Sculpting the bicyclo[3.1.0]hexane template of carbocyclic nucleosides to improve recognition by herpes thymidine kinase

Article abstract of DOI:10.1021/ja0688732

The replacement of the furanose ring by a cyclopentane in nucleosides generates a group of analogues known generically as carbocyclic nucleosides. These compounds have increased chemical and enzymatic stability due to the absence of a true glycosyl bond t

Full text of DOI:10.1021/ja0688732

Published on Web 04/24/2007
Sculpting the Bicyclo[3.1.0]hexane Template of Carbocyclic
Nucleosides to Improve Recognition by Herpes Thymidine
Kinase
Maria J. Comin,† Riad Agbaria,‡ Tsipi Ben-Kasus,‡ Mahmoud Huleihel,§
Chenzhong Liao,† Guangyu Sun,† Marc C. Nicklaus,† Jeffrey R. Deschamps,
Damon A. Parrish, and Victor E. Marquez*,†
Contribution from the Laboratory of Medicinal Chemistry, Center for Cancer Research, National
Cancer Institute at Frederick, 376 Boyles Street, Frederick, Maryland 21702, Department of
Clinical Pharmacology, Faculty of Health Sciences, Ben-Gurion UniVersity of the NegeV,
Beer-SheVa 84105, Israel, The National Institute for Biotechnology and Department of Virology,
Faculty of Health Sciences, Ben-Gurion UniVersity of the NegeV, Beer-SheVa 84105, Israel, and
NaVal Research Laboratory, Washington, DC 20375
Received December 12, 2006; E-mail: marquezv@dc37a.nci.nih.gov
Abstract: The replacement of the furanose ring by a cyclopentane in nucleosides generates a group of
analogues known generically as carbocyclic nucleosides. These compounds have increased chemical and
enzymatic stability due to the absence of a true glycosyl bond that characterizes conventional nucleosides.
The additional fusion of a cyclopropane ring to the cyclopentane produces a bicyclo[3.1.0]hexane system
that depending on its location relative to the nucleobase is able to lock the embedded cyclopentane ring
into conformations that mimic the typical north and south conformations of the furanose ring in conventional
nucleosides. These bicyclo[3.1.0]hexane templates have already provided important clues to differentiate
the contrasting conformational preferences between kinases and polymerases. Herein, we describe the
design, synthesis, and phosphorylation pattern of a new bicyclo[3.1.0]hexane thymidine analogue that seems
to possess an ideal spatial distribution of pharmacophores for an optimal interaction with herpes simplex
1 thymidine kinase. The bicyclo[3.1.0]hexane template represents a privileged rigid template for sculpting
other carbocyclic nucleosides to meet the demands of specific receptors.
Introduction
We have successfully countered this 1′-exo bias of the cyclo-
pentane ring of carbocyclic nucleosides by fusing to it a
The replacement of the furanose ring by a cyclopentane is
the hallmark of carbocyclic nucleosides.1 This apparently simple
change provides excellent chemical and enzymatic stability due
to the absence of a true glycosyl bond that characterizes
conventional nucleosides. However, the absence of the furanose
oxygen brings about a significant change in conformation due
to the loss of important gauche and anomeric effects that in
normal nucleosides maintain the ribose in the vicinity of either
a 3′-endo (north) or 2′-endo (south) conformation.2 For that
reason, carbocyclic nucleosides adopt an atypical 1′-exo con-
formation that is governed mainly by the steric bulk of the
nucleobase, which prefers to adopt an equatorial orientation.3
cyclopropane ring that, depending on the pattern of substitution,
forces the embedded cyclopentane ring to adopt either a 2′-exo
(north) or a 3′-exo (south) conformation (Figure 1), which are
18° away from the ideal north (3′-endo/2′-exo, P ) 0°) or south
(3′-exo/2′-endo, P ) 360°) conformations described in the
pseudorotational cycle of conventional nucleosides.4 These
bicyclo[3.1.0]hexane templates have already provided important
clues to differentiate the contrasting conformational preferences
between kinases and polymerases.5-7
An effective and specific interaction with appropriate viral
kinases is of paramount importance for the development of
selective antiviral agents. During the course of an earlier
investigation, we found that in the case of the herpes simplex
1 thymidine kinase (HSV1-tk), the first phorphorylation step
of the south bicyclo[3.1.0]hexane thymidine analogue (S-MCT,
† National Cancer Institute at Frederick.
‡ Department of Clinical Pharmacology, Ben-Gurion University of the
Negev.
§ The National Institute for Biotechnology and Department of Virology,
Ben-Gurion University of the Negev.
Naval Research Laboratory.
(4) Altona, C.; Sundaralingam, M. J. Am. Chem. Soc. 1972, 94, 8205-8212.
(5) Marquez, V. E.; Ezzitouni, A.; Russ, P.; Siddiqui, M. A.; Ford, H.; Feldman,
R. J.; Mitsuya, H.; George, C.; Barchi, J. J., Jr. J. Am. Chem. Soc. 1998,
120, 2780-2789.
(6) Marquez, V. E.; Ben-Kasus, T.; Barchi, J. J., Jr.; Green, K. M.; Nicklaus,
M. C.; Agbaria, R. J. Am. Chem. Soc. 2004, 126, 543-549.
(7) Marquez, V. E.; Choi, Y.; Comin, M. J.; Russ, P.; George, C.; Huleihel,
M.; Ben-Kasus, T.; Agbaria, R. J. Am. Chem. Soc. 2005, 127, 15145-
15150.
(1) (a) Marquez, V. E. AdVances in Drug Design; JAI Press, Inc.: Greenwich,
CT, 1994; Vol. 2, pp 89-146. (b) Agrofoglio, L.; Suhas, E.; Farese, A.;
Condom, R.; Challand, S. R.; Earl, R. A.; Guedj, R. Tetrahedron 1994,
50, 10611-10670.
(2) Saenger, W. Principles of Nucleic Acid Structure; Springer-Verlag: New
York, Berlin, Heilderberg, 1984; pp 9-28.
(3) Kalman, A.; Koritsanszky, T.; Beres, J.; Sagi, G. Nucleosides Nucleotides
1990, 9, 235-243.
9
6216
J. AM. CHEM. SOC. 2007, 129, 6216-6222
10.1021/ja0688732 CCC: $37.00 © 2007 American Chemical Society

Bicyclo[3.1.0]hexane Template
A R T I C L E S
Figure 3. Two-step structural “reshuffling” of bicyclo[3.1.0]hexane nucleo-
side 1 into 4. The first step allows rotation of the C-N bond to the anti
orientation, and the second step repositions the critical OH group to the
opposite tip of the ring.
Scheme 1. Retrosynthetic Analysis of Compound 4
Figure 1. Pseudorotational cycle showing the range of north and south
conformations and the locked positions of the embedded cyclopentane ring
of bicyclo[3.1.0]hexane nucleosides (E ) envelope; T ) twist; superscripted
and subscripted numbers indicate which atoms are displaced in an endo or
exo orientation, respectively).
undergo ring opening at room temperature via a retro-aldol
reaction,9 the critical 3′-OH (nucleoside numbering) was then
relocated to the opposite end of the pseudoboat ring (compare
3 vs 4) where it could engage in H-bonding with the receptor
in a manner akin to that of 1.
