Synthesis of C8-C8/C2-C8-linked triazolo pyrrolobenzodiazepine dimers by employing 'click' chemistry and their DNA-binding affinity

Article abstract of DOI:10.1016/j.tetlet.2008.04.006

A series of 1,2,3-triazole-containing pyrrolo[2,1-c][1,4]benzodiazepine dimers have been prepared efficiently by employing a 'click' chemistry protocol. This method involves 1,3-dipolar cycloaddition of terminal alkynes with organic azides using a Cu(I)-c

Full text of DOI:10.1016/j.tetlet.2008.04.006

Available online at www.sciencedirect.com
Tetrahedron Letters 49 (2008) 3620–3624
Synthesis of C8–C8/C2–C8-linked triazolo pyrrolobenzodiazepine
dimers by employing ‘click’ chemistry and their DNA-binding affinity
Ahmed Kamal *, S. Prabhakar, N. Shankaraiah, Ch. Ratna Reddy, P. Venkat Reddy
Chemical Biology Laboratory, Division of Organic Chemistry, Indian Institute of Chemical Technology, Hyderabad 500 007, India
Received 12 February 2008; revised 27 March 2008; accepted 1 April 2008
Available online 4 April 2008
Abstract
A series of 1,2,3-triazole-containing pyrrolo[2,1-c][1,4]benzodiazepine dimers have been prepared efficiently by employing a ‘click’
chemistry protocol. This method involves 1,3-dipolar cycloaddition of terminal alkynes with organic azides using a Cu(I)-catalyst.
Further, these molecules exhibited interesting DNA-binding affinity profiles.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Pyrrolo[2,1-c][1,4]benzodiazepines; 1,2,3-Triazoles; DNA-binding affinity; ‘Click’ chemistry
DNA interstrand cross-linking agents have attracted the
attention of many researchers because of their potent anti-
cancer activity as exhibited in most compounds with a pyr-
rolobenzodiazepine (PBD) ring system.1 There has been
considerable interest in the past few years in the design
and synthesis of symmetrical and unsymmetrical cross-
linking agents, particularly those based on PBDs.2 In the
literature, a number of PBD dimers have been designed
and synthesized that exhibit varying degrees of cytotoxicity
and DNA cross-linking activity.3 The PBD antitumor anti-
biotics are produced by various Streptomyces species and
are generally referred to as the anthramycin family, which
comprise of representative members including DC-81 (1),
anthramycin, tomaymycin, and chicamycin. These PBD
dimers are linked through different positions such as A-
C7/A-C70, A-C8/A-C80, and C-C2/C-C20, among these A-
C8/A-C8-linked PBD dimers have shown promising cyto-
toxicity and efficient cross-linking properties. Further,
extensive studies have been carried out on both the solu-
tion4 and solid-phase5 synthesis of PBDs, and a sound
understanding of structure–activity relationships within
the family has been developed.6 In a recent development,
Thurston and co-workers7 tethered two DC-81 units at
the C8-positions8 by using different alkane spacers to give
bisfunctional–alkylating agents capable of cross-linking
DNA. One of these dimers, DSB-120 2a, forms an irrevers-
ible interstrand cross-link between two guanine bases
within the minor groove of DNA via their exocyclic N2
atoms and spans six base pairs, thereby actively recogniz-
ing a central 50-GATC sequence.9 Moreover, in this labora-
tory, mixed imine–amide PBD dimers such as 2b have been
designed and synthesized which shows efficient DNA bind-
ing ability with significant anticancer activity in a number
of human cancer cell lines.10 In continuation of these efforts
toward the design and synthesis of nitrogen-rich PBD
dimer analogues, as well as the development of new syn-
thetic strategies,11 we became interested in exploring the
DNA-binding ability of C8–C8/C2–C8-linked 1,2,3-tri-
azole-containing PBD dimers (Fig. 1).
1,2,3-Triazoles are heterocycles with a wide range of
applications that are receiving growing attention in biolog-
ical activity studies and are employed widely as pharma-
ceuticals and agrochemicals.12 Earlier studies have
revealed that the azole group due to the aromaticity and
lone-pair electrons provides great potential for several
*
Corresponding author. Tel.: +91 40 27193157; fax: +91 40 27193189.
