A Facile Chemoenzymatic Approach to Monoterpenoid Indole Alkaloids
The synthesis of (21S)-nacycline (4) is identical to that of 12-aza-nacy-
cline, except strictosidine was used as the starting material. The final
yield was 82.3%.
Experimental Section
General Methods
Strictosidine synthase was prepared by expression of the plasmid pQE-2-
General Procedure for the Synthesis of (19S,20S)-Tetrahydroalstonines (5,
8)
STR1-pG-Tf2-His in E. coli M15 cells. Secologanin was isolated from
6
Lonicera tatarica. The 7-aza-tryptamine was synthesized from 7-aza-
indole. The 12-aza-strictosidine was obtained by conversion of 7-aza-
1
2-Aza-strictosidine (20 mg, 0.038 mmol) and b-glucosidase (5 mg) were
dissolved in a solution of acetate buffer (50 mm, pH 5.0, 2 mL). The mix-
ture was stirred at 378C for 24 h under nitrogen. After the reaction was
completed, the mixture was freeze-dried in vacuo. Then anhydrous meth-
anol (5 mL) was added to the residue and the inactivated enzyme was re-
moved by centrifugation. The supernatant was directly used for reaction
tryptamine and secologanin using the immobilized prepurified STR1-His
6
enzymatic catalytic system. Strictosidine was also synthesized by the
same method. The detailed description of these experimental procedures
is given in the Supporting Information. The MS, NMR, and NOESY
spectral data and the stereochemistry determination of 4 and 5 are also
provided in the Supporting Information. The b-glucosidase was pur-
chased from Fluka. All the other chemical reagents and biological mate-
rial were obtained from standard commercial sources and were of analyt-
ical reagent grade. ESI-MS data were recorded with a Bruker Esquire
by addition of AcOH (32 mL, 0.57 mmol) under N
stirred at RT for 15 min. NaBH (21 mg, 0.19 mmol) was added to the re-
2
and the mixture was
4
action mixture and stirred overnight. The methanol was removed in
vacuo and the reaction was quenched by addition of water (5 mL). The
aqueous layer was extracted with EtOAc (10 mLꢄ3). The combined ex-
tract was washed with water (10 mLꢄ3), brine (10 mLꢄ1), and dried
over anhydrous Na
residue was purified by semipreparative HPLC using MeOH/H
UV: 230 nm) to afford (19S,20S)-12-aza-tetrahydroalstonine (8, 4.7 mg,
3
000+ spectrometer. NMR spectra and NOESY spectroscopic data were
recorded with Bruker AVIII (500 MHz) or Bruker DRX 700 instruments
with TMS as an internal standard, and CD OD and CDCl were used as
2
SO
4
. The solvent was then removed in vacuo and the
3
3
2
O (80:20,
solvent. TLC was performed on silica gel (GF254). Column chromatogra-
phy was performed on silica gel 60 (70–230 mesh, E. Merck). All the syn-
thesized MIAs were purified by semipreparative HPLC with a LiChros-
pher RP-18 EC column (250ꢄ10 mm, 10 mm, Merck).
1
3
1
5.1%). H NMR (500 MHz, CDCl
3
): d=8.28 (d, J=5.0 Hz, 1H), 7.81 (s,
H), 7.76 (d, J=8.0 Hz, 1H), 7.56 (s, 1H), 7.04 (t, J=8.0 Hz, 1H), 4.52
(
dt, J=10.5, 6.5 Hz, 1H), 3.76 (s, 1H), 3.43 (dd, J=11.5, 2.0 Hz, 1H),
General Procedure for the Synthesis of Strictosidine Lactams (3, 6)
3.12 (dd, J=12.5, 1.5 Hz, 1H), 2.99–2.90 (m, 2H), 2.83 (dt, J=12.0,
4
1
.5 Hz, 1H), 2.76 (dd, J=12.5, 3.5 Hz, 1H), 2.70–2.56 (m, 3H), 1.72 (m,
H), 1.53 (q, J=12.5 Hz, 1H), 1.41 ppm (d, J=6.5 Hz, 1H); C NMR
1
2-Aza-strictosidine (20 mg, 0.038 mmol) was dissolved in a water solu-
13
tion of Na CO (5%, 2 mL). The mixture was stirred at 758C for 30 min
2
3
(
3
125 MHz, CDCl ): d=168.0, 155.8, 149.2, 142.3, 135.5, 126.2, 120.1,
under nitrogen. After the reaction was completed, the mixture was ex-
tracted by EtOAc (10 mLꢄ3). The combined extract was washed with
water (10 mLꢄ3), brine (10 mLꢄ1), and dried over anhydrous Na SO .
2 4
The solvent was then removed in vacuo and the residue was dissolved in
methanol (2.0 mL). After centrifugation, the supernatant was subjected
to semipreparative HPLC to afford 12-aza-strictosidine lactam (6, 18 mg,
1
1
15.7, 109.7, 106.6, 72.5, 59.9, 56.6, 53.5, 51.3, 38.6, 34.3, 31.5, 21.8,
8.7 ppm; MS (ESI): m/z: 354 [M+H] .
