A glycal based approach to the synthesis of (+)-bulgecinine, 3-hydroxy-2,5-dihydroxymethylpyrrolidine and 2-oxapyrrolizidin-3-one

Article abstract of DOI:10.1016/j.carres.2020.107931

A glycal based synthesis of (+)-bulgecinine, 3-hydroxy-2,5-dihydroxymethylpyrrolidine and 2-oxapyrrolizidin-3-ones proceeding through a common intermediate is reported. The key step in the work presented here is a two-step conversion of 4,6-di-O-benzyl-D-glucal to 2,3-dideoxy-2-tosylamido-D-glucose. This manuscript reports the first carbohydrate based approach to the synthesis of (+)-bulgecinine and the whole sequence has been accomplished with complete stereochemical integrity without the formation of mixture of products in any of these steps.

Full text of DOI:10.1016/j.carres.2020.107931

Carbohydrate Research 489 (2020) 107931
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Carbohydrate Research
journal homepage: www.elsevier.com/locate/carres
A glycal based approach to the synthesis of (+)-bulgecinine, 3-hydroxy-2,5-
dihydroxymethylpyrrolidine and 2-oxapyrrolizidin-3-one
∗
Umesh K. Mishra, Namakkal G. Ramesh
Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016, India
A R T I C L E I N F O
A B S T R A C T
Keywords:
A glycal based synthesis of (+)-bulgecinine, 3-hydroxy-2,5-dihydroxymethylpyrrolidine and 2-oxapyrrolizidin-
3-ones proceeding through a common intermediate is reported. The key step in the work presented here is a two-
step conversion of 4,6-di-O-benzyl-D-glucal to 2,3-dideoxy-2-tosylamido-D-glucose. This manuscript reports the
first carbohydrate based approach to the synthesis of (+)-bulgecinine and the whole sequence has been ac-
complished with complete stereochemical integrity without the formation of mixture of products in any of these
steps.
Bulgecinine
Glycal
Glycosidase inhibitors
Natural product
Pyrrolizidine
1
. Introduction
−)-Bulgecinine 1, a non-proteinogenic amino acid, is a common
reported to be potential glycosidase inhibitors by Lin and Chang [15].
(
2. Results and discussion
constituent of naturally occurring glycopeptides bulgecins 2 (A, B and
C), isolated from Pseudomonas mesoacidophila and Pseudomonas acid-
ophila [1] (Fig. 1). Although bulgecins do not possess any antibacterial
activity by themselves, they show co-operative effect along with β-
lactam antibiotics by inducing the characteristic morphological changes
through formation of a bulge in the cell wall of gram-negative bacteria.
These morphological changes effectively enhance the antibiotic activity
of β-lactam [2], resulting in an improved inhibition of bacterial growth
even at low concentration of the drug. (−)-Bulgecinine 1, a trisub-
stituted pyrrolidine, is the core constituent of bulgecin 2. (−)-Bulge-
The retrosynthetic analysis of our proposed synthesis of (+)-bul-
gecinine 3, 2-oxapyrrolizidin-3-one 11 and 12, as well as 3-hydroxy-
2,5-dihydroxymethylpyrrolidine 13 is depicted in Scheme 1. All three
of them could be synthesized from the common intermediate 7. Desi-
lylation of 7 followed by oxidation of the resulting primary hydroxyl
group, esterification to 6, stereoselective inversion at C-4 carbon after
appropriate synthetic manipulations and subsequent deprotection
would lead to the formation of (+)-bulgecinine 3. Treatment of com-
pound 10 with 1,1′-carbonydiimidazole followed by deprotection
would yield a new stereoisomer of 2-oxapyrrolizidin-3-one 11. Inver-
sion of stereochemistry at C-7 carbon of 11 and further deprotection
would provide another stereoisomer of 2-oxapyrrolizidin-3-one 12. On
the other hand, N-detosylation followed by deprotection would give 3-
hydroxy-2,5-dihydromethylpyrrolidine 13 (Scheme 1).
cinine
1 is chemically and crystallographically characterized as
(
4S,5R)-3-hydroxy-5-hydroxymethyl-L-proline [3] (Fig. 1). As a con-
sequence of structural novelty, total synthesis of various stereoisomers
of both bulgecins 2 [4–7] and (−)-bulgecinine 1 [8] have become the
topic of great interest among organic chemists. In this context, synth-
eses of (+)-bulgecinine 3, the enantiomer of 1, have also gained sig-
nificant attention [9–14]. Surprisingly, strategies utilizing naturally
occurring carbohydrates, that are endowed with inherent chiral centers
and functional groups congruent to (+)-bulgecinine, are missing.
This void has paved a way for us to conceive and successfully accom-
plish a glycal based strategy to (+)-bulgecinine that proceeds with
complete stereochemical integrity. In the course, our route also
allowed us to accomplish the synthesis of hitherto unreported stereo-
isomers 2-oxapyrrolizidin-3-ones 11, 12 and 3-hydroxy-2,5-dihydrox-
ymethylpyrrolidine 13, whose other stereoisomers 4 and 5 were
2.1. Synthesis of common intermediate 7
In order to synthesize (+)-bulgecinine 3, which does not contain
any substituent at C-3 position of the pyrrolidine ring, it was thought
that 4,6-di-O-benzyl-D-glucal 9 [16] would be the most ideal substrate.
The success of our approach to (+)-bulgecinine 3 mainly relied on the
conversion of 4,6-di-O-benzyl-D-glucal 9 to 2,3-dideoxy-2-tosylamido-D-
glucose 8, through an initial iodo-sulfonamidation on 9 to 14 followed
by 1,2-transposition of the amino group. Even though this two-step
∗
Corresponding author.
E-mail address: ramesh@chemistry.iitd.ac.in (N.G. Ramesh).
https://doi.org/10.1016/j.carres.2020.107931
Received 6 January 2020; Received in revised form 29 January 2020; Accepted 29 January 2020
Available online 31 January 2020
0008-6215/ © 2020 Elsevier Ltd. All rights reserved.

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
by refluxing it with sodium hydroxide in methanol and water to give
the diol 23 (the N-tosyl analogue of (+)-bulgecinine) in 86% yield. The
structure of compound 23 was also characterized through single crystal
X-ray analysis (Fig. 2), that unambiguously confirmed the stereo-
chemical inversion at C-4 position. N-Tosyl (+)-bulgecinine 23 was
finally subjected to Birch type reduction (sodium in liquid ammonia) to
get the (+)-bulgecinine 3 in 78% yield. The spectral data of (+)-bul-
gecinine 3 were found to be in consistent with the literature reported
values [15] (Scheme 3).
2
.3. Synthesis of 2-oxapyrrolizidin-3-ones and 3-hydroxy-2,5-
Fig. 1. Structures of (+) and (−)-bulgecinine, bulgecins and structurally re-
dihydroxymethylpyrrolidine
lated iminosugars.
Towards the synthesis of 2-oxapyrrolizidin-3-one 12 and 3-hydroxy-
2
,5-dihydroxymethylpyrrolidine 13, compound 7 was N-detosylated
reaction sequence was well-explored in our group on tri-O-benzyl-D-
glucal [17], the same has never been tested on 4,6-di-O-benzyl-D-glucal
with sodium amalgam in DMF and MeOH to get free amine 10 in 75%
yield. During this process, it was observed that the silyl group also got
cleaved. Compound 10 was then treated with 1,1′-carbonyldiimidazole
in dichloromethane to get bicyclic compound 24 in 89% yield. Further,
debenzylation of compound 24 through hydrogenolysis in presence of a
catalytic amount of 10% Pd/C delivered a new stereoisomer of 2-ox-
apyrrolizidine-3-one 11 in 88% yield. On the other hand, synthesis of 3-
hydroxy-2,5-dihydroxymethylpyrrolidine 13, was achieved by exposing
9
. With this background, we attempted to perform the iodosulfonami-
dation reaction of 9 with p-toluenesulfonamide in presence of N-iodo-
succinimide (NIS) at −20 °C. The reaction proceeded to completion in
1
2
h (vide TLC), affording a yellowish liquid 14. Analysis of the H NMR
spectrum indicated the formation of the expected iodo-sulfonamidated
product 14. Without any purification, the crude reaction mixture was
taken forward for the next step. Exposure of the iodo adduct 14 to
triethylamine in THF and water (4:1) afforded 4,6-di-O-benzyl-2-deoxy-
1
0 to BCl in dichloromethane. The debenzylation reaction proceeded
3
smoothly to afford 13 in 75% yield (Scheme 4).
