Methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo- [3′,4′:1,2]pyridin[3,4-b]-indol-2-substituted acetates: Synthesis and three-dimensional quantitative structure-activity relationship investigation as a class of novel vasodilators

Article abstract of DOI:10.1021/jm800249j

To find selective inhibitor of phosphodiesterase type 5 (PDE5), the essential structure elements of clinically used drugs sildenafil, vardenafil, and tadalafil were combined and a tetracyclic parent was constructed to which in 2-positions substituted acet

Full text of DOI:10.1021/jm800249j

J. Med. Chem. 2008, 51, 4715–4723
4715
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]-
indol-2-Substituted Acetates: Synthesis and Three-Dimensional Quantitative Structure-Activity
Relationship Investigation as a Class of Novel Vasodilators
Jiawang Liu, Ming Zhao,* Guohui Cui, Xiaoyi Zhang, Jun Wang, and Shiqi Peng*
College of Pharmaceutical Sciences, Capital Medical UniVersity, Beijing 100069, PR China
ReceiVed March 7, 2008
To find selective inhibitor of phosphodiesterase type 5 (PDE5), the essential structure elements of clinically
used drugs sildenafil, vardenafil, and tadalafil were combined and a tetracyclic parent was constructed to
which in 2-positions substituted acetic acid methylesters were introduced to form 17 novel vasodilators,
methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:1,2]- pyridin[3,4-b]indol-2-
substituted acetates. By molecular field analysis (MFA), an equation of three-dimensional quantitative
structure-activity relationship (3D QSAR) was established, which not only revealed the dependence of the
in vitro vasorelaxation activities on the structures but also pointed out the way to design new lead compounds
properly. Docking these novel vasodilators into the hydrophobic pocket of phosphodiesterase type 5 (PDE5)
revealed that their adaptabilities to this pocket did significantly affect on their vasorelaxation activity. Actually,
the docking adaptabilities of these novel vasodilators to PDE5 were consistent with the conformational
requirements of them to MFA and with the crystal conformation of two representatives.
Introduction
of 11 classes of human cyclic nucleotide phosphodiesterases,
among which the PDE5 enzyme is selective for cGMP.13,14
PDE5 is importantly expressed in human corpus cavernosum
tissue.15 In the literature, three PDE5 inhibitors sildenafil,16
vardenafil,17 and tadalafil18 were reported to be capable of
treating erectile dysfunction. Their structures are shown in
Figure 1.
Regardless of the initiating process, cardiovascular disease,1
sickle cell disease,2 cerebral vasospasm,3 stroke,4 ischemic heart
disease,5 and atherosclerosis6 manifest themselves as the most
common causes of death in developed countries and represent
a substantial burden to the healthcare systems around the world.
For instance, cardiac infarction alone may be responsible for
about 30% of all deaths of cardiovascular disease in some
countries. In these diseases, properties of blood vessels are
usually changed, which may be the results of vasoconstriction.
Vasoconstriction may result in disturbances of the vascular
tone and blood flow and subsequently spread the supply of
organs’ oxygen and nutrients. Discovering vasorelaxation
substances have been of importance and attracted a number of
interests. A series of endogenous substances are involved in
vasorelaxation, among which cyclic adenosine monophosphate
(cAMP)a and cyclic guanosine monophosphate (cGMP) play a
critical role.7–9 Increasing the concentration of cAMP and cGMP
causes the activation of protein kinase A and protein kinase G,
which phosphorylate a variety of substrates regulating a myriad
of physiological processes including cardiac and smooth muscle
contraction.10 Besides, phosphodiesterases (PDEs) hydrolyze
cAMP and cGMP into 5′-nucleotide monophosphates and
consequently regulate their cellular levels. PDE inhibition may
block phosphodiester hydrolysis and result in higher levels of
cyclic nucleotides. Thus PDE inhibitors may have a large variety
of therapeutic utilities including vasodilators.11,12 PDEs consist
The high-resolution cocrystal structures of PDE5 and inhibi-
tors reveal its active site as a pocket having a surface area of
approximately 675 Å2 and a volume of 927 Å3.19 This pocket
has a narrow side as its hydrophobic clamp and a wider side as
its binuclear metal ion center. These lead to a structural
requirement for the inhibitor bound to PDE5, that is, the inhibitor
should contain a planar heterocyclic ring that is not only capable
of sandwiching into the hydrophobic clamp but also forming
an H bond with Q817. To meet this requirement, 17 novel
methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-
imidazo[3′,4′:1,2]pyridin[3,4-b]indol-2-substituted acetates were
designed here. We hope that they interact as vasorelaxation
agents with the metal ions mediated through water, the protein
residues involved in nucleotide recognition and the hydrophobic
residues lining the cavity of the active site. Therefore, their in
vitro vasodilation assay, molecular field analysis (MFA), and
docking studies were performed. Besides, the crystal structures
of two compounds 4f,h were also reported in this study.
Results and Discussion
Synthesis of 4a-q. The synthetic route of methyl (11aS)-
1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:
1,2]pyridin[3,4-b]indol-2-substituted acetates (4a-q) is sum-
marized in Scheme 1. At 0 °C, (S)-2-(tert-butoxycarbonyl)-
2,3,4,9-tetrahydro-1H-pyrido-[3,4-b]indole-3-carboxylic acid were
coupled with L-amino acid methylesters providing substituted
(S)-tert-butyl 3-(2-methoxy-2-oxoethylcarbamoyl)-3,4-dihydro-
1H-pyrido[3,4-b]indole-2(9H)-carboxylate 3a-q in 76-99%
yields. After removing the tert-butoxycarbonyl (Boc) group, the
formed substituted (S)-tert-butyl 3-(2-methoxy-2-oxoethylcar-
bamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
* To whom correspondence should be addressed. For S.P.: Phone, 86-
10-8391-1528; Fax, 86-10-8391-1528; E-mail, sqpeng@mail.bjmu.edu.cn.
For M.Z.: Phone, +86 10 8280 2482; fax, +86 10 8280 2482;
E-mail,mingzhao@mail.bjmu.edu.cn.
a Abbreviations: 3D-QSAR, three-dimensional quantitative structure-acti-
vity relationship; PDEs, phosphodiesterases; PDE5, phosphodiesterase type
5; MFA, molecular field analysis; Boc, tert-butoxycarbonyl; DMSO,
dimethyl sulfoxide; NE: noradrenaline; THF: tetrahydrofuran; HOBt:
N-hydroxybenzotriazole; DCC: dicyclohexylcarbodiimide; DMF, N,N-
dimethyl formamide; NMM, N-methyl morpholine; MCS, maximum
common subgraph; G/PLS, genetic partial least-squares; TLC, thin layer
chromatography; cAMP, cyclic adenosine monophosphate; cGMP, cyclic
guanosine monophosphate; Ach, acetylcholine
10.1021/jm800249j CCC: $40.75
2008 American Chemical Society
Published on Web 07/11/2008

4716 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15
Liu et al.
Figure 1. Structures of three PDE5 inhibitors.
Scheme 1. Synthetic Route of Methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-
Substituted Acetatesa
a (i) Formaldehyde and sulfuric acid. (ii) (Boc)2O, DMF. (iii) DCC, HOBt, NMM. (iv) Hydrogen chloride in ethyl acetate (4N), methanol, acetone,
triethylamine. In 3a,4a R ) CH(CH3)CH2CH3; 3b,4b R ) CH(CH3)2; 3c,4c R ) CH2CH(CH3)2; 3d,4d R ) CH3; 3e,4e R ) H; 3f,4f R ) CH2C6H5; 3g,4g
R ) CH2C6H4-OH-p; 3h,4h R ) indole-3-ylmethyl; 3i,4i R ) CH2CO2Me; 3j,4j R ) CH2CH2CO2Me; 3k,4k R ) CH2OH; 3l,4l R ) CH(OH)CH3;
3m,4m R ) CH2CONH2; 3n,4n R ) CH2CH2CONH2; 3o,4o R ) CH2CH2CH2NHC(NH)NH2; 3p,4p R ) imidazole-4-ylmethyl; 3q,4q R ) CH2CH2SCH3.
Figure 2. ORTEP representation of 4f and 4h, the vasodilation inactive and active compounds.
late were directly treated with acetone to give methyl (11aS)-
1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:
1,2]pyridin[3,4-b]indol-2-substituted acetates in 35-65% total
yields. These results suggest that a two-step-procedure with a
simple wash is able to provide the goal products satisfactorily.
2, the orientation of the 2-benzyl of vasorelaxation inactive 4f
is different from that of the 2-indole of vasorelaxation active
4h, the benzyl group points the upper face of the 1,2,3,5,11,11a-
hexahydro-3,3-dimethyl-1-oxo-6H-imidazo- [3′,4′:1,2]pyridin[3,4-
b]indole ring, while the indole group points the under face of
this ring. The distinct orientations of 2-benzyl and indole groups
and various vasorelaxation activities of 4f,h imply that the
conformations of the 2-substituents of 4a-q greatly affect their
vasorelaxation activities.
Crystal structures of 4f,h. Two single crystals of 4f, the
vasorelaxation inactive compound with benzyl side chain, and
4h, the vasorelaxation potent compound with indole-3-ylmethyl
side chain, were prepared by evaporating their dimethyl sul-
foxide (DMSO) solutions. Their crystal structures were deter-
mined by X-ray diffractometry and the intensities were collected
at 291.2 K on a Rigaku Raxis2IV diffractometer with graphite
monochromated Mo KR radiation (λ ) 0.71073 Å). The data
collection, cell refinement, and reduction were carried out with
SMART and SAINT programs. Software used for structure
solution, refinement, analysis, and drawing include SHELXL97,
SHELXL97 all handled by the WINGX package.
