Novel N-chloroheterocyclic antimicrobials

Article abstract of DOI:10.1016/j.bmcl.2011.03.035

Antimicrobial compounds with broad-spectrum activity and minimal potential for antibiotic resistance are urgently needed. Toward this end, we prepared and investigated a novel series of N-chloroheterocycles. Of the compounds examined, the N-chloroamine series were found superior over N-chloroamide series in regards to exhibiting high antimicrobial activity, low cytotoxicity, and long-term aqueous stability.

Full text of DOI:10.1016/j.bmcl.2011.03.035

Bioorganic & Medicinal Chemistry Letters 21 (2011) 3029–3033
Contents lists available at ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Novel N-chloroheterocyclic antimicrobials
Charles Francavilla, Eric D. Turtle, Bum Kim, Donogh J. R. O’Mahony, Timothy P. Shiau, Eddy Low,
Nichole J. Alvarez, Chris E. Celeri, Louisa D’Lima, Lisa C. Friedman, Francis S. Ruado, Ping Xu,
⇑
Meghan E. Zuck, Mark B. Anderson, Ramin (Ron) Najafi, Rakesh K. Jain
NovaBay Pharmaceuticals Inc., 5980 Horton St. Suite 550, Emeryville, CA 94608, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Antimicrobial compounds with broad-spectrum activity and minimal potential for antibiotic resistance
are urgently needed. Toward this end, we prepared and investigated a novel series of N-chloroheterocy-
cles. Of the compounds examined, the N-chloroamine series were found superior over N-chloroamide ser-
ies in regards to exhibiting high antimicrobial activity, low cytotoxicity, and long-term aqueous stability.
Ó 2011 Elsevier Ltd. All rights reserved.
Received 13 January 2011
Accepted 10 March 2011
Available online 16 March 2011
Keywords:
N-Chloroheterocyclic
Antimicrobials
Broad-spectrum
Many antimicrobial compounds used for the prevention or treat-
ment of infections have been rendered less effective through
evolved bacterial drug resistance.1 This has engendered an urgent
need for new antimicrobial compounds which display both broad-
spectrum activity and reduced potential for development of antibi-
otic resistance. Here, we present results on a new series of N-chloro-
heterocycles being developed for various topical applications.
N-Chlorotaurine 2 and N,N-dichlorotaurine 3 (Scheme 1), which
are part of the innate mammalian response to infection, provide an
advantageous starting point for novel antibiotic drug development.
During the oxidative burst in human granulocytes and monocytes,
myeloperoxidase enzyme (MPO; EC 1.11.1.7) produces hypochlo-
rite, which rapidly oxidizes amino acids.2 Because of the abun-
dance of taurine 1 in white blood cells, the mono-chlorinated 2
and di-chlorinated 3 compounds are produced and utilized by hu-
man neutrophils to destroy invading microorganisms to protect
the body.3 Although these compounds have been utilized as effec-
tive antimicrobials throughout the evolutionary process, there is
no known bacterial resistance to this class of compounds.
obtain a product which can be manufactured and stored for
extended periods of time. We previously reported that b,b-disubsti-
tuted chlorotaurines exhibit improved aqueous stability and main-
tain desired biological activity.6 This observation had ultimately
led to 2,2-dimethyl-N,N-dichlorotaurine, NVC-422, now in phase 2
clinical trials for impetigo. We have evidence that the mechanism
of action (MOA) for N,N-dichloroamines involves a very rapid inacti-
vation of sulfur-containing proteins.7 This results in dysfunction or
dysregulation, leading to the death of the pathogen; we expect this
to be also the case for N-chloroheterocycles. In consideration of the
probable MOA and the influence of structure on the physiochemical
properties of N-chloramines, we examined a new generation of re-
lated compounds which may provide new clinical candidates for
various topical applications including uncomplicated skin and soft
tissue infections, onychomycosis, and impetigo.
