Synthesis and evaluation of febrifugine analogues as potential antimalarial agents

Article abstract of DOI:10.1016/j.bmcl.2006.01.009

Febrifugine is an alkaloid isolated from Dichroa febrifuga Lour as the active component against Plasmodium falciparum. Strong liver toxicity has precluded febrifugine as a potential clinical drug. In this study novel febrifugine analogues were designed an

Full text of DOI:10.1016/j.bmcl.2006.01.009

Bioorganic & Medicinal Chemistry Letters 16 (2006) 1854–1858
Synthesis and evaluation of febrifugine analogues
as potential antimalarial agents
Shuren Zhu,* Li Meng, Quan Zhang and Lai Wei
Radix Pharmaceuticals, Inc., 880 College Pkwy, Rockville, MD 20850, USA
Received 7 December 2005; revised 27 December 2005; accepted 4 January 2006
Available online 24 January 2006
Abstract—Febrifugine is an alkaloid isolated from Dichroa febrifuga Lour as the active component against Plasmodium falciparum.
Strong liver toxicity has precluded febrifugine as a potential clinical drug. In this study novel febrifugine analogues were designed
and synthesized. Lower toxicity was achieved by reducing or eliminating the tendency of forming chemically reactive and toxic inter-
mediates and metabolites. Synthesized compounds were evaluated in vitro against chloroquine sensitive (D6) and chloroquine resis-
tant (W2) P. falciparum strains for efficacy and in freshly isolated rat hepatocytes for potential cytotoxicity. The IC50’s of the best
compounds were superior to their parent compound febrifugine. Noticeably, these compounds were also over 100 times less toxic
than febrifugine. These compounds, as well as the underlying design rationale, may find usefulness in the discovery and development
of new antimalarial drugs.
ꢀ 2006 Elsevier Ltd. All rights reserved.
Malaria is one of the major parasitic infections in many
tropical and subtropical regions. Worldwide, malaria
infects 300–600 million people and kills about three
million in a year.1 The malaria parasite has now become
resistant to the best antimalarial drugs.2,3 Therefore,
medicinal agents based on novel mode of action are
required to overcome the emergence of resistance and
to control an ever-increasing number of epidemics
caused by the malaria parasite.
Figure 1.
moiety plays an essential role in the appearance of activ-
ity; and that the presence of a 100-amino group and C-20,
C-300 O-functionalities is crucial in the antimalarial activ-
ity of febrifugine.9–11 Structure–activity relationship
studies have also demonstrated that attaching any elec-
tron-withdrawing group to the 100-nitrogen decreases
activity.10
Febrifugine (1) and isofebrifugine (2), as shown in
Figure 1, were isolated as the active components against
malaria in the Chinese herb Chang Shan (Dichroa febrif-
uga Lour),4,5 which has been employed by the local
people as medicine against fevers caused by malaria
parasites for a long time. Febrifugine acts by impairing
haemazoin formation required for maturation of the
parasite at the trophozoite stage.6 Subsequent pre-clini-
cal researches have found that febrifugine possesses
adverse side effects. Strong liver toxicity has precluded
febrifugine as a potential clinical drug.7,8
Febrifugine could be metabolized to the corresponding
arene oxide 3 by cytochrome P-450 enzymes (Scheme
1). When arene oxide 3 escapes deactivation process
by certain enzymes such as epoxide hydrase or glutathi-
one S-transferase, toxicity can result because this reac-
tive electrophile will form covalent adducts with DNA,
RNA, proteins, or other biomolecules of the host. Such
binding can cause mutations and result in cell damage.
In a recent metabolic study of febrifugine, Oshima and
co-workers isolated metabolite 4.12 This study indicates
that arene oxide 3 is most probably a short-lived reactive
metabolic intermediate because metabolite 4 would have
Some febrifugine analogues have been synthesized; most
of the structural modifications were focused on side-
chain alterations. It is known that the 4-quinazolinone
*
Corresponding author. Tel.: +1 301 675 3714; fax: +1 301 424 1927;
e-mail: shuren.zhu@gmail.com
0960-894X/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2006.01.009

S. Zhu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1854–1858
1855
Scheme 1.
been derived from intermediate 3 through the rearrange-
ment known as NIH shift.13
(compounds 5–13) or the increase of the oxidation po-
tential of the molecule (compounds 5–11, 14–16).
