The total synthesis of neoamphimedine

Article abstract of DOI:10.1021/jo7017813

(Chemical Equation Presented) Neoamphimedine, a pyridoacridine alkaloid from Xestospongia sp., is a potent antitumor agent both in vitro and in vivo. Neoamphimedine can efficiently induce topoisomerase II mediated catenation of plasmid DNA in vitro and is

Full text of DOI:10.1021/jo7017813

The Total Synthesis of Neoamphimedine
Daniel V. LaBarbera, Tim S. Bugni, and Chris M. Ireland*
Department of Medicinal Chemistry, UniVersity of Utah, Salt Lake City, Utah 84112
cireland@pharm.utah.edu
ReceiVed August 14, 2007
Neoamphimedine, a pyridoacridine alkaloid from Xestospongia sp., is a potent antitumor agent both in
vitro and in vivo. Neoamphimedine can efficiently induce topoisomerase II mediated catenation of plasmid
DNA in vitro and is the only member of more than one hundred pyridoacridines thus far to have this
mechanism of action. Herein we report the first total synthesis of neoamphimedine.
CHART 1. The Structures of Amphimedine and
Neoamphimedine
Introduction
Pyridoacridines are a large and diverse family of marine
alkaloids first described in 1983 with the report of the parent
derivative amphimedine (1) (Chart 1).1 Since then over one
hundred derivatives have been characterized and studied dis-
playing antitumor, antibacterial, antiviral, and antiparasitic
activity.2,3 The major biological activity of pyridoacridines
described in the literature is in vitro cytotoxicity in mammalian
cells. This activity is attributed to nonspecific intercalation of
DNA as a result of the highly planar electron deficient aromatic
ring system of the pyridoacridine pharmacophore. Although
DNA intercalation is an important mechanistic feature of the
pyridoacridines it is becoming evident that the range of
biological activity is due to other mechanisms. These include
generating reactive oxygen species (ROS), binding to transition
metals, and inhibiting topoisomerases.2-4
cycle arrest in both the S and G2 phases suggesting a checkpoint
for the completion of top2-mediated decatenation of catenated
DNA.7 Top2 poisons that stabilize the cleavable complex, such
as etoposide and doxorubicin, have had the most clinical
success.2,7 Pyridoacridine derivatives have been shown to target
topoisomerase function; while a few can stabilize the top2
cleavable complex, most inhibit top2 catalytic function.2-4
Recently we reported the antineoplastic and novel top2
mediated cytotoxicity of neoamphimedine (2) (Chart 1).8,9 In
vitro, 2 has top2 dependent cytotoxicity in JN394T2 yeast cells
as well as potent cytotoxicity in mammalian tumor cells,
particularly the HCT116 cell line and the MDR1 expressing
A2780AD cell line.6,9 In vivo studies demonstrated that 2 is as
efficacious as Etoposide at inhibiting the growth of epidermoid-
nasopharyngeal KB tumors in nude mice. Interestingly, the
Topoisomerase II (top2) is an important molecular target for
chemotherapeutic drug discovery.4-7 Besides the ability to relax
supercoiled DNA, top2 also catalyzes the decatenation and
catenation of DNA.5,7 Topoisomerase II mediated decatenation
of DNA is essential for G2 to M cell cycle progression. Inhibition
of top2 in mammalian cells has been shown to result in cell
(1) Schmitz, F. J.; Agarwal, S. K.; Gunasedera, S. P.; Schmidt, P. G.;
Shoolery, J. N. J. Am. Chem. Soc. 1983, 105, 4835-4836.
(2) Marshall, K. M.; Barrows, L. R. Nat. Prod. Rep. 2004, 21, 731-
751.
(3) Molinski, T. F. Chem. ReV. 1993, 93, 1825-1838.
(4) Dias, N.; Vezin, H.; Lansiaux, A.; Bailly, C. Top. Curr. Chem. 2005,
253, 89-108.
(5) Champoux, J. J. Annu. ReV. Biochem. 2001, 70, 369-413.
