The first total synthesis of lymphostin

Article abstract of DOI:10.1016/j.tetlet.2004.01.140

Lymphostin (1), a novel immunosuppressant, has been synthesized from tryptophan through six kinds of regioselectively oxidative reactions.

Full text of DOI:10.1016/j.tetlet.2004.01.140

Tetrahedron
Letters
Tetrahedron Letters 45 (2004) 2847–2850
The first total synthesis of lymphostin
Kuniaki Tatsuta,* Keisuke Imamura, Sayaka Itoh and Soko Kasai
Department of Applied Chemistry, School of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku,
Tokyo 169-8555, Japan
Received 15 January 2004; accepted 28January 2004
Abstract—Lymphostin (1), a novel immunosuppressant, has been synthesized from tryptophan through six kinds of regioselectively
oxidative reactions.
Ó 2004 Elsevier Ltd. All rights reserved.
Lymphostin (1) was isolated by the Kyowa Hakko
group from a culture broth of Streptomyces sp. as an
immunosuppressant to show potent inhibitory activity
against lymphocyte kinase.1 The structure was eluci-
dated by thorough NMR studies to be a novel tricyclic
aromatic alkaloid with a pyrroloquinoline skeleton.2 In
addition to its novel mechanism of action, impinging on
a crucial biological cascade, the structure of 1 interested
us as a focused target for total synthesis. We have
proposed lymphostin (1) to be biogenetically produced
from tryptophan.
In the event, the starting N-carbobenzyloxy-L-trypto-
phan methyl ester (2) was converted to the racemic keto-
alcohol 3 in a quantitative yield by hydride reduction
and DDQ oxidation (Scheme 2 and Table 1). The
selective introduction of a hydroxyl group onto the
phenyl portion proceeded on oxidative reaction with
Tl(OCOCF3)3 followed by treatment with CuSO4Æ5H2O
to give the phenol 4.3;4 This was deoxygenated by
NaBH3CN to give 5,5 which was oxidized by
NO(SO3K)2 to the quinone 6 in high yield.
Regioselective reaction of 6 with benzylamine to afford
76 was followed by hydrogenolysis to the diamino
derivative 8. This was cyclized concomitant with aro-
matization by heating in DMF with air to give the
desired iminoquinone 9, which was acetylated to 10.7
Herein, we report the implementation of a novel
biomimetic strategy for the first total synthesis of lym-
phostin (1). The critical element of the synthetic plan was
inspired by our proposed biosynthetic sequence as shown
in the retrosynthetic perspective to assemble the tricyclic
core 14 from the quinone 8 through cyclization and
oxidation to give the intermediary iminoquinone 9
(Scheme 1).
The transformation of the quinone 10 to the diamino-
pyrroloquinoline 12 was examined under a variety of
conditions, and realized by the introduction of an azido
O
N
OMe
OH
CHO
OH
CO2Me
N
N
O
NH2
NHZ
H2N
AcHN
AcHN
H2N
N
N
NH
N
N
H
H
NH2
NHNs
O
O
Lymphostin (1)
14
9
8
2
Scheme 1.
Keywords: Total synthesis; Immunosuppressant; Pyrroloquinoline; Tricyclic alkaloid.
* Corresponding author. Tel./fax: +81-3-3200-3203; e-mail: tatsuta@waseda.jp
0040-4039/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2004.01.140