A previous experiment with a simpler version of compound
3, lacking the 3′-OH entirely, was encouraging to the extent
that monophosphorylation by HSV-tk proceeded more efficiently
than monophosphorylation of either 1 or 2.7 Unfortunately,
phosphorylation to the diphosphate level, also catalyzed by
HSV1-tk, did not proceed at all pointing to the critical role of
the OH group.
Figure 2. Structures of bicyclo[3.1.0]hexane nucleosides S-MCT (1) and
N-MCT (2). The normal south-syn conformational bias in 1 is reinforced
by the restricted rotation of the C-N bond. The preferred orientation in 2
(north) is anti.
1) was not very efficient and the amount of the 5′-monophos-
phate produced was comparable to that of the corresponding
north counterpart (N-MCT, 2), apparently with the enzyme
making no clear distinction between the south and north
antipodes.6 We hypothesized that the expected south confor-
mational penchant of HSV1-tk was being affected by other
factors that countered this preference, such as a higher syn /
anti energy barrier, that restricted free rotation of the C-N bond
in 1 (Figure 2).6,7
Indeed, we have demonstrated that south bicyclo[3.1.0]hexane
pyrimidine nucleosides have a high syn / anti energy barrier,
which is directly related to the fusion of the cyclopropane ring
immediately adjacent to the C-N bond.6 The bicyclo[3.1.0]-
hexane scaffold significantly enhances the normal south-syn
conformational bias typical of south nucleosides2 and forces the
thymine ring to remain in the syn range as demonstrated both
by crystallography and NOE studies of 1 in solution.6-8 In an
effort to alleviate this problem, we decided to reposition the
fused cyclopropane ring in 1 to the other end of the molecule
generating a new compound (3) that still maintained an intact
southlike conformation but allowed the thymine ring to sample
the anti range (Figure 3). Because compound 3 was prone to
Results and Discussion
Synthesis. Preparation of target compound 4 required the
development of a new synthetic approach. The retrosynthetic
analysis is shown in Scheme 1. The thymine ring could be built
in a linear fashion from the hydroxy-protected trans amino
alcohol 5. The synthesis of the key pseudosugar ring involved
four fundamental steps: (1) a Baylis-Hillman reaction11 to
assemble the 5′-hydroxymethyl side chain; (2) a radical deoxy-
genation reaction12 to eliminate the allylic hydroxyl group; (3)
a vicinal-diol directed cyclopropanation reaction; (4) the regi-
oselective opening of a cyclic sulfite to introduce the nitrogen
substituent at the correct position and with the desired stereo-
chemistry.13
The execution of the plan was carried out as outlined in
Scheme 2. Plentiful D-ribose was converted into cyclopentenone
10 after six steps on a 10 g scale according to the literature.10
(9) Creary, X. J. Org. Chem. 1975, 40, 3326-3331.
(10) Moon, H. R.; Choi, W. J.; Kim, H. O.; Jeong, L. S. Tetrahedron: Asymmetry
2002, 13, 1189-1193.
(11) Basavaiah, D.; Rao, P. D.; Hynma, R. S. Tetrahedron 1996, 52, 8001-
8062.
(12) Barton, D. H. R.; McCombie, S. W. J. Chem. Soc., Perkin Trans. 1 1975,
1574-1585.
(13) Moon, H. R.; Kim, H. O.; Chun, M. W.; Jeong, L. S.; Marquez, V. E. J.
Org. Chem. 1999, 64, 4733-4741.
(8) Schelling, P.; Claus, M. T.; Johner, R.; Marquez, V. E.; Schulz, G. E.;
Scapozza, L. J. Biol. Chem. 2004, 279, 32832-32838.
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A R T I C L E S
Comin et al.
Scheme 2. Synthesis of Target Compound (()-4
With the use of a modality of the Baylis-Hillman reaction,14
treatment of cyclopentenone 10 with imidazole generated in situ
a stabilized nucleophilic anion that reacted with formaldehyde.
After the elimination of the amine catalyst, the effective addition
of a hydroxymethyl group resulted in the formation of cyclo-
pentenone 9. Protection of the primary alcohol as a benzoyl
ester proceeded smoothly, and stereospecific hydride reduction
of the carbonyl group afforded exclusively the allylic alcohol
8. Unfortunately, radical deoxygenation through the intermediate
xanthate proceeded with racemization due to the energetic
equivalence of the two possible radical intermediates. We forged
ahead nonetheless and continue the synthesis from racemate 13
because a racemic target compound would still allow testing of
our fundamental hypothesis. Thus, cleavage of the ketal ring
and treatment of the corresponding diol under modified Sim-
mons-Smith cyclopropanation conditions proceeded with the
desired diastereoselectivity to afford the critical bicylo[3.1.0]-
hexane skeleton 6 (relative stereochemistry shown). Reaction
of 6 with thionyl chloride gave almost quantitatively the
corresponding cyclic sulfite that underwent nucleophilic attack
with sodium azide to afford an easily separable 5:1 mixture of
regioisomers in favor of the desired azido alcohol 16. After
protection of the free hydroxyl group as a silyl ether, reduction
of the azide provided the requisite carbocyclic amine 5 in
quantitative yield. In summary, the pseudosugar ring was
prepared from cyclopentenone 10 after 11 synthetic steps in
15% overall yield. Subsequently, the thymine ring was readily
constructed from amine 5 following conventional published
methods.15
place: (1) the anti disposition of the thymine ring and (2) the
location of the OH group at the other extreme of the concave
face of the bicyclo[3.1.0]hexane template.
Phosphorylation by HSV1-tk. Compound (()-4 was radio-
labeled in the same manner as compound 1.6,7 The course of
phosphorylation of (()-4 and 1 to the mono- (MP), di- (DP),
and triphosphate (TP) stages in HSV-1-infected Vero cells was
measured by HPLC (Table 1). The efficient phosphorylation
of (()-4 relative to S-MCT (1) confirmed the success of our
reshuffling strategy for all three important phosphorylation steps.
Because the first two key phosphorylations are catalyzed by
HSV1-tk, our results confirmed that this new compound has
all the structural attributes for an effective and improved
recognition by the viral enzyme. Because 5′-triphosphate levels
are also more elevated for the new compound, it is safe to infer
that its molecular architecture is favorably recognized by the
cellular dinucleotide kinase as well.
Molecular Modeling and Conformational Analysis. Pre-
liminary docking experiments showed that only one enantiomer
of (()-4 closely matches the crystal structure of S-MCT (1) at
the active site of HSV1-tk by forming a similar network of
hydrogen bonds (Figure 5). In contrast to compound 1 (Figure
5A), which shows a hydrogen bond to Glu225, the new
compound does not form a hydrogen bond to this amino acid
(Figure 5B). However, it does show a stronger hydrogen bond
to Glu83 and an additional hydrogen bond to Arg163 not seen
with 1. Both compounds form a hydrogen bond to Tyr101. The
hydrogen bond network to the thymine nucleobase in both cases
is nearly identical. Another reason that explains the superior
substrate properties of (()-4 versus 1, which motivated the
execution of this work, is entropic. The orientation of the
thymine ring in both 1 and (()-4 at the active site of HSV1-tk
is anti. Compound 1 in solution has been shown to have the
thymine ring in the syn orientation; however, the repositioning
X-ray Structure. The crystal structure of (()-4 (Figure 4)
confirmed that all the desired stereochemical elements were in
(14) Luo, S.; Zhang, B.; He, J.; Janczuk, A.; Wang, P. G.; Cheng, J.-P.
