Asymmetric total synthesis of three stereoisomers of (-)-renieramycin G and their cytotoxic activities

Article abstract of DOI:10.1016/j.tet.2015.04.064

(-)-Renieramycin G, a marine antitumor natural product, is a typical member of the bis-tetrahydroisoquinoline alkaloid family. In this paper, an efficient protocol of asymmetric total synthesis of its three stereoisomers, (+)-renieramycin G, 11,13-epi-(+)-renieramycin G and 11,13-epi-(-)-renieramycin G was established by the use of a combination of l- and/or d-tyrosine as the starting materials. The preliminary cytotoxicity assays tested on human cancer cell lines revealed that the L-shaped topological configuration of (-)-renieramycin G played a critical role in its cytotoxic activity.

Full text of DOI:10.1016/j.tet.2015.04.064

Tetrahedron 71 (2015) 4296e4303
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Asymmetric total synthesis of three stereoisomers of
(ꢀ)-renieramycin G and their cytotoxic activities
Enming Du, Wenfang Dong, Baohe Guan, Xuan Pan, Zheng Yan, Li Li, Nan Wang,
*
Zhanzhu Liu
State Key Laboratory of Bioactive Substance and Function of Natural Medicines, Institute of Materia Medica, Peking Union Medical College and Chinese
Academy of Medical Sciences, Beijing 100050, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 March 2015
Received in revised form 17 April 2015
Accepted 20 April 2015
Available online 6 May 2015
(ꢀ)-Renieramycin G,
a marine antitumor natural product, is a typical member of the bis-
tetrahydroisoquinoline alkaloid family. In this paper, an efficient protocol of asymmetric total synthe-
sis of its three stereoisomers, (þ)-renieramycin G, 11,13-epi-(þ)-renieramycin G and 11,13-epi-(ꢀ)-re-
nieramycin G was established by the use of a combination of L- and/or D-tyrosine as the starting
materials. The preliminary cytotoxicity assays tested on human cancer cell lines revealed that the L-
shaped topological configuration of (ꢀ)-renieramycin G played a critical role in its cytotoxic activity.
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
(ꢀ)-Renieramycin G
Stereoisomers
Cytotoxicity
Topological configuration
1. Introduction
(ꢀ)-renieramycin G displayed equipotent cytotoxicity activities
against the A549 and HCT-116 cell lines.8a This finding attracted us
The pharmacological activities of chiral drugs depend mainly on
their interaction with drug targets, most of which are also chiral
such as antibodies, enzymes, DNA. The stereoisomers of chiral
drugs, possessing complex three-dimensional structures, may dis-
play different biological and pharmacological activities in chiral
living organisms.1e3 Possessing several chiral centers, bis-
tetrahydroisoquinoline alkaloids such as ecteinascidin 743, safra-
mycin A, renieramycin G, and jorumycin, have attracted consider-
able interest due to their unique structures and potent biological
activities.4e6 Generally, hemiaminal or aminonitrile at C-21 posi-
tion are believed to be the essential functional groups for their
potent biological activities through the formation of covalent bonds
to DNA and possibly other biomacromolecules (Fig. 1).4
to investigate the stereochemical effect on the antitumor activity of
(ꢀ)-renieramycin G, which would be helpful to further understand
the mechanisms of its cytotoxic effect. To date, six total synthesis of
(ꢀ)-renieramycin G have been reported,8e13 but less attention has
However, (ꢀ)-renieramycin G,
tetrahydroisoquinoline alkaloids, still retained moderate cytotox-
icity (MIC: 0.5 and 1.0 g/mL against KB and LoVo cell lines, re-
a typical member of bis-
m
spectively) despite lacking the essential functional groups at C-21
position.7 Interestingly, Williams and co-workers reported that
3-epi-(ꢀ)-jorumycin exhibited an approximate 2e3 orders of
magnitude decrease in the cytotoxicity compared with natural
product (ꢀ)-jorumycin, while 3-epi-(ꢀ)-renieramycin
G and
* Corresponding author. Tel.: þ86 (0)10 6316 5253; fax: þ86 (0)10 6301 7757;
e-mail address: liuzhanzhu@imm.ac.cn (Z. Liu).
Fig. 1. Structures of the bis-tetrahydroisoquinoline alkaloids.
http://dx.doi.org/10.1016/j.tet.2015.04.064
0040-4020/Ó 2015 Elsevier Ltd. All rights reserved.

E. Du et al. / Tetrahedron 71 (2015) 4296e4303
4297
been paid to the synthesis of its stereoisomers. Williams et al. have
firstly developed a convergent asymmetric synthesis of 3-epi-
(ꢀ)-jorumycin and 3-epi-(ꢀ)-renieramycin G.8b Lemaire has re-
ported the synthesis of 3-epi-pentacyclic framework using bis-
(þ)/(ꢀ)-3 with TBSCl and imidazole in DMF. The absolute stereo-
chemistry of the C-1 carbon of (þ)/(ꢀ)-2a/2b was determined by
their NOESY spectra.
A strong correlation was observed between C-1 H and C-3 H in
NOESY thus indicating a cis relationship of the C-1 H and C-3 H in
compounds (þ)/(ꢀ)-2a. In contrast, the NOE effect between C-1 H
and C-3 H in the trans isomer (þ)/(ꢀ)-2b was absent (Scheme 2).
The absolute configurations of compounds (þ)/(ꢀ)-2a/2b were
further confirmed through their circular dichroism (CD) spectra,
which showed perfect mirror images, respectively (Fig. 2).
tetrahydroisoquinoline as
a
key intermediate.14 In addition,
Saito12 and Fukuyama15 have described the synthesis of 1-epi-
pentacyclic framework.
Previously, we reported an efficient approach to asymmetrically
synthesize the bis-tetrahydroisoquinoline alkaloids including
(ꢀ)-renieramycin G, (ꢀ)-saframycin A, and (ꢀ)-jorumycin and their
analogs using L
-tyrosine as the chiral starting material.10 Appar-
ently, this methodology can be extended to the synthesis of the
stereoisomers of the bis-tetrahydroisoquinoline alkaloids simply by
the combinatorial use of L- and/or D-tyrosine as the chiral starting
materials (Scheme 1). It should be noted that although there would
theoretically exist eight pairs of stereoisomers of (ꢀ)-renieramycin
G, which bears four chiral centers, four pairs could actually be
achieved since the intramolecular PicteteSpengler reaction affor-
ded solely the 11,13-cis-diastereomer as is required by the rigidity
of the pentacyclic skeleton. Herein we would report the synthesis
and cytotoxicity of three stereoisomers of (ꢀ)-renieramycin G,
namely (þ)-renieramycin G, 11,13-epi-(þ)-renieramycin G, and
11,13-epi- (ꢀ)-renieramycin G. Furthermore, the preliminary ste-
reochemical effect on the antitumor activity of the renieramycin G
isomers was disclosed.
ꢀ
Scheme 2. Synthesis of compounds (þ)/(ꢀ)-3: (i) BnOCH2CHO, HOAc, 4 A M.S., CH2Cl2/
TFE (7:1), 0 ꢁC, 7 h; (ii) TBSCl, imidazole, DMF, rt, 12 h.
