Total synthesis and assignment of configuration of lissoclinamide 7

Article abstract of DOI:10.1021/ja962859f

The first total synthesis of lissoclinamide 7, a 21-membered cyclopeptide isolated from Lissoclinum bistratum, was accomplished in 23 steps and 4.4% overall yield. The extraordinary configurational lability of the thiazoline segments was overcome by a novel strategy combining the use of the Burgess reagent for multiple simultaneous oxazoline and thiazoline formations and an efficient oxazoline → thiazoline heterocycle interconversion. In addition to the total synthesis, this work highlights the scope of alternative strategies toward Lissoclinum peptides and presents the preparation of analogues for SAR studies of the cytotoxic effects of this family of marine natural products.

Full text of DOI:10.1021/ja962859f

12358
J. Am. Chem. Soc. 1996, 118, 12358-12367
Total Synthesis and Assignment of Configuration of
Lissoclinamide 7
Peter Wipf* and Paul C. Fritch
Contribution from the Department of Chemistry, UniVersity of Pittsburgh,
Pittsburgh, PennsylVania 15260
ReceiVed August 14, 1996X
Abstract: The first total synthesis of lissoclinamide 7, a 21-membered cyclopeptide isolated from Lissoclinum
bistratum, was accomplished in 23 steps and 4.4% overall yield. The extraordinary configurational lability of the
thiazoline segments was overcome by a novel strategy combining the use of the Burgess reagent for multiple
simultaneous oxazoline and thiazoline formations and an efficient oxazoline f thiazoline heterocycle interconversion.
In addition to the total synthesis, this work highlights the scope of alternative strategies toward Lissoclinum peptides
and presents the preparation of analogues for SAR studies of the cytotoxic effects of this family of marine natural
products.
As part of our program toward the total synthesis of marine
natural products,1,2 we were particularly intrigued by the densely
functionalized macrocyclic ring structures in a group of ascidian
(“sea squirt”) metabolites from the genus Lissoclinum (Figure
1).3,4 Characterized by an alternating sequence of five-
membered heterocycles and hydrophobic amino acid residues,
these highly backbone-modified cyclopeptides assume molecular
“triangle”, “square”, and “twisted eight” conformations in
solution and the solid state.5 Their almost symmetrical array
of oxazolines, oxazoles, thiazolines, and thiazoles is reminiscent
of ring-extended porphyrins6 and aza-crown ethers7 and nurtures
speculation about ion-carrier functions.8 Indeed, interesting
X Abstract published in AdVance ACS Abstracts, November 15, 1996.
(1) Wipf, P.; Miller, C. P. J. Am. Chem. Soc. 1992, 114, 10975.
(2) (a) Wipf, P.; Xu, W. J. Org. Chem. 1996, 61, 6556. (b) Wipf, P.;
Venkatraman, S. J. Org. Chem. 1996, 61, 6517. (c) Wipf, P.; Lim, S. J.
Am. Chem. Soc. 1995, 117, 558. (d) Wipf, P.; Kim, H. Y. J. Org. Chem.
1993, 58, 5592.
(3) For a recent review of metabolites of ascidians, see: Davidson, B.
S. Chem. ReV. 1993, 93, 1771.
(4) Recently, structurally closely related compounds have also been
isolated from other ascidians, sea hares, and cyanobacteria. (a) Dolastatin
E (from Dolabella auricularia): Ojika, M.; Nemoto, T.; Nakamura, M.;
Yamada, K. Tetrahedron Lett. 1995, 36, 5057. (b) Cyclodidemnamide (from
Didemnum molle): Toske, S. G.; Fenical, W. Tetrahedron Lett. 1995, 36,
8355. (c) Nostocyclamide (from Nostoc sp. 31): Todorova, A. K.; Ju¨ttner,
F.; Linden, A.; Plu¨ss, T.; von Philipsborn, W. J. Org. Chem. 1995, 60,
7891. Westiellamide (cycloxazoline) was also isolated from the terrestrial
cyanophyte Westiellopsis prolifica: Prinsep, M. R.; Moore, R. E.; Levine,
I. A.; Patterson, G. M. L. J. Nat. Prod. 1992, 55, 140.
(5) (a) Ishida, T.; Inoue, M.; Hamada, Y.; Kato, S.; Shioiri, T. J. Chem.
Soc., Chem. Commun. 1987, 370. (b) Ishida, T.; Tanaka, M.; Nabae, M.;
Inoue, M.; Kato, S.; Hamada, Y.; Shioiri, T. J. Org. Chem. 1988, 53, 107.
(c) Schmitz, F. J.; Ksebati, M. B.; Chang, J. S.; Wang, J. L.; Hossain, M.
B.; Helm, D. v. d.; Engel, M. H.; Serban, A.; Silfer, J. A. J. Org. Chem.
1989, 54, 3463. (d) Ishida, T.; Ohishi, H.; Inoue, M.; Kamigauchi, M.;
Sugiura, M.; Takao, N.; Kato, S.; Hamada, Y.; Shioiri, T. J. Org. Chem.
1989, 54, 5337. (e) Hambley, T. W.; Hawkins, C. J.; Lavin, M. F.; Brenk,
A. v. d.; Watters, D. J. Tetrahedron 1992, 48, 341. (f) Ishida, T.; In, Y.;
Doi, M.; Inoue, M.; Hamada, Y.; Shioiri, T. Biopolymers 1992, 32, 131.
(g) McDonald, L. A.; Foster, M. P.; Phillips, D. R.; Ireland, C. M.; Lee, A.
Y.; Clardy, J. J. Org. Chem. 1992, 57, 4616. (h) In, Y.; Doi, M.; Inoue,
M.; Ishida, T.; Hamada, Y.; Shioiri, T. Chem. Pharm. Bull. 1993, 41, 1686.
(i) In, Y.; Doi, M.; Inoue, M.; Ishida, T.; Hamada, Y.; Shioiri, T. Acta
Crystallogr. 1994, C50, 432. (j) Ishida, T.; In, Y.; Shinozaki, F.; Doi, M.;
Yamamoto, D.; Hamada, Y.; Shioiri, T.; Kamigauchi, M.; Sugiura, M. J.
Org. Chem. 1995, 60, 3944.
Figure 1. Cyclic peptides of the genus Lissoclinum.
metal-chelation properties have been detected for several
Lissoclinum peptides.9,10
Most Lissoclinum peptides display moderate to high levels
of cytotoxicity that have been linked to the presence of oxazoline
functions.11,5g Table 1 illustrates some representative structure-
activity relationships for 21-membered Lissoclinum peptides.
With IC50 values of 40, 60, and 80 ng/mL in MRC5CV1,
T24, and lymphocytes cell assays, respectively, lissoclinamide
(8) Michael, J. P.; Pattenden, G. Angew. Chem., Int. Ed. Engl. 1993, 32,
1.
(9) Wipf, P.; Venkatraman, S.; Miller, C. P.; Geib, S. J. Angew. Chem.,
Int. Ed. Engl. 1994, 33, 1516.
(10) (a) Brenk, A. L. v. d.; Byriel, K. A.; Fairlie, D. P.; Gahan, L. R.;
Hanson, G. R.; Hawkins, C. J.; Jones, A.; Kennard, C. H. L.; Moubaraki,
B.; Murray, K. S. Inorg. Chem. 1994, 33, 3549. (b) Brenk, A. L. v. d.;
Fairlie, D. P.; Hanson, G. R.; Gahan, L. R.; Hawkins, C. J.; Jones, A. Inorg.
Chem. 1994, 33, 2280.
(11) (a) Shioiri, T.; Hamada, Y.; Kato, S.; Shibata, M.; Kondo, Y.;
Nakagawa, H.; Kohda, K. Biochem. Pharm. 1987, 36, 4181. (b) Kohda,
K.; Ohta, Y.; Kawazoe, Y.; Kato, T.; Suzumura, Y.; Hamada, Y.; Shioiri,
T. Biochem. Pharm. 1989, 38, 4500. (c) Kohda, K.; Ohta, Y.; Yokoyama,
Y.; Kawazoe, Y.; Kato, T.; Suzumura, Y.; Hamada, Y.; Shioiri, T. Biochem.
Pharm. 1989, 38, 4497.
(6) For a review, see: Sessler, J. L.; Burrell, A. K. Top. Curr. Chem.
1991, 161, 177.
(7) Bradshaw, J. S.; Krakowiak, K. E.; Izatt, R. M. In Aza-crown
Macrocycles; Wiley: New York, 1993.
S0002-7863(96)02859-4 CCC: $12.00 © 1996 American Chemical Society

Total Synthesis of Lissoclinamide 7
J. Am. Chem. Soc., Vol. 118, No. 49, 1996 12359
Table 1. Cytotoxic Activity of Some 21-Membered Lissoclinum
Peptides
Figure 2. Thiazoline epimerization.
IC50
R1
R2
X
Y
[µg/mL]
lissoclinamide 1 L-Val D-Ile thiazole
lissoclinamide 6 D-Val D-Phe thiazole
thiazole
thiazoline
>1019
720
lissoclinamide 7 Val
ulicyclamide L-Ile
Phe
thiazoline thiazoline
thiazole
0.0620
721
D-Ala thiazole
7 is next to ulithiacyclamide21 the most cytotoxic Lissoclinum
derivative. It is also the only L. patella metabolite that contains
two thiazoline rings in addition to the oxazoline heterocycle.
Since the mechanistic link between the presence of oxazolines
and cytocidal action is unclear,11,12 we were interested in testing
this hypothesis through the synthesis and biological analysis of
lissoclinamide 7 and its structural variants. We expect that
analogues with selective replacements of the heterocyclic
moieties will provide fundamental information about the relative
cytotoxic potential of oxazolines vs thiazolines.
The total synthesis of lissoclinamide 7 poses new and
challenging synthetic problems. Among the large number of
published syntheses of Lissoclinum peptides and structurally
related macrocycles, thiazoline-containing target molecules are
conspicuously rare.13,14 Indeed, only very recently did Pattenden
and Boden succeed in the first preparation of a thiazoline-
containing Lissoclinum peptide, lissoclinamide 4.15 Also in
1995, the structurally related cyclic hexapeptide dolastatin E
was prepared by Yamada et al.16 The difficulties in the
formation of the sensitive thiazoline heterocycles represent the
major impediments for total synthesis. In the presence of mild
Figure 3. Conversion of serines to thiazolines.
acid or base, thiazolines are readily epimerized exocyclic to C(2)
as well as at C(4) (Figure 2).17,18
We have recently shown that thiazolines can be prepared in
high yield and diastereomeric purity by cyclodehydration of
â-hydroxy thioamides.17 In short peptide sequences, the neces-
sary thioamides can be obtained by thionation of protected serine
residues with the Lawesson reagent or by thioacylation.18,22,23
For larger peptides, direct thionation lacks regioselectivity and
the thiolysis of oxazolines becomes the method of choice (Figure
3).24 The bisthiazoline-containing lissoclinamide 7 now rep-
resents a formidable demonstration of this new synthetic
methodology.
