Cancer preventive agents, Part 2: Synthesis and evaluation of 2-phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine derivatives as novel antitumor promoters

Article abstract of DOI:10.1016/j.bmc.2005.04.078

2-Phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine derivatives were synthesized and screened as potential antitumor promoters by examining the ability of the compounds to inhibit Epstein-Barr virus early antigen (EBV-EA) activation induced by the tumor p

Full text of DOI:10.1016/j.bmc.2005.04.078

Bioorganic & Medicinal Chemistry 13 (2005) 4396–4401
Cancer preventive agents, Part 2: Synthesis and evaluation
of 2-phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine
derivatives as novel antitumor promotersq
Seikou Nakamura,a Mutsuo Kozuka,a Kenneth F. Bastow,a Harukuni Tokuda,b
Hoyoku Nishino,b Madoka Suzuki,a Jin Tatsuzaki,a Susan L. Morris Natschke,a
Sheng-Chu Kuoc and Kuo-Hsiung Leea,*
aNatural Products Laboratory, School of Pharmacy, University of North Carolina, Chapel Hill, NC 27599, USA
bDepartment of Biochemistry, Kyoto Prefectural University of Medicine, Kamigyo-ku, Kyoto 602-0841, Japan
cGraduate Institute of Pharmaceutical Chemistry, China Medical University, Taichung, Taiwan
Received 10 February 2005; accepted 20 April 2005
Available online 23 May 2005
Abstract—2-Phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine derivatives were synthesized and screened as potential antitumor
promoters by examining the ability of the compounds to inhibit Epstein–Barr virus early antigen (EBV-EA) activation induced
by the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in Raji cells. Interestingly, compounds 14, 15, and 17 showed
similar inhibitory effects (89–92%, 66–69%, and 24–29% at 1000, 500, and 100 mol ratio to TPA, respectively) against EBV-EA with
potencies comparable to those of glycyrrhetic acid, a known natural antitumor-promoter.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
500, 100, and 10 mol ratio to TPA, respectively) and
cytotoxicity (ED50 values ranging from 0.001 to
0.36 lg/mL).
In the search for cancer chemopreventive agents from
natural products, many plants and plant-derived com-
pounds have been screened using the in vitro synergistic
assay for inhibitory effects on the induction of Epstein–
Barr virus early antigen (EBV-EA) by 12-O-tetradeca-
noylphorbol-13-acetate (TPA). Recently, we reported
that myricanone (1), a cyclic diarylheptanoid derived
from Myrica rubra, exhibited significant antitumor-pro-
moting activity (100%, 75%, and 24% inhibition of acti-
vation at 1000, 500, and 100 mol ratio to TPA,
respectively).1,2 In addition, we have reported that sev-
eral rotenoids showed potent antitumor-promoting
activity and cytotoxicity against neoplastic cell lines.3,4
Particularly, tephrosin (2), which has a biaryl structure
consisting of rings A and B linked by interposed C
and D rings, exhibited significant antitumor-promoting
activity (74%, 40%, and 11% inhibition of activation at
In addition, it was reported that flavone acetic acid (3,
FAA), a synthetic biaryl compound composed of rings
A and B linked by an interposed C ring, displayed
remarkable activity against marine colon adenocarci-
noma 38 and a broad spectrum of slow-growing solid tu-
mors that are usually insensitive to most cytotoxic
drugs.5,6 Xanthenone-4-acetic acid (5, XAA) has also
been shown to have an activity profile similar to that
of FAA.7,8 We have previously reported on the synthesis
and evaluation of substituted 2-phenyl-4-quinolones,
which are FAA analogues, for cytotoxicity against hu-
man tumor cell lines (HTCL).9–12 For example, 2-phen-
yl-4-quinolone-8-acetic acid (4) displayed potent
cytotoxicity, with ED50 values ranging from 0.04 to
0.44 lg/mL.9 These data prompted us to investigate
new FAA and XAA analogues as antitumor promoters
and cytotoxic agents (see Fig. 1).
Keywords: Cancer preventive agents; Antitumor-promoters; 2-Phenyl-
4-quinolones; 9-Oxo-9,10-dihydroacridines.
q For part 1 in the series, see Ref. 16.
