Synthesis and structure determination of some oxadiazole-2-thione and triazole-3-thione galactosides

Article abstract of DOI:10.1081/NCN-100105903

The syntheses of 5-pyridyl-3(β-D-galactopyranosyl)-1,3,4-oxadiazole-2-thiones 3a-3c and 5-pyridyl-2(β-D-galactopyranosyl)-4-benzyl-l,2, 4-triazole-3-thiones 6a-6c are reported. The existence of N-galactosides - not S-galactosides - was proven by IR and ¹⁵N NMR spectroscopy. The structures of the final products and the intermediates were elucidated by IR, ¹H, ¹³C and ¹⁵N NMR spectroscopy and mass spectrometry.

Full text of DOI:10.1081/NCN-100105903

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SYNTHESIS AND STRUCTURE DETERMINATION OF SOME
OXADIAZOLE-2-THIONE AND TRIAZOLE-3-THIONE
GALACTOSIDES
Roshan Ahmad a , Rashid Iqbal a , Humaira Akhtar a , Zia-ul-Haq a , Helmut Duddeck b , Lech
Stefaniak† c & Jerzy Sitkowski c
a Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
b Institut für Organische Chemie der Universität Hannover, Schneiderberg 1B, Hannover,
D-30167, Germany
c Polish Academy of Sciences, Institute of Organic Chemistry, ul. Kasprzaka 44-22, Warsaw,
PL-01-224, Poland
Published online: 21 Aug 2006.
To cite this article: Roshan Ahmad , Rashid Iqbal , Humaira Akhtar , Zia-ul-Haq , Helmut Duddeck , Lech Stefaniak† & Jerzy
Sitkowski (2001): SYNTHESIS AND STRUCTURE DETERMINATION OF SOME OXADIAZOLE-2-THIONE AND TRIAZOLE-3-THIONE
GALACTOSIDES, Nucleosides, Nucleotides and Nucleic Acids, 20:9, 1671-1682
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NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS, 20(9), 1671ꢀ1682(2001)
SYNTHESIS AND STRUCTURE
DETERMINATION OF SOME OXADIAZOLE-
2-THIONE AND TRIAZOLE-3-THIONE
GALACTOSIDES
Roshan Ahmad,1,* Rashid Iqbal,1 Humaira Akhtar,1 Zia-ul-Haq,1
Helmut Duddeck,2,* Lech Stefaniak,3,{ and Jerzy Sitkowski3
1Department of Chemistry, Quaid-i-Azam University,
Islamabad, Pakistan
2Institut fur Organische Chemie der Universitat Hannover,
Schneiderberg 1B, D-30167 Hannover, Germany
3Polish Academy of Sciences, Institute of Organic Chemistry, ul.
Kasprzaka 44-22, PL-01-224 Warsaw, Poland
ABSTRACT
The syntheses of 5-pyridyl-3(b-D-galactopyranosyl)-1,3,4-oxadiazole-
2-thiones 3aꢀ3c and 5-pyridyl-2(b-D-galactopyranosyl)-4-benzyl-1,2,
4-triazole-3-thiones 6aꢀ6c are reported. The existence of N-galactosides ꢀ
not S-galactosides ꢀ was proven by IR and 15N NMR spectroscopy. The
structures of the final products and the intermediates were elucidated by
1
IR, H, 13C and 15N NMR spectroscopy and mass spectrometry.
During the last thirty years and especially since the discovery of 20,30-
dideoxycytidine (DDC)1, 20,30-dideoxyinosine (DDI)2 and azidothymidine
(AZT)3 as anti-HIV agents, a large number of nucleosides have been syn-
thesized. The nucleosides of N-substituted azoles constitute a special class
both for their biological significance4 and for the particular synthetic meth-
ods involved in their preparation. Amongst the new synthetic nucleosides,
*Corresponding authors.
{Deceased.
1671
Copyright # 2001 by Marcel Dekker, Inc.
www.dekker.com

