Synthesis and antimicrobial activity of imidazole and pyridine appended cholestane-based conjugates

Article abstract of DOI:10.1016/j.bmcl.2013.05.098

A series of 3α-amino-5α-cholestane and 3α,7α- diamino-5α-cholestane derivatives containing imidazole and pyridine rings were synthesized by simple and effective reductive amination, and their in vitro activities against a range of Gram-positive and Gram-negative strains were evaluated. Most of the compound exhibited enhanced activity against MRSA pathogen. 3α,7α-Di(pyridylmethyl)amino-5α-cholestane 10 showed the highest potency in these series toward the Gram-positive bacteria, Staphylococcus epidermidis 887E, with the lowest MIC value of 1 μg/mL.

Full text of DOI:10.1016/j.bmcl.2013.05.098

Bioorganic & Medicinal Chemistry Letters 23 (2013) 4315–4318
Contents lists available at SciVerse ScienceDirect
Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis and antimicrobial activity of imidazole and pyridine
appended cholestane-based conjugates
a
b
b
Hong-Seok Kim a, , Jyoti R. Jadhav , Sung-Ji Jung , Jin-Hwan Kwak
⇑
a Department of Applied Chemistry, Kyungpook National University, 80 University Road, Buk-gu, Daegu 702-701, Republic of Korea
b School of Life Science, Handong Global University, Pohang 791-708, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of 3a-amino-5a-cholestane and 3a,7a-diamino-5a-cholestane derivatives containing imidazole
and pyridine rings were synthesized by simple and effective reductive amination, and their in vitro activ-
ities against a range of Gram-positive and Gram-negative strains were evaluated. Most of the compound
Received 15 March 2013
Revised 17 May 2013
Accepted 31 May 2013
Available online 7 June 2013
exhibited enhanced activity against MRSA pathogen. 3
showed the highest potency in these series toward the Gram-positive bacteria, Staphylococcus epidermidis
887E, with the lowest MIC value of 1 g/mL.
a,7a-Di(pyridylmethyl)amino-5a-cholestane 10
l
Keywords:
Cholestane
Ó 2013 Elsevier Ltd. All rights reserved.
Imidazole
Pyridine
Antimicrobial activity
The rapid increase in the prevalence of multiple drug-resistance
Gram-positive bacteria has highlighted the urgent need to discover
novel active agents against a range of Gram-positive pathogens.
One of the strategies to overcome this problem is to identify new
drugs with a new molecular target.1 Methicillin-resistant Staphylo-
coccus aureus (MRSA) and Vancomycin-resistant entercocci (VRE)
are of particular concern.2 Initially, MRSA was observed only in
hospital settings, but it is now apparent that community-acquired
MRSA (CA-MRSA) infections can occur in individuals without any
identifiable risk factors. Moreover, the prevalence of CA-MRSA is
increasing,3a particularly in children.3b,c This is currently recog-
nized as a growing problem worldwide.3d These factors make the
treatment of Gram-positive infections a greater challenge than in
the past.
