Synthetic and spectroscopic studies on the structures of uniflorines A and B: structural revision to 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine alkaloids

Article abstract of DOI:10.1016/j.tet.2008.02.110

The diastereoselective synthesis of the C-2 epimer and the C-1, C-2 di-epimers of the putative structure of the alkaloid uniflorine A has been achieved. The synthesis of the latter di-epimers employed a novel pyrrolo[1,2-c]oxazin-1-one precursor to allow for the reversal of π-facial diastereoselectivity in an osmium(VIII)-catalyzed syn-dihydroxylation (DH) reaction. The NMR spectral data of these epimeric compounds and that of related isomers did not match that of the natural product. From a comparison of the NMR data of uniflorines A and B with that of casuarine and the known synthetic 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine isomers we concluded unequivocally that uniflorine B is the known alkaloid casuarine. Although we cannot unequivocally prove the structure of uniflorine A, without access to the original material and data, the published data suggest that the natural product is also a 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine with the same relative C-7-C-7a-C-1-C-2-C-3 stereochemistry as casuarine. We thus suggest that uniflorine A is 6-epi-casuarine. Crown Copyright

Full text of DOI:10.1016/j.tet.2008.02.110

Available online at www.sciencedirect.com
Tetrahedron 64 (2008) 4868e4879
www.elsevier.com/locate/tet
Synthetic and spectroscopic studies on the structures
of uniflorines A and B: structural revision to
1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine alkaloids
*
Andrew S. Davis, Thunwadee Ritthiwigrom, Stephen G. Pyne
School of Chemistry, University of Wollongong, Wollongong, NSW 2522, Australia
Received 2 October 2007; received in revised form 20 February 2008; accepted 28 February 2008
Available online 18 March 2008
Abstract
The diastereoselective synthesis of the C-2 epimer and the C-1, C-2 di-epimers of the putative structure of the alkaloid uniflorine A has been
achieved. The synthesis of the latter di-epimers employed a novel pyrrolo[1,2-c]oxazin-1-one precursor to allow for the reversal of p-facial
diastereoselectivity in an osmium(VIII)-catalyzed syn-dihydroxylation (DH) reaction. The NMR spectral data of these epimeric compounds
and that of related isomers did not match that of the natural product. From a comparison of the NMR data of uniflorines A and B with that
of casuarine and the known synthetic 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine isomers we concluded unequivocally that uniflorine
B is the known alkaloid casuarine. Although we cannot unequivocally prove the structure of uniflorine A, without access to the original material
and data, the published data suggest that the natural product is also a 1,2,6,7-tetrahydroxy-3-hydroxymethylpyrrolizidine with the same relative
C-7eC-7aeC-1eC-2eC-3 stereochemistry as casuarine. We thus suggest that uniflorine A is 6-epi-casuarine.
Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
HO
HO
8
1. Introduction
OH
OH
H
N
H
8a
N
HO
HO
HO
HO
1
3
OH
The alkaloid uniflorine Awas isolated in 2000 from the leaves
of the tree Eugenia uniflora L.1e3 The water-soluble extract of
these leaves has been used as an antidiabetic agent in Para-
guayan traditional medicine. Uniflorine Awas found to be an in-
hibitor of the a-glucosidases, rat intestinal maltase and sucrase,
with IC50 values of 12 and 3.1 mM, respectively. The structure of
uniflorine Awas deduced from NMR analysis to be that shown as
structure 1.1 The proposed structure of uniflorine A is similar to
that of castanospermine 2, except for the stereochemistry at C-1
and the extra hydroxyl substitution at C-2 (Fig. 1).
As part of our program concerned with the synthesis of
polyhydroxylated indolizidine and pyrrolizidine alkaloids4e11
we reported an efficient nine-step synthesis of purported
uniflorine A from L-xylose.10 The structure of our synthetic
1 was unequivocally established by a single-crystal X-ray
crystallographic study of its pentaacetate derivative.10 The
5
1
2
Figure 1. Proposed structure of uniflorine A (1) and the structure of castano-
spermine (2).
1H and 13C NMR spectral data for synthetic 1, however, did
not match with those reported for uniflorine A; the latter
showed many more downfield peaks in the 1H NMR spectrum,
perhaps consistent with the amine salt. The 1H NMR spectrum
of the hydrochloride salt of synthetic 1, however, did not
match the literature spectral data either. We therefore con-
cluded that the structure assigned to uniflorine A was not cor-
rect.10 We also indicated that the coupling constant J1,8a of
4.5 Hz for uniflorine A was more consistent with the relative
syn-H-8a, H-1 stereochemistry, suggesting that uniflorine A,
if it was an indolizidine alkaloid, had the same H-1 stereo-
chemistry as castanospermine 2.
In 2006, Dhavale et al.12 also reported the synthesis of
compound 1; their sample had NMR spectral data identical
* Corresponding author. Fax: þ61 242 214287.
E-mail address: spyne@uow.edu.au (S.G. Pyne).
0040-4020/$ - see front matter Crown Copyright Ó 2008 Published by Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.02.110

A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
4869
HO
8
HO
HO
OH
OH
H
N
H
N
H
B(OH)2
NH2
HO
HO
HO
HO
HO
HO
Ph
Ph
L-xylose
3 steps
ref 10
1
3
8a
OH
OH
5
HN
HO
1
1,2-di-epi-1
Proposed structure
for uniflorine A
Synthesis:
3
Fleet, et al. 199614
Mariano et al. 200513
Pyne, et al. this paper
HO
HO
BnO
Synthesis:
H
H
Pyne et al. 200410
BnO
BnO
NaH, BnBr, Bu4NI
THF, 50 °C, 4d
Dhavale et al. 200612
N
N
Boc
56%
HO
OH
H
HO
OH
H
HO
Boc
HO
HO
HO
HO
TrO
TrO
OH
OH
5
4
N
N
2-epi-1
Synthesis:
Pyne, et al. this paper
1-epi-1
.
K2OsO4 2H2O, NMO
acetone/H2O
rt, 72 h
BnO
TrO
Synthesis:
OH
SO2Cl2, Et3N
CH2Cl2,
H
Mariano et al. 200513
BnO
BnO
OH
N
Boc
0 °C to rt
75%
BnO
Figure 2.
6
to ours. This paper also reported the synthesis of 1,2,8a-tri-epi-
1 and 8a-epi-1; these compounds also had NMR spectral data
significantly different from that of uniflorine A. In 2005, Ma-
riano et al.13 reported the synthesis of 1-epi-1, while 1,2-di-
epi-1 was reported by Fleet et al.14 in 1996 (Fig. 2), before
uniflorine was even isolated These indolizidine molecules
also had NMR spectral data different from that of uniflorine
A. Thus if uniflorine A was epimeric at C-1 and/or C-2 with
compound 1 then the only remaining possible structure for
the natural product was 2-epi-1. Thus we report here the
diastereoselective synthesis of 2-epi-1 and a comparison of
its NMR spectral data with that of uniflorine A. We also report
the synthesis of 1,2-di-epi-1 to demonstrate the versatility and
flexibility of our earlier synthetic strategy for preparing
1,2,6,7,8-pentahydroxyindolizidines.10
BnO
1. PhCO2Cs,
DMSO,
40 °C, 19 h
2. H2SO4,
H2O, THF,
rt, 20 h
OH
H
O
H
BnO
BnO
SO2
O
BnO
BnO
OR
N
Boc
N
Boc
TrO
TrO
7
8; R = Bz
54% of 8 from 6
MeOH, K2CO3,
rt, 24 h, 44%
9; R = H
BnO
BnO
OH
OH
H
TFA
anisole
H
BnO
BnO
BnO
BnO
+
OH
OH
HN
HO
10 (66%)
N
rt, 20 h
11 (8%)
DIAD, Ph3P, pyridine, THF,
0-5 °C, 48 h, 25%
2. Results and discussion
HO
OH
H
1. PdCl2, H2
2.1. Synthesis of 2-epi-1
HO
HO
MeOH, rt, 4 h
2. ion-exchange
72%
OH
11
N
The amino-tetraol 3, obtained from the boronic acid-
Mannich reaction (Petasis reaction)10 of L-xylose, allylamine,
and (E)-styrene boronic acid, was converted in three steps to
the 2,5-dihydropyrrole 4, the precursor we used earlier in our
synthesis of 1 (Scheme 1).10 The triol 4 was readily converted
to its tri-O-benzyl derivative 5 in 56% yield under standard
conditions.15 The relatively low yield for this step was in
part due to the competitive formation of the corresponding
O-dibenzyl-oxazolidin-2-one 20 (3%) and oxazin-2-one 21
(9%) (Scheme 3). Osmium(VIII)-catalyzed syn-dihydroxyla-
tion (DH) of 5 furnished the diol 6 as a single diastereomer
in 75% yield. The stereochemical outcome of this DH reaction
was expected due to the stereodirecting effect of the C-2 pyr-
rolidine substituent in 5.4,5,10 The diol 6 was then converted
directly to the cyclic sulfate 7 using sulfuryl chloride under
basic conditions (SO2Cl2, Et3N).16 This method was more
efficient than the two-step method involving first formation
of the corresponding cyclic sulfite (SOCl2, Et3N) followed
by oxidation with catalytic ruthenium tetraoxide (RuCl2,
NaIO4).8,16 The cyclic sulfate 7 was found to be sensitive to
purification on silica gel and was thus taken through the
2-epi-1
Scheme 1.
next step without purification. Treatment of 7 with cesium
benzoate in DMSO at 40 ꢀC for 19 h followed by acid hydro-
lysis of the resulting adduct gave the benzoate 8 in 54% yield
from the diol 6.8,16 The benzoate 8 resulted from the regio-
selective nucleophilic ring opening of the cyclic sulfate 7 at
the less hindered C-4 pyrrolidine position giving rise to inver-
sion of stereochemistry at C-4. This reaction also produced a
small amount (7%) of the corresponding O-trityl deprotected
analog of 8 (see Section 4 for details), formed under the acidic
hydrolysis conditions. The benzoate group of 8 was removed
by methanolysis to give the diol 9. Selective liberation of
the secondary amino and primary hydroxyl groups of 9 was
achieved by exposure of 9 to TFA in the presence of anisole,
as a cation scavenger, at rt.17 This reaction gave a mixture of
the desired amino-alcohol 10 (66%) and the indolizidine 11
(8%) (Scheme 1). We observed the formation of products

4870
A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
related to 10 and 11 from the TFA/anisole deprotection reac-
tion on 1,2-O-dibenzyl-2-epi-9 during our synthesis of 1.10
The amino-alcohol 10 underwent cyclization under Mitsunobu
reaction conditions in THF/pyridine as solvent to give the
same indolizidine 11 in a modest yield of 25%.6,18 The use
of the Appel cyclization reaction conditions (Ph3P/CBr4/
Et3N),19 that worked well for the cyclization of 1,2-O-diben-
zyl-2-epi-9, gave a complex mixture of products. Only the
Mitsunobu reaction using pyridine as the solvent gave the de-
sired product. Debenzylation of 11 under hydrogenolysis con-
resulting from attack of OsO4 from the concave (endo) face
of 12 (Scheme 2). To explain this stereochemical outcome
we suggested that the b-face would be sterically hindered
to attack by OsO4 by the pseudo-axial protons H-7a and
H-5b.6,7,9,21 A similar stereochemical argument has been
used to explain the stereochemical preference of the DH reac-
tions of 1,2-didehydroindolizidines.5 Parsons has performed
semi-empirical calculations (6-31G*) on 12, which suggested
that the HOMO of 12 is not symmetric about the alkene
moiety but has more electron density on the endo-face of the
molecule.23 This may be the major reason for the high endo-
selectivity of reactions on 12. Whatever the reasons for the
p-facial selectivity of 12, this compound and its substituted
derivatives have been successfully used by our group,6e9,21
and that of Parsons,23,24 to diastereoselectively prepare poly-
hydroxylated indolizidine and pyrrolizidine alkaloids and their
epimers. When planning our synthesis of 1,2-di-epi-1 we were
interested in employing a pyrrolo[1,2-c]oxazin-1-one similar
to 14 as a precursor and examining the diastereoselectivity
of its DH reactions (Scheme 2). To the best of our knowledge
such substrates have not been employed in natural product
synthesis.
