Synthesis and antimicrobial activity of some novel nucleoside analogues of adenosine and 1,3-dideazaadenosine

Article abstract of DOI:10.1016/j.bmcl.2007.09.028

A number of nucleoside analogues have been synthesized and evaluated for their antibacterial and antifungal activities against Staphylococcus aureus, Group D Streptococcus, Pseudomonas aeruginosa, Proteus spp., Salmonella spp., Aspergillus fumigatus, Penicillium marneffei, Candida albicans, Cryptococcus neoformans, and Mucor spp. The compounds 1, 4, and 6 emerged as potent antibacterial agents with MIC values of 0.75, 0.38, and 0.19 μM, respectively, against group D Streptococcus. Further, the results suggest that the molecules 4, 6, and 7 would be potent antifungal agents as they show substantial degree of inhibition toward the growth of pathogenic fungi with MICs of 0.75, 0.38, and 0.38 μM, respectively.

Full text of DOI:10.1016/j.bmcl.2007.09.028

Available online at www.sciencedirect.com
Bioorganic & Medicinal Chemistry Letters 17 (2007) 6239–6244
Synthesis and antimicrobial activity of some novel
nucleoside analogues of adenosine and 1,3-dideazaadenosine
Richa Srivastava,a, Anudita Bhargavab and Ramendra K. Singha,*
aNucleic Acids Research Laboratory, Department of Chemistry, University of Allahabad, Allahabad 211 002, India
bHead, Microbiology Department, Moti Lal Nehru Medical College, University of Allahabad, Allahabad 211002, India
Received 16 June 2007; revised 31 August 2007; accepted 5 September 2007
Available online 8 September 2007
Abstract—A number of nucleoside analogues have been synthesized and evaluated for their antibacterial and antifungal activities
against Staphylococcus aureus, Group D Streptococcus, Pseudomonas aeruginosa, Proteus spp., Salmonella spp., Aspergillus fumiga-
tus, Penicillium marneffei, Candida albicans, Cryptococcus neoformans, and Mucor spp. The compounds 1, 4, and 6 emerged as potent
antibacterial agents with MIC values of 0.75, 0.38, and 0.19 lM, respectively, against group D Streptococcus. Further, the results
suggest that the molecules 4, 6, and 7 would be potent antifungal agents as they show substantial degree of inhibition toward
the growth of pathogenic fungi with MICs of 0.75, 0.38, and 0.38 lM, respectively.
ꢀ 2007 Elsevier Ltd. All rights reserved.
The increasing prevalence of life-threatening fungal dis-
eases and rapidly growing trend of antimicrobial resis-
tance shown especially by Gram positive bacteria
necessitate the development of new and more effective
antimicrobial agents. Identification of novel antimicro-
bial drug with unique modes of action is desirable, since
microbes resistant to available antimicrobial agents
would unlikely be cross-resistant to these newer drugs.1
The use of nucleoside analogues can be considered as a
novel option as they are expected to act at genomic level,
and thereby interfere with transcription or replication
processes required for microbial survival. Since there
are no alternative pathways in the pathogens for these
basic metabolic processes, the nucleoside analogues, by
inhibiting these basic pathways, can prove to be effective
and better antimicrobial agents. Based on the diverse
biological activity and chemical application of benz-
imidazole derivatives,2–4 we set out to find a new class
of drugs derived from benzimidazoles that may be
targeted against major enzymes involved in the fungal
and bacterial growth. All the newly synthesized
analogues have structural similarity with the naturally
occurring nucleoside, S-adenosylhomocysteine or SAH,
which plays a key role in biological transmethylation
reactions. SAH is removed by an enzyme SAH hydro-
lase,5 and inhibition of this enzyme, in turn, causes feed
back inhibition of biological transmethylation, resulting
in the production of uncapped mRNAs and, as a result,
less efficient translational process. So, targeting SAH
hydrolase is useful in developing antifungal agents.6–8
SAH is also a substrate for SAH nucleosidase found
in bacterial methionine salvage pathway which catalyzes
the conversion of methylthioadenosine into methylthi-
oribose and adenine.9 Targeting SAH nucleosidase
may result in new antimicrobial agents and provide an
alternative to the problem of resistance faced by most
of the existing antibiotics. Further, since SAH nucleosi-
dase is not found in humans, its inhibitors are expected
to be non-toxic to human beings.
