Total synthesis of the benzo[c]phenanthridine alkaloids, terihanine and isoterihanine, and their antitumor activity

Article abstract of DOI:10.3987/COM-13-S(S)16

A new total synthesis of terihanine (2a) and isoterihanine (2b) was established by our new bond formation between the C4b and N5 positions of the benzo[c]phenanthridine ring based on a microwave-assisted thermal electrocyclic reaction of 2-cycloalkenylbenzaldoxime as an aza 6π-electron system. In addition, the antitumor activity of these synthesized compounds, including nitidine and nornitidine was evaluated in HCT-116 cells.

Full text of DOI:10.3987/COM-13-S(S)16

HETEROCYCLES, Vol. 88, No. 1, 2014
297
HETEROCYCLES, Vol. 88, No. 1, 2014, pp. 297 - 308. © 2014 The Japan Institute of Heterocyclic Chemistry
Received, 23rd May, 2013, Accepted, 7th June, 2013, Published online, 11th June, 2013
DOI: 10.3987/COM-13-S(S)16
TOTAL
SYNTHESIS
OF
THE
BENZO[c]PHENANTHRIDINE
ALKALOIDS, TERIHANINE AND ISOTERIHANINE, AND THEIR
ANTITUMOR ACTIVITY
Yuhki Kurata,a Tominari Choshi,a* Yuhsuke Ishihara,a Noriyuki Hatae,b
Takashi Nishiyama,a and Satoshi Hibinoa*
aFaculty of Pharmacy and Pharmaceutical Sciences, Fukuyama University,
a
Fukuyama, Hiroshima 729-0292, Japan; Faculty of Pharmaceutical Sciences,
Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido 061-0293,
Japan
E-mail; hibino@fupharm.fukuyama-u.ac.jp and choshi@fupharm.fukuyama-u.ac.jp
This paper is dedicated to Professor Victor Sniekus for his 77th birthday.
Abstract – A new total synthesis of terihanine (2a) and isoterihanine (2b) was
established by our new bond formation between the C4b and N5 positions of the
benzo[c]phenanthridine ring based on a microwave-assisted thermal electrocyclic
reaction of 2-cycloalkenylbenzaldoxime as an aza 6!-electron system. In addition,
the antitumor activity of these synthesized compounds, including nitidine and
nornitidine was evaluated in HCT-116 cells.
INTRODUCTION
Fully aromatized quaternary benzo[c]phenanthridine alkaloids occur naturally in Rutaceous and
Papaveraceous plants.1 Among these alkaloids, nitidine (1), fagaronine, and NK109
(7-hydroxy-8-methoxy-5-methyl-2,3-methylenedioxybenzo[c]phenanthridinium hydrogensulfate), have
attracted the interest of chemists due to their important pharmacologic properties.2 NK109, the
quarternary base of isodecarine, is a promising topoisomerase inhibitor.2,3 NK314, exhibiting significant
antitumor activity against drug-resistant human tumor cell lines, is a synthetic benzo[c]phenanthridine
fused with a pyrrolidine ring at the N5-C6 positions that is now in entered clinical trials.3,4
Many synthetic approaches to the benzo[c]phenanthridine nucleus have been clarified and summarized in
excellent reviews.1,5 In 1984, a new phenolic benzo[c]phenanthridine alkaloid, oxyterihanine was isolated
from Xanthoxylum nitidum (Japanese name: teriha-zansho).6 To determine the structure of oxyterihanine,
the first total synthesis of terihanine (2a) and isoterihanine (2b) as biogenetic precursors of the

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HETEROCYCLES, Vol. 88, No. 1, 2014
oxy-quaternary base was achieved by Ishikawa and co-workers in 1987 using a Bischler-Napieralski
reaction.7 In 2000, terihanine (2a) was isolated from the bark of Zanthoxylum nitidum for the first time by
the same group.8 Subsequently, a mixture of terihanine (2a) and isoterihanine (2b) was discovered in
Zanthoxylum ovalifolium in 2006 by Waterman and co-workers (Figure 1).9
O
O
O
O
O
O
MeO
MeO
MeO
HO
HO
N
N
N
Me
Me
terihanine (2a)
Figure 1
MeO
Me
nitidine (1)
isoterihanine (2b)
topoisomerases I/II inhibitor
antimalarial activity
Our research program is aimed at developing synthetic strategies for bioactive nitrogen-containing
fused-heteroaromatic compounds including natural products based on a thermal electrocyclic reaction
either a 6!- or an aza 6!-electron system involving an aromatic or heteroaromatic double bond in
principle.10 We recently reported the total synthesis of furoisoquinoline,11 phenanthridine,12 "-carboline,13
azaanthraquinone,14 benzo[c]phenanthridine,15 and indoloquinoline16 alkaloids by the construction of
fused pyridine ring systems using a microwave-assisted17 thermal electrocyclic reaction of an aza
6!-electron system. In this report, we describe the new total synthesis of two phenolic
benzo[c]phenanthridine alkaloids, terihanine (2a) and isoterihanine (2b), using our methodology,10-16 and
an evaluation of the antitumor activity in HCT-116 cells compared with nitidine (1).
