Synthesis of dihydroxymethyl dihydroxypyrrolidines and steviamine analogues from C-2 formyl glycals

Article abstract of DOI:10.1021/jo401613v

Synthesis of dihydroxymethyl dihydroxypyrrolidines from C-2 formyl d-glycals has been described via a common dicarbonyl intermediate. The hence obtained pyrrolidines have been further utilized for the synthesis of some steviamine analogues. The newly synthesized molecules have been evaluated for glycosidase inhibition against 6 commercially available enzymes and found to be active in the micromolar range, where one of the steviamine analogues showed good and selective inhibition of β-mannosidase (Helix pomatia).

Full text of DOI:10.1021/jo401613v

Article
pubs.acs.org/joc
Synthesis of Dihydroxymethyl Dihydroxypyrrolidines and Steviamine
Analogues from C‑2 Formyl Glycals
Alafia A. Ansari and Yashwant D. Vankar*
Department of Chemistry, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208 016, India
S
* Supporting Information
ABSTRACT: Synthesis of dihydroxymethyl dihydroxypyrro-
lidines from C-2 formyl D-glycals has been described via a
common dicarbonyl intermediate. The hence obtained
pyrrolidines have been further utilized for the synthesis of
some steviamine analogues. The newly synthesized molecules
have been evaluated for glycosidase inhibition against 6 commercially available enzymes and found to be active in the micromolar
range, where one of the steviamine analogues showed good and selective inhibition of β-mannosidase (Helix pomatia).
steviamine analogues, and to evaluate their glycosidase inhibitory
behavior.
INTRODUCTION
■
Iminosugars form an important class of compounds with
interesting structures and immense biological significance,
especially as glycosidase inhibitors,1 making them important
targets for organic synthesis. Synthesis of naturally occurring
monocyclic and bicyclic iminosugars and design and synthesis of
their analogues is of utmost importance,2 since glycosidase
inhibitors are useful for the treatment of diseases such as
diabetes,3a Gaucher’s disease,3b Fabry’s disease,3b AIDS,3c,d etc.
Among the monocyclic iminosugars, numerous 5-, 6-, and 7-
membered compounds, either naturally occurring or synthetic,
have been reported in the literature as potent glycosidase
inhibitors.4 Further, among 5-membered iminosugars, pyrroli-
dines such as 2,5-dihydroxymethyl-3,4-dihydroxypyrrolidine
(DMDP) 1, 1,4-dideoxy-1,4-imino-D-arabinitol (DAB) 2,
codonopsinine 3, and radicamine A 4 (Figure 1) are popular
examples of inhibitors.2a DMDP 1 was the first pyrrolidine
iminosugar to be isolated from natural sources5a and is a good
inhibitor of both α- and β-glucosidases.5b As a consequence,
several synthetic routes toward DMDP and its analogues have
been reported in the literature.6
Among the bicyclic compounds, indolizidines such as
lentiginosine 5, swainsonine 6, and castanospermine 7 (Figure
2) are of continued interest, owing to their biological importance
and therapeutic value.2d As a result, several syntheses of these
molecules and their analogues have been reported in the
literature.7 More recently, (−)-steviamine 8 has been isolated
from the leaves of Stevia rebaudiana8a and was found to be a good
β-galactosidase inhibitor (IC50 = 35 μM, rat intestinal lactase)
and a weak inhibitor of α-galactosaminidase,8b which may
provide leads for the treatment of cancer.8c This molecule has
also attracted the attention of organic chemists, and a few
synthesis have been reported in the recent past.8b,d,e
RESULTS AND DISCUSSION
■
C-2 formyl glycals are versatile synthons in organic chemistry,10a
as has been illustrated in the synthesis of sugar β-amino acids,10b
iminosugars,10c,d potential anticancer10e and anti-inflammatory
compounds,10f and other important intermediates.10g−j We
envisaged the synthesis of polyhydroxylated pyrrolidines from
C-2 formyl glycals, using a simple and efficient strategy as
outlined in the retrosynthesis (Scheme 1). The key steps of the
synthesis would include dihydroxylation, oxidative cleavage of
the resulting diol to ketoformate, followed by reduction and
double nucleophilic displacement by amine.
Synthesis of the monocyclic azasugars commenced from 3,4,6-
tri-O-benzyl-D-glucal 9a (Scheme 2), which was converted to the
vinyl aldehyde 10a, using the Vilsmeier−Haack reaction.11,12a
Reduction of 10a was carried out using sodium borohydride in
methanol resulting in the corresponding allylic alcohol 11a.12b
The primary hydroxyl group in alcohol 11a was protected using
trityl chloride and triethylamine as a base, giving trityl ether 12a
in 92% yield (Scheme 2). The olefin moiety was now subjected to
dihydroxylation using OsO4 and NMO,13 giving a mixture of
diols 13a (dr = 5.5:1) in almost quantitative yield. The diols were
not stable during column chromatography, and hence only a
small portion was purified for analytical purpose, by quickly
filtering through a short silica gel column and immediate
evaporation. The crude mixture was subsequently exposed to
oxidative cleavage using sodium metaperiodate in CH3CN/H2O
(4:1) medium at room temperature. The reaction proceeded to
completion in a facile manner, when sodium metaperiodate was
added in portions over 2 h, followed by vigorous stirring for 3 h at
room temperature to afford compound 14a in 74% yield (over 2
steps). The keto-formate 14a typically showed a peak at δ 7.83 in
1H NMR spectrum corresponding to −OCHO proton and peaks
In continuation with our efforts in the design and synthesis of
new glycosidase inhibitors,2a,9 we became interested in designing
a new general strategy for the synthesis of dihydroxymethyl
dihydroxypyrrolidines, to utilize them in the synthesis of
Received: July 25, 2013
Published: August 28, 2013
© 2013 American Chemical Society
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Figure 1. Pyrrolidine glycosidase inhibitors.
Figure 2. Indolizidine glycosidase inhibitors.
Scheme 1
Scheme 2
Scheme 3
at δ 207 and 160 ppm in 13C NMR spectrum corresponding to
ketone and formate groups, respectively.14 Using the same series
of reactions as described above, C-2 formyl galactal 10b, obtained
from 3,4,6-tri-O-benzyl-D-galactal 9b,11 was converted to
ketoformate 14b.
Compound 14a was then reduced using NaBH4 in methanol,
affording a 1.8:1 mixture of diols 15a and 15b (Scheme 3). The
diols were chromatographically separated and then converted to
compounds 16a and 16b using mesyl chloride and triethylamine
and a catalytic amount of DMAP at 0 °C. The dimesylates were
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then treated with neat benzylamine for double nucleophilic
displacements leading to pyrrolidines 17a and 17b, respectively.
The reaction took place only at around 140 °C, probably because
both the mesylate groups are secondary in nature causing
sufficient steric hindrance for two displacement reactions.
Attempts for double nucleophilic displacement using tert-butyl
carbamate, benzyl carbamate, or tosylamine failed, possibly
because of the reduced nucleophilicity of these amines as
compared to benzylamine. The formation of 17a and 17b was
confirmed by the disappearance of the 2 mesylate peaks at δ 2.9
in 1H NMR spectrum and appearance of 2 characteristric
doublets corresponding to −NCH2Ph at δ 3.9.14 The trityl
protecting group was removed using 3 equiv of trifluoroacetic
acid in dichloromethane at 0 °C. The resulting alcohols 18a and
18b were then completely deprotected using Pd(OH)2/C under
1 atm H2 pressure, in acidic medium for 2 days to obtain 19a15a
and 19b15b in 10.4 and 8.4% overall yield from C-2 formyl glucal
10 using simple organic transformations.
ment using benzyl amine, followed by complete deprotection,
pyrrolidines 25a and 25b were obtained in 9.5 and 10.6% overall
yields, respectively, from D-galactal 9b.
The alcohols 24a and 24b were converted to PNB analogue
26a and acetate 26b, respectively, in order to study stereo-
chemistry of new stereocenters (Figure 4) (26a: NOE
experiment of H-2/H-4, H-2/H-5; 26b: NOE experiment of
H-2/H-4, H-2/H-5; J2,3 = 2.8 Hz).14
Figure 4. NOE correlations of compounds 26a and 26b.
The protection of compounds 18a and 18b was initially
attempted with acetate protecting group in order to study the
stereochemistry of the newly generated stereocenters. However,
Because of its interesting biological properties, the recently
isolated (−)-steviamine 8 has garnered considerable interest
among glycochemists and glycobiologists. With this easy and
practical synthesis at hand, which allowed us to prepare
pyrrolidines in a scalable manner, we next targeted synthesis of
steviamine analogues. The retrosynthetic plan is illustrated in
Scheme 5. The key steps involved are aza-Michael addition of the
secondary amine on crotonaldehyde followed by Wittig
olefination and ring closing metathesis.
1
the H NMR spectra of the resulting products did not help in
stereochemical analysis since the required protons were found to
merge with other protons. This problem was overcome by
switching to PNB protection. Hence, alcohols 18a and 18b were
converted to the corresponding p-nitrobenzoate analogues 20a
and 20b using p-nitrobenzoyl chloride and triethylamine
1
(Scheme 3). Their stereochemistry was analyzed by H NMR,
COSY, NOE, and decoupling experiments (Figure 3).14 (20a:
NOE experiment of H-5/H-2, H-4/H-2, J2,3 = 4.3 Hz; 20b: NOE
experiment of H-2/H-4, H-2/H-5, J2,3 = 11.3 Hz)14
Scheme 5
Figure 3. NOE correlations of compounds 20a and 20b.
Compounds 24a and 24b were converted to Boc amines in
order to reduce the nucleophilicity of the amine group for
facilitation of further reactions. The benzyl group on the amine
was removed successfully using Pd(OH)2/C and 1 atm H2
Reduction of 14b gave a 1.3:1 mixture of diols 21a and 21b, as
shown in Scheme 4. Following the same sequence of steps as
described earlier, viz. mesylation, double nucleophilic displace-
Scheme 4
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Scheme 6
Scheme 7
(Scheme 6) in just one hour, without affecting any of the benzyl
ethers present in the compound.16 The crude amine was
subsequently protected as tert-butylcarbamate using Boc2O in
the presence of Na2CO3 to obtain 27a and 27b. The 1H NMR
spectrum of 27a and 27b showed a sharp singlet peak at δ 1.2
ppm, which is characteristic of tert-butyl protons, and the 13C
NMR spectrum showed peaks at 156 and 30 ppm,14
corresponding to carbonyl group and tert-butyl carbons of
carbamate, respectively. Next, the free primary alcohol was
oxidized using CrO3−Py−Ac2O reagent system,17 and the
resulting aldehyde was subjected to Wittig olefination using
methyl triphenylphosphonium bromide and KOtBu resulting in
alkenes 28a and 28b. The carbamate protection was then
removed using trifluoroacetic acid in dichloromethane at room
temperature over 8 h. The free amine so obtained was studied for
aza-Michael reaction with crotonaldehyde using different
conditions. Addition of bases such as KOtBu or NaH did not
help in conversion even under reflux. The zinc/NH4Cl system18
worked best for this reaction in terms of yield, reaction time, and
cleaner reaction profile. The reaction furnished the aldehydes,
which were unstable and hence immediately converted to dienes
30a/31a and 30b/31b using Wittig salt and KOtBu. These
dienes were chromatographically inseparable at this stage, and
hence the mixtures were subjected to ring-closing metathesis
reaction.
subjected to one-pot double bond reduction and deprotection of
benzyl groups, using Pd(OH)2/C in 10% HCl/MeOH under 1
atm H2 for 3 days to afford steviamine analogues 33a and 33b in
70 and 64% yields, respectively.
The free hydroxyl groups were protected as acetates using a
1:1 mixture of acetic anhydride and pyridine over 8 h (Scheme
7), hence affording 34a and 34b for stereochemistry studies
(Figure 5) (NOE experiments of 34a: H-8a/H-5, H-8a/H-3;
34b: H-3/H-5, H-3/H-8a).14
Figure 5. NOE correlations of acetates 34a and 34b.
The other mixture of dienes 30b and 31b was subjected to
ring-closing metathesis (Scheme 8) to obtain ring-closed
products 35a and 35b in 1.4:1 ratio and total 48% yield over 4
steps. On hydrogenation as shown in Scheme 8, steviamine
analogues 36a and 36b were obtained.
Ring-closing metathesis of the resulting dienes proved to be a
formidable task. Using Grubbs’ first or second generation catalyst
at room temperature and even reflux in toluene did not give the
desired products. However, the mixture of dienes 30a and 31a
underwent smooth ring-closing metathesis reaction with 6 mol %
of Grubbs’ second generation catalyst in the presence of 2 equiv
of p-TsOH,19 in refluxing toluene, giving the products 32a and
32b in 1.2:1 ratio and total 52% yield over 4 steps (Scheme 7).
The so obtained cyclized products were easily separable by
column chromatography. Each isomer 32a and 32b was then
Again, acetates 37a and 37b were prepared from 36a and 36b,
respectively, to carry out stereochemical studies (Figure 6)
(NOE experiments of 34a: H-8a/H-5, H-5/H-3; 34b: H-5/H-3,
H-5/H-8a).14
Inhibition Studies. The synthesized dihydroxymethyl
dihydroxypyrrolidines and steviamine analogues were tested
against six commercially available enzymes, and the inhibitory
values (IC50) are listed in Table 1. Pyrrolidine 19a showed good
activity against β-mannosidase (Helix pomatia, IC50 = 40 μM),
but it was not selective, while pyrrolidine 19b is already reported
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Scheme 8
against six commercially available enzymes, of which 36a was
found to be a good and selective β-mannosidase inhibitor, while
the other steviamine analogues showed affinity toward
galactosidases.
