Synthesis, spectral, crystal and antimicrobial studies of biologically potent oxime ethers of nitrogen, oxygen and sulfur heterocycles

Article abstract of DOI:10.1016/j.bmcl.2009.04.038

Three series of oxime ethers viz, 2,6-diarylpiperidin-4-one O-benzyloximes 5a-o, 2,6-diaryltetrahydropyran-4-one O-benzyloximes 7a-e and 2,6-diaryltetrahydrothiopyran-4-one O-benzyloximes 11a-b and 12a-c were synthesized and stereochemistry is established by their spectral and single crystal analysis. A SAR study has been carried out for the above oxime ethers against a panel of antibacterial (Pseudomonas aeruginosa, Staphylococcus aureus, Salmonella typhi and Escherichia coli) and antifungal agents (Candida albicans, Candida-51, Rhizopus sp., Aspergillus niger, Aspergillus flavus and Cryptococcus neoformans), respectively, using Ciprofloxacin and Amphotericin B as standards. Most of the chloro/methyl/methoxy substituted compounds exerted moderate to good activity against all the tested organisms; moreover, some compounds (5i, 5l, 5n, 5o, 7c2, 7d1, 7d2, 7e, 11b and 12c) exhibited promising activity than standard drugs.

Full text of DOI:10.1016/j.bmcl.2009.04.038

Bioorganic & Medicinal Chemistry Letters 19 (2009) 2981–2985
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis, spectral, crystal and antimicrobial studies of biologically potent
oxime ethers of nitrogen, oxygen and sulfur heterocycles
Paramasivam Parthiban a,b, Gopalakrishnan Aridoss a,b, Paramasivam Rathika c, Venkatachalam Ramkumar d,
Senthamaraikannan Kabilan a,
*
a Department of Chemistry, Annamalai University, Annamalainagar, Chidambaram 608 002, India
b Division of Image Science and Information Engineering, Pukyong National University, Busan 608 739, Republic of Korea
c Department of Microbiology, Annamalai University, Annamalainagar, Chidambaram 608 002, India
d Department of Chemistry, Indian Institute of Technology-Madras, Chennai 600 036, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Three series of oxime ethers viz, 2,6-diarylpiperidin-4-one O-benzyloximes 5a–o, 2,6-diaryltetrahydro-
pyran-4-one O-benzyloximes 7a–e and 2,6-diaryltetrahydrothiopyran-4-one O-benzyloximes 11a–b
and 12a–c were synthesized and stereochemistry is established by their spectral and single crystal anal-
ysis. A SAR study has been carried out for the above oxime ethers against a panel of antibacterial (Pseu-
domonas aeruginosa, Staphylococcus aureus, Salmonella typhi and Escherichia coli) and antifungal agents
(Candida albicans, Candida-51, Rhizopus sp., Aspergillus niger, Aspergillus flavus and Cryptococcus neofor-
mans), respectively, using Ciprofloxacin and Amphotericin B as standards. Most of the chloro/methyl/
methoxy substituted compounds exerted moderate to good activity against all the tested organisms;
moreover, some compounds (5i, 5l, 5n, 5o, 7c2, 7d1, 7d2, 7e, 11b and 12c) exhibited promising activity
than standard drugs.
Received 5 March 2009
Revised 9 April 2009
Accepted 10 April 2009
Available online 18 April 2009
Keywords:
Heterocycles
Oxime ethers
Stereochemistry
Antibacterial activity
Antifungal activity
Ó 2009 Elsevier Ltd. All rights reserved.
Though infections caused by microorganisms are common, it is
very serious and often leads to death.1 Up to 19% patients are in-
fected from hospital visits throughout the world.2 Most of the nos-
ocomial infections are associated with urinary tract and cause a
wide range of severe infections including pneumonia, bloodstream
and surgical wounds and infections of immunocompromised pa-
tients such as AIDS, cancer and organ transplant recipients. Major-
ity of the nosocomial pathogens are resistant to most of the
antibiotics.3 Beside the antibacterial, there are many studies fo-
cused on antifungal research due to the need of new, safe and po-
tent antifungal molecules. The use of available antifungal drugs,
polyene macrolides, azoles, flucytosine and candins are not ideal
in terms of efficacy, antifungal spectrum and safety; and the inva-
sive candidiasis and aspergillosis has increased dramatically.4
Though Amphotericin B is efficacious against both candidiasis
and aspergillosis, it shows severe renal toxicity.5 Hence, the urgent
need of new molecules to combat bacterial and fungal infections is
immense.
