Development of a new class of inhibitors for the malarial aspartic protease plasmepsin II based on a central 7-azabicyclo[2.2.1]heptane scaffold

Article abstract of DOI:10.1002/hlca.200390176

Plasmepsin II (PMII), a malarial aspartic protease involved in the catabolism of hemoglobin in parasites of the genus Plasmodium, and renin, a human aspartic protease, share 35% sequence identity in their mature chains. Structures of 4-arylpiperidine inhibitors complexed to human renin were reported by Roche recently. The major conformational changes, compared to a structure of renin, with a peptidomimetic inhibitor were identified and subsequently modeled in a structure of PMII (Fig. 1). This distorted structure of PMII served as active-site model for a novel class of PMII inhibitors, according to a structure-based de novo design approach (Fig. 2). These newly designed inhibitors feature a rigid 7-azabicyclo[2.2.1]heptane scaffold, which, in its protonated form, is assumed to undergo ionic H-bonding with the two catalytic Asp residues at the active site of PMII. Two substituents depart from the scaffold for occupancy of either the S1/S3 or S2′-pocket and the hydrophobic flap pocket, newly created by the conformational changes in PMII. The inhibitors synthesized starting from N-Boc-protected 7-azabicyclo[2.2.1]hept-2-ene (6; Schemes 1-5) displayed up to single-digit micromolar activity (IC₅₀ values) toward PMII and good selectivity towards renin. The clear structure-activity relationship (SAR; Table) provides strong validation of the proposed conformational changes in PMII and the occupancy of the resulting hydrophobic flap pocket by our new inhibitors.

Full text of DOI:10.1002/hlca.200390176

Helvetica Chimica Acta Vol. 86 (2003)
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Development of a New Class of Inhibitors for the Malarial Aspartic
Protease Plasmepsin II Based on a Central 7-Azabicyclo[2.2.1]heptane
Scaffold
by David A. Carcache, Simone R. Hˆrtner, Paul Seiler, and FranÁois Diederich*
Laboratorium f¸r Organische Chemie der Eidgenˆssischen Technischen Hochschule, ETH-Hˆnggerberg, HCI,
CH-8093 Z¸rich (e-mail: diederich@org.chem.ethz.ch)
and
Arnulf Dorn and Hans Peter M‰rki
Pharma Research, F. Hoffmann-La Roche Ltd., CH-4070 Basel
and
Christoph Binkert and Daniel Bur
Actelion Pharmaceuticals Ltd., Gewerbestrasse 16, CH-4123 Allschwil
Dedicated to Professor Andrea Vasella on the occasion of his 60th birthday
Plasmepsin II (PMII), a malarial aspartic protease involved in the catabolism of hemoglobin in parasites of
the genus Plasmodium, and renin, a human aspartic protease, share 35% sequence identity in their mature
chains. Structures of 4-arylpiperidine inhibitors complexed to human renin were reported by Roche recently.
The major conformational changes, compared to a structure of renin, with a peptidomimetic inhibitor were
identified and subsequently modeled in a structure of PMII (Fig. 1). This distorted structure of PMII served as
active-site model for a novel class of PMII inhibitors, according to a structure-based de novo design approach
(Fig. 2). These newly designed inhibitors feature a rigid 7-azabicyclo[2.2.1]heptane scaffold, which, in its
protonated form, is assumed to undergo ionic H-bonding with the two catalytic Asp residues at the active site of
PMII. Two substituents depart from the scaffold for occupancy of either the S1/S3 or S2'-pocket and the
hydrophobic flap pocket, newly created by the conformational changes in PMII. The inhibitors synthesized
starting from N-Boc-protected 7-azabicyclo[2.2.1]hept-2-ene (6; Schemes 1 5) displayed up to single-digit
micromolar activity (IC50 values) toward PMII and good selectivity towards renin. The clear structureÀactivity
relationship (SAR; Table) provides strong validation of the proposed conformational changes in PMII and the
occupancy of the resulting hydrophobic flap pocket by our new inhibitors.
1. Introduction. Malaria, a life-threatening disease caused by parasites of the
genus Plasmodium, kills each year more than one million people, and more than 500
millions clinical cases are annually registered [1]. The recent emergence of multi-drug-
resistant strains of Plasmodium falciparum, the parasite that causes the deadliest form
of malaria, demands the urgent development of new therapeutic agents with novel
modes of action [2 7].
The malarial parasite undergoes a complicated life cycle, which requires stages both
in a human host and a female Anopheles mosquito [8][9]. During its stay in the human
body, the parasites infect erythrocytes and catabolize hemoglobin (Hb) to provide
nutrients for its own growth and maturation, as well as for prevention of premature red

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blood cell lysis that might occur were parasite growth not compensated by reduced
host-cell volume [10]. Several proteinases have been isolated from acidic food vacuoles
[11][12], where degradation processes take place. These enzymes are believed to play
crucial roles in an ordered Hb degradation pathway. The most-recent studies suggest
that plasmepsins I and II (PMI, EC 3.4.23.38, and PMII, EC 3.4.23.39) [13][14], two
aspartic proteases, initiate the degradation process by cleaving Hb in a hinge region
without known sequence variations. After the initial cut, unraveling of Hb is possible,
thereby facilitating further proteolysis by plasmepsin IV (PMIV) [15], another aspartic
protease, and a histo-aspartic protease (HAP) [16]. Falcipain-2 [17], a cystein protease,
and falcilysin [18], a metallo-protease, should act further downstream, degrading large
fragments to small peptides, which are thought to be transported into the cytoplasm for
terminal degradation to amino acids [19]. Because degradation of Hb is vital for
parasite survival, inhibition of this degradation pathway offers a valid approach for the
development of new therapeutic agents.
Plasmepsin I and II have been identified as suitable targets for blocking this
degradation process [20]. In fact, a variety of inhibitors of PMII have been described in
recent years. They include statine- [21] and hydroxyethylamine-based [22] peptidomi-
metic inhibitors [23] generated by combinatorial-chemistry approaches, substrate
analogs based on allophenylnorstatin [24] and mannitol scaffolds [25], and amino-
piperidines discovered at Actelion by high-throughput-screening of large compound
libraries [26]. In several lead-optimization cycles, activities of the latter compound class
were improved to IC50 values (concentration of inhibitor at which 50% Vmax is
observed) in the single-digit nanomolar range. Selectivities over cathepsin D, the most
closely related human aspartic protease, were higher than 1000-fold (for a review on
PMII inhibitors, see [27]). The X-ray crystal structure of recombinant PMII complexed
to pepstatin A, a nonspecific aspartic protease inhibitor, has been solved at 2.7-ä
resolution [28]. Therefore, this enzyme was selected to serve as the structural matrix for
an X-ray structure-based de novo design approach as already pursued by the ETH
group in a variety of medicinal-chemistry projects [29 31].
High-throughput screening of the Roche compound library identified 3-
substituted 4-arylpiperidines as novel inhibitors of the human aspartic proteinase
renin (EC 3.4.23.15) [32]. The X-ray crystal structures of recombinant human renin
complexed with several representatives of this new class of inhibitors have been
determined, providing crucial structural information, which might be the basis of a
novel paradigm for the inhibition of monomeric aspartic proteases. Binding of the 4-
arylpiperidine derivatives, in their N-protonated form, to the two Asp residues of
the catalytic dyad is accompanied by a major induced-fit adaptation around the
active site of the enzyme. The long b-hairpin loop (flap), tightly covering the
catalytic dyad when inhibited by a peptidomimetic inhibitor, is shifted into a more-
open conformation, with several residues changing side-chain conformation. This
structural rearrangement unlocks a new hydrophobic pocket that is occupied by the
residue in position 4 of the piperidine scaffold. Rich and co-workers postulated
recently a similar binding mode for piperidinium-based inhibitors of pepsin (EC
3.4.23.1), another human aspartic protease [33], hinting at the possibility that such
conformational changes might also be operative in other eucaryotic aspartic
proteases.

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The remarkable interdomain flexibility of PMII observed by Silva et al. [28], as
well as the sequence identity of 35% between mature renin and PMII, prompted
us to hypothesize that an induced-fit adaptation as observed in renin might also be
effective in PMII. Further evidence for the high conformational flexibility of PMII
arose from the crystal structure of proplasmepsin II [34]. Also, some of the
3-substituted 4-arylpiperidines of the Roche group were reported in a patent to possess
high antimalarial activity, presumably by inhibiting one of the plasmepsin enzymes
[35].
The conformational changes observed in structures of human renin complexed to 4-
arylpiperidine derivatives were introduced to an available crystal structure of PMII
(PDB: 1SME), providing a new active-site matrix, which was subsequently exploited in
our design strategy (Fig. 1,a). The modeled active site of this distorted PMII structure
features three major binding pockets next to the catalytic dyad (Fig. 1,b) namely i) the
large hydrophobic S1/S3 pocket (Phe120, Phe111, Met15), ii) the more-hydrophilic S2'
pocket (Leu131, Tyr192), and iii) the lipophilic flap pocket, narrow at its entry and
spacious at its rear. The unlocking of the latter sub-site results after a cascade-like
reaction, including a lifting of the flap and side-chain rearrangements of Leu73, Tyr75,
and Trp39(pepsin numbering), as well as the disruption of the H-bond between the
latter two amino acids (Fig. 1,b).
With a modified structure of PMII, featuring conformational properties of a renin
4-arylpiperidine inhibitor complex and serving as active-site template, we designed two
classes of nonpeptidic PMII inhibitors. Synthesis and in vitro evaluation of these new
lead compounds, showing up to single-digit micromolar activities, are described in this
and the following paper [36] (for a preliminary communication of parts of this work,
see [37]).
2. Results and Discussion. 2.1. Design of the First Lead Structure. With the Roche-
in-house molecular-modeling program MOLOC [38], we identified 7-azabicyclo[2.2.1]-
heptane as a suitable central scaffold for new PMII inhibitors (for antimalarial activity
of some 8-azabicyclo[3.2.1]octane derivatives, see [35]). This bicyclus has a pKa value
of 10.8 [39] and should be fully protonated in the acidic vacuoles (estimated pH 5.0
5.4 [40]) where Hb degradation takes place. The protonated N-atom was expected
to form two charge-re-inforced H-bonds to the Asp residues of the catalytic dyad,
by analogy with the renin complexes of the 4-arylpiperidinium inhibitors from Roche
[32].
To produce inhibitors with molecular weights not exceeding 500 [41], we decided to
decorate the scaffold with two residues only, assuming that they should be pointing into
the more hydrophobic S1/S3 and flap pockets, while leaving the less-hydrophobic S2'
pocket empty. Modeling suggested that C(2) and C(3) of the bicyclic scaffold would
furnish suitable anchoring points for these substituents. Thus, compound (Æ)-1 (Fig. 2)
was designed as initial lead. In a PMII complex of (2S,3R)-1, the naphthyl moiety
should occupy the S1/S3 pocket, establishing Van der Waals contacts with the side
chains of Phe111, Phe120, and Met15 (for a review on sulfur aromatic interactions, see
[42]). The narrow entry of the flap pocket should be occupied by the benzyloxy moiety,
establishing Van der Waals contacts with the side chains of Met75, Phe111, and Tyr77.
The rather spacious lipophilic environment at the rear end of the flap pocket would be

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Fig. 1. Structural basis for inhibitor design. a) Superposition of the X-ray crystal structure of PMII (orange) with
the modeled structure (green), where the flap has been moved away from the catalytic dyad, consisting of
Asp34 and Asp214. b) Schematic representation of the active site of the modeled structure. Shown in blue is the
original location of the H-bonded side chains of Trp41 and Tyr77 before the flap moves.

