Chemistry of renieramycins. Part 11: Total synthesis of (±)-cribrostatin 4

Article abstract of DOI:10.1016/j.tet.2011.09.076

A 19-step synthesis of (±)-cribrostatin 4 (1) from readily available piperazine-2,5-dione derivative 6 is described. The synthesis features the concise construction of a pentacyclic framework, followed by the base-catalyzed epimerization of the C-1 stereo center of aldehyde (11). The results of cytotoxicity studies are also presented.

Full text of DOI:10.1016/j.tet.2011.09.076

Tetrahedron 67 (2011) 9185e9192
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Chemistry of renieramycins. Part 11: Total synthesis of (ꢀ)-cribrostatin 4
*
Masashi Yokoya, Hiroshi Ito, Naoki Saito
Graduate School of Pharmaceutical Sciences, Meiji Pharmaceutical University, 2-522-1 Noshio, Kiyose, Tokyo 204-8588, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 August 2011
Received in revised form 17 September 2011
Accepted 18 September 2011
Available online 24 September 2011
A 19-step synthesis of (ꢀ)-cribrostatin 4 (1) from readily available piperazine-2,5-dione derivative 6 is
described. The synthesis features the concise construction of a pentacyclic framework, followed by the
base-catalyzed epimerization of the C-1 stereo center of aldehyde (11). The results of cytotoxicity studies
are also presented.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
Total synthesis
Marine natural product
Isoquinoline
Cribrostatin 4
Cytotoxicity
1. Introduction
In 1988, Parameswaran et al. reported the discovery of renier-
amycin H (2h), which was isolated from the methanol extract of the
Natural products belonging to the tetrahydroisoquinoline-
quinone family and their reduced forms, including saframycins,1
renieramycins, and the most notable example, ecteinascidin 743
(YondelisÔ, trabectedin),2,3 have generated wide chemical and bi-
ological interest because of their unique structures and meager
availability in nature, and for their potent antitumor activity.4 Fol-
lowing the discovery of renieramycins AeD (2aed) from the Mexi-
can blue sponge Reniera sp. in 1982,5 more than ten renieramycin
marine natural products,6e12 along with cribrostatin 4 (1),13 jor-
umycin (4),14 and jorunnamycin C (5),15 were isolated from several
kinds of marine organisms (Fig. 1). Because of their novel structures
and remarkable biological activities, renieramycins are expected to
be one of the candidates for new anticancer drugs. However, most
renieramycins are isolable in only trace amounts and relatively un-
stable, decomposing during extraction and isolation.
bright blue sponge Haliclona cribricutis collected from the intertidal
region of Okha, Gujarat (India), along with renieramycin I (2i).8 The
structure of 2h sparked much interest because it is the first example
of renieramycins having a hydroxyl group at bridgehead position C-
13. We have revised the structure of renieramycin H (2h) to that of
cribrostatin 4 (1), which was independently isolated from the blue
sponge Cribrochalina sp. in reef passages in the Republic of Mal-
dives,13 based on 13C NMR studies of our model compounds, such as
3a19 and 3b.20,21 We are also very interested in the structure of
cribrostatin 4 (1) because it is one of the very few examples of
renieramycins having an unsaturated carbonecarbon bond be-
tween C-3 and C-4. We have focused our attention on the synthetic
studies of cribrostatin 4 (1) in order to acquire evidence that 1 re-
tains its cytotoxicity despite the lack of an essential hemiaminal or
aminonitrile functional group at C-21 position, and to reassign all
proton and carbon signals to establish our proposed structure of
renieramycin H (2h) as some original signals are missing. To date,
three total syntheses of cribrostatin 4 (1)22e24 have been reported
and all of them include the construction of a bicyclic AB ring system
with a cis relationship at C-1 and C-3 positions, followed by the
condensation of the E ring part and the elaboration of the central
CD ring. We have just completed our total synthesis of 1 via a dif-
ferent approach that involved the key transformations outlined in
Scheme 1: (1) stereoselective cyclization of lactam nitrogen of
readily available 3,6-bisarylpiperazine-2,5-dione derivative 625,26
with diethoxyethyl benzoate, (2) construction of the D ring to
generate the pentacyclic framework, (3) and epimerization of C-1
As part of our search for new metabolites through the isolation
and characterization of biologically active compounds from Thai
marine animals, specifically the Thai blue sponge, Xestospongia sp.,
we were able to solve the above problem by converting original
natural products having a very unstable amino alcohol function-
ality at C-2116 into stable
a-aminonitrile compounds via pre-
treatment with KCN.9 We have shown that this procedure yields
renieramycin M (2m) in gram scale and reported some structur-
eeactivity relationships (SARs) of renieramycins.17,18
* Corresponding author. Tel./fax: þ81 42 495 8794; e-mail address: naoki@
my-pharm.ac.jp (N. Saito).
0040-4020/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2011.09.076

9186
M. Yokoya et al. / Tetrahedron 67 (2011) 9185e9192
OMe
OMe
17
18
HO
H
Me
O
H
Me
O
OMe
Me
OMe
Me
16
E
O
O
15
HO
H
Me
OH
4
O
H
Me
O
Me
6
7
OH Me
MeO
5
8
11
3
N
Me
N
Me
X
A
C
H
H
21
N
14 O
N
13
H
Z
MeO
N
N
1
O
O
O
O
O
O
N
N
OMe
22
25
H
O
Me
O
Me
Me
OH
Me
O
O
26
24
O
H
H
3a
3b
Me
cribrostatin 4 (1)13
Me
renieramycins8
H (2h): X = Z = OH
I (2i): X = OMe, Z = H
OMe
OMe
OMe
Me
17
18
O
H
Me
O
H
Me
O
O
H
Me
O
16
O
O
O
15
H
N
H
N
H
N
4
Me
6
O
Me
MeO
Me
5
8
11
N
Me
X
N
Me
X
N
3
H
H
H
14
H
X
13
7
H
H
MeO
MeO
1
21
O
O
O
O
O
O
O
Y
22
25
O
Me
O
Me
O
Me
26
24
H
H
H
Me
Me
Me
renieramycins5
A (2a): X = OH
B (2b): X = OEt
renieramycins
renieramycins
E (2e)6: X = H, Y = OH
M (2m)9: X = H, Y = CN
C (2c)5: X = OH
D (2d)5: X = OEt
G (2g)7: X = H
O (2o)10: X = OH, Y = CN
P (2p)11: X = OMe, Y = OH
R (2r)10: X = OMe, Y = CN
OMe
OMe
Me
OMe
O
H
Me
HO
Me
OH
O
H
Me
O
O
O
H
HO
H
N
H
H
Me
O
Me
Me
N
Me
N
N
Me
H
H
H
X2
N
N
X
H
H
MeO
H
MeO
X1
O
Y
CN
CN
O
O
O
O
O
O
O
O
Me
O
Me
R
H
H
Me
Me
renieramycins10
jorumycin (4)14: R = H, Y = OH
jorunnamycin C (5)15
R = Me, Y = CN
renieramycins12
U (2u): X = H
V (2v): X = OH
N (2n): X1 = OH, X2 = H
Q (2q): X1, X2 = O
Fig. 1. Structures of renieramycin marine natural products.
center, followed by regio- and stereoselective selenium oxide
(SeO2) hydroxylation at C-14 position of bis p-quinones using our
procedure.20,27 This approach should provide a variety of novel
analogues of cribrostatin 4 as well as a 1-epi-pentacyclic compound
for the detailed study of SARs of these classes of antitumor marine
natural products.
