Synthesis of a dysidiolide-inspired compound library and discovery of acetylcholinesterase inhibitors based on protein structure similarity clustering (PSSC)

Article abstract of DOI:10.1016/j.tet.2008.02.106

Biologically relevant compound collections are a major prerequisite for efficient protein ligand development and ultimately for drug discovery. We herein describe the development of a compound collection inspired by the decalin core motif of two natural products, dysidiolide 1 and sulfiricin 2, both inhibitors of the Cdc25A phosphatase. Several keto-functionalized decalinols were synthesized in solution, immobilized on Merrifield resin equipped with a dihydropyranyl linker, and then subjected to aldol condensation reactions with different aldehydes leading to exocyclic E-configured olefins. Further diversity-increasing transformations on the solid support included Sonogashira, Suzuki, and Heck reactions, Cu-catalyzed conjugate addition and Grignard reactions, alkylation reactions in the α-position to a ketone, Wittig reactions, and reductive animations. In total, 483 compounds were synthesized. Cdc25A and AChE exhibit structural similarity in their ligand-sensing cores and were thus grouped into a protein structure similarity cluster (PSSC). A screen for AChE inhibition of a subset of 162 compounds yielded three micromolar inhibitors of AChE with IC₅₀ values <20 μM.

Full text of DOI:10.1016/j.tet.2008.02.106

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 4792e4802
www.elsevier.com/locate/tet
Synthesis of a dysidiolide-inspired compound library and discovery
of acetylcholinesterase inhibitors based on protein structure
similarity clustering (PSSC)
Michael Scheck a,b, Marcus A. Koch a,b, Herbert Waldmann a,b,
*
a Department of Chemical Biology, Max-Planck-Institut fu¨r molekulare Physiologie, Otto-Hahn-Straße 11, D-44227 Dortmund, Germany
b TU Dortmund, Fachbereich 3, Chemische Biologie, Germany
Received 30 August 2007; received in revised form 13 November 2007; accepted 29 February 2008
Available online 18 March 2008
Abstract
Biologically relevant compound collections are a major prerequisite for efficient protein ligand development and ultimately for drug discov-
ery. We herein describe the development of a compound collection inspired by the decalin core motif of two natural products, dysidiolide 1 and
sulfiricin 2, both inhibitors of the Cdc25A phosphatase. Several keto-functionalized decalinols were synthesized in solution, immobilized on
Merrifield resin equipped with a dihydropyranyl linker, and then subjected to aldol condensation reactions with different aldehydes leading
to exocyclic E-configured olefins. Further diversity-increasing transformations on the solid support included Sonogashira, Suzuki, and Heck
reactions, Cu-catalyzed conjugate addition and Grignard reactions, alkylation reactions in the a-position to a ketone, Wittig reactions, and
reductive animations. In total, 483 compounds were synthesized.
Cdc25A and AChE exhibit structural similarity in their ligand-sensing cores and were thus grouped into a protein structure similarity cluster
(PSSC). A screen for AChE inhibition of a subset of 162 compounds yielded three micromolar inhibitors of AChE with IC50 values <20 mM.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Solid-phase synthesis; Protein structure similarity clustering (PSSC); Acetylcholinesterase; Biology-oriented synthesis
1. Introduction
structure- and natural product-guided,2e4 and biology-orien-
ted5e16 or diversity-oriented17 synthesis have emerged.
The efficient identification of small molecules that modu-
late protein function in vitro and in vivo is at the heart of
chemical biology and medicinal chemistry research, and the
development of new therapies and diagnostics for disease.
Key to the discovery of novel modulators of protein function
is the identification of appropriate starting points in chemical
structure space for compound library development, which could
serve as ‘leitmotifs’ for the synthesis of biologically relevant
compound collections. To gain access to novel chemical struc-
tures in library formats, several new strategies for library design
that focus for instance on natural product-guided,1 protein
Natural products (NPs) can be regarded as evolutionarily
selected ligands for the ligand-sensing cores of proteins. They
emerge via biosynthesis by proteins and often fulfill various
biological functions through interaction with multiple pro-
teins.4,18 Their underlying structures define structural prerequi-
sites for binding to proteins and biological activity. While the
entire biologically relevant chemical space may be larger than
the structural space occupied by natural products, their struc-
tural scaffolds represent the biologically relevant and pre-
validated fractions of chemical structure space explored by
nature so far. Consequently, compound collections designed
to mimic the structures and properties of NP classes will have
greater biological relevance than the libraries obtained on the
basis of chemical feasibility alone,1,19e21 and it is expected
that NP guided compound library development1,4 will persist
* Corresponding author. Fax: þ49 231 133 2499.
E-mail
Waldmann).
address:
herbert.waldmann@mpi-dortmund.mpg.de
(H.
0040-4020/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.106

M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
4793
NaO3SO
similarity clustering (PSSC) led to the identification of novel
acetylcholinesterase inhibitors.
2. Results and discussion
O
HO
O
H
2.1. Synthesis of decalin building blocks in solution
OH
Dysidiolide (1)
Sulfiricin (2)
O
Differently functionalized decalin derivatives were synthe-
sized in solution as building blocks for further derivatization
on the solid support as shown in Scheme 1.
Figure 1. The natural products dysidiolide 1 and sulfiricin 2 served as struc-
tural guiding principles for the synthesis of a decalin scaffold-based compound
library.
Unsaturated decalinols 12e16 were synthesized employing
the enantioselective Robinson annulation25e27 as the key CeC
bond forming step (Scheme 1). In addition, intermediate 6 was
further derivatized. The carbonyl functionality was protected
as 1,3-dioxolane (6a) followed by hydrogenation of the double
bond leading to ketal 6b. Treatment with sodium methoxide
and reduction of the carbonyl group yielded alcohol 6c. After
cleavage of the 1,3-dioxolane, alcohol 11 was obtained. A fur-
ther decalinol building block (17) was synthesized starting
from alcohol 12, which was achieved by catalytic hydrogena-
tion and subsequent treatment with sodium methoxide.
as a guiding principle for the identification of small molecules
for chemical biology and medicinal chemistry research.18
Both dysidiolide 1 and sulfiricin 2 (Fig. 1) are natural prod-
ucts known to inhibit Cdc25A (IC50 values of 9.4 and 7.8 mM,
respectively).22,23 A systematic study with sulfiricin, varying
the scaffold of the compound, revealed that with analogs
bearing benzimidazole, benzothiazole or naphthalene moieties
instead of the decalin moiety, phosphatase-inhibiting activity
completely disappeared. Thus, we hypothesized that the deca-
lin moiety may represent a ‘privileged’24 core structure, which
conveys biological relevance to compound collections derived
thereof. We thus headed for the synthesis of a compound col-
lection on the solid support using the decalin moiety as ‘leit-
motif’, which we describe herein in full experimental detail.
