A general methodology for automated solid-phase synthesis of depsides and depsipeptides. Preparation of a valinomycin analogue

Article abstract of DOI:10.1021/jo981580+

A general methodology is described that allows the solid-phase synthesis of depsides and depsipeptides from chiral α-hydroxy- and α-amino acids. The results of studies with different protecting groups for the α-hydroxy acids and coupling systems for depsi

Full text of DOI:10.1021/jo981580+

J . Org. Chem. 1999, 64, 8063-8075
8063
A Gen er a l Meth od ology for Au tom a ted Solid -P h a se Syn th esis of
Dep sid es a n d Dep sip ep tid es. P r ep a r a tion of a Va lin om ycin
An a logu e†
Oliver Kuisle, Emilio Quin˜oa´, and Ricardo Riguera*
Departamento de Quı´mica Orga´nica, Facultad de Qu´ımica, and Instituto de Acuicultura,
Universidad de Santiago de Compostela, E-15706 Santiago de Compostela, Spain
Received August 4, 1998 (Revised Manuscript Received J uly 21, 1999)
A general methodology is described that allows the solid-phase synthesis of depsides and
depsipeptides from chiral R-hydroxy- and R-amino acids. The results of studies with different
protecting groups for the R-hydroxy acids and coupling systems for depside bond formation are
presented. The oligomers were prepared using a Wang-type linker with final TFA/CH2Cl2 cleavage.
Depside linkage of the THP-protected acids (THP ) tetrahydropyranyl) to the resin-bound chains
was achieved with DIC/DMAP (DIC ) diisopropylcarbodiimide, DMAP ) 4-(dimethylamino)pyridine)
and monitored by a color test with 4-(p-nitrobenzyl)pyridine. THP deprotection was achieved with
p-TsOH in CH2Cl2/MeOH and was monitored by GC. Following the established procedure, depsides
made up from the same enantiomer (i.e., H-[L-Man]8-OH, 25), by both enantiomers (i.e., H-[D-Man-
L-Man]4-OH, 26), or by different hydroxy acids in the same chain (i.e., H-[L-Lac-L-Hiv]3-OH, 27)
were prepared with an average yield of 95-97% per cycle. The linear precursor of the valinomycin
analogue 30 ([L-Val-D-Man-D-Val-L-Lac]3) was entirely synthesized on resin and cyclized in solution.
Cyclization of the open-chain depsides is the final step in the preparation of a new class of chiral
R-hydroxyester macrocycles.
In tr od u ction
by hydroxy acids, so that amide and ester bonds are
present along the chain. One of the most representative
examples of depsipeptides is the fungal antibiotic vali-
nomycin (1),6 a symmetric cyclodepsipeptide isolated from
Streptomyces fulvissimus, which is formed by three
repeating units of a sequence of four R-amino and
R-hydroxy acids. It shows the best K+/Na+ selectivity of
all K+-ionophores known to date.7 Onchidin B (2),8
isolated from a tunicate from the South Pacific, is an
example of a highly symmetric cyclodepsipeptide that
contains R- and â-amino and hydroxy acids.
Both valinomycin and onchidin B share with many
bioactive peptides a characteristic that explains the
bioactivity of many of these compounds: they present a
cyclic structure with the polar groups oriented toward
the central cavity, whereas the rest of the molecule is
relatively nonpolar. This enables them to complex ions
and act as selective ion transporters through cellular
membranes. A different biological mechanism has been
identified for another type of cyclic depsipeptide, the
quinomycins,9 which are well-known DNA bisintercala-
tors with potent antitumor activity.
In recent years, the development of combinatorial
chemistry1 and the synthesis of a wide variety of non-
polymeric substrates2 on resin has greatly increased the
interest of researchers in the practical advantages of
solid-phase synthesis. Since the pioneering work of
Merrifield et al., this technique has become standard for
the preparation of certain families of natural oligomers,
such as nucleotides,3 oligosaccharides,4 and peptides.5
However, no general solid-phase approach equivalent to
that applied to peptides has been established for the
preparation of depsides and depsipeptides, two structur-
ally related classes of compounds that are present in
terrestrial and marine sources.
Depsipeptides are oligomers that are similar to pep-
tides but in which some of the amino acids are replaced
* To whom correspondence should be addressed. Fax: + 34 981
591091.
† Abbreviations used for R-hydroxy acids and depsides are consistent
with those used for R-amino acids and peptides in the nomenclature
of peptides, with “H-” representing the hydroxy group and “-OH”
representing the carboxy group: H-Hiv-OH ) R-hyroxyisovaleric acid;
H-Lac-OH ) lactic acid; H-Man-OH ) mandelic acid.
Naturally, since ester and amide groups have certain
common structural elements, but at the same time differ
significantly in their hydrogen-bonding capacity, the
incorporation of hydroxy acids into a peptide chain is a
(1) Szostak, J . Chem. Rev. 1997, 97, 347-510.
(2) For reviews covering the period from 1992 to 1997, see: Booth,
S.; Hermkens, P. H. H.; Ottenheijm, H. C. J .; Rees. D. C. Tetrahedron
1998, 54, 15385-15443, and the previous review cited therein.
(3) (a) Eckstein, F. Nucleotides and Analogues: A Practical Ap-
proach; Rickwood, D., Hames, B. D., Eds.; IRL Press: Oxford, 1991.
For a recent review, see: (b) Beaucage, S. L.; Radhakrishnan, P. I.
Tetrahedron 1992, 48, 2223-2311.
(6) Dietrich, B.; Viout, P.; Lehn, J .-M. Macrocyclic Chemistry;
VCH: Weinheim, 1993.
(7) Izatt, R. M.; Bradshaw, J . S.; Nielsen, S. A.; Lamb, J . D.;
Christensen, J . J . Chem. Rev. 1985, 85, 271-339.
(8) Ferna´ndez, R.; Rodr´ıguez, J .; Quin˜oa´, E.; Riguera, R.; Mun˜oz,
L.; Ferna´ndez-Sua´rez, M.; Debitus, C. J . Am. Chem. Soc. 1996, 118,
11635-11643.
(9) Dell, A.; Williams, D. H.; Morris, H. R.; Smith, G. A.; Feeney,
J .; Roberts, G. C. K. J . Am. Chem. Soc. 1975, 97, 2497-2506.
(10) Adang, A. E. P.; Hermkens, P. H. H.; Linders, J . T. M.;
Ottenheijm, H. C. J .; van Staveren, C. J . Recl. Trav. Chim. Pays-Bas
1994, 113, 63-78.
(4) For a review on earlier works in the field, see: Fre´chet, J . M. J .
Polymer-Supported Reactions in Organic Synthesis; Wiley: New York,
1980; Chapter 8, p 407. For more recent examples, see: (a) Seeberger,
P. H.; Beebe, X.; Sukenick, G. D.; Pochapsky, S.; Danishefsky, S. J .
Angew. Chem., Int. Ed. Engl. 1997, 36, 491-493. (b) Nicolaou, K. C.;
Winssinger, N.; Pastor, J .; DeRoose, F. J . Am. Chem. Soc. 1997, 119,
449-450.
(5) Stewart, J . M.; Young, J . D. Solid-Phase Peptide Synthesis, 2nd
ed.; Pierce Chemical Co.: Rockford, IL, 1984.
10.1021/jo981580+ CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/04/1999

8064 J . Org. Chem., Vol. 64, No. 22, 1999
Kuisle et al.
storage materials in prokaryotic microorganisms, in
which they can constitute up to 90% of the dry cell
weight. In a lower molecular weight form, poly[(R)-
hydroxybutyrate] has also been found in prokaryotic and
eukaryotic cell walls, where it presumably participates
in the formation of ion channels. Cyclic oligomers15 of
3-hydroxybutyric acid and long chains of up to 128 units16
have been prepared and studied by Seebach et al. Other
synthetic polyesters derived from R- and â-hydroxy acids
have gained considerable economic interest in the past
few years and are produced on a large scale by biotech-
nological methods. These polymeric depsides show prop-
erties that are comparable to those of polypropylene but
are accompanied by biodegradability and biocompatabil-
ity, which makes them ideal as biodegradable substitutes
for conventional plastics17 or as surgical implants.18
Nevertheless, until now, no general and successful
methodology for the solid phase synthesis of depside
chains has been reported in the literature. Some solid-
phase approaches have been described for the synthesis
of depsipeptides, but these methods describe the intro-
duction of hydroxy acids into a peptide chain. However,
in these approaches either the ester bonds were created
beforehand in solution and only the peptide bonds were
formed on the resin19 or the hydroxy acids were not
protected at all20 and the method relied on the greater
reactivity of the amino group, which is a reasonable
assumption when the substrate contains only one hy-
droxy acid. While our work was in progress, Davies et
al.21 proposed a combination of TBDMS (tert-butyldi-
methylsilyl) and Fmoc (9-fluorenylmethyloxycarbonyl)
protection for the hydroxy and amino groups of a penta-
depsipeptide synthesized on resin. However, the reported
yields of 52% for this relatively small substrate, contain-
ing two standard peptide bonds and only two ester bonds,
were relatively moderate and the monitoring of the
completion of the ester bond formation so complex that
its use for the synthesis of longer chains would probably
become cumbersome.
In this paper, we wish to report our studies on the
development of a general methodology for the creation
of depsides and depsipeptides on solid support. The
methodology gives high yields, ensures total preservation
of the stereochemistry of the repeating units, and there-
fore permits the construction of long chains of R-hydroxy
acids or combinations of R-hydroxy and R-amino acids.22
The automated solid-phase synthesis of a depsipeptide
analogue to valinomycin is described.
useful tool for the preparation of peptidomimetics10 and
for gaining a better understanding of their structural
properties.11
For their part, the depsides are oligomers resembling
peptides but are entirely built up by hydroxy acids rather
than amino acids, and these hydroxy acids are connected
through ester bonds. A representative example of natu-
rally occurring depsides is nonactin (3), a member of the
nactin family.6 These macrocycles were isolated from
actinomyces and all have the same cyclic structure
formed by four units of an ω-hydroxy acid linked through
ester bonds, and they differ only in the substitution
pattern of the side chains.
Cyclic depsides derived from R-, â-, and γ-hydroxyacids
have been isolated from the antibiotic extract of Strep-
tomyces fradiae,12 while some lichens produce the hexa-
depside H-(R-hydroxyisovalerate)6-OMe.13 For their part,
polymeric substances derived from hydroxy acids such
as poly[(R)-hydroxybutyrate]14 are known to be common
(14) Mu¨ller, H.-M.; Seebach, D. Angew. Chem., Int. Ed. Engl. 1993,
32, 477-502.
(15) Plattner, D. A.; Brunner, A.; Dobler, M.; Mu¨ller, H.-M.; Petter,
W.; Zbinden, P.; Seebach, D. Helv. Chim. Acta 1993, 76, 2005-2033.
(16) Lengweiler, U. D.; Fritz, M. G.; Seebach, D. Helv. Chim. Acta
1996, 79, 670-701, and references therein.
(17) Doi, Y. Microbial Polyesters; VCH: Weinheim, 1990.
(18) Polymers of Biological and Biomedical Significance; Shalaby,
S. W., Ikada, Y., Langer, R., Williams, J ., Eds.; ACS Symposium Series
540; American Chemical Society: Washington, DC, 1994.
(19) For a recent example, see: Byung, H. L. Tetrahedron Lett. 1997,
38, 757-760.
(20) For
a recent example, see: Miyashita, M.; Nakamori, T.;
Akamatsu, M.; Murai, T.; Miyagawa, H.; Ueno, T. Pept. Chem. 1996,
34, 137-140.
(11) (a) Seebach, D.; Ciceri, P. E.; Overhand, M.; J aun, B.; Rigo, D.
Helv. Chim. Acta 1996, 79, 2043-2066. (b) Yang, J .; Gellman, S. H. J .
Am. Chem. Soc. 1998, 120, 9090-9091. (c) Gallo, E. A.; Gellman, S.
H. J . Am. Chem. Soc. 1993, 115, 9774-9788.
(21) Davies, J . S.; Howe, J .; J ayatilake, J .; Riley, T. Lett. Pept. Sci.
1997, 441-445.
(22) For a brief account of these results, see: Kuisle, O.; Quin˜oa´,
E.; Riguera, R. Tetrahedron Lett. 1999, 40, 1203-1206.
(23) Neises, B.; Steglich, W. Angew. Chem., Int. Ed. Engl. 1978, 17,
522-524.
(12) Takeda, Y.; Masuda, T.; Matsumoto, T.; Takeshi, Y.; Shingu,
T.; Floss, H. G. J . Nat. Prod. 1998, 61, 978-981.
(13) Bruun, T. Phytochemistry 1976, 15, 1261-1263.

