Total syntheses of conformationally constrained didemnin B analogues. Replacements of N2O-dimethyltyrosine with L-1,2,3,4-tetrahydroisoquinoline and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline

Article abstract of DOI:10.1021/jo0105991

The design and synthesis of two conformationally constrained analogues of didemnin B are described. The [N,O-Me₂Tyr⁵]residue of didemnin B was replaced with L-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid (Tic) and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline-3-carboxylic acid (MeO-Tic), which mimic the N,O-dimethylated tyrosine while constraining the conformation of the molecule. Preliminary results indicate that the conformation of the [N,O-Me₂Tyr⁵]residue closely matches the conformation imposed by the Tic replacement.

Full text of DOI:10.1021/jo0105991

J . Org. Chem. 2001, 66, 7575-7587
7575
Tota l Syn th eses of Con for m a tion a lly Con str a in ed Did em n in B
An a logu es. Rep la cem en ts of N,O-Dim eth yltyr osin e w ith
L-1,2,3,4-Tetr a h yd r oisoqu in olin e a n d
L-1,2,3,4-Tetr a h yd r o-7-m eth oxyisoqu in olin e
J ames E. Tarver J r., Amy J . Pfizenmayer, and Madeleine M. J oullie´*
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323
mjoullie@sas.upenn.edu
Received J une 13, 2001
The design and synthesis of two conformationally constrained analogues of didemnin B are described.
The [N,O-Me2Tyr5]residue of didemnin B was replaced with L-1,2,3,4-tetrahydroisoquinoline-3-
carboxylic acid (Tic) and L-1,2,3,4-tetrahydro-7-methoxyisoquinoline-3-carboxylic acid (MeO-Tic),
which mimic the N,O-dimethylated tyrosine while constraining the conformation of the molecule.
Preliminary results indicate that the conformation of the [N,O-Me2Tyr5]residue closely matches
the conformation imposed by the Tic replacement.
In tr od u ction
Didemnin B (1, Figure 1), a cyclic depsipeptide, is the
lead member of a class of marine natural products
isolated from tunicates.1 This family of natural products
exhibits potent antitumor, antiviral, and immuno-
suppressive activities.2 Didemnin B has the ability to
inhibit protein biosynthesis in vitro,3,4 to induce rapid
apoptosis,5-10 and to interfere with phosphoinositol up-
take.11 The mechanisms by which didemnin B effects
these biological activities are still under investigation,
but some progress has been reported in this area.12
Peptides can exist in a large number of conformations,
making their structural investigations a challenging goal.
One approach to analogue design is to restrict rotation
around certain bonds in order to minimize the number
of low energy conformations that can be observed. This
strategy aids in the determination of conformations
important for receptor binding, since the introduction of
the proper constraints in the ligand should reduce the
entropy cost of the receptor-ligand complex and result
in greater stability.
F igu r e 1. Didemnin B (1).
Conformational analyses for individual amino acids in
a peptide have many aspects. Torsion angles within the
backbone of a peptide (characterized by the dihedral
angles φ and ψ) and within the side chains of amino acids
(characterized by the dihedral angles ø1 and ø2 about CR-
Câ and Câ-Cγ, respectively) may be constrained. The
strategy of constraining the ø1 and ø2 bonds of tyrosine
(Tyr) or phenylalanine (Phe) is accomplished by replacing
these groups with moieties such as L-1,2,3,4-tetrahy-
droisoquinoline-3-carboxylic acid (Tic), and L-1,2,3,4-
tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid (HO-
Tic). The manner in which ø1 and ø2 may be restricted is
shown in Figure 2 using L-MeO-Tic (L-1,2,3,4-tetrahydro-
7-methoxyisoquinoline-3-carboxylic acid) as an example.
The Newman projections show the three staggered
conformations possible when looking down the R-â bond
(ø1) of an L-amino acid. Note that an unconstrained amino
acid can reach all three conformers, but due to its tether,
MeO-Tic cannot reach conformer II.
(1) Rinehart, K. L., J r.; Gloer, J . B.; Cook, J . C., J r.; Mizsak, S. A.;
Scahill, T. A. J . Am. Chem. Soc. 1981, 103, 1857-1859.
(2) Sakai, R.; Rinehart, K. L.; Kishore, V.; Kundu, B.; Faircloth, G.;
Gloer, J . B.; Carney, J . R.; Namikoshi, M.; Sun, F.; Hughes, J ., R. G.;
Gravalos, G.; de Quesada, T. G.; Wilson, G. R.; Heid, R. M. J . Med.
Chem. 1996, 39, 2819-2834.
(3) Ahuja, D.; Vera, M. D.; SirDeshpande, B. V.; Morimoto, H.;
Williams, P. G.; J oullie´, M. M.; Toogood, P. L. Biochemistry 2000, 39,
4339-4346.
(4) Ahuja, D.; Geiger, A.; Ramanjulu, J . M.; Vera, M. D.; SirDesh-
pande, B. V.; Pfizenmayer, A.; Abazecd, M.; Krosky, D. J .; Beidler, D.;
J oullie´, M. M.; Toogood, P. L. J . Med. Chem. 2000, 43, 4212-4218.
(5) Grubb, D. R.; Wolvetang, E. J .; Lawen, A. Biochem. Biophys. Res.
Commun. 1995, 215, 1130-1136.
(6) Beidler, D. R.; Ahuja, D.; Wicha, M. S.; Toogood, P. L. Biochem.
Pharmacol. 1999, 58, 1067-1074.
The strategy of constraining the ø1 and ø2 bond angles
of tyrosine or phenylalanine by replacing them with a
Tic moiety has been used extensively by Hruby et al. to
prepare analogues of somatostatin which have signifi-
cantly enhanced opioid receptor activity in comparison
to somatostatin itself.13,14 Tic analogues of N-methylated
amino acids constrain the side chain yet do not affect the
degree of substitution at the amino group, making Tic-
based analogues ideal to use as mimics of N-methylated
amino acids.
(7) J ohnson, K. L.; Vaillant, F.; Lawen, A. FEBS Lett. 1996, 383,
1-5.
(8) J ohnson, K. L.; Grubb, D. R.; Lawen, A. J . Cellular Biochem.
1999, 72, 269-278.
(9) J ohnson, K. L.; Lawen, A. Immunol. Cell Biol. 1999, 77, 242-
248.
(10) Grubb, D. R.; Ly, J . D.; Vaillant, F.; J ohnson, K. L.; Lawen, A.
Oncogene 2001, 20, 4085-4094.
(11) Dominice, C.; Dufour, M.-N.; Patino, N.; Maanzoni, O.; Grazzini,
E.; J ouin, P.; Guillon, G. J . Pharm. Exp. Ther. 1994, 271, 107-117.
(12) Vera, M. D. Ph.D. Dissertation, University of Pennsylvania,
2000 and references therein.
10.1021/jo0105991 CCC: $20.00 © 2001 American Chemical Society
Published on Web 10/20/2001

7576 J . Org. Chem., Vol. 66, No. 23, 2001
Tarver et al.
of didemnin B were used as the basis for the minimiza-
tion. The minimizations were generated using PRCG
(Conjugate gradient minimization using the Polak-
Ribiere first derivative method) followed by FMNR (Full
matrix Newton Raphson minimization) with the MM2
force field. This lowest energy conformation was manipu-
lated so that the [N,O-Me2Tyr5]residue was replaced with
Tic and was minimized again with the same procedure.
The overlay of didemnin B and [Tic5]didemnin B (2)
showed that the torsional angle (ø1) of Tic was very
similar to that in the tyrosine moiety of didemnin B.
Therefore, the torsional angles of both compounds were
close to that of conformer I, the lowest energy conformer.
Note that conformer II cannot be reached by Tic ana-
logues and conformer III is much higher in energy.
Although the torsional angles (ø1) of Tic and Tyr (in 2
and 1, respectively) were very similar, the torsional
angles (ø2) for the same moieties were different. The
aromatic ring in the Tyr side chain of 1 was perpendicu-
lar to that of the aromatic ring in the Tic side chain of 2.
Analogues 2 and 3 were designed to investigate the
effects of constraining the tyrosine side chain in didemnin
B. Although 3 closely mimics the natural product’s [N,O-
Me2Tyr5] moiety, we also prepared analogue 2 (with no
methoxy group) since its biological activity would be
directly comparable to that of the N-MePhe analogue.18
In addition, the synthesis of 2 was expected to be more
facile than that of 3 which would allow us to obtain
biological activity results more rapidly.
F igu r e 2. Newman projections of the torsional angle (ø1) of
the CR-Câ bond of MeO-Tic.
Our synthesis of 1 affords stereocontrol and conver-
gence allowing modification at any point in construc-
tion.20 This approach has permitted the synthesis of
several analogues of didemnin B, which contain modifi-
cations in the side chain peptide,21-23 the macrocyclic
peptide,24,25 or the nonpeptidic HIP-isostatine fragment.26
Thus, tyrosine was replaced with Tic and MeO-Tic to
probe the importance of free rotation of the side chain
moiety. Additionally, these analogues provide constraint
without loss of R-nitrogen substitution.
F igu r e 3. Constrained analogues (2 and 3) of didemnin B.
Structural studies and chemical modifications2 at the
[N,O-Me2Tyr5]residue of the didemnins have shown that
changes in this position are tolerated. The tyrosine side
chain in didemnin B is thought to be involved in binding
to the receptor because it protrudes outward from the
center of the interior of the molecule both in solid state
and in solution phase.15,16 We prepared two didemnin B
analogues in which the tyrosine moiety was replaced with
N-Me-leucine (N-MeLeu) and N-Me-phenylalanine (N-
MePhe).17,18 These analogues exhibited biological activity
comparable to that of didemnin B analogues. This
similarity led us to synthesize other analogues in which
the tyrosine moiety was replaced with Tic and MeO-Tic.
According to the numbering shown in Figure 1 these two
analogues are designated as [Tic5]didemnin B and [MeO-
Tic5]didemnin B (2 and 3, Figure 3) and will be referred
to as the Tic and MeO-Tic analogues, respectively.
Before beginning the synthetic process, molecular
modeling studies were conducted.19 The X-ray coordinates
Resu lts a n d Discu ssion
The retrosyntheses of the Tic and MeO-Tic analogues
(Figure 4) paralleled that of the natural product.20 After
the initial side chain removal, the molecule was divided
into a tetrapeptide and a nonpeptidic HIP-isostatine
portion. The HIP-isostatine fragment construction has
previously been described.20,21 The tetrapeptide was
formed by a series of classical peptide couplings of
protected natural amino acids and the constrained ty-
rosine analogues Tic and MeO-Tic.
Syn th eses of Lin ea r P r ecu r sor s. The synthesis of
the tetrapeptide of 2 began with a Pictet-Spengler
condensation27 performed on L-phenylalanine to yield the
(13) Hruby, V. J . In Conformationally Directed Drug Design: Pep-
tides and Nucleotides as Templates or Targets; Vida, J . A., Gordon,
M., Eds.; American Chemical Society: Washington, D. C., 1983; pp
9-28.
(14) Hruby, V. J .; Cody, W. L.; Castrucci De Lauro, A. M.; Hadley,
M. E. Collect. Czech. Chem. Commun. 1988, 53, 2549-2573.
(15) Hossain, M. B.; Van der Helm, D.; Antel, J .; Sheldrick, G. M.;
Weinheimer, A. J .; Sanduka, S. K. Int. J . Pept. Protein Res. 1996, 47,
20-27.
(16) Kessler, H.; Will, M.; Antel, J .; Beck, H.; Sheldrick, G. M. Helv.
Chim. Acta 1989, 72, 530-555.
(17) 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-
2716.
(18) Pfizenmayer, A. J .; Ramanjulu, J .; Vera, M. D.; Ding, X.; Xiao,
D.; Chen, W.-C.; J oullie´, M. M. Tetrahedron 1999, 55, 313-334.
(19) Mayer, S. C. Ph.D. Dissertation, University of Pennsylvania,
1995.
(20) Li, W.-R.; Ewing, W. R.; Harris, B. D.; J oullie´, M. M. J . Am.
Chem. Soc. 1990, 112, 7659-7672.
(21) Mayer, S. C.; Ramanjulu, J .; Vera, M. D.; Pfizenmayer, A.;
J oullie´, M. M. J . Org. Chem. 1994, 59, 5192-5205.
(22) Ding, X.; Vera, M. D.; Liang, B.; Zhao, Y.; Leonard, M. S.;
J oullie´, M. M. Bioorg. Med. Chem. Lett. 2001, 11, 231-234.
(23) Vera, M. D.; Pfizenmayer, A. J .; Ding, X.; Ahuja, D.; Toogood,
P. L.; J oullie´, M. M. Bioorg. Med. Chem. Lett. 2001, 11, 1871-1874.
(24) Ramanjulu, J .; Ding, X.; Li, W.-R.; J oullie´, M. M. J . Org. Chem.
1997, 62, 4961-4969.
(25) Vera, M. D.; Pfizenmayer, A. J .; Ding, X.; Xiao, D.; J oullie, M.
M. Bioorg. Med. Chem. Lett. 2001, 11, 13-16.
(26) Xiao, D.; Vera, M. D.; Liang, B.; J oullie´, M. M. J . Org. Chem.
2001, 66, 2734-2742.
(27) Cox, E. D.; Cook, J . M. Chem. Rev. 1995, 95, 1797-1842.

Conformationally Constrained Didemnin B Analogues
J . Org. Chem., Vol. 66, No. 23, 2001 7577
F igu r e 4. Retrosynthetic analysis of the constrained analogues (2 and 3).
Sch em e 1a
salt of Tic, which was neutralized to form L-Tic in 38%
yield (4, Scheme 1). The nitrogen of L-Tic was protected
with a benzyloxycarbonyl group (Cbz) under standard
conditions (97% yield). Coupling of the Cbz-Tic (5) to the
alcohol of Boc-Thr-OSEM using isopropenyl chlorofor-
mate afforded dipeptide 6 in 89% yield. Removal of the
Cbz group under hydrogenolysis afforded a secondary
amine (7) in 86% yield, which was coupled directly to the
dipeptide acid Cbz-Leu-Pro-OH using bis(2-oxo-3-oxazo-
lidinyl)phosphinic chloride (BOP-Cl) to form the fully
protected tetrapeptide (8) in 60% yield. Removal of the
2-(trimethylsilyl)ethoxymethyl (SEM) group with mag-
nesium bromide etherate provided 9 in quantitative yield.
Reaction of 9 with the protected non-peptide portion, Hip-
isostatine (10), was achieved using isopropenyl chloro-
formate and N-methylmorpholine to provide the pro-
tected linear precursor (11) in 47% yield. The Hip-
isostatine unit (10) was derived from protected Hip-
acetate and Cbz-D-alloisoleucine.20,21 The tert-butyl-
dimethylsilyl (TBDMS) group of the Hip-isostatine moi-
ety was removed with a mixture of acetic acid, THF, and
water to give the primary alcohol (12) in 73% yield.
The synthesis of MeO-Tic tetrapeptide began from the
a
Reagents and conditions: (a) 1. 37% aq CH2O, concentrated
HCl, 60 °C; 2. aq EtOH, NH4+OH-, 38%; (b) NaHCO3, H2O, CbzCl,
97%; (c) isopropenyl chloroformate, Boc-Thr-OSEM, Et3N, DMAP,
CH2Cl2, 89%; (d) H2, Pd/C, EtOAc, MeOH, 86%; (e) 1. Cbz-Leu-
Pro-OH, BOP-Cl, NMM, CH2Cl2, -15 °C; 2. amine (7), NMM, 0
°C, 60%; (f) MgBr2‚Et2O, CH2Cl2, -20 °C, quant. (g) NMM, iso-
propenyl chloroformate, 10, 47%; (h) AcOH, THF, H2O, 16 h, 73%.
commercially available 3′,5′-diiodo-L-tyrosine dihydrate
(Scheme 2). This substrate was chosen to avoid polym-
erization, which is known to occur when the Pictet-
Spengler reaction is carried out on tyrosine unprotected
at the ortho-positions.28 Although the iodo groups could
be removed immediately before the carbamate protection,
this reaction did not proceed well on the free amine.
Therefore the iodo groups were carried through the next
(28) Vert, M. Eur. Polym. J . 1972, 8, 513-524.

