An expedient diastereoselective synthesis of pyrrolidinyl spirooxindoles fused to sugar lactone via [3+2] cycloaddition of azomethine ylides

Article abstract of DOI:10.1016/j.tetlet.2011.12.025

Synthesis of pyrrolidinyl-spirooxindoles fused to sugar lactone has been achieved by a one pot three component 1,3-dipolar cycloaddition (1,3-DC) reaction. A unique dipolarophile (α,β-unsaturated lactone) derived from d-glucose/d-galactose reacted with az

Full text of DOI:10.1016/j.tetlet.2011.12.025

Tetrahedron Letters 53 (2012) 854–858
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An expedient diastereoselective synthesis of pyrrolidinyl spirooxindoles
fused to sugar lactone via [3+2] cycloaddition of azomethine ylides
⇑
J. Naga Siva Rao, R. Raghunathan
Department of Organic Chemistry, University of Madras, Guindy Campus, Chennai 600 025, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis of pyrrolidinyl-spirooxindoles fused to sugar lactone has been achieved by a one pot three
Received 3 August 2011
Revised 30 November 2011
Accepted 7 December 2011
Available online 14 December 2011
component 1,3-dipolar cycloaddition (1,3-DC) reaction. A unique dipolarophile (
a,b-unsaturated lactone)
derived from -glucose/ -galactose reacted with azomethine ylide generated in situ from isatin/N-substituted
D
D
isatin and secondary amino acids (sarcosine/proline/piperidine-2-carboxylic acid) to give the corresponding
cycloadducts in good yield. The cycloaddition was found to be highly regio- and diastereoselective.
Ó 2011 Elsevier Ltd. All rights reserved.
Keywords:
1,3-Dipolar cycloaddition
Azomethine ylide
Pyrrolidinyl-spirooxindoles
a,b-Unsaturated sugar lactones
In recent years, synthesis of new substituted spirooxindole
derivatives through 1,3-DC reaction of azomethine ylide with a,b-
derivatives1 has attracted the attention of synthetic organic chem-
ists due to their remarkable biological activity.2,3 Moreover spiro-
oxindole frame work has been found as core structure of many
pharmacological agents and alkaloids,4 such as horsifiline, spirot-
ryprostatine A and B, pteropodine, isopteropodine (Fig. 1). It is an
important structural motif which acts as potent non-peptide inhib-
itor of the p53–MDM2 interaction.5,6
unsaturated lactones (1a, 1b) derived from D-glucose and D-
galactose.15
In a prototype experiment, the reaction of dipolarophile 1a with
azomethine ylide generated in situ from N-methyl isatin and pro-
line in refluxing toluene under Dean–Stark reaction conditions,
afforded the cycloadduct 916 in good yields (88%) with high regio-
and stereoselectivities through an intermolecular 1,3-DC reaction
Developing efficient synthetic methods for the synthesis of
oxindoles derivatized at C3 with spirocarbocycles, spiroheterocy-
cles, spirolactones, and spirocyclic ethers are particularly impor-
tant in organic synthesis. Among the different synthetic
strategies, 1,3-dipolar cycloaddition reaction of azomethine ylide7
plays a key role in the construction of spirooxindoles.8
1,3-DC reaction of azomethine ylide is a powerful tool for the
synthesis of a variety of natural products9 containing a pyrrolidine
structure. And it has been widely used as an important carbon–car-
bon bond forming reaction. 1,3-DC reactions of nitrone,10 nitrile
oxide11 and azide12 with carbohydrate scaffolds are well known
in the literature, whereas only very few reports are available
involving azomethine ylide13 with carbohydrates. To the best of
our knowledge, there is no report in the literature on the synthesis
of pyrrolidinyl spirooxindoles fused to sugar lactone through 1,3-
DC reaction.
O
Me
N
H
O
N
O
l
H
H
C
NH
O
N
H
OMe
O
N
H
Cl
Pteropodine
A potent inhibitor of
the p53-MDM2 interaction
N
O
Me
O
N
N
MeO
MeO
O
O
As part of our ongoing research in the area of 1,3-dipolar
cycloaddition14 herein we report a short and efficient protocol
for the synthesis of sugar lactone fused pyrrolidinyl-spirooxindole
N
H
N
H
Spirotryprostatine
Horsfilline
Figure 1. Naturally occurring and biologically active 3,30-pyrrolidinyl-spirooxindole
natural products.