There are two possible ways to make this process unfa-
vorable: (I) Blocking the C-5 or C-6 position of the qui-
nazolinone ring; and (II) increasing the oxidation
potential of the molecule. As part of an ongoing malaria
chemotherapy project in our laboratory, we undertook
the synthesis and antimalarial activity evaluation of
the following febrifugine analogues (compounds 5–20,
shown in Fig. 2). Compounds 5–16 are designed to
block the aforementioned unwarranted metabolic path-
way. Introduction of an extra nitrogen atom on position
5 or 6 of the quinazolinone ring in febrifugine furnishes
compounds 5 and 6. Compounds 7–11 each bear one or
two electron-withdrawing group(s), while compounds 12
and 13 bear a bulky group on C-5 or C-6 position of the
quinazolinone ring. Compounds 14 and 15 have an extra
nitrogen atom on position 7 or 8 of the aromatic ring,
and compound 16 has an electron-withdrawing group
(fluoride) attached to C-8 position of the quinazolinone
ring. For compounds 14–16, the C-5 and C-6 positions
are now exposed to oxidation, but such a process will
be hampered because the oxidation potential of the mol-
ecule is increased due to the introduction of an extra
nitrogen atom or an electron-withdrawing group on
the quinazolinone ring. Overall, these compounds close-
ly resemble febrifugine itself by possessing a planar aro-
As a comparative study, compounds 17–20 were also de-
signed. These compounds have a methyl group or an
electron-donating methoxy group attached to the C-7
or C-8 of the aromatic ring. These compounds have
comparable or even greater tendency to undergo oxida-
tion. Biological data from these compounds should
further validate, or nullify, the hypothesis that some oxi-
dized febrifugine metabolites have contributed to the
observed toxicity.
The synthesis of compound 5 is shown in Scheme 2. Pre-
viously published procedure was adopted to synthesize
the aromatic moiety: 3H-pyrido[3,2-d]pyrimidin-4-one
(21).14 Compound 21 condensed with the known epox-
ide 22,15 to furnish corresponding alcohol 23, as a pair
of diastereomers, which follows the methods of Tanigu-
chi and Ogasawara.15 Compound 23 then underwent
TPAP oxidation16 to give ketone 24 as a single enantio-
mer. Finally, compound 24 underwent hydrogenolysis
to afford compound 5.17,18 The synthesis of compounds
6–2018 follows a similar route. The respective aromatic
moieties are available from previously published proce-
dures.19–21
Synthesized compounds (5–20) were tested in vitro
against two P. falciparum malaria parasite clones: W2
and D6, following the procedures of Desjardins et al.22
and Chulay et al.23 Both strains are from the Malaria
Research and Reference Reagent Resource Center
(MR4). The W2 clone is susceptible to mefloquine but
matic ring,
a
100-amino group, and C-20, C-300
O-functionality, and are therefore expected to possess
the same or a similar mode of action. Meanwhile, they
would be much less likely to produce toxic intermediates
because of the blocking of C-5 and C-6 positions
Figure 2.

1856
S. Zhu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1854–1858
Scheme 2.
resistant to chloroquine, sulfadoxine, pyrimethamine,
and quinine, whereas the D6 clone is naturally resistant
to mefloquine but susceptible to chloroquine, sulfadox-
ine, pyrimethamine and quinine. For in vitro toxicolog-
ical studies, synthesized compounds were evaluated in
freshly isolated rat hepatocytes by the measuring of
lysosomal (neutral red assay) functions as cytotoxicity
parameter, as described by Fontaine et al.24 Freshly iso-
lated rat hepatocytes are widely used in drug metabo-
lism and toxicity studies. Chloroquine and febrifugine
were also screened in W2, D6, and rat hepatocytes as
positive controls. Their IC50 values are summarized in
Table 1.
chloroquine-sensitive malarial strain (D-6) and chloro-
quine-resistant malarial strain (W-2). Noticeably, these
compounds were over 100 times less toxic than febrifu-
gine. On the other hand, compounds with an electron-
withdrawing group on C-6 alone (7 and 10) or a bulky
substitution (12 and 13) have both decreased antimalar-
ial activity and toxicity.
Although compounds 14–16 were also much less toxic
than febrifugine, these compounds were less active, sug-
gesting that increasing the oxidation potential of the
molecule alone reduces both toxicity and antimalarial
activity.
Compounds 5 and 6 with an extra nitrogen atom on the
position 5 or 6 of the aromatic ring and compound 8
with a fluoride substitution on C-5 possess antimalarial
activity comparable to that of febrifugine. Compounds 9
and 11 with difluoride attached to C-5 and C-6 or tri-
fluoromethyl substitution at C-5 have antimalarial activ-
ity superior to that of parent compound febrifugine.