Tetrahedron Lett. 2002, 43, 7369-7371.
(15) Shealey, Y. F.; O’Dell, C. A.; Thorpe, M. C. J. Heterocycl. Chem. 1981,
18, 383-389.
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Bicyclo[3.1.0]hexane Template
A R T I C L E S
Table 1. Phosphorylation Levels of 1 and (()-4 in HSV-1-Infected
Vero Cells (pmoles/106 Cells)a,b
S-MCT (1)
uninfected
(±)-4
metabolite
infected
uninfected
infected
MP
DP
TP
0.15 ( 0.06
0.30 ( 0.07
1.61 ( 0.24
54 ( 14
74 ( 17
153 ( 10
0.28 ( 0.11
0.08 ( 0.04
0.08 ( 0.63
252 ( 32
187 ( 15
342 ( 26
a Cells were infected 2 h before treatment, and the metabolites were
measured after 6 h. b MP ) monophosphate; DP ) diphosphate; TP )
triphosphate. Cells were treated with 10 µM, 10 µCi/mL of drug. Data are
mean ( SD (n ) 3).
Figure 6. Superimposed docked poses of both enantiomers of (()-4 to
that of docked S-MCT (1) at the active site of HSV-tk. Distances between
critical OH groups are in angstroms.
conformers. Indeed, as a result of freeing 1 from its syn bias,
according to Figure 3, it was necessary to include the cyclo-
propane ring and a virtual bond between 1′ and 5′ in (()-4 in
order to consider the system to be south, thus violating some
important pseudorotational rules.16 Furthermore, the repositioned
OH group is removed from its natural location relative to
conventional 2′-deoxynucleosides.
To visualize the importance of the new added OH group in
directing the docking of the compounds at the active site, we
superimposed the individual docked poses of both enantiomers
to that of S-MCT (1) at the active site of HSV-tk (Figure 6). It
can be appreciated that the axial OH in one enantiomer appears
displaced 2.76 Å from the axial OH in S-MCT (1) (Figure 6A),
whereas the axial OH of the other enantiomer, corresponding
to the one with the better fit, is displaced only 1.67 Å (Figure
6B). The displacement of the 5′-OH, although somewhat greater
for the enantiomer with the best fit (1.17 Å), permits the
formation of an additional hydrogen bond to Arg163 which
maybe key to explaining why the compound is such a good
substrate for HSV-tk (see Table 1).
Figure 4. Crystal structure of compound (()-4 represented as one
enantiomer (displacement ellipsoid plot drawn at the 50% probability level).
The numbering system used corresponds to the IUPAC name.
One caveat about the docking predictions is that we are
dealing with a static X-ray structure of an enzyme that executes
two phosphorylation steps. For the first phosphorylation step,
the enzyme appears to be more forgiving about the presence or
absence of the OH group, since a simpler version of compound
3, lacking the 3′-OH entirely, could be efficiently phosphory-
lated.7 However, the presence and correct disposition of the OH
becomes critical for phosphorylation to proceed beyond the
monophosphate level.
Figure 5. (A) HSV1-tk in complex with compound S-MCT (1) (result of
redocking 1 into the crystal structure; rmsd from crystal coordinates: 0.278
Å). (B) Result of docking one enantiomer of (()-4 at the same active site.
Conclusions
of the cyclopropane ring leading to (()-4 flips this ring into
the anti range. Therefore, relative to S-MCT (1), compound
(()-4 has already prepaid the entropic penalty incurred in the
flipping of the thymine ring in 1 from syn to anti when it binds
to HSV-tk.
Surprisingly, the enantiomer of (()-4 shown to have the
best fit at the active site of HSV-tk (Figure 5B) is the optical
antipode of the compound derived according to the strategy
outlined in Figure 3. Because this strategy was supposed to
generate a southlike conformation, the better fit of the optical
antipode, which should correspond to a northlike conformation,
appears counter to our rationale. The problem is that because
of the two-step reshuffling, the established rules of pseudoro-
tation do not apply,16 and the enantiomers of nucleosides (()-4
can no longer be described as canonical south and north
We have shown that changes in the substitution pattern of
rigid bicyclo[3.1.0]hexane nucleosides, which relative to normal
nucleosides appear unconventional, can lead to the spatial
optimization of pharmacophores and a vastly improved kinase
activity by HSV1-tk. These changes include the relocation of
the cyclopropane ring to relieve the molecule from the unusually
high syn / anti energy barrier and the presence of a free
hydroxyl group structurally equivalent to the 3′-hydroxyl group
in nucleosides. These changes more than doubled the amount
of triphosphate metabolite formed in HSV-1-infected cells
(Table 1).
The enantioselective synthesis of both enantiomers of com-
pound (()-4 is currently under way to identify the optimal
substrate for HSV-tk. The results presented here support the
concept that the bicyclo[3.1.0]hexane template of carbocyclic
nucleosides is a privileged rigid scaffold that can be ap-
propriately sculpted to fit the specific structural demands of an
active site, such as HSV-tk, to improve enzyme recognition.
(16) The calculated pseudorotational angle including the cyclopropane ring and
the virtual bond between 1′ and 5′ gave a value of P ) 198.3°, which
corresponds to a south (3′E) conformation. However, the maximum out-
of-plane pucker (ν2), which normally fluctuates between 35° and 45°, comes
completely out of range as 100.07°.
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A R T I C L E S
Comin et al.
Isco instrument, and analytical TLC was performed on Analtech
Uniplates silica gel GF. Unless otherwise indicated, NMR spectra were
determined in CDCl3 (99.8%) with residual CHCl3 as the reference
peak (7.26 and 77.0 ppm) and were recorded on a Varian 400 MHz
spectrophotometer. The coupling constants are reported in Hertz, and
the peak shifts are reported in the δ (ppm) scale; abbreviations s
(singlet), d (doublet), dd (doublet-of-doublets), ddd (doublet-of-doublet-
of-doublets), t (triplet), q (quartet), and m (multiplet). Positive-ion fast
atom bombardment mass spectra (FABMS) were obtained on a VG
7070E mass spectrometer at an accelerating voltage of 6 kV and a
resolution of 2000. Glycerol was used as the sample matrix, and
ionization was effected by a beam of xenon atoms. Elemental analyses
were performed by Atlantic Microlab. Inc., Norcross, GA. Infrared
spectroscopy data was obtained neat with a Jasco FT-IR/615 spec-
trometer. Specific optical rotations were measured in a Perkin-Elmer
model 241 polarimeter. All reaction glassware was oven-dried and
cooled to room temperature in an argon atmosphere prior to use.