We also demonstrate how the application of protein structure
2.2. Immobilization on solid support and first diversification
As shown in Scheme 2 for decalinol 12 as a representative
example, the decalin-derived alcohols were immobilized on
Merrifield resin equipped with a dihydropyranyl linker 18.28
O
O
R2
R2
R1
O
R3
b)
a)
O
R1
O
c)
R3
O
3
4
5
R3
H
H
H
O
O
O
OH
f)
OH
d)
e)
O
O
O
R1
O
O
O
O
R2
6-10
6a
6b
6c
11
O
g)
R3
H
O
O
h)
R1
R2
OH
OH
12-16
6
17
7
8
9
10
Compound
R1 =
12
13
14
15
16
Me
Me
Me
Benzyl
Allyl
R2 =
R3 =
H
Me
H
H
H
H
Me
H
Me
Me
Scheme 1. Solution phase synthesis of decalin-based building blocks. (a) 1.0 equiv 1,3-dione, 1.5 equiv enone, water, rt, 7 days; (b) 0.66 equiv D-CSA, 0.97 equiv
L-phenylalanine, DMF, rt to 70 ꢀC in 6 days; (c) 2 ml/mM 2-ethyl-2-methyl-1,3-dioxolane/ethylene glycol (cat.), p-toluenesulfonic acid (cat.), rt, 2 days, 90%; (d)
5 mol % Pd/C, H2 (12 bar), 65 ꢀC, 3 days, then 1.3 equiv NaOMe in MeOH, reflux, 2 h, 82%; (e) 1.01 equiv DIBAH, Et2O, ꢁ78 ꢀC to rt, 1 h, then rt, 15 min, 89%;
(f) 2.5 equiv PPTS, acetone/water (1:1), 70 ꢀC, 2 h, 82%; (g) 0.3 equiv NaBH4, EtOH, rt, yields over three steps: 43e49%; (h) 5 mol % Pd/C, H2 (1 bar), rt, 1 day,
then 1.3 equiv NaOMe in MeOH, reflux, 2 h, 62%.

4794
M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
O
O
Further
diversification
O
a), b)
c)
O
O
O
R1
OH
R2
O
18
19
19a
Scheme 2. Attachment of the scaffolds to Merrifield resin and functionalization by means of aldol condensation. (a) 1.0 equiv resin, 0.5 equiv p-TsOH, 5.0 equiv
alcohol (12e17), CH2Cl2, rt, 1 day, cleaning: 3ꢂCH2Cl2, 3ꢂCH2Cl2/MeOH¼1:1 (v/v), 3ꢂMeOH, 3ꢂCH2Cl2/MeOH¼1:1 (v/v), 3ꢂCH2Cl2 (dry), drying in
vacuum, loading level: 1.06 mmol gꢁ1; (b) 0.95 equiv LDA, 1.1 equiv aldehyde, 0 ꢀC to rt, 2 h; (c) 5% TFA in CH2Cl2, rt, 10 min (three times).
The immobilized ketones were then subjected to aldol conden-
sation reactions with different aldehydes leading to exocyclic
E-configured olefins, e.g., 19. After further derivatization (see
next chapter), the synthesized products (19a) were cleaved
from the solid support using 5% trifluoroacetic acid in DCM.
After release from the solid support by treatment with
trifluoroacetic acid the desired compounds were obtained in
purities of 23e98% and purified to homogeneity by means
of preparative HPLC. In total, 483 compounds were obtained
in multimilligram amounts. Typical overall yields were 40e
60% after the 3e5 step reaction sequences on the polymeric
carrier using the tea bag method in combination with radio
frequency coding to increase efficiency.
2.3. Diversification of aldol condensation products on solid
support
The immobilized aldol condensation products were then sub-
jected to a variety of different transformations to increase the
diversity of the library. As shown in Scheme 3 for one represen-
tative scaffold (compound 19), these reactions included Sonoga-
shira, Suzuki, and Heck reactions, Cu-catalyzed conjugate
addition and Grignard reactions, alkylation reactions in a-posi-
tion to a ketone, Wittig reactions, and reductive animations.
2.4. PSSC-guided discovery of acetylcholinesterase inhibitors
Based on the protein structure similarity clustering (PSSC)
concept developed by us,4 Cdc25A, the target protein of the
two guiding compounds of the library described here, dysidio-
lide 1 and sulfiricin 2, was found to exhibit significant
structural similarity with the ligand-sensing core of
R6
R3
R8
O
NH
23
OH
R1
OH
R1
24
OH
R1
22
R3
O
NH
h,
a)
i), a)
j), a)
OH
g), a)
OH
21
c), j), a)
O
25
R7
19 R1
f), a)
O
R2
O
a), b)
c), a)
e), a)
d), a)
OH
R1
26
OH
R1
20
O
O
O
OH
R5
OH
29
27
OH
R1
28
R9
R2
Scheme 3. (a) 10% TFA in CH2Cl2, rt, 10 min (three times); (b) 5 equiv TBAF, THF, rt, overnight; (c) 1.0 equiv CuI, 0.5 equiv Pd(PPh3)4, 20 equiv DIPEA,
15 equiv alkyne, DMF, 90 ꢀC, overnight; (d) 4.5 equiv EtMgBr, 0.35 equiv CuBr, 14 equiv DMPU, THF, ꢁ20 ꢀC to 0 ꢀC, 3 h; (e) 2.0 equiv Na2CO3, 0.5 equiv
Pd(PPh3)4, 2.0 equiv boronic acid, THF, 60 ꢀC, overnight; (f) 5.5 equiv EtMgBr, THF, ꢁ20 ꢀC to rt, 3 h; (g) 5.0 equiv alkene, 0.2 equiv Pd(OAc)2, 2.0 equiv
PPh3, 1.5 equiv TMEDA, DMF, 70 ꢀC overnight; (h) 5.0 equiv KH, THF, rt, 30 min then add 8 equiv primary bromide, rt to 50 ꢀC, 3 h; (i) 10 equiv triphenylphos-
phonium bromide, 8 equiv BuLi, toluene, 100 ꢀC, overnight; (j) 1.6 equiv TiCl4, 3.8 equiv amine, toluene, 90 ꢀC, overnight, then 1.5 equiv NaBH3CN, THF, rt,
overnight.

M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
4795
Figure 2. The two catalytic cores of Cdc25A and AChE exhibit significant structural similarity. (A) Superimposed catalytic cores of AChE (blue) and Cdc25A
˚
(red). The ligand-sensing cores of both enzymes were aligned with a rms deviation of 2.74 A at an alignment length of 49 residues. The sequence identities amount
to 8.2%. Also shown, in CoreyePaulingeKoltun (CPK) representation, are the catalytic residues, Ser-200 (AChE) and Cys-430 (Cdc25A) that are collocated in
space. (B) Structure-based sequence alignment of the two superimposed catalytic cores. The catalytic key residues (Cys-430 and Ser-200) are correlated and gray-
shaded.
acetylcholinesterase (Fig. 2). The catalytic residues, Ser-200
(for AChE) and Cys-430 (for Cdc25A), of both enzymes share
the same location in space. This structural similarity also
translates well into sequence similarity between the two cata-
lytic cores where the key catalytic residues are correlated.
In the light of this structural similarity, a subset of this com-
pound collection (in total 162 compounds) was subjected to
biochemical investigation for possible inhibition of AChE
screen. Compounds displaying IC50 values <20 mM were con-
sidered as hits. Three compounds were qualified as hits in the
AChE with IC50 values ranging from 3.7 to 15.9 mM (see
Table 1). Thus, the hit rate in the AChE inhibition screen
amounts to w2%, which is an acceptable value for an initial
screen aimed exclusively at identifying hit classes. None of
the identified compounds and the compound class in general
have been described as AChE inhibitors before.
means of a combination of both solution phase and solid phase
methodologies. Employing the PSSC concept we have proven
that the synthesized compounds are valuable and biologically
relevant starting points in chemical space for the development
of protein inhibitors for medicinal chemistry and chemical
biology research.