and position of substituents were considerably important factors
to effect the biological actions.7
On the other hand, oxime ether function of various heterocycles
is reported to possess microbiological properties. Particularly, O-
benzyl oxime ether functionality (Fig. 1) shows very significant
antimicrobial activities.8 With a view of above, we have incorpo-
rated bio-active N, O and S heterocycles with O-benzyl moiety to
make biologically potent oxime ether pharmacophore C@N–O–Bn.
As illustrated in Scheme 1, the oxime ethers 5a–o were synthe-
sized. Conversion of ketone into oxime ether primarily depends
upon the substitution on active methylene carbons and phenyl.
The C-3, C-5 unsubstituted and C-3 substituted ketones yield the
corresponding oxime ethers respectively within 6 and 7–25 h,
depending on nature and size of the substituent. But ketones with
methyl substitution at C-3 and C-5 take more than 30 h for the
conversion. All 3,5-unsubstituted/3-substituted compounds adopt
chair conformation as in Figure 2 (refer Supplementary data for
further details).
Widespread interest in the chemistry of piperidones, pyrans
and thiopyrans in a large number of natural products has attracted
due to their biological activities.6 Structure–activity relationship
(SAR) studies from piperidone heterocycles indicated that nature
Single crystal XRD study has been carried out for 5b to confirm
the stereochemistry established by NMR studies.9 Analysis of tor-
sion angles, asymmetry parameters and least-squares plane calcu-
lation10 shows that the piperidine ring adopts a chair conformation
with deviation of ring atoms N1 and C9 from C7/C8/C10/C11 plane
by ꢀ0.672(4) and 0.597(2) Å, respectively (Fig. 3). The smallest dis-
placement parameters q2 = 0.068(2) and q3 = ꢀ0.566(2) Å, total
* Corresponding author.
E-mail address: prskabilan@rediffmail.com (S. Kabilan).
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.04.038

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P. Parthiban et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2981–2985
Figure 1. Structure of oxiconazole 1, nafimidone oxime ether 2, chromonone oxime
ether 3 and target compounds.
Figure 3. ORTEP of compound 5b with atoms represented as 30% probability
ellipsoids; exists in chair conformation with equatorial disposition of methyl and
phenyl groups. The asymmetric unit of 5b contains two crystallographically
independent molecules; for clarity, one is eliminated.
While look at the chemical shifts and coupling constants, we
can identify the variation in stereochemistry of 3,5-dimethyl
substituted piperidone oxime ethers 5f, 5i, 5l and 5o. Among the
four, 5f gave two isomers 5f1 and 5f2. Due to their close Rf values,
the isomers could not be separated by TLC and hence are separated
by HPLC11a followed by their 1D (1H–1H COSY, NOESY) and 2D
NMR (HSQC, HMBC) characterization. Since the chemical shifts
and coupling constants of 5i, 5l and 5o are similar to that of 5f2,
they should also adopt the same conformation as 5f2 (Fig. 4).
In the minor isomer 5f1, doublets at 5.12 and 5.16 ppm are due
to diastereotopic nature of methylene protons (ꢀO–CH2–Ph). The
3
3
observed vicinal couplings J2,3 = 5.3 and J5,6 = 9.0 Hz are drasti-
cally deviated from its parent ketone (3J2a,3a = 3J5a,6a = 10.3 Hz),
which exists in chair conformation with equatorial orientation of
Scheme 1. Reagents and conditions: (a) EtOH, warm; (b) C6H5CH2–O–NH2ꢁHCl,
CH3COONaꢁ3H2O, MeOH, reflux.
