Synthesis of a reduced ring analog of didemnin B

Article abstract of DOI:10.1021/jo9623696

As part of investigations directed toward the determination of the essential/nonessential structural features for the bioactivities of didemnin B, we designed a reduced ring analog in which three moieties, namely the tyrosine side chain, the isostatine hydroxyl, and the side chain (L-lactyl- L-prolyl-N-Me-D-leucine), were in their presumed bioactive conformation. In designing the reduced ring analog, we eliminated the leucine-proline portion of the macrocycle core and replaced it with an n-butyl linker in order to elucidate its role. According to MM2 calculations (MacroModel molecular modeling), this analog was of lower energy than the natural product didemnin B, and both structures were superimposable. The synthetic strategy involved four disconnections. Macrocyclization was accomplished at the activated carboxylic acid of the α-(α-hydroxyisovaleryl)-propionyl unit (HIP) and the protected amine of the n-butyl linker using a modification of Schmidt's protocol. After selective deprotection of the hydroxyl and amino groups of the macrocycle, the peptide side chain was introduced using (benzotriazol-1- yloxy)tris(dimethylamino)phosphonium hexafluorophosphate (BOP) as the activating reagent.

Full text of DOI:10.1021/jo9623696

J . Org. Chem. 1997, 62, 4961-4969
4961
Syn th esis of a Red u ced Rin g An a log of Did em n in B
J oshi M. Ramanjulu, Xiaobin Ding, and Madeleine M. J oullie´*
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323
Wen-Ren Li
Department of Chemistry, National Central University, Chung-Li, Taiwan 32054, Republic of China
Received December 18, 1996X
As part of investigations directed toward the determination of the essential/nonessential structural
features for the bioactivities of didemnin B, we designed a reduced ring analog in which three
moieties, namely the tyrosine side chain, the isostatine hydroxyl, and the side chain (L-lactyl-L-
prolyl-N-Me-D-leucine), were in their presumed bioactive conformation. In designing the reduced
ring analog, we eliminated the leucine-proline portion of the macrocycle core and replaced it with
an n-butyl linker in order to elucidate its role. According to MM2 calculations (MacroModel
molecular modeling), this analog was of lower energy than the natural product didemnin B, and
both structures were superimposable. The synthetic strategy involved four disconnections.
Macrocyclization was accomplished at the activated carboxylic acid of the R-(R-hydroxyisovaleryl)-
propionyl unit (HIP) and the protected amine of the n-butyl linker using a modification of Schmidt’s
protocol. After selective deprotection of the hydroxyl and amino groups of the macrocycle, the peptide
side chain was introduced using (benzotriazol-1-yloxy)tris(dimethylamino)phosphonium hexafluo-
rophosphate (BOP) as the activating reagent.
In tr od u ction
The didemnins are an interesting class of cyclodep-
sipeptides isolated from a marine tunicate of the family
Didemnidae.1 Didemnins possess a varied degree of bio-
activities: antiviral, antitumor, and immunosuppres-
sive.2-7 Didemnin B (1b, Figure 1) was tested exten-
sively. Until now, 1b was thought to be the most active
didemnin.4-9 Recently isolated dehydrodidemnin B (1c),
an oxidized form of didemnin B, glutaminyldidemnin B,
and didemnin M have shown comparable or superior
cytotoxic activity.10,11 Most didemnins contain a common
macrocycle and differ only in the side chains attached to
the backbone through the amino group of threonine.
Didemnin B has undergone phase II clinical trials for
antitumor activity.8,12-16 Both didemnins A (1a ) and B
X Abstract published in Advance ACS Abstracts, J uly 1, 1997.
(1) Rinehart, K. L., J r.; Gloer, J . B.; Hughes, R. G., J r.; Renis, H.
E.; McGovren, J . P.; Swynenberg, E. B.; Stringfellow, D. A.; Kuentzel,
S. L.; Li, L. H. Science 1981, 212, 933.
(2) Rinehart, K. L., J r.; Gloer, J . B.; Wilson, G. R.; Hughes, R. G. J .;
Li, L. H.; Renis, H. E.; McGovren, J . P. Fed. Proc., Fed. Am. Soc. Exp.
Biol. 1983, 42, 87.
(3) 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.
(4) Rinehart, K. L., J r.; Cook, J . C., J r.; Pandey, R. C.; Gaudioso, L.
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 .
P.; Canonico, P. G. Pure Appl. Chem. 1982, 54, 2409.
(5) Montgomery, D. W.; Celniker, A.; Zukoski, C. F. Transplant.
Proc. 1987, 19, 1295.
(6) Canonico, P. G.; Pannier, W. L.; Huggins, J . W.; Rienehart, K.
L. Antimicrob. Agents Chemother. 1982, 22, 696.
(7) Legrue, S. J .; Sheu, T.-L.; Carson, D. D.; Laidlaw, J . L.; Sanduja,
S. K. Lymphokine Res. 1988, 7, 21.
(8) Malfetano, J . H.; Blessing, J . A.; Homesley, H. D.; Look, K. Y.;
McGehee, R. Am. J . Clin. Oncol. Cancer Clin. Trials 1996, 19, 184.
(9) Kucuk, O.; Young, M.; Hochster, H.; Haberman, T.; Wolf, B.;
Casileth, P. Proc. Am. Soc. Clin. Oncol. 1996, 15: Abstr. 1269.
F igu r e 1. Some naturally occurring didemnins.
(10) Sakai, R.; Stroh, J . G.; Sullins, D. W.; Rinehart, K. L. J . Am.
Chem. Soc. 1995, 117, 3734.
(11) Katauskas, A. J .; Rinehart, K. L. Abstracts of Papers, 213th
National Meeting of the American Chemistry Society, San Francisco,
CA, 1997; American Chemical Society: Washington, DC, 1997; ORG
348.
(1b) show antiviral activity against DNA and RNA
viruses,6,17 with didemnin B being more active. Didemnin
(12) Dorr, F. A.; Kuhn, J . G.; Phillips, J .; Von Hoff, D. D. Eur. J .
Cancer Clin. Oncol. 1988, 24, 1699.
(13) J acobs, A. J .; Blessing, J . A.; Munoz, A. Gynecol. Oncol. 1992,
44, 268.
S0022-3263(96)02369-9 CCC: $14.00 © 1997 American Chemical Society

4962 J . Org. Chem., Vol. 62, No. 15, 1997
Ramanjulu et al.
Sch em e 1
B has significantly greater immunosuppressive activity
than cyclosporin A, but it does not bind to the same
receptor site.18 Three sites were originally proposed as
being essential to biological activity on the basis of their
spatial relationship as determined from X-ray analysis19
and solution conformation of didemnin B:20 the tyrosine
side chain of the tetrapeptide region, the hydroxyl group
of isostatine, and the side chain attached to the amino
group of threonine. These three moieties lie on the
periphery of the highly irregular “bent figure eight”
macrocycle.
Previous experimental work has indeed shown that
biological activity is sensitive to changes in these pro-
posed areas. Removal of the O-methyl of the tyrosine
side chain reduced potency in all areas of activity21 and
the macrocycle salt (1d ) without the side chain was
essentially inactive.22 Acetylation of the isostatine hy-
droxyl group and of side-chain functionalities caused
several changes in the activity of didemnin B.10,17 Fi-
nally, natural didemnin B and nordidemnin B, which
differ in the isostatine region of the macrocycle where
isobutyl is replaced by isopropyl, were shown to have
comparable activity.23
The mechanism of action of the didemnins has not yet
been established. However, recent studies of possible
binding sites have yielded important results. In 1992,
Shen and co-workers reported that the immunosuppres-
sive activity of didemnin B is mediated through binding
to a site on Nb2 node lymphoma cells.21 In 1994,
Schreiber and co-workers found that a didemnin A
derivative binds to elongation factor 1R (eEF-1R) in a
GTP-dependent manner, which in turn inhibits protein
synthesis.24 Recently, Toogood and co-workers reported
that didemnin B inhibits the ability of eEF-2 to catalyze
polypeptide elongation, which demonstrates that it is an
inhibitor of ribosomal translocation.25
Resu lts a n d Discu ssion
spectra of didemnin B,20 we opted to replace the leucine
and proline residues with a covalent linker to introduce
conformational constraints and eliminate amino acids
that are not essential to biological activity. Elimination
of the proline-leucine portion might also reduce the
toxicity of didemnin B and increase its oral activity.
Various bridging units, needed to replace the only trans-
annular hydrogen bond present in the macrocycle, were
examined as options for connecting the free ends of the
isostatine-HIP unit. After examination of several bridg-
ing units, a n-butyl linker was found to be a suitable
replacement. The resulting structure is a 15-membered
ring (2, Scheme 1). This modification left all three
potentially active sites in a presumed “bioactive confor-
mation”. Visualization of this process was aided by using
a structure superposition program (MacroModel molec-
ular modeling). Calculations were performed using Mac-
roModel v3.1X on a Silicon Graphics Iris 4D/320S com-
puter. Minimizations were generated using PRCG,
followed by FNMR with MM2 force field. The proposed
structure was then compared to the presumed bioactive
didemnin B conformation. The two structures proved to
be remarkably similar by visual overlap comparison. In
an effort to compare this overlap by other means, we also
used MacroModel’s superposition subroutine, which cal-
culates the best fit and overlap standard deviation of the
selected atoms in the molecule. On a 3-D computer
screen, the overlay of the above-designed structure and
In recent years, introduction of covalent linkers replac-
ing amino acids that do not participate in receptor
occupation or activation has led to the syntheses of
comparable or more active analogs. This method was
used to develop analogs of smaller molecules such as
jaspamide and large peptides such as atrial natriuretic
factor.26 Upon examining the X-ray structure19 and NMR
(14) J ones, D. V.; Ajani, J . A.; Blackburn, R.; Daugherty, K.; Levin,
B.; Patt, Y. Z.; Abbruzzese, J . L. Investigational New Drugs 1992, 10,
211.