4. Experimental section
4.1. General
Unless otherwise noted, chemicals were obtained from Al-
drich, Acros or Fluka and were used without further purification.
Regular Merrifield resin (1.7 mmol gꢁ1, 1% DVB, 100e200
mesh) was purchased from Novabiochem. All solvents were
distilled by standard procedures. All reactions were performed
under argon with freshly distilled and dried solvents. Analytical
chromatography was performed using Merck silica gel 60 F254
aluminum sheets. Flash chromatography was performed using
3. Conclusion
1
In conclusion, we have synthesized a natural product-in-
spired compound collection based on the decalin scaffold by
Merck silica gel 60. H and 13C NMR data were recorded on
a Bruker DRX 500 or Bruker DRX 400 spectrometer at room

4796
M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
GCeMS, m/z (rel int. %): 210 (49) [Mþ], 192 (18), 181
(21), 153 (15), 139 (82), 111 (100), 97 (45), 69 (43), 57 (64).
Table 1
Identified AChE inhibitors
Compound
Structure
IC50 [mm]
3.7ꢃ0.4
4.2.2. (S )-3,4,8,8a-Tetrahydro-5,8a-dimethylnaphthalene-
1,6(2H,7H )-dione, 6
OH
30
L-Phenylalanine (37.0 g, 224 mmol) and D-camphorsulfonic
acid (27.0 g, 166 mmol) were added to a solution of 2-methyl-
2-(3-oxopentyl)cyclohexane-1,3-dione 5 (49.0 g, 233 mmol)
in DMF (400 ml). The solution was stirred overnight at
room temperature, and then the temperature was elevated by
10 ꢀC every 24 h until 70 ꢀC is reached. The reaction was
cooled to 0 ꢀC and satd NaHCO3 (600 ml) was added. After
stirring for 30 min, the aqueous phase was extracted with
Et2O (3ꢂ400 ml). The combined organic phases were washed
with brine and dried over MgSO4. The solvent was evaporated
under reduced pressure and the product purified by flash chro-
matography to yield a white solid (32.0 g, 71%). Melting
point: 46 ꢀC. Rf value: 0.24 (cyclohexane/EtOAc 3:1, v/v).
O
O
31
5.3ꢃ1.1
OH
O
OH
32
15.9ꢃ6.7
[a]2D0 þ136 (c 1.00, CHCl3). H NMR (400 MHz, CDCl3):
1
d 1.41 (s, 3H), 1.80 (s, 3H), 2.02e2.21 (m, 4H), 2.38e2.59
(m, 4H), 2.81e2.94 (m, 2H). GCeMS, m/z (rel int. %): 192
(34) [Mþ], 177 (38), 149 (57), 136 (100), 121 (41), 107
(74), 93 (82), 79 (49), 55 (31), 39 (23).
F
4.2.3. (4aS,5S )-4,4a,5,6,7,8-Hexahydro-5-hydroxy-1,4a-
dimethylnaphthalene-2(3H )-one, 12
Sodium borohydride (1.68 g, 44.4 mmol) in EtOH (70 ml)
was added over 3 h to a solution of (S )-3,4,8,8a-tetrahydro-
temperature. NMR spectra were calibrated to the solvent signals
of CDCl3 (7.26 ppm and 77.00 ppm) and the following abbrevi-
ations are used to indicate signal multiplicities: s (singlet),
d (doublet), t (triplet), q (quartet), quint (quintet), sext (sextet),
sept (septet), br (broad), ap (apparent). GCeMS (EI) analysis
was performed on a HewlettePackard 5890 series II gas chro-
matograph connected to a HewlettePackard 5973 series mass
spectrometer; column: H&W 19091s-102 HP-5MS, capillary:
0.2 mm, 25 mꢂ0.2 mm nominal. LCeMS was performed on
a HewlettePackard 1100 series connected to a Finnigan LCQ
ESI-spectrometer. High resolution mass spectra (HRMS) were
measured on a Finnigan MAT 8200 spectrometer. The optical
rotation was determined with a PerkineElmer polarimeter 241.
5,8a-dimethylnaphthalene-1,6(2H,7H )-dione
6
(32.0 g,
166.7 mmol) in distilled EtOH (250 ml). After an additional
30 min of stirring, acetic acid was added until gas evolution
has stopped. The solution was then coevaporated in vacuo
with toluene (50 ml). The residue was redissolved in chloroform
(500 ml), washed twicewith brine, dried over MgSO4, and evap-
orated under reduced pressure. The crude mixture is purified by
flash chromatography to yield the product as a colorless oil
(25.2 g, 78%). Rf value: 0.12 (cyclohexane/EtOAc 3:1, v/v).
1H NMR (400 MHz, CDCl3): d 1.11 (s, 3H), 1.21e1.35 (m,
1H), 1.69 (s, 3H), 1.58e1.92 (m, 4H), 1.94e2.10 (m, 2H),
2.30e2.39 (m, 2H), 2.55e2.65 (m, 1H), 3.34 (dd, J¼4.5,
7.2 Hz, 1H), 3.60 (br s, 1H). 13C NMR (125.6 MHz, CDCl3):
d 11.5, 16.0, 23.1, 27.3, 30.1, 33.6, 42.2, 78.3, 129.9, 161.8,
199.6. GCeMS, m/z (rel int. %): 194 (81) [Mþ], 179 (7), 151
(12), 138 (100), 123 (41), 110 (34), 91 (27), 77 (19), 67 (9),
55 (11) 41 (11).
4.2. Synthesis of decalin-based building blocks
4.2.1. 2-Methyl-2-(3-oxopentyl)cyclohexane-1,3-dione, 5
(R1¼Me, R2¼H, R3¼Me)
Pent-1-en-3-one 4 (R2¼H, R3¼Me) (50.0 ml, 512.4 mmol)
was added to a solution of 2-methylcyclohexane-1,3-dione 3
(R1¼Me) (37.5 g, 297.5 mmol) in water (75 ml). EtOH
(2.5 ml) was added to improve the solubility. The resulting
suspension was stirred for 7 days at room temperature (after
6 days the solid dissolved entirely). Toluene (300 ml) was
added to the reaction mixture and the aqueous phase extracted
with DCM (3ꢂ300 ml). The combined organic phases were
washed with brine and dried over MgSO4. The solvent was
evaporated under reduced pressure and the product purified
by flash chromatography to provide the product as a colorless
oil (53.7 g, 86%). Rf value: 0.16 (cyclohexane/EtOAc 3:1,
v/v). 1H NMR (400 MHz, CDCl3): d 1.02 (t, J¼7.4 Hz,
3H), 1.24 (s, 3H), 1.98e2.10 (m, 2H), 2.2e2.58 (m, 10H).
4.2.4. (1S,4aS,5S,8aR)-Octahydro-5-hydroxy-1,4a-
dimethylnaphthalene-2(1H )-one, 17
A solution of (4aS,5S )-4,4a,5,6,7,8-hexahydro-5-hydroxy-
1,4a-dimethylnaphthalen-2(3H )-one 12 (18.0 g, 92.8 mmol)
in pyridine (100 ml) and Pd/C (0.4 g) was stirred vigorously
overnight under a H2 atmosphere. DCM (250 ml) was added
and the suspension was filtered over Celite. The filtrate was
then washed with satd NH4Cl solution followed by brine and
evaporated under reduced pressure. The crude mixture was re-
dissolved in MeOH (150 ml) and heated for 2 h at reflux with
a 5.4 M solution of sodium methoxide (23.0 ml, 124 mmol).

