Synthesis of polyhydroxylated pyrrolizidine and indolizidine compounds and their glycosidase inhibitory activities

Article abstract of DOI:10.1016/j.tet.2010.10.008

The synthesis of the natural product 3-epi-casuarine and two tricyclic ether bridged analogues, plus 7-deoxy-3,6-diepi-casuarine, 7-epi-australine, 1-epi-castanospermine and 1,6-diepi-castanospermine is described. The glycosidase inhibitory activities of

Full text of DOI:10.1016/j.tet.2010.10.008

Tetrahedron 66 (2010) 9340e9347
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis of polyhydroxylated pyrrolizidine and indolizidine compounds
and their glycosidase inhibitory activities
,
Thunwadee Ritthiwigrom a, Robert J. Nash b, Stephen G. Pyne a
*
a School of Chemistry, University of Wollongong, Wollongong, New South Wales 2522, Australia
b Phytoquest Limited, IBERS, Plas Gogerddan, Aberystwyth, Ceredigion, SY23 3EB, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 July 2010
Received in revised form 17 September 2010
Accepted 4 October 2010
The synthesis of the natural product 3-epi-casuarine and two tricyclic ether bridged analogues, plus
7-deoxy-3,6-diepi-casuarine, 7-epi-australine, 1-epi-castanospermine and 1,6-diepi-castanospermine is
described. The glycosidase inhibitory activities of these compounds, along with that of uniflorine A and
other polyhydroxylated pyrrolizidines and indolizidines that we have published before, are reported.
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
resulted in the formation of two tricyclic bridged ether analogues
of 3-epi-casuarine. The synthesis of 7-deoxy-3,6-diepi-casuarine,
The polyhydroxylated 3-hydroxymethylpyrrolizidine group of
natural products includes, uniflorine A 1,1,2,3 casuarine 2,4 australine
3,5 3-epi-australine 46,7 (Fig. 1), alexine8 (7a-epi-australine), several
other epi-australines (1-epi-australine, 3-epi-australine, 2,3-
7-epi-australine, 1-epi-castanospermine and 1,6-diepi-castano-
spermine is also described. The glycosidase inhibitory activities of
these compounds, along with that of uniflorine A 1 and other
polyhydroxylated pyrrolizidine and indolizidines that we have
published before, are reported.
diepi-australine, 2,3,7-tri-epi-australine),9 1-epi-australine-2-O-
b-
glucoside, 3-epi-casuarine,10 and casuarine-6-O- -glucoside.11 The
a
hyacinthacine alkaloids are a more recent addition to this group of
which nineteen novel compounds have been identified.12 This group,
along with the polyhydroxylated pyrrolidine, piperidine, indolizidine
and nortropane alkaloids, have glycosidase inhibitory activities and
thus have potential utility as antiviral, anticancer, antidiabetic and
antiobesity drugs.7 Three structurally related synthetic compounds
have been marketed as antidiabetic drugs to treat type-2 diabetes
2. Results and discussion
Our anticipated synthesis of 3-epi-casuarine 7 from the epoxide
6 (Scheme 2) involved a regioselective ring-opening reaction of the
epoxide moiety of 6 with NaHSO4,14 a reagent that we had suc-
cessfully applied to the synthesis of casuarine 2 from 3-epi-6.13
The epoxy-pyrrolizidine 6 was treated with NaHSO4/CH2Cl2
under the conditions that we described before13 except that heat-
ing at 50 ꢀC was continued for 7 days (Scheme 3). We attribute the
slower rate of epoxide ring-opening of 6, when compared to that of
based on their potent a-glucosidase inhibitory activities while others
have been identified as candidates for therapeutics to treat type-1
Gaucher disease.7 These potentially useful biological activities along
with the stereochemical richness of these alkaloids have made these
compounds attractive and important synthetic targets.13
3-epi-6, to the increased steric hindrance of the
oxide moiety due to the 3- -CH2OTBS substituent. Because of the
a-face of the ep-
a
WerecentlyreportedthesynthesisofuniflorineA 1fromthechiral
2-substituted-2,5-dihydropyrrole 5 (Scheme 1), which is readily
slow reaction rate hydrolytic cleavage of the OTBS group also oc-
curred resulting in a mixture of products that was difficult to sep-
arate. Acetylation of this mixture and then separation by column
chromatography gave the desired acetylated product 8 (7% yield),
the epoxide 9 in 9% yield and the undesired tricyclic bridged ether
products 10 (8%) and 11 (17%) (Scheme 3). The isolation of epoxide 9
indicated that OTBS cleavage was faster than either the in-
termolecular or intramolecular (leading to tricyclic bridged ether
products) epoxide ring-opening reactions. Unfortunately, several
attempts to improve the yield of the desired compound 8 were not
successful. While the use of a more stable protecting group for the
primary alcohol group in 6 may have been more efficient this var-
iation was not examined.
prepared in four synthetic steps from L
-xylose.13 We also demon-
strated that compound 5 is a versatile precursor for the diaster-
eoselective synthesis of the alkaloids casuarine 2, australine 3 and
3-epi-australine 4 and the unnatural epimer, 3,7-epi-australine.13
In this paper we describe our attempts to prepare the natural
product 3-epi-casuarine 710 from the epoxide 6 that we have syn-
thesized previously in seven steps from 5.13 This synthesis also
* Corresponding author. E-mail address: spyne@uow.edu.au (S.G. Pyne).
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.10.008

T. Ritthiwigrom et al. / Tetrahedron 66 (2010) 9340e9347
9341
HO
7
OH
HO
OH
H
OBn
OBn
H
H
N
O
1
7a
N
HO
OH
OH
HO
OH
N
3
5
8
OH
casuarine
2
uniflorine A
1
6
OTBS
(70%)
L
-xylose
OH
O
a
H
+
4 steps
O
NH2
+
AcO
AcO
OBn
OBn
OAc
NBoc OH
5
OBn
OBn
OAc
H
N
H
B(OH)2
Ph
O
N
HO
OH
HO
H
OH
H
N
9
8
OH
OH
OH
N
(7%)
(9%)
+
OH
australine
3
3-epi-australine
4
OBn
OBn
OBn
AcO
O
H
H
N
7
6
Scheme 1.
1
OBn
AcO
5
N
3
OBn
O
H
O
10
11
7 steps
(8%)
OBn
(17%)
5
N
c
6
d
OTBS
OH
HO
O
OH
H
N
H
N
OH
HO
OH
HO
OH
H
N
O
HO
OH
13
12
(53%)
(82%)
OH
3-epi-casuarine
7
Scheme 2.
HO
OH
OH
H
N
b
8
Hydrogenolysis of 8 over PdCl2/H2 in MeOH for 4 days gave
diastereomerically pure 3-epi-casuarine 7 ([
HO
25
a]
þ2.0 (c 0.4, H2O),
D
lit.10
[
a]
þ5.7 (c 0.5, H2O)) in 77% yield after purification by ion-
23
D
OH
exchange chromatography (Scheme 3). The 1H NMR spectroscopic
data (D2O) of 7 and those of the natural product were essentially
identical (DdH¼0.01e0.02 ppm) as were the 13C NMR chemical
shifts (DdC¼0.0e0.1 ppm).10 The reasons for the difference in the
magnitude of the optical rotation between our synthetic 7 and the
natural isolate were perhaps due to the relatively small amount of
sample we had, compared to that obtained from the natural source,
which may have lead to difficulties in drying (slightly hydroscopic)
and weighing our sample.