(6) Liu, L. F. Annu. ReV. Biochem. 1989, 58, 351-75.
(7) Wang, J. C. Annu. ReV. Biochem. 1996, 65, 635-692.
(8) Guzman, F. S. D.; Carte, B.; Troupe, N.; Faulkner, D. J.; Harper, M.
K.; Concepcion, G. P.; Mangalindan, G. C.; Matsumoto, S. S.; Barrows, L.
R.; Ireland, C. M. J. Org. Chem. 1999, 64, 1400-1402.
(9) Marshall, K. M.; Matsumoto, S. S.; Holden, J. A.; Concepcion, G.
P.; Tasdemir, D.; Ireland, C. M.; Barrows, L. R. Biochem. Pharmacol. 2003,
66, 447-458.
10.1021/jo7017813 CCC: $37.00 © 2007 American Chemical Society
Published on Web 09/27/2007
J. Org. Chem. 2007, 72, 8501-8505
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LaBarbera et al.
SCHEME 1. Retrosynthesis of Neoamphimedine
parent compound 1 was inactive at all doses studied, both in
vitro and in vivo. Mechanism of action studies with 2 revealed
that it is not a top2 cleavable complex poison; however, it
efficiently induces top2-mediated catenation of plasmid DNA
in vitro. Thus far, 2 is the only member of the pyridoacridine
family to have this unique mechanism of action and more
importantly the only small molecule known to induce top2-
mediated catenation of DNA at low concentrations.9
The unique biological activities of the pyridoacridine family
and diverse structural features have resulted in numerous
synthetic studies and total syntheses. As a result, significant
advances have been made with respect to synthetic methodolo-
gies in preparing pyridoacridines.3,10-12 Despite these advances
and two reported total syntheses of the parent derivative 1,13-15
the total synthesis of 2 has not been reported. We now report
the first total synthesis of neoamphimedine.
which can be derivatized with methylamino acetaldehyde
dimethyl acetal to form the diazaanthracene 13. It is important
to note that this methodology facilitates derivatization of the E
ring and would be useful to conduct SAR studies with various
N-substituted amino acetals. The key acid intermediate 11 can
be obtained from 5 through a series of reductions, amide
formations, and acid-catalyzed ring closures.
The synthesis of 2 began with the known compound 5.16,17
Although the preparation of 5 was accomplished as described
in the literature, some improvements to the synthetic procedures
have been made (Supporting Information). Briefly, commercially
available 4-methoxy-2-nitrophenol was nitrated with 70% nitric
acid in acetic acid to afford 3 in 84-90% yield. The dinitro-
phenol was methylated with diazomethane to afford 4 in
quantitative yield followed by selective reduction of one nitro
group with 10% palladium on carbon in a boiling solution of
cyclohexene and ethanol.18 Subsequent acetylation of the
resulting amine by treatment with acetic anhydride afforded 5
in 77% yield for two steps.
Results and Discussion
Retrosynthetic analysis of 2 (Scheme 1) began with discon-
nection of the B ring. This disconnection has been described in
numerous pyridoacridine syntheses giving intermediates such
as 13. Reduction of the nitro group of 13 and subsequent
oxidation gives a reactive quinone intermediate that dehydrates
in the presence of the amine to give 2. In the previous synthesis
reported for 1 a key hetero Diels-Alder reaction was utilized
to form the 3-(2H)-isoquinolone E ring. There is no precedent
for a hetero Diels-Alder formation of a 1-(2H)-isoquinolone
required for the E ring of 2, thus a different approach was taken.