We have recently described an eleven-step preparation of 1-epi-
pentacyclic alcohol 8 through the modified PicteteSpengler cycli-
zation of lactam nitrogen with diethoxyethyl benzoate, followed by
the stereoselective hydrogenation of 7 to generate 8.28 In this paper,
we describe the total synthesis of (ꢀ)-cribrostatin 4 (1) from 8 via
Williams intermediate 9.23 The results of cytotoxicity measure-
ments are also presented.
steps based on the procedure of Gallina and Liberatori in 80e90%
overall yield.29,30 Hydrolysis of 6 with a base gave deacetylated
compound 10a (Fig. 2), which was subsequently treated with 2,2-
diethoxyethyl benzoate via O-trimethylsilyllactim intermediate to
afford 10b stereoselectively in 83% overall yield. X-ray crystallo-
graphic analysis was used to determine its structure and the ste-
reochemistry between the two methine protons was found to be
trans. Reduction of the double bond of 10b occurred from the a face,
and this was followed by acylation to afford 7 in 76% overall yield.
Partial reduction of 7 with lithium-tri-tert-butoxyaluminum hy-
dride in tetrahydrofuran (THF) gave a diastereomeric mixture of
aminal that was converted into cyclization product 10c by treat-
ment with formic acid at 60 ꢁC for 14 h in 80% overall yield.
Deprotection of 10c with trifluoroacetic acid (TFA) and H2SO4 gave
secondary amine 10d in 96% yield. Reductive methylation of 10d,
followed by hydrolysis gave pentacyclic alcohol 8 in 97% overall
yield. We have succeeded in the 11-step transformation of 8 from 6
in 47% overall yield.28
2. Results and discussion
Substrate 625 was easily prepared from 1,4-diacetylpiperazine-
2,5-dione and 2,4,5-trimethoxy-3-methylbenzaldehyde in four

M. Yokoya et al. / Tetrahedron 67 (2011) 9185e9192
9187
i
CO2Pr
MeO
MeO
O
OMe
MeO
O
OMe
Me
H
OMe
4
H
N
N
Me
OMe
Me
5 steps
N
H
3
N
H
MeO
Ac
Me
MeO
O
OMe
ref. 28
MeO
O
O
OMe
O
25, 26
6
7
OMe
MeO
H
Me
MeO
MeO
Me
OMe
5 steps
ref. 28
N
Me
14
H
N
MeO
H
1
O
OH
8
OMe
Me
O
H
Me
O
O
Me
MeO
N
cribrostatin 4
1
H
14
N
1
H
O
O
OH
9
Scheme 1. Strategy for total synthesis of cribrostatin 4 (1).
OMe
MeO
Me
MeO
Me
H
MeO
Me
O
O
OMe
OMe
OMe
MeO
Me
O
O
OMe
OMe
N
R
H
N
H
H
H
N
N
N
MeO
MeO
H
H
N
MeO
MeO
Me
OMe
O
MeO
MeO
H
Me
OMe
O
O
O
10a
O
10b
i
10c: R = CO2 Pr
10d: R = H
Fig. 2. Structures of compounds 10aed.
Having established the pentacyclic framework of 1, the next
hurdle was the isomerization at C-1 position of 8. The Swern oxi-
dation of alcohol 8 gave 11 in 92% yield (Scheme 2). Treatment of 11
with 1.0 equiv of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)31e33 in
THF at 25 ꢁC for 1 h afforded 12 in 66% yield, and 26% of starting
material 11 was recovered. Their ratio could not be varied by
changing the reaction conditions, such as the reaction time, or the
ratio of substrate to base. This reaction presumably attained equi-
librium fairly rapidly via enolate I. Accordingly, isomerization of
recovered 11 by repeating the procedure gave 12 and 11 in 81.0%
and 6.0% yields, respectively. Reduction of 12 with sodium cyano-
borohydride (NaBH3CN) in the presence of acetic acid (AcOH) gave
13 in 73% yield.
and then at ꢂ20 ꢁC for 39 h gave 14 in 46% yield.34 All the protons
and carbons of 14 were assigned after extensive NMR measure-
ments using correlation spectroscopy (COSY), 1H-detected hetero-
nuclear multiple bond coherence (HMBC), and 1H-detected
heteronuclear multiple-quantum coherence (HMQC) techniques.
The phenolic hydroxyl groups in 14 were found at C-8 and C-15 on
the basis of selected HMBC correlation data (Scheme 4).35 Oxida-
tion of 14 with 10 N HNO3 at 25 ꢁC for 10 min gave Williams in-
termediate 9 in 90% yield. On the other hand, treatment of 13 with
6.0 equiv of BBr3 in CH2Cl2 at ꢂ78 ꢁC for 1 h afforded the crude
product, which was subjected to oxidative demethylation with 10 N
HNO3 at 25 ꢁC for 30 min to give 9 in 55% overall yield. Both 1H and
13C NMR spectroscopic data were identical with the authentic data
of (ꢂ)-9.
The conversion of polymethoxyarene 13 into cribrostatin 4 in-
termediate 923 was accomplished by partial demethylation with
boron tribromide (BBr3), followed by oxidative demethylation.
Treatment of 13 with 8.0 equiv of BBr3 in CH2Cl2 at ꢂ78 ꢁC for 1 h
With our target in hand, we directed our efforts toward the
conversion of 9 into cribrostatin 4 (1) according to the procedure of
Vincent and Williams23 (Scheme 3). Treatment of 9 with angeloyl

OMe
OMe
MeO
H
Me
MeO
H
Me
MeO
MeO
MeO
H
O
b
Me
OMe
Me
OMe
N
Me
H
N
Me
H
N
Me
H
R
H
N
O
N
N
H
MeO
MeO
H
MeO
a
O
H
O
O
I
8: R = CH2OH
11: R = CHO
12
OMe
OMe
MeO
H
Me
MeO
Me
MeO
HO
H
15
OH
11
Me
OMe
Me
c
d
5
N
Me
H
N
Me
H
H
14
11
N
O
N
MeO
MeO
H
13
1
MeO
HO
MeO
HO
O
13
14
e
Me
f
HO
OMe
OMe
O
H
Me
O
Me
H
O
O
OMe
H
OH
MeO
MeO
HO
H
Me
N
Me
H
H
H
N
MeO
N
O
1
Me
O
N
HO
H
H
9
Selected HMBC correlation data of
compound 14
Scheme 2. Reagents and conditions: (a) (COCl)2, TEA, DMSO, ꢂ40 ꢁCe25 ꢁC, 92%; (b) DBU, THF, 25 ꢁC twice, 81%; (c) NaBH3CN, AcOH/MeOH, 25 ꢁC, 73%; (d) BBr3 (8 equiv),
CH2Cl2, ꢂ78 ꢁC to ꢂ20 ꢁC, 46%; (e) 10 N HNO3, 25 ꢁC, 90%; (f) BBr3 (6 equiv), CH2Cl2, ꢂ78 ꢁC to ꢂ20 ꢁC and then 10 N HNO3, 55%.