1672
AHMAD ET AL.
pyrazoles, oxadiazoles, oxatriazoles and triazoles are the significant
counterparts of sugars. Ribavirin5 the first synthetic broad-spectrum non-
interferon inducing antiviral agent has been prepared and tested against a
variety of both DNA and RNA viruses in tissue culture. Then, the ribonu-
cleoside antibiotics pyrazomycin and formycin6 have also demonstrated
antiviral activity in vitro. Some other triazole nucleosides7 having haloalkyl
groups were reported to be effective against ECA and P388 tumor systems.
N-Glycosides of oxadiazoles are not very well known but 2-b-D-ribofur-
anosyl-1,2,4-oxadiazole-3,5-dione8 showed significant antiviral activity
against herpes simplex HSV type 1, HSV type 2and parainfluenza virus
type 3. Glucosides of structurally similar heterocycles have been reported
before9ꢀ11
.
In continuation of our work on the synthesis of novel nucleosides as
potential antiviral agents and keeping in mind the biological significance of
pyridyl substituted triazoles12,13 and mercapto-oxadiazoles14,15, we synthe-
sized new pyridyl-substituted azoles and prepared their nucleosides. We
hereby report the synthesis and spectroscopy of 5-pyridyl-3-(b-D-galacto-
pyranosyl)-1,3,4-oxadiazole-2-thiones 3aꢀ3c and 5-pyridyl-2-(b-D-galacto-
pyranosyl)-4-benzyl-1,2,4-triazole-3-thiones 6aꢀ6c.
The mercapto-oxadiazoles 1aꢀ1c were synthesized by the reaction of
pyridyl-substituted hydrazides with CS2=KOH (Scheme 1). The syntheses of
some structurally related compounds have been reported earlier using slightly
different procedures16.
Scheme 1. Synthesis of oxadiazole-2-thione galactosides.

TRIAZOLE-3-THIONE GALACTOSIDES
1673
The mercaptotriazoles 4aꢀ4c were synthesized as shown in Scheme 2,
and the compounds showed the physical data in accordance with the data
reported in literature12.
Scheme 2. Synthesis of triazole-3-thione galactosides.
The mercapto-oxadiazoles and triazoles were then coupled with aceto-
bromogalactose in the presence of mercuric cyanide=nitromethane to give the
corresponding nucleosides 2aꢀ2c and 5aꢀ5c, respectively. The structure of
the compounds was established by IR, 1H NMR, 13C NMR, COSY,
HETCOR and mass spectrometry. IR spectra showed a peak at 1224 cmꢀ1
indicative of C¼S. This shows that the glycosides are N-glycosides and not
S-glycosides (Scheme 3).
In the 1H NMR spectra of the compounds 2aꢀ2c and 5aꢀ5c (Table 1)
the protons of the acetyl groups appear as singlets in the region
d=1:84ꢀ2:25. H-50 and H-60=60a resonate as multiplets in the range
d ¼ 4:13ꢀ4:28. The b configuration of these nucleosides was assigned by
NMR measurements; the anomeric proton H-10 signals appear as doublets
with coupling constants of 9ꢀ10 Hz in all compounds which clearly indicates
the diaxial orientation of H-10 and H-20. In case of the compounds 5a>ꢀ5c,

1674
AHMAD ET AL.

TRIAZOLE-3-THIONE GALACTOSIDES
1675
Scheme 3. Conceivable isomeric galactosides.
the diastereotopic methylene protons of benzyl group resonate as doublets in
the region ¼ 5:35ꢀ5:97 and ¼ 5:41ꢀ6:09 with geminal coupling constants of
1
14.3 Hz. The remaining galactose H signals appear as doublets with the
expected chemical shifts and coupling constants JðH-20; 30Þ ¼ 10:0ꢀ10:3 Hz;
JðH-30; 40Þ ¼ 3:4ꢀ3:7 Hz and JðH-40; 50Þ ꢂ 1 Hz. The pyridyl ring protons
resonate as expected for respective monosubstituted pyridines and reveal the
expected coupling splittings17. The coupling interactions between different
protons were confirmed by COSY experiments.
The 13C NMR spectra of all the isolated nucleosides (Table 2) exhibit
signals for the methyl carbon atoms of acetyl groups in the range d ¼
20:5ꢀ20:8; the carbonyl carbon atoms resonated in the region d ¼ 169:0ꢀ
170:4. In each case the anomeric carbon atom resonated at d ¼ 83:2ꢀ83:7
indicating its linkage with the N-atom of the heterocyclic moiety. The C-2
atom 2aꢀ2c and 3aꢀ3c as well as 5a, 5c, 6aꢀ6c of the heterocyclic moieties
resonate in the region ¼ 170:6ꢀ178:9 indicating its linkage with sulfur atom.
All proton-carbon connectivities were proven by HETCOR.
In the mass spectra of all the compounds, molecular ion peaks appeared
with low intensities (3ꢀ14%). Base peaks were formed by the successive loss
of CH3COOH and CH3CO from the molecular ion. Other prominent peaks
were present due to removal of either sugar moiety or heterocyclic moiety
from the molecular ion.
The deacetylation of compounds 2aꢀ2c and 5aꢀ5c was carried out
successfully in methanolic ammonia to get the corresponding deblocked
nucleosides 3aꢀ3c and 6aꢀ6c. IR spectra of all the deacetylated products
showed free OH stretching vibrations in the region 3250ꢀ3500 cmꢀ1 and
lacked any signal due to carbonyl stretching vibrations indicating complete
deacetylation of the compounds.
1
In H NMR spectra of all the compounds (Table 1), doublets were
observed due to anomeric protons which resonated in the region
d ¼ 6:48ꢀ6:94 with coupling constants of 9ꢀ10 Hz giving a clear indication