(15) Queisser, W. Onkologie 1992, 15, 454.
(16) Malfetano, J . H.; Blessing, J . A.; J acobs, A. J . Am. J . Clin.
Oncol. (CCT) 1993, 16, 47.
(17) Rinehart, K. L., J r. In U.S. Patent 4, 493, 796, 1985; p 1.
(18) Montgomery, D. W.; Zukoski, C. F. Transplantation 1985, 40,
49.
(19) 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.
(20) Kessler, H.; Will, M.; Antel, J .; Beck, H.; Sheldrick, G. M. Helv.
Chim. Acta 1989, 72, 530.
(21) Shen, G. K.; Zukoski, C. F.; Montgomery, D. W. Int. J .
Immunopharmacol. 1992, 14, 63.
(22) Mayer, S. C.; Carroll, P. J .; J oullie´, M. M. Acta Crystallogr.
1995, C51, 1609.
(23) J ouin, P.; Poncet, J .; Dufour, M.-N.; Aumelas, A.; Pantaloni,
A. J . Med. Chem. 1991, 34, 486.
(24) Crews, C. M.; Collins, J . L.; Lane, W. S.; Snapper, M. L.;
Schreiber, S. L. J . Biol. Chem. 1994, 269, 15411.
(25) SirDeshpande, B. V.; Toogood, P. L. Biochemistry 1995, 34,
9177.
(26) Kahn, M.; Su, T. In Proceedings of the Tenth American Peptide
Symposium; ESCOM; Leiden: St. Louis, MO, 1987; p 109.

Synthesis of an Analog of Didemnin B
J . Org. Chem., Vol. 62, No. 15, 1997 4963
F igu r e 2. (a) View of the minimized structure of didemnin B showing the fold of the cyclic peptide ring and the disposition of
possible interacting groups: the tyrosine side chain, the lactylproline moiety, and the hydroxyl group in isostatine. (b) Minimized
structure of reduced ring analog 2. (c) Overlay of didemnin B with reduced ring analog 2. (d) Another view (Chem 3D) of the
reduced ring analog 2 showing the intramolecular H-bond pattern. (e) Structure of reduced ring analog 2a .
didemnin B shows a rather remarkable correspondence
of the important functionalities, particularly the tyrosine
side chain, the lactyl proline moiety, and the hydroxyl
group of isostatine, as shown in Figure 2c. We retained
three hydrogen bonds (d, Figure 2) present in the natural
product. The side chain is held onto the main macrocycle
by means of a strong hydrogen bond between the carbonyl
of the side chain D-leucine and the amide of the n-butyl
linker. The conformation of the â(II) turn is dictated by
a hydrogen bond between the lactyl carbonyl and the
amide group of the threonine, and the turn is further
stabilized by the third hydrogen bond between the lactyl
hydroxyl and the tyrosine carbonyl.
Figure 2), which does not contain the N,O-dimethyl-
tyrosine portion, will be prepared in order to confirm that
the active region is the â(II)-turn region, as was observed
in jaspamide analogs.26 Preliminary biological testing of
a didemnin B analog in which the N,O-dimethyltyrosine
portion was replaced with N-MeLeu retained both cyto-
toxic and protein synthesis inhibition activities.27
Syn th etic Str a tegy. Our synthetic strategy involved
four disconnections that afforded four subunits: the
methyl 4-(azidobutyl)-Boc-D-leucinate (3); the dipeptide
N,O-diMeTyr-Thr (4); acetylated R-(R-hydroxyisovaleryl)-
propionyl) unit (acetylated HIP, 5); and didemnin B side
chain (6, Scheme 1). We introduced the optically pure
peptide side chain on the macrocycle as a separate step
at the end of the synthesis so that it could be easily
functionalized. The linear precursor leading to the
macrocycle was prepared in a stereoselective manner,
specifically preserving the stereochemistry of the 2-meth-
yl group of the HIP unit. We introduced the 3-keto group
of the HIP unit masked as a methoxymethyl (MOM)
ether to preserve the stereochemistry of the HIP unit,
so that deprotection and oxidation to the corresponding
ketone would occur only after macrocyclization. In the
macrocycle, the 3-keto group and the amide cannot lie
in the same plane; therefore, racemization at the 2-posi-
tion cannot occur readily.
At this time, we would like to emphasize two points:
1. The conformation of the threonine residue plays a
critical role in shaping the overall molecular conforma-
tion. Rotation of the tyrosine-threonine portion dramati-
cally interferes with two hydrogen bonds in the lactyl-
prolyl D-(NMe)-leucyl side chain and increases the
molecular mechanics energy (conformer energies vary
from 23 to 42 kcal/mol). Local conformation searching
has been carried out and has proven that b in Figure 2
is the local minimum conformer (E ) 23.03 kcal/mol, rms
(root mean square) ) 0.014 kJ /Å mol), even lower than
didemnin B (E ) 36.57 kcal/mol, rms ) 0.014 kJ /Å-mol).
2. After the role of the tetrapeptide is elucidated, and
if it is established that the N,O-dimethyltyrosine is not
essential to the specific biological activity, analog 2a (e,
(27) Pfizenmayer, A. J .; Ramanjulu, J .; Vera, M. D.; Ding, X.; Xiao,
D.; Chen, W.-C.; J oullie´, M. M. Bioorg. Med. Chem. Lett. 1996, 6, 2713.

4964 J . Org. Chem., Vol. 62, No. 15, 1997
Ramanjulu et al.
Sch em e 2
to be oxidized to a carboxylic acid. This operation was
accomplished by first removing the tert-butyldimethyl-
silyl group with HOAc/THF/H2O (3:1:1) to give the
corresponding alcohol 16, in 89% yield (Scheme 2). The
primary alcohol was then oxidized to its corresponding
carboxylic acid by a two-step oxidation method. Conver-
sion of the alcohol to the aldehyde was accomplished
using Dess-Martin periodinane reagent.32 The resulting
aldehyde was further oxidized without purification using
Masamune’s procedure.33 Treatment of the aldehyde
with potassium permanganate in tert-butyl alcohol,
buffered with 5% sodium hydrogen phosphate, gave the
carboxylic acid 17, in excellent yield.
To accomplish the cyclization, various phosphorus
coupling reagents as well as substituted carbodiimides
were used. However, macrocyclization proved far from
trivial. BOP, DPPA, 1,3-dicyclohexylcarbodiimide (DCC),
and BOP-Cl were unsuccessful. O-Benzotriazolyl-N,N,-
N′,N′-tetramethyluronium hexafluorophosphate (HBTU)
only gave minute amounts of product. Although pen-
tafluorophenyl diphenylphosphinate (FDPP) had been
used successfully in the macrocyclization of didemnin B,34
in this case, only a 20% yield could be obtained. As a
last resort, we utilized a modification of Schmidt’s
method.35 The Z-protected acid was treated with pen-
tafluorophenol to form the pentafluorophenyl ester. The
cyclization of the active ester to the desired macrocyle
was effected by in situ removal of the Z-protecting group
using cyclohexene or cyclohexadiene as the hydrogen
source to produce a slow evolution of hydrogen in the
presence of the catalyst (10% Pd/C), under high dilution
conditions, in dioxane at 95 °C, and with 4-pyrrolidi-
nopyridine as the base. The desired macrocycle (18) was
obtained in 59% yield (Scheme 2).
The next task was the deprotection of the various
protecting groups in a selective manner (Scheme 3). The
MOM group was removed with dimethylboron bromide
to give the corresponding secondary alcohol (19). Dess-
Martin oxidation32 of 19 afforded the ketone 20 in 99%
yield. Both the triisopropylsilyl group and the Boc group
were removed with hydrogen chloride gas in EtOAc, at
-30 to 0 °C, to yield the corresponding hydrochloride salt
of the macrocycle 21.
Syn th esis of th e P ep tid e Sid e Ch a in . Our ap-
proach to the peptide side chain began with Z-L-tyrosine
(Scheme 4). Treatment of Z-L-tyrosine in THF with
dimethyl sulfate and powdered KOH in the presence of
a phase-transfer catalyst, tetrabutylammonium hydrogen
sulfate, gave the ester 22 in good yield (Scheme 4).30 The
Z-protecting group was removed to yield 23,36 and the
secondary amine functionality was acetylated to give 24,
using acetic anhydride. Saponification of the methyl
ester of 24 gave the corresponding acid (25). Reaction
of the acid with Boc-Thr-OBn in presence of isopropenyl
chloroformate gave ester 26, which upon hydrogenation
provided the corresponding acid 4.
Syn th esis of th e Ma cr ocycle. Preparation of the
macrocycle began with the reductive amination28,29 of
D-leucine methyl ester (7) with 4-azidobutanal (prepared
by a two-step sequence: nucleophilic substitution of
4-chloro-1-butanol, followed by Swern oxidation of the
corresponding alcohol) to afford a secondary amine (8,
Scheme 2). The amine functionality was immediately
protected as its Boc derivative, and the azide was reduced
to a primary amine (9), which was converted to its
N-(benzyloxycarbonyl) (Z) derivative (10). The methyl
ester was saponified to afford the corresponding acid (11).
The acid was activated using pentafluorophenol and
DCC, and the resulting pentafluorophenyl ester (12) was
directly condensed with the lithium enolate of the HIP-
acetate to produce the â-keto ester 13 in 71% yield.
HIP-acetate was synthesized using previous methodol-
ogy.30 The reduction of the â-keto ester was accomplished
with selectivity for the anti diastereomer, using potas-
sium borohydride in ethanol31 to afford a diastereomeric
mixture of alcohols (14, Scheme 2), which was not
separated but treated with triisopropylsilyl triflate, to
give a chromatographically separable mixture of two silyl
ethers. The ratio of these two diastereomers was found
to be 6:1 (15, Scheme 2). To effect cyclization, the
protected primary hydroxyl group in the HIP-unit had
With the macrocycle salt 21 and the peptide side chain
4 in hand, we used the BOP reagent to provide 27 in 67%
yield (Scheme 3). The Boc group was removed under
(32) Dess, D. B.; Martin, J . C. J . Am. Chem. Soc. 1991, 113, 7277.