+
The synthesis of (19S,20S)-tetrahydroalstonine (5) is identical to that of
2-aza-tetrahydroalstonine, except the starting material was substituted
1
with strictosidine. The final yield was 80.6%.
yield: 95.0%) using MeOH/H
5:45; 10–20 min: 75:25; 20–35 min: 80:20; UV: 254 nm). H NMR
700 MHz, CD OD): d=8.12 (brs, 1H), 7.83 (dd, J=7.7, 1.4 Hz, 1H),
2
O as the eluent (gradient: 0–10 min:
1
5
(
3
7
2
1
1
3
.36 (s, 1H), 7.11 (dd, J=7.7, 4.9 Hz, 1H), 5.64 (m, 1H), 5.39 (d, J=
.1 Hz, 1H), 5.36 (dd, J=16.8, 1.4 Hz, 1H), 5.30 (dd, J=10.5, 2.1 Hz,
H), 5.09 (m, 1H), 4.93 (dd, J=12.6, 5.6 Hz, 1H), 4.55 (d, J=8.4 Hz,
H), 3.84 (dd, J=11.9, 2.8 Hz, 1H), 3.61 (dd, J=11.9, 5.6 Hz, 1H), 3.29–
.10 (m, 4H), 2.96–2.90 (m, 2H), 2.78 (m, 1H), 2.69–2.66 (m, 1H), 2.54
Acknowledgements
We would like to give our hearty thanks to Dr. Manfred Wagner from
Max Planck Institute for Polymer Research (Mainz, Germany) for his
help in measuring some of the NMR spectroscopic data and Dr. Matthias
Unger from Julius Maximilians University Wꢁrzburg (Germany) for part
of the MS measurements. This study was supported by Deutsche For-
schungsgemeinschaft (Bonn, Bad Godesberg, Germany), Fonds der
Chemischen Industrie (Frankfurt/Main, Germany), the National Natural
Science Foundation of China (no. 20802066), the Science Foundation of
Chinese University, the China Postdoctoral Science Foundation, National
Science & Technology Major Project “Key New Drug Creation and Man-
ufacturing Program” of China (no. 2009ZX09501-010), and K.P. Chaoꢀs
High-Tech Foundation.
(
ddd, J=13.3, 4.2, 2.1 Hz, 1H), 2.05 ppm (dt, J=14.0, 6.3 Hz, 1H);
1
3
C NMR (175 MHz,): d=167.1, 149.6, 149.3, 143.0, 136.2, 134.3, 127.8,
1
5
21.9, 120.6, 116.7, 109.7, 109.1, 100.4, 98.0, 78.3, 78.0, 74.3, 71.4, 62.9,
4.9, 44.7, 44.5, 27.2, 25.0, 21.7 ppm; MS (ESI): m/z: 500 [M+H] .
+
The synthetic scheme of strictosidine lactam (3) is identical to that of 12-
aza-strictosidine lactam, except the starting material was substituted with
strictosidine. The final yield was 76.5%.
General Procedure for the Synthesis of (21S)-Nacyclines (4, 7)
1
H
2-Aza-strictosidine (20 mg, 0.038 mmol) was dissolved in a solution of
SO (2m, 0.4 mL). The mixture was stirred at 85–908C for 30 min
2
4
under nitrogen. After the reaction was completed, saturated sodium car-
bonate was added (under cooling with an ice bath) into the solution to
adjust the pH to 8–9. The aqueous layer was extracted by EtOAc
[4] a) A. Echalier, K. Bettayeb, Y. Ferandin, O. Lozach, M. Clꢅment,
A. Bargiotti, M. G. Brasca, A. Ciavolella, N. Colombo, G. Fachin, A.
Isacchi, M. Menichincheri, A. Molinari, A. Montagnoli, A. Pillan, S.
(
10 mLꢄ3). The combined extract was washed with water (10 mLꢄ3),
brine (10 mLꢄ1), and dried over anhydrous Na SO . The solvent was
then removed in vacuo and the residue was purified by semipreparative
HPLC using MeOH/H O (80:20, UV: 230 nm) to afford (21S)-12-aza-na-
cycline (7, 8.8 mg, yield: 65.7%). H NMR (500 MHz, CDCl
2
4
2
1
3
): d=10.21
s, 1H), 8.33 (d, J=4.5 Hz, 1H), 7.79 (d, J=7.5 Hz, 1H), 7.54 (s, 1H),
(
7
.07 (dd, J=7.5, 4.5 Hz, 1H), 6.18 (s, 1H), 4.64 (q, J=6.5 Hz, 1H), 4.34
(
d, J=11.5 Hz, 1H), 3.76 (m, 1H), 3.71 (d, J=9.0 Hz, 1H), 3.68 (s, 1H),
3
2
.58 (dd, J=10.5, 4.5 Hz, 1H), 3.34 (m, 1H), 3.30 (m, 1H), 3.24 (m, 1H),
.89 (m, 1H), 2.71 (d, J=14.5 Hz, 1H), 1.75 (m, 1H), 1.52 ppm (m, 1H);
C NMR (125 MHz, CDCl ): d=167.9, 154.5, 148.9, 142.2, 133.8, 126.2,
3
1
3
1
1
19.8, 115.5, 107.3, 106.8, 76.4, 52.3, 50.9, 49.0, 33.6, 27.5, 21.9, 20.3,
8.7 ppm; MS (ESI): m/z: 352 [M+H] .
+
Chem. Asian J. 2010, 5, 2400 – 2404
ꢃ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
2403