Synthesis of novel ageladine A analogs showing more potent matrix metalloproteinase (MMP)-12 inhibitory activity than the natural product

Article abstract of DOI:10.1016/j.bmcl.2009.07.099

By employing a previously established synthetic scheme, the synthesis described in the title was carried out in order to explore the substituent effects in the pyrrole ring of ageladine A on MMP-12 inhibitory activity. It became evident that a halogen ato

Full text of DOI:10.1016/j.bmcl.2009.07.099

Bioorganic & Medicinal Chemistry Letters 19 (2009) 5461–5463
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Bioorganic & Medicinal Chemistry Letters
journal homepage: www.elsevier.com/locate/bmcl
Synthesis of novel ageladine A analogs showing more potent matrix
metalloproteinase (MMP)-12 inhibitory activity than the natural product
b
Naoki Ando a, , Shiro Terashima
*
a Discovery Research Laboratories, Kyorin Pharmaceutical Co., Ltd, 2399-1, Nogi, Nogi-machi, Shimotsuga-gun, Tochigi 329-0114, Japan
b Sagami Chemical Research Center, Hayakawa 2743-1, Ayase, Kanagawa 252-1193, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
By employing a previously established synthetic scheme, the synthesis described in the title was carried
out in order to explore the substituent effects in the pyrrole ring of ageladine A on MMP-12 inhibitory
activity. It became evident that a halogen atom (Br or Cl) at the 2-position and an additional bromine
atom at the 4-position are highly effective for improving the inhibitory activity. These studies led us to
discover three novel ageladine A analogs (4a, c, o) showing more potent MMP-12 inhibitory activity than
the natural product.
Received 25 June 2009
Revised 16 July 2009
Accepted 18 July 2009
Available online 23 July 2009
Keywords:
Ageladine A
Ó 2009 Elsevier Ltd. All rights reserved.
Matrix metalloproteinase (MMP)-12
In 2003, Fusetani et al. isolated ageladine A (1), one of the pyr-
rol-2-aminoimidazole alkaloids, from the marine sponge Agelas
nakamurai.1 It was also reported that 1 exhibits inhibitory activity
against various subtypes of matrix metalloproteinases (MMPs)
such as MMP-1, 2, 8, 9, 12 and 13.1 Accordingly, we envisioned that
1 has potential as the new lead compound for our ongoing project
aimed at exploring novel MMP-12 inhibitors. It has been antici-
pated that MMP-12 closely associates with inflammatory diseases
caused by macrophage infiltration such as skin diseases,2 athero-
sclerosis,3 aneurysms4 and cancers.5
Recently, we completed the total synthesis of 1 and reported
the MMP-12 inhibitory activity of 1 and its analogs.6 The latter
analogs were prepared by featuring the synthetic route established
for 1.6 Quite interestingly, it was disclosed that, as shown in Figure
1, two debromo-ageladine A analogs, 2 and 3, showed no inhibitory
activity against MMP-12. This result strongly suggested that a
slight change of the substituent on the pyrrole ring affords great
influence on the inhibitory activity. Therefore, we continued syn-
thetic studies on ageladine A analogs to reveal more detailed sub-
stituent effects for the pyrrole ring and to find analogs showing
improved inhibitory activity. These studies revealed novel aspects
of the structure–activity relationships for ageladine A analogs,
especially concerning substituents on the pyrrole ring, and led us
to discover three novel types of ageladine A analogs 4a, c, o exhib-
iting more potent MMP-12 inhibitory activity than 1.
target molecules we planned to synthesize. We achieved the syn-
thesis of these analogs using the synthetic scheme previously
established.6 Thus, as outlined in Scheme 1, the Pictet–Spengler
reaction of 2-(N-t-butoxycarbonylamino)histamine (5)7 with the
pyrrole-2-aldehydes 6a–p (vide infra) gave the corresponding tet-
rahydro-ageladine A derivatives 7. Sequential two-step dehydroge-
nations of 7 using IBX and activated MnO2 afforded the protected
ageladine A derivatives 8. Depending upon the structures of the
Br
Y
3
4
Br
X
N
N
2
N
H
N
H
N
N
NH
NH
H2N
H2N
ageladine A (1)
debromo-ageladine A
2: X = Br, Y = H
3: X = H, Y = Br
MMP-12 inhibitory activity IC50
1
µ
2
µ
3
µ
: 3.66 M, : >100 M, : >100 M
Figure 1. Structures of ageladine A (1) and its previously synthesized analogs 2, 3.