Solid-Phase Synthesis of Depsides and Depsipeptides
J . Org. Chem., Vol. 64, No. 22, 1999 8065
Sch em e 1a
Ta ble 1. HP LC An a lysis of Cou p lin g Rea ction betw een
8a a n d 5a
a
compd
R
n
tR
% yield (%)
9
10
11
12
13
OMe
OMe
N-acylurea
OMe
0
1
0
2
1
10 min 05 sec
13 min 45 sec
17 min 35 sec
20 min 10 sec
26 min 25 sec
38
17
10b
4
N-acylurea
4b
a
HPLC conditions: µ-Porasil (7.8 ‚ 300 mm), hexane/EtOAc (9:
b
1), 2.0 mL/min. The yields for the N-acylurea derivatives are
based on the amount of 5a (1.2 eq), since they are formed from 5a
and not 8a .
Sch em e 2
Sch em e 3
a
Key: (a) (1) TBDMSCl (2.2 equiv), imidazole (2.4 equiv), THF,
3 h; (2) K2CO3 in THF/H2O/MeOH (1:1:3), 2 h; (b) FmocCl (1.2
equiv), pyridine, THF, 15 h; (c) DHP (1.4 equiv), p-TsOH cat.,
CHCl3, 2 h.
Resu lts a n d Discu ssion
Assessm en t of Cou p lin g Con d ition s a n d P r otec-
tion . First of all, model coupling reactions were carried
out in solution to find the most suitable protection for
the hydroxy group of the R-hydroxy acids. Mandelic acid
(4) was chosen as a monomer for these experiments
because both enantiomers are commercially available.
The OR-protected L-mandelic acid derivatives 5a -7a were
prepared (Scheme 1) and submitted to depside coupling
(DIC/DMAP,23 THF, rt) with L-mandelic acid methyl ester
(8a ). Once we had decided which protecting group to use,
we started a second series of experiments in order see if
other coupling systems were superior to DIC/DMAP and
compatible with the protective group. The results of these
studies are described below.
Hyd r oxyl P r otection . In our choice of a suitable
protection method for the hydroxy group of the R-hydroxy
acids we had to take into account the limited stability of
the ester bonds, the possibility of racemization if basic
conditions were to be used, and compatibility of the
deprotection conditions with the resin linkage. We de-
cided to work with a Wang-type linker because of the
relatively smooth, acidic cleavage conditions, and so the
range of possible protective groups was even more
limited. For these reasons, we chose our protecting group
among those that can be cleaved under mild acidic or
basic conditions.
as shown in Scheme 2, a rather complex mixture of
products was obtained (Table 1). When this mixture was
submitted to semipreparative HPLC analysis, the desired
product, didepside 9, was isolated in 38% yield along with
substantial amounts of the tri- (10, 17%) and tetradep-
sides (12, 4%) and other derivatives, mainly the N-
acylurea-derived side products 11 and 13. This means
that the TBDMS group was not sufficiently stable under
the esterification conditions used for coupling and was
therefore abandoned.
Limited stability of this protecting group might also
provide an explanation for the difficulties encountered
by Davies et al. in their synthesis of the dolastatin D
analogues.21
As Fmoc has been widely used to protect amino groups,
we investigated its use to protect the hydroxy group of
R-hydroxy acids. Thus, 6a was prepared directly from 4a
with FmocCl/pyridine and was subsequently purified by
crystallization (58% yield). The Fmoc-protected tridepside
16a could be easily prepared by subsequent coupling-
deprotection-coupling (Scheme 3). Nevertheless, when
we tried to deprotect 16a using the same conditions as
before, two products were obtained that could be sepa-
rated by HPLC and were apparently diastereomers
resulting from racemization of one of the three mandelic
acid units: in the 1H NMR spectrum, both of the
compounds showed three signals in the region of the HR
proton and the same molecular mass in LRFAB-MS.
Intrigued by the fact that one racemization product was
observed almost exclusively (assuming that the other one
was the “intact” deprotected product) even though three
The first protecting group to be tested was the TBDMS
group. Protection was accomplished using an excess of
TBDMSCl to protect both the hydroxyl and the acid
function of mandelic acid. The TBDMS ester was easily
hydrolyzed to give OR-TBDMS-L-mandelic acid (5a ) in
89% yield. When 5a was submitted to coupling with 8a ,

8066 J . Org. Chem., Vol. 64, No. 22, 1999
Kuisle et al.
tion times and required higher base concentrations, and
they did not suppress racemization. When L-mandelic
acid was replaced by L-R-hydroxyisovaleric acid (4b),
tridepside 16b could be obained by the same procedure
as used for 16a (Scheme 3). In this case, no racemization
could be observed during deprotection of 16b. Only one
product, 17b, was obtained.
Although Fmoc could probably be used for the solid-
phase synthesis of depsides devoid of mandelic acid or
other base-sensitive hydroxy acids, we decided to look for
another protecting group because the risk of racemization
limits the versatility of the methodology.
Finally, we elected to protect the hydroxyl group of the
hydroxy acids as THP ethers and found it to be the
protecting group of choice for depside synthesis. 7a was
obtained either from methyl ester 8a by protection with
dihydropyran/p-TsOH and subsequent hydrolysis of the
methyl ester, by protection of the free acid 4a with excess
dihydropyran and hydrolysis of the THP ester, or also
directly from 4a with only a slight excess of dihydropy-
ran. The best results were obtained with the last
method: the yield (79%) is good and needs only one
reaction step. Neither undesired deprotection nor race-
mization was observed during the coupling and depro-
tection steps leading to tridepside 17a (Scheme 5). The
major inconvenience of THP-protected chiral alcohols is
the complexity of the NMR spectra due to formation of
diastereoisomers, and this only interferes in the identi-
fication of those compounds that are prepared in solution
(7a -c, 23a , and 24a ). Since the THP-protected resin-
bound intermediates do not have to be isolated and
identified, this potential complication does not represent
a problem in solid-phase synthesis.
Com p a r ison of Cou p lin g System s. Following our
preliminary studies in solution, DIC/DMAP was chosen
for the depside couplings because it was found to be very
efficient in esterification reactions carried out in our
group.24 Nevertheless, many more methods for the es-
terification of carboxylic acids are known. The growing
popularity of uronium and phosphonium-salt based cou-
pling reagents in peptide synthesis25 led us to consider
whether these reagents, alone or in combination with
DMAP, might be useful for ester bond formation. Thus,
a series of different coupling systems was tested to assess
their utility in depside bond formation. The results are
summarized in Table 3.
All the peptide coupling reagents that were tested
(DIC, HBTU, HATU, PyBroP) gave poor results if no
auxiliary reagent was used. Addition of HOBt in the case
of DIC couplings helped to improve the yields but
required rather long reaction times and the yields were
strongly dependent on the water content of HOBt: when
commercial (nondried) HOBt was used, which contains
1 equiv of water, hardly any product was isolated.
Consequently, HOBt was not added for the other re-
agents tested.
HBTU, HATU, and PyBroP were virtually ineffective,
either with or without DMAP, when 2,4,6-trimethylpy-
ridine (collidine) was used in equimolar amounts in
relation to the uronium salt, conditions that have been
recommended to avoid racemization.26 A 2-fold increase
1
F igu r e 1. Racemization of 17a followed by H NMR (30 mg
of 17a , 10 µL of piperidine in 1 mL of CDCl3/D2O). The signals
of the racemizing HR at 6.18 and 6.15 ppm decrease due to
interchange with deuterium.
chiral centers were present, we decided to study this
reaction in more detail.
To this end, 17a was dissolved in 1% piperidine in CD3-
OD with a drop of D2O in an NMR tube and the reaction
followed by NMR. We expected to observe one of the HR-
singlets interchanging with deuterium and therefore
disappearing. Unfortunately, under these conditions
several reactions were observed, including hydrolysis of
the ester bonds, and the spectra were too complex to be
analyzed. When the same experiment was carried out in
CDCl3 with a drop of D2O (Figure 1), two new compounds
were the main products: one of these was methyl ester
8a , which means that under the reaction conditions
hydrolysis took place, and the other showed the expected
second set of signals for the racemization product.
However, most importantly, the intensities of the two
singlets at 6.18 and 6.15 ppm, which correspond to the
racemizing HR, began to decrease slowly, as one would
expect. At 1h 40 min, these signals had shrunk to about
one-third of the intensity of the other HR singlets, which
belonged to the protons that were not affected by the
base. By the same time, the ratio of the two products was
3:7. Consequently, in CDCl3/D2O essentially the same
reaction could be observed as in THF, although it was
slower and complicated by the concurrent hydrolysis of
the ester bonds.
To find out which one of the three centers underwent
racemization, we synthesized the model compounds 20a ,
21a , and 22a (Scheme 4). The deprotection products 17a
and 18a were methylated and compared with 20a , 21a ,
and 22a by NMR and optical rotation. In this way, we
determined that 18a represented the “intact” deprotec-
tion product and that 17a arose from racemization in the
second mandelic acid residue.
In an attempt to suppress racemization, we carried out
experiments with weaker bases such as morpholine,
N-methylmorpholine, and imidazole (Table 2). Unfortu-
nately, these modifications only served to prolong reac-
(24) Latypov, S. K.; Seco, J . M.; Quin˜oa´, E.; Riguera, R. J . Am. Chem.
Soc. 1998, 120, 877-882.
(25) Carpino, L. A.; El-Faham, A.; Minor, C. A.; Albericio, F. J .
Chem. Soc., Chem. Commun. 1994, 201-203, and references therein.

Solid-Phase Synthesis of Depsides and Depsipeptides
J . Org. Chem., Vol. 64, No. 22, 1999 8067
Sch em e 4
a
MPA ) R-methoxyphenylacetic acid.
Ta ble 2. Ra cem iza tion d u r in g Dep r otection of 16a w ith
Differ en t Ba ses
Ta ble 3. Rea ction Tim es a n d Yield s for Differ en t
Cou p lin g System s in Dep sid e Bon d F or m a tion betw een
8a a n d 7a
a
base
pKa
treac
ratiob
coupling systema,b
solventc
treac (h)
yield (%)
piperidine 1-2%
morpholine 2%
4-Me-morpholine 8%
imidazole 10%
11.12
8.33
7.41
6.95
40 min
4-5 h
10 h
65:35
86:14
81:19
c
DIC/HOBt‚H2Od
A
A
A
A
A
A
A
A
A
A
B
B
A
B
B
B
B
B
2
4
20
2
28
7
2
19 h
DIC/HOBte
DIC/DMAPf
19
23
64
79
92
90
16
5
46
5
3
18
49
6
a
Weast, R. C. Handbook of Chemistry and Physics, 56th ed.;
4
b
CRC Press: Cleveland, OH, 1975; pp D147-149. Ratio of 17a :
20
0.5
2
4
15
4
4
4
4
4
18a was determined by NMR (integration of the HR signals in the
region of 5.0-6.2 ppm). c More than two products.
Sch em e 5
HBTUg
HBTUg
HBTU/DMAPf,h
HATUg
HATUg
HATU/DMAPf,g
HATU/DMAPf,h
PyBroPh
4
4
4
PyBroP/DMAPf,h
60
a
Abbreviations used: Bpoc ) 2-(4-biphenylyl)-2-propyloxycar-
bonyl; DIC ) diisopropylcarbodiimide; DMAP ) 4-(dimethylami-
no)pyridine; HATU ) O-(7-Azabenzotriazol-1-yl)-N,N,N′,N′-tet-
ramethyluronium hexafluorophosphate; HBTU ) O-(7-benzotriazol-
1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate; HOBt
) 1-hydroxybenzotriazol; PyBrop ) bromotripyrrolidinophospho-
a
nium hexafluorophosphate. Reaction conditions: 8a (1 equiv,
0.36 M), 7a (1.2 equiv, 0.43 M), coupling reagent (1.4 equiv, 0.43
b
M), rt. A: THF. B: CH2Cl2/DMF (1:1). c 1.4 equiv of commercial
d
HOBt‚H2O (not dried). 1.4 equiv of dried HOBt (8 h at 130 °C).
e 0.1 equiv of DMAP. f With 1.4 equiv of 2,4,6-trimethylpyridine.
With 2.8 equiv of 2,4,6-trimethylpyridine.
in the amount of base significantly improved the results,
and good yields within reasonable reaction times could
be obtained in the presence of DMAP. Nevertheless, none
of the coupling methods led to the yields obtained with
DIC/DMAP. In addition, the presence of 3 equiv of a base
whose pKa is similar to N-methylmorpholine (7.43, see
footnote a, Table 2) represents an additional risk of
racemization.
The best results were therefore obtained with DIC/
DMAP. Studies with different reaction times have shown
that 2 h is generally sufficient to obtain the maximum
yield, and longer reaction times do not lead to increased
g
yields. The yields obtained in solution with only a slight
excees of OR-protected hydroxy acid are good, and such
reactions should almost reach completion on the resin
when more equivalents of protected acid are employed.
Solid -P h a se Syn th esis. Among the existing solid
supports, Wang resin was chosen and it proved to meet
our needs well. The first THP-protected hydroxy acid was
linked to the resin using the same conditions and
reagents employed for all the other couplings, and this
significantly simplifies the whole automatic process. The
following reagents, ratios and conditions were employed
for the depside couplings: for each equivalent of resin-
attached substrate, 3.0 equiv of THP-protected hydroxy
(26) Han, Y.; Albericio, F.; Barany, G. J . Org. Chem. 1997, 62, 4307-
4312.