EXPERIMENTAL SECTION
■
General Experimental Methods. All experiments have been
performed in oven-dried apparatus and under nitrogen atmosphere in
dry solvents, unless indicated otherwise. Commerical grade solvents
were dried by known methods, and dry solvents were stored over 4 Å
molecular sieves. IR spectra were recorded as a thin film and expressed in
cm−1. High resolution mass spectra were recorded by Q-TOF using
Figure 6. NOE correlations of acetates 37a and 37b.
in literature to be a good yet nonselective glycosidase
inhibitor.15b On the other hand, compounds 25a and 25b
showed a broad range of inhibition properties. Among
steviamine analogues, 33a and 36a were found to be good
inhibitors of β-mannosidase (Helix pomatia) with an IC50 of 45.6
and 45.9 μM, respectively, but 36a was more selective in nature.
The inversion of stereochemistry of methyl substituent at C-5 in
36a and 36b has proved detrimental to the inhibition against
galactosidases. However, steviamine analogues 33a and 36a are
good inhibitors of β-mannosidase, while 33b and 36b do not
show inhibition activity. Even though the structure of 33b is
more similar to that of 36a, the methyl group at C-5 position is
equatorially oriented in 33a and 36a and axially oriented in 33b
and 36b, respectively, indicating that axial methyl group could
adversely affect mannosidase binding because of more steric
hindrance. Hence it is possible that steviamine analogues without
methyl group could be better inhibitors. Moreover, all the
steviamine analogues except 36a showed preferable affinity
toward galactosidases. This is probably due to the β-
configuration of the hydroxyl groups at C-1 and C-2, which is
comparable to similar configurations at C-1 and C-2 of
(−)-steviamine, a good β-galactosidase inhibitor. Compound
33b, which differs from (−)-steviamine only in the configuration
of hydroxymethyl group at C-3, shows activity toward β-
galactosidase from bovine liver, while (−)-steviamine is inactive
toward this enzyme.8d These results indicate that structural
modifications in naturally occurring glycosidase inhibitors can
lead to different and/or improved activity.
electrospray ionization (ESI) method. H NMR (500 MHz) and 13C
1
NMR (125 MHz) spectra were recorded using CDCl3 or D2O as a
solvent. Chemical shifts have been reported in ppm downfield to
tetramethylsilane and coupling constants expressed in Hertz (Hz);
splitting patterns have been assigned as s (singlet), d (doublet), dd
(doublet of doublet), dt (doublet of triplet), td (triplet of doublet), quin
(quintet), m (multiplet), or br (broad). The NMR peaks of compounds
20a, 20b, 26a, 26b, 34a, 34b, 37a, and 37b were assigned with the help
of 1H, COSY, NOE and homonuclear decoupling experiments. Optical
rotations were measured at 28 °C in indicated solvents. TLC plates were
prepared using thin layers of silica gel on microscopic slides, and
visualization of spots was effected by exposure to iodine or spraying with
10% H2SO4 and charring. Column chromatography was performed over
silica gel (100−200 Mesh) using hexane and ethyl acetate as eluents.
(2R,3S,4R)-3,4-Bis(benzyloxy)-2-(benzyloxymethyl)-5-(trityloxy-
methyl)-3,4-dihydro-2H-pyran (12a). To a stirred solution of alcohol
11a (1.5 g, 3.37 mmol) in dry CH2Cl2 (15 mL) at room temperature
under N2 atmosphere was added Et3N (1.17 mL, 8.42 mmol), followed
by trityl chloride (1.135 g, 4.04 mmol), and a catalytic amount of 4-
dimethylaminopyridine (DMAP) (41 mg, 0.38 mmol), and the mixture
was stirred for 3 h. On completion of reaction, saturated NaHCO3
solution (10 mL) was added, and the mixture was stirred for 10 min.
Extraction was done with CH2Cl2 (3 × 10 mL), and combined organic
extracts were washed with water (1 × 30 mL) and brine (1 × 30 mL) and
then dried over Na2SO4. Concentration in vacuo gave a crude residue,
which was purified by column chromatography to obtain 2.13g (92%) of
12a as a colorless thick oil: Rf = 0.7 (hexane/EtOAc = 4:1); [α]2D8 = +10.9
(c 2.65, CH2Cl2); IR (neat) νmax 3030, 2922, 2868, 1667, 1492, 1449,
1088, 1068, 1028, 698 cm−1; 1H NMR (500 MHz, CDCl3) δ 7.46−7.44
(m, 6H), 7.32−7.20 (m, 22H), 7.02−7.01 (m, 2H), 6.47 (s, 1H), 4.75
(d, J = 11.3 Hz, 1H), 4.64 (d, J = 11.3 Hz, 1H), 4.54 (s, 2H), 4.50 (d, J =
11.0 Hz, 1H), 4.46 (d, J = 11.0 Hz, 1H), 4.38 (d, J = 5.2 Hz, 1H), 4.26−
4.23 (m, 1H), 3.89 (dd, J = 5.5, 7.3 Hz, 1H), 3.77 (dd, J = 5.5, 10.6 Hz,
1H), 3.74−3.69 (m, 2H), 3.58 (d, J = 10.6 Hz, 1H); 13C NMR (125
MHz, CDCl3) δ 144.2, 142.8, 138.3, 138.1, 138.0, 128.8, 128.5, 128.4,
128.3, 128.0, 127.8, 127.7, 127.5, 127.0, 111.0, 86.8, 76.9, 75.1, 74.3,
73.5, 73.4, 72.6, 68.4, 61.7; HRMS calcd for C47H44NaO5 [M + Na]+
711.3086, found 711.3080.
CONCLUSION
■
In conclusion, we have devised a new strategy for the
construction of pyrrolidine azasugars from C-2 formyl glycals,
which has been successfully employed for the synthesis of four
dihydroxymethyl dihydroxypyrrolidines viz. 19a, 19b, 25a, and
25b. This strategy can be further utilized for the preparation of
other pyrrolidine azasugars. Further, four novel analogues of
steviamine, 33a, 33b, 36a, and 36b have been synthesized using
aza-Michael addition and ring-closing metathesis as key steps. All
the molecules obtained were examined for glycosidase inhibition
(4S,5R,6R)-4,5-Bis(benzyloxy)-6-(benzyloxymethyl)-3-
(trityloxymethyl)tetrahydro-2H-pyran-2,3-diol (13a). Compound 12a
(1.5 g, 2.18 mmol) was dissolved in acetone/tBuOH/H2O (14 mL,
5:1:1). NMO (280 mg, 2.4 mmol) was added to it, followed by a
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a
Table 1. IC50 (μM) Values of the Synthesized Compounds against Tested Glycosidases
a
E1 = α-glucosidase (Baker’s yeast), E2 = β-glucosidase (almonds), E3 = α-galactosidase (coffee beans), E4 = β-galactosidase (bovine liver), E5 = α-
mannosidase (Jack beans), E6 = β-mannosidase (Helix pomatia).
catalytic amount of OsO4 (0.02 mmol), and the mixture was stirred
overnight at room temperature. Saturated sodium metabisulphite (10
mL) was then added to it, and stirring was continued for 1 h, followed by
filtration of the reaction mixture through a Celite pad. The filtrate was
extracted with ethyl acetate (3 × 15 mL), and combined organic extracts
were washed with brine (1 × 30 mL), dried over Na2SO4, and
concentrated under a vacuum. The crude product was used as such
without purification for the next step, while a small portion was taken
and purified by passing through a short silica gel column for analytical
purpose. Compound 13a was a thick viscous liquid: Rf = 0.6 (hexane/
EtOAc = 2:1); IR (neat) νmax 3405, 3086, 2924, 2878, 1647, 1492, 1449,
1238, 1097; 1H NMR (500 MHz, CDCl3, 5.5:1 mixture of isomers) δ
7.47−7.44 (m, 6H, both isomers), 7.34−7.12 (m, 22H, both isomers),
7.13−7.10 (m, 2H, both isomers), 5.47 (d, J = 2.7 Hz, 1H, major
isomer), 5.34 (d, J = 10.7 Hz, 1H, minor isomer), 4.86−4.35 (m, 6H,
both isomers), 4.10 (dt, J = 3.3, 9.4 Hz, 1H, major isomer), 4.05−4.01
(m, 1H, minor isomer), 3.96 (d, J = 8.8 Hz, 1H, major isomer), 3.90−
3.70 (m, 4H, minor isomer), 3.65−3.48 (m, 4H, major isomer, 1H,
minor isomer), 3.51−3.48 (m, 1H, minor isomer), 3.41 (t, J = 9.1 Hz,
1H, major isomer), 3.37−3.31 (m, 1H, both isomers), 3.07 (s, 1H,
minor isomer), 2.94 (s, 1H, major isomer); 13C NMR (125 MHz,
CDCl3, 5.5:1 mixture of isomers) δ 143.6, 143.3, 143.1, 142.8, 138.6,
138.3, 138.2, 137.9, 128.9−127.2 (m, aromatic C), 100.0, 93.4, 88.8,
87.3, 85.9, 82.2, 80.7, 76.7, 76.5, 76.1, 76.0, 75.9, 75.7, 75.4, 75.1, 74.8,
74.5, 73.3, 70.8, 68.9, 68.6, 63.8, 62.3, 62.0; HRMS (ESI) calcd for
C47H46NaO7 [M + Na]+ 745.3141, found 745.3143.
(2R,3R,4S)-1,3,4-Tris(benzyloxy)-5-oxo-6-(trityloxy)hexan-2-yl for-
mate (14a). The crude diol 13a was dissolved in CH3CN/H2O (4:1)
mixture (20 mL). Sodium metaperiodate (1.4 g, 6.54 mmol) was added
to the vigorously stirred solution in portions over 2 h at room
temperature, followed by stirring for another 3 h. The reaction mixture
was then filtered, and the filtrate was extracted with CH2Cl2 (3 × 15
mL). Combined organic extracts were washed once with brine (1 × 30
mL), dried over Na2SO4, and concentrated in vacuo. The residue was
purified by a short silica gel column to afford 1.17g (74% over 2 steps) of
14a as a colorless oil: Rf = 0.6 (hexane/EtOAc = 7:3); [α]2D8 = +0.8 (c
2.50, CH2Cl2); IR (neat) νmax 3031, 2869, 1726, 1596, 1492, 1450, 1169,
1095, 1028, 746, 698 cm−1; 1H NMR (500 MHz, CDCl3) δ 7.83 (s, 1H),
7.48−7.39 (m, 6H), 7.31−7.17 (m, 20H), 7.09−7.07 (m, 2H), 7.05−
7.03 (m, 2H), 5.22−5.20 (m, 1H), 4.47 (d, J = 11.9 Hz, 1H), 4.41−4.28
(m, 5H), 4.23 (d, J = 2.7 Hz, 1H), 4.19 (d, J = 11.3 Hz, 1H), 4.03 (d, J =
18.0 Hz, 1H), 3.94 (d, J = 18.0 Hz, 1H), 3.77 (dd, J = 2.4, 11.3 Hz, 1H),
3.68 (dd, J = 4.6, 11.3 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 207.3,
159.9, 143.3, 137.6, 137.1, 136.4, 128.9, 128.6, 128.5, 128.4, 128.3, 128.1,
127.9, 127.8, 127.3, 87.4, 82.3, 77.4, 74.6, 73.9, 73.3, 71.5, 69.5, 67.8;
HRMS (ESI) calcd for C47H44NaO7 [M + Na]+ 743.2985, found
743.2987.
(2R,3R,4R,5S)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-diol
(15a) and (2R,3R,4R,5R)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-
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2,5-diol (15b). The dicarbonyl compound 14a (1.12 g, 1.56 mmol) was
dissolved in dry MeOH (15 mL) and cooled to 0 °C. Then, NaBH4 (185
mg, 4.88 mmol) was added to the reaction mixture in portions over 15
min, and stirring was continued for 1 h. Subsequently, aq. NH4Cl (10
mL) was added dropwise to the reaction mixture until the effervescence
ceased. Extraction was done using CH2Cl2 (3 × 15 mL), and the extracts
were washed with brine (1 × 30 mL) and dried over Na2SO4. Removal of
solvent under a vacuum furnished a crude residue, which was subjected
to column chromatography to separate the 2 isomers. 15a: Yield 540 mg,
48%; Rf = 0.6 (hexane/EtOAc = 2:1); [α]2D8 = +25.7 (c 0.35, CH2Cl2); IR
mmol) was dissolved in 8 mL of benzylamine and heated up to 140 °C
for 6 h. The reaction mixture was cooled to room temperature, and 1 N
HCl (15 mL) was added to it. Extraction was done using EtOAc (3 × 10
mL) followed by washing of organic layer with brine and drying over
Na2SO4. Concentration under a vacuum gave a residue, which was
purified by column chromatography to give 1.03 g (78%) of 17a as a pale
yellow oil: Rf = 0.7 (hexane/EtOAc = 4:1); [α]2D8 = −12.7 (c 0.55,
CH2Cl2); IR (neat) νmax 3377, 1596, 1449, 1408, 1088, 1026 cm−1; 1H
NMR (500 MHz, CDCl3) δ 7.45−7.43 (m, 6H), 7.35−7.34 (m, 2H),
7.30−7.12 (m, 25H), 6.95−6.94 (m, 2H), 4.74 (d, J = 12.0 Hz, 1H), 4.68
(d, J = 12.0 Hz, 1H), 4.62 (t, J = 4.6 Hz, 1H), 4.57−4.48 (m, 4H), 4.29 (t,
J = 7.3 Hz, 1H), 3.99 (d, J = 14.3 Hz, 1H), 3.78 (dd, J = 4.6, 9.7 Hz, 1H),
3.57−3.47 (m, 3H), 3.29−3.28 (m, 2H), 3.20 (dd, J = 4.6, 11.0 Hz, 1H).