Disconnection of the E ring gives the acid functionality 11,
Catalytic reduction of 5 followed by heating the resulting
amine in m-xylene with commercially available ethyl (2-nitro-
benzoyl) acetate gave the â-keto amide 6 in 96% yield for two
steps.19 Knorr cyclization of 6 with polyphosphoric acid at 75
°C gave the quinolone 7 in 52% yield. Above 75 °C the 7-acet-
amido group hydrolyzes, which can influence the yield. Quino-
line 9 was obtained in two steps via base-catalyzed conversion
of 7 with trifluoromethanesulphonic anhydride giving the aryl
triflate 8 in 70% yield.20 The triflate ester of 8 was then removed
by hydrogenolysis. In situ generation of triethyl ammonium
formate in the presence of palladium catalyst and phosphine
ligand gave the quinoline 9 in 87% yield (Scheme 2).20,21
A crucial step in this synthesis is the formation of the acid
intermediate 11, prepared via the Sandmeyer reaction (Scheme
(10) Ciufolini, M. A. Development and Application of New Preparative
Reactions in Heterocyclic Chemistry. In Heterocyclic Natural Product
Synthesis; JAI Press Inc.: Greenwich, Connecticut, 1996; Vol. 3, pp 1-55.
(11) Echavarren, A. M. Recent Developments In The Synthesis of Marine
Pyridoacridine Alkaloids. In AdVances in Nitrogen Heterocycles; Moody,
C. J., Ed.; JAI Press Inc.: Greenwich, Connecticut, 1996; Vol. 2, pp 211-
250.
(16) Burger, A.; Fitchett, G. T. J. Am. Chem. Soc. 1952, 75, 1359-
1362.
(17) Kawano, N.; Hirai, M.; Kaneko, A. Chem. Pharm. Bull. 1965, 13,
890-891.
(12) Koller, A.; Rudi, A.; Gravalos, M. G.; Kashman, Y. Molecules 2001,
6, 300-322.
(18) Entwistle, I. D.; Johnstone, R. A. W.; Povall, T. J. J. Chem. Soc.,
Perkin Trans. 1 1975, 13, 1300-1301.
(13) Echavaren, A. M.; Stille, J. K. J. Am. Chem. Soc. 1988, 110, 4051-
4053.
(19) Szczepankiewicz, B. G.; Heathcock, C. H. J. Org. Chem. 1994, 59,
3512-3513.
(14) Kubo, A.; Nakahara, S. Heterocycles 1988, 27, 2095-2098.
(15) Nakahara, S.; Tanaka, Y.; Kubo, A. Heterocycles 1996, 43, 2113-
2123.
(20) Cacchi, S.; Ciattini, P. G.; Morera, E.; Ortar, G. Tetrahedron Lett.
1986, 27, 5541-5544.
8502 J. Org. Chem., Vol. 72, No. 22, 2007

Total Synthesis of Neoamphimedine
SCHEME 2. The Synthesis of Quinoline Intermediate 9
SCHEME 3. The Synthesis of Neoamphimedine
3). In one pot, the 7-acetanilide protecting group of 9 was
hydrolyzed in a refluxing solution of glacial acetic acid, water,
and sulfuric acid for 2 h. The corresponding aniline was then
diazatized at 0 °C with sodium nitrite. The neutralized diazonium
salt was added to a freshly prepared solution of potassium cupric
cyanide22 at 50 °C affording 10 in 50-58% yield. The nitrile
of 10 was converted to the acid 11 by first generating the
primary amide in situ at 70 °C for 3 h with concentrated sulfuric
acid. The reaction was cooled and diluted in half with water
followed by heating at 120 °C for 2 h to afford 11 in 80% yield.
The acid 11 was functionalized to the amide 12 with EDC
and methylamino acetaldehyde dimethylacetal in 87% yield. The
key isoquinolone ring of the diazaanthracene 13 was formed
by converting the acetal to the aldehyde with sulfuric acid at
room temperature. Once converted to the aldehyde the isoqui-
nolone ring formation occurred smoothly at 150 °C in sulfuric
acid within 10 min to form 13 in 43% yield. When ring closure
of the dimethyl acetal was attempted at temperatures above 100
°C no product formed, and the compound decomposed. Neo-
amphimedine (2) was obtained by catalytic reduction of the nitro
group of 13 followed by CAN oxidation in 30% yield for the
(21) Nakahara, S.; Tanaka, Y.; Kubo, A. Heterocycles 1993, 36, 1139-
1144.