8068 J . Org. Chem., Vol. 64, No. 22, 1999
Kuisle et al.
Sch em e 6
Ch a r t 1
acid (0.3 mmol/mL), 3.0 equiv of DIC, and 0.1 equiv of
DMAP for 2 h at room temperature in either THF or
DMF.
and has shown to be a quick and reliable method for the
detection of small amounts of resin-bound alcohol groups.
The details of the procedure are described in the Experi-
mental Section.
Scheme 6 summarizes, in a general way, the different
steps of the solid-phase preparation of R-hydroxy acid-
derived depsides. Several depside chains were prepared
following this methodology. To test the versatility of the
approach, different synthetic targets were chosen, which
included the same enantiomer (i.e., H-[L-Man]8-OH, 25),
both enantiomers (i.e., H-[D-Man-L-Man]4-OH, 26), or
different hydroxy acids in the same chain (i.e., H-[L-Lac-
L-Hiv]3-OH, 27).
Small resin samples were removed and cleaved at
different stages of the syntheses of depsides 25-27
(Chart 1). In each case, the crude product mixture was
purified by HPLC and the isolated depsides analyzed by
NMR. Since the HR protons of different diastereomers of
the same depside, that may arise from racemization,
show different signals in 1H NMR, they can be easily
distinguished and quantified. Thus, for all the synthetic
intermediates and end products, the content of other
diastereoisomers was established and found to be lower
than 1%. Figure 2 shows the CD spectra of six depsides
(from two to seven units) obtained from L-mandelic acid.
The overall yields for depsides 25, 26, and 27 lie
between 72 and 75% (after HPLC isolation). This corre-
sponds to an average value of 95-97% per cycle. The side
products accounting for the remaining 3-5% per cycle
were isolated by HPLC and identified as the (n + 1)
oligomer (∼1%) and the depsides lacking one or more
residues.
While p-TsOH/MeOH was used to deprotect the THP
group in solution,27 it proved to be ineffective in the solid
phase, probably due to poor swelling of the resin.
Monitoring of the deprotection reactions by GC28 revealed
that introduction of CH2Cl2 as a cosolvent eliminated this
problem, and a mixture of p-TsOH (5 mg/mL) in CH2Cl2/
MeOH (97:3) was found to give the best results. With this
solution, deprotection was complete after 45-70 min.
Once the necessary minimum reaction time was known,
and the absence of resin cleavage during this process was
demonstrated by NMR of the concentrated washings,
deprotections were carried out for 2 × 60 min. Final
cleavage of the depside chain from the resin was ac-
complished with TFA/CH2Cl2 (1:1) and did not affect the
depside bonds, as shown by the absence of depside
fragments in the solution (checked by HPLC).
We have tried to find a simple procedure similar to the
ninhydrin test for assessing the efficiency of coupling in
depside bond formation. To this end, we developed an
adaptation of a scarcely known TLC spray reagent for
alcohols29 that can be carried out directly on the resin
(27) Greene, T. W. Protective Groups in Organic Synthesis; Wiley:
New York, 1981.
(28) Small samples of the deprotection solution were directly taken
from the reaction vessel and injected onto a capillary column (Ultra-
1, 25 m × 0.32 mm × 0.52 µm) at 60 °C. The peak area of the acetal
resulting from cleavage of the THP group (tR ) 8.96 min) was compared
to an internal standard (toluene, tR ) 5.89 min). Deprotection was
complete when the ratio of these two areas was constant.
(29) Pomonis, J . G.; Severson, R. F.; Freeman, P. J . J . Chromatogr.
1969, 40, 78-84.
Cyclization of these open-chain depsides leads to a new

Solid-Phase Synthesis of Depsides and Depsipeptides
J . Org. Chem., Vol. 64, No. 22, 1999 8069
(Scheme 7), and then converted into the pentafluorophe-
nol ester. Unfortunately, despite our efforts, we were not
able to selectively cleave the Cbz group without damaging
the substrate, which also bears benzyl moieties in its
mandelic acid units. Therefore, depsipeptide 32 was
prepared by the same procedure (Scheme 7) with the only
difference being that Bpoc-L-valine instead of Cbz-L-
valine was used for the final coupling step. Final cleavage
of the product from the resin simultaneously cleaves the
Bpoc group to give the unprotected linear depsipeptide
32 in 47% overall yield. The lower yield for 32, compared
to that obtained for 31, is explained by the more difficult
HPLC purification.
As far as the use of the Bpoc group for solid-phase
preparation of depsipeptides is concerned, we found it to
be more difficult to cleave than expected. In fact, when a
resin sample obtained after four steps was cleaved and
purified by HPLC, two main products were observed and
could be identified by NMR as the tridepsipeptides H-D-
Man-D-Val-L-Lac-OH and H-L-Val-D-Val-L-Lac-OH. Since
all the depside/peptide coupling reactions had been
monitored by the test described before and the Kaiser
test and found to be complete, the problem must have
arisen from incomplete deprotection. Indeed, we found
that the Bpoc deprotection of resin-bound Bpoc-D-Val-L-
Lac had not gone to completion in 20 min as noted in
the literature.34 Monitoring of Bpoc deprotection by
analysis of the washings indicated that at least a 1 h
treatment with 0.5% TFA was necessary to ensure
complete deprotection. This does not represent a problem
for the preparation of medium-sized molecules, but it can
complicate the synthesis of larger chains because re-
peated deprotections of 1 h duration will cause a certain
degree of cleavage of the anchoring bond,32 thus forcing
a change of linker or of protective groups.
Macrolactamization of 32 was accomplished by two
different procedures: via the acid chloride method35 and
with HATU,36 thus obtaining 30 in 14% and 24% yield,
respectively. In the case of the acid chloride method, we
suspect that the acid chloride hydrochloride of 32 reacts
spontaneously in the syringe, before addition of base. This
would explain the presence of relatively large amounts
of oligomerization products that were isolated in spite
the high dilution. 30 represents a novel valinomycin
derivative, and its bioactivity is currently under inves-
tigation.
F igu r e 2. CD spectra of the intermediate depsides (from 2
to 7 units of L-mandelic acid) in the synthesis of 25.
class of chiral macrocycles. In this way, when hexadep-
side 28 was made to undergo the Mitsunobu reaction30
(diethyl azodicarboxylate, triphenylphosphine), cyclo-
hexadepside 29, a chiral ester analogue of 18-crown-6,
was obtained.
To show the reliability of the method for the prepara-
tion of depsipeptides, total synthesis of the valinomycin
analogue 30 ([L-Val-D-Man-D-Val-L-Lac]3) was under-
taken. The corresponding linear precursor was entirely
synthesized on solid support as outlined in Scheme 7 and
cyclized in solution. In this derivative, D-R-hydroxyisova-
leric acid is replaced by D-mandelic acid, thus obtaining
a new analogue while maintaining the favorable confor-
mation of the authentic valinomycin. This represents a
challenging target because of its six depside and peptide
bonds. Bpoc (2-(4-biphenylyl)-2-propyloxycarbonyl)31 was
chosen as the protecting group for the R-amino groups
because the deprotecting conditions (0.5% TFA/CH2Cl2,
20 min) are mild enough to be compatible with the Wang
resin,32 which in turn was selected on the basis of the
relatively mild final cleavage conditions.
The initial idea was to use the pentafluorophenol ester
protocol for the final cyclization, in combination with in
situ release of the amino functionality by hydrogenolysis
of a benzyloxycarbonyl group. These conditions have been
shown to minimize polymerization and gave very good
results in the synthesis of valinomycin analogues.33 Thus,
the Cbz-protected (Cbz ) benzyloxycarbonyl) linear
precursor 31 was synthesized, in 63% overall yield
In conclusion, we have developed a general methodol-
ogy for the solid-phase synthesis of depsides and dep-
sipeptides. The method gives high yields, ensures the
stereochemical integrity of the products, and therefore,
allows the preparation of relatively large substrates. The
versatility of the method has been demonstrated by the
preparation of different hydroxy and amino acid-contain-
ing substrates. Cyclization of the linear depsides leads
(34) The CH2Cl2 washings from the deprotection steps, which had
been collected separately, were concentrated and analyzed by 1H NMR
spectroscopy. The washings from the deprotection of the resin-bound
tridepsipeptide THP-D-Man-D-Val-L-Lac gave a white solid instead of
the usual brownish oil that results from cleavage of the THP group.
The 1H NMR spectrum of this solid was compared to that obtained
from the Bpoc protection and showed the same signals. This means
that Bpoc deprotection of the resin-bound didepsipeptide Bpoc-D-Val-
L-Lac had not gone to completion and was accomplished in the
subsequent THP cleavage with p-TsOH/MeOH.
(35) Losse, G.; Klengel, H. Tetrahedron 1971, 27, 1423-1434, and
references therein.
(36) J ou, G.; Gonza´lez, I.; Albericio, F.; Lloyd-Williams, P.; Giralt,
E. J . Org. Chem. 1997, 62, 354-366.
(30) Mitsunobu, O. Synthesis 1981, 1-80.
(31) Sieber, P.; Iselin, B. Helv. Chim. Acta 1968, 51, 622-632.
(32) Wang, S. S. J . Org. Chem. 1975, 40, 1235-1239.
(33) For synthesis of valinomycin analogues in solution, see: Dory,
Y. L.; Mellor, J . M.; McAleer, J . F. Tetrahedron 1996, 52, 1343-1360,
1361-1378, and 1379-1388.

