Gaining diversity in solid-phase synthesis by modulation of cleavage conditions from hydroxymethyl-based supports. Application to lamellarin synthesis

Article abstract of DOI:10.1016/j.tet.2004.05.119

The application of a number of Lewis acids as a cleavage/deprotection method in the solid-phase synthesis of organic molecules can render several analogues, which, after purification, can be submitted for biological evaluation.

Full text of DOI:10.1016/j.tet.2004.05.119

Tetrahedron 60 (2004) 8669–8675
Gaining diversity in solid-phase synthesis by modulation of
cleavage conditions from hydroxymethyl-based supports.
Application to lamellarin synthesis
a,b
Pablo Cironi, Carmen Cuevas, Fernando Albericio
c
a,d,*
a,b,*
´
and Mercedes Alvarez
a
Barcelona Biomedical Research Institute, Barcelona Science Park, University of Barcelona, Josep Samitier 1, E-08028-Barcelona, Spain
Laboratory of Organic Chemistry, Faculty of Pharmacy, University of Barcelona, Avda. Joan XXIII s/n, E-08028 Barcelona, Spain
b
c
Pharma Mar, Avda Reyes Cat o´ licos 1, E-28770 Colmenar Viejo, Madrid, Spain
Department of Organic Chemistry, University of Barcelona, Mart ´ı i Franqu e´ s 1, E-08028-Barcelona, Spain
d
Received 9 December 2003; accepted 4 May 2004
Available online 10 August 2004
Abstract—The application of a number of Lewis acids as a cleavage/deprotection method in the solid-phase synthesis of organic molecules
can render several analogues, which, after purification, can be submitted for biological evaluation.
q 2004 Elsevier Ltd. All rights reserved.
1
. Introduction
distinct analogues of a natural product can be obtained by
using different cleavage conditions, and even by modulating
these conditions.
Although combinatorial chemistry has evolved greatly since
its early days in peptide chemistry, it is undoubtedly an
essential tool in modern programs of medicinal chemistry.
Combinatorial chemistry is currently being redirected
towards the rapid and rational preparation of small and
medium sized libraries of compounds based on a determined
1
For this study, lamellarins were chosen as substrates. These
hexacyclic alkaloids were first isolated from Lamellarina sp
1
2
in 1985 by Faulklner et al. Some lamellarins exhibit a
wide array of interesting and significant biological
activities, which include cell division inhibition, cyto-
toxicity, HIV-1 integrasa inhibition and immunomodula-
2
scaffold.
3
13
Library preparation can be carried out in solid-phase or in
solution, by mainly taking advantage of the solid-phase
mode through the use of supported reagents and/or
tion. While the first synthesis of lamellarins was carried
out in 1997, our group has recently reported the first solid-
1
4
phase synthesis of these hexacyclic alkaloids (Fig. 1).
4
supported purification probes. Library diversity is normally
introduced during the incorporation of the building blocks.
However, when the library is prepared in solid-phase,
diversity can also be introduced during cleavage. Thus,
5
there are resins specially designed for this purpose. These
resins usually release the final compounds by means of a
nucleophile. The oxime resin developed by Kaiser and
6
DeGrado and the ‘safety-catch’ resins developed by
7
8
Kenner and Ellman, and the aryl hydrazine linker of
9
10
Lowe are examples of it.
Another new concept
introduced by combinatorial chemistry is that any side-
product is valuable because after purification it can be
submitted for biological screening.
Figure 1. General formula of lamellarins.
1
1
2. Results and discussion
Here we describe an example of how the synthesis of the
0
1
Some lamellarins have phenol functions at C3 and C3 (R ,
3
R ¼H), therefore a plausible way to start solid-phase
Keywords: Combinatorial chemistry; Diversity; Libraries; Acidolytic
cleavage.
0
synthesis is by anchoring the phenol at C3 to a solid
*
Corresponding authors. Tel.: þ34-93-403-70-86; fax: þ34-93-403-71-26
support. Merrifield and Wang resins are convenient for this
process because they shown a good mechanical and
´
M.A.); e-mail addresses: albericio@pcb.ub.es; malvarez@pcb.ub.es
(
0040–4020/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2004.05.119

8670
P. Cironi et al. / Tetrahedron 60 (2004) 8669–8675
Figure 2. Incorporation and cleavage of the first building block.
chemical stability, highest loading and the lowest cost,
which make these resins the most suitable solid supports for
a multi-step solid-phase synthesis. These resins, which are
the process was repeated once), and to the hydroxy resins
via Mitsunobu conditions (PPh , DIEA, DEAD in THF at
3
5
25 8C for 3 h). Furthermore, Merrifield-Cl was also rejected
because the incorporation of the phenol required more
drastic conditions (double process at 50 8C for 24 h) and
because the reaction cannot be followed by any colorimetric
widely used in peptide synthesis for the preparation of acid
peptides, release the final compounds after an acid
treatment. While TFA (for the Wang resin), which is the
method of choice for peptide cleavage, is a convenient
reagent for combinatorial chemistry, its counterparts for
Merrifield resin, anhydrous HF or TFMSA, do not appear to
be appropriate. During recent years several methods based
on the use of Lewis acids have been used to cleave small
1
9
test or FT-IR.