Vasorelaxation Activities of 4a-q. To examine the vasore-
laxation activities of 4a-q, the in vitro vasodilation assays were
performed and the data are listed in Table 1. These assays
explored that 59 µM of noradrenaline (NE) induced hypertonic
contraction of the vessel strip may be effectively counteracted
by 50 µM of 4a,d,e,h,o. It was also found that, compared to
the reference compound acetylcholine (Ach), 4d,h were more
potential, and compared to the reference drug tadalafil, 4d was
equally active. However, these activities were from the pre-
liminary in vitro evaluations and the in vivo assays remain to
Their crystal data are given as Supporting Information. Their
ORTEP representations in Figure 2 show the molecular struc-
tures and the atom numbering schemes.20 As seen from Figure

Methyl Indol-2-Substituted Acetates
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15 4717
Table 1. Effect of 3a-q and 4a-q on NE Induced Vasoconstrictiona
R
compd vasorelaxation compd vasorelaxation
CH(CH3)CH2CH3
CH(CH3)2
CH2CH(CH3)2
CH3
3a
3b
3c
3d
3e
3f
10.9 ( 1.9
4a
4b
4c
4d
4e
4f
34.0 ( 4.3e
24.2 ( 1.8
15.7 ( 1.6
91.8 ( 5.6b,f
45.5 ( 3.2d
0
8.9 ( 1.4
7.8 ( 2.7
18.8 ( 2.2
H
13.5 ( 1.7
CH2C6H5
0
CH2C6H4-OH-p
indole-3-ylmethyl
CH2CO2CH3
CH2CH2CO2CH3
CH2OH
CH(OH)CH3
CH2CONH2
CH2CH2CONH2
3g
3h
3i
3j
3k
3l
7.4 ( 2.6
4g
4h
4i
4j
4k
4l
4m
4n
4o
4p
4q
16.3 ( 1.5
63.5 ( 4.4c,f
6.3 ( 1.6
9.9 ( 2.1
16.9 ( 1.2
0
15.2 ( 2.1
0
0
6.1 ( 1.8
0
0
0
11.3 ( 1.9
0
6.0 ( 2.4
Figure 4. Alignment stereoview of 4a-q used for molecular field
generation.
3m
3n
0
0
(CH2)3NHC(NH)NH2 3o
imidazole-4-ylmethyl 3p
CH2CH2SCH3
36.7 ( 3.1e
0
used for performing the alignment was the maximum common
subgraph (MCS).21 MCS looks at molecules as points and lines
and uses the techniques out of graph theory to identify the
patterns. Then MCS finds the largest subset of atoms in 4d that
shared by 4a-c,e-q. This subset was used for the alignment.
A rigid fit of atom pairings was performed to superimpose each
structure onto the target model 4d. Stereoview of aligned 4a-q
is shown in Figure 4. The alignment stereoview explores that
to superimpose onto 4d the side chains of each structure has to
take individual conformation. This individual side chain con-
formation will affect on the vasorelaxation activity.
3q
15.1 ( 2.0
tadalafil 89.9 ( 5.2b Achg
42.3 ( 2.9d
ethanol
0
a Vasorelaxation activity is represented by the percent of NE induced
hypertonic contraction of the vessel strip X ( SD%, n ) 6; final concentra-
tion: 3a-q ) 5 mM, 4a-q ) 50 µM, tadalafil, Ach ) 50 µM. b Compared
to 4a-c,e-q P < 0.01. c Compared to 4a-c,e-g,i-q P < 0.01. d Compared
to 4a-c,f,g,i-q P < 0.01. e Compared to 4b,c,e-g,i-n,q P < 0.01.
f Compared to Ach P < 0.01. g Ach: acetylcholine.
QSAR module of Cerius2 based MFA of 4a-q. Molecular
field analysis (MFA) was performed for 4a-q using the QSAR
module of Cerius2.22 A five-step procedure consisted of generat-
ing conformers, energy minimization, matching atoms and
aligning molecules, setting preferences, and regression analysis
was automatically practiced in MFA. Molecular electrostatic
and steric fields were created by use of proton and methyl groups
as probes, respectively. These fields were sampled at each point
of a regularly spaced grid of 1 Å. An energy cutoff of ( 30.0
kcal/mol was set for both electrostatic and steric fields. The
total grid points generated were 672. Although the spatial and
structural descriptors such as dipole moment, polarizability,
radius of gyration, number of rotatable bonds, molecular volume,
principal moment of intertia, AlogP98, number of hydrogen
bond donors and acceptors, and molar refractivity were also
considered, only the highest variance holder proton and methyl
descriptors were used. Regression analysis was carried out using
the genetic partial least-squares (G/PLS) method consisting of
50000 generations with a population size of 100. The number
of components was set to 5. Cross-validation was performed
with the leave-one-out procedure. PLS analysis was scaled, with
all variables normalized to a variance of 1.0.
Figure 3. Vasorelaxation activities of 4a,d,h at different concentrations.
be done. Furthermore, to really identify if PDE5 is the target,
the enzyme inhibition studies are also worthwhile.
To understand the contribution of the imidazo ring to the
vasorelaxation activities, 3a-q were used as reference com-
pounds, the vasorelaxation activities were tested using the same
in vitro vasodilation model, and the data are also listed in Table
1. The data indicated that even increasing the final concentration
by 100-fold 3a-q exhibited weaker vasodilation. This com-
parison demonstrated that the imidazo ring had a great contribu-
tion to the vasorelaxation activity.
To explore the possible dose-dependent relaxation of 4a-q
the activities of 50, 5, and 0.5 µM of 4a,d,h were evaluated on
a NE constrict aortic strip and the results are shown in Figure
4. The data demonstrate that the activities of different dose
4a,d,h are significantly different from each other and they
exhibit dose-dependent vasorelaxation (Figure 3).
Alignment of 4a-q. Establishing the valid 3D-QSAR models
a proper alignment procedure of 4a-q was practiced using the
target model align strategy in the align module within Cerius2.
On the basis of the assumption that each structure of 4a-q
exhibits activity at the same binding site of the receptor, they
were aligned in a pharmacologically active orientation. To obtain
a consistent alignment, the most vasorelaxation potent 4d was
selected as the template for superposing 4a-c,e-q. The method
The regions where variations in the steric or electrostatic
features of 4a-q in the training set lead to increase or decrease
activities were specified. Proton descriptor with positive coef-
ficient indicates a region favorable for electropositive group,
while negative coefficient indicates electronegative group
required at the position. The MFA model for the activity of
4a-q (Figure 5) in terms of the most relevant descriptors proton
and methyl group is expressed by eq 1.
Activity ) 1.79841 - 0.049782(H+ ⁄ 241) -
0.0181689(H+ ⁄ 248) + 0.03947(H+ ⁄ 138) -
0.045626(CH3 ⁄ 137) - 0.042326(H+ ⁄ 137) +
0.046705(CH3 ⁄ 139) + 0.04427(CH3 ⁄ 87) +
0.04753(H+ ⁄ 199) - 0.040812(CH3 ⁄ 264) (1)
The correlation of the activities tested on the in vitro
vasodilation model and the activities calculated using eq 1 is

4718 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15
Liu et al.
Leu765, Val782, Phe786, Leu804, and Phe820 and forming an
H bond with Tyr612. On the other hand, however, when 4f
sandwiches into PDE5′s hydrophobic clamp consisted of
hydrophobic amino acids Leu765, Val782, Phe786, Leu804, and
Phe820, the hydrophobic part of its tetracycle is more near the
hydrophilic amino acids Gln775 and Gln817 of the pocket,
which is unfavorable to the formation of the H bond. Besides,
its side chain benzyl has an endo-orientation toward its
tetracycle, which is unfavorable to sandwiching into PDE5′s
hydrophobic clamp. The docking results are completely con-
sistent with that of the crystal structures of 4f,h.
Conclusion
Structural similarity of 17 novel methyl (11aS)-1,2,3,5,11,11a-
hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:1,2]pyridin[3,4-
b]indol-2-substituted acetates (4a-q) to sildenafil, vardenafil,
and tadalafil lends themselves the capacities of relaxing smooth
muscle and blood vessel. Using docking study, we implied that
PDE5 should be their target, and their capacities of relaxing
smooth muscle and blood vessel essentially relied on their
adaptability to the pocket of PDE5. For instance, the most potent
4d is capable of sandwiching into PDE5′s hydrophobic clamp
consisted of hydrophobic amino acids Leu765, Val782, Phe786,
Leu804, and Phe820 and forming H bond with Tyr612, while
the inactive 4f is neither capable of sandwiching into this pocket
nor capable of forming this H bond. We demonstrated that the
conformations of 4f,h from the docking, MFA, and crystal
studies consistently reflected the importance of adapting the
pocket of PDE5. These results should be useful for designing
vasodilators with PDE5 as target.
Figure 5. Graph of tested versus predicted activities of 4a-q.
explained by Figure 6 (r2, 0.905). In eq 1, the data points (n),
correlation coefficient (r), square correlation coefficient (r2),
cross-validated correlation coefficient (r2cV), bootstrap correla-
tion coefficient (r2BS), and least-squares error (LSE) were 17,
0.951, 0.905, 0.838, 0.616, and 0.045, respectively.
Equation 1 contains 5 terms from proton descriptor. Among
them term 0.04753 (H+/199) has the highest positive coefficient,
which means that at this position an electron withdrawing group
will affect on the activity negatively. Figure 7a gives two
representatives, of which 4a has no electron withdrawing group
at this position and is vasorelaxation active, while 4n has an
electron withdrawing group at this position and is vasorelaxation
inactive.