OMe
OMe
O
H
Me
O
O
H
Me
O
O
O
g
h
Me
Me
N
Me
14
H
N
Me
9
H
1
H
1
N
N
OH
MeO
MeO
H
O
O
O
O
O
O
O
Me
O
Me
H
H
15
16
Me
Me
OMe
Me
OMe
O
H
Me
O
HO
H
Me
O
O
O
Me
i, j
Me
OH
Me
N
N
H
H
1
O
N
O
N
MeO
H
MeO
1
H
O
O
O
O
O
Me
O
Me
H
O
H
17
Me
Me
1 (cribrostatin 4)
Scheme 3. Reagents and conditions: (g) (Z)-MeCH]C(Me)COCl, CH2Cl2, 25 ꢁC, 21 h, 84%; (h) SeO2 (5 equiv), dioxaneeH2O, 80 ꢁC, 6 h, 71%; (i) DMP (10.5 equiv), CH2Cl2, 25 ꢁC, 3 h;
(j) Na2S2O3, THFeH2O, 25 ꢁC, 2 h, then work-up under air, 84% (two steps).

M. Yokoya et al. / Tetrahedron 67 (2011) 9185e9192
9189
We have already reported the revised structure of renieramycin
OMe
OMe
H (2h) in which both C-1 (
d
56.2) and C-19 (
d
108.6) signals should
MeO
H
Me
MeO
H
Me
OH
119.2), respectively.21
BBr3 (2 equiv)
CH2Cl2, -78oC
be replaced with C-11 ( 46.9) and C-20 (
d
d
With synthetic 1 in hand, we present here all proton and carbon
assignments of 1 by extensive NMR measurements using COSY,
HMQC, and HMBC techniques (Table 1).
Natural cribrostatin 4 (1) has mean panel GI50 values of
(5.01ꢀ0.28)ꢂ3 mM.13 Danishefsky and co-workers reported that the
assay performed with synthetic (ꢂ)-cribrostatin 4 (1) corroborated
the results obtained by Pettit and co-workers.39 Thus, the com-
pounds synthesized above, including natural renieramycin M
OMe
N
Me
H
N
Me
H
N
O
N
O
72 %
Me
Me
18
19
Scheme 4. Partial demethylation of model compound 18.
Table 1
1H and 13C NMR assignments for cribrostatin 4 (1) in CDCl3
Atom no
Synthetic 1
Natural 113
13C NMR
d
(125 MHz)
1H NMR (500 MHz)
d
(multi, integral, J in Hz)
HMBC correlations from C no.
13C NMR (125 MHz)
1H NMR (500 MHz)
6.18
1
3
4
5
6
7
8
9
10
11
13
14
15
16
17
18
19
20
21
22
46.9
124.2
100.0
185.0
127.1
156.4
179.9
134.6
139.8
56.2
CH
C
CH
C
C
C
C
C
C
CH
CH
C]O
C
C
C
C
C
C
C
6.20 (dd, 1H, 6.2, 3.1)
56.2
124.2
100.0
185.0
127.1
156.3
179.9
134.6
139.8
46.9
1-H, 4-H
11-H
4-H, 6-Me
6-Me
6.23 (s, 1H)
6.22
6-Me, 7-OMe
1-H,
1-H, 4-H
4.87 (d, 1H, 1.1)
4.11 (d, 1H, 1.1)
4-H, 13-H, N-Me
11-H, N-Me
13-H
15-OH, 16-Me
16-Me, 15-OH
16-Me, 17-OMe, 18-OH
11-H, 18-OH
11-H, 18-OH
11-H, 13-H, 15-OH
13-H
4.10
4.85
72.5
72.5
192.7
156.3
119.1
153.2
138.1
119.8
108.6
161.1
62.1
192.7
156.2
119.8
153.3
138.1
108.6
119.2
161.1
62.0
CH2
4.06 (dd, 1H, 12.0, 6.2)
3.83 (dd, 1H, 12.0, 3.1)
4.06
3.81
24
25
26
27
166.8
126.6
139.3
15.4
19.9
8.6
C]O
C
CH
CH3
CH3
CH3
CH3
22-H
26-H
166.8
126.6
139.3
15.4
19.9
8.6
5.91 (qq, 1H, 7.1, 1.4)
1.75 (dq, 1H, 7.1, 1.4)
1.47 (quint, 1H, 1.4)
1.95 (s, 3H)
4.06 (s, 3H)
11.35 (s, 1H)
5.59 (s, 1H)
2.16 (s, 3H)
3.86 (s, 3H)
2.57 (s, 3H)
5.9 (qu)
1.73 (d)
1.45
1.93
4.04
28
6-Me
7-OMe
15-OH
18-OH
16-Me
17-OMe
N-Me
61.1
61.2
9.0
61.2
41.3
CH3
CH3
CH3
9.0
61.1
41.2
2.14
3.84
2.56
11-H, 13-H
chloride in CH2Cl2 and dimethylformamide (DMF) afforded 15 in
84% yield. The reaction of 15 with SeO2 (10 equiv) in dioxane at
80 ꢁC for 8 h gave 16 in 53% yield along with recovered 15 (26%)
under our original conditions.20 The addition of water was found to
accelerate the reaction; for example, the oxidation of 15 with SeO2
in dioxaneeH2O at 80 ꢁC for 6 h proceeded through the chemo- and
diastereoselective introduction of a hydroxyl group at C-14 position
to afford 16 in 71% yield. Oxidation of 16 with DesseMartin peri-
odinate (DMP)36,37 in CH2Cl2 at 25 ꢁC for 3 h gave ketone 17 in good
yield. However, when the crude product was allowed to stand in
organic solvent at 25 ꢁC for several hours, it was converted into an
8:1 mixture of 17 and cribrostatin 4 (1).38 After extensive in-
vestigation of the reaction conditions, the following procedure was
found to be optimal in terms of product yield and reproducibility of
the reaction: Treatment of 16 with 10.5 equiv of DMP in CH2Cl2 at
25 ꢁC for 3 h, followed by sodium thiosulfate reduction and selec-
tive air oxidation of the resulting bishydroquinone afforded cri-
brostatin 4 (1) in 84% overall yield. The high stability of the
hydroquinone E ring is attributable to the presence of a hydrogen
bond between C-14 carbonyl (dC 192.7 ppm) and 15-OH (dH
11.35 ppm).
(2m), were tested in vitro for cytotoxicity using three represen-
tative human solid tumor cell lines (HCT116 human colon carci-
noma, QG56 human lung carcinoma, and DU145 prostate
carcinoma) following the standard MTT method (Table 2). Com-
pounds 9 and 16 displayed micromolar inhibitory effects, but
Table 2
Cytotoxicity of cribrostatin 4 (1) and related compounds to various cancer cell lines
(IC50 m
M)a
Compound
HCT116
QG56
DU145
8
>2
>2
>2
11
>2
>2
>2
12
>2
>2
>2
13
>2
>2
>2
14
>2
>2
>2
9
15
0.51
>2
0.97
>2
1.4
>2
16
17
0.30
>2
0.90
>2
0.39
>2
(ꢀ)-1 (Cribrostatin 4)
>2
>2
>2
(ꢂ)-2m (Renieramycin M)
7.0ꢃ10ꢂ3
21.0ꢃ10ꢂ3
1.5ꢃ10ꢂ3
a
HCT116¼human colon carcinoma; QG56¼human lung carcinoma;
DU145¼human prostate carcinoma.

