Total synthesis of uniflorine A, casuarine, australine, 3-epi-australine, and 3,7-di-epi-australine from a common precursor

Article abstract of DOI:10.1021/jo902355p

(Chemical Equation Presented) Aflexible method for the diastereoselective total synthesis of the pyrrolizidine alkaloids uniflorine A, casuarine, australine, and 3-epi-australine and the unnatural epimer 3,7-di-epi-australine from a common chiral 2,5-dihydropyrrole precursor is described. 2009 American Chemical Society.

Full text of DOI:10.1021/jo902355p

pubs.acs.org/joc
Total Synthesis of Uniflorine A, Casuarine, Australine, 3-epi-Australine,
and 3,7-Di-epi-australine from a Common Precursor
Thunwadee Ritthiwigrom,† Anthony C. Willis,‡ and Stephen G. Pyne*,†
†School of Chemistry, University of Wollongong, Wollongong, New South Wales, 2522, Australia and
‡Research School of Chemistry, Australian National University, Canberra, ACT, 0200, Australia
spyne@uow.edu.au
Received November 4, 2009
A flexible method for the diastereoselective total synthesis of the pyrrolizidine alkaloids uniflorine A,
casuarine, australine, and 3-epi-australine and the unnatural epimer 3,7-di-epi-australine from a
common chiral 2,5-dihydropyrrole precursor is described.
Introduction
(7a-epi-australine), several other epi-australines (1-epi-austra-
line, 3-epi-australine, 2,3-di-epi-australine and 2,3,7-tri-epi-
australine),9 1-epi-australine-2-O-β-glucoside, 3-epi-casuar-
ine,10 casuarine-6-O-R-glucoside,11 and the more recently
isolated hyacinthacine alkaloids of which 19 novel com-
pounds have been identified.12 This group, along with the
polyhydroxylated pyrrolidine, piperidine, indolizidine, and
Uniflorine A (1, 6-epi-casuarine),1-3 casuarine (2),4 austra-
line (3),5 and 3-epi-australine (4)6 are members of the expand-
ing group of polyhydroxylated 3-hydroxymethylpyrrolizidine
natural products (Figure 1).7 This group also includes alexine8
(1) Matsumura, T.; Kasai, M.; Hayashi, T.; Arisawa, M.; Momose, Y.;
Arai, I.; Amagaya, S.; Komatsu, Y. Pharm. Biol. 2000, 38, 302–307.
(2) Davis, A. D.; Ritthiwigrom, T.; Pyne, S. G. Tetrahedron 2008, 64,
4868–4879.
(3) For a preliminary communication on the synthesis of (þ)-uniflorine
A, see: Ritthiwigrom, T.; Pyne, S. G. Org. Lett. 2008, 10, 2769–2771.
(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, 7849–
7852.
(5) Molyneux, R. J.; Benson, M.; Wong, R. Y.; Tropea, J. E.; Elbein, A.
D. J. Nat. Prod. 1988, 51, 1198–1206.
(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, 5959–
5964.
(7) Asano, N. In Modern Alkaloids: Structure, Isolation, Synthesis and
Biology; Fattorusso, E., Taglialatela-Scafati, O., Eds.; Wiley-VCH Verlag:
Weinheim, Germany, 2008; pp 111-138.
(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,
2487–2490.
(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, 325–331.
(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, 2702–2712.
(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, 169–174.
(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, 95–103. 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, 1–8. 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, 1875–1881. 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, 993–997. Asano, N.; Ikeda, K.;
Kasahara, M.; Arai, Y.; Kizu, H. J. Nat. Prod. 2004, 67, 846–850.
DOI: 10.1021/jo902355p
r
Published on Web 12/22/2009
J. Org. Chem. 2010, 75, 815–824 815
2009 American Chemical Society

Ritthiwigrom et al.
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SCHEME 1
FIGURE 1. Structures of uniflorine A (1), casuarine (2), australine
(3), and 3-epi-australine (4).
nortropane alkaloids, have glycosidase inhibitory activities
and thus have potential utility as antiviral, anticancer, anti-
diabetic, and antiobesity drugs.7 Three structurally related
synthetic compounds have been marketed as antidiabetic
drugs to treat type-2 diabetes based on their potent R-gluco-
sidase inhibitory activities while others have been identified as
candidates for therapeutics to treat type-1 Gaucher disease.7
A comparative study of the inhibitory activities of alexine,
australine, casuarine, and their aforementioned epimers and
O-R- and O-β-glucoside derivatives against a panel of glyco-
sidase enzymes revealed that casuarine and 1-epi-australine-
2-O-β-glucoside were the most potent compounds.9 These
alkaloids showed low micromolar activities against several
R-glucosidases while casuarine had an IC50 value of 0.7 μM
against amylglucosidase from Aspergillus niger. In a separate
study, uniflorine A (1) was shown to have moderate inhibitory
activity against the R-glucosidases, rat intestinal maltase and
sucrase, with IC50 values of 12 and 3.1 μM, respectively.1
These potentially useful biological activities along with the
stereochemical richness of these alkaloids (uniflorine A and
casuarine have six contiguous stereogenic carbons) have made
these compounds attractive and important synthetic targets.13-15
We recently reported the revised structures of uniflorines
A and B from initially proposed pentahydroxyindolizi-
dines1 to 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizi-
dines from a reinvestigation of their originally published
NMR spectroscopic data.2 Uniflorine B was the known
alkaloid casuarine (2), while uniflorine A was tentatively
assigned as 6-epi-casuarine (1); this was confirmed in a
preliminary communication by the total synthesis of its
enantiomer, (þ)-uniflorine A (ent-1), from D-xylose.3 In this
paper, we report the full details of the synthesis of natural (-)-
uniflorine A (1) from the chiral 2-substituted-2,5-dihydropyr-
role 8 (Scheme 1), which is readily prepared in four synthetic
stepsfromL-xylose. Wealsodemonstrate here thatcompound
8 is a versatile precursor for the diastereoselective synthesis of
the alkaloids casuarine (2), australine (3), and 3-epi-australine
(4) and the unnatural epimer, 3,7-epi-australine 36.
Results and Discussion
Total Synthesis of (-)-Uniflorine A (1). The synthesis of
(-)-uniflorine A (1) is shown in Schemes 1 and 2. The known
tetrol 516 was prepared in one step from the boronic acid-
Mannich reaction (Petasis reaction)16,17 of L-xylose, allyla-
mine, and (E)-styrene boronic acid and then converted to its
N-Boc derivative 616 (Scheme 1). The terminal diol function-
ality of 6 was selectively protected as the acetonide derivative
7 under standard conditions. The modest yield (64%) for this
step was a result of the poor regioselectivity of this reaction.
The other regioisomer was recycled back to 6 by hydrolysis
with TFA (0.5 equiv) in MeOH/water (3:1, 10 mL/mmol) at
rt for 36 h and the crude product was reprotected to give 7 in
49% overall yield. A ring-closing metathesis reaction of the
diene 7 with use of Grubbs’ first generation ruthenium
catalyst provided the 2,5-dihydropyrrole 8 in 97% yield
(Scheme 1). This intermediate can be readily prepared on a
4 g scale from L-xylose in 4 steps and in 46% overall yield.
The 2,5-dihydropyrrole 8 underwent an osmium(VIII)-
catalyzed syn-dihydroxylation (DH) reaction to furnish the
tetrol 9 as a single diastereomer in 72% yield (Scheme 2).
The stereochemical outcome of this DH reaction was
expected due to the stereodirecting effect of the C-2 pyrroli-
dine substituentin8.2,16,18,19 The configuration of this diol was
established from ROESY NMRstudies onthe final product 1.
The tetrol 9was readily converted to its per-O-benzyl-protected
derivative 10 in 96% yield, using standard reaction condi-
tions.16 Treatment of 10 under acidic conditions (HCl/MeOH)
(13) For previous syntheses of casuarine see: Denmark, S. E.; Hurd, A. R.
Org. Lett. 1999, 1, 1311–1314. Denmark, S. E.; Hurd, A. R. J. Org. Chem.
2000, 65, 2875–2886. Izquierdo, I.; Plaza, M. T.; Tamayo, J. A. Tetrahedron
2005, 61, 6527–6533. Cardona, F.; Parmeggiani1, C.; Faggi, E.; Bonaccini,
C.; Gratteri, P.; Sim, L.; Gloster, T. M.; Roberts, S.; Davies, G. J.; Rose, D.
R.; Goti, A. Chem.;Eur. J. 2009, 15, 1627–1636.
(14) For previous syntheses of australine see: (a) Pearson, W. H.; Hines,
J. V. Tetrahedron Lett. 1991, 32, 5513–5516. (b) White, J. D.; Hrnciar, P.;
Yokochi, A. F. T. J. Am. Chem. Soc. 1998, 120, 7359–7360. (c) Denmark, S.
E.; Martinborough, E. A. J. Am. Chem. Soc. 1999, 121, 3046–3056. (d)
Pearson, W. H.; Hines, J. V. J. Org. Chem. 2000, 65, 5785–5793. (e) White, J.
D.; Hrnciar, P. J. Org. Chem. 2000, 65, 9129–9142. (f) Romero, A.; Wong, C.-
H. J. Org. Chem. 2000, 65, 8264–8268. (g) Ribes, C.; Falomir, E.; Carda, M.;
Marco, J. A. Org. Lett. 2007, 9, 77–80. (h) Trost, B. M.; Aponick, A.; Stanzl,
B. N. Chem.;Eur. J. 2007, 13, 9547–9560. (i) For a synthesis of australine
from castanospermine see: Furneaux, R. H.; Gainsford, G. J.; Mason, J. M.;
Tyler, P. C. Tetrahedron 1994, 50, 2131–2160.
(16) Davis, A. S.; Pyne, S. G.; Skelton, B. W.; White, A. H. J. Org. Chem.
2004, 69, 3139–3143.
(17) Petasis, N. A.; Zavialov, I. A. J. Am. Chem. Soc. 1998, 120, 11798–
11799.
(18) Lindsay, K. B.; Tang, M.; Pyne, S. G. Synlett 2002, 731–734.
(19) Lindsay, K. B.; Pyne, S. G. J. Org. Chem. 2002, 67, 7774–7780.
(15) For previous syntheses of 3-epi-australine see: refs 14c and 14f.
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SCHEME 2
FIGURE 2. ROESY NMR correlations for uniflorine A (1).