Retrosynthetic Strategy
Due to epimerization of the amino acids adjacent to the
thiazoline rings, the structure elucidation of lissoclinamide 7
by Watters and co-workers tentatively assigned the D-stereo-
chemistry at C(21).20a This assignment was based on the large
proportion of D-phenylalanine obtained after exhaustive hy-
drolysis (D/L ) 0.64), and the assumption that the phenylalanine
at C(11) is always of the L-configuration. In contrast, D- and
L-valine were obtained in equal proportions; therefore, no
specific stereochemistry was proposed for C(31). Initially, we
decided arbitrarily to use D-valine for lissoclinamide 7 in our
retrosynthetic approach (Figure 4). Selective thiolysis of the
two serine-derived heterocycles in trisoxazoline 3 was thought
to provide thioamide 2 which could subsequently be cyclode-
hydrated with the Burgess reagent to avoid epimerization.17
Macrolactamization at the valine-trans-oxazoline peptide bond
of 3 was chosen to minimize epimerization at the C-terminus
and to take advantage of the turn-inducing effect of the oxazoline
moiety that should facilitate ring closure.1 The resulting
secoheptapeptide 4 could be obtained by segment condensation
of a tetrapeptide and a tripeptide oxazoline, with the remaining
two serine-derived oxazolines being introduced either before
or after the macrocyclization. In general, similar yields for ring
closure of Lissoclinum peptides have been obtained in the
presence or absence of some of the heterocyclic residues in the
linear sequence.13,15
(12) Wipf, P.; Venkatraman, S. Synlett In press.
(13) For a review, see: Wipf, P. Chem. ReV. 1995, 95, 2115.
(14) Ascidiacyclamide (2 oxazolines, 2 thiazoles): Hamada, Y.; Kato,
S.; Shioiri, T. Tetrahedron Lett. 1985, 26, 3223. Bistratamide C (1 oxazole,
2 thiazoles): Aguilar, E.; Meyers, A. I. Tetrahedron Lett. 1994, 35, 2477.
Dolastatin 3 (2 thiazoles): Pettit, G. R.; Kamano, Y.; Holzapfel, C. W.;
van Zyl, W. J.; Tuinman, A. A.; Herald, C. L.; Baczynskyj, L.; Schmidt, J.
M. J. Am. Chem. Soc. 1987, 109, 7581. Schmidt, U.; Utz, R.; Lieberknecht,
A.; Griesser, H.; Potzolli, B.; Bahr, J.; Wagner, K.; Fischer, P. Synthesis
1987, 236. Lissoclinamide 5 (1 oxazoline, 2 thiazoles): Boden, C.;
Pattenden, G. Tetrahedron Lett. 1994, 35, 8271. Patellamides A, B, and C
(2 oxazolines, 2 thiazoles): Hamada, Y.; Shibata, M.; Shioiri, T. Tetrahedron
Lett. 1985, 26, 5159. Hamada, Y.; Shibata, M.; Shioiri, T. Tetrahedron
Lett. 1985, 26, 6501. Schmidt, U.; Griesser, H. Tetrahdron Lett. 1986, 27,
163. Ulicyclamide (1 oxazoline, 2 thiazoles): Schmidt, U.; Gleich, P. Angew.
Chem., Int. Ed. Engl. 1985, 24, 569. Sugiura, T.; Hamada, Y.; Shioiri, T.
Tetrahedron Lett. 1987, 28, 2251. Ulithiacyclamide (2 oxazolines, 2
thiazoles): Kato, S.; Hamda, Y.; Shioiri, T. Tetrahedron Lett. 1986, 27,
2653. Schmidt, U.; Weller, D. Tetrahedron Lett. 1986, 27, 3495. Westiel-
lamide (3 oxazolines): ref 1.
(15) Boden, C. D. J.; Pattenden, G. Tetrahedron Lett. 1995, 36, 6153.
(16) Nakamura, M.; Shibata, T.; Nakane, K.; Nemoto, T.; Ojika, M.;
Yamada, K. Tetrahedron Lett. 1995, 36, 5059.
(17) Wipf, P.; Fritch, P. C. Tetrahedron Lett. 1994, 35, 5397.
(18) Boden, C. D. J.; Pattenden, G.; Ye, T. Synlett 1995, 417.
(19) Wasylyk, J. M.; Biskupiak, J. E.; Costello, C. E.; Ireland, C. M. J.
Org. Chem. 1983, 48, 4445. This activity was determined in L1210 cells.
(20) (a) Hawkins, C. J.; Lavin, M. F.; Marshall, K. A.; Brenk, A. L. v.
d.; Watters, D. J. J. Med. Chem. 1990, 33, 1634. (b) Degnan, B. M.;
Hawkins, C. J.; Lavin, M. F.; McCaffrey, E. J.; Parry, D. L.; Brenk, A. L.
v. d.; Watters, D. J. J. Med. Chem. 1989, 32, 1349. This activity was
determined in T24 cells.
Results and Discussion
Preparation of the heptapeptide oxazoline 4 was initiated by
coupling of the mixed anhydride of benzyloxycarbonyl(Cbz)-
(21) Ireland, C. M.; Durso, A. R.; Newman, R. A.; Hacker, M. P. J.
Org. Chem. 1982, 47, 1807. This activity was determined in L1210 cells.

12360 J. Am. Chem. Soc., Vol. 118, No. 49, 1996
Wipf and Fritch
Scheme 2
Scheme 3
Figure 4. Retrosynthetic plan for lissoclinamide 7.
Scheme 1
phenylalanine (5) with proline methyl ester using the Anderson
conditions (Scheme 1).25 The resulting dipeptide 6 was saponi-
fied and condensed with threonine methyl ester to give tripeptide
7 in 93% yield. The synthesis of this tripeptide from the
C-terminus rather than the more standard N-terminal elongation
strategy was chosen to allow the use of side chain-unprotected
threonine and to circumvent a low yield in the coupling of Cbz-
phenylalanine and prolylthreonine methyl ester. The (2S,3R)-
configuration of the natural threonine residue was now selec-
tively inverted to the (2S,3S)-configuration of nonproteinogenic
allo-threonine by formation of the oxazoline with the Burgess
reagent (8),26 followed by selective hydrolysis and in situ O f
N-acyl shift.27 This straightforward protocol was readily scaled
up to multigram quantities and provided the allo-threonine-
containing tripeptide segment 9 in 80% yield.
D-phenylalanine (10) (Scheme 2). To avoid misacylation or
peptide backbone rearrangements, the serine side chain hydroxyl
functions were protected as TBDMS (tert-butyldimethylsilyl)
ethers.
Segment condensation of the carboxylic acid derived from
tetrapeptide 13 with the primary amine derived from tripeptide
9 in the presence of pentafluorophenyl diphenylphosphinate
(FDPP)28 gave the desired heptapeptide 14 in 81% yield
(Scheme 3). The C-terminal trans-oxazoline was now intro-
duced in 89% by cyclodehydration of the allo-threonine residue
with the Burgess reagent.26 In preparation for the formation of
In an analogous series of isobutyl chloroformate-mediated
condensation reactions, the D-valine-containing tetrapeptide
segment 13 was obtained in an overall yield of 51% from Cbz-
(22) (a) Clausen, K.; Thorsen, M.; Lawesson, S.-O. Tetrahedron 1981,
37, 3635. (b) Lajoie, G.; Lepine, F.; Maziak, L.; Belleau, B. Tetrahedron
Lett. 1983, 24, 3815. (c) Jensen, O. E.; Senning, A. Tetrahedron 1986, 42,
6555. (d) Cava, M. P.; Levinson, M. I. Tetrahedron 1985, 41, 5061.
(23) (a) Hoeg-Jensen, T.; Holm, A.; Sorensen, H. Synthesis 1996, 383.
(b) Zacharie, B.; Sauve, G.; Penney, C. Tetrahedron 1993, 49, 10489.
(24) Wipf, P.; Miller, C. P.; Venkatraman, S.; Fritch, P. C. Tetrahedron
Lett. 1995, 36, 6395.
(25) Anderson, G. W.; Zimmerman, J. E.; Callahan, F. M. J. Am. Chem.
Soc. 1967, 89, 5012.

Total Synthesis of Lissoclinamide 7
J. Am. Chem. Soc., Vol. 118, No. 49, 1996 12361
Scheme 4. First Approach toward Lissoclinamide 7
Figure 5. Rate of thiolysis of model oxazolines A (serine-derived)
and B (threonine-derived).
Scheme 5. Second Approach toward Lissoclinamide 7
the 21-membered macrocycle, hydrogenolysis of 15 with Pd-
(OH)2 and saponification in aqueous base led to an intermediate
amino acid that was immediately subjected to FDPP in CH2Cl2
and DMF. After 2.5 d at 40 °C, the silyl ethers were cleaved
with TBAF (tetrabutylammonium fluoride) in THF, and the
cycloheptapeptide oxazoline 16 was isolated in 21% overall
yield. Closure of the two serine-derived oxazolines under
Mitsunobu conditions29 led to the trisoxazoline derivative 17,
which was of interest to us as an analog for biological testing
beyond its role as a key synthetic intermediate toward lissocli-
namide 7.
In earlier model studies,24 we had noted distinctive differences
in the rate of thiolysis of serine-derived vs threonine-derived
oxazolines. A kinetic study confirmed that for model oxazolines
A and B, thiolysis with H2S at room temperature in MeOH/
NEt3 was considerably faster for the less-substituted serine-
derived oxazoline A (Figure 5).
Therefore, we hoped that the selective opening of trisoxazo-
line 17 would provide the desired bisthioamide 2 with good
selectivity and yield. However, even after considerable variation
of the reaction conditions, we were unable to prevent the
thiolysis of the threonine-derived oxazoline and the formation
of tristhioamide 18 as the major reaction product (Scheme 4).
The structure of this sensitive thiolysis product was confirmed
by reaction with an excess of the Burgess reagent to give the
tristhiazoline 19. The lack of chemoselectivity in the oxazoline
opening of 17 can be explained by an increased stability of the
serine-derived oxazolines embedded in the macrocyclic scaffold
as compared to the acyclic model oxazoline A. At room
temperature, no thiolysis occurred, and ring opening of the
heterocycles was only detected after extended exposure to H2S
in MeOH/NEt3 1:1 at elevated temperature (36 °C). Under these
conditions, both serine- and threonine-derived oxazolines con-
verted with similar rates to the corresponding thioamides.
Accordingly, in our second-generation approach toward
lissoclinamide 7, we sought to perform the selective thiolysis
step on an acyclic trisoxazoline (e.g., the secoderivative of 17).
On the basis of the revised structure of lissoclinamide 4, reported
by Boden and Pattenden concomitant to our work,15 we also
decided to use L-valine as a precursor. Acylation of the primary
amine derived from tripeptide 12 with Cbz-valine followed by
segment condensation with 9 gave heptapeptide 21 in high yield
(Scheme 5). Oxazoline formation, silyl ether deprotection, and
exposure to an excess of the Burgess reagent provided a linear
trisoxazoline that was highly susceptible to hydrolysis and
therefore immediately subjected to hydrogenolysis of the Cbz-
carbamate and thiolysis in a solution of H2S in methanol/
triethylamine at room temperature. Indeed, after 8 h, the
bisthioamide 23 was isolated in 41% yield and only traces of
thioamide derived from ring-opening of the trisubstituted
oxazoline were detected. This confirmed our hypothesis that
the lack of reactivity of the serine-derived oxazolines in 17 was
due to the macrocycle conformation.
After cleavage of the methyl ester in 23, macrocyclization
with FDPP proceeded sluggishly unless a large excess of
coupling agent was added to the reaction mixture. To our
(26) (a) Wipf, P.; Miller, C. P. Tetrahedron Lett. 1992, 33, 907. (b)
Atkins, G. M.; Burgess, E. M. J. Am. Chem. Soc. 1968, 90, 4744.

12362 J. Am. Chem. Soc., Vol. 118, No. 49, 1996
Wipf and Fritch
Scheme 6. Third Approach toward Lissoclinamide 7
Figure 6. Lissoclinamide 7 epimers.
surprise, under these conditions cyclodehydration of the â-hy-
droxy thioamides and macrolactamization proceeded competi-
tively, and the resulting product contained all three heterocycles.