2
-(p-toluenesulfonamido)-α-D-gluco pyranose 8, in 42% yield over two
In order to invert the stereochemistry at C-7 position of 2-ox-
apyrrolizidin-3-one 11, with a view of obtaining another stereoisomer,
chemoselective protection of primary hydroxyl group of 11 was carried
out with tert-butyldimethylsilyl chloride and imidazole to get the silyl
ether 25 in 85% yield. Inversion of stereochemistry of the secondary
hydroxyl group of 25 was carried out as before under Mitsunobu con-
steps, as a colorless solid, that could be readily crystallized from the
reaction mixture without the need for any purification by column
chromatography. Compound 8 was thoroughly characterized by various
spectroscopic and analytical techniques. The stereochemistry at the
anomeric carbon of 8 was deduced as α from the coupling constant
1
value of H-1 in its H NMR spectrum, which resonated at δ 4.77 as a
1
9
dition with para-nitrobenzoic acid in presence of DIAD and PPh to
3
triplet with J = 3.6 Hz due to its coupling with H-2 and –OH protons.
The smaller J value between H-1 and H-2 thus confirmed the α-ste-
reochemistry. Next, reductive ring opening of hemiacetal 8 was carried
get para-nitrobenzoyl derivative 26 in 88% yield. Subsequent hydro-
lysis of para-nitrobenzoyl group with sodium carbonate in MeOH gave
compound 27, which when exposed to catalytic amount of cam-
phorsulphonic acid in methanol delivered another stereoisomer of 2-
oxapyrrolizidin-3-one 12 in 88% yield (Scheme 5).
out by refluxing it with LiAlH in THF to get diol 15 in 83% yield.
4
Chemoselective protection of the primary hydroxyl group of diol 15 as
its silyl ether 16 (88% yield) was then smoothly accomplished by ex-
posing it to imidazole and TBSCl in dichloromethane. Intramolecular
Mitsunobu [17,18] cyclization reaction of compound 16 in presence of
3
. Conclusion
PPh and DEAD successfully delivered the protected pyrrolidine 7, the
3
In conclusion, we have reported an efficient synthesis of (+)-bul-
key intermediate in our approach to all the three targets (Scheme 2).
gecinine starting from 4,6-di-O-benzyl-D-glucal through the inter-
mediacy of 2,3-dideoxy-2-tosylamido-D-glucose. The orthogonally pro-
tected polyhydroxypyrrolidine 10 allowed for diversification leading to
the synthesis of three different class of compounds namely, (+)-bul-
gecinine 3, 3-hydroxy-2,5-dihydroxymethylpyrrolidine 13 and 2-ox-
apyrrolizidin-3-one 11 and 12. We believe that this strategy would find
applications in the synthesis of other structurally related natural pro-
ducts as well as unnatural cyclic amino acids and alcohols. Research in
this direction is currently under progress.
2.2. Synthesis of (+)-Bulgecinine 3
In our efforts towards the synthesis of (+)-bulgecinine 3, desiliy-
lation of 7 was carried out with a catalytic amount of camphorsulfonic
acid (CSA) in methanol to get the alcohol 17 in 91% yield. Oxidation of
the hydroxyl group of 17 to carboxylic acid 18 (90% yield) was then
accomplished with Jones reagent. In order to realize the synthesis of
(
+)-bulgecinine 3, it was necessary to selectively invert the stereo-
chemistry at C-4 of compound 18. Towards this end, acid 18 was
converted into its ethyl ester 6 in 85% yield using thionyl chloride and
ethanol. Catalytic hydrogenolysis of 6 in presence of 10% Pd/C resulted
in the cleavage of the benzyl groups to give the diol 19 in 97% yield.
Chemoselective silylation of the primary hydroxyl group of 19 with tert-
butyldimethylsilyl chloride in presence of imidazole in di-
chloromethane afforded the silyl ether 20 in 92% yield. The stereo-
chemistry of secondary hydroxyl group at C-4 position of compound 20
was then inverted through Mitsunobu [19] reaction using para-ni-
trobenzoic acid (PNAB) in presence of diisopropyl azodicarboxylate
4. Experimental
4.1. (4,6)-di-O-benzyl-2,3-dideoxy-2-(p-toluenesulfonamido)-α-D-
glucopyranose (8)
4,6-Di-O-benzyl-D-glucal 9 (2.50 g, 8.05 mmol), was dissolved in dry
dichloromethane (30 mL) and cooled to −20 °C. N-Iodosuccinimide
(1.99 g, 8.86 mmol) and p-toluenesulfonamide (1.51 g, 8.86 mmol)
were added successively. The reaction mixture was stirred for 2 h under
argon atmosphere. On completion, the reaction mixture was quenched
with a saturated solution of sodium thiosulfate (150 mL) and extracted
with dichloromethane (3 × 50 mL). The combined organic layer was
washed with brine (100 mL) and dried over anhydrous sodium sulfate.
The solvent was evaporated under vacuum to give a brown colour li-
quid which was passed over a filter column to remove unreacted p-
(
DIAD) and PPh . The expected p-nitrobenzoyl derivative 21, with in-
3
version of stereochemistry, was obtained in 80% yield. Exposure of
compound 21 to a catalytic amount of CSA in methanol delivered the
alcohol 22 in 80% yield. In the next step, both the p-nitrobenzoyl group
as well as the ethyl ester of 22 were hydrolyzed through saponification
2

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
Scheme 1. Retrosynthetic analysis of (+)-bulgecinine, 3-hydroxy-2,5-dihydroxymethylpyrrolidine and 2-oxapyrrolizidin-3-ones.
4
.89 (d, 1H exchangeable with D
J = 3.6 Hz), 4.56–4.45 (m, 3H), 4.32 (d, 1H, J = 10.8 Hz), 3.89–3.86
m, 1H), 3.64–3.56 (m, 2H), 3.45–3.39 (m, 2H), 2.91 (d, 1H ex-
2
O, J = 10.0 Hz), 4.77 (t, 1H,
(
changeable with D
2
O, J = 3.2 Hz), 2.42 (s, 3H), 2.19 (dt, 1H, J = 12.0,
1
3
4
.4 Hz), 1.68 (q, 1H, J = 12.0 Hz) ppm; C NMR (75 MHz, CDCl
3
): δ
1
43.7 (s), 138.2 (s), 137.89 (s), 137.83 (s), 129.9 (d), 128.5 (d), 128.1
(
d), 127.9 (d), 127.8 (d), 127.0 (d), 90.1 (d), 73.6 (t), 72.0 (d), 70.9 (t),
7
0.3 (d), 69.2 (t), 51.2 (d), 31.0 (t), 21.6 (q) ppm; HRMS [ESI] m/z
calcd for C27
H
31NO
6
SK [M+K]+ 536.1504 found 536.1497.
4.2. 4,6-Di-O-benzyl-2,3-dideoxy-2-(p-toluenesulfonamido)-D-glucitol (15)
Scheme 2. Synthesis of key intermediate 7 from 9.
Hemiacetal 8 (1.20 g, 2.41 mmol) was taken in a round bottomed
flask and dissolved with dry THF (20 mL). To this, LiAlH (0.14 g,
4
3
.62 mmol) was added and the reaction mixture was refluxed for 8 h.
The reaction mixture was then quenched with 2 M HCl (100 mL) and
extracted with ethyl acetate (2 × 100 mL). The combined organic layer
was dried over anhydrous sodium sulfate, filtered and concentrated.
The residue was purified by flash chromatography using a mixture of
ethyl acetate and hexane (1:3) to give compound 15 (1.00 g, 83%) as a
2
8
colourless liquid. R
f
: 0.25 (ethyl acetate/hexane, 4:6); [ ] +6.47 (c
D
0
1
.51, CHCl ); IR (KBr); ῡ 3467, 3064, 3033, 2924, 1600, 1495, 1453,
−1 1
3
325, 1157, 1092, 815, 742, 700, 668 cm
): δ 7.71 (d, 2H, J = 8.0 Hz), 7.33–7.20 (m, 12H), 5.55 (br s, 1H
O), 4.49–4.38 (m, 4H), 3.75 (d, 1H, J = 3.6 Hz),
.58–3.41 (m, 6H), 2.74 (br s, 2H exchangeable with D O), 2.37 (s, 3H),
): δ 143.4 (s), 137.7
; H NMR (300 MHz,
CDCl
3
exchangeable with D
2
3
1
2
1
3
.78 (m, 2H) ppm; C NMR (75 MHz, CDCl
3
(
2 × s), 137.6 (s), 129.8 (d), 128.6 (2 × d), 128.0 (d), 128.0 (2 × d),
1
27.2 (d), 76.4 (d), 73.5 (t), 71.68 (d), 71.63 (t), 70.9 (t), 64.4 (t), 52.9
(
d), 32.5 (t), 21.6 (q) ppm; HRMS [ESI] m/z calcd for C27
H
33NNaO S
6
[
M+Na]+ 522.1921 found 522.1924.
