A study on the synthesis of antiangiogenic (+)-coronarin A and congeners from (+)-sclareolide

Article abstract of DOI:10.1016/S0960-894X(03)00345-7

Coronarin A 1, epi-coronarin A 2 and some synthetic intermediates 14a and 14b synthesized from sclareolide exhibit good growth inhibition activities on HUVEC proliferation. In particular, coronarin A 1 and epi-coronarin A 2 effectively suppressed the growth factor induced tube formation of HUVEC at the concentration of 10 μg/mL.

Full text of DOI:10.1016/S0960-894X(03)00345-7

Bioorganic & Medicinal ChemistryLetters 13 (2003) 2009–2012
A Study on the Synthesis of Antiangiogenic (+)-Coronarin A and
Congeners from (+)-Sclareolide
Sangtae Oh,a In Howa Jeong,a Woon-Seob Shinb,* and Seokjoon Leec,*
aDepartment of Chemistry, Yonsei University, Wonju 220-710, South Korea
bDepartment of Microbiology, Kwandong University College of Medicine, Gangneung 210-701, South Korea
cDepartment of Premedical Science, Kwandong University College of Medicine, Gangneung 210-701, South Korea
Received 26 February2003; revised 20 March 2003; accepted 20 March 2003
Abstract—Coronarin A 1, epi-coronarin A 2 and some synthetic intermediates 14a and 14b synthesized from sclareolide exhibit
good growth inhibition activities on HUVEC proliferation. In particular, coronarin A 1 and epi-coronarin A 2 effectivelysup-
pressed the growth factor induced tube formation of HUVEC at the concentration of 10 mg/mL.
# 2003 Elsevier Science Ltd. All rights reserved.
Introduction
ability, biostability and effectiveness. Therefore, it is
veryimportant to discover the antiangiogenic small
molecules that might be suitable as clinical therapies.
Angiogenesis, the development process of the formation
of new blood vessels from existing host capillaries, in
normal vascular system is involved in wound healing,
embryonic development, and the female reproductive
cycle under elaborate regulations. On the other hand, in
abnormal systems, angiogenesis is believed to be
responsible for rheumatoid arthritis, ocular retinopathy
and tumors.1 In particular, tumor angiogenesis caused
byangiogenic inducers, such as the fibroblast growth
factor (FGF), the vascular endothelial growth factor
(VEGF), angiogenin, transforming growth factors
(TGF-a and TGF-b), the platelet-derived growth factor
(PDGF), the tumor necrosis factor a (TNF-a), inter-
leukins, chemokines, and angiopectins.2 Angiogenesis
plays a key role in the growth of the solid tumors, their
invasion, and metastasis. Therefore, the control of
angiogenesis maybe a promising therapeutic strategy
for the related diseases.3
The initial and keysteps in tumor angiogenesis are
mainlythe roles of the endothelial cells (ECs), the
migration, differentiation and tube formation of the
ECs.7 Therefore, in order to search for a novel small
angiogenesis inhibitor, this studytested the inhibitory
effects of promising natural products and their related
compounds against the proliferation of human umbili-
cal vein endothelial cells (HUVEC) in response to the
various growth factors.
The furanolabdane diterpenoids, coronarin A (1) and
coronarin B-F, are isolated from rhizomes of the Brazi-
lian antirheumatic medicinal plant, Hedychium Cor-
onarium (Zingiberaceae).8,9 These compounds exhibit a
significant cytotoxic effect against V-79 cells and sar-
coma 180 ascites in mice.8 Because rheumatoid arthritis,
complex chronic inflammatorydisease in the joints, are
basicallycaused byangiogenesis, the components in
antirheumatic Hedychium C. are predicted to show
antiangiogenic activity.
Strategies for regulating angiogenesis have been carried
out mainlyin molecular biology, such as the isolation
and identification of the endogenous inhibitor,4 as well
6
as gene5 and antibodytherapy. However, it has been
insufficientlycarried out to develop small molecule
antiangiogenic agents despite the settlement of bioavail-
In the process of synthesizing those natural products,
Jung and Lee reported the synthesis10 and biological
properties11 of 7-epi-coronarin A (2), coronarin E (3)12
and cytotoxic intermediates from (ꢀ)-sclareol (4).
However theycould not snythesize coronarin A ( 1).
Therefore, this studyreports the first snythesis of
*Corresponding author. Tel.:+82-33-649-7454; fax: +82-33-641-
1074; e-mail: sjlee@kwandong.ac.kr
0960-894X/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0960-894X(03)00345-7