1
Moreover, H and 13C NMR analyses revealed the isolated
material to be identical to lissoclinamide 7.30 At this point we
tentatively assigned the structure of the natural material as 24
(Figure 6). However, in light of the extraordinary ease of
epimerization of thiazolines,17,18 and since FDPP had not
previously been applied for thiazoline formation, we performed
a series of control experiments on model â-hydroxy thioamides17
that indeed routinely led to considerable epimerization exocyclic
to C(2) of the resulting thiazoline. Accordingly, we were unable
to exclude structure 25 or even 26 and 27 for our synthetic
material, and a third-generation synthesis was needed to clarify
the stereochemistry.
A comparison of the 1H NMR data for lissoclinamide 7 and
the D-valine-containing tristhiazoline 19 revealed very similar
chemical shifts at the right side, valine portion of the macro-
cycles. This observation cast additional doubt on the stereo-
chemical integrity of the route shown in Scheme 5, leading,
presumably, to the L-valine isomer 24. As a control, we then
used the D-valine heptapeptide 14 for the formation of the
cyclopeptide 28 in 48% yield (Scheme 6). Since we had been
unable to achieve chemoselectivity in the thiolysis of macro-
cyclic serine- and threonine-derived oxazolines, the side chain
protective groups on 28 were switched from serine to threonine
residues in 29 before exposure to 2.5 equiv of the Burgess
reagent. The resulting bisoxazoline was thiolyzed in methanol/
triethylamine, and desilylation gave bisthioamide 30. Triple
cyclodehydration of this compound with an excess of the
Burgess reagent was extremely efficient, providing the two
thiazolines and the oxazoline in lissoclinamide 7 in 90% yield!31
Scheme 7
Due to the superior efficiency of this last route and since the
configurationally labile thiazoline residues were only introduced
in the last step of the synthesis, we were confident that the
isomer shown in Scheme 6, an epimer at C(31) of 24, was
indeed representative of the structure of the natural product.
On the basis of the spectral data, as well as optical rotation and
[R]D, both routes incorporating L-valine (Scheme 5) or D-valine
(Scheme 6) produced material identical to the natural product.
In order to further substantiate our structure assignment of
lissoclinamide 7, we embarked on an independent synthesis of
24 according to our successful third-generation strategy.
Deprotection of L-valine-containing heptapeptide 21 and
macrolactamization under high dilution conditions provided
cyclopeptide 31 in 25% yield (Scheme 7). The lower yield in
the conversion of 21 to 31 as compared to 14 f 28 (25 vs
48%) is a consequence of the decrease in the rate of cyclization
as a function of the presence of an L- vs a D-amino acid at the
N-terminus of the linear peptide precursors.32 Analogous to
28, 31 was converted to the 21-membered heterocyclic cyclo-
peptide 24 in six steps and 15% overall yield.
With 24 in hand, the spectral differences between lissocli-
namide 7 and its L-epimer at C(31) became obvious. Indeed,
(27) Wipf, P.; Miller, C. P. J. Org. Chem. 1993, 58, 1575.
(28) (a) Chen, S.; Xu, J. Tetrahedron Lett. 1991, 32, 6711. (b) Dudash,
J.; Jiang, J.; Mayer, S. C.; Joullie´, M. M. Synth. Commun. 1993, 23, 349.
(29) (a) Wipf, P.; Miller, C. P. Tetrahedron Lett. 1992, 33, 6267. (b)
Galeotti, N.; Montagne, C.; Poncet, J.; Jouin, P. Tetrahedron Lett. 1992,
33, 2807.

Total Synthesis of Lissoclinamide 7
J. Am. Chem. Soc., Vol. 118, No. 49, 1996 12363
Conclusions
Scheme 8
In spite of the considerable body of synthetic, structural and
biological work toward Lissoclinum peptides,13 major challenges
in the design of stereoselective protocols for heterocycle
formation and effective macrocyclization strategies have re-
mained. In addition, a better understanding of the effects of
amino acid-derived thiazoline and oxazoline heterocycles on
the conformation of cyclopeptides might facilitate the de noVo
design of conformationally preorganized macrocycles. Our
work toward lissoclinamide 7 highlights the potential pitfalls
in the synthesis of configurationally labile natural products and
the concomitant structural correlation between synthetic and
isolated material. Several new strategies for Lissoclinamide
peptide synthesis have been explored, and the successful total
synthesis establishes the cyclodehydration of â-hydroxy amides
and thioamides with the Burgess reagent as a versatile and
stereochemically reliable method for the preparation of complex
oxazolines and thiazolines. The oxazoline f thiazoline conver-
sion via thiolysis of oxazolines offers a novel and convenient
strategy for the preparation of the natural product as well as a
series of analogues that will provide useful information on the
structure-activity relationships of Lissoclinum peptides. Bio-
logical evaluation of these compounds is currently in progress.
Scheme 9
Experimental Section
General Methods. NMR spectra were recorded at 300 MHz in
CDCl3 unless otherwise noted. IR spectra of solid samples were
prepared by spreading a solution of the solid in CHCl3 over a NaCl
disk, slow evaporation, and measurement of the resulting dispersion.
Anhydrous solvents were freshly distilled from either sodium ben-
zophenone ketyl, P2O5, or CaH2. All reactions were performed in oven-
dried glassware under an argon or nitrogen atmosphere. Analytical
TLC was performed with Merck silica gel 60 F-254 plates, and flash
chromatography was used to separate and purify the crude reaction
mixtures.
Cbz-Phe-Pro-allo-Thr-OMe (9). A solution of 1.03 g (2.02 mmol)
of Cbz-Phe-Pro-Thr-OMe (7) in 20 mL of THF was treated at room
temperature with 0.58 g (2.43 mmol) of the Burgess reagent (8). The
reaction mixture was stirred at room temperature for 10 min and then
heated to 75 °C for 2.5 h, cooled to room temperature, and concentrated.
Chromatography on SiO2 (90% EtOAc/hexanes) afforded 891 mg of
Cbz-Phe-Pro-Thr(oxaz)-OMe as a white foam.
A solution of 891 mg (1.805 mmol) of Cbz-Phe-Pro-Thr(oxaz)-OMe
in 60 mL of THF was treated with 18 mL of 0.3 M HCl. After 10 min
the pH was adjusted to 9.5 with solid K2CO3, and the solution was
stirred for 2 h. After addition of 20 mL of H2O, THF was removed in
vacuo. The solution was acidified with 1 M HCl and extracted with
EtOAc (3 × 90 mL). The combined organic layers were washed with
H2O (50 mL) and brine (50mL), dried (Na2SO4), and concentrated.
Chromatography on SiO2 (90% EtOAc/hexanes) afforded 829 mg (80%)
of 9 as a white foam: [R]D -10.2° (c 1.1, CHCl3, 22 °C); IR (neat)
3314, 1686, 1637 cm-1; 1H NMR (major rotamer) δ 7.39-7.18 (m, 11
H), 5.77 (d, 1 H, J ) 8.5 Hz), 5.08 (d, 1 H, J ) 12.4 Hz), 5.03 (d, 1
H, J ) 12.4 Hz), 4.76-4.63 (m, 2 H), 4.46-4.40 (m, 1 H), 4.30-4.18
(m, 1 H), 3.79 (s, 3 H), 3.67-3.60 (m, 1 H), 3.30-3.18 (m, 1 H),
3.09-3.00 (m, 1 H), 2.97-2.88 (m, 1 H), 2.16-1.70 (m, 4 H), 1.25-
1.20 (m, 3 H); 13C NMR (major rotamer) δ 171.5, 171.2, 170.5, 155.8,
136.2, 135.8, 129.4, 128.3, 127.9, 127.7, 126.7, 68.2, 66.6, 60.3, 58.3,
47.4, 38.3, 28.4, 25.0, 18.9; MS (FAB) m/e (rel intensity) 534 ([M +
Na]+, 20), 512 (M + H, 35).
the FDPP-induced thiazoline formation in 23 shown in Scheme
5 had led to a selective isomerization of the C(31)-configuration
from the L- to the D-series. Therefore, the caution that is
necessary in the structure assignment of Lissoclinum peptides
by hydrolysis of natural material has to be extended to the
correlation of the stereochemistry of synthetic compounds with
the natural product. The final structural proof for the identity
of lissoclinamide 7 was provided by the X-ray structure of
synthetic product.33
In summary, an efficient total synthesis of lissoclinamide 7
was accomplished in 18 linear steps and in 4.4% overall yield.
In addition to the natural product, we have been able to prepare
a series of analogs that should shed light on the structural basis
of the very high levels of cytotoxicity found for Lissoclinum
peptides in general and lissoclinamide 7 in specific. The
preparation of the trisoxazoline analog 17 was further optimized
by conversion of the readily available 28 to the triol 34 followed
by triple cyclodehydration (Scheme 8). Analogously, the C(31)-
epimeric trisoxazoline 36 was obtained in five steps and 36%
yield from 22 (Scheme 9).
(30) Due to the dearth of natural product, we were unable to obtain an
authentic sample of lissoclinamide 7. However, comparisons were performed
with the actual 1H NMR and 13C NMR spectra of natural lissoclinamide 7.
We thank Prof. D. Watters for providing us with copies of her data.
(31) For an example of the simultaneous formation of an oxazoline and
a thiazoline using this methodology, see: Boden and Pattenden (ref 18). In
the cyclopeptide area, the simultaneous formation of two oxazolines was
reported by Shioiri et al. and Schmidt et al. (refs 13 and 14). For the
simultaneous formation of multiple thiazolines or oxazolines in linear
polyazoles, see: Parsons, R. L.; Heathcock, C. H. Tetrahedron Lett. 1994,
35, 1383. Parsons, R. L.; Heathcock, C. H. J. Org. Chem. 1994, 59, 4733.
Wipf, P.; Venkatraman, S. J. Org. Chem. 1995, 60, 7224.
Cbz-D-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-OMe (13). A solu-
tion of 4.15 g (5.80 mmol) of Cbz-Ser(TBDMS)-D-Phe-Ser(TBDMS)-
OMe (12) in 140 mL of MeOH was treated with Pd/C and H2 gas for
2 h and then filtered through a plug of Celite and concentrated. The
residue was dried by azeotropic distillation of benzene to afford the
amine D-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-OMe as a white solid.
(32) For comparison, see: Boger, D. L.; Zhou, J. J. Org. Chem. 1996,
61, 3938 and references cited therein.
(33) The coordinates and a detailed discussion of the three-dimensional
structure of lissoclinamide 7 will be reported elsewhere.
A solution of 1.60 g (6.38 mmol) of Cbz-D-valine in 125 mL of
CH2Cl2 was treated with 0.83 mL (7.54 mmol) of N-methylmorpholine

12364 J. Am. Chem. Soc., Vol. 118, No. 49, 1996
Wipf and Fritch
and cooled to -20 °C, and 0.83 mL (6.38 mmol) of isobutyl
chloroformate was added dropwise. The reaction mixture was stirred
for 15 min at -15 °C. A solution of the amine prepared above in 20
mL of CH2Cl2 was added slowly, and the mixture was warmed to 0 °C
over 1.5 h and then to room temperature over another 1 h. The solution
was washed with 1 M NaH2PO4 (90 mL), H2O (90 mL), and brine (90
mL), dried (Na2SO4), and concentrated. Chromatography on SiO2 (30%
EtOAc/hexanes) afforded 4.39 g (93%) of 13 as a colorless solid: mp
132-133 °C (EtOAc/hexanes); [R]D +20.2° (c 1.2, CH2Cl2, 24 °C);
1.64 (m, 4 H), 1.28 (d, 2.1 H), J ) 6.3 Hz), 0.97-0.69 (m, 24 H), 0.00
to -0.16 (m, 12 H); 13C NMR (MeOH-d4, mixture of rotamers) δ 174.5,
173.0, 172.6, 172.4, 171.7, 171.5, 171.3, 170.3, 158.7, 138.4, 138.1,
137.6, 130.7, 130.4, 129.5, 128.9, 128.3, 127.9, 81.9, 81.2, 74.9, 67.7,
64.1, 63.9, 62.5, 56.8, 56.6, 56.3, 55.9, 53.9, 53.0, 47.6, 40.9, 38.8,
38.6, 32.2, 31.8, 31.6, 30.7, 26.4, 25.4, 23.0, 20.9, 20.0, 19.1, -5.2;
MS (FAB) m/e (rel intensity) 1165 ([M + Na]+, 24), 1143 ([M + H]+,
100).