E-mail addresses: ahmedkamal@iict.res.in, ahmedkamal@iictnet.org
(A. Kamal).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.04.006

A. Kamal et al. / Tetrahedron Letters 49 (2008) 3620–3624
3621
10
9
A
6
11
N
HO
N
N
O
O
H
H
H
8
B11a
1
C
7
N
H3CO
N
N
5
2
OCH3 H3CO
4
3
O
O
O
2a
1
H
N
O
H
N
O
O
H
N
N
OCH3 H3CO
O
O
2b
R1
N
H
N
N
N
N
O
H
N
O
N
R2
H
O
N
N
N
n
N
O
H
O
O
N
OCH3
H3CO
N
N
H3CO
O
4a; R1, R2 = H
4b; R1, R2 = OCH3
4c; R1 = OBn, R2 = OCH3
3a; n = 3
3b; n = 4
3c; n = 5
3d; n = 6
3e; n = 8
Fig. 1. Chemical structures of DC-81 (1), DSB-120 (2a), imine-amide PBD dimer (2b), and 1,2,3-triazole-PBD dimer analogues (3a–e and 4a–c).
applications. Interestingly, the in situ generated triazole
unit is revealed as a very active pharmacophore instead
of a passive linker.13a Furthermore, dimerization of biolog-
ically useful molecules having a triazole moiety can take
place easily.13b In recent years, alkylating agents have been
studied extensively with regard to cancer chemotherapy,
and this has led to the development of many new and more
selective alkylating agents including molecules that are
based on the triazole moiety.14 The conventional route to
1,2,3-triazoles is the Huisgen dipolar cycloaddition of
alkynes with organic azides.15 This process provides bio-
logically diverse molecules in a single-step and is also an
example of ‘click’ chemistry. In this connection, we herein
report a new class of C8–C8/C2–C8-linked pyrrolo[2,1-c]-
[1,4]benzodiazepine dimers that are linked through 1,2,3-
triazoles units, which are prepared by employing the ‘click’
reaction. Moreover, one of compound 3d has shown
enhanced DNA binding ability compared to the previously
reported PBD dimer, DSB-120.
reduction employing DIBAL-H and protection with
TMSCl/EtSH followed by deprotection using BF3ꢀOEt2/
EtSH gave sulfide 6. The etherification of 6 with propargyl
bromide in the presence of K2CO3 afforded the required
intermediate 7 in excellent yield (93%) as shown in
Scheme 1.
The synthesis of the other starting substrates 8a–e was
accomplished using the similar procedures. Etherification
of compound 6 with various dibromoalkanes followed by
azidation with NaN3 gave azides 8a–e. Alkyne 7 and azides
8a–e underwent the ‘click’ reaction in the presence of Cu(I)
catalyst (1 mol %) and sodiumascorbate (5 mol %) to afford
1,2,3-triazole-containing PBD intermediates 9a–e. Next,
9a–e were reduced with SnCl2ꢀ2H 2O followed by deprotec-
tion with HgCl2/CaCO3 to give the target molecules 3a–e17
in good yields as depicted in Scheme 2.
We next turned our attention to the exploration of
the diversity at the C2-position. The C2–C8-linked tri-
azole-containing PBD dimers 4a–c were thus prepared by
employing substrates 11a–c , which were prepared using a
reported method.18 Thus, mesylation of the C2-hydroxy
group of 11a–c followed by azidation via SN2 reaction with
NaN3 afforded azides. These upon selective reduction with
DIBAL-H followed by protection with TMSCl/EtSH gave
The synthesis of these 1,2,3-triazole-containing C8–C8-
linked PBD dimers 3a–e was carried out by employing
the (2S)-N-[4-benzyloxy-5-methoxy-2-nitrobenzoyl]proline
methyl ester (5), which was obtained according to the liter-
ature method starting from vanillin.16 This, upon selective
NO2
NO2
NO2
CH(SEt)2
BnO
COOCH3
HO
O
CH(SEt)2
iv
i, ii, iii
N
N
N
H3CO
H3CO
H3CO
O
O
O
5
6
7
Scheme 1. Reagents and conditions: (i) DIBAL-H, dry CH2Cl2, ꢁ78 °C, 1 h, 72%; (ii) TMSCl/EtSH, dry CH2Cl2, rt, 12 h, 92%; (iii) BF3ꢀOEt2/EtSH, dry
CH2Cl2, rt, 12 h, 85%; (iv) K2CO3, propargyl bromide, dry DMF, rt, 12 h, 93%.

