DBU assisted expeditious synthesis of glycosyl dienes via glycosylated β-hydroxy esters

Article abstract of DOI:10.1016/j.carres.2006.04.021

DBU catalyzed condensation of 3-O-benzyl(methyl)-5,6-dideoxy-1,2-O-isopropylidene-β-l-threo-hept-4-enofuranuronates with different aldehydes produces the corresponding 3-O-benzyl(methyl)-6-carbethoxy-5,6-dideoxy-1,2-O-isopropylidene-7-phenyl-β-l-threo-hep

Full text of DOI:10.1016/j.carres.2006.04.021

Carbohydrate Research 341 (2006) 1930–1937
Note
DBU assisted expeditious synthesis of glycosyl dienes
via glycosylated b-hydroxy estersq
Shyam S. Verma, Namrata Dwivedi, Biswajit K. Singh and Rama P. Tripathi*
Medicinal and Process Chemistry Division, Central Drug Research Institute, Lucknow 226001, India
Received 20 January 2006; received in revised form 6 April 2006; accepted 13 April 2006
Available online 15 May 2006
Abstract—DBU catalyzed condensation of 3-O-benzyl(methyl)-5,6-dideoxy-1,2-O-isopropylidene-b-L-threo-hept-4-enofuranuron-
ates with different aldehydes produces the corresponding 3-O-benzyl(methyl)-6-carbethoxy-5,6-dideoxy-1,2-O-isopropylidene-7-phen-
yl-b-L-threo-hept-4-enofuranoses. The latter on treatment with methanesulfonyl chloride followed by DBU catalyzed E2 reaction of
the methanesulfonyloxy intermediates gave the respective 3-O-benzyl(methyl)-6-carbethoxy-5,6,7-trideoxy-1,2-O-isopropylidene-7-
phenyl-b-L-threo-hept-4,6-dienofuranose in moderate to good yields.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Keywords: DBU; Aldol type condensation; Glycosyl uronates; Glycosyl dienes
Conjugated butadienes are not only synthetically impor-
tant intermediates for many cycloaddition reactions
but also biologically important structural units in
most naturally occurring molecules and synthetic poly-
mers.1–3 C-Glycosyl compounds as chiral building blocks
have been used for the synthesis of many antibiotics and
other compounds of great medicinal value.4 The enan-
tioselective cycloaddition reactions have generally been
achieved either by use of chiral catalyst5 or by chiral
dienophile.6 In addition to the reports for the synthesis
of chiral dienes,7–10 their application in such reactions
is noticed rarely primarily due to their difficult synthesis
or low yields. Synthesis of glycosyl dienes and their
applications in many cycloaddition reactions for the
synthesis of a variety of compounds have received much
attention recently.11,12 Encouraged by the above reports
we were interested to synthesize glycosyl dienes wherein
the diene fragment is at C-4 of the glycofuranose ring.
The b,c-unsaturated glycosyl uronates13 on aldol type
condensation followed by methanesulfonylation of the
hydroxyl group and subsequent E2 reaction resulted in
the required glycosyl dienes. The method is very simple
as it involves the use of inexpensive reagents and very
simple workup procedure. All the three reactions in
the synthesis viz. isomerisation, condensation and elim-
ination are catalyzed by a single base DBU. To the best
of our knowledge this is the first approach to synthesize
glycosyl dienes by aldol type condensation followed by
elimination.
The synthetic strategy is shown in Scheme 1. The b,c-
unsaturated glycosyl uronates (2a and 2b) were obtained
on heating a,b-unsaturated glycosyl uronates (1a and
1b)14 with DBU (25 mol %), in dry THF at 80 ꢁC for
5 h as reported by us earlier.13 The uronates (2a and
2b) have the Z geometry and were characterized on
the basis of their physical data and microanalysis. The
disappearance of H-4 signals (at d 4.20 and 4.15 in 1a
and 1b, respectively) and appearance of triplets at d
4.84 (J = 6.9 Hz) and 4.81 (J = 7.0 Hz) for H-5 in the
1H NMR spectral data of compounds 2a and 2b, respec-
tively; and appearance of dd at d 3.22 (J = 6.9, 2.1 Hz)
and 3.18 (J = 7.0, 2.0 Hz) for H-6 along with other usual
signals in the above compounds 2a and 2b, respectively,
evidenced the migration of double bond from a,b- to
b,c-position. In the 13C NMR spectra of 2a and 2b,
the signals for C-4 appeared at d 153.8, 153.6; C-5 at d
q CDRI Communication No. 6761.
*
Corresponding author. Tel.: +91 522 262412x4382; fax: +91 522
2624305; e-mail: rpt_56@yahoo.com
0008-6215/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.carres.2006.04.021

S. S. Verma et al. / Carbohydrate Research 341 (2006) 1930–1937
1931
R1
COOEt
COOEt
O
COOEt
6
5
HO
H
O
O
O
O
i
1
4
O
ii
3
CMe2
CMe2
CMe2
2
O
O
RO
RO
O
RO
3a-i
1a, b
2a, b
1a, 2a, R=CH2Ph
1b, 2b, R=CH3
iii
R1
3-pyridyl
2-pyridyl
Compds
R
H
CH2Ph
CH2Ph
3a, 4a
3b, 4b
3c, 4c
3d, 4d
3e, 4e
COOEt
R1
CH2Ph 3,4-dimethoxyphenyl
CH2Ph thiophene-2-yl
O
CH2Ph
CH2Ph
CH3
phenyl
O
3f, 3j
3-pyridyl
CMe2
3g, 4g
3-nitrophenyl
4-bromophenyl
3-chlorophenyl
O
RO
3h, 4h
3i, 4i
CH3
CH3
(Z, E + Z,Z)
4a-i
Scheme 1. Reagents and conditions: (i) THF, DBU, 80–90 ꢁC, 5 h; (ii) R1CHO, DBU; 0–30 ꢁC; (iii) (a) MeSO2Cl, CH2Cl2, 0 ꢁC, 0.5–1.0 h; (b) DBU,
toluene, reflux, 3–4 h.