7
)
(77%
Scheme 3. Reagents and conditions: (a) (i) NaHSO4, CH2Cl2, 50 ꢀC, 7 days; (ii) Ac2O, py,
DMAP, 24 h; (b) PdCl2, H2 (1 atm), MeOH, 4 days; ion-exchange, 77%; (c) Amberlyst OH,
MeOH, rt, 12 h; PdCl2, H2 (1 atm), MeOH, 24 h; ion-exchange, 82%; (d) Amberlyst
(OHꢁ), MeOH, rt, 16 h; PdCl2, H2 (1 atm), MeOH, 12 h; ion-exchange, 53%.
individually assigned based upon their vicinal coupling constants
to H-6 and from NOESY NMR spectra. Using PC Spartan (AM1) the
dihedral angle (
H-6 and H-5
was 0.2ꢀ. Based on the Karplus equation15 J5 ,6 should
be 3e6 Hz and J5 8.5e12.5 Hz. The larger observed vicinal cou-
4) between H-6 and H-5b
was 120.3ꢀ and between
The relative ratio of 10 and 11 (ca. 1:2) was consistent with their
relative heats of formation as calculated using PC Spartan (AM1).
The calculated heat of formation of 10 (ꢁ122.3 kcal/mol) was more
than that of 11 (ꢁ129.8 kcal/mol) suggesting 10 had more ring
strain than 11. This energy difference would be expected to be
reflected in the differences in transition state energies leading to
these regioisomeric products. The identities of 10 and 11 were
established by 1D and 2D NMR analysis. The 1H NMR spectrum of
10 showed that the most downfield proton (H-6) at 5.24 (dd, 1H,
J¼6.4, 2.8 Hz) ppm was coupled to two of the diastereotopic H-5
a
b
a
,6
pling constant (6.4 Hz) between H-6 and the two H-5 protons was
therefore assigned to J5 and the smaller one (2.8 Hz) to J5
a
,6
b,6.
While the most downfield proton in the 1H NMR spectrum of 11 (H-
7) resonated at 4.97 (br s, W1/2¼1 Hz, 1H) ppm and showed a weak
COSY cross peak to H-5
a (W-coupling). The calculated dihedral
angle from PC Spartan (AM1) between H-7 and H-6 was 99.2ꢀ and
between H-7 and H-7a was 128.8ꢀ. From the Karplus equation J6,7
should be 0e3 Hz and J7,7a 3e7 Hz. The coupling constants observed
for H-7 were consistent with the calculated J values and the
protons at 3.65 (dd, 1H, J¼14.4, 6.4 Hz, H-5
a) and 2.85 (dd, 1H,
J¼14.4, 2.8 Hz, H-5 ) ppm. The H-5 and H-5
b
a
b
protons were

9342
T. Ritthiwigrom et al. / Tetrahedron 66 (2010) 9340e9347
The acetate group of 10 was first removed using Amberlyst (OHꢁ
form) in MeOH and then hydrogenolysis over PdCl2/H2 in MeOH for
1 day gave the deprotected tricyclic bridged ether derivative 12
23
[a
]
þ8.6 (c 0.5, MeOH), in 82% yield after ion-exchange chroma-
D
tography (Scheme 3). Following the same two-step deprotection
method described above, compound 11 was converted to the tri-
23
cyclic derivative 13 [
a
]
D
þ7.6 (c 0.34, MeOH), in 53% yield after
purification by ion-exchange chromatography (Scheme 3).
In order to prepare further polyhydroxylated pyrrolizidine and
indolizidine derivatives for testing as glycosidase inhibitors several
compounds that we obtained as byproducts from our earlier
studies13 were deprotected and/or modified as indicated in the
following discussion. The alcohol 14,13 which we had obtained as
a minor regioisomeric product from the reductive ring-opening
reaction of 6 with LiAlH4, underwent hydrogenolysis over PdCl2/H2
to provide a product that was difficult to purify. This material was
subsequently acetylated by treatment with Ac2O in pyridine and
the peracetylated product was readily purified. Following deace-
tylation using Amberlyst A-26 (OHꢁ) in MeOH then pure 7-deoxy-
3,6-diepi-casuarine 15 ([
50% yield over the three steps (Scheme 4).
a
]
23 þ28.6 (c 0.23, MeOH)) was obtained in
D
OBn
H
OH
H
N
a-c
HO
OH
OH
HO
OBn
N
15
14
OTBS
(50%)
Scheme 4. Reagents and conditions: (a) PdCl2, H2 (1 atm), MeOH, rt, 3 h; then concd
HCl five drops; (b) Ac2O, py, DMAP, rt, 24 h; (c): Amberlyst A-26 (OHꢁ), MeOH, 3 h, 50%
(three steps).
The previously prepared indolizidine 1613 was treated with
LiAlH4 in THF at rt for 20 h to provide the indolizidine 17 as the only
regioisomeric product in 60% yield. Hydrogenolysis of 17 under
acidic conditions with PdCl2/H2 afforded 1,6-diepi-castanospermine
18 [
a
]
25 ꢁ74.2 (c 1.5, MeOH), lit.16
[
a
]
24 ꢁ72.0 (c 0.7, MeOH) in 95%
D
D
yield and 95% purity (Scheme 5). The 1H NMR spectroscopic data
(D2O) of 18 were consistently downfield (DdH¼0.11e0.15 ppm) from
those reported for the synthetic material prepared by Fleet et al.16
The 13C NMR spectroscopic data (in D2O with MeCN as an internal
reference at
d 1.47) of 18 and that reported in the literature for 1,6-
diepi-castanospermine were all consistently 0e0.2 ppm downfield.
Hydrogenolysis of a mixture of 19 and 20 (dr 92:8)13 over PdCl2/
H2 followed by purification and neutralized by ion-exchange
chromatography gave 7-epi-australine 21 in 90% yield (Scheme 6).
1H NMR analysis suggested that 21 was of 92% purity ([
a
]
23 ꢁ13.2 (c
D
25
1.2, H2O), lit.17
[a
]
ꢁ13.04 (c 0.55, H2O, pH 8.37)). The 1H NMR
D
spectroscopic data (D2O) of 21 were all consistently downfield
OBn
HO
OBn
HO
H
H
Fig. 1. Structures of 10 and 11 from PC Spartan (AM1).
OBn
OBn
O
a
N
N
structure of 11. The structures and relative configurations of 10 and
11 were further supported by NOESY NMR experiments (Fig. 1).
OTBS
OTBS
17
16
The NOESY correlation between H-7a and H-5
that these protons were on the same face of the ring. The correla-
tion between H-5 and H-8 indicated that H-3 was on the opposite
face to H-5 . The NOESY correlation between H-3 and H-2 in-
b in 10 indicated
(60%)
OH
H
N
a
OH
OH
b
a
dicated that they were on the same face of the ring. Furthermore
NOESY correlations between H-6 and H-8 further supported the
structure of 10 as shown in Fig. 1. NOESYexperiments on 11 showed
18
(95%)
correlations between H-7 and H-1, H-7a and H-5
H-5 showed a weak correlation to H-8. These correlations further
supported the structure assigned to 11.
b and H-2 and H-3.
a
Scheme 5. Reagents and conditions: (a) LiAlH4, THF, rt, 20 h, 60% (b) PdCl2, H2 (1 atm),
MeOH, rt, 4 days; ion-exchange, 95%.

T. Ritthiwigrom et al. / Tetrahedron 66 (2010) 9340e9347
9343
Table 1
OBn
OBn
OTBS
OBn
HO
H
N
H
N
The glycosidase inhibition of uniflorine A 1 (Mean % Inhibition at 143 mg/mL)
Enzyme
Source
pH
6.8
% Inhibitions
94
+
HO
OBn
a
-
-
-
D
D
D
-Glucosidase
S. cerevisiae
IC50 34
m
M
a
-Glucosidase
B. stearothermophilus
6.8
97
OTBS
IC50 28
m
M
19
20
a
b
a
-Glucosidase
-Glucosidase
-Galactosidase
Rice
4
5
6.5
ND
5
5
19 20
:
(
= 92:8)
-
D
Almond (Prunus sp.)
Green coffee
-
D
bean (Coffea sp.)