These compounds showed potency against both
Compounds 17–20 possess antimalarial activity compa-
rable to that of parent compound febrifugine, suggesting
that introducing a small alkyl or alkoxy substitution on
C-7 or C-8 of the aromatic ring does not change the bio-
logical potency of the molecule. Nevertheless, com-
pounds 19 and 20, with an electron-donating methoxy
substitution at C-7 or C-8 of the aromatic ring and
hence possess greater tendency to undergo oxidation,
have become 10 times more toxic. A weak electron-do-
nating methyl substitution (compounds 17 and 18) only
increases the toxicity slightly.
Table 1. In vitro activity against malarial parasite and rat hepatocytes
[IC50 (nM)]
Compound
D6 clone
W2 clone
Rat hepatocytes
In conclusion, new febrifugine analogues were designed
and synthesized. Lower toxicity was achieved by reduc-
ing or eliminating the tendency of forming chemically
reactive and toxic intermediates and metabolites. Some
of these compounds (5, 6, 8, 9, and 11) possess
significantly low cytotoxicity, while retaining potent
antimalarial activity against both chloroquine-sensitive
and -resistant strains. These compounds, as well as the
underlying design rationale, may find usefulness in the
discovery and development of new antimalarial drugs.
5
1.2
1.5
4.7
1.3
0.33
14
1.3
1.8
5.0
1.3
0.39
16
1.8 · 104
1.7 · 104
1.3 · 104
1.9 · 104
1.7 · 104
1.5 · 104
1.9 · 104
7.0 · 103
9.8 · 103
1.9 · 104
2.2 · 104
1.6 · 104
117
6
7
8
9
10
11
12
0.43
132
165
63
0.41
160
188
73
13
14
15
16
70
109
100
2.2
1.9
1.3
1.3
338
1.9
103
2.0
1.7
1.4
1.2
23
Acknowledgments
17
18
140
15
19
20
Dr. D. E. Kyle of the Walter Reed Army Institute of
Research for depositing the D6 and W2 malaria strains
at the Malaria Research and Reference Reagent Re-
source Center (MR4). Dr. B. M. Chen of the Shanghai
16
1.9 · 103
169
Chloroquine
Febrifugine
1.6

S. Zhu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1854–1858
1857
dilute aqueous HCl solution, 4–5 equiv of HCl) furnished
compound 5 (dil HCl salt) as pale-yellow crystals. Yield:
1.15 g, 61% (three steps from oxirane 22).
Institutes for Biological Sciences, Chinese Academy of
Sciences, for a sample of febrifugine. This research was
partially supported by a grant from the National
Institutes of Health (AI63734 to S.Z.).
18. All new compounds possess satisfactory analytical data.
Compound 5 (dihydrochloride salt): mp: 347–348 ꢁC
25
(dec). ½aꢀD +31.4 (c 0.3, EtOH). 1H NMR (DMSO-d6):
9.11 (d, J = 7.4 Hz, 1H), 8.48 (d, J = 7.4 Hz, 1H), 8.24 (s,
1H), 7.85 (t, J = 7.4 Hz, 1H), 5.01 (d, J = 16.8 Hz, 1H),
4.89 (d, J = 16.8 Hz, 1H), 3.45 (m, 1H), 3.23 (m, 1H), 3.15
(dd, J = 17.1 and 5.8 Hz, 1H), 2.85 (m, 2H), 2.80 (dd,
J = 17.1 and 4.7 Hz, 1H), 1.83 (m, 2H), 1.69 (m, 2H). 13C
NMR: 202.8, 168.4, 163.0, 153.1, 149.8, 143.8, 139.1,
132.5, 80.7, 71.4, 66.3, 53.4, 51.2, 37.2, 32.9. Anal. Calcd
for C15H18N4O3Æ2HCl: C, 48.01; H, 5.37; N, 14.93. Found:
C, 47.82; H, 5.43; N, 14.80. Compound 6 (dihydrochloride
References and notes
1. WHO, The World Health Report, 1999.
2. Winstanley, P. A. Parasitol. Today 2000, 16, 146.
3. Zhu, S.; Hudson, T. H.; Kyle, D. E.; Lin, A. J. J. Med.
Chem. 2002, 45, 3491.
4. Koepfly, J. B.; Mead, J. F.; Brockman, J. A., Jr. J. Am.
Chem. Soc. 1947, 69, 1837.
5. Koepfly, J. B.; Mead, J. F.; Brockman, J. A., Jr. J. Am.
Chem. Soc. 1948, 70, 1048.
6. WHO Report, Meeting on Antimalarial Drug Develop-
ment, Shanghai, China, 16–17 November 2001.
