0.815 g, 1.71 mmol) was added in THF (∼2
mL). After the solution was warmed to 0 °C with stirring for
30 min, it was stirred at rt for 3 h. The mixture was then
concentrated in vacuo. The resulting residue was diluted with
Et2O (150 mL) and washed with 5% aqueous citric acid (15
mL), 5% aqueous NaHCO3 (15 mL), and saturated aqueous
NaCl (15 mL). The organic layer was dried (Na2SO4), filtered,
and concentrated. The crude oil was purified by flash column
chromatography eluting with EtOAc:petroleum ether (15:85-
60:40) to afford the product (27, 1.25 g, 55% yield) as a clear
oil.
0.87 (d, J ) 7.9 Hz, 3H), 0.88 (s, 9H), 0.89 (d, J ) 3.0 Hz, 3H),
0.90 (d, J ) 6.4 Hz, 3H), 1.62-1.66 (m, 1H), 1.74-1.77 (m,
1H), 1.94 (ddd, J ) 6.9, 11.5, 18.2 Hz, 1H), 1.98-2.00 (m, 1H),
2.01-2.09 (m, 1H), 2.14 (dt, J ) 3.6, 13.7 Hz, 1H), 2.24 (dt, J
) 5.0, 13.6 Hz, 1H), 2.65-2.70 (m, 1H), 2.88 (dt, J ) 4.2, 10.1
Hz, 1H), 3.32 (s, 3H), 3.34 (s, 3H), 3.44-3.53 (m, 2H), 3.80
(dd, J ) 3.3, 7.1 Hz, 1H), 3.83 (dd, J ) 2.4, 3.4 Hz, 1H), 4.61
(AB, J ) 6.5, 13.7 Hz, 2H), 5.02 (dd, J ) 4.6, 7.1 Hz, 1H); 13
C
NMR (125 MHz, CDCl3) δ -5.4, -5.3, 10.9, 16.2, 18.2, 19.7,
23.0, 24.2, 25.9, 28.8, 37.4, 38.0, 49.3, 56.0, 57.8, 65.0, 78.7,
79.2, 83.7, 98.6, 171.0, 209.4; IR (neat) 2940-2970 (s), 2890-
2910 (m), 2860 (m), 1730 (s), 1465 (m), 1425 (w), 1390 (m),
1295 (w), 1255 (s), 1210 (m), 1160-1190 (m), 1135 (m), 1100
(s), 1040 (s), 920 (m) cm-1; HRMS m/ z calcd for C24H50NSiO7
(M + NH4+) 492.3357, found 492.3349; [R]20D -43.9° (c ) 0.900,
CHCl3).
(1S,2S,3R)-4-[(ter t-Bu tyldim eth ylsilyl)oxy]-1-isopr opyl-
2-(m eth oxym eth oxy)-3-m eth ylbu tyl (1S,2S)-3-(N-Ben zyl-
a m in o)-2-m eth oxycycloh exa n eca r boxyla te (25).37,38 To a
solution of ketone 24 (0.575 g, 1.21 mmol) and 1,2-dichloro-
ethane (DCE, 12.1 mL) was added benzylamine (0.145 mL,
1.33 mmol) followed by HOAc (69.3 µL, 1.21 mmol). Sodium
triacetoxyborohydride (385 mg, 1.82 mmol) was then added
to the mixture. The reaction was stirred at rt for 4 h. The
solution was quenched with saturated aqueous NaHCO3 (20
mL), and the product was extracted with EtOAc (3 × 75 mL),
dried (MgSO4), filtered, and concentrated to afford 25 (678 mg,
99% yield) as a 1:1 diastereomeric mixture: Rf 0.43 (10:90
MeOH:CHCl3); 1H NMR (500 MHz, CDCl3) δ 0.042 and 0.048
(s, 6H), 0.87-0.94 (m, 9H), 0.889 and 0.893 (s, 9H), 1.35-1.40
(m, 1H), 1.42-1.51 (m, 1H), 1.69-1.88 (m, 6H), 2.24-2.28 (m,
1H), 2.44-2.49 (m, 1H), 2.94 (ddd, J ) 4.2, 10.0, 14.1 Hz, 1H),
3.19 and 3.33 (s, 3H), 3.35 and 3.56 (s, 3H), 3.42-3.55 (m, 2H),
3.63-3.96 (m, 4H), 4.57-4.65 (m, 2H), 5.02 and 5.07 (dd, J )
3.9, 7.9 Hz, 1H), 7.22-7.38 (m, 5H); 13C NMR (125 MHz,
CDCl3) δ -5.52, -5.46, 10.6, 11.0, 15.9, 16.0, 18.2, 18.7, 19.2,
19.8, 22.0, 24.0, 25.9, 25.9, 26.9, 27.1, 28.8, 28.9, 29.8, 30.7,
37.4, 37.5, 44.6, 45.2, 47.8, 50.6, 51.0, 51.3, 55.95, 55.98, 56.1,
56.6, 65.0, 65.3, 77.8, 78.2, 78.3, 78.5, 78.6, 98.49, 98.55, 126.8,
126.9, 127.1, 128.0, 128.1, 128.3, 128.4, 141.0, 173.2, 175.0
(diastereomers present in NMR); IR (neat) 3320 (w), 3090 (w),
3070 (w), 3040 (m), 2860-2980 (s), 1730 (s), 1600 (w), 1580
(w), 1525 (w), 1495 (m), 1460 (s), 1405 (m), 1360-1390 (m),
1310 (m), 1215-1255 (s), 1200 (s), 1125-1170 (s), 1085 (s),
Meth od B. Acid 3 (0.888 g, 1.18 mmol) was dissolved in
anhydrous THF (25 mL) at 0 °C, and NMM (141 µL, 1.28
mmol) was added with stirring. To this solution was added
BOP (0.568 g, 1.28 mmol) and then amine 26 (0.511 g, 1.07