8070 J . Org. Chem., Vol. 64, No. 22, 1999
Kuisle et al.
Sch em e 7a
a
Key: (a) DIC 3 equiv, DMAP 0.1 equiv, THF, 2 h; (b) p-TsOH (5 mg/mL), MeOH/CH2Cl2 (3:97), 2 h; (c) TFA/CH2Cl2 (0.5:99.5), 20 min;
(d) (i-Pr)2EtN/CH2Cl2 (5:95), 2 × 5 min; (e) DIC, THF, 2 h; (f) 31: Cbz-L-Val; 32: Bpoc-L-Val; (g) TFA/CH2Cl2 (1:1), 1 h.
CH2Cl2, 5 min; washings (3 min each): 3 × 10 mL of CH2Cl2;
to new class of chiral ionophores. The synthesis of 31 and
3 × 10 mL of acetone; 3 × 10 mL of THF.
32 is, to our knowledge, the first entire solid-phase
preparation (including formation of depside bonds on
resin) of a depsipeptide that contains six depside bonds.
Exp er im en ta l P r oced u r e for th e Solid -P h a se Test of
Alcoh ols. After each coupling step, a suspension of a small
sample (A) of resin beads (=1-2 mg dry resin weight) in a
few drops of CH2Cl2 was placed on a silica gel TLC plate and
spread out forming a thin circle. On the same plate, two
“reference spots” were placed by the same procedure: sample
B formed by OH-bearing resin (completely deprotected depside-
linked resin) and sample C formed by fully acetylated Wang
resin. Next, the spots were successively treated with the
following reagent systems: first, 1-2 drops of 0.01 M TsCl in
toluene; second, 1-2 drops of 0.025 M PNBP in toluene, then
the TLC plate was heated with a heat gun until the orange
color disappeared; third, 10% piperidine in CHCl3 and heated
until sample B showed a deep violet color whereas sample C
remained colorless. If the coupling had been complete (no free
OH present), sample A should have appeared colorless (nega-
tive test) as sample C. If color appeared, coupling had been
incomplete and needed to be repeated. We observed a negative
test when the resin contained less than 1% free OH groups.
Exp er im en ta l Section
Gen er a l Meth od s. Unless specified, reagents were pur-
chased from Aldrich or Fluka and were used without further
purification. CH2Cl2 and THF used for solid-phase reactions
were synthesis grade, and acetone and MeCN were HPLC
grade. Solvents used for solution reactions were dried in the
appropriate manner37 and distilled prior to use. Wang resin
was purchased from Advanced Chem Tech (loading capacity
1.0 mmol/g). Solid-phase reactions were carried out on an
ACT90 peptide synthesizer. 1H and 13C NMR spectra were
recorded on Bruker DPX-250, AMX-300, and AMX-500 spec-
trometers. Coupling constants (J ) are reported in Hz. The
matrix for mass spectrometry was either thioglycerol or
m-NBA. Normal-phase HPLC was carried out using a µ-Porasil
(10 µ, 7.8 ‚ 300 mm) column, reversed-phase HPLC with
Nucleosil C18 (5 µ, 7.0 ‚ 300 mm), or Partisil M9 ODS-3 (10 µ,
9.4 ‚ 500 mm) columns. For all solid-phase reactions, yields
are referred to purified material and based upon the loading
of the starting resin.
Gen er a l P r oced u r e for Clea va ge of F m oc-P r otected
Dep sid es in Solu tion . A solution of the Fmoc-protected
depside in piperidine/THF (1:99, 20 mL/mmol depside) was
stirred at room temperature and the reaction followed by TLC.
When the starting material had completely disappeared (30-
40 min), the solution was concentrated to about 1 mL,
dissolved in CH2Cl2, washed with 1 N HCl and water, dried
(Na2SO4), filtered, and concentrated.
Or-(ter t-Bu tyld im eth ylsilyl)-L-m a n d elic Acid (L-5a ). To
a solution of L-mandelic acid (152 mg, 1 mmol) and tert-
butyldimethylsilyl chloride (331 mg, 2.2 mmol) in THF (3 mL)
was added imidazole (163 mg, 2.4 mmol) at 4 °C, and the
mixture was stirred for 1 h. The ice bath was removed, and
the mixture was stirred for a further 3 h at room temperature.
The reaction mixture was filtered, concentrated under reduced
pressure, and suspended in 1 N NaOH (3 mL). After 1.75 h,
the mixture was diluted with 3 mL of water, washed twice
with ether, acidified with concentrated HCl to pH 3-4, and
extracted three times with ether. The combined ether extracts
were dried (Na2SO4), filtered, and concentrated under reduced
pressure to give L-5a (237 mg, 89%) as a sticky, colorless oil:
[R]D ) +89.4 (c ) 1.3, CHCl3); IR (NaCl) νmax 3064, 3033, 2933,
2859, 1725, 1463, 1256, 1128, 866, 841, 781, 717, 699; 1H NMR
(250 MHz, CDCl3) δ 0.05 (s, 3 H), 0.15 (s, 3 H), 0.96 (s, 9 H),
5.26 (s, 1 H), 7.34-7.52 (m, 5 H); 13C NMR (63 MHz, CDCl3)
δ -5.3, -5.1, 18.1, 25.6, 74.2, 126.5, 128.5 (2×), 138.2, 175.9;
FABMS m/z 289 [M + Na]+ (13), 267 [M + H]+ (9), 249 (30),
221 (100). Anal. Calcd for C14H22SiO3: C, 63.12; H, 8.32.
Found: C, 62.85; H, 8.09.
Or-(9-Flu or en ylm eth yloxycar bon yl)m an delic Acid (6a).
A solution of pyridine (423 µL, 5.25 mmol) in THF (2 mL) was
added during 20 min to a solution of mandelic acid (L or d,
761 mg, 5 mmol) and 9-fluorenylmethyloxycarbonyl chloride
(1358 mg, 5.25 mmol) in THF (13 mL) at 4 °C. The mixture
was stirred for 2 h at 4 °C and then allowed to warm to room
temperature. After 15 h, the mixture was filtered and concen-
trated under reduced pressure. The crude product was dis-
solved in CH2Cl2 and washed with 1 N HCl and water. After
drying (Na2SO4), filtering, and concentration under reduced
Gen er a l P r oced u r es for Solid -P h a se Rea ction s. A.
Depside coupling conditions: DIC (3 equiv), DMAP (0.1 equiv),
THP-protected R-hydroxy acid or Bpoc-protected R-amino acid
(3 equiv), in THF (1 mL/100 mg of resin), 2 h; washings (3
min each): 3 × 10 mL of THF; 3 ×10 mL of acetone; 3 × 10
mL of CH2Cl2.
B. Peptide coupling conditions: DIC (3 equiv), THP-
protected R-hydroxy acid (3 equiv), in THF (1 mL/100 mg of
resin), 2 h; washings (3 min each): 3 ×10 mL of THF; 3 ×10
mL of acetone; 3 ×10 mL of CH2Cl2.
C. THP deprotection: 10 mL of a solution of p-TsOH (5 mg/
mL) in CH2Cl2/MeOH (97:3), 2 × 1 h, preceded by a 3 min
washing with the same solution; washings (3 min each): 3 ×
10 mL of CH2Cl2; 3 × 10 mL of acetone; 3 × 10 mL of THF.
D. Bpoc deprotection: 0.5% TFA in CH2Cl2 (10 mL), 20 min;
2 × 10 mL of CH2Cl2, 2 min each; 2 × 10 mL of 5% DIEA in
(37) Perrin, D.; Armaregeo, W. L. F. Purification of Laboratory
Chemicals; Pergamon Press: Oxford, 1988.

Solid-Phase Synthesis of Depsides and Depsipeptides
J . Org. Chem., Vol. 64, No. 22, 1999 8071
pressure, the product was crystallized from CHCl3 to give 6a
(1084 mg, 58%) as a white solid: mp ) 175 °C (toluene); [R]D
) +94.9 (c ) 1.2, CHCl3); IR (NaCl) νmax 3400 br, 3039, 1741,
H), 3.48-3.57 (m, 1 H), 3.80-3.89 (m) and 3.92-3.99 (m, 1
H), 4.25 (q, J ) 6.9) and 4.43 (q, J ) 7.0, 1 H), 4.65-4.68 and
4.72-4.74 (m, 1 H); 13C NMR (63 MHz, CDCl3) δ 17.8, 18.6,
19.1, 19.9, 24.9, 25.2, 30.3, 30.7, 62.5, 64.0, 70.0, 73.2, 97.9,
99.9, 176.1, 178.2; HREIMS m/z 174.0891 (calcd for C8H14O4
[M]+ 174.0892). Anal. Calcd for C8H14O4: C, 55.14; H, 8.10.
Found: C, 54.96; H, 8.22.
L-Ma n d elic Acid Meth yl Ester (8a ). To a stirred solution
of L-mandelic acid (3043 mg, 20 mmol) in MeOH (6 mL) was
added thionyl chloride (1.6 mL, 22 mmol) dropwise at 4 °C.
Then the solution was brought to reflux. After 4 h, the mixture
was concentrated under reduced pressure, dissolved in CH2-
Cl2, extracted with a saturated solution of NaHCO3 and water,
dried (Na2SO4), and concentrated under reduced pressure to
give 8a (2988 mg, 90%) as a slightly yellow solid: 1H NMR
(250 MHz, CDCl3) δ 3.74 (s, 3 H), 5.19 (s, 1 H), 7.28-7.48 (m,
5 H); 13C NMR (63 MHz, CDCl3) δ 53.0, 74.8, 126.5, 128.4,
128.5, 138.2, 174.0.
1590, 1448, 1390, 1252, 951, 736 cm-1 1H NMR (250 MHz,
;
CDCl3) δ 4.30 (t, J ) 7.3, 1 H), 4.40 (dd, J 1 ) 10.2, J 2 ) 7.6, 1
H), 4.54 (dd, J 1 ) 10.2, J 2 ) 7.2, 1 H), 5.92 (s, 1 H), 7.27-7.44
(m, 7 H), 7.52-7.56 (m, 2 H), 7.64 (dd, J 1 ) 7.5, J 2 ) 0.92, 1
H), 7.77 (d, J ) 7.5, 2 H); 13C NMR (63 MHz, CDCl3) δ 46.6,
70.7, 76.8, 120.1, 125.2, 125.3, 127.3, 127.7, 128.0, 129.0, 129.8,
132.7, 141.4, 143.1, 143.3, 154.5, 173.5; EIMS m/z 374 [M]+
(2), 178 (100), 165 (40); HREIMS m/z 374.1159 (calcd for
C23H18O5 [M]+ 374.1154). Anal. Calcd for C23H18O5: C, 73.77;
H, 4.85. Found: C, 73.96; H, 4.62.
Or-(9-Flu or en ylm eth yloxyca r bon yl)-L-r-h yd r oxyisova -
ler ic Acid (L-6b). L-6b was prepared as described above for
L-6a from L-R-hydroxyisovaleric acid (236 mg, 2 mmol).
Crystallization from toluene gave L-6b (259 mg, 54%) as a
white solid: [R]D ) +2.9 (c ) 2.8, CHCl3); IR (NaCl) νmax 2971,
1749, 1452, 1391, 1256, 1136, 1110, 992, 742, 674, 625 cm-1
;
Dep sid e Cou p lin g betw een L-5a a n d L-8a . A solution of
L-8a (50 mg, 0.30 mmol), L-5a (96 mg, 0.36 mmol), DIC (66
µL, 0.42 mmol), and DMAP (4 mg, 0.03 mmol) in THF (1 mL)
was stirred at room temperature for 2 h. The reaction mixture
was filtered and concentrated under reduced pressure. Puri-
fication by flash chromatography with hexane/EtOAc (7:3) gave
93 mg of a complex product mixture. This mixture was
separated by HPLC (µ-Porasil, hexane/EtOAc (91:9), 2.0 mL/
min) to give 9 (34 mg, 38%), 10 (22 mg, 17%), and 11 (7 mg,
4%). Or-(ter t-Bu tyld im eth ylsilyl)-L-m a n d elyl-L-m a n d elic
a cid m eth yl ester (9): [R]D ) +89.1 (c ) 0.9, CHCl3); 1H NMR
(250 MHz, CDCl3) δ 0.04 (s, 3 H), 0.13 (s, 3 H), 0.92 (s, 9 H),
3.59 (s, 3 H), 5.36 (s, 1 H), 5.91 (m, 1 H), 7.33-7.56 (m, 10 H);
13C NMR (63 MHz, CDCl3) δ -5.2, -5.1, 18.3, 25.7, 52.4, 74.2,
74.9, 126.6, 127.5, 128.2, 128.7, 129.2, 133.6, 138.6, 168.6,
171.4; HRFABMS m/z 415.1939 (calcd for C23H31O5Si [M + H]+
415.1941). Or-(ter t-Bu tyld im eth ylsilyl)-L-m a n d elyl-L-m a n -
d elyl-L-m a n d elic a cid m eth yl ester (10): [R]D ) +89.3 (c
) 1.2, CHCl3); 1H NMR (250 MHz, CDCl3) δ 0.02 (s, 3 H), 0.11
(s, 3 H), 0.91 (s, 9 H), 3.54 (s, 3 H), 5.37 (s, 1 H), 5.92 (s, 1 H),
6.06 (s, 1 H), 7.29-7.55 (s, 15 H); 13C NMR (63 MHz, CDCl3)
δ 18.3, 25.6, 52.4, 74.2, 74.6, 75.1, 126.6, 127.5, 127.9, 128.2,
128.3, 128.6, 128.7, 129.3, 133.2, 138.6, 167.4, 168.3, 171.2;
HRFABMS m/z 549.2307 (calcd for C31H37O7Si [M + H]+
549.2309). Or-(ter t-Bu tyld im eth ylsilyl)-L-m a n d elyl-L-m a n -
1H NMR (250 MHz, CDCl3) δ 1.11 (t, J ) 7.16, 6 H), 2.36 (m,
1 H), 4.31-4.40 (m, 2 H), 4.53 (dd, J 1 ) 9.4, J 2 ) 6.4, 1 H),
4.88 (d, J ) 4.1, 1 H), 7.33 (dt, J 1 ) 7.5, J 2 ) 1.1, 2 H), 7.42 (t,
J ) 7.5, 2 H), 7.65 (t, J ) 7.9, 2 H), 7.77 (d, J ) 7.2, 2 H); 13
C
NMR (63 MHz, CDCl3) δ 17.0, 18.5, 30.2, 46.8, 70.4, 79.5,
120.1, 125.2, 125.3, 127.2, 127.3, 127.9, 141.4, 143.2, 143.5,
155.0, 173.5; EIMS m/z 340 (3), 178 (100). Anal. Calcd for
C
20H20O5: C, 70.57; H, 5.92. Found: C, 70.20; H, 5.89.
Or-Tetr a h yd r op yr a n yl-L-m a n d elic Acid (L-7a ). Dihy-
dropyran (2.55 mL, 28 mmol) was added dropwise by syringe
to a stirred suspension of L-mandelic acid (3043 mg, 20 mmol)
and p-TsOH (76 mg, 0.4 mmol) in CHCl3 (40 mL) at 4 °C. After
5 min, the ice bath was removed and the mixture allowed to
warm to room temperature. After 15-30 min, all of the
compounds had completely dissolved and a violet color began
to appear. After 1.5 h, the reaction mixture was extracted with
0.2 N KOH (2 ‚ 50 mL). The combined KOH layers were
acidified with 6 N HCl to pH 3-4 and extracted three times
with CH2Cl2. The pH of the aqueous layer was controlled
between extractions, with more HCl added if necessary. The
combined CH2Cl2 extracts were washed with water, dried (Na2-
SO4), filtered, and concentrated under reduced pressure to give
L-7a (3734 mg, 79%) as a sticky oil that solidified slowly to
give a colorless, waxy solid: IR (NaCl) νmax 2944, 2870, 1731,
1494, 1448, 1390, 1266, 1183, 1124, 1071, 1029, 977, 907, 865,
1
d elyl-L-m a n d elyl-L-m a n d elic a cid m eth yl ester (12): H
1
704 cm-1; H NMR (250 MHz, CDCl3) δ 1.44-1.94 (m, 6 H),
NMR (250 MHz, CDCl3) δ 0.00 (s, 3 H), 0.08 (s, 3 H), 0.88 (s,
9 H), 3.51 (s, 3 H), 5.35 (s, 1 H), 5.87 (s, 1 H), 6.05 (s, 1 H),
6.06 (s, 1 H), 7.25-7.58 (s, 20 H).
3.50-3.58 (m, 1 H), 3.61-3.76 and 3.91-4.01 (m, 1 H), 4.60
(t, J ) 3.5) and 4.93 (m, 1 H), 5.25 and 5.33 (s, 1 H), 7.33-
7.52 (s, 5 H); 13C NMR (63 MHz, CDCl3) δ 18.5, 19.0, 25.0,
25.1, 30.0, 30.1, 61.9, 62.6, 75.4, 76.4, 96.7, 97.2, 127.2, 127.5,
128.5, 128.6, 128.8, 135.6, 136.1, 174.8, 176.2; FABMS m/z 259
[M + Na]+ (39), 237 [M + H]+ (50); HRFABMS m/z 237.1128
(calcd for C13H17O4 [M + H]+ 237.1127). Anal. Calcd for
Or-(9-Flu or en ylm eth yloxycar bon yl)-L-m an delyl-L-m an -
d elic Acid Meth yl Ester (14a ). A solution of L-8a (50 mg,
0.30 mmol), L-5a (135 mg, 0.36 mmol), DIC (66 µL, 0.42 mmol),
and DMAP (4 mg, 0.03 mmol) in THF (1 mL) was stirred at
room temperature for 2 h. The reaction mixture was filtered
and concentrated under reduced pressure. Purification by flash
chromatography with hexane/EtOAc (7:3) gave 14a (138 mg,
88%) as an amorphous solid: [R]D ) +78.1 (c ) 3.1, CHCl3);
IR (NaCl) νmax 3063, 3039, 2960, 1753, 1495, 1448, 1385, 1255,
C
13H16O4: C, 66.07; H, 6.83. Found: C, 66.23; H, 6.71.
Or-Tetr a h yd r op yr a n yl-L-r-h yd r oxyisova ler ic Acid (L-
7b). L-7b was prepared as described above for L-7a from L-R-
hydroxyisovaleric acid (2364 mg, 20 mmol). For the extraction
of the acidified KOH layers, CHCl3/i-PrOH (3:1) was used
instead of CH2Cl2 and the aqueous phase saturated with NaCl
before the extraction. L-7b (2987 mg, 74%) was obtained as a
sticky oil: IR (NaCl) νmax 3600-3400, 2956, 2871, 1725, 1466,
1389, 1204, 1130, 1030, 973, 910, 865, 806 cm-1; 1H NMR (250
MHz, CDCl3) δ 0.91-1.04 (m, 6 H), 1.45-1.85 (m, 6 H), 2.07-
2.20 (m, 1 H), 3.44-3.55 (m, 1 H), 3.80-4.05 (m, 1 H), 3.80 (d,
J ) 5.0) and 4.11 (d, J ) 4.9, 1 H), 4.52-4.55 and 4.68-4.70
(m, 1 H); 13C NMR (63 MHz, CDCl3) δ 17.2, 17.4, 18.5, 18.8,
19.2, 19.9, 24.9, 25.3, 30.2, 30.4, 31.2, 31.3, 62.1, 63.9, 78.3,
83.4, 96.9, 102.1, 176.1, 177.5; FABMS m/z 225 [M + Na]+
(100), 203 [M + H]+ (31). Anal. Calcd for C10H18O4: C, 59.37;
H, 8.98. Found: C, 59.41; H, 9.05.
1171, 1033, 966, 912, 738, 699 cm-1 1H NMR (250 MHz,
;
CDCl3) δ 3.61 (s, 3 H), 4.31-4.44 (m, 2 H), 4.57 (dd, J 1 ) 9.6,
J 2 ) 6.6, 1 H), 6.04 (s, 1 H), 6.10 (s, 1 H), 7.29-7.59 (m, 12 H),
7.63-7.69 (m, 4 H), 7.79 (d, J ) 7.3, 2 H); 13C NMR (63 MHz,
CDCl3) δ 46.3, 52.4, 70.4, 74.9, 77.2, 119.8, 125.0, 125.1, 127.0,
127.7, 127.8, 128.5, 128.7, 129.0, 129.4, 132.6, 133.0, 141.0,
142.9, 143.2, 154.2, 167.5, 168.2; FABMS m/z 522 [M]+ (5),
477 (17), 329 (17), 178 (100); HRFABMS m/z 522.1678 (calcd
for C32H26O7 [M]+ 522.1679). Anal. Calcd for C32H26O7: C,
73.54; H, 5.02. Found: C, 73.73; H, 5.03.
Or-(9-F lu or en ylm et h yloxyca r b on yl)-L-r-h yd r oxyiso-
va ler yl-L-r-h yd r oxyisova ler ic Acid Meth yl Ester (14b).
A solution of L-8b (53 mg, 0.40 mmol), L-5b (163 mg, 0.48
mmol), DIC (88 µL, 0.56 mmol), and DMAP (5 mg, 0.04 mmol)
in THF (1 mL) was stirred at room temperature for 2 h. The
reaction mixture was filtered and concentrated under reduced
pressure. Purification by flash chromatography with hexane/
EtOAc (4:1) gave 14b (162 mg, 90%) as an amorphous solid:
[R]D ) -27.8 (c ) 1.2, CHCl3); IR (NaCl) νmax 2967, 2883, 1751,
Or-Tetr a h yd r op yr a n yl-L-la ctic a cid (L-7c). L-7c was
prepared, as described above for L-7b, from L-lactic acid (1816
mg, 20 mmol) and was obtained as an oil (2471 mg, 71%): IR
(NaCl) νmax 3500 br, 2944, 2873, 1729, 1456, 1376, 1213, 1129,
1
1025, 984, 897, 866, 815 cm-1; H NMR (250 MHz, CDCl3) δ
1.40-1.87 (m, 6 H), 1.43 (d, J ) 6.9) and 1.48 (d, J ) 7.1, 3

