Total synthesis of the proposed structure for pochonicine and determination of its absolute configuration

Article abstract of DOI:10.1016/j.tetlet.2013.01.015

Pochonicine is a polyhydroxylated pyrrolizidine alkaloid with a powerful inhibitory activity against β-Nacetylglucosaminidases. The proposed structure for pochonicine and the three diastereomers concerning its C-1 and/or C-3 positions were synthesized from N-acetyl-D-glucosamine through construction of the pyrrolizidine skeleton by two intramolecular amino cyclizations as key steps. This synthetic study not only revised the structure of the natural product to the corresponding 1,3-di-epi-form but also determined the absolute configuration as 1R, 3S, 5R, 6R, 7S, 7aR. Copyright

Full text of DOI:10.1016/j.tetlet.2013.01.015

Tetrahedron Letters 54 (2013) 1456–1459
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Total synthesis of the proposed structure for pochonicine and determination
of its absolute configuration
Yujiro Kitamura a,c, Hiroyuki Koshino a, Takemichi Nakamura a, Aya Tsuchida b, Teruhiko Nitoda b,
Hiroshi Kanzaki b, Koji Matsuoka c, Shunya Takahashi a,
⇑
a RIKEN Advanced Science Institute, Saitama 351-0198, Japan
b Laboratory of Bioresources Chemistry, Graduate School of Environmental and Life Science, Okayama University, Okayama 700-8530, Japan
c Division of Material Science, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Pochonicine is a polyhydroxylated pyrrolizidine alkaloid with a powerful inhibitory activity against b-N-
Received 5 December 2012
Revised 28 December 2012
Accepted 7 January 2013
Available online 12 January 2013
acetylglucosaminidases. The proposed structure for pochonicine and the three diastereomers concerning
its C-1 and/or C-3 positions were synthesized from N-acetyl-D-glucosamine through construction of the
pyrrolizidine skeleton by two intramolecular amino cyclizations as key steps. This synthetic study not
only revised the structure of the natural product to the corresponding 1,3-di-epi-form but also deter-
mined the absolute configuration as 1R, 3S, 5R, 6R, 7S, 7aR.
Keywords:
Pochonicine
Ó 2013 Elsevier Ltd. All rights reserved.
GlcNAcase inhibitor
N-Acetyl-
D-glucosamine
D-Allopyranoside
Pochonicine was isolated from a solid fermentation culture of
leads it back to 5. This would be prepared from 6 via OsO4
oxidation and selective O-protection. The allyl unit in 6 might be
introduced by the a-chelation controlled addition of an allylic me-
the fungal strain Pochonia suchlasporia var. suchlasporia TAMA 87
by Usuki et al.1 The structure was shown to be a new polyhydroxy-
lated pyrrolizidine alkaloid 1 with an acetamide group by using the
NMR and MS technique (Fig. 1). Its relative stereochemistry was
tal to 7. The pyrrolidine ring could be constructed by an intramo-
lecular cyclization (position b) of an amine obtainable from 8.
3
deduced by NOE correlations and JH,H coupling constants while
We therefore selected a N-acetyl-D
-glucosamine derivative 95 as
the absolute configuration has not been determined. This natural
product exhibited a potent inhibitory activity against b-N-acetyl-
glucosaminidases (GlcNAcases) of various organisms including in-
sects, fungi, mammals, and a plant but no inhibition against b-glu-
cosidase of almond, b-glucosidase of yeast, or chitinase of Bacillus
sp. Its inhibition potency was comparable to that of a potent
GlcNAcase inhibitor, nagstatin.2 Recent studies have revealed that
GlcNAcases may be associated with several diseases such as diabe-
tes mellitus, leukemia, and cancer.3 Therefore, GlcNAcase inhibi-
tors are potentially useful tools not only for biochemical studies
but also in the design of therapeutic drugs. In connection with
our synthetic studies on enzyme inhibitors,4 described herein is
the total synthesis of 1 and its three types of diastereomers, which
dictates revision of the formula to ent-4.
the starting material. This route also enabled us to prepare three
diastereomers concerning the C-1 and/or C-3 positions6 of 1.