R2
R3
R1
R1 = Cl, Me, Ph, etc.
N
As shown in Figure 2, the general structures of the analogs bear-
ing various substituents on their pyrrole rings were designed as the
N
R2 = Cl, Me, Ph, (CH2)nPh, etc.
H
N
R
3 = Br, CH2CH2Ph
NH
H2N
4
* Corresponding author.
E-mail address: naoki.andou@mb.kyorin-pharm.co.jp (N. Ando).
Figure 2. Structures of the novel ageladine A analogs 4.
0960-894X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.bmcl.2009.07.099

5462
N. Ando, S. Terashima / Bioorg. Med. Chem. Lett. 19 (2009) 5461–5463
R2 R3
R2
R2
R2
R3
R3
R3
R1
CHO
H
N
R1
R1
R1
1)IBX
2)MnO2
N
method
Table 1
N
N
N
N
SEM
N
N
NHBoc
see
6
H
N
H
SEM
N
SEM
N
H2N
N
NH
NH
NH
5
H2N
xCF3CO2H
(x=1-2)
BocHN
BocHN
7
8
4
Scheme 1.
target molecules and the protective groups used, conversion of 8–
48 was attempted by employing various methods detailed in Table
1. Thus, analogs 4d, f–h were prepared by deprotection of the cor-
responding derivatives 8d, f–h. Analogs 4a–c, e, i–m, s, t8 were
produced by chlorination or bromination of the corresponding
derivatives 8a–c, e, i–m, s, t followed by deprotection. Analogs
4n–r, u8 were prepared by hydrogenation of 8n–r, u followed by
sequential bromination and deprotection. All of the synthesized
analogs 4a–u were isolated as their trifluoroacetate(s).6 On the
other hand, aldehyde derivatives 6a–p used for the Pictet–Spengler
reaction (vide supra) were synthesized by the methods shown in
Scheme 2. Thus, protection of 9,9 10,10 1211 and 1312 with a 2-(tri-
methylsilyl)ethoxymethyl group provided 6a, c, h, j, o and 14,
respectively. Aldehyde 6a was further converted to 6e–g by a reg-
ioselective Suzuki–Miyaura cross-coupling reaction carried out fol-
lowing the procedure reported by Handy et al.13 Aldehyde 6i was
prepared by Suzuki–Miyaura cross-coupling reaction of 6c. The
Sonogashira cross-coupling reaction of 6c and 14 gave 6k–n, p,
respectively. The synthesis of 6d was performed by bromination
of 1114 followed by protection.
The 21 structurally discrete ageladine A analogs 4a–u thus ob-
tained were subjected to MMP-12 inhibition assay.15 The results
are summarized in Table 2. As for the 2-position of the pyrrole ring,
replacement of the bromine atom with a chlorine atom obviously
increased the inhibitory activity (see 4c). However, introduction
of other groups such as methyl, phenyl and biphenyl groups clearly
decreased the activity (see 4d, f–h). From these results, it appeared
that the bromine or chlorine atom at the 2-position plays an
important role for MMP-12 inhibitory activity. On the other hand,
the 3-position of the pyrrole ring was found to show slightly
Table 1
Synthetic methods and results for the novel ageladine A analogs 4a–u
Run
Aldehyde 6
Methoda
Compound 4
No.