Bovine liver
Bovine kidney
Jack bean
(Canavalia ensiformis)
Cellullomonas fimi
Penicillium decumbens
a
b
a
a
-
-
-
D
-Galactosidase
7.3
5.5
4.5
0
ND
5
L-Fucosidase
HO
OH
D
-Mannosidase
H
b
-
D
-Mannosidase
6.5
4
4.25 13
5
5
2
ND
OH
OH
Naringinase
N
21
N-Acetyl-
N-Acetyl-
N-Acetyl-
b
b
b
-D
-D
-D
-glucosaminidase Bovine kidney
-glucosaminidase Jack bean
-hexosaminidase Aspergillus oryzae
5
ND
97
0
(90%)
Amyloglucosidase
-Glucuronidase
A. niger
Bovine liver
4.5
5
b
Scheme 6. Reagents and conditions: (a) PdCl2, H2 (1 atm), MeOH, rt, 3 h, then concd
HCl rt, 17 h, ion-exchange, 90%.
ND¼No determined.
(
DdH¼0.16e0.18 ppm) of those of the synthetic compound prepared
by Denmark and Martinborough.17 The 13C NMR signals of 21 (in
inhibition with only compounds 13, 18, 23, 25 and 27 showing
approximately 40e50% inhibition against the -glucosidase from
B. stearothermophilus at this relatively high concentration (Table 2).
1,6-Diepi-castanospermine showed similar activity against almond
D2O with MeCN as an internal reference at d 1.47) were consistently
a-D
1.0e1.1 ppm downfield of those reported earlier.17
Hydrogenolysis of 2213 over PdCl2/H2 gave diastereomerically
22
pure 1-epi-castanospermine 23 ([
a
]
D
þ3.3 (c 0.3, MeOH)), lit.18
b-
D-glucosidase and
a-D-galactosidase (coffee bean).
26
[
a]
þ3.8 (c 0.5, MeOH), in 94% yield after ion-exchange chroma-
D
tography (Scheme 7). The 1H NMR spectroscopic data (D2O) of 23
and those of the synthetic compound from Murphy19 were essen-
tially identical (DdH¼0.02e0.03 ppm). The 13C NMR signals of 23 (in
D2O with MeCN as an internal reference at 1.47 ppm) however,
were all consistently 1.7e1.8 ppm downfield of those reported
previously. However the internal reference used in the published
13C NMR spectrum was not reported.19
3. Conclusions
The total synthesis of naturally occurring 3-epi-casuarine 8 was
achieved in 13 steps and in 0.4% overall yield from -xylose. The low
L
overall yield was due to a poor yielding epoxide ring-opening re-
action due to a competing intramolecular epoxide ring-opening
reaction involving the 3-a-hydroxymethyl substituent. We also
report the synthesis of two novel tricyclic ether bridged analogues
of 3-epi-casuarine, plus 7-deoxy-3,6-diepi-casuarine, 7-epi-aus-
traline, 1-epi-castanospermine and 1,6-diepi-castanospermine. The
glycosidase inhibitory activities of these compounds, along with
that of uniflorine A and other polyhydroxylated pyrrolizidine and
indolizidines that we have published before, are reported. Uni-
OBn
OH
HO
HO
H
H
OBn
a
OH
OH
N
N
OTBS
23
22
florine A showed moderate activity against the
a
-D-glucosidases
(90%)
from S. cerevisiae and B. stearothermophilus (IC50 34 and 28
mM,
respectively). None of the other compounds tested showed any
significant inhibitory activities.
Scheme 7. Reagents and conditions: (a) PdCl2, H2 (1 atm), MeOH, rt, 3 h, then concd
HCl rt, 21 h, ion-exchange, 94%.
A comparative study of the inhibitory activities of alexine, aus-
4. Experimental
traline, casuarine and some of their epimers and O-
coside derivatives against a panel of glycosidase enzymes revealed
that casuarine and 1-epi-australine-2-O- -glucoside were the most
potent compounds.9 These alkaloids showed low
M activities
against several -glucosidases. For example, casuarine had an IC50
value of 0.7 M against rat intestinal maltase and of 0.7 M against
a- and O-b-glu-
4.1. General methods
b
m
All IR spectra were run as neat samples. All NMR spectra were
run at 500 MHz (1H NMR) or 125 MHz (13C NMR) in solutions of
CDCl3 unless otherwise noted. NMR assignments were made on the
basis of COSY, DEPT, HSQC and sometimes HMBC experiments. In
the 1H NMR assignments of some compounds the diastereotopic
H-8 (pyrrolizidine compounds) and H-5 protons (indolizidine
compounds) are referred to H-8a and H-8b and H-5a and H-5b,
respectively where the most downfield proton is labelled as ‘a’.
Petrol refers to the hydrocarbon fraction of bp 40e60 ꢀC. FCC is an
abbreviation for flash column chromatography.
a
m
m
amyloglucosidase from Aspergillus niger. In a separate study, uni-
florine A 1 wasshownto have moderate inhibitoryactivityagainst the
a
-glucosidases, rat intestinal maltase and sucrase, with IC50 values of
12 and 3.1
M, respectively.1 The results of our glycosidase inhibitor
testingforsyntheticuniflorineA113 areshowninTable 1. At143
g/mL
uniflorine A 1 showed 94e97% inhibition against the -glucosidases
m
m
a-D
of Saccharomyces cerevisiae and Bacillus stearothermophilus and
against amyloglucosidase of A. niger. The IC50 values were only de-
termined for the two aforementioned
a
-
D
-glucosidases and were
4.1.1. (1S,2S,5S,6R,7R,7aR)-5-(Acetoxymethyl)-6,7-bis(benzyloxy)-1,2-
diacetoxy-hexahy-dro-1H-pyrrolizine (8), (1aR,4S,5R,6R,6bS)-5,6-bis
(benzyloxy)-4-(acetoxymethyl)hexahydro-1aH-oxireno[2,3-a]pyrroli-
zine (9) 1,2-bis(benzyloxy)-6-acetoxy-3-methyl-7,8-epoxyindolizidine
(10) and 1,2-bis(benzyloxy)-7-acetoxy-3-methyl-6,8-epoxy-indolizidine
found to be modest at 34 and 28 M, respectively.
m
Compounds 12, 13, 15, 18 and 23 along with the pyrrolizidine
2413 and the indolizidines 25,20 262 and 272 were screened against
10 different glycosidases at 143
mg/mL. None showed strong

Table 2
The glycosidase inhibition of synthesized compounds (Mean % Inhibition at 143
m
g/mL)
-Glucosidase
Compound No.
Structures
a
-
D
-Glucosidase
b
-
D
a
-
D
-Galactosidase
b-
D
-Galactosidase
a
-D
-Mannosidase
b
-D
-Mannosidase N-acetyl-
b-
D
-Glucosaminidase
b-Glucuronidase
(Yeast) (Bacillus)
Bovine kidney
Jack bean
Bovine liver
OH
H
N
Tricyclic 12
0
24
50
0
0
6
0
0
17
24
0
OH
HO
O
OH
HO
H
Tricyclic 13
44
27
ND
19
-21
12
17
30
26
8
OH
N
O
HO
H
OH
3,7-Diepi-australine$
HCl 24$HCl13
OH
0
ꢁ9
0
ꢁ11
ꢁ38
0
0
0
0
7
0
ND
ND
N
H
OH
OH
Cl
H
N
7-Deoxy-3,6-diepi-
casuarine 15
HO
OH
ꢁ13
ꢁ16
ꢁ34
40
ꢁ29
ꢁ17
OH
OH
HO
H
N
HO
HO
1,6-Diepi-castanospermine 18
1-epi-Castanospermine 23
36
14
43
43
55
24
45
0
31
25
23
30
0
7
ꢁ12
ND
0
HO
OH
H
N
HO
HO
ꢁ10
13
17
HO
OH
H
HO
252
0
0
42
34
16
18
0
0
21
8
0
0
ꢁ11
ꢁ14
19
25
0
0
ꢁ7
OH
N
HO
HO
OH
H
N
HO
HO
262
0
OH
HO
OH
H
N
HO
HO
272
20
44
13
ꢁ7
7
ꢁ25
0
0
0
0
OH
ND¼No determined.