(33) Abiko, A.; Roberts, J . C.; Takemasa, T.; Masamune, S. Tetra-
hedron Lett. 1986, 27, 4537.
(28) Abdel-Magid, A. F.; Maryanoff, C. A.; Carson, K. G. Tetrahedron
Lett. 1990, 31, 5595.
(29) Abdel-Magid, A. F.; Maryanoff, C. A. Synlett 1990, 537.
(30) Li, W.-R.; Ewing, W. R.; Harris, B. D.; J oullie´, M. M. J . Am.
Chem. Soc. 1990, 112, 7659.
(34) Mayer, S. C.; Ramanjulu, J .; Vera, M. D.; Pfizenmayer, A.;
J oullie´, M. M. J . Org. Chem. 1994, 59, 5192.
(35) Heffner, R. J .; J iang, J .; J oullie´, M. M. J . Am. Chem. Soc. 1992,
10181.
(36) Belagali, S. L.; Mathew, T.; Himaja, M.; Kocienski, P. Indian
J . Chem. 1995, 34B, 45.
(31) Harris, B. D.; J oullie´, M. M. Tetrahedron 1988, 44, 3489.

Synthesis of an Analog of Didemnin B
J . Org. Chem., Vol. 62, No. 15, 1997 4965
Sch em e 3
amino group and cyclization in one pot via an improved
version of Schmidt’s protocol. Selective removal of the
protecting groups and the attachment of the side chain
were accomplished using previously reported methodolo-
gies.30,34 The diverse biological activities of this reduced
ring analog will be tested and compared to those of
didemnin B in the near future.
Exp er im en ta l Section
Gen er a l P r oced u r es. Materials were described previ-
ously.34 Proton and carbon magnetic resonance spectra (1H-
and 13C-NMR) were recorded on a Bruker AM-500 (500 MHz)
Fourier transform spectrometer, and chemical shifts were
expressed in parts per million (δ) relative to tetramethylsilane
(TMS 0 ppm) or CHCl3 as an internal reference (7.24 ppm for
1H and 77.0 ppm for 13C). Infrared spectra (IR) were obtained
on a Perkin-Elmer Model 281-B or a Perkin-Elmer Model 781
spectrometer. Absorptions are reported in wavenumbers
(cm-1), and the spectra are calibrated against the 1601 cm-1
band of a polystyrene film. Optical rotations (in degrees) were
recorded on a Perkin-Elmer Model 241 polarimeter at the
sodium D line. High-resolution mass spectra (HRMS) were
obtained on either a VG 70-70HS [a high-resolution double-
focusing mass spectrometer using ammonia chemical ioniza-
tion (CI) or electron impact (EI)] or a ZAB-E [using fast atom
bombardment (FAB), CI, or EI]. Gas chromatograms were
obtained on a Hewlett-Packard 5890 GC incorporating a HP-1
cross-linked methyl silicone gum capillary column. Elemental
analyses were performed by either Desert Analytics, Tucson,
AZ, or University of Pennsylvania Chemistry Department
Elemental Analysis Facility.
standard conditions, and the resulting amine was coupled
to the didemnin B side chain (6), thereby completing the
synthesis of the reduced ring analog 2.
All molecular modeling calculations were performed using
Macro Model v3.1X on
a Silicon Graphics Iris 4D/320S
computer. Minimizations were generated from X-ray coordi-
nates using PRCG followed by FNMR with the MM2 force field
to obtain overlays with rms values less than 0.050.
Con clu sion s
Meth yl N-(4-Azid obu tyl)-D-leu cin a te (8). 4-Azido-1-bu-
tanal was prepared from commercially available 4-chloro-1-
butanol. Displacement of chlorine with sodium azide, followed
by oxidation under Swern’s conditions, gave the aldehyde in
The X-ray analysis of the didemnins suggested that
three structural features are essential for their biological
activity: the side chain attached to the amino group of
threonine, the isostatine hydroxyl group, and the tyrosine
side chain. Since no modifications in the leucine-proline
dipeptide unit of the macrocycle had been reported, we
decided to elucidate its role in determining bioactivity
and overall conformation. A molecular-modeling study
revealed that the reduced ring analog (2) and didemnin
B overlaid well and that three of the four hydrogen bonds
were retained.
1
72% overall yield: Rf 0.58 (20% EtOAc/petroleum ether); H
NMR (CDCl3) δ 1.80-2.00 (m, 2H), 2.40-2.60 (m, 2H), 3.20-
3.45 (m, 2H), 9.80 (s, 1H); 13C NMR (CDCl3) δ 21.47, 40.76,
50.58, 200.80; IR (neat) 2922 (w), 2360 (w), 2099 (s), 1715 (s),
1257 (w) cm-1
.
To a solution of 7 (0.83 g, 5.71 mmol) in 20 mL of 1,2
dichloroethane (DCE) was added 4-azido-1-butanal (0.65 g,
5.75 mmol) in 3 mL of DCE. To this mixture were added acetic
acid (0.33 mL, 5.70 mmol) and sodium triacetoxyborohydride
(1.70 g, 8.02 mmol). After 12 h, the reaction was diluted with
CH2Cl2 (30 mL), and the excess reagent was quenched by
dropwise addition of ammonium chloride. The reaction mix-
ture was washed with 5% HCl, 5% NaHCO3, and saturated
The synthesis of the macrocycle was accomplished
mainly by three key reactions: reductive amination using
sodium triacetoxyborohydride, a stereoselective reduction
of the â-keto ester, and finally in situ deprotection of the
Sch em e 4

4966 J . Org. Chem., Vol. 62, No. 15, 1997
Ramanjulu et al.
NaCl solutions. The organic layer was dried (Na2SO4), filtered,
and concentrated. The resulting crude oil was purified by
column chromatography, eluting with MeOH/CHCl3 (5:95).
Pure compound 8 (1.22 g, 83%) was obtained as an oil: Rf 0.55
(10:90 MeOH:CHCl3); 1H NMR (CDCl3) δ 0.93 (d, J ) 6.6 Hz,
3H) and 0.91 (d, J ) 6.6 Hz, 3H), 1.42-1.49 (m, 2H), 1.51-
1.58 (m, 2H), 1.62-1.68 (m, 3H), 1.71-1.73 (m, 1H), 2.45 and
2.63 (ABX, J ) 6.90, 4.30 Hz, 2H), 3.25-3.29 (m, 3H), 3.72 (s,
3H); 13C NMR (CDCl3) δ 22.2, 22.7, 24.7, 24.8, 26.5, 27.2, 42.7,
47.4, 51.2, 59.8, 176.4; IR (neat) 2956 (s), 2097 (s), 1744 (s)
cm-1; HRMS m/ z calcd for C11H23N4O2 (M + H) 243.1821,
The reaction was stirred at 0 °C for 4 h, concentrated to 50
mL, and washed with ether (2 × 20 mL). The combined ether
layers were extracted with saturated NaHCO3 (10 mL) solu-
tion. The aqueous layers were combined and acidified to pH
1 with 1 N potassium hydrogen sulfate solution. The acidified
aqueous layer was extracted with ether (3 × 100 mL). The
ether extracts were dried (Na2SO4), filtered, and concentrated.
Compound 11 (6.34 g, 91%) was used directly in the next
1
step: Rf 0.60 (10:90 MeOH:CHCl3); H NMR (CDCl3) δ 0.94
(d, J ) 5.2 Hz, 6H), 1.44 (s, 9H), 1.62-1.79 (m, 7H), 3.00-
3.41 (m, 4H), 4.19-4.22 and 4.34-4.36 (m, 1H), 5.09 (m, 3H),
7.31-7.34 (m, 5H); 13C NMR (CDCl3) δ 23.1, 24.9, 25.9, 26.2,
27.3, 28.3 (3 overlapping carbons), 40.6, 46.1, 58.3, 58.5, 66.6,
80.5, 128.5, 128.0, 136.9 (3 overlapped carbons), 156.5 (over-
lapping carbon), 177.0; IR (neat) 3339 (br), 2957 (s), 1695 (br
and s) cm-1; HRMS m/ z calcd for C23H37N2O6 (M + H)
found 243.1825; [R]25 +8.89° (c ) 1.35, CHCl3).
D
Meth yl N-Boc-N-(4-a zid obu tyl)-D-leu cin a te (3). Amine
8 (4.00 g, 0.0155 mol) was dissolved in CH2Cl2 (70 mL) and
treated with triethylamine (6.59 mL, 0.047 mol) and Boc
anhydride (6.90 g, 0.032 mol). The reaction mixture was
refluxed overnight. After this time, the reaction was cooled
and diluted with ether. The organic solution was washed with
5% HCl, 5% NaHCO3, and saturated NaCl solutions. The
ether layer was dried (Na2SO4), filtered, and concentrated. The
resulting crude oil was purified by column chromatography,
eluting with EtOAc/petroleum ether (10:90). Pure compound
3 (4.63 g, 87%) was obtained as an oil: Rf 0.37 (10:90 EtOAc:
petroleum ether); 1H NMR (CDCl3) δ 0.87-0.90 (m, 6H), 1.53
(s, 9H), 1.58-1.70 (m, 5H), 2.95 (m, 1H), 3.20 (m, 2H), 3.30
(m, 2H), 3.60 (s, 3H), 4.10 and 4.50 (m, 1H); 13C NMR (CDCl3)
δ 21.8, 22.9, 24.7, 26.4, 26.7, 28.3, 45.3, 46.4, 50.7, 51.1, 51.9,
56.9, 58.1, 80.2, 155.0, 172.5; IR (neat) 2956 (s), 2870 (s), 2096
(s), 1744 (s), 1697 (s) cm-1; HRMS m/ z calcd for C16H30N4O4
437.2651, found 437.2643; [R]25 +21.99° (c ) 4.30, CHCl3);
D
Anal. Calcd for C23H36N2O6: C, 63.28; H, 8.31; N, 6.42.