97.6, 97.4 while those of C-6 appeared at d 31.4 and
31.3, respectively. The Z geometry of the double bond
in compounds 2a and 2b was evidenced by NOE experi-
ments. The above glycosyl uronates 2a and 2b were
reacted with different aldehydes (Scheme 1) separately
at 0–30 ꢁC in the presence of DBU (50 mol %) for differ-
ent interval of time to yield the respective glycosyl
b-phenyl-b-hydroxy esters 3a–i. In the above reaction
it was observed that aromatic aldehydes with electron-
withdrawing substituents gave better yields of b- hydroxy
esters than those with electron donating substituents.
Heteroaromatic aldehydes viz. 2-pridyl-, 3-pyridyl- and
thiophene-2-carboxaldehydes also gave good yields of
the respective b-hydroxy esters. Compounds 3a–i were
characterized on the basis of their IR, MS, 1H, 13C
NMR spectral data and microanalysis. Due to the dia-
stereoisomeric nature of the compounds (3a–i), duplicity
reaction. Finally, these intermediate methanesulfonyl-
oxy derivatives were refluxed in toluene in presence of
DBU (100 mol %) to give the respective glycosyl dienes
4a–i (Scheme 1) in moderate to good yields (Table 1)
and were characterized on the basis of their spectro-
scopic data and microanalysis. The glycosyl dienes were
a mixture of two geometrical isomers (ZZ and ZE),
which was evidenced on the basis of their 1H NMR
spectral data and NOE experiments. The FABMS of
compound 4a showed a (M+H)+ ion at m/z 438 while
its IR spectrum exhibited absorption band at 1729 cmꢀ1
indicating the presence of a conjugated carbethoxy
1
group. In the H NMR spectrum of the above com-
pound, the olefinic proton H-7 appeared as a singlet at
d 6.85 while H-5 was observed as two distinct singlets
at d 5.46 and 5.33, respectively, indicating the presence
of the two geometrical isomers (ZZ and ZE). The ano-
meric proton (H-1) was also observed as two doublets
at d 6.21 and 6.00 having coupling constant of 3.0 Hz
due to the presence of two geometrical isomers ZZ
1
in many 13C and H NMR signals were observed.
It is interesting to note that the above reaction of a,b-
unsaturated glycosyl uronates 1a and 1b, with the alde-
hydes in the presence of DBU did not lead to any Baylis
Hilmann adduct, instead we got the isomerized esters 2a
and 2b along with the respective aldol products in very
low yields even after 36 h.
Table 1. Synthesis of glycosyl dienes from b hydroxyl esters
Entry Diene Yield (%) Reaction time (h) ZE/ZZ (ratio)
In the next step, the glycosyl b-aryl-b-hydroxy esters
3a–i were converted into their respective O-(methane-
sulfonyl) derivatives by treatment with methanesulfonyl
chloride in anhydrous dichloromethane in the presence
of triethylamine. The crude intermediate methane-
sulfonyloxy derivatives were isolated in quantitative
yields and used as such (these compounds were not sta-
ble even at room temperature for a long time) for further
1
2
3
4
5
6
7
8
9
4a
4b
4c
4d
4e
4f
36
50
40
41
42
40
48
35
45
3.0
1.5
3.0
3.0
3.0
4.0
2.5
3.0
3.0
11/9
99/1
50/50
45/55
50/50
80/20
60/40
60/40
80/20
4g
4h
4i

1932
S. S. Verma et al. / Carbohydrate Research 341 (2006) 1930–1937
and ZE. The ratio of two geometrical isomers was deter-
mined on the basis of the integration of H-1 signal in the
two isomers and it was found to be 11:9. In the NOE
experiments with 4a, irradiation of H-5 (major isomer)
signal resulted in an enhancement of the intensity of
H-3 and H-7, indicating a ZZ geometry of the double
bonds in the major isomer while irradiation of H-5 (min-
or isomer) signal did not show any NOE with H-7 indi-
cating a ZE geometry of the diene. Similarly, all other
compounds were characterized. In the 13C NMR spec-
trum of these glycosyl dienes, duplicity of anomeric car-
bon (C-1) and some other carbons was observed due to
the presence of two geometrical isomers.
(2 · 5 mL), the organic layer was dried (Na2SO4) and
evaporated under diminished pressure to give a crude
syrup (1.30 g). The crude product, thus obtained, was
chromatographed over silica gel (230–400 mesh) using
9:1 hexane–EtOAc as eluant to give 2a (1.0 g, 84%) as
a colourless oil; [a]D +35 (c 0.10, CHCl3); IR (neat):
1730, 1600 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d
7.34–7.28 (m, 5H, ArH), 6.10 (d, J 3.2 Hz, H-1), 4.84
(t, J 6.9 Hz, 1H, H-5), 4.71, 4.51 (d, J 11.8 Hz, 2H,
CH2Ph), 4.45 (d, J 3.2 Hz, 1H, H-2), 4.25 (s, 1H, H-3)
4.16 (q, 2H, J 7.2 Hz, OCH2), 3.22 (dd, J 6.9, 2.1 Hz,
2H, H-6), 1.45, 1.30 (s, 6H, CMe2), 1.23 (t, J 7.2 Hz,
3H, Me); 13C NMR (50 MHz, CDCl3): d 172.1
(C@O), 153.8 (C–4), 137.6, 128.9, 128.3, 128.2, 127.9,
127.4 (ArC), 114.2 (CMe2), 107.1 (C-1), 97.6 (C-5),
83.6, 80.7 (C-2, C-3), 70.5 (OCH2Ph), 61.0 (OCH2),
31.1 (C-6), 28.3, 27.6 (CMe2), 14.6 (Me); FABMS:
m/z = 349 [M+H]+. Anal. Calcd for C19H24O6: C,
65.51; H, 6.89. Found: C, 65.22; H, 6.62.
In conclusion we have developed a new and simple
method for the syntheses of glycosyl dienes involving
DBU catalyzed aldol type reaction of b,c-unsaturated
glycosyl uronates with aldehydes and subsequent E2
reaction.