T. Ritthiwigrom et al. / Tetrahedron 66 (2010) 9340e9347
9345
(11). To a solution of the epoxide 6 (100.0 mg, 0.208 mmol) in an-
hydrous CH2Cl2 (5 mL) was added NaHSO4 (125 mg, 1.04 mmol). The
reaction mixture was stirred and heated at reflux for 7 days under an
atmosphereofN2. Thereactionwasquenched bytheadditionofwater
(5 mL) and stirred for 1 h. The solvent was removed under reduced
pressure and the residue was extracted with EtOAc (3ꢂ10 mL). TLC
analysis showed four major products. The crude mixture was purified
by FCC (100% EtOAc to 8.0:1.5:0.5 EtOAc/MeOH/NH3). The fractions
were not pure and they were combined, evaporated and then acety-
lated. To a solution of the crude product in pyridine (2.0 mL) was
added acetic anhydride (0.184 mL, 1.95 mmol) and a crystal of 4-
dimethylaminopyridine. The mixture was stirred at rt for 24 h. The
reaction was quenched by the addition of satd NaHCO3 solution, fol-
lowed by removal of the solvent under reduced pressure. The residue
was extracted with CH2Cl2 (3ꢂ10 mL). The combined CH2Cl2 extracts
were washed with water (10 mL), dried (Na2CO3), filtered and then
evaporated. The residue was purified by FCC (90:10 EtOAc/petrol to
8.5:1:0.5 EtOAc/MeOH/NH3) to give 8 as a pale yellow oil (7.0 mg, 7%),
10 as a colourlessoil(6.7 mg, 8%), 9 as a paleyellowoil(8.0mg, 9%)and
2929, 2873, 1735, 1378, 1237, 1120. 1H NMR
d
7.41e7.26 (m, 10H, Ar),
4.97 (br s, 1H, H-7), 4.75 (d, 1H, J 12.0 Hz, CHHPh), 4.66 (d, 1H, J
12.5 Hz, CHHPh), 4.61 (d, 1H, J 12.0 Hz, CHHPh), 4.48 (d, 1H, J
12.0 Hz, CHHPh), 4.24e4.23 (m, 2H, H-1 and H-2), 4.17 (s, 1H, H-6),
3.71 (d, 1H, J 10.5 Hz, H-8), 3.56e3.53 (m, 2H, H-3 and H-8), 3.47 (d,
1H, J 13.0 Hz, H-5
a
), 3.25 (br s, 1H, H-7a), 2.72 (dd, 1H, J 13.0, 1.0 Hz,
H-5b
), 2.05 (s, 3H, CH3). 13C NMR
d
170.0 (CO), 138.2 (C), 138.0 (C),
128.4 (CH), 128.3 (CH), 127.9 (CH), 127.8 (CH), 127.7 (CH), 127.6 (CH),
86.0 (C-1), 84.7 (C-2), 81.8 (C-7), 75.3 (C-6), 74.2 (C-7a), 72.5 (CH2),
72.1 (CH2), 62.9 (C-3), 55.7 (C-8), 49.4 (C-5), 21.0 (CH3).
4.1.2. (1R,2R,3S,6S,7S,7aR)-3-(Hydroxymethyl)-hexahydro-1H-pyr-
rolizine-1,2,6,7-tetraol (3-epi-casuarine (7)). To a solution of 8
(14 mg, 0.027 mmol) in MeOH (1 mL) was added PdCl2 (9.7 mg,
0.055 mmol). The mixture was stirred at rt under an atmosphere of
H2 (balloon) for 4 days. The mixture was filtered through a Celite
pad and the solids were washed with MeOH. The combined filtrates
were evaporated in vacuo and the residue was dissolved in water
(1 mL) and applied to a column of Amberlyst A-26 (OHꢁ) resin
11 as a pale yellow oil (14.0 mg, 17%).
(3 cm). Elution with water followed by evaporation in vacuo gave 3-
22
25
Compound 8: Rf 0.47 (50:50 EtOAc/petrol). [
a
]
þ22.3 (c 1.4,
epi-casuarine 7 as a white solid (4.3 mg, 77%). [
a
]
þ2.0 (c 0.04,
D
D
23
CHCl3). MS (ESI þve) m/z 512 (MþHþ, 100%). HRMS (ESI þve) cal-
H2O), lit.10
[a
]
þ5.7 (c 0.5, H2O). MS (ESI þve) m/z 206 (MþHþ,
D
culated for C28H34NO8 (MþHþ) 512.2284, found 512.2277. IR nmax
100%). HRMS (ESI þve) calculated for C8H16NO5 (MþHþ) 206.1028,
(cmꢁ1): 2919, 1738, 1372, 1228, 1042. 1H NMR
d 7.36e7.26 (m, 10H,
found 206.1024. IR nmax (cmꢁ1): 3300, 2924, 2901, 1361, 1027. 1H
Ar), 5.32 (app. dt, 1H, J 8.0, 6.7 Hz, H-6), 5.22 (app. t, 1H, J 6.7 Hz, H-
7), 4.61 (d, 1H, J 12.3 Hz, CHHPh), 4.55 (d, 1H, J 11.5 Hz, CHHPh), 4.48
(d,1H, J 11.5 Hz, CHHPh), 4.42 (dd,1H, J 11.1, 6.7 Hz, H-8), 4.37 (d,1H,
J 12.3 Hz, CHHPh), 4.34 (dd, 1H, J 11.1, 7.8 Hz, H-8), 4.30 (br s, 1H, H-
1), 3.95 (d, 1H, J 4.0 Hz, H-2), 3.49e3.45 (m, 1H, H-3), 3.40e3.30 (m,
NMR (D2O)
d
4.28 (br s, 1H, H-1), 4.19 (dd, 1H, J2,3¼3.5, J1,2¼1.5 Hz,
H-2), 4.11 (dt, 1H, J5,6¼7.8, J5,6¼J6,7¼8.0 Hz, H-6), 4.05 (t, 1H,
J6,7¼J7,7a¼8.0 Hz, H-7), 4.00 (dd, 1H, J8,8¼11.7, J3,8a¼6.6 Hz, H-8a),
3.94 (dd, 1H, J8,8¼11.7, J3,8b¼7.0 Hz, H-8b), 3.27 (ddd, 1H, J3,8a¼6.6,
J3,8b¼7.0, J2,3¼3.5 Hz, H-3), 3.10 (d, 3H, J7,7a¼8.0 Hz, 2ꢂH-5 and H-
1H, H-7a), 3.31 (app. t, 1H, J 7.8 Hz, H-5
H-5
), 2.11 (s, 3H, CH3), 2.05 (s, 3H, CH3), 2.01 (s, 3H, CH3). 13C NMR
170.9 (CO), 170.8 (CO), 170.3 (CO), 137.7 (C), 137.6 (C), 128.5 (CH),
b), 3.13 (app. t, 1H, J 8.0 Hz,
7a). 13C NMR (D2O)
d 80.4 (C-1), 79.7 (C-2), 79.2 (C-7), 75.9 (C-6),
a
75.5 (C-7a), 64.9 (C-3), 57.4 (C-8), 51.6 (C-5).
d
128.4 (CH), 127.9 (CH), 127.8 (CH), 127.7 (CH), 127.6 (CH), 85.7 (C-1),
85.6 (C-2), 79.0 (C-7), 76.5 (C-6), 73.8 (C-7a), 71.8 (CH2), 71.7 (CH2),
62.3 (C-3), 60.6 (C-8), 50.4 (C-5), 20.94 (CH3), 20.9 (CH3), 20.8 (CH3).
Compound 9: (NMR assignments are given based on the num-
bering system of the parent pyrrolizine (compare with 8 above) and
are not based on the systematic compound name give in the title).
Rf 0.34 (100% EtOAc). MS (ESI þve) m/z 410 (MþHþ, 100%). 1H NMR
4.1.3. 1,2-Bis(benzyloxy)-6-hydroxyl-3-methyl-7,8-epoxyindolizidine
(10a) and 3-methyl 1,2,6-trihydroxyl-7,8-epoxyindolizidine (12).