The 13C NMR signals of 1 (in D2O with MeCN as an internal
reference at δ 1.47), however, were all consistently 2.1-
2.2 ppm upfield of those reported for the natural product
(Supporting Information). We2 noted earlier that while the
1H NMR spectroscopic data reported for uniflorine B and
casuarine were also essentially identical, the 13C NMR shifts
reported for casuarine were all consistently 3.0-3.2 ppm
upfield of the corresponding 13C NMR resonances reported
for uniflorine B.1 We suggested that alternative referencing
between the two samples accounts for this consistent dis-
crepancy.2 The 13C NMR spectrum of casuarine was refer-
enced to acetone at δ 29.80 while that of uniflorines A and B
was apparently referenced to TMS as an internal standard
(a standard not known for its water (D2O) solubility).1 Thus
the consistent differences in the 13C NMR chemical shifts
between synthetic 1 and those of uniflorine A can also be
ascribed to the differences in referencing between the differ-
ent samples.24 The observed cross-peaks in the ROESY
spectrum of 1 were fully consistent with the configurational
assignment of 1 as shown in Figure 2. Thus our synthesis of 1
provides unequivocal proof that uniflorine A is 6-epi-casuar-
ine. Uniflorine A and 3-epi-casuarine therefore represent the
two known natural product epimers of casuarine.4,10
Total Synthesis of Casuarine (2). The synthesis of casuarine
(2) from the chiral 2,5-dihydropyrrole 8 is shown in Scheme 3.
This synthesis required a modified strategy to that for uni-
florine A to secure the 6R,7β-configuration of the target
molecule. To achieve this goal the synthetic plan involved a
regioselective ring-opening reaction of the epoxide 21 with an
oxygen nucleophile (Scheme 3). To obtain the key epoxide 21,
the two unprotected secondary hydroxyl groups in 8 were first
protected as their O-benzyl ethers and the resulting dibenzyl
ether 15 (92% yield) was treated under acidic conditions to
effect hydrolysis of both the acetonide and N-Boc protecting
groups and to provide amino diol 16 in 76% yield. Regio-
selective O-silylation of 16 at the primary hydroxyl group
gave the TBS ether 17 (81% yield), which was efficiently
N-protected as its Fmoc derivative 18 in 94% yield. Epoxida-
tion of the alkene moiety of 18 with 1,1,1-trifluoroacetone and
oxone25 provided the epoxide 19 in 81% yield as a single
diastereomer. Mesylation of the free secondary hydroxyl of 19
followed by treatment of the mesylate 20 (94% yield) with
piperidine resulted in smooth N-Fmoc deprotection and then
cyclization of the free cyclic secondary amine to give in 96%
yield a 91:9 mixture of the desired pyrrolizidine 21 and the
undesired indolizidine 22, respectively. We assume that 22
arose from O-TBS migration under the basic conditions of the
O-mesylation reaction; however, this was difficult to ascertain
resulted in N-Boc and acetonide hydrolysis and gave the amino
diol 11 in 81% yield. Regioselective O-silylation of 11 with
TBSCl/imidazole/DMAP gave the primary silyl ether 12 in
85% yield. In our earlier synthesis of (þ)-uniflorine A, the
compound ent-12 underwent cyclization under Mitsunobu
reaction conditions with pyridine2,20,21 as the solvent to give
a mixture (ca. 4:1) of the desired pyrrolizidine ent-13 and an
indolizidine product (structure not shown) in a combined yield
of about 30% after purification of the crude reaction mixture
by column chromatography. The undesired indolizidine pro-
duct arose from first base catalyzed O-TBS migration to the
secondary hydroxyl group in ent-12 followed by Mitsunobu
cyclization onto the primary carbon of the butyl side chain. We
have now found, using 12, that the yield of 13 could be
dramatically improved to 76% with little or no formation of
the undesired product by buffering the reaction mixture with
Et3N HCl.22 Acid hydrolysis of 13 gave the primary alcohol 14
3
2,20,23
in 90% yield, which upon hydrogenolysis with PdCl2/H2
gave uniflorine A (1) ([R]D22 -3.7 (c 1.2, H2O) {lit.1 [R]D -4.4
(c 1.2, H2O)}), in 87% yield after ion-exchange chromato-
graphy in a total of 11 synthetic steps and 13% overall yield
from L-xylose.
The 1H NMR spectral data (D2O) of 1 and those of
the natural product were essentially identical (ΔδH
=
0.00-0.02 ppm, see Table 1 of the Supporting Information).
(20) Tang, M.; Pyne, S. G. J. Org. Chem. 2003, 68, 7818–7824.
(21) Mulzer, J.; Dehmlow, H. J. Org. Chem. 1992, 57, 3194–3202.
Casiraghi, G.; Ulgheri, F.; Spanu, P.; Rassu, G.; Pinna, L.; Gasparri, F.
G.; Pelosi, F. M. G. J. Chem. Soc., Perkin Trans. I 1993, 2991–2997. Naruse,
M.; Aoyagi, S.; Kibayashi, C. J. Org. Chem. 1994, 59, 1358–1364.
(22) Anderson, J. C.; Chapman, H. A. Org. Biomol. Chem. 2007, 5, 2413–
2422.
(23) Zhao, H.; Hans, S.; Chemg, X.; Mootoo, D. R. J. Org. Chem. 2001,
66, 1761–1767. Zhou, W.-S.; Xie, W.-G.; Lu, Z.-H.; Pan, X.-F. Tetrahedron
Lett. 1995, 36, 1291–1294.
(24) Unfortunately we have not been able to obtain a copy of the NMR
spectra of uniflorine A for comparison purposes from the original authors.1
(25) Yang, D.; Wong, M.-K.; Yip, Y.-C. J. Org. Chem. 1995, 60, 3887–
3889.
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SCHEME 3
species in dichloromethane at reflux, followed by the addi-
tion of water to hydrolyze the intermediate sulfate, then
the desired diol 23 was obtained as an 86:14 crude mixture
of regioisomers. Purification of this mixture by column
chromatography gave a 92:8 mixture of the diastereomeric
diols 23 and 6,7-di-epi-23, respectively, in 51% yield. The
regiochemistry of this ring-opening reaction was consistent
with that reported on related epoxy-pyrrolizidines28 and was
expected from stereoelectronic considerations as shown in
Scheme 4. For trans-1,2-diaxial ring-opening of epoxide 21
by HSO4-, the two reactive conformations A and B are
possible. Attack on conformation A at C-7 is inhibited by
-
1,3-diaxial interactions between the nucleophile (HSO4
)
and the pseudoaxial protons H-1R and H-5R and thus
addition to conformation B at C-6 predominates resulting
in 23 as the major regioisomeric product. Hydrogenolysis of
23
23 over PdCl2/H2 gave casuarine (2) ([R]D þ18.1 (c 1.0,
24
H2O) {lit.4 [R]D þ16.9 (c 0.8, H2O)}) in 93% yield after
purification by ion-exchange chromatography in a total of
13 synthetic steps and 8% overall yield from L-xylose. The
diastereomeric purity of 2 was 95:5 from 1H NMR spectro-
scopic analysis. The 1H NMR spectroscopic data (D2O) of 2
and that of the natural product4 were essentially identical
(ΔδH = 0.00-0.01 ppm, see Table 2 of the Supporting
Information). The 13C NMR signals of 2 in D2O, however,
were all consistently 1.0-1.3 ppm downfield of those
reported for the natural product (see Table 2 of the Support-
ing Information). Consistent differences in the 13C NMR
chemical shifts of the related alkaloid australine 3 have also
been reported (see Table 3 of the Supporting Information
and the Supporting Information in ref 14g).
Total Synthesis of Australine (3). The epoxide 21 also
provided ready access to australine (3) as shown in Scheme 5.
Reductive ring-opening of a 91:9 mixture of the epoxides 21
and 22 respectively with lithium aluminum hydride at 0 °Cgave
a mixture of the pyrrolizidines 24 and 25 (27% yield, 24:25 =
88:12), a mixture of the pyrrolizidines 26 and 27 (64% yield,
26:27 = 92:8), and the indolizidine corresponding to the ring-
opening of 22 (2% yield, structure 26a in the Supporting
Information).
The regioisomeric mixture of 24 and 25 could be converted
to a mixture of 26 and 27 by treatment with TBSCl in 61%
yield. Fortunately, the regioisomers 26 and 27 could be
readily separated as their C-7R and C-6R 4-nitrobenzoate
esters, respectively, which were obtained from their Mitsunobu
reactions with 4-nitrobenzoic acid.29 In this way the 92:8
regioisomeric mixture of 26 and 27 was converted to a
mixture of the C-7 and C-6 inverted 4-nitrobenzoate esters,
respectively, from which the major regioisomer 28 was
isolated pure after separation by column chromatography.
Base hydrolysis of 28 gave the diastereomerically pure
alcohol 29 in 57% overall yield for the two synthetic steps.
Hydrogenolysis of 29 over PdCl2/H2, which also resulted in
hydrolysis of the TBS ether due to in situ formation of
since NMR analysis of the mesylate intermediate 20 was made
difficult because of N-Fmoc rotamers. A small amount of pure
21 could be obtained by further separation of the mixture
by column chromatography. Compound 22 could not be
obtained pure but was fully characterized as its deriv-
ative 26a (Supporting Information). The structure of the
epoxide 21 was confirmed by a single-crystal X-ray analysis
(Supporting Information).26
Several attempts in our laboratory to ring-open the
epoxide group of compounds related to 21 using aqueous
acid conditions (for example, H2SO4, water) led to complex
mixtures and low yields of diol products. However, when 21
was treated under the conditions reported by Saracoglu,27
using NaHSO4 as both the acid catalyst and the nucleophilic
22
HCl, gave diastereomerically pure australine 3 ([R]D þ9.4
25
(c 2.4, H2O) {lit.14d [R]D þ8 (c 0.35, H2O)}) in 86% yield
after ion-exchange chromatography in a total of 16 synthetic
1
steps and 5% overall yield from L-xylose. The H NMR
(28) Ahn, J.-B.; Yun, C.-S.; Kim, H.; Ha, D.-C. J. Org. Chem. 2000, 65,
9249–9251. Papaioannou, N.; Blank, J. T.; Miller, S. J. J. Org. Chem. 2003,
68, 2728–2734.
(26) Crystal/refinement data have been deposited with the Cambridge
Crystallographic Data Centre as CCDC 752850.
