Total synthesis of dehydrodidemnin B. Use of uronium and phosphonium salt coupling reagents in peptide synthesis in solution

Article abstract of DOI:10.1021/jo961932h

New total syntheses of didemnin A and of dehydrodidemnin B are described. The latter didemnin has the highest antiproliferative activity of all members of this family of macrocyclic depsipeptides. It was produced on coupling the side chain Pyr-Pro-OH to d

Full text of DOI:10.1021/jo961932h

354
J . Org. Chem. 1997, 62, 354-366
Tota l Syn th esis of Deh yd r od id em n in B. Use of Ur on iu m a n d
P h osp h on iu m Sa lt Cou p lin g Rea gen ts in P ep tid e Syn th esis in
Solu tion †
Gemma J ou, Isabel Gonza´lez, Fernando Albericio, Paul Lloyd-Williams,* and Ernest Giralt*
Department of Organic Chemistry, University of Barcelona, E-08028 Barcelona, Spain
Received October 15, 1996X
New total syntheses of didemnin A and of dehydrodidemnin B are described. The latter didemnin
has the highest antiproliferative activity of all members of this family of macrocyclic depsipeptides.
It was produced on coupling the side chain Pyr-Pro-OH to didemnin A, which was itself synthesized
by two novel routes. One of these was based on the elaboration of a linear heptadepsipeptide
incorporating the first amino acid of the didemnin side chain, (R)-N(Me)-Leu. Deprotection of the
amino and carboxyl terminii of this linear precursor followed by macrocyclization gave a protected
derivative of didemnin A. The second route involved synthesis of the Boc-protected didemnin
macrocycle from a linear hexadepsipeptide lacking (R)-N(Me)-Leu. Removal of the Boc group from
the macrocycle followed by its coupling with Boc-(R)-N(Me)-Leu-OH then gave Boc-didemnin A.
The overall yield was much higher for the second strategy (27% compared to 4% for the first
synthesis), but both allowed synthetic didemnin A, identical with a natural sample, to be prepared.
Extensive use was made of phosphonium and uronium salt-based coupling reagents, such as BOP,
PyBrOP, PyAOP, HBTU, and HATU for the formation of both the secondary and tertiary amide
bonds present in these complex depsipeptides.
In tr od u ction
ates the various didemnins: in the simplest member of
the family, didemnin A (1c), it consists only of (R)-N(Me)-
Leu, whereas in other cases it can be appreciably more
complex.
The didemnins1 are macrocyclic depsipeptides, first
isolated in 1981 from the marine tunicate Trididemnum
solidum by Rinehart.2,3 Subsequent studies established
that they all have have the same basic structure (1, R1
) H), consisting of a 23-membered macrocycle with an
attached side chain. The macrocycle is made up of six
subunits, (S)-Leu, (S)-Pro, (1S,2R)-Thr, (S)-N(Me)-O(Me)-
Tyr, (3S,4R,5S)-isostatine (Ist), and (2S,4S)-3-oxo-4-
hydroxy-2,5-dimethylhexanoic acid, also known as R-(R-
hydroxyisovaleryl)propionic acid (HIP). The side chain,
whose first amino acid is always (R)-N(Me)-Leu, is joined
to the Thr of the macrocycle, and its structure differenti-
* Authors to whom correspondence should be addressed.
† Abbreviations for amino acids and peptides used in this paper are
those recommended by the IUPAC-IUPAB Commission of Biochemical
Nomenclature, and published in J . Biol. Chem. 1972, 247, 977-983.
Additional abbreviations used are as follows: Boc, tert-butoxycarbonyl;
BOP, (1H-benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexaflu-
orophosphate; BOP-Cl, N,N-bis(2-oxo-3-oxazolidinyl)phosphinic chlo-
ride; Bzl, benzyl; CI, chemical ionization; DCC, N,N′-dicyclohexylcar-
bodiimide; DIEA, N,N-diisopropylethylamine; DIPCDI, N,N′-diiso-
propylcarbodiimide; DMAP, 4-(dimethylamino)pyridine; DMF, N,N-
dimethylformamide; ES, electrospray; FAB, fast atom bombardment;
HATU, N-[(dimethylamino)-1H-1,2,3-triazolo[4,5-b]pyridin-1-ylmeth-
ylene]-N-methylmethanaminium hexafluorophosphate N-oxide; HBTU,
N-[(1H-benzotriazol-1-yl)(dimethylamino)methylene]-N-methylmetha-
naminium hexafluorophosphate N-oxide; HOAt, 1-hydroxy-7-azaben-
zotriazole; HOBt, 1-hydroxybenzotriazole; HPLC, high-performance
liquid chromatography; IR, infrared; Lac, lactyl; NMR, nuclear mag-
netic resonance; PyAOP, [(7-azabenzotriazol-1-yl)oxy]tris(pyrrolidino)-
phosphonium hexafluorophosphate; PyBrOP, bromotripyrrolidinophos-
phonium hexafluorophosphate; Pyr, pyruvyl; RP, reversed phase; SEM,
[(trimethylsilyl)ethoxy]methyl; TBAF, tetra-n-butylammonium fluo-
ride; TBDMS, tert-butyldimethylsilyl; Tce, 2,2,2-trichloroethyl, TFA,
trifluoroacetic acid; THF, tetrahydrofuran; tR, retention time; TTFH,
tetramethylfluoroformamidinium hexafluorophosphate; Z, benzyloxy-
carbonyl.
Certain didemnins exhibit significant antiproliferative
and immunosuppressive activity, and didemnin B (1d ),
the most active of those hitherto isolated, was the first
marine natural product to enter phase I/II clinical trials
as a candidate drug at the U.S. National Cancer
Institute.4-9 The encouraging physiological activity of
this intriguing class of compounds together with their
structural complexity has provided the impetus for
X Abstract published in Advance ACS Abstracts, December 15, 1996.
(1) Li, W.-R.; J oullie´, M. M. In Studies in Natural Products; Atta-
ur-Rahman, Ed.; Elsevier Science Publishers: New York, 1992; Vol.
10, Part F; pp 241-302.
(2) Rinehart, K. L.; Gloer, J . B.; Cook, J . C.; Mizsak, S. A.; Scahill,
T. A. J . Am. Chem. Soc. 1981, 103, 1857-1859.
(3) Rinehart, K. L.; Gloer, J . B.; Hughes, R. G.; Renis, H. E.;
McGovren, J . P.; Swynenberg, E. B.; Stringfellow, D. A.; Kuentzel, S.
L.; Li, L. H. Science 1981, 212, 933-935.
S0022-3263(96)01932-9 CCC: $14.00 © 1997 American Chemical Society

Total Synthesis of Dehydrodidemnin B
J . Org. Chem., Vol. 62, No. 2, 1997 355
synthetic studies, culminating in the total synthesis of
several didemnins10-14 and of some analogues.15,16
More recently, while the biological activity of other
newly isolated didemnins17,18 still awaits full evaluation,
dehydrodidemnin B (1e), from Aplidium albicans,16,19,20
has shown even higher antineoplastic activity than
didemnin B, both in vitro and in vivo. It is currently the
most active didemnin known but, unfortunately, is only
present in tiny quantities in extracts of the tunicate.
Although a preliminary evaluation of its therapeutic
usefulness can be done with material obtained by semi-
synthesis from the relatively abundant natural didemnin
A (1c), a more satisfactory source of the molecule for
biological testing would be chemical synthesis. Here we
report on two new total syntheses of the didemnins that
could, in principle, provide useful quantities of dehy-
drodidemnin B.
O(Me)-Tyr and Pro was selected as the point for macro-
cyclization.12 Although formation of an amide here is,
at first sight at least, more demanding, owing to the steric
effect of the N-methylated amino group, it has the
advantages that the risks of epimerization are reduced
since the C-terminal amino acid is Pro and, more
importantly, that no other obvious side reactions are
associated with it.
Str a tegica l a n d Ta ctica l Con sid er a tion s
Didemnin A (1c) is the primary synthetic objective of
any total synthesis of this family of compounds, since all
other members can be obtained from it by attachment of
the requisite side chain to the amino terminal of (R)-
N(Me)-Leu. Two general synthetic strategies to 1c can
be envisaged, the difference between them residing in
whether or not the linear precursor to the macrocycle
incorporates the first amino acid of the side chain. Both
approaches have formed the basis of successful total
syntheses.
The key step in the synthesis of these molecules,
regardless of whether (R)-N(Me)-Leu is present in the
linear precursor, is the formation of the macrocycle. The
greater facility with which amide bonds can be formed,
a consequence of the superior nucleophilicity of the amine
over the hydroxyl group, makes macrolactamization the
preferred mode for ring closure. Successful cyclization
at all of the four possible amide bonds has been achieved
in previous syntheses of the didemnins.21 However, in
the present work, that between Pro and Leu was rejected
because of the possibility of cyclo-[(S)-Pro-(S)-N(Me)-
O(Me)-Tyr] diketopiperazine formation. That between
(S)-Leu and the HIP unit was rejected because of the
well-known tendency of â-keto acids to decarboxylate, and
that between Ist and Thr was also rejected because of
the possible cyclization of Ist to give the five-membered
γ-lactam 2. In consequence, the bond linking N(Me)-
Consideration of these factors led to the choice of the
two linear precursors, 4a and 5a , as primary synthetic
objectives. Linear precursor 4a incorporates (R)-N(Me)-
Leu whereas 5a does not, but both are diastereomeric
mixtures at C-2 of the HIP unit. Previous syntheses of
the didemnins have indicated that optically pure mac-
rocyclic products can be obtained from such mix-
tures.10,12,13,22 Removal of the protecting groups from the
amino and carboxyl functions of 4a , followed by cycliza-
tion leads to the formation of 1a , a protected derivative
of didemnin A. Similar operations on 5a give 3a , a
protected derivative of the didemnin macrocycle; attach-
ment of (R)-N(Me)-Leu or more complex side-chains is
then necessary to obtain didemnins.
(4) Dorr, F. A.; Kuhn, J . G.; Phillips, J .; von Hoff, D. D. Eur. J .
Cancer Clin. Oncol. 1988, 24, 1699-1706.
(5) Shin, D. M.; Holoye, P. Y.; Murphy, W. K.; Forman, A.; Papa-
sozomenos, S. C.; Hong, W. K.; Raber, M. Cancer Chemother. Phar-
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(6) Stewart, J . A.; Low, J . B.; Roberts, J . D.; Blow, A. Cancer 1991,
68, 2550-2554.
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213.
(8) Queisser, W. Onkologie 1992, 15, 454-462.
(9) Malfetano, J . H.; Blessing, J . A.; J acobs, A. J . Am. J . Clin. Oncol.
(CCT) 1993, 16, 47-49.
(10) Rinehart, K. L.; Kishore, V.; Nagarajan, S.; Lake, R. J .; Gloer,
J . B.; Bozich, F. A.; Li, K.-M.; Maleczka, R. E.; Todsen, W. L.; Munro,
M. H. G.; Sullins, D. W.; Sakai, R. J . Am. Chem. Soc. 1987, 109, 6846-
6848.
(11) Schmidt, U.; Kroner, M.; Griesser, H. Tetrahedron Lett. 1988,
29, 4407-4408.
(12) Hamada, Y.; Kondo, Y.; Shibata, M.; Shioiri, T. J . Am. Chem.
Soc. 1989, 111, 669-673.
(13) J ouin, P.; Poncet, J .; Dufour, M.-N.; Pantaloni, A.; Castro, B.
J . Org. Chem. 1989, 54, 617-627.
(14) Li, W.-R.; Ewing, W. R.; Harris, B. D.; J oullie´, M. M. J . Am.
Chem. Soc. 1990, 112, 7659-7672.

356 J . Org. Chem., Vol. 62, No. 2, 1997
J ou et al.
In addition to standard peptide (secondary amide)
bonds, these complex depsipeptides contain ester and
tertiary amide linkages between subunits. Peptide bond
formation between the DNA-encoded amino acids is a
highly optimized procedure that can be brought about
repetitively and reproducibly in very high yield. How-
ever, the formation of esters or of secondary amides is
more demanding, as a consequence of the poorer nucleo-
phile in the former case and of steric hindrance in the
latter. The new generation of phosphonium and uronium
salt-based coupling reagents have been used to great
effect in the solid-phase synthesis of peptides, in par-
ticular for the coupling of N-alkylated or otherwise
sterically-hindered amino acids. The synthesis of the
didemnins provided an opportunity for assessing their
suitability for the synthesis of peptides in solution, where
they have been much less frequently employed. Among
the reagents that have been used in this work are the
phosphonium and uronium23-28 reagents BOP (6), Py-
BrOP (7), PyAOP (8), HBTU (9), and HATU (10). Ad-
ditionally, the recently-described29,30 additive HOAt (11),
a structural variant of the well-known31 HOBt (12), was
also used.
N-methylated amino acids Boc-(R)-N(Me)-Leu-OH and
Boc-(S)-N(Me)-O(Me)-Tyr-OH were synthesized using
methods described by J oullie´.14 We have previously
described32 the synthesis of protected derivatives of Ist,
14 and 15, from Boc-(1R,2S)-Ile-OH.
The most challenging subunit to manage is the HIP
residue, and two protected derivatives, 16 and 17, were
employed. Both were used as mixtures of diastereomers,
and both were synthesized from H-(S)-Val-OH, as re-
ported by us.33 â-Keto ester 16 is prone to undergo
decarboxylation on hydrogenolytic deprotection of its
carboxylic acid terminus, which can complicate its syn-
thetic manipulation. Although this side reaction can
normally be controlled, alcohol 17 was prepared as an
alternative in which, after ester hydrolysis, decarbox-
ylation occurs much less readily.33
Syn th esis of Did em n in A
Str a tegy 1. The key step in the synthesis of linear
precursor 4a , whose deprotection and cyclization lead
directly to the didemnin A derivative 1a , was the union
of the eastern and western segments 21 and 29, respec-
tively, by formation of an ester bond. The synthesis of
segment 21 is outlined in Scheme 1.
Removal of the Tce group from the Bzl-HIP-Leu-OTce
unit 18, prepared from alcohol 17, as previously described
by ourselves,33 furnished carboxylic acid 19 that was
coupled with H-Pro-OTce using HBTU (9) in the presence
of HOBt (12), giving 20. Hydrogenolysis then gave
eastern segment 21.
The protection scheme for depsipeptide synthesis was
based upon the use of the Boc- and Z-groups as amino
protection, Bzl or TBDMS ethers for the protection of
alcohols, and Bzl, Tce, or SEM esters for the protection
of carboxylic acids.
The corresponding western segment 29 was synthe-
sized as outlined in Scheme 2.
Removal of the Boc group from Ist derivative 14
followed by coupling to Boc-Thr(Bzl)-OH, using HBTU
(9) in the presence of HOBt (12), gave dipeptide 22. Boc
group removal, followed by coupling with Boc-(R)-N(Me)-
Leu-OH, using BOP (6), in the presence of HOBt (12),
Syn th esis of th e Su bu n its
Of the constituents of the didemnins employed in these
syntheses, Boc-(S)-Pro-OH, Boc-(S)-Leu-OH, and Boc-
(1S,2R)-Thr(Bzl)-OH are available commercially. The
(23) Castro, B.; Dormoy, J . R.; Evin, G.; Selve, C. Tetrahedron Lett.
1975, 1219-1222.
(24) Dourtoglou, V.; Ziegler, J .-C.; Gross, B. Tetrahedron Lett. 1978,
1269-1272.
(15) Mayer, S. C.; Pfizenmayer, A. J .; J oullie´, M. M. J . Org. Chem.
1996, 61, 1655-1664.
(25) Dourtoglou, V.; Gross, B.; Lambropoulou, V.; Ziodrou, C.
Synthesis 1984, 572-574.
(16) Rinehart, K. L. US Patent No. 5294603; 1994; pp 1-25.
(17) Sakai, R.; Stroh, J . G.; Sullins, D. W.; Rinehart, K. L. J . Am.
Chem. Soc. 1995, 117, 3734-3748.
(26) Knorr, R.; Trzeciak, A.; Bannwarth, W.; Gillessen, D. Tetrahe-
dron Lett. 1989, 30, 1927-1930.
(27) Fre´rot, E.; Coste, J .; Pantaloni, A.; Dufour, M.-N.; J ouin, P.
Tetrahedron 1991, 47, 259-270.
(18) Abou-Mansour, E.; Boulanger, A.; Badre, A.; Bonnard, I.;
Banaigs, B.; Combaut, G.; Francisco, C. Tetrahedron 1995, 51, 12591-
12600.
(28) Carpino, L. A.; El-Fahan, A.; Minor, C. A.; Albericio, F. J . Chem.
Soc., Chem. Commun. 1994, 201-203.
(19) Schmitz, F. J .; Yasumoto, T. J . Nat. Prod. 1991, 54, 1469-1490.
(20) Sakai, R.; Rinehart, K. L.; Kundu, B.; Faircloth, G.; Gloer, J .
B.; Carney, J . R.; Namikoshi, M.; Sun, F.; Hughes, R. G.; Gravalos, D.
G.; de Quesada, T. G.; Wilson, G. R.; Heid, R. M. J . Med. Chem. 1996,
39, 2819-2834.
(21) Wipf, P. Chem. Rev. 1996, 95, 2115-2134.
(22) Schmidt, U.; Kroner, M.; Griesser, H. Synthesis 1991, 294-
300.
(29) Carpino, L. A. J . Am. Chem. Soc. 1993, 115, 4397-4398.
(30) Carpino, L. A.; El-Faham, A.; Albericio, F. J . Org. Chem. 1995,
60, 3561-3564.
(31) Ko¨nig, W.; Geiger, R. Chem. Ber. 1970, 103, 788-798.
(32) Lloyd-Williams, P.; Monerris, P.; Gonzalez, I.; J ou, G.; Giralt,
E. J . Chem. Soc., Perkin Trans. 1 1994, 1969-1974.
(33) Gonza´lez, I.; J ou, G.; Caba, J . M.; Albericio, F.; Lloyd-Williams,
P.; Giralt, E. J . Chem. Soc., Perkin Trans. 1 1996, 1427-1434.