⇑
Corresponding author. Tel.: +91 44 22202811; fax: +91 44 22300488.
E-mail address: ragharaghunathan@yahoo.com (R. Raghunathan).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.12.025

J. Naga Siva Rao, R. Raghunathan / Tetrahedron Letters 53 (2012) 854–858
855
R2
OAc
H
R1
O
Hb
O
N
Toluene Reflux,
Yield= 88%
O
O
Ha
O
AcO
+
+
O
R1
O
COOH
N
H
12h
N
CH3
N
CH3
R2
2a
1a : R1 = H, R2 = OAc
1b : R1 = OAc, R2 = H
3b
9 : R1 = H, R2 = OAc
16 : R1 = OAc, R2 = H
Scheme 1. Synthesis of sugar lactone fused spiropyrrolizidine oxindole.
(Scheme 1). The structure of the product was confirmed by spec-
troscopic and X-ray analyses.17 A single product was isolated in
all the cases and no trace of the other isomers formed even after
prolonged reaction time. The crude 1H NMR spectra of the products
confirmed the formation of single regio and stereoisomers.
The 1H NMR spectrum of compound 9 exhibited a characteristic
singlet at d 3.15 for NCH3 protons of isatin and at d 2.08, 2.12 for
two acetyl protons of lactone which proved the incorporation of
oxindole ring into sugar lactone. Moreover the characteristic dou-
blet at d 3.87 (J = 11.7 Hz) for Ha proton proved the formation of
regioisomer 9. If regioisomer 9A had been formed, the Ha proton
would have appeared as a multiplet in the 1H NMR spectrum.
The lactone carbonyl carbon and amide carbonyl carbon showed
peaks at 176.7 and 170.6 ppm respectively in 13C NMR spectrum.
These observed chemical shift values are in agreement with the
structure of the compound 9. Furthermore, the presence of
Figure 2. ORTEP diagram of 9.
OAc
O
OAc
R1
secondary orbital intractions
O
R1
R2
O
O
Parth A
R2
Hb
Ha
CH3
9, R1 = H, R2 = OAc
16, R1 = OAc, R2 = H
O
N
N
N
N
O
CH3
O
Observed
OAc
O
OAc
R1
R1
O
O
R2
R2
ParthB
Ha
Hb
9A, R1 = H, R2 = OAc
16A, R1 = OAc, R2 = H
N
O
N
N
H3C
N
O
H3C
No secondary orbital intraction
Not Observed
Figure 3. The possible regio chemical mode of approach of azomethine ylide to the dipolarophile.

856
J. Naga Siva Rao, R. Raghunathan / Tetrahedron Letters 53 (2012) 854–858
molecular ion peak at m/z 443.18 (M++1) in the mass spectrum
confirmed the formation of the cycloadduct 9. The stereochemistry
of the product 9 was established by X-ray crystallography analysis
as shown in Figure 2.17
The possible regiochemical mode of approach of azomethine
ylide to the dipolarophile (1a and 1b) is shown in Figure 3. In path
A amide carbonyl group of azomethine ylide having secondary
orbital interaction18 with the lactone carbonyl group of dipolaro-
phile whereas in path B such kind of secondary orbital interaction
cannot take place. Hence path A is more favorable for regioselec-
tive formation of the cycloadduct 9.
Similarly path C and path D in Figure 4 explain the stereochem-
ical approach of dipole to the dipolarophile (1a and 1b). The tran-
sition state TS1 of path C shows exo mode of approach of dipole to
both faces of dipolarophile. Since dipole is having a steric repulsion
with terminal acetoxymethyl19 group in the unsaturated lactones
in Si face it preferably attacks from the face opposite to that of
the terminal acetoxymethyl group in unsaturated lactones.
Hence approach from the Re face is more favorable than Si face
of dipolarophile. Transition state TS2 of path D would be less favor-
able due to dipolar repulsion between lactone carbonyl group of
dipolarophile and amide carbonyl group of dipole. Hence dipole
favorable approach is from Re face of dipolarophile through exo
mode19 for stereoselective formation of cycloadduct 9. The acetate
group at C-4 of lactone does not seem to play any role in control-
ling the direction of approach of dipole to the dipolarophile. Since
the cycloaddition proceeded exclusively through exo mode, a single
diastereomer was observed in all cases.