Equation 1 contains also 4 terms from methyl descriptor.
Among them term (CH3/137) and (CH3/264) have negative
coefficients, which means that at this position an hydrophobic
group will affect on the activity negatively. Figure 6b gives
two representatives, of which 4d has no hydrophobic group at
this position and is vasorelaxation active, while 4f has an
hydrophobic group at this position and is vasorelaxation
nonactive.
Docking Studies on the Representatives of 4a-q. As
mentioned above, the vasorelaxation activities of 4a-q on a
NE constrict aortic strip model are significantly different from
each other and their structures are highly similar to tadalafil, a
specific inhibitor of PDE5. Thus PDE5 was considered as one
of the possible target enzymes of 4a-q to evaluate their binding
orientations and the interaction energies between PDE5 and
them. Docking studies for 4a-q were carried out using
LigandFit module of Cerius223 and the crystal structure of PDE5
(PDB ID: 1XOZ). The active site of PDE5 was defined as a
sphere of radius 6.0 A surrounding tadalafil.
Energetically, the most favorable conformation of the docked
structure was selected on the basis of the LigandFit score and
visual inspection. Initially hydrogen atoms were added to the
protein, considering all the residues at their neutral form.
Evaluation of the docking results was based on PDE5-4a-q
complementarity, the steric and electrostatic properties, the
calculated interaction energies in PDE5-4a-q complexes, and
the intramolecular energies of 4a-q. An evaluation was given
to the adaptability of 4a,d,h represented the vasorelaxation active
compounds and 4f represented the vasorelaxation inactive
compounds to PDE5′s active site. Figure 7a demonstates that
compound 4d is suitable for sandwiching into PDE5′s hydro-
phobic clamp that contains hydrophobic amino acids Leu765,
Val782, Phe786, Leu804, and Phe820 and forming an H bond
with Tyr612. Figure 7b demonstates that compounds 4a,d,h
(shown in gray) are suitable for sandwiching into PDE5′s
hydrophobic clamp consisted of hydrophobic amino acids
Experimental Section
Synthesis. General. The protected amino acids with L-config-
uration were purchased from Sigma Chemical Co. All coupling
and deprotective reactions were carried out under anhydrous
conditions. Chromatography was performed on Qingdao silica gel
H. The purities of the intermediates and the products were confirmed
on thin layer chromatography (TLC, Merck silica gel plates of type
60 F254, 0.25 mm layer thickness) and HPLC (Waters, C18 column
4.6 mm × 150 mm). 1H NMR and 13C NMR spectra were recorded
on Bruker Advance 300 and 500 spectrometers. FAB-MS was
determined by VG-ZAB-MS high resolution GC/MS/DS and HP
ES-5989x.OpticalrotationsweredeterminedwithaSchmidt+Haensch
Polartromic D instrument. The statistical analysis of all the
biological date was carried out by use of ANOVA test with p <
0.05 as significant cutoff.
(S)-2,3,4,9-Tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic Acid
(1).24 Compound 1 was prepared according to the literature.
(S)-2-(tert-Butoxycarbonyl)-2,3,4,9-tetrahydro-1H-pyrido[3,4-
b]indole-3-carboxylic Acid (2). Compound 2 was prepared ac-
cording to the literature.
General Procedure for the Preparation of Substituted (S)-
tert-Butyl 3-(2-Methoxy-2-oxoethylcarbamoyl)-3,4-dihydro-1H-
pyrido[3,4-b]indole-2(9H)-carboxylate (3a-q). At 0 °C, to the
solution of 2.0 g (6.33 mmol) (S)-2-(tert-butoxycarbonyl)-2,3,4,9-
tetrahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid in 30 mL of
anhydrous tetrahydrofuran (THF), 1.2 g (8.9 mmol) of N-hydroxy-
benzotriazole (HOBt) were added; after 10 min, 1.75 g (8.5 mmol)
of dicyclohexylcarbodiimide (DCC) were then added. The suspen-
sion of 6.61 mmol of HCl ·L-AA-OMe in 3 mL of anhydrous THF
was adjusted pH to 8-9 with N-methyl morpholine and stirred at
room temperature for another 20 min. This suspension then was
added to the solution of (S)-2-(tert-butoxycarbonyl)-2,3,4,9-tet-
rahydro-1H-pyrido[3,4-b]indole-3-carboxylic acid and the reaction
mixture was stirred at 0 °C for 2 h and at room temperature for
16 h. On evaporation, the residue was dissolved in 30 mL of ethyl
acetate. The solution was washed successively with 5% sodium

Methyl Indol-2-Substituted Acetates
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15 4719
Figure 6. (a) Electrostatic environment of 4a,n within the grid with 3D points of eq 1. (b) Steric environment of 4d,f within the grid with 3D
points of eq 1.
Figure 7. (a) Compound 4d (shown in gray) sandwiching into the hydrophobic clamp and forming an H bond with Tyr612 of PDE5′s pocket. (b)
Ensemble of 4a,d,h (shown in gray) and 4f (shown in white) sandwiching into PDE5′s pocket.
bicarbonate, 5% citric acid, and saturated sodium chloride, and the
organic phase was separated and dried over anhydrous sodium
sulfate. After filtration and evaporation under reduced pressure, the
title compound were obtained as powder.
4.5 Hz, 1H), 4.036 (dd, J ) 10.2 Hz, J ) 3.7 Hz, 1H), 3.625 (s,
3H), 2.950 (d, J ) 6.7 Hz, 2H), 1.877 (d, J ) 6.0 Hz, 2H), 1.473
(s, 9H), 1.852 (m, J ) 5.4 Hz, 1H), 1.055 (d, J ) 5.4 Hz, 6H).
20
[R]D ) -41 (c ) 0.31, CHCl3:CH3OH, 1:1, v/v).
(S)-tert-Butyl 3-((2S)-1-Methoxy-3-methyl-1-oxopentan-2-yl-
carbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
late (3a). Yield: 2.70 g (90%) as colorless powder; mp 122-125
°C. ESI/MS (m/e) 444 [M + H]+. IR (KBr): 3445, 3203, 3006,
(S)-tert-Butyl 3-((S)-1-Methoxy-1-oxopropan-2-ylcarbamoyl)-
3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxylate (3d).
Yield: 2.43 g (95.6%) as colorless powder; mp 144-146 °C. ESI/
MS (m/e) 402 [M + H]+. IR (KBr): 3451, 3011, 2949, 2847, 1730,
2953, 2842, 1727, 1644, 1607, 1452, 1394, 1372, 1062, 900 cm-1
.
1
1604, 1450, 1392, 1370, 1066, 897 cm-1. H NMR (BHSC-500,
1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 10.045 (s, 1H), 7.965
(s, 1H), 7.293 (t, J ) 7.4 Hz, 1H), 7.214 (t, J ) 7.4 Hz, 1H), 7.007
(d, J ) 7.4 Hz, 1H), 6.895 (d, J ) 7.4 Hz, 1H), 4.842 (t, J ) 5.4
Hz,1H),4.425 (d, J ) 5.4 Hz, 1H), 4.226 (dd, J ) 10.2 Hz, J )
4.5 Hz, 1H), 4.039 (dd, J ) 10.2 Hz, J ) 3.7 Hz, 1H), 3.622 (s,
3H), 2.953 (d, J ) 6.7 Hz, 2H), 2.877 (m, J ) 6.0 Hz, 1H), 1.473
(s, 9H), 1.350 (m, J ) 5.4 Hz, 2H), 1.053 (d, J ) 5.4 Hz, 3H),
1.001 (t, J ) 5.4 Hz, 3H). [R] D20 ) -49 (c ) 0.37, CHCl3:CH3OH,
1:1, v/v).
DMSO-d6): δ/ppm ) 9.891 (s, 1H), 7.980 (s, 1H), 7.323 (t, J )
7.5 Hz, 1H), 7.235 (t, J ) 7.8 Hz, 1H), 6.972 (d, J ) 7.8 Hz, 1H),
6.813 (d, J ) 7.5 Hz, 1H), 4.884 (d, J ) 5.2 Hz, 1H), 4.591 (m, J
) 5.5 Hz, 1H), 4.255 (dd, J ) 10.0 Hz, J ) 4.7 Hz, 1H), 4.172
(dd, J ) 10.1 Hz, J ) 3.5 Hz, 1H), 3.644 (s, 3H), 2.94 (d, J )
20
10.1 Hz, 2H), 1.556 (d, J ) 5.2 Hz, 3H), 1.437 (s, 9H). [R]D
-63 (c ) 0.35, CHCl3:CH3OH, 1:1, v/v).
)
(S)-tert-Butyl 3-(2-Methoxy-2-oxoethylcarbamoyl)-3,4-dihy-
dro-1H-pyrido-[3,4-b]indole-2(9H)-carboxylate (3e). Yield: 2.39 g
(97.6%) as colorless powder; mp 133-135 °C. ESI/MS (m/e) 388
[M + H]+. IR (KBr): 3448, 3010, 2945, 2843, 1732, 1600, 1453,
(S)-tert-Butyl 3-((S)-1-Methoxy-3-methyl-1-oxobutan-2-ylcar-
bamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
late (3b). Yield: 2.65 g (97%) as colorless powder; mp 138-140
°C. ESI/MS (m/e) 430 [M + H]+. IR (KBr): 3443, 3202, 3001,
1
1390, 1371, 1062, 899 cm-1. H NMR (BHSC-500, DMSO-d6):
2951, 2845, 1729, 1648, 1602, 1450, 1392, 1370, 1067, 902 cm-1
.