M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
4797
After cooling to room temperature, DCM and water (300 ml
each) were added and the phases separated. The aqueous phase
was extracted three times with DCM. The combined organic
phases were washed with satd NH4Cl, then brine and dried
over MgSO4. The solution was evaporated under reduced pres-
sure and the crude product was purified by flash chromatography
to afford the product as a colorless oil (11.2 g, 62%). Rf value:
0.15 (cyclohexane/EtOAc 3:1, v/v). [a]2D0 ꢁ98 (c 1.00,
had stopped. The solution was then coevaporated in vacuo
with toluene (20 ml). The residue was redissolved in chloro-
form (300 ml), washed twice with brine, dried over MgSO4,
and evaporated under reduced pressure. The crude mixture
was purified by flash chromatography to yield the product as
a colorless oil (12.7 g, 79%). Rf value: 0.12 (cyclohexane/
EtOAc 3:1, v/v). [a]2D0 þ88 (c 1.00, CHCl3). 1H NMR
(400 MHz, CDCl3): d 0.79 (d, J¼7.0 Hz, 3H), 1.26 (s, 3H),
1.20e1.40 (m, 1H), 1.40e1.59 (m, 1H), 1.98e2.04 (m, 2H),
2.11e2.18 (m, 1H), 2.43e2.67 (m, 6H), 6.07 (s, 1H). 13C
NMR (125.6 MHz, CDCl3): d 17.6, 18.6, 26.0, 31.6, 36.3,
37.9, 42.3, 47.6, 82.8, 127.8, 177.1, 197.9.
1
CHCl3). H NMR (400 MHz, CDCl3): d 0.96 (d, J¼5.9 Hz,
3H), 1.07 (s, 3H), 1.17e1.85 (m, 9H), 2.19e2.55 (m, 4H),
3.22 (dd, J¼4.5, 7.0 Hz, 1H). 13C NMR (125.6 MHz, CDCl3):
d 10.3, 11.7, 24.3, 25.1, 30.0, 34.0, 37.7, 39.2, 44.8, 50.8,
79.0, 213.0. GCeMS, m/z (rel int. %): 196 (26) [Mþ], 181
(21), 163 (17), 145 (10), 135 (51), 111 (100), 107 (32), 93
(12), 79 (9), 67 (11), 55 (10), 41 (9). HRMS (FAB) calcd for
C12H20O2: 196.1463, found: 197.1558 [MþH]þ.
4.2.7. (S )-3,4,8,8a-Tetrahydro-8a-methylnaphthalene-
1,6(2H,7H )-dione, 8
But-3-en-2-one 4 (R2¼H, R3¼H) (10.5 g, 150 mmol) in
MeOH (60 ml) was added to a solution of 2-methylcyclohex-
ane-1,3-dione 3 (R1¼Me) (12.6 g, 100 mmol) and benzyltri-
methylammonium hydroxide (Triton B) (2.5 M in MeOH,
4.4 ml, 11.0 mmol) in MeOH (60 ml). The suspension was
stirred for 5 h at 60 ꢀC and subsequently overnight at room
temperature. The solvent was then evaporated under reduced
pressure and the product purified by flash chromatography.
The product was dissolved in DMF (300 ml) and combined
with L-phenylalanine (23.3 g, 141 mmol) and D-camphorsul-
fonic acid (17.0 g, 105 mmol). The solution was stirred over-
night at room temperature, and then the temperature was
elevated by 10 ꢀC every 24 h until 70 ꢀC was reached. The
reaction was cooled to 0 ꢀC and satd NaHCO3 (300 ml) was
added. After stirring for 30 min, the aqueous phase was ex-
tracted with Et2O (3ꢂ250 ml). The combined organic phases
were washed with brine and dried over MgSO4. The solvent
was evaporated under reduced pressure and the product puri-
fied by flash chromatography to yield a colorless oil (12.7 g,
60%). Rf value: 0.27 (cyclohexane/EtOAc 3:1, v/v). [a]D20
4.2.5. (8S,8aS )-3,4,8,8a-Tetrahydro-8,8a-dimethyl-
naphthalene-1,6(2H,7H )-dione, 7
trans-Pent-3-en-2-one
4
(R2¼Me, R3¼H) (7.4 g,
88.2 mmol) was added to a solution of 2-methylcyclohexane-
1,3-dione 3 (R1¼Me) (10.0 g, 80.1 mmol) in water (75 ml).
EtOH (1.5 ml) was added to improve the solubility. The result-
ing suspension was stirred for 7 days at room temperature (after
6 days the solid dissolved entirely). Toluene (200 ml) was added
to the reaction mixture and the aqueous phasewas extracted with
DCM (3ꢂ200 ml). The combined organic phases were washed
with brine and dried over MgSO4. The crude was evaporated
under reduced pressure. DMF (300 ml) was added along with
L-phenylalanine (18.5 g, 112 mmol) and D-camphorsulfonic
acid (13.5 g, 83.2 mmol). The solution was stirred overnight at
room temperature, and then the temperature was elevated by
10 ꢀC every 24 h until 70 ꢀC was reached. The reaction was
cooled to 0 ꢀC and satd NaHCO3 (300 ml) was added. After stir-
ring for 30 min, the aqueous phase was extracted with Et2O
(3ꢂ250 ml). The combined organic phases were washed with
brine and dried over MgSO4. The solvent was evaporated under
reduced pressure and the product purified by flash chromatogra-
phy to yield a white solid (9.49 g, 61%). Melting point: 58 ꢀC. Rf
value: 0.22 (cyclohexane/EtOAc 3:1, v/v). [a]2D0 þ72 (c 1.00,
1
þ103 (c 1.09, CHCl3). H NMR (400 MHz, CDCl3): d 1.42
(s, 3H), 1.61e1.78 (m, 1H), 2.03e2.20 (m, 3H), 2.36e2.53
(m, 4H), 2.66e2.78 (m, 2H), 5.84 (s, 1H). 13C NMR
(125.6 MHz, CDCl3): d 23.0, 23.4, 29.7, 31.8, 33.7, 37.7,
50.6, 125.7, 165.6, 198.0, 210.7. GCeMS, m/z (rel int. %):
178 (29) [Mþ], 160 (49), 150 (16), 136 (41), 121 (100), 108
(76), 93 (83), 79 (91), 55 (34), 39 (27). HRMS (FAB) calcd
for C11H14O2: 178.0994, found: 179.1085 [MþH]þ.
1
CHCl3). H NMR (400 MHz, CDCl3): d 0.78 (d, J¼6.8 Hz,
3H), 1.36 (s, 3H), 1.52e1.65 (m, 1H), 1.94e2.03 (m, 1H),
2.09e2.15 (m, 2H), 2.31e2.38 (m, 1H), 2.43e2.67 (m, 4H),
5.85 (s, 1H). 13C NMR (125.6 MHz, CDCl3): d 16.8, 20.8,
26.2, 32.0, 35.8, 39.0, 41.5, 54.6, 124.8, 164.2, 197.9, 211.8.
GCeMS, m/z (rel int. %): 192 (15) [Mþ], 174 (17), 150 (22),
135 (100), 122 (11), 107 (13), 94 (16), 79 (16), 55 (13), 39
(11). HRMS (FAB) calcd for C12H16O2: 192.1150, found:
193.1221 [MþH]þ.