1. Experimental
1.3. (4Z) Ethyl (1,2-O-isopropylidene-3-O-methyl-b-L-
threo)-hept-4-enofuranuronate (2b)
1.1. General methods
From 1b (1.2 g, 4.83 mmol) as a colourless oil; (1.10, 91%)
27
Commercially available reagent grade chemicals were
used as received. All reactions were followed by TLC
on E. Merck Kieselgel 60 F254, with detection by UV
light and/or spraying with 20% H2SO4 in EtOH and
heating. Column chromatography was performed on
Silica Gel (230–400 mesh, E. Merck). IR spectra were
recorded as thin films or neat chloroform solution with
a Perkin–Elmer Spectrum RX-1 (4000–450 cmꢀ1) spec-
trophotometer. The 1H and 13C NMR spectra were
recorded on a Brucker DRX-300 in (D) chloroform,
shift values are in ppm relative to SiMe4 as internal ref-
erence, unless otherwise stated; signals are reported as s
(singlet), d (doublet), t (triplet), m (multiplet); J in
hertz. Fast atom bombardment mass spectra (FABMS)
were performed by the Mass Spectrometer with a Jeol
SX-102 equipment. Elemental analyses were performed
on a Perkin–Elmer 2400 II elemental analyzer. The
optical rotations were measured in a 1.0 dm tube with
a Rudolf Autopol III polarimeter in chloroform.
½aꢁD +32 (c 0.10, CHCl3); IR (neat): 1728, 1616 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d 6.04 (d, J 3.2 Hz,
H-1), 4.81 (t, J 7.0 Hz, 1H, H-5), 4.50 (d, J 3.2 Hz,
1H, H-2), 4.05 (s, 1H, H-3), 4.14 (q, J 7.2, 2H,
OCH2), 3.34 (s, 3H, OMe), 3.18 (dd, J 7.0, 2.0 Hz,
2H, H-6), 1.47, 1.30 (s, 6H, CMe2), 1.23 (t, J 7.2 Hz,
3H, Me); 13C NMR (50 MHz, CDCl3): d 172.1
(C@O), 153.6 (C–4), 114.2 (CMe2), 107.0 (C-1), 97.4
(C-5), 83.3, 80.1 (C-2, C-3), 61.9 (OCH2), 31.3 (C-6),
28.3, 27.6 (CMe2), 14.5 (Me); FABMS: m/z = 273
[M+H]+. Anal. Calcd for C13H20O6: C, 54.58; H, 7.47.
Found: C, 54.23; H, 7.28.
1.4. (4Z) 3-O-Benzyl-6-carbethoxy-5,6-dideoxy-1,2-O-
isopropylidene-7-(3-pyridyl)-b-L-threo)-hept-4-enofura-
nose (3a)
To a magnetically stirred soln of compound 2a (1.0 g,
2.87 mmol) in dry THF (5.0 mL) at 0 ꢁC, 3-pyridylcar-
boxaldehyde (0.3 mL 3.16 mmol) and DBU (0.21 mL,
50 mol %) were added sequentially. The reaction mix-
ture was stirred for 30 min at 0 ꢁC followed by an addi-
tional 9 h at ambient temperature. The solvent
evaporated and the residue was partitioned between
EtOAc and water. EtOAc layer was separated, dried
(Na2SO4) and evaporated under diminished pressure
to give a crude mass, which was chromatographed over
SiO2 (240–400 mesh) using a gradient of hexane–
EtOAc (9:1!4:1) to give compound 3a as a colourless
˚
Solvents were dried and stored over activated 4 A
molecular sieve.
1.2. (4Z) Ethyl (3-O-benzyl-1,2-O-isopropylidene-b-L-
threo)-hept-4-enofuranuronate (2a)
To a magnetically stirred soln of the above com-
pound 1a (1.2 g, 3.44 mmol) in THF (6.0 mL), DBU
(0.13 mL, 25 mol %) was added and the reaction mixture
was stirred at 80 ꢁC for 5 h. The reaction mixture was
cooled and the solvent evaporated under diminished
pressure to give a crude product. The latter was dis-
solved in EtOAc (2 · 25 mL) and washed with water
27
viscous syrup (1.10 g, 85%); ½aꢁD ꢀ29 (c 0.10, CHCl3);
IR (neat): 3397, 1726 cmꢀ1
;
1H NMR (300 MHz,
CDCl3): d 8.57 (d, J 14.7 Hz, 1H, PyH), 8.44 (s, 1H,

S. S. Verma et al. / Carbohydrate Research 341 (2006) 1930–1937
1933
PyH), 7.79–7.72 (m, 1H, PyH), 7.41–7.15 (m, 6H, PyH,
ArH), 6.08, 5.97 (each d, J 3.3 and 2.7 Hz, 1H, H-1),
5.01 (m, 1H, H-7), 4.64–4.57 (m, 1H, H-5), 4.47–4.37
(m, 2H, OCH2Ph), 4.23–4.01 (m, 4H, H-2, OCH2, H-
3), 3.89–3.68 (m, 1H, H-6), 2.05 (br s, 1H, OH), 1.39,
1.37 (s, 6H, CMe2), 1.20 (t, J 8.7 Hz, 3H, Me); 13C
NMR (50 MHz, CDCl3): d 173.5, 173.1 (C@O), 156.0,
155.0 (C-4), 149.5, 148.9, 137.5, 137.4, 135.0, (PyC),
128.9, 128.2, 128.1, 123.7, 123.4 (ArC), 114.4, 114.3
(CMe2), 107.3 (C-1), 98.9, 98.4 (C-5), 83.4, 80.7 (C-2,
C-3), 73.7 (C-7), 70.5, 70.1 (OCH2Ph), 61.5 (OCH2),
50.3, 50.1 (C-6), 28.2, 27.9, 27.7, 27.3 (CMe2), 14.4
(Me); FABMS: m/z = 456 [M+H]+. Anal. Calcd for
C25H29O7N: C, 65.93; H, 6.15; N, 3.07. Found: C,
65.80; H, 6.10; N, 3.10.
(OCH2Ph), 61.2 (OCH2Me), 56.1, 55.9 (OMe), 50.5,
50.1 (C-6), 28.2, 27.3 (CMe2), 14.5 (Me); FABMS:
m/z = 515 [M+H]+. Anal. Calcd for C28H34O9: C,
65.36; H, 6.61. Found: C, 65.30; H, 6.60.