8072 J . Org. Chem., Vol. 64, No. 22, 1999
Kuisle et al.
1451, 1387, 1289, 1256, 1197, 1132, 1024, 1001, 792, 741 cm-1
;
concentrated under reduced pressure. Purification of the
residue by flash chromatography with hexane/EtOAc (4:1) gave
16b (160 mg, 87%) as an amorphous solid: [R]D ) -32.0 (c )
1.4, CHCl3); IR (NaCl) νmax 3063, 2968, 2882, 1752, 1453, 1386,
1H NMR (250 MHz, CDCl3) δ 1.01 (dd, J 1 ) 9.3, J 2 ) 6.9, 6
H), 1.15 (dd, J 1 ) 6.9, J 2 ) 4.2, 6 H), 2.23-2.45 (m, 2 H), 3.74
(s, 3 H), 4.28-4.38 (m, 2 H), 4.44-4.51 (m, 1 H), 4.92 (d, J )
4.2, 1 H), 4.97 (d, J ) 4.3, 1 H), 7.33 (t, J ) 7.4, 2 H), 7.42 (t,
1287, 1256, 1190, 1128, 1026, 789, 741 cm-1 1H NMR (250
;
J ) 7.3, 2 H), 7.65 (t, J ) 8.2, 2 H), 7.77 (d, J ) 7.4, 2 H); 13
C
MHz, CDCl3) δ 1.00 (dd, J 1 ) 9.2, J 2 ) 6.9, 6 H), 1.09 (dd, J 1
) 6.9, J 2 ) 4.5, 6 H), 1.13 (dd, J 1 ) 6.9, J 2 ) 4.4, 6 H), 2.22-
2.47 (m, 3 H), 3.72 (s, 3 H), 4.29-4.38 (m, 2 H), 4.43-4.52 (m,
1 H), 4.91 (d, J ) 4.3, 1 H), 4.93 (d, J ) 4.5, 1 H), 5.03 (d, J )
4.1, 1 H), 7.32 (t, J ) 7.4, 2 H), 7.41 (t, J ) 7.3, 2 H), 7.64 (t,
J ) 8.2, 2 H), 7.77 (d, J ) 7.5, 2 H); 13C NMR (63 MHz, CDCl3)
δ 16.8, 16.9, 17.1, 18.5, 18.6, 30.1, 30.2, 30.3, 46.6, 52.0, 70.3,
77.2, 79.5, 120.0, 125.2, 125.4, 127.1, 127.2, 127.8, 141.2, 143.1,
143.5, 168.7, 169.1, 169.6; FABMS m/z 577 [M + Na]+ (57),
555 [M + H]+ (61), 377 (100), 345 (95); HRFABMS m/z
555.2592 (calcd for C31H39O9 [M + H]+ 555.2594). Anal. Calcd
for C31H38O9: C, 67.13; H, 6.91. Found: C, 67.28; H, 7.01.
Dep r otection of 16a . 16a (147 mg, 0.22 mmol) was treated
with piperidine/THF according to the general procedure. Flash
chromatography of the crude product with hexane/EtOAc (7:
3) gave 88 mg of a mixture. This mixture was separated by
HPLC (µ-Porasil, hexane/EtOAc (8:2), 2.0 mL/min) to give 29
NMR (63 MHz, CDCl3) δ 16.9, 17.1, 18.5, 30.1, 30.3, 46.6, 52.0,
70.3, 70.3, 79.6, 120.0, 125.2, 125.3, 125.8, 127.1, 127.2, 127.8,
141.2, 143.1, 143.5, 154.9, 169.0, 169.5; FABMS m/z 455 [M +
H]+ (11), 277 (11), 245 (12), 178 (100). Anal. Calcd for
C
26H30O7: C, 68.71; H, 6.65. Found: C, 68.97; H, 6.78.
L-Ma n d elyl-L-m a n d elic Acid Meth yl Ester (15a ). (a ) By
Dep r otection of 14a . 14a (138 mg, 0.26 mmol) was treated
with piperidine/THF according to the general procedure. Flash
chromatography of the crude product with hexane/EtOAc (7:
3) gave 15a (75 mg, 94%) as a pale yellow solid. (b) By
Dep r otection of 23a . 23a was treated with 6 mL of a solution
of p-TsOH in MeOH (1 mg/mL), and the reaction was followed
by TLC. After 1.5 h, the mixture was concentrated under
reduced pressure to 1 mL, dissolved in ether, washed with
NaHCO3 and water, dried (Na2SO4), and concentrated. Puri-
fication of the crude product by flash chromatography with
hexane/EtOAc (4:1) gave 15a (152 mg, 91%) as a pale yellow
solid: mp ) 74-75 °C; [R]D ) +117.2 (c ) 7.0, CHCl3); IR
(NaCl) νmax 3480 br, 3063, 3034, 2953, 1749, 1447, 1273, 1217,
mg of 17a (tR ) 26 h 10 min) and 54 mg of 18a (t ) 29 h 45
R
min). l-Ma n d elyl-D-m a n d elyl-L-m a n d elic a cid m eth yl es-
ter (17a ):. [R]D ) +37.8 (c ) 2.0, CHCl3); IR (NaCl) νmax 3400
br, 3063, 3034, 2953, 2924, 2854, 1751, 1495, 1449, 1259, 1210,
1171, 1041, 737, 697 cm-1; 1H NMR (250 MHz, CDCl3) δ 3.36
(s or d, J ) 5.7, 1 H), 3.71 (s, 3 H), 5.36 (d, J ) 5.7, 1 H), 5.98
(s, 1 H), 6.18 (s, 1 H), 7.27-7.44 (m, 15 H); 13C NMR (63 MHz,
CDCl3) δ 52.7, 72.9, 75.1, 75.2, 126.7, 127.2, 127.3, 128.5, 128.6,
128.7, 129.4, 129.2, 132.6, 133.0, 137.5, 167.2, 168.2, 172.5;
FABMS m/z 435 [M + H]+ (8), 369 (9), 277 (13), 195 (88), 133
(100); HRFABMS m/z 435.1443 (calcd for C25H23O7 [M + H]+
435.1444). l-Ma n d elyl-L-m a n d elyl-L-m a n d elic a cid m eth yl
ester (18a ): [R]D ) +115.3 (c ) 2.8, CHCl3); IR (NaCl) νmax
3400 br, 2918, 2853, 1750, 1587, 1456, 1205, 1167, 1044, 792,
1174, 1092, 1068, 1031, 736, 698 cm-1 1H NMR (250 MHz,
;
CDCl3) δ 3.55 (d or s, J ) 5.4 Hz, 1 H), 3.59 (s, 3 H), 5.33 (d or
s, J ) 5.4 Hz, 1 H), 6.01 (s, 1 H), 7.35-7.59 (m, 10 H); 13C
NMR (63 MHz, CDCl3) δ 52.4, 73.1, 75.6, 126.9, 127.6, 128.5,
128.6, 128.9, 129.5, 133.3, 137.8, 168.3, 172.8; FABMS m/z 301
[M + H]+ (37), 283 (26), 149 (88), 133 (90), 121 (100);
HRFABMS m/z 301.1077 (calcd for
301.1076). Anal. Calcd for C17H16O5: C, 67.98; H, 5.37.
Found: C, 67.84; H, 5.46.
C
17H17O5 [M + H]+
L-r-H yd r oxyisova ler yl-L-r-h yd r oxyisova ler ic
Acid
Meth yl Ester (15b). 14b (162 mg, 0.36 mmol) was treated
with piperidine/THF according to the general procedure. Flash
chromatography of the crude product with hexane/EtOAc (4:
1) gave 15b (77 mg, 92%) as an amorphous solid: [R]D ) -13.6
(c ) 2.0, CHCl3); IR (NaCl) νmax 3500 br, 2966, 2882, 1745,
1
738, 699 cm-1; H NMR (250 MHz, CDCl3) δ 3.41 (s or d, J )
5.8, 1 H), 3.55 (s, 3 H), 5.33 (d, J ) 5.8, 1 H), 5.93 (s, 1 H),
6.15 (s, 1 H), 7.27-7.57 (m, 15 H); 13C NMR (63 MHz, CDCl3)
δ 52.4, 73.2, 75.2, 75.4, 126.9, 127.5, 127.9, 128.6, 128.8, 129.4,
129.6, 132.9, 133.2, 137.7, 167.2, 168.2, 172.6; FABMS m/z 435
[M + H]+ (5), 369 (8), 277 (19), 185 (38), 133 (100); HRFABMS
m/z 435.1443 (calcd for C25H23O7 [M + H]+ 435.1444). Anal.
Calcd for C25H22O7: C, 69.10; H, 5.11. Found: C, 69.05; H,
5.18.
1
1463, 1370, 1280, 1208, 1135, 1029, 774 cm-1; H NMR (250
MHz, CDCl3) δ 0.94-1.08 (m, 12 H), 2.14-2.30 (m, 3 H), 2.68
(d, J ) 6.2, 1 H), 3.74 (s, 3 H), 4.12 (dd, J 1 ) 5.9, J 2 ) 3.5, 1
H), 4.91 (d, J ) 4.3, 1 H); 13C NMR (63 MHz, CDCl3) δ 15.7,
17.1, 18.6, 30.1, 32.3, 52.1, 74.8, 77.6, 169.5, 174.7; FABMS
m/z 255 [M + Na]+ (41), 233 [M + H]+ (60), 179 (100),
18a by Dep r otection of 24a . 18a was obtained, as
described above for 15a , by deprotection of 24a with 5 mL of
p-TsOH/MeOH to give an amorphous solid (170 mg, 87%).
L-r-H yd r oxyisova ler yl-L-r-h yd r oxyisova ler yl-L-r-h y-
d r oxyisova ler ic Acid Met h yl E st er (18b ). 16b (160 mg,
0.29 mmol) was treated with piperidine/THF according to the
general procedure. Flash chromatography of the crude product
with hexane/EtOAc (4:1) gave 18b (87 mg, 91%) as an
amorphous solid: [R]D ) -25.4 (c ) 0.7, CHCl3); IR (NaCl)
νmax 3540 br, 2968, 2881, 1750, 1464, 1372, 1282, 1196, 1131,
HRFABMS m/z 233.1388 (calcd for
233.1389). Anal. Calcd for C11H20O5: C, 56.88; H, 8.68.
Found: C, 56.96; H, 8.71.
C
11H21O5 [M + H]+
Or-(9-Flu or en ylm eth yloxycar bon yl)-L-m an delyl-L-m an -
d elyl-L-m a n d elic Acid Meth yl Ester (16a ). A solution of
15a (75 mg, 0.25 mmol), L-5a (85 mg, 0.36 mmol), DIC (66 µL,
0.42 mmol), and DMAP (4 mg, 0.03 mmol) in THF (1 mL) was
stirred at room temperature for 2 h. The reaction mixture was
filtered and concentrated under reduced pressure. Purification
by flash chromatography with hexane/EtOAc (7:3) gave 16a
(147 mg, 90%) as an amorphous solid: [R]D ) +81.6 (c ) 3.0,
CHCl3); IR (NaCl) νmax 3064, 3037, 2953, 1753, 1449, 1256,
1
1029, 777 cm-1; H NMR (250 MHz, CDCl3) δ 0.94-1.09 (m,
18 H), 2.12-2.44 (m, 3 H), 2.65 (d, J ) 6.4, 1 H), 3.73 (s, 3 H),
4.13 (dd, J 1 ) 6.0, J 2 ) 3.4, 1 H), 4.93 (d, J ) 4.3, 1 H), 4.99
(d, J ) 4.0, 1 H); 13C NMR (63 MHz, CDCl3) δ 15.8, 16.8, 17.1,
18.6, 18.7, 30.1, 30.2, 32.3, 52.1, 74.9, 77.2, 77.3, 168.7, 169.5,
174.7; FABMS m/z 333 [M + H]+ (52), 233 (100); HRFABMS
m/z 333.1912 (calcd for C16H29O7 [M + H]+ 333.1913). Anal.
Calcd for C16H28O7: C, 57.82; H, 8.49. Found: C, 58.08; H,
8.63.
1
1210, 1166, 1031, 737, 696 cm-1; H NMR (250 MHz, CDCl3)
δ 3.54 (s, 3 H), 4.28-4.41 (m, 2 H), 4.54 (dd, J 1 ) 9.4, J 2
)
6.4, 1 H), 5.93 (s, 1 H), 6.09 (s, 1 H), 6.16 (s, 1 H), 7.30-7.51
(m, 17 H), 7.60-7.66 (m, 4 H), 7.78 (d, J ) 7.4, 2 H); 13C NMR
(63 MHz, CDCl3) δ 46.6, 52.4, 70.7, 75.1, 75.2, 77.2, 120.0,
125.3, 125.4, 127.3, 127.5, 127.8, 127.9, 128.1, 128.8, 128.9,
129.3, 129.5, 129.7, 132.7, 133.1, 141.3, 143.1, 143.7, 154.5,
167.1, 167.8, 168.2; FABMS m/z 657 [M + H]+ (100), 611 (76),
463 (60); HRFABMS m/z 657.2114 (calcd for C40H33O9 [M +
H]+ 657.2124). Anal. Calcd for C40H32O9: C, 73.15; H, 4.91.
Found: C, 73.07; H, 4.94.
D-Ma n d elyl-L-m a n d elic Acid Meth yl Ester (19a ). 19a
was obtained by coupling between L-8a (50 mg, 0.30 mmol)
and D-5a , as described above for 14a , followed by deprotection
of the resulting Fmoc-protected didepside with piperidine/THF
according to the general procedure to give a pale yellow solid
(68 mg, 76%): mp ) 85-86 °C; [R]D ) +57.8 (c ) 9.5, CHCl3);
IR (NaCl) νmax 3420 br, 3065, 3033, 2953, 1746, 1453, 1437,
Or-(9-F lu or en ylm et h yloxyca r b on yl)-L-r-h yd r oxyiso-
valer yl-L-r-h ydr oxyisovaler yl-L-r-h ydr oxyisovaler ic Acid
Meth yl Ester (16b). A solution of 15b (77 mg, 0.33 mmol),
L-5b (135 mg, 0.40 mmol), DIC (73 µL, 0.46 mmol), and DMAP
(4 mg, 0.03 mmol) in THF (1 mL) was stirred at room
temperature for 2 h. The reaction mixture was filtered and
1217, 1172, 1093, 1067, 1028, 734, 696 cm-1 1H NMR (250
;
MHz, CDCl3) δ 3.40 (s or d, J ) 5.5, 1 H), 3.73 (s, 3 H), 5.40 (s
or d, J ) 5.5, 1 H), 5.96 (s, 1 H), 7.27-7.61 (m, 10 H); 13C
NMR (63 MHz, CDCl3) δ 52.8, 73.0, 75.4, 126.7, 127.2, 127.6,