2010
S. Oh et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2009–2012
methylene isomers (7b and 7c), respectively, in the ratio
of 3:1:1 in an 85% yield. The allylic hydroxylation of
the mixture of 7a, 7b and 7c with SeO2 and t-BuOOH in
a methylene chloride (MC) for 2 h gave 8a, the 7-a-
hydroxy isomer as the only product in 45% yields.
However after 24 h, it gave a separable mixture of 8a
(47%) and 8b (12%), which is the allylic hydroxylation
product of 7b. The treatment of 8a with PCC in MC
afforded a a, b-unsaturated ketone (9a) and an a, b-
unsaturated aldehyde (9b), which is an oxidative rear-
ranged product, in a 75% yield, respectively, in the ratio
of 8:1. The 7-b-hydroxy isomer (10) having a natural
stereochemistryof the target compound ( 1) was gained
bythe reduction of 9a with NaBH4 in MeOH in a 98%
yield. The stereochemistry of the 7-position in 8a and 10
could be conformed in comparison with the lower
NOESY effect of the 9-axial and 7-equitorial hydrogens
in 8a and the larger effect the 9-axial and 7-axial
hydrogens in 10.8 Deacetylation of 11, which was a
TBDMS protecting compound of 10, gave 12, which
was transformed byPCC oxidation to the aldehdye
molecule (13) in an 80% overall yield from 10. The
unstable aldehyde (13) was immediatelyreacted with
3-furyllithium at ꢀ78 ꢁC, which was generated
3-bromofuran with n-butyllithium at ꢀ78 ꢁC under
afforded the separable diastereomeric mixture 14a,
which is a stericallyless hindered major product, and
14b in 72% yield. The stereochemistry of the C-12 of
Figure 1.
coronarin (1) with development of more efficient syn-
thetic pathwayfrom (+)-sclareolide ( 5), which is a
cheap, commerciallyavailable and potentiallygood
chiral starting material,13 and is particularlyuseful to
construct the C-7 stereochemistryof target molecule 1
(Fig. 1).
Chemistry
Hydride reduction of 5 with LAH in THF gave diol (6)
in a quantitative yield.14 The treatment of 6 with excess
acetic anhydride in collidine afforded an inseparable
mixture of exo methylene isomer (7a), which is an anti-
feedant albicanyl acetate homologue,15 and two endo
Scheme 1. Reagents and conditions: (a) LAH, THF, reflux, 5 h, 97%; (b) Ac2O, collidine, reflux, 16 h, 85%; (c) SeO2, t-BuOOH, MC, rt, 2 h, 45%;
(d) PCC, MC, rt, 3 h, 75%; (e) NaBH4, MeOH, rt, 1 h, 98%; (f) TBDMSCl, AgNO3, DMF, rt, 1 h, 89%; (g) Na2CO3, MeOH, rt, 2 h, 92%; (h)
PCC, MC, rt, 3 h, 98%; (i) 3-bromofuran, n-BuLi, THF, ꢀ78 ꢁC to rt, 72%, 14a: 14b=3:1; (j) 2,6-lutidine, MsCl, MC, rt, 24 h and then gently
warming to evaporate solvent, 68%.