20
ditions using PdCl2/H2 gave 2-epi-1 ([a]2D5 ꢁ9.2 (c 0.17,
H2O)) in 72% yield after ion-exchange chromatography in a to-
tal of 11 synthetic steps from L-xylose. The 1H and 13C NMR
spectral data for 2-epi-1, however, did not match with those re-
ported for uniflorine A (Table 1). This data will be discussed
further in Section 2.3.
2.2. Synthesis of 1,2-di-epi-1
The synthesis of 1,2-di-epi-1 required a method of revers-
ing the stereochemical outcome of the syn-DH reaction, as
demonstrated in the diastereoselective synthesis of the
3a,4a-diol 6 from the DH reaction of 5 (Scheme 1). We
have previously shown by converting substrates like 5 into
their corresponding pyrrolo[1,2-c]oxazol-3-ones that the DH
reaction occurs with the opposite stereochemical outcome to
give mainly b-DH.6,8,9,21 Parsons demonstrated that the unsub-
stituted pyrrolo[1,2-c]oxazol-3-one 12 underwent a photo-
chemical [2þ2]-cycloaddition of the alkene group to the
unexpected endo-face of the bicyclic system.22 Our group21
and that of Parsons23 demonstrated that the DH reaction of
12 was also highly diastereoselective and gave the diol 13,
OH
H7a
H
DH
O
O
OH
N
N
H5
H
12
O
O
13
OP
H
OP
H
PO
PO
DH
?
O
N
O
14
Table 1
1H NMR spectroscopic data (D2O) for uniflorine A and epimeric 1,2,6,7,8-
pentahydroxyindolizidines
OP
H
OP
H
OH
1,2-di-epi-1
Uniflorine A1
110
1-epi-113
1-2-di-epi-114
2-epi-1
OH
O
N
Chemical shifts (ppm)
O
15
H-1
H-2
H-3
H-3
H-5
H-5
H-6
H-7
H-8
H-8a
4.18
4.35
2.98
3.04
3.61
3.76
2.76
3.81
3.94
3.14
3.82
4.08
4.25
2.63
2.88
2.96
1.91
3.42
3.13
3.48
2.01
4.06
4.24
2.54
2.71
2.95
1.91
3.42
3.12
3.47
2.01
3.96
4.14
2.76
2.87
3.11
2.16
3.64
3.29
3.47
2.11
4.11
3.26
2.20
3.01
2.09
3.46
3.20
3.25
2.08
Scheme 2.
With the aim of preparing specifically the pyrrolo[1,2-c]-
oxazin-1-one 21 (Scheme 3) and using this compound as a pre-
cursor for the synthesis of 1,2-di-epi-1, the amino-tetraol 3
was converted to its N-Troc derivative 16 (75% yield) using
trichloroethyl succinimidyl carbonate (Troc-OSu).25 The pri-
mary alcohol of 16 was then regioselectively protected as its
O-trityl compound 17 (75% yield) (Scheme 3). Treatment of
17 with sodium hydride and benzyl bromide gave a mixture
of tri-O-benzylated 17 (structure not shown) and the oxazol-
2-one 18 and the oxazin-2-one 19. These compounds were
difficult to separate by column chromatography but NMR
analysis suggested that the cyclic derivatives, 18 and 19,
were the major products. Because separation was difficult
and not efficient the mixture was treated with Grubbs’ sec-
ond-generation ruthenium catalyst21 to provide three readily
separable products. The major bicyclic derivatives, the
Coupling constants (Hz)
J1,2
J1,8a
J2,3
J2,3
J3,3
J5,5
J5,6
J5,6
J6,7
J7,8
J8,8a
4.5
4.5
7.3
7.5
6.8
6.8
0
5.8
3.5
2.5
7.5
6.3
6.3
4.4
10.3
10.9
9.1
5.2
9.1
9.1
10.2
5.1
5.1
8.1
2.6
6.7
<1
12.1
11.8
6.4
10.7
10.9
10.7
10.7
5.3
10.9
10.8
10.4
5.3
10.5
10.9
5.5
3.8
9.0
9.0
9.0
9.9
9.4
9.0
9.0
7.7
7.7
9.2
9.5
9.0

A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
4871
and then recrystallization from ethanol/water. The 1H and 13C
NMR spectral data of this compound matched closely (Dd
0.2e0.6 ppm and Dd 0.0e0.2 ppm, respectively; 1H NMR
coupling constants very also very similar) to that reported in
the literature for this compound.14 The optical rotation of
this compound ([a]D23 þ21 (c 1.5, H2O), lit.14 [a]2D3 þ66.5 (c
1.33, H2O)) was of the same sign but of a significantly differ-
ent magnitude to that reported. The hydroscopic nature of this
compound may explain this difference.14
HO
RO
H
NaH, BnBr,
Bu4NI, THF,
50 °C, 4d
HO
HO
Ph
Troc-OSu
3
N
Troc
16; R = H
NaHCO3, dioxane,
rt, 4 h
75%
TrCl, pyridine,
CH2Cl2, rt, 9h
17; R = Tr
75%
TrO
OBn
OBn
OBn
H
H
H
H
TrO
Ph
BnO
Ph
O
+
O
N
N
2.3. Proposed structure of uniflorine A and the revised
structure of uniflorine B
O
O
19
18
1
Table 1 lists the H NMR spectral data for uniflorine A,1
Grubbs' II catalyst
CH2Cl2, reflux 24 h
compound 1,10 and its three epimers, 1-epi-1,13 2-epi-1, and
1
TrO
1,2-di-epi-1.14 The H and 13C NMR spectral data for these
OBn
OBn
H
OBn
H
H
compounds do not match with those reported for uniflorine
A; the synthetic compounds show many more upfield peaks
in their 1H NMR spectra. The newly synthesized 2-epi-1
showed J1,8a (7.5 Hz) and J1,2 (2.5 Hz) values consistent with
its proposed stereochemistry and the 1,2-diaxial like arrange-
ment of H-8a and H-1 and the 1,2-diequatorial like trans-
relationship between H1 and H2.26
Uniflorine A was originally isolated along with uniflorine
B, which was assigned the structure 27 (Fig. 3).1 Our analysis
of the NMR spectral data for this compound and its optical
rotation indicated that uniflorine B is the known 1,2,6,7-tetra-
hydroxy-3-hydroxymethylpyrrolizidine alkaloid casuarine
28.27 Fleet has also noticed this structural missassignment.28
H
TrO
BnO
O
+
O
N
O
N
O
21 (31% from 17)
20 (39% from 17)
OBn
H
OBn
H
K OsO 2H O, NMO
.
4
2
2
OR1
acetone/H2O
R2O
rt, 16 h
OR1
21
67%
O
N
O
22; R1 = H, R2 = Tr
NaH, BnBr, Bu4NI, THF
67%
23; R1 = Bn, R2 = Tr
24; R1 = Bn, R2 = H
TFA, anisole
61%
1
The optical rotation and H NMR spectral data of both com-
3
pounds match very closely; the JHH values for the two sam-
BnO
H
CBr4, Ph3P, Et3N
CH2Cl2, 0 °C, 2 h
85%
OBn
OBn
ples were in very close accord as were their 1H NMR
chemical shifts (Table 2).
NaOH, MeOH
HO
H2O, 110 °C
MW, 1 h
62%
HN
HO
The 13C NMR shifts reported for uniflorine B, however,
were consistently 3.0e3.2 ppm downfield of the corresponding
13C NMR resonances for casuarine 28. Alternative referencing
between the two samples could account for this consistent dis-
crepancy. Both 13C NMR spectra were determined at 125 MHz
in D2O. The 13C NMR spectrum of casuarine 28 was refer-
enced to acetone at d 29.8027 while that of uniflorine B was
apparently referenced to TMS (a standard not known for its
water (D2O) solubility) as an internal standard.1
BnO
25
RO
HO
OR
H
OR
N
RO
PdCl2, H2
MeOH, rt, 4 h
62%
26; R = Bn
1,2-di-epi-1
Scheme 3.
pyrrolo[1,2-c]oxazol-3-one 20 and the pyrrolo[1,2-c]oxazin-1-
one 21, were obtained in yields of 39 and 31%, respectively,
from the mono-cyclic, N-Troc analog of 5 that was not charac-
terized (Scheme 3). Osmium(VIII)-catalyzed syn-DH of 21
furnished the diol 22 as a single diastereomer in 67% yield.
The diol functionality of 21 was O-benzylated (67% yield)
and the trityl group was removed by acid hydrolysis to give
the primary alcohol 24 (61% yield). Base catalyzed hydrolysis
of the oxazinone ring of 24 under microwave irradiation
conditions gave the pyrrolidine 25 in 62% yield. The amino-
alcohol 25 underwent smooth cyclization to give the indolizi-
dine 26 using Ph3P/CBr4/Et3N in 85% yield.19 Debenzylation
HO
8
OH
OH
HO
7
H
N
H
7a
N
HO
1
1
3
7
6
8a
2
HO
OH
OH
OH
5
3
5
8
OH
27
28
casuarine
Originally proposed
structure
of unflorine B
[Uniflorine B
is casuarine]
OH
HO
HO
OH
H
H
N
HO
OH
OH
OH
HO
N
OH
6,7-di-epi-28
7-epi-28
20
of 26 under hydrogenolysis conditions using PdCl2/H2 gave
1,2-di-epi-1 in 62% yield after ion-exchange chromatography
Figure 3.