O
O
O
O
R1O
R2O
R1O
R2O
N
N
Me
2a: R1=Me, R2=H
2b: R1=H, R2=Me
3
Me
Me
Me
O
O
O
B
R1O
R2O
R1O
Br
CHO
O
O
O
Me
+
NOMe
R2O
4
6
5
Scheme 1
RESULTS AND DISCUSSION
As outlined in Scheme 1, our synthetic plan was to design a 11,12-dihydrobenzophenanthridine

HETEROCYCLES, Vol. 88, No. 1, 2014
299
framework 3, which would be derived from a 2-cycloalkenylbenzaldoxime methyl ether 4 through our
new bond formation between the C4b and N5 positions of the benzo[c]phenanthridine ring5 by a
microwave-assisted aza-electrocyclic reaction.15 A 2-cycloalkenylbenzaldoxime methyl ether 4 would be
provided
by
the
Suzuki-Miyaura
reaction
of
2-bromobenzaldehyde
5
with
2-(6,7-methylenedioxy-3,4-dihydronephthyl)boronic acid pinacol ester 6. After dehydrogenation of 3, the
conversion from norbenzo[c]phenanthridine to quaternary base 2 would be performed according to the
reported procedures.7
Me
Me
Me
O
O
B
See
Table 1
R1O
R2O
R1O
R2O
Br
O
O
O
O
Me
+
CHO
CHO
6
5a: R1=Me, R2=H
5b:R1=Me, R2=MOM
5c: R1=Me, R2=iPr
5d:R1=Ac, R2=Me
1
2
7a:
7b:
7c:
R =Me, R =MOM
NaH, MOMCl, DMF, rt, 12 h
1
2
R =Me, R =iPr
iPrBr, K2CO3, MeCN, 60 oC, 48 h
1
2
R =H, R =Me
Scheme 2
Table 1. Synthesis of 2-cycloalkenylbenzaldehydes 7a-c
Products
Reagent
SM
Pd catalyst
MW
Run
No.
7a
7b
7b
7b
7b
7b
7b
7b
7c
Yield (%)
–
–
+
–
–
–
–
–
–
K2CO3
K2CO3
K2CO3
Na2CO3
CsF
1
2
3
4
5
6
7
8
9
5b
5c
5c
5c
5c
5c
5c
5c
5d
13
34
22
27
15
13
24
6
PdCl2(dppf)
PdCl2(dppf)
PdCl2(dppf)
Pd(PPh3)4
a
a
(20)
(22)
a
–
a
Pd(PPh3)4
(26)
a
NaOMe
K2CO3
AsPh3
K2CO3
PdCl2(PPh3)2
PdCl2(PPh3)2
Pd(OAc)2
–
a
(33)
(5)a
70
PdCl2(dppf)
OHC
OiPr
OMe
a: yield (%) of bisbenzaldehyde 8
MeO
iPrO
CHO
8
To synthesize the required 2-cycloalkenylbenzaldoxime methyl ether 4, we initially attempted a synthesis

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HETEROCYCLES, Vol. 88, No. 1, 2014
of 2-cycloalkenylbenzaldehyde 7 by the Suzuki-Miyaura reaction18 of O-protected benzaldehyde 5 with
2-(6,7-methylenedioxy-3,4-dihydronaphthyl)boronic acid pinacol ester (6) in the presence of a palladium
catalyst (Scheme 2, Table 1). Using O-methoxymethyl (MOM) 2-bromobenzaldehyde 5b gave the
2-cycloalkenylbenzaldehyde 7a in only a low yield (run 1). The benzaldehyde 5c, which was converted
from the MOM group into the isopropyl group, was treated with pinacol ester 6 under the same conditions.