Fig. 2. ORTEP diagram of compound N-tosyl (+)-bulgecinine 23.
4
.3. 1-O-(tert-butyldimethylsilyl)-4,6-di-O-benzyl-2,3-dideoxy-2-(p-
toluenesulfonamido)-D-glucitol (16)
toluenesulfonamide using a solvent mixture of ethyl acetate and hexane
(
15:85) to afford a pale yellow liquid 14 (3.37 g, 69% yield) that was
Compound 15 (1.30 g, 2.60 mmol) was dissolved in dry di-
chloromethane (15 mL). Imidazole (0.71 g, 10.41 mmol) and tert-bu-
tyldimethylsilyl chloride (0.47 g, 3.12 mmol) were added successively
and the reaction mixture was stirred at 33 °C for 3 h. After completion,
the reaction mixture was diluted with water (100 mL) and extracted
with dichloromethane (3 × 50 mL). The combined organic layer was
washed with brine (50 mL). Organic layer was dried over anhydrous
sodium sulfate and concentrated under reduced pressure. The residue
was purified by flash chromatography (ethyl acetate/hexane, 15:85) to
taken further for the next step without characterization. Pale yellow
liquid (3.37 g, 5.60 mmol) was dissolved in a 40 mL mixture of THF and
water (4:1) and triethyl amine (1.56 mL, 11.19 mmol) was added. The
reaction mixture was stirred at 20 °C for 4 h. Water (100 mL) was added
to the reaction mixture and it was extracted with ethyl acetate
(
2 × 100 mL). The combined organic layer was washed with brine and
solvent was evaporated to get an yellowish solid material which was
recrystallized using a mixture of ethyl acetate and hexane (3:2) to get
the product 8 as a colourless solid 1.79 g (42% yield over two-steps).
give compound 16 (1.40 g, 88%) as a colourless liquid. R : 0.45 (ethyl
f
2
8
mp 145–148 °C; R
f
: 0.38 (ethyl acetate/hexane, 4:6); [ ] +42.1 (c
28
D
acetate/hexane, 3:7); [ ] +11.16 (c 0.43, CHCl ); IR (KBr); ῡ 3506,
D
3
0
1
.70, THF); IR (KBr); ῡ 3300, 3031, 2935, 2862, 1435, 1320, 1155,
−1 1
3
1
285, 3063, 2951, 2930, 2859, 1599, 1495, 1456, 1411, 1332, 1255,
092, 1052, 896, 817, 742, 699, 664 cm ; H NMR (300 MHz, CDCl
3
):
−1 1
210, 1160, 1092, 1027, 838, 780, 741, 699, 668 cm
; H NMR
δ 7.74 (d, 2H, J = 8.0 Hz), 7.33–7.26 (m, 10H), 7.18–7.16 (m, 2H),
(
300 MHz, CDCl
3
): δ 7.77 (d, 2H, J = 8.0 Hz), 7.43–7.33 (m, 8H),
3

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
Scheme 3. Synthesis of (+)-bulgecinine 3.
7
4
1
.31–7.28 (m, 4H), 5.17 (d, 1H exchangeable with D
2
O, J = 6.4 Hz),
J = 12.0 Hz), 4.14 (d, 1H, J = 12.0 Hz), 4.02–4.00 (m, 1H), 3.92–3.89
(m, 1H), 3.81–3.72 (m, 3H), 3.66 (d, 1H, J = 10.0 Hz), 2.38–2.25 (m,
4H), 2.15 (dd, 1H, J = 11.6, 6.8 Hz), 0.83 (s, 9H), 0.00 (s, 3H), −0.01
.61–4.50 (m, 4H), 3.86–3.83 (m, 1H), 3.63–3.49 (m, 4H), 3.44 (dd,
H, J = 10.0, 3.6 Hz), 3.34 (dd, 1H, J = 10.0, 4.8 Hz), 2.58 (br s, 1H
1
3
exchangeable with D
2
O), 2.45 (s, 3H), 1.93–1.80 (m, 2H), 0.88 (s, 9H),
(s, 3H) ppm; C NMR (75 MHz, CDCl ): δ 142.75 (s), 138.79 (s), 138.5
3
1
3
0
.00 (s, 3H), −0.01 (s, 3H) ppm; C NMR (75 MHz, CDCl
3
): δ 143.2
(s), 138.1 (s), 129.31 (d), 128.37 (d), 128.0 (d), 127.6 (d), 127.3 (d),
127.1 (d), 127.03 (d), 127.00 (d), 76.5 (d), 72.7 (t), 72.1 (t), 67.0 (t),
65.0 (t), 61.1 (d), 59.6 (d), 33.6 (t), 25.9 (q), 21.3 (q), 18.2 (s), −5.3
(
(
(
(
s), 138.1 (s), 137.9 (2 × s), 129.6 (d), 128.47 (d), 128.43 (d), 127.9
d), 127.84 (d), 127.82 (d), 127.7 (d), 127.1 (d), 76.2 (d), 73.4 (t), 71.8
d), 71.4 (t), 71.0 (t), 64.1 (t), 52.4 (d), 32.5 (t), 25.8 (q), 21.5 (q), 18.2
(q), −5.4 (q) ppm; HRMS [ESI] m/z calcd for C33
H
45NO SSiNa [M
5
+
s), −5.51 (q), −5.54 (q) ppm; HRMS [ESI] m/z calcd for
+Na] 618.2680 found 618.2680.
+
C
33
H
47NNaO
6
SSi [M+Na] 636.2785 found 636.2798.
4
.5. (2S,3S,5R)-3-(Benzyloxy)-2-(benzyloxymethyl)-5-(hydroxymethyl)-
4
.4. (2S,3S,5R)-3-(Benzyloxy)-2-(benzyloxymethyl)-5-(tert-
1-N-(p-toluenesulfonyl)pyrrolidine (17)
butyldimethylsilyloxymethyl)-1-N-(p-toluenesulfonyl)pyrrolidine (7)
Compound 16 (0.300 g, 0.49 mmol) was dissolved in dry THF
Compound 7 (0.200 g, 0.336 mmol) was dissolved in MeOH (3 mL)
and camphorsulfonic acid (0.020 g, 10% w/w) was added to it. The
reaction mixture was then stirred at 30 °C for 2 h, after which the
solvent was evaporated under vacuum and the resulting residue was
dissolved in ethyl acetate (50 mL). It was then washed with saturated
solution of sodium bicarbonate (50 mL). The organic layer was dried
over anhydrous sodium sulfate, filtered and concentrated under va-
cuum. The crude product was purified by column chromatography over
silica gel using a mixture of ethyl acetate and hexane (2:8) to give 17
(
(
3 mL). Diethyl-azodicarboxylate (0.12 mL, 0.73 mmol) and PPh
3
0.19 g, 0.73 mmol) were added successively to it. The reaction mixture
was then stirred at 30 °C under nitrogen atmosphere for 4 h, after which
it was diluted with water (100 mL) and extracted with ethyl acetate
(
3 × 50 mL). The combined organic layer was washed with water,
dried over anhydrous sodium sulfate, filtered and concentrated under
vacuum. The resulting residue was purified by flash column chroma-
tography using mixture of ethyl acetate and hexane (5:95) to give
(0.147 g, 91%) as a colourless liquid. R
f
: 0.25 (ethyl acetate/hexane,
); IR (KBr); ῡ 3213, 3064, 3032, 2944,
2873, 1599, 1496, 1452, 1404, 1334, 1158, 1127, 1088, 1010, 811,
2
8
compound 7 (0.262 g, 90%) as a colourless liquid. R
f
: 0.78 (ethyl
3:7); [ ]
D
‒20.5 (c 1.14, CHCl
3
2
8
acetate/hexane, 2:8); [ ] +2.3 (c 2.00, CHCl
3
); IR (KBr); ῡ 3063,
D
−1 1
3
1
032, 2956, 2928, 2857, 1600, 1496, 1456, 1342, 1255, 1159, 1111,
734, 684 cm ; H NMR (400 MHz, CDCl ): δ 7.73 (d, 2H, J = 7.2 Hz),
3
−
1 1
041, 838, 795, 777, 736, 698, 665 cm ; H NMR (400 MHz, CDCl
3
):
7.29–7.18 (m, 8H), 7.13 (d, 2H, J = 8.4 Hz), 7.03–7.01 (m, 2H), 4.48
(s, 2H), 4.31–4.27 (m, 1H), 4.23–4.20 (m, 2H), 4.11 (d, 1H,
J = 12.0 Hz), 3.91 (dd, 1H, J = 12.0, 4.0 Hz), 3.84–3.77 (m, 2H), 3.68
δ 7.70 (d, 2H, J = 8.0 Hz), 7.30–7.19 (m, 8H), 7.13 (d, 2H, J = 8.4 Hz),
7
.09–7.07 (m, 2H), 4.53–4.46 (m, 2H), 4.33–4.28 (m, 1H), 4.22 (d, 1H,
Scheme 4. Synthesis of 3-hydroxy-2,5-dihydroxymethylpyrrolidine 13 and 2-oxapyrrolizidin-3-one 11.