Cyclo[D-Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr(oxaz)] (16). A solu-
tion of 650 mg (0.568 mmol) of Cbz-D-Val-Ser(TBDMS)-D-Phe-Ser-
(TBDMS)-Phe-Pro-allo-Thr(oxaz)-OMe (15) in 20 mL of MeOH was
treated with Pd(OH)2 and H2 gas for 10 h. The reaction mixture was
filtered through Celite and concentrated. The residue was dissolved
in 20 mL of THF/MeOH/H2O (10:2:1) and treated with 312 µL (0.625
mmol) of a 2.0 M NaOH solution. The reaction mixture was stirred at
room temperature for 4 h, treated with 105 mg (1.25 mmol) of NaHCO3
for 30 min, filtered, concentrated, and dried by azeotropic distillation
with benzene. The resulting amino acid sodium salt was dissolved in
284 mL of CH2Cl2/DMF (3:1) and treated with 860 mg (2.25 mmol)
of FDPP. The reaction mixture was stirred at 40 °C for 2.5 d and
treated with 168 mg (2.0 mmol) of NaHCO3, and the solvents were
removed at reduced pressure. The residue was dissolved in 10%
MeOH/CHCl3 and adsorbed onto SiO2. Chromatography on SiO2 (15%
EtOAc/CHCl3 followed by 5% MeOH/CHCl3) afforded 0.48 g of a
solid, which was dissolved in 12 mL of THF and treated at 0 °C with
1.25 mL (1.25 mmol) of 1 M TBAF in THF solution for 15 min. The
reaction mixture was directly chromatographed on SiO2 (4-5% MeOH/
CHCl3) to afford 90 mg (21%) of 16 as a white solid: mp 229-232
°C (MeOH); [R]D -5.6° (c 0.3, MeOH, 23 °C); IR (neat) 3302, 1670,
1
IR (neat) 3269, 1672, 1632 cm-1; H NMR δ 7.36-7.22 (m, 11 H),
6.88 (d, 1 H, J ) 6.8 Hz), 6.68 (d, 1 H, J ) 8.0 Hz), 5.56 (d, 1 H, J
) 8.0 Hz), 5.18 (d, 1 H, J ) 12.2 Hz), 5.07 (d, 1 H, J ) 12.2 Hz),
4.78 (dd, 1 H, J ) 14.6, 7.3 Hz), 4.62-4.59 (m, 1 H), 4.52-4.50 (m,
1 H), 4.10-4.02 (m, 1 H), 4.00-3.92 (m, 2 H), 3.70 (s, 3 H), 3.64
(dd, 1 H, J ) 9.3, 6.8 Hz), 3.56 (dd, 1 H, J ) 10.0, 3.2 Hz), 3.13 (dd,
1 H, J ) 13.6, 7.4 Hz), 3.04 (dd, 1 H, J ) 13.6, 6.6 Hz), 2.25-2.1 (m,
1 H), 0.99 (d, 3 H, J ) 6.7 Hz), 0.94-0.91 (m, 12 H), 0.85 (s, 9 H),
0.10 (s, 6 H), 0.01 (s, 6 H); 13C NMR δ 171.0, 170.4, 169.8, 169.2,
156.3, 136.4, 129.2, 128.1, 127.6, 126.6, 66.5, 63.0, 59.9, 54.2, 53.9,
52.0, 38.7, 31.1, 25.6, 25.4, 19.0, 18.0, 17.8, -5.8, -6.0; MS (EI) m/e
(rel intensity) 815 (M+, 90), 758 (90), 91 (100); HRMS m/e calcd for
C41H66N4O9Si2 814.4368, found 814.4376.
Cbz-D-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-
OMe (14). A solution of 1.18 g (2.31 mmol) of Cbz-Phe-Pro-allo-
Thr-OMe (9) in 125 mL of MeOH was treated with Pd/C and H2 gas
for 4 h. The reaction mixture was filtered through a plug of Celite,
concentrated, and dried by azeotropic distillation with benzene to afford
the amine as a white solid. A solution of 2.08 g (2.55 mmol) of Cbz-
D-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-OMe (13) in 40 mL of THF/
H2O (3:1) was treated with 118 mg (2.81 mmol) of LiOH‚H2O. The
reaction mixture was stirred at room temperature for 3 h, 20 mL of
H2O was added, and THF was removed in vacuo. The solution was
acidified with 1 M NaH2PO4 and extracted with EtOAc (2 × 50 mL).
The combined organic layers were washed with H2O (25 mL) and brine
(25 mL), dried (Na2SO4), and concentrated to afford 1.95 g (95%) of
acid as a white solid. A solution of 1.95 g (2.43 mmol) of this acid,
the amine prepared above, and 0.64 mL (4.62 mmol) of Et3N in 100
mL of CH2Cl2 was treated at room temperature with a solution of 1.78
mg (4.62 mmol) of FDPP in 10 mL of CH2Cl2. The reaction mixture
was stirred overnight, diluted with 150 mL of CHCl3, washed with 1
M NaH2PO4 (90 mL), H2O (90 mL), and brine (90 mL), dried (Na2-
SO4), and concentrated. Chromatography on SiO2 (25% EtOAc/CHCl3
followed by 4% MeOH/CHCl3) and a second chromatography on SiO2
(2.5% MeOH/CHCl3) afforded 2.17 g (81%) of 14 as colorless solid:
mp 106-108 °C (CHCl3); [R]D -34.2° (c 1.2, MeOH, 23 °C); IR (neat)
3289, 1659, 1525 cm-1; 1H NMR (DMSO-d6, 368 K) δ 7.8-7.6 (b, 3
H), 7.59 (d, 1 H, J ) 7.0 Hz), 7.35-7.30 (m, 3 H), 7.30-7.15 (m, 9
H), 6.73 (d, 1 H, J ) 8.2 Hz), 5.09 (d, 1 H, J ) 12.7 Hz), 5.02 (d, 1
H, J ) 12.7 Hz), 4.80 (b, 1 H), 4.68-4.58 (m, 1 H), 4.50-4.27 (m, 4
H), 4.02 (dd, 1 H, J ) 8.5, 6.3 Hz), 3.97-3.92 (m, 1 H), 3.75-3.60
(m, 6 H), 3.38 (b, 1 H), 3.07 (dd, 1 H, J ) 13.9, 5.6 Hz), 2.86 (dd, 1
H, J ) 13.9, 8.0 Hz), 2.09-2.00 (m, 1 H), 2.00-1.75 (m, 4 H), 1.17
(d, 3 H, J ) 6.3 Hz), 0.93-0.79 (m, 24 H), 0.03 (s, 6 H), 0.02 (s, 6
H); 13C NMR (DMSO-d6, 368 K) δ 170.7, 170.1, 169.1, 168.6, 168.3,
155.5, 137.0, 136.5, 128.7, 127.7, 127.0, 125.7, 66.5, 65.2, 62.7, 62.6,
61.4, 60.0, 59.0, 58.1, 54.7, 54.2, 53.7, 51.5, 50.8, 46.2, 37.6, 37.4,
29.9, 28.0, 25.2, 23.8, 19.3, 18.5, 17.4, -3.8, -6.1; MS (FAB) m/e
(rel intensity) 1182 ([M + Na]+, 58), 1060 ([M + H]+, 44).
1
1657 cm-1; H NMR (MeOH-d4, major rotamer) δ 7.28-7.09 (m, 10
H), 4.73-4.57 (m, 3 H), 4.47-4.38 (m, 2 H), 4.21-4.13 (m, 1 H),
4.13-4.07 (m, 2 H), 3.82-3.58 (m, 3 H), 3.58-3.50 (m, 1 H), 3.31
(dd, 1 H, J ) 11.0, 3.7 Hz), 3.23-3.20 (m, 1 H), 3.10-2.80 (m, 4 H),
2.38-2.08 (m, 2 H), 1.93-1.65 (m, 3 H), 1.32 (d, 3 H, J ) 6.2 Hz),
1.0-0.9 (m, 6 H); 13C NMR (MeOH-d4, major rotamer) δ 174.2, 173.6,
173.4, 172.5, 172.2, 172.0, 138.1, 137.8, 130.6, 130.3, 129.5, 127.9,
82.1, 75.1, 62.5, 62.4, 61.0, 57.6, 57.0, 56.7, 54.7, 54.5, 38.3, 37.4,
31.8, 30.5, 26.0, 21.6, 20.0, 18.7; MS (FAB) m/e (rel intensity) 770
([M + Na]+, 98), 748 ([M + H]+, 43); HRMS m/e calcd for C38H49N7O9
747.3592, found 747.3570.
Cyclo[D-Val-Ser(oxaz)-D-Phe-Ser(oxaz)-Phe-Pro-allo-Thr(ox-
az)] (17). Method A. A solution of 42.7 mg (0.057 mmol) of cyclo-
[D-Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr(oxaz)] (16) in 10 mL of THF
was treated at -60 °C with a solution of 149.5 mg (0.57 mmol) of
triphenylphosphine in 2 mL of THF and 118 µL (0.57 mmol) of DIAD
(diisopropyl azodicarboxylate). The reaction mixture was warmed to
0 °C over 45 min, concentrated, and chromatographed on SiO2 (EtOAc
to 5% MeOH/EtOAc) to afford 34.6 mg (85%) of 17 as a colorless
solid. Method B. A solution of 40.8 mg (0.0532 mmol) of cyclo[D-
Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr] (34) in 7 mL of THF was treated
at room temperature with 63.4 mg (0.266 mmol) of the Burgess reagent.
The reaction mixture was heated at 55 °C for 1 h and at 72 °C for 4 h,
cooled to room temperature, and concentrated. Chromatography on
SiO2 (EtOAc followed by 5-10% MeOH/EtOAc) and a second
chromatography on SiO2 (3-4% MeOH/CHCl3) afforded 27.9 mg
(74%) of 17 as a colorless solid: mp 212-219 °C (dec, CHCl3); [R]D
1
+149.8° (c 0.6, CHCl3, 23 °C); IR (neat) 3356, 1662, 1645 cm-1; H
NMR δ 7.35-7.02 (m, 14 H), 5.05-4.96 (m, 1 H), 4.92-4.82 (m, 2
H), 4.72-4.67 (m, 2 H), 4.55-4.39 (m, 4 H), 4.26-4.19 (m, 3 H),
3.68-3.49 (m, 1 H), 3.15-3.02 (m, 3 H), 2.87 (dd, 1 H, J ) 13.4, 6.2
Hz), 2.62-2.48 (m, 2 H), 2.30-2.18 (m, 1 H), 2.04-1.87 (m, 4 H),
1.44 (d, 3 H, J ) 6.3 Hz), 1.01 (d, 3 H, J ) 6.9 Hz), 0.91 (d, 3 H, J
) 6.8 Hz); 13C NMR δ 172.5, 171.4, 170.0, 169.9, 169.5, 169.3, 168.8,
135.3, 135.1, 129.7, 129.2, 128.5, 128.3, 127.2, 127.1, 81.3, 77.2, 75.8,
70.8, 70.2, 68.9, 67.8, 56.4, 51.5, 51.4, 47.2, 39.9, 38.3, 29.9, 28.9,
25.2, 21.7, 19.5, 16.4; MS (EI) m/e (rel intensity) 711 (M+, 100), 620
(24); HRMS m/e calcd for C38H45N7O7 711.3380, found 711.3390.