Figure 5. ORTEP diagram of 16.
Having optimized reaction conditions, we investigated the
scope of the reaction by reacting different 1,3-dipoles with the
dipolarophiles (1a and 1b). The reactions smoothly proceeded
through [3+2] cycloaddition to give the corresponding cycload-
ducts in good yields. All the compounds were thoroughly charac-
terized by 1H, 13C NMR, DEPT-135 and mass spectroscopic
methods (Fig. 5, Table 1).
In conclusion, we have developed a simple and efficient proto-
col for the synthesis of pyrrolidinyl-spirooxindoles fused to sugar
lactone through 1,3-dipolar cycloaddition methodology. This
multicomponent reaction offers high yield of the products, with
simple experimental procedure and formation of single regio and
To study the effect of solvent on cycloaddition reaction, the
reaction was carried out in different solvents and toluene was
found to be the best to get the maximum yield of the products.
O
N
N
CH3
N
N
CH3
O
(
si-face
(
si-face
OAc
OAc
O
R1
OAc
O
O
R1
disfavored
Path D
R1
favored
Path C
O
R2
O
O
R2
R2
re-face
O
N
re-face
CH3
N
CH3
N
N
O
TS1
TS2
OAc
R1
O
O
R2
Ha
Hb
N
N
O
CH3
9, R1 = H, R2 = OAc
16, R1 = OAc, R2 = H
Observed
Figure 4. The possible stereo chemical mode of approach of azomethine ylide to the dipolarophile.

J. Naga Siva Rao, R. Raghunathan / Tetrahedron Letters 53 (2012) 854–858
857
Table 1
Synthesis of 2,30-pyrrolidinyl-spirooxindole derivatives
Entry
Unsaturated sugar lactone
Isatin
Secondary amino acids
Time (h)
12
Producta
Yieldb (%)
O
O
O
H
OAc
O
R = H, 84%, 4
R = Me, 86%, 5
R = Et, 82%, 6
R = Bn, 784%, 7
OAc
AcO
AcO
N
COOH
H
Me
Me
N
3a
O
O
O
N
R
1
H
1a
2
O
N
R
O
O
O
O
O
O
OAc
O
R = H, 84%, 8
R = Me, 88%, 9
R = Et, 80%, 10
H
AcO
AcO
OAc
OAc
H
COOH
N
N
H
N
R
2
3
12
12
3b
H
1a
2
O
N
R
O
O
OAc
O
AcO
AcO
H
H
H
N
N
H
3c
COOH
N
R
R = H, 80%, 11
1a
2
O
N
R
O
O
O
O
H
OAc
R = H, 86%, 12
R = Me, 88%, 13
R = Et, 84%, 14
OAc
AcO
AcO
N
COOH
H
Me
Me
3a
N
O
N
R
O
4
5
6
12
12
12
1b
2
H
O
O
N
R
O
O
O
O
O
OAc
O
R = H, 86%, 15
R = Me, 87%, 16
R = Et, 83%, 17
OAc
H
AcO
AcO
H
COOH
COOH
N
N
H
O
O
N
R
3b
1b
2
2
H
O
O
N
R
O
OAc
OAc
H
AcO
AcO
H
N
H
N
3c
N
R
O
R = H, 84%, 18
1b
H
O
O
N
R
a
The products were characterized by IR, NMR, MS and elemental analysis.
Isolated yield after purification.
b
4. (a) Kang, T. H.; Matsumoto, K.; Murakami, Y.; Takayama, H.; Kitajima, M.; Aimi,
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stereoisomers. The biological activities of the synthesized com-
pounds are currently under investigation, and further work in this
direction is in progress.
Acknowledgments
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J.N. thanks Council of Scientific and Industrial Research (CSIR),
New Delhi, India for the award of junior research fellowship
(JRF). R.R. and J.N. thank DST (Project No. SR/S1/OC-51/2008),
New Delhi for financial support and DST-FIST program for the
NMR facility. The authors wish to thank Professors D. Velmurugan
and S. Sundaramoorthy for single crystal X-ray data.