The imidazole nucleus is an important building block in drug
discovery. Recently imidazole and imidazolium derivatives have
been the subject of extensive study of the antimicrobial activity
for their potential as effective therapeutic agents.4 Based on several
literature surveys, imidazole derivatives show a range of pharma-
cological activities, such as anti-fungal and anti-bacterial,4a,b
anti-inflammatory and analgesic,4c anti-tubercular,4a,d anti-
depressant,4e anti-cancer,4f anti-viral,4a,g and anti-lishmanial.4h
On the other hand, the high therapeutic properties of pyridine-
related drugs have encouraged medicinal chemists to synthesize
a large number of chemotherapeutic agents.5 The medicinal prop-
erties of pyridine include a variety of pharmacological applications,
such as antibacterial,5a antitumor,5b antiparacite,5c and analgesic
activity.5d
A class of cationic steroid antibiotics as steroid-polyamine con-
jugates were designed by Savage with the intension of mimicking
the antimicrobial activities of polymyxin B (PMB),6 whereas Regen
et al. described the utilization of bile acid–polyamine conjugates as
synthetic ionophore leads in the process of drug discovery.7 Over
the last decade, Kim et al. actively studied 23,24-bisnorcholane-
based sqaulamine analogs to determine the structure–activity rela-
tionship (SAR) of sqaulamine mimics.8
Resistance to membrane active antibiotics requires major
changes in the membrane structure that in turn affects the perme-
ability barrier, increasing the susceptibility to hydrophobic antibi-
otics. As a result, a variety of molecules that are active against
Gram-positive bacteria are much less active against Gram-negative
bacteria and vice versa. The general belief is that the permeability
barrier of the outer membrane is formed via cross bridging be-
tween lipid molecules and divalent cations (Ca2+ and Mg2+).9
Therefore, metal ion chelators, such as EDTA, cationic peptides,
and polyamines, which can attack the binding sites of divalent cat-
ions, can disrupt the organization of the outer membrane, increas-
ing its permeability and therefore sensitizing bacteria to
hydrophobic antibiotics.10 Although required, the hydrophilic part
is not sufficient itself to cause either permeabilization of the bacte-
rial membranes or bacteria killing.11 The hydrophobic moiety of
amphiphilic antimicrobials is responsible for their insertion into
the hydrophobic core of the bacterial lipid bilayer, leading to mem-
brane permeabilization, and eventually to amphiphilic antimicro-
bials-mediated bacteria killing.12
⇑
Corresponding author. Tel.: +82 53 9505588; fax: +82 53 9506594.
E-mail address: kimhs@knu.ac.kr (H.-S. Kim).
0960-894X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.bmcl.2013.05.098

4316
H.-S. Kim et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4315–4318
Therefore,
a
series of
3
a
-amino-5a-cholestane-7-one and
Compound 3 was four times potent against S. aureus 77 and
3
a
,7 -diamino-5
a
a
-cholestane conjugates were synthesized by
B. subtilis ATCC6633 than compound 2, whereas compound 2
exhibited two and four times higher potency against S. aureus
241 and E. faecalis ATCC29212 strain, respectively, than compound
3. 3-Ethylhistidine conjugate (4) exhibited moderate activity
toward most of the Gram-positive bacteria with a MIC value of
reductive amination with a group containing a heterocyclic ring,
such as imidazole and pyridine as shown in Figure 1, and their
antimicrobial activities against a range of human pathogens were
evaluated. The cholesterol backbone was chosen because it is an
essential metabolite required for major biological functions such
as the cell membrane structure, where the steroid combines to-
gether with phospholipids molecules, an integral part of the lipid
bilayer.13
16 lg/mL with the exception of S. aureus ATCC6538P, which was
8
lg/mL.
3,7-Di(imidazole) conjugates (7–9) improved the antimicrobial
potency 2- to 4-fold compare to that of 3-imdazole conjugates
(2–4). 3,7-Di(ethylimidazole) conjugate (7) was two times more
active toward S. aureus ATCC6538P, S. aureus giorgio, M. luteus
ATCC9341 and B. cereus ATCC27348 Gram-positive bacterial strains
Scheme 1 illustrates the synthesis of compounds 2–11. Com-
pounds 2–6 were prepared by the one step reductive amination
of 5a-cholestane-3,7-dione (1) with a variety of amines. Com-
pounds 7–11 can be obtained by one or two step reductive amina-
tion as shown in Scheme 1.14 The spectroscopic data of the
obtained compounds are in agreement with those reported in
publications.15
(MIC values of 4–16
showed 2–8 times higher activity than compound 3 with MIC val-
ues from 2 to 4 g/mL against all Gram-positive bacteria. Although
compound 4 showed moderate activity, the compound 9 showed
double the potency toward most of the Gram-positive bacteria
tested than compound 4.
lg/mL) than compound 2. Compound 8
l
Compounds 2–11 were examined for their antimicrobial activi-
ties against a wide range of Gram-positive strains, such as eleven
strains of S. aureus ATCC6538P, S. aureus ATCC25923, S. aureus gior-
gio, S. aureus 77, S. aureus 241, Staphylococcus epidermidis 887E,
Enterococcus faecalis ATCC29212, Micrococcus luteus ATCC9341,
Bacillus cereus ATCC27348, Bacillus subtilis ATCC6633, Bacillus
licheniformis EMR and a range of Gram-negative strains, such as
Escherichia coli ATCC25922, Salmonella typhimurium ATCC13311,
Klebsiella pneumoniae 2011E, Proteus vulgaris 6059, Pseudomonas
aeruginosa 6065Y, and Klebsiella aerogenes (SHV-1) 1976E with
oxacillin (OXA) and vancomycin (VAN) as a control.8h,16 Com-
pounds 2–11 exhibited excellent in vitro activity against all
Gram-positive bacteria.