Total Synthesis of Dehydrodidemnin B
J . Org. Chem., Vol. 62, No. 2, 1997 357
Sch em e 1a
Sch em e 2a
a
Reagents and conditions: (i) Zn dust, 1 M NH4Ac, 84%; (ii)
H-Pro-OTce, HBTU, HOBt, DIEA, 76%; (iii) H2/Pd-C, 78%.
gave tripeptide 23. Saponification of the methyl ester
and protection of the hydroxyl group of 24 as the TBDMS
ether afforded carboxylic acid 25 that was protected as
its Tce ester 26. Catalytic hydrogenolysis of 26 gave
alcohol 27 that was esterified with Z-N(Me)-O(Me)-Tyr-
OH using DCC in the presence of DMAP, giving 28.
Removal of the Tce group then furnished segment 29.
Formation of an ester bond between eastern and
western segments 21 and 29 proved to be challenging
and required very careful control of the reaction condi-
tions. Use of DCC or DIPCDI in the presence of DMAP
at room temperature led only to the formation of the
corresponding N-acylisourea derivatives of 29 and recu-
peration of unchanged 21. Esterification could, however,
be brought about by treatment of a mixture of 21 and 29
with DIPCDI and DMAP in the presence of DMAP‚CF3-
COOH in refluxing chloroform. This is a variation of the
procedure decribed by Boden34 and allowed the formation
of 4a in 60% yield, after chromatography.
The transformation of linear precursor 4a into didem-
nin A derivative 1a was accomplished by sequential
deprotection of its carboxyl and amino terminii, giving
4b and then 4c, respectively, followed by macrocycliza-
tion, in 28% yield, using HATU (10) in the presence of
HOAt (11). Nuclear magnetic resonance studies together
with HPLC data of the product indicated that only one
stereoisomer was present. Treatment of 1a with 5 M
HCl-dioxane gave material whose physical data were
identical with those of a natural sample of didemnin A
(1c).
a
Reagents and conditions: (i) 40% TFA-DCM (ii) Boc-(R)-
N(Me)-Leu-OH, BOP, HOBt, DIEA, 81%; (iii) 1 M NaOH, MeOH,
96%; (iv) TBDMS-Cl, imidazole, 72%; (v) Tce-OH, DCC, 80%; (vi)
H2, Pd-C, 95%; (vii) Z-(S)-N(Me)-O(Me)-Tyr-OH, DCC, DMAP,
79%; (viii) Zn dust, 1 M NH4Ac, 66%.
side chains and the formation of didemnins. The syn-
thesis of segment 34 is outlined in Scheme 3.
Dipeptide 30 was prepared by DCC-mediated coupling
between Boc-Leu-OH and H-Pro-OBzl followed by Boc
group removal. Amide bond formation between 30 and
the HIP unit was brought about by catalytic hydro-
genolysis of 16, furnishing the corresponding â-keto acid
that was coupled rapidly in situ by treatment with HBTU
(9) in the presence of HOBt (12), giving 31. Removal of
the TBDMS group then gave alcohol 32 that was esteri-
fied with Ist derivative 15, using DCC in the presence of
DMAP, affording ester 33. Simultaneous acidolytic
deprotection of the Boc and TBDMS groups then gave
segment 34.
The complementary didepsipeptide segment 38 re-
quired to form linear precursor 5a was prepared in a
Str a tegy 2. An alternative approach to the didemnins
is based upon the synthesis of linear precursor 5a , by
formation of an amide bond between segments 34 and
38. Simultaneous deprotection of the amino and carboxyl
terminii of 5a gives 5b, whose cyclization provides the
protected didemnin macrocycle 3a . Removal of the amino
protecting group from 3a then allows the attachment of
similar manner to that reported by J oullie´,14
to Scheme 4.
according
Protection of the carboxyl group of Boc-Thr(Bzl)-OH
as the SEM ester 35 followed by catalytic hydrogenolysis
gave alcohol 36, which was esterified with Z-N(Me)-
O(Me)-Tyr-OH using DCC in the presence of DMAP,
giving 37. Removal of the SEM group from 37 could not
be carried out using TBAF because of unavoidable
decomposition of the didepsideptide, presumably initiated
(34) Boden, E. P.; Keck, G. E. J . Org. Chem. 1985, 50, 2394-2395.

358 J . Org. Chem., Vol. 62, No. 2, 1997
J ou et al.
Sch em e 3a
Sch em e 5a
a
Reagents and conditions: (i) pyruvic acid, DCC, HOBt, DIEA,
36%; (ii) H2, Pd-C, 72%.
the presence of HOBt (12), giving Boc-didemnin A (1b).
Treatment of this with 5.7 M HCl-dioxane then gave
material identical both with a natural sample of didem-
nin A (1c) and with that obtained in the previously
described synthesis.
Syn th esis of Deh yd r od id em n in B
Preparation of dehydrodidemnin B requires the cou-
pling of the (S)-Pro-Pyr side chain 40 to the amino group
of the (R)-N(Me)-Leu residue of didemnin A. Side chain
40 was synthesized as shown in Scheme 5.
Amide bond formation between H-Pro-OBzl and pyru-
vic acid was brought about using DCC in the presence of
HOBt (12), giving ester 39, which was subsequently
submitted to catalytic hydrogenolysis, producing 40.
Coupling of didemnin A (1c) with 40 using PyBrOP (7)
afforded dehydrodidemnnin B (1e) in a yield of 62%. The
synthetic material obtained had physical properties
identical with those of an authentic sample.
a
Reagents and conditions: (i) TBDMS-Hip-OH (ii) HBTU,
HOBt, DIEA, 83%; (iii) TBAF, 97%; (iv) Boc-Ist(TBDMS)-OH,
DCC, DMAP, -20 °C, 84%; (v) 5.7 M HCl-dioxane, 99%.
Sch em e 4a
Discu ssion
Several interesting observations emerge from the
results obtained in these syntheses. With regard to the
formation of the different types of linkages between the
subunits of the didemnins, it appears that different types
of reagents are better suited to the formation of different
types of linkages. Of those examined, the most useful
for the formation of esters were the carbodiimides
DIPCDI and DCC, usually in the presence of DMAP.
Occasionally, in the most demanding esterifications, such
as the union of 21 and 29, the use of DMAP‚CF3COOH
in addition to DMAP and the carbodiimide was re-
quired.34 Even here, however, ester formation could be
brought about under mild conditions and in good yield.
Other reagents such as isopropenyl chloroformate35 or
BOP-Cl36,37 were much less effective in these situations,
as were the phosphonium and uronium reagents tested.
The formation of secondary amides (standard peptide
bonds) could be carried out equally efficiently using either
carbodiimides, such as DCC or DIPCDI, or phosphonium
or uronium reagents, such as BOP (6) or HBTU (9),
respectively. However, for the formation of tertiary
amides, phosphonium and uronium reagents such as
PyBrOP (7), HBTU (9), and HATU (10) consistently gave
higher yields than other reagents, including carbodiim-
ides, isopropenyl chloroformate, and even BOP-Cl, whose
use has been recommended for the formation of this type
of amide.38 When the uronium reagents HBTU (9) or
a
Reagents and conditions: (i) SEM-Cl, Li2CO3, 78%; (ii) H2, Pd-
C, 97%; (iii) DCC, DMAP, 88%; (iv) 6% aqueous HF-MeCN, 72%.
by â-elimination, and was consequently carried out
acidolytically by treatment with HF at -20 °C, furnishing
38. Careful control of the reaction conditions was neces-
sary here in order avoid concomitant removal of the Boc
group.14
The formation of precursor 5a by amide bond formation
between 34 and 38 was complicated by the formation of
the γ-lactam 2, derived from cyclization of Ist, but was
achieved in 82% yield using HBTU (9) in the presence of
HOBt (12), using DIEA as base. Catalytic hydrogenolysis
of 5a to 5b occurred quantitatively and was followed by
macrocyclization, using HATU (10) in the presence of
HOAt (11), which gave macrocycle 3a in 76% yield after
chromatography. Nuclear magnetic resonance studies
and HPLC data of the product again indicated the
presence of only one stereoisomer.
(35) J aouadi, M.; Selve, C.; Dormoy, J . R.; Castro, B. Bull. Soc. Chim.
1984, II 409-412.
(36) Cabre´-Castellv´ı, J .; Palomo-Coll, A. L. Tetrahedron Lett. 1980,
21, 4179-4182.
(37) Diago-Meseguer, J .; Palomo-Coll, A. L.; Fernandez-Lizarbe, J .
R.; Zugaza-Bilbao, A. Synthesis 1980, 547-551.
(38) van der Auwera, C.; Anteunis, M. J . O. Int. J . Peptide Protein
Res. 1987, 29, 574-588.
After removal of the Boc group, by treatment with a
5.7 M HCl-dioxane solution, macrocycle 3b was coupled
in 92% yield to Boc-(R)-N(Me)-Leu-OH using BOP (6) in

Total Synthesis of Dehydrodidemnin B
J . Org. Chem., Vol. 62, No. 2, 1997 359
HATU (10) are used to form tertiary amides they can be
added directly to the mixture of amino and carboxyl
components, functioning as true coupling reagents, with-
out the need for separate preactivation steps. The
formation of Schiff base analogues39,40 does not occur
when secondary amines are involved.
are consistent with the existence of slow cis-trans
rotational isomerism about one of the amide bonds of the
molecule. Such rotational isomerism is not commonly
observed in chromatography, although the phenomenon
is not without precedent,42 particularly for tertiary amide-
containing peptides.43-45
The yield for the macrolactamization step using HATU
(10) in the presence of HOAt (11) is, in the case of linear
precursor 5a , very high indeed (76%), and although the
corresponding yield for 4a is much lower, scarcity of
material did not permit this key step to be optimized.
Slightly lower, but still excellent, yield (70%) for the
cyclization of 5a was obtained using PyAOP (8) in the
presence of HOAt (11), whereas the use of PyBrOP (7)
gave significantly poorer results (maximum yield of
cyclized product, 37%). Rapid (less than 12 h) cyclization
of 5a using the acid-fluoride-forming41 reagent TTFH (13)
was also observed, but mass spectrometry of the product
formed indicated that fluorination of the macrocycle had
occurred. The use of this reagent was not investigated
further.
Rotational isomerism is, however, common enough on
the time scale of NMR experiments and is often observed
in spectroscopic studies on peptides and proteins.46 High-
field NMR spectroscopy of dehydrodidemnin B (1e)
indicates the presence of two predominant conformations
in CDCl3, in a ratio of approximately 55:45, consistent
with the HPLC data for 1e. Additionally, two other
minor conformations are detected in DMSO-d6. Similar
conformational equilibria have been observed in NMR
spectroscopic studies on other didemnins.47,48 The pos-
sibility that such behavior plays a part in the pronounced
biological activity of dehydrodidemnin B cannot be
discounted.
Con clu sion s
In the syntheses of didemnin A (1c) described here,
linear precursors 4c and 5b, both of which were mixtures
of diastereomers at C-2 of the HIP unit, were cyclized to
give optically pure macrocycles in which this stereogenic
carbon atom had the correct (S) configuration. This may
indicate that, in both these cases, the diastereomer of
the linear precursor having the (S) configuration at C-2
of the HIP unit undergoes macrocyclization more rapidly
than that having the (R) configuration. The (R) diaste-
reomer of the linear precursor remaining after cyclization
of the (S) diastereomer could then, under the basic
conditions of the macrocyclization reaction, undergo
epimerization, generating more (S) diastereomer that
would then cyclize. The overall effect is to convert a
diastereomeric mixture of linear precursors into a single
stereoisomer of the macrocycle with the natural (S)
configuration at C-2 of the HIP unit. An alternative
possibility is that both diastereomers of the macrocycle
are formed initially but that epimerization occurs to
provide the more thermodynamically stable stereoisomer
under the conditions of the cyclization reaction. How-
ever, no evidence for the production of diastereomeric
macrocycles was obtained at any time in this work.
J oullie´ has suggested that epimerization at C-2 of the
HIP unit in the macrocycle is not possible because of
conformational constraints.14
Both synthetic and natural dehydrodidemnin B (1e)
show two peaks in their analytical HPLC profiles, in an
approximate proportion of 55:45. Mass spectrometric
analysis of the two fractions obtained by collecting the
HPLC effluent indicates a molecular ion corresponding
to that of dehydrodidemnin B in both cases. Reinjection
of each of the isolated fractions gave identical chromato-
grams, each showing the same two peaks observed in the
initial natural or synthetic sample. Peak coalescence is
observed on heating the HPLC column to 50 °C, but
subsequent reinjection at room tempereature of the
collected analytical HPLC effluent again gives chromato-
grams showing the same two components. These data
The total synthesis of dehydrodidemnin B, the most
active didemnin discovered to date, has been carried out
by coupling the Pyr-Pro-OH unit 40 to didemnin A (1c),
itself synthesized by two novel routes. One of these,
based on linear precursor 5a , is clearly superior, taking
place in an overall yield of 27% based on H-(S)-Pro-OBzl.
The other strategy, based on linear precursor 4a , has an
overall yield of 4% based on HIP unit 17. The more
efficient synthesis could, in principle, be used to provide
sufficient quantities of dehydrodidemnin B for clinical
trials.
Extensive use has been made of several of the newer
phosphonium and uronium salt coupling reagents, more
usually applied in solid phase peptide synthesis. The
results obtained highlight the power and versatility of
these in peptide synthesis in solution.
Exp er im en ta l Section
Gen er a l P r oced u r es. All reagents were obtained com-
mercially and were purified where appropriate. Tetrahydro-
furan was distilled from sodium/benzophenone. Dichlo-
romethane and chloroform were distilled from calcium hydride
and filtered through an alumina column prior to use. Chro-
matographic purification of products was carried out by “flash”
chromatography49 using Merck silica gel 60 (230-400 mesh).
Thin layer chromatography was carried out on Merck silica
gel 60F plates, and visualization of the developed chromato-
gram was effected by ultraviolet absorption, iodine, or phos-
phomolybdic reagent (7% w/v) in absolute ethanol. Organic
solutions were concentrated by rotatory evaporation at ∼25
mmHg (water aspirator) and were dried over sodium sulfate.
Chemical shifts are quoted in δ values downfield from
tetramethylsilane, and J values are given in Hz. Fast atom
bombardment (FAB) and electrospray (ES) mass spectrometry
were performed on a VG Quattro apparatus. All melting
(42) Keller, R. A.; Giddings, J . C. J . Chromatogr. 1960, 3, 205-220.
(43) Melander, W. R.; J acobsen, J .; Horva´th, C. J . Chromatogr. 1982,
234, 269-276.
(44) Rusconi, L.; Perseo, G.; Franzoi, L.; Montecucchi, P. C. J .
Chromatogr. 1985, 349, 117-130.
(45) Gesquiere, J . C.; Diesis, E.; Cung, M. T.; Tartar, A. J . Chro-
matogr. 1989, 478, 121-129.
(39) Gausepohl, H.; Pieles, U.; Frank, R. W. In Peptides. Chemistry
and Biology. Proceedings of the 12th American Peptides Symposium;
J . A. Smith and J . E. Rivier, Eds.; ESCOM, Leiden: 1992; pp 523-
524.
(40) Story, S. C.; Aldrich, J . V. Int. J . Peptide Protein Res. 1994, 43,
292-296.
(41) Carpino, L. A.; El-Faham, A. J . Am. Chem. Soc. 1995, 117,
5401-5402.
(46) Kessler, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 512-523.
(47) Kessler, H.; Will, M.; Antel, J .; Beck, H.; Sheldrick, G. M. Helv.
Chim. Acta 1989, 72, 530-555.
(48) Kessler, H.; Mronga, S.; Will, M.; Schmidt, U. Helv. Chim. Acta
1990, 73, 25-47.
(49) Still, W. C.; Kahn, M.; Mitra, A. J . Org. Chem. 1978, 43, 2923-
2925.