Solid-Phase Synthesis of Depsides and Depsipeptides
J . Org. Chem., Vol. 64, No. 22, 1999 8073
127.9, 128.6, 128.8, 129.3, 133.1, 137.7, 168.7, 172.9; FABMS
m/z 323 [M + Na]+ (55), 301 [M + H]+ (75), 283 (100), 261
(86); HRFABMS m/z 301.1077 (calcd for C17H17O5 [M + H]+
301.1076).
reduced pressure. Purification by flash chromatography with
hexane/EtOAc (7:3) gave 23a (214 mg, 93%) as a sticky oil:
IR (NaCl) νmax 2948, 2856, 1755, 1448, 1267, 1210, 1161, 1125,
1074, 1032, 975, 733, 700 cm-1; 1H NMR (250 MHz, CDCl3) δ
1.45-1.95 (m, 6 H), 3.45-3.54 (m, 1 H), 3.57 and 3.61 (s, 3
H), 3.65-3.78 and 3.91-3.99 (m, 1 H), 4.65 and 5.02 (t, J )
2.9, 1 H), 5.36 and 5.48 (s, 1 H), 5.96 and 5.97 (s, 1 H), 7.36-
7.58 (m, 10 H); 13C NMR (63 MHz, CDCl3) δ 18.7, 25.3, 30.1,
52.4, 61.9, 74.8, 75.6, 76.4, 96.4, 97.2, 127.3, 127.4, 127.5, 127.7,
128.4, 128.5, 128.6, 128.7, 129.2, 133.4, 133.6, 135.8, 136.1,
168.6, 169.9, 170.7; FABMS m/z 407 [M + Na]+ (26), 385 [M
+ H]+ (65), 301 (59); HRFABMS m/z 385.1650 (calcd for
Or-Met h yl-L-m a n d elyl-D-m a n d elyl-L-m a n d elic Acid
Meth yl Ester (20a ). (a ) P r ep a r a tion of 20a a s a Refer en ce
Com p ou n d by Cou p lin g betw een 19a a n d Or-Meth yl-L-
m a n d elic Acid (MP A). A solution of 19a (68 mg, 0.23 mmol),
OR-methyl-L-mandelic acid (45 mg, 0.27 mmol), DIC (50 µL,
0.32 mmol), and DMAP (3 mg, 0.02 mmol) in THF (0.8 mL)
was stirred at room temperature for 2 h. The reaction mixture
was concentrated under reduced pressure and purified by flash
chromatography with hexane/EtOAc (7:3) to give 20a (89 mg,
88%) as an amorphous solid. (b) By Meth yla tion of 17a . A
mixture of 17a (29 g, 0.07 mmol) and Ag2O (8 mg, 0.04 mmol)
in MeI (1 mL) was refluxed (50 °C) for 4 h. The mixture was
evaporated to dryness, redissolved in CHCl3, and evaporated
twice to ensure complete removal of all the MeI (caution: MeI
is volatile and carcinogenic! Work in a well-ventilated hood!).
The residue was purified by flash chromatograpy from hexane/
EtOAc (7:3) and HPLC (µ-Porasil, hexane/EtOAc (8:2), 2.0 mL/
C
22H25O6 [M + H]+ 385.1651). Anal. Calcd for C22H24O6: C,
68.72; H, 6.30. Found: C, 68.63; H, 6.37.
Or-Tetr a h yd r op yr a n yl-L-m a n d elyl-L-m a n d elyl-L-m a n -
d elic Acid (24a ). A solution of L-15a (152 mg, 0.51 mmol),
L-7a (143 mg, 0.61 mmol), DIC (111 µL, 0.71 mmol), and
DMAP (6 mg, 0.05 mmol) in THF (1.5 mL) was stirred at room
temperature for 2 h. The reaction mixture was filtered and
concentrated under reduced pressure. Purification by flash
chromatography from hexane/EtOAc (7:3) gave 24a (233 mg,
89%) as a sticky oil: IR (NaCl) νmax 3067, 3031, 2947, 2869,
1756, 1496, 1450, 1347, 1266, 1205, 1164, 1034, 973, 908, 738,
min) to give 20a (23 mg, 76%) as an amorphous solid: [R]D
+33.2 (c ) 6.0, CHCl3); IR (NaCl) νmax 3062, 3033, 2949, 2833,
1755, 1495, 1451, 1352, 1205, 1166, 1108, 1026, 737, 697 cm-1
)
1
;
698 cm-1; H NMR (250 MHz, CDCl3) δ 1.50-1.95 (m, 6 H),
1H NMR (250 MHz, CDCl3) δ 3.33 (s, 3 H), 3.69 (s, 3 H), 4.90
(s, 1 H), 5.96 (s, 1 H), 6.13 (s, 1 H), 7.29-7.43 (m, 15 H); 13C
NMR (63 MHz, CDCl3) δ 52.7, 57.5, 74.7, 75.2, 82.3, 127.4,
127.6, 127.9, 128.7, 128.7, 128.9, 129.2, 129.3, 133.0, 133.3,
135.7, 167.5, 168.3, 170.0; FABMS m/z 471 [M + Na]+ (100),
449 [M + H]+ (36), 447 (33), 417 (43), 317 (25), 283 (50);
3.43-3.55 (m, 1 H), 3.53 and 3.55 (s, 3 H), 3.69-3.77 and 3.82-
3.95 (m, 1 H), 4.64 (t, J ) 3.2), 5.03 (t, J ) 2.8, 1 H), 5.37 and
5.49 (s, 1 H), 5.91 and 5.93 (s, 1 H), 6.09 and 6.12 (s, 1 H),
7.28-7.58 (m, 15 H); 13C NMR (63 MHz, CDCl3) δ 18.6, 18.8,
25.3, 29.7, 30.1, 52.4, 61.9, 62.0, 74.5, 74.6, 75.08, 75.13, 75.6,
96.5, 97.2, 127.4, 127.5, 127.7, 127.8, 128.4, 128.5, 128.6, 128.7,
129.3, 133.0, 133.1, 135.7, 136.1, 167.4, 168.2, 169.9, 170.7;
FABMS m/z 519 [M + H]+ (16), 435 (100); HRFABMS m/z
519.2018 (calcd for C30H31O8 [M + H]+ 519.2019). Anal. Calcd
for C30H30O8: C, 69.47; H, 5.83. Found: C, 69.68; H, 5.76.
H-[L-Ma n -L-Ma n ]4-OH (25). Wang resin (1.0 g, 1.0 mmol/g
loading level) was placed into a 50 mL reaction vessel of a
peptide synthesizer and subsequently submitted to eight cycles
of the following: (1) depside coupling according to general
procedure A with OR-THP-L-mandelic acid (710 mg, 3 mmol),
DIC (470 µL, 3 mmol), and DMAP (12 mg, 0.1 mmol); (2) THP
deprotection according to general procedure C. After each
depside coupling step a small sample of resin was taken and
submitted to the test described previously and the coupling
repeated if necessary. The product was cleaved from the solid
support by treatment with 10 mL of TFA/CH2Cl2 (1:1) for 1 h.
The resin was filtered off and washed five times with CH2Cl2
(10 mL). The combined rinses were washed twice with 50 mL
of water and dried over Na2SO4, and the solvent was removed
under reduced pressure to give 1152 mg of crude 25. RP-HPLC
(Nucleosil, MeCN/water (70:30) with 0.1% TFA, 2.0 mL/min)
of 115 mg of crude 25 afforded 81 mg (0.074 mmol, 74%) of
octadepside 25 (tR ) 17 min) as a white solid: IR (NaCl) νmax
3450 br, 3035, 2948, 2869, 1748, 1496, 1453, 1254, 1208, 1173,
1062, 1032, 737, 697 cm-1; 1H NMR (300 MHz, CDCl3) δ 5.28
(s, 1 H), 5.83 (s, 1 H), 5.97 (s, 1 H), 6.00 (s, 1 H), 6.01 (s, 1 H),
6.02 (s, 1 H), 6.06 (s, 1 H), 6.13 (s, 1 H), 7.18-7.43 (m, 40 H);
13C NMR (63 MHz, CDCl3) δ 73.1, 74.6, 74.8, 75.3, 126.9, 127.4,
127.7, 127.8, 127.9, 128.6, 128.7, 128.8, 129.4, 132.3, 132.5,
137.4, 166.9, 172.6; FABMS m/z 1113 [M + Na]+ (100), 1091
[M + H]+ (27). Anal. Calcd for C64H50O17: C, 70.44; H, 4.62.
Found: C, 70.10; H, 4.78.
HRFABMS m/z 449.1599 (calcd for
C
26H25O7 [M + H]+
449.1600).
Or-Met h yl-L-m a n d elyl-L-m a n d elyl-L-m a n d elic
Acid
Meth yl Ester (21a ). (a ) P r ep a r a tion of 20a a s a Refer en ce
Com p ou n d by Cou p lin g betw een 15a a n d Or-Meth yl-L-
m a n d elic Acid . A solution of 15a (45 mg, 0.15 mmol), OR-
methyl-L-mandelic acid (30 mg, 0.18 mmol), DIC (33 µL, 0.21
mmol), and DMAP (2 mg, 0.01 mmol) in THF (0.8 mL) was
stirred at room temperature for 2 h. The reaction mixture was
concentrated under reduced pressure and purified by flash
chromatography from hexane/EtOAc (7:3) to give 21a (56 mg,
84%) as an amorphous solid. (B) By Meth yla tion (See
a bove, Meth yla tion of 20a ) of 18a (54 m g, 0.12 m m ol) To
Give a n Am or p h ou s Solid (44 m g, 80%): [R]D ) +111.5 (c
) 6.0, CHCl3); IR (NaCl) νmax 3061, 3030, 2923, 2851, 1754,
1
1494, 1450, 1348, 1205, 1163, 1107, 1038, 736, 696 cm-1; H
NMR (250 MHz, CDCl3) δ 3.50 (s, 3 H), 3.55 (s, 3 H), 4.93 (s,
1 H), 5.92 (s, 1 H), 6.13 (s, 1 H), 7.29-7.51 (m, 15 H); 13C NMR
(63 MHz, CDCl3) δ 52.4, 57.6, 74.5, 75.2, 82.4, 127.4, 127.5,
127.9, 128.6, 128.7, 128.8, 128.8, 129.3, 129.4, 133.0, 133.1,
135.7, 167.5, 168.3, 170.1; FABMS m/z 471 [M + Na]+ (100),
449 [M + H]+ (16), 447 (19), 417 (22), 317 (18), 283 (62);
HRFABMS m/z 449.1599 (calcd for
449.1600). Anal. Calcd for C26H24O7: C, 69.62; H, 5.40.
Found: C, 69.81; H, 5.52.
C
26H25O7 [M + H]+
Or-Met h yl-D-m a n d elyl-L-m a n d elyl-L-m a n d elic Acid
Meth yl Ester (22a ). P r ep a r a tion of 21a a s a Refer en ce
Com p ou n d by Cou p lin g betw een 19a a n d Or-Meth yl-D-
m a n d elic Acid . 22a was prepared as described above for 21a ,
with OR-methyl-D-mandelic acid, as an amorphous solid (59
mg, 87%): [R]D ) +62.8 (c ) 5.7, CHCl3); IR (NaCl) νmax 3063,
3032, 2949, 2833, 1757, 1495, 1449, 1209, 11647, 1108, 1040,
744, 699 cm-1; 1H NMR (250 MHz, CDCl3) δ 3.49 (s, 3 H), 3.58
(s, 3 H), 4.99 (s, 1 H), 5.98 (s, 1 H), 6.11 (s, 1 H), 7.30-7.47
(m, 15 H); 13C NMR (63 MHz, CDCl3) δ 52.4, 57.6, 74.5, 75.3,
82.2, 127.3, 127.4, 127.5, 127.6, 127.9, 128.6, 128.8, 128.9,
129.3, 129.4, 132.8, 133.1, 135.7, 167.8, 168.3, 170.1; FABMS
m/z 471 [M + Na]+ (100), 449 [M + H]+ (85), 417 (42);
H-[D-Ma n -L-Ma n ]4-OH (26). Octadepside 26 was synthe-
sized as described above for octadepside 25, starting with 1.0
g of Wang resin and carrying out eight coupling-deprotection
cycles using, alternately, OR-THP-L- and OR-THP-D-mandelic
acid (710 mg, 3.0 mmol) in the coupling reactions. The crude
product, a white foam, was purified by RP-HPLC (Partisil,
MeCN/water (70:30) with 0.1% TFA, 2.0 mL/min) to obtain
817 mg (0.75 mmol, 75%) of octadepside 2 (tR ) 16 min 40 s)
as a white solid: [R]D ) +17.3 (acetone, c ) 2.4); IR (NaCl)
νmax 3500 br, 3061, 3032, 2948, 1750, 1494, 1452, 1247, 1201,
1167, 1046, 1027, 734, 696 cm-1; 1H NMR (500 MHz, acetone-
d6) δ 5.36 (s, 1 H), 5.99 (s, 1 H), 6.17 (s, 1 H), 6.19 (s, 3 H),
6.21 (s, 1 H), 6.23 (s, 1 H), 7.22-7.46 (m, 40 H); 13C NMR (63
MHz, acetone-d6) δ 73.1, 74.4, 74.8, 74.9, 75.1, 127.0, 127.4,
HRFABMS m/z 449.1599 (calcd for
449.1600).
C
26H25O7 [M + H]+
Or-Tet r a h yd r op yr a n yl-L-m a n d elyl-L-m a n d elic Acid
(23a ). A solution of L-8a (100 mg, 0.60 mmol), L-7a (170 mg,
0.72 mmol), DIC (131 µL, 0.84 mmol), and DMAP (7 mg, 0.06
mmol) in THF (2 mL) was stirred at room temperature for 2
h. The reaction mixture was filtered and concentrated under