Initially, 2-methoxy-5-iodophenol was recovered with good
yield and purity in all the cleavage cases, but in the SnCl4
cleavage the purity of the compound was not acceptable.
1
5
molecules from this type of resins. Thus, here we have
checked some of these methods in the synthesis of
lamellarins to obtain different analogues. Resins were
Thus, we discarded this reagent. When the ZnBr cleavage
2
is carried out into the presence of acetyl bromide the
corresponding acetyl derivative is obtained with good yield
and purity. Thus seems, the possibility of using another acyl
bromide to increase the diversity (Fig. 2).
1
6
17
cleaved with a Lewis acid such as AlCl , SnCl4,
3
1
8
ZnBr2 or with carboxylic acids such as TFA in DCM.
2
3
Three different polystyrene resins, chloro and hydroxy
Merrifield and Wang resins were tested. 2-Methoxy-5-
iodophenol was incorporated to Merrifield-Cl resin by the
Lamellarin U (R , R ¼H) was taken as a model and its
structure was built up in the two hydroxymethyl resins. The
hydroxyl group of the OH in position 3 was protected as
2
0
cesium salt method (CsCO , KI, in DMF at 50 8C for 24 h,
3
isopropyl ether, which can be cleaved by acids, if it is
Figure 3. Solid-phase synthesis of lamellarins.

P. Cironi et al. / Tetrahedron 60 (2004) 8669–8675
8671
desired. Other MeO groups were already introduced into the
building blocks. For the Wang resin, the scheme outlined in
Figure 3 was followed, starting with a functionalization of
of organic molecules can be used as an important diversity
point rendering several analogues, which, after purification,
can be submitted for biological evaluation.
0
cations, to that followed for the solid-phase preparation
.86 mmol/g. The process is similar, with minor modifi-
1
4
using Merrifield-OH.
3. Experimental
Cleavages were performed with the reagents discussed
above. As expected, cleavage with ZnBr (4 equiv.) in dry
3.1. General procedure
2
DCM in the presence of AcBr (overnight, 10 equiv.) gave
the acetyl derivatives corresponding to 3,3 -di-O-acetyl-
Hydroxymethyl poly(styrene-co-1% divinylbenzene) resin
(Merrifield-OH, 100–200 mesh material, nominal loading:
0.68 mmol/g); chloromethyl poly(styrene-co-1% divinyl-
benzene)resin (Merrifield-Cl resin, 100–200 mesh material,
nominal loading: 0.61 mmol/g), 4-hydroxymethylphenoxy-
methyl poly(styrene-co-1% divinylbenzene) resin (Wang
resin, 100–200 mesh material, nominal loading:
0.86 mmol/g) were from NovaBiochem (L a¨ ufelfingen,
Switzerland).
0
lamellarin U. Cleavage with AlCl in dry DCM (10 equiv.)
3
produced mainly lamellarin U, accompanied by lamellarin
L (free hydroxy at C11) and 12-O-demethoxylamellarin U
(
free hydroxy at C12). Although the main product was
always Lamellarin U, the proportion of other derivatives can
be increased by extending cleavage times (3–6 h). With a
shorter cleavage time, the compound with an isopropoxy
group at C3 was also obtained. This derivative (3-O-
isopropyllamellarin U) was the main product when the
cleavage was performed with TFA on Wang resin. In this
cleavage, an unexpected derivative containing a chlorine
Tetrahydrofuran (THF) was freshly distilled from sodium/
benzophenone. Dichloromethane was distilled from calcium
hydride prior to use. DMF (99.99% anhydrous) was
purchased from SDS and used as received.
0
0
atom at C2 (2 -chloro-3-O-isopropyllamellarin U) was also
2
1
obtained. The purity of compounds obtained with the
Merrifield resin is greater than when the Wang resin is used.
Therefore, although cleavages carried out with Lewis acids
can also be performed on Wang resin, the results obtained
with Merrifield resins were better (Fig. 4).
1
H NMR and heterocorrelations (600 MHz) spectra were
1
3
recorded on Bruker spectrometer, C NMR (100 MHz)
spectra were recorded on a Varian Mercury 400 spec-
trometer. Chemical shift (d) are expressed in parts per
million downfield from CDCl as internal standard.
3
In conclusion, the application of a number of Lewis acids as
a cleavage/deprotection method in the solid-phase synthesis
Analytical HPLC was carried out on a Watersw 2695
Figure 4. Lewis acid cleavage of solid-phase supported lamellarins.