3622
A. Kamal et al. / Tetrahedron Letters 49 (2008) 3620–3624
R1
R2
O2N
OH
OCH3
(EtS)2HC
NO2
N
COOCH3
OH
N
O
6
11a; R1, R2 = H
O
11b; R1, R2 = OCH3
11c; R1 = OBn, R2 = OCH3
i, ii
i, ii, iii, iv
R1
R2
NO2
CH(SEt)2
NO2
O2N
O
H3CO
CH(SEt)2
O
n
N3
(EtS)2HC
+
N
+
N3
NO2
O
CH(SEt)2
N
O
N
OCH3
12a-c
7
O
O
N
H3CO
"Click" Reaction
8a-e
iii
"Click Reaction"
O
7
R1
R2
v
NO2
CH(SEt)2
N
N
N
NO
O
O2N
2 CH(SEt)2
N
O
N
(EtS)2HC
N
N
n
O
O
NO
2 CH(SEt)2
N
H3CO
N
OCH3
9a-e
13a-c
O
O
iv
N
H3CO
vi
N
O
N
N
n
R1
R2
NH2
CH(SEt)2
NH
O
H2N
2 CH(SEt)2
O
(EtS)2HC
N
N
N
H3CO
N
OCH3
10a-e
N
N
O
O
O
O
NH
2 CH(SEt)2
v
14a-c
H3CO
vii
N
3a; n = 3
3b; n = 4
3c; n = 5
3d; n = 6
3e; n = 8
O
4a; R1, R2 = H
Scheme 2. Reagents and conditions: (i) K2CO3, dibromo alkane spacers,
dry DMF, rt, 12 h, 88%; (ii) NaN3 (0.5 M in DMSO), 80 °C, 4 h, 83–90%;
(iii) CuSO4ꢀ5H2O (1 mol %), sodium ascorbate (5 mol %), t-BuOH/H2O
(1:1), rt, 12 h, 82–88%; (iv) SnCl2ꢀ2H2O, MeOH, reflux, 6 h, 80%; (v)
HgCl2–CaCO3, CH3CN–H2O (4:1), rt, 12 h.
4b; R1, R2 = OCH3
4c; R1 = OBn, R2 = OCH3
Scheme 3. Reagents and conditions: (i) mesyl chloride, Et3N, CH2Cl2, 0
°C–rt, 6 h, 88%; (ii) NaN3, dry DMF, 50–60 °C, 6 h, 82–90%; (iii)
DIBAL-H, dry CH2Cl2, ꢁ78 °C, 1 h, 78%; (iv) TMSCl/EtSH, dry CH2Cl2,
rt, 12 h, 92%; (v) CuSO4ꢀ5H2O (1 mol %), sodium ascorbate (5 mol %),
t-BuOH/H2O (1:1), rt, 12 h, 78–85%; (vi) SnCl2ꢀ2H 2O, MeOH, reflux,
6 h, 78%; (vii) HgCl2–CaCO3, CH3CN–H2O (4:1), rt, 12 h.
12a–c , which were subjected to cycloaddition with 7 by
employing the ‘click’ chemistry protocol to produce tri-
azoles 13a–c . The reduction of 13a–c followed by deprotec-
tive cyclization gave the required dimers 4a–c17 in good
yields (72–78%) as illustrated in Scheme 3.
illustrates the significant effect of introducing the 1,2,3-tri-
azole moiety between the two DC-81 PBD subunits
through different alkane spacers. Further, it was interesting
to observe that as the linker chain increased from three to
four carbons, there was a decrease in the DNA-binding
ability, while on further increase from five to six carbons
in the chain, DNA stabilization was enhanced, as in the
case of 3d. Further, increase in the chain length up to eight
carbons led to a decline in the DNA-binding ability, as in
the case of 3e. These results indicate that the incorporation
of a 1,2,3-triazole moiety in the alkane spacer enhances the
DNA-binding ability, particularly in the case of 3d (Table
1). The length of the linker and the triazole moiety may
play an important role in the DNA-binding ability. Fur-
thermore, the C2–C8-linked 1,2,3-triazole PBD dimer of
compound 4b showed a noticeable DTm, that is, 3.9 °C at
The DNA-binding ability of C8–C8/C2–C8-linked
1,2,3-triazole-PBD dimers 3a–e and 4a–c was examined
by thermal denaturation studies19 using calf thymus (CT)
DNA at pH 7.0, with incubation at 37 °C, and DNA/ligand
molar ratios of 5:1. The increase in the helix melting tem-
perature (DTm) for each compound was examined after 0
and 18 h of incubation at 37 °C. Further, the data for com-
pounds 1 and 2 are included in Table 1 for comparison.