13C NMR (125 MHz, CDCl3) δ 144.0, 140.1, 138.9, 138.7, 129.1, 128.3,
1
(neat) νmax 3467, 2923, 2867, 1493, 1450, 1089, 1069, 689 cm−1; H
NMR (500 MHz, CDCl3) δ 7.42−7.40 (m, 4H), 7.33−7.22 (m, 24H),
7.09−7.08 (m, 2H), 4.51−4.44 (m, 5H), 4.37 (d, J = 10.9 Hz, 1H), 4.07
(br s, 1H), 4.00 (br s, 1H), 3.90 (dd, J = 2.1, 7.3 Hz, 1H), 3.79 (dd, J =
2.1, 7.3 Hz, 1H), 3.61 (dd, J = 3.4, 9.4 Hz, 1H), 3.55 (dd, J = 5.2, 9.4 Hz,
1H), 3.41 (dd, J = 3.9, 9.4 Hz, 1H), 3.28 (dd, J = 5.5, 9.1 Hz, 1H), 2.86
(d, J = 4.6 Hz, 1H), 2.79 (d, J = 4.9 Hz, 1H); 13C NMR (125 MHz,
CDCl3) δ 143.8, 137.9, 137.8, 128.8, 128.5, 128.4, 128.3, 128.0, 127.9,
127.8, 127.7, 127.2, 86.8, 78.1, 77.9, 73.6, 73.4, 71.2, 70.1, 69.9, 64.8;
HRMS calcd for C46H46NaO6 [M + Na]+ 717.3192, found 717.3193.
128.2, 128.0, 127.7, 127.6, 127.4, 126.8, 126.4, 87.7, 83.8, 83.1, 73.4,
72.9, 70.3, 60.8, 59.3, 52.8; HRMS calcd for C53H52NO4 [M + H]+
766.3896, found 766.3898.
(2S,3R,4R,5R)-1-Benzyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-
5-(trityloxymethyl)-pyrrolidine (17b). In a similar manner, as described
for 17a above, compound 16b (665 mg, 0.787 mmol) was converted to
pyrrolidine 17b (460 mg, 0.60 mmol, 76%) as a pale yellow oil: Rf = 0.7
(hexane/EtOAc = 4:1); [α]2D8 = +20.0 (c 0.35, CH2Cl2); IR (neat) νmax
15b: Yield 385 mg, 34%; Rf = 0.6 (hexane/EtOAc = 2:1); [α]D28
=
+10.0 (c 0.20, CH2Cl2); IR (neat) νmax 3428, 2922, 2854, 1492, 1449,
1
3029, 1493, 1450, 1364, 1093, 1072, 698 cm−1; H NMR (500 MHz,
1
1071, 745, 689 cm−1; H NMR (500 MHz, CDCl3) δ 7.42−7.40 (m,
CDCl3) δ 7.28−7.11 (m, 35H), 4.56−4.50 (m, 2H), 4.38 (s, 2H), 4.30
(d, J = 12.0 Hz, 1H), 4.20 (d, J = 12.3 Hz, 1H), 3.94−3.85 (m, 3H),
3.74−3.66 (m, 2H), 3.45 (dd, J = 4.9, 9.4 Hz, 1H), 3.34−3.31 (m, 1H),
3.13 (dd, J = 4.9, 8.3 Hz, 1H), 3.00−2.91 (m, 2H); 13C NMR (125 MHz,
CDCl3) δ 144.3, 139.4, 138.5, 138.4, 129.3, 128.7, 128.4, 128.3, 128.2,
128.1, 127.7, 127.6, 127.5, 127.4, 126.9, 126.7, 86.4, 82.7, 82.2, 73.3,
71.5, 70.8, 69.7, 65.9, 65.0, 59.7; HRMS calcd for C53H52NO4 [M + H]+
766.3896, found 766.3898.
((2S,3R,4R,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methanol (18a). The trityl ether 17a (800 mg, 1.046
mmol) was dissolved in dry CH2Cl2 (10 mL) and cooled to 0 °C under
N2 atmosphere. To this solution was added trifluoroacetic acid (0.40
mL, 5.23 mmol), and the mixture was stirred at the same temperature for
1 h. Solvent was evaporated, and the residue diluted with EtOAc (10
mL) and quenched with satd. NaHCO3 solution (10 mL). The
compound was extracted with EtOAc (3 × 10 mL), and the organic layer
washed with brine (1 × 25 mL) and dried over Na2SO4. Concentration
in vacuo gave a residue, which was purified by column chromatography
to give 464 mg (85%) of 18a as a pale yellow oil: Rf = 0.3 (hexane/
EtOAc = 3:1); [α]D28 = −20.0 (c 1.50, CH2Cl2); IR (neat) νmax 3444,
3029, 2864, 1495, 1453, 1363, 1207, 1098 cm−1; 1H NMR (500 MHz,
CDCl3) δ 7.37−7.23 (m, 20H), 4.77 (d, J = 11.9 Hz, 1H), 4.63 (d, J =
11.9 Hz, 1H), 4.56−4.51 (m, 4H), 4.46 (d, J = 14.9 Hz, 1H), 4.22 (t, J =
7.0 Hz, 1H), 3.85 (s, 2H), 3.67−3.60 (m, 3H), 3.47 (dd, J = 1.8, 10.0 Hz,
1H), 3.39−3.36 (m, 1H), 3.32−3.31 (m, 1H); 13C NMR (125 MHz,
CDCl3) δ 138.4, 128.5, 128.4, 127.7, 127.6, 127.0, 84.5, 83.2, 77.6, 73.4,
73.0, 72.7, 66.2, 63.5, 60.3, 58.2, 52.7; HRMS calcd for C34H38NO4 [M +
H]+ 524.2801, found 524.2803.
6H), 7.32−7.16 (m, 22H), 7.10−7.08 (m, 2H), 4.56−4.46 (m, 5H), 4.37
(d, J = 11.3 Hz, 1H), 4.11 (br s, 1H), 4.05 (br s, 1H), 3.92 (dd, J = 2.4, 4.8
Hz, 1H), 3.70−3.61 (m, 3H), 3.31 (dd, J = 5.8, 9.1 Hz, 1H), 3.12 (dd, J =
7.3, 9.1 Hz, 1H), 2.94 (br s, 1H), 2.83 (br s, 1H); 13C NMR (125 MHz,
CDCl3) δ 143.9, 138.0, 137.8, 128.7, 128.5, 128.4, 128.0, 127.9, 127.8,
127.3 127.1, 86.8, 78.4, 78.1, 76.8, 74.4, 73.6, 73.5, 71.2, 71.0, 69.7, 64.4;
HRMS calcd for C46H46NaO6 [M + Na]+ 717.3192, found 717.3191.
(2R,3S,4S,5S)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-diyl di-
methanesulfonate (16a). To a stirred solution of diol 15a (950 mg,
1.37 mmol) in dry CH2Cl2 (10 mL) at 0 °C under N2 atmosphere was
added Et3N (0.95 mL, 6.85 mmol), followed by DMAP (2 mg, 0.02
mmol) and MsCl (0.26 mL, 3.43 mmol). The reaction was allowed to
stir at the same temperature for 1 h, following which aq. NaHCO3 (10
mL) was added. The mixture was extracted with CH2Cl2 (3 × 10 mL),
and combined organic extracts were washed with water (1 × 20 mL) and
brine (1 × 20 mL) and then dried over Na2SO4. Concentration in vacuo
gave an oily residue, which was purified by column chromatography to
give 1.03 g (89%) of compound 16a as a colorless oil: Rf = 0.6 (hexane/
EtOAc = 2:1); [α]D28 = +16.0 (c 1.75, CH2Cl2); IR (neat) νmax 3529,
1
3031, 2935, 1597, 1493, 1449, 1353, 1174, 1090, 917, 700 cm−1; H
NMR (500 MHz, CDCl3) δ 7.44−7.43 (m, 6H), 7.34−7.23 (m, 20H),
7.20−7.19 (m, 2H), 7.14−7.12 (m, 2H), 5.11 (quin, J = 3.7 Hz, 1H),
5.02 (quin, J = 3.7 Hz, 1H), 4.54−4.51 (m, 5H), 4.48 (d, J = 11.6 Hz,
1H), 3.99 (t, J = 4.0 Hz, 1H), 3.92 (t, J = 4.0 Hz, 1H), 3.86 (dd, J = 2.7,
11.3 Hz, 1H), 3.77 (dd, J = 6.7, 11.3 Hz, 1H), 3.58 (dd, J = 3.7, 11.0 Hz,
1H), 3.52 (dd, J = 7.3, 11.0 Hz, 1H), 2.95 (s, 3H), 2.92 (s, 3H); 13C
NMR (125 MHz, CDCl3) δ 143.3, 137.4, 137.3, 137.2, 128.8, 128.6,
128.5, 128.4, 128.3, 128.1, 128.0, 127.3, 87.6, 81.4, 81.3, 78.3, 78.2, 74.3,
74.2, 73.5, 68.7, 62.6, 38.8; HRMS calcd for C48H50NaO10S2 [M + Na]+
873.2743, found 873.2749.
(2R,3S,4S,5R)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-diyl di-
methanesulfonate (16b). The same procedure used to convert 15a to
16a was employed for 570 mg (0.838 mmol) of 15b to obtain 668 mg
(92%) of 16b as a thick viscous liquid: Rf = 0.6 (hexane/EtOAc = 2:1);
[α]2D8 = +4.0 (c 1.25, CH2Cl2); IR (neat) νmax 3407, 2924, 1597, 144,
1356, 1175, 1089, 970, 913, 699 cm−1; 1H NMR (500 MHz, CDCl3) δ
7.40−7.38 (m, 6H), 7.34−7.21 (m, 22H), 7.03−6.99 (m, 2H), 4.91−
4.85 (m, 2H), 4.69 (s, 2H), 4.53−4.43 (m, 3H), 4.16 (dd, J = 4.2, 6.1 Hz,
1H), 4.01 (d, J = 11.3 Hz, 1H), 3.91 (dd, J = 3.4, 11.3 Hz, 1H), 3.79 (t, J =
3.7 Hz, 1H), 3.70 (dd, J = 7.0, 11.3 Hz, 1H), 3.61 (dd, J = 2.7, 11.3 Hz,
1H), 3.19 (dd, J = 5.2, 11.3 Hz, 1H), 2.96 (s, 3H), 2.89 (s, 3H); 13C
NMR (125 MHz, CDCl3) δ 143.1, 137.5, 137.3, 137.2, 128.7, 128.5,
128.4, 128.1, 128.0, 127.9, 127.3, 87.1, 82.2, 81.7, 78.7, 77.7, 75.2, 74.3,
73.5, 68.7, 62.5, 38.5, 38.4; HRMS calcd for C48H54NO10S2 [M + NH4]+
868.3184, found 868.3183.
((2R,3R,4R,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methanol (18b). The same method for deprotection of
17a was used for 710 mg (0.928 mmol) of trityl ether 17b to obtain 427
mg (88%) of 18b as a pale yellow oil: Rf = 0.3 (hexane/EtOAc = 3:1);
[α]2D8 = +20.0 (c 0.15, CH2Cl2); IR (neat) νmax 3324, 2920, 2851, 1602,
1
1495, 1453, 1364, 1094, 1027, 736, 697 cm−1; H NMR (500 MHz,
CDCl3) δ 7.33−7.25 (m, 20H), 4.60−4.56 (m, 2H), 4.50−4.47 (m, 2H),
4.43 (s, 2H), 4.04 (t, J = 3.3 Hz, 1H), 3.99 (dd, J = 3.0, 5.5 Hz, 1H), 3.91
(d, J = 14.0 Hz, 1H), 3.78 (d, J = 14.0 Hz, 1H), 3.59 (dd, J = 6.4, 9.1 Hz,
1H), 3.47−3.44 (m, 2H), 3.40−3.34 (m, 2H), 2.98 (br s, 1H); 13C NMR
(125 MHz, CDCl3) δ 139.2, 138.3, 138.2, 138.0, 128.8, 128.5, 128.4,
128.0, 127.8, 127.6, 127.2, 82.7, 81.8, 73.4, 72.2, 72.0, 70.3, 69.7, 65.1,
60.9, 58.4; HRMS calcd for C34H38NO4 [M + H]+ 524.2801, found
524.2795.
(2S,3R,4R,5S)-2,5-Bis(hydroxymethyl)pyrrolidine-3,4-diol (19a).