OBn
H
7
1
HO
OBn
3
5
N
8
O
d
7.41e7.23 (m, 10H, Ar), 4.58 (d, 1H, J 12.0 Hz, CHHPh), 4.54 (d, 1H, J
10a
11.5 Hz, CHHPh), 4.53 (d, 1H, J 11.5 Hz, CHHPh), 4.43 (dd, 1H, J 11.3,
6.5 Hz, H-8), 4.37 (dd, 1H, J 11.3, 4.5 Hz, H-8), 4.36 (d, 1H, J 11.5 Hz,
CHHPh), 4.03 (d, 1H, J 4.0 Hz, H-2), 3.81 (d,1H, J 4.0 Hz, H-1), 3.71 (d,
2H, J 5.0 Hz, H-7a and H-6 or H-7), 3.63 (d, 1H, J 3.0 Hz, H-6 or H-7),
3.57 (app. dd, 1H, J 11.0, 7.0 Hz, H-3), 3.25 (d, 1H, J 11.3 Hz, H-5), 3.15
To a solution of 10 (13.4 mg, 0.033 mmol) in MeOH (1 mL) was
added Amberlyst A-26 (OHꢁ) resin (40 mg). The reaction was stir-
red for 12 h at rt then filtered through a Celite pad and the solids
were washed with MeOH (10 mL). The filtrate was evaporated in
vacuo to give 10a as a pale yellow oil that was used to next step
without purification. MS (ESI þve) m/z 368 (MþHþ, 100%). HRMS
(ESI þve) calculated for C22H26NO4 (MþHþ) 368.1844, found
368.1862. IR nmax (cmꢁ1): 3385, 2925, 2863, 1454, 1362, 1099, 1070.
(d, 1H, J 11.3 Hz, H-5), 2.03 (s, 3H, CH3). 13C NMR
d 170.9 (CO), 137.6
(C), 137.4 (C), 128.6 (CH), 128.5 (CH), 128.1 (CH), 127.9 (CH), 127.6
(CH), 127.5 (CH), 87.4 (C-2), 84.8 (C-1), 72.2 (C-7a), 71.8 (CH2), 71.7
(CH2), 62.4 (C-3), 60.3 (C-8), 57.4 (C-6 or C-7), 57.2 (C-6 or C-7), 48.1
(C-5), 20.9 (CH3).
Compound 10: Rf 0.50 (100% EtOAc). [
a
]
25 ꢁ14.9 (c 0.7, CHCl3). MS
1H NMR
d 7.37e7.26 (m,10H, Ar), 4.63 (d,1H, J 12.0 Hz, CHHPh), 4.59
D
(ESI þve) m/z 410 (MþHþ, 100%). HRMS (ESI þve) calculated for
(d, 1H, J 11.5 Hz, CHHPh), 4.57 (d, 1H, J 11.5 Hz, CHHPh), 4.54 (d, 1H, J
12.0 Hz, CHHPh), 4.49 (dd, 1H, J 6.2, 2.5 Hz, H-6), 4.36 (d, 1H, J
4.0 Hz, H-1), 4.33 (dd, 1H, J 5.5, 4.0 Hz, H-2), 3.80 (d, 1H, J 2.0 Hz, H-
7), 3.68 (d, 1H, J 12.0 Hz, H-8), 3.53 (dd, 1H, J 13.0, 6.2 Hz, H-5), 3.50
(dd, 1H, J 12.0, 2.5 Hz, H-8), 3.24 (br s, 1H, H-7a), 3.02 (br d, 1H, J
C24H28NO5 (MþHþ) 410.1967, found 410.1984. IR nmax (cmꢁ1): 2929,
2868,1737,1237,1102,1046.1H NMR
d 7.38e7.26(m,10H, Ar), 5.24 (dd,
1H, J 6.4, 2.8 Hz, H-6), 4.62 (d, 1H, J 12.0 Hz, CHHPh), 4.59 (d, 2H, J
12.0 Hz, 2xCHHPh), 4.55 (d,1H, J 12.0 Hz, CHHPh), 4.37 (d,1H, J 4.0 Hz,
H-1), 4.30 (dd,1H, J 5.5, 4.0 Hz, H-2), 3.95 (d,1H, J 2.0 Hz, H-7), 3.73 (d,
1H, J 12.0 Hz, H-8), 3.65 (dd,1H, J 14.4, 6.4 Hz, H-5), 3.59 (dd,1H, J 12.0,
1.8 Hz, H-8), 3.10 (d,1H, J 2.0 Hz, H-7a), 3.07 (dd,1H, J 5.0,1.8 Hz, H-3),
3.0 Hz, H-3), 2.86 (dd, 1H, J 13.0, 2.5 Hz, H-5). 13C NMR
d 138.0 (C),
137.9 (C), 128.3 (CH), 127.9 (CH), 127.8 (CH), 127.7 (CH), 127.6 (CH),
85.5 (C-2), 82.0 (C-1), 81.5 (C-7), 75.1 (C-6), 72.2 (CH2), 71.7 (CH2),
67.8 (C-7a), 62.3 (C-3), 59.8 (C-8), 57.9 (C-5).
2.85(dd,1H, J 14.4, 2.8Hz, H-5), 2.03 (s, 3H, CH3).13C NMR
d 170.0 (CO),
138.0(C),137.8(C),128.4(CH),128.3(CH),127.9(CH),127.87(CH),127.8
(CH),127.7(CH), 85.5 (C-2), 81.9 (C-1), 78.7(C-7), 77.1 (C-6), 72.2(CH2),
71.8 (CH2), 68.6 (C-7a), 62.3 (C-3), 59.8 (C-8), 56.1 (C-5), 20.9 (CH3).
Compound 11: Rf 0.32 (100% EtOAc). MS (ESI þve) m/z 410
To a solution of crude 10a in MeOH (1 mL) was added PdCl2
(8.71 mg, 0.05 mmol). The mixture was stirred at rt under an at-
mosphere of H2 (balloon) for 24 h The mixture was filtered through
a Celite pad and the solids were washed with MeOH. The combined
filtrates were evaporated in vacuo and the residue was dissolved in
water (1 mL) and applied to a column of Amberlyst A-26 (OHꢁ)
(MþHþ, 100%). [
a
]
25 ꢁ16.7 (c 1.6, CHCl3). HRMS (ESI þve) calculated
D
for C24H28NO5 (MþHþ) 410.1967, found 410.1974. IR nmax (cmꢁ1):

9346
T. Ritthiwigrom et al. / Tetrahedron 66 (2010) 9340e9347
resin (3 cm). Elution with water followed by evaporation in vacuo
a white solid (4.0 mg). However, the 1H NMR spectrum of this
compound showed an impure product and therefore this compound
was acetylated. To a solution of the above product in pyridine
gave 12 as a pale yellow solid (5.0 mg, 82%). [
a
]
23 þ8.6 (c 0.5, H2O).
D
MS (ESI þve) m/z 188 (MþHþ, 100%). HRMS (ESI þve) calculated for
C8H14NO4 (MþHþ) 188.0923, found 188.0928. IR nmax (cmꢁ1): 3395,
(0.5 mL) was added acetic anhydride (20
mL, 0.254 mmol) and
2965, 2934, 1316, 1033. 1H NMR (D2O)
d
4.41 (dd, 1H, J5,6¼6.0,
a crystal of 4-dimethylaminopyridine. The mixture was stirred at rt
for 24 h. The reaction was quenched by the addition of satd NaHCO3
solution, followed by removal of the solvent under reduced pressure
and the residue was extracted with CH2Cl2 (3ꢂ5 mL). The combined
CH2Cl2 extracts were washed with brine, dried (Na2CO3) and evap-
orated. The crude product was purified by FCC (70:30 EtOAc/petrol to
8.5:1:0.5 EtOAc/MeOH/NH3) to give the tetraacetate derivative of 15
2.3 Hz, H-6), 4.27 (br d, 1H, J1,2¼4.3 Hz, H-1), 4.20 (br dd, 1H,
J2,3¼5.3, J1,2¼4.3 Hz, H-2), 3.87 (br s, 1H, H-7), 3.62e3.54 (m, 3H,
2ꢂH-8 and H-5 ), 2.96 (br s, 1H, H-7a), 2.94 (br d, 1H, J2,3¼5.3 Hz,
a
H-3), 2.63 (dd, 1H, J5,5¼14.5, J5,6¼2.3 Hz, H-5
81.4 (C-7), 79.9 (C-2), 75.8 (C-1), 74.4 (C-6), 70.6 (C-7a), 63.7 (C-3),
59.5 (C-8), 56.8 (C-5).
b
). 13C NMR (D2O)
d
as a pale yellow oil (3.6 mg). Rf 0.49 (90:10 EtOAc/MeOH). MS (ESI
23
4.1.4. 1,2-Bis(benzyloxy)-7-hydroxyl-3-methyl-6,8-epoxyindolizidine
(11a) and 3-methyl-1,2,7-trihydroxyl-6,8-epoxyindolizidine (13).