R1
R2
R3
R1
R2
R3
No. (yield)d
1
2
3
4
5
6
7
8
9
10
11
12
13
14
6a
6b
6c
6d
6d
6e
6f
6g
6h
6h
6i
Br
H
H
Me
Me
Ph
3-Ph–Ph
4-Ph–Ph
H
H
H
H
H
H
Br
H
Br
Br
Br
Br
Br
Br
Me
Me
Ph
PhCH2
PhCH2
H
H
H
H
H
H
H
H
H
H
H
H
H
H
A–D
Bb–D
B–D
D
A–E
D
Br
Cl
Cl
Me
Me
Ph
3-Ph–Ph
4-Ph–Ph
Br
Br
Br
Br
Br
Br
Br
Cl
Br
Br
Br
Br
Br
Br
Br
H
H
H
Br
H
H
H
H
Br
H
H
Br
H
4a (43%)
4b (14%)
4c (10%)
4d (29%)
4e (27%)
4f (34%)
4g (39%)
4h (37%)
4i (26%)
4j (10%)
4k (13%)
41 (41%)
4m (40%)
4n (37%)
D
D
A–E
A–A–E
A–D
A–D
A–A–D
C–A–E
Me
Me
Ph
PhCH2
PhCH2
Ph(CH2)2
6j
6j
6k
Ph
15
16
6k
61
H
H
H
H
C–A–A–E
C–Ac–D
Br
Br
Ph(CH2)2
Br
Br
4o (25%)
4p (47%)
Ph
o-CF3–Ph(CH2)2
m-CF3–Ph(CH2)2
p-CF3–Ph(CH2)2
o-CF3-Ph
17
18
6m
6n
H
H
H
H
C–Ac–D
C–Ac–D
Br
Br
Br
Br
4q (29%)
4r (12%)
m-CF3-Ph
p-CF3-Ph
19
20
21
6o
6o
6p
H
H
H
Ph(CH2)3
Ph(CH2)3
H
H
H
A–E
Br
Br
Br
Ph(CH2)3
Ph(CH2)3
Br
H
Br
4s (47%)
4t (37%)
4u (11%)
A–A–E
C–Ac–F
Ph(CH2)2
Ph
a
Method A: tetra-n-butylammonium tribromide (1 equiv), method B: NCS (1 equiv), method C: H2, Pd/C, method D: (1) BF3OEt2, (2) Na2CO3aq, (3) TFA, method E: (1) TFA,
(2) Na2CO3aq, (3) TFA, method F: (1) NaOHaq, (2) TFA.
b
NCS (2 equiv).
Tetra-n-butylammonium tribromide (2 equiv).
Isolated yield based on 5.
c
d

N. Ando, S. Terashima / Bioorg. Med. Chem. Lett. 19 (2009) 5461–5463
5463
Br
Br
Br
ships, it was also disclosed that a halogen atom such as bromine or
chlorine atom was indispensable at the 2-position and that intro-
duction of a bromine atom into the 4-position was highly promis-
ing for improving MMP-12 inhibitory activity. Taking into account
these results, further studies aimed at discovering even more po-
tent ageladine A analogs are in progress.
Br
Br
a
a
b
CHO
CHO
CHO
Ar
CHO
N
H
9
N
N
SEM
SEM
6e-g
6a
Br
Br
Ph
c
CHO
CHO
SEM
N
H
10
N
N
SEM
Acknowledgements
6c
6i
Ar
Ar
We are grateful to Drs. T. Ishizaki and Y. Fukuda, Kyorin Phar-
maceutical Co. Ltd, for their many valuable suggestions and
encouragement. We would also like to thank Dr. Y. Kohno, Kyorin
Pharmaceutical Co. Ltd, for his helpful suggestions and discussions.
The MMP-12 inhibition assay was performed by Dr. Emme C. K. Lin,
ActivX Biosciences, to whom our thanks are also due.
d
CHO
SEM
6k-n
N
R2
R2
Br
e, a
a
Me
CHO
N
H
Me
CHO
SEM
CHO
CHO
SEM
6h, j, o
N
N
N
H
References and notes
11
6d
12
Ph
1. Fujita, M.; Nakao, Y.; Matsunaga, S.; Seiki, M.; Itoh, Y.; Yamashita, J.; van Soest,
R. W. M.; Fusetani, N. J. Am. Chem. Soc. 2003, 125, 15700.
Ph
Br
CHO
Br
d
a
2. (a) Vaalamo, M.; Kariniemi, A. L.; Shapiro, S. D.; Saarialho-Kere, U. J. Invest.