Among the 3,7-di(imidazole) conjugates (7–9), the best antimi-
crobial results were observed for compound 8 with the lowest MIC
value of 2
ATCC25923 and MIC value of 4
l
g/mL toward S. aureus ATCC6538P and S. aureus
g/mL toward S. aureus giorgio, S.
l
aureus 77, S. aureus 241, S. epidermidis 887E, E. faecalis ATCC29212,
M. luteus ATCC9341, B. subtilis ATCC6633 and B. licheniformis EMR
Gram-positive bacteria. Compound 8 was 2–4 times more potent
than compounds 7 and 9.
A comparative study of 3-pyridine conjugates (5, 6) showed
that, 3-methylpyridine conjugate (5) exhibited the reasonable
activity with a MIC value of 2
lg/mL toward S. aureus ATCC6538P
The structures of compounds 2–6 and 7–12 were similar in all
aspects with stereochemistry at the C3, C5 and C7-positions except
for the amino groups at 3 and 3,7-positions. Most of the 3-amino-
and 3,7-diaminocholestane conjugates containing imidazole and
pyridine groups exhibited good in vitro activity against most of
the Gram-positive bacteria. Table 1 lists the minimum inhibitory
concentrations (MICs).
and 4 g/mL toward S. aureus ATCC25923, S. aureus giorgio, S. epi-
l
dermidis 887E and B. subtilis ATCC6633, which was 2–4 times high-
er than that of the 3-ethylpyridine conjugate (6). Moderate
antimicrobial activity was encountered with compound 6 with a
MIC value in range of 8–32
with the 3,7-di(methylpyridine) conjugate (10) with the lowest
MIC value of 1 g/mL against S. epidermidis 887E and 2 g/mL all
lg/mL. Superior activity was observed
l
l
The antimicrobial activity of 3-imdazole conjugates (2–4)
showed a reasonable value toward most of the Gram-positive bac-
teria. 3-Ethylimidazole conjugate (2) and 3-propylimidazole conju-
gate (3) showed similar activity toward the majority of the tested
against S. aureus strains, B. subtilis, M. luteus ATCC9341 and B.
licheniformis EMR bacteria. The MIC values encountered for com-
pound 10 was 2–8 times higher than compound 5, and 4–8 times
more potent than 3,7-di(ethylpyridine) conjugate (11). Compound
11 showed improved MIC values toward M. luteus ATCC9341, B.
Gram-positive strains with the lowest MIC value of 8
lg/mL.
HN
O
HN
O
HN
O
H
H
4
H
n
n
N
N
HN
N
N
2: n = 1
3: n = 2
5: n = 0
6: n = 1
HN
N
NH
N
HN
NH
HN
NH
N
H
9
H
H
n
n
n
n
N
N
HN
NH
N
N
N
7: n = 1
8: n = 2
10: n = 0
11: n = 1
Figure 1. Structures of the imidazole and pyridine appended cholestane-based conjugates.

H.-S. Kim et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4315–4318
4317
SC
SC
SC
i
i or ii
O
O
HN
O
HN
NH
H
1
H
H
n
n
n
R1
7-11
R1
R2
2-6
2: n = 1, R1 = Im
3: n = 2, R1 = Im
7: n = 1, R1, R2 = Im
8: n = 2, R1, R2 = Im
SC =
4: n = 1, R1 = Histamine
5: n = 0, R1 = Py
9: n = 1, R1, R2 = Histamine
10: n = 0, R1, R2 = Py
6: n = 1, R1 =Py
11: n = 1, R1, R2 =Py
Scheme 1. Reagents and conditions: (i) amine, NaBH(OEh)3, THF, rt; (ii) amine, NaBH3CN, THF:MeOH (1:1), rt.