Fig. 2. CD spectra of compounds (þ)/(ꢀ)-2a/2b.
2.2. Synthesis of the pentacyclic skeletons (D)/(L)-6a/6b
Tyrosine derivatives (þ)/(ꢀ)-4 were obtained as illustrated in
our previous synthesis of (ꢀ)-renieramycin G.10a Condensation of
tetrahydroisoquinoline precursors (þ)/(ꢀ)-3 with tyrosine de-
rivatives (þ)/(ꢀ)-4 in the presence of BOPCl and Et3N gave four
chiral amides (þ)/(ꢀ)-5a/5b. Subsequent deprotection of the TBS
ethers followed by oxidation with DesseMartin periodinane and
then removal of the aryl TBS group with TBAF gave the cyclization
precursors. Transformation of the cyclization precursors into
pentacyclic frameworks was achieved by the intramolecular Pic-
teteSpengler condensation reaction. Treatment of the cyclization
precursors with trifluoromethanesulfonic acid (TFSA) afforded the
corresponding pentacyclic frameworks (þ)/(ꢀ)-6a/6b as single
stereoisomers (Scheme 3).10
2.3. Synthesis of the stereoisomers of (L)-renieramycin G
Scheme 1. Retro-synthesis of (ꢀ)-renieramycin G10a and the synthesis of its three
stereoisomers by the combinatorial use of L- and/or D-tyrosine as the chiral starting
materials.
With the pentacyclic frameworks (þ)/(ꢀ)-6a/6b in hand, ef-
forts were then directed toward the synthesis of the stereoisomers
of (ꢀ)-renieramycin G. Reductive methylation of compounds
(þ)/(ꢀ)-6a and (þ)-6b with 37% aqueous formaldehyde solution
and sodium cyanoborohydride in the presence of acetic acid gave
compounds (þ)/(ꢀ)-7a and (þ)-7b, respectively, which were
subsequently subjected to catalytic hydrogenation via H2 (50 psi)
and Pd(OH)2/C to afford alcohols (þ)/(ꢀ)-8a and (þ)-8b. Salcomine
oxidation of (ꢀ)-8a gave quinone 9 in 71% yield. Acylation of the
primary alcohol group with angelic acid was achieved under mild
Yamaguchi conditions to afford the stereoisomer of 11,13-epi-
(ꢀ)-renieramycin G in 59% yield. In order to improve the synthetic
efficiency of the last two steps, we adopted a different sequence
2. Results and discussion
2.1. Synthesis of 1,3-cis-tetrahydroisoquinoline (D)/(L)-2a
The synthetic routes basically followed our previously reported
procedures.10 In this work, 1,3-cis-tetrahydroisoquinoline
(þ)/(ꢀ)-2a, prepared from
L or D-tyrosine was used to synthesize
the three stereoisomers of (ꢀ)-renieramycin G. The highly dia-
stereoselective PicteteSpengler cyclization reaction afforded a pair
of diastereomers (2a/2b¼7:1). Tetrahydroisoquinolines (þ)/(ꢀ)-2a
were then transformed into the corresponding TBS ethers

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E. Du et al. / Tetrahedron 71 (2015) 4296e4303
Coupling partners
product
Coupling partners
product
(+)-3 (–)-4
(–)-3 (+)-4
(–)-3 (–)-4
(+)-3 (+)-4
Scheme 3. Synthesis of pentacyclic frameworks (þ)/(ꢀ)-6a/6b: (i) BOPCl, Et3N, CH2Cl2, rt, 72 h, 86%; (ii) HCOOH, H2O, THF, rt, 10 h, 90%; (iii) DesseMartin periodinane, CH2Cl2, rt,
2 h, 91%; (iv) TBAF, THF, 0 ꢁC, 1 h, 90%; (v) TFSA, rt, 2 h, 80%.
for the synthesis of the other two stereoisomers, namely con-
verting alcohols 8 into the angelica esters before oxidation of the
phenol units. Thus, selective acylation of alcohols (þ)-8a/8b with
angelic acid, followed by oxidation, gave the stereoisomers 11,13-
stable configuration of the natural product (ꢀ)-renieramycin G and
the synthetic isomer 11,13-epi-(þ)-renieramycin G was optimized
by DFT calculations. It showed that the topological configuration of
the pentacyclic skeleton of (þ)/(ꢀ)-renieramycin G was L-shaped
while that of 11,13-epi-isomers are S-shaped (Fig. 4). It is thus
reasonable to believe that the decrease of 11,13-epi-isomers in their
cytotoxic activities might be attributed to the changes of topolog-
ical configuration of the pentacyclic skeleton from the L-shaped to
the S-shaped. Interestingly, a similar study of Williams’ group
found that the antiproliferative activities of (ꢀ)-renieramycin G and
3-epi-(ꢀ)-renieramycin G against HCT-116 and A549 cancer cell
lines were nearly the same. It is in full agreement with our con-
clusion in that the L-shaped topological configuration of 3-epi-
(ꢀ)-renieramycin G remained almost unchanged despite the C-3
epimerization, which was proved by the X-ray analysis.8
epi-(þ)-renieramycin
G
and (þ)-renieramycin G, respectively
(Scheme 4). CD spectra were used to determine the absolute
configurations of (ꢀ)-renieramycin G and its three stereoisomers.
As expected for the two pairs of enantiomers, the CD traces
exhibited excellent mirror-image relationships, respectively
(Fig. 3). The measured optical rotations for the two pairs of
(þ)/(ꢀ)-renieramycin
G
and 11,13-epi-(þ)/(ꢀ)-renieramycin
G
were found to be close to each other in the absolute value but with
opposite signs.
2.4. Biological evaluations
The cytotoxicity of (ꢀ)-renieramycin G and its three stereoiso-
mers against the HCT-8, HELA, A549, KB, BGC-803 cell lines were
tested by the standard MTT method (Table 1). Preliminary results
indicated that (þ)-renieramycin G possessed similar cytotoxicity to
that of the natural product (ꢀ)-renieramycin G. The pair of 11,13-
epi-isomers were substantially less cytotoxic and, particularly,
11,13-epi-(þ)-renieramycin G showed nearly no cytotoxic effects,
which implied the importance of the stereochemistry factor for the
antitumor activity of these renieramycin G stereoisomers. The
3. Conclusions
In summary, a systematic and efficient protocol was established
for the synthesis of the stereoisomers of (ꢀ)-renieramycin G
through the combinatorial use of L- and/or D-tyrosine as the chiral
starting materials. The utility was illustrated by the total asym-
metric synthesis of three stereoisomers of (ꢀ)-renieramycin G,
namely (þ)-renieramycin G, 11,13-epi-(ꢀ)-renieramycin G, and
11,13-epi-(þ)-renieramycin G. This methodology could also be

E. Du et al. / Tetrahedron 71 (2015) 4296e4303
4299
Scheme 4. Reagents and conditions: (i) HCHO, NaBH3CN, HOAc, CH3OH, rt, 2 h; (ii) H2 (50 psi), Pd(OH)2/C, CH3OH, 12 h; (iii) salcomine, CH3CN, rt, 2 h; (iv) angelic acid, 2,4,6-
trichlorobenzoyl chloride, Et3N, toluene, 90 ꢁC, 12 h.