7578 J . Org. Chem., Vol. 66, No. 23, 2001
Tarver et al.
Sch em e 2a
Sch em e 3a
a
Reagents and conditions: (a) aq CH2O, concentrated HCl, 1,2-
a
Reagents and conditions: (a) 1. Dess-Martin periodinane,
dimethoxyethane, 72 °C, 54%; (b) CH2Cl2, Et3N, Cbz- succinimide,
79%; (c) THF, KOH, dimethyl sulfate, nBu4N+HSO4-, 91%; (d)
MeOH, Cu2Cl2, NaBH4, 0 °C, 87%; (e) LiOH‚H2O, THF, H2O,
MeOH, 97%; (f) isopropenyl chloroformate, Boc-Thr-OSEM, Et3N,
DMAP, CH2Cl2, 78%; (g) H2, Pd/C, EtOAc, MeOH, 87%; (h) 1. Cbz-
Leu-Pro-OH, BOP-Cl, NMM, CH2Cl2, -15 °C; 2. amine 19, NMM,
0 °C, 64%; (i) MgBr2, CH2Cl2, 98%; (j) HATU, DIEA, CH2Cl2, 10,
63%; (k) AcOH, THF, H2O, 24 h, 75%.
CH2Cl2; 2. NaClO2, aq NaH2PO4, in H2O/DMSO/CH3CN or in
t-BuOH/2-methyl-2-butene, 84%; (b) EDC‚HCl, DMAP, CH2Cl2,
pentafluorophenol, 67%; (c) EtOAc, EtOH, Pd/C, 4-pyrrolidinopy-
ridine, H2, 58% for 26; 1. H2, Pd/C, EtOH; 2. HATU, DIEA, CH2Cl2,
61% for 28; (d) Me2BBr, CH2Cl2, 82% for 28; 87% for 30; (e) Dess-
Martin periodinane, CH2Cl2, 68-94%.
of acetic acid, THF, and water to give the primary alcohol
(23) in 75% yield.
few steps until their removal was convenient. 3′,5′-Diiodo-
L-tyrosine hydrate was treated with formaldehyde and
hydrochloric acid to form the trisubstituted tetrahy-
droisoquinoline hydrochloride salt (13) in 54% yield.
Protection of nitrogen as a carbamate using triethylamine
and Cbz-succinimide afforded 14 in 79% yield. Concomi-
tant methylation of the free hydroxyl group and the
carboxylic acid was achieved using dimethyl sulfate and
potassium hydroxide to provide 15 in 91% yield. A simple
procedure using cuprous chloride and sodium borohy-
dride cleanly reduced the diiodide in 87% yield by a
mechanism, which is believed to proceed through the
copper hydride intermediate.29 The resulting ester (16)
was saponified to carboxylic acid 17 using lithium
hydroxide (97% yield). The depsipeptide linkage of N-Boc-
Thr-OSEM ester and Cbz-MeOTic was achieved by
preactivation of the acid via the mixed anhydride gener-
ated with isopropenyl chloroformate (78% yield). Cata-
lytic hydrogenation of 18 removed the Cbz group to form
19 in 87% yield. The ensuing coupling with Cbz-Leu-Pro-
OH was mediated by BOP-Cl to give 20 in 64% yield.
Removal of the SEM group with magnesium bromide
provided 21 in 98% yield. Reaction of 21 with the
protected non-peptide portion, Hip-isostatine (10) was
achieved using O-(7-azabenzotriazol-1-yl)N,N,N′,N′-tet-
ramethyluronium hexafluorophosphate (HATU) to afford
the linear precursor (22) in 63% yield. The TBDMS group
of the Hip-isostatine moiety was removed with a mixture
Cyclization . With linear precursor 12 in hand (Scheme
1), the next step was the oxidation of the primary alcohol
to an acid (Scheme 3) using the two-step oxidation we
had devised for the synthesis of other didemnins.30 This
protocol involved oxidation to the aldehyde with the
Dess-Martin periodinane reagent,31,32 followed by oxida-
tion to the acid with buffered potassium permanganate.33
An intense spot appearing on the TLC plate when
visualized under a UV lamp indicated the presence of
aromatized product. It was known that several oxidation
reagents are too strong to be used in the presence of a
1,2,3,4-tetrahydroisoquinoline. Reagents such as potas-
sium permanganate,34,35 molecular oxygen with lead
tetraacetate,36 copper chloride,37 nitric acid, mercuric
acetate, sulfur, selenium, thionyl chloride, Fremy’s salt,
sodium hypochlorite, NBS, and manganese dioxide35,38
are known to oxidize tetrahydroisoquinolines to 3, 4-di-
(30) Pfizenmayer, A. J .; Ramanjulu, J .; Vera, M. D.; Ding, X.; Xiao,
D.; Chen, W.-C.; J oullie´, M. M.; Tandon, D.; Toogood, P. L. Bioorg. Med.
Chem. Lett. 1998, 8, 3653-3656.
(31) Dess, D. B.; Martin, J . C. J . Org. Chem. 1983, 48, 4155-4156.
(32) Dess, D. B.; Martin, J . C. J . Am. Chem. Soc. 1991, 113, 7277-
7287.
(33) Abiko, A.; Roberts, J . C.; Takemasa, T.; Masamune, S. Tetra-
hedron Lett. 1986, 27, 4537-4540.
(34) Venkov, A. P.; Statkova-Abeghe, S. M. Tetrahedron 1996, 52,
1451-1460.
(35) Dyke, S. F.; Kinsman, R. G. Properties and Reactions of
Isoquinolines and their Hydrogenated Derivatives; J ohn Wiley &
Sons: New York, 1981; Vol. 38.
(36) Umezawa, B.; Hoshino, O. Heterocycles 1975, 3, 1005-1033.
(37) Shimizu, M.; Orita, H.; Hayakawa, T.; Suzuki, K.; Takehira,
K. Heterocycles 1995, 41, 773-779.
(29) Narisada, M.; Horibe, I.; Watanabe, F.; Takeda, K. J . Org.
Chem. 1989, 54, 5308-5313.

Conformationally Constrained Didemnin B Analogues
J . Org. Chem., Vol. 66, No. 23, 2001 7579
Sch em e 4a
a
Reagents and conditions: (a) HCl, EtOAc, -30 °C to 0 °C, 100%. (b) BOP, NMM, CH2Cl2, 33, 0 °C to room temperature, 63% for 2;
HATU, DIEA, CH2Cl2, 33; 0 °C to room temperature, 74% for 3.
hydroisoquinolines, fully aromatized isoquinolines, or
other degradation or ring-opened products. After model
studies of the oxidation of tetrahydroisoquinolines with
a variety of oxidizing reagents at various stages of the
synthesis,39 we achieved the desired oxidation using
sodium chlorite in the presence of a chlorine scavenger,
either DMSO or 2-methyl-2-butene. Other chlorine scav-
engers are also available, and their advantages and
disadvantages have been discussed by Dalcanale and
Montanari.40
deprotect the amino group, and 4-pyrrolidinopyridine was
used as base. This protocol afforded a 58% yield of
cyclized product (27). The MOM ether was removed with
dimethylboron bromide, and the resulting secondary
alcohol (29) was oxidized to a ketone (31) with Dess-
Martin periodinane (Scheme 3). Removal of the TIPS
ether and Boc groups with hydrogen chloride provided
the macrocycle salt. The side chain of didemnin B was
attached to the macrocycle salt to give 2 in 63% yield
using the BOP reagent (Scheme 4).
Cyclization of linear precursor 23 (Scheme 2) proceeded
in a similar manner (Scheme 3). Deprotection of the
primary TBDMS afforded a free hydroxyl group, which
could be oxidized with Dess-Martin reagent to the
corresponding aldehyde. Further oxidation to the acid
was accomplished using sodium chlorite and DMSO as
the chlorine scavenger and solvent in 84% yield for both
steps. Chromatographic purification of the acid (25) was
necessary to effect the subsequent hydrogenation. Several
conditions, including transfer hydrogenation with pal-
ladium hydroxide, palladium, and ammonium formate
and direct hydrogenolysis in various solvents, were
attempted. Only hydrogenation with 10% palladium on
carbon in absolute ethanol and a heavy catalyst loading
was successful. Ethanol/EtOAc mixtures proceeded more
slowly, but methanol could not replace ethanol. The
unstable intermediate was successfully cyclized (28) with
HATU and 3-(diethoxyphosphoryloxy)-1, 2, 3-benzotri-
azin-4(3H)-one45 (DEPBT) reagents in dichloromethane,
but HATU proved superior as cyclization with DEPBT
produced complex reaction mixtures and difficulties in
purification. The postcyclization modifications proved
similar to those outlined for Tic. The MOM deprotection
afforded the free hydroxyl (30) in 87% yield. This
compound was oxidized to the corresponding ketone (32)
in 94% yield. The final sequence involved the simulta-
neous removal of the TIPS ether and Boc protecting
groups with hydrogen chloride to afford the macrocycle
amine hydrochloride salt, which was coupled to the
didemnin B side chain (33) to give 3 in 74% yield using
HATU (Scheme 4).
The linear precursor 12 was oxidized with Dess-
Martin reagent to the corresponding unstable aldehyde,
which was directly oxidized to the acid (24) in 84% yield
using sodium chlorite and DMSO40,41 as both solvent and
chlorine scavenger (Scheme 3). Due to difficulties in
removing DMSO, 2-methyl-2-butene42 was employed as
an alternate scavenger.
Cyclization attempts began after removal of the Cbz
group of 24 by hydrogenolysis. Coupling reagents such
as O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluro-
nium tetrafluoroborate43 (TBTU) in methylene chloride
and pentafluorophenyl diphenyl phosphinate21 (FDPP) in
dimethylformamide were utilized and produced the de-
sired cyclized product only in low yield. As we had
previously employed a modification44 of the Schmidt
cyclization for a leucine analogue of didemnin B,17 we
opted for a similar approach. Acid 24 was converted to
the corresponding pentafluorophenyl ester (26) by treat-
ment with pentafluorophenol and EDC hydrochloride
with a catalytic amount of DMAP. A dilute solution of
the pentafluorophenyl ester (26) in ethyl acetate with a
small amount of ethanol was used for the cyclization at
room temperature, instead of at 95 °C as in the Schmidt
protocol. An external source of hydrogen was used to
(38) Sotomayor, N.; Dominguez, E.; Lete, E. Tetrahedron 1995, 51,
12721-12730.
(39) Pfizenmayer, A. J . Ph.D. Dissertation, University of Pennsyl-
vania, 1998.
(40) Dalcanale, E.; Montanari, F. J . Org. Chem. 1986, 51, 567-569.
(41) Lindgren, B. O.; Nilsson, T. Acta Chem. Scand. 1973, 27, 888-
890.
(42) Kraus, G. A.; Roth, B. J . Org. Chem. 1980, 45, 4825-4830.
(43) Pettit, G. R.; Taylor, S. R. J . Org. Chem. 1996, 61, 2322-2325.
(44) Heffner, R. J .; J iang, J .; J oullie´, M. M. J . Am. Chem. Soc. 1992,
114, 10181-10189.
(45) Haitao, L.; Xiaohui, J .; Yun-hua, Y.; Chongxu, F.; Romoff, T.;
Goodman, M. Org. Lett. 1999, 1, 91-93.