Table 1
Antimicrobial activities of compounds 2–11 against wide ranges of bacteriaa
Entry
Strains
2
3
4
5
6
7
8
9
10
11
OXAb
VANc
1
2
3
S. aureus ATCC6538P
S. aureus ATCC25923
S. aureus giorgio
8
8
8
8
8
8
8
16
16
2
4
4
8
8
8
4
8
4
2
2
4
4
8
8
2
2
2
8
8
8
0.25
0.25
0.5
2
2
2
4
5
6
7
8
9
10
11
12
13
14
15
16
17
S. aureus 77
S. aureus 241
>32
16
16
8
8
16
32
16
16
16
32
32
32
>32
>32
>32
>32
>32
>32
32
32
4
8
8
32
>32
16
16
32
>32
32
32
>32
>32
>32
>32
>32
>32
4
4
4
4
4
4
8
4
4
>32
>32
>32
>32
>32
>32
8
8
8
8
2
2
1
4
2
8
2
2
>32
>32
>32
>32
>32
>32
16
8
8
16
8
32
8
4
2
2
2
2
32
16
32
8
16
8
32
>32
>32
>32
>32
>32
>32
16
16
16
4
16
8
32
>32
>32
>32
>32
>32
>32
>32
>32
32
0.03
>32
16
>32
>32
>32
>32
>32
>32
>32
S. epidermidis 887E
E. faecalis ATCC29212
M. luteus ATCC9341
B. cereus ATCC27348
B. subtilis ATCC6633
B. lichenifomis EMR
E. coli ATCC25922
S. typhimurium ATCC13311
K. pneumoniae 2011E
P. vulgaris 6059
8
16
32
>32
>32
>32
>32
>32
>32
>32
>32
1
>32
2
>32
>32
>32
>32
>32
>32
>32
32
32
32
>32
>32
>32
>32
>32
>32
16
4
32
>32
>32
>32
>32
>32
>32
8
>32
>32
>32
>32
>32
>32
P. aeruginosa 6065Y
K. aerogenes (SHV-1) 1976E
a
b
c
MIC values are reported in
Oxacillin.
Vancomycin.
lg/mL.
subtilis and B. licheniformis EMR bacteria, which was four times bet-
ter than compound 6.
The relative study in between the single strand and double
strand imidazole and pyridine appended 5a-cholestane conjugates
less negatively charged. Therefore, the precise mode of action of
antimicrobial agents on Gram-positive bacteria is unknown. On
the other hand, it has been proposed and widely believed that
the compounds interact with and disrupt the cytoplasmic mem-
brane, leading to a dissolution of the proton motive force and a
leakage of essential molecules, resulting in cell death.19
Compounds 2–11 showed moderate to excellent activity to-
wards a range of Gram-positive bacteria. In contrast, none of the
Gram-negative bacteria were resistant to the compounds, due to
a different mechanism by which Gram-negative bacteria produce
their cell walls and various factors relating to the outer membrane
of Gram-negative organisms.17,18
showed that cholestane bearing a double strand moiety was more
potent than a single strand toward the majority of Gram-positive
bacteria. The antimicrobial activity was also varied by the chain
length between the amino and hetero aromatic ring attached to
cholestane through a N–H linkage. 3,7-Di(propylimidazole) conju-
gate 8 showed superior activity to 3-propylimidazole conjugate (3)
and 3,7-di(ethylimidazole) conjugates (7, 9). In the case of pyridine
conjugates, 3,7-di(methylpyridine) conjugate (10) showed the
higher activity than 3-methylpyridine conjugate (5), 3-ethylpyri-
dine conjugate (6) and 3,7-di(ethylpyridine) conjugate (11). The
conjugate 10 showed similar potency compare to vancomycin,
but less potent than oxacillin against S. aureus ATCC6538P, S. aur-
eus ATCC25923, S. aureus giorgio and M. luteus ATCC9341. In the
case of S. epidermidis 887E, conjugate 10 exhibited very strong
activity compare to oxacillin and vancomycin having a MIC value
In summary, a series of 3a-amino- and 3a,7a-diamino-5a-cho-
lestane conjugates appended with imidazolyl and pyridyl moieties
at the 3- and 7-positions of cholestane were synthesized and their
antimicrobial activity against selected human pathogenic bacterias
were evaluated. Most of the compounds showed excellent antimi-
crobial activity over a wide range of Gram-positive bacteria. The
presence of an alkyamino moiety along with a heterocyclic unit
is essential for the antimicrobial activity. The compounds 8 and
10 can be developed further as antibiotic drugs because they exhi-
bit better antibacterial activity against most of the tested MRSA
of 1 lg/mL.