In this study, we prepared several 2-phenyl-4-quinolone
and 9-oxo-9,10-dihydroacridine derivatives. These syn-
thetic compounds were evaluated for antitumor-pro-
*
Corresponding author. Tel.: +919 962 0066; fax: +919 966 3893;
e-mail: khlee@unc.edu
0968-0896/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmc.2005.04.078

S. Nakamura et al. / Bioorg. Med. Chem. 13 (2005) 4396–4401
4397
Figure 1. Structures of compounds 1–5.
moting activity and for in vitro cytotoxic activity against
HTCL.
15 and 16 were obtained by reacting 13 with N,N-dieth-
ylethylenediamine or b-alanine benzyl ester, respec-
tively. On the other hand, it was difficult to prepare
amide 14 directly from 11 because the intramolecular
cyclization reaction proceeded readily. Subsequent
reductive removal of the benzyl group of 16 by hydro-
genation gave the acid 17.
2. Chemistry
Scheme 1 shows the preparation of the 2-phenyl-4-
quinolone derivatives. The esters 109 and 11 were syn-
thesized by condensation of benzoylacetate with amine
8,13 which was readily prepared from commercially
available (o-nitrophenyl)acetic acid in two steps.
Hydrolysis of esters 10 and 11 under basic conditions
gave acids 49 and 12, respectively. Compound 12
smoothly underwent an intramolecular cyclization to
give 13 using standard EDCI/DMAP conditions. Com-
pound 13 was treated with N,N-dimethylethylenedi-
amine to produce amide 14. The product showed the
characteristic carbonyl carbon signal in the 13C NMR
The synthesis of 9-oxo-9,10-dihydroacridine derivatives
is outlined in Scheme 2. Compound 18 was synthesized
according to a literature method.8 Employing the same
method shown in Scheme 1 furnished 19 and 20 from
acid 18.
3. Results and discussion
2-Phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine
derivatives 4, 12–15, and 17–20 were evaluated for their
inhibitory effects on EBV-EA activation induced by
1
data and the structure of 14 was confirmed from H
NMR and mass spectral data. Similarly, compounds
Scheme 1. Reagents and conditions: (a) MeOH, concd H2SO4, reflux. (b) H2, 10% Pd–C, MeOH. (c) H2, 10% Pd–C, K2CO3, MeOH. (d)
Polyphosphoric acid (PPA), 90–100 ꢁC, 11; 12%. (E) 10% NaOH aq, EtOH, reflux, 12; 58%. (f) 1-(3-Dimethylaminopropyl)-3-ethylcarbodiimide
hydrochloride (EDCI), 4-dimethylaminopyridine (DMAP), CH2Cl2, 93%. (g) N,N-Dimethyl ethylenediamine, toluene, reflux, 14; 73%. (h) N,N-
Dimethylethylenediamine, toluene, reflux, 16; 55%. (h) H2, 10% Pd–C, MeOH, 94%.

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S. Nakamura et al. / Bioorg. Med. Chem. 13 (2005) 4396–4401
Scheme 2. Reagents and conditions: (a) (i) K2CO3, CuI, Cu, DMSO, 120 ꢁC; (ii) H2SO4, 90 ꢁC. (b) EDCI, DMAP, CH2Cl2, 73%. (c) Toluene, reflux,
83%.
Table 1. Inhibitory effects on TPA-induced EBV-EA activation
Compound
EBV-EA-positive cells (% viability)a
Compound concentration (mol ratio/32 pmol TPA)b
1000
500
100
10
IC50
4
12
10.8 (60)
17.2 (60)
15.4 (60)
8.8 (60)
7.5 (70)
8.3 (60)
15.7 (60)
19.6 (60)
11.4 (60)
7.4 (60)
33.6 (>80)
39.4 (>80)
35.2 (>80)
31.4 (>80)
30.6 (>80)
30.2 (>80)
37.2 (>80)
45.7 (>80)
35.1 (>80)
35.7 (>80)
66.1 (>80)
71.5 (>80)
64.5 (>80)
61.2 (>80)
60.9 (>80)
60.4 (>80)
69.7 (>80)
73.5 (>80)
68.4 (>80)
83.2 (>80)
100 (>80)
100 (>80)
100 (>80)
97.6 (>80)
96.6 (>80)
97.0 (>80)
100 (>80)
100 (>80)
100 (>80)
100 (>80)
452
487
460
406
405
403
480
489
456
413
13
14
15
17
18
19
20
Glycyrrhetic acidc
a Values represent relative percentage to the control value (100%). Values in parentheses represent the surviving Raji cells measured through trypan
blue staining. At least 60% surviving Raji cells 2 days after treatment with compounds is required for an accurate result.
b Mole ratio/TPA (32 pmol = 20 ng/mL), 1000 mol ratio = 32 nmol, 500 mol ratio = 16 nmol, 100 mol ratio = 3.2 nmol, and 10 mol
ratio = 0.32 nmol.
c Positive control on TPA-induced EBV-EA activation.