mmol).46 A catalytic amount of DMAP (26.1 mg, 0.214 mmol)
was added, followed by stirring at 0 °C for 30 min. The
mixture was stirred at rt overnight and then quenched with
saturated aqueous NaCl (5 mL). The mixture was diluted with
EtOAc (100 mL), and the layers were separated. The organic
layer was washed with 5% aqueous HCl (10 mL), 5% aqueous
NaHCO3 (10 mL), and saturated aqueous NaCl (10 mL). The
organic layer was then dried (MgSO4), filtered, and concen-
trated to an oil. The crude residue was purified by flash
column chromatography, eluting with EtOAc:petroleum ether
(15:85-60:40). Compound 27 was obtained (0.845 g, 65%
yield) as a clear oil: Rf 0.71 (50:50 EtOAc:petroleum ether);
1H NMR (500 MHz, CDCl3) δ 0.036-0.045 (s, 6H), 0.82-0.99
(m, 15H), 0.890 and 0.892 (s, 9H), 1.22-1.30 (m, 1H), 1.24 and
1.26 (s, 3H), 1.32 and 1.35 (s, 9H), 1.41-1.50 (m, 1H), 1.52-
1.63 (m, 2H), 1.64-1.84 (m, 6H), 1.84-1.96 (m, 3H), 2.12-
2.25 (m, 2H), 2.32-2.41 (m, 1H), 2.70 and 2.71 (s, 3H), 2.72-
2.93 (m, 2H), 3.19 and 3.30 (s, 3H), 3.20-3.29 (m, 1H), 3.32
and 3.35 (s, 3H), 3.42-3.53 (m, 2H), 3.58-3.76 (m, 3H), 3.73
and 3.79 (s, 3H), 3.97-4.02 (m, 1H), 4.23-4.46 (m, 1H), 4.51-
4.68 (m, 3H), 4.70-4.76 (m, 1H), 4.83-4.99 (m, 2H), 5.02-
5.28 (m, 3H), 5.67-5.70 (m, 1H), 6.68-6.72 (m, 1H), 6.79-
6.84 (m, 2H), 7.00-7.05 (m, 1H), 7.06-7.11 (m, 2H), 7.25-

1662 J . Org. Chem., Vol. 61, No. 5, 1996
Mayer et al.
7.38 (m, 5H); 13C NMR (125 MHz, CDCl3) δ -5.46, -5.52, 10.5,
10.6, 11.0, 11.2, 14.0, 14.6, 15.8, 16.2, 18.15, 18.20, 18.8, 19.3,
19.8, 19.9, 21.0, 21.4, 22.9, 23.4, 23.7, 23.8, 24.5, 24.7, 24.9,
25.2, 25.3, 25.9, 28.0, 28.1, 28.2, 28.7, 28.87, 28.90, 29.5, 29.7,
30.3, 30.4, 33.6, 34.0, 37.4, 38.1, 38.7, 39.2, 44.3, 46.2, 46.9,
47.7, 51.3, 51.7, 54.7, 55.1, 55.2, 55.4, 55.7, 55.9, 56.0, 56.9,
57.3, 61.7, 65.2, 65.5, 66.1, 66.3, 66.8, 68.1, 71.7, 71.9, 78.1,
78.4, 78.65, 78.74, 79.2, 80.1, 80.2, 80.8, 98.5, 98.7, 113.9, 114.0,
127.5, 127.7, 127.8, 128.18, 128.25, 130.1, 130.2, 130.3, 130.5,
136.8, 155.1, 155.3, 156.1, 156.7, 158.4, 158.5, 168.8, 169.1,
169.2, 169.6, 171.2, 171.5, 171.6, 172.0, 172.3, 173.8 (diaster-
eomers present in NMR); IR (CHCl3) 3420 (w), 3330 (w), 2960
(m), 2940 (m), 1725 (s), 1705 (s), 1660 (m), 1640 (s), 1545 (w),
1510 (m), 1450 (m), 1365 (m), 1250 (s), 1160 (m), 1095 (m),
1035 (m) cm-1; HRMS m/ z calcd for C63H101N5SiO16Na (M +
Et2O (160 mL) was added. After the solution was cooled to 0
°C, saturated aqueous Na2SO3 (274 drops) was added with
efficient stirring. A 10% aqueous HCl solution was added until
the aqueous layer was pH 3 (use caution not to go below). The
aqueous layer was extracted with EtOAc (100 mL), and the
combined organic layers were dried (MgSO4), filtered, and
concentrated to obtain the product (704 mg, 99% yield) as a
white solid. The crude material (29) from this oxidation
sequence was used directly in the next step without purifica-
tion: mp 102-104 °C; Rf 0.55 (10:90 MeOH:CHCl3); 1H NMR
(500 MHz, MeOH-d4) δ 0.83 (d, J ) 6.7 Hz) and 0.89-1.00
(m, 12H), 1.11 and 1.17 (dd, J ) 7.1 Hz, 3H), 1.22-1.30 (m,
3H), 1.30-1.38 (m, 1H), 1.38 and 1.40 (s, 9H), 1.42-1.50 (m,
2H), 1.52-1.87 (m, 8H), 1.93-2.10 (m, 2H), 2.11-2.28 (m, 2H),
2.43-2.91 (m, 3H), 2.80 and 2.83 (s, 3H), 3.12-3.24 (m, 1H),
3.24 and 3.30 (s, 3H), 3.29 and 3.37 (s, 3H), 3.45-3.81 (m, 2H),
3.761 and 3.764 (s, 3H), 4.01-4.12 (m, 2H), 4.48-4.68 (m, 4H)