4872
A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
Table 2
NMR (D2O) and optical rotation data for casuarine 28 and that reported for
uniflorine B
Table 3
1
The H NMR chemical shifts (ppm, D2O) for casuarine 28,27 6,7-di-epi-28,30
and 7-epi-2830 and that reported for uniflorine A1
Chemical shifts (ppm)
Coupling constants (Hz)
Nucleus
Casuarine 28
6,7-di-epi-28
7-epi-28
Uniflorine A
Nucleus Casuarine27 Uniflorine B1
Casuarine27 Uniflorine B1
H-1
H-2
H-3
H-5
H-50
H-6
H-7
H-7a
H-8
H-80
a
4.16
3.80
3.04
2.91
3.27
4.21
4.19
3.07
3.77
3.61
4.23
3.86
2.67
2.85
3.00
4.15
4.08
3.36
3.55
3.73
4.29
3.75
2.73
2.54
3.18
4.15
4.07
3.16
3.50
3.70
3.94 (H-8)a
3.81 (H-7)
2.76 (H-6)
2.98 (H-3b)
3.04 (H-3a)
4.35 (H-2)
4.18 (H-1)
3.14 (H-8a)
3.61 (H-5a)
3.76 (H-5b)
b
H-1
H-2
4.16
3.80
3.04
2.91
3.27
4.21
4.19
3.07
3.77
3.61
4.17 (H-8)b J1,2
8.0
8.0
8.0
3.8
6.6
4.0
4.7
8.1 (J7,8)
8.1 (J8,8a
Multiplet
3.79 (H-7)
3.04 (H-5)
2.92 (H-3)
3.26 (H-3)
4.22 (H-2)
4.19 (H-1)
J1,7a
J2,3
J3,8
)
H-3
H-5a
H-5b
H-6
3.7 (J5,6
6.8 (J6,7
3.9 (J2,3
4.5 (J2,3
4.5 (J1,2
)
)
)
0
0
J3,8
J5a,6
J5b,6
H-7
H-7a
)
a
3.06 (H-8a) J6,7
)
H-8
H-80
3.78 (H-6)
3.61 (H-6)
J7,7a
0
3.5
3.2 (J1,8a
00
11.3 (J6,6
)
J8,8
J5,5
11.9
12.2
)
Original assignments based on an indolizidine structure.1
0
0
12.2 (J3,3
)
A comparison of the coupling constants for the protons in
casuarine 28, 6,7-di-epi-28, and 7-epi-28 with those observed
for uniflorine A revealed a strong correlation between several
nuclei (Table 4). Specifically, the originally assigned J8,8a
value for uniflorine A was consistent with the J1,7a values
of 28, 7-epi-28, and 6,7-di-epi-28. Similarly, the originally
assigned J7,8 value of uniflorine A was consistent with the
J1,2 values of 28, 7-epi-28, and 6,7-di-epi-28, while the origi-
nally assigned J6,7 value of uniflorine A was also consistent
with the J2,3 values of 28, 7-epi-28, and 6,7-di-epi-28. These
high 3JH,H values (7.9e9.6 Hz) describe a trans-diaxial config-
uration between the contiguous protons (Table 4).26 On this
basis, we propose that uniflorine A has the same C-7aeC-
1eC-2eC-3 relative configuration as casuarine 28, 7-epi-28,
and 6,7-di-epi-28. A comparison of the last four rows of
coupling constants in Table 4 revealed a poorer correlation
between the four compounds. Clearly J7,7a was relatively
insensitive to the stereochemistry at C-7 since this coupling
constant ranged from 3.5 to 4.5 Hz in 28, 7-epi-28, and 6,7-
di-epi-28. However, care must be taken in such an analysis
as the change of configuration at one or more stereogenic cen-
ters can significantly change the conformation of the molecule
making stereochemical predictions difficult.26 The pH of the
NMR sample can also influence the chemical shifts and thus
a comparison of the above compounds under identical sample
and referencing conditions would be required before further
conclusions can be drawn. Although we cannot unequivocally
prove the structure of uniflorine A, without access to the orig-
inal material and data, the published data suggests that the
natural product is 6-epi-casuarine 29 (Fig. 4).32
Chemical shifts (ppm)
Nucleus Casuarine27 Uniflorine B1 Dd
(ppm)
3.1
Optical rotation
Casuarine27
C-1
77.8
80.9 (C-8)b
[a]2D4 þ16.9
(c 0.8, H2O)
C-2
C-3
C-5
76.6
70.0
58.0
79.8 (C-7)
73.0 (C-5)
61.1 (C-3)c
3.2
3.0
3.1
Uniflorine B1 [a]D þ16.3
(c 1.1, H2O)
C-6
C-7
C-7a
C-8
a
77.4
78.8
72.1
62.2
80.6 (C-2)
81.9 (C-1)
75.2 (C-8a)
65.5 (C-3)c
3.2
3.1
3.1
3.1
Could not be determined due to peak overlap.
Original assignment based on an indolizidine structure.1
Both signals were assigned as C-3 in the original paper.1
b
c
Further support for these compounds being the same was
the fact that both casuarine and uniflorine B inhibit the
a-glycosidase, rat intestinal maltase with low mM activities.
The reported IC50 values for uniflorine B and casuarine were
0.729 and 4.0 mM,1 respectively, from experiments in different
laboratories.
The 13C NMR chemical shifts of the methylene carbons
reported for uniflorine A at d 65.3 and 60.0 correspond more
closely to C-3 and C-5, respectively, of a 1,2,6,7-tetrahydroxy-
3-hydroxymethylpyrrolizidine (cf. casuarine C-3 (d 70.0) and
C-5 (d 58.0), Table 2) than to C-3 and C-5 of a 1,2,6,7,8-penta-
hydroxyindolizidine (the methylene resonances in 1 are at C-3 (d
59.2) and C-5 (d 55.4)). Thus it would be reasonable to assume
that uniflorine A, like uniflorine B, is also a 1,2,6,7-tetrahy-
droxy-3-hydroxymethylpyrrolizidine alkaloid. On this assump-
tion we have reassigned the published 1H NMR data for
uniflorine A as shown in Table 3 by analogy with the known
chemical shifts, coupling constants and assignments for casuar-
ine 28.27 A comparison of this reassigned NMR data for uniflor-
ine A with that of casuarine 28 and its known synthetic
diastereomers, 7-epi-2830 and 6,7-di-epi-2830,31 (Fig. 3), indicated
that these three compounds were clearly different. However,
Table 4
J values (Hz) for casuarine diastereomers and that reported for uniflorine A
Casuarine 28
6,7-di-epi-28
7-epi-28
Uniflorine A
b
J1,7a
J1,2
J2,3
8.0
8.0
8.0
7.2
8.1
9.6
7.6
7.9
9.6
7.7 (J8,8a)
7.7 (J7,8
)
)
9.0 (J6,7
J5,6
0
J5 ,6
4.0
4.7
4.2
1.8
2.3
4.5
9.6
6.4
3.8
4.2
5.1 (J2,3b
5.1 (J2,3a
)
)
1
their H NMR spectral data showed a much better correlation
a
than that between the reported data for uniflorine A and the epi-
meric 1,2,6,7,8-pentahydroxyindolizidines shown in Table 1.
This NMR reassignment required the numbering of uniflorine
A to be transposed to that indicated in brackets in Table 3.
J6,7
J7,7a
a
4.5 (J1,2
)
3.5
4.5 (J1,8a
)
Could not be determined due to peak overlap.
Original assignments based on an indolizidine structure.1
b

A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
4873
HO
*
H
reaction. The NMR spectral data of these compounds and
that of 1 and 2-epi-1 did not match that of the natural product.
From a comparison of the NMR data of uniflorine A and uni-
florine B with that of casuarine 28 and its synthetic epimers,
we have concluded unequivocally that uniflorine B is the
known alkaloid casuarine (28). Although we cannot unequiv-
ocally prove the structure of uniflorine A, without access to
the original material and data, the published data suggest
that the natural product is also a 1,2,6,7-tetrahydroxy-3-
hydroxymethylpyrrolizidine with the same relative C-7eC-
7aeC-1eC-2eC-3 as casuarine 28. We suggest that uniflorine
A is 6-epi-casuarine (29). This structure is also consistent with
the published NOE and our re-referenced 13C NMR data.1
OH
H
H
H
OH
H
HO
HO
HO
8
7
5 N
1
3
7
OH
1
3
7a
5
2
HO
N
*
OH
8
H
Originally proposed
structure
of unflorine A
H H
*
H
OH
29
6-epi-casuarine
Our proposed structure of
uniflorine A
*reported NOE
correlations
Figure 4. Our proposed structure for uniflorine A.
Further support for this structure came from the results of
the reported NOE studies and 13C NMR data of uniflorine
A.1 The original paper reported NOE correlations for uniflor-
ine A between H-1 and H-8, H-3 and H-6, and H-5 and H-7.
This would correspond to NOE correlations between H-7
and H-1, H5 and H-3, and H-8 and H-2 in the proposed struc-
ture 29 (Fig. 4). These NOE correlations are consistent with
the proposed relative stereochemistries at C-1, C-2, C-3, and
C-7 in 29. However, they do not provide information on the
relative stereochemistry of H-6 and H-7a, although the later
4. Experimental
4.1. General
General methods were as described previously.5,6 All H
1
NMR spectra were performed at 500 MHz and all 13C NMR
(DEPT) spectra at 125 MHz in CDCl3 solution, unless other-
wise noted. NMR assignments are based on COSY, DEPT
and HSQC NMR experiments and sometimes HMBC and
NOESY experiments. The 13C NMR spectra of 2-epi-1 and
1,2-di-epi-1 in D2O were referenced to internal acetonitrile
at d 1.47. IR spectra were determined as neat samples. Petrol
refers to petroleum spirit, bp 40e60 ꢀC. Compounds are
numbered as shown below.
is inferred from the magnitude of J1,7a
.
Analysis of the 13C NMR chemical shifts for casuarine
28,27 7-epi-28,30 and 6,7-di-epi-2831 and that reported for uni-
florine A1 (Table 5) indicated that casuarine 28 and uniflorine
A had the closest matching chemical shifts. If one assumes
that the 13C NMR spectrum of uniflorine A was also incor-
rectly referenced by 3 ppm then the chemical shifts of these
compounds are even more similar, except for the chemical
shift of C-6 (d 77.4 for 28 and d 74.2ꢁ3¼71.2) for uniflorine
A, again consistent with uniflorine A being 6-epi-casuarine 29.