8074 J . Org. Chem., Vol. 64, No. 22, 1999
Kuisle et al.
127.7, 128.1, 128.3, 128.6, 129.0, 129.2, 133.2, 133.3, 133.5,
134.0, 139.0, 166.7, 166.8, 167.0, 167.2, 168.4, 171.7; FABMS
m/z 1113 [M + Na]+ (100), 979 (10), 663 (8), 491 (12), 403 (22),
357 (34); HRFABMS m/z 1113.3000 (calcd for C64H50O17Na1
[M + Na]+ 1113.2946). Anal. Calcd for C64H50O17: C, 70.44;
H, 4.62. Found: C, 70.15; H, 4.80.
four coupling-deprotection cycles: (i) depside coupling ac-
cording to general procedure A with NR-Bpoc-D-valine31 (533
mg, 1.5 mmol), DIC (235 µL, 1.5 mmol), and DMAP (6 mg,
0.05 mmol), followed by Bpoc deprotection according to general
procedure D; (ii) peptide coupling according to general proce-
dure B with OR-THP-D-mandelic acid (D-7a ) (355 mg, 1.5 mmol)
and DIC (235 µL, 1.5 mmol) followed by THP deprotection
according to general procedure C; (iii) depside coupling ac-
cording to general procedure A with NR-Bpoc-L-valine31 (533
mg, 1.5 mmol), DIC (235 µL, 1.5 mmol), and DMAP (6 mg,
0.05 mmol), followed by Bpoc deprotection according to general
procedure D; and (iv) peptide coupling according to general
procedure B with D-7a (261 mg, 1.5 mmol) and DIC (235 µL,
1.5 mmol) followed by THP deprotection according to general
procedure C. The whole series, from i to iv, was effected three
times, except for the last peptide coupling (iv), which was only
carried out twice. In the last depside coupling (iii), NR-Cbz-L-
valine was used instead of the Bpoc derivative. Depside
couplings were monitored by the test described previously and
peptide couplings with the ninhydrin test,38 and in both cases,
couplings were repeated if necessary. The product was cleaved
from the solid support by treatment with 10 mL of TFA/CH2-
Cl2 (1:1) for 1 h. The resin was filtered and washed five times
with CH2Cl2 (10 mL). The combined rinses were washed twice
with 50 mL of water and dried over Na2SO4, and the solvent
was removed under reduced pressure. The crude depsipeptide
was purified by RP-HPLC (Nucleosil, MeCN/water (62:38) with
0.1% TFA, 2.0 mL/min) to obtain 429 mg (0.31 mmol, 63%) of
protected depsipeptide 6 (tR ) 43 h 55 min) as a white solid:
[R]D -36.0 (CHCl3, c ) 4.0); IR (NaCl) νmax 3320 br, 3035, 2968,
2933, 2871, 1747, 1670, 1536, 1167, 1145, 755, 697, 667, 481
H-[L-La c-L-Hiv]3-OH (27). Hexadepside 27 was synthe-
sized as described above for octadepside 25, starting with 1.0
g of Wang resin and carrying out six coupling-deprotection
cycles using, alternately, OR-THP-L-R-hydroxyisovaleric acid
(606 mg, 3.0 mmol) and OR-THP-L-lactic acid (522 mg, 3.0
mmol) in the coupling reactions. The crude product, a white
foam, was purified by RP-HPLC (Nucleosil, MeCN/water (50:
50) with 0.1% TFA, 1.8 mL/min) to obtain 384 mg (0.72 mmol,
72%) of hexadepside 3 (tR ) 24 h 45 min) as a white solid:
[R]D ) -83.9 (acetone, c ) 1.8); IR (NaCl) νmax 3480 br, 2970,
2942, 1739, 1468, 1208, 1134, 1098, 1033 cm-1; 1H NMR (300
MHz,CDCl3) δ 0.99-1.06 (m, 18 H), 1.50 (d, J ) 6.8, 3 H), 1.57
(d, J ) 6.8, 3 H), 1.60 (d, J ) 6.8, 3 H), 2.22-2.46 (m, 3 H),
4.39 (q, J ) 6.9, 1 H), 4.36 (d, J ) 3.9, 1 H), 4.98 (d, J ) 3.9,
1 H), 4.99 (d, J ) 3.9, 1 H), 5.18 (q, J ) 6.9, 1 H), 5.21 (q, J )
6.9, 1 H); 13C NMR (63 MHz, CDCl3) δ 16.6, 16.7, 16.8, 16.9,
18.5, 18.6, 18.7, 20.4, 29.9, 30.0, 66.7, 68.9, 69.0, 76.8, 76.9,
77.1, 168.4, 169.9, 173.7, 175.4; FABMS m/z 557 [M + Na]+
(100), 535 [M + H]+ (7), 337 (19), 245 (39); HRFABMS m/z
557.2189 (calcd for C24H38O13Na1 [M+ + Na] 557.2210). Anal.
Calcd for C24H38O13: C, 53.91; H, 7.17. Found: C, 54.01; H,
7.23.
H-[L-Ma n ]6-OH (28). Hexadepside 28 was synthesized as
described above for octadepside 25, starting with 1.0 g of Wang
resin and carrying out six coupling-deprotection cycles using
OR-THP-L-mandelic acid (710 mg, 3.0 mmol) in the coupling
reactions. The crude product, a white foam, was purified by
RP-HPLC (Partisil, MeCN/water (65:35) with 0.1% TFA, 2.0
mL/min) to obtain 690 mg (0.84 mmol, 84%) of hexadepside 5
(tR ) 15.5 min) as a white solid: IR (NaCl) νmax 3034, 2948,
1
cm-1; H NMR (300 MHz, CDCl3 + D2O) δ 0.84-1.17 (m, 36
H), 1.50 (td, 9 H), 2.06-2.35 (m, 6 H), 4.06-4.57 (m, 6 H),
5.04 (d, J ) 12.2, 1 H), 5.23 (d, J ) 12.2, 1 H), 5.17 (q, J ) 7.1,
1 H), 5.38 (q, J ) 6.5, 1 H), 6.00 (d, J ) 7.8, 1 H), 6.14 (s, 1 H),
6.17 (s, 1 H), 6.21 (s, 1 H), 7.36-7.55 (m, 20 H), 7.76 (m, 3 H),
7.90 (d, J ) 6.3, 1 H); 13C NMR (63 MHz, CDCl3) δ 16.8, 17.5,
17.6, 18.3, 18.4, 19.0, 19.1, 19.2, 29.2 (‚ 2), 29.3, 29.7, 30.0,
30.2, 57.8, 59.1, 59.5, 59.7, 59.8, 60.3, 67.4, 69.3, 70.5, 70.8,
75.6, 76.0, 77.3, 127.5, 127.6, 128.2, 128.5, 128.6, 128.7, 129.0,
134.9, 135.2, 135.3, 136.2, 157.2, 169.1, 170.1, 170.2, 170.4,
170.5, 170.6, 170.8, 171.4, 171.5, 171.8, 171.9, 172.0; FABMS
m/z 1387 [M + Na]+ (100), 1365 [M + H]+ (20), 1316 (30). Anal.
Calcd for C71H92N6O21: C, 62.43; H, 6.79; N, 6.16. Found: C,
62.58; H, 6.70; N, 6.04.
H-[L-Va l-D-Ma n -D-Va l-L-La c]3-OH (32). Depsipeptide 32
was synthesized as described above for 31, starting with 0.3 g
of Wang resin (1.0 mmol/g loading level) and using NR-Bpoc-
L-valine for the last depside coupling step. The crude product
was purified by RP-HPLC (Partisil, MeCN/water (55:45) with
0.1% TFA, 2.5 mL/min) to obtain 189 mg (0.14 mmol, 47%) of
32 (tR ) 37 h 40 min) as a white solid: [R]D -31.1 (CHCl3, c )
1.0); IR (NaCl) νmax 2969, 2937, 2878, 1748, 1665, 1534, 1460,
1195, 1145, 756, 699 cm-1; 1H NMR (300 MHz, CDCl3 + D2O)
δ 0.74-1.02 (m, 36 H), 1.33-1.52 (m, 9 H), 2.00-2.38 (m, 6
H), 4.03-4.66 (m, 6 H), 5.03 (q, J ) 7.3, 1 H), 5.23-5.31 (m,
1 H), 6.08 (s, 1 H), 6.14 (s, 1 H), 6.21 (s, 1 H), 7.30-7.53 (m,
20 H); 13C NMR (63 MHz, CDCl3) δ 16.6, 17.5, 17.6, 17.8, 17.9,
18.0, 18.4, 18.6, 18.7, 18.8, 19.0, 29.3, 29.5, 29.7, 30.6, 57.2,
58.1, 58.2, 58.4, 58.5, 58.7, 69.8, 70.9, 72.0, 75.7, 76.1, 77.2,
127.3, 127.5, 127.6, 128.7, 128.8, 129.1, 129.2, 131.9, 134.5,
135.2, 166.9, 168.8, 169.0, 169.7, 170.9, 171.1, 171.2 (‚ 2), 171.3,
171.4, 171.8, 173.1; FABMS m/z 1253 [M + Na]+ (20), 1231
[M + H]+ (100), 1159 (17). Anal. Calcd for C63H86N6O19: C,
61.45; H, 7.04; N, 6.82. Found: C, 61.63; H, 6.91; N, 6.71.
Cyclo[L-Va l-D-Ma n -D-Va l-L-La c]3 (30). (a ) Cycliza tion
via th e Acid Ch lor id e. 32 (88 mg, 0.065 mmol) was dissolved
in SOCl2 (0.5 mL) and kept at room temperature for 30 min.
The solution was concentrated under reduced pressure and
redissolved twice in toluene. The resulting acid chloride was
dissolved in 5 mL of toluene and added by syringe during 2 h
to a stirred solution of DIEA (20 µL) in 5 mL of toluene. After
2869, 1752, 1497, 1454, 1254, 1206, 1167, 1032, 737, 696 cm-1
;
1H NMR (300 MHz, acetone-d6) δ 5.36 (s, 1 H), 5.88 (s, 1 H),
6.11 (s, 1 H), 6.14 (s, 1 H), 6.15 (s, 1 H), 6.16 (s, 1 H), 7.31-
7.55 (m, 30 H); 13C NMR (63 MHz, acetone-d6) δ 72.9, 74.4,
74.7, 75.1, 127.0, 127.6, 128.0, 128.1, 128.2, 128.5, 128.6, 129.1,
129.2, 129.3, 133.0, 133.1, 133.4, 133.9, 138.9, 166.8, 166.9,
167.3, 168.3, 171.9; FABMS m/z 867 [M + 2Na]+ (14), 845 [M
+ Na]+ (100), 800 (9), 711 (9), 583 (9), 557 (36), 329 (25);
HRFABMS m/z 845.2208 (calcd for C48H38O13Na1 [M + Na]+
845.2210). Anal. Calcd for C48H38O13
Found: C, 70.22; H, 4.81.
: C, 70.07; H, 4.65.
Cyclo[(L-Ma n )5-D-Ma n ] (29). To a suspension of hexadep-
side 28 (411 mg, 0.5 mmol), triphenylphosphine (170 mg, 0.65
mmol), and NaClO4 (61 mg, 0.5 mmol) in toluene (15 mL) at
0 °C was added a solution of DEAD (101 µL, 0.65 mmol) in
0.5 mL of toluene by syringe. The mixture was maintained
for 15 min at 0 °C and then allowed to warm to room
temperature, and stirring was continued for a further 8 h. The
mixture was filtered and concentrated under reduced pressure,
and the crude product was purified by flash chromatography
(hexane/EtOAc (65:35) with 0.3% i-PrOH) to give 4 (60 mg,
15%) as a white solid: 1H NMR (300 MHz, CDCl3) δ 5.94 (s, 1
H), 6.04 (s, 1 H), 6.06 (s, 1 H), 6.10 (s, 1 H), 6.15 (s, 2 H), 7.17-
7.48 (m, 30 H); 13C NMR (63 MHz, CDCl3) δ 74.5, 75.3, 75.5,
75.8, 76.4, 77.0, 127.5, 127.9, 128.0, 128.2, 128.4, 129.0, 129.2,
129.5, 129.7, 129.8, 129.9, 130.0, 131.4, 132.2, 132.5, 133.0,
133.3, 133.5, 166.7, 166.9, 167.1, 167.8, 167.9, 168.3; FABMS
m/z 827 [M + Na]+ (100), 355 (8), 327 (17), 281 (33); HRFABMS
m/z 827.2074 (calcd for C48H36O12Na1 [M + Na]+ 827.2104).
Anal. Calcd for C48H36O12: C, 71.64; H, 4.51. Found: C, 71.51;
H, 4.66.
Cbz-[L-Va l-D-Ma n -D-Va l-L-La c]3-OH (31). Wang resin (0.5
g, 1.0 mmol/g loading level) was placed into a 25 mL reaction
vessel of a peptide synthesizer and washed with 10 mL of THF.
The first unit, OR-THP-L-lactic acid (7c) (261 mg, 1.5 mmol),
was coupled to the resin according to general procedure A with
DIC (235 µL, 1.5 mmol) and DMAP (6 mg, 0.05 mmol), followed
by THP deprotection according to general procedure C. The
resin was subsequently submitted to the following series of
(38) Kaiser, E.; Colescott, R. L.; Bossinger, C. D.; Cook, P. I. Anal.
Biochem. 1970, 34, 595-598.