Here, we report the synthesis and structure activity/stability
relationships of novel five- and six-membered N-chloroheterocy-
cles, expanding on what we learned in the N,N-dichloroamine
series.8 Although limited studies on N-chloroheterocyclics have
been reported9,10 our work encompasses a systematic effort to
incorporate important pharmaceutical properties such as aqueous
solubility, long-term solution stability, potent and rapid antimicro-
bial activity, and improved safety.
Nagl et al. had focused on elucidating the bacterial, fungicidal,
and virucidal activity as well as the clinical safety of N-chlorotaurine
2.4 A major challenge to our efforts has been to extend the aqueous
solution half-life of N-chlorotaurine 2 under acidic conditions5 to
We initially looked at N-chlorohydantoins, since they have
found applications in biocidal coatings;11 however, their suitability
for human therapeutics required chemical modifications to obtain
better ‘drug-like’ properties. In this series (6–11 and 15), the amide
nitrogen is chlorinated and the water solubilizing group, R, is
linked to the imide nitrogen or the ring’s 5-position. Scheme 2 out-
lines the synthesis of a variety of water soluble N-chlorohydanto-
ins, synthesized from dimethylhydantoin 4. The hydantoin was
Cl
SO3Na
SO3Na
Cl
SO3Na
N
Cl
H2N
N
H
2
3
1
Scheme 1. Taurine, N-chlorotaurine, and N,N-dichlorotaurine.
⇑
Corresponding author. Tel.: +1 510 899 8871.
E-mail address: rjain@novabaypharma.com (R.K. Jain).
0960-894X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2011.03.035

3030
C. Francavilla et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3029–3033
O
1,2-bromochloroethane. Substitution of the chloride with potas-
sium thioacetate, oxidation to the sulfonate, and N-chlorination
gave the ethylsulfonate analog 9. Displacement of the chloride in
5 with potassium thioacetate, de-S-acetylation with sodium
O
f
Cl
N
NH
HN
HN
85%
O
5
O
4
hydroxide, S-alkylation with propane sultone, oxidation to the sul-
fonate, and N-chlorination gave 10. Compound 11 was obtained by
reaction of 5 with pyridine, followed by N-chlorination.
O
O
Synthesis of the trimethylammonium salt 15 (Scheme 3) re-
quired a different synthetic approach. N-Acetonylphthalimide 12
was treated with ammonium carbonate and potassium cyanide
to give intermediate 13. The amide of the intermediate was hydro-
lyzed, and the product was N-methylated to give the trimethylam-
monium chloride 14. Treatment of 14 with t-butyl hypochlorite
gave the desired N-chlorinated hydantoin 15. Hydantoins (6–11
and 15) in Table 1 exhibited moderate antibacterial activity, but
generally lacked antifungal activity.
From the hydantoin results in Table 1, it can be seen that the
sulfonate substitution affords compounds with improved solution
stability compared to the quaternary ammonium substituted ana-
logs, cf. 9 and 6 versus 7 and 8. Additionally, longer chain lengths
between the hydantoin and the charged water-solubilizing group
improved antibacterial activity but lowered antifungal activity,
cf. 9 versus 6.
To examine the effect of expanding the size of the ring, two
piperazinediones and an oxazinan-2-one were synthesized
(Scheme 4). For the piperazinediones, 2-aminoisobutyric acid
methyl ester 16 was acylated with 2-chloroacetyl chloride and
the adduct was reacted with ethanol amine at elevated tempera-
tures to give the cyclized 2,5-diketopiperazine intermediate 17.