Found: C, 63.45; H, 8.03; N, 6.09.
P en ta flu or op h en yl N-Boc-N-[4-[N-(ben zyloxyca r bon -
yl)a m in o]bu tyl]-D-leu cin a te (12). To the solution of 11
(0.45 g, 1.28 mmol) in CH2Cl2 (3 mL) were added DCC (0.32
g, 1.53 mmol) and pentafluorophenol (0.24 g, 1.53 mmol). The
reaction was stirred at room temperature for 12 h. After this
time, the reaction mixture was diluted and the solid material
collected by filtration. The solid was washed with ether, and
the organic layer was washed with 5% HCl, 5% NaHCO3
, and
saturated NaCl solutions. The ether layer was dried (Na2SO4),
filtered, and concentrated. The resulting crude oil was purified
by column chromatography, eluting with EtOAc/petroleum
ether (20:80). Pure compound 12 (0.67 g, 67%) was obtained
as an oil: Rf 0.60 (20:80 EtOAc:petroleum ether); 1H NMR
(CDCl3) δ 0.92-0.99 (m, 6H), 1.46 (s, 9H), 1.50-2.00 (m, 7H),
3.15-3.25 (m, 2H), 3.71-3.78 (m, 2H), 4.50-4.80 (m, 1H), 4.90
(m, 1H), 5.10 (s, 2H), 7.25-7.40 (m, 5H); 13C NMR (CDCl3) δ
22.0, 23.1, 24.9, 25.9, 26.17, 27.3, 28.3, 40.6, 46.1, 66.6, 80.5,
125.5, 127.9, 128.0, 128.3, 134.9, 136.8, 136.8, 138.3, 140.0,
142.2, 154.5 (overlapping carbon), 154.7, 156.5, 169.1; IR (neat)
3336 (m), 2960 (m), 1789 (s), 1697 (s) cm-1; HRMS m/ z calcd
(M + H) 343.2345, found 343.2348; [R]25 +36.89° (c ) 5.45,
D
CHCl3).
Meth yl N-Boc-N-(4-a m in obu tyl)-D-leu cin a te (9). To a
CH3OH/EtOAc solution (1:1, 20 mL) was added 10% Pd/C (1.0
g). To the resulting suspension was added compound 3 (3.50
g, 9.78 mmol) in CH3OH (5 mL). The solution was subjected
to an atmosphere of hydrogen (40 psi) and shaken for 3 h in a
Parr hydrogenation apparatus. The reaction mixture was
filtered through Celite. The Celite bed was washed with CH3-
OH, and the filtrate was concentrated. The resulting amine
9 (3.0 g, 97%) was used directly in the next step: 1H NMR
(CDCl3) δ 0.84 (d, J ) 6.56 Hz, 6H), 1.32 (s, 9H), 1.41-1.66
(m, 7H), 2.87-2.92 (m, 1H) and 3.15-3.22 (m, 3H), 3.31-3.32
(m, 2H), 3.58 (s, 3H), 4.01-4.07 and 4.78-4.81 (m, 1H); 13C
NMR (CDCl3) δ 21.6, 23.0, 24.7, 25.6, 27.1, 28.0, 44.7, 51.0,
51.9, 57.3, 58.1, 80.1, 155.1, 171.2; IR (neat) 3364 (br), 2955
(s), 1743 (m), 1695 (s), cm-1; HRMS m/ z calcd for C16H33N2O4
for C29H39N3O6F5 (M+NH4) 620.2759, found 620.2752; [R]25
+21.20° (c ) 1.37, CHCl3).
D
(4R)-4-[[4-[(Ben zyloxyca r bon yl)a m in o]bu tyl](ter t-bu -
t oxyca r b on yl)a m in o]-6-m et h yl-3-oxoh ep t a n oic
Acid
(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 (13). To the
solution of HIP-Ac (5, 6.50 g, 0.018 mol) in dry THF (50 mL)
at -78 °C was added LDA (90 mL, 0.018 mol). The solution
was stirred at -78 °C for 1 h. The solution containing the
enolate of HIP-Ac was then added dropwise, with vigorous
stirring, to the solution containing the pentafluorophenyl ester
12 (2.32 g, 4.48 mmol). The reaction mixture was stirred for
4 h at -78 °C. After this time, saturated ammonium chloride
(100 mL) and ether (500 mL) were added. The aqueous layer
was separated and extracted with ether (2 × 100 mL), and
the combined ether layers were washed with 5% HCl, 5%
(M + H) 317.2440, found 317.2447. [R]25 +39.90° (c ) 4.52,
D
CHCl3).
Met h yl N-Boc-N-[4-[N-(b en zyloxyca r b on yl)a m in o]-
bu tyl]-D-leu cin a te (10). The primary amine 9 (1.07 g, 3.37
mmol) was dissolved in CH2Cl2 (20 mL) and cooled to 0 °C. To
this solution were added N-[(benzyloxycarbonyl)oxy]succinim-
ide (1.0 g, 4.04 mmol) and triethylamine (0.56 mL, 4.04 mmol).
The reaction was stirred overnight and diluted with ether (100
mL). The organic solution was washed with 5% HCl, 5%
NaHCO3, and saturated NaCl solutions. The ether layer was
dried (Na2SO4), filtered, and concentrated. The resulting crude
oil was purified by column chromatography, eluting with
EtOAc/petroleum ether (30:70). Pure compound 10 (1.41 g,
93%) was obtained as an oil: Rf 0.53 (30:70 EtOAc:petroleum
NaHCO3
, and saturated NaCl solutions. The ether layer was
dried (Na2SO4), filtered, and concentrated. The resulting crude
oil was purified by column chromatography, eluting with
EtOAc/petroleum ether (20:80). Pure compound 13 (2.21 g,
71%) was obtained as an oil: Rf
0.58 (20:80 EtOAc:petroleum
1
1
ether); H NMR (CDCl3) δ 0.86 (d, J ) 3.2 Hz, 3H) and 0.87
ether); H NMR (CDCl3) δ 0.02 (s, 6H), 0.74-0.98 (m, 21H),
1.21-1.62 (m, 18H), 1.74-1.88 (m, 3H), 2.92-3.26 (m, 4H),
3.29 (s, 3H), 3.63-3.67 and 3.30-3.48 (m, 4H), 3.78 (d, J )
5.9 Hz, 1H), 4.58-4.61 (m, 3H), 4.89-5.21 (m, 4H), 7.26-7.34
(d, J ) 3.0 Hz, 3H), 1.35 (s, 9H), 1.42-1.67 (m, 6H), 1.68-
1.70 (m, 1H), 2.90-2.92 (m, 1H), 3.12-3.20 (m, 3H), 3.59 (s,
3H), 4.01-4.07 and 4.49-4.54 (m, 1H), 5.00 (s, 2H), 6.07 (s,
1H), 7.20-7.29 (m, 5H); 13C NMR (CDCl3) δ 21.7, 22.9, 24.6,
25.7, 26.6, 27.1, 28.2 (3 overlapping carbons), 44.7, 46.4, 51.9,
56.9, 66.4, 80.2, 128.4, 129.1, 133.3, 133.5, 134.6, 136.6, 155.1,
156.6, 169.4; IR (neat) 3353 (m), 2955 (s), 2869 (m), 1741 (s),
1697 (s) cm-1; HRMS m/ z calcd for C24H39N2O6 (M + H)
(m, 5H);
13C NMR (CDCl3) δ -5.49 (3 overlapping carbons),
10.5, 15.8, 18.1, 19.8, 24.8, 28.3 (3 overlapping carbons), 28.8
(3 overlapping carbons), 37.4, 37.5, 37.7, 40.4, 45.05, 46.1, 55.9,
62.4, 64.5 66.6, 78.9, 79.7, 81.3, 98.9, 128.0, 128.5, 128.6, 136.6
(3 overlapping carbons), 156.4, 157.0, 167.3, 200.8; IR (neat)
3343 (br), 2958 (s), 2933 (s), 1710 (s), 1696 (s), 1643 (w) cm-1
451.2808, found 451.2803; [R]25 +32.29° (c ) 1.25, CHCl3).
;
D
HRMS m/ z calcd for C41
H72N2O10Si (M + Na) 803.4854, found
Anal. Calcd for C24H38N2O6: C, 63.98; H, 8.50; N, 6.22.
Found: C, 63.93; H, 8.23; N, 5.89.
803.4869; [R]25
+19.97° (c ) 1.89, CHCl3).
D
N-Boc-N-[4-[N-(ben zyloxycar bon yl)am in o]bu tyl]-D-leu -
cin e (11). Compound 10 (8.01 g, 0.018 mol) was dissolved in
THF/H2O (1:1, 100 mL). The reaction was cooled to 0 °C, and
lithium hydroxide monohydrate (4.45 g, 0.106 mol) was added.