3
all substituents. Hence, the observed coupling constants J2,3 and
3J5,6 suggest that 5f1 is not in chair form. If it adopts a normal chair
conformation with equatorial orientation of all substituents, the
3
3
observed coupling constants J2a,3a and J5a,6a should be around
10.5 Hz. Moreover, the coupling constants are not favorable for
boat conformation also. If it exists in a rigid boat form, the vicinal
Figure 2. Chair conformation of compounds 5a–e, 5g–h, 5j–k, 5m–n, 7a–b and
11a–b with equatorial orientation of substituents at C-2, C-3 and C-6.
puckering amplitude, QT = 0.570(2) Å and h = 172.9 (2)°. Dihedral
angle between the two phenyl rings C1/C2/C3/C4/C5/C6 and C12/
C13/C14/C15/C16/C17 is 56.56(4)°. Torsion angle of C6/C7/C8/C9
and C9/C10/ C11/C12 are 174.27(4) and 178.27(4)°, respectively.
Figure 4. Chair conformation of compounds 5f2, 5i, 5l, 5o and 7c2–d2. The phenyl
at C-2, C-6 and methyl at C-3 adopt equatorial orientation while methyl at C-5
occupies axial position to avoid A1,3 interaction.

P. Parthiban et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2981–2985
2983
coupling constants should be about 4 Hz. Hence, the abnormal vic-
inal coupling constants indicate that piperidone ring adopts nei-
ther chair nor boat conformation and hence we suggest a twist
boat conformation (Fig. 5). As well, carbon chemical shifts also sup-
port the existence of 5f1 in twist boat conformation.12
The synthetic method of 2,6-diaryltetrahydropyran-4-one O-
benzyloximes is depicted in Scheme 2. With respect to substituent
on para position of the phenyl at C-2 and C-6, 6c–e required about
25–30 h reflux for the conversion to oxime ethers. However, the
ketone without substitution on phenyl did not undergo oximina-
tion even at higher mole ratio of O-benzylhydroxylamine hydro-
chloride up to 120 h; and cannot lead to the desired product by
other bases viz, pyridine or amberlyst A-2113 instead of sodium
acetate.
The proton and carbon chemical shifts of 7a and 7b are assigned
similar to that of piperidone analogs 5b and 5c. Due to the increase
in electronegativity of oxygen than nitrogen, the benzylic protons
(H-2, H-6) and carbons (C-2, C-6) are deshielded about 0.7–0.8
and 17–18 ppm, respectively. On the basis of observed coupling
constants, chair conformation (Fig. 2) is suggested for both 7a
and 7b; the conformation of the methyl and ethyl groups also same
as in 5b and 5c (refer Supplementary data). Among the 3,5-di-
methyl compounds 7c–e, 7e gave single isomer while 7c and 7d
gave two isomers; of the two, 7d separated as 7d1 and 7d2 by
TLC whereas 7c separated by HPLC.11b Chemical shift pattern and
coupling constants of 7c1, 7d1 and 7e suggest that these com-
pounds adopt twist boat conformation like 5f1 whereas 7c2 and
7d2 adopt chair conformation with the stereochemistry as in Fig-
ure 4.
The synthesis of cis and trans-isomers of 2,6-diaryltetrahydro-
thiopyran-4-one O-benzyloximes 11a–b and 12a–c are shown in
Scheme 3. The proton and carbon chemical shifts of the cis-isomers
11a–b were assigned similar to that of corresponding piperidone
oxime ethers; thereby adopt the similar conformation of corre-
Scheme 3. Reagents and conditions: (a) EtOH, 10% NaOH, cold condition, stirring;
(b) fast stream of H2S gas, excess of CH3COONa, EtOH, reflux, 30 min.; (c) slow
stream of H2S gas, CH3COONa, EtOH, reflux, 6 h; (d) C6H5CH2–O–NH2ꢁHCl,
CH3COONaꢁ3H2O, MeOH, reflux, 5 h.
sponding piperidone oxime ethers as in Figure 2. However the
trans-isomers 12a–c, differ drastically in their coupling constants,
which indicates that these compounds are not in twist boat form
instead exist in a small contribution of boat form along with the
predominant chair form. Moreover, there are two possibilities in
chair conformation according to NMR data; one with axial orienta-
tion of the phenyl syn to oximino group another is anti to oximino
group. Of the two, syn axial phenyl should be populated largely
(Fig. 6) since in anti axial phenyl, steric interactions experienced
by the ortho protons of phenyl with axial proton at C-3, destabilize
that conformation.
Figure 5. Twist boat conformation for compounds 5f1, 7c1, 7d1 and 7e.