The alcohol 17 was converted to a sulfonic acid by reaction with
thioacetic acid under Mitsunobu reaction conditions, followed by
oxidation with hydrogen peroxide in formic acid. N-chlorination
gives the desired product 18. Alternatively, intermediate 17 was
directly N-chlorinated to give 19. For the oxazinan-2-one, carbox-
ylic acid 208 was reacted with CDI followed by (2-ethoxy-2-oxo-
N
N
R
N
( )x
R
N
Cl
Cl
O
O
a,b
c,d,b
e,d,b
g,h,b
g,i,j,h,b
k,b
6: x=1, R=SO3Na; 3%
9: R=SO3Na; 54%
10: R=SO2(CH3)3SO3Cs; 17%
11
: R=pryridinium Cl ; 48%
7: x=1, R=N(CH3)3+Cl-; 2%
: x=3, R=N(CH3)3+Cl-; 22%
+
-
8
Scheme 2. Reagents and conditions: (a) NaH, DMF, rt, 1 h followed by; propane
sultone, rt, 18 h; (b) t-BuOCl, MeOH, 0 °C, 1 h; (c) NaH, DMF, rt, 1 h;
BrCH2CH2CH2NðCH3Þ þBrꢀ, rt, 18 h; (d) (i) Ag2O, water, rt 30 min, (ii) HCl, water,
3
rt, 30 min; (e) NaH, DMF, rt, 1 h followed by BrCH2ðCH2Þ CH2NðCH3Þ þBrꢀ, rt, 18 h;
3
3
(f) BrCH2CH2Cl, NaOH, EtOH, reflux, 18 h; (g) KSAc, DMF, 70 °C, 18 h; (h) H2O2,
HCO2H, 4 °C, 4 h; (i) NaOH, MeOH, 0 °C to rt, 18 h; (j) propane sultone, Cs2CO3 DMF,
rt, 18 h; (k) pyridine, 18 h, 90 °C.
H
O
O
Cl
H
N
Cl-
N+
N
Cl-
N+
O
O
N
N
a
d
b,c
47%
HN
NH
O
N
N
50%
O
O
61%
O
O
O
14
O
12
13
15
OH
Scheme 3. Reagents and conditions: (a) (NH4)2CO3, KCN, ethanol, 75 °C, 18 h; (b)
HCl, water, 100 °C, 18 h; (c) (1) MeI, Cs2CO3, methanol, rt, 72 h; then HCl, water; (d)
t-BuOCl, MeOH, 5 °C, 2 h.
deprotonated with NaH and reacted with propane sultone, fol-
lowed by N-chlorination with t-butyl hypochlorite, to give sulfonic
acid 6. Compounds 7 and 8 were synthesized by alkylation of the
hydantoin with the appropriate bromoalkylammonium salt, fol-
lowed by halogen exchange with silver oxide and hydrogen chlo-
ride, and N-chlorination with t-butyl hypochlorite.
ethyl)lithium, to give
a keto-ester. Reduction with sodium
borohydride gave diol 21. Treatment of the diol with sodium
hydride effected cyclization to provide the thermodynamically
Other hydantoin analogs (9–11) were synthesized from the
chloride intermediate 5, obtained by alkylation of hydantoin 4 with
Table 1
Heterocyclic N-chloramides
O
Cl
N
V
Z
a
MBC or MFC (lg/mL)
Compound
t
(days at 40 °C) CT50 (mM)
½
Y
X
b
b
b
V
X
Y
Z
Escherichia coli
Staphylococcus aureus
Candida albicans
9
6
7
8
––
––
––
––
––
––
H
H
H
H
H
H
C@O N–CH2CH2SO3Na
128
16
128
128
––
256
16
128
––
128
32
>128
128
––
>256
64
128
––
––
64
32
128
16
128
>256
>1024
>1024
––
>256
>256
>256
––
––
>256
––
––
8
65
>14
4
22
4
>7
5
90
< 1
> 14
>92
>112
126
>58
0.7
0.4
––
0.6
––
0.4
––
1.3
––
––
4.3
3.2
0.5
0.3
C@O N–CH2CH2CH2SO3Na
N-CH2CH2NðCH3Þ3þClꢀ
C@O
N-CH2CH2CH2CH2CH2NðCH3Þ3þClꢀ
C@O
11
10
15
18
19
22
28
30
33
37
C@O N–CH2CH2(N-pyridinium)+
C@O N-CH2CH2SO2CH2CH2CH2SO3ꢀCs
–– N+(CH3)3 C@O N–CH3
CH2
CH2
O
––
––
H
H
H
H
H
H
C@O N–CH2CH2SO3Na
C@O N–CH2CH2OH
CH2 CH–CH2CH2OH
CH2 N–CH2CH2SO3Na
––
32
CH2 N-CH2CH2SO2CH2CH2CH2ðSOÞ3ꢀCs 64
N-CH2CH2NðCH3Þ3þClꢀ
––
–– OH
CH2
CH2 N–CH3
512
16
a
Minimum Bactericidal Concentration (MBC) was determined using a modified standard method described in CLSI M26-A whereby isotonic buffered saline at pH 4 is
substituted for Mueller–Hinton broth (MHB) to compensate for the reactivity of chlorine to certain components of MHB. Due to the rapid cidal nature of chlorinated
derivatives, the assay was shortened from 24 h at 35 °C to 1 h at room temperature.