(27) Cavdar, H.; Saracoglu, N. Tetrahedron 2009, 65, 985–989.
(29) Martin, S. F.; Dodge, J. A. Tetrahedron Lett. 1991, 32, 3017–3020.
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SCHEME 4. Formation of 23 (R1 = Bn, R2 = TBS or OH)
SCHEME 6
SCHEME 5
with those made by Denmark and differ from those reported
on the natural product (see Table 3 of the Supporting
Information).
Total Synthesis of 3-epi-Australine (4) and 3,7-Di-epi-aus-
traline (36). The syntheses of naturally occurring 3-epi-
australine (4) and the unnatural analogue 3,7-d-iepi-austra-
line (36) from the epoxide 19 are shown in Scheme 6. These
syntheses required an inversion of configuration of the butyl
side-chain secondary hydroxyl group in 19. This was
achieved by the Mitsunobu reaction of 19 with 4-nitroben-
zoic acid.29 Base treatment (K2CO3/MeOH, rt, 1 d) of the
resulting secondary 4-nitrobenzoate ester resulted in benzo-
ate hydrolysis and N-Fmoc cleavage giving the amino alco-
hol 30 in 55% overall yield for the two synthetic steps. This
compound underwent cyclization under Mitsunobu reaction
conditions with toluene as the solvent to give a separable
mixture of the desired pyrrolizidine 31 in 70% yield and the
indolizidine product 32 in 4% yield. Reductive ring-opening
of the epoxide 31 with lithium aluminum hydride at rt gave a
separable mixture of the regioisomeric pyrrolizidines 33 and
34, in yields of 41% and 9%, respectively. In contrast to the
reductive ring-opening reaction of 21, the more hindered
TBS group in these products remained intact. In the final
steps of the synthesis, the configuration at C-7 in 33 was
spectroscopic data (D2O) of 3and that of the natural product30,31
were essentially identical (ΔδH = 0.06-0.10 ppm, see Table 3 of
the Supporting Information). The 13C NMR signals of 3 in
D2O, however, were all consistently 2.0-2.3 ppm upfield of
those reported for the natural product9,30 (see Table 3 of the
Supporting Information). Our 13C NMR signals, however,
matched more closely with those reported for synthetic australine
by Pearson (ΔδC = 0.1-0.4 ppm)14d and Denmark (ΔδC
=
0.8-1.3 ppm).14c Our 13C NMR assignments, based on 2D
NMR experiments (COSY, HSQC, and HMBC), also agreed
(30) Wormald, M. R.; Nash, R. J.; Hrnciar, P.; White, J. D.; Molyneux,
R. J.; Fleet, G. W. J. Tetrahedron: Asymmetry 1998, 9, 2549–2558.
(31) For a comparison of the differences in the 1H and 13C NMR chemical
shifts for natural and synthetic australine see the Supporting Information in
ref 14g.
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JOCArticle
inverted by the two-step sequence described above for the
synthesis of australine. Thus treatment of 33 under the
Mitsunobu reaction conditions with 4-nitrobenzoic acid
followed by base treatment of the resulting 4-nitrobenzoate
gave the C-7 inverted alcohol 35 in 64% overall yield. This
compound underwent hydrogenolysis under acidic condi-
tions with PdCl2/H2 to deliver diastereomerically pure 3-epi-
australine (4) ([R]D23 -10.5 (c 0.7, H2O)) in 88% yield after
ion-exchange chromatography in a total of 16 synthetic steps
and 1.7% overall yield from L-xylose. Its hydrochloride salt,
(Scheme 3). This methodology should prove versatile for
the synthesis of other, more complex pyrrolizidine alkaloids
and stereodefined epimeric derivatives for future structure-
activity relationship studies.34
Experimental Section35
(1R,2R,3R,6R,7S,7aR)-1,2,6,7-Tetrabenzyloxy-3-((tert-butyl-
dimethylsilyloxy)methyl)hexahydro-1H-pyrrolizine, 13. To a solu-
tion of 12 (0.792 g, 1.136 mmol) in pyridine (11 mL) was
added triphenylphosphine (0.301 g, 1.148 mmol), triethylamine
3
4 HCl, had [R]D23 -37 (c 0.7, H2O), which was of the same
hydrochloride (0.156 g, 1.136 mmol), and diisopropyl azodicar-
boxylate (0.56 mL, 2.841 mmol). The mixture was stirred at rt for
3 days. The volatiles were removed in vacuo then satd CuSO4
solution (20 mL) was added. The reaction mixture was extracted
with CH2Cl2 (3 ꢀ 25 mL). The combined CH2Cl2 extracts were
washed with satd CuSO4 solution (20 mL) and water (20 mL),
dried (Na2CO3), filtered, and then evaporated. Flash column
chromatography (FCC) (100% petrol to 20:80 EtOAc/petrol)
gave 13 as a yellow viscous oil (0.587 g, 76%). [R]D20 -34 (c 0.4,
CHCl3). vmax/cm-1 3070, 3040, 2924, 2852, 1454, 1120, 1097. This
compound had the same Rf, MS, and NMR spectroscopic data as
reported for (þ)-13.3
3
sign as the natural product but significantly larger in magni-
20
tude {lit.6 for 3-epi-australine HCl, [R]D -3.5 (c 1.35,
H2O)}. The H NMR spectroscopic data (D2O) of 4 and
3
1
those of the natural product6 matched closely (ΔδH
=
0.13-0.19 ppm, see Table 4 of the Supporting Information).
The 13C NMR signals of 4 in D2O, however, were all
consistently 0.4-0.9 ppm downfield of those reported for
the natural product (see Table 4 of the Supporting
Information).
For the synthesis of 3,7-di-epi-australine (36), the direct
hydrogenolysis of 33 under acidic conditions gave diastereo-
merically pure 3,7-di-epi-australine (36) ([R]D24 -9.3 (c 1.1,
H2O)) in 90% yield after ion-exchange chromatography in a
((1R,2R,3R,6R,7S,7aR)-1,2,6,7-Tetrabenzyloxyhexahydro-1H-
pyrrolizin-3-yl)methanol, 14. To a solution of 13 (1.417 g, 2.087
mmol) in MeOH (50 mL) was added dropwise concd HCl solution
(12.5 mL) and the mixture was stirred at rt for 18 h. The mixture
was basified at 0 °C with aqueous NH3 solution (28%). The
mixture was extracted with EtOAc, dried (Na2CO3), evaporated,
and purified by FCC (50:50 EtOAc/petrol) to give 14 (1.058 g,
90%) as a pale yellow viscous oil. Rf 0.11 (50:50 EtOAc/petrol).
total of 14 synthetic steps and 2.6% overall yield from
21
L-xylose. Its hydrochloride salt, 36 HCl, had [R]D -21
(c 0.63, H2O), which was of oppositesign to that of its synthetic
3
20
enantiomer, 1,2-di-epi-alexine HCl {lit.32 [R]D þ33 (c 0.1,
3
1
H2O)}. The H NMR spectroscopic data (D2O) of 36 HCl
20
23
3
[R]D -35 (c 1.3, CHCl3) [lit.3 for (þ)-14; [R]D þ34 (c 1.3,
CHCl3)]. vmax/cm-1 3446, 3050, 2893, 2858, 1449, 1107, 1097. This
compound had the same Rf, MS, and NMR spectroscopic data as
reported for (þ)-14.
and those reported in the literature for 1,2-di-epi-alexine HCl
were essentially identical (ΔδH = 0.03-0.04 ppm, see Table 5
3
of the Supporting Information). The 13C NMR signals of
(1R,2R,3R,6R,7S,7aR)-Hexahydro-3-(hydroxymethyl)-1H-
pyrrolizine-1,2,6,7-tetraol (Uniflorine A, 1). To a solution of 14
(0.636 g, 1.126 mmol) in MeOH (12 mL) was added PdCl2
(0.300 g, 1.690 mmol). The mixture was stirred at rt under an
atmosphere of H2 (balloon) for 1 day. 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 (3 mL) and applied to a column
of Amberlyst (OH-) A-26 resin (7 cm). Elution with water
followed by evaporation in vacuo gave uniflorine A (1) (0.201 g,
87%) as a white solid, mp 163.2-164.8 °C (lit.1 mp 174-178 °C).
36 HCl in D2O, however, were all consistently 1.7-2.1 ppm
3
upfield of those reported for its enantiomer (see Table 5 of the
Supporting Information).
Conclusions
In conclusion, we have developed a flexible method to
prepare the pyrrolizidine alkaloids uniflorine A, casuarine,
australine, and 3-epi-australine and the unnatural epimer
3,7-di-epi-australine from the common chiral 2,5-dihydro-
pyrrole precursor 8, which is available in gram quantities in
four synthetic steps from L-xylose.33 The synthesis of 1
confirmed our earlier configurational assignment to this
natural product.3 The synthesis of the latter four target
compounds involved regioselective epoxide ring-opening
reactions which proceeded with diastereoselectivities ran-
ging from 91:9 (Scheme 5) to 82:18 (Scheme 6) in favor of the
desired regioisomeric products. In contrast to our earlier
work3,20 efficient methods for the cyclization of 2-substituted
pyrrolidines to pyrrolizidines have been developed by using
23
[R]D -3.7 (c 1.2, H2O) [lit.1 for (-)-uniflorine A: [R]D -4.4
(c 1.2, H2O)]. This compound had the same Rf, MS, IR, and
NMR spectroscopic data as reported for (þ)-1.1
(R)-(9H-Fluoren-9-yl)methyl 2-((1R,2R,3S)-1,2-Bis(benzyloxy)-
4-(tert-butyldimethylsilyloxy)-3-hydroxybutyl)-2,5-dihydro-1H-
pyrrole-1-carboxylate, 18. To a solution of 17 (6.05 g, 0.013 mol)
in THF (125 mL) and satd Na2CO3 solution (60 mL) was added
9-fluorenylmethyl chloroformate (3.89 g, 15.03 mmol) at 0 °C.
The reaction mixture was stirred at 0 °C for 3 h. Water (20 mL)
was added and the solvent was removed under reduced pressure
and the residue was extracted with CH2Cl2 (3 ꢀ 70 mL). The
combined extracts were washed with brine, dried (Na2CO3),
and then evaporated to leave a residue that was chromato-
graphed on silica gel by FCC (10:90 to 30:70 EtOAc/petrol) to
the Mitsunobu reaction with either Et3N HCl as an additive
3
(Scheme 2) or by using toluene as the solvent (Scheme 6).