The crystal analysis shows that thiopyran ring adopts a dis-
torted chair conformation with deviation of ring atoms S1 and C3
from C1/C2/C4/C5 plane by ꢀ0.953 and 0.575 Å, respectively
(Fig. 7). The ring puckering parameters q2 and q3 = 0.1697(17)
and 0.6279(18) Å; QT = 0.6505(2) Å and h = 15.14(15)°. Dihedral
angle between the two phenyl rings C6/C7/C8/C9/C10/C11 and
Figure 6. Predominant chair conformation of compounds 12a–c with equatorial
and axial orientations of aryl groups, respectively, at C-2 and C-6, in solution.
Scheme 2. Reagents and conditions: (a) KOH, aqueous EtOH, vigorous stirring; (b)
C6H5CH2–O–NH2ꢁHCl, CH3COONaꢁ3H2O, MeOH, reflux.

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P. Parthiban et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2981–2985
of synthesized compounds against the bacterial strains viz, Pseudo-
monas aeruginosa, Staphylococcus aureus, Salmonella typhi and Esch-
erichia coli with comparison of MICs of Ciprofloxacin in Table 1
provides an understandable structure–activity relationship. In all
N, O and S heterocycles, irrespective of the nature of hetero atom,
the compounds with substitution neither on active methylene cen-
ters C-3/C-5 nor phenyl at C-2/C-6 show poor or negligible activity.
And the substitution of Me/Et/iPr/COOEt at C-3 also does not show
any significant enhancement in their antibacterial activity. How-
ever, activity increased with incorporation of alkyl substituent at
C-3 along with the substitution of Cl/Me/OMe at C-20000 and C-60000
of compounds 5g, 5j and 5m. Further, inhibition potency increased
with the introduction of methyl substituent on both active methy-
lene carbons C-3 and C-5 of 5g, 5j and 5m.
Among the three sets of compounds 5g, 5j, 5m (no Me at C-3
and C-5), 5h, 5k, 5n (Me at C-3) and 5i, 5l, 5o (Me at C-3 and C-
5) with substituted phenyl at C-2 and C-6, the introduction of Me
group at C-3 and C-5 shows constant increase in inhibition effi-
ciency of oxime ethers 5i, 5l and 5o than 5h, 5k, 5n and 5g, 5j,
5m. Noticeably, compounds 5i and 5l are eightfold potent than
5h and 5k against S. aureus and E. coli, respectively. As well, 5i is
fourfold potent than 5h against P. aeruginosa and E. coli. Distinctly
5i, which possess the electron withdrawing chloro substituent at
C-20000 and C-60000 along with methyl at C-3 and C-5 is better than
other similar compounds 5l and 5o, respectively having methyl
and methoxy substituents, instead of chlorine. Compound 5i is
twofold potent against S. aureus, S. typhi and E. coli and fourfold
stronger against P. aeruginosa than Ciprofloxacin to inhibit the vis-
ible growth of organisms. Like 5i, compound 5l also respectively
two and four times potent than standard, against E. coli and P. aeru-
ginosa while register a twofold less inhibition potency against S.
aureus.
Figure 7. ORTEP of compound 12a with atoms represented as 30% probability
ellipsoids. The molecule exists in chair conformation with axial and equatorial
dispositions of phenyl groups, respectively syn and anti to oximino group.
C12/C13/C14/C15/C16/C17 is 73.01(4)°. Torsion angle of C3/C2/C1/
C6 and C3/C4/C5/C12 are ꢀ73.13(4)° and 177.51(4)°, respectively.
All the synthesized compounds were screened for their in vitro
antimicrobial activity against pathogenic bacteria and fungi by
twofold serial dilution method.14 A prudent perusal of the MICs
In the pyran series also, compounds 7a and 7b with unsubsti-
tuted phenyl at C-2 and C-6 show poor activity; but, the oxygen
heteroatom in place of NH shows an increase in activity for com-
pounds 7a and 7b than corresponding nitrogen analogs 5b and
5c. Among the pyran oxime ethers 7a–e, compounds with methyl
substituents at C-20000 and C-60000 in addition to C-3 and C-5 (7d1,
7d2) are better than chloro or methoxy compounds 7c1 and 7e.