4

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
Scheme 5. Synthesis of 2-oxapyrrolizidin-3-one 12.
(
d, 1H, J = 10.0 Hz), 3.63–3.60 (m, 1H), 2.90 (br s, 1H exchangeable
CDCl ): δ 173.1 (s), 143.4 (s), 138.3 (s), 137.8 (s), 137.7 (s), 129.4 (d),
3
with D O), 2.37 (q, 1H, J = 10.4 Hz), 2.25 (s, 3H), 2.14–2.09 (m, 1H)
2
128.5 (d), 128.2 (d), 127.9 (d), 127.5 (d), 127.4 (d), 127.3 (d), 127.1
1
3
ppm; C NMR (75 MHz, CDCl
3
): δ 143.1 (s), 138.1 (s), 137.9 (s), 137.0
(d), 76.7 (d), 72.9 (t), 72.6 (t), 66.8 (t), 61.5 (t), 59.7 (d), 59.1 (d), 35.2
(
s), 129.3 (d), 128.2 (d), 127.9 (d), 127.5 (d), 127.3 (d), 127.1 (d),
(t), 21.6 (q), 14.1 (q); HRMS [ESI] m/z calcd for C29
H
33NO SNa [M
6
+
1
27.0 (d), 126.7 (d), 76.3 (d), 72.6 (t), 72.0 (t), 66.6 (t), 65.1 (t), 61.6
+Na] 546.1921 found 546.1918.
(
d), 59.8 (d), 35.0 (t), 21.3 (q) ppm; HRMS [ESI] m/z calcd for
C
27
H
31NO
5
SNa [M+Na]+ 504.1815 found 504.1826.
4
.8. (2R,4S,5S)-ethyl-4-(hydroxy)-5-(hydroxymethyl)-1-N-(p-
toluenesulfonyl)pyrrolidine-2-carboxylate (19)
4
.6. (2R,4S,5S)-4-(Benzyloxy)-5-(benzyloxymethyl)-1-N-(p-
toluenesulfonyl)pyrrolidine-2-carboxylic acid (18)
In a three necked round bottomed flask (50 mL), compound 6
(
0.24 g, 0.46 mmol) was taken and dissolved with MeOH (20 mL). 10%
A solution of 17 (2.00 g, 4.15 mmol) in 20 mL of acetone was placed
in a 50 mL round-bottomed flask and cooled to 0 °C (ice-water bath). A
solution containing of 8 mL of 8 N Jones reagent was added over a
period of 10 min and it was stirred at 0 °C for 2 h. Isopropyl alcohol was
then added dropwise to destroy the excess Jones reagent present. The
reaction mixture was then extracted with ethyl acetate (2 × 50 mL),
and washed with water (100 mL). The organic layer was dried over
anhydrous sodium sulfate and concentrated. The crude material was
purified by column chromatography over silica gel using a mixture of
ethyl acetate and hexane (4:6) to give 18 (1.85 g, 90%) as a colourless
Pd/C (48 mg, 20% w/w) was added and hydrogen gas was continuously
purged for 6 h at 20 °C. The reaction mixture was then filtered through
a sintered funnel and the filtrate was concentrated under vacuum. The
resulting was residue purified by column chromatography over silica
gel using a mixture of ethyl acetate and hexane (3:7) to get 19 (0.154 g,
9
7%) as a colourless liquid. R
f
: 0.22 (ethyl acetate/hexane, 4:6).
28
Specific rotation: [ ] +36.3 (c 0.58, CHCl
3
). IR (KBr) ῡ: 3494, 2941,
D
1
6
7
1
740, 1599, 1451, 1376, 1335, 1201, 1158, 1096, 1039, 817,
−1 1
71 cm . H NMR (400 MHz, CDCl ): δ = 7.75 (d, J = 8.4 Hz, 2H),
3
.30 (d, J = 8.0 Hz, 2H), 4.63–4.61 (m, 1H), 4.52 (dd, J = 8.8, 1.6 Hz,
2
8
liquid. R
f
: 0.15 (ethyl acetate/hexane, 8:2); [ ] 18.0 (c 0.36, CHCl
3
);
D
H), 4.18–3.99 (m, 3H), 3.86–3.83 (m, 1H), 3.80–3.76 (m, 1H), 3.61
IR (KBr); ῡ 3441, 3229, 3063, 3032, 2925, 2868, 1725, 1599, 1496,
(
br s, 1H exchangeable with D
2
O), 3.05 (br. s, 1H exchangeable with
−1 1
1
453, 1403, 1343, 1158, 1118, 1031, 815, 788, 739, 700, 671 cm ; H
): δ 8.40 (br s, 1H exchangeable with D O), 7.77
D
2
O), 2.42 (s, 3H), 2.30–2.15 (m, 2H), 1.23 (t, J = 7.2 Hz, 3H) ppm.
NMR (400 MHz, CDCl
3
2
1
3
C NMR (75 MHz, CDCl ): δ = 172.5 (s), 144.0 (s), 136.4 (s), 129.6
3
(
d, 2H, J = 8.00 Hz), 7.28–7.19 (m, 10H), 7.04 (m, 2H), 4.59–4.36 (m,
(
d), 127.6 (d), 71.4 (d), 61.6 (t), 61.4 (d), 60.6 (t), 59.5 (d), 37.6 (t),
4
H), 4.24–4.03 (m, 3H), 3.60 (m, 2H), 2.57 (q, 1H, J = 10.8 Hz), 2.34
13
2
1.6 (q), 14.0 (q) ppm. HRMS [ESI]: m/z calcd for C15
H
21NO SNa [M
6
(
s, 3H), 2.26 (dd, 1H, J = 11.6, 6.8 Hz) ppm; C NMR (100 MHz,
+
+
Na] 366.0982 found 366.0987.
CDCl
3
): δ 178.5 (s), 143.6 (s), 138.2 (s), 137.8 (s), 137.6 (s), 129.5 (d),
1
28.5 (d), 128.2 (d), 127.8 (d), 127.5 (d), 127.4 (d), 127.3 (d), 127.0
(
(
d), 76.7 (d), 72.8 (t), 72.7 (t), 66.5 (t), 59.8 (d), 58.9 (d), 35.1 (t), 21.5
4.9. (2R,4S,5S)-ethyl-4-(hydroxy)-5-(tert-butyldimethylsilyloxymethyl)-1-
q) ppm; HRMS [ESI] m/z calcd for
C
27
H29NO
6
SNa [M+Na]+
N-(p-toluenesulfonyl)pyrrolidine-2-carboxylate (20)
5
18.1608 found 518.1613.
Compound 19 (0.154 g, 0.45 mmol) was dissolved in dry di-
chloromethane (2 mL). Imidazole (0.122 g, 1.79 mmol) and tert-bu-
tyldimethylsilyl chloride (0.074 g, 0.49 mmol) were added successively
and the reaction mixture was stirred for 3 h at 33 °C. Water (50 mL) was
added to the reaction mixture and it was extracted with di-
chloromethane (3 × 30 mL). The combined organic layer was washed
with brine (50 mL), dried over anhydrous sodium sulfate, filtered and
concentrated under reduced pressure. The residue was purified by flash
chromatography over silica gel using a mixture of ethyl acetate and
hexane (2:8) to get compound 20 (0.19 g, 92%) as a colourless liquid.