Alternatively, the cyclization of an Fmoc-protected pyrroli-
dine having a tethered O-mesylate to the corresponding
pyrrolizidine worked efficiently upon exposure to base
(34) After submission of this manuscript an alternative synthesis of
uniflorine A was published, see: Parmeggiani, C.; Martella, D.; Cardona,
F.; Goti, A. J. Nat. Prod. 2009, 72, 2058–2060.
(35) For general experimental details see the Supporting Information. All
1H (500 MHz) and 13C NMR (125 MHz) spectra were run in CDCl3 solution
unless otherwise indicated. NMR assignments are based upon COSY and
HSQC, and sometimes HMBC and NOESY, NMR experiments. All IR
spectra were run on neat samples.
(32) Chikkanna, D.; Singh, O. V.; Kong, S. B.; Han, H. Tetrahedron Lett.
2005, 46, 8865–8868.
(33) For a flexible synthetic strategy for preparing several hyacinthacine
alkaloids and epimers and 2,3,7-tri-epi-australine see: Donohoe, T. J.;
Thomas, R. E.; Cheeseman, M. D.; Rigby, C. L.; Bhalay, G.; Linney, I. D.
Org. Lett. 2008, 10, 3615–3618.
820 J. Org. Chem. Vol. 75, No. 3, 2010

Ritthiwigrom et al.
JOCArticle
give 18 (8.31 g, 94%) as a colorless viscous oil. Rf 0.47 (20:80
dried (Na2CO3), and then evaporated to leave a residue that was
chromatographed on silica gel by FCC (10:90 to 30:70 EtOAc/
petrol) to give 20 (0.433 g, 94%) as a pale yellow oil. Rf 0.5 (30:70
24
EtOAc/petrol). [R]D þ125 (c 2.0, CHCl3). vmax/cm-1 3061,
3028, 2945, 2924, 1700, 1413, 1107. δH (major rotamer)
7.78-7.59 (m, 4H, Ar), 7.42-7.16 (m, 14H, Ar), 5.97-5.95
(m, 1H, H-3), 5.92-5.89 (m, 1H, H-4), 4.90 (d, 2H, J = 11.0 Hz,
2 ꢀ CHHPh), 4.91-4.89 (m, 1H, H-2), 4.67-4.63 (m, 1H,
CHHPh), 4.47 (d, 1H, J = 12.0 Hz, CHHPh), 4.45 (d, 1H,
J = 8.0 Hz, H-10 or H-20), 4.39 (dd, 2H, J = 7.0, 2.3 Hz, CH2
(Fmoc)), 4.26-4.20 (m, 1H, CH (Fmoc)), 4.26-4.07 (m, 2H,
2 ꢀ H-5), 3.88 (dd, 1H, J = 13.5, 7.5 Hz, H-30), 3.77 (d, 1H, J =
7.5 Hz, H-10 or H-20), 0.90 (s, 9H, t-Bu), 0.07 (s, 3H, CH3), 0.06
(s, 3H, CH3). δC (major rotamer) 154.3 (CO), 144.0 (C), 143.9
(C), 141.3 (C), 141.2 (C), 138.4 (C), 138.2 (C), 128.3 (CH), 128.2
(CH), 128.1 (CH), 127.9 (CH), 127.6 (CH), 127.5 (CH), 126.9
(CH), 125.0 (CH), 119.9 (CH), 78.3 (C-10), 77.8 (C-20), 74.7
(CH2), 74.3 (CH2), 70.8 (C-30), 66.9 (CH2 (Fmoc)), 66.2 (C-2),
63.6 (C-40), 53.4 (C-5), 47.2 (CH (Fmoc)), 25.8 (C(CH3)3), 18.1
(C), -5.4 (CH3), -5.5 (CH3). δC (minor rotamer) 154.3, 144.0,
143.8, 141.3, 141.2, 138.3, 138.2, 128.2, 127.8, 127.7, 127.6,
126.7, 126.5, 125.5, 124.7, 119.9, 80.2, 78.6, 74.9, 74.8, 71.0,
65.9, 65.5, 63.5, 54.2, 47.7, 25.7, 18.0, -5.4. HRMS (ESIþve)
calcd for C43H52NO6Si (M þ H)þ 706.3564, found 706.3537.
(1S,2S,5R)-(9H-Fluoren-9-yl)methyl 2-((1R,2R,3S)-1,2-Bis-
(benzyloxy)-4-(tert-butyldimethylsilyloxy)-3-hydroxybutyl)-6-
oxa-3-azabicyclo[3.1.0]hexane-3-carboxylate, 19. To a solution of
the olefin 18 (2.37 g, 3.37 mmol) in MeCN (35 mL) was added
Na2EDTA (13.5 mL, 4 ꢀ 10-4 M) and CF3C(O)CH3 (6.8 mL,
7.60 mmol). The reaction was chilled to 0 °C before the portion-
wise addition of a mixture of NaHCO3 (4.24 g, 50.47 mmol) and
oxone (4.14 g, 6.73 mmol) over 15 min. After stirring for 2 h at
0 °C, the mixture was poured into water followed by removed of
the volatiles under reduced pressure. The residue was extracted
with CH2Cl2 (3 ꢀ 40 mL) and the combined extracts were
washed with brine, dried (Na2CO3), and then evaporated to
leave a residue that was chromatographed on silica gel by FCC
(10:90 to 20:80 EtOAc/petrol) to give 19 (1.95 g, 81%) as a pale
EtOAc/petrol). [R]D þ64 (c 1.1, CHCl3). vmax/cm-1 2950, 2924,
25
2888, 2852, 1695, 1360, 1328, 1175, 1110. δH (major rotamer)
7.70-7.66 (m, 2H, Ar), 7.45 (app t, 2H, J =6.8 Hz, Ar),
7.35-7.11 (m, 14H, Ar), 4.76-4.73 (m, 1H, H-30), 4.64 (d, 1H,
J =10.5 Hz, CHHPh), 4.64-4.61 (m, 2H, 2 ꢀ CHHPh), 4.34 (d,
1H, J =11.5 Hz, CHHPh), 4.31-4.29 (m, 2H, CH2 (Fmoc)), 4.16
(br s, 1H, H-2), 4.13 (app t, 1H, J = 7.0 Hz, CH (Fmoc)),
4.02-4.00 (m, 2H, H-10 and H-20), 3.97-3.94 (m, 2H, 2 ꢀ H-40),
3.74-3.72 (m, 1H, H-3), 3.68 (d, 1H, J = 12.0 Hz, H-5),
3.58-3.56 (m, 1H, H-4), 3.20 (d, 1H, J = 13.0 Hz, H-5), 3.04
(s, 3H, CH3 (Ms)), 0.82 (s, 9H, t-Bu), 0.04 (s, 6H, CH3). δC (major
rotamer) 154.9 (CO), 144.0 (C), 143.7 (C), 141.3 (C), 141.2 (C),
137.9 (C), 137.5 (C), 128.5 (CH), 128.4 (CH), 128.1 (CH), 128.0
(CH), 127.8 (CH), 127.7 (CH), 127.0 (CH), 125.0 (CH), 124.9
(CH), 120.0 (CH), 81.5 (C-30), 79.1 (C-10), 78.6 (C-20), 75.7 (CH2),
75.0 (CH2), 67.1 (CH2 (Fmoc)), 61.1 (C-40), 60.6 (C-2), 56.0 (C-3),
55.6 (C-4), 47.8 (C-5), 47.2 (CH (Fmoc)), 38.4 (CH3 (Ms)), 25.8
(C(CH3)3), 18.1 (C), -5.4 (CH3), -5.5 (CH3). HRMS (ESIþ)
calcd for C44H54NO9SSi (M þ H)þ 800.3289, found 800.3273.
(1aR,4R,5R,6R,6aS,6bS)-5,6-Bis(benzyloxy)-4-((tert-butyldi-
methylsilyloxy)methyl)hexahydro-1aH-oxireno[2,3-a]pyrrolizine, 21.
To a solution of 20 (470.3 mg, 0.589 mmol) in MeCN (6 mL) was
added piperidine (0.12 mL, 1.12 mmol). The reaction was stirred for
15 h at rt, the volatiles were removed under reduced pressure, and
the residue was purified by FCC (10:90 to 30:70 EtOAc/petrol) to
give a mixture of 21 and 22 (91:9) as a pale yellow oil (271.0 mg,
96%). A pure sample of 21 was obtained by further purification of
this mixture by FCC to give 21 as yellow needles. Rf 0.27 (30:70
24
EtOAc/petrol). Mp 40.9-43.1 °C (yellow needles). [R]D þ12
(c 1.0, CHCl3). vmax/cm-1 3032, 2945, 2924, 2858, 1255, 1109. δH
7.36-7.24 (m, 10H, Ar), 4.61 (d, 1H, J = 12.0 Hz, CHHPh), 4.60
(d, 1H, J = 11.5 Hz, CHHPh), 4.54 (d, 1H, J = 12.0 Hz, CHHPh),
4.51 (d, 1H, J = 12.0 Hz, CHHPh), 4.15 (app t, 1H, J = 3.8 Hz,
H-2), 3.91 (dd, 1H, J = 7.3, 3.8 Hz, H-1), 3.69-3.68 (m, 1H, H-6),
3.66 (dd, 1H, J = 10.0, 6.0 Hz, H-8), 3.64-3.62 (m, 2H, H-7 and
H-7a), 3.50 (app t, 1H, J = 10.0 Hz, H-8), 3.45 (d, 1H, J = 11.5 Hz,
H-5), 3.08-3.04 (m, 1H, H-3), 2.98 (d, 1H, J = 12.0 Hz, H-5), 0.88
(s, 9H, t-Bu), 0.04 (s, 3H, CH3), 0.03 (s, 3H, CH3). δC 138.1 (C),
137.7 (C), 128.4 (CH), 128.3 (CH), 127.8 (CH), 127.7 (CH), 127.64
(CH), 127.6 (CH), 88.7 (C-2), 85.9 (C-1), 72.1 (CH2), 71.8 (CH2),
70.8 (C-3), 69.0 (C-7a), 64.4 (C-8), 58.5 (C-7), 57.0 (C-6), 55.6 (C-5),
25.9 (C(CH3)3), 18.2 (C), -5.4 (CH3), -5.43 (CH3). HRMS (CIþ)
calculated for C28H40NO4Si (M þ H)þ 482.2727, found 482.2729.