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suitably filled by a piperonyl (ˆ1,3-benzodioxol) ring sandwiched between the side
chains of Val105 and Tyr115 and linked by a propyl chain to the para-position of the
benzyloxy moiety.
Fig. 2. Representation of (2S,3R)-1 in the active site of the modeled structure of PMII
2.2. Synthesis of (Æ)-1. Synthesis of the lead compound started with the
DielsÀAlder reaction between N-Boc-protected 1H-pyrrole 2 [43] and alkyne 3 [44],
furnishing (Æ)-4 in 80% yield [45] (Scheme 1). Selective hydrogenation of the more
electron-rich CˆC bond under mild conditions provided (Æ)-5 in quantitative yield.
Desulfonylation of (Æ)-5 with Na/Hg afforded 6 in acceptable yield (53%), by analogy
with the work of Liang et al. [46]. However, the large excess of Na/Hg (20 equiv.)
required for this one-step reductive cleavage of the Ts group prompted us to investigate
an alternative route to 6.

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Scheme 1. Synthesis of the Central Scaffold 6
a) 808, 24 h; 80%. b) Ni2B, EtOH, r.t., 3 h; 100%. c) Na/Hg (2.5%), Na2HPO4/NaH2PO4, AcOEt/t-BuOH, r.t.,
24 h; 53%. Boc ˆ (tert-butoxy)carbonyl.
The three-step desulfonylation described by Kaufmann and co-workers appeared to
be a more suitable solution [47]. Initial hydrosilylation of (Æ)-5, reported to proceed in
high yield, however, afforded (Æ)-7 in 28% yield only. On the other hand, metallation
(BuLi/TMEDA) followed by reaction with TMSCl gave (Æ)-7 in 53% yield along with
side product (Æ)-8 (19%; Scheme 2). Hydrogenation of (Æ)-7 and (Æ)-8 with diimide,
generated in situ from dipotassium azodicarboxylate, afforded with complete endo-
selectivity (Æ)-9 and (Æ)-10 in 92 and 90% yield, respectively. Treatment of (Æ)-9 or
(Æ)-10 with Bu4NF ¥ 3 H2O furnished 6 in 72 and 81% yield, respectively (Scheme 2).
Scheme 2. Alternative Route to 6
a) TMEDA, BuLi, TMSCl, THF, À 788, 1 h; 53% ((Æ)-7), 19% ((Æ)-8). b) N2H2, MeOH, r.t., 12 h 6 d; 92%
((Æ)-9), 90% ((Æ)-10). c) Bu4NF ¥ 3 H2O, THF, r.t., 12 h; 72 81%. TMEDA ˆ N,N,N',N'-Tetramethylethyle-
nediamine; TMS ˆ Me3Si.
Dihydroxylation of 6 with OsO4/NMO cleanly led to the exo-cis-diol 11 (100%)
[48], and Williamson ether synthesis (2-(bromomethyl)naphthalene/NaH) provided
mono-ether (Æ)-12 (68%) together with di-ether 13 (16%) (Scheme 3). A second
Williamson ether synthesis of (Æ)-12 with 4-bromobenzyl bromide afforded (Æ)-14 in
97% yield. Subsequent Suzuki cross-coupling with borane 15 produced (Æ)-16 (49%),
which was deprotected to the target compound (Æ)-1 in 86% yield. For comparison, 13
and (Æ)-14 were also deprotected, furnishing 17 and (Æ)-18 in 60 and 89% yield,
respectively.

Helvetica Chimica Acta Vol. 86 (2003)
Scheme 3. Synthesis of (Æ)-1
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a) NMO, OsO4, NaHCO3, H2O/t-BuOH/THF, r.t., 2 d; 100%. b) 2-(Bromomethyl)naphthalene, NaH, THF,
08 ! r.t., 1 d; 68% ((Æ)-12), 16% (13). c) 4-Bromobenzyl bromide, NaH, THF, 08 ! r.t., 12 h; 97%. d)
[PdCl2(dppf)], MeONa, THF, D, 50 h; 49%. e) TFA, CH2Cl2, r.t., 30 min, 60 89%. NMO ˆ 4-Methylmorpho-
line 4-oxide; dppf ˆ 1,1'-bis(diphenylphosphino)ferrocene; TFA ˆ trifluoroacetic acid.
2.3. Biological Activity. The in vitro activity of compounds (Æ)-1, 17, and (Æ)-18
toward PMII was determined in a fluorescence assay (Table; for details, see the Exper.
Part). Target compound (Æ)-1 (IC50 ˆ 70 mm) was found to bind much better than 17
(700 mm) or (Æ)-18 (>1000 mm; limit of the assay). The shorter substituents of 17 and
(Æ)-18, proposed to point into the flap pocket, probably leave the rear of this subsite
unoccupied, leading to a substantial loss in activity. On the other hand, the affinity
measured for (Æ)-1 corroborated the suitability of the 7-azabicyclo[2.2.1]heptane
scaffold for the development of more-potent inhibitors of PMII.
2.4. Second-Generation Inhibitors. Considering the binding data obtained with the
first series of inhibitors, we intended to specifically occupy the rear of the flap pocket,
which appeared to have a strong influence on biological activity. According to
molecular modeling, the 1,3-benzothiazole residue, as seen in (Æ)-19, seemed to

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Table. Biological Activities of Designed Inhibitors of Plasmepsin II
Inhibitor
IC50
PMIIa) [mm]
PMIVb) [mm]
CatDc) [mm]
CatEd) [mm]
Renin [mm]
(Æ)-1
17
70
700
> 1000
939
10
n.d.e)
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
n.d.
> 100
> 100
> 100
> 100
(Æ)-18
(Æ)-19
(Æ)-20
(À)-19
(‡)-19
15
20
61
61
61
16
8
12
35
16
25
5
4
a) Plasmepsin II. b) Plasmepsin IV. c) Cathepsin D. d) Cathepsin E. e) Not determined.
be superior over the 1,3-benzodioxole moiety (in (Æ)-1), thereby inverting the
orientation of the heterocycle to present the benzene ring directly to the hydrophobic
residues at the rear of the pocket. Furthermore, a different linker to the naphthyl
substituent, possibly favoring its positioning in the S1/S3-pocket, was explored in (Æ)-
20.
Starting from p-cresol, a sequence of nucleophilic substitutions furnished aryl ether
21, which was brominated with NBS to afford 22 (Scheme 4). Williamson ether
synthesis of 22 with (Æ)-12 provided the protected inhibitor (Æ)-23. Subsequent N-Boc
deprotection under standard conditions (TFA, CH2Cl2) yielded unexpected results.
The desired removal of the Boc protecting group was accompanied by cleavage of the
4-alkoxy-substituted benzyl ether moiety. Selective Boc-group removal by the mild and
selective method reported by Nigam et al. [49], with anhydrous ZnBr2 in CH2Cl2, was
not successful either. Finally, a two-step procedure led to target compound (Æ)-19
under very mild conditions. Conversion of (Æ)-23 to a moisture- and acid-sensitive (tert-
butyl)dimethylsilyl carbamate [50], followed by immediate treatment of the crude
product with FÀ, provided (Æ)-19 in 82% yield. By analogy, target compound (Æ)-20
was prepared starting from 11, via (Æ)-24 and (Æ)-25.
Biological activity of the two new target compounds toward PMII and PMIV, as
well as the three human aspartic proteases cathepsin D (CatD; EC 3.4.23.5), cathepsin
E (CatE; EC 3.4.23.34), and renin, was determined in an automated assay (see Exper.
Part). Inhibitors (Æ)-19 and (Æ)-20 exhibited IC50 values of 9and 10 mm, respectively,
thereby showing substantially enhanced activity compared with first-generation
compound (Æ)-1 (Table). Apparently, the spacious S1/S3 pocket can accommodate
naphthyl residues in different orientations ((Æ)-19 vs. (Æ)-20). Most importantly, a
modeling-predicted increase in binding affinity upon better occupancy of the flap
pocket was validated experimentally ((Æ)-1 vs. (Æ)-19). This provides an encouraging
boost for future modeling-driven lead-optimization cycles.
This second series of PMII inhibitors showed good selectivity towards renin, but
poor selectivity with respect to CatD and CatE. These findings suggest that the latter
two human aspartic proteases may also undergo induced-fit adaptations, thereby
forming a flap pocket that can be occupied by the 1,3-benzothiazole residue of (Æ)-19
and (Æ)-20.

Helvetica Chimica Acta Vol. 86 (2003)
Scheme 4. Synthesis of (Æ)-19 and (Æ)-20
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a) 1,2-Dibromoethane, NaOH, H2O, D, 6 h; 98%. b) 2-Sulfanylbenzothiazole, NaH, DMF, 808, 1 h; 90%. c)
NBS, AIBN, CHCl3, D, 4 h; 19%. d) 22, NaH, THF, 08 ! r.t., 16 h; 37 82%. e) TBDMSOTf, 2,6-lutidine,
CH2Cl2, r.t., 30 min. f) Bu4NF, THF, r.t., 1 2 h; 71 82% over 2 steps. g) 1-(Bromomethyl)naphthalene, NaH,
THF, 08 ! r.t., 15 h; 43%. NBS ˆ N-Bromosuccinimide; AIBN ˆ azobis(isobutyronitrile); TBDMS ˆ (tert-
butyl)dimethylsilyl; TfO ˆ trifluoromethanesulfonate.
2.5. Optical Resolution of (Æ)-19. Initial attempts to form esters of (À)-d-mandelic
acid with alcohol (Æ)-12 and to separate the mixture of diastereoisomers by column
chromatography were unsuccessful. In contrast, esterification of (À)-camphanic acid
with (Æ)-12 furnished a mixture of diastereoisomers, which could be separated by
column chromatography, to afford 26 and 27 (Scheme 5). The X-ray crystal structure of
26 was subsequently determined, which allowed the assignment of the absolute
configuration to the two diastereoisomers (Fig. 3). Basic ester hydrolysis finally led to
optically pure (‡)-12 and (À)-12, which were further processed according to the
synthetic route described above (Scheme 4) to yield (‡)-(2S,3R)-19 and (À)-(2R,3S)-
19, respectively.
Both antipodes displayed similar IC50 values ((À)-19: 5 mm and (‡)-19: 4 mm;
Table); they are within the uncertainty of the biological assay identical to the activity of
racemate (Æ)-19 (9 mm). This result leads us to conclude that either the spacious active
site of PMII may undergo major conformational changes upon complexation of small

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Fig. 3. ORTEP Representation of 26 with vibrational ellipsoids shown at the 30% probability level. Arbitrary
numbering.
molecules or that hydrophobic inhibitors can sufficiently adapt to spatial conditions
dictated by the enzyme active site. Both enantiomers can be fit into the active site of the
modeled structure of PMII, with the 1,3-benzothiazole moiety apparently being located
in the flap pocket in both cases. Consequently, the naphthyl moiety should be
positioned either in the S1/S3 pocket for the first enantiomer, or in the S2' subsite for
the other antipode. Molecular modeling indeed suggests that the S1/S3 and S2' pockets
should both be able to accommodate the naphthyl residue.
3. Conclusions. In this study on the rational development of plasmepsin II (PMII)
inhibitors, we report a successful extension of our program on X-ray-structure-based
design of nonpeptidic enzyme inhibitors. In previous work [29 31], the X-ray crystal
structures of enzymeÀinhibitor complexes were used unchanged for design purposes.
In contrast, in this work, the crystal structure of PMII was adapted to a more-open
conformation, based on observations made for the structurally related human aspartic
protease renin and the 35% sequence identity between mature renin and PMII,
respectively.
Based on this modified PMII structure, which features a new hydrophobic flap
pocket, we designed a new class of inhibitors with promising biological activity. They
feature a rigid 7-azabicyclo[2.2.1]heptane scaffold, which, in protonated form, is
assumed to undergo ionic H-bonding with the two catalytic Asp residues at the active
site of PMII. Optimization of the two inhibitor substituents, which are assumed to point
into the flap pocket and the S1/S3 or S2'-pocket (depending on the enantiomer of the
chiral inhibitors), led to (Æ)-19, which displayed an IC50 value of 9 mm.