7. Chien, P. L.; Cheng, C. C. J. Med. Chem. 1970, 13, 867.
8. Chang, H. M.; But, P. P. H. Eds.; Pharmacology and
Applications of Chinese Material Medicine; World Scien-
tific Publishing: Singapore, 1986–1987.
9. Takaya, Y.; Tasaka, H.; Chiba, T.; Uwai, K.; Tanitsu, M.;
Kim, H. S.; Wataya, Y.; Miura, M.; Takeshita, M.;
Oshima, Y. J. Med. Chem. 1999, 42, 3163.
10. Kikuchi, H.; Tasaka, H.; Hirai, S.; Takaya, Y.; Iwabuchi,
Y.; Ooi, H.; Hatakeyama, S.; Kim, H. S.; Wataya, Y.;
Oshima, Y. J. Med. Chem. 2002, 45, 2563.
11. Jiang, S.; Zeng, Q.; Gettayacamin, M.; Tungtaeng, A.;
Wannaying, S.; Lim, A.; Hansukjariya, P.; Okunji, C. O.;
Zhu, S.; Fang, D. Antimicrob. Agents Chemother. 2005, 49,
1167.
12. Hirai, S.; Kikuchi, H.; Kim, H. S.; Begum, K.; Wataya,
Y.; Tasaka, H.; Miyazawa, Y.; Yamamoto, K.; Oshima,
Y. J. Med. Chem. 2003, 46, 4351.
13. Guroff, G.; Daly, J. W.; Jerina, D. M.; Renson, J.;
Witkop, B.; Udenfriend, S. Science 1967, 157, 1524.
14. Price, C. C.; Curtin, D. Y. J. Am. Chem. Soc. 1946, 68,
914.
15. Taniguchi, T.; Ogasawara, K. Org. Lett. 2000, 2, 3193.
16. Ley, S. V.; Norman, J.; Griffith, W. P.; Marsden, S. P.
Synthesis 1994, 8, 639.
17. Synthesis procedure: Potassium hydride (30% in mineral
oil, 1.33 g) was suspended in 10 mL DMF. It was cooled in
an ice-water bath, and solid 3H-pyrido[3,2-d]pyrimidin-4-
one (21, 1.47 g) was added in. After 30 min, a solution of
oxirane 22 (1.91 g) in 2 mL DMF was added in. The
reaction mixture was then heated at 80 ꢁC for 12 h under
nitrogen atmosphere. It was partitioned between EtOAc
(80 mL) and water (80 mL), and separated organic layer
was washed with water (3 · 60 mL), then brine (40 mL),
dried over anhydrous sodium sulfate, and evaporated in a
rotary evaporator under reduced pressure to furnish the
crude product. Flash chromatography (5% MeOH/
EtOAc) furnished 23. A solution of alcohol 23 (2.1 g) in
5 mL of CH2Cl2 was added into a stirred slurry of
tetrapropylammonium perruthenate (TPAP, 70 mg), N-
methylmorpholine N-oxide (NMO, 936 mg), and ground
molecular sieve (800 mg) in 10 mL of CH2Cl2 at room
temperature. After 1 h, the reaction mixture was loaded
directly into a short column of silica gel and eluted with
5% MeOH/EtOAc. Concentration of the eluant under
reduced pressure afforded 24. Ketone 24 (1.88 g) was
dissolved in 15 mL of 95% EtOH/H2O. 300 mg of 10% Pd
on carbon was added in. It was then treated with hydrogen
(60 psi) in a Parr apparatus for 12 h. Solid was filtered off
and the solution was evaporated under vacuum to dryness.