7580 J . Org. Chem., Vol. 66, No. 23, 2001
Tarver et al.
1, 1M NaOH; before recrystallization) or [R]2D5 -172 (after
recrystallization from EtOH).
Biologica l Activity a n d Con clu sion s
Analogue 2 was tested at the National Cancer Institute
against various cell lines in vitro.46 The NCI-60 mean
data from the NCI-60 tumor cell screen46 for 2 and 1 gave
the following values: GI50 0.40 µM; TGI 7.8 µM; LC50 81
µM (2); GI50 0.013 µM; TGI 0.066 µM; LC50 3.8 µM (1).
This result shows that 2 is less active but also less toxic
than didemnin B (1), which may result in a better
therapeutic window as a growth inhibitor. In a protein
synthesis inhibition assay, the IC50 value for rabbit
reticulocyte lysates was 2.68 µM ( 0.17 µM whereas the
IC50 value for 1 was 4.4 µM ( 0.1 µM.47 X-ray and
modeling suggest similar conformations. The biological
data supports the hypothesis that this residue exists in
a hydrophobic pocket in the target protein that must be
filled in the protein ligand complex for optimal binding.4
N-Cb z-L-1,2,3,4-Tet r a h yd r oisoq u in olin e-3-ca r b oxylic
Acid (5). To a 2 M aqueous solution of NaHCO3 (8.31 g, 99.0
mmol in 49.5 mL of H2O) were added 4 (7.01 g, 39.6 mmol)
and benzyl chloroformate (6.2 mL, 43.5 mmol) in portions over
a period of 30 min. The reaction was stirred at room temper-
ature for 1.5 h before diluting and washing with Et2O. The
aqueous layer was cooled to 0 °C and acidified to pH 2 with 2
N KHSO4. This solution was extracted into EtOAc. The
combined organic layers were washed with saturated NaCl
solution, dried (MgSO4), filtered, and concentrated. Acid 5
(11.92 g, 97%) was obtained as a white foam and used directly
in the next step without purification. However, column chro-
matography was performed with acetone/hexanes (10:90 to 15:
85) to obtain the characterization data listed below; 5: Rf 0.50
1
(40:60 acetone:hexanes); H NMR (500 MHz, CDCl3) δ 3.16-
3.28 (m, 2H), 4.58 (d, J ) 17.1 Hz, 1H), 4.77 (d, J ) 16.3 Hz,
1H), 4.97 (t, J ) 5.0 Hz) and 5.17-5.24 (m, 3H, RI), 7.06-
7.40 (m, 9H); 13C NMR (125 MHz, CDCl3) δ 30.8 and 31.2 (RI),
44.3 and 44.4 (RI), 53.0, 67.6 and 67.8 (RI), 126.2 and 126.4
(RI), 126.9, 127.0, 127.9, 127.98, 128.09, 128.2, 128.46, 128.54,
131.3, 132.2 and 132.9 (RI), 136.2, 155.4, 176.7 (RI); IR (neat)
3033, 1702, 1684, 1420, 1319, 1122, 747 cm-1; HRMS (CI)
m/z calcd for C17H17N2O6 (M + H)+ 312.1236, found 312.1235;
[R]2D5 +8.47 (c 1.21, CHCl3).
Exp er im en ta l Section
Gen er a l Meth od s. Reactions requiring air-sensitive ma-
nipulations were conducted under an argon atmosphere.
Methylene chloride was distilled from calcium hydride, and
tetrahydrofuran and diethyl ether were distilled from sodium/
benzophenone ketyl. Petroleum ether refers to the fraction
boiling in the range 40-60 °C. Analytical TLC was performed
on 0.25 mm E. Merck silica gel 60 F254 plates. Merck silica gel
(60, particle size 0.040-0.063 mm) was used for flash column
chromatography. Proton and carbon magnetic resonance spec-
tra (1H, 13C NMR) were recorded on a Bruker AM-500 [500
MHz (125 MHz for 13C NMR)] Fourier transform spectrometer.
Chemical shifts (δ) were measured in parts per million, and
coupling constants (J values) are in hertz (Hz). A range of
pseudorotations are often present in cyclic peptides48 and their
chemical shifts are indicated by RI (rotational isomers).
Infrared spectra (IR) were recorded on a Perkin-Elmer 1600
series FT-IR spectrometer. Unless otherwise indicated, high-
resolution mass spectra (HRMS) were recorded on a Micromass
AutoSpec spectrometer using electron impact (EI). Optical
rotations were recorded on a Perkin-Elmer Model 341 pola-
rimeter at the sodium D line.
L-1,2,3,4-Tetr ah ydr oisoqu in olin e-3-car boxylic Acid (4).49
A mixture of L-Phe (5 g, 30.3 mmol), 37 wt % aqueous
formaldehyde (12.1 mL), and concentrated aqueous HCl (36.4
mL) was stirred at 60 °C for 1 h. An additional 4.9 mL of
formaldehyde and 9.7 mL of HCl were added, and the reaction
was stirred (still at 60 °C) for 3 h. After cooling to room
temperature, the mixture was left to stand overnight at 5 °C.
(Note: the combination of concentrated HCl and aqueous
formaldehyde forms a potent carcinogen, so the compound
should be cooled in the hood instead of the refrigerator before
filtration). The precipitated salt was collected by filtration,
washed with a small amount of ice cold water and dried in
vacuo over solid KOH. The crude salt was dissolved in 181
mL of refluxing aqueous EtOH (60%). While hot, the solution
was neutralized to pH 6-7 with aqueous ammonia. After this
solution was cooled, it was left standing at 5 °C for 5 h. The
precipitate was collected by filtration, washed with cold
aqueous EtOH, and dried in a desiccator. Acid 4 (2.02 g, 38%)
was obtained as a solid. The product was normally used
without purification but was recrystallized from aqueous EtOH
(60%) in order to obtain the following data. 4: Rf 0.49 (4:1:1
CH3CN:MeOH:H2O); HRMS (CI) m/z calcd for C10H12NO2 (M
+ H)+ 178.0868, found 178.0871; [R]2D5 -169.4 (c 0.55, 1 M
NaOH). Anal. Calcd for C10H11NO2: C, 67.78; H, 6.26; N, 7.90.
Found: C, 67.92; H, 6.30; N, 7.87. lit.49 [R]D25 -160 to -162 (c
N-Cbz-L-3-Ca r boxy-1,2,3,4-tetr a h yd r oisoqu in olin e-O-
Boc-th r eon in e-OSEM (6). To acid 5 (2.07 g, 6.64 mmol) in
CH2Cl2 (25 mL) was added Boc-threonine[(2-trimethylsilyl)-
ethoxy]methyl ester (2.21 g, 6.32 mmol) at 0 °C. To the
resulting solution were added triethylamine (2.03 mL. 14.5
mmol), DMAP (0.16 g, 1.3 mmol), and isopropenyl chlorofor-
mate (0.80 mL, 7.3 mmol). The reaction was stirred at 0 °C
for 1 h and diluted with Et2O. The organic layer was washed
sequentially with 10% HCl, 5% NaHCO3 and saturated NaCl
solutions. The Et2O layer was dried (MgSO4), filtered, and
concentrated. The crude oil was purified by column chroma-
tography eluting with EtOAc/petroleum ether (16:84 to 20:80).
The dipeptide (3.62 g, 89%) was obtained as a thick yellow
1
oil. 6: Rf 0.81 (30:70 EtOAc:petroleum ether); H NMR (500
MHz, CDCl3) δ 0.0 (s, 9H), 0.88 (t, J ) 8.4 Hz, 2H), 1.03 (d, J
) 6.4 Hz) and 1.13 (d, J ) 6.4 Hz, 3H, RI), 1.46 and 1.47 (s,
9H, RI), 3.10-3.21 (m, 2H), 3.50-3.69 (m, 2H), 4.33-4.39 (m,
1H), 4.53 and 4.73 (AB, J ) 16.4 Hz, 2H), 4.85-4.88 (m) and
4.95 (t, J ) 4.8 Hz, 1H, RI), 4.97-5.15 (m, 2H), 5.17-5.38 (m,
4H), 7.08-7.23 and 7.27-7.42 (m, 9H); 13C NMR (125 MHz,
CDCl3) δ -1.4, 16.6, 17.8, 28.3, 30.9 and 31.4 (RI), 44.4 and
44.6 (RI), 53.3 and 53.8 (RI), 56.7 and 57.0 (RI), 67.5 and 67.7
(RI), 68.1, 71.6 and 71.7 (RI), 80.2, 90.3 and 90.4 (RI), 126.3,
126.8, 126.9, 127.1, 127.95, 128.01, 128.1 and 128.2, 128.4,
128.5, 131.5, 132.2, 136.3, 155.8, 156.0, 169.3, 169.8 and 170.0
(RI); IR (neat) 3449, 2952, 1719, 1714, 1575, 1497, 1408, 1322,
1249, 1169, 1118, 914, 837 cm-1; HRMS (FAB) m/z calcd for
C
33H46N2O9SiNa (M + Na)+ 665.2871, found 665.2900; [R]2D5
+28.66 (c 0.71, CHCl3).
L-3-Car boxy-1,2,3,4-tetr ah ydr oisoqu in olin e-O-Boc-th r e-
on in e-OSEM (7). To a MeOH/EtOAc solution (1:1, 22 mL)
under N2 in a thick-walled Parr test tube was added 10% Pd/C
(1.1 g). To the resulting suspension was added 6 (3.49 g, 5.4
mmol) in MeOH (6 mL). The solution was shaken for 3 h in a
Parr hydrogenator under 40 psi of H2. The mixture was filtered
through Celite, and the Celite was washed with CH3OH. After
the filtrate was concentrated, the resulting amine 7 (0.125 g,
86%) was obtained as a yellow oil and was used directly in
the next step without purification. 7: Rf 0.67 (10:90 MeOH:
CHCl3); 1H NMR (500 MHz, CDCl3) δ -0.01 (s, 9H), 0.89-
0.93 (m, 2H), 1.11 (d, J ) 6.3 Hz) and 1.32 (d, J ) 6.4 Hz, 3H,
RI), 1.45 (s, 9H), 2.48 (brs, 1H), 2.85-3.13 (m, 2H), 3.59-3.76
(m, 2H), 3.86-4.08 (m, 2H), 4.33 (d, J ) 9.6 Hz) and 4.47 (d,
J ) 9.7 Hz, 1H, RI), 5.13-5.47 (m, 4H), 6.99-7.13 (m, 4H);
13C NMR (125 MHz, CDCl3) δ -1.6 and -1.4 (RI), 16.9, 18.0,
28.3, 31.5, 47.0, 55.8, 57.1, 68.2 and 68.3 (RI), 71.2, 80.3, 90.2
and 90.4 (RI), 126.1, 126.2, 126.3, 128.4 and 129.0 (RI), 132.8,
134.1 and 134.7 (RI), 155.8, 169.7, 171.9; IR (neat) 2954, 1730,
(46) Boyd, M. R.; Paull, K. D. Drug Dev. Res. 1995, 34, 91-109.
(47) SirDeshpande, B. V.; Toogood, P. L. Biochemistry 1995, 34,
9177-9184.
(48) Kessler, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 512-523.
(49) Majer, P.; Slaninova´, I.; Lebl, M. Int. J . Pept. Protein Res. 1994,
43, 62-68.

Conformationally Constrained Didemnin B Analogues
J . Org. Chem., Vol. 66, No. 23, 2001 7581
1720, 1503, 1454, 1367, 1249 1167, 1082, 1062, 937, 860, 837,
749 cm-1; HRMS (CI) m/z calcd for C25H41N2O7Si (M + H)+
509.2683, found 509.2672; [R]2D5 +7.72 (c 0.745, CHCl3).
9H), 1.47-1.57 (m, 1H), 1.71-2.23 (m, 8H), 2.24-2.28 (m, 1H),
2.61-2.68 (m, 2H), 3.07-3.11 (m, 1H), 3.19-3.24 (m, 1H), 3.28
(s, 3H), 3.41-3.48 (m, 2H), 3.66-3.67 (m, 1H), 3.76-3.79 (m,
2H), 4.08-4.11 (m, 1H), 4.34-4.38 (m, 1H), 4.51-4.59 (m, 5H),
4.67 and 4.89 (AX, J ) 15.1 Hz, 2H), 4.99-5.12 (m, 5H), 5.34-
5.43 (m, 2H), 6.30 (d, J ) 10.0 Hz, 1H), 7.06-7.18 and 7.27-
7.31 (m, 9H); 13C NMR (125 MHz, CDCl3) δ -5.5, 10.3, 11.8,
12.7, 14.5, 15.8, 16.1 (cont.), 17.9, 18.2, 20.0, 21.6, 23.4, 24.6,
24.7, 25.8, 27.6, 28.1, 28.3, 28.7, 30.7, 34.8, 37.5, 40.7, 41.7,
45.5, 47.0, 50.9, 51.9, 56.0, 56.3, 57.1, 57.6, 65.0, 66.8, 70.1,
71.2, 78.7, 78.8, 79.9, 98.6, 155.3, 156.3, 168.3, 169.7, 171.0,
171.1 (overlap); IR (neat) 3333, 2958, 2867, 1721, 1681, 1640,
1498, 1453, 1367, 1250, 1173, 1040, 919, 734 cm-1; HRMS m/z
calcd for C71H119O15N5Si2Na (M + Na)+ 1360.8139, found
1360.8162; [R]2D5 -25.78 (c 0.64, CHCl3). Anal. Calcd for
C71H119O15N5Si2: C, 63.69; H, 8.96; N, 5.23; Found: C, 63.65;
H, 8.89; N, 4.96.
Cb z-Leu cylp r olyl-L-(3-ca r b oxy-1,2,3,4-t et r a h yd r oiso-
qu in olin e)-O-Boc-th r eon in e-OSEM (8). Cbz-Leu-Pro-OH
(1.91 g, 5.26 mmol) was dissolved in CH2Cl2 (58 mL), and the
solution was cooled to -15 °C. To this solution was added BOP-
Cl (1.48 g, 5.79 mmol), followed by the dropwise addition of
NMM (0.64 mL, 5.79 mmol). After stirring for 0.5 h at -15
°C, the reaction mixture was concentrated to half of its volume
(using a rotary evaporator with a water bath at 0 °C), and
amine 7 (2.23 g, 4.39 mmol) was added followed by NMM (0.64
mL, 5.79 mmol). The solution was kept at 0 °C for 6 h and
then diluted with Et2O. The organic layer was washed
sequentially with 10% HCl, 5% NaHCO3, and saturated NaCl
solutions. The Et2O layer was dried (MgSO4), filtered, and
concentrated. The crude oil was purified by column chroma-
tography eluting with acetone/CH2Cl2 (7:93 to 10:90). The fully
protected tetrapeptide 8 (2.22 g, 60%) was obtained as a white
N-[N-[N-[(Ben zyloxy)ca r bon yl]-L-leu cyl]-L-p r olyl]-L-(3-
ca r b oxy-1,2,3,4-t et r a h yd r oisoq u in olin e), E st er w it h
(3S,4R,5S)-3-[(Tr iisop r op ylsilyl)oxy]-4-[(2S,3R)-2-[(ter t-
bu toxyca r bon yl)a m in o]-3-h yd r oxybu tyr a m id o]-5-m eth -
ylh 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 (12). To TBDMS
ether 11 (328 mg, 0.245 mmol) in THF (0.69 mL) was added
HOAc/H2O (3:1, 2.76 mL). After stirring 16 h, the reaction was
diluted with toluene (14 mL) and concentrated. The resulting
oil was again diluted with toluene and concentrated. This
operation was repeated until no HOAc remained. The crude
oil was purified by column chromatography, eluting with
acetone/hexanes (35:65 to 40:60). Compound 12 (250.4 mg,
83%) was obtained as a white solid. 12: mp 86-88 °C; Rf 0.375
1
solid. 8: mp 75 °C; Rf 0.45 (5:95 acetone:hexanes); H NMR
(500 MHz, CDCl3) δ -0.03 (s, 9H), 0.76-0.84 (m, 2H), 0.91 (d,
J ) 6.7 Hz) and 0.95 (d, J ) 6.7 Hz) and 0.98 (d, J ) 6.4 Hz)
and 1.03 (d, J ) 6.4 Hz, 6H, RI), 1.09 (d, J ) 6.4 Hz) and 1.21-
1.29 (m, 3H, RI), 1.44 (s, 9H), 1.73-1.91 (m, 3H), 2.02-2.32
(m, 4H), 3.06-3.2 (m, 2H), 3.44-3.59 (m, 2H), 3.67-3.82 (m,
2H), 4.27-4.30 (m, 1H), 4.53-4.86 (m, 3H), 4.87-5.08 (m, 4H),
5.05 and 5.18 (AB, J ) 6.0 Hz, 2H), 5.20-5.22 (m, 1H), 5.33-
5.40 (m, 2H), 7.07-7.30 (m, 9H); 13C NMR (125 MHz, CDCl3)
δ -2.5, 15.6, 16.8, 20.5, 22.3, 23.5, 23.8, 27.2, 29.5, 30.1, 40.5,
44.3, 45.6 and 45.9 (RI), 49.9 and 50.6 (RI), 53.4, 55.8 and 56.0
(RI), 56.6, 65.6 and 65.7 (RI), 67.0, 70.8, 79.2, 88.9 and 89.4
(RI), 125.2, 125.8 and 125.9 (RI), 126.2, 126.8, 126.9, 127.0,
127.28 and 127.30 (RI), 127.37, 127.40, 130.3, 130.8 and 131.2
(RI), 135.3, 154.6, 155.2 and 155.5 (RI), 168.1, 168.4, 168.6,
170.2; IR (neat) 3302, 2956, 1720, 1715, 1656, 1642, 1528,
1501, 1451, 1366, 1249, 1168, 860, 837, 753 cm-1; HRMS m/z
calcd for C44H64O11N4Si (M + Na)+ 875.4239, found 875.4220;
[R]2D5 -11.64 (c 1.1, CHCl3). Anal. Calcd for C44H64O11N4Si: C,
61.95; H, 7.56; N, 6.57; Found: C, 61.67; H, 7.82; N, 6.63.
Cb z-Leu cylp r olyl-L-(3-ca r b oxy-1,2,3,4-t et r a h yd r oiso-
qu in olin e)-O-Boc-th r eon in e (9).50 The fully protected tet-
rapeptide 8 (1.77 g, 2.08 mmol) was dissolved in CH2Cl2 (117
mL) and cooled to -20 °C. Magnesium bromide etherate (1.61
g, 6.24 mmol) was added, and the reaction was stirred at -20
°C for 1 h and then at 0 °C for 3.5 h. The reaction was diluted
with EtOAc and washed sequentially with 5% HCl and
saturated NaCl solutions. The organic layer was dried (Mg-
SO4), filtered, and concentrated. The crude foam was used
without purification in the next step (1.5 g, 100%).
1
(30:70 acetone:hexanes); H NMR (500 MHz, CDCl3) δ 0.84-
0.99 (m, 21H), 1.04-1.06 (m, 21H), 1.12-1.28 (m, 3H), 1.41
(s, 9H), 1.42-1.54 (m, 3H), 1.74-1.93 (m, 4H), 2.01-2.14 (m,
5H), 2.65-2.67 (m, 2H), 3.13-3.23 (m, 2H), 3.36 (s, 3H), 3.46-
3.49 (m, 2H), 3.64-3.67 and 3.76-3.79 (m, 2H), 4.09-4.11 (m,
2H), 4.31-4.32 (m, 1H), 4.52-4.62 (m, 6H), 4.67-4.69 and
4.98-5.00 (m, 9H), 5.02-5.13 (m, 4H), 5.33-5.51 (m, 2H),
6.55-6.60 (m, 1H), 7.06-7.31 (m, 9H); 13C NMR (125 MHz,
CDCl3) δ 10.8, 11.8, 12.8, 14.5, 18.1 (overlap), 20.0, 20.5, 21.47
and 21.53 (RI), 23.4, 24.6, 24.7, 27.6, 28.2, 28.3, 28.5, 30.9,
34.9 and 35.1 (RI), 36.8, 40.6, 41.7, 45.6, 47.0, 50.9, 51.9, 56.3
(overlap), 57.1, 64.2, 65.9, 66.8, 69.4, 70.8, 78.4 (overlap), 79.3,
98.5, 126.3, 127.03, 127.1, 127.9, 128.0, 128.2, 128.5, 131.8,
132.2, 136.4, 155.2, 156.3, 168.4, 169.5 (overlap), 171.2, 171.8;
IR (neat) 3334, 2961, 2868, 1720, 1680, 1639, 1498, 1453, 1367,
1248, 1171, 1111, 1042, 918 cm-1; HRMS m/z calcd for
C
65H105O15N5SiNa (M + Na)+ 1246.7274, found 1246.7270;
[R]2D5 -23.08 (c 6.15 CHCl3). Anal. Calcd for C65H105O15N5Si:
C, 63.75; H, 8.64; N, 5.72; Found: C, 63.60; H, 8.60; N, 5.71.
N-[N-[N-[(Ben zyloxy)ca r bon yl]-L-leu cyl]-L-p r olyl]-L-(3-
ca r b oxy-1,2,3,4-t et r a h yd r oisoq u in olin e), E st er w it h
(3S,4R,5S)-3-[(Tr iisop r op ylsilyl)oxy]-4-[(2S,3R)-2-[(ter t-
bu toxyca r bon yl)a m in o]-3-h yd r oxybu tyr a m id o]-5-m eth -
ylh ep ta n oic Acid , (1S,2S,3R)-4-[(ter t-Bu tyld im eth ylsilyl)-
oxy]-1-isopr opyl-2-(m eth oxym eth oxy)-3-m eth ylbu tyl Ester
(11). To the tetrapeptide acid 9 (161 mg, 0.222 mmol) in THF
(1.8 mL) at -15 °C was added dropwise NMM (24.5 µL, 0.222
mmol) followed by isopropenyl chloroformate (24.3 µL, 0.222
mmol). After the mixture was stirred for 3 min, protected
amine 10 (128 mg, 0.202 mmol) was added. The reaction was
warmed to 0 °C and stirred for 1 h. After 3 h at room
temperature, the reaction was concentrated in vacuo. The
resulting oil was diluted with Et2O and washed sequentially
with 5% citric acid, 5% NaHCO3, and saturated NaCl solutions.
The Et2O layer was dried (MgSO4), filtered, and concentrated.
The crude oil was purified by column chromatography eluting
with EtOAc/petroleum ether (30:70 to 35:65). Compound 11
(0.138 g, 47%) was obtained as a white solid. 10: mp 77-79
°C; Rf 0.46 (30:70 EtOAc:petroleum ether); 1H NMR (500 MHz,
CDCl3) δ 0.02 (s, 6H), 0.81-0.99 (m, 30H), 1.04-1.09 (m, 21H),
1.11-1.17 and 1.28-1.35 (m, 2H), 1.23-1.25 (m, 3H), 1.41 (s,
N-[N-[N-[(Ben zyloxy)ca r bon yl]-L-leu cyl]-L-p r olyl]-L-(3-
ca r b oxy-1,2,3,4-t et r a h yd r oisoq u in olin e), E st er w it h
(3S,4R,5S)-3-[(Tr iisop r op ylsilyl)oxy]-4-[(2S,3R)-2-[(ter t-
bu toxyca r bon yl)a m in o]-3-h yd r oxybu tyr a m id o]-5-m eth -
ylh ep t a n oic Acid , (1S,2S,3S)-1-Isop r op yl-2-(m et h oxy-
m eth oxy)-3-m eth ylbu ta n oic Acid Ester (24). To a solution
of the linear precursor alcohol 12 (339.2 mg, 0.277 mmol) in
CH2Cl2 (15 mL) was added the Dess-Martin periodinane
reagent (294 mg, 0.693 mmol). After 2 h the reaction was
diluted with Et2O and poured onto a solution of Na2S2O3‚5H2O
in saturated aqueous NaHCO3 solution (1.2 g in 10 mL). This
mixture was stirred for about 10 min, and when the upper
Et2O layer became clear, the layers were separated. The Et2O
layer was washed sequentially with saturated aqueous NaH-
CO3, H2O, and saturated NaCl solutions. The Et2O layer was
dried (MgSO4), filtered, and concentrated. The resulting
unstable aldehyde could then be treated in one of two manners.
Meth od A.40,51,52 To the aldehyde (339 mg, 0.277 mmol)
dissolved in DMSO:H2O:CH3CN (1:1:1, 13 mL) at room tem-
perature was added NaH2PO4‚2H2O (8.64 mg, 55.2 µmol)
(51) Rich, R. H.; Bartlett, P. A. J . Org. Chem. 1996, 61, 3916-3919.
(52) Wood, J . L.; Porco, J . A.; Tuanton, J .; Lee, A. Y.; Clardy, J .;
Schreiber, S. L. J . Am. Chem. Soc. 1992, 114, 5898-5900.
(50) Chen, W.-C.; Vera, M. D.; J oullie´, M. M. Tetrahedron Lett. 1997,
38, 4025-4028.