8672
P. Cironi et al. / Tetrahedron 60 (2004) 8669–8675
Separations Module instrument, Waterw 996 Photodiode
Array Detector. UV detection from 210 to 500 nm and
linear gradients of CH CN into H O were run at 1.0 ml/min
or 1C (100 mg, 0.5 mmol/g theoretical loading) was swelled
with dry DCM for 30 min, SnCl (10 equiv.) was added and
the reaction mixture was shaken under Ar overnight. After
this time the resin was filtered off and washed with DCM
4
3
2
flow rate from: 70:30 to 0:100 over 15 min, with a
Symmetryw C-18 5.0 mm 4.6 mm£150 mm column.
w
(5£5 ml). The filtrates were washed with H O (6£15 ml),
2
w
Preparative HPLC was carried out on a Waters 600
Multisolvent Delivery System instrument, Waters 2700
dried (MgSO anhydrous), and concentrated under reduced
4
pressure to give 5-iodo-2-methoxyphenol (12 mg of crude
1
w
Sample Manager and a Water 2487 Dual Absorbance UV
Detector; detection at 277.0 and 315.0 nm. Linear gradients
of CH CN into H O were run at 25.0 ml/min flow rate from:
material, 70% of purity by HPLC). H NMR (400 MHz,
CDCl ) d 7.23 (d, J¼2.2 Hz, 1H, H-6), 7.15 (dd, J¼8.4,
13
3
2.2 Hz, 1H, H-4), 6.59 (d, J¼8.4 Hz, H-3), 5.60 (bs, 1H,
3
2
w
7
3
0:30 to 40:60 over 60 min, with a Symmetry C-8 5.0 mm
0 mm£100 mm column.
OH), 3.87 (s, 3H, OCH ); C NMR (75 MHz, CDCl ) d
3
3
146.6 (s), 146.5 (s), 129.0 (d, C-3), 123.4(d, C-4), 112.4 (d,
C-6), 83.0 (s, C-5), 56.0 (q, OCH3).
þ
APCI -MS analysis of crude material and final compounds
were performed in a Mass spectrometer VG Platform II,
Micromass.
3.4. Typical procedure for the cleavage with anhydrous
ZnBr2
þ
FAB HR-MS were performed on a Autospec FABþby
3.4.1. 5-Iodo-2-methoxyphenol (3). The resin 1A or 1B or
1C (100 mg, 0.5 mmol/g theoretical loading) was swelled
for 30 min with dry DCM 1 ml). After this time anhydrous
Unidade de Espectrometr ´ı a de Masas (Universidad de
Santiago de Compostela).
ZnBr (4 equiv.) were added and the reaction mixture was
2
3
.2. Typical procedure for iodophenol anchorage to the
then shaken under Ar for 4 h at room temperature. The resin
was filtered off and washed with DCM (5£5 ml). The
hydroxy type resins (hydroxy Merrifield and Wang
resins)
filtrates were washed with aq. 5% NaHCO (5£15 ml), 2 M
3
HCl (3£15) and brine (3£15 ml). The organic solution was
3
.2.1. 5-Iodo-2-methoxyphenoxy-resin (1b, 1c). The
dried (MgSO anhydrous), filtered and concentrated under
4
2
2
procedure described by Spatola et al. for the incorporation
of Tyr trough a Mitsunobu reaction has been repeated here
for the incorporation of 2-methoxy-5-iodophenol to
Merrifield-OH and Wang resins. Merrifield-OH resin
reduced pressure to give 5-iodo-2-methoxyphenol (10.5 mg,
84%); CIMS m/z (relative intensity): 250 ([M ],100).
þ
Spectroscopic data were the same as in the example above.
(
1.0 g of 100–200 mesh material, 0.68 mmol/g loading)
3.4.2. 5-Iodo-2-methoxyphenol acetate (2). The resin 1A
or 1B or 1C (100 mg, 0.5 mmol/g theoretical loading) was
swelled for 30 min with dry DCM (1 ml). After this time
anhydrous ZnBr2 (4 equiv.) and AcBr (10 equiv.) were
added and the reaction mixture was then shaken under Ar
overnight at room temperature. The resin was filtered off
and washed with DCM (5£5 ml). The filtrates were washed
was washed with DCM (1£10 ml) and THF (1£10 ml). The
dried resin was then treated with THF (15 ml), 2-methoxy-
5
-iodophenol (510 mg, 2.04 mmol, 3 equiv.), and tri-
phenylphosphine (535 mg, 2.04 mmol, 3 equiv.), diiso-
propylethylamine (1.05 ml, 6.12 mmol, 9 equiv.) and the
resulting mixture was stirred and cooled at 0 8C. Diethyl
azodicarboxylate (320 ml, 2.04 mmol, 3 equiv.) was then
added dropwise and the resulting mixture was stirred 3 h at
room temperature. The solvent was then removed. The resin
was washed with DMF, DCM, methanol and diethyl ether
with aq. 5% NaHCO (5£15 ml), 2 M HCl (3£15) and brine
3
(3£15 ml). The organic solution was dried (MgSO
4
anhydrous), filtered and concentrated under reduced
pressure to give 5-iodo-2-methoxyphenol acetate (13 mg,
1
(5£15 ml each) and dried under reduced pressure. IR (KBr,
cm ), in the IR spectrum it is possible to see the absence of
89%). H NMR (200 MHz, CDCl ) d 7.49 (dd, J¼8.8,
3
2
1
2.0 Hz, 1H, H-4), 7.33 (d, J¼2.0 Hz, 1H, H-6), 6.72 (d,
J¼8.8 Hz, H-3), 3.81 (bs, 3H, OCH ), 2.30 (s, 3H, COCH );
2
1
at 3450 and 3580 cm proper of hydroxyl groups of the
1
3
3
3
13
resin; C NMR-MAS (125 MHz) d 149.8, 149.2, 130.1
C-3), 122.7 (C-4), 113.7 (C-6), 82.2 (C-5), 55.9 (OCH3).