and 4.75-4.82 (m, 1H), 4.82-4.92 (m, 3H) 4.92-5.12 (m, 3H),
6.61-6.70 (m, 1H), 6.83-6.91 (m, 2H), 6.68-7.24 and 7.41-
7.46 (m, 1H), 7.10-7.18 (m, 2H), 7.24-7.40 (m, 5H); 13C NMR
(125 MHz, MeOH-d4) δ 11.8, 12.3, 15.5, 17.3, 17.5, 19.8, 20.1,
21.3, 21.4, 23.8, 23.9, 25.9, 26.4, 28.66, 28.69, 29.4, 29.9, 30.0,
34.5, 39.3, 40.7, 42.2, 46.2, 46.9, 48.2, 52.7, 53.3, 55.7, 56.3,
57.4, 57.6, 58.6, 62.3, 66.1, 67.48, 67.55, 72.7, 72.9, 79.2, 79.4,
80.1, 80.4, 80.8, 99.1, 114.97, 115.0, 128.71, 128.75, 128.9,
129.36, 129.42, 130.7, 131.0, 131.3, 131.5, 138.0, 157.4, 158.48,
158.54, 160.0, 160.3, 170.8, 171.3, 172.0, 172.8, 173.5, 173.6,
174.2, 176.0, 177.6, 177.7 (diastereomers present in NMR); IR
(CHCl3) 3440 (w), 3330 (m), 3010 (m), 2980 (s), 2950 (s), 2880
(m), 1730 (s), 1710 (s), 1645 (s), 1585 (w), 1550 (m), 1530 (m),
1515 (s), 1470 (m), 1455 (s), 1370 (m), 1250 (s), 1165 (s), 1105
(m), 1035 (s) cm-1; HRMS m/ z calcd for C57H85N5O17Na (M +
Na+) 1234.6910, found 1234.6887; [R]20 -52.8° (c ) 0.895,
D
CHCl3).
N-[N-[N-(Ben zyloxyca r bon yl)-L-leu cyl]-L-p r olyl]-3-(p-
m eth oxyp h en yl)-N-m eth yl-L-a la n in e, Ester w ith (1S,2S)-
3-[(2S,3R)-2-[(ter t-Bu toxyca r bon yl)a m in o]-3-h yd r oxybu -
t yr a m id o]-2-m et h oxycycloh exa n eca r b oxylic
Acid ,
(1S,2S,3R)-4-Hyd r oxy-1-isop r op yl-2-(m eth oxym eth oxy)-
3-m eth ylbu tyl Ester (28). To compound 27 (0.822 g, 0.678
mmol) in THF (3.00 mL) was added HOAc:H2O (3:1, 12.0 mL)
dropwise. The reaction was stirred at rt for 24 h and then
diluted with toluene (100 mL) and concentrated. The residue
was diluted with toluene (100 mL) again and azeotroped until
no HOAc remained. The crude oil was purified by flash
column chromatography, eluting with EtOAc:petroleum ether
(50:50) followed by MeOH:CHCl3 (5:95-10:90) to afford 28
(0.702 g, 94% yield) as a solid: mp 86-88 °C; Rf 0.19 (50:50
1
EtOAc:petroleum ether); H NMR (500 MHz, CDCl3) δ 0.80-
Na+) 1134.5838, found 1134.5892; [R]20 -53.8° (c ) 0.960,
0.99 (m, 15H), 1.26 and 1.27 (s, 3H), 1.31 and 1.35 (s, 9H),
1.35-1.50 (m, 2H), 1.52-1.94 (m, 11H), 2.02-2.09 (m, 1H),
2.12-2.41 (m, 2H), 2.70 and 2.71 (s, 3H), 2.74-2.94 (m, 2H),
3.20 and 3.35 (s, 3H), 3.23-3.34 (m, 1H), 3.43-3.52 (m, 2H),
3.395 and 3.403 (s, 3H), 3.57-3.76 (m, 3H), 3.77 and 3.79 (s,
3H), 3.97-4.17 (m, 1H), 4.23-4.43 (m, 1H), 4.49-4.57 (m, 2H),
4.60-4.73 (m, 3H), 4.82-4.96 (m, 2H), 5.07-5.28 (m, 3H),
5.58-5.71 (m, 1H), 6.68-6.85 (m, 1H), 6.79-6.85 (m, 2H),
7.00-7.04 and 7.68-7.73 (m, 1H), 7.05-7.09 (m, 2H), 7.25-
7.38 (m, 5H); 13C NMR (125 MHz, CDCl3) δ 9.9, 10.2, 14.1,
14.6, 14.2, 15.4, 15.5, 18.8, 19.4, 19.9, 20.0, 21.0, 23.4, 23.5,
24.7, 24.8, 24.9, 25.2, 25.4, 26.7, 27.8, 28.1, 28.4, 28.6, 29.0,
29.4, 29.5, 29.7, 33.6, 33.7, 36.3, 38.1, 38.8, 39.1, 39.7, 44.2,
46.3, 46.9, 47.2, 51.0, 51.7, 54.7, 55.1, 55.2, 55.4, 56.4, 56.5,
57.3, 60.4, 64.2, 65.7, 66.1, 66.3, 71.7, 71.9, 78.5, 78.7, 78.9,
79.1, 79.3, 80.2, 98.8, 99.2, 113.9, 114.0, 127.5, 127.7, 127.8,
128.2, 128.3, 130.0, 130.2, 130.3, 130.4, 136.7, 155.1, 155.3,
156.7, 158.4, 158.5, 158.8, 168.7, 169.2, 169.7, 171.1, 171.2,
171.5, 171.6, 172.2, and 173.6 (diastereomers present in NMR);
IR (CHCl3) 3420 (w), 3330 (m), 2950 (s), 2930 (s), 2870 (m),
1720 (s), 1700 (s), 1635 (s), 1515 (m), 1505 (s), 1450 (s), 1365
(m), 1300 (m), 1245 (s), 1205 (s), 1155 (s), 1100 (m), 1020 (s)
cm-1; HRMS m/ z calcd for C57H87N5O16Na (M + Na+)
1120.6046, found 1120.6083; [R]20D -53.4° (c ) 0.810, CHCl3).