þve) m/z 358 (MþHþ, 100%). [
a]
D
ꢁ10.6 (c 0.3, CHCl3). IR nmax
(cmꢁ1): 2924, 2825,1736, 1372,1221, 1039. 1H NMR
d 5.40 (app. t, 1H,
J 4.5 Hz, H-6), 5.35 (dd,1H, J 5.0,1.5 Hz, H-2), 4.83 (br d,1H, J 1.5 Hz, H-
1), 4.38 (dd, 1H, J 12.0, 6.5 Hz, H-8), 4.23 (dd, 1H, J 12.0, 7.0 Hz, H-8),
3.75 (app. dt, 1H, J 6.3, 5.0 Hz, H-3), 3.59e3.55 (ddd, 1H, J 7.5, 3.0,
3.0 Hz, H-7a), 3.27 (dd, 1H, J 10.5, 4.0 Hz, H-5), 2.99 (d, 1H, J 10.5 Hz,
H-5), 2.35 (dd, 1H, J 14.3, 7.8 Hz, H-7), 2.13e2.05 (m, 13H, 4ꢂCH3 and
HO
O
OBn
H
N
7
5
1
3
OBn
8
H-7). 13C NMR
d 170.8 (CO), 170.6 (CO), 170.1 (CO),169.3 (CO), 82.7 (C-
11a
1), 79.8 (C-2), 75.6 (C-6), 69.3 (C-7a), 61.0 (C-3), 59.6 (C-8), 53.6 (C-5),
36.3 (C-7), 21.3 (CH3), 20.9 (2ꢂCH3), 20.8 (CH3).
To a solution of 11 (14.0 mg, 0.034 mmol) in MeOH (1 mL) was
added Amberlyst A-26 (OHꢁ) resin (42 mg). The reaction was stir-
red for 16 h at rt, the mixture was filtered through a Celite pad and
the solids were washed with MeOH (10 mL). The filtrate was
evaporated in vacuo to give 11a as a pale yellow oil that was used to
next step without purification. MS (ESI þve) m/z 368 (MþHþ,100%).
HRMS (ESI þve) calculated for C22H26NO4 (MþHþ) 368.1844, found
368.1862. IR nmax (cmꢁ1): 3365, 2919, 2863, 1440, 1115, 1014. 1H
To a solution of the above tetraacetate (3.6 mg, 0.010 mmol) in
MeOH (1 mL) was added Amberlyst A-26 (OHꢁ) resin (15 mg). The
reaction was stirred for 3 h at rt, the mixture was then filtered
through a Celite pad and the solids were washed with MeOH
(10 mL). The combined filtrates were evaporated in vacuo to give 7-
deoxy-3,6-diepi-casuarine 15 as a pale yellow solid (2.3 mg, 50%).
23
[a
]
þ28.6 (c 0.23, MeOH). MS (ESI þve) m/z 190 (MþHþ, 100%).
D
HRMS (ESI þve) calculated for C8H16NO4 (MþHþ) 190.1079, found
NMR d 7.42e7.26 (m,10H, Ar), 4.73 (d,1H, J 12.0 Hz, CHHPh), 4.61 (d,
190.1074. IR nmax (cmꢁ1): 3400, 2923, 2852, 1460, 1053, 1038. 1H
1H, J 12.0 Hz, CHHPh), 4.56 (d, 1H, J 12.0 Hz, CHHPh), 4.49 (d, 1H, J
12.0 Hz, CHHPh), 4.24 (app. t, 1H, J 6.3 Hz, H-2), 4.07 (dd, 1H, J 7.0,
3.8 Hz, H-1), 3.98 (s, 1H, H-6), 3.91 (s, 1H, H-7), 3.66 (app d, 1H, J
10.5 Hz, H-8), 3.54e3.51 (m, 2H, H-3 and H-8), 3.40 (d, 1H, J 13.0 Hz,
H-5), 3.07 (d,1H, J 3.8 Hz, H-7a), 2.77 (d,1H, J 13.0 Hz, H-5). 13C NMR
NMR (D2O) d 4.57 (br s, 1H, H-6), 4.22 (br s, 1H, H-2), 4.09 (br s, 1H,
H-1), 4.00 (dd, 1H, J8a,8a¼11.4 Hz, J3,8a¼6.7 Hz, H-8a), 3.92 (dd, 1H,
J8a,8b¼11.4, J3,8b¼6.7 Hz, H-8b), 3.59 (t, 1H, J1,7a¼J7,7a¼7.8 Hz, H-7a),
3.41 (br s,1H, H-3), 3.31 (dd,1H, J5,5¼10.5, J5,6¼2.5, H-5), 2.92 (d,1H,
J5,5¼10.5 Hz, H-5), 2.22e2.17 (m, 1H, H-7), 2.04e2.00 (m, 1H, H-7).
d
138.3 (C), 138.0 (C), 128.5 (CH), 128.4 (CH), 128.2 (CH), 127.9 (CH),
13C NMR (D2O)
d 81.1 (C-1), 79.7 (C-2), 72.9 (C-6), 71.4 (C-7a), 65.0
127.7 (CH), 127.6 (CH), 85.6 (C-1), 84.7 (C-2), 81.0 (C-7), 77.3 (C-6),
76.0 (C-7a), 72.6 (CH2), 72.5 (CH2), 62.7 (C-3), 55.4 (C-8), 48.6 (C-5).
To a solution of crude 11a inMeOH(1mL)wasaddedPdCl2 (9.1mg,
0.051 mmol). The mixture was stirred at rt under an atmosphere of H2
(balloon) for 24 h. The mixture was filtered through a Celite pad and
the solids were washed with MeOH. The filtrate was evaporated in
vacuo and the residue was dissolved in water (1 mL) and applied to
a column of Amberlyst A-26 (OHꢁ) resin (3 cm). Elution with water
followed by evaporation in vacuo gave 13 as a yellow solid (3.4 mg,
(C-3), 57.5 (C-8), 56.2 (C-5), 38.0 (C-7).
4.1.6. (1R,6R,7S,8R,8aR)-7,8-Bis(benzyloxy)-6-(tert-butyldimethylsily-
loxy)octahydroindolizin-1-ol (17). To a solution of the epoxide 1613
(20.0 mg, 0.042 mmol) in anhydrous THF (1 mL) was added drop-
wise a 1 M solution of lithium aluminium hydride in THF (62.4 mL,
0.062 mmol). The reaction was stirring for 20 h at rt and then
evaporated to leave a residue, which was chromatographed on silica
gel by FCC (20:80 EtOAc/petrol to 100% EtOAc) to give 17 as a yellow
25
53%). [
a
]
23 þ7.6 (c 0.34, H2O). MS (ESI þve) m/z 188 (MþHþ, 100%).