C NMR (50 MHz, CDCl ) d 168.5 (s, CvO), 151.3 (s,
3
(
C-2), 140.4 (s, C-1), 135.6 (d, C-4), 131.5 (d, C-6), 114.2 (d,
C-3), 81.3 (s, C-5), 56.0 (q, OCH ), 20.6 (q, COCH ).
3
3
3
.2.2. 5-Iodo-2-methoxyphenoxy-resin (1a). Merrifield-Cl
0
resin (1.0 g of 100–200 mesh material, 0.61 mmol/g
loading) was washed with DCM (1£10 ml). The dried
resin was then swelled in DMF (10 ml) for 30 min, then
cesium 2-methoxy-5-iodo-phenolate (1.38 g, 3.6 mmol,
6
0
stirred at 50 8C for 24 h. It was then filtered and washed with
DMF, DCM, MeOH and diethyl ether (5£15 ml each) and
dried under reduced pressure. Spectroscopic data were
similar as described in the previous example.
3.4.3. 3,3 -Di-O-acetyllamellarin U. The resin 4B (180 mg,
0.48 mmol/g theoretical loading) was swelled for 30 min
with dry DCM (1 ml). After this time anhydrous ZnBr2
(225 mg, 4 equiv.) and AcBr (111 mg, 10 equiv.) were
added and the reaction mixture was then shaken under Ar
overnight at 25 8C. The resin was filtered off and washed
with DCM (5£5 ml). The filtrates were washed with aq. 5%
equiv.) was added in DMF (dry), finally KI (20 mg,
12 mmol, 0.2 eq.) was added. The resulting mixture was
NaHCO (5£15 ml), 2 M HCl (3£15) and brine (3£15 ml).
3
The organic solution was dried (MgSO anhydrous),
4
filtered and concentrated under reduced pressure. The
crude was analyzed by HPLC-MS [C18-APCI using
þ
H O (5 mM AcNH ): acetonitrile gradient 30–100%
3.3. Typical procedure for the cleavage with anhydrous
SnCl4
2
4
acetonitrile in 15 min]: retention time 9.73 min, molecular
þ
weight 599.58; found 600.6 [MþH] . MSMS (Q-TOF)
.3.1. 5-Iodo-2-methoxyphenol (3).23 The resin 1A or 1B
calcd 599.18; found 600.20 [MþH] , 557, 22
þ
3

P. Cironi et al. / Tetrahedron 60 (2004) 8669–8675
8673
þ
crude product was purified by HPLC and the 3,3 -di-O-
þ
13
23
[
(MþH) 2C H O], 515.29 [(MþH) 22£C H O]. The
5.7 Hz, 2H, H-9); C NMR (150 MHz, CDCl3) d 151.4
(C-3 ), 149.3 (C-11), 147.9 (C-12), 146.8 (C-4 ), 145.8
2
2
2 2
0
acetyllamellarin U (4 mg, 8.5% overall yield) was obtained.
0
(C-4a), 143.6 (C-2), 136.3 (C-13b), 129.2 (C-1 ), 128.6
0
0
(C-14a), 127.1 (C-9a), 123.4 (C-6 ), 120.5 (C-13a), 117.4
1
0
0
H NMR (600 MHz, CDCl ) d 7.30 (dd, J¼8.2, 2 Hz,
3
0
0
H, H-5 ), 7.06 (s, 1H, H-4), 6.74 (s, 1H, H-10), 6.72 (s, 1H,
0
(C-14b),108.8 (C-13), 104.1 (C-1), 103.3 (C-4), 56.2
1
1
H, H-6 ), 7.22 (d, J¼2 Hz, 1H, H-2 ), 7.12 (d, J¼8.2 Hz,
(C-2 ), 114.9 (C-14), 111.1 (C-5 ), 110.9 (C-10), 110.7
0
H-1), 6.62 (s, 1H, H-13), 4.95 (m, 1H, H-8), 4.64 (m, 1H,
0
(C -OCH ), 55.8 (C -OCH ), 55.5 (C -OCH ), 55.0
4
11
2
3
3
3
0
H-8), 3.87 (s, 6H, C -OCH and C -OCH ), 3.44 (s, 3H,
1
2
4
12
(C -OCH ), 42.8 (C-8), 28,6 (C-9). (þ)-HRMS m/z
3
3
3
2
11
þ
C -OCH ), 3.40 (s, 3H, C -OCH ), 3.15 (m, 1H, H-9), 3.05
3
516.1683 (calcd for C H NO [MþH] 516.1166, D
3
3
29 26
8
(
C OOCCH ); C NMR (150 MHz, CDCl ) d 168.8
m, 1H, H-9), 2.29 (s, 3H, C OOCCH ), 2.27 (s, 3H,
13
24.8 ppm).