Synthesis of 1 began with the configurational inversion4a,7 of 9
at the 3-position (Scheme 2). The D-allosamine derivative 10 thus
obtained was hydrolyzed to give 11 after benzyloxycarbonylation.
Regioselective cleavage of the benzylidene group in 11 was accom-
plished by treating it with Me3NꢀBH3–AlCl3 in the presence of
MS4A in tetrahydrofuran (THF)8 to provide the corresponding
6-O-benzyl derivative in high yield.9 The 1,2-diol moiety was
protected by an acetonide to afford 12. Treatment of 12 with
N-bromosuccinimide and subsequent reduction with sodium boro-
hydride gave an acyclic diol 13. This compound was transformed
into the 5-O-mesylate 8 in 2 steps. Removal of the N-protecting
group by hydrogenation was accompanied by the intramolecular
cyclization to give a pyrrolidine derivative, which was isolated as
the corresponding tert-butylcarbamate 14. After debenzylation of
14, the resulting alcohol was oxidized by Swern’s method to afford
an aldehyde 7. Introduction of the allyl group into 7 was performed
by the action of allylmagnesium chloride in the presence of ZnCl2
in dichloromethane–THF at ꢁ78 °C to afford a 77:23 of mixture
of a threo alcohol 6 and an erythro isomer 15 in 87% yield.10,11
Since the absolute configuration of pochonicine was unknown,
the structure 1 shown in Figure 1 of the original paper1 was tenta-
tively chosen as the synthetic target. The retrosynthetic plan of 1 is
shown in Scheme 1. Cleavage of the C–N bond (position a) in 1
⇑
Corresponding author. Tel.: +81 48 467 9223; fax: +81 48 462 4627.
E-mail address: shunyat@riken.jp (S. Takahashi).
0040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.01.015

Y. Kitamura et al. / Tetrahedron Letters 54 (2013) 1456–1459
1457
Figure 1. Proposed structure for pochonicine.
Scheme 2. Reagents and conditions: (a) (i) MsCl, pyridine, 0 °C–>rt, 94%; (ii) NaOAc,
2-methoxyethanol–water, 120 °C, 95%; (b) (i) NaOH, 2-methoxyethanol–water,
120 °C, 74%; (ii) ZCl, Na2CO3, CH2Cl2–MeOH–water, 0 °C–>rt, 95%; (c) (i) Me3NꢀBH3,
AlCl3, MS4A, THF, rt, 89%; (ii) 2,2-dimethoxypropane, CSA, CH2Cl2, rt, 90%; (d) (i)
NBS, THF–water, 0 °C; (ii) NaBH4, EtOH, 0 °C, 78% in 2 steps; (e) (i) TBDPSCl,
imidazole, DMF, 0 °C–>rt; (ii) MsCl, DMAP, pyridine, 0 °C–>rt, 96% in 2 steps; (f) (i)
10% Pd/C, H2, EtOH, rt; (ii) Boc2O, DIPEA, DMF, rt, 63% in 2 steps; (g) (i) 20% Pd(OH)2/
C, H2, EtOH, 98%; (ii) Swern oxid., quant.; (h) allylMgCl, ZnCl2, CH2Cl2–THF, ꢁ78 °C,
87% (6/15 = 77/23).
Scheme 1. Synthetic plan of the proposed structure 1 for pochonicine.
These isomers could be separated by chromatography on silica gel.
The stereochemistry was determined by the modified Mosher
method12 of the corresponding MTPA esters of 6.13
As we secured the key intermediate 6, our attention next turned
to the construction of the pyrrolizidine ring system (Scheme 3).
Prior to the cyclization, the second nitrogen functional group was
introduced through the nucleophilic displacement reaction of a
primary tosylate 16 with sodium azide. Since diastereoselective
dihydroxylation of 17 with AD-mix15 could not be achieved, the
olefin was oxidized with OsO4-N-methylmorpholine N-oxide to
provide a ca. 1:1 mixture of diols, which were transformed into
the corresponding mesylates 5 and 18. Each isomer was separated
by chromatography on silica gel, and their stereochemistry was
determined by the detailed NMR analysis of the following pyrro-
lizidine derivatives 19 and 20.16 Formation of the second ring sys-
tem was effected by the treatment of 5 (the less polar isomer) with
TMSOTf-2,6-lutidine17 followed by heating in the presence of tri-
ethylamine, affording 19 in high yield. Finally, installation of the
acetamide group and deprotection with HCl yielded 110 as a hydro-
chloride salt. 1H, and 13C NMR data of 1ꢀHCl or 1 were inconsistent
with those of the natural product. Furthermore, the reported NOEs
between H-5/H-8 and H-5/H-80 were not observed. These results
suggest that the structure of natural pochonicine should be re-
vised. With the expectation of the NOE reported, we prepared
the 3-epimer 2 from the more polar isomer 18. However, 1H, and
13C NMR data of 210 did not match those of the natural product.