2848
K. Tatsuta et al. / Tetrahedron Letters 45 (2004) 2847–2850
OH
OH
CO2Me
NHZ
O
R1
OH
e
f
a, b
NHZ
NHZ
N
N
N
H
H
H
5
2
3: R1=H
c,d
4: R1=OH
OAc
R4
OH
R3
O
O
N
N
R2
R2
AcHN
m, n
i
k, l
NH
O
N
N
H
N3
6: R2=H, R3=NHZ
9: R2=NH2, R4=CH2OH
11
g
h
j
7: R2=NHBn, R3=NHZ
8: R2=NH2, R3=NH2
10: R2=NHAc, R4=CH2OAc
TMS
O
O
N
OMe
OMe
R4
N
N
q, r
s
t
AcHN
AcHN
AcHN
N
N
N
NHNs
NHNs
NHNs
12: R4=CH2OAc
13: R4=CH2OH
14: R4=CHO
15
16
o
p
O
OMe
OMe
O
N
OMe
O
S
N
Ns=
u
AcHN
AcHN
O
NO2
N
N
NH2
NH2
Lymphostin (1)
17
Scheme 2. Reagents and conditions: (a) LiBH4/THF, rt, 1 h then reflux, 1 h; (b) DDQ/aq THF, rt, 1 h, 95% in two steps; (c) Tl(OCOCF3)3/TFA, rt,
1 h; (d) CuSO4 Æ 5H2O/DMF, 130 °C, 10 min, 59% in two steps; (e) NaBH3CN, BF3 Æ Et2O/THF, rt, 4 h, 85%; (f) NO(SO3K)2/acetone-pH 7 phosphate
buffer, rt, 2 h, 82%; (g) BnNH2, air/PhH, rt, 4 h, 79%; (h) H2, Pd–C/EtOH, rt, 2 h, quant.; (i) air/DMF, 70 °C, 1 h; (j) C6F5OAc/DMF, rt, 12 h, 66% in
two steps; (k) Tf2O, Py/CH2Cl2, )78 °C, 1 h; (l) n-Bu4NN3/CH2Cl2, )78 °C to rt, 12 h, 68% in two steps; (m) H2, Lindlar cat./EtOH, rt, 2 h; (n) NsCl,
Py/ClCH2CH2Cl, 50 °C, 1 h, 75% in two steps; (o) aq acetone, rt, 5 days, quant.; (p) PCC, Al2O3/AcOH/CH2Cl2, rt, 4 h, 80%; (q) trimethylsilyl-
acetylene, n-BuLi/THF, )78 °C, 2 h; (r) MnO2/acetone/CH2Cl2, rt, 12 h, 69% in two steps; (s) K2CO3/MeOH, rt, 5 h, 73%; (t) PhSH, K2CO3/DMF, rt,
12 h, 75%; (u) MS 4A/DMSO, 90 °C, 7 days, 64%.
group, and subsequent reduction. Treatment of 10 with
Tf2O followed by n-Bu4NN3 afforded the tautomerized
azide 11, which was reduced on the Lindlar catalyst and
protected by an o-nitrobenzenesulfonyl (Ns) group8 to
afford 12. De-O-acetylation of 12 to 13 was quantita-
tively carried out only with aqueous acetone. The alco-
hol 13 was oxidized to the aldehyde 14, which was
followed successively by reaction with trimethylsilyl-
acetylene and oxidation with MnO2 to give the ethynyl
ketone 15.9 This was transformed to the dimethyl acetal
16 by alkaline methanol and de-N-protected by alkaline
thiophenol to the amine 17.
In the final stage, methanol was eliminated from 1710 to
give lymphostin (1). This was identical in all respects with
the natural product,11 completing the total synthesis.
At the heart of the synthesis of lymphostin (1) described
herein are six kinds of oxidative reactions, which were
regioselectively accomplished.