7582 J . Org. Chem., Vol. 66, No. 23, 2001
Tarver et al.
followed by NaClO2 (43.8 mg (80%), 0.387 mmol). After being
stirred overnight at room temperature, the mixture was
diluted with Et2O and cooled to 0 °C. It was then acidified
with 5% HCl until the pH of the aqueous layer was 3. The
layers were separated, and the aqueous layer was washed with
EtOAc. The combined organic layers were washed with
saturated NaCl solution, dried (MgSO4), filtered, and concen-
trated. Most residual DMSO could be removed by lyophilizing
with H2O/CH3CN or by dissolving the compound in ether and
washing the solution with water. The acid (24) was obtained
(326 mg, 95%) as a white powder and was used without
purification in the next step.
(m, 9H); 13C NMR (125 MHz, CDCl3) δ 11.7, 12.7, 14.5, 16.0,
17.0, 18.1, 19.6, 21.5, 23.4, 24.6, 24.7, 27.6, 28.1, 28.2, 28.8,
30.7, 34.9, 37.0, 40.0, 41.3, 41.7, 45.5, 47.0, 50.9, 51.8, 56.2,
56.4, 57.1, 66.3, 66.8, 69.9, 71.3, 78.3, 78.5, 79.9, 98.2, 126.2,
126.9, 127.1, 127.8, 127.9 (overlap), 128.0, 128.3, 128.5 (over-
lap), 131.5, 132.2, 136.1, 136.4, 138.8, 140.2, 142.2, 142.7,
156.1, 156.3, 168.3, 169.7, 169.8, 170.1, 171.1, 171.2; IR (neat)
3328, 2961, 1785, 1719, 1681, 1639, 1251, 1456, 1367, 1247,
1169, 1033, 861 cm-1; HRMS m/z calcd for C71H102O16N5SiF5-
Na (M + Na)+ 1426.6909, found 1426.6943; [R]2D5 -18.25 (c
0.92, CHCl3).
Cyclo[N-(ter t-b u t yloxyca r b on yl)-O-[[N-[(2S,3S,4S)-4-
[(3 S ,4 R ,5 S )-4 -a m i n o -3 -[(t r i i s o p r o p y l s i l y l )o x y ]-5 -
m e t h y l h e p t a n o y l ]-o x y -3 -(m e t h o x y m e t h o x y )-2 ,5 -
dim eth ylh exan oyl]-L-leu cyl]-L-pr olyl-L-(3-car boxy-1,2,3,4-
tetr a h yd r oisoqu in olyl)]-L-th r eon yl] (27).17,44,53,54 To a solu-
tion of activated ester 26 (100 mg, 71.1 µmol) in EtOAc and
EtOH (98:2, 71.1 mL) at 0 °C were added 10% Pd/C (0.242 g)
and 4-pyrrolidinopyridine (31.65 mg, 0.21 mmol). The flask
was evacuated and then placed under a H2 atmosphere. The
reaction was allowed to warm to room temperature and was
stirred under H2 for 6 h before filtering through Celite. The
filtrate was washed sequentially with 10% HCl, 5% NaHCO3,
and saturated NaCl solutions. The organic layer was dried
(MgSO4), filtered, and concentrated. The residue was purified
by column chromatography eluting with acetone/hexanes (15:
85). Compound 27 (44.5 mg, 58%) was obtained as a white
foam. 27: Rf 0.57 (30:70 acetone:hexanes); 1H NMR (500 MHz,
CDCl3) δ 0.79-1.04 (m, 18H), 1.05-1.07 (m, 21H), 1.26 (d, J
) 6.3 Hz, 3H), 1.30 (d, J ) 6.9 Hz, 3H), 1.39 and 1.42 (s, 9H,
RI), 1.43-1.56 (m, 2H), 1.64-1.66 (m, 3H), 1.85-2.20 (m, 6H),
2.50-2.60 (m, 2H), 2.76 (q, J ) 8.5 Hz, 1H), 2.92 (dd of ABX,
J ) 18.6, 2.0 Hz, 1H), 3.00 (dd of ABX, J ) 17.0, 4.1 Hz, 1H),
3.37 and 3.39 (s, 3H, RI), 3.63-3.70 (m, 2H), 3.73 (dd, J )
12.4, 4.2 Hz, 1H), 3.88-3.92 (m, 1H), 4.09-4.19 (m, 1H), 4.31-
4.33 (m, 1H), 4.43-4.58 (m, 3H), 4.61-4.69 (m, 2H), 4.70-
4.87 (m, 2H), 4.90-4.95 (m, 1H), 5.02 (d, J ) 10.5 Hz, 1H),
5.18-5.20 (m, 1H), 7.01-7.21 (m, 4H), 7.47 (d, J ) 9.6 Hz,
1H, cont.), 7.86 (d, J ) 8.4 Hz, 1H); 13C NMR (125 MHz, CDCl3)
δ 12.0, 13.0, 13.55 and 13.62, 14.6, 17.7 and 18.3 (RI), 18.4
and 18.5 (RI), 19.0, 19.1, 20.8, 23.6 and 24.7 (RI), 25.0 and
25.1 (RI), 27.9, 28.1 and 28.2 (RI), 28.3, 28.8 and 28.9 (RI),
29.2, 31.7, 34.4, 39.8, 40.6 and 40.9 (RI), 42.8 and 43.3 (RI),
44.6, 47.1, 48.4 and 48.7 (RI), 53.7 and 54.1, 55.1 and 55.2
(RI), 56.2, 56.3 and 56.4 (RI), 57.1 and 57.8 (RI), 68.8, 71.1,
78.7, 79.2, 80.2 and 80.4 (RI), 98.7, 125.3 and 126.5 (RI), 126.8
and 127.2 (RI), 127.7 and 127.8 (RI), 130.1, 132.3 and 132.7
(RI), 133.5, 155.3 and 156.0 (RI), 167.9, 169.0 and 169.7 (RI),
170.7, 171.5, 172.2, 174.3; IR (neat) 3346, 2961, 1742, 1668,
1642, 1534, 1515, 1450, 1380, 1367, 1247, 1166, 1016, 821, 754
cm-1; HRMS m/z calcd for C57H95O13N5Si (M + Na)+ 1108.6593,
found 1108.6575; [R]2D5 -20.58 (c 1.82, CHCl3). Anal. Calcd for
Meth od B.42 To the aldehyde (109 mg, 89.1 µmol) dissolved
in tert-butyl alcohol (2.2 mL) was added 2-methyl-2-butene (1.9
mL, 17.8 mmol) followed by 5% NaH2PO4 (0.733 mL) and
NaClO2 (12.1 mg (80%), 0.107 mmol). After stirring overnight
at room temperature, the reaction was diluted with Et2O (15
mL) and cooled to 0 °C before adding a few drops of Na2S2O3‚
5H2O to quench excess oxidant. The mixture was acidified with
5% HCl until the aqueous layer reached pH 2. The layers were
separated, and the aqueous layer was extracted with EtOAc.
The combined organic layers were washed with saturated NaCl
solution, dried (MgSO4), filtered, and concentrated. Acid 24
was obtained (0.11 g, 100%) as a white powder and used
without purification in the next step. Although a large excess
of 2-methyl-2-butene has to be used, this scavenger’s boiling
point is much lower than that of DMSO and it is easier to
remove it. 24: mp 77-80 °C; Rf 0.34 (30:70 acetone:hexane);
1H NMR (500 MHz, CDCl3) δ 0.84-1.00 (m, 8H), 1.03-1.09
(m, 21H), 1.12-1.15 (m, 3H), 1.20-1.26 (m, 3H), 1.25 and 1.40
(s, 9H), 1.44-1.74 (m, 3H), 1.75-1.82 (m, 2H), 2.04-2.15 (m,
5H), 2.24-2.27 (m, 1H), 2.51-2.73 (m, 3H), 3.11-3.18 (m, 2H),
3.40 (s, 3H), 3.69-3.83 (m, 3H), 4.01-4.08 (m, 2H), 4.38-4.40
(m, 2H), 4.53-4.77 (m, 4H), 4.77-4.79 and 4.89-4.92 (m, 2H),
5.00-5.13 (m, 4H), 5.33-5.50 (m, 2H), 6.76 (d, J ) 10.3 Hz,
1H), 7.02-7.44 (m, 9H); 13C NMR (125 MHz, CDCl3) δ 11.7,
12.7, 14.7, 15.8, 17.7, 18.06 and 18.13 (RI), 19.0 and 19.2 (RI),
21.6, 23.4, 24.6, 24.8, 27.3, 28.1, 28.3 and 28.4 (RI), 29.7, 30.7,
35.6, 39.5, 41.1, 41.5, 45.7, 47.0, 51.0, 52.3, 56.4, 56.9, 57.2,
58.3, 66.8, 68.7, 70.6, 78.3, 78.9, 80.2, 97.9, 126.2, 127.1, 127.3,
127.7, 127.95, 128.04, 128.3, 128.5, 131.6, 132.2, 136.4, 155.5,
156.3, 168.7, 169.4, 171.4, 171.9 (overlap), 175.9; IR (neat)
3322, 2960, 1722, 1678, 1640, 1529, 1453, 1367, 1171, 1041
cm-1; HRMS m/z calcd for C65H104O16N5Si (M + H)+ 1260.7247,
found 1260.7294; [R]2D5 -16.95 (c 0.64, CHCl3).
N-[N-[N-[(Ben zyloxy)ca r bon yl]-L-leu cyl]-L-p r olyl]-L-(3-
ca r b oxy-1,2,3,4-t et r a h yd r oisoq u in olin e), E st er w it h
(3S,4R,5S)-3-[(Tr iisop r op ylsilyl)oxy]-4-[(2S,3R)-2-[(ter t-
bu toxyca r bon yl)a m in o]-3-h yd r oxybu tyr a m id o]-5-m eth -
ylh ep ta n oic Acid , P en ta flu or op h en yl (1S,2S,3S)-1-Iso-
p r op yl-2-(m et h oxym et h oxy)-3-m et h ylb u t a n oa t e E st er
(26). Acid 24 (157.7 mg, 0.127 mmol) and pentafluorophenol
(25.7 mg, 0.14 mmol) were dissolved in CH2Cl2 (3 mL) and
cooled to 0 °C. To this solution were added EDC‚HCl (26.8 mg,
0.14 mmol) and catalytic DMAP. After being stirred at 0 °C
for 1 h, the reaction was stirred at room temperature for 12
h. The solution was concentrated, and the residue was diluted
with EtOAc and washed sequentially with 10% HCl, 5%
NaHCO3, and saturated NaCl solutions. The EtOAc layer was
dried (MgSO4), filtered, and concentrated. The crude material
was purified by column chromatography eluting with acetone/
hexanes (18:82). Compound 26 (119 mg, 67%) was obtained
as a white solid. 26: mp 73-75 °C; Rf 0.55 (30:70 acetone:
C
57H95O13N5Si: C, 63.01; H, 8.81; N, 6.45; Found: C, 62.66;
H, 8.87; N, 6.09.
Cyclo[N -(t er t -b u t oxyca r b on yl)-O-[[N -[(2S ,3S ,4S )-4-
[(3S,4R,5S)-4-a m in o-3-[(tr iisop r op ylsilyl)oxy]-5-m eth yl-
h eptan oyl]oxy-3-h ydr oxy-2,5-dim eth ylh exan oyl]-L-leu cyl]-
L-p r olyl-L-(3-ca r b oxy-1,2,3,4-t et r a h yd r oisoq u in olyl)]-L-
th r eon yl] (29). To a cold (-78 °C) stirred solution of the MOM
ether 27 (45 mg, 41.4 µmol) in dry CH2Cl2 (1 mL) was added
dropwise a solution of dimethylboron bromide (1.5 M, 0.138
mL) in CH2Cl2. After 2 h, the reaction was not complete so
the same amount of dimethylboron bromide was added again.
After 2 additional h at -78 °C, a solution of THF (2 mL) and
saturated aqueous NaHCO3 was added with vigorous stirring.
After 5 min, the mixture was diluted with ether and the
reaction warmed to room temperature. The organic layer was
separated and washed sequentially with water, 10% KHSO4,
and saturated NaCl solutions. The Et2O layer was dried
(MgSO4), filtered, and concentrated. The residue was purified
1
hexanes); H NMR (500 MHz, CDCl3) δ 0.83-0.98 (m, 18H),
1.04-1.07 (m, 21H), 1.12-1.26 (m, 3H), 1.35 (d, J ) 7.0 Hz,
3H), 1.40 (s, 9H), 1.41-1.56 (m, 2H), 1.68-1.82 (m, 3H), 1.95-
2.29 (m, 6H), 2.61-2.70 (m, 2H), 2.95-2.99 (m, 1H), 3.10 (dd
of ABX, J ) 15.7, 5.1 Hz, 1H), 3.21 (dd of ABX, J ) 15.7, 3.3
Hz, 1H), 3.29 (s, 3H), 3.65-3.67 and 3.76-3.80 (m, 2H), 4.08-
4.10 (m, 2H), 4.14-4.16 (m, 1H), 4.33-4.36 (m, 1H), 4.53-
4.55 (m, 1H), 4.56-4.64 (m, 2H), 4.66-4.68 (m, 1H), 4.90 (d,
J ) 15.1 Hz, 1H), 4.92-5.02 (m, 2H), 5.04-5.08 (m, 3H), 5.28-
5.30 (m, 1H), 5.35 (d, J ) 9.0 Hz, 1H), 5.42-5.44 (m, 1H), 6.38
(d, J ) 10.0 Hz, 1H), 7.06-7.08 and 7.13-7.18 and 7.27-7.32
(53) Schmidt, U.; Lieberknecht, A. Angew. Chem., Int. Ed. Engl.
1981, 20, 281-282.
(54) Schmidt, U.; Griesser, H. Angew. Chem., Int. Ed. Engl. 1981,
20, 280-281.