Experimental Methods
Preparation of Cell Extract for Metabolite Analysis. Vero cells
cultures (4 × 106/25 mL flask) were infected with 1 PFU/cell of HSV-
1. After a 2 h incubation period, the cells were incubated with
radioactive [Me-3H]-1 or [Me-3H]-(()-4, 10 µM, 5 µCi/mL. These
compounds were radiolabeled by Moravek Biochemicals, Brea, CA
(specific activities 1100 and 1250 dpm/pmol for 1 and (()-4,
respectively). As a control, uninfected cells were treated with the
radioactive compounds. At the end of a 6 h incubation period, the cells
were washed three times with PBS, trypsinized, and recovered by
centrifugation. The dry pellets were suspended in 250 µL of 60%
methanol (HPLC grade) and heated at 95 °C for 3 min. After
centrifugation at 12 000g for 10 min, the clear supernatant fractions
were evaporated under nitrogen and redissolved in 250 µL of water.
Aliquots of this solution were analyzed by anion-exchanged (SAX-
10) HPLC.
HPLC Separation of Metabolites. The separation of 1, (()-4, and
their phosphorylated metabolites was carried out using a Hewlett-
Packard 1100 HPLC with a diode array UV absorption detector. A
Partisil-10 SAX column (250 mm × 4.6 mm) was used with the
following elution program: 0-5 min, 100% buffer A (0.01 M
ammonium phosphate, native pH); 5-20 min, linear gradient to 25%
buffer B (0.7 M ammonium phosphate with 10% methanol); 20-30
min, linear gradient to 100% buffer B; 30-40 min, 100% buffer B;
40-55 min, linear gradient to 100% buffer A and equilibration. The
flow rate was 2 mL/min. One minute fractions were collected, and
radioactivity was measured by scintillation spectrometry. Fractions
containing radiolabeled compounds were quantitated on the basis of
the known specific activity of the parent tritiated compounds.
Molecular Modeling. Docking of compound 1 and both enantiomers
of (()-4 (only the one that binds effectively is shown in Figure 5B)
was performed on the crystal structure 1OF18 complexed with S-MCT
(1) using the program Glide 4.0,17-19 part of the First Discovery suite,
and run via the Maestro interface (Schro¨dinger, New York, NY).
Because the crystal structure of 1OF1 is a dimer, duplicate parts were
deleted. All water molecules were deleted too, except 70 and 165, both
of which form critical hydrogen bond bridges between ligand 1 and
the protein. The bound ligand (1) was adjusted manually and then the
protein was prepared to produce a new receptor file in which all residues
are neutralized except for those that are relatively close to the ligand
or form salt bridges. A series of restrained energy minimizations were
performed using the Impact20 utility until the average root-mean-square
deviation (rmsd) of the non-hydrogen atoms reached 0.3 Å. In order
to study the binding modes of the inhibitors, grid files representing
shape and properties of the receptor were generated. The three-
dimensional structures of compounds 1 and 4 were constructed using
the builder tool available through the Maestro interface. Their initial
geometries were optimized using the OPLS_2005 force field, allowing
up to 5000 steps of conjugate gradient energy minimization. The
compounds were subjected to flexible docking using the precomputed
grid files. For each compound, the 100 top-scored poses were saved
and analyzed. The rmsd between the native conformation in crystal
structure 1OF1 and the best (lowest energy) docked conformation as
shown in Figure 5A was 0.278 Å, suggesting that Glide 4.0 predicts
the binding modes quite well.
(3aR,6aR)-5-(Hydroxymethyl)-2,2-dimethyl-3a,6a-dihydrocyclo-
penta[1,2-d]1,3-dioxolan-4-one (9). To a solution of 10 (1.90 g, 12.30
mmol) in 1:1 THF/H2O (40 mL) 37% formaldehyde (4.8 mL, 64.94
mmol) and imidazole (420 mg, 6.23 mmol) were added. The mixture
was stirred at 0 °C for 4 h. The reaction mixture was extracted with
ethyl acetate (3 × 100 mL), and the combined organic phases were
dried (MgSO4) and concentrated in vacuo. The residue was purified
by column chromatography (silica gel) employing hexanes/ethyl acetate
(7:3) as eluant to give 1.80 g (79% yield) of pure compound 9 as a
20
colorless oil: [R<abv>]D ) -11 (c 0.5, CHCl3); IR (neat) 3459,
1718 cm-1; 1H NMR δ 7.43 (m, 1 H, H-6), 5.24 (m, 1 H, H-6a), 4.54
(d, J ) 5.4 Hz, 1 H, H-3a), 4.40 (mAB, 2 H, -CH2OH), 1.42 (s, 3 H,
-CH3), 1.41 (s, 3 H, -CH3); 13C NMR δ 202.4 (C-4), 152.9 (C-6),
145.8 (C-5), 115.6 (-C(CH3)2), 77.6 (C-3a), 77.0 (C-6a), 57.3 (-CH2-
OH), 27.4 (CH3), 26.0 (CH3); FABMS m/z (relative intensity) 185 (95),
127 (100). Anal. Calcd for C9H12O4‚0.1H2O: C, 58.16; H, 6.63.
Found: C, 58.12; H, 6.71.
((3aR,6aR)-2,2-Dimethyl-4-oxo-3a,6a-dihydrocyclopenta[1,2-d]1,3-
dioxolan-5-yl)methyl Benzoate (11). To a solution of 9 (1.5 g, 8.20
mmol) in CH2Cl2 (50 mL) benzoyl chloride (1.25 mL, 10.66 mmol)
and pyridine (0.9 mL, 10.66 mmol) were added at 0 °C. The reaction
mixture was stirred at the same temperature for 1 h and at room
temperature for 1 h when NH4Cl (ss, 30 mL) was added, and the
aqueous phase was extracted with dichloromethane (2 × 30 mL). The
combined organic phases were washed with NH4Cl (ss, 30 mL), dried
(MgSO4), and concentrated. The residue was purified by Combi-flash
column chromatography (silica gel) employing hexanes/ethyl acetate
(17:3) as eluant to give 2.03 g (86% yield) of pure compound 11 as a
20
colorless oil: [R<abv>]D ) 37.8 (c 0.80, CHCl3); IR (neat) 1726
1
cm-1; H NMR δ 8.05 (m, 2 H, Ph), 7.59 (m, 1 H, Ph), 7.49 (q, J )
2.0 Hz, 1 H, H-6), 7.47 (m, 2 H, Ph), 5.25 (m, 1 H, H-6a), 5.07 (dt, J
) 15.0, 1.6 Hz, 1 H, -CHaHOBz), 5.02 (dt, J ) 15.0, 1.2 Hz, 1 H,
-CHHbOBz), 4.57 (d, J ) 5.5 Hz, 1 H, H-3a), 1.41 (s, 6 H, -CH3);
13C NMR δ 200.8 (C-4), 165.9 (COOPh), 154.1 (C-6), 142.1 (C-5),
133.4 (Ph), 129.7 (Ph), 129.4 (Ph), 128.5 (Ph), 115.6 (-C(CH3)2), 77.4
(C-3a), 77.0 (C-6a), 58.2 (-CH2OBz), 27.4 (CH3), 26.1 (CH3); FABMS
m/z (relative intensity) 289 (74), 231 (47). Anal. Calcd for C16H16O5:
C, 66.66; H, 5.59. Found: C, 66.85; H, 5.66.
