Short-step synthesis and structure-activity relationship of cortistatin A analogs

Article abstract of DOI:10.1016/j.tet.2017.01.042

An improved method for synthesizing structurally simplified analogs of cortistatin A (1), a novel anti-angiogenic steroidal alkaloid from a marine sponge, was developed. In contrast to previous methods, step- and redox-economical synthesis was achieved us

Full text of DOI:10.1016/j.tet.2017.01.042

Accepted Manuscript
Short-step synthesis and structure-activity relationship of cortistatin A analogs
Naoyuki Kotoku, Aoi Ito, Shunichi Shibuya, Kanako Mizuno, Aki Takeshima, Masaki
Nogata, Motomasa Kobayashi
PII:
S0040-4020(17)30065-0
10.1016/j.tet.2017.01.042
TET 28412
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 12 December 2016
Revised Date: 16 January 2017
Accepted Date: 18 January 2017
Please cite this article as: Kotoku N, Ito A, Shibuya S, Mizuno K, Takeshima A, Nogata M, Kobayashi M,
Short-step synthesis and structure-activity relationship of cortistatin A analogs, Tetrahedron (2017), doi:
10.1016/j.tet.2017.01.042.
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ACCEPTED MANUSCRIPT
O
O
P
N
O
O
OMe
OMe
N2
MeO
K2CO3, MeOH
O
H
H
Br
OMe
H
O
O
• Second-generation synthetic method
considering step- and redox-economy
• Generation of novel cortistatin A analog
with dramatically enhanced bioactivity
NHAc