Dermatol. 1999, 112, 499; (b) Saarialho-Kere, U.; Kerkela, E.; Jeskanen, L.;
Hasan, T.; Pierce, R.; Starcher, B. J. Invest. Dermatol. 1999, 113, 664; (c) Suomela,
S.; Kariniemi, A. L.; Snellman, E.; Saarialho-Kere, U. Exp. Dermatol. 2001, 10, 175.
3. Matsumoto, S.; Kobayashi, T.; Katoh, M.; Saito, S.; Ikeda, Y.; Kobori, M. Am. J.
Pathol. 1998, 153, 109.
CHO
SEM
CHO
N
N
N
SEM
H
13
14
6p
Scheme 2. Reagents and conditions: (a) SEMCl, tBuOK/DMF, 0 °C, 1 h; (b) ArB(OH)2,
Pd(OAc)2, K2CO3/DMF, 100 °C, 7–8 h; (c) PhB(OH)2, Pd(PPh3)4, K2CO3/DMF, 100 °C,
8 h; (d) PdCl2(PPh3)2, CuI, TEA/DMF, 100 °C, 5 h; (e) NBS/THF.
4. Curci, J. A.; Liao, S.; Huffman, M. D.; Shapiro, S. D.; Thompson, R. W. J. Clin.
Invest. 1998, 102, 1900.
5. (a) Cornelius, L. A.; Nehring, L. C.; Harding, E.; Bolanowski, M.; Welgus, H. G.;
Kobayashi, D. J. Immunol. 1998, 161, 6845; (b) Kerkela, E.; Bohling, T.; Herva, R.;
Uria, J. A.; Saarialho-Kere, U. Bone 2001, 29, 487; (c) Kerkela, E.; Ala-Aho, R.;
Jeskanen, L.; Rechardt, O.; Grenman, R.; Shapiro, S. D. J. Invest. Dermatol. 2000,
114, 1113.
Table 2
MMP-12 inhibitory activity of ageladine A (1) and its analogs 2, 3 and 4a–u
6. Ando, N.; Terashima, S. Bioorg. Med. Chem. Lett. 2007, 17, 4495.
7. Ando, N.; Terashima, S. Synlett 2006, 2836.
Compound
MMP-12 IC50
(lM)
Compound
MMP-12 IC50 (lM)
8. 4a/CF3CO2H: pale yellow powder; mp 185 °C (decomp.); IR (KBr) 3333, 3179,
1
2
3
3.66
>100
>100
1.24
5.02
4j
4k
4l
4m
4n
4o
4p
4q
4r
5.02
1681, 1661, 1636, 1433, 1205, 1184, 1115, 720 cmÀ1 1H NMR (CD3OD,
;
18.7
>100
>100
10.2
2.99
>100
>100
>100
>100
>100
>100
400 MHz) d 7.53 (1H, d, J = 6.4 Hz), 8.24 (1H, d, J = 6.4 Hz); 13C NMR (CD3OD,
100 MHz) d 103.0, 104.3, 106.7, 108.5, 116.8, 119.7, 122.4, 126.4, 135.4, 162.3;
LRMS (ESI+) 434 [M+H]+; HRMS (ESI+) Calcd for C10H7Br3N5 433.82516, found:
433.82799; Anal. Calcd for C10H6Br3N5, C2HF3O2: C, 26.21; H, 1.28; N, 12.74.