((4S,3aS,6aR)-4-Hydroxy-2,2-dimethyl-4,3a,6a-trihydrocyclopenta-
[1,2-d]1,3-dioxolan-5-yl)methyl Benzoate (8). A solution of 11 (1.24
g, 4.30 mmol) in MeOH (30 mL) was treated with CeCl3·7H2O (800
mg, 2.15 mmol) and NaBH4 (162 mg, 4.30 mmol) at 0 °C. The reaction
mixture was stirred at that temperature for 30 min, pH was adjusted to
7 with acetic acid, and the solution was concentrated in vacuo. The
residue was dissolved in CHCl3 (3 × 50 mL), and the organic layer
was washed with brine (2 × 20 mL), dried (MgSO4), and concentrated.
The crude product was purified by Combi-flash column chromatography
(silica gel) employing hexanes/ethyl acetate 4:1 as eluant solvent to
afford 1.27 mg (92% yield) of 8 as a white solid: mp 74 °C,
Synthetic Methods. General. All chemical reagents were com-
mercially available. Melting points were taken on a Fisher-Jones
apparatus and are uncorrected. Combi-flash column chromatography
was performed on silica gel 60 (230-240 mesh) employing a Teledyne
(17) Glide, version 4.0; Schrodinger, LLC: New York, 2005.
(18) Friesner, R. A.; Banks, J. L.; Murphy, R. B.; Halgren, T. A.; Klicic, J. J.;
Mainz, D. T.; Repasky, M. P.; Knoll, E. H.; Shelley, M.; Perry, J. K.;
Shaw, D. E.; Francis, P.; Shenkin, P. S. J. Med. Chem. 2004, 47, 1739-
1749.
(19) Halgren, T. A.; Murphy, R. B.; Friesner, R. A.; Beard, H. S.; Frye, L. L.;
Pollard, W. T.; Banks, J. L. J. Med. Chem. 2004, 47, 1750-1759.
(20) Impact, version 4.0; Schro¨dinger, LLC: New York, 2005.
9
6220 J. AM. CHEM. SOC. VOL. 129, NO. 19, 2007

Bicyclo[3.1.0]hexane Template
A R T I C L E S
[R<abv>]D20 ) 22.9 (c 0.60, CHCl3); IR (neat) 3506, 1724 cm-1; 1H
NMR δ 8.06 (m, 2 H, Ph), 7.57 (m, 1 H, Ph), 7.45 (m, 2 H, Ph), 5.88
(m, 1 H, H-6), 5.04 (m, 1 H, H-6a), 5.01 (m, 2 H, -CH2OBz), 4.80 (t,
J ) 5.7 Hz, 1 H, H-3a), 4.58 (d, J ) 5.7 Hz, 1 H, H-4), 2.80 (bs, 1 H,
OH), 1.45 (s, 3 H, -CH3), 1.41 (s, 3 H, -CH3); 13C NMR δ 166.1
(COOPh), 144.3 (C-5), 133.1 (Ph), 129.9 (Ph), 129.6 (Ph), 128.4 (Ph),
127.6 (C-6), 112.4 (-C(CH3)2), 82.2 (C-6a), 77.4 (C-3a), 73.6 (C-4),
60.9 (-CH2OBz), 27.6 (CH3), 26.4 (CH3); FABMS m/z (relative
intensity) 291 (24), 275 (12). Anal. Calcd for C16H18O5: C, 66.19; H,
6.25. Found: C, 66.33; H, 6.30.
diiodomethane (1.10 mL, 14.50 mmol) in dichloromethane (10 mL)
were added to a solution of 14 (1.29 g, 5.52 mmol) in dichloromethane
(20 mL) at 0 °C. The reaction mixture was stirred at room temperature
for 48 h. NH4Cl (ss, 15 mL) was added, and the mixture was extracted
with dichloromethane (3 × 30 mL). The organic phase was dried and
concentrated in vacuo. The residue was purified by Combi-flash column
chromatography (silica gel) employing hexanes/ethyl acetate (3:2) as
eluant to give 699 mg (51% yield) of 6 as a colorless oil and 385 mg
(30% yield) of a regioisomeric mixture of monoylated alcohols.
1
Compound 6: IR (neat) 3423, 1714 cm-1; H NMR δ 8.04 (m, 2 H,
Ph), 7.57 (m, 1 H, Ph), 7.45 (m, 2 H, Ph), 4.54 (t, J ) 5.4 Hz, 1 H,
H-4), 4.29 (ABq, J ) 11.6 Hz, 2 H, -CH2OBz), 4.16 (t, J ) 6.2 Hz,
1 H, H-3), 2.26 (ddd, J ) 14.1, 6.6, 1.8 Hz, 1 H, H-2a), 2.12 (d, J )
14.1 Hz, 1 H, H-2b), 2.05 (bs, 2 H, OH), 1.65 (m, 1 H, H-5), 1.36 (t,
J ) 4.4 Hz, 1 H, H-6a), 0.68 (m, 1 H, H-6b); 13C NMR δ 166.6
(-COOPh), 133.0 (Ph), 130.2 (Ph), 129.6 (Ph), 128.4 (Ph), 75.3 (C-
4), 71.3 (C-3), 69.1 (-CH2OBz), 37.0 (C-2), 27.8 (C-5), 26.9 (C-1),
13.3 (C-6); FABMS m/z (relative intensity) 249 (34), 231 (44). Anal.
Calcd for C14H16O4: C, 67.73; H, 6.50. Found: C, 67.43; H, 6.54.
[(3aR,6aR)-2,2-Dimethyl-4-(methylthiothioxomethoxy)-4,3a,6a-
trihydrocyclopenta[3,4-d]1,3-dioxolan-5-yl]methyl Benzoate (12). A
solution of 8 (1.12 mg, 3.48 mmol) in anhydrous THF (20 mL) was
treated with CS2 (1.50 mL, 24.22 mmol) at 0 °C. After stirring for 5
min, NaH (420 mg, 10.46 mmol) was added portionwise, and the
reaction mixture was stirred for 30 min at room temperature. MeI (2.82
mL, 45.34 mmol) was added, and the mixture was stirred for extra 30
min. Then, it was cooled to 0 °C and water was added (10 mL). The
mixture was extracted with ethyl acetate (3 × 30 mL). The organic
phase was dried (MgSO4) and concentrated in vacuo. The residue was
purified by Combi-flash column chromatography (silica gel) employing
hexanes/ethyl acetate (19:1) as solvent to give 1.22 g (92% yield) of
12 as a white solid: mp 77 °C, [R<abv>]D20 ) -49.6 (c 0.50, CHCl3);
((4S,6S,1R,2R)-8-Oxo-7,9-dioxa-8-thiatricyclo[4.3.0.0 2,4 ]non-4-
yl)methyl Benzoate (15). Et3N (1.20 mL, 8.70 mmol) and SOCl2 (0.24
mL, 3.26 mmol) were added to a solution of 6 (540 mg, 2.18 mmol)
in dichloromethane (10 mL) at 0 °C. The reaction mixture was stirred
at the same temperature for 10 min and was then partitioned between
water (20 mL) and ethyl ether (40 mL). The organic phase was washed
with brine (2 × 10 mL), dried (MgSO4), and concentrated in vacuo.