Fig. 4. The stable conformers for (ꢀ)-renieramycin G and 11,13-epi-(þ)-renieramycin G
were optimized by DFT calculations.
Fig. 3. CD traces of (þ)/(ꢀ)-renieramycin G and 11,13-epi-(þ)/(ꢀ)-renieramycin G.
ꢀ
distilled and dried over 4 A molecular sieves prior to use. Optical
extended to the asymmetric synthesis of other stereoisomers and
analogs of bis-tetrahydroisoquinoline alkaloids. Besides, it was
revealed for the first time that the L-shaped topological configu-
rotations were measured with a PerkinElmer Polarimeter 341LC at
589 nm and 20 ꢁC. High-resolution mass spectra (HRMS) were
obtained on an Agilent LC/MSD TOF or Thermo Exactive Plus
ration of the pentacyclic skeleton was of critical importance for the
spectrometer. 1H NMR and 13C NMR spectra were recorded on
cytotoxicity of renieramycin G stereoisomers.
Varian Mercury 300, Varian Mercury 400, Bruker AV 500 or Varian
INOVA 600 MHz spectrometers as indicated.
4. Experimental section
4.2. (1S,3R)-(D)-2a and (1R,3R)-(D)-2b
4.1. General
To a solution of (þ)-1 (630 mg, 3.0 mmol), HOAc (0.44 mL,
ꢀ
Unless otherwise stated, solvents and reagents were obtained
from commercial suppliers and used without further purification.
Molecular sieves were activated at 450 ꢁC for 10 h and stored under
nitrogen. Anhydrous CH2Cl2, THF, Et3N, DMF, and toluene were
7.5 mmol), and 4 A molecular sieves (0.60 g) in CH2Cl2/TFE (7:1,
12 mL) at 0 ꢁC was added benzyloxyacetaldehyde (1.0 M in CH2Cl2,
3.3 mL) dropwise over 60 min under argon. The reaction mixture
was then stirred for 6 h at 0 ꢁC and subsequently diluted with
Table 1
Cytotoxic activity of (ꢀ)-renieramycin G and its three stereoisomers
Compounds
IC50
(
m
M) values in indicated cell linesa
HCT-8
HELA
A549
KB
BGC-803
(ꢀ)-Renieramycin G
(þ)-Renieramycin G
11,13-epi-(ꢀ)-Renieramycin G
11,13-epi-(þ)-Renieramycin G
Cisplatin
8.91ꢂ0.43
10.92ꢂ0.57
84.87ꢂ2.76
>100
3.88ꢂ0.32
6.92ꢂ0.34
49.73ꢂ2.32
>100
5.70ꢂ0.27
9.46ꢂ0.43
80.96ꢂ3.38
>100
3.50ꢂ0.15
5.23ꢂ0.23
35.54ꢂ2.75
>100
5.37ꢂ0.36
21.73ꢂ1.51
71.90ꢂ3.55
>100
2.92ꢂ0.33
1.43ꢂ0.15
1.42ꢂ0.03
3.23ꢂ0.30
0.83ꢂ0.05
a
Mean valueꢂSD (standard deviation from three experiments).

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E. Du et al. / Tetrahedron 71 (2015) 4296e4303
CH2Cl2. The mixture was filtered and the organic phase was washed
with saturated aq NaHCO3, dried, and concentrated in vacuo to give
a residue that was subjected to chromatography on silica gel
(CH2Cl2/MeOH¼100:2) to give (1S,3R)-(þ)-2a as a white solid
temperature and stirred for 72 h. The reaction mixture was
quenched with 1 N aq HCl (20 mL) and diluted with CH2Cl2 (20 mL).
The organic phase was separated, washed with brine (10 mL), dried
over anhydrous Na2SO4, and concentrated in vacuo. The residue
was purified by column chromatography on silica gel (PET/
(750 mg, 73.2%) and (1R,3R)-(þ)-2b (100 mg, 9.7%) as a white solid.
20
(1S,3R)-(þ)-2a: mp 132e134 ꢁC; [
a
]
þ125 (c 2.0, CH3OH); HRMS
EtOAc¼20:1) to afford amide (ꢀ)-5a (13.37 g, 86.0%) as a colorless
D
20
calcd for C20H26NO4 [MþH]þ 344.1856, found 344.1846; 1H NMR
oil. [a
]
ꢀ2.0 (c 0.1, CH3OH); HRMS calcd for C54H88BrN2O9Si3
D
(400 MHz, DMSO-d6):
d
8.65 (s, 1H), 7.42e7.22 (m, 5H), 6.37 (s, 1H),
[MþH]þ 1071.4976, found 1071.4988; 1H NMR (500 MHz, CDCl3):
4.70 (t, J¼4.8 Hz,1H), 4.52 (d, J¼12.4 Hz,1H), 4.47 (d, J¼12.4 Hz,1H),
4.31 (d, J¼6.0 Hz, 1H), 4.13 (dd, J¼8.4, 2.4 Hz, 1H), 3.59 (s, 3H),
3.51e3.38 (m, 2H), 3.38e3.30 (m, 1H), 2.69 (m, 1H), 2.46e2.38 (m,
1H), 2.34e2.24 (m, 1H), 2.14 (s, 3H); 13C NMR (100 MHz, DMSO-d6):
d 7.30e7.16 (m, 5H), 6.63 (s, 1H), 6.57 (s, 1H), 6.23 (m, 1H), 5.57 (s,
1H), 5.25e5.17 (m, 2H), 4.57 (m, 1H), 4.52e4.45 (m, 2H), 4.32 (m,
1H), 3.88 (m, 1H), 3.65 (s, 3H), 3.62 (s, 3H), 3.22 (m, 1H), 3.10 (m,
1H), 2.92 (m, 2H), 2.73 (m, 1H), 2.35 (s, 1H), 2.25 (s, 3H), 2.23 (s, 3H),
1.44 (s, 9H), 1.26 (s, 9H), 1.02 (s, 18H), 0.32 (s, 3H), 0.19 (s, 3H), 0.18
(s, 3H), 0.13 (s, 3H), 0.07 (s, 3H), 0.01 (s, 3H); 13C NMR (125 MHz,
d
146.7, 143.8, 138.7, 132.6, 128.1 (2C), 128.0, 127.3 (2C), 127.2, 121.1,
121.0, 73.9, 72.1, 65.2, 59.9, 53.9, 53.0, 33.0, 15.4.
(1R,3S)-(ꢀ)-2a: [
a
]
20 ꢀ102 (c 3.0, CH3OH).