Recrystallization from ethanol–water (with addition of
25
1
salt): mp: 336–337 ꢁC (dec). ½aꢀD +21.8 (c 0.5, EtOH). H
NMR: 9.04 (s, 1H), 8.68 (d, J = 7.3 Hz, 1H), 8.22 (s, 1H),
7.84 (d, J = 7.3 Hz, 1H), 5.04 (d, J = 16.9 Hz, 1H), 4.85 (d,
J = 16.9 Hz, 1H), 3.45 (m, 1H), 3.26 (m, 1H), 3.11 (dd,
J = 17.0 and 5.9 Hz, 1H), 2.83 (m, 2H), 2.78 (dd, J = 17.0
and 4.6 Hz, 1H), 1.81 (m, 2H), 1.64 (m, 2H). 13C NMR:
203.1, 167.5, 163.6, 158.0, 154.8, 148.8, 133.1, 129.4, 81.3,
70.6, 65.9, 54.1, 51.8, 36.7, 31.3. Anal. Calcd for
C15H18N4O3Æ2HCl: C, 48.01; H, 5.37; N, 14.93. Found:
C, 48.11; H, 5.27; N, 15.04. Compound 7 (hydrochloride
25
salt): mp: 306–307 ꢁC. ½aꢀD +26.3 (c 0.5, EtOH). 1H NMR:
8.24 (s, 1H), 7.86 (d, J = 7.1 Hz, 1H), 7.55 (s, 1H), 7.48 (d,
J = 7.1 Hz, 1H), 5.04 (d, J = 16.7 Hz, 1H), 4.91 (d,
J = 16.7 Hz, 1H), 3.46 (m, 1H), 3.29 (m, 1H), 3.26 (dd,
J = 17.1 and 5.6 Hz, 1H), 2.91 (m, 2H), 2.79 (dd, J = 17.1
and 4.8 Hz, 1H), 1.81 (m, 2H), 1.67 (m, 2H). 13C NMR:
202.9, 167.9, 163.6, 147.1, 133.2, 129.7, 128.9, 128.0, 127.7,
81.1, 71.3, 64.5, 55.6, 51.3, 37.3, 32.2. Anal. Calcd for
C16H18FN3O3ÆHCl: C, 54.01; H, 5.38; N, 11.81; Cl, 9.96.
Found: C, 54.19; H, 5.34; N, 11.75; Cl, 9.82. Compound 8
25
(hydrochloride salt): mp: 302–303 ꢁC. ½aꢀD +21.5 (c 0.5,
1
EtOH). H NMR: 8.20 (s, 1H), 8.15 (d, J = 7.2 Hz, 1H),
7.65 (d, J = 7.2 Hz, 1H), 7.54 (t, J = 7.2 Hz, 1H), 5.05 (d,
J = 16.8 Hz, 1H), 4.85 (d, J = 16.8 Hz, 1H), 3.44 (m, 1H),
3.31 (m, 1H), 3.29 (dd, J = 17.2 and 5.5 Hz, 1H),2.93 (m,
2H), 2.82 (dd, J = 17.2 and 4.7 Hz, 1H), 1.84 (m, 2H), 1.71
(m, 2H). 13C NMR: 205.4, 167.5, 164.1, 146.9, 141.2,
133.1, 129.9, 128.1, 127.9, 81.0, 72.1, 63.5, 55.8, 51.5, 37.4,
31.8. Anal. Calcd for C16H18FN3O3ÆHCl: C, 54.01; H,
5.38; N, 11.81; Cl, 9.96. Found: C, 54.15; H, 5.32; N,
11.70; Cl, 9.79. Compound 9 (hydrochloride salt): mp:
25
294–295 ꢁC. ½aꢀD ꢁ11.5 (c 0.45, EtOH). 1H NMR: 8.25 (s,
1H), 7.88 (d, J = 6.9 Hz, 1H), 7.71 (d, J = 6.9 Hz, 1H),
5.09 (d, J = 16.7 Hz, 1H), 4.88 (d, J = 16.7 Hz, 1H), 3.41
(m, 1H), 3.35 (m, 1H), 3.27 (dd, J = 17.3 and 5.6 Hz, 1H),
2.90 (m, 2H), 2.86 (dd, J = 17.3 and 4.8 Hz, 1H), 1.86 (m,
2H), 1.69 (m, 2H). 13C NMR: 203.8, 166.8, 164.7, 158.9,
152.5, 147.6, 136.9, 129.1, 128.9, 81.2, 71.9, 63.7, 55.4,
52.0, 37.6, 31.6. Anal. Calcd for C16H17F2N3O3ÆHCl: C,
51.41; H, 4.85; N, 11.24; Cl, 9.48. Found: C, 51.33; H,
4.82; N, 11.20; Cl, 9.39. Compound 10 (hydrochloride
25
1
salt): mp: 326–327 ꢁC (dec). ½aꢀD +16.7 (c 0.5, EtOH). H
NMR: 8.23 (s, 1H), 7.82 (d, J = 7.2 Hz, 1H), 7.71 (s, 1H),
7.59 (d, J = 7.2 Hz, 1H), 5.05 (d, J = 16.9 Hz, 1H), 4.93 (d,
J = 16.9 Hz, 1H), 3.48 (m, 1H), 3.26 (m, 1H), 3.20 (dd,
J = 17.3 and 5.7 Hz, 1H), 2.82 (m, 2H), 2.77 (dd, J = 17.3
and 4.9 Hz, 1H), 1.80 (m, 2H), 1.68 (m, 2H). 13C NMR:
203.3, 167.8, 162.6, 147.3, 137.1, 133.5, 129.8, 128.1, 127.4,
119.2, 80.1, 70.7, 64.2, 54.7, 51.0, 36.9, 33.1. Anal. Calcd
for C17H18F3N3O3Æ1.5HCl: C, 48.15; H, 4.64; N, 9.91.