(1S,2S,5R,6R,7R,7aR)-6,7-Bis(benzyloxy)-5-(hydroxymethyl)-
hexahydro-1H-pyrrolizine-1,2-diol, 23. To a solution of the epoxide
21 (37.4 mg, 0.078 mmol) in anhydrous CH2Cl2 (4 mL) was added
NaHSO4 (46.7 mg, 0.389 mmol). The reaction mixture was stirred
and heated at reflux for 2 days under an atmosphere of N2. The
reaction was quenched by the addition of water (5 mL) and stirred
for 1 h. The solvent was removed under reduced pressure and the
residue was extracted with EtOAc (3 ꢀ 10 mL). The combined
extracts were dried (MgSO4) and evaporated. NMR analysis of
this crude reaction mixture showed an 86:14 mixture of regio-
isomers. The crude mixture was purified by FCC (100% EtOAc to
8.5:1:0.5 EtOAc/MeOH/NH3) to give 23 (as a 92:8 mixture of
diastereomers) as a pale yellow oil (15.3 mg, 51%). 23 (as a 92:8
mixture of diastereomers): Rf 0.34 (8.6:1.0:0.4 EtOAc/MeOH/
25
yellow oil. Rf 0.42 (20:80 EtOAc/petrol). [R]D þ99 (c 1.1,
CHCl3). vmax/cm-1 3062, 2945, 2924, 2858, 1700, 1454, 1110.
δH (major rotamer) 7.76-7.54 (m, 4H, Ar), 7.41-7.16 (m, 14H,
Ar), 4.86 (d, 1H, J = 10.5 Hz, CHHPh), 4.67 (d, 1H, J = 12.0 Hz,
CHHPh), 4.64 (d, 1H, J = 11.5 Hz, CHHPh), 4.36 (d, 1H, J =
11.0Hz, CHHPh), 4.36-4.30 (m, 3H, CH2 (Fmoc) andH-2), 4.26
(br s, 1H, H-10), 4.19-4.15 (m, 1H, CH (Fmoc)), 3.91-3.86 (m,
1H, H-30), 3.86-3.80 (m, 2H, H-20 and H-3), 3.74-3.67 (m, 2H,
H-40 and H-5), 3.63 (d, 1H, J = 2.0 Hz, H-4), 3.59-3.53 (m, 1H,
H-40), 3.24-3.20 (m, 1H, H-5), 0.88 (s, 9H, t-Bu), 0.04 (s, 3H,
CH3), 0.03 (s, 3H, CH3). δC (major rotamer) 154.9 (CO), 143.7
(C), 141.3 (C), 138.0 (C), 137.8 (C), 128.7 (CH), 128.2 (CH), 127.9
(CH), 127.8 (CH), 127.6 (CH), 127.1 (CH), 127.0 (CH), 125.0
(CH), 124.9 (CH), 119.9 (CH), 79.1 (C-10), 77.2 (C-20), 74.9
(CH2), 74.4 (CH2), 70.6 (C-30), 67.1 (CH2 (Fmoc)), 63.5 (C-40’),
60.1 (C-2), 56.3 (C-3), 55.6 (C-4), 47.8 (C-5), 47.1 (CH (Fmoc)),
25.8 (C(CH3)3), 18.1 (C), -5.4 (CH3), -5.5 (CH3). δC (minor
rotamer) 155.0, 144.0, 141.2, 137.9, 137.7, 127.8, 127.7, 127.69,
127.64, 127.63, 127.5, 127.4, 125.0, 124.7, 120.0, 80.6, 78.0, 75.0,
74.8, 70.8, 66.2, 63.4, 59.8, 56.4, 54.9, 48.2, 47.6, 25.7, 18.07,
-5.45, -5.48. HRMS (ESIþ) calcd for C43H51NO7SiNa (M þ
Na)þ 744.3333, found 744.3360.
(1S,2S,5R)-(9H-Fluoren-9-yl)methyl 2-((1R,2S,3S)-1,2-Bis-
(benzyloxy)-4-(tert-butyldimethylsilyloxy)-3-(methylsulfonyloxy)-
butyl)-6-oxa-3-azabicyclo[3.1.0]hexane-3-carboxylate, 20. To a
solution of 19 (0.414 g, 0.574 mmol) in anhydrous CH2Cl2
(6 mL) was added anhydrous Et3N (0.24 mL, 1.723 mmol) and
methanesulfonyl chloride (0.089 mL, 1.148 mmol). The reaction
mixture was stirred at 0 °C under an atmosphere of N2 for 3 h,
followed by the evaporation of all volatiles in vacuo. Water
(20 mL) was added and the residue was extracted with CH2Cl2
(3 ꢀ 20 mL). The combined extracts were washed with brine,
23
NH3). [R]D þ19 (c 1.1, CHCl3). vmax/cm-1 3390, 3027, 2929,
2873, 1449, 1103, 1063. δH (CD3OD) δ 7.36-7.24 (m, 10H, Ar),
4.68 (d, 2H, J = 12.0 Hz, 2 ꢀ CHHPh), 4.60 (d, 1H, J = 11.5 Hz,
CHHPh), 4.54 (d, 1H, J = 12.0 Hz, CHHPh), 4.19 (app t, 1H, J =
5.3 Hz, H-1), 4.08 (dd, 1H, J = 10.5, 5.5 Hz, H-2), 4.04 (app t, 1H,
J = 5.3 Hz, H-7), 3.98 (dd, 1H, J =6.5, 5.5 Hz, H-6), 3.62 (dd, 1H,
J = 11.0, 4.8 Hz, H-8), 3.51 (dd, 1H, J = 11.3, 5.8 Hz, H-8), 3.30
(m, 1H, H-5), 3.27 (app t, 1H, J = 5.0 Hz, H-7a), 3.18 (app dt, 1H,
J. Org. Chem. Vol. 75, No. 3, 2010 821

Ritthiwigrom et al.
JOCArticle
J = 5.8, 5.0 Hz, H-3), 2.87 (dd, 1H, J = 11.3, 5.8 Hz, H-5). δC
(CD3OD) 139.6 (C), 139.5 (C), 129.4 (CH), 129.3 (CH), 128.95
(CH), 129.5 (CH), 128.7 (CH), 128.5 (CH), 87.2 (C-1), 85.6 (C-6),
81.4 (C-7), 79.2 (C-2), 75.2 (C-7a), 73.3 (CH2), 72.9 (CH2), 72.6
(C-3), 63.5 (C-8), 60.1 (C-5). HRMS (ESIþ) calcd for C22H28NO5
(M þ H)þ 386.1967, found 386.1967.
and then evaporated to give 30a as a pale yellow oil that was used in
the next step without further purification. (1S,2S,5R)-(9H-Fluo-
ren-9-yl)methyl 2-((1R,2S,3R)-1,2-bis(benzyloxy)-4-(tert-butyl-
dimethylsilyloxy)-3-(4-nitrobenzoyloxy)butyl)-6-oxa-3-azabicyclo-
[3.1.0]hexane-3-carboxylate (30a): Rf 0.41 (30:70 EtOAc/petrol).
22
[R]D þ35 (c 2.6, CHCl3). vmax/cm-1 2950, 2940, 2857, 1720, 1701,
(1R,2R,3R,6S,7S)-3-(Hydroxymethyl)hexahydro-1H-pyrroli-
zine-1,2,6,7-tetraol (Casuarine, 2). To a solution of 92% diaster-
eomerically pure 23 (21.0 mg, 0.055 mmol) in MeOH (2 mL) was
added PdCl2 (10.0 mg, 0.055 mmol). The mixture was stirred at
rt under an atmosphere of H2 (balloon) for 1.5 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 (OH-) A-26 resin (3 cm). Elution with
water followed by evaporation in vacuo gave casuarine (2) (dr =
1529, 1271, 1101. δH 8.29-8.23 (m, 2H, Ar), 7.79-7.57 (m, 2H,
Ar), 7.42-7.20 (m, 18H, Ar), 5.45 (dd, 1H, J = 9.0, 5.5 Hz, H-30),
4.91 (d, 1H, J = 11.0 Hz, CHHPh), 4.84 (d, 1H, J = 11.5 Hz,
CHHPh), 4.60 (d, 1H, J = 11.0 Hz, CHHPh), 4.45 (d, 2H, J =
6.5 Hz, CH2 (Fmoc)), 4.37 (d, 1H, J = 11.5 Hz, CHHPh),
4.28-4.14 (m, 5H, H-10 or H-20, H-3 or H-4, 2 ꢀ H-40 and CH
(Fmoc)), 4.07 (d, 1H, J = 3.0 Hz, H-3 or H-4), 3.78 (br s, 1H, H-10
or H-20), 3.76 (d, 1H, J= 12.0, Hz, H-5), 3.68 (br d, 1H, J=2.0Hz,
H-2), 3.25 (d, 1H, J = 11.5 Hz, H-5), 0.91 (s, 9H, t-Bu), 0.08 (s, 3H,
CH3), 0.07 (s, 3H, CH3). δC 163.9 (CO), 154.8 (CO), 150.5 (C),
143.8 (C), 143.5 (C), 141.2 (C), 141.1 (C), 137.6 (C), 137.4 (C), 135.2
(C), 130.7 (CH), 128.4 (CH), 128.3 (CH), 128.1 (CH), 128.0 (CH),
127.9 (CH), 127.8 (CH), 127.7 (CH), 127.5 (CH), 127.0 (CH), 126.9
(CH), 124.7 (CH), 123.4 (CH), 119.9 (CH), 80.7 (C-10), 79.0 (C-20),
75.8 (C-30), 74.5 (CH2), 74.8 (CH2), 67.0 (CH2 (Fmoc)), 61.8 (C-2),
60.5 (C-40), 56.4 (C-3 or C-4), 55.7 (C-3 or C-4), 47.6 (C-5), 47.1
(CH (Fmoc)), 25.7 (C(CH3)3), 18.0 (C), -5.4 (CH3), -5.5 (CH3).