HO
OBn
H
3 4a
OBn
H
H
3
HO
HO
5
1'
3'
TrO
1'
1
N
Boc
7
1
5
O
N
TrO
O
Table 5
13C NMR (D2O) chemical shifts (ppm) for casuarine and its epimers and uni-
florine A
4.1.1. tert-Butyl (2R)-2-[(1R,2R,3R)-1,2,3-tris(benzyloxy)-4-
triphenylmethyloxybutyl]-2,5-dihydro-1H-pyrrole-1-
carboxylate (5)
Casuarine 2827 6,7-di-epi-2831 7-epi-2830 Uniflorine A1 Uniflorine
Ad3 ppm
To a solution of 410 (12.41 g, 23.37 mmol) in dry THF
(240 mL) at 0 ꢀC was added NaH (3.702 g, 77.12 mmol, 50%
in mineral oil). After H2 evolution had ceased (10 min), BnBr
(16.68 mL, 140.2 mmol) and n-Bu4NI (863 mg, 2.337 mmol)
were added. The reaction mixture was stirred at rt for 3 days,
then treated with MeOH (20 mL) followed by evaporation of
all volatiles in vacuo. The residue was dissolved in Et2O and fil-
tered through Celite, followed by further washings of the solids
with Et2O. The solvent was evaporated and the residue was pu-
rified by flash column chromatography (5e30% EtOAc/petrol)
to give 5 as a brown oil (10.48 g, 56%), 20 (0.45 g, 3%) as
a brown oil, and 21 (1.34 g, 9%) as a brown oil. Compound 5:
Rf 0.46 (20% EtOAc/petrol). [a]2D9 þ73 (c 4.6, CHCl3). MS
(ESIþ) m/z 824 (MþNaþ, 100%). HRMS (ESIþ) calcd for
C53H55NO6Na (MþNaþ) 824.3926, found 824.3925. IR nmax
(cmꢁ1): 1700, 1449, 1110, 1060. 1H NMR (300 MHz) d 7.46e
7.05 (m, 30H, Ar), 5.84e5.80 (m, 1H, H-4), 5.76e5.74 (m,
1H, H-3), 4.84 (d, 1H, J 11.4 Hz, Bn), 4.73 (d, 1H, J 11.4 Hz,
Bn), 4.66 (d, 1H, J 11.4 Hz, Bn), 4.59 (d, 1H, J 11.4 Hz, Bn),
C-1 77.8
C-2 76.6
C-3 70.0
C-5 58.0
C-6 77.4
74.4
80.1
73.0
60.6
79.3
73.9
78.6
71.7
56.8
75.5
81.2 (C-8)a
79.9 (C-7)
72.5 (C-6)
60.0 (C-3)
74.2 (C-2)
78.2
76.9
69.5
57.0
71.2
C-7 78.8
C-7a 72.1
C-8 62.2
a
75.5
71.7
63.0
70.6
69.1
63.2
78.1 (C-1)
73.6 (C-8a)
65.3 (C-5)
75.9
70.6
62.3
Original assignments based on an indolizidine structure.1
3. Conclusions
We have successfully developed a diastereoselective syn-
thesis of the C-2 (2-epi-1) and C-1, C-2 (1,2-di-epi-1) epimers
of the putative structure of the alkaloid uniflorine A. The syn-
thesis of the latter epimer employed a novel pyrrolo[1,2-c]-
oxazin-1-one (21) to allow for the reversal of p-facial
diastereoselectivity in an osmium(VIII)-catalyzed syn-DH

4874
A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
4.49e4.46 (m, 1H, H-2), 4.33 (d, 1H, J 11.0 Hz, Bn), 4.21 (d,
1H, J 11.0 Hz, Bn), 4.09 (dq, 1H, J 1.8, 15.3 Hz, H-5), 4.01e
3.97 (m, 1H, H-10), 3.96e3.91 (m, 2H, H-30, H-5), 3.66 (t, 1H,
J 5.4 Hz, H-20), 3.47 (dd, 1H, J 3.9, 10.2 Hz, H-40), 3.39 (dd,
1H, J 5.3, 10.4 Hz, H-40), 1.45 (s, 9H, t-Bu). 13C NMR
(75 MHz) d 153.9 (CO), 144.0, 138.7, 138.5, 138.2 (q Ar),
128.2, 128.1, 128.0, 127.9, 127.8, 127.7, 127.6, 127.5, 127.4,
127.3, 127.2 (Ar), 126.9 (C-4), 126.5 (C-3), 86.9 (q C Tr),
80.9 (C-20), 80.3 (C-10), 79.7 (q C, Boc), 79.3 (C-30), 74.8,
74.6, 73.4 (Bn), 67.0 (C-2), 63.8 (C-40), 53.5 (C-5), 28.4 (CH3).
J 11.5 Hz, Bn), 4.69 (d, 1H, J 11.0 Hz, Bn), 4.57 (d, 1H, J
12.0 Hz, Bn), 4.50 (d, 1H, J 11.5 Hz, Bn), 4.45 (d, 1H, J
11.5 Hz, Bn), 4.41 (br s, 1H, H-2), 4.18 (d, 1H, J 11.0 Hz,
Bn), 4.13 (m, 1H, H-20), 4.04 (br d, 1H, J 6.5 Hz H-10),
3.89e3.86 (m, 1H, H-30), 3.73e3.68 (m, 1H, H-5), 3.59e
3.55 (m, 1H, H-40), 3.46 (dd, 1H, J 4.0, 10.5 Hz, H-40), 3.39
(dd, 1H, J 6.3, 13.3 Hz, H-5), 1.44 (s, 9H, t-Bu). 13C NMR
d 152.8 (CO), 143.9, 138.2, 137.6, 137.4 (q Ar), 128.7,
128.5, 128.3, 127.9, 127.8, 127.7, 127.5, 127.2, 127.0 (Ar),
87.1 (q C Tr), 84.4 (C-3), 83.5 (C-4), 80.8 (q C, Boc), 79.6
(C-10), 79.3 (C-20), 77.7 (C-30), 75.4, 74.2, 73.7 (Bn), 64.4
(C-2), 63.3 (C-40), 51.3 (C-5), 28.4 (CH3).
4.1.2. tert-Butyl (2R,3S,4R)-3,4-dihydroxy-2-[(1R,2S,3S)-
1,2,3-tris(benzyloxy)-4-triphenylmethyloxybutyl]-
pyrrolidine-1-carboxylate (6)
4.1.4. tert-Butyl (2R,3S,4S)-3-hydroxy-4-phenylcarbonyl-
oxy-2-[(2S,3S)-1,2,3-tris(benzyloxy)-4-triphenylmethyl-
oxybutyl]pyrrolidine-1-carboxylate (8) and tert-butyl
(2R,3S,4S)-3-hydroxy-4-phenylcarbonyloxy-2-[(2S,3S)-4-
hydroxy-1,2,3-tris(benzyloxy)-butyl]pyrrolidine-1-
carboxylate (8a)
To a solution of 5 (3.43 g, 4.28 mmol) in acetone (20 mL) and
water (20 mL) were added potassium osmate$dihydrate
(78.7 mg, 0.214 mmol) and 4-morpholine-N-oxide (1.051 g,
8.985 mmol). The reaction mixture was stirred for 3 days at rt
and evaporated to give a black oil, which was purified by flash
column chromatography (30e50% EtOAc/petrol) to give 6 as
a brown foamy solid (2.69 g, 75%). Rf 0.50 (40% EtOAc/petrol).
[a]2D5 þ34 (c 0.50, CHCl3). MS (ESIþ) m/z 858 (MþNaþ, 25%),
243 (Trþ, 100%). HRMS (ESIþ) calcd for C53H57NO8Na
(MþNaþ) 858.3981, found 858.3991. IR nmax (cmꢁ1): 3400,
BnO
OH
H
N
BnO
BnO
1'
3'
3
5
OBz
1
Boc
1
1690, 1395, 1090, 1075. H NMR (300 MHz) d 7.46e7.05
HO
8a
(m, 30H, Ar), 4.86 (d, 1H, J 11.4 Hz, Bn), 4.70 (d, 1H,
J 11.4 Hz, Bn), 4.62 (d, 1H, J 11.4 Hz, Bn), 4.53 (d, 1H, J
11.4 Hz, Bn), 4.38 (d, 1H, J 10.8 Hz, Bn), 4.26e4.21 (m, 3H,
Bn, H-10, H-4), 4.12e4.04 (m, 2H, H-3, H-30), 3.83 (t, 1H, H-
20), 3.72 (m, 1H, H-2), 3.62e3.54 (m, 2H, H-4, H-40), 3.43e
3.40 (m, 1H, H-5), 3.22e3.19 (m, 1H, H-5), 1.43 (s, 9H, t-
Bu). 13C NMR (75 MHz) d 154.5 (CO), 143.9, 138.5, 137.9,
137.8 (q Ar), 128.8, 128.4, 128.3, 128.2, 128.1, 128.0, 127.9,
127.8, 127.7, 127.6, 127.4, 126.9 (Ar), 87.0 (q C, Tr), 81.2 (C-
20), 79.3 (q C, Boc), 79.0 (C-30), 78.0 (C-10), 75.2, 74.0,
73.7 (Bn), 71.2 (C-4), 70.4 (C-3), 65.1 (C-2), 64.5 (C-40), 51.7
(C-5), 28.4 (CH3).
The crude cyclic sulfate 7 obtained from the above reaction
was dissolved in DMSO (0.5 mL), and benzoic acid (0.221 g,
1.81 mmol) and cesium carbonate (0.647 g, 1.97 mmol) were
added and the solution was stirred under an atmosphere of
N2 for 20 h at 40 ꢀC. The reaction was suspended in THF
(4 mL). Water (1.5 mL) then concentrated sulfuric acid
(0.8 mL) were added and the reaction mixture was stirred at
rt for 20 h, then poured into saturated aqueous NaHCO3, and
extracted with CH2Cl2. The combined CH2Cl2 extracts were
washed with brine, dried (MgSO4), filtered, and evaporated.
The crude products were purified by flash column chromato-
graphy (15e50% EtOAc/petrol) to give 8 (183.3 mg, 54%
from 6), 8a (18.4 mg, 7% from 6), and 6 (37.2 mg, 16%).