Helvetica Chimica Acta Vol. 86 (2003)
Scheme 5. Optical Resolution of (Æ)-19
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a) (À)-Camphanoyl chloride, Et3N, CH2Cl2, r.t., 20 h; 38% (26), 30% (27). b) aq. KOH (3m), MeOH/CH2Cl2,
r.t., 30 min; 74 98%.
The following lessons can be drawn: i) the observed SAR (Table) provides strong
support for the proposed conformational changes in PMII, leading to the opening of a
hydrophobic flap pocket. Correct occupancy of this pocket in terms of shape and
electronic complementarity appears to be crucial; however, the nature of the
substituents positioned in this area must be hydrophobic. In particular, complete
occupation of this pocket seems absolutely necessary for good affinity as reflected by
the strong loss of activity in 17 and (Æ)-18 equipped with inadequate, short substituents.
Further evidence for the binding free energy to be gained in this unlocked hydrophobic
pocket was obtained from the significantly enhanced affinity displayed by (Æ)-19 and
(Æ)-20 in comparison to (Æ)-1. Our proposal for a conformational rearrangement of the
entire flap, as well as selected parts of the protein core in PMII, receives strong support
from a yet-unpublished report on an X-ray crystal structure of a complex of PMII
inhibited by a 4-arylpiperidine derivative from Roche [51]. ii) The naphthyl moieties
seem to be accepted in a number of different conformations by the spacious S1/S3
pocket. The poor enantioselectivity observed with (À)-19 and (‡)-19 can be explained
by potential adaptations of the protein or incomplete filling of the protein pockets by
these two molecules. These findings will certainly benefit future refinements of the
molecular modeling in design and synthesis of new generations of more-potent and
-selective PMII inhibitors.
We are grateful to the ETH Research Council and F. Hoffmann-La Roche for support of the work done at
the ETH. We thank Dr. R. P. Moon for helpful discussions and Dr. C. Thilgen for assistance with the
nomenclature.
Experimental Part
General. Solvents and reagents were reagent-grade, purchased from commercial suppliers, and used
without further purification unless otherwise stated. The following compounds were prepared according to

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literature procedures: 2 [43], 3 [44], (Æ)-4 [45], (Æ)-5, and 6 [46]. THF was freshly distilled from sodium
benzophenone ketyl, CH2Cl2 from CaH2. Evaporation in vacuo was conducted at H2O aspirator pressure. All
products were dried under high vacuum (10À2 Torr) before anal. characterization. Column chromatography
(CC): SiO2 60 (40 63 mm) from Fluka or Merck, 0 0.4 bar pressure; Alox ICN Alumina B, Act. II from ICN
Biochemicals. TLC: SiO2 60 F245, Merck, visualization by UV light at 254 nm or by staining with a soln. of
KMnO4 (3 g) and K2CO3 (20 g) in 5% aq. NaOH soln. (5 ml) and H2O (300 ml). M.p.: B¸chi B540 melting point
apparatus; uncorrected. Optical rotations: Perkin-Elmer 241 polarimeter; 1-dm cell, l ˆ 589nm (Na D-line). IR
[cmÀ1]: Perkin-Elmer 1600-FT spectrometer. NMR (1H,13C): Varian Gemini-200, Varian Gemini-300, or Bruker
AMX-500; spectra were recorded at r.t. with solvent peak as reference. MS (m/z (%)): EI-MS: VG-TRIBRID
spectrometer at 70 eV; ESI-MS: Perkin-Elmer Sciex API III spectrometer; HR-MALDI-MS: IonSpec Ultima
(2,5-dihydroxybenzoic acid (DHB) matrix). Elemental analyses were performed by the Mikrolabor at the
Laboratorium f¸r Organische Chemie, ETH Z¸rich.
Biological Assays. The biological activities of (Æ)-1, 17, and (Æ)-18 were determined as follows: the FRET
(fluorescence resonance energy transfer)-based assay used the quenched fluorogenic substrate 4-{[4-
(dimethylamino)phenyl]azo}benzoic acid (DABCYL)-Arg-Leu-Glu-Arg-Thr-Phe-Leu-Ser-Phe-Pro-Thr-Thr-
Asp-Arg-5-[(2-aminoethyl)amino]naphthalene-1-sulfonic acid (EDANS), whose peptide sequence is derived
from the natural Hb processing site for PMII. Incubation of PMII with the fluorogenic substrate resulted in
specific cleavage at the PheÀLeu bond and a time-dependent increase in fluorescence intensity that was linearly
related to the extent of substrate hydrolysis. The standard conditions for hydrolysis at 378 were 20 mm AcONa,
pH 4.7, containing activated PMII (2 ng; the Pro-PMII was prepared and purified as described by Hill et al. and
was activated by incubation in 20 mm AcONa, pH 4.7, at r.t. for 60 min. [14]), 20 mm peptide (stock soln.: 5 mm
in 50% Me2SO) in a total volume of 100 ml on a microtiter plate (Black ViewPlateTM, Packard). The hydrolysis
of the substrate by PMII was monitored by measuring the fluorescence at lem ˆ 530 nm and lem ˆ 360 nm in a
Fluorescence Measurement System Millipore CytoFluor 2350 immediately after starting the reaction and after an
incubation period of 7 h.
The biological activity of (Æ)-19, (Æ)-20, (‡)-19, and (À)-19 was determined in automated assays [37]. The
proteolytic activities of plasmepsins II and IV, and cathepsins D and E were determined in a FRET-based assay
with a substrate purchased from Bachem (# M-2120). Approx. 1 nm enzyme was incubated with 1 mm substrate
at 378 in 50 mm AcONa (pH 5), 12.5% (w/v) glycerol, 0.1% (w/v) BSA (bovine serum albumin), and 10%
Me2SO. Enzyme activity was derived from the turnover rate of the substrate and monitored by the increase of
the fluorescent signal over time. Fluorescence was determined with a FLUOstar Galaxy from BMG using
excitation and emission filters of 355 and 520 nm. The proteolytic activity of renin was determined in two steps.
Approx. 2 pm renin was incubated at 378 with 0.5 mm of a peptide substrate (Bachem, # M-1120), whose
sequence is derived from the renin cleavage site in angiotensinogen. The assay buffer was PBS (phosphate-
buffered saline; pH 7.4), 1 mm EDTA (ethylenediaminetetraacetic acid), 1 mm 8-hydroxyquinoline sulfate,
0.1% BSA, and 5% Me2SO. Angiotensin 1 produced by renin was subsequently quantified with an enzyme
immunoassay, by comparison with an angiotensin 1 standard curve. Test compounds were dissolved and diluted
in 100% Me2SO.
IC50 Values for some of the inhibitors in this and the following paper [36] were also determined by both
methods; good agreement between the data was found.
tert-Butyl 2-[(4-Methylphenyl)sulfonyl]-3-(trimethylsilyl)-7-azabicyclo[2.2.1]hept-2-ene-7-carboxylate
((Æ)-7) and tert-Butyl 2-(Trimethylsilyl)-3-({4-[(trimethylsilyl)methyl]phenyl}sulfonyl)-7-azabicyclo[2.2.
1]hept-2-ene-7-carboxylate ((Æ)-8). To a well-stirred soln. of TMEDA (0.70 ml, 4.64 mmol) in THF (30 ml),
a freshly titrated soln. of BuLi in hexane (1.01m, 4.58 ml, 4.64 mmol) was added dropwise under Ar at À 788. A
soln. of (Æ)-5 (1.5 g, 4.29mmol) in THF (9ml) was then added at À 788. The mixture was stirred for 1 h, and
freshly distilled TMSCl (0.59ml, 5.15 mmol) was added at À 708. After warming to r.t., an equal volume of sat.
aq. NH4Cl soln. was added, leading to the formation of a white precipitate. After separation of the org. phase,
the aq. phase was extracted with Et2O (3Â). The combined org. layers were washed with sat. aq. NaHCO3 soln.,
dried (MgSO4), and concentrated in vacuo to give a brown oil as crude product. CC (SiO2; hexane/AcOEt 3 :1)
yielded (Æ)-7 (961 mg, 53%) together with (Æ)-8 (406 mg, 19%).
Data of (Æ)-7: Yellow oil. IR (CHCl3): 3019w, 1697s, 1595w, 1297m, 1145s, 840m. 1H-NMR (CDCl3,
300 MHz): 0.36 (s, 9H); 1.21 (br. s, 9H); 1.33 1.52 ( m, 2 H); 1.87 2.02 (m, 2 H); 2.44 (s, 3 H); 4.68 4.70
(m, 1 H); 4.88 (br. s, 1 H); 7.35 (d, J ˆ 8.1, 2 H); 7.80 (d, J ˆ 8.1, 2 H). 13C-NMR (CDCl3, 75.5 MHz): 0.37; 21.64;
24.18 (2Â); 27.85; 62.98; 66.86; 80.53; 128.15 (2Â); 130.19(2 Â); 137.63; 144.76; 153.11; 155.33; 161.58. HR-
‡
‡
MALDI-MS (DHB): 444.1631 ([M ‡ Na] , C21H31NNaO4SSi ; calc. 444.1641). Anal. calc. for C21H31NO4SSi
(421.63): C 59.82, H 7.41, N 3.32; found: C 59.71, H 7.27, N 3.52.