1676
AHMAD ET AL.

TRIAZOLE-3-THIONE GALACTOSIDES
1677
of diaxial orientation of H-10 and H-20, hence confirming the b configuration
in these compounds. No signal for methyl protons of acetyl groups was
observed confirming complete deacetylation of acetylated nucleosides. H-20 in
all deblocked products resonate at somewhat lower frequencies, in the region
d ¼ 5:27ꢀ5:54, while all other protons exhibited the same pattern as in
acetylated nucleosides with only slight difference in the chemical shifts.
Analogously, in the 13C NMR spectra of these compounds, signals due to
methyl carbon atoms and carbonyl carbon atoms were not observed.
All other carbon atoms resonate in the same region as for the respective
protected nucleosides (Table 2). In the FAB mass spectra, ½M þ 1ꢃþ peaks
were observed with reasonable intensities, corresponding to the molecular
weight of deacetylated products. Other prominent peaks appeared due to loss
of sugar moiety from the molecular ion.
The formation of N-galactosides was further confirmed by 15N-NMR
spectroscopy. 15N-chemical shift values of 2a, 2c and 5a are given in Table 1.
In compounds 2a and 2c the N-4 signals are observed at ¼ ꢀ111:3 and
ꢀ110:5 while in 5a the analogous atom N-1 resonates at ¼ ꢀ104:8 which are
typical values for nitrogen atoms in such chemical environment. In all three
cases N-3 in 2a=2b and analogously N-2in 5a resonate at low frequencies,
namely at ꢂ ꢀ175 to ꢀ180, and a difference of about 70 ppm is observed in
the chemical shifts of N-3 vs. N-4 in 2a=2c and N-2 vs. N-1 in 5a. This clearly
indicates that the sugars moieties are attached to nitrogen (Scheme 3) which
exists in an sp3-rather than in an sp2-hybridization state (aromatic). The
signals of the N-100 atoms in the pyridyl groups resonate at expected -values
(Table 1); their assignment has been proven unequivocally by H, 15N HMBC
spectroscopy.
It should be noted that alkylation of five-membered heterocyclic thiols
resulted in mixtures of S- and N-alkyl products with the N-alkylated isomers
being thermodynamically more stable18. In contrast, our synthetic procedure
afforded the N-galactosides exclusively.
EXPERIMENTAL
Melting points were determined on Gallenkamp digital melting point
1
apparatus and are uncorrected. H and 13C NMR spectra were recorded at
400 MHz and 100.6 MHz, respectively, on a Bruker AM-400 spectrometer
using CHCl3 ð¼ 7:24Þ and pyridine-d4 ð¼ 8:67; highest-frequency signal) and
the central peaks of CDCl3 ð¼ 77:0Þ and pyridine-d5 ð¼ 123:4; center line of
the highest-frequency signal), respectively, as the internal standards. 15N
NMR spectra were recorded at 50.7 MHz on a Bruker AMX-500 spectro-
meter using CH3NO2 ð¼ 0Þ as external standard. COSY and HETCOR
1
spectra were recorded to confirm coupling interactions between H atoms
and 13C atoms. Analytical thin layer chromatography was performed on