Compound 8: Rf 0.48 (30% EtOAc/petrol). [a]2D4 þ36 (c 1.0,
CHCl3). MS (ESIþ) m/z 961.9 (MþNaþ, 62%). HRMS
(ESIþ) calcd for C60H61NO9Na (MþNaþ) 962.4244, found
962.4247. IR nmax (cmꢁ1): 3385, 1730, 1696, 1271, 1110,
4.1.3. tert-Butyl (3aS,4S,6aR)-4-[(1R,2S,3S)-1,2,3-tris-
(benzyloxy)-4-triphenylmethyloxybutyl]tetrahydro-5H-
[1,3,2]dioxathiolo[4,5-c]pyrrole-5-carboxylate
2,2-dioxide (7)
To a solution of 6 (301 mg, 0.361 mmol) in CH2Cl2 (3 mL)
was added Et3N (0.755 mL, 5.42 mmol) followed by sulfuryl
chloride (0.145 mL, 1.81 mmol) at 0 ꢀC. The reaction mixture
was stirred for 1 h at 0 ꢀC under an atmosphere of N2 and then
warmed up to rt for 1 h. The residue was suspended in water
(5 mL). The aqueous layer was extracted with CH2Cl2 (3ꢂ
10 mL) and washed with brine. The combined organic phases
were dried (MgSO4), filtered, and evaporated under reduced
pressure to give a brown oil that was used in the next step
without further purification (7): Rf 0.36 (20% EtOAc/petrol).
MS (ESIþ) m/z 920 (MþNaþ, 50%), 243 (Trþ, 100%).
HRMS (ESIþ) calcd for C53H55NO10SNa (MþNaþ)
920.3444, found 920.3439. IR nmax (cmꢁ1): 1700, 1395,
1
1070, 1027. H NMR d 7.99 (d, 2H, J 7.5 Hz, H-o-Bz), 7.55
(t, 1H, J 7.5 Hz, H-p-Bz), 7.42e7.07 (m, 32H, Ar), 5.10 (dd,
1H, J 14.5, 8.0 Hz, H-4), 4.79 (d, 1H, J 12.0 Hz, Bn), 4.75
(d, 1H, J 11.5 Hz, Bn), 4.72 (br t, 2H, J 5.5 Hz, H-3, Bn),
4.54 (m, 1H, Bn), 4.53 (m, 1H, Bn), 4.44 (br s, 2H, H-10,
Bn), 4.28 (br s, 1H, OH), 4.20 (br s, 1H, H-5), 4.11 (dd, 1H,
J 14.0, 7.0 Hz, H-30), 3.89 (br s, 1H, H-20), 3.85 (br s, 1H,
H-2), 3.46 (br s, 2H, H-40, H-40), 3.15 (br s, 1H, H-5), 1.44
(s, 9H, t-Bu). 13C NMR d 166.9, 153.5 (CO), 143.9, 138.1,
137.7 (q Ar), 133.3, 129.8, 129.4, 128.7, 128.3, 128.29,
128.22, 128.16, 128.13, 127.7, 127.69, 127.61, 127.2, 126.8
(Ar), 86.9 (q C Tr), 80.5 (C-20), 79.7 (C-4), 79.3 (q C, Boc),
78.7 (C-30), 78.2 (C-10), 75.0, 74.2, 73.5 (Bn), 73.2 (C-3),
64.8 (C-2), 63.6 (C-40), 49.2 (C-5), 28.3 (CH3).
1
1210, 1160, 1070. H NMR d 7.42e6.93 (m, 30H, Ar), 5.44
(d, 1H, J 5.0 Hz, H-3), 5.07 (m, 1H, H-4), 4.76 (d, 1H,

A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
4875
Compound 8a: Rf 0.29 (40% EtOAc/petrol). MS (ESIþ) m/z
697.8 (MþHþ, 30%). HRMS (ESIþ) calcd for C41H47NO9
(MþHþ) 698.3329, found 698.3340. IR nmax (cmꢁ1): 3436,
petrol and 15% MeOH/EtOAc) to give 11 as a pale yellow
solid (11 mg, 8%) and the amino-alcohol 10 (92.3 mg, 66%)
as a brown foamy solid. Compound 10: Rf 0.45 (1:19:80
NH4OH/MeOH/CHCl3). [a]2D1 ꢁ14.0 (c 0.35, MeOH). MS
(ESIþ) m/z 494 (MþHþ, 100%). HRMS (ESIþ) calcd for
C29H35NO6 (MþHþ) 494.2543, found 494.2531. IR nmax
(cmꢁ1): 3411, 3283, 1454, 1126, 1058, 1044. 1H NMR
d 7.37e7.25 (m, 15H, Ar), 4.86 (d, 1H, J 11.0 Hz, Bn), 4.71
(d, 1H, J 11.0 Hz, Bn), 4.68 (d, 1H, J 11.5 Hz, Bn), 4.65 (d,
1H, J 11.0 Hz, Bn), 4.63 (d, 1H, J 11.5 Hz, Bn), 4.57 (d, 1H,
J 11.5 Hz, Bn), 4.00 (br s, 1H, H-3), 3.90e3.88 (m, 1H, H-
4), 3.84 (m, 2H, H-10, H-40), 3.79 (m, 2H, H-20, H-40), 3.74
(m, 1H, H-30), 3.14 (br s, 1H, H-2), 3.00 (dd, 1H, J 11.5,
4.5 Hz, H-5), 2.81 (br d, 1H, J 11.5 Hz, H-5). 13C NMR
d 137.6, 137.4, 137.3 (q Ar), 128.7, 128.6, 128.5, 128.3,
128.2, 128.1 (Ar), 80.9 (C-20), 80.3 (C-10), 79.5 (C-3), 78.6
(C-30), 75.5, 74.2, 72.9 (Bn), 66.8 (C-2), 60.8 (C-40), 52.3 (C-5).
Synthesis of 11 from 10: to a solution of 10 (37.0 mg,
0.075 mmol) in pyridine (1 mL) was added triphenylphos-
phine (39.4 mg, 0.150 mmol) and diisopropyl azodicarboxy-
late (0.030 mL, 0.150 mmol) at 0 ꢀC. The reaction mixture
was stirred under an atmosphere of N2 at 0 ꢀC for 8 h, and
at 0e5 ꢀC for 40 h, then warm up to rt for 48 h. The volatiles
were removed in vacuo then 1 M HCl (5 mL) was added and
the mixture was extracted with CH2Cl2 (2ꢂ10 mL). The com-
bined CH2Cl2 extracts were washed with water dried
(MgSO4), filtered, and then evaporated to give a brown oil. Pu-
rification by flash column chromatography (2% MeOH/
CHCl3e1:4:95% NH4OH/MeOH/CHCl3) gave 11 (9.0 mg,
25%) as a pale yellow solid. Compound 11: Rf 0.31 (100%
EtOAc). [a]2D3 þ34 (c 0.26, CHCl3). MS (ESIþ) m/z 476
(MþHþ, 100%). HRMS (ESIþ) calcd for C29H33NO5
(MþHþ) 476.2437, found 476.2327. IR nmax (cmꢁ1): 3293,
1
1700, 1403, 1265, 1110, 1069. H NMR d 8.00 (d, 2H, J
7.5 Hz, H-o-Bz), 7.53 (t, 1H, J 7.5 Hz, H-p-Bz), 7.40 (t, 2H,
J 7.5 Hz, H-m-Bz), 7.37e7.18 (m, 15H, Ar), 5.14 (dd, 1H, J
14.0, 8.0 Hz, H-4), 4.83e4.44 (m, 6H, 4Bn, H-3, H-10), 4.30e
4.10 (m, 3H, H-5, Bn, H-2), 4.00e3.86 (m, 2H, H-40, H-40),
3.84e3.76 (m, 3H, H-20, H-30, Bn), 3.24e3.12 (m, 1H, H-5),
1.46 (s, 9H, t-Bu). 13C NMR d 166.7, 154.0 (CO), 143.8,
138.6, 137.5, 134.4 (q Ar), 133.3, 129.8, 129.4, 128.7, 128.5,
128.4, 128.3, 128.29, 128.21, 128.16, 128.0, 127.8, 127.6,
127.3, 126.9 (Ar), 81.0 (C-20), 80.3 (q C, Boc), 78.8 (C-4),
78.2 (C-30), 78.1 (C-10), 75.6, 74.3 (C-3), 74.2, 72.7 (Bn), 64.5
(C-2), 60.7 (C-40), 49.9 (C-5), 28.7 (CH3).
4.1.5. tert-Butyl (2R,3S,4S)-3,4-dihydroxy-2-[(1R,2S,3S)-
1,2,3-tris(benzyloxy)-4-triphenylmethyloxybutyl]-
pyrrolidine-1-carboxylate (9)
To a solution of 8 (34.9 mg, 0.037 mmol) in MeOH (1 mL)
was added K2CO3 (0.010 g, 0.075 mmol). After stirring at rt
for 1 day, the mixture was evaporated and dissolved in
CHCl3 then washed with water. The aqueous layer was ex-
tracted with CHCl3 and the combined CHCl3 extracts were
washed with brine, dried (MgSO4), and evaporated. The resi-
due was purified by PTLC (30% EtOAc/petrol) to give 9 as
a colorless oil (13.5 mg, 44%). Rf 0.16 (30% EtOAc/petrol).
[a]2D2 þ10.5 (c 0.7, CHCl3). MS (ESIþ) m/z 858 (MþNaþ,
62%), 243 (Trþ, 100%). HRMS (ESIþ) calcd for
C53H57NO8Na (MþNaþ) 858.3982, found 858.3970. IR nmax
(cmꢁ1): 3400, 1691, 1392, 1163, 1073. 1H NMR d 7.48e
7.11 (m, 30H, Ar), 4.85 (d, 1H, J 11.5 Hz, Bn), 4.68 (d, 1H,
J 11.5 Hz, Bn), 4.61e4.47 (m, 3H, Bn), 4.40 (d, 1H, J
11.5 Hz, Bn), 4.24 (d, 1H, J 8.5 Hz, H-10), 4.01 (m, 1H, H-
30), 3.78e3.76 (m, 2H, H-3, H-4), 3.72e3.62 (m, 4H, H-40,
H-20, H-40, H-2), 3.48 (dd, 1H, J 12.0, 4.5 Hz, H-5), 3.24 (d,
1H, J 11.5 Hz, H-5), 1.26 (s, 9H, t-Bu). 13C NMR d 154.5
(CO), 143.9, 137.4, 137.1, 137.08 (q Ar), 128.8, 128.7,
128.5, 128.3, 127.9, 127.8, 127.7, 127.1, 127.0 (Ar), 87.0 (q
C Tr), 81.6 (C-20), 80.0 (q C, Boc), 79.2 (C-10), 77.4 (C-30),
77.4, 77.2, 77.1 (Bn), 77.2 (C-4), 73.7 (Bn), 73.3 (C-3), 67.9
(C-2), 63.8 (C-40), 54.5 (C-5), 29.7 (CH3).