Table 1. Physico-chemical properties of compounds
1H NMR (600 MHz; d ppm; J Hz)
13C NMR (150 MHz; d ppm)
MS ðm=zÞ
1H NMR (600 MHz; d ppm; J Hz)
13C NMR (150 MHz; d ppm)
MS ðm=zÞ
Com-
pounds
Mp (°C)
Com-
pounds
Mp (°C)
IR (KBr; cmÀ1
)
IR (KBr; cmÀ1
)
1
276–277
Crystals
(i-PrOH)
1H NMR (DMSO-d6): d 2.35 (3H, s), 3.95 (3H, s), 7.64 (1H, d,
J ¼ 12:5 Hz), 7.88 (1H, d, J ¼ 12:5 Hz), 8.15 (1H, s), 8.23 (2H, br
s), 8.38 (1H, s), 8.63 (1H, s), 10.16 (1H, br s)
11
Wax
1H NMR (MeOH-d4): d 2.15 (3H, s), 2.33 (3H, s), 5.47 (2H, s),
7.78 (1H, s), 8.03 (1H, s), 8.06 (1H, s)
MALDI-TOF-MS: 325 [M+H]þ
13C NMR (DMSO-d6): d 24.3, 58.4, 101.7, 110.6, 117.3, 124.3,
124.8, 133.5, 136.4, 139.5, 145.6, 147.5, 150.1, 163.8, 169.5, 188.5
FAB-MS: 311 [M+H]þ
IR (KBr): 3428, 2346, 1735, 1658, 1560, 1540, 1457, 1421, 1388,
1236, 1218, 1106, 1087
IR (KBr): 3448, 1685, 1654, 1632, 1596, 1500, 1363, 1350, 1241,
1132, 1078
3
153
Needles
(EtOAc)
1H NMR (MeOH-d4): d 3.84 (1H, dd, J ¼ 11:5 & 6.0 Hz), 3.96
(1H, dd, J ¼ 11:5 & 5.0 Hz), 5.09 (1H, d, J ¼ 13:0 Hz), 5.11 (1H,
dd, J ¼ 6:0 & 5.0 Hz), 5.12 (1H, d, J ¼ 13:0 Hz), 7.21 (1H, ddd,
J ¼ 7:5, 7.5 & 1.0 Hz), 7.24 (1H, ddd, J ¼ 7:5, 7.5 & 1.0 Hz), 7.27–
7.38(5H, m), 7.45 (1H, ddd, J ¼ 7:5, 1.0 & 0.5 Hz), 8.25 (1H, ddd,
J ¼ 7:5, 1.0 & 0.5 Hz)
12
218(decomp.)
Needles
(MeOH)
1H NMR (MeOH-d4): d 2.09 (3H, s), 2.28(3H, s), 5.36 (2H, s),
7.80 (1H, ddd, J ¼ 8:0, 8.0 & 1.0 Hz), 8.02 (1H, dd, J ¼ 8:0 &
1.0 Hz), 8.05 (1H, dd, J ¼ 8:0 & 1.0 Hz), 8.10 (1H, s), 8.11 (1H,
ddd, J ¼ 8:0, 8.0 & 1.0 Hz), 8.14 (1H, s), 8.26 (1H, s)
FAB-MS: 484 [M+H]þ
FAB-MS: 339 [M+H]þ
4
6
196–197
Crystals
(EtOAc)
1H NMR (MeOH-d4): d 3.83 (1H, dd, J ¼ 11:0 & 6.5 Hz), 3.95
(1H, dd, J ¼ 11:0 & 6.5 Hz), 5.09 (1H, d, J ¼ 14:0 Hz), 5.13 (1H,
d, J ¼ 14:0 Hz), 5.17 (1H, dd, J ¼ 6:5 & 6.5 Hz), 6.55 (1H, d,
J ¼ 8:0 Hz), 6.91 (1H, d, J ¼ 8:0 Hz), 7.12 (1H, dd, J ¼ 8:0 &
8.0 Hz), 7.25–7.37 (5H, m), 8.31 (1H, s)
13
225 (decomp.)
Needles
(EtOAc)
1H NMR (DMSO-d6): d 2.16 (1H, br s), 2.20 (3H, s), 5.50 (2H, s),
7.88 (1H, ddd, J ¼ 8:0, 8.0 & 1.0 Hz), 8.00 (1H, br s), 8.07 (1H, dd,
J ¼ 8:0 & 1.0 Hz), 8.08 (1H, s), 8.10 (1H, dd, J ¼ 8:0 & 1.0 Hz),
8.11 (1H, s), 8.22 (1H, s), 8.23 (1H, ddd, J ¼ 8:0, 8.0 & 1.0 Hz),
10.03 (1H, br s)
FAB-MS: 355 [M+H]þ
MALDI-TOF-MS: 442 [M+H]þ
165 (decomp.)
1H NMR (MeOH-d4): d 2.81 (1H, dd, J ¼ 14:5 & 10.0 Hz), 3.04 14
194–195
(decomp.)
Amorphous
1H NMR (MeOH-d4): d 2.18(3H, s), 7.85 (1H, ddd, J ¼ 8:0, 8.0 &
1.5 Hz), 7.90 (1H, dd, J ¼ 7:5 & 1.5 Hz), 8.07 (1H, s), 8.09 (1H, s),