Found: C, 47.92; H, 4.73; N, 9.81. Compound 11
25
(hydrochloride salt): mp: 320–321 ꢁC (dec). ½aꢀD ꢁ10.5 (c
1
0.45, EtOH). H NMR: 8.18 (s, 1H), 7.85 (d, J = 7.2 Hz,
1H), 7.65 (d, J = 7.2 Hz, 1H), 7.54 (t, J = 7.2 Hz, 1H), 5.06

1858
S. Zhu et al. / Bioorg. Med. Chem. Lett. 16 (2006) 1854–1858
(d, J = 16.8 Hz, 1H), 4.84 (d, J = 16.8 Hz, 1H), 3.43 (m,
C16H18FN3O3ÆHCl: C, 54.01; H, 5.38; N, 11.81; Cl, 9.96.
Found: C, 54.11; H, 5.30; N, 11.74; Cl, 9.85. Compound
1H), 3.30 (m, 1H), 3.27 (dd, J = 17.2 and 5.6 Hz, 1H), 2.92
(m, 2H), 2.84 (dd, J = 17.2 and 4.8 Hz, 1H), 1.83 (m, 2H),
1.70 (m, 2H). 13C NMR: 203.4, 166.5, 163.3, 146.7, 134.2,
133.1, 128.9, 128.0, 126.9, 118.4, 80.7, 72.0, 63.3, 54.8,
51.2, 37.1, 31.4. Anal. Calcd for C17H18F3N3O3Æ1.5HCl:
C, 48.15; H, 4.64; N, 9.91. Found: C, 47.97; H, 4.60; N,
9.98. Compound 12 (hydrochloride salt): mp: 293–
25
17 (hydrochloride salt): mp: 276–277 ꢁC. ½aꢀD +15.4 (c
0.45, EtOH). 1H NMR: 8.17 (s, 1H), 7.81 (s, 1H), 7.62 (d,
J = 7.1 Hz, 1H), 7.47 (d, J = 7.1 Hz, 1H), 5.02 (d,
J = 16.7 Hz, 1H), 4.93 (d, J = 16.7 Hz, 1H), 3.45 (m,
1H), 3.29 (m, 1H), 3.21 (dd, J = 17.3 and 5.8 Hz, 1H), 2.80
(m, 2H), 2.74 (dd, J = 17.3 and 4.9 Hz, 1H), 2.65 (s, 3H),
1.82 (m, 2H), 1.70 (m, 2H). 13C NMR: 202.3, 167.4, 161.6,
146.3, 138.5, 133.4, 129.5, 128.6, 127.9, 80.5, 77.7, 66.2,
53.7, 51.8, 36.7, 33.0, 26.8. Anal. Calcd for
C17H21N3O3ÆHCl: C, 58.03; H, 6.30; N, 11.94; Cl, 10.08.
Found: C, 58.13; H, 6.28; N, 11.85; Cl, 10.15. Compound
25
294 ꢁC.½aꢀD +12.4 (c 0.51, EtOH). 1H NMR: 8.24 (d,
J = 7.2 Hz, 1H), 8.18 (s, 1H), 7.75 (d, J = 7.2 Hz, 1H), 7.64
(t, J = 7.2 Hz, 1H), 5.05 (d, J = 16.8 Hz, 1H), 4.85 (d,
J = 16.8 Hz, 1H), 3.44 (m, 1H), 3.31 (m, 1H), 3.29 (dd,
J = 17.2 and 5.5 Hz, 1H), 2.93 (m, 2H), 2.85 (dd, J = 17.2
and 4.7 Hz, 1H), 1.82 (m, 2H), 1.71 (m, 2H), 1.31 (s, 9H).