In re-examining the NMR data reported, we found that the sig-
nals derived from H-1 and 3 of the natural product were observed
at the low-filed rather than those of our synthetic samples, and
investigated the NMR data of the related pyrrolizidine alkaloids.
The papers reported by Kato et al.18 and Yoda and co-workers19
suggested that the chemical shift of such protons in the pyrrolizi-
Scheme 3. Reagents and conditions: (a) (i) TBAF, AcOH, THF, rt, 92%; (ii) TsCl, Et3N,
DMAP, CH2Cl2, 0 °C–>rt, 97%; (b) (i) NaN3, DMF, 60 °C, 72%; (ii) TBSOTf, 2,6-lutidine,
CH2Cl2, 0 °C, 91%; (c) (i) OsO4, NMO, acetone–water, rt, 98%; (ii) TBSCl, imidazole,
DMF, rt; (iii) MsCl, Et3N, DMAP, CH2Cl2, 0 °C–>rt, 45% for 5 and 35% for 18 (2 steps);
(d) (i) TMSOTf, 2,6-lutidine, CH2Cl2, 0 °C–>rt; (ii) Et3N, THF, rt–>70 °C, 84% from 5
for 19 and 85% from 18 for 20 (2 steps); (e) (i) Ph3P, THF–water, 60 °C; (ii) Ac2O,
pyridine, rt; (iii) HCl–MeOH, CH2Cl2, rt, 79% for 1 and 67% for 2 (3 steps).
dine alkaloids was affected by the stereochemistry of C-1 as well as
C-3. These results prompted us to compare the NMR data of the

1458
Y. Kitamura et al. / Tetrahedron Letters 54 (2013) 1456–1459
Supplementary data
Supplementary data (1H NMR data for MTPA esters of 6, 1H- and
13C NMR spectra of synthetic 4 and natural pochonicine) associated
with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.tetlet.2013.01.015.
References and notes
1. Usuki, H.; Toyo-oka, M.; Kanzaki, H.; Okuda, T.; Nitoda, T. Bioorg. Med. Chem.
2009, 17, 7248.
2. (a) Aoyagi, T.; Suda, H.; Uotani, K.; Kojima, F.; Aoyama, T.; Horiguchi, K.;
Hamada, M.; Takeuchi, T. J. Antibiot. 1992, 45, 1404; (b) Aoyama, T.; Naganawa,
H.; Suda, H.; Uotani, K.; Aoyagi, T.; Takeuchi, T. J. Antibiot. 1992, 45, 1557.
3. (a) Alhadeff, J. A.; Holzinger, R. T. Biochem. Med. 1982, 27, 214; (b) Drexler, H.
G.; Gaedicke, G.; Minowada, J. Leuk. Res. 1983, 7, 611; (c) Pluncinsky, C.; Propok,
J. J.; Alhadeff, M. D.; Alhadeff, J. A. Cancer 1986, 58, 1484; (d) Lo, C. H.;
Kritchevsky, D. J. Med. 1978, 9, 313.
4. (a) Takahashi, S.; Terayama, H.; Kuzuhara, H. Tetrahedron Lett. 1992, 33, 7565;
(b) Takahashi, S.; Kuzuhara, H. J. Chem. Soc., Perkin Trans. 1 1997, 607; (c)
Takahashi, S.; Kuzuhara, H. J. Carbohydr. Chem. 1998, 17, 117; (d) Takahashi, S.;
Nakajima, M.; Kuzuhara, H. Tetrahedron 2001, 57, 6915.