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80,10a0-decahydrospiro[indoline-3,100-pyrano[4,3-a]indolizine]-30-yl)methyl
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sugar lactone 1a (0.2 g, 0.087 mmol), isatin (0.129 g, 0.087 mmol), and
piperidine-2-carboxylic acid (0.169, 0.132 mmol),white solid. Mp = 150–
151 °C.1H NMR (CDCl3, 300 MHz): d 1.18–1.23 (m, 3H), 1.29 (s, 3H), 1.35–1.42
(m, 1H), 1.97 (s, 3H), 2.0–2.07 (m, 2H), 2.20–2.23 (m, 2H), 2.99–3.06 (m, 1H),
3.41–3.61 (m, 2H), 4.11–4.20 (m, 2H), 5.15–5.21 (m, 1H), 5.27–5.31 (m, 1H), 6.75
13
(d, J = 7.5 Hz, 1H), 7.03 (t, J = 7.5 Hz, 1H), 7.09–7.20 (m, 2H), 7.90 (s, 1H).
C
NMR (CDCl3, 75 MHz): d 19.2, 20.6, 23.7, 25.0, 32.3, 44.4, 44.6, 46.1, 61.7, 62.9,
64.5, 72.7, 73.7, 109.3, 123.5, 124.7, 128.8, 129.4, 140.9, 169.1, 169.7, 170.6,
178.3. IR (KBr)
C
+3.39 (c 0.4, CH2Cl2).
v
max: 1712, 1744, 3296 cmꢀ1. m/z 442.17. Anal. Calcd for
23H26N2O7: C, 62.43; H, 5.92; N, 6.33. Found: C, 62.53; H, 5.98; N, 6.40. ½a D27:1
ꢁ
(d) ((3S,3a0S,60R,70R,7a0R)-70-Acetoxy-20-methyl-2,40-dioxo-20,3a0,40,60,70,
7a0-hexahydro-10H-spiro[indoline-3,30-pyrano[4,3-c]pyrrole]-60-yl)methyl
acetate (12): Isolated yield: 86% (0.3 g) Synthesized from a,b-unsaturated sugar
lactone 1b (0.2 g, 0.087 mmol), isatin (0.129 g, 0.087 mmol), and sarcosine
(0.117 g, 0.132 mmol), white solid. m.p =110–111 °C.1H NMR (CDCl3, 300 MHz):
d 2.08 (s, 3H), 2.12 (s, 3H), 2.14 (s, 3H), 3.02–3.11 (m, 1H), 3.34–3.39 (m, 2H),
3.64 (d, J = 11.1 Hz, 1H), 4.26–4.30 (m, 2H), 5.19–5.20 (m, 1H), 5.25–5.29 (m,
1H), 6.84 (d, J = 7.5 Hz, 1H), 7.1 (t, J = 7.5 Hz, 1H), 7.23–7.28 (m, 2H), 8.01 (s, 1H).
13
C NMR (CDCl3, 75 MHz): d 20.7, 20.8, 34.3, 38.5, 49.9, 55.9, 62.2, 66.6, 74.0,
74.8, 110.3, 123.4, 123.9, 128.7, 129.9, 141.5, 169.1, 169.9, 170.5, 177.7. IR (KBr)
v
max: 1708, 1743, 3296 cmꢀ1. m/z 402.14; Anal. Calcd for C20H22N2O7: C, 59.70;
16. General procedure for the synthesis of pyrrolidinyl-spirooxindole
derivatives: To a solution of isatin/N-substituted isatin (1 equiv) and cyclic
H, 5.51; N, 6.69. Found: C, 59.81; H, 5.58; N, 6.74. ½a D27:6
ꢁ
+3.6 (c 0.5, CH2Cl2).
(e) ((3S,30R,40R,4a0R,4b0S,9a0S)-40-Acetoxy-1-methyl-10,2-dioxo-30,40,4a0,4b0,
50,60,70,9a0-octahydro-10H-spiro[indoline-3,90-pyrano[4,3-a]pyrrolizine]-30-
or acyclic secondary amino acid (1.4 equiv) in dry toluene, was added
a,b-
unsaturated sugar lactone (1a–b) under the nitrogen atmosphere. The solution
was refluxed for 12 h in Dean–Stark apparatus to give the cycloadducts. After
completion of the reaction as indicated by TLC, the solvent was evaporated
under reduced pressure. The crude product was extracted with
dichloromethane. The organic layer was dried with anhydrous sodium
sulphate and concentrated in vacuo. The crude product was purified by
column chromatography using hexane/EtOAc (7:3) as eluent.
yl)methyl acetate (16): Isolated yield: 87% (0.338 g) Synthesized from a,b-
unsaturated sugar lactone 1b (0.2 g, 0.087 mmol), N-methyl isatin (0.141 g,
0.087 mmol), and proline (0.151 g, 0.132 mmol), white solid. Mp = 158–159 °C.