1678
AHMAD ET AL.
aluminium sheets coated with 0.2mm layer of silica gel 60 F 254 (Merck). The
compounds were detected with UV light of 254 nm and by using spray
reagent. EI-MS spectra were recorded on a Finnigan MAT-312and positive
FAB-MS on a Fisons Autospec spectrometer.
General Procedure for the Synthesis of 5-pyridyl-2-mercapto-
1,3,4-oxadiazoles (1aꢀ1c)
The method used for the preparation of 5-pyridyl-2-mercapto-1,3,4-
oxadiazoles starting from isomeric pyridine carboxylic acid hydrazides, was
the same as reported13 for the preparation of 2-(3,4-disubstituted-1,2,4-tria-
zole-5-yl-mercaptomethyl)-5-mercapto-1,3,4-oxadiazoles from the corre-
sponding hydrazides.
The respective pyridine carboxylic acid hydrazide (0.04 moles) was dis-
solvedinabsoluteethanol ina round bottom flask; 0.05molesof carbon disulfide
were added to this solution. This was followed by the addition of 0.04 moles of
potassium hydroxide dissolved in 20mL of water. The reaction mixture was
thoroughly stirred and subjected to reflux. The progress of the reaction was
monitored by TLC in each case. The reaction mixture turned yellow during the
reaction, and hydrogen sulfide evolution took place. After reaction completion,
excessethanolwasdistilledoff. Then, the reactionmixturewas dilutedwithwater
andacidifiedwith4NHCltopH2ꢀ3incaseofcompounds1aand1candto pH 5
for 1b. This resulted in deposition of a crystalline solid in each case. The solid
separated was filtered and recrystallized from water-ethanol mixture.
5-(2-Pyridyl)-2-mercapto-1,3,4-oxadiazole (1a)
ꢄ
ꢀ1
~
Yield 83%. ꢀ M.p. 223ꢀ224 C. ꢀ IR (n; cm ; KBr): 1520, 1570,
2550ꢀ2600. ꢀ EI-MS m=z (%): 179 (Mþ), 119, 106 and 78. ꢀ C7H5N3SO (179):
calcd., C 46.93, H 2.79, N 23.46, S 17.88; found, C 46.56, H 2.79, N 23.26, S 18.25.
5-(3-Pyridyl)-2-mercapto-1,3,4-oxadiazole (1b)
Yield 85%. ꢀ M.p. 232ꢀ233 C. ꢀ IR (n, cmꢀ 1, KBr): 1530, 1630,
ꢄ
~
2540ꢀ2590. ꢀ EI-MS m=z (%): 179 (Mþ), 119, 106 and 78. ꢀ C7H5N3SO
(179): calcd., C 46.93, H 2.79, N 23.46, S 17.88; found, C 46.79, H 2.79,
N 23.57, S 17.76.
5-(4-Pyridyl)-2-mercapto-1,3,4-oxadiazole (1c)
Yield 95%. ꢀ M.p. 269ꢀ270 C. ꢀ IR (n), cmꢀ 1, KBr): 1540, 1620,
ꢄ
~
2500ꢀ2550. ꢀ EI-MS m=z (%): 179 (Mþ), 119, 106 and 78. ꢀ C7H5N3SO