1,2,3-Triazole-containing PBD dimers showed DTm values
ranging from 0.9 to 18.7 °C (Table 1). Interestingly, com-
pound 3d elevates the helix melting temperature of CT-
DNA to 18.7 °C after incubation at 37 °C for 18 h. Natu-
rally occurring DC-81 (1) shows a DTm of 0.7 °C, whereas
synthetic DC-81 dimer 2 (DSB-120) exhibits a DTm of
15.1 °C under similar experimental conditions. This result

A. Kamal et al. / Tetrahedron Letters 49 (2008) 3620–3624
3623
Table 1
Chem. Soc. 1992, 114, 4939–4941; (d) Wilson, S. C.; Howard, P. W.;
Forrow, S. M.; Hartley, J. A.; Adams, L. J.; Jenkins, T. C.; Kelland,
L. R.; Thurston, D. E. J. Med. Chem. 1999, 42, 4028–4041; (e) Reddy,
B. S. P.; Damayanthi, Y.; Reddy, B. S. N.; Lown, W. J. Anti-Cancer
Drug Des. 2000, 15, 225–238; (f) Gregson, S. J.; Howard, P. W.;
Thurston, D. E. Bioorg. Med. Chem. Lett. 2003, 13, 2277–2280.
4. (a) Kamal, A.; Shankaraiah, N.; Devaiah, V.; Reddy, K. L.; Juvekar,
A.; Sen, S.; Kurian, N.; Zingde, S. Bioorg. Med. Chem. Lett. 2008, 18,
1468–1473; (b) Kamal, A.; Shankaraiah, N.; Markandeya, N.; Reddy,
K. L.; Reddy, S. Ch. Tetrahedron Lett. 2008, 49, 1465–1468; (c)
Kamal, A.; Shankaraiah, N.; Reddy, K. L.; Devaiah, V.; Juvekar, A.;
Sen, S. Lett. Drug Des. Discovery 2007, 4, 596–604; (d) Kamal, A.;
Khan, N. A.; Reddy, K. S.; Ahmed, S. K.; Kumar, M. S.; Juvekar, A.;
Sen, S.; Zingde, S. Bioorg. Med. Chem. Lett. 2007, 17, 5345–5348; (e)
Kamal, A.; Ramu, R.; Venkatesh, T.; Khanna, R. G. B.; Barkume,
M. S.; Juvekar, A.; Zingde, S. Bioorg. Med. Chem. 2007, 17, 6868–
6875; (f) Kamal, A.; Reddy, D. R. S.; Reddy, P. S. M. M. Bioorg.
Med. Chem. Lett. 2006, 16, 1160–1163; (g) Kamal, A.; Devaiah, V.;
Reddy, K. L.; Kumar, M. S. Bioorg. Med. Chem. 2005, 13, 2021–
2029; (h) Kamal, A.; Reddy, K. L.; Devaiah, V.; Shankaraiah, N.;
Kumar, M. S.; Reddy, G. S. K. Lett. Drug Des. Discovery 2005, 1,
55–61;.
Thermal denaturation data for C8–C8/C2–C8-linked 1,2,3-triazole-con-
taining PBD dimers (3a–e and 4a–c) with calf thymus CT-DNA
PBD dimers [PBD]/[DNA]
molar ratioa
DTm (°C)b After incubation at 37 °C for
0 h
18 h
3a
3b
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
1:5
5.5
2.0
4.8
11.3
3.8
9.8
3c
3d
11.9
7.1
0.9
18.7
13.9
2.5
3e
4a
4b
4c
3.9
5.9
1.5
4.8
DC-81
DSB-120
a
0.3
0.7
10.2
15.1
For CT-DNA alone at pH 7.00 0.01, Tm = 69.6 °C 0.01 (mean
value from 10 separate determinations), all Tm values are 0.05–0.1 °C.
b
For a 1:5 molar ratio of [PBD]/[DNA], where CT-DNA concentra-
tion = 100 lM and ligand concentration = 20 lM in aqueous sodium
phosphate buffer [10 mM sodium phosphate + 1 mM EDTA, pH
7.00 0.01].