The residue was purified by Combi-flash column chromatography (silica
gel) employing hexanes/ethyl acetate (4:1) as eluant to give 615 mg
(96% yield) of a diasteriomeric mixture 15 as a colorless oil: 1H NMR
δ 8.04 (m, 2 H, Ph), 7.59 (m, 1 H, Ph), 7.46 (m, 2 H, Ph), 5.69 (t, J
) 5.9 Hz, 1 H, H-1), 5.55 (dd, J ) 7.4, 5.3 Hz, 1 H, H-1′), 5.45 (t, J
) 6.8 Hz, 1 H, H-6), 5.21 (td, J ) 7.4, 2.0 Hz, 1 H, H-6′), 4.34 (d, J
) 11.9 Hz, 1 H, -CHaHOBz), 4.33 (d, J ) 11.9 Hz, 1 H, -CHa-
HOBz′), 4.24 (d, J ) 11.9 Hz, 1 H, -CHHbOBz), 4.22 (d, J ) 11.9
Hz, 1 H, -CHHbOBz′), 2.58 (ddd, J ) 15.4, 7.2, 2.0 Hz, 1 H, H-5a),
2.51 (ddd, J ) 15.2, 7.8, 1.8 Hz, 1 H, H-5a′), 2.40 (d, J ) 15.4 Hz, 2
H, H-5b, H-5b′), 1.86 (m, 2 H, H-2, H-2′), 1.81 (dd, J ) 6.1, 4.3 Hz,
1 H, H-3a), 1.19 (m, 1 H, H-3b), 0.99 (m, 1 H, H-3a′), 0.92 (dd, J )
5.9, 4.3 Hz 1 H, H-3b′); 13C NMR δ 166.3 (-COOPh), 133.2 (Ph),
129.9 (Ph), 129.8 (Ph), 129.6 (Ph), 128.45 (Ph), 128.43 (Ph), 90.9 (C-
1′), 89.5 (C-6′), 87.9 (C-1), 84.7 (C-6), 68.5 (-CH2OBz), 67.9 (-CH2-
OBz′), 35.3 (C-5′), 33.9 (C-5), 33.3 (C-4), 33.1 (C-4′), 27.3 (C-2), 26.7
(C-2′), 18.6 (C-3), 15.5 (C-3′); FABMS m/z (relative intensity) 295
(24), 231 (21), 173 (18). Anal. Calcd for C14H14O5S: C, 57.13; H,
4.79. Found: C, 57.47; H, 4.89.
1
IR (neat) 1720, 1069, 710 cm-1; H NMR δ 8.05 (m, 2 H, Ph), 7.58
(m, 1 H, Ph), 7.45 (m, 2 H, Ph), 6.24 (m, 1 H, H-4), 6.19 (m, 1 H,
H-6), 5.08 (m, 2 H, H-6a, H-3a), 4.97 (mAB, J ) 14.2 Hz, 2 H, -CH2-
OBz), 2.58 (s, 3 H, -SCH3), 1.42 (s, 3 H, -CH3), 1.38 (s, 3 H, -CH3);
13C NMR δ 215.4 (-OC(S)SCH3), 165.9 (COOPh), 140.1 (C-5), 133.2
(Ph), 131.8 (C-6), 129.7 (Ph), 129.6 (Ph), 128.4 (Ph), 113.0 (-C(CH3)2),
82.2 (C-6a)*, 82.2 (C-4)*, 76.8 (C-3a), 60.6 (-CH2OBz), 27.4 (CH3),
26.7 (CH3), 19.2 (-SCH3); FABMS m/z (relative intensity) 381 (9),
365 (4), 323 (34). Anal. Calcd for C18H20O5S2‚0.3H2O: C, 56.08; H,
5.39; S, 16.64. Found: C, 55.85; H, 5.34; S, 16.52.
(()-(2,2-Dimethyl-4,3a,6a-trihydrocyclopenta[3,4-d]1,3-dioxolan-
5-yl)methyl Benzoate (13). A solution of 12 (1.00 g, 1.45 mmol) and
AIBN (304 mg, 0.97 mmol) in anhydrous toluene (20 mL) was heated
to 50 °C under a blanket of argon. Tri-n-butyltin hydride (3.05 mL,
5.96 mmol) was slowly added, and when the addition was completed,
the reaction mixture was stirred at 120 °C for 1.5 h. The solvent was
removed in vacuo, and the residue was purified by Combi-flash column
chromatography (silica gel) employing hexanes/ethyl acetate (19:1) as
solvent to give 621 mg (88% yield) of 13 as a colorless oil: IR (neat)
1712 cm-1; 1H NMR δ 8.06 (m, 2 H, Ph), 7.58 (m, 1 H, Ph), 7.45 (m,
2 H, Ph), 5.81 (m, 1 H, H-6), 5.15 (m, 1 H, H-6a), 4.89 (mAB, 2 H,
-CH2OBz), 4.83 (td, J ) 5.9, 1.2 Hz, 1 H, H-3a), 2.68 (m, 1 H,
H-4a),2.57 (m, 1 H, H-4b), 1.44 (s, 3 H, -CH3), 1.36 (s, 3 H, -CH3);
13C NMR δ 166.1 (COOPh), 141.1 (C-5), 133.1 (Ph), 129.9 (Ph), 129.6
(Ph), 128.4 (Ph), 126.8 (C-6), 109.9 (-C(CH3)2), 85.0 (C-6a), 78.0
(C-3a), 62.9 (-CH2OBz), 39.1 (C-4), 27.4 (CH3), 25.6 (CH3); FABMS
m/z (relative intensity) 259 (8), 217 (59). Anal. Calcd for C16H18O4:
C, 70.06; H, 6.61. Found: C, 69.69; H, 6.83.
[(()-4-(Diazoazamvinyl)-3-hydroxybicyclo[3.1.0]hexyl]methyl Ben-
zoate (16) and [(()-3-(Diazoazamvinyl)-4-hydroxybicyclo[3.1.0]-
hexyl]methyl Benzoate (17). A solution of 15 (1.74 g, 5.91 mmol) in
anhydrous DMF (20 mL) was treated with sodium azide (780 mg, 11.82
mmol) at 100 °C for 15 h. Water (20 mL) was added, and the mixture
was extracted with ethyl acetate (3 × 20 mL); the organic phase was
washed with brine (20 mL), dried (MgSO4), and concentrated in vacuo.