N-[N-[N-(Ben zyloxyca r bon yl)-L-leu cyl]-L-p r olyl]-3-(p-
m eth oxyp h en yl)-N-m eth yl-L-a la n in e, Ester w ith (1S,2S)-
3-[(2S,3R)-2-[(ter t-Bu toxyca r bon yl)a m in o]-3-h yd r oxybu -
D
CHCl3).
N-[N-(L-Leu cyl)-L-pr olyl]-3-(p-m eth oxyph en yl)-N-m eth -
yl-L-a la n in e, Ester w ith (1S,2S)-3-[(2S,3R)-2-[(ter t-Bu -
toxyca r bon yl)a m in o]-3-h yd r oxybu tyr a m id o]-2-m eth oxy-
cycloh exa n eca r boxylic Acid , (1S,2S,3S)-1-Isop r op yl-2-
(m et h oxym et h oxy)-3-m et h ylb u t a n oic Acid E st er (30).
Under a hydrogen atmosphere (40 psi), Cbz-protected amine
29 (0.662 g, 0.595 mmol) was combined with MeOH:EtOAc (1:
1, 10.0 mL) and 10% Pd/C (0.220 g, 10.3 mmol) and shaken in
a Parr apparatus for 24 h. The slurry was filtered through
Celite, followed by thorough washing with MeOH:EtOAc. The
filtrate was concentrated in vacuo, and the residue was
azeotroped with toluene several times to give the product 30
as an oil (576 mg, 99% yield): Rf 0.34 (10:90 MeOH:CHCl3);
1H NMR (500 MHz, MeOH-d4) δ 0.86-1.05 (m, 12H), 1.11-
1.19 (m, 3H), 1.28-1.43 (m, 2H), 1.43-1.56 (m, 12H), 1.56-
1.96 (m, 10H), 1.99-2.09 (m, 2H), 2.10-2.35 (m, 2H), 2.47-
2.56 (m, 2H), 2.78-3.15 (m, 6H), 3.20-3.26 (m, 1H), 3.26-3.37
(m, 3H), 3.42-3.69 (m, 2H), 3.75-3.78 (m, 3H), 4.05-4.18 (m,
2H), 4.23-4.56 (m, 3H), 4.59-4.68 (m, 3H), 4.80-4.97 (m, 3H),
5.02-5.55 (m, 1H), 6.80-6.89 (m, 2H), 7.09-7.17 (m, 2H); 13
C
NMR (125 MHz, MeOH-d4) δ 10.8, 10.9, 14.5, 17.4, 19.4, 20.2,
20.9, 21.5, 21.6, 23.8, 25.3, 25.6, 28.5, 28.69, 28.74, 29.4, 30.0,
31.9, 34.4, 41.3, 44.2, 47.1, 51.8, 55.7, 55.8, 56.5, 56.7, 61.5,
70.2, 72.8, 73.7, 80.3, 80.5, 81.1, 81.2, 99.3, 115.0, 115.3, 130.6,
131.1, 131.3, 131.8, 157.8, 160.0, 160.2, 171.0, 171.1, 173.3,
175.8, 176.1, 180.0 (diastereomers present in NMR); IR (neat)
3180-3630 (br), 2960 (s), 2940 (s), 2880 (m), 2830 (w), 1725
(s), 1660 (s), 1635 (s), 1550 (w), 1515 (s), 1440-1470 (m), 1250
t yr a m id o]-2-m et h oxycycloh exa n eca r b oxylic
Acid ,
(1S,2S,3S)-1-Isop r op yl-2-(m eth oxym eth oxy)-3-m eth ylbu -
ta n oic Acid Ester (29). To a mixture of the Dess-Martin
periodinane reagent (0.702 g, 0.639 mmol)47 and CH2Cl2 (10.0
mL) at rt was added a solution of alcohol 28 (0.352 g, 0.831
mmol) in CH2Cl2 (0.763 mL) dropwise. The reaction was
stirred for 45 min at this temperature and then diluted with
Et2O (75 mL). This slurry was poured into saturated aqueous
NaHCO3 (40 mL) containing Na2S2O3‚5H2O (1.65 g). After the
mixture was stirred for 5 min, an additional amount of Et2O
(75 mL) was added. The combined organic layers were washed
with saturated aqueous NaHCO3 (40 mL) and H2O (30 mL),
dried (MgSO4), filtered, and concentrated. The residue was
dissolved in t-BuOH (5.00 mL), keeping the temperature at
25 °C. To this solution was added 5% aqueous NaH2PO4 (3.30
mL) followed by 1 M aqueous KMnO4 (5.00 mL) dropwise.48
The reaction was stirred at 25 °C for 50 min, at which time
(s), 1200-1220 (m), 1165 (s), 1100 (m), 1080 (m), 1035 (s) cm-1
;
HRMS m/ z calcd for C49H79N5O15Na (M + Na+) 1000.5471,
found 1000.5433; [R]20 -45.4° (c ) 0.940, CHCl3).