As a result, product 7b along with bisbenzaldehyde 8 (20%) was obtained in a 34% yield (run 2). Despite
performing this reaction under microwave irradiation conditions12 the yield of 7b was not increased (run
3). Although we attempted other conditions (palladium catalysts and additive parameters) in further detail,
the yield of 7b was not improved (runs 4-8). The cross-coupling reaction of
4-acetoxy-2-bromobenzaldehyde 5d with pinacol ester
6
afforded the deacetylated
2-cycloalkenylbenzaldehyde 7c in moderate yield without byproducts (run 9). A reason for the low
reactivity of 5c with 6 on the Suzuki-Miyaura reaction is unclear (Table 1).
O
O
O
O
MeONH2•HCl
R1O
R2O
R1O
R2O
AcONa
NOMe
EtOH
80 oC, 3 h
CHO
1
2
1
2
7b:
7c:
4a:
4b:
R =Me, R =iPr (88%)
R =Me, R =iPr
1
2
1
2
R =H, R =Me (90%)
R =H, R =Me
O
O
O
O
R1O
R2O
R1O
R2O
MW
10%Pd-C
1,2-dichlorobenzene
180 oC, 7 h
1,2-dichlorobenzene
200 oC, 5 h
N
N
R1=Me, R2=iPr (75%)
10a: R1=Me, R2=H (96%)
10b: R1=H, R2=Me (65%)
3a:R1=Me, R2=iPr (84%)
3b:R1=H, R2=Me (96%)
9:
H2SO4, AcOH
110 oC, 1.5 h
O
O
1) HCO2H
R1O
R2O
80 oC, 12 h
R1O
R2O
Jones reagent
O
O
N
N
2) NaBH4
rt, 30 min
acetone
0 oC, 30 min
Me
Me
2a:terihanine: R1=Me, R2=H (32%)
2b:isoterihanine: R1=H, R2=Me (76%)
1
2
11a:
11b:
R =Me, R =H (29%)
1
2
R =H, R =Me (51%)
Scheme 3
Treatment of the obtained 2-cycloalkenylbenzaldehyde 7b and 7c with hydroxylamine methyl ether gave
benzaldoxime 4a (88%) and 4b (90%), which was subjected to the microwave-assisted thermal
aza-electrocylic reaction11-16 in 1,2-dichlorobenzene to yield the 11,12-dihydrobenzophenanthridine 3a

HETEROCYCLES, Vol. 88, No. 1, 2014
301
(84%) and 3b (96%), respectively. Subsequently, the 11,12-dihydrobenzophenanthridine 3a and 3b were
oxidized by refluxing with 10% Pd-C in 1,2-dichrolobenzene to give O-isopropyl norterihanine (9: 75%)
and norisoterihanine (10b: 65%). The O-isopropyl group of 9 was cleaved with H2SO4 in AcOH at 110 oC
to produce norterihanine (10a: 96%). Finally, conversion of norterihanine (10a) and norisoterihanine
(10b) to terihanine (2a) and isoterihanine (2b), respectively, was achieved according to the procedures of
the Ishikawa group.19 Namely, treatment of 10a,b with formic acid followed by reduction with NaBH4
gave the N-methylated 5,6-dihydrobenzophenanthridines 11a,b, which were oxidized by Jones reagent
followed by treatment with diluted hydrochloric acid to yield terihanine (2a) and isoterihanine (2b).
Physical and spectroscopic data of our synthetic terihanine (2a) and isoterihanine (2b) were identical with
those of authentic samples provided by Ishikawa7 in all respects.
The antitumor activity of the synthesized benzophenanthridines (nitidine (1), terihanine (2a),
isoterihanine (2b), and three compounds of their nor-type was assessed in HCT-116 cells20 (Table 2). At a
dose of 10 µM, nitidine (1) and isoterihanine (2b) inhibited the tumor cell viability to 33.5% and 43.7%,
respectively, whereas the other benzophenanthridines had weak antitumor activity at the same dose. The
correlation between the structure and antitumor activity will be reported elsewhere in due course.
Table 2. Effect of benzo[c]phenanthridines on HCT-116 cells viability
Benzophenanthridines
Cell viability (%) on 10µM
nornitidine
81.4
79.1
72.7
33.5
74.7
43.7
norterihanine (10a)
norisoterihanine (10b)
nitidine (1)
terihanine (2a)
isoterihanine (2b)
CONCLUSION
In conclusion, a new total synthesis of the phenolic 8,9-disubstituted benzo[c]phenanthridine alkaloids
terihanine (2a) and isoterihanine (2b) was achieved by our new bond formation between the C4b and N5
positions of the tetracyclic ring based on the microwave-assisted thermal azaelectrocyclic reaction. These
synthesized compounds including nitidine and nornitidine were evaluated for antitumor activity on
HCT-116 cells. Nitidine and isoterihanine at a dose of 10 µM inhibited tumor cell viability to 33.5% and
43.7% of the tumor cells viability, respectively.