ACCEPTED MANUSCRIPT
Short-step Synthesis and Structure-activity Relationship of
Cortistatin AAnalogs
Naoyuki Kotoku *, †, Aoi Ito †, Shunichi Shibuya, Kanako Mizuno, Aki Takeshima,
Masaki Nogata, and Motomasa Kobayashi*
Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita,
Osaka 565-0871, Japan
*Corresponding authors: Tel.: +81-6-6879-8215; Fax: +81-6-6879-8219;
E-mail: kotoku@phs.osaka-u.ac.jp and kobayasi@phs.osaka-u.ac.jp
† These authors contributed equally to this work.
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Abstract
An improved method for synthesizing structurally simplified analogs of cortistatin A
(1), a novel anti-angiogenic steroidal alkaloid from a marine sponge, was developed. In
contrast to previous methods, step- and redox-economical synthesis was achieved using
a known α-bromoketone as the starting material. The structure-activity relationship
study revealed that the isoquinoline portion was strictly recognized by the target
molecule. Surprisingly, the introduction of the acetamide moiety on the A-ring structure
dramatically enhanced the selective antiproliferative activity against endothelial cells.
This new method can be easily applied to gram-scale synthesis and enabled us to
prepare various analogs, which were focused on the participation of the side chain and
A-ring structure.
Keywords: Cortistatin A; Anti-angiogenesis; Marine sponge; Analog synthesis;
Structure-activity relationship.
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1. Introduction
Marine natural products have garnered considerable attention as a rich and promising
source of drug candidates, especially in the field of anticancer drug discovery. 1,2 In most
cases, however, the sustainable supply of active compounds has been a challenge for
further evaluation and drug development. Generally, only small amounts of bioactive
compounds can be isolated from the extracts of marine organisms such as sponges and
tunicates. Chemical synthesis of bioactive natural products and their analog compounds
can often overcome this drawback. The syntheses of truncated natural products based on
structure-activity relationship (SAR) studies would be expected to facilitate the
development of more accessible and promising drug leads with optimized activity or
chemical stability. 3,4
In our study of bioactive substances from marine organisms, we have focused on
identifying anti-angiogenic substances and isolated cortistatins,5 a family of novel
abeo-9(10-19)-androstane-type steroidal alkaloids, from the Indonesian marine sponge
Corticium simplex. Cortistatin A (1, Figure 1), a major constituent of C. simplex,
showed a potent and highly selective antiproliferative activity against human umbilical
vein endothelial cells (HUVECs). Cortistatin A (1) was also revealed to exhibit a potent
inhibitory activity against in vitro migration and tubular formation of HUVECs induced
by vascular endothelial growth factor (VEGF) or basic fibroblast growth factor (bFGF).
5d
Because of their unique chemical structure and intriguing biological properties,
cortistatins are expected to be an emerging novel chemical entity for use as
anti-angiogenic drug leads.
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However, the extremely scarce supply of natural cortistatins has hampered our
validation of the feasibility of their use as potential practical drug leads. There have
been a number of reports of the synthesis of cortistatins including six total syntheses 6,7;
however, the yields were low in most cases. Therefore, we engaged in a synthetic study
of structurally simplified analog compounds and produced a useful analog, 2 (Figure 1).
8,9
Analog 2 exhibited a comparable antiproliferative activity to that of cortistatins
against HUVECs, good selectivity, and potent in vivo antitumor activity following oral
administration. To develop a more practical and promising anticancer drug lead based
on the core structure of analog 2 as a scaffold, we focused on establishing a more
efficient synthetic method than the existing methods. In this report, our
second-generation synthetic method for producing cortistatin analogs and the generation
of a novel and potent analog 30 are presented.
Figure 1 (revised)
2. Results and Discussion
The first-generation synthetic method for producing the cortistatin analog 2
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developed by our group is depicted in Scheme 1. 8 We were able to prepare >100 mg of
analog 2 using this method without any difficulty to examine its in vivo efficacy.
However, it was far from being an efficient method 10,11 because it had the following
drawbacks: (1) The number of reaction steps and total yield were not satisfactory; in
particular, six reaction steps are needed for converting the cyclohexanone 7 to the
α,β-unsaturated aldehyde 10 (Scheme 1). (2) The aforementioned problematic steps
include iterative redox reactions. (3) The side chain portion of the structure was
introduced in an earlier step of the synthesis, and eight reaction steps were needed to
prepare each analogous compound for the optimization study of the side chain structure.
Therefore, we developed a second-generation synthesis of the cortistatin analog 2 to
modify the process for mass production and structural optimization.
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Scheme 1
The retrosynthetic analysis of the second-generation synthesis is depicted in Scheme
2. The most significant modification was the use of the α-bromoketone 11 as a starting
material. Compound 11 can be obtained from Hajos-Parrish ketone (3) 12 at a large scale
(>100 g) through a tert-butyl cuprate (t-BuCu)- or SiCu-catalyzed stereoselective
conjugate reduction and subsequent bromination using a known method, which was
previously used to generate a precursor for the synthesis of vitamin-D2 and its analogs.
13 The problematic functionalizations encountered in the first-generation synthesis, such
as the one-carbon homologation and regioselective introduction of a double bond (from
7 to 10 in Scheme 1), could be resolved through a shortened sequence. Specifically, the
one-carbon homologation through the Wittig reaction giving vinyl ether 14, and
subsequent β-elimination of the bromide (from 12 to 10) could provide the requisite
α,β-unsaturated aldehyde functionality (Scheme 2). The protection/deprotection steps
for the carbonyl group were also eliminated, which reduced the overall number of steps.
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Scheme 2 (revised)
Initially, a one-carbon homologation reaction of the α-bromoketone 11 was
attempted (Scheme 3). A Wittig reaction using (methoxymethyl)triphenylphosphonium
chloride provided an α,β-unsaturated aldehyde 15 in place of the desired vinyl ether in
moderate yield. In contrast, the use of the Ohira-Bestmann reagent in methanol in the
14
presence of potassium carbonate
provided another product in good yield. Spectral
analysis revealed that this product was α,β-unsaturated acetal 16. A plausible reaction
mechanism leading to 16 is shown in Scheme 3. The homologation product of the
Ohira-Bestmann reaction, methyl vinyl ether 14, might be formed in situ, from which
the bromide group would be eliminated as depicted, thereby providing an oxocarbenium
ion (17). Finally, the nucleophilic addition of the solvent MeOH would yield the
α,β-unsaturated acetal 16. The serendipitous but elegant reaction performed here
achieved the requisite transformation around the carbonyl group in a single reaction
step.
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Scheme 3 (revised)
Next, the introduction of an isoquinoline moiety with the desired stereochemistry
was successfully achieved using the Suzuki-Miyaura cross-coupling reaction between
isoquinolin-7-yl boronate and the enol triflate 18, obtained from 16 in good yield,
followed by subsequent hydrogenation of the double bond in 19 using the palladium on
carbon (Pd-C) catalyst (Scheme 4). To our delight, a complete chemoselectivity between
the two double bonds in 19 was fortuitously achieved in this hydrogenation step,
providing 20 as the sole product. Following the hydrolysis of the acetal moiety,
treatment of the resulting aldehyde 10 with 1,3-cyclohexanedione in the presence of
ethylenediamine yielded the desired analog 2. Thus, the second-generation synthetic
method for the generation of cortistatin analogs was developed. All the non-strategic
transformation steps in the first-generation synthesis were eliminated. This redox-,
atom-, and step-economical synthetic method can be applied to sub-gram or gram-scale
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synthesis without substantially decreasing the yield of each reaction.
Scheme 4 (revised)
To analyze the detailed SAR of the cortistatin A (1), we then focused our attention
on analog synthesis. From previous SAR analysis of the naturally occurring cortistatins,
we determined that the isoquinoline side chain is crucial for the potent growth inhibitory
activity against HUVEC, and that the functionalities on the core structure, such as the
hydroxyl group on the A-ring portion, might be not essential but important. 5d However,
scope and limitation on the modification of those parts remained unclear. To acquire
additional information, we synthesized several analogs with modified isoquinoline or
A-ring moieties.
Firstly, compounds with a varied side chain were prepared from the enol triflate 18.
As shown in Scheme 5, Suzuki coupling with the corresponding boronate ester 24 15 and
16
25,
followed by hydrogenation, hydrolysis of the acetal, and Knoevenagel
condensation, yielded analogs 23a and 23b with an isoquinolin-6-yl or an
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isoquinolin-1-one-7-yl side chain, respectively, in comparable yields with those
obtained in the synthesis of 2. In the hydrogenation of 21b, an additional reduction on
the α,β-unsaturated acetal moiety was observed at extended reaction times, whereas a
complete chemoselectivity was obtained in those of 19 and 21a. The basic nitrogen in
the isoquinoline moieties of 19 and 21a might coordinate with the Pd and weaken its
reactivity in the hydrogenation reaction.
Scheme 5 (revised)
Secondly, functionalization of the A-ring portion was attempted. Considering the
σ
-symmetric property of 1,3-diketone, 5-hydroxymethyl-1,3-cyclohexanedione 17 was
used to prepare analogs with a polar substituent. The Knoevenagel condensation
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reaction between the tert-butyldiphenylsilyl (TBDPS)-protected dione (26) and the
α,β-unsaturated aldehyde 10 proceeded smoothly, and the subsequent
tetra-n-butylammonium fluoride (TBAF) treatment yielded an analog 28 with a
hydroxymethyl moiety (Scheme 6). The hydroxyl group in 28 was further converted to
an acetamide moiety in a three-step sequence involving a Mitsunobu reaction with
diphenylphosphoryl azide (DPPA) 18, a Staudinger reaction, and acetylation, thereby
providing analog 30.
Scheme 6 (revised)
The antiproliferative activities of the synthetic analogs against HUVECs and KB3-1
cells were subsequently evaluated (Table 1). The results revealed that analogs 23a and
23b showed quite weak antiproliferative activities against HUVECs (half-maximal
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inhibitory concentration (IC50), 18 or 90 µM), which were even weaker than those
against KB 3-1 cells (IC50, 10.5 or 25 µM). These results clearly indicate that the target
molecule (protein) strictly recognized the isoquinoline moiety; only the analog with the
isoquinolin-7-yl moiety was able to interact with the target molecule. 9 In contrast, the
introduction of the additional functionality on the A-ring portion enhanced the
compound’s potency against the HUVECs. Therefore, compounds 28 and 29 with a
hydroxymethyl and an azidomethyl moiety, respectively, showed strong antiproliferative
activities against the HUVECs (IC50, 0.016 or 0.015 µM) with a high selectivity (>
500-fold) over the KB 3-1 cells (IC50, 21.2 or 10.9 µM). Furthermore, the acetamide
analog, 30, surprisingly exhibited a highly potent activity against the HUVECs (IC50,
0.0026 µM) as well as an excellent selectivity over the KB 3-1 cells (IC50, 8.2 µM, >
3000-fold), which is comparable to that of cortistatin A (1). This evidence clearly
indicates that the acetamide moiety dramatically enhanced the growth inhibitory activity
against HUVECs.
3. Conclusion
In summary, we developed a second-generation synthetic method for producing
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cortistatin A analogs. The high-yielding and short-step synthetic method also provided
us with the opportunity to prepare various analog compounds, and we produced the
acetamide analog 30 as a promising anti-angiogenic drug lead compound. Further lead
optimization studies and in vivo evaluations of the active compounds are currently
underway.
4. Experimental
4-1. General experimental
13
JEOL ECA-500 (1H: 500 MHz, 13C: 125 MHz), JEOL ECS-400 (1H: 400 MHz, C:
13
100 MHz), and Agilent NMR system (1H: 600 MHz, C: 150 MHz) spectrometer was
used to obtain 1H- and 13C-NMR data using tetramethylsilane as an internal standard. A
JASCO FT/IR-5300 infrared spectrometer was used for obtaining IR spectra. Mass
spectra were obtained with a Waters Q-Tof Ultima API using MeOH as a solvent. Silica
gel (Kanto, 40-100 µm) and pre-coated thin layer chromatography (TLC) plates (Merck,
60F254) were used for column chromatography and TLC. Spots on TLC plates were
detected by spraying phosphomolybdic acid solution (5 g phosphomolybdic acid in 100
mL of EtOH) and acidic p-anisaldehyde solution (p-anisaldehyde: 25 mL, c-H2SO4: 25
mL, AcOH: 5 mL, EtOH: 425 mL) with subsequent heating. Unless otherwise noted, all
the reactions were performed under N2 atmosphere using purchased reagents and
solvents without further purification. After workup, the organic phases were dried over
Na2SO4.
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4.2.
(3aS,7aS)-5-(Dimethoxymethyl)-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-inden-1-on
e (16)
Dimethyl (1-diazo-2-oxopropyl)phosphonate (0.44 mL, 2.9 mmol) and K2CO3 (537 mg,
3.9 mmol) were added to a solution of 11 13b (476 mg, 1.9 mmol) in MeOH (15.5 mL) at
0 °C, and the whole mixture was stirred for 1 h at rt. H2O was added to the mixture, and
the whole mixture was extracted with AcOEt. Removal of the solvent from the AcOEt
extract under reduced pressure gave a crude product, which was purified by SiO2
column (n-hexane/AcOEt = 4:1) to give 16 (350 mg, 80%) as colorless amorphous
solid.
1
[α]22 +71.8° (c = 1.38 in CHCl3). IR (KBr): 1742, 1071, 1051 cm–1. H-NMR (500
D
MHz, acetone-d6) δ: 5.87 (1H, s), 4.53 (1H, s), 3.25 (6H, s), 2.53-2.47 (1H, m), 2.47
(1H, dd, J = 18.9, 8.6 Hz), 2.16-2.08 (3H, m), 2.03-1.99 (1H, m), 1.80-1.69 (2H, m),
1.48 (1H, dd, J = 18.9, 10.9 Hz), 0.83 (3H, s). 13C-NMR (125 MHz, acetone-d6) δ:
217.7, 136.7, 125.9, 106.3, 53.6, 53.4, 48.0, 44.3, 36.5, 29.1, 23.1, 22.6, 13.2. ESI MS:
m/z 247 (M+Na)+. HR-ESI MS: m/z 247.1310, calcd for C13H20O3Na. Found: 247.1314.
4.3. (3aS,7aS)-6-(Dimethoxymethyl)-3a-methyl-3a,4,5,7a-tetrahydro-1H-inden-3-yl
trifluoromethanesulfonate (18)
KHMDS (0.5 M in toluene, 1.3 mL, 0.65 mmol) was added dropwise to a solution of 16
(100 mg, 0.45 mmol) and N-phenyltriflimide (207 mg, 0.58 mmol) in THF (4.5 mL) at
–78 °C, and the whole mixture was stirred at that temperature for 30 min. H2O was
14