3
0
3
24
3
3
0
C OOCCH ), 168.3 (C OOCCH ), 151.2 (C-4 ), 149.0
3
3
0
C-12), 147.5 (C-11), 147.4 (C-2), 144.8 (C-3), 140.7 (C-3 ),
1
(
(
3.5.4. Lamellarin L. H NMR (600 MHz, CDCl ) d 7.11 (d,
3
3
3
0
0
0
J¼1.9 Hz, 1H, H-2 ), 7.02 (d, J¼8.3 Hz, 1H, H-5 ), 6.98 (dd,
0
27.4 (C-14a), 126.4 (C-9a), 125.0 (C-2 ), 119.8 (C-13a),
0
0
H-10), 6.68 (s, 1H, H-1), 6.67 (s, 1H, H-13), 5.70 (bs, 2H),
1
1
1
1
5
38.7 (C-4a), 136.1 (C-13b), 129.5 (C-6 ), 127.7 (C-1 ),
J¼8.3, 1.9 Hz, 1H, H-6 ), 6.93 (s, 1H, H-4), 6.79 (s, 1H,
0
16.1 (C-14b), 114.1 (C-14), 112.5 (C-5 ), 111.8 (C-4),
0
10.9 (C-10), 108.5 (C-13), 105.4 (C-1), 56.0 (C -OCH ),
5.60 (bs, 1H), 4.78 (m, 1H, H-8), 4.70 (m, 1H, H-8), 3.96 (s,
12
0
0
3H, C -OCH ), 3.50 (s, 3H, C -OCH ), 3.41 (s, 3H, C -
4
4
2
3
3
3
1
2
2
11
13
23
6.0 (C -OCH ), 55.6 (C -OCH ), 55.2 (C -OCH ), 42.5
3
OCH ), 3.01 (m, 2H, H-9); C NMR (150 MHz, CDCl )
3 3
3
3
0
3
3
0
145.1 (C-12), 143.2 (C-2), 135.4 (C-13b), 128.3 (C-1 ),
0
(
C-8), 28.7 (C-9), 20.0 (C OOCCH ), 20.0 (C OOCCH ).
3
d 146.4 (C-3), 146.3 (C-3 ), 146.2 (C-4 ), 145.7 (C-11),
3
þ
0
128.2 (C-14a), 127.4 (C-9a), 122.9 (C-6 ), 119.8 (C-13a),
(
5
þ)-HRMS m/z 599.1789 (calcd for C H NO [M]
3
3
29
10
0
17.3 (C-2 ), 114.0 (C-10), 111.9 (C-5 ), 108.4 (C-13), 104.1
99.1791, D þ0.4 ppm).
.5. Typical procedure for AlCl cleavage
0
0
1
0
4
2
3
(C-1), 103.5 (C-4), 56.2 (C -OCH ), 55.5 (C -OCH ), 55.1
3 3
3
1
2
(
C -OCH ), 42.2 (C-8), 28.2 (C-9). (þ)-HRMS m/z
3
þ
3
1
.5.1. 5-Iodo-2-methoxyphenol (3). The resin 1A or 1B or
C (100 mg, 0.5 mmol/g theoretical loading) was swelled
502.1503 (calcd for C H NO [MþH] 502.1502, D
2
8
24
8
20.1 ppm).
with dry DCM for 30 min, AlCl (10 equiv.) was added and
3
the reaction mixture was shaken under Ar for 3 h. After this
time the resin was filtered off and washed with DCM
1
3.5.5. Demethyllamellarin U. H NMR (600 MHz, CDCl )
3
0
d 7.04 (d, J¼2.0 Hz, 1H, H-2 ), 7.00 (d, J¼8.0 Hz, 1H,
0
0
6.74 (s, 1H, H-13), 6.73 (s, 1H, H-10), 6.57 (s, 1H, H-1),
(
5£5 ml). The filtrates were washed with a sat. aq. solution
H-5 ), 6.94 (dd, J¼8.0, 2.0 Hz, 1H, H-6 ), 6.92 (s, 1H, H-4),
of NH Cl (1£15 ml) and H O (6£15 ml), dried (MgSO
4
2
4
anhydrous), and concentrated under reduced pressure to
give 5-iodo-2-methoxyphenol (11 mg, 88%). Spectroscopic
data were the same as in the example above.
5.68 (s, OH), 5.65 (s, OH), 5.36 (s, OH), 4.72–4.80 (m, 2H,
4
0
H-8), 3.97 (s, 3H, C -OCH ), 3.89 (s, 3H, C -OCH ), 3.49
11
3
3
2
13
(s, 3H, C -OCH ), 3.07 (m, 2H, H-9); C NMR (150 MHz,
3
2
3
0
(C-4a), 144.9 (C-3 ), 143.8 (C-12), 142.9 (C-2), 135.2
CDCl3) d 146.3 (C-11), 146.2 (C-4 ) 146.2 (C-3), 145.2
0
(C-13b), 128.1 (C-14a), 126.1 (C-9a), 122.8 (C-6 ), 120.6
3.5.2. Deprotected lamellarins. The resin 4B (220 mg,
0.44 mmol/g loading) was swelled in dry DCM (3 ml) for
30 min and AlCl3 (220 mg, 1.65 mmol, 15 equiv.) was
0
(C-13a), 117.1 (C-2 ), 115.7 (C-14), 113.1 (C-14b), 112.1
0
(C-13), 111.2 (C-5 ), 110.3 (C-10), 104.1 (C-1), 103.2 (C-4),
0
55.9 (C -OCH ), 55.7 (C -OCH ), 55.3 (C -OCH ), 42.3
added. The reaction mixture was stirred in a vibromatic
shaker at 25 8C for 6 h. It was then filtered and washed with
DCM, AcOEt and MeOH (5£10 ml, each), the organic
solvent was evaporated. The residue was taken with a sat.