δ/ppm ) 9.934 (s, 1H), 8.025 (s, 1H), 7.302 (t, J ) 7.5 Hz, 1H),
7.201 (t, J ) 7.6 Hz, 1H), 6.955 (d, J ) 7.6 Hz, 1H), 6.836 (d, J
) 7.6 Hz, 1H), 4.891 (d, J ) 5.4 Hz, 1H), 4.223 (dd, J ) 10.2 Hz,
J ) 4.5 Hz, 1H), 4.182 (s, 2H), 4.194 (dd, J ) 10.2 Hz, J ) 3.7
Hz, 1H), 3.663 (s, 3H), 2.95 (d, J ) 10.1 Hz, 2H), 1.455 (s, 9H).
1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 10.043 (s, 1H), 7.962
(s, 1H), 7.295 (t, J ) 7.4 Hz, 1H), 7.211 (t, J ) 7.7 Hz, 1H), 7.004
(d, J ) 7.7 Hz, 1H), 6.892 (d, J ) 7.4 Hz, 1H), 4.840 (t, J ) 5.4
Hz, 1H), 4.423 (d, J ) 5.4 Hz, 1H), 4.225 (dd, J ) 10.2 Hz, J )
4.5 Hz, 1H), 4.037 (dd, J ) 10.2 Hz, J ) 3.7 Hz, 1H), 3.626 (s,
3H), 3.103 (m, J ) 5.4 Hz, 1H), 2.951 (d, J ) 6.7 Hz, 2H), 1.474
(s, 9H), 1.053 (d, J ) 5.4 Hz, 6H). [R]D20 ) -32 (c ) 0.30, CHCl3:
CH3OH, 1:1, v/v).
20
[R]D ) -101 (c ) 0.36, CHCl3:CH3OH, 1:1, v/v).
(S)-tert-Butyl 3-((S)-1-Methoxy-1-oxo-3-phenylpropan-2-yl-
carbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
late (3f). Yield: 2.99 g (99.0%) as colorless powder; mp 150-152
°C. ESI/MS (m/e) 478 [M + H]+. IR (KBr): 3446, 3205, 3006,
(S)-tert-Butyl 3-((S)-1-Methoxy-4-methyl-1-oxopentan-2-yl-
carbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
late (3c). Yield: 2.78 g (99%) as colorless powder; mp 131-133
°C. ESI/MS (m/e) 444 [M + H]+. IR (KBr): 3443, 3205, 3002,
2948, 2847, 1731, 1645, 1603, 1451, 1392, 1370, 1069, 904 cm-1
.
1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 9.920 (s, 1H), 7.971
(s, 1H), 7.314 (t, J ) 7.5 Hz, 1H), 7.282 (t, J ) 7.9 Hz, 2H), 7.195
(t, J ) 7.6 Hz, 1H), 7.140 (d, J ) 7.6 Hz, 2H), 7.025 (t, J ) 7.6
Hz, 1H), 6.963 (d, J ) 7.8 Hz, 1H), 6.807 (d, J ) 7.6 Hz, 1H),
4.935 (d, J ) 5.4 Hz, 1H), 4.822 (t, J ) 5.4 Hz, 1H), 4.274 (dd, J
) 10.2 Hz, J ) 4.5 Hz, 1H), 4.185 (dd, J ) 10.2 Hz, J ) 3.4 Hz,
2954, 2845, 1724, 1642, 1605, 1455, 1392, 1370, 1065, 903 cm-1
.
1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 10.043 (s, 1H), 7.962
(s, 1H), 7.291 (t, J ) 7.4 Hz, 1H), 7.212 (t, J ) 7.4 Hz, 1H), 7.004
(d, J ) 7.4 Hz, 1H), 6.891 (d, J ) 7.4 Hz, 1H), 4.840 (t, J ) 5.4
Hz, 1H), 4.422 (d, J ) 5.4 Hz, 1H), 4.224 (dd, J ) 10.2 Hz, J )

4720 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15
Liu et al.
1H), 3.625 (s, 3H), 3.17 (d, J ) 5.4 Hz, 2H), 2.930 (d, J ) 10.2
1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 9.981 (s, 1H), 7.870
(s, 1H), 7.343 (t, J ) 7.4 Hz, 1H), 7.254 (t, J ) 7.6 Hz, 1H), 6.952
(d, J ) 7.6 Hz, 1H), 6.724 (d, J ) 7.4 Hz, 1H), 4.870 (t, J ) 5.4
Hz, 1H), 4.673 (m, J ) 5.6 Hz, 1H), 4.485 (t, J ) 5.6 Hz, 1H),
3.991 (m, J ) 5.2 Hz, 2H), 3.653 (s, 3H), 2.974 (d, J ) 5.7 Hz,
2H), 2.195 (d, J ) 3.7 Hz, 1H), 1.474 (s, 9H), 1.19(d, J ) 5.6 Hz,
20
Hz, 2H), 1.483 (s, 9H). [R]D ) -64 (c ) 0.36, CHCl3:CH3OH,
1:1, v/v).
(S)-tert-Butyl 3-((S)-3-(4-Hydroxyphenyl)-1-methoxy-1-oxo-
propan-2-ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-
carboxylate (3g). Yield: 2.87 g (92%) as colorless powder; mp
143-145 °C. ESI/MS (m/e) 494 [M + H]+. IR (KBr): 3439, 3203,
3001, 2955, 2847, 1732, 1644, 1601, 1453, 1391, 1372, 1062, 903
cm-1. 1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 9.990 (s, 1H),
8.024 (s, 1H), 7.371 (t, J ) 7.6 Hz, 1H), 7.223 (t, J ) 7.7 Hz, 1H),
7.152 (d, J ) 7.5 Hz, 2H), 7.024 (d, J ) 7.5 Hz, 1H), 6.961 (d, J
) 7.7 Hz, 1H), 6.915 (d, J ) 7.5 Hz, 2H), 4.980 (s, 1H), 4.935 (d,
J ) 5.4 Hz, 1H), 4.806 (t, J ) 5.6 Hz, 1H), 4.292 (m, J ) 5.2 Hz,
2H), 3.643 (s, 3H), 3.157 (d, J ) 5.2 Hz, 2H), 2.975 (d, J ) 5.0
Hz, 2H), 1.49 3 (s, 9H). [R]D20 ) -57 (c ) 0.32, CHCl3:CH3OH,
1:1, v/v).
20
3H). [R]D ) -65 (c ) 0.35, CHCl3:CH3OH, 1:1, v/v).
(S)-tert-Butyl 3-((S)-4-Amino-1-methoxy-1,4-dioxobutan-2-
ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-car-
boxylate (3m). Yield: 2.13 g (76%) as colorless powder; mp
127-129 °C. ESI/MS (m/e) 445 [M + H]+. IR (KBr): 3440, 3203,
3005, 2942, 2833, 1735, 1642, 1604, 1453, 1394, 1372, 1067, 903
cm-1. 1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 8.871 (s, 1H),
8.012 (s, 1H), 7.296 (t, J ) 7.4 Hz, 1H), 7.217 (t, J ) 7.4 Hz, 1H),
7.008 (d, J ) 7.4 Hz, 1H), 6.827 (d, J ) 7.4 Hz, 1H), 6.053 (s,
2H), 4.927 (d, J ) 5.5 Hz, 1H), 4.422 (t, J ) 5.5 Hz, 1H), 4.246
(d, J ) 5.6 Hz, 2H), 3.674 (s, 3H), 2.942 (d, J ) 5.4 Hz, 2H),
2.688 (t, J ) 5.5 Hz, 2H), 1.466 (s, 9H). [R]D20 ) -51 (c ) 0.38,
CHCl3:CH3OH, 1:1, v/v).
(S)-tert-Butyl 3-((S)-3-(1H-Indol-3-yl)-1-methoxy-1-oxopro-
pan-2-ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-
carboxylate (3h). Yield: 2.78 g (85%) as colorless powder; mp
161-163 °C. ESI/MS (m/e) 517 [M + H]+. IR (KBr): 3442, 3204,
3000, 2948, 2839, 1729, 1642, 1604, 1448, 1391, 1372, 1062, 900
cm-1. H NMR (BHSC-500, DMSO-d6): δ/ppm ) 9.872 (s, 1H),
9.863 (s, 1H), 8.095 (s, 1H), 7.324 (t, J ) 7.5 Hz, 1H), 7.307 (t, J
) 7.4 Hz, 1H), 7.126 (d, J ) 7.8 Hz, 1H), 7.114 (t, J ) 7.8 Hz,
1H), 7.103 (d, J ) 7.6 Hz, 1H), 7.095 (t, J ) 7.8 Hz, 1H), 7.046
(d, J ) 7.6 Hz, 1H), 6.981 (d, J ) 7.5 Hz, 1H), 6.835 (s, 1H), 4.94
(d, J ) 5.4 Hz, 1H), 4.762 (t, J ) 5.3 Hz, 1H), 4.291 (d, J ) 5.2
Hz, 2H), 3.644 (s, 3H), 3.192 (d, J ) 5.4 Hz, 2H), 2.955 (d, J )
(S)-tert-Butyl 3-((S)-5-Amino-1-methoxy-1,5-dioxopentan-2-
ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-car-
boxylate (3n). Yield: 2.38 g (82%) as colorless powder; mp
122-124 °C. ESI/MS (m/e) 459 [M + H]+. IR (KBr): 3445, 3200,
3001, 2940, 2835, 1733, 1640, 1602, 1452, 1391, 1370, 1065, 900
cm-1. 1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 9.916 (s, 1H),
8.007 (s, 1H), 7.292 (t, J ) 7.4 Hz, 1H), 7.203 (t, J ) 7.4 Hz, 1H),
7.005 (d, J ) 7.4 Hz, 1H), 6.806 (d, J ) 7.4 Hz, 1H), 6.054 (s,
2H), 4.925 (d, J ) 5.5 Hz, 1H), 4.413 (t, J ) 5.5 Hz, 1H), 4.245
(d, J ) 5.6 Hz, 2H), 3.677 (s, 3H), 2.945 (d, J ) 5.4 Hz, 2H),
2.186 (t, J ) 5.5 Hz, 2H), 2.140 (t, J ) 5.5 Hz, 2H), 1.464 (s, 9H).