1.7. (4Z) 3-O-Benzyl-6-carbethoxy-5,6-dideoxy-7-
hydroxy-1,2-O-isopropylidene-7-(thiophene-2-yl)-
b-L-threo-hept-4-enofuranose (3d)
From 2a (1.0 g, 2.87 mmol) as a colourless viscous syrup
27
(1.03 g, 78%); ½aꢁD ꢀ25 (c 0.10, CHCl3); IR (neat): 3470,
1
1722 cmꢀ1; H NMR (200 MHz, CDCl3): d 7.36–7.17
(m, 5H, ArH), 7.03 (d, J 3.2 Hz, 1H, ThiophH), 6.96–
6.88 (m, 2H, ThiophH), 6.08, 6.06 (each d, J 3.0 Hz,
1H, H-1), 5.23–5.16 (m, 1H, H-7), 4.72–4.59 (m, 1H,
H-5), 4.40, 4.25 (d, J 12.4 Hz, 2H, PhCH2), 4.16 (d, J
3.0 Hz, 1H, H-2), 4.13 (q, J 7.2, 2H, OCH2Me), 4.00
(s, 1H, H-3), 3.69 (m, 1H, H-6), 2.06 (br s, 1H, OH),
1.39, 1.35 (s, 6H, CMe2), 1.22 (t, J 7.2 Hz, 3H, Me);
13C NMR (50 MHz, CDCl3): d 173.2 (C@O), 154.7
(C-4), 137.5, 128.8, 128.7, 128.2, 128.1, 126.9, 125.4,
125.1, 124.9, 124.6 (Ar–C, ThiophC), 114.3 (CMe2),
107.4 (C-1), 99.4 (C-5), 83.5, 80.6 (C-2, C-3), 71.8 (C-
7), 70.3 (OCH2Ph), 61.3 (OCH2Me), 50.3, (C-6), 28.3,
27.6 (CMe2), 14.5 (Me); FABMS: m/z = 461 [M+H]+.
Anal. Calcd for C24H28O7S: C, 62.60; H, 6.08. Found:
C, 62.61; H, 6.03.
1.5. (4Z) 3-O-Benzyl-6-carbethoxy-5,6-dideoxy-7-
hydroxy-1,2-O-isopropylidene-7-(2-pyridyl)-b-L-
threo-hept-4-enofuranose (3b)
From 2a (1.0 g, 2.87 mmol) as a colourless viscous syrup
27
(1.05 g, 82%); ½aꢁD ꢀ40 (c 0.10, CHCl3); IR (neat): 3449,
1
1722 cmꢀ1; H NMR (200 MHz, CDCl3): d 8.53–8.42
(m, 1H, PyH), 7.67–7.17 (m, 8H, PyH, ArH), 5.94,
5.84 (each d, J 3.0 and 2.8 Hz, 1H, H-1), 5.28–5.00 (m,
1H, H-7), 4.84–4.60 (m, 1H, H-5), 4.50–4.24 (m, 2H,
PhCH2), 4.21–4.04 (m, 4H, H-2, OCH2, H-3), 3.70–
3.65 (m, 1H, H-6), 2.26 (br s, 1H, OH), 1.37 and 1.32
(each s, each 3H, CMe2), 1.13 (t, J = 6.8 Hz, 3H, Me);
13C NMR (50 MHz, CDCl3): d 172.8 (C@O), 154.6,
154.1 (C-4), 148.7, 148.1, 137.6, 136.9 (PyC), 128.8,
128.2 (ArC), 123.0, 121.8, (ArC, PyC), 114.3 (CMe2),
107.3, 107.0 (C-1), 99.7, 98.1 (C-5), 83.5, 80.6 (C-2, C-
3), 73.4 (C-7), 70.4 (OCH2Ph), 61.4, 61.1 (OCH2Me),
50.2, 49.3 (C-6), 28.2, 27.6 (CMe2), 14.5 (Me); FABMS:
m/z = 456 [M+H]+. Anal. Calcd for C25H29O7N: C,
65.93; H, 6.15; N, 3.07. Found: C, 65.90; H, 6.12; N,
3.11.
1.8. (4Z) 3-O-Benzyl-6-carbethoxy-5,6-dideoxy-7-
hydroxy-1,2-O-isopropylidene-7-phenyl-b-L-threo-
hept-4-enofuranose (3e)
From 2a (1.0 g, 2.87 mmol) as a colourless viscous syrup
27
(1.10 g, 85%); ½aꢁD ꢀ16 (c 0.10, CHCl3); IR (neat): 3470,
1
1722 cmꢀ1; H NMR (200 MHz, CDCl3): d 7.41–7.11
(m, 10H, ArH), 6.09, 6.00 (each d, J 3.2, 2.8 Hz, 1H,
H-1), 5.22–5.16 (m, 1H, H-7), 4.99–4.67 (m, 1H, H-5),
4.69 (m, 2H, PhCH2), 4.40 (d, J 3.0 Hz, 1H, H-2), 4.19
(m, 2H, OCH2Me), 4.00 (s, 1H, H-3), 3.71, 3.69 (m,
1H, H-6), 2.06 (br s, 1H, OH), 1.41, 1.39 and 1.35,1.30
(s, 6H, CMe2), 1.19 (t, J 7.0 Hz, 3H, Me); FABMS:
m/z = 455 [M+H]+. Anal. Calcd for C26H3O7: C,
68.72; H, 6.60. Found: C, 68.69; H, 6.78.