EXPERIMENTAL
All non-aqueous reactions were carried out under an atmosphere of nitrogen in dried glassware unless
otherwise noted. Solvents were dried and distilled according to standard protocols. Analytical thin-layer

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HETEROCYCLES, Vol. 88, No. 1, 2014
chromatography was performed with Silica gel 60PF254 (Merck). Silica gel column chromatography was
performed with Silica gel 60N (63-210 µm, KANTO CHEMICAL Co. Ltd.). All melting points were
determined on Yanagimoto micro melting point apparatus and are uncorrected. Proton nuclear magnetic
resonance (1H NMR) spectra were recorded on a JEOL AL-300 at 300 MHz. Chemical shifts are reported
relative to Me4Si (# 0.00). NMR spectra was measured with CDCl3 unless otherwise noted. Multiplicity is
indicated by one or more of the following: s (singlet); d (doublet); t (triplet); q (quartet); m (multiplet); br
(broad). Carbon nuclear magnetic resonance (13C NMR) spectra were recorded on a JEOL AL-300 at 75
MHz. Chemical shifts are reported relative to CDCl3 (# 77.0) and DMSO-d6 (# 39.7). Infrared spectra
were recorded with ATR method using a Shimadzu FTIR-8000 spectrophotometer and technologies
DuraScop. Low and high resolution mass spectra (HRMS) were recorded on JEOL JMS-700
spectrometers by direct inlet system.
2-(3,4-Dihydro-6,7-methylenedioxy-2-naphthyl)-5-isopropoxy-4-methoxybenzaldehyde (7b)
A mixture of 2-bromobenzaldehyde 5c (50 mg, 0.18 mmol), naphthylboronic acid pinacol ester 615 (82
mg, 0.28ꢀmmol), K2CO3 (76 mg, 0.55 mmol), and PdCl2(PPh3)2 (11 mg, 0.014 mmol) in anhyd. MeOH (8
o
mL) and DMF (2 mL) was stirred at 80 C for 1 h under N2 atmosphere. The reaction mixture was
quenched with water, and then the mixture was extracted with EtOAc. The EtOAc layer was washed with
water and brine, dried over Na2SO4, and concentrated under reduced pressure. The residue was purified
by column chromatography using EtOAc-hexane (1:19 v/v) as an eluent to give the
o
2-naphthylbenzaldehyde 7b (23 mg, 34%), mp 108–109 C (EtOAc-hexane). IR (ATR) $: 1673 cm–1.
1H-NMR (300 MHz, CDCl3) #: 1.41 (6H, d, J=6.0 Hz), 2.66 (2H, t, J=8.0 Hz), 2.91 (2H, t, J=8.0 Hz),
3.94 (3H, s), 4.67 (1H, sept, J=6.0 Hz), 5.93 (2H, s), 6.29 (1H, s), 6.62 (1H, s), 6.70 (1H, s), 6.81 (1H, s),
7.48 (1H, s), 10.08 (1H, s). 13C-NMR (75 MHz, CDCl3) !: 21.9 (2C), 28.4, 29.8, 56.2, 71.3, 100.9, 107.3,
108.4, 110.5, 112.4, 127.1, 127.8, 128.7, 130.5, 133.8, 142.1, 146.2, 146.8, 154.7, 190.7. MS (EI) m/z:
366ꢀ (M+). HRMS (EI) calcd for C22H22O5 366.1467; found 366.1478.
2-(3,4-Dihydro-6,7-methylenedioxy-2-naphthyl)-4-hydroxy-5-methoxybenzaldehyde (7c)
4-Acetoxy-2-bromo-5-methoxybenzaldehyde (5d) (167 mg, 0.61 mmol), naphthylboronic acid pinacol
ester 615 (200 mg, 0.67 mmol), K2CO3 (276 mg, 2.0 mmol) and PdCl2(PPh3)2 (24 mg, 0.03 mmol) in
anhyd. MeOH (8 mL) and DMF (2 mL) were used in the same procedure as above to give the
o
2-naphthylbenzaldehyde 7c (138 mg, 70%), mp 225-228 C (EtOAc-hexane). IR (ATR) ": 3143, 1654
1
cm–1. H-NMR (300 MHz, CDCl3) !: 2.64 (2H, t, J=7.9 Hz), 2.90 (2H, t, J=7.9 Hz), 3.98 (3H, s), 5.94
(2H, s), 6.12 (1H, s), 6.26 (1H, s), 6.62 (1H, s), 6.70 (1H, s), 6.92 (1H, s), 7.48 (1H, s), 10.07 (1H, s).