D
Cyclo[N-(ter t-bu tyloxyca r bon yl)-O-[[[N-[(2S,3S,4S)-4-
[[(1S,2S)-3-a m in o-2-m eth oxycycloh exa n eca r bon yl]oxy]-
3-(m eth oxym eth oxy)-2,5-d im eth ylh exa n oyl]-L-leu cyl]-L-
p r olyl]-N,O-d im et h yl-L-t yr osyl]-L-t h r eon yl] (31). The
unprotected linear precursor (acid 30, 0.400 g, 0.409 mmol)
was dissolved in DMF (40.5 mL). To this solution was added
i-Pr2NEt (0.169 mL, 0.969 mmol) followed by the coupling
reagent (HBTU, 0.147 g, 0.388 mmol).50 The reaction was
stirred at rt for 3 h, the solvent distilled, and the residue
diluted with EtOAc (100 mL). The ether extract was washed
with 5% aqueous HCl (10 mL), 5% aqueous NaHCO3 (10 mL),

Constrained Ring Analog of Didemnin B
J . Org. Chem., Vol. 61, No. 5, 1996 1663
and saturated aqueous NaCl (10 mL), dried (MgSO4), and
concentrated in vacuo. The crude product was purified by
flash column chromatography, eluting with acetone:CHCl3 (1:
99-25:75) to obtain the product 31 as an oil (0.254 g, 52%
yield): Rf 0.33 (20:80 acetone:CHCl3); 1H NMR (500 MHz,
CDCl3) δ 0.81 (d, J ) 2.6 Hz) and 0.84 (d, J ) 4.2 Hz, 3H),
0.82 (d, J ) 2.1 Hz) and 0.88 (d, J ) 3.1 Hz, 3H), 0.93 (d, J )
3.6 Hz) and 0.97 (d, J ) 6.5 Hz, 3H), 1.03 (d, J ) 6.6 Hz) and
1.07 (d, J ) 6.8 Hz, 3H), 1.17-1.21 (m, 3H), 1.34 (d, J ) 6.3
Hz) and 1.37 (d, J ) 6.7 Hz, 3H), 1.38-1.50 (m, 3H), 1.42 and
1.53 (s, 9H), 1.55-1.92 (m, 9H), 1.92-2.17 (m, 2H), 2.20-2.34
(m, 1H), 2.63-2.88 (m, 2H), 2.92 and 3.00 (s, 3H), 3.12-3.22
(m, 2H), 3.40 and 3.44 (s, 3H), 3.41 and 3.43 (s, 3H), 3.43-
4.59 (m, 1H), 3.63-3.97 (m, 2H), 3.77 and 3.79 (s, 3H), 3.99
(d, J ) 10.0 Hz, 1H), 4.18-4.60 (m, 2H), 4.60-5.84 (m, 4H),
4.92-5.06 (m, 2H), 5.40-5.54 (m, 1H), 6.27-6.32 (m) and 6.50
(d, J ) 8.1 Hz, 1H), 6.80 (d, J ) 8.6 Hz) and 6.84 (d, J ) 8.6
Hz, 2H), 6.99-7.19 (m, 2H), 7.35 (d, J ) 8.2 Hz) and 8.02-
8.13 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 14.2, 17.1, 17.5,
19.0, 19.4, 20.7, 21.1, 22.6, 23.7, 24.4, 25.2, 27.7, 28.2, 28.9,
29.3, 29.7, 30.7, 34.8, 41.6, 42.0, 42.5, 46.4, 48.5, 49.6, 55.2,
55.4, 56.4, 57.8, 59.0, 62.1, 72.6, 78.0, 78.8, 79.8, 81.1, 98.9,
113.8, 114.2, 129.1, 129.8, 130.8, 155.4, 158.7, 168.9, 170.4,
172.2, 172.3, 172.7, 174.4 (diastereomers present in NMR); IR
(neat) 3326 (m), 2935 (s), 1731 (s), 1645 (s), 1584 (w), 1514
(s), 1456 (m), 1367 (m), 1301 (m), 1249 (m), 1167 (s), 1090 (m),
1044 (m) cm-1; HRMS m/ z calcd for C49H77N5O14Na (M + Na+)
added, and the layers were separated. The organic layer was
washed with saturated aqueous NaHCO3 (7 mL) and H2O (7
mL), dried (MgSO4), filtered, and concentrated. The resulting
residue was purified by flash column chromatography, eluting
with acetone:CHCl3 (1:99-20:80) to afford 33 (85.4 mg, 70%
1
yield) as a clear oil: Rf 0.85 (20:80 acetone:CHCl3); H NMR
(500 MHz, CDCl3) δ 0.75-1.02 (m, 12H), 1.05-1.40 (m, 6H),
1.40-1.78 (m, 8H), 1.43 and 1.46 (s, 9H), 1.80-2.25 (m, 5H),
2.26-2.64 (m, 3H), 2.69 and 2.74 (s, 3H), 2.86-3.24 (m, 2H),
3.24-3.43 (m, 1H), 3.26 and 3.32 (s, 3H), 3.48-3.79 (m, 2H),
3.79 and 3.80 (s, 3H), 3.91-4.46 (m, 2H), 4.49-4.94 (m, 3H),