Conformationally Constrained Didemnin B Analogues
J . Org. Chem., Vol. 66, No. 23, 2001 7583
by column chromatography eluting with acetone/hexanes (22:
78) to give alcohol 29 (35.3 mg, 82%) as a white foam. 29: Rf
0.48 (30:70 acetone:hexanes); 1H NMR (500 MHz, CDCl3) δ
0.80-0.97 (m, 18H), 1.02-1.14 (m, 21H), 1.28 (d, J ) 6.3 Hz,
3H), 1.35 (d, J ) 6.8 Hz, 3H), 1.41 and 1.44 (s, 9H), 1.46-1.64
(m, 6H), 1.88-2.20 (m, 4H), 2.32-2.35 (m, 1H), 2.47-2.57 (m,
1H), 2.63-2.77 (m, 1H), 2.93-3.05 (m, 1H), 3.18-3.39 (m, 1H),
3.39-3.50 (m, 1H), 3.63-3.78 (m, 2H), 3.84-3.93 (m, 1H),
4.03-4.17 (m, 2H), 4.27-4.37 (m, 1H), 4.48-4.64 (m, 3H),
4.67-4.90 (m, 3H), 4.93-4.97 (m, 1H), 5.00-5.04 (m, 1H),
qu in olyl)]-L-th r eon yl] Hyd r och lor id e. A solution of ketone
31 (10 mg, 9.6 µmol) in EtOAc (0.6 mL) was cooled to -30 °C.
Gaseous HCl was introduced (via a glass pipet through a
septum in one neck of the flask) at such a rate that the
temperature of the reaction mixture was maintained between
-10 °C and -20 °C for 30 min. During this time, the second
neck of the flask was attached first to an oil bubbler and then
to a water bubbler. After stopping the flow of HCl (g) and
placing the flask under a N2 atmosphere, the solution was
stirred for 2 h at this temperature and then stirred at 0 °C for
4 h. The solution was then purged with N2 for about 30 min,
maintaining the temperature at 0 °C. After the solution was
concentrated, the residue was triturated and washed by
decantation with three 1.7 mL portions of tert-butyl methyl
ether/hexanes (1:4). The product was dried in vacuo. The salt
(8.2 mg, 100%) was obtained as a white solid: Rf 0.55 (10:90
MeOH: CH2Cl2); 1H NMR (500 MHz, CD3OD) δ 0.85-1.10 (m,
18H), 1.16-1.22 (m, 1H), 1.24-1.25 (m, 3H), 1.27-1.30 (m,
1H), 1.32 (d, J ) 6.3 Hz, 3H), 1.36-1.44 (m, 1H), 1.49-1.57
(m, 1H), 1.73-1.81 (m, 3H), 1.86-1.94 (m, 1H), 2.06-2.17 (m,
2H), 2.29-2.37 (m, 1H), 2.47 (dd, J ) 17.9, 10.5 Hz, 1H), 3.03
(dd of ABX, J ) 16.8, 4.0 Hz, 1H), 3.27-3.34 (m, 2H), 3.41-
3.46 (m, 1H), 3.64-3.67 (m, 1H) and 3.75-3.79 (m, 1H), 4.03-
4.09 (m, 2H), 4.11-4.17 (m, 2H), 4.28-4.30 (m, 1H), 4.56-
4.60 (m, 1H) and 4.73-4.78 (m, 1H), 4.86-4.88 (m, 2H), 4.98-
5.01 (m, 2H), 5.09-5.11 (m, 1H), 5.27-5.29 (m, 2H), 7.20-
7.22 (m, 4H), 7.43-7.45 (m, 1H), 8.91-8.93 (m, 1H); 13C NMR
(125 MHz, CD3OD) δ 12.4, 13.8, 14.8, 15.4, 17.2, 19.3, 21.1,
23.8, 25.8, 26.1, 28.8, 29.0, 29.8, 31.5, 35.7, 40.8, 41.4, 49.8,
51.2, 55.8, 57.3, 58.4, 59.4, 67.6, 69.0, 82.3, 126.8, 127.8, 128.5,
130.9, 134.5 (overlap), 169.2, 172.4, 172.6, 172.7, 173.2, 173.5,
207.0; IR (neat) 2960, 2878, 2358, 2340, 1730, 1639, 1454,
1389, 1312, 1247, 1225, 1166, 1087 cm-1; HRMS m/z calcd for
5.73-5.74 (m, 1H), 7.01-7.25 (m, 4H), 7.38-7.48 (m, 2H); 13
C
NMR (125 MHz, CDCl3) δ 12.0, 12.9, 13.5 and 13.6 and 13.8
(RI), 14.7, 17.6, 18.2 and 18.4 (RI), 18.5, 19.2, 20.9, 23.4 and
23.6 (RI), 24.7 and 24.8 (RI), 25.0 and 25.1 (RI), 27.9 and 28.0
(RI), 28.1 and 28.2 (RI), 28.7 and 28.9 (RI), 29.6, 34.3, 34.8,
39.8, 40.5 and 40.9 (RI), 45.1, 47.1, 48.2, 49.7, 55.2, 56.0, 57.1
and 57.8 (RI), 69.0, 71.0, 72.0, 73.0, 79.1, 80.2, 125.3, 126.5
and 126.8 (RI), 127.2 and 127.7 (RI), 130.1, 132.2, 132.7 and
133.5, 156.1, 167.8, 169.0 and 169.5 (RI), 170.7, 171.5, 172.1
and 172.2 (RI), 173.7; IR (neat) 3355, 2960, 2869, 1740, 1702,
1670, 1642, 1540, 1450, 1387, 1301, 1227, 1168, 918, 883, 732
cm-1; HRMS m/z calcd for C55H91O12N5SiNa (M + Na)+
1064.6331, found 1064.6355; [R]2D5 -24.5 (c 0.96, CHCl3).
C y c lo [N -(t er t -b u t o x y c a r b o n y l)-O -[[N -[(2S ,4S )-4-
[(3S,4R,5S)-4-a m in o-3-[(tr iisop r op ylsilyl)oxy]-5-m eth yl-
h ep ta n oyl]oxy-3-oxo-2,5-d im eth ylh exa n oyl]-L-leu cyl]-L-
p r olyl-L-(3-ca r b oxy-1,2,3,4-t e t r a h yd r oisoq u in olyl)]-L-
th r eon yl] (31). To a solution of the alcohol 29 (10 mg, 9.59
µmol) in CH2Cl2 (1 mL) was added the Dess-Martin periodi-
nane reagent (6 mg, 14.1 µmol). After 2 h, the reaction was
not complete so more reagent (5 mg, 11.8 µmol) was added.
After an additional 2 h, the solution was diluted with Et2O
and poured onto a solution of Na2S2O3‚5H2O in saturated
aqueous NaHCO3 solution (48.3 mg in 4 mL). This mixture
was stirred for about 10 min, and when the upper Et2O layer
became clear, the layers were separated. The Et2O layer was
washed sequentially with saturated aqueous NaHCO3, H2O,
and saturated NaCl solutions. The Et2O layer was dried
(MgSO4), filtered, and concentrated. The residue was purified
by column chromatography eluting with acetone/hexanes (15:
85 to 18:82) to give the desired ketone 31 (6.8 mg, 68%) as a
white foam. 31: Rf 0.55 (30:70 acetone:hexanes); 1H NMR (500
MHz, CDCl3) δ 0.78-0.98 (m, 18H), 1.01-1.08 (m, 21H), 1.16-
1.25 (m, 5H), 1.26-1.36 (m, 4H), 1.38 and 1.44 (s, 9H), 1.48-
1.71 (m, 2H), 1.82-2.24 (m, 5H), 2.55-2.76 (m, 2H), 3.00 (dd
of ABX, J ) 17.1, 4.1 Hz) and 3.15 (dd of ABX, J ) 17.6, 2.2
Hz, 1H, RI), 3.18-3.29 (m, 1H), 3.37-3.47 (m, 1H), 3.53-3.57
(m, 1H) and 3.63-3.69 (m, 1H), 3.73 (dd, J ) 12.4, 4.2 Hz)
and 3.70-3.82 (m, 1H), 3.89-3.94 (m) and 4.10-4.15 (m, 1H),
4.24-4.37 (m, 1H), 4.38-4.46 (m, 1H), 4.49-4.63 (m, 2H),
4.70-4.83 (m, 2H), 90-5.01 (m, 2H), 5.09 (d, J ) 10.3 Hz) and
5.18 (d, J ) 7.6 Hz, 1H), 5.65-5.68 (m, 1H), 6.95-7.22 (m,
4H), 7.43 (d, J ) 10.5 Hz) and 7.70 (d, J ) 9.1 Hz, 1H), 8.46
(d, J ) 8.2 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 12.0 and
12.1 (RI), 12.8 and 13.3 and 13.8 (RI), 14.4 and 14.7 (RI), 15.3
and 15.9 (RI), 17.1, 18.1 and 18.2 and 18.4 and 18.5 (RI), 20.3,
20.8 and 21.1 (RI), 23.3 and 23.6 (RI), 24.8 and 24.9 (RI), 25.2,
27.4, 27.8 and 27.9 (RI), 28.11 and 28.14 (RI), 28.3 and 28.5
(RI), 28.9 and 30.0 and 30.4 (RI), 32.8, 33.4 and 33.7 (RI), 39.5
and 39.8 and 40.3 (RI), 41.8, 46.4, 47.1 and 48.3 (RI), 49.6 and
49.9 (RI), 52.6 and 54.1 (RI), 55.3 and 55.5 (RI), 56.1 and 56.3
(RI), 57.2 and 57.4 and 57.9 (RI), 69.2 and 69.4 (RI), 80.1 and
80.3 and 80.4 (RI), 81.7, 125.5, 126.6 and 126.8 (RI), 127.4 and
127.6 and 127.7 (RI), 129.7 and 130.1 (RI), 132.2 and 132.7
(RI), 133.4, 155.6 and 156.3 (RI), 167.8, 168.5 and 169.2 (RI),
169.3 and 169.6 (RI), 170.9 and 171.6 (RI), 171.3 and 171.6
(RI), 172.0 and 172.6 (RI), 202.5 and 204.5 (RI); IR (neat) 3331,
2960, 2868, 1735, 1670, 1642, 1534, 1497, 1449, 1387, 1367,
1314, 1247, 1166, 1103, 1048, 1016, 916, 883, 732 cm-1; HRMS
m/z calcd for C55H89O12N5SiNa (M + Na)+ 1062.6175, found
1062.6143; [R]2D5 -36.34 (c 1.1, CHCl3).
C
41H61O10N5‚HClNa (M + Na - HCl)+ 806.4316, found
25
806.4330; [R]D -127.1 (c 1.26, MeOH).
Cyclo-N-L-la ct yl-L-p r olyl-N-m et h yl-D-leu cin e [O-[[N-
[(2S,4S)-4-[(3S,4R,5S)-4-a m in o-3-h yd r oxy-5-m et h ylh ep -
tan oyl]oxy-3-oxo-2,5-dim eth ylh exan oyl]-L-leu cyl]-L-pr olyl-
L -( 3 -c a r b o x y -1 ,2 ,3 ,4 -t e t r a h y d r o i s o q u i n o l y l ) ] -L -
th r eon yl] (2). To a solution of amine salt (10 mg, 12.1 µmol)
and L-lactyl-L-prolyl-N-methyl-D-leucine (5.75 mg, 18.29 µmol),
in CH2Cl2 (0.5 mL) at 0 °C, were added BOP (8.1 mg, 18.29
µmol) and NMM (5.36 µL, 48.4 µmol). After 30 min, the
solution was brought to room temperature and stirred for 3
h. The reaction mixture was treated with 1.5 mL of saturated
NaCl solution and then extracted with EtOAc. The combined
organic layers were washed successively with 5% HCl, 5%
NaHCO3, and saturated NaCl solutions. The resulting organic
layer was dried (MgSO4), filtered, and concentrated. The crude
oil was purified by column chromatography, eluting with
MeOH/CH2Cl2 (5:95) to afford 2 (8.3 mg, 63%) as a white solid.
2: Rf 0.59 (10:90 MeOH:CH2Cl2); 1H NMR (500 MHz, CDCl3)
δ 0.84-0.95 (m, 24H), 1.16-1.25 (m, 3H), 1.31 (d, J ) 6.9 Hz,
3H), 1.36 (d, J ) 6.7 Hz, 3H), 1.40 (d, J ) 6.3 Hz, 3H), 1.42-
1.44 (m, 1H), 1.52-1.57 (m, 1H), 1.58-1.67 (m, 1H), 1.69-
1.72 (m, 1H), 1.81-1.91 (m, 2H), 1.95-2.04 (m, 6H), 2.15-
2.21 (m, 2H), 2.31-2.37 (m, 1H), 2.56 (dd, J ) 18.0, 9.9 Hz,
1H), 2.9 (brs, 1H), 3.04 (dd, J ) 17.0, 4.1 Hz, 1H), 3.15 (s, 3H),
3.36 (d, J ) 12.5 Hz, 1H), 3.38-3.43 (m, 1H), 3.52 (d, J ) 18
Hz, 1H), 3.55-3.58 and 3.62-3.65 (m, 4H), 3.79 (dd, J ) 12.3,
4.0 Hz, 1H), 4.06-4.13 (m, 2H), 4.21 (q, J ) 6.8 Hz, 1H), 4.34-
4.38 (m, 2H), 4.54 and 4.66, (AB, J ) 16.9 Hz, 2H), 4.69-4.79
(m, 3H), 5.22 (d, J ) 3.4 Hz, 1H), 5.34-5.37 (m, 2H), 7.08 (d,
6.3H), 7.10-7.23 (m, 4H), 7.51 (d, J ) 5.3 Hz, 1H), 7.88 (d, J
) 9.3 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 12.0, 13.2, 15.3,
16.0, 16.7, 18.8, 20.2, 20.9, 21.4, 23.4, 23.8, 24.9, 25.2, 26.0,
27.5, 28.0, 28.2, 28.4, 29.7, 31.3, 33.6, 36.3, 39.1, 41.1, 47.0,
49.3, 49.7, 49.8 (overlap), 54.6, 54.9,56.7, 57.5, 57.7, 57.9, 65.9
(overlap), 67.4, 69.7, 81.1, 125.4, 126.8, 127.7, 130.1, 132.2,
133.5, 167.3, 168.0, 169.4, 171.2, 171.5, 171.7, 172.8 (overlap),
173.8, 205.0; IR (neat) 3346, 2958, 1732, 1641, 1535, 1449,
1217, 1166, 1089, 753 cm-1; HRMS m/z calcd for C56H85N7O14
-
Cyclo[O-[[N-[(2S,4S)-4-[(3S,4R,5S)-4-a m in o-3-h yd r oxy-
5-m et h ylh ep t a n oyl]oxy-3-oxo-2,5-d im et h ylh exa n oyl]-L-
le u c y l]-L -p r o ly l-L -(3-c a r b o x y -1,2,3,4-t e t r a h y d r o is o -
Na (M + Na)+ 1102.6052, found 1102.6046; [R]2D5 -71.81 (c
0.415, CHCl3).