1.6. (4Z) 3-O-Benzyl-6-carbethoxy-5,6-dideoxy-7-
hydroxy-1,2-O-isopropylidene-7-(3,4-dimethoxyphenyl)-
b-L-threo-hept-4-enofuranose (3c)
From 2a (1.0 g, 2.87 mmol) as a colourless viscous syrup
27
(1.21 g, 83%); ½aꢁD ꢀ37 (c 0.10, CHCl3); IR (neat): 3469,
1.9. (4Z) 6-Carbethoxy-5,6-dideoxy-7-hydroxy-1,2-O-
isopropylidene-3-O-methyl-7-(3-pyridyl)-b-L-threo-hept-
4-enofuranose (3f)
1725 cmꢀ1; H NMR (200 MHz, CDCl3): d 7.36–7.26
1
(m, 5H, ArH), 7.11–7.01 (m, 3H, ArH), 6.07, 5.99 (each
d, J 3.4 Hz, 1H, H-1), 4.96–4.89 (m, 1H, H-7), 4.69–4.50
(m, 1H, H-5), 4.50–4.40 (m, 3H, PhCH2, H-2), 4.20 (q, J
7.2 Hz, 2H, OCH2), 4.09 (s, 1H, H-3), 3.86, 3.71 (s, 3H,
OMe), 3.90 (m, 1H, H-6), 2.06 (br s, 1H, –OH), 1.41,
1.39 (s, 6H, CMe2), 1.19 (t, J 7.2 Hz, 3H, OCH2Me);
13C NMR (50 MHz, CDCl3): d 173.7, 173.5 (C@O),
154.5, 154.1 (C-4), 137.4, 134.3, 128.8, 128.7, 128.2,
128.1, 120.0, 119.4 (ArC), 114.3 (CMe2), 107.3 (C-1),
98.3 (C-5), 83.5, 80.7 (C-2, C-3), 75.3 (C-7), 70.2
From 2b (1.0 g, 2.87 mmol) as a colourless viscous syrup
27
(1.20 g, 87%); ½aꢁD ꢀ60 (c 0.10, CHCl3); IR (neat): 3469,
1
1729 cmꢀ1; H NMR (200 MHz, CDCl3): d 8.59–8.46
(m, 2H, PyH), 7.72 (d, J 8.0 Hz, PyH), 7.30–7.20 (m,
1H, PyH), 6.01, 5.89 (each d, J 3.0 and 2.8 Hz, 1H, H-
1), 5.30–5.19 (m, 1H, H-7), 4.82–4.60 (m, 1H, H-5),
4.46–4.39 (m, 1H, H-2), 4.16–4.09 (m, 2H, OCH2Me),
3.94, 3.92 (each s, each 1H, H-3), 3.70–3.65 (m, 1H,

1934
S. S. Verma et al. / Carbohydrate Research 341 (2006) 1930–1937
H-6), 3.32, 3.13 (s, 3H, OMe), 2.90 (br s, 1H, OH), 1.40,
1.35 (s, 6H, CMe2), 1.16 (m, 3H, Me). 13C NMR
(50 MHz, CDCl3): d 173.8, 173.5 (C@O), 155.5, 154.8
(C-4), 149.3, 148.7, 137.5, 134.7, 123.7 (Py-C), 114.4
(CMe2), 107.1 (C-1), 98.5 (C-5), 83.1, 82.8 (C-2, C-3),
73.6, 73.2 (C-7), 61.5 (OCH2Me), 56.5 (OMe), 52.4,
50.2 (C-6), 28.2, 27.9, 27.5, 27.3 (CMe2), 14.4 (Me);
FABMS: m/z = 380 [M+H]+. Anal. Calcd for
C19H25O7N: C, 60.15; H, 6.59; N, 3.69. Found: C,
60.11; H, 6.60; N, 3.65.
1.12. (4Z) 6-Carbethoxy-5,6-dideoxy-7-hydroxy-1,2-O-
isopropylidene-3-O-methyl-7-(3-chlorophenyl)-
b-L-threo-hept-4-enofuranose (3i)
From 2b (1.0 g, 3.67 mmol) as a colourless oil (1.36 g,
27
90%); ½aꢁD ꢀ15 (c 0.10, CHCl3); IR (neat): 3448,
1723 cmꢀ1 1H NMR (200 MHz, CDCl3): d 7.36 (s,
;
1H, ArH), 7.26–7.22 (m, 3H, ArH), 6.01, 5.94 (each d,
J 3.2 Hz, 1H, H-1), 5.12–4.91 (m, 1H, H-7), 4.74–4.59
(m, 1H, H-5), 4.45–4.40 (m, 1H, H-2), 4.18–4.07 (m,
2H, OCH2Me), 3.98 (s, 1H, H-3), 3.95–3.89 (m, 1H,
H-6), 3.35 (s, 3H, OMe), 2.90 (br s, 1H, –OH), 1.40,
1.33 (s, 6H, CMe2), 1.16 (t, J 7.0 Hz, 3H, Me). 13C
NMR (50 MHz, CDCl3): d 173.2 (C@O), 155.1, 154.2
(C-4), 140.5, 131.5, 131.3, 128.6, 128.4, 121.5 (ArC),
114.0 (CMe2), 106.9 (C-1), 98.6, 97.3 (C-5), 83.0, 82.1
(C-2 and C-3), 74.6, 73.0 (C-7), 66.1 (OCH2Me), 56.6
(OMe), 50.3, 49.4 (C-6), 27.7, 27.2 (CMe2), 15.2 (Me);
FABMS: m/z 414 [M+H]+. Anal. Calcd for
C20H25O7Cl: C, 58.11; H, 6.05. Found: C, 58.10; H,
6.02.
1.10. (4Z) 6-Carbethoxy-5,6-dideoxy-7-hydroxy-1,2-O-
isopropylidene-3-O-methyl-7-(3-nitrophenyl)-b-L-threo-
hept-4-enofuranose (3g)
From 2b (1.0 g, 3.67 mmol) as a colourless viscous
27
syrup (1.50 g, 97%); ½aꢁD ꢀ50 (c 0.10, CHCl3); IR (neat):
1
3433, 1720 cmꢀ1; H NMR (200 MHz, CDCl3): d 8.23
(s, 1H, ArH), 8.14 (d, J 5.4 Hz, 1H, ArH), 7.84 (t, J
8.0 Hz, 1H, ArH), 7.62 (d, J 8.0 Hz, ArH), 6.01, 5.87
(each d, J 2.8 Hz, 1H, H-1), 5.26–4.94 (m, 1H, H-7),
4.81–4.58 (m, 1H, H-5), 4.39 (d 2.8 Hz, 1H, H-2), 4.04
(q, J 7.2 Hz, 2H, OCH2), 3.63 (s, 1H, H-3), 3.37 (s, 3H,
OCH3), 3.03–2.84 (m, 1H, H-6), 2.90 (br s, 1H, OH),
1.28, 1.20 (s, 6H, CMe2), 1.16 (t, J 7.2 Hz, Me); 13C
NMR (50 MHz, CDCl3): d 172.7, 172.3 (C@O), 148.3
(C-4), 133.8, 133.5, 132.9, 129.2, 129.1, 118.9 (ArC),
114.0 (CMe2), 106.9, 106.8 (C-1), 98.9 (C-5), 83.1, 82.7
(C-2, C-3), 74.6, 74.3 (C-7), 61.0 (OCH2), 56.2 (Me),
52.2, 51.3 (C-6), 28.1, 27.9 (CMe2), 14.4 (Me); FABMS:
m/z 424 [M+H]+. Anal. Calcd for C20H25O9N: C,
56.73; H, 5.91; N, 3.30. Found: C, 56.68; H, 5.90; N,
3.38.