13C NMR: 202.3, 169.5, 165.1, 152.9, 147.2, 143.1, 133.9,
130.1, 129.9, 81.0, 72.1, 63.5, 56.8, 51.5, 37.3, 35.6, 31.8,
30.5. Anal. Calcd for C20H27N3O3ÆHCl: C, 60.98; H, 7.16;
N, 10.67; Cl, 9.00. Found: C, 60.91; H, 7.19; N, 10.56; Cl,
9.09. Compound 13 (hydrochloride salt): mp: 290–291 ꢁC.
25
18 (hydrochloride salt): mp: 272–273 ꢁC. ½aꢀD ꢁ11.6 (c
1
0.45, EtOH). H NMR: 8.18 (s, 1H), 7.85 (d, J = 7.2 Hz,
1H), 7.64 (t, J = 7.2 Hz, 1H), 7.45 (d, J = 7.2 Hz, 1H), 5.04
(d, J = 16.7 Hz, 1H), 4.89 (d, J = 16.7 Hz, 1H), 3.40 (m,
1H), 3.39 (m, 1H), 3.25 (dd, J = 17.1 and 5.7 Hz, 1H), 2.92
(m, 2H), 2.81 (dd, J = 17.1 and 4.9 Hz, 1H), 2.61 (s, 3H),
1.80 (m, 2H), 1.71 (m, 2H). 13C NMR: 202.4, 167.2, 161.3,
147.3, 137.4, 134.4, 129.9, 129.0, 128.3, 80.2, 77.1, 66.0,
53.4, 51.5, 36.3, 33.2, 26.9. Anal. Calcd for
C17H21N3O3ÆHCl: C, 58.03; H, 6.30; N, 11.94; Cl, 10.08.
Found: C, 58.09; H, 6.35; N, 11.80; Cl, 10.25. Compound
25
½aꢀD ꢁ10.3 (c 0.45, EtOH). 1H NMR: 8.21 (s, 1H), 7.96 (d,
J = 7.1 Hz, 1H), 7.68 (d, J = 7.1 Hz, 1H), 7.55 (s, 1H), 5.06
(d, J = 16.8 Hz, 1H), 4.90 (d, J = 16.8 Hz, 1H), 3.44 (m,
1H), 3.29 (m, 1H), 3.25 (dd, J = 17.2 and 5.7 Hz, 1H), 2.89
(m, 2H), 2.77 (dd, J = 17.2 and 4.8 Hz, 1H), 1.80 (m, 2H),
1.71 (m, 2H), 1.34 (s, 9H). 13C NMR: 202.9, 167.9, 164.6,
154.1, 143.2, 134.7, 129.9, 128.8, 128.4, 81.1, 71.2, 65.5,
55.7, 52.3, 37.4, 35.5, 32.7, 30.2. Anal. Calcd for
C20H27N3O3ÆHCl: C, 60.98; H, 7.16; N, 10.67; Cl, 9.00.
Found: C, 60.89; H, 7.13; N, 10.60; Cl, 9.12. Compound
25
19 (hydrochloride salt): mp: 281–282 ꢁC.½aꢀD +18.3 (c 0.5,
EtOH). 1H NMR: 8.11 (s, 1H), 7.71 (s, 1H), 7.22 (d,
J = 7.2 Hz, 1H), 7.42 (d, J = 7.2 Hz, 1H), 5.05 (d,
J = 16.7 Hz, 1H), 4.90 (d, J = 16.7 Hz, 1H), 3.81 (s, 3H),
3.49 (m, 1H), 3.28 (m, 1H), 3.20 (dd, J = 17.1 and 5.8 Hz,
1H), 2.80 (m, 2H), 2.74 (dd, J = 17.1 and 4.9 Hz, 1H), 1.82
(m, 2H), 1.72 (m, 2H). 13C NMR: 202.5, 168.3, 165.5,
161.3, 188.5, 138.4, 134.5, 130.6, 128.9, 81.5, 77.5, 66.0,
58.7, 53.5, 52.8, 37.1, 32.2. Anal. Calcd for
C17H21N3O4ÆHCl: C, 55.51; H, 6.03; N, 11.42; Cl, 9.64.
Found: C, 55.63; H, 6.08; N, 11.55; Cl, 9.75. Compound
25
14 (dihydrochloride salt): mp: 341–342 ꢁC (dec). ½aꢀD
+27.4 (c 0.43, EtOH). 1H NMR: 9.25 (s, 1H), 8.76 (d,
J = 7.3 Hz, 1H), 8.48 (d, J = 7.3 Hz, 1H), 8.26 (s, 1H), 5.07
(d, J = 16.7 Hz, 1H), 4.93 (d, J = 16.7 Hz, 1H), 3.42 (m,
1H), 3.27 (m, 1H), 3.28 (dd, J = 17.3 and 5.8 Hz, 1H), 2.92
(m, 2H), 2.78 (dd, J = 17.3 and 4.7 Hz, 1H), 1.81 (m, 2H),
1.70 (m, 2H). 13C NMR: 202.6, 167.9, 164.6, 159.1, 155.2,
154.7, 139.9, 134.8, 81.0, 71.9, 66.5, 55.6, 52.1, 37.6, 32.5.