Helvetica Chimica Acta Vol. 86 (2003)
2185
Data of (Æ)-8: Pale-yellow solid. M.p. 878. IR (KBr): 2944s, 1706s, 1583w, 1293s, 1270s, 1162s, 1150s, 844s.
1H-NMR (CDCl3, 300 MHz): 0.35 (s, 9H); 0.43 ( s, 9H); 1.12 1.21 ( m, 2 H); 1.33 (br. s, 9H); 1.86 2.02
(m, 2 H); 2.42 (s, 2 H); 4.52 4.53 (m, 1 H); 4.92 (br. s, 1 H); 7.25 7.27 (m, 2 H); 7.57 7.60 (m, 2 H). 13C-NMR
(CDCl3, 75.5 MHz): À 0.40; 1.46; 21.72; 24.53 (2Â); 28.06; 62.74; 66.79; 80.57; 129.64 (2 Â); 130.35; 137.57
‡
‡
(2Â); 140.10; 142.69; 155.13; 160.93. HR-MALDI-MS (DHB): 516.2026 (100, [ M ‡ Na] , C24H39NNaO4SSi2 ;
calc. 516.2036).
tert-Butyl 2-[(4-Methylphenyl)sulfonyl]-3-(trimethylsilyl)-7-azabicyclo[2.2.1]heptane-7-carboxylate ((Æ)-
9). Freshly prepared dipotassium azodicarboxylate (1.02 g, 5.27 mmol) [52] was added to a stirred soln. of (Æ)-7
(740 mg, 1.76 mmol) in anh. MeOH (18 ml) at 08. The reduction was initiated by adding few drops of aq. AcOH
(50%). The ice bath was removed, and the mixture was allowed to stir overnight. H2O was added, and the
mixture was extracted with Et2O (3Â). The combined org. phases were washed with H2O (1Â) and sat. aq. NaCl
soln. (2Â), dried (MgSO4), and concentrated in vacuo to yield (Æ)-9 (686 mg, 92%), which was used without
further purification in the next step. An anal. sample was obtained by CC (SiO2; hexane/AcOEt 3 :1). White
solid. M.p. 1458. IR (KBr): 2967s, 1700s, 1589m, 1283s, 1174s, 1133s, 850s. 1H-NMR (CDCl3, 300 MHz): 0.33
(s, 9H); 1.41 ( s, 9H); 1.44 1.49 ( m, 2 H); 1.75 1.85 (m, 2 H); 2.47 (s, 3 H); 2.60 2.69( m, 1 H); 3.79(br.
m, 1 H); 3.86 (br. s, 1 H); 4.30 (br. s, 1 H); 7.38 (d, J ˆ 8.5, 2 H); 7.77 (d, J ˆ 8.5, 2 H). 13C-NMR (CDCl3,
75.5 MHz): 0.55; 13.90; 21.63; 23.51; 27.31; 28.23; 59.31; 62.40; 67.77; 80.49; 128.05 (2Â); 130.28 (2Â); 137.59;
‡
‡
144.88; 155.02. HR-MALDI-MS (DHB): 446.1788 ([M ‡ Na] , C21H33NNaO4SSi ; calc. 446.1797).
tert-Butyl 2-(Trimethylsilyl)-3-({4-[(trimethylsilyl)methyl]phenyl}sulfonyl)-7-azabicyclo[2.2.1]heptane-7-
carboxylate ((Æ)-10). Freshly prepared dipotassium azodicarboxylate (2.32 g, 11.94 mmol) was added to a
stirred soln. of (Æ)-8 (1.18 g, 2.39mmol) in anh. MeOH (25 ml) at 0 8. The reduction was initiated by adding few
drops of 50% aq. AcOH soln. The mixture was stirred for 3 d at r.t., another portion of dipotassium
azodicarboxylate (1.81 g, 9.31 mmol) and a few drops of a 50% aq. AcOH soln. were added, and the mixture was
stirred for another 3 d. After addition of H2O, the aq. phase was extracted with Et2O (3Â). The combined org.
phases were washed with H2O (1 Â 100 ml) and sat. aq. NaCl soln. (2Â), dried (MgSO4), and concentrated in
vacuo to yield (Æ)-10 (1.06 g, 90%), which was used without further purification in the next step. An anal.
sample was obtained by CC (SiO2; hexane/AcOEt 3 :1). White solid. M.p. 1548. IR (KBr): 2969s, 1708s, 1601m,
1289s, 1272s, 1179s, 1138s, 843s. 1H-NMR (CDCl3, 200 MHz): 0.34 (s, 9H); 0.41 ( s, 9H); 1.38 (br. s, 9H); 1.43
1.49( m, 2 H); 1.77 1.83 (m, 2 H); 2.45 (s, 2 H); 2.84 2.90 (m, 1 H); 3.68 3.71 (m, 1 H); 3.80 3.87 (m, 1 H);
4.26 4.30 (m, 1 H); 7.36 (d, J ˆ 7.4, 2 H); 7.81 (d, J ˆ 7.4, 2 H). 13C-NMR (CDCl3, 75.5 MHz): 0.51; 1.57; 14.07;
21.73; 24.61 (2Â); 28.17; 59.87; 64.12; 69.11; 80.51; 129.72 (2Â); 130.46; 137.81 (2Â); 142.83; 155.09. HR-
‡
‡
MALDI-MS (DHB): 518.2182 ([M ‡ Na] , C24H41NNaO4SSi2 ; calc. 518.2192).
tert-Butyl 7-Azabicyclo[2.2.1]hept-2-ene-7-carboxylate (6) [46]. Procedure A: To a stirred soln. of (Æ)-9
(1.71 g, 4.04 mmol) in THF (210 ml), Bu4NF ¥ 3 H2O (7.64 g, 24.22 mmol) was added, and the mixture was stirred
for 12 h at r.t under Ar. H2O and pentane were added and, after separation of the org. phase, the aq. phase was
extracted with Et2O (2Â). The combined org. layers were dried (MgSO4) and concentrated in vacuo to yield a
brown oil. CC (SiO2; pentane/Et2O 1:1) furnished 6 (642 mg, 81%). Colorless liquid. 1H-NMR (CDCl3,
200 MHz): 1.09 1.14 ( m, 2 H); 1.44 (s, 9H); 1.84 1.90 ( m, 2 H); 4.68 (br. s, 2 H); 6.24 (br. s, 2 H).
Procedure B: To a stirred soln. of (Æ)-10 (1.08 g, 2.17 mmol) in THF (126 ml), Bu4NF ¥ 3 H2O (7.64 g,
24.22 mmol) was added, and the mixture was stirred for 12 h at r.t under Ar. Workup as described for Procedure
A afforded 6 (307 mg, 72%).
tert-Butyl 2,3-Dihydroxy-7-azabicyclo[2.2.1]heptane-7-carboxylate (11). A soln. of 6 (1.18 g, 6.04 mmol) in
THF (9ml), NMO (1.23 g, 9.08 mmol), and OsO 4 (0.6 ml of a 2.5% soln. in t-BuOH) were added in succession
to a stirred soln. of NaHCO3 (0.51 g, 6.04 mmol) in t-BuOH (48 ml) and H2O (12 ml). After stirring at r.t. for 2 d
under Ar, an aq. soln. of NaHSO4 (10%, 25 ml) was added. Stirring was continued for 1 h, and AcOEt was
added. After separation of the aq. phase, the org. phase was washed with sat. aq. NaCl soln., dried (MgSO4), and
concentrated in vacuo to yield 11 (1.38 g, 100%). Pale-yellow solid. M.p. 798. IR (CHCl3): 3432w, 3023s, 1676m,
1
1368s, 1208s, 1142m. H-NMR (CDCl3, 500 MHz): 1.27 1.32 (m, 2 H); 1.46 (s, 9H); 1.65 1.71 ( m, 2 H); 3.06
(br. s, 2 H); 3.80 (s, 2 H); 4.12 (s, 2 H). 13C-NMR (CDCl3, 75.5 MHz): 24.23 (2Â); 28.18; 62.62 (2Â); 74.85
‡
(2Â); 80.53; 158.10. EI-MS: 229( M ). Anal. calc. for C11H19NO4 (229.28): C 57.63, H 8.35, N 6.11; found: C
57.42, H 8.21, N 6.06.
tert-Butyl 2-Hydroxy-3-[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate ((Æ)-12)
and tert-Butyl 2,3-Bis[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate (13). To a stirred
suspension of NaH (60% in oil, 96 mg, 2.40 mmol) in THF (4 ml) at 08, 11 (500 mg, 2.18 mmol) in THF (6 ml)
was added. A soln. of 2-(bromomethyl)naphthalene (530 mg, 2.40 mmol) in THF (20 ml) was added dropwise
at 08, and the mixture was stirred at r.t. for 1 d. MeOH was added, and the mixture was stirred for 1 h. After