1.13. (4-Z,6-E/Z) 3-O-Benzyl-6-carbethoxy-5,6,7-tri-
deoxy-1,2-O-isopropylidene-7-(3-pyridyl)-b-L-threo-hept-
4,6-dienofuranose (4a)
To a magnetically stirred soln of compound 3a (0.5 g,
1.10 mmol) and triethylamine (1 mL) in CH2Cl2 (5 mL)
at 0 ꢁC, methanesulfonyl chloride (0.14 mL, 1.21 mmol)
was slowly added and the reaction continued for 1 h till
the disappearance of the starting material (TLC). The
solvent was evaporated and the residue thus obtained
was filtered on flash silica gel to give the intermediate
methanesulfonyloxy derivative (0.40 g) which was used
in the next step. A soln of the above methanesulfonyloxy
derivative and DBU (0.17 mL, 100 mol %) in anhydr
toluene (5 mL) was refluxed at 130 ꢁC for 3 h. The reac-
tion mixture was cooled, the solvent evaporated and the
residue was dissolved in EtOAc (2 · 25 mL) and washed
with water (2 · 12.5 mL). The organic layer was dried
(Na2SO4) and evaporated under diminished pressure to
give a residual mass (0.35 g) which was chromato-
graphed over SiO2 column using a gradient of hexane–
EtOAc (19:1!9:1) to give 4a (0.18 g, 36%) as a colour-
1.11. (4Z) 6-Carbethoxy-5,6-dideoxy-7-hydroxy-1,2-O-
isopropylidene-3-O-methyl-7-(4-bromophenyl)-b-L-
threo-hept-4-enofuranose (3h)
From 2b (1.0 g, 3.67 mmol) as a colourless syrup
27
(1.14 g, 86%); ½aꢁD ꢀ37 (c 0.10, CHCl3); IR (neat):
3481, 1731 cmꢀ1
;
1H NMR (300 MHz, CDCl3): d
7.44–7.25 (m, 2H, ArH), 7.24–7.20 (m, 2H, ArH),
5.99, 5.92 (each d, J 3.6 Hz, 1H, H-1), 5.13–5.09 (m,
1H, H-7), 4.75, 4.54 (each d, J 10.6 Hz, 1H, H-5),
4.40 (d, J 3.6 Hz, 1H, H-2), 3.99 (s, 1H, H-3), 3.68 (q,
J 7.2 Hz, 2H, OCH2), 3.48–3.43 (m, 1H, H-6), 3.31,
3.25 (each s, each 3H, OMe), 2.90 (br s, 1H, OH),
1.39, 1.35, (s, 6H, CMe2), 1.19 (t, J 7.2 Hz, Me). 13C
NMR (50 MHz, CDCl3): d 173.7 (C@O), 155.3, 154.4
(C-4), 140.5, 131.5, 131.3, 128.6, 128.4, 121.5 (ArC),
114.1 (CMe2), 107.0 (C-1), 98.7, 97.1 (C-5), 83.0, 82.2
(C-2, C-3), 75.0, 73.0 (C-7), 66.0 (OCH2Me), 56.4
(OMe), 50.1, 49.6 (C-6), 27.7, 27.1 CMe2, 15.4 (Me);
FABMS: m/z = 458 [M+H]+. Anal. Calcd for
C20H25O7Br: C, 52.51; H, 5.47. Found: C, 52.50; H,
5.42.
27
less foam; ½aꢁD ꢀ50 (c 0.10, CHCl3); IR (neat):
1
1729 cmꢀ1; H NMR (200 MHz, CDCl3): d 8.63–8.52
(m, 3H, PyH), 7.82–7.45 (m, 6H, PyH, ArH), 6.85 (s,
1H, H-7), 6.21, 6.00 (d, J 3.0 Hz, 1H, H-1), 5.46, 5.33
(s, 1H, H-5), 4.98 (d, J 11.2 Hz, 1H, CH2Ph), 4.87 (d, J
3.0 Hz, 1H, H-2), 4.77 (d, J 11.2 Hz, 1H, CH2Ph), 4.60
(s, 1H, H-3), 4.35 (q, J 7.2 Hz, 2H, OCH2), 1.62 and
1.51 (s, 6H, CMe2), 1.32 (t, J 7.2 Hz, 3H, Me); 13C
NMR (50 MHz, CDCl3): d 169.1 (C@O), 154.4 (C-4),
148.7, 148.4 (C-6), 137.4, 136.8, 132.4, 132.3 (PyC),
130.7, 128.9, 128.9, 128.4, 128.3, 123.4 (PyC), 127.6
(ArC), 115.3 (CMe2), 108.6 (C-1), 102.8 (C-7), 96.1 (C-

S. S. Verma et al. / Carbohydrate Research 341 (2006) 1930–1937
1935
5), 82.8, 82.1 (C-2, C-3), 71.0 (OCH2Ph), 61.8 (OCH2),
28.2, 27.6 (2 · Me), 14.6 (Me); FABMS: m/z = 438
[M+H]+. Anal. Calcd for C25H27O6N: C, 68.64; H,
5.94; N, 3.20. Found: C, 68.62; H, 5.90; N, 3.10.