Anal. Calcd for C15H18N4O3Æ2HCl: C, 48.01; H, 5.37; N,
14.93. Found: C, 48.12; H, 5.33; N, 14.84. Compound 15
25
20 (hydrochloride salt): mp: 282–283 ꢁC. ½aꢀD ꢁ15.6 (c 0.5,
1
EtOH). H NMR: 8.13 (s, 1H), 7.54 (t, J = 7.3 Hz, 1H),
7.35 (d, J = 7.3 Hz, 1H), 7.15 (d, J = 7.3 Hz, 1H), 5.02 (d,
J = 16.9 Hz, 1H), 4.89 (d, J = 16.9 Hz, 1H), 3.77 (s, 3H),
3.41 (m, 1H), 3.36 (m, 1H), 3.27 (dd, J = 17.4 and 5.7 Hz,
1H), 2.92 (m, 2H), 2.81 (dd, J = 17.4 and 4.9 Hz, 1H), 2.64
(s, 3H), 1.79 (m, 2H), 1.68 (m, 2H). 13C NMR: 203.1,
166.2, 162.3, 160.5, 147.3, 137.4, 132.9, 129.9, 128.7, 80.1,
76.1, 66.5, 58.9, 53.1, 51.3, 36.7, 33.0. Anal. Calcd for
C17H21N3O4ÆHCl: C, 55.51; H, 6.03; N, 11.42; Cl, 9.64.
Found: C, 55.44; H, 6.05; N, 11.52; Cl, 9.55.
25
(dihydrochloride salt): mp: 341–342 ꢁC (dec). ½aꢀD ꢁ19.6
1
(c 0.42, EtOH). H NMR: 8.93 (d, J = 6.8 Hz, 1H), 8.78
(d, J = 6.8 Hz, 1H), 8.31 (s, 1H), 8.25 (t, J = 6.8 Hz, 1H),
4.92 (d, J = 17.2 Hz, 1H), 4.81 (d, J = 17.2 Hz, 1H), 3.51
(m, 1H), 3.33 (m, 1H), 3.21 (dd, J = 17.2 and 5.6 Hz, 1H),
2.81 (m, 2H), 2.78 (dd,J = 17.2 and 4.5 Hz, 1H), 1.89 (m,
2H), 1.67 (m, 2H). 13C NMR: 204.1, 171.8, 167.3, 162.8,
152.1, 142.6, 133.1, 130.9, 81.4, 70.8, 65.8, 52.7, 50.9, 37.6,
31.8. Anal. Calcd for C15H18N4O3Æ2HCl: C, 48.01; H,
5.37; N, 14.93. Found: C, 47.90; H, 5.45; N, 14.81.
19. Williams, E. J.; Kenny, P. W.; Kettle, J. G.; Mwashimba,
P. G. Tetrahedron Lett. 2004, 45, 3737.
20. Alexandre, F. R.; Berecibar, A.; Besson, T. Tetrahedron
Lett. 2002, 43, 3911.
21. Armarego, W. L. F.; Smith, J. I. C. J. Chem. Soc. B 1967,
449.
22. Desjardins, R. E.; Canfield, C. J.; Haynes, D. E.; Chulay,
J. D. Antimicrob. Agents Chemother. 1979, 16, 710.
23. Chulay, J. D.; Haynes, J. D.; Diggs, C. L. Exp. Parasitol.
1983, 55, 138.
25
Compound 16 (hydrochloride salt): mp: 298–299 ꢁC. ½aꢀD
+14.6 (c 0.5, EtOH). 1H NMR: 8.21 (s, 1H), 7.85 (d,
J = 7.2 Hz, 1H), 7.64 (t, J = 7.2 Hz, 1H), 7.55 (d,
J = 7.2 Hz, 1H), 5.03 (d, J = 16.8 Hz, 1H), 4.87 (d,
J = 16.8 Hz, 1H), 3.41 (m, 1H), 3.34 (m, 1H), 3.26 (dd,
J = 17.1 and 5.5 Hz, 1H), 2.90 (m, 2H), 2.84 (dd, J = 17.1
and 4.7 Hz, 1H), 1.83 (m, 2H), 1.70 (m, 2H). 13C NMR:
204.4, 167.8, 164.8, 149.9, 142.2, 134.3, 130.9, 129.1, 127.6,
81.1, 72.4, 64.5, 54.8, 51.8, 37.2, 31.6. Anal. Calcd for
24. Fontaine, F.; de Sousa, G.; Duchene, P.; Rahmani, R.
Toxicology In Vitro 1998, 12, 545.