The mechanism of the action for Gram-negative bacteria can be
explained as follows: the positively charged amino groups of ami-
nosteroid derivatives interact with the negatively charged bacterial
LPSs (lipopolysaccharide) resulting in a disruption of the outer
membrane and subsequent cell death.17,18 The mechanism of ac-
tion of the same compound against Gram-positive bacteria cannot
be explained by this fact because the membrane of Gram-positive
bacteria are essentially constituted of peptidoglycans, which are
and CA-MRSA pathogens with the lowest MIC value of 1 lg/mL.
Acknowledgment
This study was supported by the Kyungpook National Univer-
sity Research Fund, 2012.

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H.-S. Kim et al. / Bioorg. Med. Chem. Lett. 23 (2013) 4315–4318
9. (a) Vaara, M. Antimicrob. Agents Chemother. 1993, 37, 354; (b) Djouhri-Bouktab,
References and notes
L.; Vidal, N.; Rolain, J. M.; Brunel, J. M. J. Med. Chem. 2011, 54, 7417.
10. Zasloff, M. Perspect. Immun. Insect Host Def. 1994, 31.
11. (a) Katsu, T.; Nakagawa, H.; Yasuda, K. Antimicrob. Agents Chemother. 2002, 46,
1073; (b) Savage, P. B.; Li, C.; Taotafa, U.; Ding, B.; Gua, Q. FEMS Microbiol. Lett.
2002, 217, 1.
1. (a) Caminero, J. A.; Sotgiu, G.; Zumla, A.; Battia Migliori, G. Lancet Infect. Dis.
2010, 101, 621; (b) Tomasz, A. N. Engl. J. Med. 1994, 330, 1247; (c) Wiesch, P. A.;
Kouyos, R.; Engelst€adter, J.; Regoes, R. R.; Bonhoeffer, S. Lancet Infect. Dis. 2011,
11, 236; (d) Bax, R.; Bywater, R.; Cornaglia, G.; Goossens, H.; Hunter, P.; Isham,
V.; Jarlier, V.; Jones, R.; Phillips, I.; Sahm, D.; Senn, S.; Struelens, M.; Taylor, D.;
White, A. Clin. Microbiol. Infect. 2001, 7, 316.
2. (a) Diekema, D. J.; Pfaller, M. A.; Schmitz, F. J. Clin. Infect. Dis. 2001, 32, S132; (b)
National Nosocomial Infections Surveillance (NNIS) System Report Am. J. Infect.
Control. 2004, 32, 470.
12. Pasquale, E. D.; Salmi-Smail, C.; Brunel, J.-M.; Sanchez, P. Chem. Phys. Lipids
2010, 163, 131.
13. (a) Spector, A. A.; Yorek, M. A. J. Lipid Res. 1985, 26, 1015; (b) Roux, C.; Wolf, C.;
Mulliez, N.; Gaoua, W.; Cormier, V.; Chevy, F.; Citadelle, D. Am. J. Clin. Nutr.
2000, 71, 1270; (c) Wolfrum, C.; Shi, S.; Narayanannair, J. K.; Muthusamy, J.;
Wang, G.; Pandey, R. K.; Kallanthottathil, G. R.; Nakayama, T.; Charrise, K.;
Ndungo, E. M.; Zimmermann, T.; Koteliansky, V.; Manoharan, M.; Stoffel, M.
Nat. Biotechnol. 2007, 25, 1149.
3. (a) Herold, B. C.; Immergluck, L. C.; Maranan, M. C. J. Am. Med. Assoc. 1998, 279,
593; (b) Zetola, N.; Francis, J. S.; Nuermberger, E. L.; Bishai, W. R. Lancet Infect.