5. (a) Kamal, A.; Reddy, K. L.; Devaiah, V.; Shankaraiah, N.; Reddy,
D. R. S. Mini-Rev. Med. Chem. 2006, 6, 53–68; (b) Kamal, A.; Reddy,
K. L.; Devaiah, V.; Shankaraiah, N.; Reddy, G. S. K.; Raghavan, S.
J. Comb. Chem. 2007, 9, 29–42; (c) Kamal, A.; Shankaraiah, N.;
Devaiah, V.; Reddy, K. L. Tetrahedron Lett. 2006, 47, 6553–6556; (d)
Kamal, A.; Shankaraiah, N.; Reddy, K. L.; Devaiah, V. Tetrahedron
Lett. 2006, 47, 4253–4257; (e) Kamal, A.; Reddy, K. L.; Devaiah, V.;
Shankaraiah, N. Synlett 2004, 1841–1843.
0 h while the melting temperature increased to 5.9 °C upon
incubation for 18 h at 37 °C. The C2–C8-linked triazole
PBD dimers have shown appreciable affinity; however,
the binding ability is not that significant, probably due to
the structural rigidity at C2 of the PBD subunit.
6. Kamal, A.; Rao, M. V.; Laxman, N.; Ramesh, G.; Reddy, G. S. K.
Curr. Med. Chem.—Anti-Cancer Agents 2002, 2, 215–254.
In conclusion, the synthesis of a new class of C8–C8/
7. Bose, D. S.; Thompson, A. S.; Ching, J. A.; Hartley, J. A.; Berardini,
M. D.; Jenkins, T. C.; Neidle, S.; Hurley, L. H.; Thurston, D. E. J.
Am. Chem. Soc. 1992, 114, 4939–4941.
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J. A.; Jenkins, T. C.; Neidle, S.; Thurston, D. E. J. Chem. Soc., Chem.
Commun. 1992, 1518–1520.
C2–C8-linked
1,2,3-triazole-containing
pyrrolo[2,1-c]
[1,4]benzodiazepine dimers has been demonstrated through
‘click’ chemistry. These compounds have been evaluated
for their DNA-binding affinity using DNA thermal dena-
turation studies. Representative dimer 3d has shown signif-
icant DNA-binding ability. Detailed studies on the
mechanistic aspects, and anticancer activity and molecular
modeling investigations on these dimers are in progress.
9. Smellie, M.; Kelland, L. R.; Thurston, D. E.; Souhami, R. L.;
Hartley, J. A. Brit. J. Cancer 1994, 70, 48–53.
10. (a) Kamal, A.; Ramesh, G.; Laxman, N.; Ramulu, P.; Srinivas, O.;
Neelima, K.; Kondapi, A. K.; Srinu, V. B.; Nagarajaram, H. A. J.
Med. Chem. 2002, 45, 4679–4688; (b) Kamal, A.; Ramesh, G.;
Srinivas, O.; Ramulu, P.; Laxman, N.; Rehana, T.; Deepak, M.;
Achary, M. S.; Nagarajaram, H. A. Bioorg. Med. Chem. 2004, 12,
5427–5436; (c) Kamal, A.; Reddy, P. S. M. M.; Reddy, D. R. S.
Bioorg. Med. Chem. Lett. 2004, 14, 2669–2672; (d) Kamal, A.;
Srinivas, O.; Ramulu, P.; Ramesh, G.; Kumar, P. P. Bioorg. Med.
Chem. 2004, 14, 4107–4111.
11. (a) Kamal, A.; Laxman, N.; Ramesh, G.; Neelima, K.; Kondapi, A.
K. Chem. Commun. 2001, 437–438 ; (b) Kamal, A.; Reddy, K. L.;
Devaiah, V.; Shankaraiah, N. Synlett 2004, 2533–2536; (c) Kamal, A.;
Devaiah, V.; Reddy, K. L.; Shankaraiah, N. Adv. Synth. Catal. 2006,
348, 249–254.
12. (a) Hardman, J.; Limbird, L.; Gilman, A. Goodman and Gilman’s The
Pharmacological Basis of Therapeutics, 9th ed.; McGraw-Hill: New
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Acknowledgment
The authors S.P.R., N.S. Ch.R.R., and P.V.R. are grate-
ful to the CSIR, New Delhi, for the award of Research
fellowships.