9190
M. Yokoya et al. / Tetrahedron 67 (2011) 9185e9192
almost all synthetic compounds, including (ꢀ)-1, did not show any
cytotoxicity.
(200 mL), dried, and concentrated in vacuo, and the residue
(607 mg) was subjected to silica gel (75 g) chromatography with
hexane to hexaneeethyl acetate¼2:1 to afford 11 (141.0 mg, 26%
recovery). Further elution with hexaneeethyl acetate¼2:1 to ethyl
acetate gave 12 (374.0 mg, 66.0% yield).
Recovered 11 (141.0 mg, 0.262 mmol) was treated again with
DBU (39.2 uL, 0.262 mmol) in THF (150 mL) at 25 ꢁC for 1 h. Per-
forming the same work-up and separation described above affor-
ded 12 (82.0 mg) and 11 (32.2 mg). Thus, 456 mg of 12 (81.0%) could
be obtained from 11 (560.0 mg) along with recovered 11 (32.3 mg,
6.0%).
In summary, the stereoselective total synthesis of (ꢀ)-cri-
brostatin 4 (1) has been realized in 19 steps from readily available
compound 6 in 9.5% overall yield. Efforts to refine the synthesis of 1,
including its optically active forms, and to prepare analogues for
biological screening and studies of the mechanism of action are
under way.
3. Experimental section
3.1. General
IR (KBr) 3435, 2941, 1740, 1676, 1641, 1466, 1412, 1356, 1269,
1184, 1128, 1065, 1007, 964 cmꢂ1; 1H NMR (CDCl3, 400 MHz)
d 8.99
IR spectra were obtained with a Shimadzu Prestige 21/IRA
Affinity-1 FT-IR spectrometer. 1H and 13C NMR spectra were
recorded on a JEOL-JNM-ECA500 FT NMR spectrometer at 500 MHz
for 1H and 125 MHz for 13C, on a JEOL-JNM-AL400 NMR spec-
trometer at 400 MHz for 1H and 100 MHz for 13C, and on a JEOL-
JNM-AL300 NMR spectrometer at 300 MHz for 1H and 75 MHz
for 13C (ppm, J in Hz with TMS as internal standard). All proton and
carbon signals were assigned by extensive NMR measurements
using COSY, HMBC, and HMQC techniques. Mass spectra were
recorded on a JEOL JMS 700 instrument with a direct inlet system
operating at 70 eV.
(1H, s, CHO), 6.43 (1H, s, 9-H), 6.18 (1H, s, 14-H), 4.71 (1H, s, 15-H),
3.91 (3H, s, OMe), 3.81 (3H, s, OMe), 3.76 (3H, s, OMe), 3.75 (3H, s,
OMe), 3.74 (3H, s, OMe), 3.74 (1H, m, 6-H, signals overlapped with
OMe), 3.68 (3H, s, OMe), 3.23 (1H, dd, J¼17.1, 5.9 Hz, 5-H
dd, J¼17.1, 2.3 Hz, 5-H ), 2.58 (3H, s, NMe), 2.21 (3H, s, ArMe), 2.20
(3H, s, ArMe); 13C NMR (CDCl3, 100 MHz)
192.8 (CHO), 167.9 (C-7),
a), 3.17 (1H,
b
d
152.3 (C-4), 150.4, 149.8 (C-2, C-11), 149.6 (C-13), 146.2 (C-1), 146.1
(C-10), 134.2 (C-14a), 126.4 (C-3 or C-12), 125.9 (C-15a), 124.6 (C-3
or C-12), 121.1 (C-4a), 119.6 (C-9a), 115.8 (C-13a), 101.8 (C-14), 61.4
(OMe), 60.6 (OMe), 60.4 (C-6), 60.1 (OMe), 60.1 (OMe), 60.1 (OMe),
59.9 (OMe), 59.5 (C-9), 56.3 (C-15), 41.6 (NMe), 29.0 (C-5), 9.6
(ArMe), 9.5 (ArMe); EIMS m/z (%) 538 (Mþ, 4), 509 (34), 481 (100),
248 (48); HRMS m/z 538.2311 (Mþ, calcd for C29H34N2O8, 538.2315).
3.1.1. 1,2,4,10,11,13-Hexamethoxy-9-carboxaldehyde-3,12,16-
trimethyl-7-oxo-(6S*,9S*,15R*)-5,6,9,15-tetrahydro-6,15-
iminoisoquino[3,2-b][3]-benzazocine (11). A solution of oxalyl
chloride (0.67 mL, 8.0 mmol) and DMSO (1.14 mL, 16.0 mmol) in
CH2Cl2 (60 mL) was stirred for 10 min at ꢂ78 ꢁC. A solution of 8
(540.0 mg, 1.0 mmol) in CH2Cl2 (20 mL) was added to the above
reaction mixture over 30 min and the entire mixture was stirred at
the same temperature for 2 h. Triethylamine (2.79 mL, 20 mmol)
was then added dropwise and the reaction mixture was stirred for
5 min at ꢂ78 ꢁC and an additional 70 min at 0 ꢁC. After the reaction
mixture was diluted with saturated aqueous NaHCO3 solution
(300 mL), the resulting solution was extracted with CHCl3
(300 mLꢃ3). The combined extracts were washed with brine
(300 mL), dried, and concentrated in vacuo, and the residue was
subjected to silica gel chromatography with hexaneeethyl
acetate¼2:1 to ethyl acetate to afford 11 (496.0 mg, 92%) as a col-
orless amorphous powder.
3.1.3. 1,2,4,10,11,13-Hexamethoxy-9-hydroxymethyl-3,12,16-
trimethyl-7-oxo-(6S*,9R*,15R*)-5,6,9,15-tetrahydro-6,15-
iminoisoquino[3,2-b][3]-benzazocine (13). To a THF solution of so-
dium cyanoborohydride (1 M, 76.4 m
L, 0.764 mmol) at 0 ꢁC were
added 12 (274.0 mg, 0.51 mmol) and AcOH (3.8 mL, 66.2 mmol) in
THF (70 mL), and the mixture was stirred at 25 ꢁC for 2 h. The re-
action mixture was poured into saturated aqueous NaHCO3
(300 mL) and extracted with CHCl3 (300 mLꢃ3). The combined
extracts were washed with brine (300 mL), dried, and concentrated
in vacuo to give a residue (295.0 mg). Chromatography on a silica
gel column with CHCl3 to CHCl3eMeOH¼50:1 gave 13 (201.0 mg,
73%) as a colorless amorphous powder.