7584 J . Org. Chem., Vol. 66, No. 23, 2001
Tarver et al.
L-1,2,3,4-Tetr a h yd r o-7-h yd r oxy-6,8-d iiod oisoqu in olin e-
3-ca r boxylic Acid Hyd r och lor id e (13).55 Concentrated HCl
(248.6 mL), 1, 2-dimethoxyethane (16.6 mL), and formaldehyde
(37 wt %, 18.2 mL) were added under nitrogen to 3′,5′-diiodo-
L-tyrosine‚2H2O (25 g, 53.3 mmol) with stirring with a me-
chanical stirrer. CAUTION: the combination of concentrated
HCl and aqueous formaldehyde forms a potent carcinogen. The
resulting suspension was heated slowly to 72 °C for 30 min.
After 30 min at this temperature, additional concentrated HCl
(110 mL), 1,2-dimethoxyethane (8.3 mL), and formaldehyde
(37 wt %, 9.1 mL) were added. Stirring was continued for 18
h at 72-75 °C. The suspension was cooled in an ice bath, and
the solids were collected by filtration. The filter cake was
washed thoroughly with cold 1,2-dimethoxyethane until the
color lightened, and the solid was dried in vacuo overnight.
The resulting salt 13 (13.8 g, 54%) was obtained as a tan solid.
Although this product could be recrystallized from MeOH/H2O,
it was normally used without purification; [R]2D5 -79.44 (c
0.27, glacial HOAc); lit.55 [R]2D5 -88.83 (c 0.20, glacial HOAc).
2952, 1741, 1703, 1412, 1324, 1210 cm-1; HRMS (FAB) m/z
calcd for C20H20I2NO5 (M + H)+ 607.9434, found 607.9425;
[R]2D5 +35.19 (c 1.05, CHCl3). Anal. Calcd for C20H19I2NO5: C,
39.56; H, 3.15; N, 2.31; Found: C, 39.73; H, 3.22; N, 2.00.
Met h yl N-Cb z-N-L-1,2,3,4-Tet r a h yd r o-7-m et h oxyiso-
qu in olin e-3-ca r boxyla te (16). Methyl ester 15 (4.32 g, 7.12
mmol) was slowly dissolved in HPLC grade methanol (230
mL). The solution was cooled to 0 °C, and CuCl (1.04 g, 5.26
mmol) was added with stirring, turning the solution green.
Sodium borohydride (2.70 g, 71.2 mmol) was added in portions
over a period of 15 min, and the solution turned brown, then
black. After no starting material remained, the reaction
mixture was filtered through a Celite/MeOH slurry to obtain
a clear yellow solution. The solution was concentrated to afford
an orange residue that was dissolved in ethyl acetate. The
organic layer was washed with 10% HCl, 5% NaHCO3, and
brine and then dried over MgSO4. After removal of the drying
agent, the solution was concentrated and the crude oil was
purified by flash column chromatography, eluting with EtOAc/
petroleum ether (22:78) to afford 16 as a yellow oil (2.20 g,
87%). 16: Rf 0.63 (25:75 EtOAc:petroleum ether); 1H NMR (500
MHz, CDCl3) δ 3.08-3.22 (m, 2H), 3.54 and 3.62 (s, 3H, RI),
3.76 and 3.77 (s, 3H, RI), 4.54 (d, J ) 16.3 Hz) and 4.59 (d, J
) 16.4 Hz) and 4.77 (d, J ) 16.4 Hz) and 4.77 (d, J ) 16.4 Hz,
2H, RI), 4.94 (t, J ) 5.0 Hz) and 5.14-5.26 (m, 3H, RI), 6.61
and 6.69 (s, 1H, RI) and 6.72 (d, 8.3 Hz, 1H), 7.04 (d, J ) 8.3
Hz, 1H), 7.26-7.42 (m, 5H); 13C NMR (125 MHz, CDCl3) δ 30.3
and 30.7 (RI), 44.6 and 44.8 (RI), 52.2 and 52.3 (RI), 53.4 and
54.0 (RI), 55.3, 67.5 and 67.6 (RI), 111.0 and 111.2 (RI), 113.2,
123.6, 123.7, 127.9, 128.0, 128.1, 128.5 and128.6 (RI), 129.0,
129.5, 133.5, 155.9, 158.5, 171.7 and 171.92 (RI); IR (neat)
1742, 1702, 1613, 1505, 1410, 1321 cm-1; HRMS (CI) m/z calcd
for C20H25N2O (M + NH4)+ 373.1763, found 373.1758; [R]2D5
+13.95 (c 1.14, CHCl3).
N-Cbz-L-1,2,3,4-Tetr a h yd r o-7-m eth oxyisoqu in olin e-3-
ca r boxylic Acid (17). Methyl ester 16 (1.822 g, 5.13 mmol)
was dissolved in a 1:1:1 THF-water-MeOH mixture and
cooled to 0 °C. While stirring, lithium hydroxide hydrate (0.538
g, 12.82 mmol) was added. The reaction was allowed to stir
and was warmed to room temperature after 4 h. After stirring
for another 14 h, the reaction mixture was concentrated and
treated with NaHCO3. The solution was extracted twice with
EtOAc. The aqueous layer was acidified to pH 3 using 2 N
KHSO4 solution. The resulting acid was extracted into EtOAc
three times and washed with brine. After drying over MgSO4,
the solution was filtered and concentrated to afford the acid
(17) as a white foam (1.70 g, 97%). The acid was usually used
directly in the next step without purification. However, a small
amount was purified by column chromatography eluting with
MeOH/CH2Cl2 (7:93) to obtain a sample for characterization.
17: mp 52-54 °C; Rf 0.46 (25:75 EtOAc:petroleum ether); 1H
NMR (500 MHz, CDCl3) δ 3.09 (d, J ) 6.0 Hz) and 3.13 (d, J
) 6.0 Hz) and 3.20-3.23 (m, 2H, RI), 3.76 and 3.77 (s, 3H,
RI), 4.52-4.57 and 4.72-4.76 (m, 2H), 4.97-4.99 and 5.18-
5.23 (m, 3H, RI), 6.62-6.74 (m, 2H), 7.04-7.07 (m, 1H), 7.31-
7.46 (m, 5H); 13C NMR (125 MHz, CDCl3) δ 30.0 and 30.5 (RI),
44.5 and 44.7 (RI), 53.3 and 53.7 (RI), 55.2, 67.6 and 67.8 (RI),
111.0 and 111.2 (RI), 113.3, 123.4, 127.9, 128.0, 128.1 and
128.2, 128.5, 129.1 and 129.5 (RI), 133.3, 134.0, 136.3, 156.3,
158.5, 176.5; IR (neat) 2954, 1700, 1680, 1613, 1505, 1263,
1428, 1321 cm-1; HRMS (CI) m/z calcd for C19H23N2O5 (M +
NH4)+ 359.1607, found 359.1601; [R]D25 +16.42 (c 0.14, CHCl3).
Cbz-L-1,2,3,4-Tetr a h yd r o-7-h yd r oxy-6,8-d iiod oisoqu in -
olin e-3-ca r boxylic Acid (14). The hydrochloride salt (13,
6.00 g, 12.44 mmol) was dissolved in anhydrous CH2Cl2 (150
mL) and the solution cooled to 0 °C while stirring. Triethy-
lamine (3.78 g, 37.44 mmol) was added dropwise, and after 5
min Cbz-succinimide (3.41 g, 13.68 mmol) was added. The
reaction was monitored by TLC. At the end of the reaction,
the mixture was concentrated and washed first with NaHCO3
solution and then with EtOAc. The solution was extracted
three times into EtOAc. TLC comparison of aqueous vs organic
layers showed that the product remained at the baseline while
the undesired product had an Rf 0.60 (30%EtOAc/petroleum
ether). The aqueous layer was acidified to pH 2 using 2 N
KHSO4. The carboxylic acid was extracted into ethyl acetate
three times, and the solution was dried over MgSO4 and
filtered. The filtrate was concentrated to provide 5.67 g of 14
as a white/gray solid, 79%. yield. mp 94-96 °C; Rf 0.50 (10:90
1
MeOH:CH2Cl2); H NMR (500 MHz, CDCl3) δ 3.08-3.19 (m,
2H), 4.32 (d, J ) 17.6 Hz) and 4.38 (d, J ) 17.3 Hz) and 4.69
(d, J ) 11.8 Hz) and 4.73 (d, J ) 13.1 Hz, 2H, RI), 5.06-5.32
(m, 3H), 5.82 (br, 1H), 7.32-7.50 (m, 6H); 13C NMR (125 MHz,
CDCl3) δ 29.7 and 30.1 (RI), 50.7, 52.3 and 52.6 (RI), 68.0, 80.2
(overlap), 126.8, 127.2, 127.7, 128.1, 128.2, 128.3, 128.6,136.1,
138.5 and 138.7 (RI), 152.5, 156.1,175.0; IR (KBr) 3424, 1682,
1424, 1324 cm-1; HRMS (FAB) m/z calcd for C18H15I2NO5Na-
(M + Na)+ 601.8938, found 601.8953; [R]2D5 +44.08 (c 0.52,
CHCl3).
Meth yl N-Cbz-L-1,2,3,4-Tetr a h yd r o-7-h yd r oxy-6,8-d i-
iod o-isoqu in olin e-3-ca r boxyla te (15). Acid 14 (5.00 g, 8.63
mmol) was dissolved in anhydrous THF under N2. Potassium
hydroxide (3.19 g, 56.9 mmol) was added in portions to the
stirring solution, and then tetrabutylammonium hydrogen
sulfate (0.500 g, 1.48 mmol) was added. After initiating
vigorous stirring, dimethyl sulfate was added dropwise. Once
the reaction was judged complete by TLC, the KOH was
collected and the filtrate was stirred with 50% ammonium
hydroxide solution at 0 °C to quench any excess dimethyl
sulfate (CAUTION: toxic and potent carcinogen). The mixture
was concentrated and extracted with ethyl acetate twice. The
organic layer was washed with 10% HCl, 5% NaHCO3, and
brine. The organic layer was dried over MgSO4. The crude oil
was purified by flash column chromatography, eluting with
EtOAc:petroleum ether (18:82) to afford the ester (15) as a
white solid (4.77 g, 91%) Recrystallization of the solid from
ether/petroleum ether was done prior to elemental analysis.
N-Cb z-L-3-Ca r b oxy-1,2,3,4-t et r a h yd r o-7-m et h oxyiso-
qu in olin e-O-Boc-th r eon in e-OSEM (18). Acid 18 (3.34 g,
9.65 mmol) and Boc-Thr-OSEM (2.34 g, 8.98 mmol) were
dissolved in CH2Cl2 (1.85 mL, Note: Solution should be no
more concentrated than 0.25 M). The solution was cooled to 0
°C, and then triethylamine (2.9 mL, 20.65 mmol), DMAP
(0.274 g, 2.25 mmol), and isopropenyl chloroformate (1.1 mL,
9.88 mmol) were added, in that order. After stirring at 0 °C
for 1.5 h, the reaction was diluted with ether (20 mL) and
washed with 10% HCl, 5% NaHCO3, and brine and then dried
over MgSO4. After removal of the drying agent, the solution
was concentrated under reduced pressure to afford 18 as a
1
15: mp 47-49 °C; Rf 0.32 (30:70 acetone/hexanes); H NMR
(500 MHz, CDCl3) δ 3.13-3.21 (m, 2H), 3.60 and 3.66 (s, 3H,
RI), 3.84 (s, 3H), 4.29-4.39 (m) and 4.75-4.81 (m, 2H), 5.03
and 5.20-5.31 (m, 3H), 7.35-7.58 and 7.56-7.57 (m, 6H); 13
C
NMR (125 MHz, CDCl3) δ 30.0 and 30.4 (RI), 50.9, 52.3 and
52.6 (RI), 52.8, 60.6, 67.8, 87.7, 95.1, 127.7, 128.0, 128.1, 128.2,
128.5, 131.2, 136.7, 139.1, 139.5, 155.9, 157.7, 170.9; IR (neat)
(55) Verschueren, K.; Toth, G.; Tourwe´, D.; Lebl, M.; Van Binst, G.;
Hruby, V. J . Synthesis 1992, 458-460.

