Highly efficient diastereoselective biocatalytic acylation of a diastereotopic furanose diol and synthesis of key intermediates for amino derivatized bicyclonucleosides

Article abstract of DOI:10.1016/S0040-4020(02)01632-0

The selectivity of Candida antarctica lipase has been demonstrated and employed in the manipulation of a diastereotopic furanose diol as the key step in the synthesis of a novel bicyclo 3-amino-3-deoxy furanose derivative, which is an important intermedia

Full text of DOI:10.1016/S0040-4020(02)01632-0

Tetrahedron 59 (2003) 1333–1338
Highly efficient diastereoselective biocatalytic acylation of a
diastereotopic furanose diol and synthesis of key intermediates for
amino derivatized bicyclonucleosides
Ashok K. Prasad,a Sucharita Roy,a,b Rajesh Kumar,a,c Neerja Kalra,a Jesper Wengel,d
Carl E. Olsen,e Ashok L. Cholli,b Lynne A. Samuelson,b Jayant Kumar,b Arthur C. Watterson,b
Richard A. Grossc and Virinder S. Parmara,b,c
,
*
aBioorganic Laboratory, Department of Chemistry, University of Delhi, Delhi 110 007, India
bDepartment of Chemistry, Institute for Nano Science and Engineering Technology, University of Massachusetts, One University Avenue,
Lowell, MA 01854, USA
cNSF Center for Biocatalysis and Bioprocessing of Macromolecules, Department of Chemistry, Polytechnic University,
Six Metrotech Center, Brooklyn, NY 11201, USA
dDepartment of Chemistry, University of Southern Denmark, DK-5230 Odense M, Denmark
eDepartment of Chemistry, Royal Veterinary and Agricultural University, DK-1871 Copenhagen, Denmark
Received 30 July 2001; revised 28 November 2002; accepted 12 December 2002
Dedicated to the cherished memory of our collaborator and friend (Late) Professor Sukant K. Tripathy
Abstract—The selectivity of Candida antarctica lipase has been demonstrated and employed in the manipulation of a diastereotopic
furanose diol as the key step in the synthesis of a novel bicyclo 3-amino-3-deoxy furanose derivative, which is an important intermediate for
the synthesis of bicyclic analogs of AZT. The asymmetrization of the diol has been achieved with preferred formation of a monoacylated
product with 100% diastereoselectivity. An efficient synthesis of an intermediate in the synthesis of amino derivatized bicyclonucleosides is
also described, two such novel compounds containing cycloamino residues have been prepared. q 2003 Elsevier Science Ltd. All rights
reserved.
1. Introduction
known to possess strong antibacterial and anticancer
properties.7 Further, amine-modified oligonucleotides have
displayed increased thermal affinities towards complemen-
tary ON’s and excellent hybridization properties.8–10
Recent years have seen the emergence of sugar modified
nucleoside analogs as promising chemotherapeutic agents.1
The importance of anti-sense and anti-gene oligonucleotides
(ON’s) as potential and selective inhibito0rs 0 of gene
expression along with the discovery of 2 ,3 -dideoxy
nucleosides, like AZT, ddC and d4T as anti-HIV agents
have proved to be significant developments in this field.
Reports have shown the anti-inhibitory activity of confor-
mationally locked AZT analogs against HIV-1 reverse
transcriptase.2 In addition, a family of related molecules
named locked nucleic acids (LNAs) have elicited much
interest due to having enhanced duplex stability and higher
binding affinity to complementary single stranded DNA and
RNA.3,4 The modified nucleosides have also attracted much
attention as potential antiviral and anticancer agents.5,6 Of
these, particularly amino sugar nucleosides have long been
Although there has been a growing demand for the
development of nucleoside-based therapeutics, this class
of compounds remains to some extent unexplored because
the manipulation of polyhydroxy functionalities in carbo-
hydrate moieties is a major limitation using conventional
methods. In our studies, directed towards the synthesis of
40-C-branched AZT analogs, the selective protection of a
single hydroxyl group in the prochiral intermediate 3-azido-
3-deoxy-4-C-hydroxymethyl-1,2-O-isopropylidene-a-D-
erythro-ribofuranose (1), gave unsatisfactory results using
the classical chemical methods. Our continued interest11 in
regio- and stereoselective reactions on different types of
compounds using enzymes led us to embark on a novel
chemo-enzymatic strategy to overcome this problem.