HRMS (ESIþ) calcd for C50H55N2O10Si (M þ H)þ 871.3626,
found 871.3611. To a solution of crude 30a (0.131 mmol) in MeOH
(2 mL) was added K2CO3 (0.015 g, 0.109 mmol). After stirring at rt
for 1 day, the mixture was evaporated and dissolved in CH2Cl2. The
solution was washed with water (5 mL) and the aqueous layer was
extracted with CH2Cl2 (3 ꢀ 10 mL). The combined extracts were
washed with brine, dried (Na2CO3), and evaporated. The residue
was purified by FCC (50:50 EtOAc/petrol to 100% EtOAc) to give
30 as a yellow oil (36 mg, 55%). Rf 0.08 (30:70 EtOAc/petrol).
23
95:5) as a brown foamy solid (10.4 mg, 93%). [R]D þ18.1 (c 1.0,
24
H2O) [lit.4 [R]D þ16.9 (c 0.8, H2O)]. vmax/cm-1 3284, 2919,
1378, 1128, 1102, 1029. δH (D2O) 4.22-4.18 (m, 2H, H-6 and
H-7), 4.16 (t, 1H, J1,2 = J1,7a = 8.7 Hz, H-1), 3.79 (t, 1H, J1,2 =
0
2,3 = 8.0 Hz, H-2), 3.77 (dd, 1H, J8,8 = 10.0, J3,8 = 3.5 Hz,
J
H-8), 3.61 (dd, 1H, J8,8 = 11.3, J3,8 = 6.8 Hz, H-8 ), 3.27 (dd,
0
0
0
1H, J5R,5β = 12.3 Hz, J5β,6 = 4.3 Hz, H-5β), 3.06 (dd, 1H,
J1,7a = 8.0 Hz, J7,7a = 3.0 Hz, H-7a), 3.04-3.00 (m, 1H, H-3),
2.90 (dd, 1H, J5R,5β = 11.8 Hz, J5R,6 = 4.3 Hz, H-5R). δC (D2O)
79.9 (C-7), 78.9 (C-1), 78.5 (C-6), 77.8 (C-2), 73.1 (C-7a), 71.0
(C-3), 63.5 (C-8), 59.0 (C-5). HRMS (ESIþ) calcd for
C8H16NO5 (M þ H)þ 206.1028, found 206.0953.
(1R,2R,3R,7S,7aR)-3-Hydroxymethylhexahydro-1H-pyrroli-
zine-1,2,7-triol (Australine, 3). To a solution of 29 (74.6 mg,
0.155 mmol) in MeOH (3 mL) was added PdCl2 (41.1 mg, 0.232
mmol). The mixture was stirred at rt under an atmosphere of H2
(balloon) for 3 h, follow by the dropwise addition of concd HCl
(10 drops) and stirring was continued 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 (2 mL) and applied to a
column of Amberlyst (OH-) A-26 resin (4 cm). Elution with
water followed by evaporation in vacuo gave australine 3 as
23
[R]D þ53 (c 2.8, CHCl3). vmax/cm-1 3362, 2930, 1449, 1250, 1100.
δH (major rotamer) 7.33-7.25 (m, 10H, Ar), 4.86 (d, 1H, J =
11.0 Hz, CHHPh), 4.71 (d, 1H, J = 11.5 Hz, CHHPh), 4.62 (d, 1H,
J= 11.0 Hz, CHHPh), 4.57 (d, 1H, J=11.0Hz, CHHPh), 3.81 (br
s, 3H, H-20, H-30, and H-40), 3.73 (dd, J = 9.5, 3.5 Hz, 1H, H-40),
3.67 (d, 1H, J = 2.5 Hz, H-3 or H-4), 3.55 (dd, 1H, J = 9.5, 2.0 Hz,
H-10), 3.42 (d, 1H, J = 9.5 Hz, H-2), 3.39 (d, 1H, J = 2.5 Hz, H-3
or H-4), 3.02 (d, 1H, J = 13.5 Hz, H-5), 2.70 (d, 1H, J = 13.0 Hz,
H-5), 0.91 (s, 9H, t-Bu), 0.08 (s, 6H, 2 ꢀ CH3). δC (major rotamer)
138.3 (C), 138.2 (C), 128.4 (CH), 128.3 (CH), 128.22 (CH), 128.2
(CH), 128.1 (CH), 128.0 (CH), 127.8 (CH), 127.7 (CH), 79.4 (C-20),
78.5 (C-10), 74.52 (CH2), 74.5 (CH2), 71.7 (C-30), 64.4 (C-40), 59.9
(C-2), 58.0 (C-3 or C-4), 55.8 (C-3 or C-4), 46.9 (C-5), 25.9
(C(CH3)3), 18.3 (C), -5.28 (CH3), -5.3 (CH3). HRMS (ESIþ)
calcd for C28H42NO5Si (M þ H)þ 500.2832, found 500.2836.
(1aR,4S,5R,6R,6bS)-5,6-Bis(benzyloxy)-4-((tert-butyldimethyl-
silyloxy)methyl)hexahydro-1aH-oxireno[2,3-a]pyrrolizine, 31, and
(1aR,5R,6S,7R,7aS,7bS)-6,7-Bis(benzyloxy)-5-(tert-butyldimethyl-
silyloxy)octahydrooxireno[2,3-a]indolizine, 32. To a solution of 30
(0.500 g, 1.002 mmol) in toluene (10 mL) was added triphenylphos-
phine (0.657 g, 2.505 mmol). The mixture was cooled to 0 °C and
diisopropyl azodicarboxylate (0.49 mL, 2.505 mmol) was added.
The mixture was heated and stirred at 80 °C for 12 h. The volatiles
were removed in vacuo then satd CuSO4 solution (20 mL) was
added. The mixture was extracted with CH2Cl2 (3 ꢀ 25 mL). The
combined extracts were washed with water (20 mL), dried
(Na2CO3), filtered, and then evaporated. The residue was purified
by FCC (50:50 EtOAc/petrol to 100% EtOAc) to give 31 as a
yellow oil (0.337 g, 70%) and 32 as a yellow oil (0.02 g, 4%). 31:
a yellow oil (25.1 mg, 86%). [R]D þ9.4 (c 2.4, H2O) [lit.14d
22
25
[R]D þ8 (c 0.35, H2O)]. vmax/cm-1 3318, 2944, 2873, 2484,
1388, 1332, 1123, 1041. δH (D2O) 4.37-4.35 (m, 1H, H-7), 4.22
(t, 1H, J1,2 = J1,7a = 7.8 Hz, H-1), 3.89 (dd, 1H, J2,3 = 9.5 Hz,
0
J1,2 = 8.0 Hz, H-2), 3.79 (dd, 1H, J8,8 = 12.0 Hz, J3,8 = 3.5 Hz,
H-8), 3.61 (dd, 1H, J8,8 = 11.5 Hz, J3,8 = 7.0 Hz, H-80), 3.17
(dd, 1H, J1,7a = 7.8 Hz, J7,7a = 4.8 Hz, H-7a), 3.15-3.12 (m,
1H, H-5), 2.74-2.69 (m, 2H, H-3 and H-5), 2.05-2.00 (m, 1H,
H-6), 1.97-1.89 (m, 1H, H-6). δC NMR (D2O) 79.5 (C-2), 73.7
(C-1), 71.3 (C-7a), 71.1 (C-3), 70.1 (C-7), 63.5 (C-8), 52.4 (C-5),
0
0
35.8 (C-6). 3 HCl salt: δH (D2O) 4.72-4.69 (m, 1H, H-7), 4.51
3
(app t, 1H, J = 7.5 Hz, H-1), 4.18 (dd, 1H, J = 10.0, 8.0 Hz,
H-2), 4.02 (dd, 1H, J = 13.0, 2.5 Hz, H-8), 3.95-3.92 (m, 1H,
H-7a), 3.92 (dd, 1H, J = 13.8, 4.3 Hz, H-8), 3.84 (app br t, 1H,
J = 9.8 Hz, H-5), 3.45-3.38 (m, 2H, H-5 and H-3), 2.36-2.31
(m, 1H, H-6), 2.05-2.00 (m, 1H, H-6), 2.29-2.27 (m, 1H, H-6).
δC (D2O) 76.2 (C-2), 73.3 (C-7a), 72.1 (C-1), 71.4 (C-3), 68.7
(C-7), 56.5 (C-8), 52.9 (C-5), 35.0 (C-6). HRMS (EI) calcd for
C8H15NO4 (M þ) 189.1001, found 189.0994.
((2R,3R,4R)-3,4-Bis(benzyloxy)-4-((1S,2S,5R)-6-oxa-3-azabi-
cyclo[3.1.0]hexan-2-yl)-1-(tert-butyldimethylsilyloxy)butan-2-ol, 30.
To a solution of 19 (0.095 g, 0.131 mmol) in toluene (2 mL) was
added triphenylphosphine (0.086 g, 0.328 mmol) and p-nitroben-
zoic acid (0.055 g, 0.328 mmol). The mixture was cooled to 0 °Cand
diisopropyl azodicarboxylate (64.5 μL, 0.28 mmol) was added. The
mixture was stirred at rt for 5 h. The volatiles were removed in
vacuo then satd CuSO4 solution (20 mL) was added. The reaction
mixture was extracted with CH2Cl2 (3 ꢀ 10 mL). The combined
extracts were washed with water (5 mL), dried (Na2CO3), filtered
Rf 0.26 (70:30 EtOAc/petrol). [R]D þ43 (c1.6, CHCl3). vmax/cm-1
25
2952, 2930, 2850, 1447, 1250, 1095. δH 7.38-7.25 (m, 10H, Ar),
4.55 (d, 1H, J = 12.0 Hz, CHHPh), 4.53 (d, 1H, J = 12.0 Hz,
CHHPh), 4.51 (d, 1H, J = 11.5 Hz, CHHPh), 4.48 (d, 1H, J =
12.0 Hz, CHHPh), 4.09 (d, 1H, J = 4.0 Hz, H-2), 3.99 (app t, 1H,
J = 9.3 Hz, H-8), 3.91 (dd, 1H, J = 10.0, 5.0 Hz, H-8), 3.80 (d, 1H,
J = 4.5 Hz, H-1), 3.68-3.66 (m, 2H, H-6 or H-7 and H-7a), 3.60
822 J. Org. Chem. Vol. 75, No. 3, 2010

Ritthiwigrom et al.