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Helvetica Chimica Acta Vol. 86 (2003)
removal of the solvent in vacuo, the residue was taken up in Et2O and washed with H2O (1Â). Drying (MgSO4)
and concentration in vacuo gave a yellow oil, which was purified by CC (SiO2; hexane/AcOEt 4 :1) to afford
(Æ)-12 (545 mg, 68%) and 13 (177 mg, 16%).
Data of (Æ)-12: White solid. M.p. 1178. IR (KBr): 3504s, 3056m, 2972s, 1682s, 1507m, 1416s, 1361s, 1110s,
1
757s, 617s. H-NMR (CDCl3, 500 MHz): 1.17 1.27 (m, 2 H); 1.44 (s, 9H); 1.67 (br. s, 2 H); 3.33 (br. s, 1 H);
3.60 (d, J ˆ 6.2, 1 H); 3.84 (dd, J ˆ 7.7, 6.2, 1 H); 4.11 (br. s, 1 H); 4.28 (br. s, 1 H); 4.79 4.81 ( m, 2 H); 7.46 7.53
(m, 3 H); 7.79 7.87 ( m, 4 H). 13C-NMR (CDCl3, 125 MHz): 24.08 (2Â); 28.28; 58.17; 62.47; 72.62; 74.81; 79.78;
80.51; 125.74; 126.08; 126.24; 126.71; 127.72; 127.89; 128.35; 133.11; 133.21; 134.71; 156.34. HR-MALDI-MS
‡
‡
(DHB): 392.1835 ([M ‡ Na] , C22H27NNaO4 ; calc. 392.1838). Anal. calc. for C22H27NO4 (369.46): C 71.52, H
7.37, N 3.79; found: C 71.52, H 7.42, N 3.81.
Data of 13: White solid. M.p. 1318. IR (KBr): 2972s, 1698s, 1600w, 1509w, 1355s, 1080s, 742m, 620w.
1H-NMR (CDCl3, 500 MHz): 1.18 1.30 (m, 2 H); 1.43 (s, 9H); 1.64 1.73 ( m, 2 H); 3.65 (s, 2 H); 4.26 (br.
s, 1 H); 4.42 (br. s, 1 H); 4.82 (s, 4 H); 7.41 7.50 (m, 6 H); 7.68 7.82 (m, 8 H). 13C-NMR (CDCl3, 125 MHz):
24.08; 25.17; 28.31; 58.37; 59.75; 72.27 (2Â); 79.59; 81.78; 82.35; 125.74 (2Â); 125.97 (4Â); 126.49(2 Â); 127.65
(2Â); 127.88 (2Â); 128.00 (2Â); 132.96 (2Â); 133.25 (2Â); 135.81 (2Â); 156.21. HR-MALDI-MS (DHB):
‡
‡
532.2456 ([M ‡ Na] , C33H35NNaO4 ; calc. 532.2464). Anal. calc. for C33H35NO4 (509.64): C 77.77, H 6.92, N
2.75; found: C 77.93, H 6.94, N 2.78.
tert-Butyl (2R,3S)-2-Hydroxy-3-[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate
((‡)-12). To 26 (34 mg, 0.06 mmol) in MeOH (0.3 ml) and CH2Cl2 (0.1 ml), 3m KOH (0.1 ml, 0.30 mmol)
was added. The mixture was stirred for 30 min, diluted with H2O, and extracted with Et2O (2Â). The combined
org. phases were dried (MgSO4) and concentrated in vacuo to afford a colorless turbid oil. CC (SiO2; hexane/
24
D
AcOEt 2 :1) yielded (‡)-12 (17 mg, 74%). Colorless oil. ‰aŠ ˆ ‡25.5 (c ˆ 0.85, CHCl3).
tert-Butyl (2S,3R)-2-Hydroxy-3-[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate
((À)-12). To 27 (66 mg, 0.12 mmol) in MeOH (0.7 ml) and CH2Cl2 (0.2 ml), 3m KOH (0.2 ml, 0.60 mmol)
24
D
was added. Workup as described for (‡)-12 provided (À)-12 (43 mg, 98%). Colorless oil. ‰aŠ ˆ À19.3 (c ˆ 0.7,
CHCl3).
tert-Butyl 2-[(4-Bromobenzyl)oxy]-3-[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane-7-carbox-
ylate ((Æ)-14). A soln. of (Æ)-12 (100 mg, 0.27 mmol) in THF (0.7 ml) was added dropwise to a suspension
of NaH (60% in oil, 12 mg, 0.29mmol) in THF (2.2 ml) at 0 8, and the mixture was stirred for 1 h at r.t. 4-
Bromobenzyl bromide (73 mg, 0.29mmol) in THF (0.5 ml) was added at 0 8, and the mixture was stirred at r.t.
for 12 h. MeOH was then added, and the mixture was stirred for 30 min. Concentration in vacuo yielded a white
solid, which was taken up in Et2O. Washing with H2O (1Â), drying (MgSO4), and concentration in vacuo
afforded (Æ)-14 (140 mg, 97%). White solid. M.p. 1268. IR (KBr): 2970s, 1698s, 1354s, 1111s, 1079s, 862m, 751m,
620m. 1H-NMR (CDCl3, 500 MHz): 1.20 1.29( m, 2 H); 1.42 (s, 9H); 1.61 1.72 ( m, 2 H); 3.60 (d, J ˆ 5.7, 1 H);
3.65 (d, J ˆ 5.7, 1 H); 4.19 4.28 ( m, 1 H); 4.32 4.43 (m, 1 H); 4.60 (s, 2 H); 4.75 (s, 2 H); 7.22 (br. s, 2 H); 7.39
(br. s, 2 H); 7.45 7.49( m, 3 H); 7.74 7.84 (m, 4 H). 13C-NMR (CDCl3, 125 MHz): 23.95; 25.14; 28.28; 58.45;
59.82; 71.42; 72.19; 79.61; 81.56; 82.19; 121.28; 125.81 (2Â); 126.06; 126.45; 127.66; 127.83; 127.99; 129.35 (2Â);
‡
131.31 (2Â); 132.94; 133.21; 135.65; 137.41; 156.08. HR-MALDI-MS (DHB): 560.1401 ([M ‡ Na] ,
‡
C29H32BrNNaO4 ; calc. 560.1412).
tert-Butyl 2-({4-[3-(1,3-Benzodioxol-5-yl)propyl]benzyl}oxy)-3-[(naphthalen-2-yl)methoxy]-7-azabicy-
clo[2.2.1]heptane-7-carboxylate ((Æ)-(16)). A soln. of 15 in THF (0.37 ml, 0.17 mmol; prepared by stirring
safrol (1 equiv.) and 0.5n 9-borabicyclo[3.3.1]nonane (9-BBN) (1 equiv.) in THF) was added to a degassed soln.
of (Æ)-14 (85 mg, 0.16 mmol), [PdCl2(dppf)] (4 mg, 4 mmol), and NaOMe (23 mg, 0.43 mmol). The mixture was
heated to reflux for 50 h, then H2O was added. The aq. phase was extracted with Et2O (2Â), and the combined
org. phases were washed with sat. aq. NaCl soln., dried (MgSO4), and concentrated in vacuo to give a brown oil.
CC (SiO2; hexane/AcOEt 3 :1) furnished (Æ)-16 (48 mg, 49%). White solid. M.p. 1468. IR (CHCl3): 2984s,
1686s, 1609w, 1516m, 1107s, 9 43w, 854w. 1H-NMR (CDCl3, 300 MHz): 1.15 1.19( m, 2 H); 1.42 (s, 9H); 1.60
1.68 (m, 2 H); 1.84 1.94 (m, 2 H); 2.53 2.64 (m, 4 H); 3.58 (d, J ˆ 5.9, 1 H); 3.61 (d, J ˆ 5.9, 1 H); 4.19 4.27
(m, 1 H); 4.32 4.40 (m, 1 H); 4.63 (s, 2 H); 4.79( s, 2 H); 5.92 (s, 2 H); 6.63 6.74 (m, 3 H); 7.11 (d, J ˆ 7.4,
2 H); 7.27 (d, J ˆ 7.4, 2 H); 7.43 7.49( m, 3 H); 7.73 7.82 (m, 4 H). 13C-NMR (CDCl3, 125 MHz): 23.95; 25.21;
28.29; 33.22; 34.98; 35.12; 58.52; 59.73; 72.20 (2Â); 79.54; 81.54; 82.09; 100.70; 108.06; 108.86; 121.12; 125.70
(2Â); 125.94; 126.46; 127.64; 127.85; 127.93; 128.25 (2Â); 128.32 (2Â); 132.93; 133.24; 135.67; 135.84; 136.13;
‡
‡
141.55; 145.52; 147.52; 156.19. HR-MALDI-MS (DHB): 644.2979 ([M ‡ Na] , C39H43NNaO6 ; calc. 644.2988).
2,3-Bis[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane (17). A soln. of 13 (52 mg, 0.10 mmol) and
TFA (0.27 ml, 3.57 mmol) in CH2Cl2 (4 ml) was stirred for 30 min at r.t. under Ar. The crude TFA salt of 17,
obtained after evaporation in vacuo, was taken up in sat. aq. NaCl soln., and the pH of the soln. was adjusted to

Helvetica Chimica Acta Vol. 86 (2003)
2187
10 with 10% aq. K2CO3 soln. The aq. phase was extracted with CHCl3/i-PrOH 3 :1 (2Â). The combined org.
phases were dried (MgSO4) and concentrated in vacuo to yield a brown solid. CC (SiO2; AcOEt/NEt3 99 :1)
yielded 17 (25 mg, 60%). Colorless oil. IR (CHCl3): 3289w, 2977w, 1602w, 1509w, 1101s. 1H-NMR (CDCl3,
300 MHz): 1.07 1.11 (m, 2 H); 1.61 1.65 (m, 2 H); 2.31 (br. s, 1 H); 3.60 3.62 (m, 2 H); 3.72 (s, 2 H); 4.79
(s, 4 H); 7.41 7.51 (m, 6 H); 7.67 7.86 (m, 8 H). 13C-NMR (CDCl3, 50 MHz): 24.02 (2Â); 59.79 (2Â); 72.56
(2Â); 83.41 (2Â); 125.92 (2Â); 126.02 (2Â); 126.11 (2Â); 126.65 (2Â); 127.73 (2Â); 127.95 (2Â); 128.21 (2Â);
‡
‡
133.03 (2Â); 133.35 (2Â); 135.86 (2Â). HR-MALDI-MS (DHB): 432.1923 ([M ‡ Na] , C28H27NNaO2 ; calc.
432.1939).
2-[(4-Bromobenzyl)oxy]-3-[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]heptane ((Æ)-18). A soln. of
(Æ)-14 (100 mg, 0.19mmol) and TFA (0.50 ml, 6.50 mmol) in CH 2Cl2 (7.5 ml) was stirred for 30 min at r.t. under
Ar. Workup as described for 17 provided (Æ)-18 (72 mg, 89%). Colorless oil. IR (CHCl3): 3292w, 2954m, 2512w,
1662w, 1595w, 1508w, 1103s, 1072s, 862w. 1H-NMR (CDCl3, 500 MHz): 1.08 1.13 (m, 2 H); 1.68 1.72 (m, 2 H);
3.02 (br. s, 1 H); 3.60 3.65 (m, 2 H); 3.65, 3.71 (AB, J ˆ 5.5, 2 H); 4.53, 4.57 (AB, J ˆ 11.8, 2 H); 4.71, 4.76
(AB, J ˆ 11.9, 2 H); 7.20 (d, J ˆ 8.3, 2 H); 7.41 (d, J ˆ 8.3, 2 H); 7.39 7.50 ( m, 3 H); 7.72 7.84 (m, 4 H).
13C-NMR (CDCl3, 125 MHz): 23.82; 23.92; 59.82; 60.06; 71.80; 72.57; 83.03; 83.29; 121.51; 125.80; 125.95;
126.18; 126.56; 127.68; 127.83; 128.15; 129.41 (2Â); 131.46 (2Â); 132.99; 133.22; 135.49; 137.24. HR-MALDI-MS
‡
‡
(DHB): 460.0876 ([M ‡ Na] , C24H24NNaO2 ; calc. 460.0888).
2-({4-[3-(1,3-Benzodioxol-5-yl)propyl]benzyl}oxy)-3-[(naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]hep-
tane ((Æ)-1). A soln. of (Æ)-16 (45 mg, 0.07 mmol) and TFA (0.20 ml, 2.6 mmol) in CH2Cl2 (3 ml) was stirred for
30 min at r.t. under Ar. Workup as described for 17 followed by CC (SiO2; AcOEt/NEt3 99 :1) yielded (Æ)-1
(32 mg, 86%). Colorless oil. IR (CHCl3): 3250w, 2928m, 2476w, 1666w, 1605w, 1504m, 1099s, 9 33w, 860w.
1H-NMR (CDCl3, 500 MHz): 1.09 1.13 ( m, 2 H); 1.72 1.74 (m, 2 H); 1.89( m, 2 H); 2.56 (t, J ˆ 7.7, 2 H); 2.61
(t, J ˆ 7.8, 2 H); 3.00 (br. s, 1 H); 3.64 3.67 (m, 2 H); 3.67, 3.70 (AB, J ˆ 5.5, 2 H); 4.59, 4.60 (AB, J ˆ 11.9, 2 H);
4.73, 4.74 (AB, J ˆ 11.9, 2 H); 5.92 (s, 2 H); 6.61 6.73 (m, 3 H); 7.12 (d, J ˆ 7.9, 2 H); 7.26 (d, J ˆ 7.9, 2 H); 7.42
7.47 (m, 3 H); 7.74 7.82 (m, 4 H). 13C-NMR (CDCl3, 125 MHz): 23.69; 23.74; 33.20; 34.98; 35.13; 60.08; 60.15;
72.47; 72.59; 82.76; 82.79; 100.71; 108.07; 108.84; 121.11; 125.87; 125.90; 126.07; 126.61; 127.66; 127.86; 128.05
(2Â); 128.12; 128.47 (2Â); 132.99; 133.23; 135.43; 135.55; 136.07; 141.84; 145.54; 147.53. HR-MALDI-MS
‡
‡
(DHB): 544.2450 ([M ‡ Na] , C34H35NNaO4 ; calc. 544.2464).
2-{[2-(4-Methylphenoxy)ethyl]sulfanyl}-1,3-benzothiazole (21). NaH (60% in oil, 240 mg, 6.0 mmol) was
added to a soln. of 1-(2-bromoethoxy)-4-methylbenzene (1.19g, 5.4 mmol) [53] and 2-sulfanyl-1,3-benzothia-
zole (1.00 g, 6.0 mmol) in dry DMF (13 ml), and the yellow mixture was heated to 808 for 1 h. H2O was added,
and the turbid soln. was extracted with Et2O (2Â). The combined org. phases were washed with sat. aq. NaCl
soln. and H2O, dried (MgSO4), and concentrated in vacuo to furnish a yellow solid. CC (SiO2; hexane/AcOEt
21:4) yielded 21 (1.48 g, 90%). Pale-yellow solid. M.p. 648. IR (CHCl3): 3005w, 2923w, 2872w, 1610w, 1511s,
1463m, 1429s, 1303w, 1292w, 1240s, 1174w, 1072w, 1026w, 9 9 8w, 822w. 1H-NMR (CDCl3, 300 MHz): 2.29( s, 3 H);
3.74 (t, J ˆ 6.6, 2 H); 4.36 (t, J ˆ 6.6, 2 H); 6.86 6.89( m, 2 H); 7.08 7.12 (m, 2 H); 7.28 7.33 (m, 1 H); 7.40
7.46 (m, 1 H); 7.75 7.78 (m, 1 H); 7.86 7.89( m, 1 H). 13C-NMR (CDCl3, 50 MHz): 20.37; 32.14; 66.49; 114.68
(2Â); 121.09; 121.60; 124.40; 126.11; 130.02 (2 Â); 130.52; 135.22; 153.22; 156.33; 166.20. HR-MALDI-MS
‡
‡
(DHB): 302.0670 (MH , C16H16NOS2 ; calc. 302.0673). Anal. calc. for C16H15NOS2 (301.43): C 63.75, H 5.02, N
4.65; found: C 63.78, H 5.04, N 4.60.
2-({2-[4-(Bromomethyl)phenoxy]ethyl}sulfanyl)-1,3-benzothiazole (22). A dried flask was charged with 21
(416 mg, 1.44 mmol) in dry CHCl3 (6 ml), freshly recrystallized NBS (274 mg, 1.54 mmol), and AIBN (1.6 mg,
0.01 mmol). The mixture was heated to reflux for 4 h, then cooled to r.t. and filtered. The filtrate was washed
with 0.5m NaHCO3 and H2O, dried (MgSO4), and evaporated in vacuo to provide a light-yellow solid. CC (SiO2;
hexane/AcOEt 7:1) yielded 22 (103 mg, 19%). White solid. M.p. 1058. IR (CHCl3): 1610s, 1512s, 1456s, 1428s,
1
1306m, 9 9 s8. H-NMR (CDCl3, 300 MHz): 3.75 (t, J ˆ 6.7, 2 H); 4.39( t, J ˆ 6.7, 2 H); 4.50 (s, 2 H); 6.94 6.96
(m, 2 H); 7.29 7.35 ( m, 3 H); 7.42 7.46 (m, 1 H); 7.75 7.78 (m, 1 H); 7.86 7.89( m, 1 H). 13C-NMR (CDCl3,
75.5 MHz): 31.88; 33.69; 66.44; 115.07 (2 Â); 121.14; 121.62; 124.50; 126.20; 130.60 (3Â); 135.49; 153.17; 158.61;
‡
‡
166.02. HR-MALDI-MS (DHB): 379.9778 (MH , C16H15BrNOS2 ; calc. 379.9778). Anal. calc. for
C16H14NOS2Br (380.33): C 50.53, H 3.71, N 3.68; found: C 50.46, H 3.88, N 3.65.
tert-Butyl 2-[{4-{2-[(1,3-Benzothiazol-2-yl)sulfanyl]ethoxy}benzyl)oxy]-3-[(naphthalen-2-yl)methoxy]-7-
azabicyclo[2.2.1]heptane-7-carboxylate ((Æ)-23). A soln. of (Æ)-12 (111 mg, 0.3 mmol) in THF (3 ml) was
added to NaH (60% in oil, 16 mg, 0.39mmol) at 0 8 under Ar. After stirring for 30 min at 08, 22 (120 mg,
0.3 mmol) in THF (1.5 ml) was added dropwise. After 16 h at r.t., MeOH was added, and the mixture was stirred
for 15 min. The residue obtained by evaporation in vacuo was taken up in Et2O, and the soln. was washed with
H2O, dried (MgSO4), and concentrated in vacuo to give a white solid. CC (SiO2; CH2Cl2/AcOEt 199 :1 ! 19:1)