Keywords: biocatalysis; lipase; acylation; diastereoselectivity;
bicyclonucleoside.
2. Results and discussion
*
Corresponding author. Address: Bioorganic Laboratory, Department of
Chemistry, University of Delhi, Delhi 110 007, India. Tel.: þ91-11-2766-
6555; fax: þ91-11-2766-7206; e-mail: virparmar@yahoo.co.in
The synthetic route designed by us for the preparation of the
0040–4020/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0040-4020(02)01632-0

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A. K. Prasad et al. / Tetrahedron 59 (2003) 1333–1338
target intermediate compounds useful in the synthesis of
bicyclic analogs of AZT starts with 1, which was prepared
from D-glucose by a multiple step sequence.12,13 As per our
scrutiny of literature, there has been no report on the
successful monoprotection of the diol 1 other than a report
involving its stereoselective protection by reaction with
TBDPSCl in the presence of triethylamine and dichloro-
methane. This reaction, however yielded the monosilyl
ether in a low 62% yield.13 Our previous results have shown
that the asymmetrization of 3-O-benzyl-4-C-hydroxy-
methyl-1,2-O-isopropylidene-b-L-threo-pentofuranose
(6)14,15 can be easily carried out in organic solvents by two
enzymes, namely Pseudomonas cepacia and Candida
antarctica lipase.14 The latter lipase was seen to exhibit
high diastereoselectivity (de) optimized to 79% de yielding
the 5-O-acetyl-a-D-xylofuranose derivative, while the
former lipase yielded the epimeric 4-C-(acetoxy)methyl-
a-D-xylofuranose derivative in relatively lower diastereos-
electivity. We describe here a similar enzymatic strategy for
the selective protection of 1 as part of our chemosynthetic
approach targeted towards the formation of modified
nucleosides. A screening of lipases, e.g. C. antarctica
lipase (CAL), Candida rugosa lipase (CRL), porcine
pancreatic lipase (PPL) and Amano PS lipase in different
organic solvents was employed for the optimization of the
reaction conditions; CAL in toluene was found to be the
most suitable system for selective acetylation of compound
1. It was observed that C. antarctica lipase catalysed the
preferential acetylation of the C-5 hydroxy group of 1
giving rise to the 5-O-acetyl-a-D-ribofuranose derivative 3
in 98% yield and in impressive 100% de (Scheme 1). We
thus report here a promising, convenient and practical route
for the monoacetylation of the diastereotopic diol 1 in a
single step.
wherein the anomeric proton appeared as a single doublet at
d 5.76 (J¼3.7 Hz).
Repeated attempts to pinpoint the position of acetylation,
however, gave unsatisfactory results using NOE and COSY
experiments. The structure of the monoacetylated epimer
was therefore established on the basis of further chemical
transformations starting with the tosylation of the remaining
hydroxyl group in 3 to yield 4 in 95% yield. This was
followed by a one pot reduction and cyclization, achieved
by refluxing the tosyl derivative 4 with 10% Pd–C in ethyl
acetate in an atmosphere of hydrogen to afford the novel
cyclized derivative 5 in 65% yield, whose structure was
ascertained unambiguously on the basis of its spectral data.
The bicyclic compound 5 is important as it could serve as a
valuable synthon for the synthesis of AZT analogs and other
sugar modified nucleosides and oligonucleotides.
We had earlier reported a reversal of stereoselectivity in the
CAL-catalyzed acylation reaction on 3-O-benzyl-4-C-
hydroxymethyl-1, 2-O-isopropylidene-b-L-threo-pento-
furanose (6)14,15 by changing the acylating agent from
vinyl acetate to the more bulky 2,2,2-trifluoroethyl butyrate.
This factor however, was not observed in the enzymatic
butanoylation of 1 with 2,2,2-trifluoroethyl butyrate, this
reaction gave the monobutyrate 2 involving the same site of
esterification as in the formation of the monoacetate 3
(Scheme 1). This observation was concluded based on the
similar splitting pattern of the C-5 methylene protons of the
butanoyloxymethyl moiety in the proton NMR spectrum of
the monobutanoylated 2 as observed for the corresponding
protons of the acetyloxymethyl moiety in the 1H NMR
spectrum of the monoacetylated compound 3. We speculate
that the non-occurrence of reversal of selectivity in the
biocatalytic acylation of 1 by change of the acylating agent
is due to the polar nature and opposite configuration of the
azido substituent at the C-3 position in 1 as compared to the
benzyloxy substituent at the C-3 position in 6, which
perhaps is able to allow the reversal in the site of acylation
in the latter compound by change of the acylating agent due
to its bulk, non-polar nature and preferred stereochemistry
appropriate for the active site of the Candida antactica
lipase.