(4R)-4-[[4-[(Ben zyloxyca r bon yl)a m in o]bu tyl](ter t-bu -
toxyca r bon yl)a m in o]-3-h yd r oxy-6-m eth ylh ep ta n oic Acid
(1S,2S,3R)-4-[(ter t-Bu tyld im eth ylsilyl)oxy]-1-isop r op yl-
2-(m et h oxym et h oxy)-3-m et h ylb u t yl E st er (14). Potas-

Synthesis of an Analog of Didemnin B
J . Org. Chem., Vol. 62, No. 15, 1997 4967
sium borohydride (0.58 g, 0.011 mol) was added in portions to
â-keto ester 13 (1.66 g, 2.39 mmol) in absolute ethanol (20 mL)
and at 0 °C. The reaction mixture was stirred at 0 °C for 1 h
and then at ambient temperature for 24 h. A 1 N HOAc
solution was added dropwise until the aqueous layer was
neutral to litmus. The resulting solution was concentrated,
dissolved in ether, and washed with 5% HCl, 5% NaHCO3, and
saturated NaCl solutions. The ether layer was dried (Na2SO4),
filtered, and concentrated. The resulting crude oil was purified
by column chromatography eluting with EtOAc/petroleum
ether (20:80). Pure compound 14 (1.46 g, 78%) was obtained
as an oil: Rf 0.49 (20:80 EtOAc:petroleum ether); 1H NMR
(CDCl3) δ 0.05 (s, 6H), 0.89-0.92 (m, 24H), 1.45 (s, 9H), 1.16-
1.76 (m, 9H), 2.50-2.55 (m, 2H), 3.08-3.17 (m, 5H), 3.34 (s,
3H), 3.39-3.82 (m, 3H), 3.96-4.00 (brs, 1H), 4.20-4.31 (m,
1H), 4.59-4.64 (m, 2H), 5.04-5.08 (m, 4H), 7.26-7.34 (m, 5H);
13C NMR (CDCl3) δ -5.5 (3 overlapping carbons), 10.4, 15.8,
18.1, 19.9, 20.1, 20.4, 20.6, 20.9, 22.7, 25.8, 28.4 (3 overlapping
carbons), 28.7 (3 overlapping carbons), 37.5, 37.5, 39.1, 39.5,
40.4, 42.3, 42.5, 46.1, 48.1, 56.0, 64.9, 66.5, 78.6, 78.8, 78.9,
79.3, 99.0, 127.9, 128.4, 128.4, 136.7 (2 overlapping carbons)
155.1, 156.4, 170.8; IR (CHCl3) 3344 (br), 2958 (s), 2932 (s),
1693 (br and s), 1534 (m), 1516 (s) cm-1; HRMS m/ z calcd for
bu toxyca r bon yl)a m in o]-6-m eth yl-3-[(tr iisop r op ylsilyl)-
oxy]h ep ta n oic Acid (1S,2S,3R)-3-Ca r boxy-1-isop r op yl-2-
(m eth oxym eth oxy)bu tyl Ester (17). To a solution of the
alcohol 16 (27 mg, 0.033 mmol) in CH2Cl2 (1.0 mL) was added
1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-3(1H)-one (Dess-
Martin periodinane reagent, 19 mg, 0.05 mmol). The reaction
was stirred for 0.5 h and diluted with ether (5.5 mL). This
slurry was poured into saturated aqueous NaHCO3 (2.1 mL)
containing Na2S2O3‚5H2O (86.38 mg). After the slurry was
stirred for 5 min, an additional amount of Et2O (5 mL) was
added. The combined organic layers were washed with
saturated aqueous NaHCO3 (2.1 mL) and H2O (2.1 mL), dried
(Na2SO4), filtered, and concentrated. The residue was dis-
solved in tert-BuOH (1.91 mL), keeping the temperature at
25 °C. To this solution was added 5% aqueous NaH2PO4 (1.26
mL) followed by 1 M aqueous KMnO4 (1.91 mL) dropwise. The
reaction was stirred at 25 °C for 1 h at which time Et2O (66
mL) was added. After the solution was cooled to 0 °C,
saturated aqueous Na2SO3 (30 drops) was added with efficient
stirring. A 10% aqueous HCl solution was added until the pH
of the aqueous layer reached exactly 3 (use caution not to go
below). The aqueous layer was extracted with EtOAc (30 mL),
and the combined organic layers were dried (Na2SO4), filtered,
and concentrated to obtain the product 17 (27 mg) in 99%
C41H74N2O10Si (M + Na) 805.5011, found 805.5003. [R]25
D
1
+17.68° (c ) 6.55, CHCl3).
yield: Rf 0.71 (12:4:1 CHCl3:MeOH:NH3); H NMR (CDCl3) δ
0.83-1.12 (m, 34H), 1.23-1.82 (m, 16H), 1.98-2.05 (m, 1H),
2.53-2.74 (m, 2H), 2.81-2.88 (m, 1H), 3.03-3.40 (m, 8H), 3.39
(s, 3H), 3.95-3.97 (m, 1H), 4.25-4.41 (m, 2H), 4.65-4.78 (m,
3H), 5.09 (s, 2H), 7.33-7.36 (m, 5H); 13C NMR (CDCl3) δ 12.6
(9 overlapping carbons), 17.7, 18.3, 19.1, 22.1, 28.4 (3 overlap-
ping carbons), 28.8, 28.7, 29.7, 39.6, 40.4, 40.8, 41.1, 43.1 56.1,
59.7, 66.6, 72.2, 72.6, 73.1, 78.5, 79.6, 98.3, 128.1, 128.3, 128.4,
128.5, 129.9, 130.1, 156.3, 156.8, 169.6, 176.5; IR (neat) 3400
(br), 2946 (s), 1733 (s), 1690 (s) cm-1; HRMS m/ z calcd for
C44H78N2O11 (M + Na) 861.1967, found 861.1957; [R]25D +3.31°
(c ) 0.83, CHCl3).
(3S,4R)-4-[[4-[(Ben zyloxyca r bon yl)a m in o]bu tyl](ter t-
bu toxyca r bon yl)a m in o]-6-m eth yl-3-[(tr iisop r op ylsilyl)-
oxy]h ep t a n oic Acid (1S,2S,3R)-4-[(ter t-Bu t yld im et h yl-
silyl)oxy]-1-isop r op yl-2-(m e t h oxym e t h oxy)-3-m e t h yl-
bu tyl Ester (15). To alcohol 14 (0.69 g, 0.88 mmol), in CH2-
Cl2 (5 mL) and at 0 °C, was added 2,6-lutidine (0.31 mL, 2.66
mmol). To the resulting solution was added dropwise triiso-
propylsilyl triflate (0.36 mL, 1.34 mmol). The reaction mixture
was stirred at 0 °C for 6 h. After the reaction was complete,
it was diluted with 20 mL of ether. The organic layer was
washed with 5% HCl, 5% NaHCO3, and saturated NaCl
solutions. The ether layer was dried (Na2SO4), filtered, and
concentrated. The resulting crude oil was purified by column
chromatography eluting with EtOAc/petroleum ether (5:95).
Pure compound 15 (1.46 g, 78%) was obtained as an oil: Rf
5(R)-Isobu tyl-15(S)-isopr opyl-14(S)-(m eth oxym eth oxy)-
13(S)-m et h yl-2,12-d ioxo-4(S)-[(t r iisop r op ylsilyl)oxy]-1-
oxa -6,11-d ia za cyclop en ta d eca n e-6-ca r boxylic Acid ter t-
Bu tyl Ester (18). Acid 17 (30 mg, 0.036 mmol) was dissolved
in CH2Cl2 (2 mL). To this solution were added DCC (9 mg,
0.043 mmol), pentafluorophenol (8 mg, 0.043 mmol), and
DMAP (2 mg, 0.016 mmol) sequentially. The reaction was
stirred at room temperature for 12 h. The reaction mixture
was diluted with ether (5 mL) and filtered. The solid was
washed with an additional 5 mL of ether, and the organic layer
was washed with 5% HCl, 5% NaHCO3, and saturated NaCl
solutions. The ether layer was dried (Na2SO4), filtered, and
concentrated. The resulting crude oil was purified by column
chromatography eluting with EtOAc/petroleum ether (20:80).
The corresponding pure pentafluorophenyl ester (0.025 g, 68%)
was used in the next step. To a mixture of freshly distilled
dioxane (22 mL) containing 10% palladium on carbon (8.4 mg),
absolute ethanol (0.52 mL), and 4-pyrrolidinopyridine (9 mg,
0.065 mmol) at 95 °C was added over a period of 1.5 h a
solution of the activated ester (22 mg, 0.022 mmol) and
cyclohexene (1.97 mL) in dioxane (4 mL). After the addition,
the reaction was allowed to stir for 48 h, at which time it was
cooled to 25 °C and filtered through a bed of Celite. The
filtrate was concentrated under reduced pressure to afford a
crude oil. This oil was purified by column chromatography
eluting with EtOAc/petroleum ether (50:50) to provide pure
macrocycle 18 (8.6 mg, 58%): Rf 0.57 (50% EtOAc/petroleum
ether); 1H NMR (CDCl3) δ 0.91-1.23 (m, 36H), 1.37-1.38 (m,
2H), 1.46 (s, 9H), 1.57-1.94 (m, 5H), 2.06-2.10 (m, 1H), 2.31-
2.33 and 2.45-2.48 (m, 2H), 2.63-2.64 and 2.82-2.84 (m, 2H),
2.84-2.86 (m, 1H), 3.16-3.20 and 3.40-3.43 (m, 2H), 3.45 (s,
3H), 3.78-3.80 (m, 1H), 3.90 (d, J ) 6.5 Hz, 1H), 4.23 (dd, J
1
0.25 (20:80 EtOAc:petroleum ether); H NMR (CDCl3) δ 0.04
(s, 6H), 0.89-1.08 (m, 47H), 1.41 (s, 9H), 1.41-1.95 (m, 7H),
2.42-2.50 and 2.70-2.85 (m, 2H), 3.05-3.50 (m, 7H), 3.34 (s,
3H), 3.79 (m, 1H), 4.27-4.35 (m, 1H), 4.57-4.64 (m, 3H), 4.91-
4.97 (m, 1H), 5.09 (s, 2H), 7.26-7.35 (m, 5H); 13C NMR (CDCl3)
δ 12.7 (9 overlapping carbons), 16.3, 17.7, 18.2, 18.3, 19.7, 20.1,
20.4, 20.6, 20.9, 22.1, 28.4 (3 overlapping carbons), 28.7 (3
overlapping carbons), 37.6, 39.1, 40.9, 41.0, 43.0, 55.9, 56.0,
65.2, 66.6, 72.6, 78.7, 78.8, 79.9, 98.4, 127.9, 128.0, 128.4, 136.8
(2 overlapping carbon) 156.3 (overlapping carbon), 170.8; IR
(neat) 3356 (w), 2955 (s), 2867 (m), 1731 (m), 1691 (s), 1591
(s) cm-1; HRMS m/ z calcd for C50H94N2O10Si2 (M + Na)
961.6345, found 961.6301; [R]25 -8.19° (c ) 2.02, CHCl3).