Cbz-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-OMe (20). A solution
of 4.45 g (6.22 mmol) of Cbz-Ser(TBDMS)-D-Phe-Ser(TBDMS)-OMe
(12) in 120 mL of MeOH was treated with Pd/C and H2 gas for 2 h
and then filtered through a plug of Celite and concentrated. The residue
was dried by azeotropic distillation with benzene to afford the amine
Cbz-D-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-
(oxaz)-OMe (15). A solution of 0.75 g (0.64 mmol) of Cbz-D-Val-
Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-OMe (14) in 25
mL of THF was treated at room temperature with 253 mg (1.06 mmol)
of the Burgess reagent. The solution was warmed from room
temperature to 65 °C over 30 min and kept at 65 °C for 2 h. The
reaction mixture was cooled to room temperature and concentrated.
Chromatography on SiO2 (2.5% MeOH/CHCl3) afforded 659 mg (89%)
of 15 as a colorless solid: mp 145-146 °C (MeOH); [R]D -12.0° (c
1.4, MeOH, 22 °C); IR (neat) 3289, 1652, 1646 cm-1
;
1H NMR
(MeOH-d4, major rotamer) δ 7.28-7.00 (m, 15 H), 5.09-4.90 (m, 2
H), 4.75-4.68 (m, 1 H), 4.60-4.49 (m, 3 H), 4.27 (dd, 1 H, J ) 5.3,
5.2 Hz), 4.18 (dd, 1 H, J ) 7.7, 7.2 Hz), 3.92 (d, 1 H, J ) 6.9 Hz),
3.85-3.32 (m, 9 H), 3.12-2.94 (m, 2 H), 2.94-2.72 (m, 2 H), 2.12-

Total Synthesis of Lissoclinamide 7
J. Am. Chem. Soc., Vol. 118, No. 49, 1996 12365
as a white solid. A solution of 1.72 g (6.83 mmol) of Cbz-valine in
125 mL of CH2Cl2 was treated with 0.89 mL (8.07 mmol) of
N-methylmorpholine, cooled to -20 °C, and treated with 0.89 mL (6.83
mmol) of isobutyl chloroformate. The reaction mixture was stirred
for 15 min at -15 °C. A solution of the amine prepared above in 20
mL of CH2Cl2 was added slowly, and the reaction mixture was warmed
to 10 °C over 1 h. The solution was diluted with 100 mL of CH2Cl2,
washed with 1 M NaH2PO4 (90 mL), H2O (90 mL), and brine (90 mL),
dried (Na2SO4), and concentrated. Chromatography on SiO2 (30%
EtOAc/hexanes) afforded 4.77 g (94%) of 20 as a colorless solid: mp
118-120 °C (CHCl3); [R]D +19.8° (c 1.0, CH2Cl2, 22 °C); IR (neat)
2.79 (m, 2.2 H), 2.08-1.65 (m, 4.4 H), 1.62-1.44 (m, 0.6 H), 1.35 (d,
1 H, J ) 6.2 Hz), 1.29 (d, 2 H, J ) 6.2 Hz), 0.95-0.84 (m, 6 H),
0.84-0.73 (m, 18 H), 0.00 to -0.09 (m, 12 H); 13C NMR (MeOH-d4,
mixture of rotamers) δ 174.2, 172.8, 172.6, 172.4, 171.9, 171.8, 171.7,
171.5, 171.3, 171.1, 170.3, 170.1, 158.0, 138.3, 138.2, 138.0, 137.6,
81.8, 81.1, 75.1, 68.0, 64.0, 62.6, 62.4, 56.7, 56.4, 56.3, 55.8, 53.8,
52.9, 48.0, 47.5, 41.0, 38.8, 38.7, 38.5, 32.1, 31.8, 26.4, 25.3, 23.0,
20.9, 20.8, 19.8, 19.1, 18.8, 9.2, -5.2; MS (FAB) m/e (rel intensity)
1142 ([M + H]+, 100), 1084 (28).
Cyclo[D-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-
Thr] (28). A solution of 1.05 g (0.901 mmol) of Cbz-D-Val-Ser-
(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-OMe (14) in 175 mL
of MeOH was treated with Pd/C and H2 gas for 24 h. The reaction
mixture was filtered through a plug of Celite and concentrated.
Chromatography on SiO2 (5-12% MeOH/CHCl3) afforded 0.85 g
(92%) of amine. A solution of 265 mg (0.258 mmol) of this amine in
THF/MeOH/H2O (10:2:1) was treated with 142 µL (0.284 mmol) of a
2.0 M NaOH solution. The reaction was stirred at room temperature
for 4 h and then treated with 47.7 mg (0.568 mmol) of NaHCO3. After
30 min, the reaction mixture was filtered, concentrated, and dried by
azeotropic distillation with benzene. A solution of the amino acid
sodium salt, 86 mg (1.02 mmol) of NaHCO3, and 393 mg (1.02 mmol)
of FDPP in 129 mL of DMF was heated at 40 °C for 3 d. DMF was
removed by distillation under reduced pressure at 45 °C. The remaining
residue was dissolved in 10% MeOH/CHCl3 and adsorbed onto SiO2.
Chromatography on SiO2 (25% EtOAc/hexanes followed by 5-10%
MeOH/CHCl3) and a second chromatography on SiO2 (4-7% MeOH/
CHCl3) afforded 123 mg (48%) of 28 as a white solid: mp 143-145
°C (CHCl3); [R]D -43.7° (c 1.0, MeOH, 22 °C); IR (neat) 3296, 1643,
1
3289, 1697, 1633 cm-1; H NMR δ 7.38-7.16 (m, 13 H), 7.12 (b, 1
H), 5.58 (b, 1 H), 5.11 (s, 2 H), 5.03 (b, 1 H), 4.62-4.57 (m, 1 H),
4.45-4.35 (m, 1 H), 4.35-4.25 (m, 1 H), 3.93 (dd, 1 H, J ) 9.9, 4.2
Hz), 3.85 (dd, 1 H, J ) 9.4, 2.3 Hz), 3.67 (s, 3 H), 3.58 (dd, 1 H, J )
9.9, 4.1 Hz), 3.51-3.45 (m, 1 H), 3.09 (dd, 1 H, J ) 13.6, 6.8 Hz),
2.96 (dd, 1 H, J ) 13.6, 7.0), 2.05-1.95 (m, 1 H), 0.93 (s, 9 H), 0.91-
0.82 (m, 6 H), 0.81 (s, 9 H), 0.14 (s, 3 H), 0.13 (s, 3 H), -0.02 (s, 6
H); 13C NMR δ 171.3, 170.2, 169.0, 156.5, 136.5, 129.6, 128.1, 127.8,
127.7, 126.3, 66.5, 63.9, 63.0, 58.6, 54.1, 53.8, 53.6, 51.7, 40.1, 32.6,
25.7, 25.4, 18.9, 18.0, 17.9, 17.2, -5.6, -5.8, -5.9; MS (EI) m/e (rel
intensity) 814 (M+, 60), 796 (80), 755 (69), 91 (100); HRMS m/e calcd
for C41H66N4O9Si2 814.4368, found 814.4340.
Cbz-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-
OMe (21). A solution of 1.17 g (2.29 mmol) of Cbz-Phe-Pro-allo-
Thr-OMe (9) in 125 mL of MeOH was treated with Pd/C and H2 gas
for 4 h. The reaction mixture was filtered through a plug of Celite,
concentrated, and dried by azeotropic distillation with benzene to afford
the amine as a white solid. A solution of 2.12 g (2.60 mmol) of Cbz-
Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-OMe (20) in 40 mL of THF/
H2O (3:1) was treated with 120 mg (2.86 mmol) of LiOH‚H2O. The
reaction mixture was stirred at room temperature for 3 h. After addition
of 20 mL of H2O, THF was removed in vacuo. The solution was
acidified with 1 M NaH2PO4 and extracted with EtOAc (2 × 50 mL).
The combined organic layers were washed with H2O (25 mL) and brine
(25 mL), dried (Na2SO4), and concentrated to afford 2.08 g (100%) of
acid as a white solid. A solution of 1.84 g (2.29 mmol) of this acid,
the amine prepared above, and 0.64 mL (4.58 mmol) of Et3N in 90
mL of CH2Cl2 was treated at room temperature with a solution of 1.76
g (4.58 mmol) of FDPP in 10 mL of CH2Cl2. The reaction mixture
was stirred overnight, diluted with 150 mL of CHCl3, washed with 1
M NaH2PO4 (90 mL), H2O (90 mL), and brine (90 mL), dried (Na2-
SO4), and concentrated. Chromatography on SiO2 (25% EtOAc/CHCl3
followed by 3% MeOH/CHCl3) and a second chromatography on SiO2
(2.5% MeOH/CHCl3) afforded 2.37 g (89%) of 21 as colorless solid:
mp 175-176 °C (MeOH); [R]D -48.2° (c 1.1, MeOH, 21 °C); IR (neat)
1
1510, cm-1; H NMR (MeOH-d4, major rotamer) δ 7.40 (d, 2 H, J )
7.1 Hz), 7.23-7.09 (m, 8 H), 4.71-4.55 (m, 2 H), 4.35 (d, 1 H, J )
6.4 Hz), 4.32-4.18 (m, 3 H), 4.07-3.98 (m, 2 H), 3.96-3.71 (m, 4
H), 3.56 (dd, 1 H, J ) 9.4, 5.1 Hz), 3.44-3.33 (m, 1 H), 3.20-3.12
(m, 2 H), 2.96-2.88 (m, 2 H), 2.32-2.13 (m, 2 H), 2.07-1.85 (m, 3
H), 1.13 (d, 3 H, J ) 6.3 Hz), 0.87-0.83 (m, 6 H), 0.78 (s, 9 H), 0.61
(s, 9 H), -0.01 to -0.11 (m, 6 H), -0.22 (s, 3 H), -0.31 (s, 3 H); 13
C
NMR (MeOH-d4, major rotamer) δ 174.4, 173.5, 173.0, 172.9, 172.7,
171.2, 139.0, 137.7, 130.4, 130.2, 129.6, 128.1, 127.9, 68.0, 63.9, 63.4,
63.3, 60.3, 60.0. 58.6, 55.8, 55.6, 55.1, 37.40, 31.8, 30.1, 26.4, 26.3,
26.0, 20.1, 20.0, 19.1, 18.9, 18.5, -5.2, -5.4; MS (FAB) m/e (rel
intensity) 1016 ([M + Na]+, 54), 994 ([M + H]+, 100).