(22) Gattermann, L. The Practical Methods of Organic Chemistry, 2nd
Am. from the 4th Ger. ed.; MacMillian & CO., Ltd.: London, 1909; Vol.
1, pp 216-223.
J. Org. Chem, Vol. 72, No. 22, 2007 8503

LaBarbera et al.
°C under argon. After the addition the reaction was stirred an
additional 5 min, diluted with 100 mL of H2O, and made basic
with saturated aqueous NaHCO3. The aqueous phase was extracted
with dichloromethane 3× (50 mL). The combined dichloromethane
extracts were dried with Na2SO4 and concentrated in vacuo. The
resulting residue was chromatographed on silica gel eluting with
1:1 ethyl acetate and hexanes to afford 8 as yellow crystals (8 g,
final two steps. The synthetic product was compared with the
natural product using H NMR in chloroform and 2D NMR
gHMBC and gHSQC in 2:1 chloroform/methanol. The splitting
patterns, chemical shifts, and 2D proton carbon correlations were
identical to the natural product.8
The concise synthesis of 2 was achieved in 12 steps from
readily available 5. Another important feature of this synthesis
is the chemistry used to form the E ring of 2. This ring system
has proved to be the most challenging step for both the synthesis
of 1 and 2. The chemistry used in the synthesis of 2 allows for
derivatization that can be useful in studying structure-activity
relationships of the more biologically active 2. Currently, we
are scaling up the synthesis to conduct in vivo studies to further
understand the biological mechanism of action of neoamphi-
medine.
1
1
70% yield): mp 127-128 °C; TLC (ethyl acetate) Rf ) 0.56. H
NMR (400 MHz, CDCl3): δ 8.21 (d, J ) 8.0 Hz, 1H), 8.18 (s,
1H), 8.15 (s, 1H), 7.69 (t, J ) 8.0 Hz, 1H), 7.60 (t, J ) 8.0 Hz,
1H), 7.30 (d, J ) 8.0 Hz, 1H), 6.86 (s, 1H), 4.14 (s, 3H), 3.45 (s,
3H), 2.27 (s, 3H). IR (NaCl plate): 846, 910, 1062, 1211, 1415,
1526, 1613, 1696, 2941, 3387 cm-1. HRMS (m/z): [M+H]+ calcd
for C20H17N3O8F3S, 516.0688; found, 516.0671.
7-Acetamido-5,8-dimethoxy-4-(2-nitrophenyl)quinoline (9).
Formic acid (99%) was added dropwise over 10 min to a solution
mixture consisting of 8 (6.5 g, 12.6 mmol), triethyl amine (11.1
mL, 80 mmol), palladium(II) acetate (600 mg, 2.7 mmol) and 1,1-
bis(diphosphino)ferrocene in 130 mL of dry DMF at 0 °C under
argon. The reaction mixture was slowly warmed to 60 °C over 2
h, poured into 1.5 L of water, and made basic with saturated aqueous
NaHCO3. The aqueous phase was extracted 3× (400 mL) with
dichloromethane. The dichloromethane extracts were combined,
washed with 200 mL of saturated aqueous NaCl, dried with
Na2SO4, and concentrated in vacuo resulting in a crude solid. The
solid was purified by silica chromatography eluting with 1:1 DCM/
ethyl acetate to afford 9 as yellow crystals (4 g, 87% yield): mp
237-238 °C; TLC (ethyl acetate) Rf ) 0.20. 1H NMR (400 MHz,
CHCl3): δ 8.96 (d, J ) 4.2 Hz, 1H), 8.19 (d, J ) 8.0 Hz, 1H),
8.16 (s, 1H), 8.13 (s, 1H), 7.67 (t, J ) 8.0 Hz, 1H), 7.57 (t, J )
8.0 Hz, 1H), 7.29 (d, J ) 8.0 Hz, 1H), 7.13 (d, J ) 4.2 Hz, 1H),
4.14 (s, 3H), 3.46 (s, 3H), 2.29 (s, 3H). IR (NaCl plate): 858, 1257,
1347, 1391, 1419, 1456, 1522, 1616, 1684 cm-1. HRMS (m/z):
[M+H]+ calcd for C19H18N3O5, 368.1246; found, 368.1256.