Dis. 2005, 5, 275; (c) Buescher, E. S. Curr. Opin. Pediatr. 2005, 17, 67; (d)
Vandenesch, F.; Naimi, T.; Enright, M. C. Emerg. Infect. Dis. 2003, 9, 978.
4. (a) Shingalapur, R. V.; Hosamani, K. M.; Keri, R. S. Eur. J. Med. Chem. 2009, 44,
4244; (b) Sharma, D.; Narasimhan, B.; Kumar, P.; Judge, V.; Narang, R.; De
Clercq, E.; Balzarini, J. Eur. J. Med. Chem. 2009, 44, 2347; (c) Zampieri, D.;
Mamolo, M. G.; Vio, L.; Banfi, E.; Scialino, G.; Fermeglia, M.; Ferrone, M.;
Pricl, S. Bioorg. Med. Chem. 2007, 15, 7444; (d) Olender, D.; Zwawiak, J.;
Lukianchuk, V.; Lesyk, R.; Kropacz, A.; Fojutowski, A.; Zaprutko, L. Eur. J. Med.
Chem. 2009, 44, 645; (e) Puratchikodya, A.; Doble, M. Bioorg. Med. Chem.
2007, 15, 1083; (f) Achar, K. C. S.; Hosamani, K. M.; Seetharamareddy, H. R.
Eur. J. Med. Chem. 2010, 45, 2048; (g) Gupta, P.; Hameed, S.; Jain, R. Eur. J.
Med. Chem. 2004, 39, 805; (h) Pandey, J.; Tiwari, V. K.; Varma, S. S.;
Chaturvedi, V.; Bhatnagar, S.; Sinha, S.; Gaikwad, A. N.; Tripathi, R. P. Eur. J.
Med. Chem. 2009, 44, 3350; (i) Hadizadeh, F.; Hosseinzadeh, H.; Motamed-
Shariaty, V. S.; Seifi, M.; Kazemi, S. Iranian J. Pharm. Res. 2008, 7, 29; (j)
Özkay, Y.; Tunali, Y.; Karaca, H.; Isikdag, I. Eur. J. Med. Chem. 2010, 45, 3293;
(k) Refaat, H. M. Eur. J. Med. Chem. 2010, 45, 2949; (l) Congiu, C.; Cocco, M.
T.; Onnis, V. Bioorg. Med. Chem. Lett. 2008, 18, 989; (m) Tonelli, M.; Simone,
M.; Tasso, B.; Novelli, F.; Boido, V.; Sparatore, F.; Paglietti, G.; Pricl, S.;
Giliberti, G.; Blois, S.; Ibba, C.; Sanna, G.; Loddo, R.; La Colla, P. Bioorg. Med.
Chem. 2010, 18, 2937; (n) Bhandari, K.; Srinivas, N.; Marrapu, V. K.; Verma,
A.; Srivastava, S.; Gupta, S. Bioorg. Med. Chem. Lett. 2010, 20, 291.
5. (a) Jo, Y. W.; Im, W. B.; Rhee, J. K.; Shim, M. J.; Kim, W. B.; Choi, E. C. Bioorg. Med.
Chem. 2004, 12, 5909; (b) Nicolaou, K. C.; Scarpelli, R.; Bollbuck, B.; Werschkun,
B.; Pereira, M. M. M.; Wartmann, M.; Altmann, K.-H.; Zaharevitz, D.; Gussio, R.;
Giannakakou, P. Chem. Biol. 2000, 7, 593; (c) Fortuna, G. C.; Barresi, V.; Berellini,
G.; Musumarra, G. Bioorg. Med. Chem. 2008, 16, 4150; (d) Bernardino, A. M. R.;
Pinheiro, L. C. S.; Rodrigues, C. R.; Loureiro, N. I.; Castro, H. C.; Lanfredi-Rangel,
A.; Sabatini-Lopes, J.; Borges, J. C.; Carvalho, J. M.; Romeiro, G. A.; Ferreira, V. F.;
Frugulhetti, I. C. P. P.; Vannier-Santos, M. A. Bioorg. Med. Chem. 2006, 14, 5765;
(e) Manegatti, R.; Silva, G. M. S.; Zapata-Sudo, G. Z.; Raimundo, J. M.; Sudo, R. T.;
Barreiro, E. J.; Fraga, C. A. M. Bioorg. Med. Chem. 2006, 14, 632.