2188
Helvetica Chimica Acta Vol. 86 (2003)
provided (Æ)-23 (75 mg, 37%). Viscous colorless oil. IR (CHCl3): 2951w, 2882w, 1694s, 1611m, 1511m, 1463m,
1429m, 1367s, 1324m, 1174m, 1148s, 1123m, 1082m, 9 9 m7 , 89 0w, 859w. 1H-NMR (CDCl3, 300 MHz): 1.15 1.17
(br. m, 2 H); 1.41 (s, 9H); 1.62 1.64 (br. m, 2 H); 3.57, 3.61 (AB, J ˆ 5.7, 2 H); 3.74 (t, J ˆ 6.5, 2 H); 4.13 4.24
(br. m, 1 H); 4.34 4.38 (br. m, 3 H); 4.59(br. s, 2 H); 4.78 (br. s, 2 H); 6.88 6.91 (m, 2 H); 7.25 7.33 (m, 3 H);
7.39 7.49( m, 4 H); 7.74 7.82 (m, 5 H); 7.86 7.89( m, 1 H). 13C-NMR (CDCl3, 75.5 MHz): 23.91; 24.85; 28.17;
31.79; 58.31; 59.67; 66.34; 71.69; 72.16; 79.51; 81.81 (2 Â); 114.52 (2Â); 121.09; 121.58; 124.42; 125.80 (2 Â);
126.04; 126.15; 126.58; 127.71; 127.93; 128.03; 129.57 (2Â); 131.01; 133.00; 133.31; 135.44; 135.89; 153.19; 156.35;
‡
‡
158.00; 166.12. HR-MALDI-MS (DHB): 691.2268 (22, [M ‡ Na] , C38H40N2NaO5S2 ; calc. 691.2276). Anal.
calc. for C38H40N2O5S2 (668.88): C 68.24, H 6.03, N 4.19; found: C 68.09, H 6.12, N 4.12.
tert-Butyl (2R,3S)-2-[(4-{2-[(1,3-Benzothiazol-2-yl)sulfanyl]ethoxy}benzyl)oxy]-3-[(naphthalen-2-yl)-
24
D
methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate ((À)-23). ‰aŠ ˆ À2.0 (c ˆ 0.75, CHCl3).
tert-Butyl (2S,3R)-2-[(4-{2-[(1,3-benzothiazol-2-yl)sulfanyl]ethoxy}benzyl)oxy]-3-[(naphthalen-2-yl)-
24
D
methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate ((‡)-23). ‰aŠ ˆ ‡1.9( c ˆ 0.75, CHCl3).
2-[(2-{4-[({3-[(Naphthalen-2-yl)methoxy]-7-azabicyclo [2.2.1]hept-2-yl}oxy)methyl]phenoxy}ethyl)sulfan-
yl]-1,3-benzothiazole ((Æ)-19). To (Æ)-23 (50 mg, 0.08 mmol) in CH2Cl2 (140 ml), 2,6-lutidine (17 ml, 0.15 mmol)
and TBDMSOTf (26 ml, 0.11 mmol) were added, and the mixture was stirred for 30 min. Sat. aq. NH4Cl soln.
was added, and the mixture was extracted with Et2O (2Â). The combined org. layers were washed with sat. aq.
NaCl soln. and H2O, dried (MgSO4), and evaporated in vacuo to yield a turbid yellow oil. This oil was dissolved
in THF (135 ml), Bu4NF (1m in THF, 132 ml, 0.13 mmol) was added, and the mixture was stirred at r.t. for 1 h
under Ar. Sat. aq. NH4Cl soln. was added, and the mixture was extracted with CHCl3 (3Â). The combined org.
layers were washed with sat. aq. NaCl soln., dried (MgSO4), and evaporated in vacuo to afford a turbid yellow
oil. CC (basic Al2O3, act. II; AcOEt/MeOH 25 :1) yielded (Æ)-19. Pale-yellow oil (38 mg, 82% over 2 steps). IR
(CHCl3): 2971m, 1601w, 1527w, 1458w, 1425m, 1253s, 1091s, 1021s. 1H-NMR (CDCl3, 300 MHz): 1.03 1.09
(m, 2 H); 1.58 1.64 (m, 2 H); 1.93 (br. s, 1 H); 3.53 3.58 (m, 2 H), 3.64, 3.68 (AB, J ˆ 5.3, 2 H); 3.75 (t, J ˆ 6.6,
2 H); 4.36 (t, J ˆ 6.6, 2 H); 4.56 (s, 2 H); 4.75 (s, 2 H); 6.87 6.92 (m, 2 H); 7.26 7.33 (m, 3 H); 7.38 7.48
(m, 4 H); 7.74 7.89( m, 6 H). 13C-NMR (CDCl3, 75.5 MHz): 23.54 (2Â); 31.99; 59.69 (2Â); 66.39; 72.08; 72.50;
82.63; 82.84; 114.67 (2Â); 121.12; 121.61; 124.46; 125.96; 125.99; 126.17 (2Â); 126.70; 127.76; 127.97; 128.21;
129.63 (2Â); 130.85; 133.08; 133.32; 135.47; 135.67; 153.21; 158.16; 166.12. HR-MALDI-MS (DHB): 591.1740
‡
‡
([M ‡ Na] , C33H32N2NaO3S2 ; calc. 591.1752).
2-[(2-{(2R,3S)-4-[({3-[(Naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]hept-2-yl}oxy)methyl]phenoxy}ethyl)-
24
D
sulfanyl]-1,3-benzothiazole ((À)-19). ‰aŠ ˆ À2.6 (c ˆ 0.3, CHCl3).
2-[(2-{(2S,3R)-4-[({3-[(Naphthalen-2-yl)methoxy]-7-azabicyclo[2.2.1]hept-2-yl}oxy)methyl]phenoxy}ethyl)-
24
D
sulfanyl]-1,3-benzothiazole ((‡)-19). ‰aŠ ˆ ‡2.4 (c ˆ 0.9, CHCl3).
tert-Butyl 2-Hydroxy-3-[(naphthalen-1-yl)methoxy]-7-azabicyclo[2.2.1]heptane-7-carboxylate ((Æ)-24. A
soln. of 11 (500 mg, 2.18 mmol) in THF (6 ml) was added at 08 to a suspension of NaH (60% in oil, 96 mg, 2.40
mmol) in THF (4 ml), and the mixture was stirred at 08 for 15 min. A soln. of 1-(bromomethyl)naphthalene
(530 mg, 2.40 mmol) in THF (20 ml) was added dropwise, and the mixture was stirred for 15 h at r.t. under Ar.
After addition of MeOH, stirring was continued for 20 min. Evaporation in vacuo gave a residue, which was
taken up in Et2O. The soln. was washed with H2O, dried (MgSO4), and concentrated in vacuo to give an oil. CC
(SiO2; hexane/AcOEt 4 :1) yielded (Æ)-24 (371 mg, 43%). Colorless oil. IR (CHCl3): 3517w, 3008m, 2980m,
2872w, 1693s, 1390s, 1368s, 1257w, 1171m, 1143s, 1113m, 1071m, 1020w, 9 0w5, 889w. 1H-NMR (CDCl3,
300 MHz): 1.15 1.24 (m, 2 H); 1.42 (s, 9H); 1.61 1.73 ( m, 2 H); 3.27 (m, 1 H); 3.63 (m, 1 H); 3.83 (m, 1 H);
4.04 4.18 (m, 1 H); 4.21 4.37 (m, 1 H); 5.03 5.12 (m, 2 H); 7.42 7.58 (m, 4 H); 7.82 7.89( m, 2 H); 8.10
8.14 (m, 1 H). 13C-NMR (CDCl3, 50 MHz): 23.94; 24.27; 28.14; 58.72; 62.49; 70.94; 74.84; 79.73; 80.52; 123.95;
125.22; 126.02; 126.59; 126.81; 128.65; 129.09; 131.76; 132.81; 133.82; 156.46. HR-MALDI-MS (DHB): 392.1837
‡
‡
([M ‡ Na] , C22H27NNaO4 ; calc. 392.1838). Anal. calc. for C22H27NO4 (369.46): C 71.52, H 7.37, N 3.79; found:
C 71.50, H 7.34, N 3.81.
tert-Butyl 2-[(4-{2-[(1,3-Benzothiazol-2-yl)sulfanyl]ethoxy}benzyl)oxy]-3-[(naphthalen-1-yl)methoxy]-7-
azabicyclo[2.2.1]heptane-7-carboxylate ((Æ)-25). A mixture of (Æ)-24 (150 mg, 0.41 mmol), NaH (60% in oil,
25 mg, 0.62 mmol), and THF (3 ml) in a dried flask was stirred for 45 min at 08 under Ar, then a soln. of 22
(500 mg, 1.31 mmol) was added dropwise. After stirring at r.t. for 16 h, MeOH was added, and stirring was
continued for 15 min. Evaporation in vacuo left a residue, which was taken up in Et2O (30 ml) and washed with
H2O (2Â), dried (MgSO4), and concentrated in vacuo to afford a turbid yellow oil. CC (SiO2; hexane/AcOEt
3 :1) provided (Æ)-25 (226 mg, 82%). Colorless oil. IR (CHCl3): 3009m, 2951w, 1694s, 1610w, 1511m, 1464m,
1428m, 1368s, 1324w, 1240m, 1174m, 1148s, 1087m, 9 9m9. 1H-NMR (CDCl3, 300 MHz): 1.13 1.16 (m, 2 H);
1.42 (s, 9H); 1.61 1.74 ( m, 2 H); 3.53, 3.59( AB, J ˆ 6.2, 2 H); 3.74 (t, J ˆ 6.4, 2 H); 4.12 4.24 (m, 1 H);