360 J . Org. Chem., Vol. 62, No. 2, 1997
J ou et al.
points are uncorrected. Reversed-phase HPLC was performed
using a Shimadzu apparatus. Detection was by ultraviolet
absorption at 220 nm, and Nucleosil C18 (25 × 0.4 cm, 10 µm,
120 Å) or Nucleosil C4 (25 × 0.4 cm, 10 µm, 120 Å) columns
were used as indicated.
30.60, 41.52, 41.66, 46.69, 46.75, 49.03, 49.10, 49.23, 49.60,
58.58, 58.63, 72.84, 73.25, 74.00, 89.18, 89.66, 127.67, 127.73,
127.91, 128.35, 128.42, 137.62, 137.46, 168.94, 170.23, 171.00,
208.82, 209.97; m/ z (FAB) 611.1 [(M′′′ + H)+, 5], 608.8 [(M′′
+ H)+, 30], 607.2 [(M′ + H)+, 100], 605.3 [(M + H)+, 100].
H-Hip -Leu -P r o-OTce (21). Ester 20 (110 mg, 0.30 mmol)
in dry THF (4 mL) was hydrogenolyzed in the presence of 10%
Pd-C (110 mg) for 60 min at rt and atmospheric pressure.
Filtration through Celite and solvent removal gave an oil that
was purified by chromatography (silica gel, AcOEt-hexanes,
1:1), giving the two diastereomers of 21 (approximate propor-
tions, 1:1) as a white solid (80 mg, 78%): mp 100-103 °C; RP-
HPLC tR 16.82 and 17.70 min, Nucleosil C18 column, linear
gradient from 10% B in A to 100% B over 20 min, followed by
isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN/0.036% TFA, at a flow rate of 1
mL min-1; IR (film) ν 3313, 2962, 2921, 2871, 1763, 1719, 1636,
1540, 1449, 1369, 1153, 1097, 1022 cm-1; 1H NMR (300 MHz,
CDCl3) δ 0.73 (3H, d, J ) 6.6), 0.82 (3H, d, J ) 6.9), 0.94 (6H,
d, J ) 6.6), 0.95 (6H, d, J ) 6.6), 0.96 (6H, d, J ) 6.6), 0.99
(6H, d, J ) 6.3), 1.01 (3H, d, J ) 6.9), 1.09 (3H, d, J ) 6.9),
1.31 (3H, d, J ) 6.9), 1.38 (3H, d, J ) 7.2), 1.54-1.78 (3H, m),
2.04-2.16 (5H, m), 3.58-3.68 (3H, m), 3.72-3.84 (3H, m), 3.66
(1H, q, J ) 6.9), 3.91 (1H, q, J ) 7.2), 3.96-4.00 (1H, m), 4.22-
4.26 (1H, m), 4.60-4.82 (2H, m), 4.67 (1H, d, J ) 12.1), 4.68
(1H, d, J ) 12.1), 4.86 (1H, d, J ) 12.1), 4.87 (1H, d, J ) 12.1),
6.63-6.68 (2H, m); 13C NMR (75 MHz, CDCl3) δ 13.54, 13.71,
15.21, 16.00, 19.45, 19.91, 21.43, 21.68, 23.36, 23.41, 24.78,
24.89, 28.87, 28.94, 30.97, 31.44, 40.62, 41.80, 46.78, 46.80,
49.30, 50.18, 50.31, 50.45, 58.70, 58.79, 74.04, 80.44, 81.29,
94.71, 168.80, 170.08, 170.12, 171.04, 172.11, 209.18, 210.01;
m/ z (FAB) 521.6 [(M′′′ + H)+, 15], 519.1 [(M′′ + H)+, 25], 517.1
[(M′ + H)+, 80], 515.2 [(M + H)+, 85] 497.2 (100); m/ z
(FABHRMS) 515.145 730, C21H33Cl3N2O6 requires (M + H)+
515.148 245.
Boc-P r o-OTce. DCC (1.51 g, 5.58 mmol) in CH2Cl2 (5 mL)
was added over 5 min to a solution of Boc-Pro-OH (1.01 g, 4.65
mmol), DMAP (110 mg, 0.93 mmol) and 2,2,2-trichloroethanol
(0.53 mL, 5.58 mmol) in CH2Cl2 (5 mL) at 0 °C. After being
stirred for 7 h at 0 °C, the mixture was filtered, the solvent
removed, and the residue taken up in AcOEt (70 mL). This
solution was washed with 10% citric acid (2 × 15 mL), 5%
aqueous NaHCO3 solution (2 × 15 mL), and saturated aqueous
NaCl solution (2 × 15 mL). Drying and filtration, followed by
solvent removal, gave an oil (1.87 g) that was purified by
chromatography (silica gel, AcOEt-hexanes, 1:6), giving Boc-
Pro-OTce as white prisms (1.61 g, 99%): mp 50-52 °C; [R]D
-45.0 (c 1.4, CHCl3); IR (film) ν 3000-2800, 1770, 1700, 1390,
1370, 1265, 1150, 1090 cm-1 1H NMR (200 MHz, CDCl3) δ
;
1.42 (9H, s), 1.47 (9H, s), 1.90-2.40 (4H, m), 3.35-3.66 (2H,
m), 4.34-4.50 (1H, m), 4.65 (2H, d, J ) 12.9), 4.76 (2H, s),
4.94 (2H, d, J ) 12.9); 13C NMR (50 MHz, CDCl3) 23.97, 24.74,
28.88, 30.35, 31.34, 46.78, 47.00, 59.23, 59.43, 74.58, 80.03,
80.07, 154.00, 172.00; m/ z (FAB) 371.9 [(M′′ + Na)+, 5], 369.9
[(M′ + Na)+, 19], 367.9 [(M + Na)+, 20], 349.9 [(M′′ + H)+, 7],
348.0 [(M′ + H)+, 20], 346.0 [(M′ + H)+, 22], 289.9 (100); m/ z
(FABHRMS) 346.039 351, C12H18Cl3NO4 requires (M + H)+,
346.037 967. Anal. Calcd for C12H18Cl3NO4: C, 41.74; H, 5.22;
N, 4.06%. Found: C, 41.73; H, 5.31, N, 3.81.
Bzl-Hip -Leu -OH (19). Zinc dust (90 mg, 13.70 mmol) was
added, portionwise, to a solution of ester 18 (150 mg, 0.29
mmol) in THF (2 mL), followed by 1 M aqueous NH4OAc
solution (0.40 mL), and the mixture was stirred vigorously
under Ar for 24 h. After filtration and solvent removal the
residue was taken up in AcOEt (50 mL), and this solution was
washed with 5% aqueous KHSO4 (5 mL) and with saturated
aqueous NaCl solution (5 mL). Drying and filtration followed
by solvent removal gave the two diastereomers of 19 (90 mg,
85%) as a clear oil: IR (film) ν 3314, 2962, 2950, 2875, 1719,
Boc-Th r (Bzl)-Ist-OMe (22). A 40% solution of TFA in
CH2Cl2 (10 mL) was added to 14 (970 mg, 3.36 mmol) in
CH2Cl2 (5 mL), and after 20 min, the solvent was removed
and chased with Et2O. The solid obtained was dissolved in
dry MeCN (8 mL) and was added to a solution of Boc-Thr-
(Bzl)-OH (1.56 g, 5.04 mmol), HOBt (770 mg, 5.04 mmol), and
HBTU (1.91 g, 5.04 mmol) in dry MeCN (8 mL). DIEA (1.43
mL, 8.39 mmol) was added over 40 min, and the mixture was
stirred for 24 h at rt. The solvent was removed and the residue
taken up in AcOEt (125 mL), and this solution was washed
with 5% aqueous KHSO4 (3 × 15 mL), 5% aqueous NaHCO3
(3 × 15 mL), and saturated aqueous NaCl solution (3 × 15
mL). Drying and filtration followed by solvent removal gave
an oil (3.41 g) that was purified by chromatography (silica gel,
AcOEt-hexanes, 1:2), giving 22 as a colorless semisolid (1.10
g, 69%): [R]D -5.3 (c 0.7, CHCl3); IR (film), 3500-3100, 3000-
2800, 1720, 1700, 1630, 1610, 1530, 1490, 1450, 1430, 1380,
1654, 1540, 1457, 1389, 1369, 1208, 1071, 1028 cm-1 1 H NMR
;
(200 MHz, CDCl3) δ 0.85-0.98 (12H, m), 1.20-1.40 (1H, m),
1.36 (3H, d, J ) 7.2), 1.40-1.80 (2H, m), 2.00-2.20, (1H, m),
3.70 (1H, d, J ) 6.0), 3.90 (1H, q, J ) 7.1), 3.92 (1H, q, J )
7.1), 4.38 (1H, d, J ) 11.0), 4.41 (1H, d, J ) 11.6), 4.40-4.58
(1H, m), 4.59 (1H, d, J ) 11.4), 4.63 (1H, d, J ) 11.6), 6.71
(1H, d, J ) 7.2), 6.75 (1H, d, J ) 8.5), 7.25-7.45 (m, 5H); 13C
NMR (75 MHz, CDCl3) δ 15.88, 16.11, 17.56, 17.66, 18.94,
21.47, 21.58, 22.79, 24.80, 24.86, 30.36, 30.44, 40.46, 40.61,
48.89, 49.39, 50.89, 50.97, 72.88, 73.37, 89.13, 89.86, 127.64,
127.74, 127.93, 127.96, 128.20, 128.28, 128.46, 137.26, 169.51,
176.95, 210.35, 210.85; m/ z (FAB) 400.2 [(M + Na)+, 10], 378.2
[(M + H)+, 100]; m/ z (FABHRMS) 378.229 519. C21H31NO5
requires: (M + H)+, 378.228 048.
Bzl-Hip -Leu -P r o-OTce (20). TFA (0.89 mL) was added
to Boc-Pro-OTce (140 mg, 0.41 mmol) in CH2Cl2 (2 mL), and
after 20 min, the solvent was removed and chased with Et2O.
The solid obtained was dissolved in dry MeCN (1 mL) at 0 °C
and added to a solution of 19 (72 mg, 0.19 mmol) in MeCN (1
mL). HOBt (29 mg, 0.19 mmol), HBTU (73 mg, 0.19 mmol),
and DIEA (0.10 mL, 0.60 mmol) were then added successively
to the mixture, and after 3 h stirring at rt, the solvent was
removed and the residue taken up in AcOEt (50 mL). This
solution was washed with 5% aqueous KHSO4 (2 × 5 mL), with
5% aqueous NaHCO3 (2 × 5 mL), and with saturated aqueous
NaCl solution (2 × 5 mL). Drying and filtration followed by
solvent removal gave an oil (160 mg) that was purified by
chromatography (silica gel, AcOEt-hexanes, 2:3), giving the
two diastereomers of 20 (88 mg, 76%) as a clear colorless oil:
IR (film) ν 3303, 2960, 2950, 2873, 1765, 1725, 1634, 1530,
1453, 1368, 1269, 1153, 1095, 1070 cm-1; 1H NMR (200 MHz,
CDCl3) δ 0.85-0.98 (12H, m), 1.32 (3H, d, J ) 7.1), 1.34 (3H,
d, J ) 6.9), 1.40-1.70 (3H, m), 1.95-2.40 (5H, m), 3.50-3.95
(4H, m), 4.33-4.42 (1H, m), 4.51-4.75 (1H, m), 4.36-4.90 (4H,
m), 6.63 (1H, d, J ) 8.4), 6.75 (1H, d, J ) 9.0), 7.27-7.36 (5H,
m); 13C NMR (75 MHz, CDCl3) δ 14.97, 15.50, 17.61, 17.73,
18.93, 19.09, 21.63, 21.69, 23.34, 24.61, 24.86, 28.93, 30.49,
1
1365, 1170 cm-1; H NMR (200 MHz, CDCl3) δ 0.71 (3H, d, J
) 6.7), 0.88 (3H, t, J ) 7.2), 1.20 (3H, d, J ) 6.8), 1.15-1.35
(2H, m), 1.46 (9H, s), 1.83-2.00 (1H, qd, J 1 ) 6.7, J 2 ) 2.6);
2.35-2.55 (2H, m), 3.67 (3H, s), 3.85 (1H, td, J 1 ) 7.8, J 2
)
3.9), 3.99 (1H, td, J 1 ) 8.8, J 2 ) 3.1), 4.50-4.63 (1H, m), 4.52
(1H, d, J ) 11.1), 4.62 (1H, d, J ) 11.1), 5.50 (1H, m), 6.43 (d,
J ) 9.4), 7.32 (5H, m); 13C NMR (75 MHz, CDCl3) δ 11.64,
13.04, 15.32, 27.02, 28.24, 33.66, 38.26, 51.72, 51.72, 55.31,
57.80, 68.70, 71.50, 74.52, 80.07, 127.47, 127.63, 127.87,
127.96, 128.20, 128.30, 128.39, 137.61, 155.51, 170.16, 173.57;
m/ z (FAB) 481.4 [(M + H)+, 51], 381.4 (100).
Boc-(R)-N(Me)-Leu -Th r (Bzl)-Ist-OMe (23). A 5 M solu-
tion of HCl in dioxane (12 mL) was added to 22 (880 mg, 1.83
mmol) in dioxane (3 mL), and after 50 min, the solvent was
removed and chased with Et2O. The solid obtained was
dissolved in DMF (4 mL) and added to a solution of Boc-(R)-
N(Me)-Leu-OH (670 mg, 2.75 mmol) in DMF (8 mL) at 0 °C.
HOBt (460 mg, 3.03 mmol), BOP (1.34 g, 3.03 mmol), and
DIEA (1.29 mL, 7.62 mmol) were added successively, and this
mixture was stirred for 24 h at rt. The solvent was removed
and the residue taken up in AcOEt (150 mL). This solution
was washed with 5% aqueous KHSO4 (3 × 20 mL), 5% aqueous
NaHCO3 (3 × 20 mL), and saturated aqueous NaCl solution
(3 × 20 mL). Drying and filtration followed by solvent removal