In a successful reaction, a solution of compound 1 (100 mg)
and an equimolar amount of vinyl acetate in toluene (4 mL)
was incubated with C. antarctica lipase (20 mg) at 25–288C
and the progress of the reaction was monitored by TLC. On
completion of the reaction, the enzyme was filtered off, the
solvent removed under reduced pressure and the product
was purified by column chromatography on silica gel using
a gradient solvent system of petroleum ether–ethyl acetate
to afford compound 3 as an yellow oil. The formation of a
1
single epimer was confirmed from its H NMR spectrum
A set of chemical reactions was also carried out starting
Scheme 1. Reagents and conditions: (i) C. antarctica lipase, toluene, 2,2,2-trifluoroethyl butyrate, 25–288C; (ii) C. antarctica lipase, toluene, vinyl acetate,
25–288C; (iii) p-toluene sulphonyl chloride, pyridine, 08C; (iv) H2, 10% Pd–C, ethyl acetate, 608C.

A. K. Prasad et al. / Tetrahedron 59 (2003) 1333–1338
1335
Scheme 2. Reagents and conditions: (i) p-toluene sulphonyl chloride, pyridine, 08C; (ii) H2, 10% Pd–C, ethyl acetate, 25–288C; (iii) sodium hydride,
dimethylformamide, toluene 42–458C; (iv) piperidine/pyrrolidine, triethylamine, methanol, reflux.
with 6 towards the synthesis of key synthons for amino-
derivatized bicyclonucleosides (Scheme 2). Treatment of 6
with p-toluene sulphonyl chloride gave the ditosylate 7 in
76% yield. The next step involved debenzylation by
hydrogenolysis in the presence of palladium on activated
charcoal to yield 8 in 63% yield. Subsequent cyclization of 8
was carried out in the presence of sodium hydride giving
rise to the oxabicyclo compound 9 with a pendant tosyl
group in 61% yield. This tosyl group could then be used as a
handle for the introduction of various heterocyclic amines at
the 4-C-hydroxymethyl position. We report here two
different novel bicyclo compounds 10 and 11 thus
synthesized having pyrrolidine and piperidine moieties,
respectively as attached pendant amino functionalities.
recorded on a JEOL JMS-AX505W high resolution mass
spectrometer in positive mode using the matrix HEDS (bis-
hydroxyethyldisulfide) doped with sodium acatate, except
for compound 5 for which the matrix NBA (5-nitrobenzyl
alcohol) was used. The C. antarctica lipase immobilized on
accurel was gifted by Novozymes Inc. and used as such. The
enzymes porcine pancreatic lipase (PPL, Type II) and C.
rugosa lipase (CRL, Type VII) were purchased from Sigma
Chemical Co. (USA) and used after storing in vacuo over
P2O5 for 24 h. The lipase ‘Amano PS’ was a gift from
Amano Co., Japan and used as such. The organic solvents
˚
used were distilled over activated molecular sieves (4 A).
Analytical TLCs were performed on precoated Merck silica
gel 60F254 plates; the spots were detected either by UV light
or by charring with 4% alcoholic H2SO4. Reactions were
monitored at l254 nm on a Shimadzu LC-10AS HPLC
instrument with SPD-10A UV-VIS detector and Shimpack
CLC-ODS (4.6£150 mm2) reverse phase column; solvent
system used was methanol–water (3:2) at a flow rate of
0.50 mL/min.
3. Conclusion
We have explored complementary synthetic and chemo-
enzymatic routes for the synthesis of key synthons towards
novel modified bicyclonucleosides, including the synthesis
of nine novel compounds, hitherto unknown in literature. It
can thus be seen in the present study that biocatalytic
transformations can be used to tailor the course of the
reaction to yield desired products. Further, this approach
also has advantages with respect to high stereoselectivity
and better yields obtained through eco-friendly routes.