20
6.4 Hz, 2H), 1.496 (s, 9H). [R]D ) -79 (c ) 0.34, CHCl3:
CH3OH, 1:1, v/v).
(S)-Dimethyl 2-((S)-2-(tert-Butoxycarbonyl)-2,3,4,9-tetrahy-
dro-1H-pyrido[3,4-b]-indole-3-carboxamido)succinate
(3i).
20
Yield: 2.79 g (96%) as colorless powder; mp 158-160 °C. ESI/
[R]D ) -56 (c ) 0.38, CHCl3:CH3OH, 1:1, v/v).
MS (m/e) 460 [M + H]+. IR (KBr): 3441, 3210, 3004, 2955, 2841,
1
1732, 1643, 1604, 1453, 1390, 1371, 1061, 903 cm-1. H NMR
(S)-tert-Butyl 3-((S)-5-Guanidino-1-methoxy-1-oxopentan-2-
ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-car-
boxylate (3o). Yield: 2.43 g (79%) as colorless powder; mp
168-170 °C. ESI/MS (m/e) 487 [M + H]+. IR (KBr): 3443, 3207,
3001, 2948, 2842, 1731, 1645, 1602, 1453, 1390, 1372, 1061, 904
cm-1. 1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 10.221 (s, 1H),
8.452 (s, 2H), 8.270 (s, 1H), 8.224 (s, 1H), 8.017 (s, 1H), 7.293 (t,
J ) 7.6 Hz, 1H), 7.185 (t, J ) 7.7 Hz, 1H), 7.044 (d, J ) 7.7 Hz,
1H), 6.961 (d, J ) 7.6 Hz, 1H), 4.905 (d, J ) 5.3 Hz, 1H), 4.426
(t, J ) 4.2 Hz, 1H), 4.251 (d, J ) 5.0 Hz, 2H), 3.655 (s, 3H),
2.947 (d, J ) 4.1 Hz, 2H), 2.680 (t, J ) 5.4 Hz, 2H), 1.925 (m, J
(BHSC-500, DMSO-d6): δ/ppm ) 10.050 (s, 1H), 8.051 (s, 1H),
7.373 (t, J ) 7.4 Hz, 1H), 7.252 (t, J ) 7.4 Hz, 1H), 7.006 (d, J
) 7.6 Hz, 1H), 6.954 (d, J ) 7.4 Hz, 1H), 4.926 (d, J ) 5.5 Hz,
1H), 4.773 (t, J ) 5.5 Hz, 1H), 4.242 (d, J ) 5.6 Hz, 2H), 3.625
(s, 3H), 3.581 (s, 3H), 2.917 (d, J ) 5.2 Hz, 2H), 2.855 (d, J ) 5.4
20
Hz, 2H), 1.494 (s, 9H). [R]D ) -52 (c ) 0.35, CHCl3:CH3OH,
1:1, v/v).
(S)-Dimethyl 2-((S)-2-(tert-Butoxycarbonyl)-2,3,4,9-tetrahy-
dro-1H-pyrido[3,4-b]-indole-3-carboxamido)pentanedioate (3j).
Yield: 2.93 g (98%) as colorless powder; mp 154-156 °C. ESI/
MS (m/e) 474 [M + H]+. IR (KBr): 3441, 3203, 3000, 2944, 2831,
20
) 5.5 Hz, 2H), 1.583 (m, J ) 5.5 Hz, 2H), 1.576 (s, 9H). [R]D
) -45 (c ) 0.35, CHCl3:CH3OH, 1:1, v/v).
1
1731, 1645, 1604, 1455, 1390, 1372, 1067, 903 cm-1. H NMR
(BHSC-500, DMSO-d6): δ/ppm ) 9.890 (s, 1H), 8.044 (s, 1H),
7.393 (t, J ) 7.6 Hz, 1H), 7.282 (t, J ) 7.6 Hz, 1H), 7.015 (d, J
) 7.7 Hz, 1H), 6.844 (d, J ) 7.6 Hz, 1H), 4.906 (d, J ) 5.4 Hz,
1H), 4.437 (t, J ) 5.6 Hz, 1H), 4.225 (d, J ) 5.5 Hz, 2H), 3.663
(s, 3H), 3.647 (s, 3H), 2.968 (d, J ) 5.4 Hz, 2H), 2.281 (t, J ) 5.6
(S)-tert-Butyl 3-((S)-3-(1H-Imidazol-4-yl)-1-methoxy-1-oxo-
propan-2-ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-
carboxylate (3p). Yield: 2.36 g (80%) as colorless powder; mp
162-164 °C. ESI/MS (m/e) 468 [M + H]+. IR (KBr): 3442, 3206,
3004, 2949, 2839, 1730, 1643, 1601, 1454, 1391, 1368, 1062, 902
cm-1. 1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 12.980 (s, 1H),
9.962 (s, 1H), 8.053 (s, 1H), 7.475 (s, 1H), 6.85 (s, 1H), 7.362 (t,
J ) 7.4 Hz, 1H), 7.206 (t, J ) 7.7 Hz, 1H), 7.164 (d, J ) 7.7 Hz,
1H), 6.985 (t, J ) 7.4 Hz, 1H), 4.937 (t, J ) 5.3 Hz, 1H), 4.835 (t,
J ) 5.4 Hz, 1H), 4.266 (d, J ) 5.2 Hz, 2H), 3.645 (s, 3H), 3.194
20
Hz, 2H), 2.245 (t, J ) 5.7 Hz, 2H), 1.434 (s, 9H). [R]D ) -45
(c ) 0.37, CHCl3:CH3OH, 1:1, v/v).
(S)-tert-Butyl 3-((S)-3-hydroxy-1-methoxy-1-oxopropan-2-yl-
carbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
late (3k). Yield: 2.43 g (92%) as colorless powder; mp 139-141
°C. ESI/MS (m/e) 418 [M + H]+. IR (KBr): 3442, 3200, 3001,
2952, 2845, 1730, 1644, 1606, 1455, 1392, 1370, 1067, 900 cm-1
.
(d, J ) 5.4 Hz, 2H), 2.925 (d, J ) 5.2 Hz, 2H), 1.493 (s, 9H).
1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 9.950 (s, 1H), 7.972
(s, 1H), 7.291 (t, J ) 7.6 Hz, 1H), 7.224 (t, J ) 7.9 Hz, 1H), 6.995
(d, J ) 7.9 Hz, 1H), 6.830 (t, J ) 7.6 Hz, 1H), 4.872 (d, J ) 5.4
Hz, 1H), 4.526 (t, J ) 5.6 Hz, 1H), 4.197 (d, J ) 5.2 Hz, 2H),
20
[R]D
) -47 (c ) 0.30, CHCl3:CH3OH, 1:1, v/v).
(S)-tert-Butyl 3-((S)-1-Methoxy-4-(methylthio)-1-oxobutan-
2-ylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-car-
boxylate (3q). Yield: 2.80 g (97%) as colorless powder; mp
159-161 °C. ESI/MS (m/e) 462 [M + H]+. IR (KBr): 3441, 3203,
3004, 2953, 2847, 1732, 1641, 1603, 1454, 1390, 1372, 1061, 900
cm-1. 1H NMR (BHSC-500, DMSO-d6): δ/ppm ) 10.04 (s, 1H),
7.97 (s, 1H), 7.32 (t, J ) 7.5 Hz, 1H), 7.22 (t, J ) 7.8 Hz, 1H),
6.99 (d, J ) 7.8 Hz, 1H), 6.81 (d, J ) 7.5 Hz, 1H), 4.86 (t, J ) 5.3
Hz, 1H), 4.45 (t, J ) 5.5 Hz, 1H), 4.28 (d, J ) 5.1 Hz, 2H), 3.68
(s, 3H), 2.93 (d, J ) 5.3 Hz, 2H), 2.42 (t, J ) 5.4 Hz, 2H), 2.28
4.133 (d, J ) 5.6 Hz, 2H), 3.634 (s, 3H), 2.95 (d, J ) 5.6 Hz, 1H),
20
2.925 (d, J ) 5.6 Hz, 1H), 2.288 (s, 1H), 1.454 (s, 9H). [R]D
-57 (c ) 0.38, CHCl3:CH3OH, 1:1, v/v).
)
(S)-tert-Butyl 3-((2S)-3-Hydroxy-1-methoxy-1-oxobutan-2-yl-
carbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-carboxy-
late (3l). Yield: 2.37 g (87%) as colorless powder; mp 140-142
°C. ESI/MS (m/e) 432 [M + H]+. IR (KBr): 3437, 3200, 3002,
2951, 2844, 1735, 1649, 1600, 1450, 1392, 1370, 1065, 901 cm-1
.

Methyl Indol-2-Substituted Acetates
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15 4721
20
(d, J ) 5.6 Hz, 2H), 2.10 (s, 3H), 1.44 (s, 9H). [R]D ) -48 (c
) 0.33, CHCl3:CH3OH, 1:1, v/v).