The compounds used in the present study are synthe-
sized as shown in Scheme 1. For the synthesis of
ribosides of 1,3-dideazaadenine (ii), 6-nitro-1,3-dide-
azaadenine, (iii) and 8-ethyl-1,3-dideazaadenine (iv),
silylation of the corresponding substituted bases was
performed using hexamethyldisilazane (HMDS) and tri-
chloromethylsilane (TCS) in acetonitrile (CH3CN) at its
reflux point. Excess of HMDS and TCS was removed in
vacuo after completion of the reaction. The resultant si-
lyl derivatives were used, without further purification for
coupling with suitably protected sugar, 1-O-acetyl-2,3,5-
tri-O-benzoyl-b-D-ribofuranose (ABR). The coupling
reactions were carried out in the presence of SnCl4 as
Keywords: Adenosine; Dideazaadenosine; SAH analogues; Antifungal;
Antibacterial.
*
Corresponding author. Tel./fax: +91 532 2461005; e-mail:
singhramk@rediffmail.com
Present address: Molecular Biophysics Unit, Indian Institute of
Science, Bangalore 560012, India.
0960-894X/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2007.09.028

6240
R. Srivastava et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6239–6244
HO
HOOCCH CH
2
S
C H OOCCH CH S
2 5 2 2
Cl
2
base
base
base
base
O
O
O
O
f
H
H
H
H
H
H
H
H
a
c
H
H
H
H
H
H
b
OH
OH
OH
OH
OH
OH
OH
OH
1 or 4
3 or 6
g
d
OOCCH CH
S
2
2
NH OCCH CH
S
CH =CH-CH -S
2
2
2
base
2
2
base
base
O
O
O
H
H
H
H
H
H
e
H
H
H
OH
OH
OH
OH
OH
OH
NO
2
7 or 8
2 or 5
A
NO2
NH2
NH2
NO2
N
N
N
N
N
C2H5
N
H
N
H
N
H
N
H
N
(iv)
(i)
(ii)
(iii)
for 1-3, base = (i) adenine
for 4-6, base = (ii) 1,3-dideazaadenine
for 7,
for 8,
base = (iii) 6-nitro-1,3-dideazaadenine
base = (iv) 6-nitro-8-ethyl-1,3-dideazaadenine
Scheme 1. Reagents: (a) SOCl2/HMPA, dry pyridine; (b) dowex (H+), 2 N NH4OH; (c) mercaptopropionic acid, DMAP/pyridine; (d) DCC,
p-nitrophenol, dioxan; (e) NH3; (f) DCC, EtOH, concd H2SO4; (g) allyl disulfide, triphenyl phosphine.
catalyst using Vorbruggen and Bennua procedure.10 The
¨
and triphenylphosphine to give 7 and 8. This one step
procedure is more convenient than the multistep proce-
dure used earlier for 50-sulfur generation and the yield is
also considerably improved. The advantageous points of
this reaction were high yield and absence of side reac-
tions, such as the formation of cyclonucleoside, etc.13
products were purified on silica gel column using DCM/
MeOH and deprotected using ammonia (25%) for 5 h at
60 ꢁC. The products were further washed several times
with ether and recrystallized using aq ethanol. Adeno-
sine and 9-(10-b-D-ribofuranosyl) 1,3-dideazaadenine
were converted to their 50-chloro-50-deoxy derivatives
by treating them with thionyl chloride (SOCl2) and
hexamethylphosphoramide (HMPA).11 50-Chloro-50-
deoxynucleosides were further treated with mercapto-
propionic acid to give 50-S-(propionic acid) 50-deoxy-9-
(10-b-D-ribofuranosyl) adenine (1) and 50-S-(propionic
acid) 50-deoxy-9-(10-b-D-ribofuranosyl) 1,3-dideazaade-
nine (4), respectively. The –COOH function of 1 and 4
was activated by a reaction with p-nitrophenol and dic-
yclohexylcarbodiimide (DCC) in pyridine and triethyl-
amine to get the corresponding activated ester A. The
completion of the reaction was assessed by precipitation
of dicyclohexylurea (DCU). The activated phenyl esters
were then treated with ammonia to get the correspond-
ing amides—50-S-(propionamide) 50-deoxy-9-(10-b-D-
ribofuranosyl) adenine (2) and 50-S-(propionamide)