13C-NMR (75 MHz, CDCl3) !: 28.3, 29.5, 56.2, 100.9, 107.3, 108.4, 108.9, 113.7, 127.0, 127.8, 128.7,
130.8, 133.3, 143.0, 146.0, 146.2, 146.8, 150.6, 190.7. MS (EI) m/z: 324 (M+). HRMS (EI) calcd for
C19H16O5 324.0998; found 324.0978.

HETEROCYCLES, Vol. 88, No. 1, 2014
303
2-(3,4-Dihydro-6,7-methylenedioxy-2-naphthyl)-5-isopropoxy-4-methoxybenzaldehyde
O-methyloxime (4a)
A mixture of 2-naphthylbenzaldehydes 7b (194 mg, 0.53 mmol), MeONH2•HCl (80 mg, 0.95 mmol), and
AcONa (78 mg, 0.95 mmol) in EtOH (10 mL) was stirred at 80 oC for 3 h. After removal of solvent, the
mixture was extracted with EtOAc. The EtOAc layer was washed with water and brine, dried over
Na2SO4, and concentrated under reduced pressure. The residue was purified by column chromatography
o
using EtOAc-hexane (1:19 v/v) as an eluent to give the oxime ether 4a (185 mg, 88%), mp 86-87 C
(EtOAc-hexane). 1H-NMR (300 MHz, CDCl3) #: 1.41 (6H, d, J=6.0 Hz), 2.55 (2H, t, J=8.1 Hz), 2.86 (2H,
t, J=8.1 Hz), 3.88 (3H, s), 3.94 (3H, s), 4.66 (1H, sep, J=6.0 Hz), 5.92 (2H, s), 6.24 (1H, s), 6.61 (1H, s),
6.68 (1H, s), 6.72 (1H, s), 7.41 (1H, s), 8.23 (1H, s). 13C-NMR (75 MHz, CDCl3) !: 22.0 (2C), 28.4, 29.6,
55.9, 61.8, 71.2, 100.8, 107.1, 108.3, 110.8, 111.9, 121.7, 128.1, 128.4, 128.5, 135.7, 136.8, 146.0, 146.3,
146.4, 147.9, 151.4. MS (EI) m/z: 395 (M+). HRMS (EI) calcd for C23H25NO5 395.1733; found 395.1740.
2-(3,4-Dihydro-6,7-methylenedioxy-2-naphthyl)-4-hydroxy-5-methoxybenzaldehyde
O-methyloxime (4b)
2-Naphthylbenzaldehyde 7c (163 mg, 0.50 mmol), MeONH2•HCl (65 mg, 0.78 mmol), and AcONa (64
mg, 0.78 mmol) in EtOH (10 mL) were used in the same procedure as above to give the oxime ether 4b
(160 mg, 90%), mp 133-134 oC (EtOAc-hexane). 1H-NMR (300 MHz, CDCl3) !: 2.52 (2H, t, J=8.3 Hz),
2.84 (2H, t, J=8.3 Hz), 3.94 (3H, s), 3.97 (3H, s), 5.78 (1H, s), 5.92 (2H, s), 6.21(1H, s), 6.60 (1H, s), 6.67
13
(1H, s), 6.82 (1H, s), 7.38 (1H, s), 8.25 (1H, s). C-NMR (75 MHz, CDCl3) !: 28.4, 29.4, 56.1, 61.8,
100.8, 107.2, 107.7, 108.3, 113.6, 121.3, 128.1, 128.5, 128.8, 135.3, 137.5, 145.8, 146.0, 146.4, 147.0,