Cyclo[D-Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr(TIPS)] (29). A so-
lution of 162 mg (0.163 mmol) of cyclo[D-Val-Ser(TBDMS)-D-Phe-
Ser(TBDMS)-Phe-Pro-allo-Thr] (28) in 4 mL of CH2Cl2 was treated
at room temperature with 25 µL (0.212 mmol) of 2,6-lutidine and 57
µL (0.212 mmol) of TIPS-OTf (triisopropylsilyl triflate). The reaction
mixture was stirred for 6 h, diluted with 45 mL of EtOAc, washed
with 1 M NaH2PO4 (15 mL) and brine (15 mL), dried (Na2SO4), and
concentrated. Chromatography on SiO2 (1-3% MeOH/CHCl3) af-
forded 156 mg (83%) of cyclo[D-Val-Ser(TBDMS)-D-Phe-Ser(TB-
DMS)-Phe-Pro-allo-Thr(TIPS)] as a colorless solid. A solution of 15.4
mg (0.0134 mmol) of this silyl ether in 1 mL of THF/H2O (20:1) was
treated with 0.4 mg (0.002 mmol) of TsOH‚H2O and stirred at room
temperature overnight. After addition of 0.4 mg (0.004 mmol) of
NaHCO3, the reaction mixture was stirred for another 15 min. The
volume of the solution was reduced to about one-third of the original
volume, and the remainder was directly chromatographed on SiO2 (6-
8% MeOH/CHCl3). Further purification by HPLC on SiO2 (4.5%
MeOH/CHCl3) afforded 9.0 mg (73%) of 29 as a colorless solid: mp
155-157 °C (CHCl3); [R]D -39.0° (c 0.8, MeOH, 22 °C); IR (neat)
1
3283, 1676, 1630 cm-1; H NMR (DMSO-d6, 368 K) δ 7.76-7.50
(m, 5 H), 7.35-7.27 (m, 4 H), 7.24-7.16 (m, 11 H), 6.72 (d, 1 H, J
) 8.2 Hz), 5.07 (d, 1 H, J ) 12.7 Hz), 5.04 (d, 1 H, J ) 12.7 Hz),
4.77 (b, 1 H), 4.62 (dd, 1 H, J ) 8.0, 5.7 Hz), 4.55 (b, 1 H), 4.43-
4.25 (m, 4 H), 3.98-3.90 (m, 2 H), 3.68-3.55 (m, 9 H), 3.4-3.3 (m,
1 H), 3.06 (dd, 2 H, J ) 13.9, 5.5 Hz), 2.85 (dd, 2 H, J ) 13.9, 7.9
Hz), 2.05-1.95 (m, 1 H), 1.95-1.70 (m, 4 H), 1.16 (d, 3 H, J ) 6.4
Hz), 0.89-0.78 (m, 24 H), 0.02 (s, 6 H), 0.02 (s, 6 H); 13C NMR
(MeOH-d4) δ 174.1, 173.9, 172.8, 172.2, 172.0, 171.9, 171.4, 158.0,
138.2, 130.5, 130.3, 129.5, 129.0, 127.8, 69.0, 68.0, 64.0, 62.4, 61.4,
59.9, 56.6, 56.3, 54.0, 52.5, 39.0, 38.7, 32.1, 30.1, 26.4, 25.7, 20.1,
19.8, 19.1, 18.6, -5.2; MS (FAB) m/e (rel intensity) 1182 ([M + Na]+,
45), 1160 ([M + H]+, 97), 1101 (100).
Cbz-Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-
(oxaz)-OMe (22). A solution of 138.6 mg (0.119 mmol) of Cbz-Val-
Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-OMe (21) in 2.5
mL of THF was treated at room temperature with 44.2 mg (0.185 mmol)
of the Burgess reagent and stirred for 15 min. The reaction mixture
was heated to 60 °C for 2.5 h, cooled to room temperature, and
concentrated. Chromatography on SiO2 (3% MeOH/CHCl3) afforded
126.8 mg (93%) of 22 as a colorless solid: [R]D -23.7° (c 1.2, MeOH,
23 °C); IR (neat) 3287, 1693, 1678 cm-1; 1H NMR (MeOH-d4, mixture
of rotamers) δ 7.27-7.08 (m, 15 H), 5.11-4.96 (m, 2 H), 4.76-4.69
(m, 1 H), 4.60-4.48 (m, 1.6 H), 4.45-4.25 (m, 2 H), 4.24-4.16 (m,
1 H), 4.01 (d, 0.3 H, J ) 6.6 Hz), 3.89 (d, 0.7 H, J ) 6.5 Hz), 3.84-
3.39 (m, 8.8 H), 3.39-3.29 (m, 0.6 H), 3.14-3.01 (m, 1.8 H), 2.99-
1
3291, 1680, 1651 cm-1; H NMR (MeOH-d4, mixture of rotamers) δ
7.40 (d, 0.5 H, J ) 7.2 Hz), 7.34 (d, 1 H, J ) 7.3 Hz), 7.30-7.10 (m,
8.5 H), 4.58-4.20 (m, 6.2 H), 4.15-4.03 (m, 0.8 H), 3.98-3.70 (m,
2 H), 3.70-3.45 (m, 3.3 H), 3.45-3.28 (m, 2 H), 3.15-2.77 (m, 2.8
H), 2.30-2.20 (m, 0.8 H), 2.17-1.85 (m, 3.2 H), 1.65-1.42 (m, 0.8
H), 1.23 (d, 1.5 H, J ) 6.2 Hz), 1.20-1.10 (m, 2.6 H), 1.00 (s, 16.2
H), 0.97-0.80 (m, 5.8 H), 0.79-0.74 (m, 3.H); 13C NMR (MeOH-d4,
mixture of rotamers) δ 174.62, 174.0, 173.8, 173.6, 173.4, 173.3, 173.2,
173.0, 172.6, 172.5, 172.1, 171.5, 171.3, 139.0, 138.4, 138.0, 137.4,
130.4, 129.8, 129.7, 128.8, 128.1, 69.0, 63.7, 63.5, 63.4, 62.8, 62.4,
62.2, 60.9, 60.3, 58.7, 58.1, 56.5, 55.7, 47.9, 39.1, 38.1, 37.4, 37.0,
32.6, 32.4, 32.0, 26.4, 22.8, 20.4, 20.0, 19.6, 19.1, 18.6, 18.2, 13.8,

12366 J. Am. Chem. Soc., Vol. 118, No. 49, 1996
Wipf and Fritch
13.6; MS (ES) m/e (rel intensity) 944.5 ([M + Na]+, 100), 922.5 ([M
+ H]+, 10); HRMS (ES) m/e calcd for C47H71N7O10NaSi 944.4929,
found 944.4969.
remaining residue was dissolved in 10% MeOH/CHCl3 and adsorbed
onto SiO2. Chromatography on SiO2 (30% EtOAc/CHCl3 followed
by 4-7% MeOH/CHCl3) and subsequent HPLC on SiO2 (4% MeOH/
CHCl3) afforded 211 mg (25%) of 31 as a white solid: mp 155-160
°C (MeOH); [R]D -53.4° (c 0.6, MeOH, 24 °C); IR (neat) 3273, 1639,
1560 cm-1; 1H NMR (MeOH-d4, mixture of rotamers) δ7.28-7.02 (m,
10 H), 4.99-4.90 (m, 0.4 H), 4.52 (dd, 0.9 H, J ) 9.2, 5.5 Hz), 4.49-
4.30 (m, 2.6 H), 4.30-4.14 (m, 2 H), 4.14-4.02 (m, 0.8 H), 4.00-
3.90 (m, 1.8 H), 3.90-3.76 (m, 1.4 H), 3.76-3.68 (m, 0.6 H), 3.67-
3.58 (m, 1.1 H), 3.55-3.44 (m, 1.7 H), 3.31-3.23 (m, 1.6 H), 3.15-
2.96 (m, 2 H), 2.95-2.78 (2.2 H), 2.22-2.10 (m, 0.9 H), 2.04-1.78
(m, 1.8 H), 1.65-1.51 (m, 0.6 H), 1.50-1.32 (m, 0.7 H), 1.23-1.08
(m, 3.5 H), 0.98-0.60 (m, 25 H), 0.03 to -0.03 (m, 4 H), -0.03 to
-0.12 (m, 6.2 H), -0.12 to -0.20 (m, 1.8 H); 13C NMR (MeOH-d4,
318 K, major rotamer) δ 174.2, 173.9, 173.1, 172.2, 172.1, 171.8, 170.9,
138.7, 137.2, 130.6, 130.3, 129.9, 129.5, 128.5, 127.7, 67.3, 64.7, 63.7,
62.1, 61.9, 56.4, 56.2, 56.0, 55.0, 47.6, 39.4, 37.8, 31.8, 30.4, 26.5,
26.4, 23.1, 21.7, 19.7, 19.1, 18.1, -5.2, -5.4; MS (FAB) m/e (rel
intensity) 1032 ([M+K]+, 6), 1016 ([M + Na]+, 100), 994 ([M + H]+,
6).
Cyclo[D-ValΨ{(CdS)NH}-Ser-D-PheΨ{(CdS)NH}-Ser-Phe-Pro-
allo-Thr] (30). A solution of 40.5 mg (0.0439 mmol) of cyclo[D-Val-
Ser-D-Phe-Ser-Phe-Pro-allo-Thr(TIPS)] (29) in 4 mL of THF was
treated at room temperature with 32.0 mg (0.134 mmol) of the Burgess
reagent. The mixture was stirred at 65 °C for 2.5 h, cooled to room
temperature, and concentrated. The residue was dissolved in 5 mL of
MeOH/Et3N (1:1) and saturated with H2S gas. The solution was stirred
at room temperature for 4 d and then concentrated. Chromatography
on SiO2 (CHCl3 to 4% MeOH/CHCl3) afforded 40.6 mg of thiolysis
products. The crude material was dissolved in 1 mL of THF, treated
with 49 µL (0.049 mmol) of 1 M TBAF in THF, and heated at 37 °C
for 3 h. The solution was cooled to room temperature and directly
chromatographed on SiO2 (6% MeOH/CHCl3). Further purification
by HPLC on SiO2 (2% MeOH/EtOAc) afforded 14.4 mg (41%) of 30
as a colorless solid: mp 195-197 °C (dec, MeOH); [R]D -118° (c
0.9, MeOH, 23 °C); IR (neat) 3292, 1657, 1649 cm-1 1H NMR
;
(MeOH-d4, major rotamer) δ 7.39 (d, 2 H, J ) 7.2 Hz), 7.35-7.05
(m, 8 H), 5.25 (dd, 1 H, J ) 7.9, 5.1 Hz), 4.87-4.81 (m, 2 H), 4.70
(dd, 1 H, J ) 10.7, 3.2 Hz), 4.66-4.50 (m, 2 H), 4.28-4.22 (m, 1 H),
4.10-3.94 (m, 3 H), 3.86-3.76 (m, 2 H), 3.75-3.50 (m, 5 H), 3.45-
3.35 (m, 1 H), 3.35-3.26 (m, 2 H), 3.16-2.87 (m, 4 H), 2.41-2.28
(m, 1 H), 2.24-2.10 (m, 1 H), 2.00-1.85 (m, 4 H), 1.05 (d, 3 H, J )
6.3 Hz), 0.87 (d, 3 H, J ) 6.7 Hz), 0.80 (d, 3 H, J ) 6.7 Hz); 13C
NMR (MeOH-d4, major rotamer) δ 208.2, 204.8, 174.7, 173.3, 171.9,
171.8, 171.2, 139.0, 138.1, 130.6, 130.6, 129.8, 129.6, 129.6, 128.0,
68.4, 67.8, 65.2, 64.1, 63.6, 62.1, 61.5, 61.1, 55.8, 55.4, 40.3, 37.8,
33.5, 30.3, 26.2, 23.0, 20.7, 19.9, 19.4; MS (FAB) m/e (rel intensity)
820 ([M + Na]+, 45), 798 ([M + H]+, 100).