5. Cai, L.; Guan, W.; Kitaoka, M.; Shen, J.; Xia, C.; Chen, W.; Wang, P. G. Chem.
Commun. 2009, 2944.
6. The carbon-numbering system was conveniently according to the original
Letter.1
7. Baker, B. R.; Schaub, R. E. J. Org. Chem. 1954, 19, 646.
8. Ek, M.; Garegg, P. J.; Hultberg, H.; Oscarson, S. J. Carbohdr. Chem. 1983, 2, 305.
9. The regioisomer was not detected by TLC analysis.
Scheme 4. Reagents and conditions: (a) (i) TBAF, AcOH, THF, rt, 84%; (ii) TsCl, Et3N,
DMAP, CH2Cl2, 0 °C–>rt, 92%; (b) (i) NaN3, DMF, 60 °C, 75%; (ii) TBSOTf, 2,6-lutidine,
CH2Cl2, 0 °C, quant.; (c) (i) OsO4, NMO, acetone–water, rt, 92% in 2 steps; (ii) TBSCl,
imidazole, DMF, rt, 90%; (iii) MsCl, Et3N, DMAP, CH2Cl2, 0 °C–>rt, 38% for 23 and 36%
for 24 (2 steps); (d) (i) TMSOTf, 2,6-lutidine, CH2Cl2, 0 °C–>rt; (ii) Et3N, THF, 70 °C,
82% from 23 for 25 and 87% from 24 for 26 (2 steps); (e) (i) 10% Pd/C, H2, EtOAc, rt;
(ii) Ac2O, pyridine, rt; (iii) HCl–MeOH, CH2Cl2, rt, 50% for 3 and 66% for 4 (3 steps).
10. Spectral data of representative compounds:
1:½a 2D4
ꢂ
ꢁ13.6 (c = 0.34, MeOH); 1H NMR (600 MHz, CD3OD): d 4.44 (1H, ddd,
J = 5.0, 5.0, 3.3 Hz, H-1), 4.27 (1H, dd, J = 5.5, 5.0 Hz, H-7), 3.77 (1H, dd, J = 6.5,
5.0 Hz, H-6), 3.53 (1H, dd, J = 5.5, 5.0 Hz, H-7a), 3.50 (1H, dd, J = 11.0, 4.2 Hz, H-
8), 3.40 (1H, dd, J = 11.0, 6.0 Hz, H-80), 3.31 (2H, m, H-9 and 90), 3.27 (1H, dddd,
J = 8.7, 6.9, 6.0, 4.2 Hz, H-3), 3.02 (1H, ddd, J = 6.5, 5.1, 5.1 Hz, H-5), 2.02 (1H,
ddd, J = 12.9, 6.9, 3.3 Hz, H-2), 1.95 (3H, s, MeCO), 1.75 (1H, ddd, J = 12.9, 8.7,
5.0 Hz, H-20); 13C NMR (150 MHz, CD3OD): d 173.5 (CO), 76.8 (C-6), 74.4 (C-1),
74.1 (C-7), 71.4 (C-5), 70.7 (C-7a), 68.4 (C-3), 66.6 (C-8), 43.1 (C-9), 40.0 (C-2),
22.6 (Me); HRMS (ESI+) calcd for C11H21N2O5 [M+H]+ 261.1450, found:
261.1458.
Table 1
Inhibition of 4 against a couple of GlcNAcases
2: ½a 2D5
ꢂ
ꢁ16.9 (c = 0.36, MeOH); 1H NMR (600 MHz, CD3OD): d 4.42 (1H, ddd,
Origin of enzymes
IC50 (nM)
J = 6.0, 5.5, 4.1 Hz, H-1), 4.19 (1H, dd, J = 4.2, 4.1 Hz, H-7), 3.98 (1H, dd, J = 11.5,
7.3 Hz, H-8), 3.79 (1H, dd, J = 7.8, 4.2 Hz, H-6), 3.78 (1H, dd, J = 11.5, 3.7 Hz, H-
80), 3.51 (1H, m, H-5), 3.49 (1H, dd, J = 6.0, 4.1 Hz, H-7a), 3.45 (1H, dd, J = 13.3,
5.1 Hz, H-9), 3.39 (1H, m, H-3), 3.28 (1H, dd, J = 13.3, 5.0 Hz, H-90), 2.12 (1H,
ddd, J = 12.8, 7.3, 6.0 Hz, H-2), 1.87 (1H, ddd, J = 12.8, 5.5, 4.1 Hz, H-20), 1.95
(3H, s, MeCO); 13C NMR (150 MHz, CD3OD): d 173.6 (CO), 78.8 (C-6), 74.0 (C-7),
73.8 (C-1), 68.9 (C-7a), 63.4 (C-8), 62.4 (C-3), 61.6 (C-5), 43.7 (C-9), 40.8 (C-2),
22.6 (Me); HRMS (ESI+) calcd for C11H21N2O5 [M+H]+ 261.1450, found:
261.1455.