4
.7. (2R,4S,5S)-ethyl-4-(benzyloxy)-5-(benzyloxymethyl)-1-N-(p-
toluenesulfonyl)pyrrolidine-2-carboxylate (6)
Compound 18 (1.60 g, 3.23 mmol), was dissolved in a EtOH (20 mL)
and cooled to 0 °C. Thionyl chloride (0.47 mL, 6.46 mmol) was added
dropwise. After 10 min, the reaction flask was removed from ice and
refluxed for 5 h. The reaction was stopped and solvent was con-
centrated. To the resulting residue, an aqueous solution of sodium bi-
carbonate (100 mL) was added and it was extracted with ethyl acetate
2
8
(
3 × 50 mL). The combined organic layer was dried over anhydrous
R
f
: 0.58 (ethyl acetate/hexane, 4:6); [ ]
D
+43.6 (c 0.52, CHCl ); IR
3
sodium sulfate, filtered and concentrated under vacuum. The residue
was purified by column chromatography over silica gel using a mixture
of ethyl acetate and hexane (15:85) to give 6 (1.44 g, 85%) as a col-
(KBr); ῡ 3517, 2955, 2932, 2858, 1737, 1599, 1469, 1341, 1278, 1257,
−
1
1
1191, 1157, 1095, 1047, 853, 811, 780, 683, 664 cm
(400 MHz, CDCl
; H NMR
3
) δ 7.63 (d, 2H, J = 8.0 Hz), 7.21 (d, 2H, J = 7.6 Hz),
4.58–4.54 (m, 1H), 4.36 (d, 1H, J = 8.0 Hz), 4.06–3.99 (m, 2H),
3.97–3.90 (m, 1H), 3.84 (m, 2H), 3.08 (d, 1H exchangeable with D O,
J = 8.8 Hz), 2.34 (s, 3H), 2.22–2.11 (m, 2H), 1.14 (t, 3H, J = 7.2 Hz),
2
8
ourless liquid. R
f
: 0.49 (ethyl acetate/hexane, 3:7); [ ] +21.0 (c 0.19,
D
CHCl
3
); IR (KBr); ῡ 2925, 2865, 1742, 1499, 1453, 1344, 1187, 1159,
2
−
1 1
1
115, 1029, 795, 699, 666 cm ; H NMR (400 MHz, CDCl
3
): δ 7.75 (d,
1
3
2
H, J = 8.0 Hz), 7.33–7.20 (m, 10H), 7.09–7.06 (m, 2H), 4.53 (d, 1H,
0.79 (s, 9H), 0.00 (s, 3H), −0.05 (s, 3H); C NMR (75 MHz, CDCl ): δ
3
J = 12.0 Hz), 4.49 (d, 1H, J = 12.0 Hz), 4.43 (dt, 1H, J = 10.8,
172.3 (s), 143.6 (s), 137.2 (s), 129.5 (d), 127.5 (d), 71.5 (d), 62.1 (t),
61.4 (t), 60.6 (d), 59.3 (d), 37.9 (t), 25.8 (q), 21.5 (q), 18.0 (s), 14.0 (q),
6
.8 Hz), 4.37 (dd, 1H, J = 9.6, 0.8 Hz), 4.23–4.09 (m, 5H), 3.66–3.60
(
m, 2H), 2.51 (dt, 1H, J = 12.0, 10.4 Hz), 2.35 (s, 3H), 2.10 (ddd, 1H,
−5.4 (q), −5.6 (q); HRMS [ESI]] m/z calcd for C21
H
35NNaO SSi [M
6
1
3
+
J = 12.0, 6.8, 1.2 Hz), 1.28 (t, 3H, J = 7.20 Hz); C NMR (100 MHz,
+Na] 480.1847 found 480.1848.
5

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
4
.10. (2R,4R,5S)-ethyl-4-(p-nitrobenzoyloxy)-5-(tert-
reduced pressure. Purification of crude compound was done by column
chromatography over silica gel using a mixture of methanol and
chloroform (5:95) as an eluent to get 23 (0.14 g, 86%) as a colourless
butyldimethylsilyloxymethyl)-1-N-(p-toluenesulfonyl)pyrrolidine-2-
carboxylate (21)
2
8
solid. mp 146–148 °C; R
f
: 0.25 (methanol/chloroform, 1:9); [ ] +36.4
D
Compound 20 (0.198 g, 0.43 mmol), was dissolved in dry THF
(c 0.22, MeOH); IR (KBr); ῡ 3515, 3287, 2964, 2931, 2885, 2756, 2644,
−1
(
(
4 mL). Diisopropyl azodicarboxylate (0.171 mL, 0.86 mmol), PPh
3
2566, 1707, 1456, 1334, 1232, 1157, 1096, 1048, 961, 814, 681 cm
;
1
0.23 g, 0.86 mmol) and p-nitrobenzoic acid (0.108 g, 0.65 mmol) were
H NMR (400 MHz, DMSO‑d
6
+D O): δ 7.72 (d, 2H, J = 8.4 Hz), 7.35
2
added successively and the reaction mixture was stirred at 30 °C, under
nitrogen atmosphere, for 5 h. It was then diluted with water (50 mL)
and extracted with ethyl acetate (3 × 30 mL). The organic layer was
washed with water, dried over anhydrous sodium sulfate, filtered and
concentrated under vacuum. The resulting residue was purified by flash
column chromatography over silica gel using a mixture of ethyl acetate
and hexane (1:9) to get compound 21 (0.21 g, 80%) as a colourless
(d, 2H, J = 8.0 Hz), 4.41 (d, 1H, J = 9.2 Hz), 4.18 (d, 1H, J = 4.0 Hz),
3.53–3.51 (m, 2H), 3.07 (dd, 1H, J = 11.6, 8.8 Hz), 2.45–2.39 (m, 1H),
1
3
2.36 (s, 3H), 1.90 (d, 1H, J = 13.6 Hz) ppm; C NMR (100 MHz,
DMSO‑d ): δ 174.1 (s), 143.2 (s), 138.9 (s), 129.7 (d), 127.4 (d), 72.9
6
(d), 70.1 (d), 61.6 (d), 60.6 (t), 37.1 (t), 21.4 (q) ppm; HRMS [ESI] m/z
calcd for C13
H
17NNaO
6
S [M+Na]+ 338.0669 found 338.0670.
2
8
liquid. R
f
: 0.80 (ethyl acetate/hexane, 3:7); [ ] ‒13.6 (c 0.46, CHCl
3
);
D
4
.13. (2R,4R,5S)-4-(Hydroxy)-5-(hydroxymethyl)-pyrrolidine-2-
IR (KBr); ῡ 2930, 2859, 1755, 1725, 1604, 1526, 1467, 1347, 1286,
1
carboxylic acid {(+)-bulgecinine (3)}
1
255, 1186, 1157, 1123, 1058, 838, 782, 719, 668 cm-1; H NMR
(
400 MHz, CDCl
3
): 8.26 (d, 2H, J = 8.8 Hz), 8.15 (d, 2H, J = 8.4 Hz),
Liquid ammonia (~20 mL) was condensed in to a three necked
round-bottomed flask at −70 °C. Sodium metal (0.074 g, 3.17 mmol)
was cut into small pieces and added to liquid ammonia. Compound 23
7
.87 (d, 2H, J = 8.0 Hz), 7.29 (d, 2H, J = 8.0 Hz), 5.51 (d, 1H,
J = 4.4 Hz), 4.71 (d, 1H, J = 9.2 Hz), 4.22–4.19 (m, 2H), 4.07 (br m,
1
H), 3.88 (m, 2H), 2.89–2.82 (m, 1H), 2.41 (s, 3H), 2.30 (d, 1H,
(
0.10 g, 0.32 mmol) was then added to the blue coloured solution. The
J = 14.8 Hz), 1.26 (t, 3H, J = 7.2 Hz), 0.88 (s, 9H), 0.06 (s, 3H), 0.00
1
3
reaction mixture was stirred at −70 °C for 3 h. Benzene was then added
to the reaction mixture until blue colour of reaction mixture dis-
appeared, after which water (10 mL) was added and the reaction
mixture was stirred at room temperature till all ammonia got evapo-
rated. The aqueous layer was separated from the organic layer and the
aqueous layer was washed with ethyl acetate. The aqueous layer was
neutralized with 10% aq. HCl (~pH 5) and purified by ion-exchange
chromatography (Dowex 50WX8 resin, 200–400 mesh) using water as
an eluent initially followed by a mixture of water and ammonia solution
(
s, 3H); C NMR (75 MHz, CDCl ): δ 171.7 (s), 164.1 (s), 150.7 (s),
3
1
7
1
43.5 (s), 138.0 (s), 135.2 (s), 131.0 (d), 129.4 (d), 127.7 (d), 123.5 (d),
8.1 (d), 67.6 (d), 62.2 (t), 61.5 (t), 61.4 (d), 35.9 (t), 25.8 (q), 21.5 (q),
8.1 (s), 14.2 (q), −5.5 (q), −5.6 (q); HRMS [ESI] m/z calcd for
+
C
28
H
38
N
2
NaO
9
SSi [M+Na] 629.1959 found 629.1944.