D
(3S,4R)-4-[[4-[(Ben zyloxyca r bon yl)a m in o]bu tyl](ter t-
bu toxyca r bon yl)a m in o]-6-m eth yl-3-[(tr iisop r op ylsilyl)-
oxy]h ep ta n oic 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 (16). To compound
15 (0.15 g, 0.16 mmol) in THF (2 mL) was added HOAc/H2O
(3:1, 8 mL). After 16 h, the reaction was diluted with toluene
(40 mL) and concentrated until no HOAc remained. The crude
oil was then purified by column chromatography eluting with
EtOAc/petroleum ether (20:80). Pure compound 16 (0.12 g,
89%) was obtained as an oil: Rf 0.22 (20:80 EtOAc:petroleum
1
ether); H NMR (CDCl3) δ 0.83-0.99 (m, 15H), 1.09 (s, 21H),
1.42 (s, 9H), 1.43-1.89 (m, 9H), 2.41-2.53 and 2.83-2.88 (m,
2H), 3.06-3.56 (m, 8H), 3.40 (s, 3H), 3.37-3.84 (m, 1H), 4.21-
4.40 (m, 2H), 4.55 (d, J ) 6.0 Hz, 1H) and 4.68-4.72 (m, 2H),
5.07-5.09 (m, 2H), 7.31-7.35 (m, 5H); 13C NMR (CDCl3) δ 10.3,
12.5 (9 overlapping carbons), 12.7, 15.9, 18.3, 19.8, 20.2, 20.3,
20.9, 22.3, 28.6 (3 overlapping carbons), 35.4, 39.2, 39.4, 40.8,
40.9, 42.8, 54.0, 56.2, 64.5, 66.6, 72.6, 78.6, 79.1, 98.6, 127.9,
128.1, 128.1, 128.3, 128.5, 136.0, 156.2, 156.4, 170.4; IR
) 8.8, 10.8 Hz, 1H), 4.76-4.78 (m, 3H) and 6.03 (brs, 1H); 13
C
NMR (CDCl3) δ 13.1 (9 overlapping carbons), 14.2, 17.6, 18.3,
18.3, 19.9, 19.2, 21.8, 23.3, 23.9, 24.7, 27.1, 28.3 (3 overlapping
carbons), 28.8, 33.5, 36.7, 40.8, 41.4, 42.3, 56.4, 59.1, 73.9, 75.7,
80.3, 98.1, 155.8, 170.9, 173.3; IR (CHCl3) 3282 (br), 2943 (s),
2868 (s), 2359 (s), 1739 (s), 1693 (s), 1633 (s), 1157 (s), 1027
(s) cm-1; HRMS m/z calcd for C36H70N2O8Si (M + Na) 709.4803,
found 709.4861; [R]25D -16.48° (c ) 1.07, CHCl3). Anal. Calcd
(CHCl3) 3354 (br), 2946 (s), 2868 (s), 1729 (s), 1691 (s) cm-1
;
HRMS m/ z calcd for C44H80N2O10Si (M + Na) 847.5480, found
847.5461; [R]25 -16.51° (c ) 1.89, CHCl3).
D
(3S,4R)-4-[[4-[(Ben zyloxyca r bon yl)a m in o]bu tyl](ter t-

4968 J . Org. Chem., Vol. 62, No. 15, 1997
Ramanjulu et al.
for C36H70N2O8Si: C, 62.94; H, 10.27; N, 4.08. Found: C,
62.97; H, 9.95; N, 4.03.
1.32-1.92 (m, 8H), 2.19-2.29 (m, 1H), 2.78-3.28 (m, 8H), 3.78
(m, 1H), 4.15 (m, 1H), 5.18 (m, 1H), 6.69 (s, 1H); 13C NMR
(500 MHz, CDCl3) δ 14.2, 16.6, 17.6, 17.6, 19.5, 21.9, 22.9, 24.8,
25.8, 28.3, 38.8, 39.4, 39.5, 46.3, 51.6 and 58.9 (RI), 66.1, 84.3
and 84.4 (RI), 168.2, 172.8, 205.5; IR (neat) 3251 (br), 2962
(s), 2359 (m), 1723 (s), 1652 (s) cm-1; HRMS m/ z calcd for
C20H36N2O5 (M + H) 385.2702, found 385.2715.
14(S)-Hyd r oxy-5(R)-isobu tyl-15(S)-isop r op yl-14-(m eth -
o x y m e t h o x y )-13(S )-m e t h y l-2,12-d io x o -4(S )-[(t r iis o -
pr opylsilyl)oxy]-1-oxa-6,11-diazacyclopen tadecan e-6-car -
boxylic Acid ter t-Bu tyl Ester (19). To a cold (n-78 °C),
stirred solution of the MOM ether 18 (35 mg, 0.05 mmol) in
dry CH2Cl2 (1 mL) was added dropwise a solution of dimeth-
ylboron bromide (1.40 M, 0.11 mL) in CH2Cl2. After 1 h at
-78 °C, a mixture of THF/NaHCO3 (2:1) was added dropwise
into a vigorously stirring reaction mixture. After 5 min, the
mixture was diluted with ether (5 mL), and the organic layer
was separated and washed successively with water, 10%
aqueous sodium bisulfate, and saturated NaCl solutions. The
aqueous layers were reextracted with ether (5 mL), and the
organic layers were combined, dried (Na2SO4), and concen-
trated. The residue was purified by column chromatography
eluting with EtOAc/petroleum ether (50:50). Pure compound
19 (0.023 g, 77%) was obtained as an oil: Rf 0.55 (50% EtOAc/
petroleum ether); 1H NMR (CDCl3) δ 0.84-1.21 (m, 34H),
1.31-1.39 (m, 2H), 1.39 (s, 9H), 1.44-1.97 (m, 5H), 2.07-2.09
(m, 1H), 2.37-2.44 (m, 2H), 2.74-2.91 (m, 3H), 3.10-3.16 (m,
2H), 3.78-3.80 (m, 1H), 3.89 (d, J ) 5.6 Hz, 1H), 4.04-4.15
(m, 1H), 4.66 (d, J ) 6.9 Hz, 1H), 5.76 (m, 1H); 13C NMR
(CDCl3) δ 13.1 (9 overlapping carbons), 13.3, 13.6, 17.7, 18.3,
18.4, 18.7, 19.8, 21.7, 23.9, 24.3, 24.8, 26.7, 28.4, 29.4, 33.7,
36.8, 40.3 (overlapping carbon), 42.2, 43.9, 59.3, 61.0, 72.4,
73.2, 80.3, 155.8, 171.2 (overlapping carbon); IR (neat) 3318
Z-N,O-d im eth yltyr osin e Meth yl Ester (22).30 To N-Z-
L-tyrosine (1.00 g, 0.32 mmol) at ambient temperature was
added THF (16 mL). Finely powdered KOH (1.77 g, 0.032 mol)
was then added in portions, followed by the addition of
tetrabutylammonium hydrogen sulfate (0.10 g, 10% by weight).
Rapid stirring was initiated, and dimethyl sulfate (1.8 mL,
0.019 mol) was added dropwise over a period of 15 min. After
1 h, the solid material was collected by filtration and washed
with ethyl acetate. The filtrate was washed with 10% HCl,
5% NaHCO3, and saturated NaCl solutions. The ethyl acetate
layer was dried (Na2SO4), filtered, and concentrated. The
crude oil was purified by column chromatography eluting with
EtOAc/petroleum ether (15:85). The ester (22, 0.97 g, 85%
yield) was obtained as an oil: Rf 0.55 (30:70 EtOAc:petroleum
1
ether); H NMR (CDCl3) δ 2.80 (d, J ) 12.90 Hz, 3H), 2.91-
3.01 (m, 1H), 3.10-3.17 (m, 1H), 3.71, 3.64 and 3.75 (s, 3H,
RI), 3.92 (s, 3H), 4.72-5.08 (m, 3H), 6.76-7.32 (m, 9H); 13C
NMR (CDCl3) δ 31.5, 32.0, 33.9 and 34.4 (RI), 52.1 and 55.1
(RI), 58.5, 60.7, 60.3, 67.3, 67.4, 113.9, 113.9, 136.4, 136.7,
127.4, 127.8, 127.9, 128.3, 128.9, 129.8, 136.4, 136.6, 155.9,
156.5 and 158.3 (RI), 171.5 and 171.2 (RI); IR (neat) 2400 (m),
1750 (s), 1710 (s), 1513 (s), 1247(m) cm-1; HRMS m/ z calcd
(br), 2960 (m), 2868 (m), 1739 (s), 1692 (s), 1643 (s) cm-1
;
HRMS m/ z calcd for C34H66N2O7Si (M + H) 643.4717, found
for C20H24NO5 (M + H) 358.1654, found 358.1640; [R]25
-51.00° (c ) 0.59, CHCl3).
D
643.4738; [R]25 -0.13° (c ) 4.64, CHCl3). Anal. Calcd for
D
C34H65N2O7Si: C, 63.61; H, 10.21; N, 4.36. Found: C, 63.45;
H, 10.25; N, 4.39.
N-Acetyl-N,O-d im eth yl-L-tyr osin e Meth yl Ester (24).