1H, H-7), 6.20, 6.12 (each d, J 3.2 Hz, 1H, H-1), 5.48,
5.32 (each s, 1H, H-5), 4.89, 4.68 (d, J 11.6 Hz, 2H,
PhCH2), 4.56 (m, 1H, H-2), 4.60 (s, 1H, H-3), 4.33 (q,
J 6.8 Hz, 2H, OCH2), 1.60, 1.38 (s, 6H, CMe2), 1.32
(t, J 6.8 Hz, 3H, OCH2Me); 13C NMR (50 MHz,
CDCl3): d 168.9, 167.8 (C@O), 155.9 (C-4), 152.9 (C-
6), 139.5, 137.7, 137.5, 137.5 132.5, 128.9, 128.6, 127.4,
125.4, 123.6 (ArC, ThiophC), 114.8, 114.6 (CMe2),
107.9 (C-1), 103.4 (C-7), 98.8 (C-5), 83.4, 82.1 (C-2, C-
3), 70.9 (OCH2Ph), 61.8, 51.3 (OCH2Me), 30.7, 30.0,
28.3, 28.1 (CMe2), 14.7, 14.4 (Me). FABMS: m/z =
443 [M+H]+. Anal. Calcd for C24H26O6S: C, 65.16; H,
5.88. Found: C, 65.08; H, 5.75.
1.14. (4-Z,6-E/Z) 3-O-Benzyl-6-carbethoxy-5,6,7-tri-
deoxy-1,2-O-isopropylidene-7-(2-pyridyl)-b-L-threo-hept-
4,6-dienofuranose (4b)
From 3b (0.5 g, 1.10 mmol) as a colourless foam (0.20 g,
27
50%); ½aꢁD ꢀ14 (c 0.10, CHCl3); IR (neat): 1728 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d 8.50 (d, J 4.0 Hz, 1H,
PyH), 7.58 (m, 1H, PyH), 7.38, 7.08 (m, 7H, ArH,
PyH), 6.70 (s, 1H, H-7), 6.22 (d, J 3.2 Hz, 1H, H-1),
5.28 (s, 1H, H-5), 4.73–4.48 (m, 4H, OCH2Ph, H-2, H-
3), 4.39–4.33 (q, J 7.2 Hz, OCH2Me), 1.44 and 1.38 (s,
6H, CMe2), 1.32 (t, J 7.2 Hz, 3H, OCH2Me); 13C
NMR (50 MHz, CDCl3): d 170.0 (C@O), 154.4 (C-4),
149.5 (C-6), 142.4 (PyC), 137.4, 136.5, 135.0, 133.6,
128.9, 128.4, 128.2 127.6 (ArC, PyC), 123.9, 122.8
(PyC), 114.9 (CMe2), 108.7 (C-1), 103.2 (C-7), 98.3 (C-
5), 82.8, 82.2 (C-2, C-3), 70.9 (OCH2Ph), 61.4
(OCH2Me), 28.2, 27.6 (CMe2), 14.6 (Me); FABMS:
m/z = 438 [M+H]+. Anal. Calcd for C25H27O6N: C,
68.64; H, 5.94; N, 3.20. Found: C, 68.62; H, 6.01; N, 3.16.
1.17. (4-Z,6-E/Z) 3-O-Benzyl-6-carbethoxy-5,6,7-tri-
deoxy-1,2-O-isopropylidene-7-(phenyl)-b-L-threo-hept-
4,6-dienofuranose (4e)
From 3e (0.5 g, 1.08 mmol) as a colourless foam (0.21 g,
27
42%); ½aꢁD ꢀ49 (c 0.10, CHCl3); IR (neat): 1706 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d 7.34–7.21 (m, 10H,
ArH,), 6.70 (s, 1H, H-7), 6.20, 6.12 (each d, J 3.4 Hz,
1H, H-1), 5.48 (s, 1H, H-5), 4.89, 4.66 (d, J 11.2 Hz,
2H, PhCH2), 4.56 (m, 1H, H-2), 4.09 (s,1H, H-3), 4.33
(q, J 7.0 Hz, 2H, (OCH2), 1.60, 1.38 (s, 3H, CMe2),
1.32 (t, J 7.0 Hz, 3H, Me); FABMS: m/z = 437
[M+H]+. Anal. Calcd for C26H28O6: C, 71.55; H, 6.42.
Found: C, 71.52; H, 6.41.
1.15. (4-Z,6-E/Z) 3-O-Benzyl-6-carbethoxy-5,6,7-tri-
deoxy-1,2-O-isopropylidene-7-(3,4-dimethoxyphenyl)-b-
L-threo-hept-4,6-dienofuranose (4c)
1.18. (4-Z,6-E/Z) 6-Carbethoxy-5,6,7-trideoxy-1,2-O-
isopropylidene-3-O-methyl-7-(3-pyridyl)-b-L-threo-
hept-4,6-dienofuranose (4f)
From 3c (0.5 g, 1.07 mmol) as a colourless foam (0.20 g,
27
40%) yield; ½aꢁD ꢀ58 (c 0.10, CHCl3); IR (neat):
1
1724 cmꢀ1; H NMR (200 MHz, CDCl3): d 7.44–6.92
(m, 8H, ArH), 6.68 (s, 1H, H-7), 6.21, 6.04 (each d, J
3.0 Hz, 1H, H-1), 5.48, 5.28 (each s, 1H, H-5), 4.98 (d,
J 11.2 Hz, 1H, PhCH2), 4.87 (d, J 3.0 Hz, 1H, H-2),
4.77 (d, J 11.2 Hz, 1H, PhCH2), 4.60 (s, 1H, H-3),
4.35 (q, J 7.2 Hz, 2H, OCH2Me), 1.50 and 1.37 (s, 6H,
(CMe2), 1.28 (t, J 7.2 Hz, 3H, OCH2Me); 13C NMR
(50 MHz, CDCl3): d 170.1 (C@O), 154.8 (C–4), 152.6
(C-6), 137.6, 135.0, 132.4, 128.9, 128.3, 127.2, 124.6,
121.9 (ArC), 114.7 (CMe2), 108.4, 107.7 (C-1), 104.0
(C-7), 99.5 (C-5), 83.2, 82.1 (C-2, C-3), 71.0 (OCH2Ph),
61.6 (OCH2), 56.5, 56.2 (OMe), 28.3, 28.2, (CMe2), 14.7,
14.3 (Me). FABMS: m/z = 497 [M+H]+. Anal. Calcd
for C28H32O8: C, 67.74; H, 6.45. Found: C, 67.68; H,
6.42.
From 3f (0.5 g, 1.31 mmol) as a colourless foam (0.18 g,
27
40%); ½aꢁD ꢀ30 (c 0.10, CHCl3); IR (neat): 1722 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d 8.71 (s, 1H, PyH),
8.50–8.44 (m, 1H, PyH), 7.36–7.25 (m, 2H, PyH), 6.83
(s, 1H, H-7), 6.17, 5.94 (each d, J 3.2 Hz, 1H, H-1),
5.36, 5.30 (s, 1H, H-5), 4.52 (d, J 3.2 Hz, 1H, H-2),
4.29–4.16 (m, 2H, OCH2), 3.82 (each s, 1H, H-3), 3.44,
3.40 (s, 3H, OMe), 1.48, 1.45 (s, 6H, CMe2), 1.22 (t, J
7.2 Hz, Me); FABMS: m/z = 362 [M+H]+. Anal. Calcd
for C19H23O6N: C, 63.16; H, 6.37; N, 3.88. Found: C,
63.10; H, 6.42. N, 3.80.