4
.11. (2R,4R,5S)-ethyl-4-(p-nitrobenzoyloxy)-5-(hydroxymethyl)-1-N-(p-
toluenesulfonyl) pyrrolidine-2-carboxylate (22)
(
1:1). The aqueous solution fraction from the column were con-
Compound 21 (0.436 g, 0.72 mmol), was dissolved in a MeOH
centrated under vacuum to get acid 3 (0.040 g, 78%) as a colourless
(
3 mL) and camphorsulfonic acid (0.043 g, 10% w/w) was added to it.
15
2
8
liquid. R
f
: 0.60 (water/methanol, 2:8); [ ] +15.5 (c 0.18, H
2
O), lit.
D
The reaction mixture was stirred at 35 °C for 5 h, after which the solvent
was evaporated under vacuum and the resulting residue was dissolved
in ethyl acetate (50 mL). It was then washed with saturated solution of
sodium bicarbonate (50 mL). The organic layer was dried over anhy-
drous sodium sulfate, filtered and concentrated under vacuum. The
crude product was purified by column chromatography over silica gel
using a mixture of ethyl acetate and hexane (2:8) to get 22 (0.28 g,
‒
1
15.1; IR (KBr); ῡ 3379, 3235, 3058, 2951, 2929, 1622, 1404, 1323,
−1 1
084, 1045, 990 cm
;
H NMR (400 MHz, D O): δ 4.23 (q, 1H,
2
J = 4.4 Hz), 4.07 (dd, 1H, J = 8.8, 6.8 Hz), 3.75 (dd, 1H, J = 14.4,
6
.8 Hz), 3.63–3.58 (m, 2H), 2.51 (ddd, 1H, J = 14.0, 8.8, 5.6 Hz), 2.01
13
(
dt, 1H, J = 14.0, 5.2 Hz) ppm; C NMR (100 MHz, D
2
O): δ 174.0 (s),
7
0.4 (d), 66.7 (d), 59.2 (d), 57.9 (t), 36.3 (t) ppm; HRMS [ESI] m/z
[M+Na]+ 184.0580 found 184.0580.
calcd for C
6
H
11NNaO
4
8
0%) as a colourless solid. mp 139–142 °C; R
f
: 0.25 (ethyl acetate/
2
8
hexane, 3:7); [ ] ‒53.5 (c 0.26, CHCl
3
); IR (KBr); ῡ 3512, 3111, 2930,
D
1
8
745, 1725, 1604, 1526, 1332, 1277, 1217, 1157, 1100, 1052, 1020,
−1 1
4
.14. (2S,3S,5R)-4-(Benzyloxy)-5-(benzyloxymethyl)-2-(hydroxymethyl)
37, 808, 716, 695 cm
;
H NMR (400 MHz, CDCl ): δ 8.26 (d, 2H,
3
pyrrolidine (10)
J = 8.8 Hz), 8.09 (d, 2H, J = 8.8 Hz), 7.93 (d, 2H, J = 8.0 Hz), 7.29 (d,
2
4
H, J = 8.0 Hz), 5.50 (d, 1H, J = 5.2 Hz), 4.90 (dd, 1H, J = 9.6 Hz),
.25–4.12 (m, 2H), 4.02 (dd, 1H, J = 12.8 Hz), 3.82 (d, 1H,
To a solution of 7 (1.40 g, 2.35 mmol) in a 20 mL mixture of DMF
and methanol (6:1), anhydrous disodium hydrogen phosphate (1.66 g,
J = 12.4 Hz), 3.75 (br m, 1H), 2.81 (ddd, 1H, J = 14.8, 10.0, 5.6 Hz),
1
1.75 mmol), 3% Na–Hg (27.01 g, 35.24 mmol) were added and re-
2
.40 (s, 3H), 2.33 (d, 1H, J = 14.8 Hz), 2.22 (br s, 1H exchangeable
13
action mixture was stirred for 5 h at 60 °C. The reaction mixture was
diluted with water (100 mL) and extracted with ethyl acetate
with D
2
O), 1.23 (t, 3H, J = 7.2) ppm; C NMR (75 MHz, CDCl ): δ
3
1
1
71.7 (s), 164.1 (s), 150.8 (s), 144.3 (s), 136.3 (s), 135.0 (s), 130.9 (d),
(
(
3 × 50 mL). The combined organic layer was washed with brine
50 mL), dried over anhydrous sodium sulfate and the solvent was
29.7 (d), 128.1 (d), 123.6 (d), 79.3 (d), 67.5 (d), 61.8 (t), 61.6 (t), 61.5
(
d), 35.8 (t), 21.6 (q), 14.2 (q) ppm; HRMS [ESI] m/z calcd for
concentrated under vacuum to give a residue, which was purified by
column chromatography over silica gel using a mixture of ethyl acetate
and hexane (6:4) as an eluent to get 10 (0.58 g, 75%) as a colourless
+
C
22
H
24
N
2
NaO
9
S [M+Na] 515.1095 found 515.1086.
2
8
4
.12. (2R,4R,5S)-4-(Hydroxy)-5-(hydroxymethyl)-1-N-(p-
toluenesulfonyl)-pyrrolidine-2-carboxylic acid {N-tosyl-(+)-bulgecinine
23)}
liquid. R
f
: 0.29 (ethyl acetate/hexane, 8:2); [ ] +18.6 (c 1.03, CHCl
3
);
D
IR (KBr); ῡ 3398, 3062, 3032, 2927, 2876, 1599, 1454, 1339, 1156,
−
1 1
(
1093, 1028, 815, 739, 700, 664 cm
;
H NMR (400 MHz, CDCl
3
2
): δ
O),
7
.33–7.22 (m, 10H), 5.07–4.91 (br m, 2H, exchangeable with D
In a 50 mL round bottomed flask containing 5 mL of methanol and
water (1:1), compound 22 (0.255 g, 0.52 mmol) and NaOH (0.062 g,
4.54–4.47 (m, 3H), 4.35 (d, 1H, J = 12.0 Hz), 4.01 (m, 1H), 3.75–3.63
(m, 3H), 3.52 (dd, 1H, J = 11.2, 6.4 Hz), 3.40 (dd, 2H, J = 11.2,
6.0 Hz), 1.99 (dd, 1H, J = 13.6, 7.2 Hz), 1.59 (ddd, 1H, J = 13.6, 8.8,
1
.55 mmol) were added. The mixture was refluxed for 3 h after which
1
3
the reaction mixture was gradually brought to room temperature and
acidified with 10% aq. HCl until the pH of the solution reached 6. It was
then extracted with ethyl acetate (2 × 50 mL). The combined organic
layer was dried over anhydrous sodium sulfate and concentrated under
5.2 Hz) ppm; C NMR (75 MHz, CDCl ): δ 138.0 (s), 128.49 (d), 128.47
3
(d), 127.9 (d), 127.8 (d), 127.5 (d), 78.8 (d), 73.4 (t), 71.3 (t), 67.7 (t),
63.0 (t), 61.7 (d), 58.3 (d), 32.6 (t) ppm; HRMS [ESI] m/z calcd for
C
20
H26NO
3
[M+H]+ 328.1907 found 328.1918.