Compound 18a (120 mg, 0.23 mmol) was dissolved in 10% HCl/
MeOH (3 mL). To this solution was added Pd(OH)2/C (20% w/w, 30
mg). The solution was degassed and subsequently stirred vigorously
under 1 atm of H2 (balloon) for 2 days, after which it was filtered
(2S,3R,4R,5S)-1-Benzyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-5-
(trityloxymethyl)-pyrrolidine (17a). Compound 16a (1.03 g, 1.22
9389
dx.doi.org/10.1021/jo401613v | J. Org. Chem. 2013, 78, 9383−9395

The Journal of Organic Chemistry
Article
through a Celite pad and washed with MeOH. The solvent was
evaporated, and the residue dissolved in 5 mL of MeOH and passed
through Amberlite IRA 120 (H+) resin. The eluent was evaporated, and
residue washed repeatedly with EtOAc/Hexane (1:1) to obtain 23 mg
(62%) of 19a. Spectral data was found to be identical with the data
reported in the literature.15a
(2S,3R,4R,5R)-2,5-Bis(hydroxymethyl)pyrrolidine-3,4-diol (19b).
Using the same procedure for complete deprotection of 18a to 19a,
18b (100 mg, mmol) gave 68% (21 mg) of 19b as a pale yellow oil. Data
was found to be matching with the literature report.15b
isomers) δ 7.34−7.12 (m, 28H, both isomers), 6.97−6.95 (m, 2H, both
isomers), 5.41 (s, 1H, major isomer), 5.23 (d, J = 10.7 Hz, 1H, minor
isomer), 4.75−4.56 (m, 3H, both isomers), 4.53−4.38 (m, 2H, major
isomer, 3H, minor isomer), 4.33−4.28 (m, 1H, both isomers), 4.25−
4.18 (m, 1H, both isomers), 4.05 (d, J = 6.1 Hz, 1H, minor isomer), 3.98
(d, J = 10.4 Hz, 1H, major isomer), 3.83−3.80 (m, 2H, major isomer,
1H, minor isomer), 3.75 (dd, J = 1.2, 3.0 Hz, 1H, minor isomer), 3.63 (d,
J = 10.4 Hz, 1H, major isomer), 3.58−3.53 (m, 2H, both isomers), 3.48−
3.45 (m, 1H, minor isomer), 3.38 (s, 1H, major isomer), 3.20 (s, 1H,
major isomer), 2.55 (d, J = 7.0 Hz, 1H, minor isomer); 13C NMR (125
MHz, CDCl3, 5.5:1 mixture of isomers) δ 143.6, 142.8, 138.8, 138.7,
138.6, 138.0, 137.9, 128.7−127.1 (m, aromatic C), 100.8, 94.0, 88.6,
87.3, 82.6, 78.4, 75.8, 75.2, 75.0, 74.7, 74.5, 73.9, 73.6, 73.4, 71.4, 69.5,
69.1, 68.7, 68.2, 63.1, 62.1; HRMS (ESI) calcd for C47H46NaO7 [M +
Na]+ 745.3141, found 745.3143.
(2R,3S,4S)-1,3,4-Tris(benzyloxy)-5-oxo-6-(trityloxy)hexan-2-yl for-
mate 14b. The same procedure for oxidative cleavage of 13a to 14a was
followed for crude 13b to afford 14b (2.61 g, 78% after 2 steps) as a
viscous liquid: Rf = 0.6 (hexane/EtOAc = 7:3); [α]2D8 = −7.1 (c 1.40,
CH2Cl2); IR (neat) νmax 3061, 3031, 2924, 2870, 1728, 1493, 1451,
1173, 1098, 737, 699 cm−1; 1H NMR (500 MHz, CDCl3) δ 7.97 (s, 1H),
7.40−7.39 (m, 6H), 7.27−7.20 (m, 22H), 7.10−7.06 (m, 30H), 5.34 (d,
J = 4.2 Hz, 1H), 4.48 (dd, J = 2.4, 11.3 Hz, 1H), 4.44 (dd, J = 2.1, 11.3 Hz,
1H), 4.40 (br s, 2H), 4.35−4.33 (m, 2H), 4.14 (dd, J = 2.4, 4.9 Hz, 1H),
4.11−4.09 (m, 1H), 4.04 (dd, J = 2.7, 18.0 Hz, 1H), 3.98 (dd, J = 2.7,
18.0 Hz, 1H), 3.65 (ddd, J = 2.4, 5.2, 10.7 Hz, 1H), 3.57 (ddd, J = 2.4, 4.3,
10.7 Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 206.4, 160.5, 143.3,
137.5, 137.4, 136.7, 128.8−127.1 (m, aromatic), 87.4, 81.0, 78.2, 74.5,
73.2, 72.7, 72.3, 69.7, 68.2; HRMS calcd for C47H44NaO7 [M + Na]+
743.2985, found 743.2982.
((2S,3R,4S,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methyl 4-nitrobenzoate (20a). To a solution of alcohol
18a (60 mg, 0.115 mmol) in dry CH2Cl2 (2 mL) under N2 at room
temperature was added 4-nitrobenzoyl chloride (32 mg, 0.172 mmol)
along with Et3N (0.05 mL, 0.344 mmol) and a catalytic amount of
DMAP, following which the reaction mixture was stirred for 1 h. The
reaction was then treated with satd. NaHCO3 solution (2 mL) and
extracted with CH2Cl2 (3 × 2 mL), and the combined organic extracts
were washed with H2O (1 × 5 mL) and brine (1 × 5 mL) and finally
dried over Na2SO4. The solvent was evaporated, and the residue purified
by column chromatography to afford 64 mg (83%) of 20a as a colorless
oil: Rf = 0.6 (hexane/EtOAc = 4:1); [α]2D8 = −12.0 (c 0.50, CH2Cl2); IR
(neat) νmax 2918, 2854, 1723, 1605, 1526, 1495, 1453, 1346, 1272, 1101,
1
697 cm−1; H NMR (500 MHz, CDCl3) δ 8.19−8.17 (m, 2H, ArH),
8.04−8.02 (m, 2H, ArH), 7.31−7.19 (m, 20H, ArH), 4.71−4.49 (m, 8H,
H-7, H-7′, −OCH2Ph), 4.35−4.31 (m, 1H, H-3), 4.24−4.20 (m, 1H, H-
4), 4.07 (dd, J = 3.0, 14.3 Hz, 1H, −NCH2Ph), 3.89 (dd, J = 2.7, 14.3 Hz,
1H, −NCH2Ph), 3.69−3.60 (m, 2H, H-2, H-6), 3.48 (dt, J = 2.7, 9.8 Hz,
1H, H-6′), 3.30 (td, J = 3.0, 6.4 Hz, 1H, H-5); 13C NMR (125 MHz,
CDCl3) δ 164.6, 150.4, 139.4, 138.5, 138.4, 138.3, 135.9, 130.6, 128.4,
128.3, 128.1, 127.7, 127.6, 127.5, 127.4, 126.9, 123.5, 83.2, 82.6, 73.5,
73.0, 72.6, 67.1, 64.2, 60.7, 58.8, 53.0; HRMS calcd for C41H41N2O7 [M
+ H]+ 673.2914, found 673.2912.
(2R,3S,4R,5R)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-diol
21a and (2R,3S,4R,5S)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-
diol (21b). The procedure followed for the reduction of compound 14a
was followed for 2.60 g (3.62 mmol) of 14b, to provide 21a and 21b,
which were separated by column chromatography.
((2R,3R,4S,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methyl 4-nitrobenzoate (20b). Using the same
procedure as described for protection of 18a, alcohol 18b (45 mg,
0.086 mmol) was converted to its pNB ester 20b (46 mg, 79%), which
was a colorless oil: Rf = 0.6 (hexane/EtOAc = 4:1); [α]2D8 = +23.0 (c 0.65,
CH2Cl2); IR (neat) νmax 3029, 2919, 2857, 1724, 1606, 1527, 1495,
1453, 1346, 1271, 1100 cm−1; 1H NMR (500 MHz, CDCl3) δ 8.14−8.12
(m, 2H, Ar-H), 7.94−7.92 (m, 2H, Ar-H), 7.32−7.19 (m, 20H, Ar-H),
4.54−4.46 (m, 5H, −OCH2Ph), 4.41 (d, J = 12.3 Hz, 1H, −OCH2Ph),
4.22 (dd, J = 8.0, 11.3 Hz, 1H, H-3), 4.08−4.02 (m, 3H, H-4, H-7, H-7′),
3.87−3.83 (m, 2H, −NCH2−), 3.78 (dd, J = 7.7, 9.1 Hz, 1H, H-6), 3.51
(dd, J = 4.9, 9.1 Hz, 1H, H-6′), 3.45 (t, J = 4.9, 7.4 Hz, 1H, H-5), 3.25−
3.22 (m, 1H, H-2); 13C NMR (125 MHz, CDCl3) δ 164.3, 150.4, 139.5,
138.4, 138.2, 137.9, 135.6, 130.7, 128.9, 128.4, 128.3, 127.8, 127.7, 127.6,
127.5, 127.2, 123.4, 82.5, 82.3, 73.5, 72.7, 71.1, 69.7, 68.3, 66.3, 59.7;
HRMS calcd for C41H41N2O7 [M + H]+ 673.2914, found 673.2911.
(2R,3R,4R)-3,4-Bis(benzyloxy)-2-(benzyloxymethyl)-5-(trityloxy-
methyl)-3,4-dihydro-2H-pyran (12b). Following the same procedure
for the preparation of 12a from 11a, compound 12b (3.20 g, 95%) was
obtained from 11b (2.18 g, 4.90 mmol) as a colorless oil: Rf = 0.6
(hexane/EtOAc = 4:1); [α]2D8 = +16.4 (c 2.20, CH2Cl2); IR (neat) νmax
21a: Yield 950 mg, 38%; Rf = 0.4 (hexane/EtOAc = 7:3); [α]2D8 = −2.2
(c 1.85, CH2Cl2); IR (neat) νmax 3435, 3060, 2925, 2870, 1597, 1493,
1449, 1397, 1323, 1210, 1073, 1028 cm−1; 1H NMR (500 MHz, CDCl3)
δ 7.44−7.42 (m, 6H), 7.35−7.21 (m, 22H), 7.08−7.06 (m, 2H), 4.74 (d,
J = 11.3 Hz, 1H), 4.63 (d, J = 11.0 Hz, 1H), 4.55−4.51 (m, 2H), 4.46 (d,
J = 11.9 Hz, 1H), 4.31 (d, J = 10.7 Hz, 1H), 4.09−4.01 (m, 2H), 3.96
(dd, J = 1.2, 7.6 Hz, 1H), 3.78 (dd, J = 1.8, 7.6 Hz, 1H), 3.55 (dd, J = 6.4,
9.4 Hz, 1H), 3.46 (dd, J = 6.1, 9.4 Hz, 1H), 3.39 (dd, J = 6.1, 9.1 Hz, 1H),
3.12 (dd, J = 7.3, 8.8 Hz, 1H), 2.51 (d, J = 7.3 Hz, 1H), 2.39 (d, J = 8.2
Hz, 1H); 13C NMR (125 MHz, CDCl3) δ 143.8, 138.0, 137.8, 128.5,
128.4, 128.2, 128.0, 127.9, 127.8, 127.1, 86.9, 77.5, 74.6, 74.5, 73.4, 71.5,
69.8, 69.5, 64.6; HRMS calcd for C46H46NaO6 [M + Na]+ 717.3192,
found 717.3198.
21b: Yield 1.19 g, 48%; Rf = 0.3 (hexane/EtOAc = 7:3); [α]2D8 = −7.7
(c 2.85, CH2Cl2); IR (neat) νmax 3432, 3060, 2926, 2871, 1597, 1492,
1
1449, 1397, 1212, 1074, 1028 cm−1; H NMR (500 MHz, CDCl3) δ
7.43−7.41 (m, 6H), 7.30−7.21 (m, 22H), 7.06−7.05 (m, 2H), 4.64−
4.59 (m, 2H), 4.51−4.44 (m, 3H), 4.38 (d, J = 11.0 Hz, 1H), 4.08−4.04
(m, 2H), 3.87 (t, J = 3.5 Hz, 1H), 3.78 (dd, J = 3.7, 7.0 Hz, 1H), 3.57−
3.50 (m, 2H), 3.45 (dd, J = 3.0, 9.7 Hz, 1H), 3.28 (dd, J = 6.7, 9.7 Hz,
1H), 3.19 (br s, 1H), 2.85 (br s, 1H); 13C NMR (125 MHz, CDCl3) δ
143.9, 138.0, 137.8, 128.8, 128.4, 128.1, 128.0, 127.9, 127.8, 127.7, 127.1,
86.8, 80.5, 77.9, 73.8, 73.7, 73.4, 71.1, 70.8, 70.2, 64.9;HRMS calcd for
C46H46NaO6 [M + Na]+ 717.3192, found 717.3195.
1
3030, 2870, 1665, 1492, 1450, 1090, 669 cm−1; H NMR (500 MHz,
CDCl3) δ 7.47−7.46 (m, 6H), 7.36−7.23 (m, 22H), 7.16 (br s, 2H),
6.39 (s, 1H), 4.81 (d, J = 12.0 Hz, 1H), 4.73 (d, J = 11.4 Hz, 1H), 4.65 (d,
J = 11.7 Hz, 1H), 4.55−4.49 (m, 2H), 4.44−4.41 (m, 2H), 4.35 (br s,
1H), 4.02 (s, 1H), 3.84−3.80 (m, 1H), 3.75 (d, J = 10.3 Hz, 1H), 3.68 (d,
J = 8.9 Hz, 1H), 3.58 (d, J = 10.3 Hz, 1H); 13C NMR (125 MHz, CDCl3)
δ 144.3, 142.2, 138.7, 138.3, 138.1, 128.8, 128.5, 128.3, 128.1, 128.0,
127.9, 127.8, 127.7, 127.5, 127.4, 127.0, 111.0, 86.8, 75.9, 73.5, 73.4,
73.2, 72.5, 71.6, 68.4, 62.0; HRMS calcd for C47H44NaO5 [M + Na]+
711.3086, found 711.3086.