1H), 7.437 (t, J ) 7.2 Hz, 1H), 7.256 (d, J ) 7.2 Hz, 1H), 7.053
(d, J ) 7.2 Hz, 1H), 7.000 (d, J ) 7.2 Hz, 1H), 4.431 (t, J ) 4.8
Hz, 1H), 3.990 (t, J ) 5.4 Hz, 1H), 3.660 (s, 3H), 3.423 (dd, J )
4.3 Hz, J ) 10.0 Hz, 1H), 3.088 (dd, J ) 4.3 Hz, J ) 10.0 Hz,
1H), 2.741 (d, J ) 5.4 Hz, 2H), 1.490 (d, J ) 4.8 Hz, 3H), 1.433
(s, 3H), 1.271 (s, 3H). 13C NMR (CDCl3, 75 MHz) δ/ppm )
173.555, 170.811, 136.706, 131.442, 127.725, 122.304, 120.113,
118.905, 111.202, 108.890, 70.879, 60.131, 51.011, 44.551, 42.107,
30.113, 29.107, 25.004, 14.115. [R]D20 ) -87 (c ) 0.28, acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-acetate (4e). Yield:
0.76 g (45%) as colorless powder. ESI/MS (m/e) 329 [M + H]+.
1H NMR (CDCl3, 300 MHz) δ/ppm ) 8.522 (s, 1H), 7.439 (t, J )
7.4 Hz, 1H), 7.260 (d, J ) 7.4 Hz, 1H), 7.058 (d, J ) 7.4 Hz, 1H),
7.007 (d, J ) 7.4 Hz, 1H), 4.335 (s, 2H), 3.977 (t, J ) 5.6 Hz,
1H), 3.662 (s, 3H), 3.431 (dd, J ) 4.1 Hz, J ) 10.2 Hz, 1H), 3.092
(dd, J ) 4.1 Hz, J ) 10.2 Hz, 1H), 2.744 (d, J ) 5.6 Hz, 2H),
1.430 (s, 3H), 1.276 (s, 3H). 13C NMR (CDCl3, 75 MHz) δ/ppm
) 172.167, 170.825, 136.651, 131.224, 124.333, 121.922, 120.400,
119.113, 111.363, 109.223, 71.112, 61.166, 50.958, 44.551, 42.867,
General Procedure for the Preparation of Methyl (11aS)-
1,2,3,5,11,11a- hexahydro-3,3-dimethyl-1-oxo-6H-imidazo[3′,4′:
1,2]pyridin[3,4-b]indol-2-substituted Acetate (4a-q). At 0 °C to
the solution of 4.51 mmol of substituted (S)-tert-butyl 3-(2-methoxy-
2-oxoethylcarbamoyl)-3,4-dihydro-1H-pyrido[3,4-b]indole-2(9H)-
carboxylate (3) in 8 mL of ethyl acetate 16 mL of hydrogen
chloride/ethyl acetate (4N) were added dropwise. The reaction
solution was stirred at 0 °C for 90min and evaporated under reduced
pressure. The residue was dissolved in 60 mL of methanol and 20
mL of acetone. The reaction solution was adjusted to pH 9 with
triethylamine, stirred at room temperature and in dark for 240 h,
and TLC (CHCl3/MeOH, 10/1) indicated the complete disappear-
ance of 3. On evaporation, the residue was dissolved in 200 mL of
ethyl acetate. The solution was washed successively with 5%
sodium bicarbonate, 5% citric acid, and saturated sodium chloride,
and the organic phase was separated and dried over anhydrous
sodium sulfate. After filtration and evaporation under reduced
pressure, the residues of 4a-l,n,q were dissolved in 5 mL of
methanol to purify via direct crystallization, while the residues of
4m,o,p were purified on silica column chromatography (CHCl3/
CH3OH, 10:1).
20
30.200, 29.535, 25.531. [R]D ) -74 (c ) 0.30, acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-benzylacetate
(4f). Yield: 0.98 g (45%) as colorless powder. ESI/MS (m/e) 418
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S, 3′S)-but-2-ylac-
etate (4a). Yield: 0.8 g (46%) as yellowish crystals. ESI/MS (m/e)
1
[M + H]+. H NMR (CDCl3, 300 MHz) δ/ppm ) 8.807 (s, 1H),
7.416 (t, J ) 7.2 Hz, 1H), 7.271 (t, J ) 7.5 Hz, 2H), 7.259 (d, J
) 7.2 Hz, 1H), 7.144 (d, J ) 7.5 Hz, 2H), 7.079 (t, J ) 7.5 Hz,
1H), 7.058 (d, J ) 7.2 Hz, 1H), 7.006 (d, J ) 7.2 Hz, 1H), 4.988
(t, J ) 4.5 Hz, 1H), 4.372 (dd, J ) 4.5 Hz, J ) 10.5 Hz, 1H,),
3.689 (s, 3H), 3.564 (d, J ) 4.5 Hz, 2H), 3.275 (d, J ) 5.5 Hz,
2H), 2.910 (d, J ) 4.5 Hz, 2H), 1.281 (s, 3H), 1.344 (s, 3H). 13C
NMR (DMSO-d6, 75 MHz) δ/ppm ) 171.144, 170.443, 138.284,
136.042, 135.886, 132.540, 132.391, 129.804, 128.279, 126.606,
120.548, 118.422, 112.551, 105.754, 77.955, 56.766, 56.049,
52.299, 41.198, 33.789, 24.319, 23.346, 22.882. [R]D20 ) -152 (c
) 0.25, acetone).
1
384 [M + H]+. H NMR (CDCl3, 300 MHz) δ/ppm ) 8.100 (s,
1H), 7.425 (t, J ) 7.5 Hz, 1H), 7.252 (t, J ) 7.5 Hz, 1H), 7.093
(d, J ) 7.5 Hz, 1H), 7.060 (d, J ) 7.5 Hz, 1H), 4.391 (t, J ) 6.6
Hz, 1H), 3.914 (t, J ) 6.6 Hz, 1H), 3.763 (dd, J ) 10.5 Hz, J )
4.2 Hz, 2H), 3.666 (s, 3H), 2.931 (m, J ) 6.2 Hz, 1H), 2.725 (d,
J ) 6.6 Hz, 2H), 1.489 (m, J ) 6.0 Hz, 2H), 1.440 (s, 3H), 1.209
(s, 3H), 0.922 (d, J ) 6.6 Hz, 3H), 0.853 (t, J ) 6.6 Hz, 3H). 13
C
NMR (CDCl3, 75 MHz) δ/ppm ) 171.911, 171.243, 136.257,
131.082, 127.109, 121.612, 119.519, 118.076, 110.749, 108.013,
78.953, 60.665, 57.410, 52.135, 41.569, 33.937, 25.457, 24.929,
23.883, 18.657, 16.391, 11.207. [R]D20 ) -94 (c ) 0.26, acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b] indol-2-(2′S)-isopropylac-
etate (4b). Yield: 0.96 g (56%) as colorless powder. ESI/MS (m/
e) 370 [M + H]+. 1H NMR (CDCl3, 300 MHz) δ/ppm ) 8.251 (s,
1H), 7.503 (t, J ) 7.5 Hz, 1H), 7.313 (t, J ) 7.5 Hz, 1H), 7.127
(d, J ) 7.5 Hz, 1H), 7.102 (d, J ) 7.5 Hz, 1H), 3.981 (d, J ) 6.5
Hz, 1H), 3.844 (t, J ) 5.5 Hz, 1H), 3.735 (s, 3H), 3.477 (dd, J )
4.5 Hz, J ) 10.8 Hz, 1H), 3.194 (dd, J ) 4.5 Hz, J ) 10.8 Hz,
1H), 2.951 (m, J ) 5.5 Hz, 1H), 2.726 (d, J ) 5.5 Hz, 2H), 1.505
(s, 3H), 1.442 (s, 3H), 1.206 (m, J ) 6.6 Hz, 3H), 0.999 (m, J )
6.6 Hz, 3H). 13C NMR (CDCl3, 75 MHz): δ/ppm ) 172.637,
170.185, 136.249, 130.974, 127.175, 121.736, 119.650, 118.183,
110.700, 108.326, 78.846, 61.728, 57.393, 52.193, 41.652, 33.937,
27.773, 23.899, 20.504, 19.828, 18.814. [R]D20 ) -105 (c ) 0.22,
acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(p-hydroxyl-
benzyl)acetate (4g). Yield: 0.76 g (43%) as colorless powder; mp
212-214 °C. ESI/MS (m/e) 434 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 8.792 (s, 1H), 7.405 (t, J ) 7.2 Hz,1H), 7.272 (t,
J ) 7.2 Hz,1H), 7.257 (t, J ) 7.5 Hz, 2H), 7.149 (d, J ) 7.5 Hz,
2H), 7.056 (d, J ) 7.2 Hz, 1H), 7.017 (d, J ) 7.2 Hz, 1H), 5.638
(s, 1H), 4.800 (dd, J ) 4.8 Hz, J ) 10.8 Hz, 1H), 3.823 (t, J ) 5.8
Hz, 1H), 3.664 (s, 3H), 3.661 (d, J ) 5.8 Hz, 2H), 3.237 (d, J )
4.8 Hz, 2H), 2.890 (d, J ) 5.8 Hz, 2H), 1.433 (t, 3H), 1.268 (s,
3H). 13C NMR (DMSO-d6, 75 MHz) δ/ppm ) 171.003, 170.534,
155.987, 136.034, 132.573, 130.710, 128.271, 126.688, 120.540,
118.414, 117.466, 115.035, 110.897, 105.804, 78.021, 56.807,
20
56.321, 52.217, 41.255, 30.681, 24.841, 23.355, 17.989. [R]D
-143 (c ) 0.26, acetone).