JOCArticle
(d, 1H, J = 2.0 Hz, H-6 or H-7), 3.39 (app dt, 1H, J = 8.5, 4.3 Hz,
H-3), 3.19 (d, 1H, J = 10.5 Hz, H-5), 3.03 (d, 1H, J = 11.5 Hz,
H-5), 0.09 (s, 9H, t-Bu), 0.06 (s, 6H, 2 ꢀ CH3). δC 138.3 (C), 137.6
(C), 128.5 (CH), 128.3 (CH), 127.9 (CH), 127.6 (CH), 127.5 (CH),
127.3 (CH), 86.9 (C-2), 85.3 (C-1), 72.2 (CH2), 71.9 (C-7a), 71.7
(CH2), 65.7 (C-3), 58.5 (C-8), 57.6 (C-6 or C-7), 57.3 (C-6 or C-7),
48.1 (C-5), 25.9 (C(CH3)3), 18.2 (C), -5.4 (CH3), -5.5 (CH3). 32:
Rf 0.25 (70:30 EtOAc/petrol). δH 7.78-7.26 (m, 10H, Ar), 4.97 (d,
1H, J = 11.5 Hz, CHHPh), 4.73 (d, 1H, J = 11.5 Hz, CHHPh),
4.65 (d, 2H, J = 11.5 Hz, 2 ꢀ CHHPh), 4.15 (m, 1H, H-6), 3.63
(app t, 1H, J = 7.8 Hz, H-8), 3.55 (d, 1H, J = 3.0 Hz, H-1 or H-2),
3.52 (d, 1H, J = 10.5 Hz, H-3), 3.45 (d, 1H, J = 3.0 Hz, H-1 or
H-2), 3.38 (dd, 1H, J = 10.0, 3.0 Hz, H-7), 3.20 (d, 1H, J =
10.5 Hz, H-3), 3.15 (d, 1H, J = 9.5 Hz, H-8a), 2.96 (dd, 1H, J =
15.0, 1.5 Hz, H-5), 2.86 (br d, 1H, J = 15.0 Hz, H-5), 0.91 (s, 9H,
t-Bu), 0.10 (s, 3H, CH3), 0.07 (s, 3H, CH3). δC 138.5 (C), 138.3 (C),
133.2 (CH), 133.0 (CH), 128.6 (CH), 128.4 (CH), 128.2 (CH), 127.8
(CH), 127.6 (CH), 127.5 (CH), 84.1 (C-7), 75.0 (CH2), 72.7 (C-8),
72.2 (CH2), 71.3 (C-6), 61.8 (C-8a), 57.8 (C-1 or C-2), 54.7 (C-1 or
C-2), 52.0 (C-3), 50.3 (C-5), 28.6 (C(CH3)3), 18.2 (C), -4.6 (CH3),
-4.7 (CH3). HRMS (ESIþ) calcd for C28H40NO4Si (M þ H)þ
482.2727, found 482.2717.
diisopropyl azodicarboxylate (41.1 μL, 0.021 mmol) was added.
The mixture was stirred at rt for 8 h. The volatiles were removed
in vacuo then satd CuSO4 solution (20 mL) was added. The
reaction mixture was extracted with CH2Cl2 (3 ꢀ 10 mL). The
combined extracts were washed with water (5 mL), dried
(Na2CO3), filtered, and then evaporated to give 35a as a brown
oil that was used in the next step without further purification.
(1S,5S,6R,7R,7aR)-6,7-Bis(benzyloxy)-5-((tert-butyldimethyl-
silyloxy)methyl)hexahydro-1H-pyrrolizin-1-yl-4-nitrobenzoate (35a):
26
Rf 0.39 (50:50 EtOAc/petrol). [R]D þ31 (c 3.0, CHCl3). vmax/cm-1
2926, 2853, 1726, 1528, 1272, 1096. δH 7.95 (s, 4H, Ar), 7.37-7.12(m,
10H,Ar),5.63(appt,1H,J=5.8Hz, H-7),4.56(d, 1H,J=12.0Hz,
CHHPh), 4.51 (d, 1H, J = 12.0 Hz, CHHPh), 4.49 (d, 1H, J =
13.0 Hz, CHHPh), 4.47 (d, 1H, J = 13.5 Hz, CHHPh), 4.13 (dd, 1H,
J = 4.5, 1.5 Hz, H-2), 4.07 (dd, 1H, J = 10.3, 7.3 Hz, H-8), 4.05 (dd,
1H, J = 4.3, 2.3 Hz, H-1), 4.00 (dd, 1H, J = 10.3, 6.8 Hz, H-8), 3.68
(appt,1H,J= 4.8 Hz, H-7a), 3.40 (app dt, 1H, J= 6.0, 5.0 Hz, H-3),
3.30-3.25 (m, 1H, H-5), 2.81 (app br t, 1H, J = 6.5 Hz, H-5),
2.30-2.23 (m, 1H, H-6), 2.05 (br d, 1H, J = 12.0 Hz, H-6), 0.90 (s,
9H, t-Bu), 0.08 (s, 3H, CH3), 0.07 (s, 3H, CH3). δC 163.8 (CO), 150.4
(C), 138.3 (C), 137.7 (C), 135.2 (C),130.6 (CH), 128.4 (CH), 128.3
(CH), 127.6 (CH), 127.5 (CH), 126.9 (CH), 123.3 (CH), 86.9 (C-2),
81.7 (C-1), 74.3 (C-7), 73.7 (C-7a), 72.3 (CH2), 71.7 (CH2),65.4(C-3),
59.9 (C-8), 46.2 (C-5), 34.7 (C-6), 25.9 (C(CH3)3), 18.3 (C), -5.3
(CH3), -5.4 (CH3). HRMS (ESIþ) calcd for C35H45N2O7Si (M þ
H)þ 633.2996, found 633.2986. To a solution of crude 35a (0.083
mmol) in MeOH (2 mL) was added K2CO3 (0.023 g, 0.1669 mmol).
After stirring at rt for 4 h, the mixture was evaporated and dissolved in
CH2Cl2 then washed with water. The aqueous layer was extracted
with CH2Cl2 and the combined extracts were washed with brine, dried
(Na2CO3), and evaporated. The residue was purified by FCC (80:20
EtOAc/petrol to 10:90 MeOH/EtOAc) to give 35 as a pale yellow
oil (26 mg, 64%). Rf 0.19 (10:90 MeOH/EtOAc). [R]D24 -5.3 (c 1.2,
CHCl3). vmax/cm-1 3418, 2930, 2850, 1673, 1250, 1089. δH 7.36-7.26
(m, 10H, Ar), 4.68 (d, 1H, J = 11.5 Hz, CHHPh), 4.62 (d, 1H, J =
12.0 Hz, CHHPh), 4.57 (d, 1H, J = 11.5 Hz, CHHPh), 4.56 (d, 1H,
J=12.0Hz, CHHPh), 4.25 (app t, 1H, J=5.0Hz, H-1), 4.23(appt,
1H, J = 5.0 Hz, H-2), 4.12 (app br t, 1H, J = 2.5 Hz, H-7), 3.97 (dd,
1H, J = 10.8, 5.3 Hz, H-8), 3.82 (dd, 1H, J = 10.8, 5.3 Hz, H-8), 3.49
(appt,1H,J= 4.3 Hz, H-7a), 3.31 (app dt, 1H, J= 4.8, 4.0 Hz, H-3),
3.04-2.99 (m, 1H, H-5), 2.81 (br t, 1H, J = 7.8 Hz, H-5), 1.96-1.94
(m, 2H, 2 ꢀ H-6), 0.88 (s, 9H, t-Bu), 0.05 (s, 3H, CH3), 0.04 (s, 3H,
CH3). δC 138.4 (C), 137.9 (C), 128.4 (CH), 128.3 (CH), 128.0 (CH),
127.8 (CH), 127.6 (CH), 127.5 (CH), 85.5 (C-2), 79.5 (C-1), 73.2
(C-7a), 73.0 (CH2),71.9(CH2),71.2(C-7),62.5(C-3),59.3(C-8),43.9
(C-5), 36.9 (C-6), 26.0 (C(CH3)3), 18.6 (C), -5.3 (CH3), -5.8 (CH3).
HRMS (ESIþ) calcd for C28H42NO4Si (M þ H)þ 484.2883, found
484.2882.
(1R,5S,6R,7R,7aR)-6,7-Bis(benzyloxy)-5-((tert-butyldimethyl-
silyloxy)methyl)hexahydro-1H-pyrrolizin-1-ol, 33, and (2S,5S,6R,
7R,7aR)-6,7-Bis(benzyloxy)-5-((tert-butyldimethylsilyloxy)methyl)-
hexahydro-1H-pyrrolizin-2-ol, 34. To a solution of crude 31 (0.037 g,
0.098 mmol) in anhydrous THF (2 mL) was added dropwise a
solution of lithium aluminum hydride (1 M in THF, 0.1 mL, 0.
1 mmol). The mixture was stirred at rt for 12 h. The solvent was
evaporated and the mixture was chromatographed on silica gel by
FCC (80:20 EtOAc/petrol to 10:90 MeOH/EtOAc) to give 33 as a
pale yellow oil (15.3 mg, 41%) and 34 (3.3 mg, 9%) as a pale yellow
22
oil. 33: Rf 0.31 (5:95 MeOH/EtOAc). [R]D -4 (c 1.4, CHCl3).
v
max/cm-1 3390, 2923, 2858, 1260, 1095. δH 7.34-7.25 (m, 10H,
Ar), 4.59 (d, 1H, J = 11.5 Hz, CHHPh), 4.57 (d, 1H, J = 10.5 Hz,
CHHPh), 4.52 (d, 1H, J = 12.0 Hz, CHHPh), 4.48 (d, 1H, J =
11.5 Hz, CHHPh), 4.16 (app dt, 1H, J= 6.5, 5.5 Hz, H-7), 4.04 (dd,
1H, J = 4.5, 2.0 Hz, H-2), 3.95 (dd, 1H, J = 10.0, 7.3 Hz, H-8),
3.89-3.86 (m, 2H, H-1 and H-8), 3.35 (app dt, 1H, J = 6.5, 4.8 Hz,
H-3), 3.30 (app t, 1H, J = 4.5 Hz, H-7a), 3.09 (ddd, 1H, J = 9.3,
7.0, 6.5 Hz, H-5), 2.91-2.87 (m, 1H, H-5), 2.19-2.13 (m, 1H, H-6),
1.84-1.78 (m, 1H, H-6), 0.88 (s, 9H, t-Bu), 0.40 (s, 6H, 2 ꢀ CH3).