0
4
11
2
3
3
3
(C-8), 28.8 (C-9). (þ)-HRMS m/z 502.1508 (calcd for
þ
C H NO [MþH] 502.1502, D 21.1 ppm).
2
8
24
8
aq. solution of NH Cl and extracted with ethyl acetate
4
(
fraction was dried and evaporated. The HPLC/MS [C18-
5£20 ml), then washed with brine (1£30 ml). The organic
þ
0–100% acetonitrile in 15 min] shown three lamellarin
3.6. Typical procedure for TFA cleavage of Wang resin
APCI using H O (5 mM AcNH ): acetonitrile gradient
2
3.6.1. 5-Iodo-2-methoxyphenol (3). A solution of TFA in
DCM (1:1, 2 ml) was added to the Wang conjugate phenol
1C resin (56 mg, 0.71 mmol/g theoretical loading) and the
mixture was shaken for 2 h at room temperature. The
resulting suspension was filtered of, the same acid solution
was added and the mixture was shaken for 2 h. This process
was repeated two times. Finally the resin was washed
several times with DCM. The filtrates were washed with
H O (3£25 ml), dried (MgSO anhydrous), and concen-
4
3
derivatives: lamellarin U, retention time 8.0 min, calcd
þ
retention time 6.9 min, calcd 501.14; found 502.15
5
15.16; found 516.19 [MþH] ; demethyllamellarin U,
þ
[
5
MþH] , and lamellarin L, retention time 6.6 min, calcd
þ
01.14; found 502.15 [MþH] . The crude product was
purified by HPLC. Lamellarin U (4.5 mg, 9.2%), demethyl-
lamellarin L (1 mg, 2.0%), and lamellarin L (1.5 mg, 3.1%)
were obtained.
2
4
trated under reduced pressure to give a very clean 5-iodo-2-
methoxyphenol (8 mg, 81%). Spectroscopic data were the
same as in the example above.
1
3
.5.3. Lamellarin U. H NMR (600 MHz, CDCl ) d 7.11 (d,
3
0
0
J¼1.9 Hz, 1H, H-2 ), 7.02 (d, J¼8.2 Hz, 1H, H-5 ), 6.99 (dd,
0
H-10), 6.70 (s, 1H, H-13), 6.69 (s, 1H, H-1), 5.69 (s, 1H, C3-
J¼8.2, 1.9 Hz, 1H, H-6 ), 6.94 (s, 1H, H-4), 6.73 (s, 1H,
3.6.2. Hydroxy protected lamellarins. Following the
general procedure of cleavage with TFA described above,
from 4C (300 mg) a reaction crude was obtained. The
0
4
OH), 5.66 (s, 1H, C3 -OH), 4.80 (m, 1H, H-8), 4.72 (m, 1H,
11
0
H-8), 3.95 (s, 3H, C -OCH ), 3.87 (s, 3H, C -OCH ), 3.51
þ
HPLC/MS [C18-APCI using H O (5 mM AcNH ):
4
3
3
2
2
12
(
s, 3H, C -OCH ), 3.37 (s, 3H, C -OCH ); 3.08 (dd, J¼6.6,
acetonitrile gradient 30–100% acetonitrile in 15 min]
3
3

8674
P. Cironi et al. / Tetrahedron 60 (2004) 8669–8675
0
isopropyllamellarin U retention time 11.07 min, calcd
shown two different lamellarins derivatives: 2 -chloro-3-O
2002, 6, 287–288. (d) Lebl, M. In Integrated Drug Discovery
Technologies; Mei, H.-Y., Czarnik, A. W., Eds.; Marcel
Dekker: New York, NY, 2002; pp 395–405.
3
5
þ
37
5
91.17; found 592.23 [ Cl MþH] , 594.23 [ Cl
þ
MþH] , 3-O-isopropyllamellarin
U
retention time
2. (a) Goodnow, R. Drugs Future 2002, 27, 1165–1180.
(b) Sauer, W. H. B.; Schwarz, M. K. Chimia 2003, 57,
276–283.
þ
1
1.3 min, calcd 557.20; found 558.30 [MþH] . The crude
0
product was purified by HPLC. 2 -Chloro-3-O-isopropyl-
lamellarin U (2 mg, 2% overall yield), and 3-O-isopropyl-
lamellarin U (8.5 mg, 9%, overall yield) were obtained.