1H NMR (CDCl3, 300 MHz): d 1.84–1.85 (m, 1H), 1.97–2.00 (m, 2H), 2.11 (s, 3H),
2.12 (s, 3H), 2.21–2.23 (m, 1H), 2.56–2.64 (m, 1H), 2.71–2.81(m, 2H), 3.15 (s,
3H), 3.78 (d, J = 11.4 Hz, 1H), 4.21–4.24 (m, 1H), 4.27–4.31 (m, 2H), 5.21–5.13
(m, 1H), 5.37–5.40 (m, 1H), 6.85 (d, J = 7.8 Hz, 1H), 7.09 (t, J = 7.5 Hz, 1H), 7.33–
7.36 (m, 2H). 13 C NMR (CDCl3, 75 MHz): d 20.8, 20.9, 24.2, 26.3, 27.8, 46.4, 48.0,
49.6, 62.2, 66.5, 66.7, 73.9, 75.3, 108.8, 122.7, 124.9, 127.1, 130.1, 144.6, 169.3,
(a) ( ( 3 S , 3 a 0S,60R,70S,7a0R)-70-Acetoxy-20-methyl-2,40-dioxo-20,3a0,40,60,70,
7a0-hexahydro-10H-spiro[indoline-3,30-pyrano[4,3-c]pyrrole]-60-yl)methyl
acetate (4): Isolated yield: 84% (0.296 g) Synthesized from
a,b-unsaturated
170.1, 170.5, 176.7. IR (KBr)
C
v
max: 1745, 1698 cmꢀ1. m/z 442.19. Anal. Calcd for
sugar lactone 1a (0.2 g, 0.087 mmol), isatin (0.129, 0.087 mmol), and sarcosine
(0.117 g, 0.132 mmol),white solid. Mp = 115–116 °C. 1H NMR (CDCl3,
300 MHz): d 2.06 (s, 3H), 2.12 (s, 3H), 2.15 (s, 3H), 3.01–3.06 (m, 1H), 3.40–
3.49 (m, 1H), 3.55–3.61 (m, 1H), 3.70 (d, J = 11.1 Hz, 1H), 4.21–4.25 (m, 1H),
23H26N2O7: C, 62.43; H, 5.92; N, 6.33. Found: C, 62.33; H, 5.82; N, 6.41. ½a D26:9
ꢁ
+1.78 (c 0.3, CH2Cl2).
(f) ((3S,30R,40R,4a0R,4b0S,10a0S)-40-Acetoxy-10,2-dioxo-10,30,40,4a0,4b0,50,60,70,
80,10a0-decahydrospiro[indoline-3,100-pyrano[4,3-a]indolizine]-30-yl)methyl
4.40–4.46 (m, 1H), 5.21–5.24 (m, 1H), 5.31–5.34 (m, 1H), 6.79 (d, J = 7.5 Hz,
acetate (18): Isolated yield: 84% (0.326 g) Synthesized from a,b-unsaturated
13
1H), 7.07 (t, J = 7.5 Hz, 1H), 7.18–7.28 (m, 2H), 8.58 (s, 1H).