CDCl3) d 172.5, 171.2, 154.8, 154.5, 148.8, 148.7, 147.8, 145.3, 138.6,
D
20
(1R,3R)-(þ)-2b: mp 179e181 ꢁC; [
a
]
þ0.83 (c 1.2, CH3OH);
132.5, 131.6, 131.3, 128.4, 128.2, 127.4, 127.3, 127.2 124.1, 123.3, 121.9,
119.5, 79.0, 72.9, 70.8, 64.9, 64.7, 60.2, 59.9, 52.6, 51.9, 49.6, 41.4,
37.4, 29.6, 29.4, 28.0, 26.5, 26.2, 25.9 (3C), 25.6 (3C), 18.7, 18.2, 18.1,
16.9, 15.9, ꢀ3.7, ꢀ4.2, ꢀ4.5, ꢀ5.3, ꢀ5.5.
D
HRMS calcd for C20H26NO4 [MþH]þ 344.1856, found 344.1847; 1H
NMR (400 MHz, CD3OD):
d 7.45e7.25 (m, 5H), 6.50 (s, 1H), 4.63 (s,
2H), 4.26 (dd, J¼10.0, 3.2 Hz, 1H), 3.71 (m, 1H), 3.70 (s, 3H), 3.61 (t,
J¼10.4 Hz, 1H), 3.50 (dd, J¼10.4, 3.2 Hz, 1H), 3.42 (dd, J¼10.8, 8.4 Hz,
1H), 3.27 (m, 1H), 2.61 (dd, J¼16.4, 4.4 Hz, 1H), 2.40 (dd, J¼16.4,
4.6. Amide (L)-5b
11.6 Hz,1H), 2.13 (s, 3H); 13C NMR (150 MHz, CD3OD):
d 150.0,146.0,
139.7, 131.4, 129.6, 129.5 (2C), 129.0 (2C), 128.8, 124.9, 115.4, 74.1,
Following the general reaction protocol, (1S,3R)-(þ)-3 (7.50 g,
13.13 mmol) was reacted with BOPCl (4.34 g, 17.08 mmol), Et3N
(4.70 mL, 34.06 mmol), and (R)-(þ)-4 (8.80 g,17.03 mmol) in CH2Cl2
(180 mL), which provided amide (ꢀ)-5b (11.31 g, 80.5%) as a color-
69.6, 66.9, 60.4, 54.7, 48.9, 31.9, 11.6.
20
(1S,3S)-(ꢀ)-2b: [
a
]
ꢀ0.67 (c 1.5, CH3OH).
D
4.3. (1S,3R)-(D)-3
less oil. [
a
]
D
20 ꢀ10.2 (c 1.5, CHCl3); HRMS calcd for C54H88BrN2O9Si3
[MþH]þ 1071.4976, found 1071.4978; 1H NMR (500 MHz, CDCl3):
To a solution of (1S,3R)-(þ)-2a (5.0 g, 15.58 mmol) in anhydrous
DMF (15 mL) were added imidazole (7.93 g,116.62 mmol) and TBSCl
(8.74 g, 58.27 mmol). The reaction mixture was stirred at room
temperature for 24 h. It was then quenched with water and
extracted with EtOAc (40 mLꢃ3). The combined organic phase was
washed with brine, dried over anhydrous Na2SO4, and concentrated
in vacuo to give the crude product. Purification by chromatography
d
7.32e7.16 (m, 5H), 6.63 (s, 1H), 6.59 (s, 1H), 6.09 (dd, J¼6.5, 4.0 Hz,
1H), 5.53 (d, J¼8.5 Hz, 1H), 5.08 (dd, J¼14.0, 9.0 Hz, 1H), 4.55 (d,
J¼12.0 Hz, 1H), 4.37 (d, J¼12.0 Hz, 1H), 3.73e3.67 (m, 2H), 3.64 (s,
3H), 3.62 (s, 3H), 2.99 (dd, J¼13.5, 5.0 Hz, 1H), 2.92e2.85 (m, 1H),
2.76 (dd, J¼13.0, 9.0 Hz, 1H), 2.65 (dd, J¼16.0, 7.0 Hz, 1H), 2.36e2.32
(m, 2H), 2.28 (s, 3H), 2.23 (s, 3H), 1.32 (s, 6H), 1.22 (s, 3H), 1.02 (s,
9H), 0.98 (s, 9H), 0.92 (s, 3H), 0.85 (s, 6H), 0.27 (s, 3H), 0.18 (s, 3H),
0.14 (s, 3H), 0.10 (s, 3H), 0.003 (s, 3H), ꢀ0.043 (s, 3H); 13C NMR
on silica gel (PET/EtOAc¼10:1) give (1S,3R)-(þ)-3 (7.25 g, 87.1%) as
20
a
C
colorless oil.
[
a
]
D
þ58.6 (c 3.8, CHCl3); HRMS calcd for
(125 MHz, CDCl3): d 172.5, 154.5, 149.0, 147.8, 147.4, 145.2, 138.7,
32H54NO4Si2 [MþH]þ 572.3586, found 572.3581; 1H NMR
132.6, 132.0, 130.4, 128.7, 128.3, 127.5, 127.2, 127.1, 124.4, 123.5,
123.3, 121.9, 119.4, 78.7, 72.8, 71.9, 65.6, 60.3, 60.0, 59.8, 52.6, 50.6,
49.1, 41.3, 29.6, 28.2, 26.2 (3C), 25.9 (3C), 25.6 (3C), 18.7, 18.2, 16.9,
15.8, 14.2, ꢀ0.02, ꢀ3.6, ꢀ3.7, ꢀ4.2, ꢀ4.5, ꢀ4.6, ꢀ5.3.
(300 MHz, CDCl3):
d 7.28e7.26 (m, 5H), 6.57 (s, 1H), 4.51 (d,
J¼11.7 Hz, 1H), 4.45 (d, J¼11.7 Hz, 1H), 4.49e4.47 (m, 1H), 4.16 (d,
J¼8.7 Hz, 1H), 3.75e3.68 (m, 2H), 3.62 (s, 3H), 3.62e3.58 (m, 1H),
2.84 (s, 1H), 2.62e2.50 (m, 2H), 2.22 (s, 3H), 0.95 (s, 9H), 0.90 (s,
9H), 0.24 (s, 3H), 0.08 (s, 9H); 13C NMR (125 MHz, CDCl3):
d
147.7,
4.7. General protocol for the preparation of pentacyclic
145.9, 138.7, 133.0, 129.5, 128.2 (2C), 127.6 (2C), 127.3, 125.6, 124.1,
73.4, 73.2, 67.0, 59.9, 54.2, 53.9, 33.3, 26.2 (2C), 25.9 (2C), 25.6, 18.6,
framework (1S,3R,11R,13S)-(D)-6a
18.3, 15.7, ꢀ3.6, ꢀ3.7, ꢀ4.4, ꢀ5.3, ꢀ5.3.
(1) The starting amide (ꢀ)-5a (8.60 g, 8.00 mmol) was dissolved in
THF/HCOOH/H2O (6:3:1, 130 mL) and stirred at room temper-
ature for 10 h. The mixture was then concentrated in vacuo,
dissolved in EtOAc, washed with saturated aq NaHCO3 and
brine, dried over anhydrous Na2SO4, and re-concentrated in
vacuo. Flash chromatography on silica gel (PET/EtOAc¼8:1)
afforded primary alcohol (6.90 g, 89.8%) as a white solid.