TRIAZOLE-3-THIONE GALACTOSIDES
1679
(179): calcd., C 46.93, H 2.79, N 23.46, S 17.88; found, C 46.90, H 2.87, N
23.73, S 17.77.
General Procedure for the Preparation of Nucleosides
To a mixture of 2mmoles of acetobromogalactose (,23,4,6-tetra- O-
acetyl-a-D-galactopyranosyl bromide), 2mmoles of mercuric cyanide and 2g
of anhydrous calcium sulfate (or molecular sieve) in 80ꢀ100 ml of dry
nitromethane was added 1 mmole of the appropriate heterocyclic compound.
The mixture was refluxed for 5ꢀ6 hours. Then, it was filtered while still hot in
order to remove an insoluble residue which was washed with more hot
nitromethane, and the filtrate was evaporated to dryness in vacuo. The pro-
duct obtained was treated with dichloromethane and filtered to separate a
solid (a complex formed by mercuric halide and the corresponding hetero-
cycle). The dichloromethane extract was washed with 30% aqueous potas-
sium iodide, water and then dried over anhydrous sodium sulfate. The
solution was filtered, and the solvent was evaporated to dryness. The crude
solid obtained was recrystallized from absolute ethanol.
N-(2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl)-5-(2-pyridyl)-1,3,4-
oxadiazole-2-thione (2a)
Yield 64%. ꢀ M.p. 183 C. ꢀ IR (n, cmꢀ 1, KBr): 3464, 1752, 1652,
ꢄ
~
1588, 1468, 1420, 1368, 1316, 1224, 1124, 1028, 920, 792. ꢀ For NMR data
see Tables 1 and 2 ꢀ EI-MS m=z (%): 509 (Mþ, 4), 331 (galAc4, 91), 180 (34),
169 (100), 127 (38), 109 (71), 97 (13), 78 (23).
N-(2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl)-5-(3-pyridyl)-1,3,4-
oxadiazole-2-thione (2b)
Yield 58%. ꢀ M.p. 142 C. ꢀ IR (n, cmꢀ 1, KBr): 3464, 2972, 1752,
ꢄ
~
1624, 1588, 1560, 1472, 1424, 1368, 1320, 1224, 1124, 1076, 1016, 920. ꢀ For
NMR data see Tables 1 and 2 ꢀ EI-MS m=z (%): 509 (Mþ, 4), 331 (galAc4,
85), 169 (100), 127 (40), 109 (78), 81 (19).
N-(2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl)-5-(4-pyridyl)-1,3,4-
oxadiazole-2-thione (2c)
Yield 75%. ꢀ M.p. 201 C. ꢀ (n, cmꢀ 1, KBr): 3464, 2972, 1752, 1636,
ꢄ
~
1592, 1552, 1496, 1412, 1368, 1320, 1224, 1124, 1060, 952. ꢀ For NMR data
see Tables 1 and 2 ꢀ EI-MS m=z (%): 509 (Mþ, 3), 331 (galAc4, 89), 169
(100), 127 (42), 109 (88), 81 (18).

1680
AHMAD ET AL.
N-(2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl)-5-(2-pyridyl)-
4-benzyl-1,2,4-triazole-2-thione (5a)
Yield 57%. ꢀ M.p. 177 C. ꢀ IR (n, cmꢀ 1, KBr): 3464, 3444, 3060,
ꢄ
~
1752, 1652, 1588, 1496, 1456, 1424, 1368, 1224, 1172, 1124, 1088, 1060, 952.
ꢀ For NMR data see Tables 1 and 2 ꢀ EI-MS m=z (%): 598 (Mþ, 13.3), 330
(galAc4-H, 19), 269 (72), 268 (33), 169 (52), 128 (25), 109 (38), 91 (100).
N-(2,3,4,6-Tetra-O-acetyl-b-D-galactopyranosyl)-5-(3-pyridyl)-
4-benzyl-1,2,4-triazole-2 thione (5b)
This compound could not be separated and was directly subjected to
deacetylation to get the corresponding deblocked nucleoside.
N-(2,3,4,6-Tetra-O-Acetyl-b-D-galactopyranosyl)-5-(4-pyridyl)-
4-benzyl-1,2,4-triazole-2-thione (5c)
Yield 60%. ꢀ M.p. 163ꢀ4 C. ꢀ IR (n, cmꢀ 1, KBr): 3444, 3060, 1752,
ꢄ
~
1652, 1588, 1456, 1408, 1368, 1224, 1060, 952. ꢀ For NMR data see Tables 1
and 2 ꢀ FAB-MS m=z (%): 599 (M þ Hþ; 67), 331 (galAc4, 50), 269 (100),
179 (38), 169 (72), 139 (23), 127 (50).
Deprotection of Acetylated Nucleosides
Deprotection of the galactosides was accomplished by the following
general procedure: the protected galactosides (1 mmole) were dissolved in dry
methanol and a fairly rapid stream of dry ammonia was passed into the
solution for 2ꢀ3 hours with stirring until TLC (dry methanol) indicated
completion of the reaction. The solution was kept for 20 hours at 0ꢀ4ꢄC.
Removal of the solvent in vacuo yielded a sirup which was dissolved in dry
ethanol and then recrystallised by adding a few drops of ethyl acetate.
N-(b-D-Galactopyranosyl)-5-(2-pyridyl)-1,3,4-oxadiazole-2-thione (3a)
Yield 33%. ꢀ M.p. 170ꢀ3 C (decomp). ꢀ IR (n, cmꢀ 1, KBr): 3340 (br),
ꢄ
~
2924, 1656, 1612, 1524, 1004, 832. ꢀ For NMR data see Tables 1 and 2 ꢀ
FAB-MS m=z (%) 341 (Mþ, 21), 179 (Mþ-galþH, 34). Analysis
C18H15N3O6S (341.34) Calculated: C, 45.74; H, 4.42and N, 12.31. Found: C,
45.64; H, 4.50 and N, 12.29.
N-(b-D-Galactopyranosyl)-5-(3-pyridyl)-1,3,4-oxadiazole-2-thione (3b)
Yield 30%. ꢀ M.p. 161ꢀ3 C (decomp). ꢀ IR (n, cmꢀ 1, KBr): 3376 (br),
ꢄ
~
2928, 1676, 1596, 1524, 1220, 980, 936. ꢀ For NMR data see Tables 1 and 2