To a CH3OH/EtOAc solution (1:1, 15 mL) was added 10% Pd/C
(0.34 g). To the resulting suspension was added Z-N,O-
dimethyltyrosine methyl ester (22, 1.14 g, 3.16 mmol) in CH3-
OH (2.00 mL). The solution was subjected to an atmosphere
of hydrogen (40 psi) in a Parr apparatus and shaken for 3 h.
The reaction mixture was filtered through Celite. The Celite
was washed with CH3OH, and the filtrate was concentrated.
The resulting amine (1.00 g, 91% yield) was used directly in
the next step.36 The crude secondary amine was dissolved in
methylene chloride and cooled to 0 °C. To this solution was
added triethylamine (0.62 mL, 4.70 mmol) followed by acetic
anhydride (0.47 mL, 4.93 mmol) and the reaction stirred for
12 h. After the reaction was complete, it was diluted with
ether and washed with 10% HCl, 5% NaHCO3, and saturated
NaCl solutions. The organic layer was dried (Na2SO4), filtered,
and concentrated. The resulting crude oil was purified by
column chromatography eluting with acetone/hexane (30:70).
Compound 24 (1.04 g, 87% yield) was obtained as an oil: Rf
5(R)-Isob u t yl-15(S)-isop r op yl-14-(m et h oxym et h oxy)-
13(S)-m eth yl-2,12,14-tr ioxo-4(S)-[(tr iisop r op ylsilyl)oxy]-
1-oxa-6,11-diazacyclopen tadecan e-6-car boxylic Acid ter t-
Bu tyl Ester (20). To a mixture of the 1,1,1-triacetoxy-1,1-
dihydro-1,2-benziodoxol-3(1H)-one (Dess-Martin periodinane
reagent, 0.021 g, 0.048 mmol) and CH2Cl2 (1 mL) was added
the alcohol 19 (0.023 g, 0.036 mmol) in CH2Cl2 (1 mL). The
reaction was stirred for 1 h and diluted with ether (5 mL).
This slurry was poured into saturated aqueous NaHCO3 (2.5
mL) containing Na2S2O3‚5H2O (90 mg). After the mixture was
stirred for 5 min, an additional amount of Et2O (5 mL) was
added. The combined organic layers were washed with
saturated aqueous NaHCO3 (2.5 mL) and H2O (2.5 mL), dried
(Na2SO4), filtered, and concentrated. The crude oil was
purified by column chromatography eluting with EtOAc/
petroleum ether (40:60). Pure compound 20 (0.023 g, 99%)
was obtained as an oil. Rf 0.36 (40% EtOAc/petroleum ether);
1H NMR (CDCl3) δ 0.85-1.30 (m, 35H), 1.30-1.33 (m, 2H),
1.46 (s, 9H), 1.60-1.82 (m, 5H), 2.05-2.11 (m, 1H), 2.50-2.92
(m, 5H), 3.12-3.20 and 3.41-3.55 (m, 2H), 3.63-3.75 (m, 1H),
4.20-4.21 (m, 1H), 5.08-5.10 (m, 1H), 5.48 (brs, 1H); 13C NMR
(CDCl3) δ 12.2, 12.8 (3 overlapping carbons), 18.0, 18.2, 18.3,
21.8, 23.9, 24.7, 27.15, 25.1 28.4 (3 overlapping carbons), 35.0,
37.9, 38.4, 40.0, 42.0, 51.8, 59.5, 72.7, 81.1, 156.4, 168.7 and
170.1, 204.1; IR (neat) 3302 (br), 2944 (s), 2868 (s), 2360 (m),
1751 (s), 1693 (s), 1638 (s) cm-1; HRMS m/ z calcd for
1
0.30 (30:70 acetone:hexane); H NMR (CDCl3) δ 1.95 (s, 3H),
2.78 and 2.84 (s, 3H, RI), 2.92-2.95 and 3.22-3.26 (m, 2H),
3.67 (s, 3H), 3.73 (s, 3H), 4.49-4.52 and 5.10-5.20 (m, 1H),
6.70 and 7.05 ([AX]2, J ) 8.2 Hz, 4H); 13C NMR (CDCl3) δ 21.0
and 21.6 (RI), 34.3 (33.8 and 33.5, (RI), 52.1 and 52.4 (RI),
55.1, 58.0, 62.7, 113.8, 114.2, 128.9, 129.6, 129.8, 158.3, 171.2,
171.4; IR (neat) 3000 (w), 2359 (s), 1739 (s), 1651 (s), 1513 (s)
cm-1; HRMS m/ z calcd for C14H20NO4 (M + H) 266.1392, found
266.1403; [R]25 -63.53° (c ) 0.40, CHCl3).
D
C34H64N2O7Si (M + H) 641.4561, found 641.4550; [R]25
-23.58° (c ) 1.65, CHCl3).
N-Acetyl-N,O-d im eth yl-L-tyr osin e (25). N-Acetyl-N,O-
dimethyl-L-tyrosine methyl ester (24, 0.24 g, 0.902 mmol) was
dissolved in 20 mL of THF. The reaction mixture was cooled
to 0 °C, and 20 mL of 0.2 M LiOH was added. The reaction
was stirred for 6 h, concentrated to 20 mL, and washed with
ether (2 × 20 mL). The combined organic layers were
extracted with saturated NaHCO3 solution. The aqueous
layers were combined and acidified to pH 1 with 2 N KHSO4
solution. The acidified aqueous layer was extracted with ethyl
acetate (3 × 25 mL). The organic layers were dried (Na2SO4),
filtered, and concentrated. The acid (25, 0.213 g, 94% yield)
was obtained as a white foam: Rf 0.11 (40:60 acetone:hexane);
1H NMR (CDCl3) δ 1.71 and 1.95 (s, 3H, RI), 2.75 and 2.85 (s,
3H, RI), 2.96-3.01 and 3.23-3.26 (m, 2H), 3.71 (s, 3H), 4.40-
4.49 and 5.04-5.07 (m, 1H), 6.74-6.77 and 7.00-7.04 (m, 4H);
13C NMR (CDCl3) δ 21.6, 33.6 and 34.2 and 34.5 (RI), 55.2,
59.6, 62.1, 114.3, 114.0, 128.6, 129.7, 129.8, 158.4, 172.6, 174.0;
D
4(S)-Hydr oxy-5(R)-isobu tyl-15(S)-isopr opyl-13(S)-m eth -
yl-1-oxa -6,11-d ia za cyclop en ta d eca n e-2,12,14-tr ion e (21).
A solution of ketone 20 (0.023 g, 0.036 mmol) in 3.0 mL of
EtOAc was cooled to -30 °C. Gaseous HCl was then intro-
duced at such a rate that the temperature of the reaction
mixture was maintained between -10 and -20 °C at satura-
tion. The solution was kept for 2 h at this temperature and
then kept at 0 °C for 4 h. The solution was then purged with
nitrogen (g) 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 3-mL por-
tions of tert-butyl methyl ether/hexane (1:4). The product was
collected by filtration and dried. Compound 20 (0.015 g, 90%)
was obtained as a white solid: Rf 0.30 (15:85 MeOH:chloro-
form); 1H NMR (CDCl3) δ 0.84-1.19 (m, 12H), 1.27 (s, 3H),

Synthesis of an Analog of Didemnin B
J . Org. Chem., Vol. 62, No. 15, 1997 4969
IR (neat) 2957 (br), 1731 (s), 1595 (s), 1513 s), 1249 (s) cm-1
;
1735 (s), 1717 (s), 1652 (s), 1513 (s), 1173 (s) cm-1; HRMS calcd
for C42H66O12N4 (M + Na) m/ z 841.4779, found 841.4795; [R]25
HRMS m/ z calcd for C13H18NO4 (M + H) 252.1236, found
D
252.1229; [R]25 -56.64 (c ) 0.52, CHCl3). Anal. Calcd for
D
-1.62° (c ) 1.79, CHCl3).
C13H17NO4: C, 62.14; H, 6.82; N, 5.57. Found: C, 62.02; H,
6.71; N, 5.91.