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Chem. 2001, 44, 737–748; (b) Gregson, S. J.; Howard, P. W.;
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3624
A. Kamal et al. / Tetrahedron Letters 49 (2008) 3620–3624
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1020.7; 871.5; 786.4. 1H NMR (200 MHz, CDCl3): d 7.66 (dd, 2H,
J = 1.16, 2.57 Hz); 7.50 (d, 2H, J = 3.49 Hz); 6.98 (s, 1H); 6.79 (s,
2H); 5.30 (s, 2H); 4.30–4.37 (t, 2H, J = 7.18 Hz); 3.99–4.09 (m, 2H);
3.92 (s, 6H); 3.70–3.83 (m, 4H); 3.50–3.63 (m, 2H); 2.27–2.37 (m, 4H);
2.01–2.11(m, 2H); 1.82–1.88 (m, 4H); 1.25–1.35 (m, 10H); 13C NMR
(150 MHz, CDCl3): 164.6; 164.4; 162.5; 162.4; 159.2; 150.7; 143.2;
140.5; 140.4; 123.1; 123.0; 119.9; 111.5; 111.3; 110.2; 68.8; 62.8; 62.2;
56.3; 56.2; 50.4; 46.9; 46.8; 33.3; 32.2; 30.1; 29.6; 29.5; 29.3; 29.0; 28.8;
28.7; 26.3; 25.7. FABMS: m/z 684 [M+ +H]; HRMS calcd For
16. Thurston, D. E.; Murthy, V. S.; Langley, D. R.; Jones, G. B.
Synthesis 1990, 81–84.
17. Spectral data: Compound 3a: Yield: 72%; FT-IR: cmꢁ1 2928.3;
1655.3; 1613.1; 1505.5; 1463.1; 1431.5; 1260.7; 1220.2; 1134.7; 1020.7;
871.5; 786.4. 1H NMR (200 MHz, CDCl3):
d 7.60 (d, 2H,
J = 3.47 Hz); 7.45 (s, 2H); 6.90 (s, 1H); 6.69 (s, 1H); 5.22 (s, 2H);
4.51–4.57 (m, 4H); 3.91–4.06 (m, 2H); 3.87 (s, 6H); 3.47–3.80 (m, 6H);
2.35–2.43 (m, 2H); 2.20–2.26 (m, 3H); 1.88–2.05 (m, 4H); FABMS:
m/z 613 [M++H]. HRMS calcd For C32H35N7O6 [M++H] 613.3042,
found 613.3036. Compound 3b: Yield: 68%; FT-IR: cmꢁ1 2927.3;
1655.3; 1613.1; 1505.5; 1463.1; 1431.5; 1260.7; 1220.2; 1134.7; 1020.7;
C
37H45N7O6 [M+ +H] 684.3044, found 684.3036. Compound 4a:
Yield: 78%; FT-IR: cmꢁ1 2998.5; 1693.1; 1636.1; 1505.5; 1463.1;
1431.5; 1260.7; 1220.2; 1134.7; 1020.7; 871.5; 756.4. 1H NMR (300
MHz, CDCl3): d 7.63–7.70 (m, 3H); 7.52 (d, 2H, J = 2.80 Hz); 7.34 (d,
2H, J = 3.15 Hz); 6.92–7.00 (m, 2H); 5.31 (s, 2H); 5.10–5.29 (m, 2H);
4.23–4.30 (m, 1H); 3.91 (s, 3H); 3.77–3.88 (m, 2H); 3.70–3.74 (m, 2H);
3.52–3.61 (m, 2H); 2.62–2.83 (m, 2H); 2.30–2.32 (m, 2H). FABMS:
m/z 526 [M++H]; HRMS calcd for C28H28N7O4 [M++H] 526.2202,
found 526.2212. Compound 4b: Yield: 76%; FT-IR: cmꢁ1 2998.3;
1693.3; 1636.1; 1505.5; 1463.1; 1431.5; 1260.7; 1220.2; 1134.7; 1020.7;
871.5; 786.4; 647.5. 1H NMR (300 MHz, CDCl3): d 7.63–7.69 (dd,