Total Synthesis of Dehydrodidemnin B
J . Org. Chem., Vol. 62, No. 2, 1997 361
gave an oil (1.50 g) that was purified by chromatography (silica
gel, AcOEt-hexanes, 1:1), giving 23 as a white solid (910 mg,
81%): mp 94-96 °C; RP-HPLC tR 19.67 min, Nucleosil C18
column, linear gradient from 10% B in A to 100% B over 20
min, followed by isocratic elution with 100% B for 10 min,
where A is H2O/0.045% TFA and B is MeCN/0.036% TFA, at
a flow rate of 1 mL min-1; [R]D +22.8 (c 1.2, CHCl3); IR (film)
ν 3441, 3338, 2960, 2950, 2900, 2900, 1671, 1497, 1456, 1387,
gradient from 10% B in A to 100% B over 20 min, followed by
isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN/0.036% TFA, at a flow rate of 1
mL min-1; [R]D +31.7 (c 0.9, CHCl3), IR (film) ν 3332, 2960,
2933, 2900, 1867, 1684, 1507, 1457, 1472, 1389, 1368, 1322,
1254, 1154, 1096 cm-1; 1H NMR (300 MHz, CDCl3) δ 0.03 (3H,
s), 0.07 (3H, s), 0.65 (3H, d, J ) 6.9), 0.87 (9H, s), 0.88 (3H, t,
J ) 7.5), 0.92 (3H, d, J ) 6.9), 0.94 (3H, d, J ) 6.9), 1.12 (3H,
d, J ) 6.6), 1.10-1.25 (2H, m), 1.45 (9H, s), 1.40-1.50 (1H,
m), 1.66-1.71 (2H, m), 1.77-1.84 (1H, m), 2.35-2.55 (2H, m),
2.82 (3H, bs), 4.01-4.11 (2H, m), 4.50-4.62 (4H, m), 4.70-
4.75 (1H, m), 6.33 (1H, d, J ) 9.6), 6.99 (1H, d, J ) 7.8), 7.28-
7.32 (5H, m); 13C NMR (75 MHz, CDCl3) δ -4.29, -4.91, 11.88,
13.01, 15.74, 17.86, 21.48, 23.26, 24.94, 25.70, 27.35, 28.28,
29.68, 30.76, 33.84, 36.75, 37.08, 40.59, 56.31, 56.92, 69.19,
71.68, 73.81, 80.86, 127.58, 127.83, 128.08, 128.39, 137.76,
156.98, 169.23, 169.82, 171.92, 172.45, 173.32, 173.86; m/ z
(FAB) 708.4 [(M + H)+, 21], 608.4 (100).
1368, 1322, 1254, 1158 cm-1 1H NMR (300 MHz, CDCl3) δ
;
0.62-0.72 (3H, m), 0.82-0.85 (3H, t, J ) 7.2), 0.90 (3H, d, J
) 6.6), 0.93 (3H, d, J ) 6.6), 1.12 (3H, d, J ) 5.4), 1.07-1.30
(2H, m), 1.39-1.54 (1H, m), 1.39 (9H, s), 1.64-1.74 (1H, m),
1.84 (1H, qd, J 1 ) 6.9, J 2 ) 3.6), 2.30-2.45 (2H, m), 2.80 (3H,
bs), 3.30 (1H, bs), 3.63 (3H, s), 3.75-3.85 (1H, m), 3.96 (1H,
td, J 1 ) 9.2, J 2 ) 2.7), 4.12-4.20 (1H, m), 4.40-4.45 (1H, m),
4.47-4.65 (3H, m), 6.36 (1H, d, J ) 10.8), 6.47 (1H, d, J )
9.2), 6.93 (1H, bs) , 7.00 (1H, d, J ) 6.8), 7.26-7.37 (m, 5H);
13C NMR (75 MHz, CDCl3) δ 11.68, 13.23, 14.97, 15.50, 21.32,
21.63, 23.22, 24.60, 24.94, 27.03, 28.21, 29.50, 31.72, 33.76,
36.77, 38.03, 51.74, 55.47, 56.06, 56.61, 57.51, 57.85, 68.75,
71.63, 72.03, 73.98, 80.62, 81.00, 127.90, 128.00, 128.44,
168.00, 169.78, 171.82, 171.5, 173.57; m/ z (FAB) 630.6 [(M +
Na)+, 9], 608.6 [(M + H)+, 50], 508.6 (100); m/ z (FABHRMS)
608.391 288, C32H53N3O8 requires (M + H)+ 608.391091. Anal.
Calcd for C32H53N3O8: C, 63.26; H, 8.73; N, 6.91. Found: C,
63.02; H, 8.77; N, 6.63.
Boc-(R)-N(Me)-Leu -Th r (Bzl)-Ist (TBDMS)-OTce (26).
DCC (70 mg, 0.34 mmol) was added over 5 min to a solution
of 25 (200 mg, 0.28 mmol), 2,2,2-trichloroethanol (32 µL, 0.34
mmol), and DMAP (7 mg, 0.056 mmol) in CH2Cl2 (2 mL) at 0
°C. The mixture was allowed to attain rt and, after being
stirred for 24 h, was filtered. The solvent was removed and
the residue taken up in AcOEt (100 mL) and washed with 10%
citric acid solution (2 × 20 mL), 5% aqueous NaHCO3 solution
(2 × 20 mL), and saturated aqueous NaCl solution (2 × 20
mL). Drying and filtration followed by solvent removal gave
an oil that was purified by chromatography (silica gel, AcOEt-
hexanes, 1:6), giving 26 as a clear, viscous oil (189 mg, 80%):
RP-HPLC tR 27.42 min, C4 Nucleosil column, linear gradient
from 10% B in A to 100% B over 20 min, followed by isocratic
elution with 100% B for 10 min, where A is H2O/0.045% TFA
Boc-(R)-N(Me)-Leu -Th r (Bzl)-Ist-OH (24). A 1.1 M NaOH
solution (1.76 mL, 1.93 mmol) was added dropwise to 23 (470
mg, 0.77 mmol) in MeOH (3.4 mL) at 0 °C, and after 4 h the
mixture was allowed to attain rt over 60 min and was diluted
with H2O (50 mL). The solution was extracted with AcOEt (2
× 20 mL), and the combined organic phases were extracted
with saturated aqueous NaHCO3 (2 × 15 mL). The combined
aqueous phases were taken to pH 3 by addition of 2 M aqueous
KHSO4 and extracted with AcOEt (4 × 50 mL). The combined
organic phases were washed with saturated aqueous NaCl
solution (2 × 10 mL), dried, and filtered. Solvent removal gave
24 as an oil (440 mg, 96%): RP-HPLC tR 18.41 min, Nucleosil
C18 column, linear gradient from 10% B in A to 100% B over
20 min, followed by isocratic elution with 100% B for 10 min,
where A is H2O/0.045% TFA and B is MeCN/0.036% TFA, at
a flow rate of 1 mL min-1; [R]D +26.0 (c 0.7, CHCl3); IR (film)
and B is MeCN/0.036% TFA, at a flow rate of 1 mL min-1
;
[R]D+ 21.5 (c 1.3, CHCl3); IR (film) ν 3855, 3345, 2959, 2859,
1753, 1694, 1597, 1472, 1387, 1368, 1321, 1258, 1225, 1157
1
cm-1; H NMR (200 MHz, CDCl3) δ 0.03 (6H, s), 0.64 (3H, d,
J ) 6.6), 0.83 (9H, s), 0.84 (3H, t, J ) 7.5), 0.93 (3H, d, J )
6.3), 0.95 (3H, d, J ) 6.2), 1.11 (3H, d, J ) 6.4), 1.10-1.36
(2H, m), 1.38-1.54 (1H, m), 1.64-1.82 (3H, m), 1.47 (9H, s),
2.51 (1H, dd, J 1 ) 16.3, J 2 ) 5.2), 2.64 (1H, dd, J 1 ) 16.4, J 2
) 5.1), 2.79 (3H, bs), 4.00-4.20 (3H, m), 4.47 (1H, dd, J 1
)
ν 3492, 2959, 2866, 1734, 1635, 1456, 1425, 1200, 1170 cm-1
;
6.1, J 2 ) 3.7), 4.58-4.76 (5H, m), 6.37 (1H, bd, J ) 9.1), 7.09
(1H, m), 7.34 (5H, m); 13C NMR (50 MHz, CDCl3) δ -4.85,
-4.52, 11.78, 13.40, 14.54, 14.73, 21.56, 24.61, 24.70, 24.87,
25.69, 27.40, 28.29, 33.76, 36.59, 37.00, 40.03, 55.78, 55.87,
56.20, 69.56, 71.70, 73.79, 73.99, 80.05, 128.00, 128.12, 128.49,
156.00, 168.92, 170.08, 171.57, 171.64, 171.83; m/ z (FAB)
840.5 [(M′ + H)+, 32], 838.5 [(M + H)+, 30], 740.4 (100); m/ z
(FABHRMS) 838.377 458, C39H66Cl3N3O8Si requires (M + H)+
838.376 098.
1H NMR (200 MHz, CDCl3) δ 0.69 (3H, d, J ) 6.9), 0.81-0.88
(3H, t, J ) 7.0), 0.91 (3H, d, J ) 6.1), 0.94 (3H, d, J ) 6.2),
1.14 (3H, d, J ) 6.2), 1.10-1.60 (3H, m), 1.41 (9H, s), 1.65-
1.75 (2H, m), 1.80-1.97 (1H, m), 2.25-2.50 (2H, m), 2.78 (3H,
s), 2.84 (3H, s), 3.75-3.88 (1H, m), 3.92-4.04 (1H, m), 4.10-
4.18 (1H, m), 4.50-4.70 (4H, m), 6.50-6.70 (2H, m), 7.27-
7.31 (5H, m); 13C NMR (50 MHz, CDCl3) δ 12.15, 13.74, 16.04,
16.34, 21.81, 22.16, 23.68, 25.13, 25.45, 27.56, 28.74, 30.19,
32.00, 34.29, 37.25, 37.61, 38.83, 56.35, 57.28, 57.97, 68.98,
72.31, 74.61, 81.34, 128.62, 129.00, 170.00, 172.50, 176.01; m/ z
(FAB) 616.4 [(M + Na)+, 27], 594.4 [(M + H)+, 30], 494.4 (100);
m/ z (FABHRMS) 616.352 980, C31H51N3O8 requires (M + Na)+
616.357 380.
Boc-(R)-N(Me)-Leu -Th r -Ist(TBDMS)-OTce (27). Com-
pound 26 (180 mg, 0.22 mmol) in dry THF (1.5 mL) was
hydrogenolyzed for 90 min in the presence of 10% Pd-C (72
mg) at rt and atmospheric pressure. The mixture was filtered,
and solvent removal gave 27 as an oil (150 mg, 90%): RP-
HPLC tR 24.35 min, C4 Nucleosil column, linear gradient from
10% B in A to 100% B over 20 min, followed by isocratic elution
with 100% B for 10 min, where A is H2O/0.045% TFA and B
is MeCN/0.036% TFA, at a flow rate of 1 mL min-1; [R]D +11.7
(c 1.0, CH2Cl2); IR (film) ν 3360, 2960, 2920, 2860, 1750, 1700,
1680, 1660, 1525, 1510, 1500, 1460, 1385, 1365, 1320, 1250,
Boc-(R)-N(Me)-Leu -Th r (Bzl)-Ist(TBDMS)-OH (25).
A
suspension of 24 (110 mg, 0.19 mmol), TBDMS-Cl (170 mg,
1.16 mmol), and imidazole (210 mg, 3.09 mmol) in DMF (0.10
mL) was stirred for 36 h under nitrogen. The resulting
solution was diluted with AcOEt (50 mL) and washed with
cold 1 M KHSO4 solution (2 × 5 mL) and saturated aqueous
NaCl solution (2 × 5 mL). After drying, filtration, and solvent
removal, the residue was taken up in dioxane (2 mL). This
solution was taken to pH 9.5 by addition of aqueous 1 M NaOH
and after 0.5 min the pH was adjusted to 7.0 by addition of 1
M KHSO4 solution. The solvent was removed and the residue
taken up in H2O (20 mL) and extracted with AcOEt (2 × 10
mL). The aqueous phase was taken to pH 3 by addition of 2
M KHSO4 solution and extracted with AcOEt (3 × 20 mL).
The combined organic phases were washed with saturated
aqueous NaCl solution (1 × 10 mL), dried, and filtered.
Solvent removal gave an oil (170 mg) that was purified by
chromatography (silica gel, 1% MeOH in CH2Cl2 f 5% MeOH
in CH2Cl2, gradient elution), giving 25 as an oil (100 mg,
72%): RP-HPLC tR 24.30 min, Nucleosil C18 column, linear
1
1150, 1095 cm-1; H NMR (200 MHz, CDCl3) δ 0.06 (3H, s),
0.09 (3H, s), 0.86 (9H, s), 0.89-0.98 (12H, m), 1.14 (3H, d, J )
6.3), 1.20-1.50 (2H, m), 1.60-1.90 (4H, m), 2.55 (1H, dd, J 1
)
16.0, J 2 ) 5.5), 2.68 (1H, dd, J 1 ) 12.1, J 2 ) 4.1), 2.79 (3H,
bs), 3.25 (1H, bs), 4.04-4.25 (3H, m), 4.34-4.46 (1H, m), 4.64-
4.70 (1H, m), 4.69 (1H, d, J ) 12.1), 4.79 (1H, d, J ) 12.0),
4.65 (1H, m), 7.00 (1H, m); 13C NMR (50 MHz, CDCl3) δ -4.81,
-4.47, 11.62, 13.90, 18.31, 18.38, 23.25, 24.87, 24.93, 25.72,
27.16, 28.32, 29.60, 30.60, 34.37, 36.72, 39.68, 56.38, 57.32,
57.48, 66.37, 69.24, 74.27, 170.80, 170.99, 172, 90, 173.08; m/ z
(FAB) 751.9 [(M′′ + H)+, 12], 750.4 [(M′ + H)+, 22], 748.6 [(M′
+ H)+, 19] 650.5 (100); m/ z (FABHRMS) 748.329 538, C32H60
Cl3N3O8Si requires (M + H)+ 748.329 353.
-
Boc-(R)-N(Me)-Leu -Th r [Z-N(Me)-O(Me)-Tyr ]-Ist (TB-