TRIAZOLE-3-THIONE GALACTOSIDES
1681
ꢀ FAB-MS m=z (%) 342( Mþ þ H, 26), 197 (28), 179 (Mþ-galþH, 33).
Analysis C18H15N3O6S (341.34) Calculated: C, 45.74; H, 4.42and N, 12.31.
Found: C, 45.70; H, 4.49 and N, 12.32.
N-(b-D-Galactopyranosyl)-5-(4-pyridyl)-1,3,4-oxadiazole-2-thione (3c)
Yield 49%. ꢀ M.p. 149-52 C (decomp). ꢀ IR (n, cmꢀ 1, KBr): 3388
ꢄ
~
(br), 2924, 1688, 1688, 1620, 1552, 1216, 1020, 884. ꢀ For NMR data see
Tables 1 and 2 ꢀ FAB-MS m=z (%) 342( Mþ þ H, 60), 180 (Mþ-gal+2H,
80). Analysis C18H15N3O6S (341.34) Calculated: C, 45.74; H, 4.42and N,
12.31. Found: C, 45.80; H, 4.40 and N, 12.40.
N-(b-D-Galactopyranosyl)-5-(2-pyridyl)-4-benzyl-1,2,4-triazole-2-thione (6a)
Yield 53%. ꢀ M.p. 190ꢀ3 C (decomp). ꢀ IR (n, cmꢀ 1, KBr): 3404 (br),
ꢄ
~
3004, 2924, 1656, 1632, 1552, 1244, 1024, 880. ꢀ For NMR data see Tables 1
and 2 ꢀ FAB-MS m=z (%) 431 (Mþ þ H, 21), 269 (Mþ-galþ2H, 100).
Analysis C20H22N4O5S (430.46) Calculated: C, 55.81; H, 5.14 and N, 13.02.
Found: C, 55.79; H, 5.05 and N, 13.00.
N-(b-D-Galactopyranosyl)-5-(3-Pyridyl)-4-Benzyl-1,2,4-Triazole-2-thione (6b)
Yield 40%. ꢀ M.p. 142ꢀ3 C (decomp). ꢀ (n, cmꢀ 1, KBr): 3372(br),
ꢄ
~
3064, 2920, 1604, 1576, 1542, 1264, 1028, 880, 832. ꢀ For NMR data see
Tables 1 and 2 ꢀ FAB-MS m=z (%) 431 (Mþ þ H, 19), 269 (Mþ-galþ2H, 77).
Analysis C20H22N4O5S (430.46) Calculated: C, 55.81; H, 5.14 and N, 13.02.
Found: C, 55.84; H, 5.18 and N, 13.05.
N-(b-D-Galactopyranosyl)-5-(4-pyridyl)-4-benzyl-1,2,4-triazole-2-thione (6c)
Yield 35%. ꢀ M.p. 170ꢀ2 C (decomp). ꢀ IR (n, cmꢀ 1, KBr): 3351 (br),
ꢄ
~
3042, 2924, 1612, 1567, 1538, 1220, 998, 881. ꢀ For NMR data see Tables 1
and 2 ꢀ FAB-MS m=z (%) 431 (Mþ þ H, 67), 269 (Mþ-galþ2H, 100), 154
(47). Analysis C20H22N4O5S (430.46) Calculated: C, 55.81; H, 5.14 and N,
13.02. Found: C, 55.86; H, 5.15 and N, 12.92.
ACKNOWLEDGMENTS
This work has been supported by the Quaid-i-Azam University Research
Funds, the German Academic Exchange Service (DAAD) and the Fonds der Che-
mischen Industrie.

1682
AHMAD ET AL.
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Received April 27, 1999
Accepted February 20, 2001