Helvetica Chimica Acta Vol. 86 (2003)
2189
4.29 4.40 ( m, 1 H); 4.36 (t, J ˆ 6.4, 2 H); 4.50 4.53 (m, 2 H); 5.06 (br. s, 2 H); 6.85 6.87 (m, 2 H); 7.13 7.25
(m, 2 H); 7.28 7.34 (m, 1 H); 7.37 7.49( m, 5 H); 7.75 7.89( m, 4 H); 8.15 8.19( m, 1 H). 13C-NMR (CDCl3,
50 MHz): 24.46 (2Â); 28.21; 32.05; 59.67 (2Â); 66.40; 70.40; 71.67; 79.51; 81.44 (2Â); 114.52 (2Â); 121.09;
121.60; 124.43; 124.52; 125.19; 125.79; 126.17 (2 Â); 126.75; 128.46; 128.55; 129.51 (2Â); 131.06; 131.89; 133.79
‡
‡
(2Â); 135.48; 153.22; 156.33; 157.95; 166.11. HR-MALDI-MS (DHB): 691.2270 ([M ‡ Na] , C38H40N2NaO5S2 ;
calc. 691.2276).
2-[(2-{4-[({3-[(Naphthalen-1-yl)methoxy]-7-azabicyclo[2.2.1]hept-2-yl}oxy)methyl]phenoxy}ethyl)sulfan-
yl]-1,3-benzothiazole ((Æ)-20). To (Æ)-24 (182 mg, 0.27 mmol) in CH2Cl2 (0.5 ml), 2,6-lutidine (63 ml,
0.54 mmol) and TBDMSOTf (94 ml, 0.41 mmol) were added, and the mixture was stirred for 30 min. After
addition of sat. aq. soln. of NH4Cl, the mixture was extracted with Et2O. The combined org. layers were washed
with sat. aq. NaCl soln. and H2O, dried (MgSO4), and evaporated to give a turbid yellow oil. This oil was
dissolved in THF (0.5 ml), Bu4NF (1m in THF, 0.38 ml, 0.38 mmol) was added, and the mixture was stirred at r.t.
for 2 h. After addition of sat. aq. NH4Cl soln., extraction with CHCl3 (3Â), washing the combined org. layers
with sat. aq. NaCl soln., drying (MgSO4), and evaporation in vacuo afforded a turbid yellow oil. CC (basic
Al2O3, act. II; AcOEt/MeOH 25 :1) provided (Æ)-20 (110 mg, 71%). Pale-yellow oil. IR (CHCl3): 2962m,
1
1610w, 1513w, 1462w, 1431w, 1261s, 1097s, 1015s. H-NMR (CDCl3, 300 MHz): 1.04 1.13 (m, 2 H); 1.79 2.14
(m, 3 H); 3.57 3.60 (m, 2 H); 3.64, 3.70 (AB, J ˆ 5.4, 2 H); 3.74 (t, J ˆ 6.6, 2 H); 4.36 (t, J ˆ 6.6, 2 H); 4.50
(s, 2 H); 5.00, 5.06 (AB, J ˆ 11.7, 2 H); 6.86 6.89( m, 2 H); 7.18 7.21 (m, 2 H); 7.28 7.33 (m, 1 H); 7.37 7.49
(m, 5 H); 7.75 7.89( m, 4 H); 8.14 8.16 (m, 1 H). 13C-NMR (CDCl3, 75.5 MHz): 23.55; 23.66; 31.99; 58.13;
60.35; 66.39; 70.92; 72.00; 82.74; 82.94; 114.65 (2Â); 121.12; 121.60; 124.39; 124.45; 125.24; 125.87; 126.17;
126.26; 126.81; 128.53; 128.74; 129.63 (2Â); 130.84; 131.91; 133.72; 133.83; 135.47; 153.20; 158.12; 166.11. HR-
‡
‡
MALDI-MS (DHB): 591.1745 (43, [M ‡ Na] , C33H32N2NaO5S2 ; calc. 591.1752).
tert-Butyl (2S,3R)-2-[(Naphthalen-2-yl)methoxy]-3-({[(1S,4R)-4,7,7-trimethyl-3-oxo-2-oxabicyclo[2.2.1]-
hept-1-yl]carbonyl}oxy)-7-azabicyclo[2.2.1]heptane-7-carboxylate (26) and tert-Butyl (2R,3S)-2-[(Naphtha-
len-2-yl)methoxy]-3-({[(1S,4R)-4,7,7-trimethyl-3-oxo-2-oxabicyclo[2.2.1]hept-1-yl]carbonyl}oxy)-7-azabicy-
clo[2.2.1]heptane-7-carboxylate (27). To (Æ)-12 (200 mg, 0.54 mmol) in CH2Cl2 (2 ml) at 08, Et3N (0.15 ml,
1.08 mmol) and (À)-camphanoyl chloride (132 mg, 0.61 mmol) in CH2Cl2 (0.8 ml) were added, and the mixture
was stirred for 20 h at r.t. CH2Cl2 and H2O were added, and the separated org. phase was washed with 2n HCl
(2Â), 1m NaHCO3 (10 ml), and sat. aq. NaCl soln (2Â). Drying (MgSO4) and concentration in vacuo afforded a
cloudy oil. CC (SiO2; PhMe/AcOEt 2: 1) yielded 26 (111 mg, 38%) and 27 (90 mg, 30%).
Data of 26: White solid. M.p. 1668. IR (KBr): 2967m, 1789s, 1739s, 1694s, 1383s, 1261s, 1083s. 1H-NMR
(CDCl3, 300 MHz): 0.86 1.06 (m, 9H); 1.23 1.28 ( m, 2 H); 1.35 1.44 (m, 10 H); 1.62 1.82 (m, 4 H); 2.21
2.30 (m, 1 H); 3.82 3.83 (m, 1 H); 4.23 4.42 (br. s, 2 H); 4.60 4.64 (m, 1 H); 4.73 4.76 (m, 1 H); 4.82 4.91
(br. s, 1 H); 7.44 7.49( m, 3 H); 7.77 7.84 (m, 4 H). 13C-NMR (CDCl3, 75.5 MHz): 9.70; 16.70; 16.93; 24.37
(2Â); 28.35; 28.95; 30.70; 54.11; 55.00; 58.48 (2Â); 72.83 (2Â); 79.87; 81.92; 91.55; 126.24; 126.41; 126.48;
‡
127.19; 127.94; 128.18; 128.41; 133.36; 133.42; 135.10; 155.10; 167.56; 178.50. ESI-MS: 588 (15, [ M ‡ K] ), 572
‡
‡
(100, [M ‡ Na] ), 567 (16, [M ‡ NH4] ). X-Ray: see Fig 3.
Data of 27: White solid. M.p. 1418. IR (KBr): 2961m, 1787s, 1751s, 1702s, 1390s, 1170s, 1087s. 1H-NMR
(CDCl3, 300 MHz): 0.78 (br. s, 3 H); 0.94 (br. s, 3 H); 1.00 (br. s, 3 H); 1.22 1.25 (m, 2 H); 1.43 1.48 (m, 10 H);
1.73 1.79( m, 4 H); 2.38 2.46 (m, 1 H); 3.81 3.83 (m, 1 H); 4.25 4.38 (br. s, 2 H); 4.53 4.86 (m, 3 H); 7.45
7.49( m, 3 H); 7.77 7.84 (m, 4 H). 13C-NMR (CDCl3, 75.5 MHz): 9.65; 16.30; 16.46; 24.50 (2Â); 28.45; 28.97;
30.89; 54.08; 54.90; 58.45 (2 Â); 72.51 (2Â); 79.93; 81.44; 91.37; 126.24; 126.43 (2Â); 127.26; 127.94; 128.15;
‡
128.41; 133.34; 133.44; 135.06; 154.86; 167.50; 178.56. HR-MALDI-MS (DHB): 572.2614 ([M ‡ Na] ,
‡
C32H39NNaO7 ; calc. 572.2624).
X-Ray Crystal Structure of 26. Crystals were grown by slow diffusion of hexane into a soln. of 26 in CH2Cl2.
X-Ray crystal data for C32H39NO7 (Mr 549.64): orthorhombic space group P212121 (No. 19), Dc ˆ 1.254 g/cmÀ3
,
Z ˆ 4, a ˆ 6.326(1), b ˆ 11.317(1), c ˆ 40.658(5) ä, Vˆ 2910.8(6) ä3, CuKa radiation, l ˆ 1.5418 ä, 2.178 ꢀ q ꢀ
49.928, 1785 unique reflections, Tˆ 183 K, crystal size ca. 0.1  0.05  0.05 mm. The structure was solved by
direct methods (SIR92) [54] and refined by full-matrix least-squares analysis (SHELXL-97) [55], using an
À
À
ÁÁ
À
Á
isotropic extinction correction and w ˆ 1= s2 Fo2 ‡ (0.070P)2 ‡ 0.075P), where P ˆ Fo2 ‡ 2F2c /3. All heavy
atoms were refined anisotropically, H-atoms isotropically, whereby H-positions are based on stereochemical
considerations. Final R(F) ˆ 0.0351, wR(F2) ˆ 0.0976 for 401 parameters and 1628 reflections with I > 2s(I).
Crystallographic data (excluding structure factors) for 26 have been deposited with the Cambridge
Crystallographic Data Centre as deposition No. CCDC-201544. Copies of the data can be obtained, free of
charge, on application to the CCDC, 12 Union Road, Cambridge CB21EZ UK (fax: ‡ 44(1223)336033; e-mail:
deposit@ccdc.cam.ac.uk).