TPA in Raji cells as a primary screening test for anti-
tumor-promoters (Table 1).1,2,14 Glycyrrhetic acid, a
known natural antitumor promoter, was used as the
reference standard.14 In this assay, all of the com-
pounds tested showed inhibitory effects on EBV-EA
activation without cytotoxicity on Raji cells, and the
effects of 14, 15, and 17 were almost equivalent to
that of glycyrrhetic acid. In particular, compound 15
exhibited remarkable inhibitory effects (92, 69, and
29 at 1000, 500, and 100 mol ratio to TPA, respec-
tively) on EBV-EA induction. In addition, the follow-
ing conclusions were drawn: (a) The presence of an
alkyl amide moiety in the side chain, such as in com-
pounds 14, 15, and 17, is important for activity. (b)
Compared with 9-oxo-9,10-dihydroacridine 20, 2-
phenyl-4-quinolone 14 showed enhanced activity. (c)
Lactam compounds 13 and 19 showed reduced
activity.
4. Conclusion
2-Phenyl-4-quinolone and 9-oxo-9,10-dihydroacridine
derivatives, including 11 newly synthesized compounds,
were prepared and evaluated as cytotoxic agents and
antitumor promoters. Although target compounds 11–
20 were not cytotoxic against HTCL, compounds 14,
15, and 17 displayed significant antitumor-promoting
activity. Further investigation of this series of com-
pounds is ongoing in our laboratory.
5. Experimental
All chemicals and solvents were used as purchased. Melt-
ing point was measured on a Fisher–Johns melting point
1
apparatus without correction. H NMR and 13C NMR
spectra were recorded on Varian Gemini 2000
(300 MHz) NMR spectrometer with TMS as the internal
standard. All chemical shifts are reported in parts per mil-
lion. NMR spectra were referenced to the residual solvent
peak; chemical shifts d in parts per million; apparent sca-
lar coupling constants J in Hz. Mass spectral data were
obtained on a TRIO 1000 or a JEOL JMS BU-20 mass
spectrometer, respectively. IR spectra were recorded on
Perkin-Elmer 1320 spectrophotometer. Analytical thin-
Compounds 11–20 were also tested for cytotoxicity
against a HTCL panel.15 Compounds 11–16 and 18–20
were essentially inactive at 16 lg/mL, with compound
17 having the lowest mean IC50 of 4.2 0.7 lg/mL
and at least fourfold lower activity against KB-VIN,
suggesting that it was
(P-glycoprotein).
a
substrate for pgP

S. Nakamura et al. / Bioorg. Med. Chem. 13 (2005) 4396–4401
4399
layer chromatography (TLC) was carried out on Merck
precoated aluminum silica gel sheets (Kieselgel 60 F-
254). All target compounds were characterized by H
128.5, 129.9, 132.2, 143.8, 147.4, 170.6, 179.0; EI-HRMS
m/z: Calcd for C17H11NO2: M, 261.0790. Found: M+,
261.0782.
1
and IR spectral analyses and MS analyses.
5.3.2. 2H-Pyrrolo[3,2,1-de]acridine-1,6-dione (19). Start-
ing with 632 mg (2.50 mmol) of 18, EDCI (574 mg,
2.99 mmol), and DMAP (31 mg, 0.25 mmol); yield
428 mg, 73%; pale yellow powder; IR (KBr) 1743,
5.1. [2-(3-Fluorophenyl)-4-oxo-1,4-dihydroquinolin-8-
yl]acetic acid methyl ester (11)
Methyl 2-aminophenylacetate (283 mg, 1.71 mmol) was
suspended in 1.5 mL of polyphosphoric acid (PPA). The
mixture was warmed to 90–100 ꢁC, and ethyl (3-fluor-
obenzoyl)acetate (300 mg, 1.43 mmol) was added drop-
wise. The resulting mixture was further stirred for 1 h.