C NMR (CDCl3,
sugar lactone 1b (0.2 g, 0.087 mmol), isatin (0.129 g, 0.087 mmol), and
piperidine-2-carboxylic acid (0.169 g, 0.132 mmol), white solid. mp = 157–
158 °C.1H NMR (CDCl3, 300 MHz): d = 1.19–1.25 (m, 2H), 1.25–1.28 (m, 1H),
1.45–1.46 (m, 1H), 1.68 (s, 3H), 2.02 (s, 3H), 2.04–2.08 (m, 1H), 2.21–2.18 (m,
2H), 2.32–2.35 (m, 1H), 2.84–2.90 (m, 1H), 2.95–3.02 (m, 1H), 3.52–3.58 (m, 1H),
4.12–4.26 (m, 2H), 4.91–4.96 (m, 1H), 5.11–5.14 (m, 1H), 6.77 (d, J = 7.5 Hz, 1H),
7.03 (t, J = 7.5 Hz, 1H), 7.15–7.21 (m, 2H), 8.23 (s, 1H). 13 C NMR (CDCl3, 75 MHz):
d 19.2, 19.7, 22.5, 24.1, 31.2, 44.3, 44.5, 47.4, 61.1, 61.5, 64.9, 72.8, 74.0, 108.8,
75 MHz): d 20.4, 26.6, 34.2, 35.2, 51.6, 53.6, 61.4, 65.2, 73.4, 74.8, 110.1, 123.1,
123.7, 128.5, 129.6, 141.4, 169.4, 169.6, 170.4, 177.7. IR (KBr) vmax: 1710, 1743,
3290 cmꢀ1. HRMS (ESI) m/z [M+H]+ calcd for C20H23N2O7 403.1505, found
403.1509. Anal. Calcd for C20H22N2O7: C, 59.70; H, 5.51; N, 6.69. Found: C,
59.85; H, 5.63; N, 6.62. ½a D27:3
ꢁ
+3.5 (c 2.3, CH2Cl2).
(b) ((3S,30R,40S,4a0R,4b0S,9a0S)-40-Acetoxy-1-methyl-10,2-dioxo-30,40,4a0,4b0,
50,60,70,9a0-octahydro-10H-spiro[indoline-3,90-pyrano[4,3-a]pyrrolizine]-30-
yl)methyl acetate (9): Isolated yield: 88% (0.34 g) Synthesized from
a
,b-
122.3, 123.0, 127.9, 128.5, 140.2, 168.2, 168.6, 169.6, 176.4. IR (KBr) vmax: 1712,
unsaturated sugar lactone 1a (0.2 g, 0.087 mmol), N-methyl isatin (0.141 g,
0.087 mmol), and proline (0.151 g, 0.132 mmol), white solid. Mp = 164–165 °C.
1H NMR (CDCl3, 300 MHz): d 1.54–1.57 (m, 1H), 1.84–1.97 (m, 2H), 1.93–1.96
(m, 1H), 2.08 (s, 3H), 2.12 (s, 3H), 2.58–2.62 (m, 1H), 2.71–2.80 (m, 1H), 2.95–
3.01 (m, 1H), 3.15 (s, 3H), 3.87 (d, J = 11.7 Hz, 1H), 4.24–4.29 (m, 1H), 4.40–4.51
(m, 2H), 5.40–5.41 (m, 2H), 6.84 (d, J = 7.5 Hz, 1H), 7.09 (t, J = 7.5 Hz, 1H), 7.33–
7.38 (m, 2H). 13 C NMR (CDCl3, 75 MHz): d 20.7, 25.2, 26.2, 28.9, 42.0, 48.5, 52.0,
61.5, 65.1, 65.5, 73.4, 74.1, 108.8, 122.8, 124.7, 127.3, 130.0, 144.4, 169.3, 169.8,
1746, 3297 cmꢀ1. HRMS (ESI) m/z [M+H]+ calcd or C23H27N2O7 443.1818, found
443.1820. Anal. Calcd for C23H26N2O7: C, 62.43; H, 5.92; N, 6.33. Found: C, 62.51;
H, 5.86; N, 6.40. ½a D27:1
ꢁ
+ 1.10 (c 0.35, CH2Cl2).
17. The detailed X-ray crystallographic data (CCDC numbers for 9 and 16 are
827985 and 822189 respectively) are available from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.
18. Vidhya Lakshmi, N.; Thirumurugan, P.; Perumal, P. T. Tetrahedron Lett. 2010, 51,
1064–1068.
170.6, 176.7. IR (KBr)
v
max: 1698, 1745 cmꢀ1. HRMS (ESI) m/z [M+H]+ calcd for
19. Pas niczek, K.; Socha, D.; Jurczak, M.; Frelek, J.; Suszczyn ska, A.; Lipkowska, Z.
U.; Chmielewski, M. J. Carbohydr. Chem. 2003, 22, 613–629.
C23H27N2O7 443.1818, found 443.1824. Anal. Calcd for C23H26N2O7: C, 62.43; H,
5.92; N, 6.33. Found: C, 62.54; H, 5.99; N, 6.41. ½a D26:7
ꢁ
+4 (c 0.55, CH2Cl2).