viscous oil (12 mg, 60%). Rf 0.59 (5:95 MeOH/EtOAc).[
a]
ꢁ31.1 (c
D
D
HRMS (ESI þve) calculated for C8H14NO4 (Mþ) 188.0923, found
1.8, CHCl3). MS (ESI þve) m/z 484 (MþHþ, 100%). HRMS (ESI þve)
188.0928. IR nmax (cmꢁ1): 3380, 2919,1114,1054,1033. 1H NMR (D2O)
calculated for C28H42NO4Si (MþHþ) 484.2883, found 484.2871.IR
d
4.25 (t,1H, J1,2¼J2,3¼7.3 Hz, H-2), 4.22 (s, 2H, H-6 and H-7), 4.16 (dd,
nmax (cmꢁ1): 3390, 3030, 2922, 2850,1248,1092.1H NMR
d 7.40e7.25
1H, J1,2¼7.3, J1,7a¼4.3Hz, H-1), 3.76 (dd,1H, J8a,8b¼12.5, J3,8a¼7.3Hz,H-
8a), 3.69 (d, 1H, J8a,8b¼12.5 Hz, H-8b), 3.63 (d, 1H, J5,5¼14.0 Hz, H-5),
3.54 (t,1H, J2,3¼J3,8a¼7.3 Hz, H-3), 3.08 (d,1H, J1,7a¼4.3 Hz, H-7a), 2.80
(m, 10H, Ar), 4.96 (d, 1H, J 12.0 Hz, CHHPh), 4.73 (d, 1H, J 12.0 Hz,
CHHPh), 4.70 (d,1H, J 12.0 Hz, CHHPh), 4.60 (d,1H, J 12.0 Hz, CHHPh),
4.15 (br s, 1H, H-6), 4.01 (app. dt, 1H, J 9.4, 4.8 Hz, H-1), 3.80 (app. t,
1H, J 9.2 Hz, H-8), 3.35 (dd, 1H, J 9.2, 3.0 Hz, H-7), 2.94e2.90 (m, 2H,
H-5 and H-3), 2.40 (app. dt, 1H, J 8.8, 8.0 Hz, H-3), 2.22e2.14 (m, 2H,
H-5 and H-2),1.95 (dd,1H, J 9.4, 5.8 Hz, H-8a),1.59e1.53 (m,1H, H-2),
(d, 1H, J5,5¼14.0 Hz, H-5). 13C NMR (D2O)
d 80.2 (C-6), 79.5 (C-1), 77.9
(C-7), 77.7 (C-2), 76.5 (C-7a), 64.3 (C-3), 54.9 (C-8), 47.7 (C-5).
4.1.5. (1R,2R,3S,6S,7aR)-3-(Hydroxymethyl)hexahydro-1H-pyrrolizine-
1,2,6-triol (15). To a solution of 14 (12 mg, 0.025 mmol) in MeOH
(1 mL) was added PdCl2 (6.6 mg, 0.037 mmol). The mixture was
stirred at rt under an atmosphere of H2 (balloon) for 3 h, followed by
the dropwise addition of concd HCl (five drops). The mixture was
stirred at rt for 21 h. The mixture was filtered through a Celite pad
and the solids were washed with MeOH. The combined filtrates were
evaporated in vacuo and the residue was dissolved in water (1 mL)
and applied to a column of Amberlyst A-26 (OHꢁ) resin (3 cm).
Elution with water followed by evaporation in vacuo gave product as
0.90 (s, 9H, t-Bu), 0.08 (s, 3H, CH3), 0.04 (s, 3H, CH3). 13C NMR
d 138.6
(C), 138.5 (C), 128.5 (CH), 128.4 (CH), 128.3 (CH), 127.8 (CH), 127.5
(CH),127.4 (CH), 85.2 (C-7), 78.5 (C-8), 75.2 (C-1), 74.7 (CH2), 73.4 (C-
8a), 71.7 (CH2), 68.2 (C-6), 56.3 (C-5), 51.5 (C-3), 31.8 (C-2), 25.8 (C
(CH3)3), 18.2 (C), ꢁ4.5 (CH3), ꢁ4.53 (CH3).
4.1.7. (1R,6R,7R,8R,8aR)-Octahydroindolizine-1,6,7,8-tetraol(1,6-diepi-
castanospermine (18)). To a solution of 17 (37.9 mg, 0.079 mmol) in
MeOH (2 mL) was added PdCl2 (20.9 mg, 0.112 mmol). The mixture
was stirred at rt under an atmosphere of H2 (balloon) for 12 h,

T. Ritthiwigrom et al. / Tetrahedron 66 (2010) 9340e9347
9347
followed by the dropwise addition of concd HCl (10 drops), The
1312, 1086. 1H NMR (D2O)
d
4.26e4.22 (m, 1H, H-1), 3.61 (ddd, 1H,
mixture was stirred at rt for 3 days. The mixture was filtered through
a Celite pad and the solids were washed with MeOH. The filtrate was
evaporated in vacuo and the residue was dissolved in water (1.5 mL)
and applied to a column of Amberlyst A-26 (OHꢁ) resin (3 cm).
Elution with water followed by evaporation in vacuo gave 1,6 diepi-
castanospermine 18 in 95% purity, as a yellow viscous oil (14 mg).
J5a,6¼10.8, J6,7¼9.3, J5b,6¼5.7 Hz, H-6), 3.39 (app. t, 1H, J7,8¼
J8,8a¼9.3 Hz, H-8), 3.33 (app. t, 1H, J6,7¼J7,8¼9.3 Hz, H-7), 3.16 (dd,
1H, J5a,5b¼10.8, J5a,6¼5.7 Hz, H-5a), 2.95 (ddd, 1H, J3,3¼9.4, J2,3¼8.0,
1.5 Hz, H-3), 2.57 (dt, 1H, J3,3¼9.4, J2,3¼8.5 Hz, H-3), 2.34e2.28 (m,
1H, H-2), 2.24 (t, 1H, J5a,5b¼J5b,6¼10.8 Hz, H-5b), 2.12 (dd, 1H,
J8,8a¼9.3, J1,8a¼6.5 Hz, H-8a), 1.70 (app. t, 1H, J¼11.5 Hz, H-2).
25
24
[
a
]
ꢁ74.2 (c 1.5, MeOH), lit.16
[
a
]
ꢁ72.0 (c 0.7, MeOH). MS (ESI
13C NMR (D2O)
d 79.3 (C-7), 74.3 (C-1), 74.0 (C-8), 73.4 (C-8a), 70.5
(C-6), 55.5 (C-5), 51.4 (C-3), 33.0 (C-2).
D
D
þve) m/z 190 (MþHþ, 100%). HRMS (ESI þve) calculated for
C8H16NO4 (MþHþ) 190.1079, found 190.1072. IR nmax (cmꢁ1): 3365,
3308, 2914, 2888, 1444, 1202, 1060. 1H NMR (D2O)
d 4.29e4.25 (m,
Acknowledgements
1H, H-1), 4.03 (br s, 1H, H-6), 3.68 (t, 1H, J7,8¼J8,8a¼9.4 Hz, H-8), 3.53
(dd, 1H, J7,8¼9.4, J6,7¼3.5 Hz, H-7), 3.05 (dd, 1H, J5a,5b¼12.7,
J5a,6¼2.5 Hz, H-5a), 2.92 (app. t, 1H, J¼8.5 Hz, H-3), 2.48 (dt, 1H,
J2,3¼J3,3¼9.3, J2,3¼9.0 Hz, H-3), 2.42 (d, 1H, J5a,5b¼12.7 Hz, H-5b),
2.34e2.25 (m, 1H, H-2), 1.99 (dd, 1H, J8,8a¼9.4, J1,8a¼6.5 Hz, H-8a),
We thank the Australian Research Council and the University of
Wollongong for financial support and Chiang Mai University and
the Thai Government for a Ph.D. scholarship to T.R.
1.67e1.62 (m, 1H, H-2). 13C NMR (D2O)
d 75.8 (C-7), 74.6 (C-1), 74.0
Supplementary data
(C-8a), 72.2 (C-8), 69.3 (C-6), 55.7 (C-5), 51.7 (C-3), 32.9 (C-2).
Supplementary data associated with this article can be found in
online version at doi:10.1016/j.tet.2010.10.008.