Cyclo[Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr(TIPS)] (32). A solu-
tion of 108 mg (0.109 mmol) of cyclo[Val-Ser(TBDMS)-D-Phe-Ser-
(TBDMS)-Phe-Pro-allo-Thr] (31) in 6 mL of CH2Cl2 was treated at
room temperature with 16.5 µL (0.142 mmol) of 2,6-lutidine and 38
µL (0.142 mmol) of TIPS-OTf. The reaction mixture was stirred at
room temperature for 8 h, diluted with 45 mL EtOAc, washed with 1
M NaH2PO4 (10 mL) and brine (10 mL), dried (Na2SO4), and
concentrated. Chromatography on SiO2 (1-3% MeOH/CHCl3) af-
forded 97.6 mg (78%) of cyclo[Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-
Phe-Pro-allo-Thr(TIPS)] as a colorless solid. A solution of 97.6 mg
(0.0848 mmol) of this silyl ether in 3 mL of THF/H2O (20:1) was treated
with 2.4 mg (0.0127 mmol) of TsOH‚H2O, stirred at room temperature
overnight, and treated with 2.1 mg (0.0254 mmol) of NaHCO3. The
reaction mixture was stirred for another 15 min. The volume of the
solution was reduced to about one-third under reduced pressure, and
the reaction mixture was directly chromatographed on SiO2 (6-8%
MeOH/CHCl3). Further purification by HPLC on SiO2 (4.5% MeOH/
CHCl3) afforded 61 mg (78%) of 32 as a colorless solid: mp 162-165
°C (MeOH); [R]D -36.4° (c 0.5, MeOH, 23 °C); IR (neat) 3294, 1649,
Cyclo[D-Val-Ser(thiaz)-D-Phe-Ser(thiaz)-Phe-Pro-allo-Thr(ox-
az)] (Lissoclinamide 7 (25)). A solution of 18.2 mg (0.0228 mmol)
of cyclo[D-ValΨ{(CdS)NH}-Ser-D-PheΨ{(CdS)NH}-Ser-Phe-Pro-
allo-Thr] (30) in 3 mL of THF was treated at room temperature with
27.2 mg (0.114 mmol) of the Burgess reagent. The mixture was stirred
at room temperature for 10 min and then heated to 40 °C for 20 min
and to 70 °C for 1.5 h. The solution was cooled, filtered, concentrated,
and chromatographed on SiO2 (3% MeOH/CHCl3). Further purification
with HPLC (2% MeOH/CHCl3) afforded 15.3 mg (90%) of lissocli-
namide 7 (25) as a colorless solid: mp 242-247 °C (dec, MeOH);
1
1632 cm-1; H NMR (MeOH-d4, mixture of rotamers) δ 7.26-6.94
(m, 10 H), 4.99 (dd, 0.4 H, J ) 7.4, 7.2 Hz), 4.69-4.55 (m, 0.7 H),
4.53-4.39 (m, 1 H), 4.39-4.29 (m, 1.3 H), 4.29-4.12 (m, 1.8 H),
4.12-4.00 (m, 1.4 H), 4.00-3.60 (m, 3.4 H), 3.56-3.38 (m, 3.1 H),
3.38-3.26 (m, 1.4 H), 3.10-3.00 (m, 0.9 H), 3.00-2.84 (m, 1.9 H),
2.77 (dd, 0.6 H, J ) 14.3, 11.0 Hz), 2.58 (dd, 0.3 H, J ) 13.7, 6.6
Hz), 2.35-1.76 (m, 3.9 H), 1.76-1.43 (m, 0.9 H), 1.38-0.69 (m, 30
H); 13C NMR (MeOH-d4, mixture of rotamers) δ 177.1, 175.1, 174.4,
173.5, 173.1, 172.9, 172.8, 172.4, 172.2, 171.6, 171.4, 170.1, 139.9,
139.2, 138.3, 138.0, 137.2, 130.6, 130.2, 130.0, 129.7, 129.4, 129.2,
128.6, 127.8, 127.6, 69.5, 69.1, 68.7, 64.4, 63.0, 62.7, 62.3, 61.5, 60.4,
58.9, 58.3, 58.0, 57.3, 56.3, 55.4, 54.8, 53.6, 47.5, 39.6, 38.2, 37.5,
32.6, 31.2, 30.9, 30.3, 26.5, 25.9, 22.9, 20.0, 19.7, 19.5, 19.2, 18.6,
18.2, 13.6; MS (FAB) m/e (rel intensity) 944 ([M + Na]+, 17), 922
([M + H]+, 100).
Cyclo[ValΨ{(CdS)NH}-Ser-D-PheΨ{(CdS)NH}-Ser-Phe-Pro-
allo-Thr] (33). A solution of 73.0 mg (0.079 mmol) of cyclo[Val-
Ser-D-Phe-Ser-Phe-Pro-allo-Thr(TIPS)] (32) in 8 mL of THF was
treated with 56.5 mg (0.237 mmol) of the Burgess reagent. The reaction
mixture was stirred at room temperature for 15 min, heated at 70 °C
for 2.5 h, cooled to room temperature, and concentrated. Chromatog-
raphy through two short plugs of SiO2 (4-6% MeOH/EtOAc and 5%
MeOH/CHCl3) afforded 65.9 mg of crude product as a colorless solid.
This solid was dissolved in 5 mL of MeOH/Et3N (1:1) and saturated
with H2S gas. The solution was stirred at room temperature for 4 d
and then concentrated. Chromatography on SiO2 (CHCl3 to 4% MeOH/
CHCl3) afforded 51 mg of thiolysis products. This material was
dissolved in 2 mL of THF, treated with 58 µL (0.058 mmol) of TBAF
(1 M in THF), and heated at 37 °C for 28 h. The mixture was cooled
to room temperature and directly chromatographed on SiO2 (6% MeOH/
CHCl3). Further purification by HPLC on SiO2 (2% MeOH/EtOAc)
afforded 22.0 mg (35%) of 33 as a white solid: mp 192-197 °C (dec,
MeOH); [R]D -131.6° (c 1.0, MeOH, 22 °C); IR (neat) 3250, 1670,
[R]D +172° (c 0.6, CHCl3, 22 °C); IR (neat) 3379, 1674, 1651 cm-1
;
1H NMR δ 7.74 (d, 1 H, J ) 10.1 Hz), 7.36-7.11 (m, 9 H), 7.09 (d,
2 H, J ) 6.7 Hz), 6.91 (d, 1 H, J ) 9.2 Hz), 5.30-5.21 (m, 2 H),
5.00-4.87 (m, 3 H), 4.64 (dd, 1 H, J ) 10.6, 9.9 Hz), 4.56 (dd, 1 H,
J ) 8.0, 7.6 Hz), 4.27 (d, 1 H, J ) 4.6 Hz), 3.68-3.52 (m, 4 H), 3.21
(dd, 1 H, J ) 11.3, 11.1 Hz), 3.09 (d, 2 H, J ) 5.2 Hz), 3.07-2.98 (m,
1 H), 2.91 (dd, 1 H, J ) 13.5, 6.2 Hz), 2.69 (dd, 1 H, J ) 13.4, 8.6
Hz), 2.54-2.44 (m, 1 H), 2.30-2.22 (m, 1 H), 2.04-1.86 (m, 3 H),
1.43 (d, 3 H, J ) 6.4 Hz), 0.97 (d, 3 H, J ) 6.9 Hz), 0.64 (d, 3 H, J
) 6.8 Hz); 13C NMR δ 179.9, 172.9, 172.1, 170.8, 169.6, 169.4, 135.7,
134.7, 129.7, 129.6, 128.6, 128.4, 127.4, 127.0, 81.1, 79.7, 78.2, 75.8,
56.4, 51.9, 51.6, 47.1, 39.4, 38.8, 36.2, 34.8, 30.8, 28.8, 25.4, 21.8,
19.7, 15.9; MS (FAB) m/e (rel intensity) 744 ([M + H]+, 100); HRMS
m/e calcd for C38H45N7O5S2 743.2924, found 743.2960; HRMS (FAB)
m/e calcd for C38H46N7O5S2 ([M + H]+) 744.3027, found 744.3002.
Cyclo[Val-Ser(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-
Thr] (31). A solution of 1.23 g (1.060 mmol) of Cbz-Val-Ser-
(TBDMS)-D-Phe-Ser(TBDMS)-Phe-Pro-allo-Thr-OMe (21) in 400 mL
of MeOH was treated with Pd(OH)2/C and H2 gas for 24 h. The
reaction mixture was filtered through a plug of Celite and concentrated.
The residue was purified by chromatography through a short plug of
SiO2 (5-10% MeOH/CHCl3) to afford 0.88 g (81%) of amine as a
solid. This amine was dissolved in 26 mL of THF/MeOH/H2O (10:
2:1) and treated with 0.64 mL (1.28 mmol) of a 2.0 M NaOH solution.
The reaction mixture was stirred at room temperature overnight and
then treated with 196 mg (2.33 mmol) of NaHCO3. After 30 min, the
suspension was filtered, concentrated, and dried by azeotropic distil-
lation with benzene. A solution of the resulting amino acid sodium
salt, 288 mg (3.428 mmol) of NaHCO3, and 1.32 g (3.43 mmol) of
FDPP in 429 mL of DMF was heated at 45 °C for 4.5 d. Volatiles
were removed by distillation under reduced pressure at 45 °C. The

Total Synthesis of Lissoclinamide 7
J. Am. Chem. Soc., Vol. 118, No. 49, 1996 12367
1
1657 cm-1; H NMR δ (MeOH-d4, major rotamer) δ 7.26-7.02 (m,
mg (88%) of amine as a solid. This amine was dissolved in 10 mL of
THF/MeOH/H2O (10:2:1), treated with 0.24 mL of a 2.0 M NaOH
solution and stirred at room temperature for 2 h. After addition of 81
mg (0.96 mmol) of NaHCO3, the reaction mixture was stirred for an
additional 30 min, filtered, concentrated, and dried by azeotropic
distillation with benzene. The amino acid sodium salt was dissolved
in 218 mL of DMF and treated with 358 mg (1.86 mmol) of NaHCO3
and 717 mg (1.86 mmol) of FDPP. The reaction mixture was stirred
at 40 °C for 4 d, and DMF was removed under reduced pressure. The
residue was dissolved in 10% MeOH/CHCl3 and adsorbed onto SiO2.
Chromatography on SiO2 (15% EtOAc/CHCl3 followed by 5-7%
MeOH/CHCl3) afforded 264 mg of crude product, which was dissolved
in 4.5 mL of THF, cooled to 0 °C, and treated for 15 min with 0.65
mL of a 1 M TBAF solution in THF. The reaction mixture was directly
chromatographed on SiO2 (4 to 10% MeOH/CHCl3) to afford 176 mg
(54%) of 35 as a colorless solid: mp 171-177 (dec, MeOH); [R]D
10 H), 5.11 (dd, 1 H, J ) 4.7, 4.6 Hz), 4.92 (dd, 1 H, J ) 5.7, 5.6 Hz),
4.86-4.81 (m, 1 H), 4.58-4.41 (m, 2 H), 4.30-4.17 (m, 1 H), 4.13-
3.92 (m, 2 H), 3.69-3.54 (m, 3 H), 3.50 (dd, 1 H, J ) 11.1, 4.6 Hz),
3.34-3.20 (m, 2 H), 3.12-2.92 (m, 4 H), 2.79 (dd, 1 H, J ) 12.2,
11.9 Hz), 2.69-2.55 (m, 1 H), 1.99-1.72 (m, 2 H), 1.61-1.47 (m, 1
H), 1.36-1.20 (m, 1 H), 1.07 (d, 3 H, J ) 5.9 Hz), 0.93 (d, 3 H, J )
7.0 Hz), 0.71 (d, 3 H, J ) 7.0 Hz); 13C NMR (MeOH-d4, major rotamer)
δ 203.7, 203.6, 173.2, 173.1, 172.0, 171.2, 170.8, 138.8, 136.7, 130.8,
130.5, 130.1, 129.3, 128.7, 127.6, 68.7, 67.2, 62.5, 62.2, 61.7, 61.2,
60.8, 60.6, 55.7, 47.6, 41.1, 38.8, 32.9, 31.0, 22.6, 22.3, 20.2, 19.7,
15.6; MS (FAB) m/e (rel intensity) 820 ([M + Na]+, 18), 798 ([M +
H]+, 30), 697 (100).