)
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(indole-3-yl-me-
thyl)acetate (4h). Yield: 0.80 g (45%) as colorless powder; mp
204-206 °C. ESI/MS (m/e) 457 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 8.862 (s, 1H), 8.775 (s, 1H), 7.567 (t, J ) 7.8 Hz,
1H), 7.415 (t, J ) 7.8 Hz, 1H), 7.325 (t, J ) 7.8 Hz, 1H), 7.268 (t,
J ) 7.8 Hz, 1H), 7.262 (d, J ) 7.8 Hz, 1H), 7.247 (t, J ) 7.8 Hz,
1H), 7.022 (d, J ) 7.8 Hz, 1H), 7.010 (d, J ) 7.8 Hz, 1H), 6.779
(s, 1H), 4.691 (dd, J ) 4.5 Hz, J ) 9.9 Hz, 1H), 3.781 (t, J ) 4.7
Hz, 1H), 3.694 (s, 3H), 3.480 (m, J ) 4.0 Hz, 2H), 3.199 (d, J )
4.5 Hz, 2H), 2.911 (d, J ) 4.7 Hz, 2H), 1.500 (s, 3H), 1.232 (s,
3H). 13C NMR (DMSO-d6, 75 MHz) δ/ppm ) 170.855, 170.641,
136.034, 135.985, 132.532, 132.383, 127.595, 126.663, 124.389,
120.894, 120.556, 118.447, 118.002, 117.482, 111.400, 110.864,
110.551, 105.787, 77.972, 56.882, 56.654, 52.217, 41.223, 27.690,
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-isobutylace-
tate (4c). Yield: 1.14 g (65%) as colorless powder; mp 204-206
1
°C. ESI/MS (m/e) 384 [M + H]+. H NMR (CDCl3, 300 MHz)
δ/ppm ) 8.503 (s, 1H), 7.434 (t, J ) 7.2 Hz, 1H), 7.254 (d, J )
7.2 Hz, 1H), 7.064 (d, J ) 7.2 Hz, 1H), 7.007 (d, J ) 7.2 Hz, 1H),
4.438 (t, J ) 4.9 Hz, 1H), 3.997 (t, J ) 5.2 Hz, 1H), 3.664 (s, 3H),
3.430 (dd, J ) 4.2 Hz, J ) 10.5 Hz, 1H), 3.089 (dd, J ) 4.2 Hz,
J ) 10.5 Hz, 1H), 2.734 (d, J ) 5.2 Hz, 2H), 2.189 (m, J ) 4.9
Hz, 2H), 1.888 (m, J ) 4.9 Hz, 1H), 1.432 (s, 3H), 1.273 (s, 3H),
0.921 (d, J ) 4.9 Hz, 6H). 13C NMR (CDCl3, 75 MHz) δ/ppm )
171.647, 171.342, 136.266, 131.123, 127.159, 121.637, 119.535,
118.093, 110.758, 108.087, 78.475, 57.360, 52.852, 52.465, 41.668,
20
39.064, 25.210, 25.061, 23.611, 22.473, 22.374, 19.787. [R]D
-89 (c ) 0.25, acetone).
)
20
24.434, 23.750, 23.363. [R]D ) -128 (c ) 0.25, acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-methylace-
tate (4d). Yield: 0.69 g (41%) as colorless powder. ESI/MS (m/e)
Dimethyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-
oxo-6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-succinate
(4i). Yield: 0.97 g (56%) as colorless powder; mp 234-236 °C.
ESI/MS (m/e) 400 [M + H]+. 1H NMR (CDCl3, 300 MHz) δ/ppm
1
342 [M + H]+. H NMR (CDCl3, 300 MHz) δ/ppm ) 8.328 (s,

4722 Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15
Liu et al.
) 8.782 (s, 1H), 7.411 (t, J ) 7.5 Hz, 1H), 7.301 (t, J ) 7.5 Hz,
1H), 7.007 (d, J ) 7.5 Hz, 1H), 6.995 (d, J ) 7.5 Hz, 1H), 4.439
(t, J ) 4.5 Hz, 1H), 3.971 (t, J ) 5.4 Hz, 1H), 3.648 (s, 3H), 3.639
(s, 3H), 3.443 (dd, J ) 4.2 Hz, J ) 10.8 Hz, 1H), 3.274 (dd, J )
4.2 Hz, J ) 10.8 Hz, 1H), 2.886 (d, J ) 4.5 Hz, 2H), 2.796 (d, J
) 4.2 Hz, 2H), 1.465 (s, 3H), 1.377 (s, 3H). 13C NMR (DMSO-d6,
75 MHz) δ/ppm ) 171.020, 170.979, 169.866, 135.911, 134.762,
132.424, 121.631, 120.606, 118.463, 113.515, 110.914, 71.054,
56.511, 52.637, 51.747, 50.074, 41.223, 34.407, 24.583, 23.501,
111.033, 71.107, 56.583, 51.145, 46.220, 45.588, 34.996, 24.617,
23.511, 23.289. [R]D ) -57 (c ) 0.24, acetone).
20
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(aminocarbo-
nylethyl)acetate (4n). Yield: 0.78 g (45%) as colorless powder;
mp 234-236 °C. ESI/MS (m/e) 399 [M + H]+. 1H NMR (CDCl3,
300 MHz) δ/ppm ) 8.771 (s, 1H), 7.468 (t, J ) 7.5 Hz, 1H), 7.290
(t, J ) 7.5 Hz, 1H), 7.072 (d, J ) 7.5 Hz, 1H), 7.041 (d, J ) 7.5
Hz, 1H), 6.231 (s, 2H), 4.132 (t, J ) 4.8 Hz, 1H), 3.913 (t, J ) 5.5
Hz, 1H), 3.681 (s, 3H), 3.482 (dd, J ) 4.4 Hz, J ) 10.1 Hz, 1H),
3.120 (dd, J ) 4.4 Hz, J ) 10.1 Hz, 1H), 2.745 (d, J ) 5.5 Hz,
2H), 2.683 (m, J ) 4.8 Hz, 2H), 2.492 (t, J ) 4.8 Hz, 2H), 1.475
(s, 3H), 1.363 (s, 3H). 13C NMR (DMSO-d6, 75 MHz) δ/ppm )
176.021, 172.987, 170.872, 135.933, 134.776, 132.438, 121.641,
20
23.280. [R]D ) -76 (c ) 0.23, acetone).
Dimethyl 1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-6H-
imidazo-[3′,4′:1,2]- pyridin[3,4-b]indol-2-glutarate (4j). Yield:
0.84 g (48%) as colorless powder; mp 234-236 °C. ESI/MS (m/e)
1
414 [M + H]+. H NMR (CDCl3, 300 MHz) δ/ppm ) 8.775 (s,
120.636, 118.503, 113.765, 111.205, 71.154, 56.549, 52.687,
20
50.682, 44.898, 31.433, 25.881, 24.908, 23.514, 23.296. [R]D
-63 (c ) 0.25, acetone).
)
1H), 7.472 (t, J ) 7.5 Hz, 1H), 7.293 (t, J ) 7.5 Hz, 1H), 7.078
(d, J ) 7.5 Hz, 1H), 7.046 (d, J ) 7.5 Hz, 1H), 4.134 (t, J ) 4.7
Hz, 1H), 3.904 (t, J ) 5.6 Hz, 1H), 3.716 (s, 3H), 3.677 (s, 3H),
3.486 (dd, J ) 4.2 Hz, J ) 10.3 Hz, 1H), 3.116 (dd, J ) 4.2 Hz,
J ) 10.3 Hz, 1H), 2.749 (d, J ) 5.6 Hz, 2H), 2.681 (d, J ) 4.7
Hz, 2H), 2.496 (d, J ) 4.7 Hz, 2H), 1.473 (s, 3H), 1.367 (s, 3H).
13C NMR (DMSO-d6, 75 MHz) δ/ppm ) 171.026, 170.983,
169.870, 135.915, 134.770, 132.430, 121.637, 120.612, 118.469,
113.521, 110.922, 71.062, 56.517, 52.643, 51.751, 50.080, 41.231,
34.415, 26.887, 24.599, 23.507, 23.288. [R]D20 ) -58 (c ) 0.24,
acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(3-guanidino-
propyl)acetate (4o). Yield: 0.79 g (45%) as colorless powder; mp
196-197 °C. ESI/MS (m/e) 427 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 8.787 (s, 2H), 8.722 (s, 1H), 8.224 (s, 1H), 7.360
(t, J ) 7.5 Hz, 1H), 7.279 (t, J ) 7.5 Hz, 1H), 7.003 (d, J ) 7.5
Hz, 1H), 6.957 (d, J ) 7.5 Hz, 1H), 6.504 (s, 1H), 4.661 (t, J )
5.6 Hz, 1H), 4.018 (t, J ) 4.8 Hz, 1H), 3.815 (dd, J ) 4.2 Hz, J
) 10.3 Hz, 1H), 3.628 (s, 3H), 3.439 (dd, J ) 4.2 Hz, J ) 10.3
Hz, 1H), 2.863 (d, J ) 4.8 Hz, 2H), 2.589 (t, J ) 4.6 Hz, 2H),
1.900 (m, J ) 4.6 Hz, 2H), 1.574 (m, J ) 4.6 Hz, 2H), 1.376 (s,
3H), 1.313 (s, 3H). 13C NMR (CDCl3, 75 MHz) δ/ppm ) 173.402,
173.337, 172.194, 135.748, 135.100, 132.499, 122.600, 120.679,
119.643, 113.555, 111.717, 71.333, 60.706, 51.903, 50.417, 47.007,
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(hydroxyme-
thyl)acetate (4k). Yield: 0.89 g (52%) as colorless powder; mp
196-197 °C. ESI/MS (m/e) 358 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 8.857 (s, 1H), 7.409 (t, J ) 7.4 Hz, 1H), 7.293 (t,
J ) 7.4 Hz, 1H), 7.014 (d, J ) 7.4 Hz, 1H), 6.971 (d, J ) 7.4 Hz,
1H), 5.012 (t, J ) 5.4 Hz, 1H), 4.176 (t, J ) 5.4 Hz, 2H), 4.094 (t,
J ) 4.4 Hz, 1H), 3.814 (dd, J ) 4.2 Hz, J ) 10.2 Hz, 1H), 3.623
(s, 3H), 3.440 (dd, J ) 4.2 Hz, J ) 10.2 Hz, 1H), 2.879 (d, J )
4.4 Hz, 2H), 2.453 (s, 1H), 1.375 (s, 3H), 1.307 (s, 3H). 13C NMR
(CDCl3, 75 MHz) δ/ppm ) 170.987, 169.446, 135.911, 132.556,
126.663, 120.573, 118.438, 117.499, 110.897, 105.886, 78.137,
58.390, 56.816, 56.511, 52.044, 41.445, 24.492, 23.338, 19.275.