IR (KBr) 3460, 2940,1672,1636,1466,1412,1364,1341,1248,1113,
1007, 964 cmꢂ1; 1H NMR (CDCl3, 400 MHz)
d 6.26 (1H, s, 14-H), 6.09
(1H, dd, J¼7.8, 5.0 Hz, 9-H), 4.68 (1H, br s,15-H), 3.88 (3H, s,10-OMe),
3.86 (3H, s, 1-OMe), 3.78 (3H, s, 11-OMe), 3.76 (3H, s, 13-OMe), 3.75
(3H, s, 2-OMe), 3.70 (1H, dt, J¼4.7, 1.2 Hz, 6-H), 3.66 (4-OMe), 3.32
(1H, ddd, J¼11.0, 6.2, 5.0 Hz, 9-CH), 3.19 (1H, ddd, J¼11.0, 7.8, 6.2 Hz,
9-CH), 3.18 (2H, d, J¼4.7 Hz, 5-H2), 2.55 (3H, s, NMe), 2.19 (3H, s, 12-
Me), 2.18 (3H, s, 3-Me), 1.38 (1H, t, J¼6.2 Hz, OH); 13C NMR (CDCl3,
IR (KBr) 3447, 2940, 2833, 1738, 1676, 1639, 1465, 1412, 1354,
1269, 1248, 1113, 1066, 1007 cmꢂ1; 1H NMR (CDCl3, 400 MHz)
d 9.41
(1H, s, CHO), 6.48 (1H, s, 9-H), 6.19 (1H, s,14-H), 4.84 (1H, d, J¼1.7 Hz,
15-H), 3.97 (3H, s, OMe), 3.95 (3H, s, OMe), 3.91 (1H, m, 6-H), 3.78
(3H, s, OMe), 3.70 (6H, s, OMeꢃ2), 3.67 (3H, s, OMe), 3.20 (1H, dd,
J¼17.6, 7.6 Hz, 5-H
a
), 3.07 (1H, dd, J¼17.6, 1.1 Hz, 5-H
b
d
), 2.83 (3H, s,
191.3 (CHO),
100 MHz) d 169.0 (C-7), 152.4 (C-4), 150.5 (C-11), 149.9 (C-2), 149.5
NMe), 2.15(6H, s, ArMeꢃ2); 13C NMR(CDCl3,100 MHz)
(C-13), 146.1 (C-1), 145.6 (C-10), 132.7 (C-14a), 126.0 (C-15a), 125.3
(C-12),124.9 (C-3),121.1 (C-4a),120.5 (C-9a),119.4 (C-13a),102.7 (C-
14), 64.6 (9-CH2), 61.4 (11-OMe), 60.7 (10-OMe), 60.6 (C-6), 60.2 (1-
OMe), 60.2 (4-OMe), 60.1 (13-OMe), 59.9 (2-OMe), 56.6 (C-15), 49.1
(C-9), 41.7 (NMe), 29.5 (C-5), 9.6 (3-Me), 9.4 (12-Me); EIMS m/z (%)
540 (Mþ,10), 509 (28), 481 (100), 248 (41); HRMS m/z 540.2473 (Mþ,
calcd for C29H36N2O8, 540.2472).
168.9 (C-7), 152.1 (C-4), 149.9, 149.8 (C-2, C-11), 149.4 (C-13), 145.8
(C-1), 145.7 (C-10), 134.8 (C-14a), 127.2 (C-15a), 126.4, 124.6 (C-3, C-
12), 121.0 (C-4a), 120.2 (C-9a), 114.0 (C-13a), 98.7 (C-14), 61.1 (OMe),
60.4 (OMe), 60.3 (OMe), 60.0 (OMe), 59.9 (C-6), 59.8 (OMe), 59.8
(OMe), 59.6 (C-9), 55.3 (C-15), 41.9 (NMe), 27.2 (C-5), 9.5 (ArMe), 9.4
(ArMe); EIMS m/z (%) 538 (Mþ, 5), 509 (33), 481 (100), 248 (51);
HRMS m/z 538.2310 (Mþ, calcd for C29H34N2O8, 538.2315).
3.1.4. 1,2,10,11-Tetramethoxy-9-hydroxymethyl-3,12,16-trimethyl-7-
oxo-(6S*,9R*,15R*)-5,6,9,15-tetrahydro-6,15-iminoisoquino[3,2-b][3]-
benzazocine (14). To a stirred solution of 13 (10.8 mg, 0.02 mmol) in
CH2Cl2 (1.2 mL) at ꢂ78 ꢁC was added a CH2Cl2 solution of BBr3
3.1.2. 1,2,4,10,11,13-Hexamethoxy-9-carboxaldehyde-3,12,16-
trimethyl-7-oxo-(6S*,9R*,15R*)-5,6,9,15-tetrahydro-6,15-
iminoisoquino[3,2-b][3]-benzazocine (12). DBU (156 mL, 1.04 mmol)
was added over 5 min to a stirred solution of 11 (560.0 mg,
1.04 mmol) in THF (170 mL) at 0 ꢁC and the reaction mixture was
stirred at 25 ꢁC for 1 h. After the reaction mixture was concentrated
in vacuo, the resulting residue was diluted with 5% aqueous
NaHCO3 solution (200 mL) and then extracted with CHCl3
(200 mLꢃ3). The combined extracts were washed with brine
(1.0 M, 160.0 mL, 0.16 mmol) over 5 min. Stirring was continued at
the same temperature for 1 h, and then at ꢂ20 ꢁC for 39 h. The
reaction mixture was diluted with water (20 mL) and extracted
with CHCl3 (20 mLꢃ6). The combined extracts were washed with
5% NaHCO3 solution (20 mL), dried, and concentrated in vacuo and
the residue (7.0 mg) was purified by silica gel column

M. Yokoya et al. / Tetrahedron 67 (2011) 9185e9192
9191
chromatography with CHCl3eMeOH¼100:1 to afford 14 (4.7 mg,
dd, J¼5.7, 2.9 Hz, 9-H), 5.92 (1H, qq, J¼7.4,1.4 Hz, 20-H), 4.50 (1H, br s,
15-H), 4.21 (1H, dd, J¼11.9, 5.7 Hz, 9-CH), 4.05 (3H, s, 11-OMe), 4.01
(3H, s, 2-OMe), 4.01 (1H, dd, J¼11.9, 2.9 Hz, 9-CH), 3.72 (1H, dt, J¼6.8,
46.1%) as a pale purple amorphous powder.