362 J . Org. Chem., Vol. 62, No. 2, 1997
J ou et al.
DMS)-OTce (28). Z-N(Me)-O(Me)-Tyr-OH (157 mg, 0.46
mmol) in CH2Cl2 (1 mL), DMAP (8 mg, 0.066 mmol) in CH2Cl2
(100 µL), and DCC (104 mg, 0.50 mmol) in CH2Cl2 (0.3 mL)
were added to a solution of 27 (154 mg, 0.21 mmol) in CH2Cl2
(0.8 mL) at 0 °C. The mixture was allowed to attain rt and
stirred for 24 h. After filtration and solvent removal, the
residue was taken up in AcOEt (100 mL) and washed with
10% citric acid (2 × 20 mL), 5% aqueous NaHCO3 solution (2
× 20 mL), and saturated aqueous NaCl solution (2 × 20 mL).
Drying and filtration followed by solvent removal gave an oil
that was purified by chromatography (silica gel, AcOEt-
hexanes, 1:4), giving 28 as a clear, colorless oil (174 mg,
79%): RP-HPLC tR 20.75 min, C4 Nucleosil column, linear
gradient from 10% B to 100% B over 20 min, followed by
isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN + 0.036% TFA), at a flow rate of
1 mL min-1; [R]D +16.9 (c 0.9, CHCl3); IR (film) ν 3347, 2957,
2930, 2900, 1748, 1692, 1514, 1458, 1389, 1321, 1250, 1153,
1036 cm-1; 1H NMR (300 MHz, CDCl3) δ 0.04 (3H, s), 0.09 (3H,
s), 0.84 (9H, s), 0.88-1.00 (12H, m), 1.19 (3H, d, J ) 6.6), 1.13-
1.27 (2H, m), 1.46 (9H, s), 1.40-1.50 (1H, m), 1.58-1.70 (2H,
m), 1.72-1.82 (1H, m), 2.57-2.74 (2H, m), 2.75 (3H, bs), 2.95
(3H, bs), 2.92-3.00 (1H, m), 3.11-3.20 (1H, m), 3.77 (3H, s),
4.06-4.15 (1H, m), 4.28-4.41 (2H, m), 4.64 (1H, d, J ) 12.0),
4.71 (1H, d, J ) 12.0), 4.76-4.84 (2H, m), 5.06 (1H, d, J )
12.1), 5.16 (1H, d, J ) 12.0), 5.18-5.22 (1H, m), 6.74 (1H, bd,
J ) 7.5), 6.75 (2H, d, J ) 8.4), 6.99 (1H, bd, J ) 8.9), 7.07
(2H, d, J ) 9.1), 7.26-7.32 (5H, m); 13C NMR (75 MHz, CDCl3)
δ -4.70, -7.52, 11.40, 14.50, 17.94, 21.5, 23.24, 24.90, 25.76,
27.04, 28.32, 29.60, 30.60, 34.11, 34.46, 36.50, 39.30, 55.21,
56.50, 57.00, 60.01, 67.50, 68.97, 74.11, 77.20, 80.05, 113.97,
127.67, 127.97, 128.44, 129.80, 136.30, 157.00, 158.00, 168.00,
170.00, 172.00; m/ z (FAB) 1076.0 [(M′ + H)+, 5], 1074.0 [(M
+ H)+, 5], 976.0 (100).
was purified by chromatography (silica gel, AcOEt-hexanes,
1:4), giving the two diastereomers of 4a (approximate propor-
tions 1:1) as a semisolid, (21 mg, 60%): RP-HPLC tR 22.91
min, C4 Nucleosil column, linear gradient from 10% B in A to
100% B, over 20 min, followed by isocratic elution with 100%
B for 10 min, where A is H2O/0.045% TFA and B is MeCN/
0.036% TFA), at a flow rate of 1 mL min-1; IR (film) ν 3317,
2960, 2933, 2900, 2861, 1746, 1700, 1661, 1636, 1538, 1514,
1455, 1387, 1361, 1322, 1250, 1156, 1100 cm-1; 1H NMR (500
MHz, CDCl3) δ -0.04 (3H, s), 0.10 (3H, s), 0.78 (3H, d, J )
6.5), 0.81 (9H, s), 0.85-0.89 (21H, m), 1.12 (3H, d, J ) 6.5),
1.95-1.26 (2H, m), 1.26 (3H, d, J ) 6.1), 1.29 (3H, d, J ) 7.0),
1.43 (9H, s), 1.40-1.48 (2H, m), 1.50-1.68 (4H, m), 1.94 (1H,
q, J ) 7.0), 1.99-2.15 (2H, m), 2.32-2.43 (4H, m), 2.74-2.82
(7H, m), 2.90-2.98 (1H, m), 3.14-3.34 (1H, m), 3.63-3.68 (1H,
m), 3.75 (3H, s), 3.91-3.95 (2H, m), 4.11-4.26 (2H, m), 4.51
(1H, d, J ) 12.0), 4.52 (1H, d, J ) 12.0), 4.76-4.82 (4H, m),
4.82-5.14 (5H, m), 5.24-5.30 (1H, m), 6.72 (2H, d, J ) 8.5),
6.76 (2H, d, J ) 8.5), 6.98 (2H, d, J ) 8.1), 7.06 (2H, d, J )
8.1), 7.14-7.24 (2H, m), 7.25-7.31 (5H, m), 7.42 (1H, d, J )
10.0); 13C NMR (75 MHz, CDCl3) δ -4.86, -3.80, 12.13, 13.21,
14.30, 14.89, 16.44, 17.49, 18.11, 19.28, 21.42, 22.23, 22.91,
23.39, 24.64, 25.93, 27.61, 28.24, 29.22, 29.69, 30.01, 33.63,
34.07, 34.36, 39.73, 41.07, 47.62, 48.23, 48.63, 55.16, 55.99,
57.60, 58.82, 60.40, 67.04, 67.33, 67.80, 70.85, 73.87, 80.6,
80.95, 113.83, 127.40, 127.76, 127.88, 128.34, 129.77, 156.16,
158.00, 169.20, 169.93, 171.58, 171.80, 205.23; m/ z (FAB)
1464.8 [(M′ + Na)+, 6], 1462.8 [(M + Na)+, 7], 1442.9 [M′ +
H)+, 8], 1440.9 [M + H)+, 8] 1342.8 (100). Anal. Calcd for
C70H109Cl3N6O17Si: C, 58.41; H, 7.58; N, 5.84. Found: C,
58.23; H, 7.37; N, 5.91.
Boc-(R)-N(Me)-Leu -Th r [Z-N(Me)-O(Me)-Tyr ]-Ist (TB-
DMS)-Hip -Leu -P r o-OH (4b). Zinc dust (32 mg, 0.48 mmol)
was added portionwise to a solution of 4a (21 mg, 0.015 mmol)
in THF (600 µL), followed by 1 M NH4OAc solution (115 µL),
and the mixture stirred vigorously under Ar for 24 h. AcOEt
(10 mL) was added, the mixture filtered, and the filtrate
washed with saturated aqueous NaCl solution (2 × 10 mL)
and dried. Filtration and solvent removal gave 4b as an oil
(16 mg, 81%): RP-HPLC tR 22.27 min, C4 Nucleosil column,
linear gradient from 10% B to 100% B over 20 min, followed
by isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN/0.036% TFA, at a flow rate of 1
mL min-1; IR (film) ν 3309, 2964, 2931, 2890, 280, 1746, 1704,
1659, 1632, 1547, 1515, 1452, 1385, 1368, 1321, 1262, 1100,
1021cm-1; 1H NMR (300 MHz, CDCl3) δ 0.07 (6H, s), 0.82 (9H,
s), 0.83-0.91 (24H, m), 1.14 (3H, d, J ) 6.3), 1.18-1.28 (2H,
m), 1.28 (3H, d, J ) 7.2), 1.32 (3H, d, J ) 7.2), 1.48 (9H, s),
1.40-1.50 (2H, m), 1.52-1.68 (4H, m), 1.90-2.50 (8H, m), 2.78
(3H, bs,), 2.80 (3H, bs), 2.80-2.92 (1H, m), 3.20-3.30 (1H, m),
3.56-3.68 (2H, m), 3.77 (3H, s), 3.92-4.20 (3H, m), 4.49-4.94
(3H, m), 4.97-5.17 (4H, m), 5.20-5.25 (1H, m), 6.72-6.80 (2H,
m), 7.00-7.20 (4H, m), 7.26-7.32 (5H, m), 7.40-7.45 (1H, m);
m/ z (ES) 1332.03 [(M + Na)+, 33], 1310.14 [(M + H)+, 100].
Boc-(R)-N(Me)-Leu -Th r [H -N(Me)-O(Me)-Tyr ]-Ist (TB-
DMS)-Hip -Leu -P r o-OH (4c). Acid 4b (15 mg, 0.01 mmol)
in THF (300 µL) was hydrogenolyzed in the presence of 10%
Pd-C (17 mg) for 4 h at rt and atmospheric pressure.
Filtration followed by solvent removal gave 4c as a white solid
(13 mg, 95%): mp 75-77 °C; RP-HPLC tR 18.96 min, C4
Nucleosil column, linear gradient from 10% B in A to 100% B
over 20 min, followed by isocratic elution with 100% B for 10
min, where A is H2O/0.045% TFA and B is MeCN/0.036% TFA,
at a flow rate of 1 mL min-1; IR (film) ν 3313, 2963, 2931,
2858, 1731, 1661, 1632, 1515, 1455, 1387, 1368, 1322, 1260,
1162, 1096, 1022 cm-1; 1H NMR (500 MHz, CDCl3) δ 0.05 (6H,
s), 0.81-0.94 (33H, m), 1.08 (3H, d, J ) 6.6), 1.13 (3H, d, J )
6.6), 1.18-1.34 (2H, m), 1.26 (3H, d, J ) 7.0), 1.29 (3H, d, J )
7.0), 1.44-1.50 (2H, m), 1.48 (9H, s), 1.60-1.80 (4H, m), 1.90-
2.10 (4H, m), 2.24-2.43 (4H, m), 2.73-2.77 (6H, m), 2.80-
3.07 (2H, m), 3.53-3.64 (2H, m), 3.75 (3H, s), 3.91-4.16 (3H,
m), 4.62-4.84 (4H, m), 5.04-5.11 (2H, m), 6.77-6.82 (3H, m),
7.00-7.07 (4H, m), 7.33 (1H, d, J ) 10.1); m/ z (ES) 1175.08
[(M + H)+, 100].
Boc-(R)-N(Me)-Leu -Th r [Z-N(Me)-O(Me)-Tyr ]-Ist (TB-
DMS)-OH (29). Zinc dust (118 mg, 1.80 mmol) was added
portionwise to a solution of 28 (59 mg, 0.05 mmol) in THF (1.6
mL), followed by 1 M aqueous NH4OAc solution (0.28 mL), and
the mixture was stirred vigorously under nitrogen for 24 h.
After filtration and solvent removal, the residue was taken
up in AcOEt (50 mL) and washed with 5% aqueous KHSO4
solution (2 × 10 mL) and saturated aqueous NaCl solution (2
× 10 mL). Drying and filtration followed by solvent removal
gave an oil that was purified by chromatography (silica gel,
CH2Cl2/MeOH, 99:1 f CH2Cl2/MeOH, 98:2, gradient elution),
giving 29 as a colorless semisolid (34 mg, 66%): RP-HPLC tR
19.12 min, C4 Nucleosil column, linear gradient from 10% B
in A to 100% B over 20 min, followed by isocratic elution with
100% B for 10 min, where A is H2O/0.045% TFA and B is
MeCN/0.036% TFA, at a flow rate of 1 mL min-1; [R]D +16.3
(c 0.6, CHCl3); IR (film) 3428, 3328, 2960, 2943, 1743, 1707,
1655, 1515, 1457, 1389, 1322, 1300, 1250, 1152, 1093 cm-1
;
1H NMR (300 MHz, CDCl3) δ 0.07 (3H, s), 0.09 (3H, s), 0.82
(3H, d, J ) 6.6), 0.87 (9H, s), 0.88 (3H, t, J ) 6.5), 0.94 (3H, d,
J ) 6.9), 0.96 (3H, d, J ) 6.9), 1.14-1.30 (3H, m), 1.18 (3H, d,
J ) 6.3), 1.46 (9H, s), 1.41-1.90 (3H, m), 1.80-1.90 (1H, m),
2.40-2.60 (2H, m), 2.75-3.00 (7H, m), 3.20-3.35 (1H, m), 3.78
(3H, s), 4.03-4.18 (2H, m), 4.50-4.58 (1H, m), 4.80-4.90 (1H,
m), 5.00-5.16 (1H, m), 5.01 (1H, d, J ) 12.0), 5.13 (1H, d, J )
12.0), 6.74-6.83 (2H, m), 6.98-7.26 (4H, m), 7.27-7.35 (5H,
m); 13C NMR (75 MHz, CDCl3) δ -4.94, -4.31, 11.93, 13.31,
17.82, 21.26, 21.45, 23.16, 25.03, 25.66, 27.27, 28.30, 30.36,
30.97, 34.16, 34.30, 37.58, 41.16, 55.16, 55.92, 56.36, 57.67,
59.63, 67.43, 68.60, 69.50, 70.08, 81, 113.91, 127.45, 127.87,
128.38, 129.76, 135.41, 157.17, 158.37, 168.7, 169.89, 172.6,
173.6, 173.8; m/ z (FAB) 966.2 [(M + Na)+, 65], 940.1 (100).
Boc-(R)-N(Me)-Leu -Th r [Z-N(Me)-O(Me)-Tyr ]-Ist (TB-
DMS)-Hip -Leu -P r o-OTce (4a ). Acid 29 (23 mg, 0.024 mmol)
and alcohol 21 (15 mg, 0.03 mmol) in CHCl3 (500 µL) were
added to a solution of DMAP‚CF3COOH (6 mg, 0.025 mmol),
DMAP (4 mg, 0.036 mmol), and DIPCDI (3.75 µL, 0.01 mmol)
in CHCl3 (100 µL) under nitrogen and the mixture heated to
reflux. After 8 h, DMAP‚CF3COOH (6 mg, 0.25 mmol), DMAP
(4 mg, 0.036 mmol), and DIPCDI (3.75 µL, 0.01 mmol) in
CHCl3 (100 µL) were added and stirring continued for a further
16 h at rt. The solvent was removed, and the crude residue
Cyclo-[N(Me)-O(Me)-Tyr -O-[Boc-(R)-N(Me)-Leu -]-Th r -
Ist(TBDMS)-Hip -Leu -P r o-] (1a ). HATU (12 mg, 0.031