4
Pochonicinea
PUGNAcb
Spodoptera liturac
Jack bean
>14200
3130
5.96
0.288
714
678
a
These data were referred from the previous paper.1
b
O-(2-Acetamido-2-deoxy-
D-glucopyranosylidene)amino
N-phenylcarbamate
(PUGNAc)24 was used as a positive control.
c
A crude enzyme was employed for the assay.
3ꢀHCl: ½a 2D6
ꢂ
ꢁ10.4 (c = 0.53, MeOH); 1H NMR (600 MHz, CD3OD): d 4.74 (1H,
ddd, J = 6.0, 4.4, 2.5 Hz, H-1), 4.25 (1H, dd, J = 3.6, 3.6 Hz, H-7), 4.06 (1H, dd,
J = 9.5, 3.6 Hz, H-6), 4.03 (1H, dd, J = 3.6, 2.5 Hz, H-7a), 3.95 (1H, dd, J = 15.1,
3.3 Hz, H-9), 3.86 (3H, m, H-3, 8, and 80), 3.56 (1H, ddd, J = 9.5, 6.0, 3.3 Hz, H-5),
3.49 (1H, br dd, J = 15.1, 6.0 Hz, H-9’), 2.52 (1H, ddd, J = 13.8, 7.4, 6.0 Hz, H-2),
2.02 (3H, s, MeCO), 1.90 (1H, ddd, J = 13.8, 6.0, 4.4 Hz, H-20); 13C NMR
(150 MHz, CD3OD): d 175.9 (CO), 78.1 (C-7a), 75.0 (C-6), 74.1 (C-3), 70.9 (C-7),
70.7 (C-5), 70.2 (C-1), 61.8 (C-8), 39.6 (C-9), 38.3 (C-2), 22.3 (Me); HRMS (ESI+)
1-epimers of 1 and 2 with that of the natural product. The epimers
3 and 4 were synthesized via 25 and 26 from alcohol 15 according
to the method described for the preparation of
1 and 2
(Scheme 4).16 Comparing the data of both compounds with those
of the natural product, we found that the NMR data of 4 were con-
sistent with those of natural pochonicine.20 However, the sign of
the specific rotation value of 4ꢀHCl was opposite to that of natural
pochonicineꢀHCl.21 Furthermore, we examined the inhibitory activ-
ity of 4 against a couple of GlcNAcases.22 As shown in Table 1, the
inhibitory potency of 4 against GlcNAcases from Spodoptera litura,
and Jack bean was very weak compared to that of the natural prod-
uct. Based on these results, we concluded that 4 was an enantiomer
of the natural product, and that the structure of pochonicine
should be revised to be ent-4.
calcd for C11H21N2O5 [M+H]+ 261.1450, found: 261.1454.