Water was added, then aqueous NaOH (10%) was added
slowly until pH 6 and the solution was extracted with
CHCl3. The organic layer was dried over Na2SO4 and
concentrated in vacuo. The residue was purified by silica
gel column chromatography eluting with EtOAc/n-hex-
ane = 1:1 to afford 11 (51 mg, 12%); brown amorphous
solid; IR (KBr) 3000, 1725, 1609, 1583, 1514, 1266,
1649, 1599, 1497, 1153 cmÀ1 1H NMR (CDCl3): d
;
3.96 (s, 2H, ArCH2), 7.41 (dd, 1H, J = 7.1, 8.0, Ar-H),
7.51 (ddd, 1H, J = 0.8, 7.1, 8.0, Ar-H), 7.63 (dd, 1H,
J = 0.8, 7.1, Ar-H), 7.81 (ddd, 1H, J = 1.7, 7.1, 8.5,
Ar-H), 8.18 (dd, 1H, J = 0.8, 8.0, Ar-H), 8.52 (dd, 1H,
J = 1.7, 8.0, Ar-H), 9.08 (dd, 1H, J = 0.8, 8.5, Ar-H);
ESI-MS m/z 236 (M++1).
5.4. General procedure for synthesizing target compounds
14 and 15
To a solution of 13 in toluene was added the appropriate
diamine. The reaction mixture was heated to reflux for
4 h, quenched with saturated NH4Cl aq, and extracted
with CHCl3. The extract was washed with brine, dried
over Na2SO4, and concentrated in vacuo. The residue
was purified by silica gel column chromatography elut-
ing with CHCl3 to CHCl3/MeOH = 3:1.
1
756 cmÀ1; H NMR (CDCl3): d 3.78 (s, 2H, COOCH3),
3.96 (s, 2H, ArCH2), 6.62 (d, 1H, J = 1.7, Ar-H), 7.21–
7.34 (m, 2H, Ar-H), 7.50–7.63 (m, 4H, Ar-H), 8.36 (d,
1H, J = 7.1, Ar-H), 10.20 (s, 1H, NH); ESI-MS m/z 311
(M+).
5.2. [2-(3-Fluorophenyl)-4-oxo-1,4-dihydroquinolin-8-
yl]acetic acid (12)
5.4.1. N-(2-Dimethylaminoethyl)-2-(4-oxo-2-phenyl-1,4-
dihydroquinolin-8-yl)-acetamide (14). Starting with
25 mg (0.096 mmol) of 13 and 0.5 mL N,N-dimethylethy-
lenediamine; yield 24 mg, 73%; pale yellow amorphous
solid; IR (KBr) 3177, 3007, 2901, 1628, 1603, 1575,
Acetate 11 (45 mg, 0.15 mmol) was suspended in 50%
aqueous EtOH (2 mL) containing 2 mL of aqueous
NaOH (10%). The reaction mixture was heated to reflux
for 18 h. After cooling, the solution was slowly acidified
with aqueous HCl (10%). The precipitate was collected
and washed with water to provide 12 (25 mg, 58%); yel-
1
1544, 1507, 1443, 1325, 767 cmÀ1; H NMR (CDCl3): d
2.22 [s, 6H, N(CH3)2], 2.42 (t, 2H, J = 5.8, CH2CH2N),
3.33 [dt, 2H, J = 5.8, 6.0, NHCH2CH2N, after addition
of D2O, 3.33 (t, J = 5.8)], 3.85 (s, 2H, ArCH2CO), 6.68
(s, 1H, Ar-H), 6.93 (br s, 1H, NH, D2O exchange),
7.23–7.28 (m, 1H, Ar-H), 7.45–7.59 (m, 4H, Ar-H), 7.91
(dd, 2H, J = 1.4, 8.0, Ar-H), 8.32 (dd, 1H, J = 1.1, 8.1,
Ar-H), 11.76 (br s, 1H, NH, D2O exchange); 13C NMR
(CDCl3): d 37.2, 42.6, 45.0, 57.2, 108.3, 123.2, 123.4,
125.9, 126.3, 126.8, 129.4, 130.5, 133.4, 134.7, 139.9,
150.4, 171.1, 179.0; EI-HRMS m/z: Calcd for
C21H23N3O2: M, 349.1790. Found: M+, 349.1789.
1
low amorphous solid; H NMR (DMSO-d6): d 4.11 (s,
2H, CH2), 7.30–7.46 (m, 3H, Ar-H), 7.55–7.65 (m, 2H,
Ar-H), 7.84–8.00 (m, 2H, Ar-H), 8.07 (dd, 1H, J = 1.4,
8.2, Ar-H); ESI-MS m/z 298 (M++1).