δC 138.4 (C), 138.1 (C), 128.4 (CH), 128.3 (CH), 127.7 (CH), 127.6
(CH), 127.5 (CH), 127.3 (CH), 85.9 (C-1), 85.6 (C-2), 77.7 (C-7a),
75.6 (C-7), 72.1 (CH2), 71.4 (CH2), 65.3 (C-3), 58.8 (C-8), 46.1
(C-5), 35.6 (C-6), 25.9 (C(CH3)3), 18.3 (C), -5.4 (CH3), -5.5
(CH3). HRMS(ESIþ) calcdforC28H42NO4Si (M þ H)þ 484.2883,
25
found 484.2868. 34: Rf 0.1 (5:95 MeOH/EtOAc). [R]D þ10.3
(c 1.1, CHCl3). vmax/cm-1 3236, 2952, 2923, 1250, 1096. δH
7.36-7.24 (m, 10H, Ar), 4.56 (d, 1H, J = 12.0 Hz, CHHPh),
4.53 (d, 1H, J = 12.0 Hz, CHHPh), 4.48 (d, 1H, J = 12.0 Hz,
CHHPh), 4.45 (d, 1H, J = 12.0 Hz, CHHPh), 4.43 (br t, 1H, J =
4.0 Hz, H-6), 4.10 (dd, 1H, J = 4.5, 2.0 Hz, H-2), 3.91 (d, 2H, J =
6.0 Hz, 2 ꢀ H-8), 3.88-3.83 (m, 2H, H-1 and H-7a), 3.54 (app dt,
1H, J= 6.0, 5.0 Hz, H-3), 3.23 (dd, 1H, J= 10.0, 3.5 Hz, H-5), 2.96
(d, 1H, J = 10.0 Hz, H-5), 2.18 (dd, 1H, J = 13.0, 7.3 Hz, H-7),
1.86-1.81 (m, 1H, H-7), 0.89 (s, 9H, t-Bu), 0.05 (s, 6H, 2 ꢀ CH3).
δC 138.0 (C), 137.9 (C), 128.5 (CH), 128.4 (CH), 127.8 (CH), 127.7
(CH), 127.6 (CH), 127.4 (CH), 86.8 (C-1), 85.7 (C-2), 73.7 (C-6),
72.4 (CH2), 71.5 (CH2), 68.7 (C-7a), 64.5 (C-3), 58.5 (C-8), 56.2 (C-
5), 39.5 (C-7), 25.9 (C(CH3)3), 18.3 (C), -5.4 (CH3), -5.5 (CH3).
HRMS (ESIþ) calcd for C28H42NO4Si (M þ H)þ 484.2883, found
484.2863.
(1R,2R,3S,7S,7aR)-3-(Hydroxymethyl)hexahydro-1H-pyrro-
lizine-1,2,7-triol (3-epi-Australine, 4). To a solution of 35 (21 mg,
0.045 mmol) in MeOH (1 mL) was added PdCl2 (12 mg, 0.065
mmol). The mixture was stirred at rt under an atmosphere of H2
(balloon) for 3 h, follow by the dropwise addition of concd HCl
(5 drops). Stirring at rt was continued 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 (OH-) A-26 resin (3 cm). Elution with
water followed by evaporation in vacuo gave 3-epi-australine (4)
as a brown viscous oil (7.2 mg, 88%). [R]D23 -10.5 (c 0.7, H2O).
v
max/cm-1 3279, 2924, 2888, 1429, 1357, 1058. δH (D2O) 4.41
(br t, 1H, J6,7 = J7,7a = 4.0 Hz, H-7), 4.30 (t, 1H, J1,2 = J1,7a
3.3 Hz, H-1), 4.15 (t, 1H, J1,2 = J2,3 = 4.0 Hz, H-2), 4.01 (dd,
=
0
1H, J8,8 = 11.8 Hz, J3,8 = 5.8 Hz, H-8), 3.92 (dd, 1H, J8,8
0
=
11.8 Hz, J3,8 = 6.3 Hz, H-8 ), 3.38 (t, 1H, J1,7a = J7,7a = 4.3 Hz,
(1S,5S,6R,7R,7aR)-6,7-Bis(benzyloxy)-5-((tert-butyldimethyl-
silyloxy)methyl)hexahydro-1H-pyrrolizin-1-ol, 35. To a solution
of 33 (0.040 g, 0.083 mmol) in toluene (2 mL) was added
triphenylphosphine (0.055 g, 0.021 mmol) and p-nitrobenzoic
acid (0.035 g, 0.021 mmol). The mixture was stirred at 0 °C and
0
0
0
H-7a), 3.30 (dt, 1H, J3,8 = 5.3 Hz, J2,3 = J3,8 = 4.5 Hz, H-3),
3.15-3.10 (m, 1H, H-5R), 2.88 (t, 1H, J5,5 = J5,6 = 8.0 Hz,
H-5β), 2.00-1.87 (m,2H, 2 ꢀ H-6). 13C NMR(D2O)δ79.3 (C-2),
J. Org. Chem. Vol. 75, No. 3, 2010 823

Ritthiwigrom et al.
JOCArticle
75.2 (C-7a), 74.7 (C-1), 70.4 (C-7), 63.9 (C-3), 57.8 (C-8), 45.3
H-5R), 3.06 (dd, 1H, J7,7a = 2.0 Hz, J1,7a = 5.5 Hz, H-7a), 2.98
(t, 1H, J5,5 = J5,6 = 8.5 Hz, H-5β), 2.23-2.18 (m, 1H, H-6R),
1.80-1.72 (m, 1H, H-6β). δH (D2O) 80.5 (C-1), 79.8 (C-2), 78.2
(C-7a), 75.1 (C-7), 64.9 (C-3), 57.6 (C-8), 46.4 (C-5), 34.5 (C-6).
(C-5), 35.6 (C-6). HRMS (ESIþ) calcd for C8H16NO4 (M þ H)þ
190.1079, found 190.1086. 4 HCl salt: [R]D23 -37 (c 0.7, H2O).
3
[lit.6 [R]D -3.5 (c 1.35, H2O)]. δH (D2O) 4.77-4.73 (m, 1H,
20
36 HCl salt: [R]D -21 (c 0.63, H2O), HCl salt [lit.31 for ent-
21
H-7), 4.65 (s, 1H, H-1), 4.34 (d, 1H, J = 3.5 Hz, H-2), 4.29 (d, 1H,
J = 5.5 Hz, H-7a), 4.16 (dd, 1H, J = 12.0, 4.5 Hz, H-8),
4.13-4.04 (m, 2H, H-8 and H-3), 3.74 (dd, 1H, J = 11.3, 5.3
Hz, H-5), 3.71-3.65 (m, 1H, H-5), 2.28 (dd, 1H, J = 14.0, 5.0 Hz,
H-6), 2.21-2.13 (m, 1H, H-6). δC (D2O) 79.3 (C-7a), 77.4 (C-2),
74.2 (C-1), 69.3 (C-7), 67.1 (C-3), 56.1(C-8), 48.4(C-5), 35.0 (C-6).
(1R,2R,3S,7R,7aR)-3-(Hydroxymethyl)hexahydro-1H-pyrro-
lizine-1,2,7-triol (3,7-Di-epi-australine, 36). To a solution of 33
(20 mg, 0.041 mmol) in MeOH (1 mL) was added PdCl2 (11 mg,
0.062 mmol). The mixture was stirred at rt under an atmosphere
of H2 (balloon) for 3 h, followed by the dropwise addition of
concd HCl (5 drops) at rt for 15 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 (OH-) A-26 resin (3 cm). Elution with water fol-
lowed by evaporation in vacuo gave 3,7-di-epi-australine (36) as
3
3
20
36 HCl; [R]D þ33 (c 0.1, H2O)]. δH (D2O) 4.63 (dt, 1H, J6,7
=
8.0 Hz, J6,7 = J7,7a = 6.0 Hz, H-7), 4.41 (br s, 1H, H-1), 4.35
0
(d, 1H, J1,2 = 2.5 Hz H-2), 4.13 (dd, 1H, J8,8 = 12.5 Hz, J3,8
=
0
5.0 Hz, H-8), 4.10 (d, 1H, J8,8 = 9.0 Hz, H-8), 4.06-4.02 (m,
1H, H-3), 3.84 (d, 1H, J7,7a = 6.5 Hz, H-7a), 3.75 (dd, 1H, J5,5
11.3 Hz, J5,6 = 6.3 Hz, H-5), 3.73 (dd, 1H, J5,5 = 10.8 Hz, J5,6
=
=
6.3 Hz, H-5), 2.54-2.48 (m, 1H, H-6), 2.07-1.99 (m, 1H, H-6).
δC (D2O) 80.1 (C-7a), 77.6 (C-1), 77.1 (C-2), 73.1 (C-7), 67.7
(C-3), 55.8 (C-8), 48.6 (C-5), 33.1 (C-6). HRMS (ESIþ) calcd for
C8H16NO4 (M þ H)þ 190.1079, found 190.1074.
Acknowledgment. We thank the Australian Research
Council and the University of Wollongong for financial
support and Chiang Mai University and the Thai Govern-
ment for a Ph.D. scholarship to T.R.
24
a white solid (7.0 mg, 90%). [R]D -9.3 (c 1.1, H2O). vmax/cm-1
3370, 3309, 2509, 1454, 1202, 1060. δH (D2O) 4.30 (dt, 1H, J6,7
=
7,7a = 6.5 Hz, J6,7 = 6.0 Hz, H-7), 4.16 (br d, 1H, J2,3 = 3.5 Hz,
Supporting Information Available: General experimental
procedures and full experimental procedures and characteriza-
tion data as well as copies of the 1H NMR and 13C NMR spectra
of all new compounds and crystal/refinement data and an
ORTEP plot of compound 21 (CCDC 752850). This material
is available free of charge via the Internet at http://pubs.acs.org.
J
0
H-2), 4.13 (s, 1H, H-1), 3.97 (dd, 1H, J8,8 = 11.8 Hz, J3,8 = 7.0
Hz, H-8), 3.92 (dd, 1H, J8,8 = 12.0 Hz, J3,8 = 7.0 Hz, H-80),
3.28 (ddd, 1H, J2,3 = 9.0 Hz, J3,8 = 7.0 Hz, J2,3 = 4.0 Hz, H-3),
3.11 (ddd, 1H, J5,5 = 10.0 Hz, J5,6 = 10.0 Hz, J5,6 = 6.0 Hz,
0
0
824 J. Org. Chem. Vol. 75, No. 3, 2010