(2) To a solution of the primary alcohol (4.10 g, 4.28 mmol) from
the previous step dissolved in CH2Cl2 (100 mL) was added
DesseMartin periodinane (3.20 g, 7.52 mmol). The reaction
mixture was stirred at room temperature for 2 h under argon
and then washed with saturated aq NaHCO3 and brine. The
organic phase was dried over anhydrous Na2SO4 and concen-
trated in vacuo. Flash chromatography on silica gel (PET/
EtOAc¼10:1) afforded the hemiaminal product (3.70 g, 90.5%)
as a white solid.
20
(1R,3S)-(ꢀ)-3: [
a
]
ꢀ47.8 (c 7.4, CHCl3).
D
4.4. (R)-(D)-4
(R)-(þ)-4 was prepared as previously described.10a
[a
]
20 þ12.9 (c
D
10.0, CHCl3); HRMS calcd for C44H72N2O12Si2Br2Na [2MþNa]þ
1057.2883, found 1057.2881; 1H NMR (500 MHz, CDCl3):
d 6.64
(s, 1H), 4.74 (m, 1H), 3.73 (s, 3H), 3.46 (m, 1H), 2.76 (m, 1H), 2.36
(s, 3H), 1.39 (s, 3H), 1.14 (s, 3H), 1.00 (s, 6H), 0.91 (s, 6H), 0.18 (s, 3H),
0.10 (s, 3H); 13C NMR (125 MHz, CDCl3):
d 175.6, 131.4, 121.9, 121.0,
119.3, 81.0, 60.1, 53.5, 41.4, 38.4, 28.2, 27.9, 18.2, 17.9, 16.8, ꢀ3.6,
ꢀ4.6.
20
(S)-(ꢀ)-4: [
a]
ꢀ9.4 (c 1.2, CH3OH).10a
D
4.5. Amide (L)-5a
(3) To a solution of the hemiaminal product (1.83 g, 1.91 mmol) in
THF (40 mL) at 0 ꢁC was added TBAF (1.0 M in THF, 5.73 mL). The
reaction mixture was stirred at 0 ꢁC for 1 h and then quenched
with saturated aq NH4Cl and extracted with EtOAc (40 mLꢃ3).
The combined organic phase was washed with brine, dried
To a solution of (1S,3R)-(þ)-3 (8.30 g, 14.50 mmol) in anhydrous
CH2Cl2 (200 mL) were added Et3N (5.20 mL, 37.70 mmol), and (S)-
(ꢀ)-4 (9.74 g, 18.85 mmol), followed by BOPCl (4.80 g, 18.85 mmol)
in two batches. The resulting mixture was then warmed to ambient

E. Du et al. / Tetrahedron 71 (2015) 4296e4303
4301
over anhydrous Na2SO4, and concentrated in vacuo to provide
the crude product. Flash chromatography on silica gel (PET/
EtOAc¼1:1) afforded the cyclization precursor (1.25 g, 89.9%) as
a white solid.
(1S,3R,11R,13S)-(þ)-7a (414 mg, 94.8%) as a white solid. Mp
20
138e140 ꢁC;
[a
]
þ153.0 (c 0.1, CH3OH); HRMS calcd for
D
C
25H30BrN2O6 [MþH]þ 533.1282, found 533.1282; 1H NMR
(500 MHz, CDCl3):
d
6.52 (s, 1H), 5.20 (s, 1H), 4.34 (s, 1H), 4.17 (s,
(4) To a solution of the cyclization precursor (970 mg, 1.33 mmol),
under argon, was added trifluoromethanesulfonic acid (8 mL).
The reaction mixture was stirred for 2 h at room temperature
and quenched with saturated aq NaHCO3 and extracted with
EtOAc (20 mLꢃ3). The combined organic phase was washed
with brine, dried over anhydrous Na2SO4, and concentrated in
vacuo. The residue was purified by column chromatography on
1H), 3.99 (d, J¼11.0 Hz, 1H), 3.90 (d, J¼5.5 Hz, 1H), 3.79 (dd, J¼11.5,
4.0 Hz, 1H), 3.71 (s, 3H), 3.65 (s, 3H), 3.35 (t, J¼13.0 Hz, 1H), 3.21 (d,
J¼11.5 Hz, 1H), 2.98e2.88 (m, 2H), 2.80 (d, J¼14.5 Hz, 1H), 2.45 (s,
3H), 2.32 (s, 3H), 2.25 (s, 3H); 13C NMR (125 MHz, CDCl3):
d 173.6,
145.7,145.0,144.2,144.1,133.5,130.2,129.0,128.0,121.7,121.3,119.5,
117.7, 68.1, 62.5, 61.2, 60.7, 60.1, 58.7, 56.1, 39.3, 36.8, 26.2, 16.6, 15.7.
(1R,3S,11S,13R)-(ꢀ)-7a: [
a
]
20 ꢀ148.2 (c 53.9, CH2Cl2).
D
silica gel (CH2Cl2/CH3OH¼100:2) to afford (1S,3R,11R,13S)-
20
(þ)-6a (550 mg, 79.6%) as a white solid. Mp 183e185 ꢁC; [
a]
D
4.10. (1S,3R,11S,13R)-(D)-7b
þ198 (c 0.5, CH3OH); HRMS calcd for C24H28BrN2O6 [MþH]þ
519.1125, found 519.1125; 1H NMR (500 MHz, DMSO-d6):
d 9.20
Following the general reaction protocol (1S,3R,11S,13R)-(þ)-6b
(500 mg, 0.97 mmol) was reacted with HCHO (37%, 5.18 mL),
NaBH3CN (612 mg, 9.71 mmol), and HOAc (9.29 mL) in CH3OH
(47 mL). Workup and purification afforded (1S,3R,11S,13R)-(þ)-7b
(s, 1H), 8.79 (s, 1H), 6.47 (s, 1H), 5.00 (s, 1H), 4.41 (dd, J¼8.5,
5.0 Hz, 1H), 4.32 (s, 1H), 4.20 (ddd, J¼11.0, 4.5, 2.5 Hz, 1H), 3.78
(s, 1H), 3.58 (s, 3H), 3.55 (s, 3H), 3.32e3.29 (m, 1H), 3.21 (t,
J¼13.0 Hz, 1H), 2.94 (d, J¼11.5 Hz, 1H), 2.77e2.73 (m, 2H), 2.60
(d, J¼13.0 Hz, 1H), 2.22 (s, 3H), 2.16 (s, 3H); 13C NMR (125 MHz,
(460 mg, 89.6%) as a white solid. Mp 155e157 ꢁC; [
a
]
20 þ55.7 (c 5.3,
D
CH2Cl2); HRMS calcd for C25H30BrN2O6 [MþH]þ 533.1282, found
533.1292; 1H NMR (400 MHz, CDCl3):
d 6.51 (s, 1H), 6.17 (s, 1H), 6.05
DMSO-d6):
d 174.8, 145.9, 145.1, 144.7, 144.2, 134.9, 129.3, 128.1,
127.0, 120.4, 119.9, 115.7, 61.9, 61.0, 60.5, 59.9, 54.8, 54.6, 53.6,
49.5, 36.3, 32.2, 16.2, 15.3.