5.3. General procedure for synthesizing target compounds
13 and 19
A solution of 4 or 18 in anhydrous CH2Cl2 at room tem-
perature under argon was treated with 1-(3-dimethylami-
nopropyl)-3-ethylcarbodiimide hydrochloride (EDCI)
and 4-dimethylaminopyridine (DMAP). After 4 h, the
mixture was diluted with CH2Cl2 and washed with water
and brine, dried over Na2SO4, and concentrated in vacuo.
The residue was purified by silica gel column chromatog-
raphy eluting with CHCl3 to CHCl3/MeOH = 10:1 to af-
ford 13 or 19.
5.4.2.
N-(2-Diethylaminoethyl)-2-(4-oxo-2-phenyl-1,4-
dihydroquinolin-8-yl)-acetamide (15). Starting with
25 mg (0.096 mmol) of 13 and 0.2 mL N,N-diethylethyl-
enediamine; yield 27 mg, 75%; pale yellow amorphous so-
lid; 1H NMR (CDCl3): d 1.07 (t, 6H, J = 7.1,
CH2CH3 · 2), 2.68 (t, 4H, J = 7.1, NCH2CH3 · 2), 2.71
(t, 2H, J = 5.2, CH2CH2NEt2), 3.41 (dt, 2H, J = 5.2,
5.8, NHCH2CH3), 3.90 (s, 2H, ArCH2), 6.67 (s, 1H, Ar-
H), 7.26 (t, 1H, J = 7.6, Ar-H), 7.52–7.59 (m, 4H, Ar-
H), 7.91 (dd, 2H, J = 1.4, 7.4, Ar-H), 8.32 (dd, 1H,
J = 1.4, 8.2, Ar-H), 11.70 (br s, 1H, NH); ESI-MS m/z
378 (M++1).
5.3.1.
4-Phenyl-1H-pyrrolo[3,2,1-ij]quinoline-2,6-dione
(13). Starting with 95 mg (0.34 mmol) of 4, EDCI
(78 mg, 0.41 mmol), and DMAP (4 mg, 0.034 mmol);
yield 83 mg, 93%; pale yellow powder; mp 224.0–
226.0 ꢁC (CHCl3–MeOH–n-hexane); IR (KBr) 1772,
1639, 1606, 1492, 1406, 1384, 1186 cmÀ1
;
1H NMR
5.5. 3-[2-(4-Oxo-2-phenyl-1,4-dihydroquinolin-8-yl)-ace-
tylamino]propionic acid benzyl ester (16)
(CDCl3): d 3.93 (s, 2H, ArCH2), 6.30 (s, 1H, Ar-H),
7.41–7.51 (m, 6H, Ar-H), 7.61 (dd, 1H, J = 0.8, 7.1, Ar-
H), 8.12 (d, 1H, J = 8.0, Ar-H); 13C NMR (CDCl3): d
36.5, 118.4, 122.1, 123.5, 123.6, 125.8, 127.3, 128.0,
To a solution of 13 (50 mg, 0.191 mmol) of toluene
(2 mL) were added b-alanine benzyl ester p-toluenesulf-

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S. Nakamura et al. / Bioorg. Med. Chem. 13 (2005) 4396–4401
onate salt (202 mg, 0.574 mmol) and Et3N (0.08 mL,
0.574 mmol). The reaction mixture was refluxed for 4 h
and concentrated in vacuo. The residue was diluted with
CHCl3 and washed with water and brine, dried over
Na2SO4, and concentrated in vacuo. The crude product
was purified by silica gel column chromatography elut-
ing with CHCl3/MeOH = 50:1 to afford 16 (46 mg,
55%); white powder; IR (KBr) 3228, 3064, 1734, 1629,
acid (4 mM, inducer), TPA (32 pM), and various
amounts of test compounds dissolved in 5 lL DMSO.
Smears were made from the cell suspension. The EBV-
EA inducing cells were stained with high titer EBV-
EA-positive serum from NPC patients and detected by
an indirect immunofluorescence technique. In each as-
say, at least 500 cells were counted, and the number of
strained cells (positive cells) was recorded. Triplicate as-
says were performed for each data point. The EBV-EA
inhibitory activity of the test compounds was expressed
by comparison with that of the positive control experi-
ment (100%), which was carried out with n-butyric acid
(4 mM) plus TPA (32 nM). In the experiments, the
EBV-EA induction was normally around 35%, and this
value was taken as the positive control (100%). n-Butyric
acid (4 mM) alone induced 0.1% EA-positive cells. The
viability of treated Raji cells was assayed by the try-
pan-blue staining method.