4.99-5.18 (m, 2H), 5.47-5.69 (m, 1H), 6.05-6.22 (m, 1H),
6.80-6.97 (m, 2H), 7.02-7.15 (m, 2H), 7.33 (d, J ) 8.6 Hz)
and 8.35 (s, 1H); 13C NMR (125 MHz, CDCl3) δ 13.2, 13.5, 15.1,
16.8, 17.4, 18.0, 18.4, 18.9, 19.0, 21.0, 21.3, 23.4, 23.8, 24.0,
24.3, 24.6, 26.0, 28.1, 28.3, 29.2, 29.7, 30.2, 32.5, 33.2, 38.6,
39.2, 40.3, 43.8, 46.2, 46.5, 46.8, 48.8, 49.0, 50.2, 50.3, 53.3,
55.22, 55.25, 55.3, 55.9, 56.7, 57.7, 57.8, 66.5, 67.3, 70.8, 71.2,
79.3, 79.7, 79.9, 81.0, 81.7, 84.2, 113.8, 114.0, 129.9, 130.0,
130.1, 130.4, 155.1, 158.4, 158.7, 168.9, 169.0, 170.1, 171.1,
171.3, 172.2, 203.4, 204.3 (diastereomers present in NMR); IR
(neat) 3306 (m), 2935 (m), 2871 (w), 1741 (s), 1640 (s), 1514
(s), 1452 (m), 1367 (m), 1302 (m), 1248 (s), 1168 (s), 1124 (w),
1098 (m) cm-1; HRMS m/ z calcd for C47H71N5O13Na (M + Na+)
936.4946, found 936.4930; [R]20 -80.5° (c ) 0.940, CHCl3).
D
Cyclo[O-[[[N-[(2S,3S,4S)-4-[(1S,2S)-3-a m in o-2-m eth oxy-
cycloh exa n eca r bon yl]oxy]-3-oxo-2,5-d im eth ylh exa n oyl]-
L-leu cyl]-L-pr olyl]-N,O-dim eth yl-L-tyr osyl]-L-th r eon yl] Hy-
d r och lor id e (34). A solution of ketone 33 (70.0 mg, 76.6
µmol) in EtOAc (7.4 mL) was cooled to -30 °C. Gaseous HCl
was introduced at such a rate that the temperature of the
mixture was maintained between -10 and -20 °C at satura-
tion. After being stirred for 1 h at this temperature, it was
stirred at 0 °C for 1 h. The solution was then purged with N2
for about 30 min, maintaining the temperature at 0 °C. After
the solution was concentrated, the residue was triturated and
washed by decantation with three 1.0 mL portions of tert-butyl
methyl ether:hexane (1:4). The product was collected by
filtration and dried in vacuo after recrystallization from
MeOH:toluene to provide the hydrochloride salt (34, 58.6 mg,
90% yield) as a white solid: mp 183-185 °C; Rf 0.31 and 0.34
(10:90 MeOH:CHCl3); 1H NMR (500 MHz, CDCl3) δ 0.73-1.11
(m, 12H), 1.11-1.18 (m, 1H), 1.22-1.47 (m, 6H), 1.47-1.97
(m, 10H), 1.97-2.47 (m, 4H), 2.68 (s, 3H), 2.69-2.91(m, 1H),
2.91-3.30 (m, 2H), 3.30 and 3.41 (s, 3H), 3.40-3.63 (m, 3H),
3.63-3.74 (m, 1H), 3.77 and 3.79 (s, 3H), 3.80-4.01 (m, 1H),
4.13-4.98 (m, 4H), 5.03-5.11 (m, 1H), 5.13-5.27 (m, 1H),
6.71-6.88 (m, 2H), 6.94-7.14 (m, 2H), 7.63-7.75 and 8.05-
8.20 (m, 1H), 8.20-9.24 (m, 3H); 13C NMR (125 MHz, CDCl3)
δ 14.1, 14.7, 17.6, 17.8, 18.0, 18.3, 18.9, 19.3, 20.4, 20.6, 21.3,
21.5, 22.6, 23.5, 23.8, 24.7, 26.4, 26.9, 28.1, 28.5, 28.9, 29.7,
30.4, 31.2, 31.5, 32.6, 32.9, 33.3, 38.6, 39.5, 41.3, 41.6, 42.2,
43.4, 46.1, 46.8, 47.4, 47.6, 49.4, 49.7, 49.1, 50.2, 52.4, 55.2,
54.0, 55.2, 56.9, 57.9, 58.0, 58.8, 66.3, 69.4, 71.7, 73.0, 79.2,
81.6, 81.8, 83.8, 114.0, 114.2, 129.5, 129.7, 130.0, 130.4, 158.5,
158.9, 166.5, 166.8, 168.6, 169.3, 170.7, 170.9, 171.0, 171.5,
172.4, 172.8, 174.2, 174.5, 203.6, 204.5 (diastereomers present
in NMR); IR (neat) 3310 (br), 2960 (s), 1732 (s), 1634 (s), 1558
(m), 1514 (s), 1456 (m), 1388 (w), 1369 (w), 1302 (w), 1248 (m),
982.5365, found 982.5379; [R]20 -17.4° (c ) 1.17, CHCl3).