1
1460, 1103, 1071. H NMR d 7.38e7.27 (m, 15H, Ar), 5.00
(d, 1H, J 10.5 Hz, Bn), 4.94 (d, 1H, J 11.0 Hz, Bn), 4.82
(d, 1H, J 11.0 Hz, Bn), 4.70 (d, 1H, J 11.5 Hz, Bn), 4.67 (d,
1H, J 12.5 Hz, Bn), 4.64 (d, 1H, J 11.5 Hz, Bn), 4.04 (dd,
1H, J 5.0, 2.0 Hz, H-2), 3.73 (dd, 1H, J 6.5, 2.0 Hz, H-1),
3.69 (m, 1H, H-6), 3.53 (m, 1H, H-7), 3.52 (m, 1H, H-8),
3.18 (dd, 1H, J 10.5, 5.5 Hz, H-5), 2.85 (d, 1H, J 10.5 Hz,
H-3), 2.61 (dd, 1H, J 10.5, 6.5 Hz, H-3), 2.04 (t, 1H, J
10.5 Hz, H-5), 1.96 (dd, 1H, J 9.0, 7.0 Hz, H-8a). 13C NMR
d 138.6, 138.2, 138.1 (q Ar), 128.7, 128.43, 128.41, 128.19,
128.14, 127.9, 127.8, 127.7, 127.6 (Ar), 87.3 (C-7), 84.1 (C-
1), 81.6 (C-8), 79.4 (C-6), 78.0 (C-2), 75.5, 74.8, 72.9 (Bn),
72.6 (C-8a), 60.4 (C-3), 54.1 (C-5).
4.1.6. (2S,3S,4R)-4-[(2R,3S,4S)-3,4-Dihydroxypyrrolidin-2-
yl]-2,3,4-tribenzyloxybutan-1-ol (10) and (1S,2S,6S,7R,
8R,8aR)-1,2-dihydroxy- 6,7,8-tribenzyloxyoctahydro-
indolizine (11)
To a solution of 9 (237 mg, 0.284 mmol) in anhydrous
CH2Cl2 (2.8 mL) were added anisole (0.289 mL, 2.841 mmol)
and TFA (2.19 mL, 28.41 mmol). The reaction mixture was
stirred under an atmosphere of N2 at rt for 20 h, followed by
the evaporation of all volatiles in vacuo. The residue was dis-
solved in CH2Cl2 (5 mL) and washed with saturated Na2CO3
solution (10 mL). The aqueous layer was extracted with
CH2Cl2 (3ꢂ10 mL). The combined CH2Cl2 layers were dried
(Na2CO3) and evaporated to give a brown oil, which was pu-
rified by flash column chromatography (50e100% EtOAc/
4.1.7. (1S,2S,6S,7R,8R,8aR)-Octahydroindolizine-1,2,6,7,8-
pentol (2-epi-1)
To a solution of 11 (11.0 mg, 0.023 mmol) in EtOAc
(0.5 mL) and MeOH (0.5 mL) was added PdCl2 (6.16 mg,
0.035 mmol). The reaction mixture was stirred at rt under an
atmosphere of H2 (balloon) for 4 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 and applied to a column
of Amberlyst (OHꢁ) A-26 resin. Elution with water followed

4876
A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
1
by evaporation in vacuo gave compound 4 (3.4 mg, 72%) as a
pale yellow, foamy solid. [a]2D5 ꢁ9.2 (c 0.17, H2O). MS
(ESIþ) m/z 206 (MþHþ, 100%). HRMS (ESIþ) calcd for
C8H15NO5 (MþHþ) 206.1028, found 206.0990. IR nmax
found 732.1631. H NMR (major rotamer inter alia) d 7.44e
7.21 (m, 20H, Ar), 6.59 (d, 1H, J 16.2 Hz, H-7), 6.44 (dd,
1H, J 7.5, 15.8 Hz, H-6), 5.83 (dddd, 1H, J 6.2, 6.2, 10.8,
16.5 Hz, H-20), 5.17 (d, 1H, J 17.1 Hz, H-30), 5.10 (d, 1H, J
10.5 Hz, H-30), 4.77 (d, 1H, J 11.7 Hz, CH2CCl3), 4.70 (d,
1H, J 11.7 Hz, CH2CCl3), 4.37 (t, 1H, J 7.8 Hz, H-5), 4.07
(m, 1H, H-4), 3.96 (m, 2H, H-10, H-10), 3.91 (m, 1H, H-2),
3.71 (m, 1H, H-3), 3.34 (dd, 1H, J 4.8, 9.6 Hz, H-1), 3.24
(dd, 1H, J 5.7, 9.6 Hz, H-1). 13C NMR d 154.9 (CO), 143.6
(q Ar), 136.2 (C-7), 135.0 (C-20), 133.7 (q Ar), 128.6, 127.9,
127.1, 126.6 (Ar), 123.9 (C-6), 118.1 (C-30), 95.3 (CCl3),
86.9 (q C, Tr), 75.1 (CH2CCl3), 73.0 (C-4), 72.4 (C-2), 69.5
(C-3), 64.6 (C-1), 62.1 (C-5), 50.0 (C-10).
1
(cmꢁ1): 3308, 1073, 1043. H NMR (D2O) d 4.14 (br d, 1H,
J2,3b 7.0 Hz, H-2), 3.96 (dd, 1H, J1,8a 7.0, J1,2 2.5 Hz, H-1),
3.64 (ddd, 1H, J5b,6 10.0, J6,7 9.0, J5a,6 5.3 Hz, H-6), 3.47 (t,
1H, J7,8¼J8,8a 9.0 Hz, H-8), 3.29 (t, 1H, J6,7¼J7,8 9.0 Hz, H-
7), 3.11 (dd, 1H, J5a,5b 10.8, J5a,6 5.3 Hz, H-5a), 2.87 (br d,
1H, J3a,3b 11.0 Hz, H-3a), 2.76 (dd, 1H, J3a,3b 10.8, J2,3b
6.3 Hz, H-3b), 2.16 (t, 1H, J5a,5b¼J5b,6 10.8 Hz, H-5b), 2.11
(dd, 1H, J8,8a 9.0, J1,8a 8.0 Hz, H-8a). 13C NMR (D2O)
d 82.7 (C-1), 79.2 (C-7), 78.1 (C-2), 74.1 (C-8), 72.1 (C-8a),
70.3 (C-6), 59.7 (C-3), 55.6 (C-5).
4.1.10. (1R,7aR)-1-[(1R,2S)-1,2-Bis(benzyloxy)-3-triphenyl-
methyloxypropyl]-5,7a-dihydro-1H-pyrrolo[1,2-c][1,3]-
oxazol-3-one (20) and (3S,4R,4aR)-3-[(1S)-1-(benzyloxy)-
2-triphenylmethyloxyethyl]-4-(benzyloxy)-3,4,4a,7-tetra-
hydropyrrolo[1,2-c][1,3]oxazin-1-one (21)
4.1.8. (6E)-5-{Allyl[(2,2,2-trichloroethoxy)carbonyl]-
amino}-5,6,7-trideoxy-7-phenyl-D-gluco-hept-6-enitol (16)
To a solution of 310 (4.94 g, 16.9 mmol) in 1,4-dioxane
(50 mL) were added NaHCO3 solution (34 mL, 2 M) and suc-
cinimidyl-2,2,2-trichloroethyl carbonate (4.90 g, 16.9 mmol).
The reaction mixture was stirred at rt for 5 h then diluted
with water (100 mL) and extracted with EtOAc (2ꢂ100 mL).
The combined EtOAc extracts were washed with 10% HCl
(2ꢂ100 mL) and brine (100 mL) before being dried
(MgSO4) and evaporated, giving a clear oil. The residue was
purified by flash column chromatography (100% EtOAc) to
give 16 as a clear oil (5.75 g, 75%). Rf 0.30 (100% EtOAc).
[a]2D2 ꢁ35 (c 2.0, CHCl3). MS (ESIþ) m/z 490 (MþNaþ,
60%), 243 (Trþ, 100%). HRMS (ESIþ) calcd for
C19H24Cl3NO6Na (MþNaþ) 490.0567, found 490.0566. IR
To a solution of triol 17 (14.0 g, 19.74 mmol) in dry THF
(200 mL) were added n-Bu4NI (730 mg, 1.974 mmol) and
BnBr (14.10 mL, 118.48 mmol). The reaction mixture was
stirred at rt for 10 min then cooled to 0 ꢀC before the addition
of NaH (7.3 g, 78.98 mmol, 30% dispersion in mineral oil).
The mixture was then warmed to rt and stirred for 1 h before
the addition of MeOH (2 mL). After stirring for 10 min, the
mixture was filtered through Celite followed by the washing
of the solids with CH2Cl2. The filtrate was evaporated. Oxazo-
lidinone 18 and oxazinanone 19 were obtained as a mixture
(12.0 g) and separated from tri-O-benzylated 17 (which was
not isolated) by flash column chromatography (25% EtOAc/
petrol). The mixture of 18 and 19 was dissolved in dry
CH2Cl2 (900 mL) and Grubbs II catalyst (687 mg, 0.81 mmol)
was added and the reaction mixture was stirred and heated
at reflux for 24 h, then cooled to rt and evaporated. The residue
was purified by flash column chromatography (40% EtOAc) to
give oxazolone 20 (4.85 g 39%) and oxazinone 21 (3.85 g,
31%) as oils.
1
nmax (cmꢁ1): 3400, 1697, 1412, 1244, 1141, 1050. H NMR
d 7.39e7.22 (m, 5H, Ar), 6.62 (d, 1H, J 16.2 Hz, H-7), 6.45
(dd, 1H, J 7.8, 15.9 Hz, H-6), 5.86 (dddd, 1H, J 2.7, 7.1,
10.2, 17.0 Hz, H-20), 5.22 (d, 1H, J 17.4 Hz, H-30), 5.16 (d,
1H, J 10.2 Hz, H-30), 4.83 (d, 1H, J 12.0 Hz, CH2CCl3),
4.74 (d, 1H, J 12.0 Hz, CH2CCl3), 4.42 (t, 1H, J 7.7 Hz,
H-5), 4.13 (m, 1H, H-4), 4.00 (m, 2H, H-10, H-10), 3.86 (q,
1H, J 4.2 Hz, H-2), 3.72 (m, 2H, H-1, H-1), 3.65 (m, 1H,
H-3). 13C NMR d 154.8 (CO), 136.3 (q Ar), 135.1 (C-7),
133.7 (C-20), 128.5, 127.9, 126.5 (Ar), 124.1 (C-6), 118.1
(C-30), 95.3 (CCl3), 75.0 (CH2CCl3), 73.2 (C-2), 72.2 (C-4),
70.0 (C-3), 63.9 (C-1), 61.6 (C-5), 49.7 (C-10).