Conformationally Constrained Didemnin B Analogues
J . Org. Chem., Vol. 66, No. 23, 2001 7585
yellow oil (4.75 g, 78%). Compound 18 was purified by column
chromatography, eluting with 5%-10% acetone/hexanes gradi-
ent. 18: Rf 0.71 (20:80 EtOAc:petroleum ether); 1H NMR (500
MHz, CDCl3) δ 0.0 (s, 9H), 0.86 (t, J ) 8.2 Hz, 2H), 1.04 (d, J
) 6.3 Hz) and 1.12 (d, J ) 6.3 Hz, 3H, RI), 1.44 and 1.45 (s,
9H, RI), 3.01-3.14 (m, 2H), 3.51-3.63 (m, 2H), 3.73 and 3.75
(s, 3H, RI), 4.34-4.39 (m, 1H), 4.48 and 4.69 (AB quartet, J )
16.4 Hz, 2H), 4.85 (d, J ) 5.7 Hz) and 4.91 (t, J ) 4.7 Hz, 1H,
RI), 5.00 (d, J ) 8.5 Hz, 1H), 5.05-5.14 (m, 1H), 5.17 and 5.20
(s, 2H, RI), 5.24-5.28 (m, 2H), 6.60 and 6.68-6.71 (m, 2H),
7.01 (d, J ) 8.5 Hz, 1H), 7.28-7.40 (m, 5H); 13C NMR (125
MHz, CDCl3) δ -1.6 and -1.4 (RI), 16.6, 17.9, 28.3, 30.2 and
30.7 (RI), 44.6 and 44.9 (RI), 53.5 and 54.0 (RI), 55.2, 56.9 and
57.0 (RI), 67.5 and 67.7 (RI), 68.1, 71.6 and 71.7 (RI), 80.3,
90.3, and 90.4 (RI), 111.1 and 111.3 (RI), 113.2, 123.3 and 123.5
(RI), 128.0, 128.1, 128.5, 129.0, 129.3, 133.4, 134.0, 136.3 and
136.4 (RI), 155.8, 156.0, 158.5, 169.5, 170.0; IR (neat) 1730,
1713, 1504, 1413, 1163 cm-1; HRMS (FAB) m/z calcd for
N-[N-[N-[(Ben zyloxy)ca r bon yl]-L-leu cyl]-L-p r olyl]-L-(3-
ca r boxy-1,2,3,4-tetr a h yd r o-7-m eth oxyisoqu in olin e), Es-
ter w ith (3S,4R,5S)-3-Hyd r oxybu tyr a m id o]-5-m eth ylh ep -
ta n oic Acid , (1S,2S,3R)-4-[(ter t-Bu tyld im eth ylsilyl)oxy]-
1-isopr opyl-2-(m eth oxym eth oxy)-3-m eth ylbu tyl Ester (22).
To a solution of tetrapeptide acid 21 (1.01 g, 1.34 mmol) and
protected HIP-isostatine (0.663 g, 1.04 mmol) in CH2Cl2 (2 mL,
0.6M) was added HATU (0.566 g, 1.49 mmol). The reaction
was cooled to 0 °C, DIEA (0.65 mL, 3.72 mmol) was added,
and the reaction was allowed to warm slowly to room temper-
ature. After 14 h, the reaction color changed from yellow to
dark reddish brown. The reaction was diluted with ether,
washed with 10% HCl, saturated NaHCO3, and brine, and then
dried over Na2SO4. The solvent was removed under reduced
pressure to leave an orange foam. The residue was purified
by column chromatography, eluting with acetone/hexanes
gradient, to afford 1.84 g of 22 as a white solid (63% yield).
22: mp 77-80 °C; Rf 0.71 (30:70 EtOAc:petroleum ether); 1H
NMR (500 MHz, CDCl3) δ 0.02 (s, 6H), 0.83-0.99 (m, 30H),
1.04-1.06 (m, 21H), 1.07-1.34 (m, 3H), 1.40 (s, 9H), 1.44-
1.56 (m, 3H), 1.71-1.88 (m, 3H), 1.90-2.16 (m, 5H), 2.21-
2.27 (m, 1H), 2.65-2.66 (m, 2H), 3.02 (dd, J ) 15.5, 5.6 Hz,
1H), 3.14 (dd, J ) 15.5, 3.2 Hz, 1H), 3.28 (s, 3H), 3.39-3.47
(m, 2H), 3.65-3.72 (m, 1H), 3.74 (s, 3H), 3.75-3.77 (m, 2H),
4.08-4.11 (m, 2H), 4.34-4.37 (m, 1H), 4.50-4.67 (m, 2H),
4.84-4.87 (m, 1H), 4.92-5.13 (m, 6H), 5.36-5.40 (m, 2H), 6.34
(d, J ) 10.1 Hz, 1H), 6.59-6.70 (m, 2H), 6.97 (d, J ) 8.4 Hz,
1H), 7.23-7.32 (m, 5H); 13C NMR (125 MHz, CDCl3) δ -5.5,
0.3, 17.7, 17.9, 18.1, 20.0, 21.5, 23.4, 24.5, 24.7, 25.8, 27.6, 28.1,
28.2, 28.6, 29.9, 34.8, 37.5, 40.6, 41.7, 45.6, 47.0, 50.9, 52.1,
55.2, 55.9, 56.3, 57.1, 57.5, 65.0, 66.7, 70.1, 71.1, 78.6, 78.8,
79.8, 98.6, 111.0, 113.3, 124.3, 127.9, 128.0, 128.4, 129.2, 132.8,
136.4, 155.3, 156.3, 158.5, 168.3, 169.8, 171.0, 171.1, 171.4;
IR (neat) 3330, 2958, 1719, 1680, 1640 cm-1; HRMS m/z calcd
for C72H121N5O16Si2Na (M + Na)+ 1390.8245, found 1390.8284;
[R]2D5 -19.95 (c 2.9, CHCl3). Anal. Calcd for C72H121N5O16Si2:
C, 63.17; H, 8.91; N, 5.12; Found: C, 63.06; H, 8.93; N, 5.28.
C
34H48N2O10SiNa (M + Na)+ 695.3076, found 695.3071; [R]2D5
+29.85 (c 1.37, CHCl3).
Cb z-Leu cylp r olyl-L-(3-ca r b oxy-1,2,3,4-t et r a h yd r o-7-
m eth oxy-isoqu in olin e)-O-Boc-th r eon in e-OSEM (20). A
solution of carbamate 18 (3.45 g, 5.13 mmol) and 10% Pd on
carbon (0.080 g) in 1:1 MeOH/EtOAc solvent (25 mL) was
placed in a Parr hydrogenator vessel under 50 psi for 8 h. After
all the starting material had been consumed, the reaction was
filtered through a Celite/MeOH slurry and concentrated under
reduced pressure. The resulting yellow oil (19) was used
without purification in the next step. Crude yield 87%. To a
solution of Cbz-Leu-Pro-OH (2.13 g, 5.89 mmol) in CH2Cl2 (12
mL) cooled to -15 °C were added BOP-Cl (1.66 g, 6.52 mmol)
and N-methylmorpholine (0.7 mL, 6.52 mmol). The reaction
was stirred for 40 min and then warmed to 0 °C for 5 min
before adding a stirred, cooled solution of amine 19 (2.76 g,
5.13 mmol) in CH2Cl2 (12 mL) and NMM (0.7 mL, 6.52 mmol).
The reaction was stirred at 0 °C for 6 h, diluted with ether
(50 mL), washed with 10% HCl, saturated NaHCO3, and brine,
and then dried over MgSO4. The solvent was removed under
reduced pressure to provide 20 as a white foam. Compound
20 was purified by column chromatography, eluting with
acetone/hexanes gradient, to afford 2.90 g of a solid, 64% yield.
20: mp 66-68 °C; Rf 0.45 (30:70 EtOAc:petroleum ether); 1H
NMR (500 MHz, CDCl3) δ -0.02 (s, 9H), 0.80-0.89 (m, 2H),
0.92 (d, J ) 6.6 Hz) and 0.95 (d, J ) 6.7 Hz, 3H, RI) and 0.99
(d, J ) 6.4 Hz) and 1.03 (d, J ) 6.5 Hz, 6H, RI), 1.10 (d, J )
6.3 Hz) and 1.23 (d, J ) 6.1 Hz, 3H, RI), 1.38-1.40 (m, 2H),
1.42 and 1.44 (s, 9H, RI), 1.48-1.60 (m, 1H), 1.83-1.86 and
2.01-2.32 (m, 4H), 3.00-3.14 (m, 2H), 3.47-3.59 (m, 2H),
3.60-3.68 and 3.80-3.82 (m, 2H), 3.74 and 3.75 (s, 3H, RI),
4.33-4.38 (m, 1H), 4.50-4.69 (m, 2H), 4.75-5.03 (m, 4H),
5.05-5.17 (m, 2H), 5.20-5.22 (m, 2H), 5.29-5.40 (m, 2H),
6.60-6.63 and 6.69-6.73 (m, 2H), 7.02 (d, J ) 8.4 Hz, 1H),
7.27-7.32 (m, 5H); 13C NMR (125 MHz, CDCl3) δ -1.3, 16.7,
17.9, 21.5, 23.4, 24.6, 24.9, 28.3 and 28.5 (RI), 29.9, 30.4 and
30.5 (RI), 41.7, 45.6, 47.0, 51.9, 55.2, 55.3, 57.3, 57.7, 66.8, 68.1,
71.9, 80.3, 90.4, 111.2, 113.4, 124.2, 127.9, 128.0, 128.2, 128.4,
128.5, 129.3, 129.4, 132.4, 155.6, 156.3, 158.6, 169.4, 169.8,
N-[N-[N-[(Ben zyloxy)ca r b on yl]-L-leu cyl]-L-p r olyl]-L-
(3-ca r b oxy-1,2,3,4-t et r a h yd r o-7-m et h oxyisoq u in olin e),
Ester w ith (3S,4R,5S)-3-Hyd r oxybu tyr a m id o]-5-m eth yl-
h ep t a n oic Acid , (1S,2S,3R)-4-H yd r oxy-1-isop r op yl-2-
(m eth oxym eth oxy)-3-m eth ylbu tyl Ester (23). To a stirred
solution of TBDMS ether 22 (0.900 g, 0.660 mmol) in “wet”
THF (1.6 mL, distilled but not anhydrous) at ambient tem-
perature was added a 3:1 HOAc:water solution (6.4 mL) in a
steady stream. The reaction was allowed to stir 24 h then
worked up by removing solvent as an azeotrope with toluene
until no acetic acid remained. The compound was purified by
column chromatography, eluting with acetone/hexanes gradi-
ent, affording 23 as a white solid (0.619 g, 75%); 23: mp 86-
1
87 °C; Rf 0.33 (50:50 EtOAc:petroleum ether); H NMR (500
MHz, CDCl3) δ 0.86-0.94 (m, 21H), 0.97-1.07 (m, 21H), 1.13
(m, 3H), 1.42 (s, 9H), 1.45-1.56 (m, 3H), 1.77-1.83 (m, 3H),
1.91-1.96 (m, 4H),2.04-2.26 (m, 3H), 2.66-2.68 (m, 2H),
3.06-3.18 (m, 2H), 3.38 (s, 3H), 3.43-3.49 (m, 2H), 3.68-3.80
(m, 3H), 3.76 (s, 3H), 4.09-4.14 (m, 2H), 4.32-4.34 (m, 1H),
4.55-4.56 (m, 2H), 4.66-4.68 (m, 2H), 4.90 (d, J ) 4.90, 15.0
Hz, 1H), 4.99-5.16 (m, 5H), 5.36-5.52 (m, 3H), 6.62-6.73 (m,
3H), 6.99 (d, J ) 8.4 Hz, 1H), 7.26-7.31 (m, 5H); 13C NMR
(125 MHz, CDCl3) δ 11.8, 12.7, 12.9, 14.5, 15.8, 18.1, 19.8, 21.5,
23.4, 24.6, 24.7, 27.5, 27.6, 28.1, 28.3, 28.5, 30.0, 35.2, 36.8,
40.6, 41.6, 45.8, 47.0, 50.9, 52.0, 55.3, 56.3, 57.1, 64.1, 64.2,
66.8, 69.3, 70.5, 70.7, 77.5, 78.3, 79.4, 98.5, 111.1, 113.3, 124.1,
127.9, 128.0, 128.4, 129.2, 132.8, 136.4, 155.0, 156.3, 158.6,
167.9, 168.2, 169.6, 171.2, 171.8; IR (neat) 3334, 2961, 2868,
1718, 1682, 1638, 1506, 1455, 1367, 1253, 1174, 1040, 919
cm-1; HRMS m/z calcd for C66H107N5O16SiNa (M + Na)+
1276.7380, found 1276.7361; [R]2D5 -27.55 (c 1.1, CHCl3).
Anal. Calcd for C66H107N5O16Si: C, 63.18; H, 8.60; N, 5.58;
Found: C, 62.83; H, 8.58; N, 5.46.
170.8, 171.2; IR (neat) 3287, 2955, 2360, 1715, 1644 cm-1
;
HRMS m/z calcd for C45H66N4O12SiNa (M + Na)+ 905.4344,
found 905.4368; [R]2D5 -9.36 (c 0.55, CHCl3). Anal. Calcd for
C
45H66N4O12Si: C, 61.20; H, 7.53; N, 6.34; Found: C, 60.82;
H, 7.45; N, 5.94.
Cb z-Leu cylp r olyl-L-(3-ca r b oxy-1,2,3,4-t et r a h yd r o-7-
m eth oxyisoqu in olin e)-O-Boc-th r eon in e (21). To a solution
of SEM ester 20 (1.21 g, 1.37 mmol) in CH2Cl2 (14 mL) cooled
to 0 °C was added MgBr2 (0.757 g, 4.11 mmol) in one portion.
After stirring at 0 °C for 3 h, no starting material remained.
The reaction was diluted with ethyl acetate (25 mL) and
washed with 10%HCl. The aqueous layer was extracted with
ethyl acetate. The organic layers were combined and dried over
Na2SO4. The solvent was removed under reduced pressure,
affording 21 as a yellow foam which was used without
purification in the next step. (1.01 g, crude yield 98%).
N-[N-[N-[(Ben zyloxy)ca r bon yl]-L-leu cyl]-L-p r olyl]-L-(3-
ca r boxy-1,2,3,4-tetr a -h yd r o-7-m eth oxyisoqu in olin e), Es-
ter w ith (3S,4R,5S)-3-Hyd r oxybu tyr a m id o]-5-m eth ylh ep -
tan oic Acid, (1S,2S,3R)-1-Isopr opyl-2-(m eth oxym eth oxy)-