Total Synthesis of Dehydrodidemnin B
J . Org. Chem., Vol. 62, No. 2, 1997 363
mmol), HOAt (4 mg, 0.031 mmol), and DIEA (8.65 µL, 0.05
mmol) were added to 4c (30 mg, 0.025 mmol) in THF (23 mL)
at 0 °C, and the mixture was stirred for 3 h under Ar. The
solvent was removed and the residue taken up in AcOEt (75
mL) and washed with 5% aqueous KHSO4 solution (2 × 10
mL), 5% aqueous NaHCO3 solution (2 × 10 mL), and saturated
aqueous NaCl solution (2 × 10 mL). Drying and filtration,
followed by solvent removal, gave an oil that was purified by
chromatography (silica gel, CH2Cl2-AcOEt, 8:1), giving 1a as
an oil (8 mg, 28%): RP-HPLC tR 21.16 min, C4 Nucleosil, linear
gradient from 10% B in A to 100% B, over 20 min, followed by
isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN/0.036% TFA, at a flow rate of 1
mL min-1; IR (film) ν 3338, 2960, 2933, 2890, 2860, 1736, 1665,
settes (3.64 g, 72%): mp 185-186 °C; [R]D -64.7 (c 2.0,
CH2Cl2); IR (film, CH2Cl2) ν 3485, 2957, 2871, 1746, 1709,
1651, 1501, 1429, 1391, 1366, 1250, 1169, 1045, 1022 cm-1
;
1H NMR (200 MHz, CDCl3) δ 0.90 (3H, d, J ) 6.6), 0.96 (3H,
d, J ) 6.5), 1.42 (9H, s), 1.75 (1H, m), 1.92-2.28 (4H, m), 3.50-
3.80 (2H, m), 4.32-4.54 (1H, m), 4.54-4.75 (1H, m), 5.05 (2H,
d, J ) 12.0), 5.23 (2H, d, J ) 12.0), 7.34 (5H, bs); 13C NMR (50
MHZ, CDCl3) δ 22.19, 23.89, 24.99, 25.38, 28.83, 29.45, 42.46,
47.18, 50.72, 59.31, 67.39, 79.99, 128.66-129.04, 136.1, 156.2,
172.32; m/ z (FAB) 419.4 [(M + H)+, 55], 319.4 (100); m/ z
(FABHRMS) 419.255 191, C23H34N2O5 requires (M + H)+,
419.254 598. Anal. Calcd for C23H34N2O5: C, 66.03; H, 8.13;
N, 6.70. Found: C, 66.11; H, 8.12; N, 6.78.
TBDMS-Hip -Leu -P r o-OBzl (31). Ester 16 (1.39 g, 3.696
mmol) in THF (15 mL) was hydrogenolyzed in the presence of
10% Pd-C (235 mg) for 120 min at room rt and atmospheric
pressure. The system was cooled to -20 °C and the mixture
filtered through Celite, washing with THF (20 mL), directly
onto a solution of HBTU (1.467 g, 3.88 mmol) and HOBt (509
mg, 3.70 mmol) at -10 °C. DIEA (628 µL, 3.70 mmol) was
added, and after 3 min, a solution of 30 (2.27 g, 5.39 mmol)
[formed by treating Boc-Leu-Pro-OBzl (2.25 g, 5.39 mmol) with
60% TFA in CH2Cl2 for 2 h at rt, followed by removal of the
solvent and chasing with Et2O], in THF (7 mL) and DIEA (1.49
mL, 8.69 mmol), was added. The temperature was maintained
at -5 °C for 3 h, allowed to attain rt, and stirred for 16 h. The
solvent was removed and the residue taken up in AcOEt (50
mL) and washed with 5% aqueous KHSO4 solution, 5%
aqueous NaHCO3 solution, and saturated aqueous NaCl
solution. Drying and filtration, followed by solvent removal,
gave an oil (2.52 g) that was purified by chromatography (silica
gel, AcOEt-hexanes, 3:7), giving the two diastereomers of 31
(approximate proportions, 1:1) as a colorless caramel (1.79 g,
83%): RP-HPLC tR 22.7 min, Nucleosil C18 column, linear
gradient from 10% B in A to 100% B over 20 min, followed by
isocratic elution at 100% B for 10 min, where A is H2O/0.045%
1642, 1536, 1515, 1451, 1387, 1368, 1321, 1250, 1167 cm-1
;
1H NMR (500 MHz, CDCl3) δ -0.06 (3H, s), 0.04 (3H, s), 0.82
(9H, s), 0.80-0.92 (24H, m), 1.08-1.15 (1H, m), 1.24 (9H, s),
1.27 (3H, d, J ) 7.0), 1.32 (3H, d, J ) 7.0), 1.49 (9H, s), 1.45-
1.50 (2H, m), 1.56-1.78 (5H, m), 1.94 (1H, q, J ) 6.5), 1.98-
2.29 (2H, m), 2.40-2.48 (1H, m), 2.52 (3H, s), 2.75 (3H, s), 2.77
(3H, s), 3.13-3.18 (2H, m), 3.36 (1H, dd, J 1 ) 14.5, J 2 ) 4.5),
3.52 (1H, dd, J 1 ) 10.5, J 2 ) 4.1), 3.53-3.64 (2H, m), 3.68-
3.72 (1H, m), 3.78 (3H, s), 4.03 (1H, td, J 1 ) 10.1, J 2 ) 2.0),
4.15 (1H, dd, J 1 ) 9.0, J 2 ) 9.0), 4.58 (1H, dd, J 1 ) 7.9, J 2
)
6.0), 4.70-4.84 (3H, m), 4.94-4.98 (1H, m), 5.01 (1H, d, J )
3.5), 6.82-6.84 (1H, m), 6.83 (2H, d, J ) 8.5), 7.08 (2H, d, J )
8.3), 7.34-7.40 (1H, m), 7.87-7.93 (1H, m); 13C NMR (75 MHz,
CDCl3) δ -4.78, -3.63, 12.03, 14.21, 15.26, 16.01, 16.89, 19.08,
20.95, 22.68, 23.12, 23.79, 24.82, 25.12, 25.94, 27.73, 27.87,
28.34, 29.68, 30.37, 33.42, 34.11, 38.59, 39.79, 41.38, 47.06,
47.72, 49.35, 55.20, 55.27, 57.24, 66.01, 68.33, 70.79, 77.19,
81.48, 114.12, 128.83, 129.90, 130.38, 130.92, 158.63, 168.57,
168.96, 169.35, 170.58, 170.97, 171.81, 172.50, 205.26; m/ z
(FAB) 1180.6 [(M + Na)+, 65], 1158.6 [(M + H)+, 100]. Anal.
Calcd for C60H100N6O14Si: C, 62.28; H, 8.65; N, 7.27. Found:
C, 62.42; H, 8.63; N, 6.72.
Did em n in A (1c). Macrocycle 1a (10.2 mg, 8.65 × 10-3
mmol) was dissolved in 5 M HCl in dioxane (1 mL), and after
60 min, the solvent was removed and chased with Et2O, giving
didemnin A hydrochloride (8.4 mg, 98%): mp 141-147 °C (lit.12
mp 146-148 °C); [R]D -148.5 (c 0.4, CHCl3) [lit.12 [R]D -148.7
(c 0.4, CHCl3)]; RP-HPLC Rt 19.82 min, C4 Nucleosil column,
linear gradient from 10% B in A to 100% B over 20 min,
followed by isocratic elution with 100% B for 10 min, where A
is H2O/0.045% TFA and B is MeCN/0.036% TFA), at a flow
TFA and B is MeCN/0.036% TFA, at a flow rate of 1 mL min-1
;
IR (film, CH2Cl2) 3295, 3060 and 3040, 2957, 2934, 2880, 2858,
1736, 1634, 1528, 1454, 1387, 1252, 1171, 1070 cm-1; 1H NMR
(200 MHz, CDCl3) δ 0.01 (3H, s), 0.03 (3H, s), 0.85-0.97 (12H,
m), 0.92 (9H, s), 0.93 (9H, s), 1.33 (3H, d, J ) 7.0), 1.37 (3H,
d, J ) 7.0), 2.40-2.65 (3H, m), 1.92-2.28 (4H, m), 3.64-3.76
(1H, m), 4.69-4.82 (1H, m), 5.05 (1H, d, J ) 11.8), 5.20 (2H,
d, J ) 11.8), 6.73 (1H, d, J ) 8.9), 6.98 (1H, d, J ) 9.0), 7.34
(5H, bs); 13C NMR (75 MHz, CDCl3) δ -5.24, -4.81, 15.70,
17.43, 17.57, 18.84, 21.48, 21.61, 18.05, 23.28, 24.43, 24.55,
24.76, 25.68, 28.87, 31.36, 31.77, 41.27, 41.67, 48.68, 48.55,
48.89, 58.71, 66.84, 83.84, 83.29, 128.09, 128.47, 135.40,
169.24, 170.67, 170.89, 171.16, 171.20, 209.11, 211.62; m/ z
(FAB) 611.5 [(M + Na)+, 15], 589.5 [(M + H)+, 100]; m/ z
(FABHRMS) 589.369 045, C32H52N2O6Si requires (M + H)+,
589.367 291.
H-Hip -Leu -P r o-OBzl (32). The ester 31 (908 mg, 1.54
mmol) and TBAF (1.03 g, 3.24 mmol) were dissolved in dry
THF (17 mL) at rt, and after 30 min, H2O (30 mL) was added
and the solution extracted with AcOEt (4 × 40 mL). The
combined organic phases were washed with saturated aqueous
NaCl solution and dried. Filtration and solvent removal gave
an off-white solid that was purified by chromatography
(AcOEt-hexanes, 2:3) giving the two diastereomers of 32
(approximate proportions, 1:1) as a white solid (708 mg,
97%): mp 180-186 °C, (lit.12 mp 128-130 °C); RP-HPLC tR
17.5 and 16.5 min, Nucleosil C18 column, linear gradient from
10% B in A to 100% B over 20 min, followed by isocratic elution
with 100% B for 10 min, where A is H2O/0.045% TFA and B
is MeCN/0.036% TFA, at a flow rate of 1 mL min-1; IR (film,
CH2Cl2) ν 3450-3293, 3060 and 3040, 2961, 2946, 2883, 2852,
1746, 1632, 1533, 1454, 1357, 1387, 1265, 1173, 1095, 1045,
1018 cm-1; 1H NMR (500 MHz, CDCl3) δ 0.71 (3H, d, J ) 6.8),
0.81 (3H, d, J ) 6.6), 0.88 (3H, d, J ) 6.5), 0.91 (3H, d, J )
6.5), 0.94 (3H, d, J ) 6.5), 0.99 (3H, d, J ) 7.1), 1.07 (3H, d, J
) 6.5), 1.36 (3H, d, 6.5), 1.43-1.52 (2H, m), 1.60-1.66 (1H,
m), 1.93-1.20 (3H, m), 2.12-2.23 (2H, m), 3.53-3.58 (1H, m),
3.65 (1H, q, J ) 7.1), 3.67-3.73 (1H, m), 3.89 (1H, q, J ) 7.1),
3.96 (1H, d, J ) 4.2), 4.22 (1H, d, J ) 4.1), 4.54-4.56 (1H, m),
4.58-4.62 (1H, m), 4.69-4.73 (1H, m), 5.1 (1H, d, J ) 12.1),
1
rate of 1 mL min-1; H NMR (500 MHz, CDCl3) δ 0.82-0.92
(24H, m), 1.11-1.19 (1H, m), 1.22 (3H, d, J ) 6.9), 1.32 (3H,
d, J ) 6.8), 1.30-1.35 (1H, m), 1.35-1.63 (6H, m), 1.71-1.81
(2H, m), 1.93-2.07 (1H, m), 2.07-2.18 (2H, m), 2.28-2.34 (1H,
m), 2.49-2.52 (1H, dd, J 1 ) 11, J 2 ) 10.5), 2.54 (3H, s), 2.72
(3H, bs), 2.79 (3H, bs), 2.86-2.94 (1H, bs), 2.72-2.79 (1H, bd,
J ) 10.5), 3.15-3.18 (1H, dd, J 1 ) 14.5, J 2 ) 10.5), 3.33-3.36
(1H, dd, J 1 ) 14.5, J 2 ) 4.5), 3.54-3.57 (1H, dd, J 1 ) 10.5, J 2
) 4.5), 3.56-3.61 (1H, m), 3.78 (3H, s), 3.96-4.00 (1H, m),
4.03-4.08 (1H, m), 4.11-4.80 (1H, bs), 4.56-4.62 (1H, m),
4.68-4.81 (3H, m), 4.99-5.01 (1H, q, J ) 3.5), 5.16 (1H, bs),
6.83 (2H, d, J ) 8.5), 6.95 (1H, bs), 7.07 (2H, d, J ) 8.5), 7.21-
7.25 (1H, bs), 7.95 (1H, bs); 13C NMR (75 MHz, CDCl3) δ 11.55,
14.95, 15.26, 16.82, 18.56, 20.89, 22.00, 23.08, 23.76, 24.58,
24.85, 25.10, 27.12, 29.35, 29.35, 29.65, 29.69, 31.36, 33.96,
34.14, 38.51, 38.64, 40.14, 55.38, 55.56, 57.31, 66.17, 67.85,
70.58, 80.96, 80.98, 81.57, 114.12, 130.33, 158.63, 168.41,
169.33, 169.70, 170.38, 171.24, 172.28, 172.28, 172.93, 204.83;
m/ z 944.2 [(M + H)+, 100].
Boc-Leu -P r o-OBzl. Boc-Leu-OH (3.01 g, 12 mmol), DCC
(3.22 g, 15.6 mol), and HOBt (1.82 g, 13.2 mmol) were added
to a stirred solution of Pro-OBzl‚HCl (7.31 g, 30 mmol) and
NMM (4.63 mL, 62 mmol) in CH2Cl2 (25 mL) at 0 °C. The
mixture was allowed to attain rt and was maintained at this
temperature for 18 h. After cooling and filtration, the solvent
was removed and the residue taken up in AcOEt (80 mL) and
washed with 10% aqueous KHSO4 solution, 10% aqueous
NaHCO3 solution, and saturated aqueous NaCl solution.
Drying and filtration followed by solvent removal gave an oil
(9.65 g) that was purified by chromatography (silica gel,
AcOEt-hexanes, 1:6), giving Boc-Leu-Pro-OBzl as white ro-