All the compounds 1–8 were tested in vitro for anti-
bacterial and antifungal activity14 and they exhibited
good to moderate activity against Gram positive bac-
teria and some human pathogenic fungi, Table 1. The
positive results with compounds 1 and 4 against bac-
teria may be due to easy recognition of propionic acid
by the bacterial cells as it is structurally similar to
amino acids, the natural components of bacterial cell
wall. Thus, the structural features of these molecules
help in their better cellular uptake. In order to
increase their effectiveness, compounds 1 and 4 were
further converted into their derivatives, 3 and 6, with
biodegradable ester linkages. This modification is
likely to have made the compounds more lipophilic
in nature, which in turn may have made these mole-
cules more effective inhibitors of enzymes involved in
lipid and cell wall syntheses. The biodegradable ester
linkage gets hydrolyzed inside the cell and the
resulting carboxylate form of the drug molecule is
thus entrapped inside, resulting in its higher bioavail-
ability. The drug effect was better in its ester form, 6,
than its amide form, 5, since ester bonds are easily
hydrolyzed than amide bonds. The higher activity of
these molecules against Gram positive bacteria than
Gram negative bacteria might be due to the structural
50-deoxy-9-(10-b-D-ribofuranosyl)
1,3-dideazaadenine
(5). Compounds 1 and 4 when allowed to react with eth-
anol in the presence of DCC and catalytic amount of
concd H2SO4 gave the esters-50-S-(ethylpropionate)
50deoxy-9-(10-b-D-ribofuranosyl) adenine (3) and 50-S-
(ethylpropionate)
50-deoxy-9-(10-b-D-ribofuranosyl)
1,3-dideazaadenine (6), respectively. Similarly, glycosyl-
ation of 6-nitro-1,3-dideazaadenine (iii) and 8-ethyl-1,
3-dideazaadenine (iv) with ABR gave their respective
ribosides12 which were further treated with allyl disulfide

Table 1. In vitro antibacterial and antifungal activities as MIC (micromole)
Compounds
Structures
S. aureus
S. group D
A. fumigatus
P. marneffei
C. albicans
C. neoformans
Mucor spp.
HOOCCH CH S
2
2
adenine
O
1
nt
0.755
1.5
1.5
1.5
1.5
1.5
H
H
H
H
H
OH
OH
NH OCCH CH S
2
2
2
adenine
O
2
3
4
5
6
7
nt
nt
Nt
nt
nt
nt
nt
—
—
—
—
—
H
H
H
OH
OH
C
H OOCCH CH S
5 2 2
2
adenine
O
nt
—
—
—
—
—
H
H
H
OH
O
OH
HOOCCH CH S
2
2
dideazaadenine
0.38
0.75
0.75
0.75
0.75
0.75
H
H
OH
OH
NH OCCH CH S
2
2
2
dideazaadenine
O
nt
—
—
—
—
—
H
H
H
OH
OH
C
H OOCCH CH S
5 2 2
2
dideazaadenine
O
0.19
1.25
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
0.38
H
H
H
OH
O
OH
CH =CH-CH -S
2
2
6-nitro-1,3-dideazaadenine
H
H
OH
OH
(continued on next page)

6242
R. Srivastava et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6239–6244
differences in their cell walls. It was observed that the
antimicrobial activity was enhanced when the normal
adenine base was replaced by 1,3-dideazaadenine. This
enhanced activity establishes the hydrophobic nature
of interaction between these compounds and the en-
zymes involved in microbial proliferation, since it is
the bases of nucleosides which are primarily responsi-
ble for recognition by enzymes. Further, introduction
of 8-ethyl group in 1,3-dideazaadenine, compound 8,
showed significant loss of antimicrobial activity. This
clearly shows that any modification at C-8 position
impairs the antimicrobial activity of the molecule,
probably by proving itself a less favored substrate.