Of the two isomers in each compound 7c and 7d, the isomers
7c1 and 7d1 with twist boat conformation show better activity
than isomers 7c2 and 7d2 with chair conformation. The oxime
Table 1
Antibacterial activity of compounds 5a–o, 7a–e and 11a–12c
Compds
Minimum inhibitory concentrationa
(lg/mL)
P. aeruginosa
S. aureus
S. typhi
E. coli
5a
5b
5c
5d
200
200
100
200
50
50
200
50
25
6.25
50
50
25
>200b
200
25
100
100
50
>200
200
100
100
100
50
100
50
50
12.5
200
100
12.5
100
50
>200
200
200
100
50
100
200
100
100
100
50
5e
ether 7d1 shows MICs 12.5-25 lg/mL against all the tested patho-
5f1
5f2
5g
5h
5i
5j
5k
5l
5m
5n
gens; twice over potent than standard against S. aureus and S. typhi.
In thiopyran oxime ethers 11a–12c, the antibacterial activity
against all the tested organisms is not better than corresponding
piperidone analog except para-Me compounds. The sulfur analog
of 5j, that is, compounds 11b and 12b show good activity than
5j. Particularly, the cis-isomer 11b is far better than trans-isomer
12b; its inhibition potency against S. aureus and S. typhi is twofold
higher than Ciprofloxacin.
50
6.25
200
50
6.25
50
25
100
100
50
50
50
50
50
25
25
5o
25
25
25
Table 2 explains SAR study of synthesized compounds against a
panel of fungal strain viz, Candida albicans, Candida-51, Rhizopus
sp., Aspergillus niger, Aspergillus flavus and Cryptococcus neoformans.
The unsubstituted piperidone oxime ether does not show activity
against most of the strains, whose activity against C. albicans, Can-
7a
7b
100
100
25
50
12.5
25
25
200
25
>200
100
25
100
200
50
50
12.5
25
200
100
50
100
25
100
50
50
50
25
50
25
200
50
200
50
7c1
7c2
7d1
7d2
7e
11a
11b
12a
12b
12c
Ciprofloxacin
50
50
dida-51 and A. flavus lies in the range of 200 lg/mL. Moreover, the
50
introduction of Me/Et/iPr/COOEt at C-3 and Me at C-3, C-5 of 5a
also have no improvement in their antifungal potency, except
against a few organisms. Compounds 5c against Rhizopus sp. and
A. niger, 5d against Rhizopus sp. and C. albicans, 5e and 5f2, respec-
tively, against C. albicans and Rhizopus sp. and 5f1 against C. albi-
>200
12.5
>200
100
50
100
25
200
100
50
50
25
12.5
25
50
cans and Candida-51 show the MIC at the level of 50 lg/mL. The
a
MIC is the lowest concentration of an antimicrobial agent to significantly pre-
vent the visible growth of a pathogen after a period of incubation; MIC values are
incorporation of Cl/Me/OMe substituents at C-20000 and C-60000 of
5a (i.e., compounds 5g, 5j and 5m) shows the improvement in their
inhibition potency; 5g against C. albicans and A. niger and 5m
represented in micrograms per milliliter (lg/mL).
b
No activity up to 200 lg/mL.

P. Parthiban et al. / Bioorg. Med. Chem. Lett. 19 (2009) 2981–2985
2985
Table 2
groups at C-3 and/or C-5 positions play a significant role in eliciting
good antimicrobial properties. Hence, these classes of oxime ethers
can be used as sketch to conquer both bacterial and fungal
infections.
Antifungal activity of compounds 5a–o, 7a–e and 11a–12c
Compds
Minimum inhibitory concentration (lg/mL)
C.
Candida-
51
Rhizopus
sp.
A.
niger
A.
flavus
C.
albicans
neoformans
Acknowledgments
5a
5b
5c
5d
200
100
100
50
50
50
100
50
25
25
200
50
50
100
25
12.5
100
100
50
12.5
25
6.25
50
>200
100
200
50
200
200
100
200
100
50
100
200
50
25
100
50
6.25
50
>200
200
50
>200
200
50
200
200
100
100
50
200
100
>200
200
100
200
>200
200
50
>200
>200
200
100
100
100
200
100
50
The authors would like to acknowledge NMR research center,
IISc-Bangalore and Department of Chemistry, IIT-Madras, respec-
tively, for recording NMR and single crystal XRD. We extend our
thanks to RMMCH, Annamalai University for the antimicrobial
studies.