7-Cyano-5,8-dimethoxy-4-(2-nitrophenyl)quinoline (10). A
solution consisting of 9 (500 mg, 1.4 mmol), 15 mL of glacial acetic
acid, 5 mL of H2O, and 5 mL of concentrated H2SO4 was heated
at reflux for 2 h. The resulting orange solution was cooled to room
temperature and transferred (using ∼5 mL of ice water) to a 500
mL beaker containing 25 g of ice. The beaker was placed on an
ice bath and cooled to 0 °C. The aniline was then diazatized by the
dropwise addition of sodium nitrite (400 mg, 5.8 mmol) in 5 mL
of H2O while maintaining the temperature between 0 and 5 °C.
After the addition the color of the reaction turns from dark orange
to pale yellow, and the reaction is stirred at 0 °C for an additional
10 min followed by neutralization of the diazoinium salt to pH 5,
at 0 °C, with solid K2CO3 over 30 min. Prior to neutralizing the
diazonium salt the cupric cyanide solution was made fresh as
follows. Copper sulfate (23 g) was dissolved in 100 mL of H2O in
a 1 L beaker and warmed to 40 °C, and KCN (25 g) in 50 mL of
H2O was added dropwise with stirring. Caution!! During this
addition hydrogen cyanide is produced so this must be done in a
well-ventilated hood to avoid breathing any vapors. After the
addition of KCN the temperature was heated to 65 °C while the
diazonium salt was being neutralized. The neutralized diazonium
salt was transferred to an addition funnel and added dropwise to
the cupric cyanide solution over 15 min while maintaining the
temperature at 45-50 °C. The reaction mixture was then heated at
50 °C for 1 h, diluted with an equal volume of ethyl acetate, and
stirred for 10 min. The aqueous phase was extracted 3× (100 mL)
with ethyl acetate. The combined ethyl acetate extracts were dried
with Na2SO4 and concentrated to give a crude oil. The oil was
purified by silica flash chromatography using ethyl acetate as the
eluent to afford 10 as tan crystals (265 mg, 58% yield): mp 129-
Experimental
3-Acetamido-2,5-dimethoxy-(2-nitrobenzoyl)-acetanilide (6).
A solution consisting of 5 (9.25 g, 38.5 mmol), 4.6 g of 10% Pd
on carbon, 278 mL of cyclohexene, and 310 mL of absolute ethanol
was refluxed for 2 h. The solution was filtered through celite while
hot, and the catalyst was washed with ethanol. The filtrate was
concentrated in vacuo giving an oil that solidified when triturated
in hexanes. The white solid was filtered and air-dried (7.75 g, 96%
yield). Without purification a mixture consisting of 3-acetamido-
2,6-dimethoxyaniline (12 g, 57 mmol) and ethyl-(2-nitrobenzoyl)-
acetate (13.5 g, 57 mmol) in 15 mL of anhydrous m-xylene were
combined in a 100 mL round-bottom flask fitted with a short stem
distillation apparatus under argon. The reaction vessel was placed
on a sand bath preheated to 160-180 °C and stirred for 2 h. The
temperature of the distillate reached 70 °C as ethanol was distilled
off and dropped to 30 °C after distillation was complete. The
reaction was cooled to room temperature and poured into 100 mL
of diethyl ether. The resulting yellow oil was crystallized by
trituration giving a pale yellow powder. The powder was filtered
and washed 2× (25 mL) with diethyl ether and dried to afford 6
(21 g, 96% yield): mp 170-171 °C; TLC (ethyl acetate) Rf ) 0.23.