Studies on the synthetic transformations and biological
activity evaluation of these compounds are now in
progress.
4.1.1. 3-Azido-5-butanoyl-3-deoxy-4-C-hydroxymethyl-
1,2-O-isopropylidene-a-D-erythro-ribofuranose (2). A
solution of compound 112,13 (100 mg, 0.4 mmol) and an
equimolar amount of 2,2,2-trifluoroethyl butyrate (TFEB) in
toluene (4 mL) was incubated with C. antarctica lipase
(20 mg) at 25–288C and the progress of the reaction was
monitored by TLC. On completion, the enzyme was filtered
off, the solvent removed under reduced pressure and the
product was purified by column chromatography on silica
gel using a gradient solvent system of petroleum ether–
ethyl acetate (3:2) to afford compound 2 as an yellow oil
1
(95 mg) in 75% yield. H NMR (300 MHz, acetone-d6) d:
4. Experimental
4.1. General
0.93 (3H, t, J¼8.4 Hz, CO(CH2)2CH3), 1.32 and 1.54 (6H,
2s, 3H each, 2£CH3), 1.63 (2H, m, COCH2CH2CH3), 2.35
(2H, t, J¼7.5 Hz, COCH2CH2CH3), 2.93 (1H, br s, OH),
3.75 and 3.90 (2H, dd, J¼11.3 Hz each, CH2OH), 4.15 and
4.22 (2H, dd, J¼11.4 Hz each, CH2OCO(CH2)2CH3), 4.35
(1H, d, J¼5.6 Hz, C-3H), 5.00 (1H, m, C-2H) and 5.86 (1H,
d, J¼3.8 Hz, C-1H); 13C NMR (75.5 MHz, acetone-d6) d:
13.86 (COCH2CH2CH3), 19.02 (COCH2CH2CH3), 26.49
and 26.82 (C(CH3)2), 36.44 (COCH2CH2CH3), 62.63 (C-3),
64.26 (CH2OH), 65.65 (CH2OCO(CH2)2CH3), 81.55 (C-2),
87.10 (C-4), 105.52 (C-1), 114.19 (C (CH3)2) and 173.32
(CO); IR (neat film): 802, 873, 1029, 1168, 1261, 1385,
Melting points were determined on a Mettler FP62
instrument and are uncorrected. The IR spectra were
recorded either on a Perkin-Elmer model 2000 FT-IR or
RXI FT-IR spectrometer. The 1H NMR and 13C NMR
spectra were recorded on Bruker Advance-300 spectrometer
at 300 and at 75.5 MHz, respectively, using TMS as internal
standard. The chemical shift values are on d scale and the
coupling constants (J) are in Hz. The FAB-HRMS spectra
of all the compounds to measure their accurate masses were

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A. K. Prasad et al. / Tetrahedron 59 (2003) 1333–1338
1458, 1740, 2114, 2965, 3502 cm21; FAB-HRMS: m/z
338.1347 ([MþNa]þ, C13H21N3O6Na calcd 338.1328).
yield by column chromatography on elution with petroleum
1
ether–ethyl acetate (3:1).; H NMR (300 MHz, CDCl3) d:
1.32 and 1.56 (6H, 2s, 3H each, 2£CH3), 2.09 (3H, s,
OCOCH3), 3.71 (2H, s, C-7H), 3.89 and 4.08 (2H, dd,
J¼9.3 Hz each, CH2OCOCH3), 4.32 (1H, m, C-5H), 4.65
(1H, m, C-4H) and 6.03 (1H, d, J¼4.1 Hz, C-3H); 13C NMR
(300 MHz, CDCl3) d: 21.20 (COCH3), 27.03 and 27.83
(C(CH3)2), 55.30 (C-5), 65.03 (C-7), 66.51 (CH2OAc),
79.80 (C-4), 88.80 (C-1), 110.50 (C-3), 113.50 (–C(CH3)2)
and 171.51 (CO); IR (neat film): 1020, 1040,1080, 1140,
1230, 1370, 1642, 1742 (OCOCH3), 2850, 2928 and
3335(NH) cm21; FAB-HRMS: m/z 487.2303 ([M2þH]þ,
2£(C11H17NO5)þH calcd 487.2292).