b
E. coli ATCC 25922, S. aureus ATCC 29213, C. albicans ATCC 10231.

C. Francavilla et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3029–3033
3031
O
Z
Z
Z
a
b
O
O
R
a,b
HO
N
81%
N
N
H
H2N CO2Me
N
H
N
Cl
26% 42
84%
79% 44
N
38%
NH
Cl
: Z = CHN(Me)2 39: Z = CHN+(Me)3Cl-
O
38
c,d,e
e
43
16
18: R=SO3Na; 14%
19: R=OH; 80%
40
: Z = CHOH
41: Z = C=O
17
O O
S
O
c
e,b
d
O
O
OH
Cl
S
S
O
Cl
N
h,i
j,e
O
88%
100%
26%
N
Cl
Cbz
Cbz
N
N
OH
45
OH
65%
46
37%
OH
47
H
H
48
21
20
22
Scheme 4. Reagents and conditions: (a) ClCH2COCl, EtOAc, H2O, rt 2 h; (b)
ethanolamine, THF; EtOH 140 °C, 18 h; (c) DIAD, P(Ph)3, AcSH, 0 °C to rt, 26 h; (d)
HCO2H, H2O2, rt, 6 h; (e) t-BuOCl, MeOH, 0 °C to rt, 30 min to 2 h; (h) CDI, THF, rt
1 h; followed by LiCH2CO2Et, ꢀ78 °C, 2 h; (i) NaBH4, EtOH, rt, 3 h; (j) NaH, THF, rt,
4 h.
O
OH
OH
H2N HN
g,b
24%
f
N
N
24
65%
Cl
49
50
Scheme 6. Reagents and conditions: (a) (i) MeI, DCM, 0 °C, 30 min, (ii) Ag2O, water,
rt, 30 min, (iii) HCl, water, rt, 5 min; (b) t-BuOCl, MeOH, 0 °C, 1 h; (c) Na2S, H2O,
MeOH, rt to reflux, 8 h; (d) m-CPBA, DCM, 0 °C, 45 min; (e) NH4OH, 60–100 °C, 22 h;
(f) Raney NickelÒ, methanol, H2, rt, 18 h; (g) acetone, CHCl3, NaOH, rt to reflux, 19 h.
O
H
N
b,c
a
d,e
OH
OH
H2N
HN
N
O2N
OH
41%
87%
26%
23
24
25
O
O
late with potassium thioacetate, gave thioacetate 26. The desired N-
chloroamine 28 was obtained by oxidation of thioacetate 36 with
hydrogen peroxide in acetic acid to the sulfonate 27, followed by
N-chlorination. Similarly, compound 30 was prepared from 26 by
a reaction sequence consisting of saponification, S-alkylation, oxida-
tion to the sulfone, and N-chlorination. Imidazolidinone 32 was syn-
thesized from 31 by a similar route used to obtain 25 from 23.
Methylation and N-chlorination of 32 provided 33. Reaction of the
diol 34 with formaldehyde under Mannich reaction conditions gave
the 1,3-oxazinane intermediate 35.12 Acid-promoted ring opening
of 35, followed by hydrogenation, and cyclization yielded the de-
sired 2-imidazolidinone intermediate 36. Compound 37 was ob-
tained after treatment of imidazolidinone 36 with t-butyl
hypochlorite.