1H NMR (400 MHz, CDCl3): δ 9.23 (s, 1H), 8.21 (d, J ) 8.0 Hz,
1H), 7.81 (t, J ) 7.5 Hz, 1H), 7.75-7.67 (m, 3H), 7.59 (s, 1H),
7.49 (d, J ) 8.0 Hz, 1H), 3.96 (s, 2H), 3.81 (s, 3H), 3.79 (s, 3H),
2.23 (s, 3H). IR (NaCl plate): 993, 1049, 1246, 1346, 1456, 1525,
1603, 1684, 2358, 3308 cm-1. HRMS (m/z): [M+H]+ calcd for
C19H20N3O7, 402.1301; found, 402.1299.
7-Acetamido-5,8-dimethoxy-4-(2-nitrophenyl)-2-(1H)quinoli-
none (7). Polyphosphoric acid (200 g) was prewarmed to 75 °C in
a 500 mL beaker fitted with a mechanical stirrer. To the stirred
viscous acid was gradually added 6 (20 g, 50 mmol). The reaction
was kept at 75 °C until finished by TLC (ethyl acetate) ap-
proximately 5 h. The reaction was cooled to room temperature and
poured into 500 mL of ice water. The resulting yellow solid was
filtered and washed with ice water until the washings became
neutral. The solid was dried under high vacuum to give 12 g of
crude material. Recrystallization with ethanol and water afforded
7 as a yellow powder (10 g, 52% yield): mp >279 °C dec; TLC
1
(10% MeOH in ethyl acetate) Rf ) 0.25. H NMR (400 MHz,
CDCl3): δ 10.06 (s, 1H), 8.20 (d, J ) 8.0 Hz, 1H), 7.87 (s, 1H),
7.71 (s, 1H), 7.67 (t, J ) 8.0 Hz, 1H), 7.56 (t, J ) 8.0 Hz, 1H),
7.32 (d, J ) 8.0 Hz, 1H), 6.34 (s, 1H), 3.88 (s, 3H), 3.38 (s, 3H),
2.26 (s, 3H). IR (NaCl): 984, 1137, 1236, 1387, 1525, 1559, 1616,
1652, 3147 cm-1. HRMS (m/z): [M+Na]+ calcd for C19H17N3O6-
Na, 406.1015; found, 406.1025.
1
7-Acetamido-5,8-dimethoxy-4-(2-nitrophenyl)-2-(trifluo-
romethane sulfonoxy)quinoline (8). Trifluoromethane sulfonic
anhydride (8 mL, 48 mmol) was added dropwise over 25 min to a
solution consisting of 7 (8.5 g, 22.2 mmol) in 300 mL of dry
dichloromethane containing triethylamine (10 mL, 72 mmol) at -20
130 °C; TLC (ethyl acetate/MeOH, 1:1 v/v) Rf ) 0.71. H NMR
(500 MHz, CD3OD): δ 8.99 (d, J ) 4.0 Hz, 1H), 8.22 (d, J ) 8.0
Hz, 1H), 7.73 (t, J ) 8.0 Hz, 1H), 7.63 (t, J ) 8.0 Hz, 1H), 7.37
(d, J ) 4.0 Hz, 1H), 7.31 (d, J ) 8.0 Hz, 1H), 6.82 (s, 1H), 4.26
(s, 3H), 3.44 (s, 3H). 13C NMR (125 MHz, CDCl3): δ 155.5, 152.5,
8504 J. Org. Chem., Vol. 72, No. 22, 2007

Total Synthesis of Neoamphimedine
150.8, 150.4, 150.0, 147.7, 137.9, 133.3, 130.1, 128.9, 123.9, 123.9,
122.8, 116.5, 105.6, 104.3, 63.3, 55.8. IR (NaCl plate): 990, 1072,
ice water and diluted with 20 mL of ethyl acetate. The aqueous
layer was made basic to pH ) 9 with K2CO3 and extracted 3× (50
mL) with ethyl acetate. The ethyl acetate extracts were dried with
Na2SO4 and concentrated in vacuo to give a yellow green oil. The
crude oil was purified by column chromatography (1.5 cm × 2.5
cm) using alumina Brockman acitivity I neutral and ethyl acetate
as the eluent, to afford a yellow to green colored oil (10 mg, 43%
1139, 1243, 1346, 1389, 1465, 1526, 1716, 2359, 3342 cm-1
.