D
Cyclo[N-(ter t-b u t oxyca r b on yl)-O-[[[N-[(2S,3S,4S)-4-
[[(1S,2S)-3-a m in o-2-m eth oxycycloh exa n eca r bon yl]oxy]-
3-h yd r oxy-2,5-d im eth ylh exa n oyl]-L-leu cyl]-L-p r olyl]-N,O-
d im eth yl-L-tyr osyl]-L-th r eon yl] (32). To a solution of MOM
ether 31 (0.254 g, 0.265 mmol) in CH2Cl2 (5.8 mL) at -78 °C
was added dropwise a solution of dimethylboron bromide (1.5
M, 0.533 mL) in CH2Cl2.51,52 After 1 h at -78 °C, the reaction
mixture was transferred via cannula into a vigorously stirred
mixture of THF (3.7 mL) and saturated aqueous NaHCO3 (1.85
mL). After 5 min, the mixture was diluted with Et2O (75 mL)
and the resulting organic layer washed with H2O (7.5 mL),
10% aqueous NaHSO4 (7.5 mL), and saturated aqueous NaCl
(7.5 mL). The aqueous layers were extracted with Et2O, and
the combined organic layers were dried (MgSO4), filtered, and
concentrated. The residue was purified by flash column
chromatography, eluting with acetone:CHCl3 (2:98-26:74) to
afford 32 (186 mg, 77% yield) as an oil: Rf 0.20 (20:80 acetone:
CHCl3); 1H NMR (500 MHz, CDCl3) δ 0.77-0.98 (m, 9H), 1.02
(d, J ) 6.8 Hz, 3H), 1.22-1.28 (m, 1H), 1.30-1.48 (m, 6H),
1.43 and 1.53 (s, 9H), 1.53-1.74 (m, 6H), 1.74-2.02 (m, 4H),
2.02-2.20 (m, 2H), 2.22-2.41 (m, 2H), 2.52-2.80 (m, 1H), 2.91
and 2.99 (s, 3H), 2.93-3.22 (m, 3H), 3.39 and 3.48 (s, 3H),
3.42-3.67 (m, 2H), 3.70-3.94 (m, 1H), 3.78 and 3.79 (s, 3H),
4.01 (d, J ) 8.7 Hz, 1H), 4.11-4.51 (m, 2H), 4.53-4.87 (m,
3H), 4.91-5.12 (m, 2H), 5.42-5.60 (m, 1H), 6.24-6.38 (m, 1H),
6.85 (d, J ) 8.5 Hz) and 6.91 (d, J ) 8.3 Hz, 2H), 7.05 (d, J )
7.9 Hz) and 7.16 (d, J ) 6.1 Hz, 2H), 8.06-8.17 (m, 1H); 13C
NMR (125 MHz, CDCl3) δ 10.2, 17.1, 18.9, 19.1, 20.6, 22.4,
23.7, 24.4, 24.7, 25.2, 27.4, 28.3, 29.1, 29.8, 30.6, 35.1, 41.8,
42.6, 43.4, 46.3, 49.5, 55.2, 55.32, 55.34, 57.8, 58.8, 62.0, 71.8,
72.2, 78.3, 79.4, 81.1, 113.1, 114.2, 129.1, 129.7, 130.1, 155.3,
158.7, 168.1, 168.9, 170.5, 171.9, 172.1, 174.3 (diastereomers
present in NMR); IR (neat) 3295 (m), 2960 (s), 2873 (m), 1726
(s), 1659 (s), 1650 (s), 1644 (s), 1514 (s), 1454 (m), 1367 (m),
1177 (m), 1091 (m) cm-1; HRMS m/ z calcd for C42H63N5O11
-
Na (M - HCl + Na+) 836.4422, found 836.4438; [R]20 -91.5°
D
(c ) 0.865, CHCl3).
1302 (m), 1249 (s), 1215 (m), 1176 (s), 1088 (m), 1059 (m) cm-1
;
Cyclo[N-(N-L-la ctyl-L-p r olyl-N-m eth yl-D-leu cyl)-O-[[[N-
[(2S,3S,4S)-4-[[(1S,2S)-3-a m in o-2-m et h oxycycloh exa n e-
ca r b on yl]oxy]-3-oxo-2,5-d im et h ylh exa n oyl]-L-leu cyl]-L-
p r olyl]-N,O-d im eth yl-L-tyr osyl]-L-th r eon yl] (2b). To a
mixture of the constrained macrocycle amine salt (34, 30.0 mg,
35.3 µmol) and the didemnin B side chain (35, 13.3 mg, 42.4
µmol) in CH2Cl2 (2.0 mL) at 0 °C were added BOP (23.4 mg,
53.0 µmol) and NMM (8.9 mg, 9.7 µL, 88.3 µmol).46 After 30
min at 0 °C, the reaction mixture was allowed to warm to rt
and stir for an additional 4 h. The solution was then treated
with saturated aqueous NaCl (2 mL) and extracted with EtOAc
(10 mL). The organic layer was washed with 5% aqueous HCl
(1 mL), 5% aqueous NaHCO3, and saturated aqueous NaCl (1
mL), dried (MgSO4), filtered, and concentrated. The crude
HRMS m/ z calcd for C47H73N5O13Na (M + Na+) 938.5103,
found 938.5106; [R]20 -16.9° (c ) 0.850, CHCl3).