The N-chloroimidazolidin-2-ones (28, 30, 33, and 37) showed
improved antibacterial activity over analogously functionalized
hydantoin compounds (cf. 28 vs 9, 30 vs 10) with significantly re-
duced cytotoxicity (Table 1). In addition, this series showed in-
creased aqueous stability at 40 °C. However, the antibacterial and
antifungal activities were below our expectations and further stud-
ies are planned to improve the efficacy of these compounds.
At this point, all of the N-chloroheterocycles have been cyclic
N-chloroamides. From our previous work, we felt that heterocyclic
derivatives which contain the N-chloroamine functionality may
exhibit improved stability and antimicrobial activity. Thus, we pre-
pared the six-membered, N-chloroheterocycles derived from piper-
idine (42–44), thiomorpholine (48) and piperazine (50 and 54)
scaffolds. These were constructed through acyclic version of our suc-
cessful route to N-chlorotaurine.
Initially, 2,2,6,6-tetramethylpiperidine was examined (Scheme
6). Dimethylamine 38 was alkylated with methyl iodide, and the
iodide was exchanged with chloride ion to give ammonium salt
39. The N-chlorination of 39 and two other commercially available
compounds (40 and 41) gave 42, 43, and 44, respectively. Reaction
of sodium sulfide with 3-chloro-2-methylprop-1-ene 45, followed
by oxidation gave intermediate 47. Cyclization and N-chlorination
of the intermediate gave 48. Compound 50 was obtained by hydro-
genation, a Bargellini-type reaction,13 and N-chlorination of inter-
mediate 24. Although the 2,2,6,6-tetramethylpiperidine analogs
did display acceptable biological activity, the solution stability
and the CT50 values were disappointing (Table 2).
99%
f
h
SO3Na
Cl
O
SO3Na
HN
N
N N
O
42%
SAc
27
HN
N
28
g
O
26
O
O
i,j,h
100%
SH
N
HN
N
Cl
S
SO3Cs
N
N
3%
29
30
O
O
N+
a,b,k
2%
l,h
Cl
HN
N
N
N
N
H2N
65%
OAc-
31
32
33
O
O
O2N
Cl
O2N
HO
n
o,b,c
44%
h
N
N
HN
N
N
OH
55%
62%
O
OH
37
OH
34
35
36
Scheme 5. Reagents and conditions: (a) i-PrOH, CH2O, water, NO2CH(CH3)2, NaOH,
rt, 24 h; (b) Raney NickelÒ, MeOH, H2, rt, 18 h; (c) urea, 200 °C, 1 h; (d) MsCl,
pyridine, DCM, rt, 24 h; (e) KSAc, DMF, rt, 18 h; (f) H2O2, HCO2H, 0 °C to rt, 16 h; (g)
NaOH, MeOH, water, 0 °C to rt, 18 h; (h) t-BuOCl, MeOH, 0 °C, 1 h; (i) propane
sultone, Cs2CO3, DMF, rt, 18 h; (j) m-CPBA, DCM, rt, 21 h; (k) CDI, DCM, rt, 20 h; (l)
MeI, MeOH, rt, 18 h; (m) Ag2O, water, AcOH, rt, 2 h; (n) CH2O, water, CH3NH2; (o)
HCl, EtOH, reflux, 5 h.
favored oxazinan-2-one, which was N-chlorinated to give 22.
Examination of 9 versus 18 in Table 1 reveals that ring expansion
has little effect on either antifungal or antibacterial activity. It is
noteworthy that the sulfonate derivative 18 possesses a pro-
foundly greater solution stability than its alcohol counterpart 19.
To obtain a broader therapeutic index (assessed by the in vitro
CT50 vs antimicrobial activity) of the N-chloro hydantoin derivatives,
we replaced one of the hydantoin carbonyls with a methylene group
to afford imidazolidin-2-ones. In this series (28, 30, 33, and 37), chlo-
rine was bonded to the 3-position nitrogen (adjacent to the dimeth-
ylmethylene group), and the water solubilizing group was linked to
either the 1-position nitrogen or the dimethylmethylene group.