364 J . Org. Chem., Vol. 62, No. 2, 1997
J ou et al.
5.18 (1H, d, J ) 12.1), 6.57 (1H, d, J ) 8.5), 6.63 (1H, d, J )
8.5), 7.28-7.38 (5H, m); 13C NMR (75 MHz, CDCl3) δ 14.06,
14.26, 15.85, 16.48, 20.07, 20.53, 22.02, 22.25, 25.37, 25.46,
29.45, 29.53), 31.59, 32.09, 41.13, 42.29, 49.93, 50.91, 51.02,
59.52, 67.60, 81.02, 128.78, 1.29.2, 169.48, 171.58, 172.17,
209.76; m/ z (FAB) 497.4 [(M + Na)+, 12], 475.5 [(M + H)+,
100]; m/ z (FABHRMS) 497.263 162, C26H38N2O6 requires (M
+ Na)+ 497.262 757. Anal. Calcd for C26H38N2O6: C, 65.82;
H, 8.02; N, 5.91. Found: C, 65.97; H, 8.18; N, 5.76.
Boc-Th r -OSEM (36). Benzyl ether 35 (950 mg, 2.16 mmol)
in MeOH (10 mL) was hydrogenolyzed in the presence of 10%
Pd-C (146 mg) for 60 min at rt and atmospheric pressure.
The mixture was filtered through Celite and the solvent
removed, giving 36 as an oil (730 mg, 97%): RP-HPLC tR 19.5
min, Nucleosil C18 column, linear gradient from 10% B in A
to 100% B over 20 min, followed by isocratic elution with 100%
B for 10 min, where A is H2O/0.045% TFA and B is MeCN/
0.036% TFA, at a flow rate of 1 mL min-1; [R]D -8.4 (c 1.03,
CH2Cl2) [lit.14 [R]D -6.8 (c 2.1, CHCl3)]; IR (film, CH2Cl2) ν
3550-3350, 2979, 2880, 1719, 1508, 1368, 1250, 1165, 1113
Boc-Ist(TBDMS)-Hip -Leu -P r o-OBzl (33). DCC (95 mg,
0.46 mmol) in CH2Cl2 (154 µL) was added dropwise, over 15
min, to a stirred solution of 32 (195 mg, 0.41 mmol), 15 (149
mg, 0.38 mmol), and DMAP (16 mg, 0.13 mmol) in CH2Cl2 (746
µL) under Ar at between -5 and -10 °C. After 3 h, the
temperature was allowed to rise to 4 °C (refrigerator) and was
then maintained for 12 h. The mixture was filtered, the
solvent removed, and the residue taken up in AcOEt (40 mL)
and washed with 5% aqueous KHSO4 solution, 5% aqueous
NaHCO3 solution, and saturated aqueous NaCl solution.
Drying and filtration, followed by solvent removal, gave an
oil (412 mg) that was purified by chromatography (silica gel,
AcOEt-hexanes, 3:7), giving the two diastereomers of 33
(approximate proprotions, 1:1) as a clear, colorless oil, (292
mg, 84%): RP-HPLC tR 26 and 25 min, Nucleosil C18 column,
linear gradient from 10% B in A to 100% B over 20 min,
followed by isocratic elution with 100% B for 10 min, where A
is H2O/0.045% TFA and B is MeCN/0.036% TFA, at a flow rate
of 1 mL min-1; IR (film, CH2Cl2) ν 3365-3200, 3069, 3038,
2959, 2930, 2882, 2857, 1746, 1688, 1640, 1533, 1456, 1389,
1258, 1171, 1086 cm-1; 1H NMR (500 MHz, CDCl3) δ 0.01 (3H,
s), 0.03 (3H, s), 0.05 (3H, s), 0.07 (3H, s), 0.77-1.03 (18H, m),
0.84 (9H, s), 0.85 (9H, s), 1.33 (3H, d, J ) 7.4), 1.32-1.36 (2H,
m), 1.49 (3H, d, J ) 7.5), 1.38-1.62 (3H, m), 1.42 (9H, s), 1.44
(9H, s), 1.51-1.77 (1H, m), 1.88-2.37 (3H, m), 2.17-2.33 (2H,
m), 2.47-2.74 (2H, m), 3.34-3.72 (1H, m), 3.72-3.82 (1H, m),
3.99-4.40 (1H, m), 4.03-4.16 (1H, m), 4.49 (1H, d, J ) 10.3),
4.54-4.59 (1H, m), 4.63-4.70 (2H, m), 4.75 (1H, d, J ) 4.5),
4.77-4.81 (1H, m), 4.95-5.19 (2H, m), 5.22 (1H, d, J ) 5.2),
5.32 (1H, d, J ) 10.5), 6.38 (1H, d, J ) 10.9), 6.71 (1H, d, J )
7.4), 6.76 (1H, d, J ) 8.4), 8.60 (1H, d, J ) 9.5); 13C NMR (75
MHz, CDCl3) δ -5.05, -4.49, 11.83, 12.03, 13.01, 13.51, 13.83,
14.08, 16.92, 17.10, 17.85, 19.14, 19.65, 21.57, 22.09, 22.96,
23.28, 24.36, 24.60, 24.85, 25.73, 26.97, 27.33, 28.35, 28.46,
28.93, 29.09, 29.65, 34.12, 34.16, 40.45, 40.85, 41.18, 42.20,
46.74, 46.16, 47.99, 48.34, 48.90, 49.42, 57.62, 58.81, 58.96,
60.46, 66.62, 66.88, 68.18, 69.69 , 78.98, 79.24, 79.84, 82.95,
128.08-128.49, 135.48 135.61, 155.85, 158.27, 157.44, 168.40,
169.07, 170.65, 170.86, 171.42 171.79, 203.09 205.97; m/ z
(FAB) 846.6 [(M + H)+, 15], 746.6 (100); m/ z (FABHRMS)
868.516 630, C45H75N3O10Si requires (M + Na)+ 868.511 930.
Boc-Th r (Bzl)-OSEM (35). SEM-Cl (2.6 mL, 14.56 mmol)
was added to a suspension of Li2CO3 (1.08 g, 14.56 mmol) and
Boc-Thr(Bzl)-OH (3.07 g, 9.93 mmol) in DMF (10 mL), contain-
ing activated molecular sieves (1 g, 4 Å pore size), and this
mixture was stirred under Ar at rt for 18 h. The mixture was
filtered through Celite, and H2O (20 mL) was added to the
filtrate. Extraction with AcOEt (5 × 20 mL), followed by
washing the combined organic phases with saturated NaCl
solution, drying, filtration, and solvent removal, gave an oil
(3.5 g) that was purified by chromatography (silica gel,
AcOEt-hexanes, 1:9), giving 35 as a clear, colorless oil [2.42
g, 78%, based on recovered Boc-Thr(Bzl)-OH (0.95 g)]: RP-
HPLC tR 22.3 min, Nucleosil C18 column, linear gradient from
10% B in A to 100% B over 20 min, followed by isocratic elution
at 100% B for 10 min, where A is H2O/0.045% TFA and B is
MeCN/0.036% TFA, at a flow rate of 1 mL min-1; [R]D -1.35
(c 0.7, CH2Cl2); IR (film, CH2Cl2) ν 3500-3275, 2979-2875,
1721, 1501, 1368, 1250, 1167, 1070 cm-1; 1H NMR (200 MHz,
CDCl3) δ 0.02 (9H, s), 0.90-0.99 (2H, m), 1.31 (3H, d, J ) 6.3),
1.49 (9H, s), 3.65-3.72 (2H, m), 4.12-4.25 (1H, m), 4.32-4.41
(2H, m), 4.39-4.63 (1H, m), 5.28-5.34 (3H, m), 7.29-7.33 (5H,
bs); 13C NMR (50 MHz, CDCl3) δ -1.51, 16.23, 17.89, 28.26,
58.28, 68.04, 70.86, 74.56, 79.81, 89.83, 127.15, 127.31, 137.83,
156.09, 170.79; m/ z (FAB) 462.4 [(M + Na)+, 5], 440.4 [(M +
H)+, 28]; m/ z (FABHRMS) 440.244 850, C22H37NO6Si requires
(M + H)+ 440.246 842.
cm-1 1H NMR (200 MHz, CDCl3) δ 0.02 (9H, s), 0.92-1.01
;
(2H, m), 1.27 (3H, d, J ) 6.3), 1.45 (9H, s), 3.69-3.77 (2H, m),
4.22-4.41 (2H, m), 5.36-5.38 (3H, m); 13C NMR (50 MHz,
CDCl3) δ -1.46, 17.98, 19.94, 28.27, 58.47, 68.13, 68.18, 80.01,
89.89, 157.06, 171.14; m/ z (CI) 372.2 [(M + Na)+, 55], 350.2
[(M + H)+, 10], 236.0 (100).
Boc-Th r [Z-N(Me)-O(Me)-Tyr ]-OSEM (37). DCC (1 g,
0.72 mmol) in CH2Cl2 (800 µL) was added to Z-N(Me)-O(Me)-
Tyr-OH (1.53 g, 4.67 mmol), 36 (1.25 g, 3.59 mmol), and DMAP
(86 mg, 0.72 mmol) in CH2Cl2 (4 mL) at -10 °C and the
mixture allowed to attain rt and stirred for 15 h. After the
mixture was cooled to 0 °C, CH2Cl2 (15 mL) was added and
the solution filtered and washed with 5% aqueous KHSO4
solution, 5% aqueous NaHCO3 solution, and saturated aqueous
NaCl solution. Drying and filtration followed by solvent
removal gave an oil (2.62 g) that was purified by chromatog-
raphy (silica gel, AcOEt-hexanes, 1:5), giving 37 as an oil (2.08
g, 88%): RP-HPLC tR 21.4 min, Nucleosil C18 column, linear
gradient from 10% B in A to 100% B over 20 min, followed by
isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN/0.036% TFA, at a flow rate of 1
mL min-1; [R]D -10.3 (c 1.2, CH2Cl2) [lit.14 [R]D -15.2 (c 1.1,
CHCl3]; IR (film, CH2Cl2) ν 3200, 2957-2838, 1742, 1705, 1613,
1586, 1514, 1454, 1402, 1308, 1248, 1180, 1142, 1109, 1034
cm-1 1H NMR (200 MHz, CDCl3) δ 0.03 (9H, s), 0.91-1.00
;
(2H, m), 1.31 (3H, d, J ) 6.3), 1.46 (9H, s), 2.73 (3H, s), 2.81
(3H, s), 2.85-3.04 (1H, m), 3.10-3.30 (1H, m), 3.65-3.79 (2H,
m), 3.78 (3H, s), 4.43-4.51 (1H, m), 4.69-4.88 (1H, m), 5.06-
5.40 (5H, m), 5.40-5.52 (1H, m), 6.75-6.81 (2H, m), 6.99-
7.71 (2H, m), 7.31-7.32 (5H, bs.); 13C NMR (50 MHz, CDCl3)
δ -1.46, 16.74, 17.01, 17.95, 28.24, 31.64, 32.19, 33.86, 34.17,
55.14, 56.88, 57.05, 67.28, 68.24, 71.52, 71.74, 80.21, 90.40,
113.88, 127.62, 128.79, 129.40, 129.80, 138.67, 137.84, 138.53,
158.31, 169.59, 169.72; m/ z (FAB) 697.6 [(M + Na)+, 100]; m/ z
(FABHRMS) 675.330 007, C34H50N2O10 requires (M + H)+
675.331 300.
Boc-Th r [Z-N(Me)-O(Me)-Tyr ]-OH (38). Aqueous HF in
MeCN [1.383 mL of a solution of 15% HF (1 mL) in H2O (1
mL)], previously cooled to -25 °C, was added dropwise to a
solution of 37 (358 mg, 0.519 mmol) in MeCN (2.767 mL) at
-25 °C, and the temperature of the system was maintained
between -25 and -15 °C for 7 h. Cold (0 °C) solutions of 10%
aqueous KHSO4 (18 mL) and cold (0 °C) AcOEt (15 mL) were
added, and the pH of the aqueous phase was adjusted to 4 by
addition of solid NaHCO3. The aqueous phase was then
extracted with AcOEt (4 × 20 mL), dried, and filtered. Solvent
removal gave an oil (313 mg) that was purified by chroma-
tography (silica gel, MeOH-CH2Cl2, 1:32), giving 38 as a white
semisolid (204 mg, 72%): RP-HPLC tR 17.9, Nucleosil C18
column, linear gradient from 10% B in A to 100% B over 20
min, followed by isocratic elution at 100% B for 10 min, where
A is H2O/0.045% TFA and B is MeCN/0.036% TFA, at a flow
rate of 1 mL min-1; [R]D -20.5 (c 2, CH2Cl2); IR (film, CH2Cl2)
ν 3400, 3050, 2900, 1715, 1613, 1514, 1456, 1402, 1368, 1248,
1165, 1061, 1036 cm-1; 1H NMR (200 MHz, CDCl3) δ 1.29 (3H,
d, J ) 6.5), 1.45 (9H, s), 2.74 (3H, s), 2.75 (3H, s), 2.76-3.31
(2H, m), 3.77 (3H, s), 4.42-4.52 (1H, m), 4.66-4.83 (1H, m),
5.01-5.16 (2H, m), 5.30-5.53 (2H, m), 6.72-6.81 (2H, m),
6.95-7.09 (2H, m), 7.35 (5H, bs); 13C NMR (75 MHZ, CDCl3)
δ 16.44, 16.82, 28.23, 31.71, 31.97, 33.82, 33.68, 55.14, 56.87,
56.75, 60.58, 60.39, 67.51, 67.76, 71.83, 72.47, 80.40, 113.91,
127.59, 128.69, 129.77, 236.42, 156.00, 156.19, 156.71, 158.31,
159.47, 169.78; m/ z (FAB) 567.1 [(M + Na)+, 46], 545.1 [(M +
H)+, 7], 445.1 (100); m/ z (FABHRMS) 567.233 280, C28H35N2O9
requires (M + Na)+ 567.231 851.

Total Synthesis of Dehydrodidemnin B
J . Org. Chem., Vol. 62, No. 2, 1997 365
Boc-Th r [Z-N(Me)-O(Me)-Tyr ]-Ist-Hip-Leu -P r o-OBzl (5a).
A 5.7 M solution of HCl in dioxane (3 mL) was added to a
solution of 33 (141 mg, 0.17 mmol) in dioxane (1 mL) at rt,
and after 3 h the solvent was removed and chased with Et2O.
The white solid formed (34, 105 mg, 0.167 mmol) in THF (2
mL) was then added to a solution of 38 (119 mg, 0.22 mmol),
HBTU (83 mg, 0.22 mmol), HOBt (30 mg, 0.22 mmol), and
DIEA (37 µL, 0.22 mmol) in dry THF (1.2 mL) under nitrogen
at -15 °C. After being stirred for 5 min, DIEA (57 µL, 0.33
mmol) was added dropwise over 15 min, and the temperature
was maintained between -10 and -5 °C for 4 h. The solvent
was removed and the residue taken up in AcOEt (30 mL) and
washed with 5% aqueous KHSO4 solution, 5% aqueous NaH-
CO3 solution, and saturated aqueous NaCl solution. Drying
and filtration followed by solvent removal gave an oil (329 mg)
that was purified by chromatography (silica gel, AcOEt-
hexanes, 1:1) giving the two diastereomers of 5a (approximate
proportions, 1:1) as a glassy solid (159 mg, 82%): mp 89-93
°C; RP-HPLC tR 21.0 and 22.1 min, Nucleosil C18 column,
linear gradient from 10% B in A to 100% B over 20 min,
followed by isocratic elution at 100% B for 10 min, where A is
H2O/0.045% TFA and B is MeCN/0.036% TFA, at a flow rate
of 1 mL min-1; IR (film, CH2Cl2) ν 3350, 2961, 2927, 2893,
1744, 1688, 1638, 1514, 1454, 1368, 1304, 1248, 1171, 1067,
1036 cm-1; 1H NMR (500 MHz, CDCl3) δ 0.74-0.92 (18H, m),
1.05-1.15 (2H, m), 1.18-1.20 (2H, m), 1.23 (3H, d, J ) 6.8),
1.25 (3H, d, J ) 6.8), 1.29 (3H, d, J ) 6.9), 1.42 (9H, s), 1.45
(9H, s), 1.50-1.66 (3H, m), 1.89-2.02 (4H, m), 2.17-2.25 (2H,
m), 2.37-2.42 (1H, m), 2.81 (3H, s), 2.88 (3H, s), 2.91 (3H, s),
2.95 (3H, s), 2.84-2.93 (2H, m), 3.17-3.25 (1H, m), 3.53-3.59
(1H, m), 3.75 (3H, s), 3.88-3.98 (4H, m), 4.49 (1H, d, J ) 3.1),
4.51 (1H, d, J ) 3.1), 4.53-4.57 (1H, m), 4.68-4.72 (1H, m),
4.96-4.99 (1H, m), 5.02-5.33 (4H, m), 5.02 (1H, d, J ) 3.2),
5.23 (1H, d, J ) 3.1), 5.26-5.33 (1H, m), 5.47 (1H, d, J ) 9.5),
6.74 (2H, d, J ) 7.8), 6.77 (2H, d, J ) 7.7), 7.08 (2H, d, J )
7.7), 7.17 (1H, d, J ) 7.5), 7.21 (1H, d, J ) 9.5), 7.23-7.36
(10H, m,), 7.75 (1H, d, J ) 7.9), 7.79 (1H, d, J ) 8.2); 13C NMR
(75 MHz, CDCl3) δ 11.95, 13.27, 15.16, 16.47, 17.33, 18.79,
21.28, 23.65, 24.65, 24.72, 27.09, 28.08, 28.93, 31.20, 31.32,
33.62, 33.98, 38.38, 41.01, 47.12, 49.38, 54.96, 55.17, 57.89,
58.83, 60.01, 60.16, 67.18, 71.05, 71.32, 80.34, 81.24, 113.89,
127.51, 128.59, 129.69, 129.77, 135.52, 136.77, 156.93, 158.27,
169.87, 170.62, 171.15, 171.85, 172.39, 204.88; m/ z (FAB)
1181.2 [(M + Na)+, 20], 1159.2 [(M + H)+, 80], 1059.2 (100).
macrocycle 3a as a clear viscous oil (27 mg, 76%): mp 164-
168 °C; RP-HPLC tR 20.4 min, Nucleosil C18 column, linear
gradient from 10% B in A to 100% B over 20 min, followed by
isocratic elution with 100% B for 10 min, where A is H2O/
0.045% TFA and B is MeCN/0.036% TFA, at a flow rate of 1
mL min-1; [R]D -209.4 (c 0.3, CHCl3); IR (film, CH2Cl2) ν 3343,
2961, 2927, 2893, 1734, 1640, 1514, 1454, 1368, 1302, 1248,
1
1167, 1018 cm-1; H NMR (500 MHz, CDCl3) δ 0.78 (3H, d, J
) 7.1), 0.85 (3H, d, J ) 7.0), 0.87 (3H, d, J ) 7.0), 0.89-0.93
(9H, m), 1.10-1.20 (1H, m), 1.20 (3H, d, J ) 6.4), 1.30 (3H, d,
J ) 6.9), 1.36 (2H, m), 1.40 (2H, m), 1.44 (9H, s), 1.48-1.72
(2H, m), 1.72-1.78 (1H, m), 1.83-1.88 (1H, m), 2.01-2.17 (3H,
2m), 2.27-2.29 (1H, m), 2.47-2.53 (1H, m), 2.53 (3H, s), 2.93
(1H, bs), 3.14-3.19 (2H, m), 3.34-3.37 (1H, dd, J 1 ) 14.8, J 2
) 4.1), 3.54-3.56 (1H, dd, J 1 ) 10.5, J 2 ) 4.1), 3.58-3.63 (1H,
m), 3.68-3.72 (1H, m), 3.78 (3H, s), 3.94-3.98 (1H, m), 3.98
(1H, q, J ) 7.5), 4.07-4.11 (1H, 3d, J ) 3.8), 4.57-4.61 (2H,
m), 4.77-4.81 (1H, m), 4.97-4.98 (1H, q, J ) 3.5), 5.02 (1H,
d, J ) 10.5), 5.18 (1H, d, J ) 4.2), 6.81 (2H, d, J ) 8.5), 7.05
(2H, d, J ) 8.5), 7.19 (1H, d, J ) 10.2), 7.64 (1H, d, J ) 10.1);
13C NMR (75 MHz, CDCl3) δ 11.56, 14.68, 14.97, 15.27, 16.61,
18.45, 20.64, 23.50, 24.71, 24.78, 26.92, 27.73, 27.94, 31.55,
33.94, 33.94, 38.27, 38.52, 40.64, 46.86, 49.54, 49.65, 55.16,
55.19, 55.84, 57.12, 65.96, 67.30, 71.00, 80.27, 81.41, 114.02,
130.22, 158.53, 168.30, 169.31, 170.12, 170.29, 171.20, 172.38,
204.51; m/ z (FAB) 938.9 [(M + Na)+, 55], 916.9 [(M + H)+,
100]; m/ z (FABHRMS) 916.532 120, C47H73N5O13 requires (M
+ H)+ 916.528 300.
Boc-d id em n in A (1b). A 5.7 M solution of HCl in dioxane
(2.8 mL) was added to a solution of 3a (36 mg, 39.34 × 10-3
mmol) in dioxane (200 µL) at rt, and after 1 h, the solvent
was removed and chased with Et2O. The white solid formed
(3b) was dissolved in CH2Cl2 (400 µL) and added to a solution
of Boc-(R)-N(Me)-Leu-OH (24 mg, 99.28 × 10-3 mmol), BOP
(48 mg, 109.24 × 10-3 mmol), HOBt (16 mg, 109.24 × 10-3
mmol), and DIEA (16.8 µL, 99.28 × 10-3 mmol) in CH2Cl2 (250
µL) at 0 °C. The mixture was allowed to attain rt, and after
40 min, the solvent was removed and the residue taken up in
AcOEt (10 mL) and washed with 5% aqueous KHSO4 solution,
5% aqueous NaHCO3 solution, and saturated aqueous NaCl
solution. Drying and filtration followed by solvent removal
gave an oil (19 mg) that was purified by chromatography (silica
gel, AcOEt-hexanes, 1:1) giving 1b (38 mg, 92%) as a white
solid: mp 121-124 °C; RP-HPLC tR 21.2 min, Nucleosil C18
column, linear gradient from 10% B in A to 100% B over 20
min, followed by isocratic elution with 100% B for 10 min,
where A is H2O/0.045% TFA and B is MeCN/0.036% TFA, at
a flow rate of 1 mL min-1; [R]D -84.19 (c 0.37, CHCl3); IR (film,
CH2Cl2) ν 3338, 2959, 2930, 2875, 1734, 1667, 1640, 1539,
1514, 1454, 1389, 1368, 1321, 1248, 1157, 1076 cm-1; 1H NMR
(500 MHz, CDCl3) δ 0.82-0.92 (24H, m), 1.11-1.19 (1H, m),
1.22 (3H, d, J ) 6.3), 1.32 (3H, d, J ) 6.5), 1.30-1.35 (1H, m),
1.40 (s, 9H), 1.35-1.63 (6H, m), 1.71-1.81 (2H, m), 1.93-2.07
(1H, m), 2.07-2.18 (2H, m), 2.28-2.34 (1H, m), 2.49 (1H, d, J
) 10.8), 2.52 (1H, d, J ) 10.5), 2.54 (3H, s), 2.72 (3H, bs), 2.79
(3H, bs), 2.86-2.94 (1H, bs), 3.15-3.18 (1H, dd, J 1 ) 14.5, J 2
) 4.5), 3.33-3.36 (1H, dd, J 1 ) 14.5, J 2 ) 4.5), 3.54-3.57 (1H,
dd, J 1 ) 10.5, J 2 ) 4.5), 3.56-3.61 (1H, m), 3.78 (3H, s), 3.96-
4.00 (1H, m), 4.03-4.08 (1H, m), 4.11-4.80 (1H, bs), 4.56-
4.62 (1H, m), 4.68-4.81 (3H, m), 4.99-5.01 (1H, q, J ) 3.5),
5.16 (1H, bs), 6.83 (2H, d, J ) 8.5), 6.95 (1H, bs), 7.07 (2H, d,
J ) 8.5), 7.21-7.25 (1H, bs), 7.95 (1H, bs); 13C NMR (75 MHz,
CDCl3) δ 11.55, 14.95, 15.26, 16.82, 18.56, 20.89, 22.00, 23.08,
23.76, 24.58, 24.85, 25.10, 27.12, 29.35, 29.35, 29.65, 29.69,
31.36, 33.96, 34.14, 38.51, 38.64, 40.14, 55.38, 55.56, 57.31,
66.17, 67.85, 70.58, 80.96, 80.98, 81.57, 114.12, 130.33, 158.63,
168.41, 169.33, 169.70, 170.38, 171.24, 172.28, 172.28, 172.93,
204.83; m/ z (FAB) 1066.3 [(M + Na)+, 31%], 1044.3 [(M + H)+,
100]. Anal. Calcd for C49H77N6O13: C, 56.43; H, 7.39; N, 8.06.
Found: C, 56.57; H, 7.37; N, 8.07.
Anal. Calcd for C62H87N5O16
: C, 64.30; H, 7.52; N, 6.05.
Found: C, 64.14; H, 7.66; N, 5.95.
Boc-Th r [H-N(Me)-O(Me)-Tyr ]-Ist-Hip-Leu -P r o-OH (5b).
Depsipeptide 5a (45 mg, 39.12 × 10-3 mmol) in THF (1.7 mL)
was hydrogenolyzed in the presence of 10% Pd-C (39 mg) at
rt and atmospheric pressure for 3 h. The mixture was filtered
through Celite and the solvent removed, giving the two
diastereomers of 5b (approximate proportions, 1:1) as an oil
(37 mg, 99%): RP-HPLC tR 14.7 and 15.2 min, Nucleosil C18
column, linear gradient from 10% B in A to 100% B over 20
min, followed by isocratic elution with 100% B for 10 min,
where A is H2O/0.045% TFA and B is MeCN/0.036% TFA), at
a flow rate of 1 mL min-1; 1H NMR (500 MHz, CDCl3) δ 0.79-
1.08 (18H, m), 1.80-1.38 (3H, m), 1.26 (3H, bs), 1.29 (3H, d, J
) 7.1), 1.47 (9H, s), 1.50-1.66 (3H, m), 1.84-1.94 (1H, m),
1.90-2.28 (4H, m), 2.35-2.50 (4H, m), 2.30-2.35 (1H, m),
2.44-3.18 (4H, m), 2.60 (3H, m), 3.53-3.61 (1H, m), 3.77 (3H,
s), 3.88-4.07 (4H, m), 4.12-4.72 (4H, m), 5.18-5.24 (1H, m),
5.24 (1H, bs), 6.84 (2H, d, J ) 7.9), 7.08 (2H, d, J ) 8.0), 7.13
(1H, d, J ) 8.2), 7.18 (1H, d, J ) 8.2), 7.62-7.68 (1H, bs); m/ z
(FAB) 972.7 [(M+K)+, 33], 934.9 (M+, 100].
Cyclo-N(Me )-O(Me )-Tyr -O-[Boc-Th r -]-Ist -H ip -Le u -
P r o (3a ). HATU (18 mg, 46.94 × 10-3 mmol), HOAt (7 mg,
47.73 × 10-3 mmol), and DIEA (13.3 µL, 78.24 × 10-3 mmol)
were added to a stirred solution of 5b (36 mg, 39.12 × 10-3
mmol) in THF (34 µL) at 0 °C. The mixture was allowed to
attain rt, and after 17 h the solvent was removed and the
residue taken up in AcOEt (10 mL) and washed with 5%
aqueous KHSO4 solution, 5% aqueous NaHCO3 solution, and
saturated aqueous NaCl solution. Drying and filtration fol-
lowed by solvent removal gave an oil (49 mg) that was purified
by chromatography (silica gel, AcOEt-hexanes, 1:1), giving
Did em n in A (1c). A 6 M solution of HCl in dioxane (2.8
mL) was added to a solution of 1b (32 mg, 30.65 × 10-3 mmol)
in dioxane (100 µL) and the solution stirred for 30 min. The
solvent was removed and chased with Et2O, giving 1c hydro-
chloride as a white solid (31 mg, 99%). The physical and
spectroscopic data obtained for this compound were identical