The residue was purified by Combi-flash column chromatography (silica
gel) employing hexanes/ethyl acetate (3:1) as solvent to give 1.25 g
(78%) of 16 and 207 mg (13%) of undesired regioisomer 17 (91%
(()-(3,4-Dihydroxycyclopent-1-enyl)methyl Benzoate (14). A solu-
tion of 13 (536 mg, 1.96 mmol) in 60% aqueous acetic acid (5 mL)
was heated to 50 °C for 1 h. The solvent was removed in vacuo, and
the residue was purified by Combi-flash column chromatography (silica
gel) employing hexanes/ethyl acetate (2:3) as solvent to give 344 mg
1
overall yield). Compound 16: IR (neat) 3463, 2091, 1715 cm-1; H
1
(75% yield) of 14 as a colorless oil: IR (neat) 3358, 1718 cm-1; H
NMR δ 8.03 (m, 2 H, Ph), 7.53 (m, 1 H, Ph), 7.41 (m, 2 H, Ph), 4.35
(ABq, J ) 11.7 Hz, 2 H, -CH2OBz), 4.24 (d, J ) 6.8 Hz, 1 H, H-3),
4.64 (s, 1 H, H-4), 2.35 (ddd, J ) 14.2, 7.0, 2.2 Hz, 1 H, H-2a), 1.91
(d, J ) 14.2 Hz, 1 H, H-2b), 1.72 (bs, 1 H, -OH), 1.60 (ddd, J ) 9.2,
4.1, 1.6 Hz, 1 H, H-5), 1.23 (dd, J ) 5.5, 4.5 Hz, 1 H, H-6a), 0.87
(ddd, J ) 9.2, 5.3, 2.0 Hz, 1 H, H-6b); 13C NMR δ 166.6 (-COOPh),
133.0 (Ph), 130.2 (Ph), 129.6 (Ph), 128.4 (Ph), 78.1 (C-3), 69.6 (C-4),
68.5 (-CH2OBz), 37.9 (C-2), 29.2 (C-1), 26.1 (C-5), 15.0 (C-6);
FABMS m/z (relative intensity) 274 (19), 256 (15). Anal. Calcd for
C14H15N3O3‚0.1H2O: C, 61.13; H, 5.57; N, 15.28. Found: C, 61.35;
NMR δ 8.03 (m, 2 H, Ph), 7.55 (m, 1 H, Ph), 7.42 (m, 2 H, Ph), 5.78
(m, 1 H, H-2), 4.86 (mAB, 2 H, -CH2OBz), 4.63 (m, 1 H, H-3), 4.39
(m, 1 H, H-4), 2.66 (m, 1 H, H-5a), 2.42 (m, 1 H, H-5b); 13C NMR δ
166.2 (COOPh), 141.9 (C-1), 133.2 (Ph), 129.8 (Ph), 129.7 (Ph), 128.5
(Ph), 127.3 (C-2), 75.8 (C-3), 71.1 (C-4), 63.0 (-CH2OBz), 40.0 (C-
5); FABMS m/z (relative intensity) 235 (14), 217 (82). Anal. Calcd
for C13H14O4.0‚2H2O: C, 65.69; H, 6.11. Found: C, 65.62; H, 6.15.
(()-(3,4-Dihydroxybicyclo[3.1.0]hexyl)methyl Benzoate (6). Di-
ethylzinc (1.0 M in hexanes, 13 mL, 15.00 mmol) and a solution of
9
J. AM. CHEM. SOC. VOL. 129, NO. 19, 2007 6221

A R T I C L E S
Comin et al.
H, 5.76; N, 14.93. Compound 17: IR (neat) 3463, 2091, 1715 cm-1
;
MeOH, 19:1) to give 452 mg (83% yield) of pure 20 as a white solid:
mp 165-167 °C, IR (neat) 2927, 2855, 1702, 1693 cm-1; 1H NMR δ
10.09 (bs, NH), 8.03 (m, 2 H, Ph), 7.60 (m, 1 H, Ph), 7.36 (m, 2 H,
Ph), 7.36 (d, J ) 0.9 Hz, 1 H, H-6), 4.75 (d, J ) 12.1 Hz, 1 H, -CHa-
HOBz), 4.74 (s, 1 H, H-4), 4.29 (d, J ) 12.1 Hz, 1 H, -CHHbOBz),
4.16 (d, J ) 6.9 Hz, 1 H, H-3), 2.41 (dd, J ) 14.4, 6.9 Hz, 1 H, H-2a),
1.99 (d, J ) 14.4 Hz, 1 H, H-2b), 1.58 (d, J ) 0.9 Hz, 1 H, -CH3),
1.49 (m, 2 H, H-5, H-6a), 0.95 (m, 1 H, H-6b); 13C NMR δ 166.6
(-COOBz), 164.0 (C-4), 151.5 (C-2), 136.3 (C-6), 133.5 (Ph), 129.6
(Ph), 128.6 (Ph), 111.2 (C-5), 78.8 (C-3′), 67.8 (-CH2OBz), 66.0 (C-
4′), 35.8 (C-2′), 31.0 (C-1′), 25.0 (C-5′), 14.2 (C-6′), 12.3 (-CH3);
FABMS m/z (relative intensity) 357 (55), 235 (100). Anal. Calcd for
C19H20N2O5‚0.6H2O: C, 62.19; H, 5.82; N, 7.63. Found: C, 61.94; H,
5.90; N, 7.32.
1H NMR δ 8.04 (m, 2 H, Ph), 7.58 (m, 1 H, Ph), 7.46 (m, 2 H, Ph),
4.39 (dd, J ) 7.0, 5.1 Hz, 1 H, H-4), 4.30 (ABq, J ) 11.7 Hz, 2 H,
-CH2OBz), 3.37 (dt, J ) 9.8, 7.4 Hz, 1 H, H-3), 2.35 (dd, J ) 12.7,
7.6 Hz, 1 H, H-2a), 1.97 (ddd, J ) 12.7, 9.8, 1.2 Hz, 1 H, H-2b), 1.90
(bs, 1 H, -OH), 1.66 (m, 1 H, H-5), 0.97 (dd, J ) 6.1, 4.1 Hz, 1 H,
H-6a), 0.73 (m, 1 H, H-6b); 13C NMR δ 166.5 (-COOPh), 133.1 (Ph),
130.0 (Ph), 129.6 (Ph), 128.4 (Ph), 78.2 (C-4), 68.5 (-CH2OBz), 64.9
(C-3), 32.9 (C-2), 25.7 (C-5), 24.9 (C-1), 11.1 (C-6); FABMS m/z
(relative intensity) 274 (14), 256 (12). Anal. Calcd for C14H15N3O3:
C, 61.53; H, 5.53; N, 15.39. Found: C, 61.57; H, 5.59; N, 14.25.
(()-[4-(Diazoazamvinyl)-3-(1,1,2,2-tetramethyl-1-silapropoxy)-
bicyclo[3.1.0]hexyl] Methyl Benzoate (18). To a solution of 16 (484
mg, 1.77 mmol) in anhydrous dichloromethane (10 mL), pyridine (0.2
mL, 2.66 mmol) and TBDMSTf (0.61 mL, 2.66mmol) were added.