4.1.2. 3-Azido-5-acetyl-3-deoxy-4-C-hydroxymethyl-1,2-
O-isopropylidene-a-D-erythro-ribofuranose (3). A sol-
ution of compound 1 (245 mg, 1 mmol) and an equimolar
amount of vinyl acetate in toluene (10 mL) was incubated
with C. antarctica lipase (50 mg) at 25–288C and the
progress of the reaction was monitored by TLC. On
completion of the reaction, the enzyme was filtered off
and the solvent removed under reduced pressure to afford
1
compound 3 as an yellow oil (240 mg) in 98% yield. H
NMR (300 MHz, DMSO-d6) d: 1.19 and 1.59 (6H, 2s, 3H
each, 2£CH3), 2.05 (3H, s, COCH3), 3.36 (2H, br s,
CH2OH), 4.00 and 4.11 (2H, dd, J¼11.2 Hz each, CH2-
OCOCH3), 4.27 (1H, d, J¼5.6 Hz, C-3H), 4.79 (1H, m,
OH), 4.85 (1H, m, C-2H) and 5.76 (1H, d, J¼3.7 Hz, C-1H);
13C NMR (75.5 MHz, DMSO-d6) d: 20.83 (COCH3), 26.34
and 26.51 (C(CH3)2), 61.00 (CH2OH), 62.65 (C-3), 64.95
(CH2OCOCH3), 80.3 (C-2), 86.10 (C-4), 104.10 (C-1),
112.90 (C(CH3)2) and 170.21 (CO); IR (neat film): 605, 875,
1028, 1120, 1167, 1234, 1386, 1457, 1747, 2114, 2942,
2986, 3502 cm21; FAB-HRMS: m/z 310.0997 ([MþNa]þ,
C11H17N3O6Na calcd 310.1015).
4.1.5. 3-O-Benzyl-5-(O-p-toluenesulphonyl)-4-C-(p-
toluenesulphonyloxymethyl)-1,2-O-(isopropylidene)-b-
L-threo-xylofuranose (7). Diol 614,15 (245 mg, 1 mmol)
was dissolved in minimum amount of pyridine and
2 mol equiv. tosyl chloride was added, the reaction mixture
was stirred at 08C and the progress monitored by TLC. On
completion of the reaction, the contents were poured over
ice-cold water, neutralization of aqueous solution with
dilute hydrochloric acid yielded a white solid which was
chromatographed over silica gel using petroleum ether–
ethyl acetate (4:1) as eluent to yield the pure compound 7 as
a white solid (495 mg) in 76% yield, mp 78–798C; 1H NMR
(300 MHz, CDCl3) d: 1.25 and 1.35 (6H, 2s, 3H each,
2£CH3), 2.44 and 2.51 (6H, 2s, 3H each, 2£CH3C6H4), 4.00
(1H, br s, C-3H), 4.08 (4H, m, 2£CH2OTs), 4.47 (1H, d,
J¼11.6 Hz, CHaC6H5), 4.50 (2H, m, CHbC6H5 and C-2H),
5.80 (1H, d, J¼4.2 Hz, C-1H), and 7.30 and 7.70 (13H, 2m,
aromatic protons); 13C NMR (75.5 MHz, CDCl3) d: 23.65
(2£CH3C6H4), 28.10 and 28.80 (C(CH3)2), 69.51 and 69.60
(2£CH2OTs), 74.13 (OCH2Ph), 85.44 (C-2), 86.38 (C-3),
87.69 (C-4), 107.40 (C-1), 115.15 (C (CH3)2), and 129.71,
130.01, 130.05, 130.16, 130.56, 131.83, 131.98, 134.24,
134.39, 138.55, 146.92 and 147.18 (aromatic carbons); IR
(Nujol): 992, 1097, 1178, 1211, 1267, 1307, 1372, 1455,
4.1.3. 3-Azido-5-acetyl-3-deoxy-4-C-(p-toluenesulphonyl-
oxymethyl)-1,2-O-isopropylidene-a-D-erythro-ribofura-
nose (4). Compound 3 (230 mg, 0.8 mmol) was dissolved in
a minimum amount of pyridine and the solution allowed to
stir at 08C, tosyl chloride (84 mg) was added portion-wise
into the stirred solution. The reaction was monitored by
TLC and at completion, the reaction mixture was neutral-