These heterocyclic compounds were synthesized by the series of
reactions as shown in Scheme 5. Amino ethanol 23 was reacted with
2-nitropropane in a nitro-Mannich reaction to give nitro compound
24. Synthesis of 25 was accomplished by hydrogenation of the nitro
group, followed by cyclization with urea. The reaction of 25 with
methanesulfonyl chloride, and displacement of the resulting mesy-
Piperazinedione 52 (Scheme 7) was obtained by treatment of
2-amino-2-methylpropanenitrile 51 with ammonium hydroxide
and ammonium chloride at reflux temperature.14 The N-alkylation

3032
C. Francavilla et al. / Bioorg. Med. Chem. Lett. 21 (2011) 3029–3033
Table 2
Heterocyclic N-chloramines
Cl
N
V
a
MBC or MFC (lg/mL)
Compound
t
(days at 40 °C)
CT50 (mM)
½
Z
Y
b
b
b
V
Y
Z
E. coli
S. aureus
C. albicans
CHNðCH3Þ3þClꢀ
42
43
44
48
50
54
58
59
60
61
62
CH2
CH2
CH2
CH2
CH2
C@O
––
––
––
––
––
CH2
CH2
CH2
CH2
C@O
C@O
C@O
C@O
C@O
C@O
C@O
16
1
1
2
1
128
2
4
16
4
2
8
4
2
1
2
128
2
16
8
2
256
32
32
128
8
>256
256
16
28
32
<1
>113
––
1.8
0.2
0.04
0.1
0.1
1.3
2.2
14.5
23.5
8.3
CHOH
C@O
SO2
N-CH2CH2OH
N–CH2CH2SO3Na
N–CH2CH2CH2CH2OH
N–CH2CH2CH2SO3Na
N–CH2CH2CH2CH2SO3Na
N-CH2CH2CH2NðCH3Þ3þClꢀ
N-CH2CH2CH2CH2CH2NðCH3Þ3þClꢀ
90
>92
>249
>84
111
>160
32
32
16
2
9.1
a
Minimum Bactericidal Concentration (MBC) was determined using a modified standard method described in CLSI M26-A whereby isotonic buffered saline at pH 4 is
substituted for Mueller–Hinton broth (MHB) to compensate for the reactivity of chlorine to certain components of MHB. Due to the rapid cidal nature of chlorinated
derivatives, the assay was shortened from 24 h at 35 C to 1 h at room temperature.
b
E. coli ATCC 25922, S. aureus ATCC 29213, C. albicans ATCC 10231.
ton with sodium hydride followed by treatment with an alkyl bro-
R
N
R
N
O
O
mide. Compound 58 was prepared by alkylation of 57 with benzyl
4-bromobutyl ether, halogen exchange, hydrogenation, and N-chlo-
rination. Compounds(59–62) were obtainedbyalkylationof 57with
the appropriate alkyl halide, halogen exchange, and N-chlorination.
All of the imidazolidin-4-ones exhibited significant improvements
over both the hydantoins (6–11, and 15) and the 2-imidazolidinones
(28, 30, 33, and 37). Both antibacterial and antifungal activities were
improved as shown by the MBC and MFC values. These molecules
displayed excellent aqueous solution stability at elevated tempera-
tures. Additionally, the 4-imidazolidinones also had a greatly im-
proved CT50 profile over the other heterocycles.
To hopefully improve potency, safety, and physicochemical prop-
erties over our previous N,N-dichloroamine based antimicrobials,8
5- and 6-membered heterocyclic N-chloroamide and N-chloroamine
were prepared and evaluated in vitro. In the N-chloroamide series,
the hydantoins (6–11, and 15) antimicrobial activity were general
poor against all the pathogens. For the 2-imidazolidinones (28, 30,
33 and 37), compound 37 had good antibacterial and antifungal
activity; however, showed no improvement in its toxicity profile
over our previous N,N-dichloroamines. In the N-chloroamine series,
the 6-membered piperidine analogs (42–44, 48, and 50) had good
antibacterial activity and moderate antifungal activity. Cytotoxicity
profiles for these compounds were not encouraging; thus, they had a
less thanoptimal therapeuticindex. However, we had interestingre-
sults with the 5-membered analogs (58–62). All the 4-imidazolidi-
nones had good antibacterial activity, antifungal activity, and
solution stability. These compounds had a dramatically improved
therapeutic index over all compounds tested in this paper. Addi-
tional, they are an improvement over all compounds that we have
presented to date.