14. Representative synthesis: 3a-[(5-Imidazolyl)ethyl]amino-5a-cholestane-7-one
(4). A mixture of 5 -cholestane-3,7-dione (1, 100 mg, 0.45 mmol), histamine
a
hydrochloride salt (38 mg, 1.1 mmol) and triethylamine (30 mg, 1.1 mmol) in
THF (15 mL) was reacted with sodium tris(2-ethylhexanoxy)borohydride
[NaBH(OEh)3] (2 mL) at room temperature for 8 h. After work up, the residue
was chromatographed on silica gel with the elution of (CH2Cl2-MeOH-NH4OH
20:1:0.2) to give 4; 62% yield; waxy solid; TLC Rf 0.54 (CH2Cl2–MeOH–NH4OH
20:1:0.5); 1H NMR (CDCl3) d 0.58 (s, 3H, 18-CH3), 0.78 (d, J = 6.6 Hz, 26-CH3),
0.79 (d, J = 6.6 Hz, 27-CH3), 0.83 (d, J = 7.3 Hz, 21-CH3), 0.98 (s, 3H, 19-CH3),
2.17–2.33 (m, 2H), 2.70 (t, J = 7.0 Hz, 2H, –CH2), 2.77 (t, J = 7.3 Hz, 2H, –CH2),
2.86 (br s, 1H, 3b-H), 6.72 (s, 1H, Im-H4), 7.46 (s, 1H, Im-H2); 13C NMR (CDCl3)
d 11.5, 12.5, 19.2, 21.6, 22.9, 23.2, 24.2, 25.4, 26.3, 27.0, 28.4, 28.8, 32.8, 33.3,
36.0, 36.5, 37.1, 39.1, 39.9, 42.6, 42.9, 46.5, 47.4, 49.3, 50.7, 52.6, 55.4, 56.4,
118.6, 134.9, 135.2, 213.1; HR mass Calcd for C32H53ON3: 495.4189. Found: m/z
496.4268 (M+H)+.
3a
,7a
-Bis[2-(5-imidazolyl)ethyl]amino-5
a
-cholestane (9).
A
mixture of
compound
4
(100 mg, 0.21 mmol) and the histamine hydrochloride salt
(90 mg, 3 equiv) in THF–MeOH (1:1) (15 mL) was reacted with NaBH3CN
(38 mg, 3 equiv) at room temperature for 12 h. After work up, the residue was
chromatographed with the elution of (CH2Cl2–MeOH–NH4OH 20:1.0:0.2) on
silica gel to give compound 9 as an waxy solid; yield (62%); TLC Rf 0.52
(CH2Cl2–MeOH–NH4OH 20:1:0.5); 1H NMR (CDCl3) d 0.63 (s, 3H, 18-CH3), 0.79
(s, 3H, 19-CH3), 0.84 (d, J = 6.6 Hz, 26-CH3), 0.86 (d, J = 6.6 Hz, 27-CH3), 0.89 (d,
J = 7.2 Hz, 21-CH3), 2.64 (br s, 2H), 2.67–2.83 (m, 4H, –CH2), 2.85–2.98 (m, 4H, –
CH2), 6.75 (s, 2H, Im-H4), 7.43 (s, 1H, Im-H2), 7.49 (s, 1H, Im-H2); 13C NMR
(CDCl3) d 11.4, 12.2, 19.1, 21.1, 22.9, 23.2, 24.0, 24.4, 25.6, 26.1, 26.9, 28.4, 28.5,
31.9, 32.2, 32.3, 32.8, 36.2, 36.6, 36.8, 39.3, 39.7, 39.9, 43.2, 46.7, 47.4, 48.5,
51.1, 53.7, 56.2, 56.6, 117.9, 118.8, 134.8, 134.9, 135.1, 135.2; HR mass Calcd
for C37H62N6: 590.5036. Found: m/z 591.5112 (M+H)+.
15. (a) Ahmad, M. W.; Jung, Y. M.; Khan, S. N.; Kim, H.-S. Bull. Korean Chem. Soc.