50
5e
200
100
50
>200
100
50
100
25
12.5
50
25
25
200
100
50
25
50
25
25
200
50
>200
50
50
25
5f1
5f2
5g
5h
5i
5j
5k
5l
5m
5n
50
25
25
25
Supplementary data
200
100
50
100
50
100
100
25
100
50
100
200
100
50
25
50
25
100
>200
100
100
100
25
200
100
50
100
25
12.5
100
50
Complete experimental details, analytical, IR, mass and NMR
data of all compounds. Conformation of alkyl group at C-3 of 5b–
d, 5h, 5k, 5n and 7a–b. Crystal data for 5b and 12a. Supplementary
crystallographic data for 5b (CCDC No. 717888) and 12a (CCDC No.
717889) can be obtained free of charge at www.ccdc.cam.ac.uk/
conts/retrieving.html. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.bmcl.2009.04.038.
12.5
6.25
100
100
50
5o
7a
7b
25
200
200
100
50
50
50
50
100
50
200
100
25
7c1
7c2
7d1
7d2
7e
11a
11b
12a
12b
12c
Stda
25
12.5
50
25
50
6.25
12.5
200
100
>200
200
25
25
6.25
>200
200
200
50
References and notes
1. Potera, C. Science 1999, 46, 4830.
2. (a) Facts sheet-Swiss Hand Hygiene Campaign, 2007. http://www.swiss-
noso.ch.; (b) Gastmeier, P.; Sohr, D.; Geffers, C.; Behnke, M.; Rüden, H. Infect.
Control Hosp. Epidemiol. 2007, 28, 466; (c) http://www.wrongdiagnosis.com/n/
nosocomial_infections/stats-country.
3. (a) Talbot, G. H.; Bradley, J.; Edwards, J. E.; Gilbert, D.; Scheld, M.; Bartlett, J. G.
Clin. Infect. Dis. 2006, 42, 657; (b) Gastmeier, P.; Sohr, D.; Geffers, C.; Behnke,
M.; Daschner, F.; Rüden, H. Infection 2005, 33, 148.
25
25
12.5
25
25
50
50
a
Amphotericin B.
4. (a) Fridkin, S. K.; Jarvis, W. R. Clin. Microbiol. Rev. 1996, 9, 499; (b) Marr, K. A.
Oncology 2004, 18, 9; (c) Akins, R. A. Med. Mycol. 2005, 42, 285.
5. Masubuchi, M.; Ebiike, H.; Kawasaki, K.; Sogabe, S.; Morikami, K.; Shiratori, Y.;
Tsujii, S.; Fujii, T.; Sakata, K.; Hayase, M.; Shindoh, H.; Aoki, Y.; Ohtsuka, T.;
Shimma, N. Bioorg. Med. Chem. 2003, 11, 4463.
6. (a) Baliah, V.; Jeyaraman, R.; Chandrasekaran, L. Chem. Rev. 1983, 83, 379; (b)
Aridoss, G.; Parthiban, P.; Ramachandran, R.; Prakash, M.; Kabilan, S.; Jeong, Y.
T. Eur. J. Med. Chem. 2009, 44, 577; (c) Aridoss, G.; Amirthaganesan, S.; Kumar,
N. A.; Kim, J. T.; Lim, K. T.; Kabilan, S.; Jeong, Y. T. Bioorg. Med. Chem. Lett. 2008,
18, 6542; (d) Aridoss, G.; Balasubramanian, S.; Parthiban, P.; Kabilan, S. Eur. J.
Med. Chem. 2007, 42, 851; (e) Dell, L. P. Curr. Med. Chem. 1998, 5, 179; (f) Singh,
V. et al Bioorg. Med. Chem. Lett. 2003, 13, 4209.
against Candida-51 and Rhizopus sp. inhibit the visible growth of
fungi at 50 g/mL. Compounds 5g, 5j and 5m show better MICs
while incorporating methyl at C-3 (compounds 5h, 5k and 5n)
and C-5 (compounds 5i, 5l and 5o). Among those, 5l and 5o are
doubly potent than Amphotericin B against Rhizopus sp., A. flavus
and C. albicans, A. niger, C. neoformans, respectively; in specific,
l
both register their best MIC at 6.25
Pyran analogs 5b and 5c, that is, compounds 7a and 7b show
activity in the range of 50–200 g/mL. The para substitution along
with methyl at C-3 and C-5 show better activity than correspond-
lg/mL against Candida-51.
l
7. (a) Prostakov, N. S.; Gaivoronskaya, L. A. Chem. Rev. 1978, 47, 447; (b) Lijinsky,
W.; Taylor, H. W. Int. J. Cancer 1975, 16, 318.
ing piperidone analog in the range of 25–50 lg/mL for most of the
8. (a) Parthiban, P.; Balasubramanian, S.; Aridoss, G.; Kabilan, S. Med. Chem. Res.