D
Cyclo[N-(ter t-b u t oxyca r b on yl)-O-[[[N-[(2S,3S,4S)-4-
[[(1S,2S)-3-a m in o-2-m eth oxycycloh exa n eca r bon yl]oxy]-
3-oxo-2,5-d im et h ylh exa n oyl]-L-leu cyl]-L-p r olyl]-N,O-d i-
m eth yl-L-tyr osyl]-L-th r eon yl] (33). To a mixture of the
Dess-Martin periodinane reagent (73.3 mg, 0.173 mmol) and
CH2Cl2 (3.5 mL) at rt was added a solution of alcohol 32 (122
mg, 0.133 mmol) in CH2Cl2 (3.5 mL) dropwise. The reaction
was stirred for 2 h at this temperature and then diluted with
Et2O (35 mL). This mixture was poured into a saturated
aqueous NaHCO3 solution (7 mL) containing Na2S2O3‚5H2O
(416 mg) and stirred ∼5 min. Another 35 mL of Et2O was

1664 J . Org. Chem., Vol. 61, No. 5, 1996
Mayer et al.
residue was purified by flash column chromatography, eluting
with MeOH:CHCl3 (3:97) to afford the product (2b, 18.0 mg,
46% yield) as an off-white solid in a 1:1 diastereomeric
mixture: Rf 0.30 and 0.46 (20:80 acetone:CHCl3); 1H NMR (500
MHz, CDCl3) δ 0.78-1.14 (m, 18H), 1.17-1.28 (m, 6H), 1.28-
1.40 (m, 3H), 1.40-1.46 (m, 3H), 1.46-1.65 (m, 5H), 1.65-
2.27 (m, 11H), 2.27-2.41 (m, 2H), 2.41-2.54 (m, 1H), 2.63-
2.78 (m, 1H), 2.69 and 2.79 (s, 3H), 2.83-2.95 (m, 1H), 2.90
and 3.08 (s, 3H), 3.17-3.43 (m, 1H), 3.30 and 3.33 (s, 3H),
3.48-3.77 (m, 5H), 3.78 and 3.79 (s, 3H), 3.81-4.18 (m, 2H),
4.29-4.52 (m, 2H), 4.52-4.76 (m, 2H), 4.77-4.97 (m, 2H),
4.97-5.22 (m, 2H), 5.22-5.37 (m, 1H), 5.42-5.64 (m, 1H),
6.64-6.73 and 6.88-6.95 (m, 1H), 6.79-6.87 (m, 2H), 7.02 (d,
J ) 8.5 Hz) and 7.06 (d, J ) 8.5 Hz, 2H), 7.34 (d, J ) 6.8 Hz)
and 7.55-7.58 (m, 1H); 13C NMR (125 MHz, CDCl3) δ 13.5,
14.0, 14.8, 16.3, 17.7, 17.9, 18.2, 18.4, 18.8, 18.9, 19.3, 19.4,
20.3, 21.2, 21.65, 21.74, 22.0, 22.3, 22.6, 23.4, 23.7, 23.8, 24.2,
24.5, 24.9, 25.0, 25.3, 25.87, 25.93, 27.5, 28.0, 28.2, 28.3, 29.5,
29.7, 30.1, 30.6, 31.3, 31.6, 32.3, 32.8, 34.1, 34.3, 35.5, 39.3,
39.5, 43.6, 45.2, 45.9, 46.1, 46.8, 47.2, 48.8, 49.2, 49.6, 50.6,
53.1, 54.6, 55.2, 55.29, 55.33, 55.4, 55.8, 56.5, 57.0, 57.1, 57.4,
57.5, 58.8, 59.0, 62.8, 65.6, 65.9, 67.8, 70.4, 71.2, 72.7, 72.8,
75.9, 80.2, 80.9, 83.9, 113.9, 114.2, 129.2, 130.0, 130.1, 130.2,
158.3, 158.7, 168.7, 169.6, 170.5, 170.6, 171.1, 171.2, 172.2,
173.5, 174.8, 203.5 (diastereomers present in NMR); IR (neat)
3386 (br), 2957 (s), 1734 (m), 1635 (s), 1514 (m), 1451 (m), 1369
(w), 1248 (m), 1169 (m), 1098 (m) cm-1; HRMS m/ z calcd for
C57H87N7O15Na (M + Na+) 1132.6158, found 1132.6187; [R]20
D
-19.8° (c ) 0.313, CHCl3).
Ack n ow led gm en t . This investigation was sup-
ported by the National Institutes of Health (CA-40081).
We also acknowledge Dr. George T. Furst, Dr. Patrick
J . Carroll, Mr. J ohn Dykins, and Ms. Magda M. Cuevas
of the University of Pennsylvania Analytical Facilities
for their expert technical assistance.
Abbr eviation s: N-[(benzyloxy)carbonyl]-5-norbornene-
2,3-dicarboximide (BCN); N,N-bis(2-oxo-3-oxazolidinyl)-
phosphonic chloride (BOP-Cl); 1,1-carbonyldiimidazole
(CDI); tetrabutylammonium fluoride (TBAF).
Su p p or tin g In for m a tion Ava ila ble: Analytical data for
intermediates 6-18, 3, and 35 and copies of NMR spectra of
these as well as all new compounds (65 pages). This material
is contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
J O951693I