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added to the mixture at 0 °C, and the whole mixture was extracted with Et2O. Removal
of the solvent from the Et2O extract under reduced pressure gave a crude product, which
was purified by SiO2 column (n-hexane/AcOEt = 5:1) to give 18 (148 mg, 93%) as a
colorless oil.
[α]22 +51.2° (c = 1.61 in CHCl3). IR (KBr): 1213, 1144, 1059 cm–1. 1H-NMR (500
D
MHz, CDCl3) δ: 5.93 (1H, s), 5.59 (1H, s), 4.51 (1H, s), 3.33 (3H, s), 3.30 (3H, s), 2.76-
2.71 (1H, m), 2.36 (1H, ddd, J = 14.9, 6.3, 3.5 Hz), 2.26-2.21 (1H, m), 2.19-2.14
(1H,m), 1.84-1.75 (2H, m), 0.94 (3H, s). 13C-NMR (125 MHz, CD3OD) δ: 160.3, 137.1,
125.7, 116.9, 107.4, 54.3, 54.0, 47.8, 46.4, 31.1, 30.0, 22.3, 15.3. ESI MS: m/z 379
(M+Na)+. HR-ESI MS: m/z 379.0803, calcd for C14H19O5F3SNa. Found: 379.0836.
4.4.
7-((3aS,7aS)-6-(Dimethoxymethyl)-3a-methyl-3a,4,5,7a-tetrahydro-1H-inden-3-yl)
isoquinoline (19)
7-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinoline (147 mg, 0.65 mmol),
Pd(PPh3)4 (72.1 mg, 0.062 mmol) and K2CO3 (172 mg, 1.25 mmol) were added to a
solution of 18 (148 mg, 0.42 mmol) in DMF (4.2 mL), and the whole mixture was
stirred at 50 °C for 90 min. H2O was added to the mixture at rt, and the whole mixture
was extracted with Et2O. Removal of the solvent from the Et2O extract under reduced
pressure gave a crude product, which was purified by SiO2 column (toluene/acetone =
10:1) to give 19 (101 mg, 72%) as a colorless oil.
[α]22 +73.3° (c = 0.91 in CHCl3). IR (KBr): 2932, 1103, 1073 cm–1. 1H-NMR (500
D
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MHz, acetone-d6) δ: 9.31 (1H, s), 8.46 (1H, d, J = 5.7 Hz), 8.13 (1H, s), 7.89 (2H, d, J =
1.1 Hz), 7.73 (1H, d, J = 5.7 Hz), 6.25 (1H, s), 6.03 (1H, s), 4.56 (1H, s), 3.29 (3H, s),
3.28 (3H, s), 2.79-2.71 (1H, m), 2.43 (1H, ddd, J = 14.9, 6.9, 3.4 Hz), 2.39-2.35 (1H, m),
13
2.28-2.21 (3H, m), 1.78 (1H, dd, J = 19.5, 8.5 Hz) 1.12 (3H, s). C-NMR (125 MHz,
acetone-d6) δ: 153.7, 153.5, 143.8, 136.7, 136.2, 135.5, 130.6, 129.9, 129.8, 127.2,
126.2, 124.6, 120.7, 106.7, 53.5, 53.4, 50.3, 48.3, 32.9, 32.8, 22.9, 16.6. ESI MS: m/z
336 (M+H)+. HR-ESI MS: m/z 336.1964, calcd for C22H26NO2. Found: 336.1989.
4.5.
7-((1S,3aS,7aS)-5-(Dimethoxymethyl)-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-inden
-1-yl)isoquinoline (20)
Pd/C (11.0 mg) was added to a solution of 19 (36.8 mg, 0.11 mmol) in AcOEt (2.0 mL),
and the whole mixture was stirred under a H2 atmosphere for 20 h. The reaction mixture
was filtered through Celite pad, and the solvent was removed from the filtrate under
reduced pressure to give 20 (37.1 mg, quant.) as a colorless oil.
[α]24 +17.3° (c = 1.98 in CHCl3). IR (KBr): 2932, 2876, 1196, 1073, 849 cm–1.
D
1H-NMR (500 MHz, acetone-d6) δ: 9.27 (1H, s), 8.45 (1H, d, J = 5.7 Hz), 7.98 (1H, s),
7.87 (1H, d, J = 8.6 Hz), 7.73 (1H, d, J = 5.7 Hz), 7.68 (1H, d, J = 8.6 Hz), 5.88 (1H, s),
4.49 (1H, s), 3.24 (1H, s), 3.23 (1H, s), 3.07 (1H, t, J = 9.7 Hz), 2.46-2.44 (2H, m),
2.15-2.13 (2H, m), 1.96-1.93 (2H, m), 1.65-1.63 (2H, m), 1.60-1.56 (1H, m), 0.50 (3H,
s). 13C-NMR (125 MHz, acetone-d6) δ: 153.1, 143.3, 141.4, 135.7, 135.3, 133.0, 129.6,
127.3, 126.8, 126.5, 120.7, 106.7, 55.8, 53.4, 53.3, 49.0, 45.3, 34.7, 27.1, 25.6, 22.9,
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12.4. ESI MS: m/z 338 (M+H)+. HR-ESI MS: m/z 338.2120, calcd for C22H28NO2.
Found: 338.2100.
4.6.
(1S,3aS,7aS)-1-(Isoquinolin-7-yl)-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-indene-5-c
arbaldehyde (10)
Pyridinium p-toluenesulfonate (27.6 mg, 0.11 mmol) was added to a solution of 20
(37.1 mg, 0.11 mmol) in acetone/H2O (20:1, 2.1 mL), and the whole mixture was stirred
for 1 h. Sat. NaHCO3 aq. was added to the mixture, and the whole mixture was
extracted with AcOEt. Removal of the solvent from the AcOEt extract under reduced
pressure gave a crude product, which was purified by SiO2 column (n-hexane/AcOEt =
1:1) to give 10 (31.3 mg, 98%) as a colorless oil.
[α]24D +55.8° (c = 2.10 in CHCl3). IR (KBr): 2965, 2922, 1680, 850 cm–1. 1H-NMR (500
MHz, CDCl3) δ: 9.43 (1H, s), 9.24 (1H, s), 8.49 (1H, s), 7.81 (1H, s), 7.76 (1H, d, J =
8.6 Hz), 7.63 (1H, d, J = 5.2 Hz), 7.59 (1H, dd, J = 8.6, 1.7 Hz), 6.87 (1H, d, J = 1.7
Hz), 3.03 (1H, t, J = 9.7 Hz), 2.69-2.64 (1H, m), 2.45-2.38 (2H, m), 2.28-2.22 (1H, m),
13
2.17-2.09 (2H, m), 1.80-1.73 (2H, m), 1.67-1.61 (1H, m), 0.48 (3H, s). C-NMR (125
MHz, CDCl3) δ: 194.1, 152.3, 151.8, 142.5, 141.3, 139.6, 134.7, 132.0, 128.6, 126.1,
125.9, 120.1, 55.0, 50.0, 44.9, 33.1, 26.4, 24.0, 20.5, 12.3. ESI MS: m/z 292 (M+H)+.
HR-ESI MS: m/z 292.1701, calcd for C20H22NO. Found: 292.1695.
4.7.
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(3S,3aR,11aS,11bR)-3-(Isoquinolin-7-yl)-3a-methyl-1,3,3a,4,5,8,9,10,11a,11b-decahy
drocyclopenta[c]xanthen-7(2H)-one (2)
Cyclohexane-1,3-dione (16.2 mg, 0.15 mmol) and ethylenediamine (7.2 ꢀL, 0.11 mmol)
were added to a solution of 10 (21.0 mg, 0.072 mmol) in AcOEt (1.0 mL), and the
whole mixture was stirred for 19 h. H2O was added to the mixture, and the whole
mixture was extracted with CH2Cl2. Removal of the solvent from the CH2Cl2 extract
under reduced pressure gave a crude product, which was purified by SiO2 column
(n-hexane/AcOEt = 1:3) to give 2 (19.3 mg, 70%) as a colorless oil.
All the spectral data were identical to those of the previous report. 8
4.8.
6-((3aS)-6-(Dimethoxymethyl)-3a-methyl-3a,4,5,7a-tetrahydro-1H-inden-3-yl)isoqu
inoline (21a)
6-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinoline (24, 214.3 mg, 0.84 mmol),
Pd(PPh3)4 (97 mg, 0.084 mmol) and K2CO3 (232 mg, 1.70 mmol) were added to a
solution of 18 (200 mg, 0.56 mmol) in DMF (5.6 mL), and the whole mixture was
stirred at 50 °C for 1 h. H2O was added to the mixture, and the whole mixture was
extracted with Et2O. Removal of the solvent from the Et2O extract under reduced
pressure gave a crude product, which was purified by SiO2 column (n-hexane/acetone =
2:1) to give 21a (177.8 mg, 75%) as a colorless oil.
[α]27 +9.5° (c = 0.60 in MeOH). IR (KBr): 2929, 2844, 1626, 1102, 1073, 1053 cm-1.
D
1H-NMR (600 MHz, acetone-d6) δ: 9.22 (1H, s), 8.47 (1H, d, J = 5.4 Hz), 8.03 (1H, d, J
18