ized by pouring into acidified water. The solid that separated
out was purified by column chromatography (petroleum
ether–ethyl acetate 4:1) to yield compound 4 (335 mg) as a
white solid in 95% yield, mp 122–138C; 1H NMR
(300 MHz, CDCl3) d: 1.29 and 1.38 (6H, 2s, 3H each,
2£CH3), 2.05 (3H, s, COCH3), 2.44 (3H, s, CH3C6H4), 4.05
(2H, m, C-3H and CHaOAc), 4.18 (1H, d, J¼11.6 Hz,
CHbOAc), 4.28 and 4.38 (2H, dd, J¼10.4 Hz each,
CH2OTs), 4.75 (1H, m, C-2H), 5.77 (1H, d, J¼3.7 Hz,
C-1H), and 7.34 and07.82 (4H, 2d0, 2H each, J¼8.2 Hz each,
C-20H, C-30H, C-5 H and C-6 H); 13NMR (75.5 MHz,
CDCl3) d: 21.59 (COCH3), 22.51 (CH3C6H4), 26.71 and
26.85 (C(CH3)2), 65.48 (CH2OTs), 65.75 (CH2OAc), 68.93
(C-3), 80.72 (C-2), 84.65 (C-4), 105.34 (C-1)0, 115.06 (C
(CH3)2), 129.08 (C-20 and C-60), 130.73 (C-3 and C-50),
133.61 (C-10), 145.84 (C-40) and 170.94 (CO); IR (KBr):
554, 666, 789, 840, 873, 984, 1033, 1097, 1121, 1178, 1191,
1225, 1310, 1455, 1495, 1598, 1750, 2117, 2932, 2959 and
2989 cm21; FAB-HRMS: m/z 464.1110 ([MþNa]þ, C18-
H23N3O8SNa calcd 464.1103).
1598 and 2923 cm21
;
FAB-HRMS: m/z 641.1516
([MþNa]þ, C30H34O10S2Na calcd 641.1491).
4.1.6. 5-(O-p-Toluenesulphonyl)-4-C-(p-toluenesul-
phonyloxymethyl)-1,2-O-(isopropylidene)-b-L-threo-
xylofuranose (8). Compound 7 (310 mg, 0.5 mmol) was
dissolved in dry ethyl acetate (10 mL) and half molar equiv.
of palladium on activated charcoal was added to the reaction
mixture. The contents were degassed with hydrogen and
allowed to stir for 24 h at 25–288C in the presence of
hydrogen gas. The reaction was monitored by TLC and at
completion, the charcoal was filtered off and the residue
obtained on evaporation of the solvent was purified by
column chromatography using petroleum ether–ethyl
acetate (2:3) as eluent to afford the debenzylated compound
8 as a white solid (172 mg) in 63% yield, mp 164–658C; 1H
NMR (300 MHz, CDCl3) d: 1.21 and 1.28 (6H, 2s, 3H each,
2£CH3), 2.47 (6H, s, 2£CH3C6H4), 4.15 (5H, m,
2£CH2OTs and C-3H), 4.56 (1H, m, C-2H), 5.86 (1H, d,
J¼3.8 Hz, C-1H), 7.52 and 7.80 (8H, 2m, aromatic
protons); 13C NMR (75.5 MHz, CDCl3) d: 21.55
(2£CH3C6H4), 25.83 and 26.53 (C(CH3)2), 68.18 and
68.75 (2£CH2OTs), 76.35 (C-3), 86.97 (C-4), 88.03 (C-2),
106.57 (C-1), 112.93 (C(CH3)2), and 128.35, 128.77,
128.80, 129.11, 130.51, 130.83, 131.00, 131.34, 133.36,
4.1.4. 1-Acetoxymethyl-6-amino-3,4-O-isopropylidene-2-
oxabicyclo [3.2.0] heptane (5). The tosylated compound 4
(220 mg, 0.5 mmol) was dissolved in ethyl acetate in a
reaction flask degassed with hydrogen and half mol equiv
10% Pd–C (65 mg) was added and the reaction was heated
up to 608C in an atmosphere of hydrogen and monitored by
TLC. At completion, the catalyst was filtered off and from
the filtrate, the solvent was evaporated under reduced
pressure to yield the crude product. The pure bicyclo
compound 5 was obtained as a colorless oil (79 mg) in 65%