6

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
4
.15. (5R,7S,8S)-7-(Benzyloxy)-8-(benzyloxymethyl)-1-aza-3-oxabicyclo-
58.0 (d), 40.6 (t), 25.7 (q), 18.0 (s), −5.4 (q), −5.5 (q) ppm; HRMS
[
3.3.0]-octan-2-one (24)
[ESI] m/z calcd for
C
13
H
25NNaO
4
Si [M+Na]+ 310.1445 found
3
10.1457.
Compound 10 (0.661 g, 2.02 mmol), was dissolved in a di-
chloromethane (10 mL). 1,1′-Carbonyldiimidazole (0.655 g,
4.18. (5R,7R,8S)-7-(p-nitrobenzoyloxy)-8-(tert-
4
3
.04 mmol) was added to it. The reaction mixture was then stirred at
0 °C for 10 h, diluted with water (50 mL) and extracted with di-
butyldimethylsilyloxymethyl)-1-aza-3-oxabicyclo-[3.3.0]-octan-2-one (26)
chloromethane (3 × 50 mL). The combined organic layer were washed
with brine (50 mL), dried over anhydrous sodium sulfate and con-
centrated under vacuum. The resulting residue was purified by column
chromatography over silica gel using a mixture of ethyl acetate and
Compound 25 (0.52 g, 1.80 mmol), was dissolved in dry THF
(10 mL). Diisopropyl azodicarboxylate (0.532 mL, 2.71 mmol), PPh
(0.711 g, 2.71 mmol) and p-nitrobenzoic acid (0.393 g, 2.35 mmol)
were added successively, the reaction mixture was stirred at 30 °C,
under nitrogen atmosphere for 4 h. It was then diluted with water
(50 mL) and extracted with ethyl acetate (3 × 50 mL). The organic
layer was washed with brine, dried over anhydrous sodium sulfate,
filtered and concentrated under vacuum. The resulting residue was
purified by flash column chromatography over silica gel using a mixture
of ethyl acetate and hexane (15:85) to get compound 26 (0.70 g, 88%)
3
hexane (3:7) to get 24 (0.64 g, 89%) as a colourless liquid. R
f
: 0.49
2
8
(
ethyl acetate/hexane, 5:5); [ ] +75.5 (c 0.52, CHCl
3
); IR (KBr); ῡ
D
3
032, 2920, 2867, 1755, 1453, 1393, 1324, 1234, 1180, 1115, 1074,
−1 1
1
025, 742, 700, 608 cm ; H NMR (400 MHz, CDCl ): δ 7.34–7.24 (m,
3
1
0H), 4.57 (m, 2H), 4.54–4.52 (m, 2H), 4.49–4.45 (m, 1H), 4.32 (td,
H, J = 5.2, 2.0 Hz), 4.24–4.18 (m, 1H), 4.14–4.08 (m, 2H), 3.79 (dd,
H, J = 9.6, 7.6 Hz), 3.74 (dd, 1H, J = 9.6, 6.4 Hz), 2.20 (ddd, 1H,
1
1
as a colourless solid. mp 82–85 °C. R
f
: 0.75 (ethyl acetate/hexane, 4:6);
1
3
28
J = 12.8, 5.6, 1.6 Hz), 1.58 (ddd, 1H, J = 15.2, 10.0, 5.2 Hz) ppm;
C
[ ] ‒3.2 (c 0.25, CHCl ); IR (KBr); ῡ 2931, 2859, 1752, 1722, 1608,
D
3
−
1 1
NMR (75 MHz, CDCl
3
): δ 161.8 (s), 138.2 (s), 137.9 (s), 128.4 (d),
1527, 1470, 1354, 1282, 1120, 1056, 886, 884, 836, 778, 715 cm ; H
1
7
28.3 (d), 127.8 (d), 127.7 (d), 127.6 (d), 127.4 (d), 80.2 (d), 73.3 (t),
NMR (400 MHz, CDCl ): δ 8.19 (d, 2H, J = 8.8 Hz), 8.05 (d, 2H,
3
2.4 (t), 68.0 (t), 67.6 (t), 62.1 (d), 57.4 (d), 37.6 (t) ppm; HRMS [ESI]
J = 9.2 Hz), 5.57–5.54 (m, 1H), 4.52 (t, 1H, J = 8.0 Hz), 4.19–4.12 (m,
+
m/z calcd for C21
H
23NNaO
4
[M+Na] , 376.1519 found 376.1525.
3H), 3.88 (dd, 1H, J = 10.8, 3.2 Hz), 3.72 (dd, 1H, J = 10.4, 4.0 Hz),
2
.72–2.65 (m, 1H), 1.81 (ddd, 1H, J = 13.6, 6.8, 4.0 Hz), 0.81 (s, 9H),
13
4
.16. (5R,7S,8S)-7-(Hydroxy)-8-(hydroxymethyl)-1-aza-3-oxabicyclo-
0.01 (s, 3H), 0.00 (s, 3H) ppm; C NMR (75 MHz, CDCl ): δ 164.3 (s),
3
[
3.3.0]-octan-2-one (11)
161.9 (s), 150.8 (s), 134.9 (s), 130.9 (d), 123.8 (d), 79.3 (d), 69.1 (t),
6
6.7 (d), 64.3 (t), 58.3 (d), 38.9 (t), 25.9 (q), 18.2 (s), −5.43 (q),
+
In a 50 mL three necked round bottomed flask, compound 24
−5.48 (q) ppm; HRMS [ESI] m/z calcd for C20
H
28
N
2
NaO Si [M+Na]
7
(
0.15 g, 0.42 mmol) was taken and dissolved with MeOH (20 mL). 10%
459.1558 found 459.1564.
Pd/C (30 mg, 20% w/w) was added and hydrogen gas was continuously
purged for 4 h at 20 °C. The reaction mixture was then filtered through
a sintered funnel and the filtrate was concentrated under vacuum. The
resulting was residue purified by column chromatography over silica
gel using a mixture of methanol and chloroform (5:95) to get 11
4.19. (5R,7R,8S)-7-(Hydroxy)-8-(tert-butyldimethylsilyloxymethyl)-1-
aza-3-oxabicyclo-[3.3.0]-octan-2-one (27)
To a solution of compound 26 (0.30 g, 0.69 mmol) in 5 mL MeOH,
sodium carbonate (0.145 g, 1.37 mmol) was added and stirred at 30 °C
for 3 h, after which the solid was filtered through Buchner funnel. The
filtrate was dried over anhydrous sodium sulfate and concentrated
under vacuum. The resulting residue was purified by column chroma-
tography over silica gel using a mixture of ethyl acetate and hexane
(
0.065 g, 88%) as a colourless liquid. R
f
: 0.60 (methanol/chloroform,
2
8
1
1
:9); [ ] +96.7 (c 1.10, MeOH); IR (KBr); ῡ 3395, 2942, 1736, 1403,
D
−
1 1
329, 1241, 1182, 1110, 1041, 1004, 774 cm
; H NMR (400 MHz,
D
2
O): δ 4.72 (t, 1H, J = 5.2 Hz), 4.65 (t, 1H, J = 8.4 Hz), 4.40–4.33 (m,
H), 4.29 (dd, 1H, J = 8.8, 4.0 Hz), 3.90 (m, 1H), 3.80 (dd, 1H,
J = 11.2, 5.6 Hz), 3.73 (dd, 1H, J = 11.6, 7.6 Hz), 2.10 (dd, 1H,
1
(3:7) to get the alcohol 27 as a colourless liquid (0.18 g, 91%). R : 0.41
f
1
3
28
J = 13.2, 4.8 Hz), 1.89 (ddd, 1H, J = 16.0, 13.2, 5.2 Hz); C NMR
in (ethyl acetate/hexane, 4:6); [ ] +42.7 (c 0.44, CHCl ); IR (KBr); ῡ
D
3
(
(
100 MHz, D
2
O): δ 163.8 (s), 73.0 (d), 69.0 (t), 63.8 (d), 59.8 (t), 57.6
3424, 2952, 2931, 2858, 1739, 1466, 1392, 1254, 1123, 1055, 1008,
Na [M+Na]+
−1 1
d), 39.5 (t); HRMS [ESI] m/z calcd for C
7
H11NO
4
837, 777 cm ; H NMR (400 MHz, CDCl ): δ 4.49–4.43 (m, 2H), 4.14
3
1
96.0580 found 196.0579.