Compounds 20: Rf 0.51 (40% EtOAc/petrol). [a]2D5 þ13 (c
4.5, CHCl3). MS (ESIþ) m/z 660 (MþNaþ, 43%). HRMS
(ESIþ) calcd for C42H39NO5Na (MþNaþ) 660.2726, found
660.2712. 1H NMR d 7.47e7.15 (m, 25H, Ar), 5.86 (dq,
1H, J 2.0, 5.9 Hz, H-7), 5.69 (dq, 1H, J 2.0, 5.9 Hz, H-6),
4.81 (dd, 1H, J 5.7, 8.1 Hz, H-1), 4.74 (d, 1H, J 12.0 Hz,
Bn), 4.68 (d, 1H, J 11.1 Hz, Bn), 4.61 (d, 1H, J 11.1 Hz,
Bn), 4.39 (d, 1H, J 11.1 Hz, Bn), 4.27 (ddt, 1H, J 2.1, 3.6,
15.5 Hz, H-5), 4.09e4.03 (m, 1H, H-7a), 3.73e3.67 (m, 2H,
H-10, H-20), 3.63 (dddd, 1H, J 1.5, 2.7, 4.8, 15.6 Hz, H-5),
3.56 (dd, 1H, J 4.8, 10.2, H-30), 3.47 (dd, 1H, J 4.8,
10.2 Hz, H-30). 13C NMR d 162.2 (C-3), 144.0, 138.2, 138.1
(q Ar), 131.7 (C-7), 128.53, 128.49, 128.5, 128.1, 128.0,
127.9, 127.6, 127.3, 127.2 (Ar), 125.8 (C-6), 87.4 (q C, Tr),
79.0 (C-1), 78.3, 77.1 (C-10 or C-20), 74.6, 72.6 (Bn), 67.0
(C-7a), 62.5 (C-30), 54.7 (C-5).
4.1.9. (6E)-5-{Allyl[(2,2,2-trichloroethoxy)carbonyl]-
amino}-1-O-triphenylmethyl-5,6,7-trideoxy-7-phenyl-D-
gluco-hept-6-enitol (17)
To a solution of 16 (15.0 g, 32.1 mmol) in dry CH2Cl2
(150 mL) were added dry pyridine (2.85 mL, 35.3 mmol)
and TrCl (9.04 g, 32.4 mmol). The reaction mixture was
stirred at rt for 9 h, then poured into water (150 mL) and ex-
tracted with CH2Cl2 (2ꢂ100 mL). The combined CH2Cl2 ex-
tracts were washed with brine, dried (MgSO4), and
evaporated. The crude product was purified by flash column
chromatography (40% EtOAc/petrol) to give 17 (17.15 g,
75%) as a clear oil. Rf 0.60 (20% EtOAc/petrol). [a]2D5 ꢁ8 (c
1.0, CHCl3). MS (ESIþ) m/z 732 (MþNaþ, 100%). HRMS
(ESIþ) calcd for C38H38Cl3NO6Na (MþNaþ) 732.1662,
Compound 21: Rf 0.20 (40% EtOAc/petrol). [a]2D5 þ80 (c
7.8, CHCl3). MS (ESIþ) m/z 660 (MþNaþ, 45%), 243 (Trþ,
100%). HRMS (ESIþ) calcd for C42H39NO5Na 660.2726,

A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
4877
1
found 660.2710. H NMR d 7.44e7.16 (m, 25H, Ar), 5.82 (s,
1
1024. H NMR d 7.42e7.08 (m, 35H, ArH), 4.96 (d, 1H, J
11.4 Hz, Bn), 4.65 (d, 1H, J 11.7 Hz, Bn), 4.56 (dt, J 1.2,
6.0 Hz, H-3), 4.50 (d, 1H, J 12.0 Hz, Bn), 4.48 (s, 2H,
Bnꢂ2), 4.44 (d, 1H, J 11.7 Hz, Bn), 4.37 (d, 1H, J 11.4 Hz,
Bn), 4.21 (d, 1H, J 11.7 Hz, Bn), 4.14 (ddd, 1H, J 1.2, 5.9,
9.6 Hz, H-4), 3.94 (dt, 1H, J 1.0, 3.0 Hz, H-5), 3.77 (dt, 1H,
J 1.2, 3.5 Hz, H-10), 3.65 (ddd, 1H, J 3.0, 6.8, 10.2 Hz,
H-6), 3.54 (dd, 1H, J 7.5, 10.0 Hz, H-7), 3.51 (m, 4H, H-20,
H-20, H-4a, H-7). 13C NMR d 151.7 (C-1), 143.9, 138.23,
138.18, 137.4, 137.2 (q Ar), 128.6, 128.5, 128.45, 128.3,
128.2, 128.1, 128.0, 127.9, 127.8, 127.74, 127.67, 127.4,
127.3, 127.1, 126.6 (Ar), 87.5 (q C, Tr), 78.0 (C-6), 76.0
(C-5), 75.6 (C-10), 74.6 (C-3), 73.4, 72.4, 72.2, 72.1 (Bn),
67.7 (C-4), 62.7 (C-20), 59.4 (C-4a), 48.0 (C-7).
2H, H-5, H-6), 4.603 (dd, 1H, J 1.3, 6.3 Hz, H-3), 4.601 (d,
1H, J 11.5 Hz, Bn), 4.59 (d, 1H, J 11.8 Hz, Bn), 4.56 (d,
1H, J 11.8 Hz, Bn), 4.52 (dd, 1H, J 1.2, 9.5 Hz, H-4a), 4.45
(d, 1H, J 11.8 Hz, Bn), 4.39 (dd, 1H, J 4.8, 15.3 Hz, H-7),
4.01 (dd, 1H, J 5.3, 15.5 Hz, H-7), 3.86 (ddd, 1H, J 1.5, 6.3,
7.3 Hz, H-10), 3.60 (dd, 1H, J 6.0, 10.0 Hz, H-4), 3.54 (dd,
1H, J 6.0, 10.0 Hz, H-20), 3.51 (dd, 1H, J 7.0, 10.0 Hz, H-
20). 13C NMR d 151.7 (C-1), 143.8, 138.0, 136.9 (q Ar),
128.59 (C-5 or C-6), 128.55, 128.2, 128.1 (Ar), 127.8 (C-5
or C-6), 127.7, 127.6, 127.4, 127.3, 127.1, 127.0 (Ar), 87.4
(q C, Tr), 75.2 (C-10), 75.0 (C-3), 73.9 (C-4), 72.7, 72.2
(Bn), 62.8 (C-20), 62.7 (C-4a), 55.1 (C-7).
4.1.11. (3S,4R,4aR,5R,6S)-4-Benzyloxy-3-[(1S)-1-(benzyl-
oxy)-2-triphenylmethyloxyethyl]-5,6-dihydroxy-hexa-
hydropyrrolo[1,2-c][1,3]oxazin-1-one (22)
4.1.13. (3S,4R,4aR,5R,6S)-4,5,6-Tris(benzyloxy)-3-[(1S)-1-
(benzyloxy)-2-hydroxyethyl]-hexahydropyrrolo[1,2-c]-
[1,3]oxazin-1-one (24)
To a solution of 21 (3.43 g, 5.38 mmol) in acetone (20 mL)
and water (20 mL) were added potassium osmate$dihydrate
(99 mg, 0.269 mmol) and 4-morpholine-N-oxide (1.32 g,
11.30 mmol). The reaction mixture was stirred for 16 h at rt
and evaporated to give a black oil, which was purified by flash
column chromatography (60% EtOAc/petrol) to give 22 as
a brown foamy solid (2.4 g, 67%). Rf 0.10 (60% EtOAc/pet-
rol). [a]2D4 þ75 (c 2.8, CHCl3). MS (ESIþ) m/z 672 (MþHþ,
100%). HRMS (ESIþ) calcd for C42H42NO7 (MþHþ)
To a solution of 23 (1.88 g, 2.21 mmol) in dry CH2Cl2
(20 mL) was added anisole (2.41 mL, 22.1 mmol) and the mix-
ture was cooled to 0 ꢀC before the addition of TFA (1.7 mL,
22.1 mmol). The reaction mixture was stirred for 1 h at 0 ꢀC,
then poured into saturated aqueous Na2CO3 solution and ex-
tracted with CH2Cl2 (2ꢂ50 mL). The combined CH2Cl2 ex-
tracts were washed with brine, dried (MgSO4), and
evaporated. The residue was purified by flash column chroma-
tography (60% EtOAc/petrol) to give 24 (820 mg, 61%) as
a yellow oil. Rf 0.17 (60% EtOAc/petrol). [a]2D5 þ120 (c 1.5,
CHCl3). MS (ESIþ) m/z 633 (MþNaþ, 100%). HRMS
(ESIþ) calcd for C37H39NO7 (MþNaþ) 633.2702, found
1
672.2961, found 672.2941. H NMR d 7.45e7.17 (m, 25H,
Ar), 4.70 (d, 1H, J 11.5 Hz, Bn), 4.581 (d, 1H, Bn), 4.579
(dd, 1H, J 1.5, 6.0 Hz, H-3), 4.51 (d, 1H, J 12.0 Hz, Bn),
4.33 (d, 1H, J 11.5 Hz, Bn), 4.06 (dd, 1H, J 5.8, 9.3 Hz,
H-4), 3.97 (dt, 1H, J 3.9, 8.1 Hz, H-6), 3.88 (q, 1H, J
3.5 Hz, H-5), 3.84 (dt, 1H, J 1.5, 6.3 Hz, H-10), 3.54 (dd,
1H, J 6.0, 10.0 Hz, H-20), 3.52e3.48 (m, 3H, H-20, H-7, H-
4a), 3.22 (dd, 1H, J 8.3, 11.3 Hz, H-7). 13C NMR d 152.5
(C-1), 143.8, 138.1, 137.5 (q Ar), 128.6, 128.5, 128.2, 128.1,
127.84, 127.77, 127.5, 127.1, 126.9 (Ar), 87.3 (q C, Tr),
75.7 (C-10), 75.5 (C-3), 72.5 (Bn), 72.4 (Bn), 70.9 (C-5),
69.9 (C-6), 67.6 (C-4), 62.7 (C-20), 60.3 (C-4a), 50.3 (C-7).