8.13 (1H, dd, J ¼ 8:0 & 1.0 Hz), 8.16 (1H, ddd, J ¼ 8:0, 7.5 &
1.0 Hz), 8.25 (1H, s), 10.03 (1H, s)
Prisms (acetone) (1H, dd, J ¼ 14:5 & 5.0 Hz), 3.56 (1H, dd, J ¼ 11:0 & 5.0 Hz), 3.59
(1H, dd, J ¼ 11:0 & 5.5 Hz), 3.92 (1H, dddd, J ¼ 10:0, 5.5, 5.0 &
5.0 Hz), 4.92 (1H, d, J ¼ 11:5 Hz), 5.03 (1H, d, J ¼ 11:5 Hz), 6.50
(1H, d, J ¼ 10:5 Hz), 6.53 (1H, d, J ¼ 10:5 Hz), 6.96 (1H, s), 7.19–
7.31 (5H, m)
FAB-MS: 440 [M+H]þ
FAB-MS: 355 [M+H]þ
7
8
>300
Crystals
(MeOH)
1H NMR (MeOH-d4): d 2.79 (1H, dd, J ¼ 12:0 & 10.0 Hz), 3.01 15
(1H, dd, J ¼ 12:0 & 6.0 Hz), 3.56 (1H, dd, J ¼ 12:5 & 6.0 Hz), 3.57
(1H, dddd, J ¼ 10:0, 6.0, 6.0 & 2.5 Hz), 3.60 (1H, dd, J ¼ 12:5 &
2.5 Hz), 4.39 (2H, s), 4.93 (1H, d, J ¼ 13:0 Hz), 5.04 (1H, d,
J ¼ 13:0 Hz), 5.08(1H, s), 6.75 (1H, s), 7.16–7.32 (10H, m)
FAB-MS: 460 [M+H]þ
244–246
(decomp.)
Amorphous
1H NMR (MeOH-d4): d 0.06 (9H, s), 2.23 (3H, s), 8.03 (1H, ddd,
J ¼ 8:0, 8.0 & 1.0 Hz), 8.06 (1H, s), 8.08 (1H, dd, J ¼ 8:0 &
1.0 Hz), 8.12 (1H, dd, J ¼ 8:0 & 1.0 Hz), 8.15 (1H, s), 8.17 (1H,
ddd, J ¼ 8:0, 8.0 & 1.0 Hz), 8.30 (1H, s)
FAB-MS: 536 [M+H]þ
216–218
(decomp.)
Crystals
(MeOH)
1H NMR (MeOH-d4): d 2.87 (1H, dd, J ¼ 14:5 & 7.5 Hz), 2.96
(1H, dd, J ¼ 14:5 & 7.0 Hz), 3.42 (1H, dddd, J ¼ 7:5, 7.0, 6.5 &
4.0 Hz), 3.49 (1H, dd, J ¼ 11:5 & 6.5 Hz), 3.68(1H, dd, J ¼ 11:5 &
4.0 Hz), 5.39 (1H, s), 6.83 (1H, s)
16
>300
Amorphous
1H NMR (MeOH-d4): d 2.21 (3H, s), 3.28(6H, s), 3.72 (2H, d,
J ¼ 6:0 Hz), 4.93 (1H, t, J ¼ 6:0 Hz), 7.98(1H, ddd, J ¼ 8:0, 7.5 &
1.0 Hz), 8.06 (1H, s), 8.12 (1H, dd, J ¼ 8:0 & 1.0 Hz), 8.14 (1H, s),
8.15 (1H, dd, J ¼ 8:0 & 1.0 Hz), 8.20 (1H, ddd, J ¼ 8:0, 7.5 &
1.0 Hz) 8.29 (1H, s)
13C NMR (MeOH-d4): d 28.2, 54.4, 63.6, 98.2, 120.2, 121.3, 123.9,
136.5, 154.1, 180.1, 180.4
FAB-MS: 236 [M+H]þ
þ
FAB-MS: 528[M+H]

2850
K. Tatsuta et al. / Tetrahedron Letters 45 (2004) 2847–2850
It seems likely that the chemistry and insights developed
for this total synthesis will find wider application.
Acknowledgements
The present work was financially supported by Grant-
in-Aid for Specially Promoted Research and Scientific
Research A from MEXT. We are grateful to 21COE
ꢀPractical Nano-Chemistryꢁ from MEXT, Japan and
Advanced Research Institute for Science and Engineer-
ing, Waseda University for the generous supports of our
program.
References and notes
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11. An authentic sample of lymphostin (1: mp 275–277 °C)
was kindly provided by Dr. Y. Kanda, Kyowa Hakko
Kogyo Co., Ltd.