(4S,5S,6R)-4,5-Bis(benzyloxy)-6-(benzyloxymethyl)-3-
(trityloxymethyl)tetrahydro-2H-pyran-2,3-diol (13b). The method for
dihydroxylation of 12a to 13a was used for compound 12b (3.20 g, 4.65
mmol). Compound 13b was a thick colorless viscous liquid: Rf = 0.6
(hexane/EtOAc = 2:1); IR (neat) νmax 3423 (br), 3061, 2925, 1493,
1449, 1064 cm−1; 1H NMR (500 MHz, CDCl3, 4.4:1 mixture of
(2R,3R,4S,5R)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-diyl
dimethanesulfonate (22a). The diol 21a (950 mg, 1.37 mmol) was
converted to dimesylate using the same method as for 15a to 16a, to
afford 1.01 g (87%) of 22a as a colorless oil: Rf = 0.3 (hexane/EtOAc =
7:3); [α]2D8 = −8.1 (c 2.65, CH2Cl2); IR (neat) νmax 3400, 3061, 2934,
1
2874, 1597, 1492, 1449, 1357, 1175, 1095, 917 cm−1; H NMR (500
MHz, CDCl3) δ 7.41−7.39 (m,6H), 7.34−7.22 (m, 22H), 7.17−7.15
(m, 2H), 5.03 (br s, 1H), 4.79−4.76 (m, 2H), 4.66 (d, J = 11.0 Hz, 1H),
4.61 (d, J = 11.0 Hz, 1H), 4.47−4.40 (m, 3H), 4.20 (dd, J = 2.7, 6.1 Hz,
1H), 3.87−3.81 (m, 2H), 3.73−3.71 (m, 2H), 3.27 (dd, J = 5.1, 11.6 Hz,
1H), 2.91 (s, 3H), 2.78 (s, 3H); 13C NMR (125 MHz, CDCl3) δ 143.1,
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137.4, 137.3, 128.8−127.4 (m, aromatic C), 87.4, 81.5, 81.4, 77.9, 77.8,
74.7, 74.5, 73.5, 69.7, 63.6, 38.7, 38.4; HRMS calcd for C48H50NaO10S2
[M + Na]+ 873.2743, found 873.2748.
128.2, 127.8, 127.7, 127.6, 127.4, 126.9, 78.9, 77.8, 73.4, 71.8, 71.3, 67.8,
61.6, 58.4, 52.7; HRMS calcd for C34H38NO4 [M + H]+ 524.2801, found
524.2802.
(2R,3R,4S,5S)-1,3,4-Tris(benzyloxy)-6-(trityloxy)hexane-2,5-diyl di-
methanesulfonate (22b). The diol 21b (1.15 g, 1.66 mmol) was
converted to dimesylate using the same method as for 15a to 16a, to
afford 1.19 g (85%) of 22b as a colorless oil: Rf = 0.3 (hexane/EtOAc =
7:3); [α]2D8 = −0.4 (c 2.35, CH2Cl2); IR (neat) νmax 3433, 3030, 2934,
(2S,3S,4R,5R)-2,5-Bis(hydroxymethyl)pyrrolidine-3,4-diol (25a).
The same method for complete deprotection of 18a to 19a was
followed for 24a (95 mg, 0.18 mmol), affording 20 mg (67%) of 25a as a
yellow liquid: Rf = 0.4 (MeOH/EtOAc = 1:4); [α]2D8 = +21.3 (c 0.40,
CH3OH). IR (neat) νmax 3349, 3062, 1237, 1100, 1028 cm−1; 1H NMR
(500 MHz, D2O) δ 4.21−4.20 (m, 1H), 4.14 (dd, J = 4.0, 9.1 Hz, 1H),
3.88−3.82 (m, 2H), 3.77 (dd, J = 8.3, 12.0 Hz, 1H), 3.71 (dd, J = 5.7,
12.6 Hz, 1H), 3.63 (ddd, J = 3.4, 4.9, 8.3 Hz, 1H), 3.51 (ddd, J = 3.4, 5.7,
9.1 Hz, 1H); 13C NMR (125 MHz, D2O) δ 71.2, 70.1, 62.2, 61.7, 58.1,
57.5; HRMS calcd for C6H14NO4 [M + H]+ 164.0923, found 164.0922.
(2S,3S,4R,5S)-2,5-Bis(hydroxymethyl)pyrrolidine-3,4-diol (25b).
The same method for complete deprotection of 18a to 19a was
followed for 24b (105 mg, 0.20 mmol), affording 21 mg (61%) of 25b as
a yellow liquid: Rf = 0.4 (MeOH/EtOAc = 1:4); [α]2D8 = +7.5 (c 0.80,
CH3OH); IR (neat) νmax 3344, 3062, 1100, 1025 cm−1; 1H NMR (500
MHz, D2O) δ 4.27 (dd, J = 3.0, 4.2 Hz, 1H), 4.19 (s, 1H), 3.93−3.87 (m,
2H), 3.81−3.72 (m, 2H), 3.65 (br s, 1H), 3.57 (ddd, J = 3.0, 5.8, 7.8 Hz,
1H); 13C NMR (125 MHz, D2O) δ 71.9, 70.6, 62.7, 62.2, 58.6, 57.9;
HRMS calcd for C6H14NO4 [M + H]+ 164.0923, found 164.0918.
((2R,3R,4S,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methyl-4-nitrobenzoate (26a). In the same way as 18a
was converted to 20a, compound 24a (45 mg, 0.086 mmol) was
transformed to 26a (53 mg, 92%), which was a colorless oil: Rf = 0.6
(hexane/EtOAc = 4:1); [α]2D8 = +27.5 (c 3.35, CH2Cl2); IR (neat) νmax
3375, 3029, 2862, 1725, 1606, 1526, 1453, 1347, 1273, 1101, 1014 cm−1;
1H NMR (500 MHz, CDCl3) δ 8.10−8.09 (m, 2H, ArH), 7.94−7.92 (m,
2H, ArH), 7.34−7.14 (m, 20H, ArH), 4.64−4.55 (m, 3H, −OCH2Ph),
4.47 (dd, J = 4.5, 11.5 Hz, 1H, H-7), 4.35−4.30 (m, 2H, −OCH2Ph),
4.23 (d, J = 12.0 Hz, 1H, −OCH2Ph), 4.18 (dd, J = 3.7, 11.5 Hz, 1H, H-
7′), 4.02 (d, J = 8.0 Hz, 1H, −NCH2Ph), 3.95−3.94 (m, 1H, H-4), 3.86−
3.81 (m, 2H, H-3, −NCH2Ph), 3.46−3.43 (m, 1H, H-2), 3.26−3.23 (m,
1H, H-5), 3.04 (dd, J = 4.3, 9.7 Hz, 1H, H-6), 2.98 (dd, J = 7.4, 9.7 Hz,
1H, H-6′); 13C NMR (125 MHz, CDCl3) δ 164.4, 150.4, 139.2, 138.3,
138.2, 137.8, 135.6, 130.6, 129.0, 128.4, 128.3, 128.0, 127.8, 127.6, 127.4,
127.2, 123.4, 77.9, 77.0, 73.1, 71.5, 71.0, 66.8, 65.2, 64.7, 59.4; HRMS
calcd for C41H41N2O7 [M + H]+ 673.2914, found 673.2917.
((2S,3R,4S,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methyl acetate (26b). The alcohol 24b (40 mg, 0.076
mmol) was dissolved in dry CH2Cl2 (2 mL). To this solution was added
Et3N (0.012 mL, 0.09 mmol), Ac2O (0.02 mL, 0.19 mmol), and a
catalytic amount of DMAP, and the mixture was stirred at room
temperature for 1 h. The reaction was quenched with satd. NaHCO3
solution, followed by extraction with CH2Cl2 (3 × 2 mL). Organic layer
was then washed with H2O (1 × 5 mL) and brine (1 × 5 mL) and then
dried over Na2SO4. Concentration in vacuo gave a residue, which was
purified by column chromatography to yield (37 mg, 87%) of 26b as a
colorless oil: Rf = 0.4 (hexane/EtOAc = 4:1); [α]2D8 = +7.5 (c 0.80,
CH2Cl2); IR (neat) νmax 3062, 3029, 2860, 1739, 1453, 1237, 1100, 1028
cm−1; 1H NMR (500 MHz, CDCl3) δ 7.34−7.19 (m, 20H, ArH), 4.68−
4.54 (m, 5H, −OCH2Ph, H-7), 4.44−4.39 (m, 3H, H-7′, −OCH2Ph),
4.10−4.03 (m, 2H, H-3, −NCH2Ph), 3.94−3.91 (m, 2H, H-4,
−NCH2Ph), 3.55 (td, J = 2.7, 7.0 Hz, 1H, H-2), 3.30 (dd, J = 8.2,
14.3 Hz, 1H, H-6), 3.23−3.19 (m, 2H, H-5, H-6′), 1.85 (s, 3H,
OCOCH3); 13C NMR (125 MHz, CDCl3) δ 170.9, 140.1, 138.8, 138.4,
138.3, 128.4−126.8 (m, aromatic), 79.8, 78.3, 73.3, 72.1, 71.8, 70.6, 66.6,
63.1, 60.7, 53.4, 21.1; HRMS calcd for C36H40NO5 [M + H]+ 566.2906,
found 566.2903.
1
2874, 1597, 1449, 1356, 1174, 1092, 917 cm−1; H NMR (500 MHz,
CDCl3) δ 7.41−7.38 (m, 6H), 7.33−7.21 (m, 22H), 7.17−7.14 (m, 2H),
5.20−5.18 (m, 1H), 5.09 (dd, J = 5.2, 8.8 Hz, 1H), 4.60 (d, J = 11.0 Hz,
1H), 4.55 (d, J = 11.6 Hz, 1H), 4.52−4.49 (m, 3H), 4.43 (d, J = 10.6 Hz,
1H), 3.96−3.92 (m, 2H), 3.80 (dd, J = 5.8, 11.0 Hz, 1H), 3.74 (dd, J =
3.7, 11.3 Hz, 1H), 3.55 (dd, J = 2.4, 11.3 Hz, 1H), 3.47 (dd, J = 6.7, 11.0
Hz, 1H), 2.98 (s, 3H), 2.92 (s, 3H); 13C NMR (125 MHz, CDCl3) δ
143.4, 137.2, 137.1, 128.7−127.3 (m, aromatic C), 87.3, 81.4, 80.8, 77.6,
77.5, 75.1, 73.7, 72.7, 69.5, 63.1, 39.2, 38.6; HRMS calcd for
C48H50NaO10S2 [M + Na]+ 873.2743, found 873.2747.
(2S,3S,4R,5R)-1-Benzyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-5-
(trityloxymethyl)pyrrolidine (23a). The procedure for double
nucleophilic displacement as used for 16a to 17a was followed for
1.00 g (1.18 mmol) of 22a, to obtain 728 mg (81%) of 23a as a yellow
liquid: Rf = 0.6 (hexane/EtOAc = 9:1); [α]2D8 = −9.2 (c 1.20, CH2Cl2);
IR (neat) νmax 3397, 3029, 1598, 1493, 1449, 1088, 1061, 1027 cm−1; 1H
NMR (500 MHz, CDCl3) δ 7.42−7.36 (m, 6H), 7.30−7.17 (m, 29H),
4.48−4.41 (m, 4H), 4.32 (s, 2H), 3.97 (d, J = 13.5 Hz, 1H) 3.86 (d, J =
13.5 Hz, 1H), 3.75−3.72 (m, 2H), 3.30−3.19 (m, 4H), 3.02−2.95 (m,
2H); 13C NMR (125 MHz, CDCl3) δ 144.2, 139.7, 138.6, 138.4, 129.4,
128.8, 128.3, 128.2, 128.1, 127.9, 127.7, 127.5, 127.4, 126.9, 86.5, 78.1,
78.0, 73.1, 71.9, 71.2, 66.7, 66.0, 64.7, 59.9; HRMS calcd for C53H52NO4
[M + H]+ 766.3896, found 766.3891.
(2S,3S,4R,5S)-1-Benzyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-5-
(trityloxymethyl)pyrrolidine (23b). The procedure for double
nucleophilic displacement as used for 16a to 17a was followed for
1.19 g (1.40 mmol) of 22b, to obtain 902 mg (84%) of 23b as a yellow
liquid: Rf = 0.6 (hexane/EtOAc = 9:1); [α]2D8 = +3.6 (c 1.10, CH2Cl2); IR
(neat) νmax 3401, 3029, 2918, 2862, 1597, 1493, 1450, 1204, 1090, 1028
cm−1; 1H NMR (500 MHz, CDCl3) δ 7.39−7.37 (m, 6H), 7.28−7.18
(m, 29H), 4.50−4.42 (m, 4H), 4.34 (br s, 2H), 3.99 (d, J = 13.1 Hz, 1H),
3.88 (d, J = 13.1 Hz, 1H), 3.77−3.73 (m, 2H), 3.31−3.21 (m, 4H),
3.03−2.96 (m, 2H); 13C NMR (125 MHz, CDCl3) δ 144.2, 138.6, 138.5,
129.4, 128.8, 128.3, 128.2, 128.1, 127.9, 127.7, 127.6, 127.5, 127.4, 126.9,
86.5, 78.1, 78.0, 73.1, 71.9, 71.2, 66.7, 66.0, 64.7, 59.9; HRMS calcd for
C53 H52NO4 [M + H]+ 766.3896, found 766.3899.