148.2. MS (EI) m/z: 353 (M+). HRMS (EI) calcd for C20H19NO5 353.1263; found 353.1234.
11,12-Dihydro-8-isopropoxy-9-methoxy-2,3-methylenedioxybenzo[c]phenanthridine (3a)
o
A mixture of oxime ether 4a (52 mg, 0.13 mmol) in 1,2-dichlorobenzene (1.5 mL) was stirred at 200 C
for 5 h with MW-irradiation under N2 atmosphere. After removal of solvent, the residue was purified by
column chromatography (silica gel) using EtOAc (1:19 v/v) as an eluent to give the
o
1
11,12-dihydrobenzophenanthridine 3a (40 mg, 84%), mp 201-202 C (EtOAc-hexane). H-NMR (300
MHz, CDCl3) #: 1.48 (6H, d, J=6.1 Hz), 2.95 (2H, t, J=7.7 Hz), 3.19 (2H, d, J=7.7 Hz), 4.03 (3H, s), 4.76
13
(sep, J=6.1 Hz), 5.98 (2H, s), 6.75 (1H, s), 7.21 (1H, s), 7.89 (1H, s), 8.92 (1H, s). C-NMR (75 MHz,
CDCl3) !: 21.8 (2C), 23.5, 28.0, 56.0, 71.1, 100.9, 101.4, 105.6, 107.9, 108.9, 122.8, 123.8, 126.5, 130.9,
131.0, 147.0, 147.3, 147.8, 147.9, 150.5, 154.1. MS (EI) m/z: 363 (M+). HRMS (EI) calcd for C22H21NO4
363.1471; found 363.1480.
11,12-Dihydro-9-hydroxy-8-methoxy-2,3-methylenedioxybenzo[c]phenanthridine (3b)
Oxime ether 4b (80 mg, 0.23 mmol) in 1,2-dichlorobenzene (2.5 mL) with MW-irradiation were used in
the same procedure as above to give the 11,12-dihydrobenzophenanthridine 3b (70 mg, 96%), mp

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HETEROCYCLES, Vol. 88, No. 1, 2014
o
246-248 C (EtOAc-hexane). H-NMR (300 MHz, CDCl3) !: 2.93 (2H, t, J=7.5 Hz), 3.16 (2H, t, J=7.5
1
Hz), 4.08 (3H, s), 5.98 (2H, s), 6.24 (1H, br s), 6.74 (1H, s), 7.21 (1H, s), 7.41 (1H, s), 7.88 (1H, s), 8.95
13
(1H, s). C-NMR (75 MHz, CDCl3) !: 23.4, 28.0, 56.1, 100.9, 104.8, 105.6, 105.7, 107.9, 122.8, 123.6,
129.7, 131.2, 131.6, 144.7, 147.0, 147.2, 147.3, 148.3, 149.5. MS (EI) m/z: 321 (M+). HRMS (EI) calcd
for C19H15NO4 321.1001; found 321.1014.
8-Isopropoxy-9-methoxy-2,3-methylenedioxybenzo[c]phenanthridine (9)
A stirred mixture of 11,12-dihydrobenzophenanthridine 3a (40 mg, 0.11 mmol) and 10% Pd-C (60 mg) in
1,2-dichlorobenzene (3 mL) were heated at reflux for 7 h. After removal of solvent, the residue was
purified by column chromatography using the EtOAc-hexane (1:9 v/v) as an eluent to give the
o
1
benzophenanthridine 9 (30 mg, 75%), mp 220-222 C (CHCl3-hexane). H-NMR (300 MHz, CDCl3) #:
1.52 (6H, d, J=5.8 Hz), 4.14 (3H, s), 4.82 (1H, sep, J=5.8 Hz), 6.13 (2H, s), 7.26 (1H, s), 7.42 (1H, s),
13
7.84 (1H, d, J=8.2 Hz), 7.90 (1H, s), 8.31 (1H, d, J=8.2 Hz), 8.71 (1H, s), 9.21 (1H, s). C-NMR (75
MHz, DMSO-d6) #: 21.9 (2C), 56.2, 71.3, 101.3, 102.0, 102.2, 104.4, 110.2, 118.2, 119.9, 122.2, 126.4,
128.6, 129.2, 129.5, 140.5, 148.0, 148.2, 148.4, 149.7, 153.9. MS (EI) m/z: 361 (M+). HRMS (EI) calcd
for C22H19NO4 361.1314; found 361.1301.