Cyclo[Val-Ser(thiaz)-D-Phe-Ser(thiaz)-Phe-Pro-allo-Thr(oxaz)] (24).
A solution of 19.8 mg (0.0248 mmol) of cyclo[ValΨ{(CdS)NH}-Ser-
D-PheΨ{(CdS)NH}-Ser-Phe-Pro-allo-Thr] (33) in 3 mL of THF was
treated at room temperature with 29.6 mg (0.124 mmol) of the Burgess
reagent. The reaction mixture was stirred at room temperature for 10
min and heated to 40 °C for 20 min and to 70 °C for 1.5 h. The solution
was cooled, filtered, concentrated, and chromatographed on SiO2 (3%
MeOH/CHCl3). Further purification by HPLC on SiO2 (2% MeOH/
CHCl3) afforded 13.1 mg (71%) of 24 as a colorless solid: mp 163-
165 °C (CHCl3); [R]D +86.2° (c 0.6, CHCl3, 22 °C); IR (neat) 3368,
1
-2.3° (c 0.6, MeOH, 23 °C); IR (neat) 3300, 1647, 1630 cm-1; H
NMR (MeOH-d4, major rotamer) δ 7.24-7.08 (m, 10 H), 4.95 (dd, 1
H, J ) 8.3, 2.3 Hz), 4.62-4.55 (m, 1 H), 4.51-4.44 (m, 1 H), 4.24-
4.17 (m, 2 H), 4.14-3.94 (m, 4 H), 3.81-3.71 (m, 2 H), 3.64-3.59
(m, 1 H), 3.32-3.27 (m, 2 H), 3.07-2.81 (m, 3 H), 2.21-2.13 (m, 1
H), 1.95-1.80 (m, 4 H), 1.26 (d, 3 H, J ) 6.4 Hz), 0.86 (d, 3 H, J )
6.6 Hz), 0.67 (d, 3 H, J ) 6.6 Hz); 13C NMR (MeOH-d4, major rotamer)
δ 174.3, 173.2, 172.6, 172.1, 171.6, 171.5, 138.2, 138.0, 130.3, 130.1,
129.5, 127.7, 83.6, 76.0, 62.8, 62.4, 58.1, 57.4, 57.2, 56.9, 53.2, 38.1,
37.3, 34.1, 30.2, 25.9, 21.5, 19.8, 19.7; MS (FAB) m/e (rel intensity)
770 (M + Na, 33), 748 (M + H, 42), 154 (100).
1686, 1653 cm-1; H NMR δ 7.90-7.69 (b, 1 H), 7.62 (d, 1 H, J )
1
9.6 Hz), 7.49 (d, 1 H, J ) 5.3 Hz), 7.38-7.11 (m, 10 H), 5.26-5.14
(m, 1 H), 5.09-4.99 (m, 1 H), 4.88-4.49 (m, 5 H), 4.24 (d, 1 H, J )
4.1 Hz), 4.02-3.88 (b, 1 H), 3.73 (dd, 1 H, J ) 10.1, 9.8 Hz), 3.46
(dd, 2 H, J ) 10.7, 10.5 Hz), 3.31 (dd, 2 H, J ) 11.6, 11.5 Hz), 3.16-
2.95 (m, 2 H), 2.77 (dd, 1 H, J ) 12.6, 9.5 Hz), 2.48-2.23 (b, 2 H),
2.23-2.08 (m, 1 H), 1.99-1.70 (m, 3 H), 1.42 (d, 3 H, J ) 6.2 Hz),
1.00-0.90 (m, 6 H); 13C NMR δ 173.9, 171.2, 170.3, 169.5, 169.3,
169.1, 135.7, 135.4, 129.8, 129.6, 128.5, 128.2, 127.2, 127.0, 82.1,
79.6, 78.2, 75.1, 56.1, 53.9, 53.2, 47.2, 40.2, 38.4, 36.9, 33.1, 28.6,
25.1, 21.7, 19.9, 19.5; MS (EI) m/e (rel intensity) 743 (M+, 44), 700
(28), 373 (100); HRMS m/e calcd for C38H45N7O5S2 743.2924, found
743.2952.
Cyclo[Val-Ser(oxaz)-D-Phe-Ser(oxaz)-Phe-Pro-allo-Thr(oxaz)] (36).
A solution of 26.0 mg (0.0348 mmol) of cyclo[Val-Ser-D-Phe-Ser-Phe-
Pro-allo-Thr(oxaz)] (35) in 6 mL of THF at was treated at -60 °C
with a solution of 91.3 mg (0.348 mmol) of triphenylphoshine in 1
mL of THF and 69 µL (0.348 mmol) of DIAD. The reaction mixture
was warmed to -20 °C over 20 min, and a white precipitate appeared.
The suspension was warmed to room temperature, concentrated, and
purified by chromatography on SiO2 (EtOAc to 5% MeOH/EtOAc) to
afford 18.2 mg (74%) of 36 as a white solid: mp 153-160 °C (CHCl3);
[R]D +72.8° (c 0.4, CHCl3, 22 °C); IR (neat) 3330, 2966, 1657, 1533
cm-1; 1H NMR (major rotamer) δ 7.64-7.57 (m, 2H), 7.27-7.17 (m,
9 H), 7.08-7.05 (m, 2 H), 4.87-4.60 (m, 7 H), 4.49 (dd, 1 H, J )
10.8, 9.8 Hz), 4.36-4.28 (m, 2 H), 4.26 (d, 1 H, J ) 4.4 Hz), 3.37
(dd, 1 H, J ) 13.7, 6.0 Hz), 3.22-3.00 (m, 3 H), 2.72 (dd, 1 H, J )
12.6, 10.1 Hz), 2.18-2.05 (m, 3 H), 1.92-1.68 (m, 1 H), 1.43 (d, 3 H,
Cyclo[D-Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr] (34). A solution of
15.4 mg (0.0155 mmol) of cyclo[D-Val-Ser(TBDMS)-D-Phe-Ser-
(TBDMS)-Phe-Pro-allo-Thr] (28) in 0.7 mL of THF/H2O (20:1) was
treated with 0.5 mg (0.0026 mmol) of TsOH‚H2O. The mixture was
stirred overnight at room temperature, treated with 0.4 mg (0.005 mmol)
of NaHCO3, and stirred for another 15 min. The volume of the solution
was reduced to about one-third, and the residue was directly chro-
matographed on SiO2 (8% MeOH/CHCl3) to afford 10.1 mg (85%) of
34 as a white solid: mp 164-168 °C (MeOH); [R]D -55.1° (c 0.9,
J ) 6.3 Hz), 0.93 (d, 3 H, J ) 6.7 Hz), 0.87 (d, 3 H, J ) 6.8 Hz); 13
C
NMR (major rotamer) δ 171.4, 170.5, 170.4, 169.8, 169.2, 168.9, 164.0,
151.1, 135.8, 135.5, 129.6, 129.5, 128.5, 128.3, 127.2, 127.0, 82.2,
75.2, 71.4, 69.1, 68.2, 56.1, 53.4, 51.8, 49.5, 47.1, 40.3, 37.7, 34.0,
28.6, 25.1, 21.8, 19.5; MS (FAB) m/e (rel intensity) 734 ([M + Na]+,
20), 712 ([M + H]+, 100); HRMS m/e calcd for C38H45N7O7 711.3380,
found 711.3361.
MeOH, 22 °C); IR (neat) 3292, 1666, 1651 cm-1; H NMR (MeOH-
1
d4, mixture of rotamers) δ 7.38 (d, 1.2 H, J ) 7.1 Hz), 7.27-7.06 (m,
8.8 H), 4.69 (dd, 0.6 H, J ) 11.2, 7.8 Hz), 4.60 (dd, 0.5 H, J ) 9.3,
4.9 Hz), 4.53 (dd, 0.8 H, J ) 7.7, 5.0 Hz), 4.40-4.36 (m, 1.3 H),
4.36-4.23 (m, 2.2 H), 4.16 (dd, 0.7 H, J ) 4.1, 4.1 Hz), 4.06-3.96
(m, 1.6 H), 3.92 (d, 0.4 H, J ) 5.2 Hz), 3.88-3.81 (m, 0.6 H), 3.80-
3.63 (m, 2.6 H), 3.62-3.40 (m, 2.5 H), 3.39-3.23 (m, 1.7 H), 3.20-
3.10 (m, 0.9 H), 3.03-2.89 (m, 2.0 H), 2.79 (dd, 0.4 H, J ) 14.3, 8.8
Hz), 2.31-2.13 (m, 1.6 H), 2.04-1.88 (m, 2.2 H), 1.72-1.50 (m, 1.2
H), 1.20 (d, 1.6 H, J ) 6.3 Hz), 1.15 (d, 1.8 H, J ) 6.3 Hz), 0.86 (d,
3.6 H, J ) 6.8 Hz), 0.78 (d, 1.2 H, J ) 6.9 Hz), 0.49 (d, 1.1 H, J )
6.8 Hz); 13C NMR (MeOH-d4, mixture of rotamers) δ 174.5, 174.2,
174.0, 173.7, 173.4, 173.2, 173.0, 172.7, 171.6, 139.1, 138.6, 138.0,
137.5, 130.5, 129.7, 128.0, 68.4, 67.7, 64.0, 63.5, 63.0, 62.4, 61.8, 60.7,
60.1, 58.8, 58.1, 56.7, 56.3, 55.6, 39.2, 37.5, 37.1, 33.0, 31.7, 30.7,
30.3, 26.3, 23.1, 20.9, 20.4, 20.1, 18.6, 17.8; MS (FAB) m/e (rel
intensity) 788 ([M + Na]+, 15), 766 ([M + H]+, 72).
Acknowledgment. Support from the National Institutes of
Health (AI34914) is gratefully acknowledged. We would like
to thank Dr. Steven Geib (University of Pittsburgh) for the x-ray
analysis of synthetic lissoclinamide 7, and Prof. Diane J. Watters
(University of Queensland) for copies of the NMR spectra of
the natural product. P.W. is the recipient of an A. P. Sloan
Research Fellowship (1994-96), a Camille Dreyfus Teacher-
Scholar Award (1995-97), and an NSF Presidential Faculty
Fellowship (1994-1999).
Supporting Information Available: 1H NMR and 13C NMR
spectra of synthetic lissoclinamide 7 and intermediates and
experimental details for 6, 7, 11, 12, 18, 19, and 23 (57 pages).
See any current masthead page for ordering and Internet access
instructions.
Cyclo[Val-Ser-D-Phe-Ser-Phe-Pro-allo-Thr(oxaz)] (35). A solu-
tion of 567 mg (0.496 mmol) of Cbz-Val-Ser(TBDMS)-D-Phe-Ser-
(TBDMS)-Phe-Pro-allo-Thr(oxaz)-OMe (22) in 25 mL of MeOH was
treated with Pd(OH)2 and H2 gas for 10 h. The reaction mixture was
filtered through a plug of Celite, concentrated, and chromatographed
through a short plug of SiO2 (4 to 12% MeOH/CHCl3) to afford 440
JA962859F