Solid-Phase Synthesis of Depsides and Depsipeptides
J . Org. Chem., Vol. 64, No. 22, 1999 8075
24 h, the solvent was removed under reduced pressure. The
residue was dissolved in ether and filtered. The ether solution
was washed with 1 N HCl, NaHCO3, and water, dried (Na2-
SO4), and filtered. Purification of the crude product by RP-
HPLC (Nucleosil, MeCN/water (80:20) with 0.1% of TFA, 2.0
mL/min) gave 11 mg of 30 (tR ) 17 h 25 min) as a solid. (b)
Cycliza tion w ith HATU. 32 (99 mg, 0.074 mmol), HATU (56
mg, 0.147 mmol), and N,N-diisopropylethylamine (32 µL, 0.187
mmol) were dissolved in 75 mL of THF at 4 °C. The solution
was stirred at 4 °C for 1 h and then allowed to warm to room
temperature. After 24 h, the solvent was removed under
reduced pressure. Elaboration and purification as described
6.6, 1 H), 0.91 (d, J ) 6.6, 1 H), 0.97 (d, J ) 6.6, 1 H), 1.10 (d,
J ) 6.6, 1 H), 1.50 (d, J ) 6.9, 1 H), 2.13-2.36 (m, 6 H), 4.00
(dd, J 1 ) 9.7, J 2 ) 6.8, 1 H), 4.11 (dd, J 1 ) 9.6, J 2 ) 6.8, 1 H),
5.33 (q, J ) 6.8, 1 H), 6.12 (s, 1 H), 7.29-7.36 (m, 3 H), 7.40-
7.46 (m, 2 H), 7.92 (d, J ) 6.7, 1 H), 8.06 (d, J ) 6.7, 1 H); 13
C
NMR (63 MHz, CDCl3) δ 17.4, 19.2, 19.3, 19.4 (‚ 2), 28.5, 28.7,
59.6, 59.8, 70.7, 76.0, 127.4, 128.4, 128.6, 135.6, 170.2, 170.9
(‚ 2), 172.3; FABMS m/z 1251 [M + K]+ (36), 1235 [M + Na]+
(36), 1213 [M + H]+ (34). Anal. Calcd for C63H84N6O18: C,
62.36; H, 6.98; N, 6.93. Found: C, 62.18; H, 6.88; N, 7.01.
Ack n ow led gm en t. This work was supported by
grants from CICYT (PM98-0227) and XUGA (20910B96
and 20908B97).
above yielded 21 mg of 30: mp ) 201-203 °C (CHCl3); [R]D
)
-21.8 (CHCl3, c ) 0.8); IR (NaCl) νmax 3054, 2928, 2843, 1686,
1648, 1508, 1447, 1353, 1281, 1177, 1161, 1111, 1090, 823, 760,
1
720 cm-1; H NMR (300 MHz, CDCl3 + D2O) δ 0.85 (d, J )
J O981580+