3. Solid-Phase Synthesis. A Practical Guide; Kates, S. A.,
Albericio, F., Eds.; Marcel Dekker: New York, USA, 2000.
4
. Storer, R. I.; Takemoto, T.; Jackson, P. S.; Ley, S. V. Angew.
Chem., Int. Ed. 2003, 42, 2521–2525.
1
3
.6.3. 3-O-Isopropyllamellarin U. H NMR (600 MHz,
0
CDCl ) d 7.11 (d, J¼2.0 Hz, 1H, H-2 ), 7.01 (d, J¼8.3 Hz,
5. For reviews on handles/linkers, see: (a) Blackburn, C.;
Albericio, F.; Kates, S. A. Drugs Future 1997, 22,
1007–1025. (b) Guillier, F.; Orain, D.; Bradley, M. Chem.
Rev. 2000, 100, 2091–2157.
3
0
H-4), 6.73 (s, 1H, H-10), 6.72 (s, 1H, H-13), 6.71 (s, 1H,
0
1
H, H-5 ), 6.99 (dd, J¼8.3, 2.0 Hz, 1H, H-6 ), 6.90 (s, 1H,
H-1), 5.68 (bs, 1H, OH), 4.83 (m, 1H, H-8), 4.74 (m, 1H,
3
0
H-8), 4.52 (hept, 1H, C -OCH(CH ) ), 3.94 (s, 3H, C -
4
6. DeGrado, W. F.; Kaiser, E. T. J. Org. Chem. 1980, 45,
1295–1300.
3
2
1
1
2
OCH ), 3.87 (s, 3H, C -OCH ), 3.45 (s, 3H, C -OCH ),
3
3.37 (s, 3H, C -OCH ), 3.09 (m, 2H, H-9), 1.37 (d, 6H, C -
1
OCH(CH ) ); C NMR (150 MHz, CDCl3) d 148.8
3
3
1
2
3
7. Kenner, G. W.; McDermott, J. R.; Sheppard, R. C. Chem.
Commun. 1971, 636–637.
3
3
23
3
2
(
(
(
(
(
C-11), 147.4 (C-12), 147.1 (C-3), 146.4 (C-2), 146.3
C-4 ), 146.1 (C-3 ), 135.8 (C-13b), 128.6 (C-1 ), 128.1
8. Backes, B. J.; Ellman, J. A. J. Am. Chem. Soc. 1994, 116,
11171–11172.
0
C-14a), 126.5 (C-9a), 122.9 (C-6 ), 120.1 (C-13a), 117.3
0
0
0
C-2 ), 114.7 (C-14) 111.2 (C-5 ),110.9 (C-10), 110.3
9. Millington, C. R.; Quarrell, R.; Lowe, G. Tetrahedron Lett.
1998, 39, 7201–7204.
0
0
3
C-14b), 108.8 (C-13), 105.1 (C-1), 103.5 (C-4), 71.4 (C -
4
10. The ‘safety-catch’ resin requires an activation before cleavage.
11. For the first precedent described in the literature regarding the
simultaneous synthesis of a few related compounds, which are
purified before being submitted to evaluation, see Tjoeng,
F. S.; Towery, D. S.; Bulock, J. W.; Whipple, D. E.; Fok, K. F.;
Williams, M. H.; Zupec, M. E.; Adams, S. P. Int. J. Peptide
Prot. Res. 1990, 35, 141–146.
0
11
OCH(CH ) ), 56.2 (C -OCH ), 55.8 (C -OCH ), 55.4
3
3
2
3
2
12
(
C -OCH ), 55.0 (C -OCH ), 42.3 (C-8), 28.6 (C-9), 21.7
3 3
3
(C -OCH(CH ) ). (þ)-HRMS m/z 557.2067 (calcd for
C H NO [M] 557.2050, D 23.0 ppm).
3
2
þ
3
2
31
8
0
The presence of the unexpected 2 -chloro-3-O-isopropyl-
1
lamellarin U was confirmed by H NMR (600 MHz, CDCl )
3
12. Andersen, R. J.; Faulkner, D. J.; Cun-heng, H.; Duyne, G. D.;
Clardy, J. J. Am. Chem. Soc. 1985, 107, 5492–5495.
13. (a) Lindquist, N.; Fenical, W. J. Org. Chem. 1988, 53,
4570–4574. (b) Quesada, A. R.; Gr a´ valos, M. D. G.; Puentes,
J. L. F. Br. J. Cancer 1996, 74, 677–682. (c) Urban, S.; Capon,
R. J. Aust. J. Chem. 1996, 49, 711–713. (d) Reddy, M. V. R.;
Faulkner, D. J.; Venkateswarlu, Y.; Rao, M. R. Tetrahedron
1997, 53, 3457–3466. (e) Davis, R. A.; Carroll, A. R.; Pierens,
G. K.; Quinn, R. J. J. Nat. Prod. 1999, 62, 419–424. (f) Reddy,
M. V. R.; Rao, M. R.; Rhodes, D.; Hansen, M. S. T.; Rubins,
K.; Bushman, F. D.; Venkateswarlu, Y.; Faulkner, D. J. J. Med.