(s, 1H), 5.79e5.73 (m, 1H), 4.31 (s, 1H), 4.04 (d, J¼12.0 Hz, 1H),
3.81ee3.72 (m, 7H), 3.46 (m, 1H), 3.38 (m, 1H), 3.12e2.96 (m, 3H),
2.42 (s, 3H), 2.39 (m, 1H), 2.37 (s, 3H), 2.25 (s, 3H); 13C NMR
20
(1R,3S,11S,13R)-(ꢀ)-6a: [
a]
ꢀ171.2 (c 2.6, CH3OH).
(150 MHz, CDCl3):
d 172.7, 145.7, 145.5, 144.2, 143.9, 133.2, 130.8,
D
129.7, 129.5, 120.9 (2C), 118.2, 118.1, 68.2, 61.3, 60.7, 60.0, 58.9, 55.3,
52.7, 39.9, 31.8, 31.1, 16.8, 15.7.
4.8. (1S,3R,11S,13R)-(D)-6b
Following general protocol for step 1, the starting amide (ꢀ)-5b
(7.40 g, 6.92 mmol) dissolved in THFeHCOOHeH2O (6:3:1, 110 mL)
and stirred at room temperature for 10 h. Workup and purification
provided the pure alcohol (5.63 g, 84.9%) as a white solid.
Following the general protocol for step 2, the primary alcohol
(5.20 g, 5.43 mmol) was dissolved in CH2Cl2 (130 mL) and reacted
with DesseMartin periodinane (4.03 g, 9.50 mmol) for 2 h. Workup
and purification provided the hemiaminal product (4.31 g, 83.0%) as
a white solid.
Following the general protocol for step 3, the hemiaminal
product (2.10 g, 2.20 mmol) was dissolved in THF (46 mL) and
reacted with TBAF (1.0M in THF, 6.58 mL) for 1 h. Workup as in
general procedure afforded the cyclization precursor (1.45 g, 90.6%)
as a white solid.
4.11. (1S,3R,11R,13S)-(D)-8a
A solution of (1S,3R,11R,13S)-(þ)-7a (361 mg, 0.68 mmol) in
CH3OH (30 mL), HOAc (2.0 mL), and Pd(OH)2 (moist, Pd content
20%, 340 mg) were placed in a Parr apparatus. The vessel was filled
with hydrogen gas at 50 psi and the reaction mixture was vigor-
ously stirred for 10 h at room temperature. The mixture was filtered
and concentrated in vacuo. The residue was dissolved in EtOAc,
washed with saturated aq NaHCO3 and brine, dried over anhydrous
Na2SO4, and re-concentrated in vacuo. The crude product was pu-
rified by column chromatography on silica gel (PET/EtOAc¼1:2) to
afford (1S,3R,11R,13S)-(þ)-8a (287 mg, 93.2%) as a white solid. Mp
20
244e246 ꢁC;
C
[
a
]
D
þ115.0 (c 0.1, CH3OH); HRMS calcd for
25H31N2O6 [MþH]þ 455.2177, found 455.2190; 1H NMR (500 MHz,
Following the general protocol for step 4, the cyclization pre-
cursor (1.20 g, 1.65 mmol) was treated with trifluoromethane-
sulfonic acid (10 mL) under argon and warmed to rt over 2 h.
Workup and purification afforded (1S,3R,11S,13R)-(þ)-6b (710 mg,
DMSO-d6): d 8.83 (s, 1H), 8.77 (s, 1H), 6.46 (s, 1H), 6.39 (s, 1H), 5.01
(s, 1H), 4.50 (s, 1H), 4.14 (s, 1H), 4.08 (s,1H), 3.58 (s, 3H), 3.54 (s, 3H),
3.40 (d, J¼8.5 Hz, 1H), 3.31e3.26 (m, 2H), 2.98 (dd, J¼17.5, 6.5 Hz,
1H), 2.89 (d, J¼7.2 Hz,1H), 2.66 (d, J¼14.0 Hz,1H), 2.56 (d, J¼17.0 Hz,
1H), 2.42 (s, 3H),2.16 (s, 3H), 2.11 (s, 3H); 13C NMR (125 MHz,
DMSO): d 172.0, 146.2, 146.1, 144.2, 144.0, 135.3, 128.9, 128.2, 127.1,
122.7, 120.5, 119.8, 62.5, 61.0, 59.9, 59.8, 59.1, 55.4, 54.6, 37.1, 24.6,
15.4, 15.3.
83.1%) as a white solid. Mp 165e167 ꢁC; [
a
]
D
20 þ81.1 (c 2.6, CH3OH);
HRMS calcd for C24H28BrN2O6 [MþH]þ 519.1125, found 519.1100; 1H
NMR (500 MHz, DMSO-d6):
d
9.21 (s, 1H), 8.71 (s, 1H), 6.46 (s, 1H),
5.47 (t, J¼5.0 Hz, 1H), 4.44 (s, 1H), 4.32 (t, J¼5.0 Hz, 1H), 3.81e3.76
(m, 2H), 3.62 (s, 3H), 3.61 (s, 3H), 3.19 (m, 1H), 3.05 (m, 1H),
2.95e2.91 (m, 1H), 2.83 (m, 2H), 2.36e2.31 (m, 1H), 2.28 (s, 3H),
(1R, 3S, 11S, 13R)-(ꢀ)-8a: [
a]
20 ꢀ92.8 (c 44.6, CH2Cl2).
D
2.17 (s, 3H); 13C NMR (125 MHz, DMSO-d6):
d
170.2, 146.4, 146.0,
4.12. (1S,3R,11S,13R)-(D)-8b
144.5, 144.4, 132.8, 129.8, 129.7, 128.9, 122.0, 119.8, 119.6, 116.0, 63.5,
61.0, 60.3, 59.8, 53.2, 50.5, 48.3, 36.0, 32.1, 16.5, 15.5.