3(S)-[[2(S)-(Acetylm eth yla m in o)-3-(4-m eth oxyp h en yl)-
p r op ion yl]oxy]-2(S)-(2-[[[1-(2(S)-h yd r oxyp r op ion yl)p yr -
r olid in e-2(S)-ca r b on yl]m et h yl]a m in o]-4(S)-m et h ylp en -
t a n oyla m in o)b u t yr ic Acid 4(S)-Hyd r oxy-5(R)-isob u t yl-
15(S )-isop r op y l-13(S )-m e t h y l-1-o xa -6,11-d ia za c y c lo -
p en ta d eca n e-2,12,14-tr ion e (2). Compound 27 (0.013 g, 15
µM) was dissolved in 1 mL of dry methylene chloride and
cooled to 0 °C. To this solution was added trifluoroacetic acid
(0.024 mL, 0.03 mM), and the reaction was stirred for 6 h at
ambient temperature. Upon completion of the reaction, the
solution was concentrated under reduced pressure, the result-
ing residue was azeotroped (3 × 2 mL) with toluene, and the
resulting TFA salt was used in the next step without purifica-
tion. To a solution of TFA salt (0.013 g, 15 µM) and didemnin
B side chain (6, 0.005 g, 15 µM) in CH2Cl2 (1.0 mL) and at 0
°C were added BOP (8.5 mg, 19 µM) and NMM (8.0 µL, 7.16
µM). After 30 min, the solution was brought to room temper-
ature and stirred for 6 h. After this time, the reaction mixture
was diluted with 5 mL of Et2O. The organic layer was washed
successively with 5% HCl, 5% NaHCO3, and saturated NaCl
solutions. The organic layer was dried (NaSO4), filtered, and
concentrated. The resulting crude oil was purified by column
chromatography eluting with MeOH/CHCl3 (10:90) to afford
9.0 mg (53%) of pure analog 2: Rf 0.61 (15:85 MeOH:CHCl3);
1H NMR (CDCl3) δ 0.87-1.34 (m, 33H), 1.61-1.91 (m, 11H),
1.99 and 2.00 (s, 3H, RI), 2.19-2.24 (m, 1H), 2.95 and 2.82 (s,
6H), 2.94-3.23 (m, 6H), 3.15-3.32(m, 6H), 3.77 (s, 3H), 4.61-
4.90 (m, 5H), 5.10-5.53 (m, 5H), 6.81-6.83 and 7.25-7.26 (m,
4H); 13C NMR (CDCl3) δ 15.8, 19.5, 17.2, 21.1, 21.4, 21.6, 21.9,
22.3, 23.1, 23.3, 23.5, 23.7, 24.4, 24.8, 24.9, 25.1, 26.0, 28.3,
28.4, 28.4, 28.9, 29.7, 30.9, 36.0, 39.0, 39.3, 45.3, 46.9, 49.5,
55.3, 55.1, 56.9, 57.7, 61.5, 66.0, 70.5, 80.7, 83.9, 113.9, 114.1,
128.5, 129.5, 129.7, 158.3, 168.3, 168.9, 170.0, 171.1, 172.3,
172.8, 173.3, 205.1; IR (neat) 3323 (br), 2929 (s), 1738 (s), 1731
(s), 1659 (s), 1643 (s), 1632 (s), 1514 (s) cm-1; HRMS calcd for
N-Acet yl-N,O-d im et h yl-L-t yr osin e-O-Boc-L-t h r eon in e
Ben zyl Ester (26). To N-acetyl-N,O-dimethyltyrosine (25,
0.41 g, 0.16 mmol), in CH2Cl2 (5 mL) and at 0 °C, was added
Boc-threonine benzyl ester (0.50 g, 1.62 mmol). To the
resulting solution were added triethylamine (0.48 mL, 0.36
mmol), DMAP (0.04 g, 0.32 mmol), and isopropenyl chloro-
formate (0.19 mL, 0.18 mmol). The reaction was stirred at 0
°C for 1 h and diluted with ether (50 mL), and the organic
layer was washed with 5% HCl, 5% NaHCO3, and saturated
NaCl solutions. The ether layer was dried (Na2SO4), filtered,
and concentrated. The resulting crude oil was purified by
column chromatography eluting with EtOAc/petroleum ether
(40:60). Compound 26 (0.72 g, 82%) was obtained as an oil:
1
Rf 0.71 (40:60 acetone:hexane); H NMR (CDCl3) δ 1.28 (d, J
) 6.35 Hz, 3H), 1.45 (s, 9H), 1.99 (s, 3H), 2.64 (s, 3H), 2.92 (t,
J ) 10.4 Hz, 1H) and 3.15 and 3.18 (dd, J ) 5.6, 5.7 Hz, 1H),
3.78 (s, 3H), 4.40 (d, J ) 9.3 Hz, 1H), 4.86-4.87 (m, 1H), 5.12-
5.16 (m, 3H), 5.40-5.41 (m, 1H), 6.81 and 7.60 ([AX]2, J ) 8.6
Hz, 4H), 7.33-7.46 (m, 5H); 13C NMR (CDCl3) δ 16.4, 20.9,
30.1 (3 overlapping carbons), 33.8, 34.3, 55.7, 57.8, 59.5, 67.0,
71.2, 80.1, 113.9, 114.3, 127.2, 127.8, 128.9, 128.9, 129.1, 129.1,
129.9, 131.1, 137.9, 156.1, 158.1, 169.9, 170.3, 171.6; IR
(CHCl3) 3400 (br), 2950 (s), 1745 (s), 1650 (br and s), 1500 (s)
cm-1; HRMS m/ z calcd for C29H38N2O8 (M + Na) 565.2526,
found 565.2541; [R]25 -29.60° (c ) 0.38, CHCl3).
D
N-Acet yl-N,O-d im et h yl-L-t yr osin e-O-Boc-L-t h r eon in e
(4). To a CH3OH/EtOAc solution (1:1, 2 mL) was added 10%
Pd/C (0.014 g). To the resulting suspension was added
N-acetyl-N,O-dimethyl-L-tyrosine-O-Boc-L-threonine-OBn (26,
0.048 g, 0.065 mmol) in CH3OH (1.00 mL). The solution was
subjected to an atmosphere of hydrogen (40 psi) and stirred
for 3 h in a Parr apparatus. The reaction mixture was filtered
through Celite. The Celite was washed with CH3OH, and the
filtrate was concentrated. The resulting acid 4 (0.038 g, 91%
yield) was used directly in the next step: Rf 0.13 (40:60
acetone:hexane); 1H NMR (CDCl3) δ 1.29 (d, J ) 5.9 Hz, 3H),
1.49 (s, 9H), 2.01 (s, 3H), 2.77 (s, 3H), 2.96-3.01 and 3.20-
3.22 (m, 2H), 3.75 (s, 3H), 4.44 (m, 1H), 4.84 (m, 1H), 5.22 (m,
1H), 5.41 (s, 1H), 6.92 and 7.06 ([AX]2, 8.2, 4H); 13C NMR
(CDCl3) δ 16.4, 21.2, 28.2 (3 overlapping carbons), 33.3, 35.2,
55.1, 60.3, 62.9, 72.44, 80.1, 113.9, 114.3, 128.9, 129.8, 155.9
(overlapping carbon), 158.4, 169.2, 172.9; IR (CHCl3) 3350 (br),
C52H82O14N6 (M + Na) m/ z 1037.5787, found 1037.5738; [R]25
D
+9.71° (c ) 0.57, CHCl3).
Ack n ow led gm en t. Financial support by the Na-
tional Institutes of Health (CA-40081) is gratefully
acknowledged. We also thank Dr. George T. Furst, Dr.
Patrick J . Carroll, Mr. J ohn Dykins, and Dr. Rakesh
Kohli of the University of Pennsylvania Analytical
Facilities for their expert technical assistance.
2979 (m), 1740 (s), 1715 (s), 1610 (m), 1513 (s), 1165 (s) cm-1
;
HRMS m/ z calcd for C22H32N2O8 (M + Na) 475.2057, found
475.2035; [R]25 -10.57° (c ) 1.94, CHCl3).
D
2-(Ace t ylm e t h yla m in o)-3-(4-m e t h oxyp h e n yl)p r op i-
on ic Acid 2-[(ter t-bu toxyca r bon yl)a m in o]-3-(4-h yd r oxy-
5-isobu tyl-15-isop r op yl-13-m eth yl-2,12,14-tr ioxo-1-oxa -6,-
11-d ia za cyclop en ta d ec-6-yl)-1-m eth yl-3-oxop r op yl Ester
(27). To a solution of acid 4 (0.01 g, 0.02 mol) and amine 21
(0.009 g, 0.02 mmol), in CH2Cl2 (1.0 mL) and at 0 °C, were
added BOP (0.0122 g, 0.027 mmol) and NMM (0.011 mL, 0.102
mmol). After 30 min, the solution was brought to room
temperature and stirred for 6 h. After this time, the reaction
mixture was treated with 3 mL of saturated NaCl solution and
then extracted with 5 mL of Et2O. The organic layers were
combined and washed successively with 5% HCl, saturated
NaCl, 5% NaHCO3, and saturated NaCl solutions. The organic
layer was dried (NaSO4), filtered, and concentrated. The
resulting crude oil was purified by column chromatography
eluting with MeOH/chloroform (10:90) to afford 0.011 g (67%)
of pure compound 27: Rf 0.5 (90:10 chloroform:MeOH); 1H
NMR (CDCl3) 0.87-1.34 (m, 18H), 1.46 (s, 9H), 1.61-1.91 (m,
7H), 1.99 and 2.00 (s, 3H, RI), 2.19-2.24 (m, 1H), 2.77 (s, 3H),
2.94-3.23 (m, 6H), 3.15-3.32(m, 4H), 3.77 (s, 3H), 4.61-4.90
(m, 4H), 5.10-5.53 (m, 4H), 6.81-6.83 and 7.25-7.26 (m, 4H);
13C NMR (CDCl3) δ 16.2, 16.7, 17.2, 17.5, 17.6, 19.3, 20.3, 21.8,
22.0, 24.8, 25.1, 26.2, 28.2 (3 overlapping carbons), 29.7, 33.8,
34.5, 37.3, 38.9, 39.9, 46.2, 52.2, 57.7, 59.0, 66.4, 71.5, 80.3,
83.0, 113.9, 128.2, 129.0, 129.8, 137.8, 155.9, 158.4, 169.3,
169.4, 169.6, 171.1, 171.8, 205.5; IR (neat) 3310 (br), 2935 (s),
Abbr evia tion s: (1H-1,3-benzotriazol-1-yloxy)tris(di-
methylamino)phosphonium hexafluorophosphate (BOP);
N-(benzyloxycarbonyl)-5-norbornene-2,3-dicarboximide
(BCN); N,N-bis(2-oxo-3-oxazolidinyl)phosphonic chloride
(BOP-Cl); diethyl ether (Et2O); diisopropylethylamine
(DIEA); diphenyl phosphorazidate (DPPA); ethyl acetate
(EtOAc); R-(R-hydroxyisovaleryl)propionyl (HIP); isopro-
penyl chloroformate (IPCF); N-methylmorpholine (NMM);
pentafluorophenyl diphenylphosphinate (FDPP); tetra-
butylammonium fluoride (TBAF); triisopropylsilyl triflate
(TIPSOTf); 1,1,1-triacetoxy-1,1-dihydro-1,2-benziodoxol-
3(1H)-one (Dess-Martin periodinane reagent); triethyl-
amine (Et3N); rotational isomers (RI).
Su p p or tin g In for m a tion Ava ila ble: NMR data for ob-
tained compounds (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 O9623696