IR (KBr) 3421, 2938,1636,1464,1423,1354,1251,1117,1061 cmꢂ1
;
1H NMR (CDCl3, 400 MHz)
d
6.23 (1H, s, 14-H), 6.05 (1H, dd, J¼7.6,
1.4 Hz, 6-H), 2.95 (1H, dd, J¼19.8, 6.8 Hz, 5-H ), 2.84 (1H, dd, J¼19.8,
a
4.8 Hz, 9-H), 4.68 (1H, s,15-H), 3.85 (3H, s,10-OMe), 3.84 (1H, m, 6-H,
signals overlapped with those of OMe), 3.83 (3H, s,1-OMe), 3.77 (3H,
s, 11-OMe), 3.73 (3H, s, 2-OMe), 3.31 (1H, dd, J¼11.1, 4.8 Hz, 9-CH),
1.4 Hz, 5-H
1.75 (3H, dq, J¼7.4, 1.4 Hz, 20-Me),1.57 (1H, quint, J¼1.4 Hz, 19-Me);
13C NMR (CDCl3, 125 MHz)
186.5 (C-4), 184.9 (C-13), 180.5 (C-10),
b), 2.47 (3H, s, NMe),1.96 (3H, s,12-Me),1.92 (3H, s, 3-Me),
d
3.19 (1H, dd, J¼11.1, 7.6 Hz, 9-CH), 3.12 (1H, dd, J¼16.8, 5.9 Hz, 5-H
a
),
), 2.57 (3H, s, NMe), 2.13 (3H, s, 12-
Me), 2.11 (3H, s, 3-Me); 13C NMR (CDCl3, 100 MHz)
169.0 (C-7),
180.1 (C-1), 167.1 (C-7 and C-18), 156.2 (C-11), 155.2 (C-2), 140.6 (C-
14a),139.8 (C-4a),139.3 (C-20),136.2 (C-15a),134.6 (C-13a),128.5 (C-
3), 127.3 (C-12), 126.8 (C-19), 124.2 (C-9a), 101.3 (C-14), 62.4 (C-16),
61.1 (11-OMe), 61.0 (2-OMe), 59.5 (C-6), 54.3 (C-15), 47.1 (C-9), 41.1
(NMe), 28.3 (C-5), 20.2 (C-22), 15.5 (C-21), 8.7 (3-Me), 8.6 (12-Me);
EIMS m/z (%) 562 (Mþ, 5), 449 (13), 423 (15), 423 (25), 421 (100), 218
(40); HREIMS m/z 562.1952 (Mþ, calcd for C30H30N2O9, 562.1951).
3.06 (1H, dd, J¼16.8, 1.6 Hz, 5-H
b
d
150.3 (C-11), 149.6 (C-2), 147.8 (C-4), 144.9 (C-13), 143.5 (C-1), 143.1
(C-10),131.7 (C-14a),125.3 (C-15a),120.4 (C-9a),117.9 (C-3),117.8 (C-
12), 114.3 (C-4a), 113.8 (C-13a), 102.7 (C-14), 64.6 (9-CH2), 60.8 (10-
OMe), 60.5 (C-6), 60.4 (1-OMe), 60.3 (11-OMe), 60.2 (2-OMe), 56.4
(C-15), 49.4 (C-9), 41.6 (NMe), 28.8 (C-5), 9.1 (3-Me), 9.0 (12-Me);
EIMS m/z (%) 512 (Mþ, 14), 481 (28), 453 (100), 234 (76); HRMS m/z
512.2160 (Mþ, calcd for C27H32N2O8, 512.2159).
3.2.2. (5S*,6S*,9R*,15R*)-(1,5,6,7,9,10,13,15-Octahydro-5-hydroxy-
2,11-dimethoxy-3,12,16-trimethyl-1,4,7,10,13-pentaoxo-6,15-imino-
4H-isoquino[3,2-b][3]-benzazocin-9-yl)methyl (2Z)-methyl-2-
butenoate (16). Without water: A suspension of 15 (10.6 mg,
0.019 mmol) and SeO2 (21.0 mg, 0.186 mmol) in dioxane (2.5 mL)
was stirred at 80 ꢁC for 8 h. The reaction mixture was filtered and
the filter cake was washed with ethyl acetate (20 mL). The com-
bined filtrates were concentrated in vacuo to give a residue. Flash
column chromatography on silica gel (4 g) with hexaneeethyl
acetate¼1:1 afforded 16 (5.8 mg, 53.2%) as a dark red film and
starting material 15 (2.7 mg, 25.5% recovery).
With water: A suspension of 15 (7.3 mg, 0.013 mmol) and SeO2
(7.2 mg, 0.065 mmol) in dioxane (2.0 mL) and water (0.2 mL) was
stirred at 80 ꢁC for 6 h. The reaction mixture was filtered and the
filter cake was washed with ethyl acetate (20 mL). The combined
filtrates were concentrated in vacuo to give a residue (10.6 mg).
Flash column chromatography on silica gel (7 g) with hexaneeethyl
acetate¼1:1 afforded 16 (5.3 mg, 71.0%) as a dark red film and
starting material 15 (1.0 mg, 14.0% recovery).
3.1.5. (6S*,9R*,15R*)-5,6,9,15-Tetrahydro-9-hydroxymethyl-3,12,16-
trimethyl-2,11-dimethoxy- 6,15-imino-4H-isoquino[3,2-b][3]-benza-
zocine-1,4,7,10,13-pentone (9). A solution of 14 (7.5 mg,14.6 mmol) in
10 N HNO3 (0.5 mL) was stirred at 25 ꢁC for 10 min. The reaction
mixture was diluted with water (5 mL) and extracted with ethyl
acetate (20 mLꢃ3). The combined extracts were washed with brine
(20 mL), dried, and concentrated in vacuo. The residue (7.6 mg) was
subjected to purification by silica gel chromatography with ethyl
acetate to give 9 (6.3 mg, 90.0%) as a darkpurple amorphous powder.
IR (KBr) 3343, 2926, 2855, 1683, 1653, 1616, 1568, 1558, 1456,
1373, 1308, 1234, 1227, 1153 cmꢂ1 1H NMR (CDCl3, 500 MHz)
;
d
6.26 (1H, s, 14-H), 5.96 (1H, dd, J¼7.1, 4.5 Hz, 9-H), 4.55 (1H, s, 15-
H), 4.02 (3H, s, OMe), 3.97 (3H, s, OMe), 3.74 (1H, dt, J¼6.5, 1.5 Hz,
6-H), 3.50 (1H, dd, J¼11.4, 4.5 Hz, 9-CH), 3.36 (1H, dd, J¼11.4,
7.1 Hz, 9-CH), 2.96 (1H, dd, J¼19.8, 6.5 Hz, 5-H
a), 2.89 (1H, dd,
b), 2.51 (3H, s, NMe), 1.96 (3H, s, 12-Me), 1.94
J¼19.8, 1.5 Hz, 5-H
(3H, s, 3-Me), 1.62 (1H, br s, OH); 13C NMR (CDCl3, 125 MHz)
186.6 (C-4), 185.0 (C-13), 180.5 (C-10), 180.5 (C-1), 168.7 (C-7),
IR (KBr) 3446, 2930, 2857, 1654, 1616, 1570, 1456, 1341, 1307,
d
1233, 1211, 1153 cmꢂ1; 1H NMR (CDCl3, 500 MHz)
d 6.28 (1H, s, 14-
156.0 (C-11), 155.4 (C-2), 140.7 (C-14a), 140.0 (C-4a), 136.5 (C-15a),
134.5 (C-13a), 129.1 (C-3), 127.6 (C-12), 125.0 (C-9a), 101.8 (C-14),
62.9 (9-CH2), 61.1 (OMe), 61.0 (OMe), 59.6 (C-6), 54.4 (C-15), 48.4
(C-9), 41.2 (NMe), 28.7 (C-5), 8.8 (ArMe), 8.7 (ArMe); Positive
FABMS m/z 481 [Mþþ1], HRFABMS m/z 481.1623 ([MþH]þ, calcd
for C25H25N2O8, 481.1611).