Following the general reaction protocol, (1S,3R,11S,13R)-(þ)-7b
(300 mg, 0.56 mmol) was reacted with Pd(OH)2 (moist, Pd content
20%, 283 mg), HOAc (1.75 mL) and hydrogen gas at 50 psi in CH3OH
4.9. (1S,3R,11R,13S)-(D)-7a
(25 mL), which provided (1S,3R,11S,13R)-(þ)-8b (230 mg, 89.8%) as
20
To
a
stirred solution of (1S,3R,11R,13S)-(þ)-6a (425 mg,
a white solid. Mp 147e149 ꢁC; [
a
]
þ75.5 (c 2.0, CH2Cl2); HRMS
D
0.82 mmol) in 40 mL CH3OH were added HCHO (37%, 4.40 mL),
NaBH3CN (520 mg, 8.2 mmol), and HOAc (7.90 mL). The reaction
mixture was stirred for 2 h at room temperature and concentrated
in vacuo. The residue was dissolved in EtOAc, washed with satu-
rated aq NaHCO3 and brine, dried over anhydrous Na2SO4, and re-
concentrated in vacuo. The crude product was purified by column
chromatography on silica gel (CH2Cl2/CH3OH¼100:1) to afford
calcd for C25H31N2O6 [MþH]þ 455.2177, found 455.2173; 1H NMR
(400 MHz, CDCl3):
d 6.52 (s, 1H), 6.50 (s, 1H), 6.23 (s, 1H), 6.04 (s,
1H), 5.81e5.75 (m, 1H), 4.30 (s, 1H), 4.07 (d, J¼11.2 Hz, 1H), 3.76 (s,
3H), 3.75 (s, 3H), 3.74e3.70 (m, 1H), 3.54e3.43 (m, 1H), 3.39e3.31
(m, 1H), 3.22 (dd, J¼17.2, 6.8 Hz, 1H), 3.01 (dd, J¼15.2, 2.0 Hz, 1H),
2.92 (d, J¼17.6 Hz,1H), 2.47 (s, 3H), 2.38 (m,1H), 2.26 (s, 3H), 2.24 (s,
3H). 13C NMR (125 MHz, CDCl3):
d 146.5, 145.5, 144.2, 143.5, 132.2,

4302
E. Du et al. / Tetrahedron 71 (2015) 4296e4303
129.5, 122.3 (2C), 120.9 (2C), 118.2, 68.0, 60.8, 60.7, 59.7, 58.7, 55.3,
52.7, 39.9, 31.7, 30.9, 15.8, 15.7.
1.79 (d, J¼7.5 Hz, 3H), 1.72 (s, 3H); 13C NMR (125 MHz, CDCl3):
d
167.4, 145.5, 145.3, 143.7, 143.3, 137.4, 135.2, 128.6, 127.9, 122.0,
121.0, 118.2, 62.8, 62.3, 60.7 (2C), 59.9, 55.9, 52.2, 40.2, 37.3, 30.9,
29.7, 25.1, 20.4, 15.7, 15.4.
4.13. (1R,3S,11S,13R)-(L)-9
To a solution of (1R,3S,11S,13R)-(ꢀ)-8a (14.6 mg, 0.032 mmol) in
CH3CN (4.0 mL) was added salcomine (19.5 mg, 0.06 mmol) at
room temperature and the reaction mixture was stirred in air for
2 h. The mixture was filtered and concentrated in vacuo. The res-
idue was purified by column chromatography on silica gel (PET/
4.16. (1S,3R,11S,13R)-(D)-10b
Following the general reaction protocol, angelica acid (8.3 mg,
0.083 mmol) was activated by 2,4,6-trichloro-benzoyl chloride
(13.0 mL, 0.083 mmol) and Et3N (12.0 mL, 0.087 mmol) in anhydrous
EtOAc¼1:1) to afford (1R,3S,11S,13R)-(ꢀ)-9 (11.0 mg, 71.0%) as
toluene (4 mL) and then reacted with (1S, 3R, 11S, 13R)-(þ)-8b
20
a yellow solid. [
a
]
ꢀ256.2 (c 9.7, CH2Cl2); HRMS calcd for
(15 mg, 0.033 mmol), which provided (1S,3R,11S,13R)-(þ)-10b
D
C
25H27N2O8 [MþH]þ 483.1762, found 483.1745; 1H NMR (400 MHz,
(10.2 mg, 57.6%) as a white solid. [
a
]
20 þ100.5 (c 4.0, CH2Cl2); HRMS
D
CDCl3):
d
4.87 (s, 1H), 4.24e4.13 (m, 1H), 4.00 (s, 3H), 3.99 (s, 3H),
calcd for C30H37N2O7 [MþH]þ 537.2595, found 537.2593; 1H NMR
3.91 (s, 1H), 383e3.78 (m, 1H), 375e3.67 (m, 2H), 3.04 (d,
J¼16.4 Hz, 1H), 2.96 (d, J¼11.6 Hz, 1H), 2.93e2.83 (m, 1H),
2.77e2.70 (m, 2H), 2.41 (s, 3H), 1.96 (s, 3H), 1.95 (s, 3H); 13C NMR
(300 MHz, CDCl3): d 6.56e6.44 (m, 2H), 5.94e5.70 (m, 4H),
4.33e4.21 (m, 3H), 4.00 (d, J¼12.3 Hz, 1H), 3.78 (s, 3H), 3.74 (s, 3H),
3.66 (d, J¼6.9 Hz, 1H), 3.17 (dd, J¼17.4, 7.2 Hz,1H), 2.98 (m, 1H), 2.85
(m, 1H), 2.51 (m, 1H), 2.44 (s, 3H), 2.24 (s, 3H), 2.23 (s, 3H), 1.64 (d,
(125 MHz, CDCl3):
d 186.4, 185.8, 182.5, 181.4, 172.5, 155.8, 155.4,
143.2, 139.4, 137.8, 136.9, 129.5, 128.4, 63.7, 61.0, 59.2, 58.9, 58.2,
54.0, 39.2, 30.9, 29.6, 20.1, 8.8 (2C).
J¼7.2 Hz, 3H), 1.38 (s, 3H); 13C NMR (125 MHz, CDCl3):
d 167.1, 146.3,
145.6, 143.8, 143.1, 133.4, 129.1, 127.5, 122.2, 122.1, 120.7 (2C), 117.5,
64.1, 60.6 (2C), 59.9, 58.2, 55.2, 49.1, 40.2, 32.0, 28.4, 20.0, 15.7 (2C),
15.3.