HRMS (m/z): [M+H]+ calcd for C18H14N3O4, 336.0984; found,
336.0982.
5,8-Dimethoxy-4-(2-nitrophenyl)-7-quinolinecarboxcylic acid
(11). The nitrile 10 (50 mg, 0.15 mmol) was dissolved in 750 µL
of concentrated H2SO4 at room temperature. The acid solution was
stirred at 60-70 °C for 3.5 h resulting in the primary amide. The
reaction solution was cooled on ice and slowly diluted with 750
µL of ice cold water followed by heating at 120 °C under argon
for 2 h. The reaction was cooled to room temperature, poured into
10 mL of ice water, and neutralized (pH ) 5) with solid K2CO3.
The neutral solution was extracted 3× (30 mL) with ethyl acetate,
dried with Na2SO4, and concentrated in vacuo to give a pale orange
powder. Recrystallization with ethyl acetate and hexanes gave pale
orange needles (43 mg, 80% yield): mp >162 °C dec; TLC (ethyl
1
yield): TLC (30% MeOH in ethyl acetate) Rf ) 0.41. H NMR
(500 MHz, CDCl3): δ 9.02 (d, J ) 4.2 Hz, 1H), 8.27 (d, J ) 8.0
Hz, 1H), 7.72 (t, J ) 8.0 Hz, 1H), 7.63 (t, J ) 8.0 Hz, 1H), 7.48
(d, J ) 8.0 Hz, 1H), 7.26 (d, J ) 4.2 Hz, 1H), 6.97, (d, J ) 7.7
Hz, 1H) 6.53 (d, J ) 7.7 Hz, 1H), 4.23 (s, 3H), 3.50 (s, 3H), 3.02
(s, 3H). IR (NaCl plate): 1063, 1231, 1345, 1524, 1652, 2926 cm-1
.
HRMS (m/z): [M+H]+ calcd for C21H18N3O5, 392.1246; found,
392.1260.
Neoamphimedine (2). A reaction mixture consisting of 13 (10
mg, 0.025 mmol), 20 mg of 10% Pd on carbon, 500 µL of
cyclohexene, and 1 mL of absolute ethanol was refluxed for 1 h.
The reaction mixture was cooled to room temperature and filtered
through a plug of Celite. The filtrate was concentrated in vacuo
giving a pale yellow residue, which was dissolved into 1 mL of
ACN and cooled to 0 °C on an ice bath. A solution of CAN (35
mg, 0.063 mmol) in 1 mL of H2O was added dropwise to the ice
cold ACN solution and stirred at 0 °C for 15 min. The reaction
solution was allowed to warm to room temperature and stirred for
an additional 45 min. The pH of the solution was adjusted with
saturated aqueous NaHCO3 (pH ) 8) and extracted 3× (10 mL)
CHCl3. The CHCl3 extracts were combined, dried with Na2SO4,
and concentrated in vacuo to afford 2 as a yellow solid. The solid
was recrystallized with CHCl3 and hexanes to give yellow crystals
(2.4 mg, 30% yield). The original publication of the structure of
neoamphimedine NMR data was reported in trifluoroacedic acid
(TFA). It is important to note that neoamphimedine is unstable in
the presence of TFA: TLC (CHCl3/MeOH 1:1 v/v) Rf ) 0.43. 1H
NMR (400 MHz, CDCl3): δ 9.32 (d, J ) 5.5 Hz, 1H), 8.62 (d, J
) 8.0 Hz, 1H), 8.56 (d, J ) 5.5 Hz, 1H), 8.36 (d, J ) 8.0 Hz, 1H),
7.97 (t, J ) 8.0 Hz, 1H), 7.87 (t, J ) 8.0 Hz, 1H), 7.84 (d, J ) 7.0
Hz, 1H), 7.81 (d, J ) 7.0 Hz, 1H), 3.74 (s, 3H). (2D gHMBC and
gHSQC proton carbon correlations are in the Supporting Informa-
tion.) HRMS (m/z): [M+H]+ calcd for C19H12N3O2, 314.0930;
found, 314.0940.