20
40.665, 27.334, 27.008, 25.884, 24.510, 23.362. [R]D ) -82 (c
) 0.22, acetone).
Methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(imidazol-4-yl-
methyl)acetate (4p). Yield: 0.61 g (35%) as colorless powder; mp
204-206 °C. ESI/MS (m/e) 408 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 10.072 (s, 1H), 8.885 (s, 1H), 7.411 (s, 1H), 7.265
(t, J ) 7.3 Hz, 1H), 7.184 (d, J ) 7.3 Hz, 1H), 7.025 (d, J ) 7.3
Hz, 1H), 7.009 (d, J ) 7.3 Hz, 1H), 6.820 (s, 1H), 4.700 (dd, J )
4.3 Hz, J ) 9.5 Hz, 1H), 3.823 (t, J ) 4.8 Hz, 1H), 3.690 (s, 3H),
3.482 (m, J ) 4.3 Hz, 2H), 3.193 (d, J ) 4.3 Hz, 2H), 2.905 (d, J
) 4.8 Hz, 2H), 1.442 (s, 3H), 1.400 (s, 3H). 13C NMR (DMSO-d6,
75 MHz) δ/ppm ) 171.119, 170.992, 136.440,136.228, 135.175,
134.864, 132.007, 123.393, 121.800, 120.759, 120.204, 112.920,
111.432, 70.978, 59.889, 51.648, 50.971, 45.202, 27.698, 29.430,
20
[R]D ) -66 (c ) 0.22, acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S,3′R)-(1-hydroxy-
lethyl)acetate (4l). Yield: 0.72 g (42%) as colorless powder; mp
196-197 °C. ESI/MS (m/e) 372 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 8.669 (s, 1H), 7.403 (t, J ) 7.5 Hz, 1H), 7.290 (t,
J ) 7.5 Hz, 1H), 7.010 (d, J ) 7.5 Hz, 1H), 6.975 (d, J ) 7.5 Hz,
1H), 5.010 (t, J ) 5.5 Hz, 1H), 4.173 (m, J ) 5.6 Hz, 1H), 4.097
(d, J ) 4.6 Hz, 1H), 3.811 (dd, 1H, J ) 4.3 Hz, J ) 10.1 Hz, 1H),
3.620 (s, 3H), 3.435 (dd, 1H, J ) 4.3 Hz, J ) 10.1 Hz, 1H), 2.879
(d, 1H, J ) 5.5 Hz, 2H), 2.453 (s, 1H), 1.375 (s, 3H), 1.307 (s,
3H), 1.286 (d, J ) 4.6 Hz, 3H). 13C NMR (CDCl3, 75 MHz) δ/ppm
) 171.544, 170.135, 136.037, 132.598, 126.685, 120.623, 118.608,
117.637, 111.229, 106.104, 78.715, 65.466, 58.412, 57.159, 56.573,
52.119, 41.607, 24.513, 23.357, 19.286. [R]D20 ) -85 (c ) 0.28,
acetone).
20
23.758, 23.665. [R]D ) -88 (c ) 0.26, acetone).
Methyl (11aS)-1,2,3,5,11,11a-hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(2-methylthio-
ethyl)acetate (4q). Yield: 1.11 g (64%) as colorless powder; mp
190-191 °C. ESI/MS (m/e) 402 [M + H]+. 1H NMR (CDCl3, 300
MHz) δ/ppm ) 7.997 (s, 1H), 7.473 (t, J ) 7.2 Hz, 1H), 7.292 (t,
J ) 7.2 Hz, 1H), 7.088 (d, J ) 7.2 Hz, 1H), 7.023 (d, J ) 7.2 Hz,
1H), 4.137 (t, J ) 4.2 Hz, 1H), 3.928 (t, J ) 5.2 Hz, 1H), 3.721 (s,
3H), 3.480 (dd, J ) 4.5 Hz, J ) 10.8 Hz, 1H), 3.139 (dd, J ) 4.5
Hz,, J ) 10.8 Hz, 1H), 2.809 (d, J ) 5.2 Hz, 2H), 2.577 (m, J )
4.2 Hz, 2H), 2.415 (m, J ) 4.2 Hz, 2H), 2.151 (s, 3H), 1.479 (s,
3H), 1.363 (s, 3H). 13C NMR (DMSO-d6, 75 MHz) δ/ppm )
171.804, 170.913, 136.249, 131.148, 127.134, 121.637, 119.535,
118.085, 110.766, 108.005, 78.442, 57.294, 52.629, 52.514, 41.726,
31.481, 28.663, 24.806, 23.528, 22.951, 15.097. [R]D20 ) -102 (c
) 0.25, acetone).
Methyl (11aS)-1,2,3,5,11,11a-Hexahydro-3,3-dimethyl-1-oxo-
6H-imidazo-[3′,4′:1,2]pyridin[3,4-b]indol-2-(2′S)-(aminocarbo-
nylmethyl)acetate (4m). Yield: 0.69 g (40%) as colorless powder;
mp 196-197 °C. ESI/MS (m/e) 385 [M + H]+. 1H NMR (CDCl3,
300 MHz) δ/ppm ) 8.770 (s, 1H), 7.413 (t, J ) 7.4 Hz, 1H), 7.322
(t, J ) 7.4 Hz, 1H), 7.012 (d, J ) 7.4 Hz, 1H), 6.998 (d, J ) 7.4
Hz, 1H), 6.217 (s, 2H), 4.559 (t, J ) 4.7 Hz, 1H), 3.956 (t, J ) 5.6
Hz, 1H), 3.667 (s, 3H), 3.450 (dd, J ) 4.0 Hz, J ) 10.1 Hz, 1H),
3.277 (dd, J ) 4.0 Hz, J ) 10.1 Hz, 1H), 2.883 (d, J ) 5.6 Hz,
2H), 2.790 (d, J ) 4.7 Hz, 2H), 1.460 (s, 3H), 1.375 (s, 3H). 13C
NMR (DMSO-d6, 75 MHz) δ/ppm ) 177.111, 172.968, 171.875,
135.937, 134.776, 132.431, 121.650, 120.614, 118.469, 113.522,
In Vitro Vasodilation Assay. A constant temperature trough
(CS501, Chongqing YinHe Experimental Apparatus Ltd. of China)
was used to ensure the buffer warmed; a tension transducer (Hang
JZ101, Beidian Xinghang Machine and Equipment Ltd.) and a two-
channel physiological recorder (LMS-2B, Chengdu Apparatus
Manufacturer) were used to evaluate the vasodilative effect. The
male Wistar rats weighing 250-300 g (purchased from Animal
Center of Capital Medical University) were used. Immediately after
decapitation, rat aortic strips were taken and put in a perfusion bath

Methyl Indol-2-Substituted Acetates
Journal of Medicinal Chemistry, 2008, Vol. 51, No. 15 4723
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inhibitors. Int. J. Clin. Pract. 2002, 56, 453–459.
with 15 mL warmed (37 °C), oxygenated (95%O2/5%CO2) Kreb’s
solution (pH 7.4). The aortic strip was connected to a tension
transducer, and the relaxation contraction curve of muscles was
registered. Administration of 59 µM NE induced hypertonic
contraction of the vessel strip. As the contraction reaches its
maximum, NE was washed out, and the vessel strip was stabilized
for 30 min. After renewal of the solution, 59 µM NE was added.
When the hypertonic contraction value of the aortic strip reached
the peak (the highness was taken as 100% contraction), 15 µL of
ethanol (negative control), or 15 µL solution of tadalafil in ethanol
(positive control) or 15 µL solution of Ach in ethanol (positive
control) or 15 µL solution of 4a-q in ethanol was administrated
to observe the vasodilation and the percent of vasodilation was taken
as the vasorelaxation activity.
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Acknowledgment. This work was supported by Beijing Area
Major Laboratory of Peptide and Small Molecular Drugs, the
973 Project of China (2006CB708501), and the National Natural
Scientific Foundation of China (30672513).
(17) Haning, H.; Niewohner, U.; Schenke, T.; Es-Sayed, M.; Schmidt, G.;
Lampe, T.; Bischoff, E. Imidazo[5,1-f]triazin-4(3H)-ones, a new class
of potent PDE 5 inhibitors. Bioorg. Med. Chem. Lett. 2002, 12, 865–
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K. Y. J. Structural Basis for the Activity of Drugs that Inhibit
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Supporting Information Available: Summary of crystal data
and details of intensity collection of 4f,h and elemental analysis
data of 3a-q and 4a-q. This material is available free of charge
via the Internet at http://pubs.acs.org.
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