1.19. (4-Z,6-E/Z)6-Carbethoxy-5,6,7-trideoxy-1,2-O-iso-
propylidene-3-O-methyl-7-(3-nitrophenyl)-b-L-threo-hept-
4,6-dienofuranose (4g)
1.16. (4-Z,6-E/Z) 3-O-Benzyl-6-carbethoxy-5,6,7-tri-
deoxy-1,2-O-isopropylidene-7-(thiophen-2-carboxalde-
hyde)-b-L-threo-hept-4,6-dienofuranose (4d)
From 3g (0.5 g, 1.18 mmol) as a colourless foam (0.34 g,
27
48%); ½aꢁD ꢀ52 (c 0.10, CHCl3); IR (neat): 1723 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d 8.17 (t, J 3.4 Hz, 1H,
ArH), 8.08 (d, J 8.4 Hz, 1H, ArH), 7.62–7.42 (m, 2H,
ArH), 6.86 (s, 1H, H-7), 6.17 (d, J 3.0 Hz, 1H, H-1),
5.35, 5.30 (s, 1H, H-5), 4.51 (d, J 3.0 Hz, 1H, H-2),
4.28 (q, J 7.8 Hz, 2H, OCH2), 3.81 (s, 1H, H-3), 3.40,
From 3d (0.5 g, 1.08 mmol) as a colourless foam in
27
(0.20 g, 41%) yield; ½aꢁD ꢀ54 (c 0.10, CHCl3); IR (neat):
1
1706 cmꢀ1; H NMR (200 MHz, CDCl3): d 7.41 (s, 1H,
ThiophH), 7.42–7.26 (m, 7H, ArH, ThiophH), 7.05 (s,

1936
S. S. Verma et al. / Carbohydrate Research 341 (2006) 1930–1937
(s, 3H, OMe), 1.46, 1.34 (s, 6H, CMe2), 1.22 (t, J 7.8 Hz,
3H, Me); 13C NMR (50 MHz, CDCl3): d 169.0, 168.5
(C@O), 156.1 (C-4), 148.3 (C-6), 135.4, 133.7, 130.5,
130.2 (ArC), 113.9 (CMe2), 108.2, 107.6 (C-1), 102.3
(C-7), 98.6 (C-5), 83.4, 81.9 (C-3, C-2), 61.4 (OCH2),
56.4 (OMe), 27.9, 27.7 (CMe2), 13.9 (Me); FABMS:
m/z = 406 [M+H]+. Anal. Calcd for C20H23O8N: C,
59.25; H, 5.68; N, 3.45. Found: C, 59.15; H, 5.61; N,
3.38.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.carres.
2006.04.021.
References
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´
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35%); ½aꢁD ꢀ62 (c 0.25, CHCl3); IR (neat): 1726 cmꢀ1
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ArH), 7.33–7.13 (m, 2H, ArH), 6.69 (s, 1H, H-7), 6.14,
5.97 (d, J 3.0 Hz, 1H, H-1), 5.41, 5.31 (s, 1H, H-5),
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OCH2), 3.80 (s, 1H, H-3), 3.38 (s, 3H, OCH3), 1.48,
1.36(s, 6H, CMe2), 1.25 (t, J 7.2 Hz, 3H, Me); 13C
NMR (50 MHz, CDCl3): d 169.9 (C@O), 155.3 (C-4),
153.6 (C-6), 136.5, 135.1, 131.9, 129.9, 123.0, 122.2
(ArC), 114.8 (CMe2), 108.4, 107.6 (C-1), 103.2 (C-7),
98.3 (C-5), 84.5, 82.8 (C-3, C-2), 57.1 (OCH2), 52.6
(OMe), 28.1, 27.6 (CMe2), 13.9 (Me); FABMS: m/z =
439 [M+H]+. Anal. Calcd for C20H23O6Br: C, 54.66;
H, 5.24. Found: C, 54.62; H, 5.22.
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Deagostinoa, A.; Migliardia, M.; Occhiatoa, E. G.;
Prandia, C.; Zavattaroa, C.; Venturelloa, P. Tetrahedron
2005, 61, 3429–3436; (e) Vallin, K. S. A.; Larhed, M.;
Johansson, K.; Hallberg, A. J. Org. Chem. 2000, 65, 4537–
4542; (f) Ma, B.; Snyder, J. K. Tetrahedron Lett. 2005, 46,
703–706.
1.21. (4-Z,6-E/Z) 6-Carbethoxy-5,6,7-trideoxy-1,2-O-
isopropylidene-3-O-methyl-7-(3-chlorophenyl)-b-L-threo-
hept-4,6-dienofuranose (4i)
From 3i (0.5 g, 1.21 mmol) as a colourless foam(0.21 g,
27
45%); ½aꢁD ꢀ48 (c 0.10, CHCl3); IR (neat): 1725 cmꢀ1
;
1H NMR (200 MHz, CDCl3): d 7.32–7.19 (m, 4H,
ArH), 6.75 (s, 1H, H-7), 6.15 (d, J 3.2 Hz, 1H, H-1),
5.43, 5.31 (s, 1H, H-5), 4.51 (d, J 3.2 Hz, 1H, H-2),
4.25 (q, J 6.6 Hz, 2H, OCH2), 4.18 (s, 1H, H-3), 3.39
(s, 3H, OMe), 1.45, 1.39 (s, 6H, CMe2), 1.23 (t, J
6.6 Hz, 3H Me); 13C NMR (50 MHz, CDCl3): d 174.0
(C@O), 153.8 (C-4), 149.2 (C-6), 138.2, 134.5, 128.8,
128.3, 126.6 (ArC), 114.8 (CMe2), 108.5, 107.8 (C-1),
102.9 (C-7), 98.3 (C-5), 84.5, 83.9 (C-3, C-2), 61.7
(OCH2), 56.9 (OMe), 27.3, 27.6 (CMe2), 14.6 (Me);
FABMS: m/z = 395 [M+H]+. Anal. Calcd for
C20H23O6Cl: C, 60.76; H, 5.82. Found: C, 60.66; H, 5.80.
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Acknowledgements
S.S.V., N.D. and B.S. are thankful to UGC and CSIR,
for financial assistance in the form of JRF. We are
thankful to RSIC, for giving the spectral data and
analysis.
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