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Helvetica Chimica Acta Vol. 86 (2003)
REFERENCES
[1] U. Weiss, Nature 2002, 415, 669.
[2] C. Hopkins Sibley, J. E. Hyde, P. F. G. Sims, C. V. Plowe, J. G. Kublin, E. K. Mberu, A. F. Cowman, P. A.
Winstanley, W. M. Watkins, A. M. Nzila, Trends Parasitol. 2001, 17, 582.
[3] A. Bell, Curr. Opin. Anti-infect. Invest. Drugs 2000, 2, 63.
[4] P. J. Rosenthal, −Antimalarial Chemotherapy: Mechanisms of Action, Resistance, and New Directions in
Drug Discovery×, Humana Press, New Jersey, 2001.
[5] P. M. S. Chauhan, S. K. Srivastava, Curr. Med. Chem. 2001, 8, 1535.
¬
¬
¬
[6] M. Frederich, J.-M. Dogne, L. Angenot, P. DeMol, Curr. Med. Chem. 2002, 9, 1435.
[7] R. G. Ridley, Nature 2002, 415, 686.
[8] L. H. Miller, M. F. Good, G. Milon, Science 1994, 264, 1878.
[9] A. Robert, O. Dechy-Cabaret, J. Cazelles, B. Meunier, Acc. Chem. Res. 2002, 35, 167.
[10] S. E. Francis, D. J. Sullivan, D. E. Goldberg, Annu. Rev. Microbiol. 1997, 51, 9 7.
[11] R. Banerjee, J. Liu, W. Beatty, L. Pelosof, M. Klemba, D. E. Goldberg, Proc. Natl. Acad. Sci. U.S.A. 2002,
99, 990.
[12] G. H. Coombs, D. E. Goldberg, M. Klemba, C. Berry, J. Kay, J. C. Mottram, Trends Parasitol. 2001, 17, 532.
[13] R. P. Moon, L. Tyas, U. Certa, K. Rupp, D. Bur, C. Jacquet, H. Matile, H. Loetscher, F. Grueninger-Leitch,
J. Kay, B. M. Dunn, C. Berry, R. G. Ridley, Eur. J. Biochem. 1997, 244, 552.
[14] J. Hill, L. Tyas, L. H. Phylip, J. Kay, B. M. Dunn, C. Berry, FEBS Lett. 1994, 352, 155.
[15] D. M. Wyatt, C. Berry, FEBS Lett. 2002, 513, 159.
[16] C. Berry, M. J. Humphreys, P. Matharu, R. Granger, P. Horrocks, R. P. Moon, U. Certa, R. G. Ridley, D.
Bur, J. Kay, FEBS Lett. 1999, 447, 149.
[17] B. R. Shenai, P. S. Sijwali, A. Singh, P. J. Rosenthal, J. Biol. Chem. 2000, 275, 29000.
[18] K. K. Eggleson, K. L. Duffin, D. E. Goldberg, J. Biol. Chem. 1999, 274, 32411.
[19] K. A. Kolakovich, I. Y. Gluzman, K. L. Duffin, D. E. Goldberg, Mol. Biochem. Parasitol. 1997, 87, 123.
[20] R. P. Moon, D. Bur, H. Loetscher, A. D×Arcy, L. Tyas, C. Oefner, F. Grueninger-Leitch, D. Mona, K. Rupp,
A. Dorn, H. Matile, U. Certa, C. Berry, J. Kay, R. G. Ridley, Adv. Exp. Med. Biol. 1998, 436, 39 7.
[21] C. D. Carroll, H. Patel, T. O. Johnson, T. Guo, M. Orlowski, Z.-M. He, C. L. Cavallaro, J. Guo, A. Oksman,
I. Y. Gluzman, J. Conelly, D. Chelsky, D. E. Goldberg, R. E. Rolle, Bioorg. Med. Chem. Lett. 1998, 8, 2315;
C. D. Carroll, T. O. Johnson, S. Tao, G. Lauri, M. Orlowski, I. Y. Gluzman, D. E. Goldberg, R. E. Dolle,
Bioorg. Med. Chem. Lett. 1998, 8, 3203.
[22] T. S. Haque, A. G. Skillman, C. E. Lee, H. Habashita, I. Y. Gluzman, T. J. A. Ewing, D. E. Goldberg, I. D.
Kuntz, J. A. Ellman, J. Med. Chem. 1999, 42, 1428; D. J. Maly, L. Huang, J. A. Ellman, ChemBioChem 2002, 3, 16.
[23] S. Jiang, S. T. Prigge, L. Wei, Y.-E. Gao, T. H. Hudson, L. Gerena, J. B. Dame, D. E. Kyle, Antimicrob.
Agents Chemother. 2001, 45, 2577.
[24] A. Negami, I. Luque, T. Rimura, Y. Kiso, E. Freire, Biochemistry 2002, 41, 2273.
[25] K. Ersmark, I. Feierberg, S. Bjelic, J. Hulten, J. Aqvist, A. Hallberg, Drugs Future (Suppl. A: XXIIth Int.
Symp. Med. Chem.) 2002, 27, 231.
[26] C. Boss, S. Richard, T. Weller, C. Binkert, S. Meyer, P. Strickner, D. Bur, W. Fischli, BOSS-9Symposium
Namur, Belgium 2002, Poster TH 046; C. Boss, W. Fischli, S. Meyer, S. Richard-Bildstein, T. Weller,
Actelion Pharmaceuticals Ltd. 2002, WO-00224649; C. Boss, W. Fischli, S. Meyer, S. Richard-Bildstein, T.
Weller, Actelion Pharmaceuticals Ltd. 2002, WO-00238534.
[27] C. Boss, S. Richard-Bildstein, T. Weller, W. Fischli, S. Meyer, C. Binkert, Curr. Med. Chem. 2003, 10, 883.
[28] A. M. Silva, A. Y. Lee, S. V. Gulnik, P. Majer, J. Collins, T. N. Bhat, P. J. Collins, R. E. Cachau, K. E. Luker,
I. Y. Gluzman, S. E. Francis, A. Oksman, D. E. Goldberg, J. W. Erickson, Proc. Natl. Acad. Sci. U.S.A. 1996,
93, 10034.
[29] U. Obst, V. Gramlich, F. Diederich, L. Weber, D. W. Banner, Angew. Chem. 1995, 107, 1874; Angew. Chem.,
Int. Ed. 1995, 34, 1739; U. Obst, D. W. Banner, L. Weber, F. Diederich, Chem. Biol. 1997, 4, 287; U. Obst, P.
Betschmann, C. Lerner, P. Seiler, F. Diederich, V. Gramlich, L. Weber, D. W. Banner, P. Schˆnholzer, Helv.
Chim. Acta 2000, 83, 855; P. Betschmann, S. Sahli, F. Diederich, U. Obst, V. Gramlich, Helv. Chim. Acta
2002, 85, 1210.
[30] B. Masjost, P. Ballmer, E. Borroni, G. Z¸rcher, F. K. Winkler, R. Jakob-Roetne, F. Diederich, Chem. Eur.
J. 2000, 6, 971; C. Lerner, A. Ruf, V. Gramlich, B. Masjost, G. Z¸rcher, R. Jakob-Roetne, E. Borroni, F.
Diederich, Angew. Chem. 2001, 113, 4164; Angew. Chem., Int. Ed. 2001, 40, 4040; C. Lerner, B. Masjost, A.
Ruf, V. Gramlich, R. Jakob-Roetne, G. Z¸rcher, E. Borroni, F. Diederich, OrgBioChem 2003, 1, 42.

Helvetica Chimica Acta Vol. 86 (2003)
2191
[31] E. A. Meyer, R. Brenk, R. K. Castellano, M. Furler, G. Klebe, F. Diederich, ChemBioChem 2002, 3, 250.
[32] C. Oefner, A. Binggeli, V. Breu, D. Bur, J.-P. Clozel, A. D×Arcy, A. Dorn, W. Fischli, F. Gr¸ninger, R.
G¸ller, G. Hirth, H. P. Maerki, S. Mathews, M. M¸ller, R. G. Ridley, H. Stadler, E. Vieira, M. Wilhelm,
F. K. Winkler, W. Wostl, Chem. Biol. 1999, 6, 127.
[33] M. G. Bursavich, D. H. Rich, Org. Lett. 2001, 3, 2625; M. G. Bursavich, C. W. West, D. H. Rich, Org. Lett.
2001, 3, 2317.
[34] N. Khazanovich Bernstein, M. M. Cherny, H. Loetscher, R. G. Ridley, M. N. G. James, Nat. Struct. Biol.
1999, 6, 32.
[35] D. Bur, W. Fischli, H. Matile, R. G. Ridley, W. Wostl, F. Hoffman-La Roche Ltd., 1999, WO-09912532.
[36] D. A. Carcache, S. R. Hˆrtner, A. Bertogg, F. Diederich, A. Dorn, H. P. M‰rki, C. Binkert, D. Bur, Helv.
Chim. Acta 2003, 86, 2192.
[37] D. A. Carcache, S. R. Hˆrtner, A. Bertogg, C. Binkert, D. Bur, H. P. M‰rki, A. Dorn, F. Diederich,
ChemBioChem 2002, 3, 1137.
[38] P. R. Gerber, K. M¸ller, J. Comput.-Aided Mol. Design 1995, 9, 251.
[39] R. R. Fraser, R. B. Swingle, Can. J. Chem. 1970, 48, 2065.
[40] A. Yayon, Z. I. Cabantchik, H. Ginsburg, EMBO J. 1984, 3, 2695.
[41] C. A. Lipinski, F. Lombardo, B. W. Dominy, P. J. Feeney, Adv. Drug Deliv. Rev. 1997, 23, 3.
[42] E. A. Meyer, R. K. Castellano, F. Diederich, Angew. Chem. 2003, 115, 1244; Angew. Chem., Int. Ed. 2003,
42, 1210.
[43] L. Grehn, U. Ragnarsson, Angew. Chem. 1984, 96, 29 1;Angew. Chem., Int. Ed. 1984, 23, 296.
[44] Z. Chen, M. L. Trudell, Synth. Commun. 1994, 24, 3149.
[45] H.-J. Altenbach, B. Blech, J. A. Marco, E. Vogel, Angew. Chem. 1982, 94, 789; Angew. Chem., Int. Ed. 1982,
21, 778.
[46] F. Liang, H. A. Navarro, P. Abraham, P. Kotian, Y.-S. Ding, J. Fowler, N. Volkow, M. J. Kuhar, F. Ivy Carroll,
J. Med. Chem. 1997, 40, 2293.
[47] A. Otten, J. C. Namyslo, M. Stoermer, D. E. Kaufmann, Eur. J. Org. Chem. 1998, 19 9 7.
[48] R. Leung-Toung, Y. Liu, J. M. Muchowski, Y.-L. Wu, J. Org. Chem. 1998, 63, 3235.
[49] S. C. Nigam, A. Mann, M. Taddei, C.-G. Wermuth, Synth. Commun. 1989, 19, 3139.
[50] M. Sakaitani, Y. Ohfune, J. Org. Chem. 1990, 55, 870.
[51] J. Yuvaniyama, Department of Biochemistry, Mahidol University, Bangkok, Thailand, personal commu-
nication.
[52] J. T. Groves, K. W. Ma, J. Am. Chem. Soc. 1977, 99, 4076.
[53] A. R. Goldfarb, R. R. Renshaw, J. Am. Chem. Soc. 1941, 63, 2280.
[54] A. Altomare, G. Cascarano, C. Giacovazzo, A. Guagliardi, M. Burla, G. Polidori, M. Camalli, J. Appl.
Crystallogr. 1994, 27, 435.
[55] G. M. Sheldrick, −SHELXL-97 Program for the Refinement of Crystal Structures×, University of Gˆttingen,
Germany, 1997.
Received February 5, 2003