((2R,3R,4S,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methanol (24a). Using the procedure for deprotection
of trityl ether in 17a to give 18a, compound 24a (390 mg, 80%) was
obtained from trityl ether 23a (715 mg, 0.935 mmol), as a pale yellow
oil: Rf = 0.5 (hexane/EtOAc = 3:2); [α]2D8 = −8.2 (c 2.05, CH2Cl2); IR
1
(neat) νmax 3205, 3031, 1670, 1454, 1202, 1133 cm−1; H NMR (500
MHz, CDCl3) δ 7.44−7.21 (m, 20H), 4.72 (d, J = 12.5 Hz, 1H), 4.59−
4.53 (m, 3H), 4.49−4.43 (m, 3H), 4.29 (d, J = 12.8 Hz, 1H), 4.13 (dd, J
= 4.2, 7.9 Hz, 1H), 4.10−4.08 (m, 1H), 3.90 (dd, J = 8.2, 10.4 Hz, 1H),
3.83 (td, J = 3.0, 7.9 Hz, 1H), 3.71 (dd, J = 3.0, 10.1 Hz, 1H), 3.63 (br s,
1H), 3.59−3.51 (m, 2H); 13C NMR (125 MHz, CDCl3) δ 137.5, 137.3,
131.2, 129.0, 128.6, 128.5, 128.2, 128.1, 128.0, 127.9, 78.3, 73.6, 72.6,
68.1, 61.8, 59.0; HRMS calcd for C34H38NO4 [M + H]+ 524.2801, found
524.2802.
((2S,3R,4S,5S)-1-Benzyl-3,4-bis(benzyloxy)-5-(benzyloxymethyl)-
pyrrolidin-2-yl)methanol (24b). Using the procedure for deprotection
of trityl ether in 17a to give 18a, compound 24b (446 mg, 77%) was
obtained from trityl ether 23b (850 mg, 1.11 mmol), as a pale yellow oil:
Rf = 0.5 (hexane/EtOAc = 3:2). [α]2D8 = +24.3 (c 0.70, CH2Cl2); IR
(neat) νmax 3424, 3292, 2865, 1601, 1494, 1453, 1117, 1045, 1027 cm−1;
1H NMR (500 MHz, CDCl3) δ 7.35−7.20 (m, 20H), 4.73 (d, J = 12.0
(2S,3S,4R,5R)-tert-Butyl 3,4-bis(benzyloxy)-2-(benzyloxymethyl)-
5-(hydroxymethyl)pyrrolidine-1-carboxylate (27a). Compound 24a
(870 mg, 1.66 mmol) was dissolved in dry CH3OH (10 mL), and
Pd(OH)2/C (20% w/w, 44 mg) was added to it. The mixture was
degassed and then vigorously stirred under 1 atm of H2 pressure
(balloon) for 1 h. On complete consumption of starting material (TLC
monitoring), the reaction mixture was filtered through Celite. Filtrate
was evaporated to obtain the crude amine, which was used without
purification for the next step.
Hz, 1H), 4.62 (d, J = 12.0 Hz, 1H), 4.55 (d, J = 12.0 Hz, 1H), 4.51−4.42
(m, 3H), 4.14−4.09 (m, 2H), 4.01 (d, J = 6.1 Hz, 1H), 3.97−3.93 (m,
2H), 3.76 (br s, 2H), 3.45 (dd, J = 3.4, 7.1 Hz, 1H), 3.37 (dd, J = 3.7, 9.7
Hz, 1H), 3.27−3.24 (m, 1H), 3.21 (dd, J = 7.4, 9.7 Hz, 1H); 13C NMR
(125 MHz, CDCl3) δ 140.1, 138.3, 138.1, 137.6, 128.5, 128.4, 128.3,
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Article
The amine was dissolved in EtOAc (8 mL). To this solution were
added Boc2O (0.42 mL, 1.83 mmol) and solid Na2CO3 (528 mg, 4.98
mmol), and the mixture was stirred for 3 h at room temperature. The
reaction mixture was then diluted with EtOAc (5 mL) followed by
addition of H2O (8 mL). It was then extracted with EtOAc (3 × 5 mL),
washed with brine (1 × 15 mL), and dried over Na2SO4. Evaporation of
solvent gave a residue, which on column chromatography afforded 708
mg (80%) of 27a as a colorless oil: Rf = 0.6 (hexane/EtOAc = 7:3); [α]D28
= +5.1 (c 2.15, CH2Cl2); IR (neat) νmax 3447, 2928, 2867, 1694, 1496,
Hz, 1H, minor rotamer), 4.02 (d, J = 4.0 Hz, 1H, major rotamer), 3.95
(dd, J = 2.7, 6.7 Hz, 1H, minor rotamer), 3.79 (br s, 1H, minor rotamer),
3.65−3.47 (m, 2H, major rotamer), 3.34−3.30 (m, 1H, minor rotamer),
1.41 (br s, 9H, major rotamer), 1.38 (s, 9H, minor rotamer); 13C NMR
(125 MHz, CDCl3) δ 154.5, 138.3, 138.0, 136.0, 135.3, 128.5−127.5 (m,
aromatic), 118.5, 117.9, 80.0, 79.9, 78.7, 78.0, 77.7, 73.2, 72.2, 71.7, 71.5,
69.5, 68.7, 62.6, 61.9, 61.7, 61.5, 53.5, 28.5, 28.4; HRMS calcd for
C33H40NO5 [M + H]+ 530.2901, found 530.2901.
(2S,3S,4R,5S)-tert-Butyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-
5-vinylpyrrolidine-1-carboxylate (28b). In a similar manner as
described above for 28a, compound 28b (535 mg, 70%) was obtained
from 27b (770 mg, 1.44 mmol) as a colorless oil: Rf = 0.7 (hexane/
EtOAc = 4:1); [α]D28 = +14.2 (c 0.85, CH2Cl2); IR (neat) νmax 3332,
2976, 2928, 2867, 1694, 1454, 1408, 1392, 1366, 1109 cm−1; 1H NMR
(500 MHz, CDCl3, 2.5:1 mixture of rotamers) δ 7.37−7.25 (m, 13H,
both rotamers), 7.20−7.18 (m, 2H, both rotamers), 6.15−6.07 (m, 1H,
both rotamers), 5.34−5.16 (m, 2H, both rotamers), 4.75−4.40 (m, 6H
major rotamer, 7H minor rotamer), 4.32 (t, J = 8.5 Hz, 1H, major
rotamer), 4.16−4.12 (m, 2H major rotamer, 1H, minor rotamer), 4.07
(d, J = 4.0 Hz, 1H, minor rotamer), 4.03 (d, J = 4.0 Hz, 1H, major
rotamer), 3.95 (dd, J = 2.5, 6.5 Hz, 1H, minor rotamer), 3.59 (dd, J = 2.5,
9.5 Hz, 1H, major rotamer), 3.54 (dd, J = 2.5, 9.5 Hz, 1H, minor
rotamer), 3.48 (dd, J = 6.5, 9.5 Hz, 1H, major rotamer), 3.32 (dd, J = 7.0,
9.5 Hz, 1H, minor rotamer), 1.42 (s, 9H, major rotamer), 1.39 (s, 9H,
minor rotamer); 13C NMR (125 MHz, CDCl3) δ 154.5, 153.5, 138.5,
138.3, 138.2, 138.0, 137.9, 136.0, 135.3, 128.5−127.5 (m, aromatic),
118.6, 118.0, 80.0, 79.9, 78.6, 77.9, 77.6, 73.3, 73.2, 72.1, 71.7, 71.6, 71.5,
69.5, 68.7, 62.6, 61.9, 61.7, 61.4, 28.5; HRMS calcd for C33H40NO5 [M +
H]+ 530.2901, found 530.2904.
General Procedure for the Aza-Michael Reaction and Wittig
Olefination Followed by Ring-Closing Metathesis to Obtain
Compounds 32a, 32b, 35a, and 35b. An amine 28a or 28b (600 mg,
1.13 mmol) was dissolved in dry CH2Cl2 (10 mL) and cooled to 0 °C,
CF3COOH (0.26 mL, 3.39 mmol) was added, and the mixture was
stirred with gradual warming to room temperature for 8 h. Once the
starting material was consumed (TLC monitoring), the solvent was
evaporated, and the crude amine used as such for the next reaction. The
crude amine was dissolved in THF (2 mL), crotonaldehyde (0.18 mL,
2.26 mmol) was added, and to this solution Zn (368 mg, 5.65 mmol)
and saturated NH4Cl solution (5 mL) were added, and the mixture was
stirred vigorously for 3 h. The reaction mixture was then diluted with
EtOAc (5 mL) and washed with water (1 × 10 mL). Extraction with
EtOAc (3 × 5 mL) and evaporation of the solvent gave crude aldehydes,
which were used without purification for the Wittig reaction.
To a stirred suspension of methyl triphenyl phosphonium bromide
(887 mg, 2.49 mmol) in dry THF (3 mL) under N2 at room temperature
was added KOtBu (390 mg, 3.40 mmol), and the mixture was stirred for
1 h. To the resulting bright yellow mixture was added the crude aldehyde
dissolved in dry THF (2 mL), and the mixture was stirred for 2 h. The
reaction mixture was poured into ice−water and extracted with EtOAc
(3 × 5 mL). Organic extracts were dried and concentrated. The crude
diene mixture was dissolved in dry toluene under N2 atmosphere, and to
this solution was added Grubbs’ second generation catalyst (58 mg,
0.067 mmol) and pTSA (440 mg, 2.26 mmol), and the mixture was
heated to 100−110 °C, for 10−12 h. The solvent was removed by
evaporation, and the residue purified by column chromatography.
(1R,2S,3S,5R,8aR)-1,2-Bis(benzyloxy)-3-(benzyloxymethyl)-5-
methyl-1,2,3,5,6,8a-hexahydroindolizine (32a). Yield 29% (148 mg),
colorless oil: Rf = 0.7 (hexane/EtOAc = 4:1); [α]2D8 = +23.3 (c 1.50,
CH2Cl2); IR (neat) νmax 2922, 1697, 1640, 1454, 1363, 1206, 1096
cm−1; 1H NMR (500 MHz, CDCl3) δ 7.34−7.25 (m, 15H), 5.97−5.90
(m, 1H), 5.81−5.73 (m, 1H), 4.71−4.63 (m, 2H), 4.57−4.50 (m, 2H),
4.42 (s, 2H), 4.06 (dt, J = 2.4, 6.7 Hz, 1H), 3.89 (dd, J = 2.4, 5.8 Hz, 1H),
3.51 (dd, J = 6.7, 9.8 Hz, 1H), 3.07 (dd, J = 5.5, 9.1 Hz, 1H), 2.77−2.71
(m, 1H), 2.25−2.12 (m, 3H), 1.68 (br s, 1H), 1.05−1.04 (m, 3H); 13C
NMR (125 MHz, CDCl3) δ 138.3, 138.1, 136.7, 135.7, 128.5, 128.3,
127.9, 127.8, 127.7, 127.6, 119.1, 115.5, 85.2, 82.5, 71.9, 71.6, 71.0, 57.5,
53.3, 32.3; HRMS calcd for C31H35NNaO3[M + Na]+ 492.2515, found
492.2516.
1
1454, 1394, 1365, 1106 cm−1; H NMR (500 MHz, CDCl3, 1.7:1
mixture of rotamers) δ 7.32−7.29 (m, 13H, both rotamers), 7.25−7.22
(m, 2H, both rotamers), 4.55−4.53 (m, 3H, both rotamers), 4.46−4.41
(m, 3H, both rotamers), 4.21 (br s, 1H, major rotamer), 4.11−3.97 (m,
2H, both rotamers), 3.90−3.86 (m, 2H major rotamer, 3H minor
rotamer), 3.75 (br s, 1H, major rotamer), 3.50−3.45 (m, 2H, both
rotamers), 3.02 (br s, 1H, minor rotamer), 1.47−1.40 (m, 9H, both
rotamers); 13C NMR (125 MHz, CDCl3) δ 155.8, 138.0, 137.7, 137.0,
128.6, 128.5, 128.4, 128.1, 128.0, 127.9, 127.6, 80.6, 80.3, 78.2, 78.0,
77.8, 77.5, 73.4, 71.9, 71.7, 68.6, 68.4, 64.4, 63.0, 61.8, 61.4, 28.4; HRMS
calcd for C32H40NO6 [M + H]+ 534.2850, found 534.2853.