4: ½a 2D6
ꢂ
+3.0 (c = 1.74, MeOH)
[lit. 1: ½a 1D7
ꢂ
+9.2 (c = 0.89, MeOH)]; 1H NMR
21
(600 MHz, CD3OD): d 4.55 (1H, ddd, J = 6.8, 6.4, 5.0 Hz, H-1), 3.94 (1H, dd,
J = 3.7, 3.7 Hz, H-7), 3.80 (1H, dd, J = 8.2, 3.7 Hz, H-6), 3.77 (1H, dd, J = 11.9,
3.6 Hz, H-8), 3.61 (1H, dd, J = 11.9, 5.1 Hz, H-80), 3.43 (1H, m), 3.38 (1H, dd,
J = 13.3, 5.5 Hz, H-9), 3.33 (1H, dd, J = 5.0, 3.7 Hz, H-7a), 3.28 (1H, dd, J = 13.3,
5.0 Hz, H-90), 3.19 (1H, ddd, J = 8.2, 5.5, 5.0 Hz, H-5), 2.09 (1H, ddd, J = 12.4, 6.4,
4.6 Hz, H-2), 1.95 (1H, ddd, J = 12.4, 7.4, 6.8 Hz, H-20), 1.94 (3H, s, MeCO); 13C
NMR (150 MHz, CD3OD): d 173.6 (CO), 79.0 (C-6), 75.2 (C-7a), 72.2 (C-7), 69.1
(C-1), 62.9 (C-8), 62.2 (C-3), 60.7 (C-5), 43.4 (C-9), 40.4 (C-2), 22.6 (Me); HRMS
(ESI+) calcd for C11H21N2O5 [M+H]+ 261.1450, found: 261.1447.
4ꢀHCl: ½a 2D6
ꢂ
ꢁ30.6 (c = 0.82, MeOH) [natural pochonicineꢀHCl23: ½a D27
ꢂ
+33.3
(c = 0.09, MeOH)]; 1H NMR (600 MHz, CD3OD): d 4.60 (1H, br d, J = 4.1 Hz, H-1),
4.22 (1H, dd, J = 4.6, 4.1 Hz, H-7), 4.14 (1H, dddd, J = 12.8, 8.2, 5.5, 2.7 Hz, H-3),
4.06 (1H, br d, J = 4.6 Hz, H-7a), 4.06 (1H, dd, J = 13.3, 2.7 Hz, H-8), 4.03 (1H, dd,
J = 15.1, 3.7 Hz, H-9), 4.01 (1H, dd, J = 9.7, 4.1 Hz, H-6), 3.93 (1H, dd, J = 13.3,
8.2 Hz, H-80), 3.91 (1H, ddd, J = 9.7, 4.1, 3.7 Hz, H-5), 3.53 (1H, dd, J = 15.1,
4.1 Hz, H-90), 2.25 (1H, ddd, J = 12.8, 12.8, 4.1 Hz, H-2), 2.03 (3H, s, MeCO), 1.96
(1H, br dd, J = 12.8, 5.5 Hz, H-20); 13C NMR (150 MHz, CD3OD): d 176.6 (CO),
79.3 (C-7a), 74.3 (C-6), 70.0 (C-7), 69.8 (C-1), 67.8 (C-3), 63.5 (C-5), 59.1 (C-8),
39.4 (C-9), 37.5 (C-2), 22.2 (Me).
In conclusion, the structural revision of pochonicine and deter-
mination of the absolute configuration were achieved by total syn-
thesis of the proposed structure for pochonicine and its three types
of diastereomers concerning the C-1 and/or C-3 positions.
Acknowledgement
6: ½a 2D6
ꢂ
+19.0 (c = 1.20, CHCl3); 1H NMR (500 MHz, CDCl3): d 7.65–7.60 (4H, m),
This work was supported by the Chemical Genomics Project (RI-
KEN) and in part by the Ministry of Education, Culture, Sports, Sci-
ence and Technology of Japan (MEXT, No. 24580168).
7.46–7.36 (6H, m), 6.41 (1H, s), 6.07 (1H, m), 5.14 (1H, br d, J = 17.1 Hz), 5.07
(1H, br d, J = 10.2 Hz), 4.70 (2H, br s), 4.17 (1H, br s), 4.03 (1H, br s), 3.79 (1H, br
dd, J = 7.9, 2.5 Hz), 3.75–3.69 (2H, m), 2.66 (br d, J = 14.2 Hz), 2.42 (1H, m), 1.44

Y. Kitamura et al. / Tetrahedron Letters 54 (2013) 1456–1459
1459
(3H, s), 1.33 (12H, br s), 1.04 (9H, s); 13C NMR (125 MHz, CDCl3): d 155.4, 135.7,
135.6, 135.4, 132.7, 132.6, 129.92, 129.87, 127.90, 127.86, 116.5, 111.3, 80.8,
80.6, 79.6, 69.7, 68.3, 66.9, 64.1, 38.1, 28.3, 26.9, 26.8, 25.2, 19.1; HRMS (ESI+)
calcd for C33H47NO6Si [M+Na]+ 604.3070, found: 604.3069.