ACCEPTED MANUSCRIPT
= 8.4 Hz), 7.98 (1H, s), 7.79 (1H, m), 7.78 (1H, s), 6.30 (1H, s), 6.03 (1H, s), 4.56 (1H,
s), 3.29 (3H, s), 3.28 (3H, s), 2.75 (1H, t, J = 7.8 Hz), 2.44 (1H, ddd, J = 15.6, 7.2, 3.0
Hz), 2.35 (1H, dd, J = 12.0, 7.2 Hz), 2.28-2.21 (3H, m), 1.79-1.74 (1H, m), 1.12 (3H, s).
13C-NMR (125 MHz, acetone-d6) δ: 153.7, 152.6, 144.1, 139.4, 136.6, 136.1, 131.0,
128.4, 128.0, 127.5, 126.0, 123.4, 121.1, 106.5, 53.4, 53.3, 50.1, 48.2, 32.7, 32.7, 22.7,
16.5. ESI MS: m/z 336 (M+H)+. HR-ESI MS: m/z 336.1964, calcd for C22H26NO2.
Found: 336.1955.
4.9.
(1S,7aS)-1-(isoquinolin-6-yl)-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-indene-5-carb
aldehyde (22a)
Pd/C (10%, 14.2 mg) was added to a solution of 21a (42.5 mg, 0.13 mmol) in AcOEt
(2.2 mL), and the whole mixture was stirred under a H2 atmosphere for 22 h. The
reaction mixture was filtered through Celite pad, and the solvent was removed from the
filtrate under reduced
pressure to give
a
hydrogenation
product,
6-((1S,7aS)-5-(dimethoxymethyl)-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-inden-1-yl)iso
quinoline (40.9 mg, 96%) as a colorless oil.
[α]26 +17.7° (c = 1.19 in MeOH). IR (KBr): 2927, 2876, 1630, 1103, 1072 cm-1.
D
1H-NMR (600 MHz, acetone-d6) δ: 9.20 (1H, s), 8.43 (1H, d, J = 5.4 Hz), 7.96 (1H, d, J
= 8.7 Hz), 7.76 (1H, s), 7.69 (1H, d, J = 5.4 Hz), 7.54 (1H, t, J = 8.7 Hz), 5.84 (1H, s),
4.45 (1H, s), 3.20 (3H, s), 3.18 (3H, s), 2.94 (1H, t, J = 9.6 Hz), 2.39-2.34 (2H, m),
2.11-2.04 (2H, m), 1.93-1.85 (2H, m), 1.60-1.58 (2H, m), 1.56-1.48 (1H, m), 0.44 (3H,
19