8-Hydroxy-9-methoxy-2,3-methylenedioxybenzo[c]phenanthridine (10a)
A mixture of benzophenanthridine 9 (20 mg, 0.055 mmol) and H2SO4 (20 µL, 0.38 µmol) in AcOH (10
o
mL) was stirred at 110 C for 1.5 h. The mixture was diluted with water, and then the mixture was
extracted with EtOAc. The EtOAc layer was washed with water and brine, dried over Na2SO4, and
concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, 5
o
g) using EtOAc-hexane (1:9 v/v) as an eluent to give norterihanine (10a) (17 mg, 96%), mp 286-288 C
(CHCl3-hexane). 1H-NMR (300 MHz, DMSO-d6) #: 4.08 (3H, s), 6.19 (2H, s), 7.47 (1H, s), 7.49 (1H, s),
7.93 (1H, d, J=8.6 Hz), 8.14 (1H, s), 8.52 (1H, s), 8.60 (1H, d, J=8.6 Hz), 9.19 (1H, s), 10.00 (1H, br s).
13C-NMR (75 MHz, DMSO-d6) #: 57.3, 80.3, 102.1, 102.6, 103.7, 105.7, 112.0, 120.3, 121.1, 123.4,
127.4, 128.5, 129.5, 130.2, 140.2, 148.9, 149.1, 150.8, 154.0. MS (EI) m/z: 319 (M+); HRMS (EI) calcd
for C19H13NO4 319.0845; found 319.0819.
9-Hydroxy-8-methoxy-2,3-methylenedioxybenzo[c]phenanthridine (10b)
A mixture of 11,12-dihydrobenzophenanthridines 3b (80 mg, 0.25 mmol) in the presence of 10% Pd-C
o
(120 mg) in 1,2-dichlorobenzene (3 mL) was stirred at 180 C for 7 h. After removal of solvent, the
residue was purified by column chromatography using EtOAc-hexane (1:9 v/v) as an eluent to give
o
1
norisoterihanine 10b (51 mg, 65%), mp 271-273 C (CHCl3-hexane). H-NMR (300 MHz, DMSO-d6) !:
3.99 (3H, s), 6.20 (2H, s), 7.49 (1H, s), 7.68 (1H, s), 7.91 (1H, d, J=8.9 Hz), 8.01 (1H, s), 8.32 (1H, d,
J=8.9 Hz), 8.52 (1H, s), 9.25 (1H, s), 10.33 (1H, s). 13C-NMR (75 MHz, DMSO-d6) !: 55.8, 101.1, 101.5,
104.5, 105.6, 108.2, 118.7, 119.3, 121.5, 126.3, 128.4, 128.4, 129.2, 139.5, 147.9, 148.0, 149.2, 150.1,

HETEROCYCLES, Vol. 88, No. 1, 2014
305
151.5. MS (EI) m/z: 319 (M+). HRMS (EI) calcd for C19H13NO4 319.0845; found 319.0856.
5,6-Dihydro-8-hydroxy-9-methoxy-N-methyl-2,3-methylenedioxybenzo[c]phenanthridine (11a)
A mixture of norterihanine (10a) (26 mg, 0.081 mmol) in HCO2H (2.5 mL) was stirred for 12 h at 80 oC,
and then NaBH4 (288 mg, 7.61 mmol) was added to the solution at rt. After being stirred at rt for 30 min,
the mixture was adjusted to weakly alkaline with aqueous 10% NaOH solution, and then the mixture was
extracted with CHCl3. The CHCl3 layer was washed with water and brine, dried over K2CO3, and
concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, 5
g) using EtOAc-hexane (1:9, v/v) as an eluent to give the 5,6-dihydro-N-methylbenzophenanthridine 11a
(8 mg, 29%), which was used without any further purification. 1H-NMR (300 MHz, CDCl3) #: 2.59 (3H,
s), 4.00 (3H, s), 4.10 (3H, s), 5.68 (1H, br s), 6.05 (2H, s), 6.85 (1H, s), 7.11 (1H, s), 7.28 (1H, s), 7.49
(1H, d, J=8.6 Hz), 7.66 (1H, s), 7.68 (1H, d, J=8.6 Hz). MS (EI) m/z: 335 (M+).
5,6-Dihydro-9-hydroxy-8-methoxy-N-methyl-2,3-methylenedioxybenzo[c]phenanthridine (11b)
Norisoterihanine (10b) (15 mg, 0.09 mmol), HCO2H (3 mL) and NaBH4 (314 mg, 8.3 mmol) were used
in the same procedure as above to give the 5,6-dihydro-N-methylbenzophenanthridine 11b (15 mg, 51%),
mp 221-223 oC (EtOAc-hexane) (Lit.,7 mp 235-242 oC). 1H-NMR (300 MHz, CDCl3) !: 2.60 (3H, s), 3.96
(3H, s), 4.12 (2H, s), 5.60 (1H, br s), 6.05 (2H, s), 6.78 (1H, s), 7.11 (1H, s), 7.38 (1H, s), 7.49 (1H, d,
J=8.6 Hz), 7.65 (1H, s), 7.66 (1H, d, J=8.6 Hz). MS (EI) m/z: 335 (M+). HRMS (EI) calcd for C20H17NO4
335.1158; found 335.1163.