H), 6.09 (1H, dd, J¼6.0, 2.9 Hz, 9-H), 5.93 (1H, qq, J¼7.3, 1.5 Hz, 20-
H), 4.86 (1H, dd, J¼7.0, 1.7 Hz, 5-H), 4.52 (1H, d, J¼1.1 Hz, 15-H), 4.19
(1H, dd, J¼12.0, 5.9 Hz, 9-CH), 4.06 (3H, s, 11-OMe), 4.01 (3H, s, 2-
OMe), 3.99 (1H, dd, J¼12.0, 2.9 Hz, 9-CH), 3.75 (1H, dd, J¼1.7,
1.1 Hz, 6-H), 2.88 (1H, d, J¼7.0 Hz, OH), 2.55 (3H, s, NMe),1.96 (3H, s,
12-Me), 1.93 (3H, s, 3-Me), 1.75 (3H, dq, J¼7.3, 1.5 Hz, 20-Me), 1.57
(1H, quint, J¼1.5 Hz, 19-Me); 13C NMR (CDCl3, 125 MHz)
d 186.7 (C-
3.2. Oxidative demethylation of 13 in two steps
4), 184.7 (C-13), 181.0 (C-10), 180.0 (C-1), 167.1 (C-18), 163.9 (C-7),
156.1 (C-11), 155.4 (C-2), 139.3 (C-20), 138.4 (C-4a), 138.3 (C-13a),
136.9 (C-15a), 134.3 (C-14a), 128.8 (C-3), 127.4 (C-12), 126.7 (C-19),
124.8 (C-9a), 102.2 (C-14), 67.1 (C-6), 64.8 (C-5), 62.3 (C-16), 61.1
(11-OMe), 61.0 (2-OMe), 54.7 (C-15), 47.2 (C-9), 41.5 (NMe), 20.2 (C-
22), 15.5 (C-21), 8.7 (3-Me), 8.7 (12-Me); EIMS m/z (%) 578 (Mþ, 5),
465 (17), 438 (24), 437 (100), 422 (12), 421 (49), 234 (12), 218 (20);
HREIMS m/z 578.1899 (Mþ, calcd for C30H30N2O10, 578.1900).
Partial O-demethylation of 13 (21.6 mg, 0.04 mmol) in CH2Cl2
(2.4 mL) with a CH2Cl2 solution of BBr3 (1 M, 240 mL, 0.24 mmol) as
described above afforded a residue (16.6 mg). A solution of the
residue in 10 N HNO3 (0.5 mL) was stirred at 25 ꢁC for 30 min to give
9 (10.5 mg, 55%) in two steps.
3.2.1. (6S*,9R*,15R*)-(1,5,6,7,9,10,13,15-Octahydro-2,11-dimethoxy-
3,12,16-trimethyl-1,4,7,10,13-pentaoxo-6,15-imino-4H-isoquino[3,2-
b][3]-benzazocin-9-yl)methyl (2Z)-methyl-2-butenoate (15). A solu-
tion of angelic acid (60.1 mg, 0.60 mmol) in ether (3.0 mL) was cooled
3.2.3. (6S*,9R*,15R*)-(1,6,7,9,10,13,15-Heptahydro-2,11-dimethoxy-
3,12,16-trimethyl-1,4,5,7,10,13-hexaoxo-6,15-imino-4H-isoquino[3,2-
b][3]-benzazocin-9-yl)methyl (2Z)-methyl-2-butenoate (17). A 0.3 M
dichloromethane solution of DMP (0.35 mL, 0.104 mmol) was
added to a stirred solution of 16 (5.1 mg, 0.0088 mmol) in CH2Cl2
(1.0 mmol) at 25 ꢁC within 1 min, and the mixture was stirred at
25 ꢁC for 3 h. The reaction mixture was diluted with 5% aqueous
NaHCO3 solution (10 mL) and extracted with CHCl3 (10 mLꢃ3). The
combined extracts ware washed with brine (10 mL), dried, and
concentrated in vacuo to give a residue in the form of a dark red oil.
IR (KBr) 2924, 2855, 1724, 1683, 1653, 1570, 1294, 1263, 1228,
with iced waterand a solution of oxalyl chloride(50.6
mL, 0.59 mmol)
in DMF (4.6 L, 59.2 mmol) was added dropwise over 5 min. The
m
resulting solution was stirred at 25 ꢁC for 2 h and then a solution of 9
(14.2 mg, 0.030 mmol) in CH2Cl2 (1.5 mL) was added over 5 min. The
reaction mixture was concentrated to approximately 0.3 mL with
a stream of argon and CH2Cl2 (0.8 mL) was then added. The resulting
mixture was stirred at 25 ꢁC for 21 h. The reaction mixture was
purified by silica gel chromatography with hexaneeethyl
acetate¼1:2 to afford 15 (13.9 mg, 84%) as a dark purple film.
IR (KBr) 2949, 1683, 1653, 1570, 1560, 1458, 1340, 1310, 1229,
1209, 1153 cmꢂ1 1H NMR (CDCl3, 500 MHz)
; d 6.34 (1H, s, 14-H),
6.19 (1H, dd, J¼6.1, 2.8 Hz, 9-H), 5.91 (1H, qq, J¼7.1, 1.5 Hz, 20-H),
1153 cmꢂ1; 1H NMR (CDCl3, 500 MHz)
d 6.24 (1H, s, 14-H), 6.12 (1H,
4.75 (1H, d, J¼1.4 Hz, 15-H), 4.30 (1H, dd, J¼12.2, 6.1 Hz, 9-CH), 4.07

9192
M. Yokoya et al. / Tetrahedron 67 (2011) 9185e9192
(3H, s,11-OMe), 4.04 (1H, d, J¼1.4 Hz, 6-H), 4.03 (3H, s, 2-OMe), 3.96
(1H, dd, J¼12.2, 2.8 Hz, 9-CH), 2.54 (3H, s, NMe), 1.97 (3H, s, 12-Me),
1.95 (3H, s, 3-Me), 1.71 (3H, dq, J¼7.3, 1.5 Hz, 20-Me), 1.54 (1H,
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tet.2011.09.076.
quint, J¼1.5 Hz, 19-Me); 13C NMR (CDCl3, 125 MHz)
d 184.8 (C-5),
184.5 (C-13), 183.5 (C-4), 182.1 (C-1), 179.9 (C-10), 167.3 (C-18),
159.9 (C-7), 156.2 (C-11), 155.0 (C-2), 146.4 (C-15a), 139.2 (C-20),
136.6 (C-14a), 134.0 (C-13a), 130.0 (C-3), 127.4 (C-12), 126.7 (C-19),
125.2 (C-4a), 125.0 (C-9a), 103.0 (C-14), 73.0 (C-6), 62.3 (C-16), 61.2
(11-OMe), 60.9 (2-OMe), 55.9 (C-15), 47.9 (C-9), 41.2 (NMe), 20.1 (C-
22), 15.4 (C-21), 8.9 (3-Me), 8.7 (12-Me); EIMS m/z 466 (Mþꢂ100,
21), 465 (75), 438 (25), 437 (100), 234 (14); HRFABMS m/z 577.1830
(Mþþ1, calcd for C30H29N2O10, 577.1822), 437.1352 (calcd for
C23H21N2O7, 437.1349), 234.0769 (calcd for C12H12NO4, 234.0766).