(2S,3S,4R,5S)-tert-Butyl 3,4-bis(benzyloxy)-2-(benzyloxymethyl)-
5-(hydroxymethyl)pyrrolidine-1-carboxylate (27b). The same proce-
dure employed for the preparation of 27a from 24a was used for the
conversion of 24b (950 mg, mmol) to give 27b (785 mg, 81%) as a
colorless oil: Rf = 0.6 (hexane/EtOAc = 7:3); [α]2D8 = +27.5 (c 2.40,
CH2Cl2); IR (neat) νmax 3455, 2974, 2928, 2867, 1693, 1496, 1454,
1391, 1366, 1255, 1113, 1028 cm−1; 1H NMR (500 MHz, CDCl3, 1:1
mixture of rotamers) δ 7.34−7.25 (m, 13H, both rotamers), 7.23−7.21
(m, 2H, both rotamers), 4.74−4.66 (m, 1H, both rotamers), 4.55−4.48
(m, 5H, both rotamers), 4.45−4.40 (m, 2H, both rotamers), 4.28 (dd, J
= 4.5, 8.0 Hz, 1H, one rotamer), 4.25 (dd, J = 4.5, 8.5 Hz, 1H, one
rotamer), 4.16−4.09 (m, 3H, both rotamers), 4.05−3.97 (m, 2H, both
rotamers), 3.94 (dd, J = 2.5, 6.5 Hz, 1H, one rotamer), 3.88−3.85 (m,
1H, one rotamer), 3.82 (dd, J = 4.0, 9.5 Hz, 1H, one rotamer), 3.61 (dd, J
= 3.0, 10.0 Hz, 1H, one rotamer), 3.56−3.28 (m, 1H, both rotamers),
3.46−3.44 (m, 1H, one rotamer), 3.36 (dd, J = 7.0, 9.5 Hz, 1H, one
rotamer), 1.47 (s, 9H, one rotamer), 1.40 (s, 9H, one rotamer); 13C
NMR (125 MHz, CDCl3) δ 154.9, 154.2, 138.2, 137.8, 137.6, 137.5,
137.0, 128.5−127.5 (m, aromatic), 80.5, 80.3, 78.7, 77.2, 73.4, 72.3, 72.1,
71.9, 71.8, 69.3, 68.6, 61.8, 61.7, 60.9, 60.8, 59.5, 59.3, 28.5, 28.4; HRMS
calcd for C32H40NO6 [M + H]+ 534.2850, found 534.2856.
(2S,3S,4R,5R)-tert-Butyl-3,4-bis(benzyloxy)-2-(benzyloxymethyl)-
5-vinylpyrrolidine-1-carboxylate (28a). To a well-stirred, ice-cooled
suspension of CrO3 (210 mg, 2.10 mmol) in dry CH2Cl2 (5 mL), under
N2 atmosphere, was added Ac2O (0.40 mL, 4.19 mmol), and pyridine
(0.67 mL, 8.38 mmol). After stirring for 15 min, alcohol 27a (700 mg,
1.31 mmol) dissolved in dry CH2Cl2 (3 mL) was added at 0 °C, and the
mixture was stirred with gradual warming to room temperature over 1 h.
On completion of reaction (TLC monitoring), the reaction mixture was
quickly passed through a short silica gel column and washed down with
EtOAc (25 mL). Concentration of eluent gave crude aldehyde, which
was used as such without purification for the next step.
To a stirred suspension of methyl triphenylphosphonium bromide
(1.029 g, 2.88 mmol) in dry THF (3 mL) under N2 atmosphere, was
added potassium tert-butoxide (368 mg, 3.28 mmol), and the mixture
was stirred at room temperature for half an hour. The formation of ylide
was indicated by a bright yellow colored solution. Then the aldehyde
dissolved in dry THF (2 mL) was added dropwise to this mixture at 0
°C. Stirring was continued over 3 h, following which the contents were
poured into cold water (5 mL). The extraction was done using EtOAc (3
× 5 mL), and combined organic extracts were washed with brine (1 × 10
mL). Drying over Na2SO4 and concentration in vacuo gave a crude
residue, which was purified by column chromatography, to yield 515 mg
of 28a (74%, over 2 steps) as a colorless oil: Rf = 0.7 (hexane/EtOAc =
4:1); [α]2D8 = −1.3 (c 0.75, CH2Cl2); IR (neat) νmax 3331, 2976, 2929,
1
1692, 1453, 1391, 1105 cm−1; H NMR (500 MHz, CDCl3, 3.5:1
mixture of rotamers) δ 7.36−7.18 (m, 15H, both rotamers), 6.14−6.07
(m, 1H, major rotamer), 5.70 (br s, 1H, minor rotamer), 5.32−5.05 (m,
1H, both rotamers), 4.75−4.40 (7H, both rotamers), 4.31 (t, J = 8.5 Hz,
1H, major rotamer), 4.15−4.11 (m, 1H, both rotamers), 4.06 (d, J = 4.0
9392
dx.doi.org/10.1021/jo401613v | J. Org. Chem. 2013, 78, 9383−9395

The Journal of Organic Chemistry
Article
(1R,2S,3S,5S,8aR)-1,2-Bis(benzyloxy)-3-(benzyloxymethyl)-5-
methyl-1,2,3,5,6,8a-hexahydroindolizine (32b). Yield 23% (118 mg),
colorless oil: Rf = 0.7 (hexane/EtOAc = 4:1); [α]2D8 = +41.0 (c 2.20,
CH2Cl2); IR (neat) νmax 2922, 1695, 1638, 1496, 1454, 1363, 1206, 1096
cm−1; 1H NMR (500 MHz, CDCl3) δ 7.34−7.25 (m, 15H), 5.91−5.88
(m, 1H), 5.82−5.78 (m, 1H), 4.71−4.68 (m, 2H), 4.63−4.52 (m, 3H),
4.48 (s, 2H), 4.35 (dd, J = 2.4, 6.5 Hz, 1H), 4.26 (dd, J = 3.1, 8.2 Hz, 1H),
3.92 (br s, 1H), 3.50 (dd, J = 6.7, 9.8 Hz, 1H), 3.39 (d, J = 11.2 Hz, 1H),
3.14 (d, J = 11.2 Hz, 1H), 2.50 (dd, J = 5.5, 8.2 Hz, 1H), 2.25 (J = 5.5, 8.2
Hz, 1H), 1.15−1.14 (m, 3H); 13C NMR (125 MHz, CDCl3) δ 138.3,
138.2, 136.5, 135.8, 128.5, 128.3, 127.9, 127.8, 127.7, 127.6, 121.2 119.6,
82.3, 81.3, 71.9, 71.6, 71.0, 57.6, 53.5, 32.3; HRMS calcd for
C31H35NNaO3[M + Na]+ 492.2515, found 492.2512.
(1R,2S,3S,5S,8aS)-1,2-Bis(benzyloxy)-3-(benzyloxymethyl)-5-
methyl-1,2,3,5,6,8a-hexahydroindolizine (35a). Yield 28% (144 mg),
colorless oil: Rf = 0.7 (hexane/EtOAc = 4:1); [α]2D8 = −4.8 (c 1.40,
CH2Cl2); IR (neat) νmax 2922, 1695, 1638, 1496, 1454, 1363, 1206, 1096
cm−1; 1H NMR (500 MHz, CDCl3) δ 7.32−7.22 (m, 15H), 5.91−5.88
(m, 1H), 5.82−5.78 (m, 1H), 4.49−4.34 (m, 7H), 4.18−4.13 (m, 2H),
4.01−3.99 (m, 2H), 3.91−3.87 (m, 1H), 3.84 (dd, J = 4.0, 8.6 Hz, 1H),
3.39 (dd, J = 2.8, 10.3 Hz, 1H), 3.32−3.30 (m, 1H), 1.15−1.14 (m, 3H);
13C NMR (125 MHz, CDCl3) δ 138.8, 138.7, 136.4, 136.2, 128.6, 128.4,
3.74 (m, 2H), 3.49 (br s, 1H), 3.17 (br s, 1H), 2.02 (br s, 1H), 1.77−1.49
(m, 6H), 1.07−1.06 (m, 3H); 13C NMR (125 MHz, D2O) δ 77.9, 72.5,
63.9, 59.7, 57.0, 43.9, 29.6, 25.7, 22.5, 14.3; HRMS calcd for C10H20NO3
[M + H]+ 202.1443, found 202.1441.
(1R,2S,3S,5R,8aS)-3-(Hydroxymethyl)-5-methyloctahydroindoli-
zine-1,2-diol (36b). Following the same procedure for 33a, compound
36b was obtained from 35b (28 mg, 0.059 mmol), in 60% yield (7 mg),
as a colorless oil: Rf = 0.3 (EtOAc); [α]2D8 = −2.2 (c 0.40, CH3OH). IR
(neat) νmax 3351, 3064, 1229, 1101, 1027 cm−1; 1H NMR (500 MHz,
D2O) δ 4.20−4.19 (m, 2H), 4.02−3.85 (m, 3H), 3.41−3.37 (m, 1H),
2.69 (br s, 1H), 1.90−1.75 (m, 2H), 1.65−1.56 (m, 4H), 1.28−1.26 (m,
3H); 13C NMR (125 MHz, D2O) δ 76.9, 70.1, 62.6, 62.3, 56.5, 46.2,
28.3, 26.4, 23.2, 11.2; HRMS calcd for C10H20NO3 [M + H]+ 202.1443,
found 202.1440.
(1R,2S,3S,5R,8aR)-3-(Acetoxymethyl)-5-methyloctahydroindoli-
zine-1,2-diyl diacetate (34a). The triol 33a (20 mg, 0.061 mmol) was
stirred at room temperature in acetic anhydride−pyridine mixture (1:1,
2 mL) for 8 h, following which solvent was evaporated, and residue was
purified by column chromatography to afford 26 mg (80%) of acetate
34a as a pale yellow liquid: Rf = 0.4 (hexane/EtOAc = 3:1); [α]2D8 = +9.5
(c 0.20, CH2Cl2); IR (neat) νmax 3062, 3029, 2860, 1739, 1453, 1237,
1100, 1028 cm−1; 1H NMR (500 MHz, CDCl3) δ 5.46 (t, J = 6.6 Hz, 1H,
H-2), 5.37 (t, J = 6.6 Hz, 1H, H-1), 4.32 (t, J = 10.6 Hz, 1H, H-9), 4.12−
4.01 (m, 2H, H-3, H-9′), 3.38 (ddd, J = 2.8, 6.6, 13.7 Hz, 1H, H-5),
2.81−2.74 (m, 1H, H-8a), 2.11 (s, 3H, −OCOCH3), 2.07 (s, 3H,
−OCOCH3), 2.04 (s, 3H, −OCOCH3), 1.80−1.70 (m, 2H, H-6, H-6′),
1.61−1.58 (m, 1H, H-7), 1.46−1.41 (m, 1H, H-7′), 1.26−1.21 (m, 5H,
H-8, H-8′, −CH3); 13C NMR (125 MHz, CDCl3) δ 170.9, 170.7, 170.3,
75.2, 62.6, 60.1, 54.7, 45.1, 29.7, 28.3, 23.4, 21.2, 21.0, 20.8, 11.2; HRMS
calcd for C16H26NO6 [M + H]+ 328.1760, found 328.1763.
128.3, 128.1, 128.0, 127.8, 127.6, 127.4, 127.3, 126.6, 108.7, 85.6, 83.5,
74.8, 73.4, 69.3, 58.1, 51.9, 34.7; HRMS calcd for C31H35NNaO3[M +
Na]+ 492.2515, found 492.2511.
(1R,2S,3S,5R,8aS)-1,2-Bis(benzyloxy)-3-(benzyloxymethyl)-5-
methyl-1,2,3,5,6,8a-hexahydroindolizine (35b). Yield 20% (103 mg),
colorless oil: Rf = 0.7 (hexane/EtOAc = 4:1); [α]2D8 = −11.5 (c 0.90,
CH2Cl2); IR (neat) νmax 2925, 1698, 1640, 1495, 1453, 1361, 1208, 1095
cm−1; 1H NMR (500 MHz, CDCl3) δ 7.32−7.22 (m, 15H), 5.91−5.84
(m, 2H), 4.27−4.09 (m, 4H), 3.92−3.70 (m, 7H), 3.12 (dt, J = 2.1, 5.2
Hz, 1H), 3.06 (dd, J = 8.7, 14.3 Hz, 1H), 2.84−2.78 (m, 1H), 2.28−2.24
(m, 1H), 1.10−1.08 (m, 3H); 13C NMR (125 MHz, CDCl3) δ 138.2,
138.0, 136.5, 135.8, 128.5, 128.3, 127.9, 127.8, 127.7, 127.6, 115.5, 114.0,
84.2, 82.6, 71.9, 71.3, 57.5, 53.3, 32.9; HRMS calcd for
C31H35NNaO3[M + Na]+ 492.2515, found 492.2517.
(1R,2S,3S,5S,8aR)-3-(Acetoxymethyl)-5-methyloctahydroindoli-
zine-1,2-diyl diacetate (34b). Following the same procedure for 34a,
compound 34b was obtained from 33b (18 mg, 0.055 mmol), in 77%
yield (23 mg) as a colorless oil: Rf = 0.4 (hexane/EtOAc = 3:1); [α]D28
=
+2.2 (c 1.80, CH2Cl2); IR (neat) νmax 3065, 3039, 2858, 1740, 1238,
1100, 1029 cm−1; 1H NMR (500 MHz, CDCl3) δ 5.54 (dd, J = 8.0, 9.1
Hz, 1H, H-1), 5.25 (m, 1H, H-2), 5.14 (m, 1H, H-9), 4.25 (dd, J = 3.4,
12.0 Hz, 1H, H-9′), 3.76−3.74 (m, 1H, H-3), 3.36 (dd, J = 2.0, 9.1 Hz,
1H, H-5), 2.98 (ddd, J = 2.3, 8.0, 12.6 Hz, 1H, H-8a), 2.15 (s, 3H,
−OCOCH3), 2.10 (s, 3H, −OCOCH3), 2.07 (s, 3H, −OCOCH3),
1.76−1.72 (m, 1H, H-6), 1.59−1.48 (m, 3H, H-6′, H-7, H-7′), 1.38−
1.22 (m, 2H, H-8, H-8′), 1.09 (m, 3H, −CH3); 13C NMR (125 MHz,
CDCl3) δ 170.8, 170.7, 170.2, 76.0, 62.3, 61.7, 59.1, 55.5, 53.5, 38.6, 29.7,
21.3, 21.2, 21.0, 14.8; HRMS calcd for C16H26NO6 [M + H]+ 328.1760,
found 328.1758.