2009, 30, 2101; (b) Jadhav, J. R.; Ahmad, M. W.; Kim, H.-S. Tetrahedron Lett.
2010, 51, 5954; (c) Jadhav, J. R.; Bae, C.-H.; Kim, H.-S. Tetrahedron Lett. 2011, 52,
1623.
16. Clinical and Laboratory Standards Institute. Methods for dilution antimicrobial
susceptibility test for bacteria that grow aerobically; approved standards. 9th
ed. Document M07–A9. Wayne, PA: CLSI; 2012.
17. (a) Savage, P. B.; Li, C. Expert Opin. Investig. Drugs 2000, 9, 263; (b) Chin, J. N.;
Jones, R. N.; Sader, H. S.; Savage, P. B. J. Antimicrob. Chemother. 2008, 61, 365; (c)
Schmidt, E. J.; Bosewell, J. S.; Walsh, J. P.; Schellenberg, M. M.; Winter, T. W.; Li,
C.; Allman, G. W.; Savage, P. B. J. Antimicrob. Chemother. 2001, 47, 671.
18. (a) Ding, B.; Yin, J.; Liu, Y.; Cardenas-Garcia, J.; Evanson, R.; Orsak, T.; Fan, M.;
Turin, G.; Savage, P. B. J. Am. Chem. Soc. 2004, 126, 13642; (b) Salmi, C.; Loncle,
C.; Vidal, N.; Letourneux, Y.; Fantini, J.; Maresca, M.; Taieb, N.; Pages, J. M. PLoS
One 2008, 3, 2765.
6. (a) Savage, P. B. Curr. Med. Chem. 2002, 1, 293; (b) Li, C.; Peters, A. S.; Meredith,
E. L.; Allman, G. W.; Savage, P. B. J. Am. Chem. Soc. 1998, 120, 2961; (c) Li, C.;
Budge, L. P.; Driscoll, C. D.; Willardson, B. M.; Allman, G. W.; Savage, P. B. J. Am.
Chem. Soc. 1999, 121, 931; (d) Ding, B.; Guan, Q.; Walsh, J. P.; Boswell, J. S.;
Winter, T. W.; Winter, E. S.; Boyd, S. S.; Li, C.; Savage, P. B. J. Med. Chem. 2002,
45, 663.
7. Rivera, D. G.; Concepcion, O.; Pérez-Labrada, K.; Coll, F. Tetrahedron 2008, 64,
5298.
8. (a) Kim, H.-S.; Choi, B. S.; Kwon, K. C.; Lee, S. O.; Kwak, H. J.; Lee, C. H. Bioorg.
Med. Chem. 2000, 8, 2059; (b) Kim, H.-S.; Kwon, K.-C.; Kim, K. S.; Lee, C. H.
Bioorg. Med. Chem. Lett. 2001, 11, 3065; (c) Khan, S. N.; Bae, S.-Y.; Kim, H.-S.
Tetrahedron Lett. 2005, 46, 7675; (d) Khan, S. N.; Kim, H.-S.; Kim, B. J. Bioorg.
Med. Chem. Lett. 2007, 17, 5139; (e) Khan, S. N.; Cho, N. J.; Kim, H.-S. Tetrahedron
Lett. 2007, 48, 5189; (f) Khan, S. N.; Jung, Y. M.; Kim, B. J.; Cho, H.; Lee, J.; Kim,
H.-S. Bioorg. Med. Chem. Lett. 2008, 18, 2558; (g) Khan, S. N.; Kim, H.-S. J. Ind.
Eng. Chem. 2009, 15, 561; (h) Kim, H.-S.; Khan, S. N.; Jadhav, J. R. Bioorg. Med.
Chem. Lett. 2011, 18, 2558.
19. (a) Alhanout, K.; Malesinki, S.; Vidal, N.; Peyrot, V.; Rolain, J. M.; Brunel, J. M. J.
Antimicrob. Chemother. 2010, 65, 1688; (b) Alhanout, K.; Rolain, J. M.; Brunel, J.
M. Curr. Med. Chem. 2010, 17, 3909; (c) Friedrich, C. L.; Moyles, D.; Beveridge,
T.; Hancock, R. E. W. Antimicrob. Agents Chemother. 2000, 44, 2086.