Terihanine (2a) chloride
Jones reagent (50 µL) was added to a stirred solution of 5,6-dihydro-N-methylbenzophenanthridine 11a
(12 mg, 0.036 mmol) in acetone (9 mL) under cooling with ice. The mixture was stirred at the same
temperature for 30 min, and basified with aqueous 10% NaOH solution, and then the mixture was
extracted with CHCl3. The CHCl3 layer was washed with water and brine, dried over K2CO3, and
concentrated under reduced pressure. The residue was dissolved in a small amount of CHCl3, and then
diluted HCl was added dropwise to the solution under cooling with ice. The resulting precipitates were
o
collected by filtration to give terihanine (2a) chloride (4 mg, 32%), mp 246-248 C (MeOH-Et2O) (Lit.,7
o
o
o
o
mp 280 C, melted at 240-245 C and then solidified again) (Lit.,8 mp 271-278 C, melted at 242-245 C
1
and then solidified again). H-NMR (300 MHz, CF3COOD) #: 4.47 (3H, s), 5.07 (3H, s), 6.34 (2H, s),
7.61 (1H, s), 7.93 (1H, s), 8.17 (1H, s), 8.19 (1H, d, J=8.6 Hz), 8.31 (1H, s), 9.39 (1H, s). 1H-NMR (300
MHz, DMSO-d6) #: 4.21 (3H, s), 4.85 (3H, s), 6.32 (2H, s), 7.75 (2H, s), 8.25 (1H, d, J=8.6 Hz), 8.28 (1H,
13
s), 8.33 (1H, s), 8.86 (2H, d, J=8.6 Hz), 9.86 (1H, s), 11.11 (1H, s). C-NMR (75 MHz, DMSO-d6) #:
51.3, 57.2, 102.7, 103.5, 104.6, 105.8, 119.3, 119.8, 120.1, 124.3, 130.0, 131.0, 132.1, 132.3, 148.4, 148.7,
150.3, 151.4, 158.4. TOFMS (ESI) calcd for C20H16NO4 334.1074; found 334.1057.
Isoterihanine (2b) chloride

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5,6-Dihydro-N-methylbenzophenanthridine 11b (18 mg, 0.054 mmol), and Jones reagent (80 µL) in
acetone (13 mL) were used in the same procedure as above to give isoterihanine (2b) chloride (15 mg,
76%), mp 230-232 oC (MeOH-Et2O) (Lit.,7 mp 243-247 oC). 1H-NMR (300 MHz, CF3COOD) #: 4.23 (3H,
s), 4.97 (3H, s), 6.23 (2H, s), 7.50 (1H, s), 7.69 (1H, s), 8.07 (1H, s), 8.17 (1H, d, J=8.6 Hz), 8.30 (1H, s),
1
8.47 (1H, d, J=8.6 Hz), 9.30 (1H, s). H-NMR (300 MHz, DMSO-d6) !: 4.03 (3H, s), 4.82 (3H, s), 6.30
(2H, s), 7.70 (1H, s), 7.86 (1H, s), 8.18 (1H, s), 8.19 (1H, d, J=9.2 Hz), 8.24 (1H, s), 8.51 (1H, d, J=9.2
Hz), 9.71 (1H, s). 13C-NMR (75 MHz, DMSO-d6) !: 51.3, 56.5, 102.9, 104.6, 105.9, 106.5, 109.7, 118.8,
118.9, 120.2, 123.6, 130.2, 132.4, 132.5, 132.5, 148.6, 148.9, 151.3, 151.4, 158.1. TOFMS (ESI) calcd for
C20H16NO4 334.1074; found 334.1088.
ACKNOWLEDGEMENTS
We thank Professor Tsutomu Ishikawa, Graduate School of Pharmaceutical Sciences, Chiba University,
for providing the authentic terihanine (Cl) and isoterihanine (Cl). This work was partly supported by a
Grant-in Aid for Scientific Research (C) of the Japan Society for the Promotion of Science (Grant
Numbers 20590026 (S.H.) and 23590143 (N.H.).
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