2H, J = 4.38, 4.11 Hz); 7.53 (d, 1H, J = 5.11 Hz); 6.99 (s, 2H); 6.84 (s,
2H); 5.33 (s, 2H); 4.27–4.31 (m, 2H); 4.00 (d, 1H, J = 4.03 Hz); 3.96
(s, 3H); 3.94 (s, 3H); 3.92 (s, 3H); 3.83–3.86 (m, 2H); 2.29–2.36 (m,
4H); 2.01–2.11 (m, 4H). FABMS: m/z 586 [M++H]; HRMS calcd for
871.5; 786.4. 1H NMR (400 MHz, CDCl3):
d 7.68 (d, 2H,
J = 4.50 Hz); 7.51 (s, 2H); 7.00 (s, 1H); 6.80 (s, 2H); 5.31 (s, 2H);
4.46–4.56 (m, 2H); 4.04–4.16 (m, 2H); 3.92 (s, 6H); 3.79–3.88 (m, 2H);
3.69–3.74 (m, 4H); 3.54–3.60 (m, 2H); 2.32 (m, 4H); 2.04–2.17 (m,
4H); 1.85–1.90 (m, 1H); 1.59–1.67 (m, 1H). FABMS: m/z 628 [M+
+H]. HRMS calcd For C33H37N7O6 [M+ +H] 628.3034, found
628.3040. Compound 3c: Yield: 75%; FT-IR: cmꢁ1 2926.9; 1655.3;
1608.2; 1505.5; 1463.1; 1431.5; 1260.7; 1220.2; 1134.7; 1020.7; 871.7;
787.4. 1H NMR (300 MHz, CDCl3): d 7.68 (t, 1H, J = 4.26 Hz); 7.51
(d, 2H, J = 4.62 Hz); 6.99 (s, 2H); 6.78 (s, 2H); 5.31 (s, 2H); 4.37–4.41
(m, 2H); 4.00–4.11 (m, 2H); 3.93 (s, 6H); 3.78–3.86 (m, 2H); 3.70–3.75
(m, 2H); 3.53–3.62 (m, 4H); 2.29–2.34 (m, 4H); 1.89–2.10 (m, 6H);
1.52–1.60 (m, 2H). FABMS: m/z 642 [M+ +H]; HRMS calcd for
C
30H32N7O6 [M+ +H] 586.2414, found 586.2438. Compound 4c:
Yield: 72%; FT-IR: cmꢁ1 2928.3; 1655.3; 1613.1; 1505.5; 1463.1;
1431.5; 1260.7; 1220.2; 1134.7; 1020.7; 871.5; 770.4; 690.5. 1H NMR
(400 MHz, CDCl3): d 7.67 (d, 2H, J = 4.61 Hz); 7.51–7.58 (m, 7H);
7.37 (s, 1H); 6.92 (s, 2H); 5.32 (s, 2H); 5.11–5.29 (m, 2H); 4.21–4.29
(m, 1H); 3.92 (s, 3H); 3.89 (s, 3H); 3.74–3.85 (m, 2H); 3.70–3.74 (m,
2H); 3.49–3.58 (m, 2H); 2.62–2.78 (m, 2H); 2.33–2.01 (m, 4H).
FABMS: m/z 662 [M++H]. HRMS calcd for C36H35N7O6 [M++H]
662.2422, found 586.2434.
C
34H39N7O6 [M+ +H] 642.3040, found 642.3034. Compound 3d:
Yield: 73%; FT-IR: cmꢁ1 2928.3; 1655.3; 1613.1; 1505.5; 1463.1;
1431.5; 1260.7; 1220.2; 1134.7; 1020.7; 871.5; 786.4. 1H NMR
(400 MHz, CDCl3): d 7.67–7.74 (d, 2H, J = 6.34 Hz); 7.39–7.41 (m,
3H); 6.49–6.54 (m, 2H); 5.32 (s, 2H); 4.34–4.49 (m, 2H); 4.05 (d, 2H
J = 5.39 Hz); 3.88 (s, 6H); 3.72–3.82 (m, 4H); 3.56–3.63 (m, 4H); 2.73
(m, 2H); 2.28–2.35 (m, 2H); 1.93–2.01 (m, 8H); 1.77–1.83 (m, 2H).
FABMS: m/z 656 [M++H]; HRMS calcd for C35H31N7O6 [M++H]
656.3040, found 656.3034. Compound 3e: Yield: 78%; FT-IR: cmꢁ1
2928.3; 1655.3; 1613.1; 1505.5; 1463.1; 1431.5; 1260.7; 1220.2; 1134.7;
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