4.2.8. (4aR,5R)-4,4a,5,6,7,8-Hexahydro-5-hydroxy-4a-
methylnaphthalene-2(3H )-one, 14
Sodium borohydride (946 mg, 25.0 mmol) in EtOH (30 ml)
was added over 3 h to a solution of (S )-3,4,8,8a-tetrahydro-8a-
methylnaphthalene-1,6(2H,7H )-dione 8 (17.0 g, 95.5 mmol)
in distilled EtOH (150 ml). After an additional 30 min of stir-
ring, acetic acid was added until gas evolution had stopped.
The solution was then coevaporated in vacuo with toluene
(20 ml). The residue was redissolved in chloroform (300 ml),
washed twice with brine, dried over MgSO4, and evaporated
under reduced pressure. The crude mixture was purified by
flash chromatography to yield the product as a colorless oil
(13.9 g, 81%). Rf value: 0.12 (cyclohexane/EtOAc 3:1, v/v).
4.2.6. (4S,4aS,5S )-4,4a,5,6,7,8-Hexahydro-5-hydroxy-4,4a-
dimethylnaphthalene-2(3H )-one, 13
Sodium borohydride (776 mg, 20.5 mmol) in EtOH (30 ml)
was added over 3 h to a solution of (8S,8aS )-3,4,8,8a-tetra-
hydro-8,8a-dimethylnaphthalene-1,6(2H,7H )-dione 7 (15.9 g,
82.8 mmol) in distilled EtOH (150 ml). After an additional
30 min of stirring, acetic acid was added until gas evolution

4798
M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
[a]2D0 þ78 (c 1.00, CHCl3). 1H NMR (400 MHz, CDCl3):
d 1.17 (s, 3H), 1.22e1.53 (m, 6H), 1.80e2.78 (m, 5H), 3.31
(t, J¼6.4 Hz, 1H), 5.71 (s, 1H). 13C NMR (125.6 MHz,
CDCl3): 14.3, 15.5, 21.2, 27.4, 30.3, 32.3, 33.8, 41.7, 60.6,
125.4, 171.6, 200.2. GCeMS, m/z (rel int. %): 180 (44)
[Mþ], 162 (10), 152 (12), 137 (16), 124 (100), 109 (69), 91
(31), 79 (35), 67 (23), 55 (28), 43 (35). HRMS (FAB) calcd
for C11H16O2: 180.1150, found: 181.1217 [MþH]þ.
(9), 141 (8), 115 (11), 91 (100), 77 (12), 65 (12). HRMS (FAB)
calcd for C18H20O2: 268.1463, found: 269.1530 [MþH]þ.
4.2.11. (4aR,5S )-4a-Benzyl-4,4a,5,6,7,8-hexahydro-5-
hydroxy-1-methylnaphthalene-2(3H )-one, 15
Sodium borohydride (473 mg, 12.5 mmol) in EtOH (20 ml)
was added over 3 h to a solution of (R)-8a-benzyl-3,4,8,8a-tetra-
hydro-5-methylnaphthalene-1,6(2H,7H )-dione
9
(12.8 g,
47.8 mmol) in distilled EtOH (100 ml). After an additional
30 min of stirring, acetic acid was added until gas evolution
had stopped. The solution was then coevaporated in vacuo
with toluene (20 ml). The residue was redissolved in chloroform
(300 ml), washed twicewith brine, dried over MgSO4, and evap-
orated under reduced pressure. The crude mixture was purified
by flash chromatography to yield the product as a colorless oil
(13.9 g, 81%). Rf value: 0.10 (cyclohexane/EtOAc 3:1, v/v).
[a]2D0 þ72 (c 1.01, CHCl3). 1H NMR (400 MHz, CDCl3):
d 1.23e1.57 (m, 6H), 1.82 (s, 3H), 1.90e2.09 (m, 2H), 2.26e
2.51 (m, 2H), 2.74e2.87 (m, 1H), 2.95e3.02 (m, 1H), 3.20e
3.26 (m, 1H), 7.04e7.12 (m, 1H), 716e7.20 (m, 2H), 7.35e7.40
(m, 2H). 13C NMR (125.6 MHz, CDCl3): d 11.7, 23.8, 27.7,
30.9, 31.1, 33.7, 36.7, 46.8, 80.1, 126.9, 129.9 (4C), 132.7,
138.6, 157.6, 199.2. GCeMS, m/z (rel int. %): 270 (41) [Mþ],
178 (35), 161 (100), 137 (16), 105 (22), 91 (76), 79 (25), 67
(13), 55 (18), 43 (25). HRMS (FAB) calcd for C18H22O2:
270.1620, found: 271.1712 [MþH]þ.
4.2.9. 2-Benzyl-2-(3-oxopentyl)cyclohexane-1,3-dione, 5
2-Benzylcyclohexane-1,3-dione 3 (R1¼benzyl) (20.2 g,
100 mmol) in MeOH (60 ml) was added to a solution of pent-
1-en-3-one 4 (R2¼H, R3¼Me) (12.6 g, 150 mmol) and benzyl-
trimethylammonium hydroxide (Triton B) (2.5 M in MeOH,
4.4 ml, 11.0 mmol) in MeOH (60 ml). The suspension was
stirred for 5 h at 60 ꢀC and subsequently overnight at room tem-
perature. The solvent was then evaporated under reduced pres-
sure and toluene (400 ml) was added. The phases were
separated and the aqueous phase extracted three times each
with DCM (300 ml). The combined organic phases werewashed
with brine and then dried over MgSO4. The solvent was evapo-
rated under reduced pressure and the product purified by flash
chromatography to yield a colorless oil (22.9 g, 80%). Rf value:
0.21 (cyclohexane/EtOAc 3:1, v/v). 1H NMR (400 MHz,
CDCl3): d 0.99 (t, J¼7.0 Hz, 3H), 1.93e2.03 (m, 2H), 2.11e
2.64 (m, 10H), 3.66 (s, 2H), 7.17e7.37 (m, 5H). 13C NMR
(125.6 MHz, CDCl3): d 7.9, 16.1, 21.4, 35.9, 36.9 (2C), 37.1,
38.5, 70.7, 127.2, 128.1 (2C), 128.7 (2C), 135.2, 200.0, 210.0,
210.4. GCeMS, m/z (rel int. %): 286 (32) [Mþ], 258 (12), 202
(13), 187 (31), 173 (56), 158 (42), 115 (27), 91 (100), 57 (21),
42 (10). HRMS (FAB) calcd for C18H22O3: 286.1569, found:
287.1655 [MþH]þ. The 1H NMR data are in accordance with
the literature.29
4.2.12. (8S,8aS )-8a-Allyl-3,4,8,8a-tetrahydro-8-methyl-
naphthalene-1,6(2H,7H )-dione, 10
Pent-3-en-2-one 4 (R2¼Me, R3¼H) (8.2 g, 97.2 mmol) was
added to a solution of 2-allylcyclohexane-1,3-dione
3
(R1¼allyl) (13.4 g, 88.1 mmol) in water (75 ml). EtOH
(1.5 ml) was added to improve the solubility. The resulting
suspension was stirred for 7 days at room temperature (after
6 days the solid dissolved entirely). Toluene (200 ml) was
added to the reaction mixture and the aqueous phase extracted
with DCM (3ꢂ200 ml). The combined organic phases were
washed with brine and dried over MgSO4. The solvent was