Found: C, 25.99; H, 1.24; N, 12.56. 4c/2CF3CO2H: pale yellow powder; Mp
130 °C (decomp.); IR (KBr) 3147, 2923, 1719, 1664, 1474, 1438, 1202, 1135,
4a
4b
4c
4d
4e
4f
4g
4h
4i
2.02
>100
>100
>100
>100
>100
>100
794, 724 cmÀ1 1H NMR (CD3OD, 400 MHz)
; d 7.16 (1H, s), 7.42 (1H, d,
J = 6.4 Hz), 8.06 (1H, d, J = 6.4 Hz); 13C NMR (CD3OD, 100 MHz) d 98.3, 105.3,
114.8, 121.0, 123.5, 128.6, 133.0, 136.6, 146.9, 160.7; LRMS (ESI+) 312 [M+H]+;
HRMS (ESI+) Calcd for C10H8BrClN5 311.96516, found: 311.96500; Anal. Calcd
for C10H7BrClN5, 2C2HF3O2: C, 31.10; H, 1.68; N, 12.95. Found: C, 31.15; H, 1.65;
N, 13.31. 4o/1.5CF3CO2H: pale yellow powder; 1H NMR (DMSO-d6, 400 MHz) d
2.26–2.72 (2H, m), 2.76–2.81 (2H, m), 7.18–7.32 (5H, m), 7.50 (1H, d,
J = 6.1 Hz), 7.75 (2H, br s), 8.26 (1H, d, J = 6.1 Hz), 12.73 (1H, br s); 13C NMR
(DMSO-d6, 100 MHz) d 27.7, 35.3, 100.0, 102.4, 112.6, 115.6, 118.6, 121.5,
121.9, 122.2, 126.1, 128.28, 128.34, 128.36, 128.41, 140.6; LRMS (ESI+) 460
[M+H]+; HRMS (ESI+) Calcd for C18H16Br2N5 459.97725, found: 459.97738;
Anal. Calcd for C18H15Br2N5, 1.5C2HF3O2: C, 39.90; H, 2.63; N, 11.08. Found: C,
39.62; H, 2.65; N, 11.34.
4s
4t
4u
different substituent effects from the 2-position. The bromine
atom was most promising (see 4b, c), but the phenyl and phenethyl
analog also showed weak inhibitory activity (see 4k, n). The most
interesting effects were obtained by introducing a substituent into
the 4-position of the pyrrole ring. It became evident that introduc-
ing a bromine atom into the 4-position significantly increased the
inhibitory activity (see 4a, j, o). Especially, 4-bromo-ageladine A,
4a, showed the most potent activity among all the synthesized
analogs, and its activity was ca. three times as much as that of nat-
ural ageladine A (1). On the other hand, the 4-phenetyl analog, 4u,
was found to show no inhibitory activity.
In conclusion, we have succeeded in synthesizing 21 structur-
ally discrete ageladine A analogs in order to explore the substituent
effects in the pyrrole ring on MMP-12 inhibitory activity. From the
inhibitory activity assay, it became evident that three analogs, 4a,
c, o, show more potent activity than natural ageladine A (1) and
that the activity of the most potent, 4a, is ca. three times as great
as that of 1. Based on the studies of the structure–activity relation-
9. Handy, S. T.; Sabatini, J. J.; Zhang, Y.; Vulfova, I. Tetrahedron Lett. 2004, 45, 5057.
10. Laha, J. K.; Muthiah, C.; Taguchi, M.; McDowell, B. E.; Ptaszek, M.; Lindsey, J. S. J.
Org. Chem. 2006, 71, 4092.
11. Muchowski, J. M.; Hess, P. Tetrahedron Lett. 1988, 29, 3215.
12. Ghosez, L.; Franc, C.; Denonne, F.; Cuisinier, C.; Touillaux, R. Can. J. Chem. 2001,
79, 1827.
13. Handy, S. T.; Sabatini, J. J. Org. Lett. 2006, 8, 1537.
14. Muchowski, J. M.; Hess, P. Tetrahedron Lett. 1988, 29, 777.
15. The MMP-12 inhibition assay was performed as per manufacturer’s (BioMol)
protocol. Human MMP-12 catalytic domain (residues 84-255) obtained from
Biomol (Plymouth Meeting, PA) was diluted in Assay buffer (50 mM Tris pH7.5,
0.05% Brij-35, 10 mM CaCl2, 1 mM DTNB) to a concentration of 0.007 U/
MMP-12 solution (44 L) was premixed with 1 L of inhibitors dissolved in
DMSO in a 384-well plate, and the mixture was incubated for 20 min at RT.
Then, 5 L of 1 mM MMP chromogenic substrate (thiopeptolide) obtained from
Biomol was added to the mixture and the reaction mixture was incubated for
30–80 min at 37 °C. Reaction was terminated by adding 7 L of 0.2 M EDTA (pH
lL. The
l
l
l
l
8.0). The intensity of the color developed by the digested substrate was
measured at 405 nm.