The reaction mixture was stirred at 0 °C for 1 h. Brine (10 mL) and
dichloromethane (20 mL) were added, and the aqueous phase was
extracted with dichloromethane (2 × 20 mL). The organic phase was
dried (MgSO4) and concentrated. The residue was purified by Combi-
flash column chromatography (silica gel) employing hexanes as solvent
to give 685 mg (100% yield) of 18 as a colorless oil: IR (neat) 2092,
1718 cm-1; 1H NMR δ 8.07 (m, 2 H, Ph), 7.56 (m, 1 H, Ph), 7.45 (m,
2 H, Ph), 4.47 (d, J ) 11.7 Hz, 1 H, -CHaHOBz), 4.30 (d, J ) 11.7
Hz, 1 H, -CHHbOBz), 4.16 (dd, J ) 6.5, 1.5 Hz, 1 H, H-3), 3.57 (s,
1 H, H-4), 2.31 (ddd, J ) 13.8, 6.6, 2.0 Hz, 1 H, H-2a), 1.85 (d, J )
13.8 Hz, 1 H, H-2b), 1.57 (ddd, J ) 9.1, 4.1, 1.5 Hz, 1 H, H-5), 1.30
(m, 1 H, H-6a), 0.87 (s, 9 H, -C(CH3)3), 0.85 (m, 1 H, H-6b), 0.05 (s,
3 H, -CH3), 0.05 (s, 3 H, -CH3); 13C NMR δ 166.6 (-COOBz), 132.9
(Ph), 130.3 (Ph), 129.6 (Ph), 128.3 (Ph), 78.3 (C-3), 70.1 (C-4), 68.6
(-CH2OBz), 38.2 (C-2), 29.1 (C-1), 25.9 (C-5), 25.7 (C(CH3)3), 17.8
(-C(CH3)3), 14.7 (C-6), -4.9 (-CH3), -5.0 (-CH3); FABMS m/z
(relative intensity) 388 (4), 345 (4). Anal. Calcd for C20H29N3O3Si: C,
61.98; H, 7.54; N, 10.84. Found: C, 62.09; H, 7.60; N, 10.67.
(()-[3-Hydroxy-4-(5-methyl-2,4-dioxo(1,3-dihydropyrimidinyl))-
bicyclo[3.1.0]hexyl] Methyl Benzoate (20). Lindlar’s catalyst (80 mg)
was added to a solution of 18 (667 mg, 1.72 mmol) in dichloromethane/
methanol (1:1, 25 mL). The reaction mixture was stirred under H2 (g)
atmosphere (1 atm) at room temperature overnight. The suspension
was filtered through a Celite pad, and the solvent was removed in vacuo
to give 622 mg (100% yield) of 5 as a colorless oil that was used as
such in the next step. To a suspension of AgNCO (480 mg, 3.16 mmol,
dried overnight under vacuum at 100 °C) in anhydrous benzene (10
mL) a solution of (2E)-3-methoxy-2-methylprop-2-enoyl chloride (500
mg, 3.50 mmol) in anhydrous benzene (5 mL) was added dropwise
under argon. The mixture was heated at reflux for 1 h and then was
allowed to reach room temperature. The supernatant was added through
canula to a solution of 5 (610 mg, 1.72 mmol) in anhydrous benzene
(5 mL) at 10 °C. The reaction mixture was allowed to reach room
temperature and was stirred for 3 h. The solvent was removed in vacuo,
and the residue was purified by Combi-flash chromatography (hexanes/
ethyl acetate, 1:1) to afford 793 mg (94% yield) of 19 as a colorless
oil that was used as such in the next step. Thus, compound 19 (771
mg, 1.53 mmol) was dissolved in ethanol (15 mL), and 2 N HCl (1.5
mL) was added. The reaction mixture was refluxed for 15 h. The solvent
was removed in vacuo, and the residue was coevaporated with ethanol
(3 × 10 mL) and purified by Combi-flash chromatography (CH2Cl2/
(()-[3-Hydroxy-5-(hydroxymethyl)bicyclo[3.1.0]hex-2-yl]-5-methyl-
1,3-dihydropyrimidine-2,4-dione ((()-4). Compound 20 (367 mg, 1.03
mmol) was treated with methanolic ammonia (5 mL) at 70 °C for 40
h. The volatiles were removed, and the residue was purified by Combi-
flash chromatography (CH2Cl2/MeOH, 93:7) to give 224 mg (89%
yield) of pure (()-4 as a white solid: mp 114-116 °C, IR (neat) 3371,
1
3008, 1682, 1634 cm-1; H NMR (CD3OD) δ 7.93 (d, J ) 1.2 Hz, 1
H, H-6), 4.69 (s, 1 H, H-2′), 4.04 (d, J ) 7.3 Hz, 1 H, H-3′), 4.02 (d,
J ) 11.7 Hz, 1 H, -CHaHOH), 3.34 (d, J ) 11.7 Hz, 1 H, -CHHb-
OH), 2.44 (ddd, J ) 14.3, 7.3, 2.0 Hz, 1 H, H-4′a), 1.86 (d, J ) 1,2
Hz, 3 H, -CH3), 1.71 (d, J ) 14.3 Hz, 1 H, H-4′b), 1.32 (ddd, J ) 9.2,
4.0, 1.4 Hz, 1 H, H-1′), 1.16 (dd, J ) 4.9, 4.0 Hz, 1 H, H-6′a), 0.77
(ddd, J ) 9.2, 4.9, 2.0 Hz, 1 H, H-6b); 13C NMR δ 166.5 (C-4), 152.9
(C-2), 139.9 (C-6), 111.2 (C-5), 80.1 (C-3′), 66.4 (C-2′), 66.3 (-CH2-
OH), 37.1 (C-5′), 34.6 (C-4′), 26.2 (C-1′), 15.0 (C-6′), 12.4 (-CH3);
FABMS m/z (relative intensity) 253 (100). Anal. Calcd for C12H16N2O4‚
1.3H2O: C, 52.31; H, 6.81; N, 10.17. Found: C, 52.04; H, 6.53; N,
9.88. X-ray structure: diffraction quality crystals of compound (()-4
were grown by slow evaporation from water. Single-crystal X-ray
diffraction data on (()-4 were collected at 103 °K using Mo KR
radiation and a Bruker APEX II CCD area detector (see the Supporting
Information for details). Atomic coordinates for compound (()-4 have
been deposited with the Cambridge Crystallographic Data Centre (dep-
osition number 629315). Copies of the data can be obtained, free of
charge, upon application to CCDC, 12 Union Road, Cambridge, CB2
1EZ, U.K. [fax, +44(0)-1223-336033 or e-mail, deposit@ccdc.cam.ac.uk].
Acknowledgment. The authors thank Drs. James A. Kelley
and Christopher Lai of the Laboratory of Medicinal Chemistry,
NCIsFrederick, for mass spectral analyses. This research was
supported in part by the Intramural Research Program of the
NIH, Center for Cancer Research, NCIsFrederick. Crystal-
lographic studies were supported by the National Institute on
Drug Abuse (NIDA) under contract DA6002-01.
Supporting Information Available: 1H and 13C NMR spectra
of new compounds, complete crystallographic data of compound
4, and crystallographic data in CIF format. This material is free
of charge via the Internet at http://pubs.acs.org.
JA0688732
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6222 J. AM. CHEM. SOC. VOL. 129, NO. 19, 2007