evaporated under reduced pressure. DMF (400 ml) was added
along with L-phenylalanine (24.8 g, 150 mmol) and D-cam-
phorsulfonic acid (18.1 g, 111 mmol). The solution was stirred
overnight at room temperature, and then the temperature was
elevated by 10 ꢀC every 24 h until 70 ꢀC was reached. The re-
action was cooled to 0 ꢀC and satd NaHCO3 (400 ml) was
added. After stirring 30 min, the aqueous phase was extracted
with Et2O (3ꢂ300 ml). The combined organic phases were
washed with brine and dried over MgSO4. The solvent was
evaporated under reduced pressure and the product purified
by flash chromatography to yield a white solid (10.4 g,
54%). Melting point: 52 ꢀC. Rf value: 0.37 (cyclohexane/
EtOAc 3:1, v/v). [a]2D0 þ54 (c 1.00, CHCl3). 1H NMR
(400 MHz, CDCl3): d 0.84 (d, J¼7.6 Hz, 3H), 1.54e1.70
(m, 1H), 1.91e2.74 (m, 11H), 5.01e5.13 (m, 2H), 5.58e
5.71 (m, 1H). 13C NMR (125.6 MHz, CDCl3): d 17.0, 21.1,
33.2, 33.7, 40.3, 41.2, 43.8, 58.6, 119.3, 125.3, 132.7, 163.8,
197.9, 210.2. GCeMS, m/z (rel int. %): 218 (52) [Mþ], 203
(31), 190 (10), 175 (24), 161 (22), 149 (100), 135 (26), 119
4.2.10. (R)-8a-Benzyl-3,4,8,8a-tetrahydro-5-methyl-
naphthalene-1,6(2H,7H )-dione, 9
L-Phenylalanine (11.1 g, 66.9 mmol) and D-camphorsulfonic
acid (8.1 g, 49.8 mmol) were added to a solution of 2-benzyl-2-
(3-oxopentyl)cyclohexane-1,3-dione 5 (20.0 g, 69.9 mmol) in
DMF (400 ml). The solution was stirred overnight at room tem-
perature, and then the temperature was elevated by 10 ꢀC every
24 h until 70 ꢀC was reached. The reaction was cooled to 0 ꢀC
and satd NaHCO3 (500 ml) was added. After stirring for
30 min, the aqueous phase was extracted with Et2O
(3ꢂ300 ml). The combined organic phases were washed with
brine and dried over MgSO4. The solvent was evaporated under
reduced pressure and the product purified by flash chromatogra-
phy to yield a white solid (13.3 g, 71%). Melting point: 67 ꢀC. Rf
value: 0.12 (cyclohexane/EtOAc 3:1, v/v). [a]2D0 þ78 (c 1.00,
1
CHCl3). H NMR (400 MHz, CDCl3): d 1.65e1.75 (m, 1H),
1.86 (s, 3H), 1.87e1.91 (m, 1H), 1.91e2.02 (m, 2H), 2.07e2.12
(m, 1H), 2.36e2.52 (m, 5H), 2.60e2.71 (m, 1H), 2.83e2.91 (m,
1H), 6.97e7.03 (m, 1H), 7.24e7.30 (m, 2H), 7.37e7.42 (m,
2H). 13C NMR (125.6 MHz, CDCl3): d 11.8, 21.5, 27.1, 29.3,
37.0, 38.9, 43.2, 56.1, 127.2, 128.7, 129.8 (4C), 141.2, 157.9,
197.7, 211.1. GCeMS, m/z (rel int. %): 268 (17) [Mþ], 176

M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
4799
(14), 105 (41), 91 (49), 77 (36), 55 (27), 41 (23). HRMS (FAB)
calcd for C14H18O2: 218.1307, found: 219.1391 [MþH]þ.
with satd NH4Cl, then with brine and dried over MgSO4.
The solvent was evaporated under reduced pressure and the
crude product was dissolved in MeOH (20 ml). A 5.4 M solu-
tion of sodium methoxide in MeOH (2.3 ml, 12.4 mmol) was
added and the solution was heated for 2 h at reflux. After the
reaction had cooled to room temperature, DCM and water
(200 ml each) were added. The phases were separated and
the aqueous phase backwashed twice with DCM. The com-
bined organic extracts were washed with satd NH4Cl and
brine, and dried over MgSO4. The crude organic extracts
were evaporated under reduced pressure and the product puri-
fied by flash chromatography to yield a colorless oil (2.31 g,
82%). Rf value: 0.31 (cyclohexane/EtOAc 3:1, v/v). [a]D20
4.2.13. (4S,4aS,5S )-4a-Allyl-4,4a,5,6,7,8-hexahydro-5-
hydroxy-4-methylnaphthalene-2(3H )-one, 16
Sodium borohydride (48 mg, 12.8 mmol) in EtOH (20 ml)
was added over 3 h to a 0 ꢀC cooled solution of (S )-8a-ben-
zyl-3,4,8,8a-tetrahydro-5-methylnaphthalene-1,6(2H,7H )-di-
one 10 (9.9 g, 45.5 mmol) in distilled EtOH (100 ml). After an
additional 30 min of stirring, acetic acid was added until gas
evolution had stopped. The solution was then coevaporated
in vacuo with toluene (20 ml). The residue was redissolved
in chloroform (300 ml), washed twice with brine, dried over
MgSO4, and evaporated under reduced pressure. The crude
mixture was purified by flash chromatography to yield the
product as a colorless oil (13.9 g, 81%). Rf value: 0.14 (cyclo-
hexane/EtOAc 3:1, v/v). [a]2D0 þ66 (c 1.03, CHCl3). 1H NMR
(400 MHz, CDCl3): d 0.85 (d, J¼8.0 Hz, 3H), 1.28e2.74 (m,
11H), 3.21e3.26 (m, 1H), 5.04e5.17 (m, 2H), 5.58e5.70 (m,
2H). 13C NMR (125.6 MHz, CDCl3): d 16.9, 23.6, 28.5, 32.6,
35.4, 36.1, 44.7, 51.8, 79.5, 115.9, 123.8, 139.1, 170.0, 199.1.
GCeMS, m/z (rel int. %): 220 (13) [Mþ], 202 (11), 179 (22),
161 (39), 137 (61), 119 (100), 105 (29), 91 (31), 77 (28), 65
(15), 55 (14), 41 (23). HRMS (FAB) calcd for C14H20O2:
220.1463, found: 221.1551 [MþH]þ.
1
þ83 (c 1.09, CHCl3). H NMR (400 MHz, CDCl3): d 0.94
(d, J¼6.6 Hz, 3H), 1.25 (s, 3H), 1.32e1.83 (m, 8H), 1.90e
2.00 (m, 1H), 2.07e2.29 (m, 2H), 2.37e2.48 (m, 1H),
3.83e4.00 (m, 4H). 13C NMR (125.6 MHz, CDCl3): d 12.4,
17.5, 22.6, 22.8, 25.9, 29.8, 38.2, 43.1, 44.1, 49.8, 65.4
(2C), 112.6, 213.4. GCeMS, m/z (rel int. %): 238 (17)
[Mþ], 209 (31), 138 (11), 112 (74), 99 (100), 86 (78), 67
(14), 55 (21), 41 (16). HRMS (FAB) calcd for C14H22O3:
238.1569, found: 239.1659 [MþH]þ.
