V. Bala et al. / Bioorg. Med. Chem. Lett. 24 (2014) 5782–5786
5783
N
N
N
(b)
(c)
Conventional
approach
O2N
CH3
R1
(a)
N
N
HN
N
HN
N
N
NH2
1-2
N
S Na
S
Green
R
R
R
approach
S
S
S
S
S
N
R2
S
3-4
S
(i)
CH3
(ii)
(iii)
5-19
S
Scheme 1. (a) CS2, NaOH, ethyl acetate, 0–5 °C, 3–4 h; (b) alkyl/aryl halide, triethyl
amine, methanol, rt, 3–4 h; (c) distilled water, alkyl/aryl halide, 30 min.
N
S
R
R1
S
S
R
N
HN
O
S
N
S
R2
R
(vi)
(iv)
F3C
(v)
S
concentration (Table 1). Compound 9 and 10 exhibited potent sper-
micidal activity at 0.36 and 0.48 mM concentrations, respectively,
while the marketed drug N-9 had minimum effective concentration
(MEC) of 0.8 mM.
Figure 1. General structures of previously reported carbodithioates (i) metronida-
zole-carbodithioate (ii) & (iii) azole-carbodithioate (iv) fluoxetine-carbodithioate
(v) substituted carbodithioate (vi) general structure of synthesized carbamodithio-
ate derivatives.
In order to check microbicidal potential, synthesized com-
pounds (3–19) were further evaluated for anti-Trichomonas activity
against metronidazole (MTZ) susceptible and resistant TV strains
by using standard procedure.36 Sixteen compounds (except 13)
were found active against MTZ susceptible strain and fifteen
(except 13 and 15) against MTZ resistant strain (Table 1). Remark-
able activity was observed in three compounds (9, 10 and 19) at
concentration ranging from 0.054–0.056 mM comparable to MTZ
(MIC 0.019 mM). Compound 9 (MIC 0.228 mM) was also found as
active as MTZ (MIC 0.292 mM) against resistant strain.
The antifungal activity of synthesized compounds (3–19) was
also ascertained against six fungal strains (patient isolates of
Candida albicans, Cryptococcus neoformans, Sporothrix schenckii,
Trichophyton mentagrophytes, Aspergillus fumigates, and Candida
parapsilosis-ATCC-220190) and fifteen compounds (except 7 and
Recent SAR studies have revealed that a minor chemical change
into the proven structure results in significant potency enhance-
ment.24–28 Further, it has been also reported that incorporation of
one more nitrogen (N) atom into active scaffold has resulted into
improved biological activity as exemplified in N-amino rhodanine
derivatives showing strong insecticidal, antifungal and plant
growth inhibitory activity in comparison to rhodanine itself.29,30
Moreover, N-amino piperazine and N-amino morpholine have also
been reported as biologically active moieties.31,32 Therefore; it was
thought worthwhile adding one more N atom into the established
dithiocarbamate structure (1) to explore it as vaginal microbicide
with spermicidal potential (Fig. 2).
The design and synthesis of carbamodithioates (Fig. 2), their
spermicidal, anti-Trichomonas, and antifungal activity evaluation,
and subsequent safety assessment towards vaginal flora (Lactoba-
cillus) and cervical epithelium (HeLa cells) have been communi-
cated in this report. The mode of action through SH binding and
stability of most promising compound 9 in simulated vaginal fluid
(SVF) is also presented.
15) were found active at 12.5–50
lg/mL against one or more fungal
strains. Surprisingly, fourteen compounds (3, 4, 6, 8–14 and 16–19)
were active at 12.5–50 lg/mL against Trichophyton mentagrophytes
considered as opportunistic sexually transmitted infection.37 Most
potent compound 9 was also active against four fungal strains at
12.5–50 lg/mL, while N-9 was found almost inactive against them.
Structure Activity Relationship (SAR) have been compared by
virtue of the spermicidal, anti-Trichomonas and antifungal activity
results which suggested that piperidine moiety was preferred over
morpholine as all piperidin-1-yl-carbamodithioates have shown
spermicidal activity ranging from 0.36 to 57.08 mM. Compound 9
and 10 were ꢀ2-fold active than N-9 (MEC, 0.8 mM). The results
of spermicidal activity showed that the preference of substituent
(R) of piperidin-1-yl-carbamodithioates (5–11) was ethyl pyrroli-
dine (9) > ethyl piperidine (10) > hydroxy ethyl (7) > allyl
(6) > benzyl (8) > butyl (5) = ethyl morpholine (11). Whereas
among morpholin-4-yl-carbamodithioates (12–19), ethyl pyrroli-
dine (17) and ethyl piperidine (18) substituents were most
desirable.
The substituted morpholin/piperidin-1-yl-carbamodithioate
derivatives (5–19) were synthesized according to the strategy out-
lined in Scheme 1. The present study reaction was carried out in
water without addition of other base to yield substituted morphol-
in/piperidin-1-yl-carbamodithioate derivatives (5–19) in 30 min.
Significant rate enhancement was observed in water compared to
organic solvent. This acceleration is probably due to factors such
as hydrophobic effect,33 enhanced hydrogen bonding in the transi-
tion state,34 etc.
The structures of all newly synthesized compounds were con-
firmed by 1H NMR, 13C NMR, IR spectroscopy, mass spectrometry
(ESMS and HRMS) and elemental analysis. (See Supporting
information).
The anti-Trichomonas activity data against MTZ susceptible
strain suggested that among sodium salt of carbamodithioates (3
and 4), piperidine moiety (3, MIC 0.07 mM) was again preferred
over morpholine (4, MIC 0.64 mM). With piperidine moiety (5–
11), ethyl pyrrolidine (9, MIC 0.056 mM) and ethyl piperidine
(10, MIC 0.054 mM) substituents at sulfur atom possessed notable
activity. The order of preferred groups were ethyl pyrrolidine
(9) > ethyl piperidine (10) > ethyl morpholine (11) > benzyl
(8) > allyl (6) = hydroxy ethyl (7) > butyl (5). Morpholine moiety
(12–19) was again found to be less desirable as only compound
19 have shown activity at MIC 0.054 mM while others were active
at concentration 0.116–0.268 mM. The activity against MTZ resis-
tant strain was decreased as expected. Among the compounds
(3–19), Sodium morpholin-4-yl-carbamodithioate (4) was equipo-
tent for both MTZ susceptible and resistant strain while others lost
the activity by 2–8.5-folds as compared to MTZ where activity loss
was 15-folds. Piperidino derivatives (3 and 5–11) were again
preferred over morpholino compounds (4 and 12–19). Compounds
A potent spermicidal activity is a key feature of vaginal microbi-
cides to attract users. The synthesized seventeen compounds (3–19)
were subjected to spermicidal assay involving Sander-Cramer
assay35, where fourteen compounds (except 4, 12 and 16) irreversibly
immobilized 100% normal human spermatozoa at 0.36–57.08 mM
R1
S
N
NH
S
N
R2
Structure 1
S
R
S
R
(No significant
Designed carbamodithioate scaffold
(additional NH was introduced to enhance activity)
spermicidal activity)
N
O
N
=
N
R= different alkyl/aryl/heteroaryl substituents
Figure 2. Designing of carbamodithioates.