A. K. Prasad et al. / Tetrahedron 59 (2003) 1333–1338
1337
133.55, 145.96 and 146.22 (aromatic carbons); IR (Nujol):
853, 897, 976, 992, 1179, 1365, 1456, 1598, 2925 and
The reaction was worked-up by evaporation of the solvent
under reduced pressure and the crude product was purified
by column chromatography with a solvent system of
petroleum ether–ethyl acetate (1:3) to yield compound 11
as an yellow oil (16 mg) in 64% yield. 1H NMR (300 MHz,
CDCl3) d: 1.36 and 1.52 (6H, 2s, 3H each, 2£CH3), 1.83
(6H, br 0s, C-30H, C-40H and C-50H), 2.74 (4H, br s, C-20H
and C-6 H), 2.84 and 3.21 (2H, dd, J¼13.2 Hz each, NCH2),
4.40 (1H, d, J¼7.4 Hz, C-7Ha), 4.66 (1H, d, J¼3.3 Hz,
C-5H), 4.83(1H, d, J¼7.4 Hz, C-7Hb), 4.94 (1H, m, C-4H)
and 6.23 (1H, d, J¼30.3 Hz, C-3H); 13C NMR (75.5 MHz,
CDCl3) d: 23.57 (C-4 ), 27.13 and 27.93 (C(CH3)2), 29.40
and 29.74 (C-30 and C-50), 55.39 (C-20 and C-60), 59.08
(CH2N), 80.81 (C-7), 84.25 (C-4), 87.81 (C-1), 88.95 (C-5),
108.5 (C-3) and 114.52 (C(CH3)2); IR (neat film): 849, 959,
1014, 1068, 1090, 1163, 1229, 1372, 1379, 1461, 2854,
3551 cm21
C23H28O10S2Na calcd 551.1022).
;
FAB-HRMS: m/z 551.1063 ([MþNa]þ,
4.1.7. 2,6-Dioxo-3,4-isopropylidene-1-(p-toluenesul-
phonyloxymethyl)-bicyclo [3.2.0] heptane (9). Sodium
hydride (2 mol equiv., 20 mg) was taken in a three-necked
flask and stirred with a few drops of DMF, followed by
addition of toluene (10 mL) and compound 8 (160 mg,
0.3 mmol) and the reaction mixture allowed to stir under an
atmosphere of dry nitrogen for 30 min. The temperature was
slowly increased to 42–458C and the reaction monitored by
TLC. The reaction was quenched by adding methanol and
extracted with ethyl acetate to yield the crude product,
which was purified by column chromatography using
petroleum ether–ethyl acetate (4:1) as eluent to yield 9 as
a white solid (70 mg) in 61% yield, mp 80–818C; 1H NMR
(300 MHz, CDCl3) d: 1.33 and 1.40 (6H, 2s, 3H each,
2£CH3), 2.46 (3H, s, CH3C6H4), 4.19 (2H, s, CH2OTs), 4.29
and 4.63 (2H, dd, J¼7.7 Hz each, C-7H), 4.66 (1H, d,
J¼3.1 Hz, C-5H), 4.98 (1H, m, C-4H), 6.20 (1H, d,
J¼3.2 Hz, C-3H), and 7.36 and 7.81 (4H, 02d, 2H each,
J¼8.2 Hz each, C-20H, C-30H, C-50H and C-6 H); 13C NMR
(75.5 MHz, CDCl3) d: 22.00 (CH3C6H4), 26.70 and 28.00
(C(CH3)2), 68.42 (CH2OTs), 78.70 (C-7), 84.60 (C-4),
86.00 (C-1), 87.80 (C-5), 108.20 (C-3), 115.20 (C(CH3)2),
128.30 and 130.30 (C-20, C-30, C-50, C-60), 132.64 (C-40) and
145.71 (C-10); IR (Nujol): 831, 1176, 1368, 1454, 1597 and
2925 cm21
;
C14H23NO4Na calcd 292.1525).
FAB-HRMS: m/z 292.1540 ([MþNa]þ,
Acknowledgements
This work was supported by grants from the Council of
Scientific and Industrial Research (CSIR, New Delhi, India)
and Danish International Development Agency (DANIDA,
Denmark).
2929 cm21
;
C16H20O7SNa calcd 379.0827).
FAB-HRMS: m/z 379.0811 ([MþNa]þ,
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