Chem. 1999, 42, 1901–1907. (g) Boger, D.; Soenen, D. R.;
Boyce, C. W.; Hendrick, C. W.; Jin, Q. J. Org. Chem. 2000,
0
.75 (s, 1H, H-10), 6.62 (s, 1H, H-13), 6.56 (s, 1H, H-1),
0
d 7.11 (s, 1H, H-6 ), 7.07 (s, 1H, H-3 ) 6.90 (s, 1H, H-4),
6
5
4
3
.61 (bs, 1H, OH), 4.93 (m, 1H, H-8), 4.66 (m, 1H, H-8),
3
0
.51 (hept, 1H, C -OCH(CH ) ), 3.96 (s, 3H, C -OCH ),
4
3
2
3
1
1
2
.87 (s, 3H, C -OCH ), 3.48 (s, 3H, C -OCH ), 3.42 (s, 3H,
3
3
1
2
3
C -OCH ), 3.09 (m, 2H, H-9) 1.38 (d, 6H, C -
3
OCH(CH ) ); C NMR (150 MHz, CDCl ) d 148.9
2
1
3
23
3
3
0
(
(
(
(
(
5
C-11), 148.4 (C-5 ), 147.1 (C-3), 147.4 (C-12), 146.9
C-4 ), 146.5 (C-2), 145,8 (C-4a), 135.9 (C-13b), 128.3
C-14a), 126.6 (C-9a), 126.2 (C-1 ), 119.9 (C-13a), 118.6
0
0
0
24
0
25
C-3 ) 112.0 (C-6 ), 110.9 (C-10), 109.9 (C-14b), 108.2
3
C-13), 104.7 (C-1), 103.3 (C-4), 71.3 (C -OCH(CH ) ,
3
2
0
6.4 (C -OCH ), 55.7 (C -OCH ), 55.4 (C -OCH ), 55.0
4
11
2
3
3
3
65, 2479–2483.
14. Cironi, P.; Manzanares, I.; Albericio, F.; A´ lvarez, M. Org.
Lett. 2003, 5, 2959–2962.
12
3
(
C -OCH ), 45.4 (C-8), 28.6 (C-9), 21.6 (C -OCH(CH ) ).
3
3 2
þ
(
5
þ)-HRMS m/z 592.1751 (calcd for C H NO Cl [MþH]
3
2
31
8
92.1738, D 22.2 ppm.
15. Forns, P.; Albericio, F. Electronic Encyclopedia of Reagents
for Organic Synthesis; Paquette, L. A., Ed.; Wiley: Chichester,
UK, 2003, www.mrw.interscience.wiley.com/eros/.
1
6. Mata, E. G. Tetrahedron Lett. 1997, 38, 6335–6338.
7. Stones, D.; Miller, D. J.; Beaton, M. W.; Rutherford, T. J.;
Gani, D. Tetrahedron Lett. 1998, 39, 4875–4878.
Acknowledgements
1
This work was partially supported by CICYT (PBQU2000-
235) and Pharma Mar (Madrid). P.C. thanks MEC (Spain)
for a pre-doctoral fellowship.
1
8. Li, W. R.; Yo, Y. C. Tetrahedron Lett. 2000, 41, 6619–6622.
9. The quantitative disappearance of the hydroxyl groups in both
the Merrifield-OH and the Wang resins can be followed by the
Qui n˜ o a´ test (Kuisle, O.; Qui n˜ o a´ , E.; Riguera, R. Tetrahedron
0
1
1999, 55, 14807–14812) and by FT-IR, making unnecessary
any further blocking step.
References and notes
2
0. Banwell, M. G.; Flynn, B. L.; Stewart, S. G. J. Org. Chem.
1998, 63, 9139–9144.
1
. (a) Lam, K. S.; Salmon, S. E.; Hersh, E. M.; Hruby, V. J.;
Kazmierski, W. M.; Knapp, R. J.; Cuervo, J. H. Nature 1991,
54, 82–84. (b) Houghten, R. A.; Pinilla, C.; Blondelle, S. E.;
Appel, J. R.; Dooley, C. T.; Cuervo, J. H. Nature 1991, 354,
4–86. (c) Meldal, M.; Pirrung, M. Curr. Opin. Chem. Biol.
21. We believe that such unexpected chlorination could have been
achieved due to the traces of chlorine in the DCM, which
under strong acid medium as the TFA and the presence of
highly electron-rich aromatic rings facilitate this low yield
3
8

P. Cironi et al. / Tetrahedron 60 (2004) 8669–8675
8675
secondary reaction. To the best of our knowledge, there are not
precedents in the literature of this side-reaction.
2. Romanovskis, P.; Spatola, A. F. J. Pept. Res. 1998, 52,
iodophenol synthesized by Feldman, K. S. J. Org. Chem. 1997,
62, 4983–4990.
1
2–3
2
2
24. 2D JC-H
,
JC-H (observing 5 and 8 Hz JC–H couplings) and
356–374.
3. Spectroscopic data was compared with the 2-methoxy-5-
NOESY (mixing time 600 ms) correlations were performed.
25. Assignment may be reversed.