1
1580, 1512, 1171, 753 cmÀ1; H NMR (CDCl3): d 2.60
(t, 2H, J = 6.0, CH2CH2COOBn), 3.56 (dt, 2H,
J = 6.0, 6.0, NHCH2CH2), 3.85 (s, 2H, ArCH2CONH),
5.08 (s, 2H, COOCH2Ar), 6.68 (d, 1H, J = 1.7, Ar-H),
7.21 (dd, 1H, J = 7.1, 8.0, Ar-H), 7.26–7.36 (m, 4H,
Ar-H), 7.42 (dd, 1H, J = 1.4, 7.1, Ar-H), 7.51–7.58 (m,
4H, Ar-H), 7.88–7.91 (m, 2H, Ar-H), 8.32 (dd, 1H,
J = 1.4, 8.0, Ar-H), 11.82 (s, 1H, NH); ESI-MS m/z
441 (M++1).
5.6. 3-[2-(4-Oxo-2-phenyl-1,4-dihydroquinolin-8-yl)-ace-
tylamino]propionic acid (17)
5.9. Cytotoxicity assay
A solution of 16 (40 mg, 0.09 mmol) in MeOH (20 mL)
at room temperature under argon was treated with
40 mg Pd–C (10%) and placed under hydrogen
(30 psi). The mixture was shaken in a Parr apparatus
for 15 h and then the content was filtered to remove
the catalyst and evaporated to dryness in vacuo to give
17 (30 mg, 94%); pale yellow amorphous solid; 1H NMR
(DMSO-d6): d 2.40 (t, 2H, J = 6.0, CH2CH2COOH),
3.27 (dt, 2H, J = 6.0, 6.0, NHCH2CH2), 3.98 (s, 2H,
ArCH2), 6.47 (s, 1H, Ar-H), 7.28–7.34 (m, 1H, Ar-H),
7.56–7.61 (m, 3H, Ar-H), 7.96–8.00 (m, 1H, Ar-H),
8.04 (d, 1H, J = 8.2, Ar-H), 8.10–8.20 (m, 1H, Ar-H),
8.72–8.78 (m, 1H, Ar-H); ESI-MS m/z 351 (M++1).
The in vitro cytotoxicity assay was carried out according
to procedures described by Rubinstein et al.15 The hu-
man tumor cell line panel consists of ovarian carcinoma
(1A9), lung carcinoma (A549), breast cancer (MCF-7),
epidermoid carcinoma of nasopharyngeal cancer (KB),
and multi-drug resistant KB subclone expressing P-gly-
coprotein (KB-Vin).
Acknowledgment
This investigation was supported in part by a grant from
the National Cancer Institute (CA 17625) awarded to K.
H. Lee.
5.7. N-(2-Dimethylaminoethyl)-2-(9-oxo-9,10-dihydroac-
ridin-4-yl)-acetamide (20)
References and notes
To a solution of 19 (50 mg, 0.213 mmol) of toluene
(4 mL) was added 0.1 mL N,N-dimethylethylenedi-
amine. The reaction mixture was refluxed for 7 h and
concentrated in vacuo. The residue was filtered with
CHCl3/MeOH and the filtrate was evaporated to dry-
ness in vacuo. The product was collected and washed
with EtOAc to provide 20 (57 mg, 83%); pale yellow
amorphous solid; 1H NMR (CDCl3): d 2.22 [s, 6H,
N(CH3)2], 2.41 [t, 2H, J = 5.8, CH2CH2N(CH3)2], 3.33
[dt, 2H, J = 5.8, 6.3, NHCH2CH2N(CH3)2, after addi-
tion of D2O, 3.33 (t, J = 5.8)], 3.85 (s, 2H, ArCH2),
6.67 (br s, 1H, NH, D2O exchange), 7.19 (dd, 1H,
J = 7.1, 8.2, Ar-H), 7.24–7.29 (m, 1H, Ar-H), 7.49–
7.52 (m, 2H, Ar-H), 7.66 (ddd, 1H, J = 1.4, 6.9, 8.2,
Ar-H), 8.45 (br d, 2H, J = 8.2, Ar-H), 11.86 (br s, 1H,
NH, D2O exchange); ESI-MS m/z 324 (M++1).
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