17. Bastiaans, H. M. M.; van der Baan, J. L.; Ottenheijm, H. C. J. J. Org. Chem. 1997,
62, 3880.
18. Kato, A.; Kato, N.; Adachi, I.; Hollinshead, J.; Fleet, G. W. J.; Kuriyama, C.; Ikeda,
K.; Asano, N.; Nash, R. J. J. Nat. Prod. 2007, 70, 993.
19. Sengoku, T.; Satoh, Y.; Takahashi, M.; Yoda, H. Tetrahedron Lett. 2009, 50, 4937.
20. Since pochonicine is a highly polar basic compound, the chemical shifts of its
protons in the 1H NMR spectra readily change in the presence of a trace
15: ½a 2D6
ꢂ
+57.4 (c = 0.93, CHCl3); 1H NMR (500 MHz, CDCl3): d 7.63–7.57 (4H,
m), 7.47–7.37 (6H, m), 5.99 (1H, m), 5.09 (1H, br d, J = 17.3 Hz), 5.04 (1H, br d,
J = 10.3 Hz), 4.90 (1H, br d, J = 10.3 Hz), 4.88 (1H, t, J = 6.6 Hz), 4.71 (1H, br d,
J = 6.6 HZ), 4.20 (1H, br d, J = 6.4 Hz), 4.12 (1H, br t, J = 10.3 Hz), 4.00 (1H, br s),
3.90 (1H, br d, J = 10.3 Hz), 3.67 (1H, dd, J = 10.5, 2.0 Hz), 2.50 (1H, m), 2.15 (1H,
m), 1.52 (3H, s), 1.34 (12H, br s), 1.05 (9H, s); 13C NMR (125 MHz, CDCl3): d
156.1, 136.8, 135.6, 135.5, 132.6, 132.4, 130.0, 129.9, 127.93, 127.89, 115.7,
111.1, 81.1, 80.7, 80.1, 70.1, 68.2, 64.8, 64.5, 38.0, 28.3, 26.9, 25.4, 23.7, 19.1;
HRMS (ESI+) calcd for C33H47NO6Si [M+Na]+ 604.3070, found: 604.3069.
11. The ratio was determined by 1H NMR analyses. The results of allylation under
other conditions are as follows; (1) allylMgBr, Et2O, ꢁ78 °C, 84% (6/15 = 62/38);
amount of a base or acid. Therefore, it was very difficult to match the NMR data
1
of 4 or even natural pochonicine with those of the original Letter.
identification by NMR analyses, HPLC treatment of
For
4
under the same
conditions that were used at the final stage of the purification of the
authentic sample was needed. Otherwise 4 did not afford the same NMR
spectra as those of the natural sample.
21. The specific rotation value of the free amine was small and its data were found
to change around
0 by the pH (see above). On the other hand, the
corresponding hydrochloride salt23 afforded the relatively large and reliable
data.
(2) allyltributylstannane, BF3ꢀEt2O, CH2Cl2, ꢁ78 °C–>rt, 14% (6/15 = 71/29); (3)
14
allylbromide, indium,
THF, ꢁ78 °C–>rt, 37% (6/15 = 54/46).
12. Ohtani, I.; Kusumi, T.; Kashman, Y.; Kakisawa, H. J. Am. Chem. Soc. 1991, 113,
4092.
22. Usuki, H.; Nitoda, T.; Okuda, T.; Kanzaki, H. J. Pestic. Sci. 2006, 31, 41.
23. The corresponding hydrochloride salt was prepared by treatment of the free
amine with HCl in methanol.
13. See Supplementary data.
14. Beuchet, P.; Le Marrec, N.; Mosset, P. Tetrahedron Lett. 1992, 33, 5959.
15. Kolb, H. C.; VanNieuwenhze, M. S.; Sharpless, K. B. Chem. Rev. 1994, 94, 2483.
16. Selected NOEs (600 MHz, CDCl3) are shown below.
24. Horsch, M.; Hoesch, L.; Vasella, A.; Rast, D. M. Eur. J. Biochem. 1991, 197, 815.