ACCEPTED MANUSCRIPT
s). 13C-NMR (150 MHz, acetone-d6) δ: 152.6, 144.5, 143.7, 136.3, 135.5, 129.9, 128.4,
127.3, 127.0, 125.7, 120.8, 106.5, 55.8, 53.2, 53.1, 48.9, 45.2, 34.5, 26.8, 25.4, 22.7,
12.3. ESI MS: m/z 338 (M+H)+. HR-ESI MS: m/z 338.2120, calcd for C22H28NO2.
Found: 338.2104.
Pyridinium p-toluenesulfonate (20.4 mg, 0.081 mmol) was added to a solution of an
aliquot of the above product (27.4 mg, 0.081 mmol) in acetone/H2O (10:1, 1.65 mL),
and the whole mixture was stirred for 12 h. Sat. NaHCO3 aq. was added to the mixture,
and the whole mixture was extracted with AcOEt. Removal of the solvent from the
AcOEt extract under reduced pressure gave a crude product, which was purified by SiO2
column (n-hexane/AcOEt = 1:1) to give 22a (22.0 mg, 93%) as a colorless oil.
[α]26 +64.1° (c = 0.62 in MeOH). IR (KBr): 2964, 2924, 2878, 1679, 1628 cm-1.
D
1H-NMR ( 600 MHz, CDCl3 ) δ: 9.43 (1H, s), 9.22 (1H, s), 8.50 (1H, d, J = 6.0 Hz),
7.91 (1H, d, J = 8.4 Hz), 7.66 (1H, s), 7.61 (1H, d, J = 6.0 Hz), 7.51 (1H, d, J = 8.4 Hz),
6.87 (1H, s), 3.03 (1H, t, J = 9.6 Hz), 2.67-2.58 (1H, m), 2.47-2.39 (2H, m), 2.25-2.22
(1H, m), 2.17-2.09 (2H, m), 1.80-1.74 (2H, m), 1.67-1.62 (1H, m), 0.48 (3H, s).
13C-NMR (150 MHz, CDCl3) δ: 194.1, 151.9, 151.7, 143.2, 142.8, 141.3, 135.7, 129.0,
127.7, 127.0, 125.2, 120.4, 55.3, 50.1, 45.1, 33.1, 26.3, 24.0, 20.5, 12.4. ESI MS: m/z
292 (M+H)+. HR-ESI MS: m/z 292.1701, calcd for C20H22NO. Found: 292.1690.
4.10.
(3S,3aR,11aS)-3-(isoquinolin-6-yl)-3a-methyl-2,3,3a,4,5,8,9,10,11a,11b-decahydrocy
20

ACCEPTED MANUSCRIPT
clopenta[c]xanthen-7(1H)-one (23a)
Cyclohexane-1,3-dione (4.0 mg, 0.034 mmol) and ethylenediamine (5 ꢀL, 0.08 mmol)
were added to a solution of 22a (5.0 mg, 0.017 mmol) in AcOEt (0.2 mL), and the
whole mixture was stirred for 2 h. H2O was added to the mixture, and the whole mixture
was extracted with CH2Cl2. Removal of the solvent from the CH2Cl2 extract under
reduced pressure gave a crude product, which was purified by SiO2 column
(n-hexane/AcOEt = 1:2) to give 23a (4.6 mg, 69%) as a colorless oil.
[α]26D +1.7° (c = 0.57 in MeOH). IR (KBr): 2928, 2880, 2854, 1645, 1631, 1604, 1406,
1381, 1218, 1168,754 cm-1. 1H-NMR (600 MHz, CDCl3) δ: 9.21 (1H, s), 8.49 (1H, d, J
= 5.7 Hz), 7.90 (1H, d, J = 8.4 Hz), 7.63 (1H, s), 7.60 (1H, d, J = 5.7 Hz), 7.47 (1H, d, J
= 8.4 Hz), 6.19 (1H, s), 4.92 (1H, d, J = 10.2 Hz), 3.01 (1H, t, J = 9.6 Hz), 2.42-2.27
(7H, m), 2.16-2.12 (3H, m), 1.99-1.93 (2H, m), 1.74-1.72 (1H, m), 1.61-1.58 (1H, m),
13
1.50-1.47 (1H, m), 0.60 (3H, s). C-NMR (150 MHz, CDCl3) δ: 194.9, 171.4, 152.0,
143.0, 142.6, 135.6, 129.1, 128.8, 127.7, 126.9, 125.3, 120.3, 110.9, 110.7, 80.7, 56.9,
55.4, 46.8, 36.8, 36.4, 29.1, 28.0, 26.3, 23.9, 20.6, 12.4. ESI MS: m/z 386 (M+H)+.
HR-ESI MS: m/z 386.2120, calcd for C26H28NO2. Found: 386.2102.
4.11.
7-((3aS)-6-(Dimethoxymethyl)-3a-methyl-3a,4,5,7a-tetrahydro-1H-inden-3-yl)isoqu
inolin-1(2H)-one (21b)
7-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinolin-1(2H)-one (25, 93.3 mg,
0.34 mmol), Pd(PPh3)4 (78.6 mg, 0.06 mmol) and K2CO3 (158.8 mg, 1.15 mmol) were
21