366 J . Org. Chem., Vol. 62, No. 2, 1997
J ou et al.
to those reported for the didemnin A obtained in the first
synthesis described above.
HPLC tR 19.0 and 19.8 min, linear gradient from 10% B in A
to 100% B over 20 min, followed by isocratic elution with 100%
B for 10 min, where A is H2O/0.045% TFA and B is MeCN/
0.036% TFA, at a flow rate of 1 mL min-1; Rf 0.40 and 0.28
(CH2Cl2-AcOEt, 2:3), 0.52 and 0.45 (CHCl3-MeOH, 9.5:0.5);
[R]D -95.9 (c 1.8, CHCl3); 1H NMR (500 MHz, CDCl3) δ 0.84-
0.93 (24H, m), 1.16-1.70 (9H, m), 1.72-1.81 (1H, m), 1.81-
1.90 (1H, m), 1.90-2.24 (6H, m), 2.30-2.39 (1H, m), 2.49 (3H,
s) 2.51 (3H, s), 2.55 (3H, s), 2.52-2.64 (1H, m), 2.85 (1H, bs),
2.94 (1H, bs), 3.09 (3H, s), 3.13 (3H, s), 3.15-3.18 (1H, m),
3.21-3.26 (1H, dd, J ) 15.8, 6.1), 3.32-3.36 (1H, dd, J 1 ) 14.5,
J 2 ) 4.1), 3.54-3.60 (1H, m), 3.66-3.72 (1H, m), 3.78 (3H, s),
3.80-3.87 (1H, m), 3.96-3.99 (1H, m), 4.03-4.11 (2H, m),
4.15-4.23 (1H, 2q, J ) 7.5), 4.55-4.57 (1H, 2d, J ) 5.5, 2.2),
4.59-4.62 (1H, t), 4.56-4.64 (1H, dd, J 1 ) 6.5, J 2 ) 2.5), 4.68-
4.71 (1H, t), 4.76-4.81 (1H, t), 5.10-5.18 (1H, m), 5.17 (1H,
d, J ) 3.5), 5.18 (1H, d, J ) 3.5), 5.27-5.31 (2H, m), 6.82 (2H,
d, J ) 8.5), 6.83 (2H, d, J ) 8.5), 7.05 (2H, d, J ) 8.5), 7.06
(2H, d, J ) 8.5), 7.02 (1H, d, J ) 7.1), 7.16 (1H, d, J ) 9.5),
7.17 (1H, d, J ) 9.5), 7.59 (1H, d, J ) 5.5), 7.77 (1H, d, J )
9.5), 7.83 (1H, d, J ) 9.4); 13C NMR (75 MHz, CDCl3) δ 11.63,
11.68, 14.11, 14.70, 15.26, 15.30, 16.00, 16.20, 16.88, 16.93,
18.62, 18.85), 20.89, 20.94, 21.62, 21.36, 23.44, 23.57, 23.84,
23.93, 24.66, 24.77, 24.85, 25.02, 26.22, 26.34, 27.09, 27.6,
27.06, 27.30, 27.95, 27.99, 29.33, 29.69, 31.31-31.37, 33.97,
34.06, 36.02, 36.45, 38.68, 38.76, 41.01, 41.15, 47.00, 48.42,
48.48, 48.86, 49.20, 49.51, 54.65, 54.75, 55.26, 55.58, 55.61,
57.14, 57.27), 57.47, 57.79, 66.24, 33.39, 67.80, 67.99, 70.34,
70.67, 81.0, 81.52, 114.10, 130.31, 156.0, 158.65, 161.1, 161.60,
168.20, 169.53, 169.59, 170.452, 171.25, 171.80, 171.95, 172.26,
172.33, 197.5, 204.80, 204.85; m/ z (FAB) 1132.6 [(M + Na)+,
42], 1110.8 [(M + H)+, 100].
P yr -P r o-OBzl (39). Pyruvic acid (1.58 mL, 22 mmol), DCC
(5.35 g, 26 mmol), HOBt (3.27 g, 24 mmol), and DIEA (3.67
mL, 22 mmol) were added to a solution of H-Pro-OBzl‚HCl
(6.26 g, 26 mmol) in CH2Cl2 (14 mL) at 0 °C, and after 5 min,
DIEA (4.4 mL, 26 mmol) was added and stirring was continued
for 32 h at rt. The mixture was filtered, the solvent removed,
and the residue taken up in AcOEt (50 mL) and washed with
5% aqueous KHSO4 solution, 5% aqueous NaHCO3 solution,
and saturated aqueous NaCl solution. Drying and filtration,
followed by solvent removal, gave an oil that was purifed by
chromatography (silica gel, AcOEt-hexanes, 3:7), giving 39
as an off-white solid (2.04 g, 36%): mp 42-47 °C; [R]D -66.8
(c 0.1, CHCl3); IR (film, CH2Cl2) ν 3035, 2956, 2884, 1744, 1717,
1645, 1499, 1443, 1383, 1352, 1273, 1175, 1092 cm-1; 1H NMR
(200 MHz, CDCl3) δ 1.75-2.40 (4H, m), 2.37 (3H, s), 2.44 (3H,
s), 3.45-3.82 (2H, m), 4.52-4.61 (1H, m), 4.88-4.97 (1H, m),
5.14-5.15 (2H, m), 5.17-5.20 (2H, m), 7.34 (5H, bs); 13C NMR
(50 MHz, CDCl3) δ 22.11, 25.22, 26.5, 27.10, 28.53, 31.48,
47.53, 44.81, 59.76, 67.02, 67.31, 128.11, 128.64, 135.24, 170.1,
170.2, 198 (CO); m/ z (CI) 293 [(M+NH4)+, 100]. Anal. Calcd
for C15H17NO4: C, 65.44; H, 6.22; N, 5.08. Found: C, 65.04;
H, 6.01; N, 5.11.
P yr -P r o-OH (40). Ester 39 (174 mg, 0.63 mmol) in THF
(4 mL) was hydrogenolyzed in the presence of 10% Pd-C
(containing 50% H2O) (105 mg) at rt and atmospheric pressure
for 3 h. The mixture was filtered through Celite, and solvent
removal gave an oil (120 mg) that was purified by chroma-
tography (silica gel, AcOEt-hexanes, 3:2) giving 40 as a white
solid (85 mg, 72%): mp 67-69 °C; [R]D -112 (c 0.12, CHCl3);
IR (film, CH2Cl2) ν 3450-3000, 2961-2870, 1719, 1643, 1615,
1452, 1354, 1205, 1175, 1094, 1018 cm-1; 1H NMR (200 MHz,
CDCl3) δ 1.85-2.45 (4H, m), 2.43 and 2.47 (3H, s), 3.42-3.85
(2H, m), 4.52-4.61 (1H, m), 4.88-4.97 (1H, m), 7.21-7.40 (1H,
bs); 13C NMR (75 MHz, CDCl3) δ 22.03, 25.23, 26.48, 27.00,
28.23, 31.44, 47.57, 48.37, 59.61, 59.395, 162.47, 162.52,
175.04, 176.29, 197.18; m/ z (CI) 220 [(M + N2H7)+, 15], 203
Ack n ow led gm en t. We thank PharmaMar SA, Min-
isterio de Educacio´n y Ciencia, Madrid, Spain (Grant
No. PB95-1131), and Generalitat de Catalunya (Grup
Consolidat [1995 SGR 494] i Centre de Refere`ncia en
Biotecnologia) for generous financial support of this
work. Samples of the natural didemnins were kindly
supplied by PharmaMar and by Dr. K. L. Rinehart.
[(M + NH4)+, 100], 186 [(M + H)+, 16]. Anal. Calcd for C8H11
-
NO4: C, 51.88; H, 5.99; N, 7.56. Found: C, 52.13; H, 5.85; N,
7.65.
Deh yd r od id em n in B (1e). Acid 40 (60 mg, 0.35 mmol)
in CH2Cl2 (350 µL), PyBroP (160 mg, 0.35 mmol) in CH2Cl2
(400 µL), and DIEA (87 µL, 0.51 mmol) were added to 1c (80
mg, 0.09 mmol), and the mixture was cooled to -5 °C and
stirred at this temperature for 30 min. The mixture was
allowed to attain rt, and after 4 h the solvent was removed
and the residue taken up in AcOEt (10 mL) and washed with
5% aqueous KHSO4 solution, 5% aqueous NaHCO3 solution,
and saturated aqueous NaCl solution. Drying and filtration
followed by solvent removal gave an oil (200 mg) that was
purified by chromatography (silica gel, AcOEt-CH2Cl2, 1:1),
giving 1e as a white solid (60 mg, 62%): mp 152-160 °C; RP-
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
all synthetic intermediates described in the experimental
section, including synthetic and natural didemnins, 1c and 1e.
1H-1H COSY spectra for compound 3a and for natural 1e. 1H-
1H TOCSY spectra for compounds 21, 5a , 4a , and 1a -e and
for natural 1c (44 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 O961932H