4.2.16. (1S,4aS )-Decahydro-5-(1,3-dioxolan)-1,4a-
dimethylnaphthalene-2-ol, 6c
A 1 M solution of diisobutylaluminum hydride (14.5 ml,
14.5 mmol) was added at ꢁ78 ꢀC to a solution of (1S,4aS )-
octahydro-5-(1,3-dioxolan)-1,4a-dimethylnaphthalene-2(1H )-
one 6b (3.41 g, 14.3 mmol) in distilled Et2O (20 ml). The
solution was stirred at ꢁ78 ꢀC for 1 h, then left to warm up
to room temperature. The solution was stirred at room temper-
ature for 15 min before being cooled to ꢁ78 ꢀC for quenching
with a saturated solution of NH4Cl. After warming to room
temperature, the phases were separated and the aqueous phase
backwashed twice with Et2O. The combined organic extracts
were washed with brine and dried over MgSO4. The crude ex-
tract was evaporated under reduced pressure and the product
was purified by flash chromatography to yield a colorless oil
(3.05 g, 89%). Rf value: 0.33 (cyclohexane/EtOAc 3:1, v/v).
4.2.14. (S )-4,4a,5,6,7,8-Hexahydro-5-(1,3-dioxolan)-1,4a-
dimethylnaphthalene-2(3H )-one, 6a
2-Ethyl-2-methyl-1,3-dioxolan (100 ml) and catalytic
amounts of ethylene glycol and p-toluenesulfonic acid were
added to a solution of (S )-3,4,8,8a-tetrahydro-5,8a-dimethyl-
naphthalene-1,6(2H,7H )-dione
6 (10.5 g, 53.8 mmol) in
DCM (100 ml). The solution was stirred for 2 days at room
temperature, then triethylamine (4 ml) and DCM (400 ml)
were added. The organic phase was washed with brine and
then dried over MgSO4. The solution was evaporated under
reduced pressure and the crude product purified by flash chro-
matography to yield 6a (11.0 g, 90%) as a colorless oil. Rf
value: 0.33 (cyclohexane/EtOAc 3:1, v/v). [a]2D0 þ125 (c
1
1
1.39, CHCl3). H NMR (400 MHz, CDCl3): d 1.34 (s, 3H),
[a]2D0 þ113 (c 1.39, CHCl3). H NMR (400 MHz, CDCl3):
1.57e1.72 (m, 5H), 1.76 (d, J¼1.2 Hz, 3H), 2.02e2.25 (m,
2H), 2.32e2.50 (m, 2H), 2.67e2.76 (m, 1H), 3.87e4.00 (m,
4H). 13C NMR (125.6 MHz, CDCl3): d 11.5, 20.9, 21.4,
26.4, 26.5, 29.7, 33.7, 45.3, 65.0, 65.3, 112.8, 130.1, 156.0,
198.5. GCeMS, m/z (rel int. %): 236 (21) [Mþ], 180 (12),
149 (21), 121 (17), 107 (15), 99 (100), 91 (34), 77 (25), 55
(18), 41 (12). HRMS (FAB) calcd for C14H20O3: 236.1412,
found: 237.1477 [MþH]þ.
d 0.92e1.00 (m, 3H), 1.12 (s, 3H), 1.24e1.83 (m, 12H),
2.31 (br s, 1H), 3.16 (m, 1H), 3.83e4.00 (m, 4H). 13C NMR
(125.6 MHz, CDCl3): d 12.7, 16.8, 20.9, 22.8, 23.6, 29.8,
32.0, 44.2, 44.3, 44.8, 65.4 (2C), 80.0, 112.8. GCeMS, m/z
(rel int. %): 240 (11) [Mþ], 222 (13), 195 (10), 178 (12),
160 (16), 145 (15), 125 (26), 113 (22), 99 (100), 86 (71), 67
(10), 55 (18), 41 (12). HRMS (FAB) calcd for C14H24O3:
240.1725, found: 241.1817 [MþH]þ.
4.2.15. (1S,4aS )-Octahydro-5-(1,3-dioxolan)-1,4a-
dimethylnaphthalene-2(1H )-one, 6b
4.2.17. (5S,8aS )-Octahydro-6-hydroxy-5,8a-dimethyl-
naphthalene-1(2H )-one, 11
Pd/C (0.2 g) was added to a solution of (S )-4,4a,5,6,7,8-
hexahydro-5-(1,3-dioxolan)-1,4a-dimethylnaphthalene-
2(3H )-one 6a (2.79 g, 11.8 mmol) in pyridine (50 ml). The
suspension was stirred vigorously for 3 days under 12 bar
H2 atmosphere at 65 ꢀC. DCM (250 ml) was then added and
the suspension filtered over Celite. The filtrate was washed
2-Hydroxy-pyridinium
p-toluenesulfonate
(15.0 g,
56.1 mmol) was added to (1S,4aS )-decahydro-5-(1,3-dioxo-
lan)-1,4a-dimethylnaphthalene-2-ol 6c (5.30 g, 22.1 mmol) in
a 1:1 solution of acetone and water (100 ml). The mixture
was stirred for 2 h at 70 ꢀC. After cooling to room tempera-
ture, satd NaHCO3 (400 ml) was added and the phases

4800
M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
separated. The aqueous phase was backwashed three times
with DCM (500 ml each). The combined organic phases
were washed with brine and dried over MgSO4. The crude
mixture was purified by flash chromatography to yield a color-
less oil (3.51 g, 82%). Rf value: 0.33 (cyclohexane/EtOAc 3:1,
v/v). [a]2D0 þ125 (c 1.39, CHCl3). 1H NMR (400 MHz,
CDCl3): d 0.97 (d, J¼6.4 Hz, 3H), 1.27 (s, 3H), 1.38e2.05
(m, 10H), 2.12e2.31 (m, 2H), 3.10e3.17 (m, 1H). 13C
NMR (125.6 MHz, CDCl3): d 11.0, 21.4, 23.1, 27.2, 28.7,
35.6, 39.0, 45.2, 45.4, 55.2, 79.5, 214.3. GCeMS, m/z (rel
int. %): 196 (32) [Mþ], 178 (81), 163 (31), 135 (100), 111
(75), 107 (71), 95 (62), 81 (66), 67 (69), 55 (73), 41 (78).
HRMS (FAB) calcd for C12H20O2: 196.1463, found:
196.1481 [M]þ.
4.3.4. General procedure for the Sonogashira reaction on
solid support (general procedure 4)
The resin (1 equiv) was combined under an argon atmo-
sphere with CuI (1.0 equiv), Pd(PPh3)4 (0.5 equiv), DMF
(15 ml/g), diisopropylethyl amine (20 equiv), and the terminal
alkyne (15 equiv). The mixture was shaken overnight at 90 ꢀC.
The solution was filtered and the resin washed three times with
THF/H2O¼2:1, DCM/MeOH¼1:1 (v/v), MeOH, DCM/
MeOH¼1:1 (v/v), and DCM, and then dried under reduced
pressure.
4.3.5. General procedure for the reductive amination on
solid support (general procedure 5)
Dry resin (1 equiv) was combined with toluene (5 ml/g
resin), titanium(IV) chloride (1.6 equiv) in toluene, and the
amine (3.8 equiv). The mixture was shaken overnight at
60 ꢀC. The solution was then filtered and the resin washed three
times with toluene, DCM/MeOH¼1:1 (v/v), MeOH, DCM/
MeOH¼1:1 (v/v), and DCM, and then dried in vacuo. The resin
was then suspended in THF (3 ml/g resin) with sodium cyano-
borohydride (1.5 equiv) and shaken overnight at room tempera-
ture. The solution was then filtered and resin washed three times
with THF, DCM/MeOH¼1:1 (v/v), MeOH, DCM/MeOH¼1:1
(v/v), and DCM, and then dried in vacuo.