ACCEPTED MANUSCRIPT
added to a solution of 18 (82 mg, 0.23 mmol) in DMF (2.3 mL), and the whole mixture
was stirred at 50 °C for 6 h. H2O was added to the mixture, and the whole mixture was
extracted with Et2O. Removal of the solvent from the Et2O extract under reduced
pressure gave a crude product, which was purified by SiO2 column (n-hexane/acetone =
4:1) to give 21b (39.7 mg, 49%) as a colorless oil.
[α]27D +25.3° (c = 1.11 in MeOH). IR (KBr): 3165, 2926, 2848, 1652, 1635, 1613, 1101,
1073 cm-1. 1H-NMR (600 MHz, CD3OD) δ: 8.31 (1H, s), 7.74 (1H, d, J = 8.1 Hz), 7.55
(1H, d, J = 8.1 Hz), 7.13 (1H, d, J = 7.2 Hz), 6.62 (1H, d, J = 7.2 Hz), 6.09 (1H, s), 5.98
(1H, s), 4.52 (1H, s), 3.31 (3H, s), 3.30 (3H, s), 2.68-2.66 (1H, m), 2.37-2.33 (1H, ddd,
J = 15.0, 7.2, 3.0 Hz), 2.27-2.16 (3H, m), 2.15 (2H, s), 1.71-1.65 (1H, m), 1.05 (3H, s).
13C-NMR (150 MHz, CD3OD) δ: 165.0, 154.1, 138.5, 136.9, 136.3, 132.7, 129.7, 128.5,
127.5, 127.2, 126.8, 124.7, 107.8, 107.7, 54.1, 54.0, 50.7, 48.5, 33.2, 33.1, 23.0, 16.7.
MALDI MS: m/z 352 (M+H)+. HR-MALDI MS: m/z 352.1907, calcd for C22H26NO3.
Found: 352.1917.
4.12.
(1R,7aS)-7a-Methyl-1-(1-oxo-1,2-dihydroisoquinolin-7-yl)-2,3,3a,6,7,7a-hexahydro-
1H-indene-5-carbaldehyde (22b)
Pd/C (10%, 6.3 mg) was added to a solution of 21b (18.9 mg, 0.054 mmol) in AcOEt
(1.0 mL), and the whole mixture was stirred under a H2 atmosphere for 5 h. The reaction
mixture was filtered through Celite pad, and the solvent was removed from the filtrate
under
reduced
pressure
to
give
a
hydrogenation
product,
22

ACCEPTED MANUSCRIPT
7-((1S,7aS)-5-(dimethoxymethyl)-7a-methyl-2,3,3a,6,7,7a-hexahydro-1H-inden-1-yl)iso
quinolin-1(2H)-one (17.6 mg, quant.) as a colorless oil.
[α]27D +18.8° (c = 0.83 in MeOH). IR (KBr): 3164, 2926, 2874, 2830, 1652, 1636, 1614,
1103, 1070 cm-1. 1H-NMR (600 MHz, CD3OD) δ: 8.18 (1H, s), 7.58 (1H, d, J = 8.1 Hz),
7.55 (1H, d, J = 8.1 Hz), 7.11 (1H, d, J = 7.2 Hz), 6.63 (1H, d, J = 7.2 Hz), 5.85 (1H, s),
4.45 (1H, s), 3.26 (3H, s), 3.25 (3H, s), 2.88 (1H, t, J = 9.6 Hz), 2.38-2.36 (1H, m),
2.33-2.31 (1H, m), 2.12-2.06 (2H, m), 1.94-1.88 (2H, m), 1.58-1.51 (3H, m), 0.44 (3H,
s). 13C-NMR (150 MHz, CD3OD) δ: 165.1, 141.5, 138.18, 138.17, 135.8, 135.2, 128.4,
128.1, 127.0, 126.6, 107.9, 107.8, 56.2, 54.02, 54.00, 49.5, 45.5, 35.1, 27.6, 27.4, 26.0,
23.0, 12.5. ESI MS: m/z 354 (M+H)+. HR-ESI MS: m/z 354.2069, calcd for C22H28NO3.
Found: 354.2083.
Pyridinium p-toluenesulfonate (11.0 mg, 0.044 mmol) was added to a solution of an
aliquot of the above product (15.4 mg, 0.044 mmol) in acetone/H2O (10:1, 1.1 mL), and
the whole mixture was stirred for 1 h. Sat. NaHCO3 aq. was added to the mixture, and
the whole mixture was extracted with AcOEt. Removal of the solvent from the AcOEt
extract under reduced pressure gave a crude product, which was purified by SiO2
column (n-hexane/acetone = 2:1) to give 22b (16.3 mg, quant.) as a colorless oil.
[α]26D +36.8° (c = 1.44 in MeOH). IR (KBr): 3163, 2968, 2923, 2877, 1680, 1651, 1635,
754 cm-1. 1H-NMR (600 MHz, CDCl3) δ: 11.80 (1H, s), 9.41 (1H, s), 8.28 (1H, s), 7.55
(1H, d, J = 7.8 Hz), 7.51 (1H, d, J = 7.8 Hz), 7.18 (1H, d, J = 6.9 Hz), 6.85 (1H, d, J =
1.2 Hz), 6.56 (1H, d, J = 6.9 Hz), 2.98 (1H, d, J = 9.6 Hz), 2.62 (1H, m), 2.44-2.40 (2H,
23