4.1.8. (1R,2R,3R,7R,7aR)-3-Hydroxymethyl-hexahydro-pyrrolizine-
1,2,7-triol (7-epi-australine (21)). To a solution of a 92:8 mixture of
19 and 20 (37.1 mg, 0.077 mmol) MeOH (2 mL) was added PdCl2
(20.4 mg, 0.115 mmol). The mixture was stirred at rt under an at-
mosphere of H2 (balloon) for 3 h, followed by the dropwise addition
of concd HCl (eight drops). The mixture was stirred at rt for 17 h and
was then filtered through a Celite pad and the solids were washed
with MeOH. The combined filtrates were evaporated in vacuo and
the residue was dissolved in water (1.5 mL) and applied to a column
of Amberlyst A-26 (OHꢁ) resin (3 cm). Elution with water followed
by evaporation in vacuo gave 7-epi-australine 21 (dr 92:8) as a pale
References and notes
1. Matsumura, T.; Kasai, M.; Hayashi, T.; Arisawa, M.; Momose, Y.; Arai, I.; Ama-
gaya, S.; Komatsu, Y. Pharm. Biol. 2000, 38, 302e307.
2. Davis, A. D.; Ritthiwigrom, T.; Pyne, S. G. Tetrahedron 2008, 64, 4868e4879.
3. Ritthiwigrom, T.; Pyne, S. G. Org. Lett. 2008, 10, 2769e2771.
4. Nash, R. J.; Thomas, P. I.; Waigh, R. D.; Fleet, G. W. J.; Wormald, M. R.; de Q.
Lilley, P. M.; Watkin, D. J. Tetrahedron Lett. 1994, 35, 7849e7852.
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1988, 51, 1198e1206.
6. Nash, R. J.; Fellows, L. E.; Plant, A. C.; Fleet, G. W. J.; Derome, A. E.; Baird, P. D.;
Hegarty, M. P.; Scofield, A. M. Tetrahedron 1988, 44, 5959e5964.
7. Asano, N. In Modern Alkaloids: Structure, Isolation, Synthesis and Biology; Fat-
torusso, E., Taglialatela-Scafati, O., Eds.; Wiley-VCH: Weinheim, 2008;
pp 111e138.
8. Nash, R. J.; Fellows, L. E.; Dring, J. V.; Fleet, G. W. J.; Derome, A. E.; Hamor, T. A.;
Scofield, A. M.; Watkin, D. J. Tetrahedron Lett. 1988, 29, 2487e2490.
9. Kato, A.; Kano, E.; Adachi, I.; Molyneux, R. J.; Watson, A. A.; Nash, R. J.; Fleet, G.
W. J.; Wormald, M. R.; Kizu, H.; Ikeda, K.; Asano, N. Tetrahedron: Asymmetry
2003, 14, 325e331.
10. Van Ameijde, J.; Horne, G.; Wormald, M. R.; Dwek, R. A.; Nash, R. J.; Jones, P. W.;
Evinson, E. L.; Fleet, G. W. J. Tetrahedron: Asymmetry 2006, 17, 2702e2712.
11. Wormald, M. R.; Nash, R. J.; Watson, A. A.; Bhadoria, B. K.; Langford, R.; Sims, M.;
Fleet, G. W. J. Carbohydr. Lett. 1996, 2, 169e174.
23
25
yellow solid (13.0 mg, 90%). [
a
]
D
ꢁ13.2 (c 1.2, H2O), lit.17
[a]
D
ꢁ13.04 (c 0.55, H2O, pH 8.37). MS (ESI þve) m/z 190 (MþHþ, 100%).
HRMS (EI þve) calculated for C8H15NO4 (Mþ) 189.1001, found
189.0999. IR nmax (cmꢁ1): 3358, 2980, 1340, 1126, 1027. 1H NMR
(D2O)
d
4.34 (br s, 1H, H-7), 3.77 (dd, 1H, J8a,8b¼12.0, J3,8a¼4.5 Hz, H-
8a), 3.76 (t, 1H, J1,2¼J2,3¼8.5 Hz, H-2), 3.71 (t, 1H, J1,2¼J1,7a¼8.0 Hz,
H-1), 3.64 (dd, 1H, J8a,8¼11.8, J3,8b¼5.8 Hz, H-8b), 3.08 (dd, 1H,
J5,5¼J5,6 10.8, J5,6¼6.0 Hz, H-5), 3.01 (br d, 1H, J1,7a¼8.0 Hz, H-7a),
2.89e2.84 (m, 1H, H-5), 2.69e2.64 (m, 1H, H-3), 2.11e2.04 (m, 1H,
H-6), 1.80e1.74 (m, 1H, H-6). 13C NMR (D2O)
d 78.6 (C-1), 77.0 (C-2),
12. Kato, A.; Adachi, I.; Miyauchi, M.; Ikeda, K.; Komae, T.; Kizu, H.; Kameda, Y.;
Watson, A. A.; Nash, R. J.; Wormald, M. R.; Fleet, G. W. J.; Asano, N. Carbohydr.
Res. 1999, 316, 95e103; Asano, N.; Kuroi, H.; Ikeda, K.; Kizu, H.; Kameda, Y.;
Kato, A.; Adachi, I.; Watson, A. A.; Nash, R. J.; Fleet, G. W. J. Tetrahedron:
Asymmetry 2000, 11, 1e8; Yamashita, T.; Yasuda, K.; Kizu, H.; Kameda, Y.;
Watson, A. A.; Nash, R. J.; Fleet, G. W. J.; Asano, N. J. Nat. Prod. 2002, 65,
1875e1881; Kato, A.; Kato, N.; Adachi, I.; Hollinshead, J.; Fleet, G. W. J.; Kur-
iyama, C.; Ikeda, K.; Asano, N.; Nash, R. J. J. Nat. Prod. 2007, 70, 993e997;
AsanoN.; IkedaK.; KasaharaM.; AraiY.; KizuH.. J. Nat. Prod. 2004, 67, 846e850.
13. Ritthiwigrom, T.; Willis, A. C.; Pyne, S. G. J. Org. Chem. 2010, 75, 815e824 and
references cited therein.
75.8 (C-7), 74.5 (C-7a), 69.0 (C-3), 63.4 (C-8), 52.4 (C-5), 32.3 (C-6).
4.1.9. (1R,6S,7R,8R,8aR)-Octahydroindolizine-1,6,7,8-tetraol (1-epi-
castanospermine (23)). To a solution of 22 (9.0 mg, 0.019 mmol)
MeOH (1 mL) was added PdCl2 (6.6 mg, 0.037 mmol). The mixture
was stirred at rt under an atmosphere of H2 (balloon) for 3 h, fol-
lowed by the dropwise addition concd HCl (four drops). The mix-
ture was stirred at rt for 21 h and was then filtered through a Celite
pad and the solids were washed with MeOH. The filtrate was
evaporated in vacuo and the residue was dissolved in water (1 mL)
and applied to a column of Amberlyst A-26 (OHꢁ) resin (3 cm).
Elution with water followed by evaporation in vacuo gave 1-epi-
14. Cavdar, H.; Saracoglu, N. Tetrahedron 2009, 65, 985e989.
15. Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Vyvyan, J. R. Introduction to Spectros-
copy, 4th ed.; Brooks/Cole: Belmont CA, 2009; p 242.
16. Fleet, G. W. J.; Ramsden, N. G.; Nash, R. J.; Fellows, L. E.; Jacob, G. S.; Molyneux,
R. J.; di Bello, I. C.; Winchester, B. Carbohydr. Res. 1990, 205, 269e282.
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18. Ina, H.; Kibayashi, C. J. Org. Chem. 1993, 58, 52e61.
19. Cronin, L.; Murphy, P. V. Org. Lett. 2005, 7, 2691e2693.
20. Davis, A. S.; Pyne, S. G.; Skelton, B. W.; White, A. H. J. Org. Chem. 2004, 69,
3139e3143.
castanospermine 23 as a colourless solid (3.3 mg, 94%). [
a
]
22 þ3.3 (c
D
0.3, MeOH), lit.18
[
a]
þ3.8 (c 0.5, MeOH). MS (ESI þve) m/z 190
26
D
(MþHþ, 100%). HRMS (ESI þve) calculated for C8H16NO4 (MþHþ)
190.1079, found 190.1088. IR nmax (cmꢁ1): 3330, 2924, 2822, 1444,