7586 J . Org. Chem., Vol. 66, No. 23, 2001
Tarver et al.
3-m eth yl-bu ta n oic Acid Ester (25). To a solution of alcohol
23 (0.595 g, 0.474 mmol) in CH2Cl2 (9 mL) was added the
Dess-Martin periodinane reagent. After the starting material
had been consumed (TLC, 30%acetone/hexanes), the reaction
was diluted with ether (60 mL) and 1:1 saturated Na2S2O3/
saturated NaHCO3 solution or, alternatively, Na2S2O3 (898 mg,
5.68 mmol) dissolved in saturated NaHCO3 solution (20 mL)
was added. The mixture was stirred until the ether layer
became clear (10 min), and then the layers were separated.
The organic phase was washed with saturated NaHCO3, water,
and brine and then dried over MgSO4. The solvent was
removed under reduced pressure to leave an odorous tan foam.
The aldehyde was dissolved in DMSO (5 mL). To the solution
was added acetonitrile (5 mL) and water (5 mL). The stirring
solution became cloudy, and then sodium chlorite (60 mg, 0.664
mmol) and sodium monobasic phosphate hydrate (13 mg, 0.095
mmol) were added. The reaction was stirred for 16 h then
diluted with ethyl acetate and cooled to 0 °C. The cooled
solution was acidified carefully to pH 3 using 10% HCl. The
acid was extracted thrice into ethyl acetate, and the organic
phase was concentrated. The oily residue was dissolved in
ether and washed with water to remove residual DMSO. The
organic phase was dried over Na2SO4, and solvent was
removed under reduced pressure. Compound 25 was purified
by column chromatography, eluting with acetone/hexanes
gradient (10%-40%), to yield a white/tan solid (0.504 g, 84%).
and 3.39 (s, 3H, RI), 3.46 (q, 1H), 3.69 (dd, J ) 12.4, 4.3, 1H),
3.74(s) and 3.78 (s, 3H, RI), 3.88(m) and 3.91 (dd, J ) 9.0, 1.6,
1H), 4.11 (t) and 4.20 (m, 1H), 4.35 (q, J ) 7.2, 1H), 4.45 (dd,
J ) 16.4, 2.1) and 4.67 (d, J ) 17.1, 1H), 4.53-4.57 (m, 1H),
4.66 (m) and 4.69 (d, J ) 6.4, 2H), 4.78 (m,), 4.84 (m, sextet,
1H), 5.03 (d, J ) 10.6) and 5.15 (d, J ) 6.7, 1H), 5.70 (m, 1H),
6.60 (d, J ) 2.4) and 6.63 (d, J ) 2.2, 1H), 6.68 (dd, J ) 8.3,
2.4) and 6.78 (dd, J ) 8.4, 2.5, 1H), 6.93 (d, J ) 8.4) and 7.09
(d, J ) 8.5, 1H), 7.39 (d, J ) 9.5) and 7.52 (d, J ) 10.7, 1H);
13C NMR (125 MHz, CDCl3) δ 12.1, 13.0, 13.6, 13.6,14.1, 14.6,
17.4, 17.7,18.3, 18.4 18.5, 19.1, 19.1, 19.3, 20.9, 21.2, 22.7, 23.4,
23.6, 24.7, 24.8, 25.1, 25.2, 27.2, 27.4, 27.7, 27.8, 27.9, 28.2,
28.3, 28.8, 28.9, 29.2, 29.7, 31.9, 34.4, 34.7, 39.8, 40.6, 40.9,
42.8 and 43.3 (RI), 44.9, 46.5, 47.1, 48.4, 48.7, 49.9, 54.0, 55.0,
55.2, 55.4, 56.2, 56.3, 57.4, 57.8, 61.6, 68.9, 71.1, 78.7, 79.2,
79.6, 80.1, 80.4, 98.6, 110.3, 111.1, 113.2, 113.6, 122.1, 125.4,
128.9, 130.9, 131.0, 133.3, 133.9, 155.3, 156.0, 158.3, 158.8,
167.9, 168.8, 169.0, 169.4, 170.8, 171.4, 172.2, 174.1, 174.2;
HRMS m/z calcd for C58H97N5O14SiNa (M + Na)+ 1138.6699,
found 1138.6705.
Cyclo[N -(t er t -b u t oxyca r b on yl)-O-[[N -[(2S ,3S ,4S )-4-
[(3 S ,4 R ,5 S )-4 -a m i n o -3 -[(t r i i s o p r o p y l s i l y l )o x y ]-5 -
m eth ylh ep ta n oyl]oxy-3-h yd r oxy-2,5-d im eth ylh exa n oyl]-
L-leu cyl]-L-p r olyl-L-(3-ca r b oxy-1,2,3,4-t et r a h yd r o-7-m e-
th oxyisoqu in olyl)]-L-th r eon yl] (30). To a solution of MOM
ether 28 (70 mg, 62.7 µmol) in CH2Cl2 (0.6 mL) cooled to -78
°C was added 3.0 M Me2BBr solution in CH2Cl2 (0.06 mL, 0.188
mmol) dropwise. After 1 h, the reaction was treated with a
3:1 THF:saturated NaHCO3 solution (0.06 mL) at -78 °C,
stirred 5 min, and then warmed to RT and diluted with ether.
The aqueous layer was separated, and the organic phase was
washed successively with water, 10% NaHSO4, and brine and
dried over Na2SO4. The solvent was removed under reduced
pressure, and the product was purified by column chromatog-
raphy, eluting with 20% acetone/hexanes, affording 30 as a
white powder (59.6 mg, 87%). 30: Rf 0.43 (30% acetone/
hexanes); 1H NMR (500 MHz, CDCl3): δ 0.84-0.95 (m, 18H),
1.00-1.13 (m, 21H), 1.14-1.35 (m, 6H), 1.39 (s) and 1.42 (s,
9H, RI), 1.44-1.60 (m, 4H), 1.90 (m, 2H), 1.97-2.28 (m, 4H),
2.29-2.35 (m, 1H), 2.47 (dd, J ) 18.4, 6.8) and 2.53 (d, J )
17.1, 1H), 2.65 (m) and 2.73 (dd, J ) 15.4, 7.8, 1H), 2.93 (m),
3.10 (dd, J ) 16.5, 5.2) and 3.20 (d, J ) 14.8, 2H) 3.31 (dd, J
) 16.5, 12.6) and 3.46 (q, 1H), 3.62-3.76 (m, 2H), 3.73 (s) and
3.78 (s, 3H, RI), 3.86 (d, J ) 8.0) and 3.91 (d, J ) 9.1, 1H),
3.99 (m) and 4.12 (t, 1H), 4.23 (t) and 4.33 (t,1H), 4.48-4.65
(m, 3H), 4.69 (d, J ) 3.7) and 4.72 (d, J ) 7.8) and 4.76 (t,
2H), 4.85 (m, 1H), 4.92 (m, 1H), 4.97 (d, J ) 10.6) and 5.18 (d,
J ) 7.3), 5.03 (br) and 5.41 (br) and 5.69 (m,1H), 6.50 (br),
6.59 (d, J ) 2.2) and 6.63 (d)2.4, 1H), 6.67 (dd, J ) 7.2, 2.4)
and 6.78 (dd, J ) 8.5, 2.5, 1H), 6.91 (d, J ) 8.4) and 7.09 (d,
J ) 8.6, 1H), 7.37 (d, J ) 7.6) and 7.43 (dd, J ) 10.2, 3.0, 2H);
13C NMR: (125 MHz, CDCl3) δ 12.1, 12.9, 13.5, 13.6, 14.7, 17.6,
18.2, 18.4, 18.5, 18.5, 19.2, 20.9, 21.1, 23.4, 23.6, 24.7, 24.8,
25.1, 25.1, 27.2, 27.7, 28.0, 28.2, 28.3, 28.7, 29.0, 29.6, 31.8,
34.4, 34.7, 34.8, 39.8, 40.1, 41.0, 43.4, 45.0, 45.2, 46.5, 47.1,
48.2, 49.8, 54.2, 55.2, 55.2, 55.4, 56.0, 57.4, 57.8, 69.0, 71.0,
72.0, 73.1, 79.1, 80.2, 80.4, 110.4, 111.1, 113.2, 113.6, 122.1,
125.4, 128.8, 131.0, 133.3, 133.9, 155.3, 156.1, 158.3, 158.8,
167.9, 169.1, 169.5, 170.8, 171.5, 172.1, 172.2, 173.7; IR (neat)
3326, 2924, 2852, 2364, 1734, 1636 cm-1; HRMS m/z calcd for
C56H93N5O13SiNa (M + Na)+ 1094.6436, found 1094.6460;
[R]2D5 -15.17 (c 0.15, CHCl3).
1
25: mp 76-79 °C; Rf 0.38 (30:70 acetone:hexanes); H NMR
(500 MHz, CDCl3) δ 0.84-0.99 (m, 18H), 1.02-1.04 (m, 21H),
1.13-1.31 (m, 5H), 1.40 (s, 9H), 1.41-1.57 (m, 2H), 1.72-1.78
(m, 2H), 2.04-2.45 (m, 5H), 2.51-2.73 (m, 3H), 3.06 (dd, J )
15.4, 5.2 Hz, 1H), 3.12-3.15 (m, 1H), 3.39 (s, 3H), 3.75 (s, 3H),
3.77-3.83 (m, 3H), 4.06-4.08 (m, 1H), 4.37-4.39 (m, 2H),
4.55-4.70 (m, 4H), 4.78 (d, J ) 9.9 Hz, 1H), 4.87 (d, J ) 15.1
Hz, 1H), 4.92-5.14 (m, 4H), 5.39-5.50 (m, 3H), 6.61 (m, 1H),
6.71 (d, J ) 8.3 Hz, 1H), 6.77 (d, J ) 8.7 Hz, 1H), 6.98 (d, J )
7.3 Hz, 1H), 7.24-7.31 (m, 5H); 13C NMR (125 MHz, CDCl3) δ
11.7, 12.6, 14.5 and 14.7 (RI), 15.8, 17.7, 18.1, 19.0, 21.5, 23.3,
24.5, 24.6, 24.7, 27.3, 28.2, 28.4, 29.7, 29.9, 35.6, 39.5, 40.5,
41.1 and 41.3 (RI), 42.6, 45.8, 47.1, 51.0, 55.3, 56.4, 56.9, 57.3,
58.3, 66.8, 68.7, 70.6, 78.4, 78.9, 80.2, 97.8, 111.2, 113.4, 124.1,
127.7, 127.9, 128.0, 128.2, 128.4, 129.1, 132.6, 136.4, 155.5,
156.3, 158.6, 168.7, 169.5, 171.6, 171.8, 171.9, 175.6; IR (neat)
3325, 2961, 1714, 1650, 1506, 1452, 1170, 1040, 750 cm-1
;
HRMS m/z calcd for C66H106N5O17Si (M + H)+ 1268.7352, found
1268.7302; [R]D25 -16.89 (c 0.305, CHCl3).
Cyclo[N-ter t-b u t yloxyca r b on yl)-O-[[N-[(2S,3S,4S)-4-
[(3S,4R,5S)-4-a m in o-3-[(tr iisop r op ylsilyl)oxy]-5-m eth yl-
h ep t a n oyl]-oxy-3-(m et h oxym et h oxy)-2,5-d im et h ylh ex-
a n oyl]-L-leu cyl]-L-p r olyl-L-(3-ca r boxy-1,2,3,4-tetr a h yd r o-
7-m eth oxyisoqu in olyl)]-L-th r eon yl] (28). A stirred solution
of carbamate 25 (12.3 mg, 9.7 µmol) and 10% Pd/C (200 mg)
in absolute ethanol (0.7 mL) was evacuated thrice and placed
under a hydrogen atmosphere. The reaction was left under
hydrogen atmosphere for 24 h.The catalyst was then filtered
and washed with ethanol. The solvent was removed under
reduced pressure to provide a tan foam. The amine was used
without purification in the next step.
To a solution of amino acid in CH2Cl2 (1.5 mL, 0.005 M)
was added O-(7-azabenzotriazol-1-yl-N, N, N′,N′-tetramethy-
-
luronium PF6 salt (HATU) (4 mg, 0.353 mmol), and the
solution was cooled to 0 °C. DIEA (0.061 mL, 0.353 mmol) was
added dropwise, and then the reaction was allowed to warm
to room temperature. After 18 h, the reaction was diluted with
ether, washed with 10% HCl, saturated NaHCO3, and brine,
and then dried over Na2SO4. The solvent was removed under
reduced pressure, and the resulting compound was purified
by column chromatography, eluting with acetone/hexanes
gradient, to afford 28 as an orange/tan foam (6 mg, 61%); 28:
Rf 0.45 (30:70 acetone:hexanes); 1H NMR (500 MHz, CDCl3) δ
0.85 (t, 5H), 0.89-1.04 (m,13H),1.06 (m, 21H), 1.12-1.35 (m,
9H), 1.39 and 1.42 (s, 9H), 1.90-2.09 (m, 5H), 2.15-2.20 (m,
1H), 2.40 (broad, 0.5H), 2.51 (d, J ) 6.6, 0.5H), 2.54-2.60 (m,
1H), 2.63 (broad, 0.5H), 2.74-2.80 (m, 0.5H), 2.93 (dd, J )
18.7, 2.3, 1H), 3.13 (m, 1H), 3.32 (dd, J ) 16.4, 12.5), 3.37 (s)
C y c lo [N -(t er t -b u t o x y c a r b o n y l)-O -[[N -[(2S ,4S )-4-
[(3 S ,4 R ,5 S )-4 -a m i n o -3 -[(t r i i s o p r o p y l s i l y l )o x y ]-5 -
m e t h ylh e p t a n oyl]oxy-3-oxo-2,5-d im e t h ylh e xa n oyl]-L-
le u cyl]-L-p r olyl-L-(3-ca r b oxy-1,2,3,4-t e t r a h yd r o-7-m e -
th oxyisoqu in olyl)]-L-th r eon yl] (32). To a solution of alcohol
30 (27.3 mg, 25.5 µmol) in CH2Cl2 (1.8 mL) was added Dess-
Martin periodinane (DMP) (24 mg, 57 µmol). After 2 h, starting
material still remained so another 3 equiv of DMP was added,
and the reaction allowed to stir another 2 h. The reaction was
diluted with ether (7 mL) and treated with 2 mL of 1:1
saturated Na2S2O3/saturated NaHCO3 solution and added
Na2S2O3 (24 mg). The mixture was stirred until the ether layer

Conformationally Constrained Didemnin B Analogues
J . Org. Chem., Vol. 66, No. 23, 2001 7587
became clear (10 min), and then the layers were separated.
The organic phase was washed with sat. NaHCO3, water, and
brine and then dried over Na2SO4. The solvent was removed
under reduced pressure to leave a white foam. The product
was purified by column chromatography, eluting with 20%
acetone/hexanes, affording 32 as a white foam (25.7 mg, 94%).
carefully triturated three times using 4:1 hexane:methyl tert-
butyl ether solution, and the reaction was concentrated to
afford a tan powder. The salt (4.6 mg, 5.61 µmol) was dissolved
in CH2Cl2, and the didemnin B side chain (2 mg, 6.17 µmol)
was added. At room temperature, HATU (2.5 mg, 6.73 µmol)
and DIEA (4 µL, 20.4 µmol) were added to the solution. After
stirring 14 h, the reaction was diluted with ether and washed
with 10% HCl, saturated NaHCO3, and brine and then dried
over Na2SO4. The solvent was removed under reduced pres-
sure. The residue was purified by column chromatography,
eluting with 30%-50% acetone/hexanes gradient, to afford 3
a white powder (4.6 mg, 74%); Rf 0.59 (10% MeOH/CH2Cl2);
1H NMR (500 MHz, CDCl3) δ 0.82-0.95 (m, 12H), 0.98-1.05
(m, 6H), 1.08-1.49 (m, 6H), 1.53-1.68 (m, 3H), 1.71-1.92 (m,
3H), 1.96-2.05 (m, 8H), 2.21 (m, 2H), 2.26-2.38 (m, 3H), 2.54-
2.59 (m, 2H), 2.87-3.17 (m, 3H), 3.13 (s) and 3.15 (s, 3H),
3.18-3.32 (m, 1H), 3.41-3.48 (m, 1H), 3.51-3.71 (m, 4H),
3.73-3.80 (m, 2H), 3.79 (s, 3H), 4.01-4.16 (m, 4H), 4.17-4.23
(m, 1H), 4.32-4.39 (m, 2H), 4.49-4.65 (m, 2H), 4.70-4.90 (m,-
3H), 5.18-5.25 (m, 1H), 5.32-5.39 (m, 2H), 6.61 (m) and 6.70
(d, J ) 2.6, 1H), 6.79 (m, 2H), 7.07-7.13 (m, 3H), 7.25-7.34
(m, 1H), 7.47-7.53 (m, 1H), 7.68-7.77 (m, 1H), 7.90 (d, J )
9.2, 1H); 13CNMR (125 MHz, CDCl3) δ 11.8, 12.0, 13.2, 14.1,
14.1, 14.9, 15.4, 15.5, 16.1, 16.3, 16.7, 18.8, 18.8, 20.2, 20.8,
21.1, 21.2, 21.4, 22.7, 23.0, 23.4, 23.7, 23.8, 24.8, 24.8, 25.2,
26.0, 26.7, 27.1, 27.2, 27.4, 28.1, 28.2, 28.4, 28.9, 29.0, 29.1,
29.1, 29.2, 29.4, 29.5, 29.7, 30.0, 30.2, 30.3, 30.4, 31.0, 31.1,
31.3, 31.3, 31.4, 31.9, 33.6, 33.7, 33.7, 36.0, 36.2, 38.7, 41.1,
41.7, 47.1, 47.2, 49.0, 49.3, 49.8, 50.0, 54.5, 54.6, 54.8, 54.9,
55.3, 55.4, 55.4, 56.0, 56.7, 57.7, 57.8, 65.9, 66.0, 67.8, 68.6,
68.8, 71.3, 77.6, 77.8, 78.1, 78.4, 78.5, 78.7, 78.8, 79.0, 79.2,
79.3, 79.4, 79.5, 79.6, 81.0, 81.2, 110.2, 111.6, 113.1, 113.7,
113.9, 127.8, 128.8, 128.8, 130.9, 131.0,143.6, 156.2, 158.8,
167.5, 169.4, 169.9, 170.2, 170.8, 171.4, 171.6, 172.8, 173.0,-
1
Rf 0.49 (30% acetone/hexanes); H NMR (500 MHz, CDCl3) δ
0.83-0.98 (m, 18H), 1.02-1.12 (m, 21H), 1.14-1.30 (m, 9H),
1.39 and 1.44 (s, 9H), 1.52-1.71 (m, 2H), 1.78-1.90 (m, 1H),
1.98-2.25 (m, 2H), 2.55-2.63 (m, 1H), 2.67 (dd of ABX, J )
14.8, 3.2) and 2.72 (m, 1H), 2.93 (dd, of ABX, J ) 16.7, 4.1)
and 3.17 (m, 2H), 3.33 (dd, J ) 16.3, 12.5) and 3.45 (q, 1H),
3.56 (q, 1H) and 3.68 (m, 1H), 3.74 and 3.78 (s, 3H), 3.80-
3.95 (m) and 3.92 (q, 1H), 4.13 and 4.27 (t, 1H), 4.36-4.63 (m,
4H), 4.72-4.84 (m, 2H), 4.90 (m, 1H), 4.95 (d, J ) 4.0) and
5.01 (m, 1H), 5.09 (d, J ) 10.3) and 5.17 (d, J ) 7.7, 1H), 5.66
(m, 1H), 6.60-6.68 (m, 1H) and 6.78 (dd, J ) 7.4, 2.1) and
6.86 (d, J ) 8.3), 7.05 (d, J ) 6.8) and 7.09 (d, J ) 8.5, 1H),
7.38 (m) and 7.43 (d, J ) 10.6, 1H), 7.70 (d, J ) 9.0) and 8.45
(d, J ) 8.3, 1H); 13CNMR (125 MHz, CDCl3) δ 11.9, 12.0, 12.9,
13.3, 13.8,14.1, 14.4, 14.7, 15.3, 15.9, 17.2, 17.5 18.1,18.1, 18.2,
18.3,18.4, 18.4, 18.4, 18.5, 18.5, 18.7, 20.3, 20.8, 21.1, 23.3, 23.6,
24.8, 24.9, 25.2, 26.8, 27.2, 27.4, 28.1, 28.2, 28.3, 28.3, 28.4,
28.5, 28.9, 29.3, 29.4, 29.6, 29.7, 30.3, 30.4 31.9, 32.0, 33.4,
33.7, 39.5, 39.8, 40.3, 41.8, 45.2, 46.4, 47.1, 48.3, 49.6, 49.9,
50.0, 52.5, 54.1, 55.2, 55.4, 55.6, 56.1, 56.3, 57.4, 57.5, 58.0,
69.3, 69.4, 69.9, 71.0, 80.1, 80.3, 80.4, 81.8, 110.2, 111.2, 113.2,
113.8, 114.1, 121.8, 125.3, 126.9, 127.2, 127.8, 127.9, 127.9,
127.9, 128.0, 128.2, 128.7, 129.7, 131.0, 131.8, 133.2, 133.4,
133.8, 155.6, 156.4, 158.3 and 158.9 (RI), 167.8, 168.6, 169.3,
169.4, 169.7, 170.9, 171.1, 171.4, 171.4, 171.6, 172.0, 172.6,
202.5 and 204.5 (RI); IR (neat) 3341, 2961, 2868, 2361, 1733,
1716, 1700, 1683, 1670, 1652, 1646 cm-1; HRMS m/z calcd for
C
56H91N5O13SiNa (M + Na)+ 1092.6280, found 1092.6233.
Cyclo-N-L-la ct yl-L-p r olyl-N-m et h yl-D-leu cin e[O-[[N-
174.0, 205.1; IR (neat) 3316, 2963, 2922, 1726, 1641 cm-1
;
HRMS m/z calcd for C57H87N7O15Na (M + Na)+ 1132.6157,
found 1132.6155; [R]2D5 -20.85 (c 0.24, CHCl3).
[(2S,4S)-4-[(3S,4R,5S)-4-a m in o-3-h yd r oxy-5-m et h ylh ep -
tan oyl]oxy-3-oxo-2,5-dim eth ylh exan oyl]-L-leu cyl]-L-pr olyl-
L-(3-ca r boxy-1,2,3,4-tetr a h yd r o-7-m eth oxyisoqu in olyl)]-
L-th r eon yl] (3). A solution of Boc-ketone 32 (5.9 mg) in HPLC
grade EtOAc was cooled to -30 °C and purged with argon.
HCl gas was bubbled through the solution via a submerged
pipet. The reaction was equipped with an oil bubbler and then
Ack n ow led gm en t. We gratefully acknowledge the
National Institutes of Health (CA-40081), the NSF
(CHE 99-01449), UNCF‚Merck Science Initiative, and
the University of Pennsylvania for financial support. We
also thank Dr. Peter Toogood and Dr. Deepika Ahuja
at the University of Michigan for the biological testing.
a
water scrubber. As the gas bubbled the reaction was
maintained at -15 °C for 40 min, and then the flow was
stopped. A stir bar was added, and the reaction was warmed
to 0 °C and left stirring for 3.5 h. The flask was purged with
argon and the reaction mixture concentrated. The residue was
J O0105991