References and notes
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3.3. Synthesis of ( )-cribrostatin 4 (1)
A 0.3 M CH2Cl2 solution of DMP (0.31 mL, 0.092 mmol) was
added to a stirred solution of 16 (5.0 mg, 0.0087 mmol) in
dichloromethane (1.0 mmol) at 25 ꢁC within 1 min, and the mixture
was stirred at 25 ꢁC for 3 h. After the reaction mixture was diluted
with THF (5 mL), saturated aqueous Na2S2O3 solution (5 mL) was
added. The mixture was stirred vigorously at 25 ꢁC for 2 h. The
reaction mixture was diluted with water (10 mL) and extracted
with ethyl acetate (10 mLꢃ3). The combined extracts were washed
with brine (10 mL), dried, and concentrated in vacuo. The residue
(25.2 mg) was purified by silica gel (9 g) flash column chroma-
tography with hexaneeethyl acetate¼1:2 to afford cribrostatin 4
(1: 4.2 mg, 84.0%) as a dark red film.
14. Fontana, A.; Cavaliere, P.; Wahidulla, S.; Naik, C. G.; Cimino, G. Tetrahedron
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16. For simplicity, natural product numbering was used in this manuscript, but
IR (KBr) 3429, 2930, 2857, 2851, 1697, 1649, 1558, 1458, 1416,
IUPAC numbering was used in the Experimental.
1379, 1342, 1292, 1229, 1209, 1155, 1126, 1088, 845, 750 cmꢂ1 1H
;
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NMR (CDCl3, 500 MHz) d 11.35 (1H, s, 4-OH), 6.26 (1H, s, 14-H), 6.20
(1H, dd, J¼6.2, 3.1 Hz, 9-H), 5.91 (1H, qq, J¼7.1, 1.4 Hz, 20-H), 5.59
(1H, s, 1-OH), 4.87 (1H, d, J¼1.1 Hz, 15-H), 4.11 (1H, d, J¼1.1 Hz, 6-H),
4.06 (1H, dd, J¼12.0, 6.2 Hz, 9-CH), 4.06 (3H, s, 11-OMe), 3.86 (3H, s,
2-OMe), 3.83 (1H, dd, J¼12.0, 3.1 Hz, 9-CH), 2.57 (3H, s, NMe), 2.16
(3H, s, 3-Me), 1.95 (3H, s, 12-Me), 1.75 (3H, dq, J¼7.1, 1.4 Hz, 20-Me),
19. Saito, N.; Sakai, H.; Takai, R.; Muranaka, M.; Itabashi, M.; Kubo, A.; Yazawa, K.;
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2001, 55, 21e28.
1.47 (1H, quint, J¼1.4 Hz, 19-Me); 13C NMR (CDCl3, 125 MHz)
d 192.7
22. Chan, C.; Heid, R.; Zheng, S.; Guo, J.; Zhou, B.; Furuuchi, T.; Danishefsky, S. J. J.
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(C-5), 185.0 (C-13), 179.9 (C-10), 166.8 (C-18), 161.1 (C-7), 156.4 (C-
11), 156.3 (C-4), 153.2 (C-2), 139.8 (C-13a), 139.3 (C-20), 138.1 (C-1),
134.6 (C-9a), 127.1 (C-12), 126.6 (C-19), 124.2 (C-14a), 119.8 (C-15a),
119.1 (C-3), 108.6 (C-4a), 100.0 (C-14), 72.5 (C-6), 62.1 (C-16), 61.2
(2-OMe), 61.1 (11-OMe), 56.2 (C-15), 46.9 (C-9), 41.3 (NMe), 19.9 (C-
22), 15.4 (C-21), 9.0 (3-Me), 8.6 (12-Me); EIMS m/z (%) 578 (Mþ, 3),
465 (10), 438 (25), 437 (100), 234 (12); HREIMS m/z 578.1902 (Mþ,
calcd for C30H30N2O10, 578.1900).
23. Vincent, G.; Williams, R. M. Angew. Chem., Int. Ed. 2007, 46, 1517e1520; Corri-
gendum: Vincent, G.; Williams, R. M. Angew. Chem., Int. Ed. 2011, 50, 8458.
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ꢀ
~
30. Gonzalez, J. F.; de la Cuesta, E.; Avendano, C. Synth. Commun. 2004, 34,1589e1597.
31. Epimerization of 1,3-disubstituted tetrahydroisoquinoline derivatives by DBU
has been studied in the synthesis of ecteinascidin 743.30,31
4. Cell growth inhibition assay (IC50
)
A single-cell suspension (2ꢃ103 cells/well) was added to serially
diluted test compounds in a microplate. The cells were then cul-
tured for 4 days. Cells were enumerated with a cell counting kit
(DOJINDO, Osaka, Japan). IC50 was expressed as the concentration
at which cell growth was inhibited by 50% compared with the
untreated control.
32. Herberich, B.; Kinugawa, M.; Vazquez, A.; Williams, R. M. Tetrahedron Lett. 2001,
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34. Oxidative demethylation of 13 with 6.0 equiv of BBr3 gave 14 in 35% yield
and starting material 13 (4%). This transformation was unsuccessful when
less than 5.0 equiv of BBr3 was used, affording an inseparable mixture of
mono demethylated products along with a large amount of the starting
material.
35. The mechanism of the selective demethylation of 13 is unclear. Neverthe-
less, we have reported that the partial demethylation of 18 with BBr3 (2
equiv) at ꢂ78 ꢁC afforded phenol 19 (72%), the structure of which was
confirmed by X-ray crystallographic analysis (Scheme 4). See Saito, N.;
Ohira, Y.; Aihara, T.; Harada, S.; Shida, Y.; Kubo, A. Tetrahedron 1994, 50,
3915e3928.
36. The DNP oxidation method was first introduced by Danishefsky and co-
workers in their first synthesis of 1,22 and was subsequently adopted in our
conversion of saframycin G into saframycin F and renieramycin Ointo renier-
amycin Q.37
Acknowledgements
This work is supported by a Grant-in Aid (No. 23590019) for
Scientific Research from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT), Japan. This work is also partially
supported by the Japan Society for the Promotion of Science (JSPS)
Asia-Africa Science Platform Program (2010-2012) and a grant from
the High-Tech Research Center Project, MEXT, Japan (S0801043).
We are grateful to Dr. Takuo Tsukuda (Chugai Pharmaceutical
Company, Kamakura Research Center) for conducting the cytotox-
icity assay.
37. Saito, E.; Daikuhara, N.; Saito, N. Heterocycles 2007, 74, 411e420.
38. As far as we know, there is no report of any spectroscopic data of 17 in the
literature. Because 17 was difficult to isolate in its pure form, its spectroscopic
data were measured after the usual work-up.
39. Wright, B. J. D.; Chan, C.; Danishefsky, S. J. J. Nat. Prod. 2008, 71, 409e414.