Since all the nucleoside analogues are structurally sim-
ilar to SAH, studies on these molecules on the en-
zymes SAH hydrolase and SAH nucleosidase (for
which SAH is a substrate) as their inhibitor may be
helpful in fully evaluating their potential. Further
studies are in progress and the detailed work along
with mechanism of action of these molecules will be
published soon as a full paper separately. Compound
1 has already been shown as a potent anticancer agent
against cervical cancer caused by HPV-16 on the basis
of studies on HPV-16 +ve SiHa cell line.15 The syn-
thesis of the molecules studied, their characterization
16
and antimicrobial studies
tion references and notes.
are given under the sec-
Acknowledgments
The authors thank the University Grants Commission,
New Delhi, for financial support and the Regional
Sophisticated Instrumentation Centre, Central Drug
Research Institute, Lucknow, India, for providing spec-
tral data.
References and notes
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Organic layer was combined, washed with distilled water,
and dried over anhydrous Na2SO4. The resultant solution
was concentrated and the compound 2 crystallized out.
The formation of amide was also confirmed by a +ve
ninhydrin test for the amino group present at the 50
position. Yield 45%, Rf = 0.42 (DCM/MeOH 9:1). UV
1
(MeOH) kmax 238, 281, 317 nm. H NMR (DMSO-d6) d
0
4.48–4.50 (s, 2H, NH2 ); d 8.09 (s, 1H, C-2); d 8.45–8.68 (s,
9. Tyagi, A. K.; Tabor, C. W.; Tabor, H. Methods Enzymol.
1983, 94, 294.
1H, C-8); d 5.68–6.00 (d, J = 6.1, 1H, H10); d 3.49–3.69 (m,
1H, H20); d 3.46–3.63 (m, 1H, H30); d 4.33–4.62 (m, 1H,
H40); d 3.32–3.40 (m, 2H, H50); d 1.88–2.0 (s, 2H, OH); d
2.70 (t, 2H); d 2.49 (t, 2H); d 5.49–6.0 (s, 2H, NH2); MS m/z
353 (M+). Anal. Calcd for C13H18N6O4S: C, 44.07; H,
5.08; N, 23.66. Found: C, 43.93; H, 4.98; N, 23.62. 50-S-
(Ethylpropionate) 50-deoxy-9-(10-b-D-ribofuranosyl) ade-
nine (3). Compound 1 (4 mmol) dissolved in ethanol
(30 mL) was stirred for a few min with concd H2SO4
(1.5 mL). To this solution, a solution of DCC (6 mmol) in
10 mL ethanol was added dropwise. Stirring was contin-
ued for 24 h at room temperature. The completion of the
reaction was assessed by the white ppt of dicyclohexylurea,
which was filtered out, and ethanol evaporated on pump
at 45 ꢁC. Partitioning between water and ethyl acetate
gave the expected product 3 in the organic fraction which
was dried over Na2SO4, evaporated to a solid mass, and
was purified on a silica gel column using a mixture of
DCM and MeOH as eluant. Yield 36%, Rf = 0.36 (DCM/
MeOH 9:1) UV (MeOH) kmax 257, 281, 317 nm. 1H NMR
10. Vorbruggen, H.; Bennua, B. Chem. Ber. 1981, 114, 1279.
¨
11. Borchardt, R. T.; Huber, J. A.; Wu, Y. S. J. Org. Chem.
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12. Sinha, S.; Srivastava, R.; Singh, R. K. Nucleosides,
Nucleotides Nucleic Acids 2004, 23, 1815.
13. Robins, M. J.; Wnuk, S. F.; Mullah, K. B.; Dalley, N. K.;
Yuan, C. S.; Lee, Y.; Borchardt, R. T. J. Org. Chem. 1994,
59, 544.
14. (a) Baur, A. W.; Kirby, W. M. M.; Shorris, J. C.; Turk, M.
Am. J. Patnol. 1966, 45, 493; (b) Sumana, M. N.;
Rajgopal, V. Ind. J. Pathol. Microbiol. 2002, 45, 169.
15. Sinha S.; Srivastava, R.; Prusty B.; Das, B. C.; Singh, R.
K., Nucleosides, Nucleotides Nucleic Acids 2007, in press.