2005, 14, 523; (b) Ramalingan, C.; Park, Y. T.; Kabilan, S. Eur. J. Med. Chem. 2006,
41, 683; (c) Bhandari, K.; Srinivas, N.; Kesava, G. B. S.; Shukla, P. K. Eur. J. Med.
Chem. 2009, 44, 437; (d) Mixich, G.; Thiele, K. Arzneim.-Forsch./Drug Res. 1979,
29, 1510; (e) Polak, A. Arzneim.-Forsch./Drug Res. 1982, 32, 17; (f) Rossello, A.;
Bertini, S.; Lapucci, A.; Macchia, M.; Martinelli, A.; Rapposelli, S.; Herreros, E.;
Macchia, B. J. Med. Chem. 2002, 45, 4903; (g) Emami, S.; Falahati, M.;
Banifatemi, A.; Amanlouc, M.; Shafiee, A. Bioorg. Med. Chem. 2004, 12, 3971;
(h) Karakurt, A.; Dalkara, S.; Ozalp, M.; Ozbey, S.; Kendy, E.; Stables, J. P. Eur. J.
Med. Chem. 2001, 36, 421.
9. Parthiban, P.; Balasubramanian, S.; Aridoss, G.; Kabilan, S. Spectrochim. Acta Part
A 2008, 70, 11.
10. Cremer, D.; Pople, J. A. J. Am. Chem. Soc. 1975, 97, 1354.
11. (a) Semi-preparative HPLC, solvent system (mobile phase): MeOH–water
mixture, 9:1, flow rate: 5.0 mL/min, column (stationary phase): symmetry ODS
columnÒ, condition: isocratic, instrument: Waters 486 Tunable absorbance
detector, solution: 50 mg/mL; (b) solvent system: acetonitrile–water mixture,
1:1, flow rate: 3.5 mL/min..
tested pathogens. In specific, the Me substitution at C-20000 and C-
60000 show better MICs than others; of the two isomers 7d1 and
7d2, the isomer with chair conformation 7d2 is potent than 7d1.
Compounds 7d2 and 7e show remarkable MIC at 6.25 lg/mL
against C. albicans, Candida-51 and C. neoformans, respectively.
Both stereomers 11a and 12a have no activity against most of
the tested pathogenic fungi whereas the introduction of methyl
group at C-20000 and C-60000 of 11a and 12a show better activity
against all the strains. Of the two, trans-isomer 12b is more potent
than 11b. Among the synthesized thiopyran oxime ethers 11a–12c,
the trans-isomer 12c shows more potency against all the tested
fungal strains, whose MICs fall in the range of 12.5–50 lg/mL.
When compare to the cis-isomer of the piperidone analog 5m,
12. Geneste, P.; Durand, R.; Kamenka, J. M.; Beierbeck, H.; Martino, R.; Saunders, J.
K. Can. J. Chem. 1978, 56, 1940.
13. (a) Parthiban, P.; Ramachandran, R.; Aridoss, G.; Kabilan, S. Magn. Reson. Chem.
2008, 46, 780; (b) Ballini, R.; Barboni, L.; Filippone, P. Chem. Lett. 1997, 5, 475.
14. Dhar, M. L.; Dhar, M. M.; Dhawan, B. N.; Mehrotra, B. N.; Ray, C. Indian J. Expt.
Biol. 1968, 6, 232.
the MICs of the trans-isomer 12c are considerably better; espe-
cially 12c register its best MIC at 12.5 lg/mL against C. neoformans,
which is respectively two- and eightfold better than standard and
5m.
In overall, the hetero atom of synthesized compounds paved by
chloro/methyl/methoxy-phenyl on either side along with alkyl