1
acetate/MeOH, 1:1 v/v) Rf ) 0.30. H NMR (400 MHz, CDCl3):
δ 9.03 (s, 1H), 8.21 (d, J ) 7.8 Hz, 1H), 7.68 (t, J ) 7.7 Hz, 1H),
7.59 (t, J ) 7.7 Hz, 1H), 7.36 (s, 1H), 7.29 (d, J ) 7.8 Hz, 1H),
7.28 (s, 1H) 4.42 (s, 3H), 3.49 (s, 3H). IR (NaCl plate): 860, 996,
1134, 1236, 1346, 1393, 1456, 1524, 1575, 1699, 2514, 2938 cm-1
.
HRMS (m/z): [M+H]+ calcd for C18H15N2O6, 355.0930; found,
355.0947.
7-[N-(2,2-Dimethoxyethyl)-N-methyl]-carboxamide-5,8-
dimethoxy-4-(2-nitrophenyl)quinoline (12). To a solution consist-
ing of 11 (30 mg, 0.085 mmol) and EDC‚HCl (33 mg, 0.17 mmol)
in 5 mL of dichloromethane under argon, was added (methylamino)
acetaldehyde dimethyl acetal (22 µL, 20 mg, 0.17 mmol) dropwise
under argon. The reaction mixture was stirred at room temperature
for 15 h and quenched by the addition of 5 mL of H2O. The aqueous
phase was extracted 3× (20 mL) with dichloromethane, and the
dichloromethane extracts where combined, dried with Na2SO4, and
concentrated in vacuo. The resulting crude residue was purified by
column chromatography (1.5 cm × 2.5 cm) using alumina Brock-
man acitivity I neutral and ethyl acetate as the eluent to afford a
yellow colored oil (33.5 mg, 87% yield): TLC (ethyl acetate/MeOH
1
1:1 v/v) Rf ) 0.56. H NMR (500 MHz, CDCl3): δ 8.97 (d, J )
4.2 Hz, 1H), 8.23-8.11 (m, 1H), 7.65 (t, J ) 7.8 Hz, 1H), 7.55 (t,
J ) 7.8 Hz, 1H), 7.28 (m, 1H), 7.19 (d, J ) 4.2 Hz, 1H), 6.59 (s,
1H), 4.90-2.79 (This region integrates to 18 protons, but they were
not assigned because of cis-trans isomerization, 18H). IR (NaCl
plate): 732, 1072, 1121, 1238, 1385, 1461, 1526, 1636, 2934 cm-1
.
Acknowledgment. We thank the NIH (Grant CA36622) for
generous support of this work.
HRMS (m/z): [M+H]+ calcd for C23H26N3O7, 456.1771; found,
456.1790.
5,10-Dimethoxy-8-methyl-4-(2-nitrophenyl)-pyrido-[4,3-g]-
quinoline-9(8H)-one (13). Dimethyl acetal 12 (30 mg, 0.065 mmol)
was dissolved in 750 µL of ice cold H2SO4 followed by stirring at
ambient temperature for 4 h to generate the reactive aldehyde
intermediate. The acid solution containing the aldehyde was then
placed in an oil bath preheated to 150 °C and stirred at that
temperature for 10 min. The reaction was poured into 20 mL of
Supporting Information Available: General experimental
details, detailed procedures for the preparation of 3-5, 1D and 2D
NMR spectra for neoamphimedine, and 1D NMR spectra for each
intermediate. This material is available free of charge via the Internet
at http://pubs.acs.org.
JO7017813
J. Org. Chem, Vol. 72, No. 22, 2007 8505