4.3. General procedures for solid-supported synthesis
4.3.1. General procedure for resin loading (general
procedure 1)
THP-functionalized resin (1.0 equiv) was preswelled for
15 min in DCM (15 ml/g). The alcohol (5 equiv) to be coupled
was then added along with p-toluenesulfonic acid monohy-
drate (0.5 equiv) and the suspension shaken overnight. The
resin was filtered and washed three times each with DCM,
DCM/MeOH¼1:1 (v/v), MeOH, DCM/MeOH¼1:1 (v/v),
and DCM, and then dried in vacuo.
Loading determination procedure: resin was preswelled for
15 min in DCM, then a 10% solution of trifluoroacetic acid in
DCM (5 ml) was added and shaken for 10 min. The solution
was then filtered and coevaporated with toluene (3 ml). The
amount and quality of the cleaved alcohol determines the
loading of the resin.
4.3.6. General procedure for the amination of aryl iodides
on solid support (general procedure 6)
Amine (3.0 equiv) was added to the resin (1 equiv) and
combined under an argon atmosphere with CsOAc (3.6 equiv),
CuI (1.5 equiv), and DMF (8 ml/g resin). The reaction mixture
was heated to 90 ꢀC for 18 h (deep blue solution). The solution
was then filtered, and the resin washed three times with tolu-
ene, DCM/MeOH¼1:1 (v/v), MeOH, DCM/MeOH¼1:1 (v/v),
and DCM, and then dried in vacuo.
4.3.2. General procedure for the solid phase aldol reaction
(general procedure 2)
n-BuLi in hexane (9 equiv) was added to a solution of diiso-
propyl amine (10 equiv) in THF (1 ml/mmol) at ꢁ78 ꢀC. After
the solution warmed to room temperature, it was then added
to the resin (1 equiv), which was washed twice and preswelled
in THF (15 ml). The mixture was shaken at room temperature
for 30 min then cooled to 0 ꢀC. The aldehyde (12 equiv) was
then added and the mixture shaken for a further 30 min at
0 ꢀC, then 2 h at room temperature. After filtration of the sol-
vent, the resin was washed three times each with THF, DCM/
MeOH¼1:1 (v/v), MeOH, DCM/MeOH¼1:1 (v/v), and DCM,
and then vacuum dried.
4.3.7. General procedure for the alkylation on solid support
(general procedure 7)
The polymer-bound ketone (1.0 equiv) was washed twice
and preswelled in dry THF (2 ml/g resin). Potassium hydride
(5.0 equiv) in THF (3 ml/mmol) was then added and the reac-
tion shaken for 30 min at room temperature. The primary bro-
mide (8.0 equiv) was then added and the reaction shaken for
1 h at room temperature and 2 h at 50 ꢀC. After draining the
solvent, the resin was washed three times each with THF,
DCM/THF¼1:1 (v/v), MeOH, DCM/MeOH¼1:1 (v/v), and
DCM, and then vacuum dried.
4.3.3. General procedure for the cleavage (general
procedure 3)
4.3.8. General procedure for the Wittig reaction on solid
support (general procedure 8)
The dry resin (30 mg) was preswelled in DCM (2 ml) for
15 min. After filtration of the solvent, a 10% TFA solution in
DCM (3 ml) was added and the mixture shaken for 10 min.
The solution was filtered and the resin washed twice with the
TFA solution. Toluene (3 ml) was added to the combined
filtrates and the solution evaporated under reduced pressure.
The crude product was dissolved in ca. 100 ml acetonitrile and
purified by HPLC.
The polymer-bound ketone (1.0 equiv) was suspended in
toluene (2 ml/g resin) and shaken for 15 min. Triphenylphos-
phonium bromide (10 equiv) and n-BuLi (8 equiv) in toluene
were then added and the reaction shaken for 15 min at room
temperature then overnight at 100 ꢀC. The solvent was then
drained, and the resin washed three times with toluene, DCM/
toluene¼1:1 (v/v), DCM/MeOH¼1:1 (v/v), MeOH, DCM/
MeOH¼1:1 (v/v), and DCM, and then dried in vacuo.

M. Scheck et al. / Tetrahedron 64 (2008) 4792e4802
4801
4.3.9. General procedure for the cleavage of the silyl
a final assay volume of 100 ml and end concentrations of
200 mM ATC33 and 300 mM DTNB.34 Similarly, control exper-
iments in the presence of 0.01% Triton X-100 were performed.35
The reaction rate was calculated from the absorption difference
between 30 and 90 s reaction time and was determined to be
0.059ꢃ0.003 DA/min in the absence of inhibitor.34 After
screening the whole library at 20 mM inhibitor concentration,
IC50 values of the most promising candidates (best percent inhi-
bition) were determined. Different concentrations of each test
compound were assayed and the percent inhibition due to the
presence of test compound was calculated. IC50 values were
determined from log concentration versus inhibition curves by
using the IC50 fit function that is implemented in the program
GRAFIT version 5.0.4 (Erithacus, Surrey, UK).
protecting group on solid phase (general procedure 9)
The polymer-bound silyl protected alcohol was preswelled
in THF (2 ml/g resin) and shaken for 15 min. Tetrabutylam-
monium fluoride trihydrate was then added and the mixture
shaken overnight at room temperature. The solvent was
drained and the resin washed three times with THF, DCM/
THF¼1:1 (v/v), DCM/MeOH¼1:1 (v/v), MeOH, DCM/
MeOH¼1:1 (v/v), and DCM, and then dried in vacuo.
4.3.10. General procedure for the Heck reaction on solid
support (general procedure 10)
The resin (1.0 equiv) was preswelled for 15 min in DMF
(10 ml/g). Olefin (5.0 equiv), Pd(OAc)2 (0.1 equiv), PPh3
(2.0 equiv), and tetramethylethylene diamine (1.0 equiv)
were added and the suspension heated to 70 ꢀC and shaken
overnight. The solution was filtered away and the resin washed
three times with THF/H2O¼2:1, DCM/MeOH¼1:1 (v/v),
MeOH, DCM/MeOH¼1:1 (v/v), and DCM, and then dried
in vacuo.
Acknowledgements
This research was supported by the Deutsche Forschungs-
gemeinschaft, the Max Planck Gesellschaft, and the Fonds
der Chemischen Industrie. M.A.K. was the recipient of a doc-
toral scholarship from the Studienstiftung des Deutschen
Volkes.
4.3.11. General procedure for the Suzuki reaction on solid
support (general procedure 11)
The resin (1.0 equiv) was preswelled in THF (10 ml/g).
Na2CO3 (0.5 equiv), Pd(PPh3)4 (0.5 equiv), and boronic acid
(2.0 equiv) were then added and the suspension heated to
60 ꢀC and shaken overnight. The solution was filtered, the resin
washed with THF/H2O¼2:1, DCM/MeOH¼1:1 (v/v), MeOH,
DCM/MeOH¼1:1 (v/v), and DCM, and then dried in vacuo.
Supplementary data
Full analytical characterization of the whole library and
results of the AChE assay are provided. Supplementary data
associated with this article can be found in the online version,
at doi:10.1016/j.tet.2008.02.106.
4.4. Inhibition of acetylcholinesterase (AChE)
References and notes
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