4.14. 11,13-epi-(L)-Renieramycin G
To a solution of angelica acid (6.6 mg, 0.066 mmol) in anhy-
drous toluene (1 mL) at 0 ꢁC were added 2,4,6-trichlorobenzoyl
4.17. 11,13-epi-(D)-Renieramycin G
chloride (11
m
L, 0.07 mmol) and Et3N (10
m
L, 0.07 mmol) under
To a solution of (1S,3R,11R,13S)-(þ)-10a (6.5 mg, 0.012 mmol) in
CH3CN (1.5 mL) was added salcomine (3.9 mg, 0.012 mmol) at room
temperature and the reaction mixture was stirred in air for 2 h. The
mixture was filtered and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (PET/EtOAc¼1:1)
argon. After stirring for 2 h at room temperature, the solution of
(1R,3S,11S,13R)-(ꢀ)-9 (15 mg, 0.031 mmol) in anhydrous toluene
(4 mL) was added to the reaction mixture and then the reaction
mixture was stirred for 48 h at 90 ꢁC. After cooled to room tem-
perature, the reaction mixture was quenched with saturated
aq NH4Cl, extracted with EtOAc, dried over anhydrous Na2SO4,
and concentrated in vacuo. The crude product was purified
by column chromatography on silica gel to afford 11,13-epi-
to afford 11,13-epi-(þ)-renieramycin G (4.0 mg, 58.5%) as a yellow
20
solid. [
a
]
D
þ122.0 (c 0.2, CH2Cl2); HRMS calcd for C30H33N2O9
[MþH]þ 565.2181, found 565.2160; 1H NMR (500 MHz, CDCl3):
d
6.05e6.00 (m, 1H), 5.19 (s, 1H), 5.17 (s, 1H), 4.58 (dd, J¼13.0,
(ꢀ)-renieramycin G (10.4 mg, 59.3%) as a yellow solid. [
a
]
20 ꢀ123.3
3.0 Hz, 1H), 4.05 (s, 3H), 3.97 (s, 3H), 3.94 (s, 1H), 3.76e3.74 (m, 1H),
3.08 (d, J¼17.0 Hz, 1H), 2.90 (dd, J¼11.0, 2.0 Hz, 1H), 2.76e2.74 (m,
2H), 2.67 (ddd, J¼17.0, 11.0, 2.0 Hz, 1H), 2.46 (s, 3H), 1.94 (s, 6H), 1.84
(dd, J¼7.5, 1.5 Hz, 3H), 1.74 (s, 3H); 13C NMR (125 MHz, CDCl3):
D
(c 0.6, CH2Cl2); HRMS calcd for C30H33N2O9 [MþH]þ 565.2181,
found 565.2185; 1H NMR (400 MHz, CDCl3):
d
6.03 (dq, J¼7.2,
1.2 Hz, 1H), 5.22 (s, 1H), 5.13 (dd, J¼12.0, 2.4 Hz, 1H), 4.61 (dd,
J¼12.0, 2.4 Hz, 1H), 4.06 (s, 3H), 4.00 (m, 1H), 3.98 (s, 3H), 3.84 (s,
1H), 3.13 (d, J¼16.8 Hz, 1H), 2.95 (d, J¼10.4 Hz, 1H), 2.85 (s, 2H),
2.71 (m, 1H), 2.56 (s, 3H), 1.94 (s, 6H), 1.84 (dq, J¼7.2, 1.6 Hz, 3H),
d
186.5, 185.6, 182.5, 180.7, 172.7, 167.2, 156.4, 155.4, 143.2, 139.6,
139.5, 138.0, 137.1, 129.4, 127.8, 126.9, 61.0 (2C), 60.7, 58.9, 58.6, 54.1,
53.2, 39.7, 29.5, 21.1, 20.5, 15.5, 8.7, 8.6.
1.74 (t, J¼1.2 Hz, 3H); 13C NMR (125 MHz, CDCl3):
d 186.3, 185.4,
182.2, 180.6, 167.2, 156.4, 155.3, 142.9, 139.8, 139.2, 137.6, 137.0,
129.5, 127.9, 126.8, 61.0, 60.7, 58.8, 58.4, 53.9, 53.2, 39.8, 29.4, 21.6,
20.5, 15.5, 8.7 (2C).
4.18. (D)-Renieramycin G
Following the general reaction protocol, (1S,3R,11S,13R)-(þ)-10b
(6.0 mg, 0.011 mmol) was reacted with salcomine (8.0 mg,
0.025 mmol) in CH3CN (4.0 mL). Workup and purification afforded
4.15. (1S,3R,11R,13S)-(D)-10a
(þ)-renieramycin G (4.1 mg, 65.0%) as a yellow solid. [
a
]
20 þ141.7 (c
D
To a solution of angelica acid (16.5 mg, 0.165 mmol) in anhy-
drous toluene (1 mL) at 0 ꢁC were added 2,4,6-trichlorobenzoyl
chloride (25.8
0.6, CH2Cl2); HRMS calcd for C30H33N2O9 [MþH]þ 565.2181, found
565.2167; 1H NMR (400 MHz, CDCl3):
d
5.89 (dq, J¼7.2, 1.2 Hz, 1H),
mL, 0.165 mmol) and Et3N (22.9
mL, 0.165 mmol)
5.46 (d, J¼1.6 Hz, 1H), 4.69 (dd, J¼11.6, 2.4 Hz, 1H), 4.40 (dd, J¼11.6,
2.4 Hz, 1H), 4.16 (br s, 1H), 4.05 (s, 3H), 4.00 (s, 3H), 3.90 (br s, 1H),
3.74 (d, J¼5.2 Hz, 1H), 3.07 (dd, J¼16.8, 2.4 Hz, 1H), 2.90 (dd, J¼20.8,
6.4 Hz, 1H), 2.76 (d, J¼20.4 Hz, 1H), 2.40 (s, 3H), 1.94 (s, 3H), 1.93 (s,
3H), 1.69 (dq, J¼7.2, 1.6 Hz, 3H), 1.52 (t, J¼1.6 Hz, 3H), 1.47 (m, 1H);
under argon. After stirring for 2 h at room temperature, the solution
of (1S,3R,11R,13S)-(þ)-8a (30 mg, 0.066 mmol) in anhydrous tolu-
ene (4 mL) was added to the reaction mixture and then the reaction
mixture was stirred for 48 h at 90 ꢁC. After cooled to room tem-
perature, the reaction mixture was quenched with saturated
aq NH4Cl, extracted with EtOAc, dried over anhydrous Na2SO4, and
concentrated in vacuo. The crude product was purified by column
chromatography on silica gel to afford (1S,3R,11R,13S)-(þ)-10a
13C NMR (125 MHz, CDCl3):
d 186.0, 185.1, 182.1, 180.1, 170.0, 166.8,
156.1, 155.4, 143.2, 141.9, 141.2, 139.7 (2C), 136.0, 129.0, 128.0, 126.5,
62.8 (2C), 61.0, 58.9, 55.8, 53.1, 50.3, 39.8, 25.4, 23.7, 20.3, 15.4, 8.7
(2C).
ꢀ148.8 (c 0.2, CH2Cl2).10a
20
(26 mg, 73.4%) as a white solid. [
a]
20 þ118.5 (c 2.0, CH2Cl2); HRMS
(ꢀ)-Renieramycin G: [
a
]
D
D
calcd for C30H37N2O7 [MþH]þ 537.2595, found 537.2609; 1H NMR
(300 MHz, CDCl3):
d
6.49 (s, 1H), 6.46 (s, 1H), 5.94e5.89 (m, 1H),
4.19. Cytotoxicity assay
5.89 (s, 1H), 5.71 (s, 1H), 5.51 (s, 1H), 5.04 (d, J¼11.7 Hz, 1H), 4.57 (d,
J¼10.8 Hz, 1H), 4.17 (s, 1H), 3.76e3.73 (m, 1H), 3.73 (s, 3H), 3.71 (s,
3H), 3.32 (t, J¼12.9 Hz, 1H), 3.20 (d, J¼12.0 Hz, 1H), 3.10 (dd, J¼17.1,
6.6 Hz,1H), 2.88e2.79 (m, 2H), 2.55 (s, 3H), 2.25 (s, 3H), 2.21 (s, 3H),
Each sample was tested in vitro against five different cell lines,
including HCT-8 (human colon cancer cell line), HELA (Hela human
cervical cancer cell line), A549 (human lung adenocarcinoma

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Acknowledgements
This research was financially supported by Beijing Key Labora-
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Supplementary data
Supplementary data associated with this article can be found in
the online version, at http://dx.doi.org/10.1016/j.tet.2015.04.064.
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