16. Experimental: UV measurements were carried out on a
Hitachi 220S spectrophotometer. 1H NMR spectra were
recorded using a DRX 300 instrument with DMSO-d6 as
solvent. Fungal strains were obtained from SGPGI,
Lucknow, India, and bacterial strains were obtained from
clinical patients. 50-S-(Propionic acid) 50-deoxy-9-(10-b-D-
ribofuranosyl) adenine (1). 50-Chloro-50-deoxyadenosine
(10 mmol) and dimethylaminopyridine (DMAP, 0.5 equiv)
were dissolved in dry pyridine (25 mL) and stirred for a
few minutes to get a clear solution. The solution was made
basic by adding triethylamine (TEA, 1.4 equiv or 0.6 mL).
Mercaptopropionic acid (12 mmol or 1.2 equiv) in dry
pyridine (10 mL) was added to the reaction mixture and
the stirring was continued overnight at 50 ꢁC. The reaction
mixture was concentrated under vacuum (50–60 ꢁC) to get
a dry residue which was then dissolved in water (30 mL).
The aqueous solution was washed consecutively with ethyl
acetate (15· 3 mL) and was reduced to syrup using a
pump. The compound 1 which is contaminated with
unreacted mercaptopropionic acid was purified by silica
gel column chromatography. Yield 65%, Rf: 0.36 (DCM/
MeOH 9.5:05). UV (MeOH) kmax 240, 281, 317 nm. 1H
0
(DMSO-d6) d 4.52–4.54 (s, 2H, NH2 ); d 8.10 (s, 1H, C-2);
d 8.45–8.67 (s, 1H, C-8); d 5.69–6.06 (d, J = 6.1, 1H, H10);
d 3.54–3.75 (m, 1H, H20); d 3.44–3.56 (m, 1H, H30); d
4.32–4.59 (m, 1H, H40); d 3.33–3.44 (m, 2H, H50); d 1.90–
2.0 (s, 2H, OH); d 2.79–2.83 (t, 2H); d 2.55–2.62 (t, 2H); d
4.12 (q, 2H); d 1.30 (t, 3H); MS m/z 383.7 (M+). Anal.
Calcd for C15H21N5O5S: C, 47; H, 5.47; N, 18.23. Found:
C, 46.86; H, 5.42; N, 18.19. 50-Deoxy-9-(10-b-D-ribofur-
anosyl) 1,3-dideazaadenine (4) Ribo-DDA or 9-(10-b-D-
ribofuranosyl) 1,3-dideazaadenine was converted to its
50-chloro-50-deoxy derivative by treating it with thionyl
chloride (1.5 mL) and HMPA (8 mL) which was further
converted to 4 by following the procedure and molar
ratios similar to that used for the preparation of 1. TLC
indicated the formation of two isomers. One isomer
crystallized out as soon as solvent was evaporated on
pump while other was still present in mother liquor, which
was purified by silica gel column chromatography. The
product containing fractions were evaporated and the
residue recrystallized from ethanol to give 4. Yield 45%,
Rf = 0.4 (DCM/MeOH, 9.5:0.5). UV (MeOH) kmax 235,
266, 314 nm. 1H NMR (DMSO-d6) d 7.26–7.70 (m, 3H,
aro); d 7.90–8.01 (s, 1H, C-8;) d 8.48–8.70 (s, 1H, C-8); d
5.65–6.03 (d, 1H, H10); d 3.50–3.70 (m, 1H, H20); d 3.49–
3.65 (m, 1H, H30); d 4.36–4.66 (m, 1H, H40); d 3.34–3.46
(m, 2H, H50); d 1.90–2.0 (s, 2H, OH); d 2.50–2.71 (t, 2H); d
2.55–2.60 (t, 2H); MS m/z 352.4 (M+). Anal. Calcd for
C15H19N3O5S: C, 50.99; H, 5.38; N, 11.89. Found: C,
50.81; H, 5.31; N, 11.78. 50-S-(Propionamide) 50-deoxy-9-
(10-b-D-ribofuranosyl) 1,3-dideazaadenine (5) The com-
pound 5 was obtained from the compound 4 as syrup
using a procedure similar to the one used to get compound
2 from 1. Yield 30%, Rf = 0.4 (DCM/MeOH, 9.5:0.5). UV
0
NMR (DMSO-d6) d 4.50–4.52 (s, 2H, NH2 ); d 8.12 (s, 1H,
C-2); d 8.48–8.70 (s, 1H, C-8); d 5.65–6.03 (d, J = 6.2, 1H,
H10); d 3.50–3.70 (m, 1H, H20); d 3.49–3.65 (m, 1H, H03);