1
633.2690. H NMR d 7.38e7.26 (m, 16H, Ar H), 7.21e7.17
(m, 4H, Ar H), 4.97 (d, 1H, J 11.4 Hz, Bn), 4.79 (d, 1H, J
12.0 Hz, Bn), 4.58 (dd, 1H, J 2.0, 5.6 Hz, Bn), 4.53 (d, 1H, J
11.1 Hz, Bn), 4.52 (d, 1H, J 11.7 Hz, Bn), 4.51 (s, 2H,
Bnꢂ2), 4.49 (d, 1H, J 12.3 Hz, Bn), 4.40 (d, 1H, J 11.1 Hz,
Bn), 4.17 (dd, 1H, J 5.7, 9.3 Hz, H-4), 4.01 (t, 1H, J 3.0 Hz,
H-5), 3.92 (ddd, 1H, J 1.5, 5.4, 7.1 Hz, H-10), 3.84 (ddd, 1H,
J 1.2, 5.7, 10.2 Hz, H-20), 3.79 (m, 1H, H-20), 3.74 (dd, 1H, J
3.2, 7.8 Hz, H-6), 3.61 (dd, 1H, J 2.9, 9.5 Hz, H-4a), 3.58
(dd, 1H, J 7.8, 10.2 Hz, H-7), 3.50 (t, 1H, J 9.9 Hz, H-7). 13C
NMR d 152.4 (C-1), 138.1, 138.0, 137.3, 137.0 (q Ar), 128.5,
128.3, 128.2, 128.1, 128.0, 127.9, 127.8, 127.7, 127.4, 126.8
(Ar), 77.8 (C-6), 77.6 (C-10), 77.3 (C-5), 75.7 (C-3), 73.4,
72.5, 72.2, 72.1 (Bn), 67.7 (C-4), 60.6 (C-20), 59.4 (C-4a),
48.0 (C-7).
4.1.12. (3S,4R,4aR,5R,6S)-4,5,6-Tris(benzyloxy)-3-[(1S)-1-
(benzyloxy)-2-triphenylmethyloxyethyl]-hexahydro-
pyrrolo[1,2-c][1,3]oxazin-1-one (23)
To a solution of 22 (2.24 g, 3.34 mmol) in dry THF (20 mL)
at 0 ꢀC was added NaH (353 mg, 7.35 mmol, 50% in mineral
oil). After H2 evolution had ceased (10 min), BnBr (1.6 mL,
13.36 mmol) and n-BuNI (123 mg, 0.334 mmol) were added.
The mixture was brought to 50 ꢀC and stirred for 18 h, then
cooled to rt and treated with MeOH (5 mL) and Et3N
(3 mL), and stirred for 10 min. After evaporating all volatiles,
the residue was dissolved in Et2O and filtered through Celite,
followed by further washings of the solids with Et2O. The
solvent was evaporated and the residue was purified by flash
column chromatography (30% EtOAc/petrol) to give 23 as
a yellow oil (1.9 g, 67%). Rf 0.19 (30% EtOAc/petrol). [a]D24
þ64 (c 2.77, CHCl3). MS (ESIþ) m/z 874 (MþNaþ, 100%).
HRMS (ESIþ) calcd for C56H53NO7Na (MþNaþ) 874.3719,
found 874.3720. IR nmax (cmꢁ1): 1680, 1449, 1091, 1060,
4.1.14. (2S,3S,4R)-4-[(2S,3R,4S)-3,4-Dibenzyloxy-
pyrrolidin-2-yl]-2,4-dibenzyloxybutane-l,3-diol (25)
To a solution of 24 (30 mg, 49.18 mmol) in MeOH (1 mL)
were added NaOH (20 mg, 0.5 mmol) and H2O (0.5 mL) in
a 10 mL sealed microwave reactor tube. The reaction mixture
was stirred and irradiated with microwaves in a CEM micro-
wave reactor for 1 h at 110 ꢀC using a maximum applied
power of 500 W. After cooling, the mixture was poured into
water and the product was extracted with EtOAc (2ꢂ5 mL).
The combined EtOAc extracts were washed with brine, dried
(Na2SO4), and evaporated. The residue was purified by flash

4878
A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
column chromatography (100% EtOAc and 10% MeOH/
EtOAc) to give a clear oil (18 mg, 62%). Rf 0.32 (20%
MeOH/EtOAc). [a]2D1 þ75 (c 0.85, CHCl3). MS (ESIþ) m/z
584 (MþHþ, 100%). HRMS (ESIþ) calcd for C36H42NO6
recrystallized from boiling EtOH with a few drops of H2O
to give 1,2-di-epi-1 (38 mg, 62%) as transparent micro-crys-
tals. [a]2D3 þ21 (c 1.5, H2O) [lit. [a]D23 þ66.5 (c 1.33, H2O)]
MS (ESIþ) m/z 206 (MþHþ, 100%). HRMS (ESIþ) calcd
for C8H16NO5 (MþHþ) 206.1028, found 206.1036. IR nmax
1
584.3012 (MþHþ), found 584.3023. H NMR d 7.35e7.14
1
(m, 20H, Ar), 5.02 (d, 1H, J 11.5 Hz, Bn), 4.75 (d, 1H, J
10.5 Hz, Bn), 4.52 (s, 2H, Bnꢂ2), 4.50 (d, 1H, J 11.5 Hz,
Bn), 4.43 (d, 1H, J 10.5 Hz, Bn), 4.42 (s, 2H, Bnꢂ2), 4.11
(t, 1H, J 3.3 Hz, H-3), 4.08 (t, 1H, J 4.0 Hz, H-30), 4.02 (dd,
1H, J 3.5, 9.5 Hz, H-4), 3.96 (m, 1H, H-1), 3.73e3.66 (m,
3H, H-1, H-2, H-40), 3.57 (dd, 1H, J 4.8, 9.3 Hz, H-20), 2.90
(dd, 1H, J 9.3, 10.8 Hz, H-50), 2.77 (dd, 1H, J 6.8, 10.8 Hz,
H-50). 13C NMR d 138.7, 138.3, 138.04, 138.0 (q Ar),
128.43, 128.4, 128.3, 128.2, 128.1, 127.9, 127.7, 127.6,
127.5, 127.3 (Ar), 80.9 (C-2 or C-40), 77.4 (C-30), 76.9 (C-2
or C-40), 74.6 (C-4), 73.3 (C-3), 73.2, 72.11, 72.10, 71.7
(Bn), 62.7 (C-1), 61.1 (C-20), 46.4 (C-50).
(cmꢁ1): 3344, 1618, 1294. H NMR (D2O) d 4.29 (ddd, 1H,
J2,3b 2.8, J1,2 5.8, J2,3a 8.5 Hz, H-2), 4.12 (dd, 1H, J1,8a 3.8,
J1,2 6.3 Hz, H-1), 3.53 (t, 1H, J7,8¼J8,8a 9.5 Hz, H-8), 3.48
(ddd, 1H, J5a,6 5.5, J6,7 9.0, J5b,6 10.5 Hz, H-6), 3.18 (t, 1H,
J6,7¼J7,8 9.3 Hz, H-7), 3.00 (t, 1H, J5a,6 5.0, J5a,5b 11.0 Hz,
H-5a), 2.76 (dd, 1H, J2,3b 2.8, J3a,3b 10.8 Hz, H-3b), 2.50
(dd, 1H, J2,3a 8.3, J3a,3b 10.8 Hz, H-3a), 2.04 (dd, 1H, J1,8a
3.5, J8,8a 9.5 Hz, H-8a), 1.95 (t, 1H, J5a,5b¼J5b,6 10.5 Hz, H-
5b). 13C NMR (D2O) d 79.3 (C-7), 70.7 (C-8a), 70.4 (C-6),
70.2 (C-2), 69.7 (C-1), 69.3 (C-8), 59.9 (C-3), 55.7 (C-5).
Acknowledgements
4.1.15. (1R,2S,6S,7R,8R,8aR)-1,2,6,8-Tetrabenzyloxy-
octahydroindolizin-7-ol (26)
We thank the Australian Research Council for financial
support and the University of Wollongong for a Ph.D. scholar-
ship to A.S.D. and Chiang Mai University and the Thai
Government for a Ph.D. scholarship to T.R.
To a solution of amino-alcohol 25 (290 mg, 0.497 mmol) in
dry CH2Cl2 (5 mL) at 0 ꢀC were added Et3N (2.77 mL,
19.88 mmol), PPh3 (326 mg, 1.24 mmol), and CBr4 (410 mg,
1.24 mmol). The reaction mixture was stirred for 2 h at 0 ꢀC
and poured into water (20 mL). The water layer was extracted
with CH2Cl2 (2ꢂ20 mL). The combined CH2Cl2 extracts were
washed with brine, dried (K2CO3), and evaporated. The resi-
due was purified by flash column chromatography (50%
EtOAc/petrol) to give 26 as a yellow oil (240 mg, 85%). Rf
0.69 (40% EtOAc/petrol). MS (ESIþ) m/z 566 (MþHþ,
100%). HRMS (ESIþ) calcd for C36H40NO5 (MþHþ)
References and notes
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Machan, T.; Tang, M. Synlett 2004, 2670e2680.
1
566.2906, found 566.2922. H NMR d 7.37e7.20 (m, 20H,
Ar), 4.95 (d, 1H, J 11.1 Hz, Bn), 4.88 (d, 1H, J 11.4 Hz,
Bn), 4.65 (d, 1H, J 11.7 Hz, Bn), 4.58 (d, 1H, J 12.0 Hz,
Bn), 4.56 (d, 1H, J 11.7 Hz, Bn), 4.54 (d, 1H, J 12.0 Hz, Bn),
4.52 (d, 1H, J 11.1 Hz, Bn), 4.50 (d, 1H, J 12.0 Hz, Bn),
4.19 (dd, 1H, J 3.5, 5.3 Hz, H-1), 4.14 (ddd, 1H, J 3.6, 5.6,
8.0 Hz, H-2), 3.84 (t, 1H, J 9.2 Hz, H-8), 3.59 (m, 1H, H-6),
3.57 (m, 1H, H-7), 3.24 (dd, 1H, J 4.2, 10.2 Hz, H-5), 3.20
(dd, 1H, J 3.3, 9.9 Hz, H-3), 2.47 (dd, 1H, J 8.0, 10.1 Hz,
H-3), 2.17 (dd, 1H, J 3.5, 9.2 Hz, H-8a), 1.94 (t, 1H, J
10.1 Hz, H-5). 13C NMR d 139.1, 138.4, 138.1, 138.0 (q
Ar), 128.5, 128.32, 128.3, 128.2, 128.1, 127.9, 127.6, 127.5,
127.4, 127.3 (Ar), 79.2 (C-7), 78.5 (C-2), 78.2 (C-6), 77.4
(C-1), 77.0 (C-8), 74.2, 73.8, 72.4, 72.2 (Bn), 69.2 (C-8a),
57.3 (C-3), 53.4 (C-5).
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4.1.16. (1R,2S,6S,7R,8R,8aR)-Octahydroindolizine-
1,2,6,7,8-pentol (1,2-di-epi-1)
To a solution of 26 (168 mg, 0.297 mmol) in MeOH (3 mL)
was added PdCl2 (79 mg, 0.446 mmol). The reaction mixture
was stirred at rt under a H2 atmosphere (balloon) for 18 h.
The mixture was filtered through Celite and the solids were
washed with MeOH. The combined filtrates were evaporated
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by evaporation resulted in a cloudy white residue that was
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A.S. Davis et al. / Tetrahedron 64 (2008) 4868e4879
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