ACCEPTED MANUSCRIPT
m), 2.20-2.15 (1H, m), 2.06-2.05 (1H, m), 1.76-1.71 (2H, m), 1.61-1.60 (1H, m), 0.46
(3H, s). 13C-NMR (150 MHz, CDCl3) δ: 194.1, 164.5, 152.1, 141.3, 139.2, 136.6, 133.6,
127.2, 126.2, 125.7, 125.6, 106.5, 54.9, 50.0, 44.7, 33.0, 29.2, 26.4, 23.9, 20.5, 12.9.
ESI MS: m/z 308 (M+H)+. HR-ESI MS: m/z 308.1651, calcd for C20H22NO2. Found:
308.1664.
4.13.
7-((3S,3aR,11aS)-3a-Methyl-7-oxo-1,2,3,3a,4,5,7,8,9,10,11a,11b-dodecahydrocyclop
enta[c]xanthen-3-yl)isoquinolin-1(2H)-one (23b)
Cyclohexane-1,3-dione (8.0 mg, 0.071 mmol) and piperidine (10 ꢀL, 0.16 mmol) were
added to a solution of 22b (10.9 mg, 0.035 mmol) in 1,4-dioxane (0.7 mL), and the
whole mixture was stirred for 13 h. H2O was added to the mixture, and the whole
mixture was extracted with CHCl3. Removal of the solvent from the CHCl3 extract
under reduced pressure gave a crude product, which was purified by SiO2 column
(n-hexane/AcOEt = 1 : 2) to give 23b (7.3 mg, 51%) as a colorless oil.
[α]27D –8.6° (c = 0.64 in MeOH). IR (KBr): 3184, 2961, 2925, 2855, 1651, 1613, 1598,
1261, 800 cm-1. 1H-NMR (400 MHz, CDCl3) δ: 10.78 (1H, brs), 8.26 (1H, s), 7.54-7.49
(2H, m), 7.14 (1H, brs), 6.57 (1H, d, J = 6.8 Hz), 6.18 (1H, s), 4.91 (1H, d, J = 10.0 Hz),
2.96 (1H, t, J = 9.4 Hz), 2.43-2.35 (7H, m), 2.12-2.11 (3H, m), 1.98-1.92 (2H, m),
13
1.72-1.69 (1H, m), 1.59-1.55 (1H, m), 1.47-1.40 (1H, m), 0.59 (3H, s). C-NMR (150
MHz, CDCl3) δ: 194.0, 170.4, 163.3, 137.9, 135.6, 132.9, 128.0, 126.1, 125.4, 124.7,
124.6, 109.9, 109.7, 105.6, 79.8, 55.6, 54.4, 45.5, 35.8, 35.4, 28.1, 27.1, 25.4, 22.9, 19.6,
24

ACCEPTED MANUSCRIPT
11.3. ESI MS: m/z 424 (M+Na)+. HR-ESI MS: m/z 424.1889, calcd for C26H27NO3Na.
Found: 424.1886.
4.14. 5-(((tert-Butyldiphenylsilyl)oxy)methyl)cyclohexane-1,3-dione (26)
Imidazole (40 mg, 0.59 mmol) and tert-butylchlorodiphenylsilane (0.08 mL, 0.32
mmol) were added to a solution of (3,5-dimethoxycyclohexa-2,5-dien-1-yl)methanol
(50 mg, 0.29 mmol) in DMF (2.9 mL), and the whole mixture was stirred for 1 h. Sat.
NH4Cl aq. was added to the mixture, and the whole mixture was extracted with Et2O.
Removal of the solvent from the Et2O extract under reduced pressure gave a crude
product, which was purified by SiO2 column (n-hexane/AcOEt = 20:1) to give
tert-butyl((3,5-dimethoxycyclohexa-2,5-dien-1-yl)methoxy)diphenylsilane (50 mg,
53%) as a colorless oil.
1
IR (KBr): 2953, 2933, 2901, 2857, 1694, 1206, 1148, 1111, 703 cm-1. H-NMR (500
MHz, CDCl3) δ: 7.62-7.60 (4H, m), 7.35-7.28 (6H, m), 4.68-4.66 (2H, m), 3.46 (2H, d,
J = 6.9 Hz), 3.41 (6H, s), 3.13-3.08 (1H, m), 2.59-2.57 (2H, m), 0.95 (9H, s). 13C-NMR
(125 MHz, acetone-d6) δ: 153.7, 136.3, 134.6, 130.5, 128.5, 93.3, 70.5, 54.3, 40.0, 32.1,
27.2, 19.8. MALDI MS: m/z 409 (M+H)+. HR-MALDI MS: m/z 409.2194, calcd for
C22H26NO3. Found: 409.2200.
1N HCl (0.19 mL) was added to a solution of an aliquot of the above product (39.5 mg,
0.097 mmol) in THF (0.48 mL), and the whole mixture was stirred for 3 h. Removal of
the solvent from the reaction mixture under reduced pressure gave 26 (43.9 mg, quant.)
25

ACCEPTED MANUSCRIPT
as a colorless oil.
Mixture of keto-form and enol-form. IR (KBr): 2931, 2896, 2858, 1588, 1224, 1112,
1
703 cm-1. H-NMR (500 MHz, CDCl3) δ: 7.66-7.64 (4H, m), 7.44-7.35 (6H, m), 5.38
(0.5H, s), 3.70 (1.5H, s), 3.64-3.59 (2H, m), 3.57-3.34 (0.5H, m), 2.73-2.60 (0.5H, m),
13
2.47-2.26 (4H, m), 1.07 (9H, s). C-NMR (150 MHz, CDCl3) δ: 203.6, 199.8, 178.5,
135.5, 135.4, 134.8, 133.2, 133.12, 133.09, 132.4, 129.8, 129.7, 129.67, 129.4, 127.7,
127.6, 127.5, 101.9, 67.1, 66.5, 66.3, 60.3, 57.6, 55.8, 43.4, 39.5, 36.3, 36.2, 33.4, 31.7,
26.7, 26.6, 26.5, 21.0, 19.2, 19.0, 14.1. MALDI MS: m/z 403 (M+Na)+. HR-MALDI
MS: m/z 403.1700, calcd for C22H26NO3. Found: 403.1697.
4.15.
(3S,3aR,11aS)-9-(((tert-Butyldiphenylsilyl)oxy)methyl)-3-(isoquinolin-7-yl)-3a-meth
yl-2,3,3a,4,5,8,9,10,11a,11b-decahydrocyclopenta[c]xanthen-7(1H)-one (27)
5-(((tert-Butyldiphenylsilyl)oxy)methyl)cyclohexane-1,3-dione (26, 23.0 mg, 0.06
mmol) and ethylenediamine (5 ꢀL, 0.08 mmol) were added to a solution of 10 (11.7 mg,
0.04 mmol) in AcOEt (0.8 mL), and the whole mixture was stirred for 19 h. H2O was
added to the mixture, and the whole mixture was extracted with CHCl3. Removal of the
solvent from the CHCl3 extract under reduced pressure gave a crude product, which was
purified by SiO2 column (n-hexane/AcOEt = 1:2) to give 27 (14.0 mg, 53%) as a
colorless oil.
1
IR (KBr): 2957, 2929, 2856, 1648, 1607, 1111, 703 cm-1. H-NMR (600 MHz, CDCl3)
δ: 9.24 (1H, s), 8.49 (1H, d, J = 4.8 Hz), 7.80 (1H, s), 7.77 (1H, d, J = 8.4 Hz), 7.65 (4H,
26