d 4.36–4.66 (m, 1H, H40); d 3.34–3.46 (m, 2H, H50); d
1.90–2.0 (s, 2H, OH); d 2.50–2.71 (t, 2H); d 2.55–2.60 (t,
2H); MS m/z 354.5 (M+). Anal. Calcd for C13H17N5O5S:
C, 43.94; H, 4.79; N, 19.72. Found: C, 43.76; H, 4.68; N,
19.57. 50-S-(Propionamide)50-deoxy-9-(10-b-D-ribofurano-
syl) adenine (2). Compound 1 (4 mmol) was dissolved in
dry pyridine (15 mL) and was stirred for a few minutes to
get a clear solution. A solution of p-nitrophenol (300 mg)
in dioxane (10 mL) was added drop wise to the stirred
reaction mixture. After 15 min, TEA (1 mL) was added to
make the solution slightly basic. Stirring was continued for
another 30 min. DCC (550 mg or 1.2 equiv) dissolved in
DCM (10 mL) was added to the reaction vessel. The
reaction mixture was stirred overnight at room tempera-
ture after adding excess of NH3. The completion of the
reaction is assessed by precipitation of dicyclohexylurea
(DCU). The reaction mixture was filtered to separate
DCU and the filtrate evaporated to half of its volume. The
concentrated solution was poured into 5% NaHCO3
solution (to neutralize the residual acid and to separate
excess of PNP) and was extracted with DCM (4· 10 mL).
1
(MeOH) kmax 235, 266, 314 nm. H NMR (DMSO-d6) d
7.26–7.70 (m, 3H, aro); d 7.90–8.01 (s, 1H, C-8); d 8.48–
8.70 (s, 1H, C-8); d 5.65–6.03 (d, 1H, H10); d 3.50–3.70
(m, 1H, H20); d 3.49–3.65 (m, 1H, H30); d 4.36–4.66 (m,
1H, H40); d 3.34–3.46 (m, 2H, H50); d 1.90–2.0 (s, 2H,
OH); d 2.72 (t, 2H); d 2.55 (t, 2H); d 5.50–6.0 (s, 2H, NH2);
MS m/z 353 (M+). Anal. Calcd for C15H20N4O4S: C,
51.14; H, 5.68; N, 15.91. Found: C, 51.04; H, 5.55; N,

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R. Srivastava et al. / Bioorg. Med. Chem. Lett. 17 (2007) 6239–6244
15.87. 50-S-(Ethylpropionate) 50-deoxy-9-(10-b-D-ribofur-
Antimicrobial assay: all the nucleoside analogues 1–8 were
tested in vitro for antibacterial activity against a panel of
Gram negative bacilli like Pseudomonas aeruginosa, Pro-
teus spp., Salmonella spp., Gram positive cocci like
Staphylococcus aureus and Group D Streptococcus, and
for antifungal activity against human pathogenic fungi
like Aspergillus fumigatus, Penicillium marneffei, Candida
albicans, Cryptococcus neoformans, Mucor spp. A known
amount of synthesized compounds (1.5; 1.1, 0.57, 0.28,
0.14, and 0.07 lM/mL) was impregnated on sterile filter
paper discs of 6mm diameter. Each of the above-
mentioned Gram positive and Gram negative bacteria
was tested by Kirby Bauer Disc Diffusion (KBDD)
method, as per standard protocol (Bauer, et al. Am.
J. Clin. Pathol. 1966, 45, 493). The compounds showing
some inhibition zone by this method were further analyzed
by the broth-dilution assay to determine their MIC values
as per standard protocol (J. Antimicrob. Chemother. 1991,
27, Suppl. D, 1). Since none of the compounds showed any
inhibition against Gram negative bacteria by diffusion
method, their MIC values were not determined. The
synthesized compounds and reference drugs were dis-
solved in DMSO–H2O (50%) and doubling dilutions were
subsequently prepared. Equal amount of bacteria was
added into each tube to bring the turbidity level to 0.5
Mcfarlands. The tubes were incubated at 37 ꢁC for 18–
24 h and observed for any visible turbidity the next day.