(1R,2S,3S,5R,8aR)-3-(Hydroxymethyl)-5-methyloctahydroindoli-
zine-1,2-diol (33a). Compound 32a (40 mg, 0.085 mmol) was
dissolved in dry CH3OH (2 mL), and Pd(OH)2/C (8 mg, 20% w/w)
was added. The mixture was stirred under 1 atm of H2 (balloon)
overnight, following which 1 N HCl (1 mL) was added, and
subsequently the mixture was stirred under 1 atm of H2 for 2 days.
The catalyst was filtered through a Celite bed and washed with MeOH.
The solvent was removed under a vacuum, and residue washed
repeatedly with hexane. The compound was purified by washing with
excess of 50% EtOAc/Hexane solution. The solvent was decanted, and
the residue left behind was dried under a vacuum to afford pure
compound 33a (12 mg, 70%) as a pale yellow liquid: Rf = 0.3 (EtOAc);
[α]2D8 = −2.2 (c 0.40, CH3OH). IR (neat) νmax 3349, 3062, 1237, 1100,
1028 cm−1; 1H NMR (500 MHz, D2O) δ 4.20−4.19 (m, 2H), 4.02−4.00
(m, 2H), 3.90 (dd, J = 8.5, 11.3 Hz, 1H), 3.46−3.44 (m, 1H), 2.62 (br s,
1H), 1.77 (br s, 2H), 1.65−1.56 (m, 4H), 1.28−1.26 (m, 3H); 13C NMR
(125 MHz, D2O) δ 77.1, 70.2, 62.6, 62.3, 56.5, 46.2, 28.3, 26.4, 23.2, 9.4;
HRMS calcd for C10H20NO3 [M + H]+ 202.1443, found 202.1437.
(1R,2S,3S,5S,8aR)-3-(Hydroxymethyl)-5-methyloctahydroindoli-
zine-1,2-diol (33b). Following the same procedure for 33a, compound
33b was obtained from 32b (32 mg, 0.068 mmol), in 64% yield (9 mg),
as a pale yellow liquid: Rf = 0.3 (EtOAc); [α]2D8 = −7.9 (c 0.20, CH3OH).
IR (neat) νmax 3353, 3060, 1420, 1232, 1101, 1029 cm−1; 1H NMR (500
MHz, D2O) δ 4.04 (br s, 1H), 3.65−3.64 (m, 2H), 3.58−3.56 (m, 2H),
3.41 (d, J = 13.7 Hz, 1H), 3.25−3.20 (m, 1H), 1.80−1.55 (m, 5H), 1.46
(br s, 1H), 1.25−1.23 (m, 3H); 13C NMR (125 MHz, D2O) δ 77.2, 70.7,
62.1, 60.6, 57.6, 47.5, 29.2, 26.1, 20.8, 10.2; HRMS calcd for C10H20NO3
[M + H]+ 202.1443, found 202.1437.
(1R,2S,3S,5S,8aS)-3-(Acetoxymethyl)-5-methyloctahydroindoli-
zine-1,2-diyl diacetate (37a). Following the same procedure for 34a,
compound 37a was obtained from 36a (25 mg, 0.076 mmol), in 75%
yield (30 mg) as a colorless oil: Rf = 0.4 (hexane/EtOAc = 3:1); [α]D28
=
+12.5 (c 1.00, CH2Cl2); IR (neat) νmax 3058, 3030, 1738, 1428, 1240,
1103, 1026 cm−1; 1H NMR (500 MHz, CDCl3) δ 5.46−5.43 (m, 1H, H-
1), 5.34 (t, J = 6.7 Hz, 1H, H-2), 4.90−4.89 (m, 1H, H-9), 4.77 (dd, J =
4.5, 11.9 Hz, 1H, H-9′), 3.69−3.66 (m, 1H, H-3), 3.32 (dd, J = 2.4, 8.2
Hz, 1H, H-8a), 2.83 (dd, J = 2.4, 12.8 Hz, 1H, H-5), 2.11 (s, 3H,
−OCOCH3), 2.09 (s, 3H, −OCOCH3), 2.02 (s, 3H, −OCOCH3),
1.75−1.62 (m, 2H, H-8, H-8′), 1.56−1.43 (m, 3H, H-7, H-7′, H-6),
1.28−1.26 (m, 1H, H-6′), 1.09 (m, 3H, −CH3); 13C NMR (125 MHz,
CDCl3) δ 170.6, 170.4, 170.0, 76.1, 62.0, 61.5, 59.9, 59.3, 49.9, 39.1, 29.7,
21.3, 21.2, 20.8, 14.8; HRMS calcd for C16H26NO6 [M + H]+ 328.1760,
found 328.1760.
(1R,2S,3S,5R,8aS)-3-(Acetoxymethyl)-5-methyloctahydroindoli-
zine-1,2-diyl diacetate (37b). Following the same procedure for 33a,
compound 37b was obtained from 36b (12 mg, 0.037 mmol), in 77%
yield (15 mg) as a colorless oil: Rf = 0.4 (hexane/EtOAc = 3:1); [α]D28
=
−32.8 (c 0.80, CH2Cl2); IR (neat) νmax 3059, 3028, 1742, 1430, 1236,
1103, 1026 cm−1; 1H NMR (500 MHz, CDCl3) δ 5.14 (dd, J = 6.7, 14.3
Hz, 1H, H-1), 5.00−4.99 (m, 2H, H-2, H-9), 4.95 (br s, 1H, H-9′), 4.18
(dd, J = 2.4, 8.2 Hz, 1H, H-3), 3.20 (d, J = 11.3 Hz, 1H, H-8a), 2.76 (dd, J
= 2.1, 6.7 Hz, 1H, H-5), 2.13 (s, 3H, −OCOCH3), 2.10 (s, 3H,
−OCOCH3), 2.04 (s, 3H, −OCOCH3), 1.72−1.65 (m, 2H, H-6, H-6′),
(1R,2S,3S,5S,8aS)-3-(Hydroxymethyl)-5-methyloctahydroindoli-
zine-1,2-diol (36a). Using the procedure employed to obtain 33a,
compound 36a was obtained from 35a (45 mg, 0.096 mmol), in 67%
yield (13 mg), as a pale yellow liquid: Rf = 0.3 (EtOAc); [α]2D8 = +3.1 (c
0.55, CH3OH). IR (neat) νmax 3353, 3060, 1420, 1232, 1101, 1029 cm−1;
1H NMR (500 MHz, D2O) δ 4.25−4.22 (m, 1H), 4.06 (br s, 1H), 3.77−
9393
dx.doi.org/10.1021/jo401613v | J. Org. Chem. 2013, 78, 9383−9395

The Journal of Organic Chemistry
Article
1.60−1.52 (m, 2H, H-7, H-7′), 1.44−1.40 (m, 1H, H-8), 1.27−1.21 (m,
1H, H-8′), 1.12 (m, 3H, −CH3); 13C NMR (125 MHz, CDCl3) δ 171.2,
170.6, 169.9, 71.1, 62.5, 60.7, 59.6, 58.5, 32.6, 21.2, 21.1, 20.9, 15.8;
HRMS calcd for C16H26NO6 [M + H]+ 328.1760, found 328.1761.
General Procedure for Enzyme Inhibition Assay. All the
enzymes and their corresponding substrates have been procured from
Sigma-Aldrich Chemical Co. The inhibition studies of compounds (19a,
19b, 25a, 25b, 33a, 33b, 36a, 36b) have been determined by measuring
residual hydrolytic activities of the glycosidases. The substrates and
enzymes were prepared as 0.025 M solutions in the respective pH buffer
solutions of the corresponding enzyme. In all cases, the substrates used
were the corresponding p-nitrophenyl glycopyranosides. The incuba-
tion mixture consisted of 100 μL of enzyme solution, 200 μL of 1 mg
mL−1 aqueous solution of the test compound, and 100 μL of the
appropriate buffer solution of the optimum pH for the enzyme. After
incubation at 37 °C for 1 h, 100 μL of the substrate solution was added
and allowed to react for 10 min. The reaction mixture was quenched
using 2.5 mL of 0.05 M borate buffer (pH = 9.8). In all cases, control
experiments were run simultaneously in the absence of test compound.
A series of blank experiments for the substrate were also carried out in
the respective buffer solutions without the enzyme or test compounds.
The absorbance of the liberated p-nitrophenol in each reaction (both
test and control reactions) was recorded using spectrophotometer at
405 nm. Percentage inhibition was calculated as the ratio of the
difference in the observed absorbances of the control and test reactions
to the observed absorbance of the control reaction. Results have thus
been reported as IC50 values, which is the concentration of the test
compound that causes 50% inhibition of the enzyme. The assays were
performed in triplicate, and the IC50 values have been reported as mean
standard deviation, in Table 1.
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ASSOCIATED CONTENT
■
S
* Supporting Information
Copies of 1H and 13C NMR spectra for all new compounds. This
material is available free of charge via the Internet at http://pubs.
acs.org.
(8) (a) Michalik, A.; Hollinshead, J.; Jones, L.; Fleet, G. W. J.; Yu, C.-Y.;
Hu, X.-G.; van Well, R.; Horne, G.; Wilson, F. X.; Kato, A.; Jenkinson, S.
F.; Nash, R. J. Phytochem. Lett. 2010, 3, 136−138. (b) Hu, X.-G.;
Bartholomew, B.; Nash, R. J.; Wilson, F. X.; Fleet, G. W. J.; Nakagawa, S.;
Kato, A.; Jia, Y.-M.; van Well, R.; Yu, C.-Y. Org. Lett. 2010, 12, 2562−
2565. (c) Greco, M.; De Mitri, M.; Chiriaco, F.; Leo, G.; Brienza, E.;
Maffia, M. Cancer Lett. 2009, 283, 222−229. (d) Jiangseubchatveera, N.;
Bouillon, M. E.; Liawruangrath, B.; Liawruangrath, S.; Nash, R. J.; Pyne,
S. G. Org. Biomol. Chem. 2013, 11, 3826−3833. (e) Chronowska, A.;
Gallienne, E.; Nicolas, C.; Kato, A.; Adachi, I.; Martin, O. R. Tetrahedron
Lett. 2011, 52, 6399−6402.
AUTHOR INFORMATION
Corresponding Author
*Fax: 0091-512-259 0007. E-mail: vankar@iitk.ac.in.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
(9) (a) Reddy, B. G.; Vankar, Y. D. Angew. Chem., Int. Ed. 2005, 44,
2001−2004. (b) Doddi, V. R.; Vankar, Y. D. Eur. J. Org. Chem. 2008,
5583−5589. (c) Doddi, V. R.; Kokatla, H. P.; Pal, A. P. J.; Basak, R. K.;
Vankar, Y. D. Eur. J. Org. Chem. 2008, 5731−5739. (d) Kumari, N.;
Vankar, Y. D. Org. Biomol. Chem. 2009, 7, 2104−2109. (e) Pal, A. P. J.;
Gupta, P.; Reddy, Y. S.; Vankar, Y. D. Eur. J. Org. Chem. 2010, 6957−
6966. (f) Reddy, Y. S.; Kancharla, P. K.; Roy, R.; Vankar, Y. D. Org.
Biomol. Chem. 2012, 10, 2760−2773 and references cited therein.
(10) (a) Ramesh, N. G.; Balasubramaniam, K. K. Eur. J. Org. Chem.
2003, 4477−4487. (b) Rawal, G. K.; Rani, S.; Kumari, N. J. Org. Chem.
2009, 74, 5349−5355. (c) Gupta, P.; Vankar, Y. D. Eur. J. Org. Chem.
2009, 1925−1933. (d) Reddy, Y. S.; Kancharla, P. K.; Roy, R.; Vankar, Y.
D. Org. Biomol. Chem. 2012, 10, 2760−2773. (e) Sagar, R.; Park, J.; Koh,
M.; Park, S. B. J. Org. Chem. 2009, 74, 2171−2174. (f) Bharate, S. B.;
Mahajan, T. R.; Gole, Y. R.; Nambiar, M.; Matan, T. T.; Kulkarni-
Almeida, A.; Balachandran, S.; Junjappa, H.; Balakrishnan, A.;
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We thank the Department of Science and Technology, New
Delhi, for a J. C. Bose National Fellowship (JCB/SR/S2/JCB-
26/2010) to Y.D.V. We also thank the Council of Scientific and
Industrial Research (CSIR), New Delhi for financial support
[Grant No. 02(0124)/13/EMR-II)]. A.A.A. thanks the CSIR,
New Delhi, for a Senior Research Fellowship.
DEDICATION
■
Dedicated to Professor M. Periasamy on the occasion of his 60th
birthday.
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