ACCEPTED MANUSCRIPT
d, J = 6.6 Hz), 7.58 (1H, d, J = 8.4 Hz), 7.45-7.38 (6H, m), 6.19 (1/2H, s), 6.17 (1/2H, s),
4.97 (1/2H, d, J = 10.2 Hz) , 4.93 (1/2H, d, J = 10.2 Hz), 3.63-3.57 (2H, m), 3.02 (1H, t,
J = 9.0 Hz), 2.48-2.28 (7H, m), 2.19-2.12 (3H, m), 1.77-1.70 (1H, m), 1.61-1.58 (1H,
m), 1.51-1.46 (1H, m), 1.06 (9H, s), 0.62 (3/2H, s), 0.61(3/2H, s). 13C-NMR (150 MHz,
CDCl3) δ: 194.5, 194.2, 170.8, 170.7, 151.9, 141.9, 139.4, 139.4, 135.5, 135.5, 134.8,
133.3, 133.2, 133.2, 132.4, 129.7, 129.0, 128.6, 128.5, 127.7, 126.4, 126.4, 125.8, 120.3,
111.1, 110.6, 110.6, 110.0, 81.0, 80.8, 66.6, 66.4, 56.7, 55.6, 55.2, 46.8, 46.6, 39.4, 39.1,
37.0, 36.6, 35.9, 35.3, 31.0, 30.7, 29.2, 29.0, 26.8, 26.3, 26.3, 24.0, 23.8, 19.3, 12.4,
12.3. ESI MS: m/z 676 (M+Na)+. HR-ESI MS: m/z 676.3223, calcd for C43H47NO3NaSi.
Found: 676.3249.
4.16.
(3S,3aR,11aS)-9-(Hydroxymethyl)-3-(isoquinolin-7-yl)-3a-methyl-2,3,3a,4,5,8,9,10,1
1a,11b-decahydrocyclopenta[c]xanthen-7(1H)-one (28)
Acetic acid (1.8 ꢀL, 0.032 mmol) and tetra-n-butylammonium fluoride (1.0 M in THF,
32 ꢀL, 0.032 mmol) were added to a solution of 27 (14.0 mg, 0.021 mmol) in THF (0.2
mL), and the whole mixture was stirred for 16 h. Sat. NaHCO3 aq. was added to the
mixture, and the whole mixture was extracted with CHCl3. Removal of the solvent from
the CHCl3 extract under reduced pressure gave a crude product, which was purified by
SiO2 column (CHCl3/MeOH/H2O = 60:3:1, lower phase) to give 28 (9.7 mg, 100%) as a
colorless oil.
1
IR (KBr): 3367, 2925, 2880, 1639, 1601, 1420, 1407, 1381, 1208, 754 cm-1. H-NMR
27

ACCEPTED MANUSCRIPT
(600 MHz, CDCl3) δ: 9.22 (1H, s), 8.47 (1H, s), 7.79 (1H, s), 7.76 (1H, d, J = 8.4 Hz),
7.65 (1H, s), 7.57 (1H, d, J = 7.8 Hz), 6.17 (1/2H, s), 6.16 (1/2H, s), 4.95 (1/2H, d, J =
10.2 Hz), 4.91 (1/2H, d, J = 10.2 Hz), 3.67-3.58 (2H, m), 3.03-2.99 (1H, m), 2.51-2.10
(11H, m), 1.73-1.69 (1H, m), 1.59-1.58 (1H, m), 1.50-1.45 (1H, m), 0.61 (3/2H, s), 0.60
(3/2H, s). 13C-NMR (150 MHz, CDCl3) δ: 194.2, 194.0, 170.7, 170.5, 152.0, 142.0,
139.3, 134.8, 132.4, 129.1, 128.7, 126.4, 125.8, 120.3, 111.0, 110.6, 110.5, 110.1, 81.0,
80.9, 65.8, 65.5, 56.7, 55.5, 55.3, 46.7, 46.6, 39.2, 38.9, 37.0, 36.6, 35.8, 35.2, 31.0,
30.6, 29.2, 29.0, 26.3, 26.3, 23.9, 23.7, 12.3, 12.3. ESI MS: m/z 416 (M+H)+. HR-ESI
MS: m/z 416.2226, calcd for C27H30NO3. Found: 416.2231.
4.17.
(3S,3aR,11aS)-9-(Azidomethyl)-3-(isoquinolin-7-yl)-3a-methyl-2,3,3a,4,5,8,9,10,11a,
11b-decahydrocyclopenta[c]xanthen-7(1H)-one (29)
Diphenylphosphoryl azide (45 ꢀL) was added to a solution of 28 (66.1 mg, 0.16 mmol),
diethyl azodicarboxylate (2.2 M in toluene, 94 ꢀL, 0.21 mmol) and triphenylphosphine
(54.3 mg, 0.21 mmol) in THF (1.6 mL), and the whole mixture was stirred for 40 min.
MeOH was added to the mixture, and the solvent from the whole mixture was removed
under reduced pressure to give a crude product. Purification by SiO2 column
(CHCl3/MeOH/H2O = 100:3:1, lower phase) to give 29 (70.1 mg, quant.) as a colorless
oil.
IR (KBr): 2961, 2925, 2882, 2854, 2100, 1646, 1605, 1407, 1382, 1209, 755 cm-1.
1H-NMR (400 MHz, CDCl3) δ: 9.22 (1H, s), 8.49 (1H, d, J = 5.8 Hz), 7.79 (1H, s), 7.76
28