The MIC was noted as the lowest dilution of the new
synthetic compound that inhibited visible growth of the
microorganism inoculated. The MIC values are noted in
Table 1. Data were not taken for the initial solution
because of the high DMSO concentration (12.5%). For
antifungal susceptibility testing also the initial screening is
done by disc-diffusion method. The broth used is M-3
broth susceptibility test medium and the solid medium
used was corn meal agar, instead of Mueller–Hinton agar.
Thereafter, the MIC of these nucleoside analogues was
evaluated for fungal agents by broth-dilution method
(Mazens, M. F. et al. Antimicrob. Agents Chemother. 1979,
15, 475).
anosyl) 1,3-dideazaadenine (6). Compound 4 was dis-
solved in ethanol and stirred for few min to get a clear
solution and the same procedure was followed as in the
case of the analogue 3 to get the compound 6. Yield 30%,
Rf = 0.4 (DCM/MeOH, 9.5:0.5). UV (MeOH) kmax 235,
266, 314 nm. 1H NMR (DMSO-d6) d 7.26–7.70 (m, 3H,
aro); d 7.90–8.01 (s, 1H, C-8; ) d 8.48–8.70 (s, 1H, C-8); d
5.65–6.03 (d, 1H, H10); d 3.50–3.70 (m, 1H, H20); d 3.49–
3.65 (m, 1H, H30); d 4.36–4.66 (m, 1H, H40); d 3.34–3.46
(m, 2H, H50); d 1.90–2.0 (s, 2H, OH); d 2.79–2.83 (t, 2H); d
2.55–2.62 (t, 2H); d 4.12 (q, 2H); d 1.30 (t, 3H); MS m/z
380 (M+). Anal. Calcd for C17H23N3O5S: C, 53.54; H,
6.04; N, 11.02. Found: C, 53.47; H, 6.0; N, 10.96. 50-
Allylthio-50-deoxy-9-(10-b-D-ribofuranosyl) 6-nitro-1,3-
dideazaadenine (7). Ribo-NDDP or 9-(10-b-D-ribofurano-
syl) 6-nitro-1,3-dideazaadenine12 (5 mmol) is treated with
allyl disulfide (15 mmol) in the presence of Ph3P (15 mmol)
in dry pyridine (50 mL) at room temperature for 24 h. 50-
Allylthio-50-deoxyribofuranosyl nitrodideazaadenine was
obtained as a single product contaminated with unreacted
triphenylphosphine. The nucleoside analogue 7 was puri-
fied by silica gel column chromatography. Compound 7
eluted between 9 and 11% CH3OH in CH2Cl2. Yield 48%,
mp 209 ꢁC, UV (MeOH) kmax 290 nm kmin 238 nm. 1H
NMR (DMSO-d6) d 7.52–8.19 (m, 4H, aro), 2.3–2.5 (2H,
q), 1.3–1.57 (3H, t), 1.8–2.0 (2H, d), 4.0–4.2 (1H, m), 4.8–
5.02 (2H, d). MS m/z 351.6 (M+). Anal. Calcd for
C15H17O5N3S: C, 51.28; H, 4.84; N, 11.97. Found: C,
51.21; H, 4.80; N, 11.91. 50-Allylthio-50-deoxy-9-(10-b-D-
ribofuranosyl) 8-ethyl-1,3-dideazaadenine (8). Compound
8 was synthesized by a procedure similar to that described
for 7, from 9-(10-b-D-ribofuranosyl) 8-ethyl-1,3-dide-
azaadenine (prepared indigenously).12 The pure com-
pound 8 was crystallized from ethanol. Yield 58%, mp
189 ꢁC, UV (MeOH) kmax 316 nm, kmin 238 nm. 1H NMR
(DMSO-d6) d 7.52–8.09 (m, 3H, aro), 2.3–2.5 (2H, q), 1.3–
1.57 (3H, t), 1.8–2.0(2H, d), 4.0–4.2 (1H, m), 4.8–5.02 (2H,
d). MS m/z 332.8 (M+). Anal. Calcd for C15H17O5N3S: C,
61.26; H, 6.31; N, 8.41. Found: C, 61.19; H, 6.25; N, 8.37.