(dd, 1H, J = 8.8, 5.2 Hz), 4.04–4.12 (m, 1H), 3.79–3.77 (m, 1H),
3
.73–3.71 (m, 1H), 3.63–3.59 (m, 1H), 2.76 (br s, 1H exchangeable
4
.17. (5R,7S,8S)-7-(Hydroxy)-8-(tert-butyldimethylsilyloxymethyl)-1-
with D
7.6, 6.0 Hz), 0.83 (s, 9H), 0.01 (s, 3H), 0.00 (s, 3H); C NMR
100 MHz, CDCl ): δ 162.4 (s), 75.5 (d), 69.5 (t), 68.3 (d), 63.7 (t), 57.9
2
O), 2.34 (dt, 1H, J = 12.8, 6.4 Hz), 1.67 (ddd, 1H, J = 13.2,
13
aza-3-oxabicyclo-[3.3.0]-octan-2-one (25)
(
3
Compound 11 (0.495 g, 2.86 mmol) was dissolved in dry di-
chloromethane (5 mL). Imidazole (0.778 g, 11.43 mmol) and tert-bu-
tyldimethylsilyl chloride (0.560 g, 3.72 mmol) were added successively
and the reaction mixture was stirred for 6 h at 30 °C. It was then diluted
with water (100 mL) and extracted with dichloromethane (3 × 50 mL).
The combined organic layer was washed with brine (100 mL), dried
over anhydrous sodium sulfate filtered and concentrated under reduced
pressure. The residue was purified by flash chromatography over silica
gel using mixture of ethyl acetate and hexane (3:7) to get compound 25
(d), 40.4 (t), 25.9 (q), 18.2 (s), −5.45 (q), −5.47 (q); HRMS [ESI] m/z
calcd for C13
H
25NNaO
4
Si [M+Na]+ 310.1445 found 310.1449.
4.20. (5R,7R,8S)-7-(Hydroxy)-8-(hydroxymethyl)-1-aza-3-oxabicyclo-
[3.3.0]-octan-2-one (12)
Compound 27 (0.150 g, 0.52 mmol), was dissolved in MeOH (3 mL)
and camphorsulfonic acid (0.015 g, 10% w/w) was added to it. The
reaction mixture was then stirred at 30 °C for 3 h, after which the
solvent was evaporated under vacuum and the resulting residue was
purified by column chromatography over silica gel using a mixture of
(
0.70 g, 85%) as a colourless semi solid. R
f
: 0.45 (ethyl acetate/hexane,
2
8
5
1
6
:5); [ ] +74.4 (c 0.65, CHCl
3
); IR (KBr); ῡ 3467, 2933, 2861, 1742,
D
471, 1405, 1326, 1252, 1182, 1131, 1097, 1004, 976, 842, 776,
methanol and hexane (5:95) to get 12 (0.080 g, 88%) as a colourless
−
1
1
28
80 cm ; H NMR (400 MHz, CDCl
3
): δ 4.59 (q, 1H, J = 4.4 Hz), 4.41
liquid. R
f
: 0.50 (methanol/chloroform, 1:9); [ ] +40.3 (c 0.31,
D
(
dd, 1H, J = 8.4, 8.0 Hz), 4.19–4.12 (m, 1H), 4.05 (dd, 1H, J = 9.2,
.6 Hz), 3.95–3.92 (m, 1H), 3.82–3.74 (m, 2H), 3.50 (dd, 1H, ex-
changeable with D O, J = 3.6, 0.8 Hz), 2.03 (dd, 1H, J = 12.8, 5.2 Hz),
.59–1.51 (m, 1H), 0.78 (s, 9H), 0.00 (s, 3H), −0.01 (s, 3H) ppm;
NMR (75 MHz, CDCl ): δ 161.7 (s), 75.0 (d), 67.5 (t), 62.9 (d), 62.5 (t),
MeOH); IR (KBr); ῡ 3388, 2926, 1733, 1400, 1235, 1059, 1003,
−1 1
3
775 cm ; H NMR (400 MHz, MeOD): δ 4.64 (t, 1H, J = 8.8 Hz), 4.46
(td, 1H, J = 5.6, 3.2 Hz), 4.29 (dd, 1H, J = 8.8, 4.8 Hz), 4.24–4.17 (m,
1H), 3.78–3.64 (m, 3H), 2.45 (dt, 1H, J = 12.8, 6.4 Hz), 1.74 (ddd, 1H,
J = 13.2, 8.0, 6.0 Hz) ppm; 13C NMR (100 MHz, MeOD): δ 164.7 (s),
2
1
3
1
C
3
7

U.K. Mishra and N.G. Ramesh
Carbohydrate Research 489 (2020) 107931
7
5.4 (d), 71.0 (t), 70.3 (d), 62.7 (t), 58.9 (d), 41.0 (t) ppm; HRMS [ESI]
c) E.J. Van Asselt, K.H. Kalk, B.W. Dijkstra, Biochemistry 39 (2000) 1924–1934;
+
d) A.M.W.H. Thunnissen, H.J. Rozeboom, K.H. Kalk, B.W. Dijkstra, Biochemistry
m/z calcd for C
7
H
11NNaO
4
[M+Na] 196.0580 found 196.0587.
3
4 (1995) 12729–12737;
e) M.F. Templin, D.H. Edwards, J.Y. Hoeltje, J. Biol. Chem. 267 (1992)
20039–20043.
4.21. (2S,3S,5R)-3-(Hydroxy)-2,5-(dihydroxymethyl)pyrrolidine (13)
[
[
3] S. Shinagawa, F. Kasahara, Y. Wada, S. Harada, M. Ajai, Tetrahedron 40 (1984)
3
465–3470.
To a solution of compound 10 (0.300 g, 0.92 mmol) in di-
4] A.G.M. Barrett, D. Pilipauskas, J. Org. Chem. 55 (1990) 5194–5196.
chloromethane (1 mL), BCl
3
(4.58 mL, solution in di-
1
M
[5] A.G.M. Barrett, D. Pilipauskas, J. Org. Chem. 56 (1991) 2787–2800.
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chloromethane) was added dropwise at 0 °C under argon atmosphere.
The reaction mixture was stirred at 32 °C for 2 h, after which the re-
action was stopped and solvent was evaporated under vacuum. The
resulting residue was quenched with 2 mL of ammonium hydroxide
solution. After evaporation of the ammonium hydroxide, the crude
product was purified by column chromatography over silica gel using a
mixture of ammonia solution and acetonitrile (5:95) as an eluent to get
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3 (0.100 g, 75%) as a light brown liquid. R
f
: 0.45 (ammonia solution/
2
8
acetonitrile, 1:9); [ ] +6.23 (c 0.69, H
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1
1
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884, 1620, 1410, 1336, 1118, 1051, 971, 618 cm
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234–1238;
(
400 MHz, D
J = 11.6, 6.0 Hz), 3.66–3.57 (m, 2H), 3.55 (d, 1H, J = 4.4 Hz), 3.49
dd, 1H, J = 11.6, 6.8 Hz), 3.27 (td, 1H, J = 6.4, 3.6H z), 1.92 (ddd,
2
O): δ = 4.36 (dt, 1H, J = 4.8, 1.2 Hz), 3.74 (dd, 1H,
h) M. Toumi, F. Couty, G. Evano, Tetrahedron Lett. 49 (2008) 1175–1179;
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(
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H, J = 14.0, 6.8, 1.2 Hz), 1.74 (ddd, 1H, J = 14.0, 9.2, 4.8 Hz) ppm;
1
3
k) J.K. Khalaf, A. Datta, J. Org. Chem. 69 (2004) 387–390 (references cited
there in).
C NMR (75 MHz, D
2
O): δ 71.3 (d), 63.5 (t), 63.1 (d), 59.2 (t) 57.6 (d),
+
3
6.2 (t) ppm; HRMS [ESI] m/z calcd for C
6
H14NO
3
[M+H] 148.0968
[
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Declaration of competing interest
[
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
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Acknowledgments
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b) Y. Natori, S. Kikuchi, Y. Yoshimura, A. Kato, I. Adachi, H. Takahata,
Heterocycles 86 (2012) 1401–1417.
The authors are grateful to the Council of Scientific and Industrial
Research (CSIR), New Delhi, India for financial support in the form of a
research grant (02(243)/15/EMR-II) and a research fellowship to
U.K.M. The authors also thank the Department of Science and
Technology (DST) and the Indian Institute of Technology Delhi (IITD)
for funding of the ESI-HRMS at IIT Delhi.
[
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Appendix A. Supplementary data
1
130–1140;
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.carres.2020.107931.
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8