f
O
O
e
NC NH2
2%
37%
N
H
N
Cl
51
52: R=H
53: R=(CH2)3SO3Na
g
57%
54:
R=(CH2)3SO3Na
Scheme 7. Reagents and conditions: (e) t-BuOCl, MeOH, 0 °C to rt, 30 min to 2 h; (f)
NH4OH, NH4Cl, reflux, 7 h; (g) NaH, DMF, Br(CH2)3SO3Na, rt, 20 h.
O
HO
N
N
c-f
O
Cl
S
O
58
a
b
HN
HN
NH
NH
81%
100%
O
g,d,h
55
W
56
57
N
N
( )x
Cl
: x=1, W=SO Na; 24%
59
60
61
62
: x=2, W=SO3Na; 27%
3
: x=1, W=N(CH3)3+Cl-; 18%
: x=3, W=N(CH ) +Cl-; 33%
3 3
Scheme 8. Reagents and conditions: (a) NaCN, S(NH4)2, NH4Cl, water, 60 °C, 8 h; (b)
NaOH, H2O2, water, 4 °C, 4 h; (c) NaH, DMF, rt, 1 h followed by BnOCH2(CH2)2CH2Br,
DMF, rt, 18 h, 90%; (d) Ag2O, water, rt, 1 h followed by HCl, water, 93–98%; (e) 10%
Pd/C, EtOH, H2, rt, 48 h, 26%; (f) t-BuOCl, MeOH, 0 °C, 1 h, 30%; (g) NaH, DMF, rt, 1 h
followed by WCH2(CH2)xCH2Br, DMF, rt, 18 h; (f) t-BuOCl, MeOH, 0 °C, 1 h.
of intermediate 52 with 3-bromopropane-1-sulfonic acid sodium
salt followed by N-chlorination gave the desired N-chloropiper-
azine-2,6-dione 54 (Scheme 7).
These six-membered N-chloroamine heterocycles typically had
good antibacterial activity. This was a significant improvement over
both 5- and six-membered N-chloroamide heterocycles. However,
they lacked the level of solution stability which we were seeking
for topical antimicrobial applications. Since we were quite im-
pressed by the antibacterial and antifungal activity of 50, we decided
to synthesize the 5-membered derivative, imidazolidin-4-one.
In this series, (58–62), we investigated 5-membered, N-chloro-
amine heterocycles, where the water solublizing group was linked
totheamidenitrogen. ThesynthesisofN-chloroimidazolidin-4-ones
derivatives was initiated with the common intermediate 57, readily
prepared from acetone using a two step procedure (Scheme 8).15
Alkylation was accomplished through the removal of the amide pro-
In summary, we have described the synthesis, antimicrobial
activity, cytotoxicity, and aqueous stability of various 5- and 6-
membered ring N-chloroheterocycles. Of these, the N-chloroamines
analogs (Scheme 2), were found to be a significant improvement
over the N-chloroamides analogs (Scheme 1) in antimicrobial activ-
ity. Within the N-chloroamines, the 5-membered 4-imidazolidinon-
es (58–62) were superior to the six-membered heterocycles in
terms of therapeutic index. Additionally, the 4-imidazolidinone
analogs met our goal of improving antimicrobial therapeutic index
and solution stability over our previous N,N-dichloroamine bench-
mark.8 Thus, the imidazolidin-4-ones were found to have all the
desirable physicochemical properties for developing new broad-

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3033
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7. Results from the biological experiments and the kinetic data will be published
elsewhere.
Acknowledgments
The authors wish to acknowledge Drs. John Bartell, Masood
Chowhan, Howard Ketelson, and David Stroman for helpful discus-
sions. This work was supported by Alcon Laboratories, Inc.
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