S. Oh et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2009–2012
2011
14a and 14b could not be conformed bythe NOSEY
spectra because of the flexibilityof the C-9 furan side
chain. The dehydration of the diastereomeric mixture 14
with 2,6-lutidine (10 equiv) in the presence of methane-
sulfonyl chloride and then the subsequent desilyation
afforded the coronarin A (1) exclusivelyin 68% yield
via 16a (Scheme 1).
In conclusion, coronarin A (1), a constituent of the
Brazilian antirheumatic medicinal plant, its epimer (2)
and some intermediates (14a and 14b) have a high
growth inhibition effect on HUVEC. In particular, cor-
onarin A (1) and epi-coronarin A (2) have shown an
inhibition effect on the endothelial tube formation. With
the earlystudies on the structure–activityrelationship of
the coronarin analogues, this studyconfirmed that the
furanoladane-type natural product would be excellent
lead compound for use as an antiangiogenic inhibitor.
Currently, detailed studies on the structure–activity
relationships coupled with molecular modeling aimed at
developing new and efficient angiogenic inhibitors are
underway.
Biology
Initially, the antiangiogenic effect of coronarin A 1 and
its related molecules were examined on a HUVEC16
proliferation assayusing the MTT colorimetric
method.17 The results are listed in Table 1. Coronarin A
(1) and its epimer (2) showed potent inhibition activities
whereas sclareol (3) and sclareolide (4), a trans-decalin
structure with no furan moiety, exhibit no activity.
Compounds 14a and 14b, the precursors of coronarin A
with a furan group, exhibited a similar activityto 1 and
2. Although 15a, 15b and 16a, 16b have a similar struc-
ture to coronarin A (1) and its related antiangiogenic
molecules (2, 14a and 14b) theyhave no significant
inhibition effect on HUVEC growth. So, when assuming
the growth inhibition effects in Table 1, it was hypothe-
sized that the proper hydrophilic trans-decalin with a
conjugated furan group might be a lead compound for
use as angiogenic inhibitors.
Acknowledgements
We are grateful for the financial support from research
grants (KCS-KOSEF-2001-10) from the Korean Che-
mical Societyand Korea Science and Engineering
Foundation.
References and Notes
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heiro, A. J.; de Olivera, R. C. B.; Ishige, M.; Motidome, M.
Planta Medica 1988, 311.
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Next, their abilityto suppress the growth factor induced
tube formation byHUVEC was assessed at the concen-
tration of 10 mg/mL.18 As shown in Table 2, epi-cor-
onarin A (2) effectivelyinhibited the tube formation by
90% while coronarin A exhibited mild inhibition activ-
ityby55%. Compounds ( 14a, 14b, 15a, 15b, 16a and
16b) failed to inhibit the blood tube formation to some
degree.
Table 1. HUVEC proliferation inhibition assayresults for selected
compoundsa
Compd
Growth inhibition
IC50 (mg/mL)
Compd
Growth inhibition
IC50 (mg/mL)
1
2
4
5
14a
4.22
3.12
>50
>50
14b
15a
15b
16a
16b
3.76
29.67
15.03
>50
10. Jung, M.; Ko, I.; Lee, S. J. Nat. Prod. 1998, 61, 1394.
11. Jung, M.; Ko, I.; Lee, S.; Choi, S. J.; Youn, B. H.; Kim,
S. K. Bioorg. Med. Chem. Lett. 1998, 8, 3295.
12. Muller, M.; Schroder, J.; Magg, C.; Seifert, K. Tetra-
¨
¨
hedron Lett. 1998, 39, 4655.
7.71
>50
aIC50 was calculated from nonlinear regression byGraphPad Prism
software.
13. Chackalamannil, S.; Wang, Y.; Xia, Y.; Czarniecki, M.
Tetrahedron Lett. 1995, 36, 5315.
14. Zoretic, P. A.; Fang, H.; Ribeiro, A. A.; Dubay, G. J.
Org. Chem. 1998, 63, 1156.
15. Spectral data of selected compounds. 14a: white crystal,
Table 2. HUVEC tube formation assayresults for selected com-
poundsa
20
mp 109–111 ꢁC; ½ꢀꢂD ꢀ32.0 (c=0.08, CHCl3); IR (KBr pellet)
n
max 3363, 3098, 1463, 836 cmꢀ1; 1H NMR (300 MHz; CDCl3)
d7.41 (1H, t, J=1.56 Hz, H16), 7.29 (1H, t, J=0.93 Hz, H15),
6.41 (1H, dd, J=1.65 Hz, 0.63 Hz, H14), 5.32 (1H, d, J=1.35
Hz, H17), 4.85 (1H, d, J=1.35 Hz, H17), 4.73 (1H, dd,
J=9.99 Hz, 4.59 Hz, H12), 3.77 (1H, dd, J=10.89 Hz, 5.13
Hz, H7), 2.03 (1H, td, J=13.3 Hz, 4.50 Hz, H9), 1.89 (2H, m,
H11), 0.93 (9H, s, t-Butyl), 0.84, 0.79, 0.69 (each 3H, s, H20,
H19, H20) 0.07 (6H, d, J=6.57 Hz, Si-(CH3)2) ppm; 13C
NMR (75 MHz; CDCl3) d150.1, 143.6, 139.7, 128.6, 108.2,
104.5, 74.9, 65.7, 53.1, 51.2, 41.9, 39.1, 38.7, 34.5, 33.3, 31.5,
25.9, 21.6, 19.3, 18.6, 14.6, ꢀ5.0 ppm; GC/MSD (m/z) reten-
Compd
Inhibition percentage
at 10 mg/mL
Compd
Inhibition percentage
at 10 mg/mL
1
2
4
5
14a
55
90
14b
15a
15b
16a
16b
10
10
0
22
5
Not tested
Not tested
20
aValues expressed in percentage of HUVEC tube branches/well as
compared to untreated control.

2012
S. Oh et al. / Bioorg. Med. Chem. Lett. 13 (2003) 2009–2012
tion time 23.2 (min) 432 (M+), 414, 399, 375, 357, 320, 300,
16. Jaffe, E. A.; Nachman, R. L.; Becker, C. G.; Minick, C. R.
J. Clin. Invest. 1973, 52, 2745.
20
263, 141, 97, 75 (100); 14b: white crystal, mp 104–106 ꢁC; ½aꢂD
ꢀ190 (c=0.02, CHCl3); IR (KBr pellet) nmax 3421, 3098, 1462,
17. Mosmann, T. J. Immunol. Methods 1983, 65, 55. Assay
Method: HUVEC in EGM-2 medium containing the growth
factor (Cambrex, Walkersville, MD) was plated in a 48-well
plate (10,000 cells/well) for 4 h to allow cells to adhere to the
plate. The test compounds, diluted in the medium, were added
to the appropriate wells and incubated for 72 h at 37 in a 5%
CO2 humidified atmosphere. After incubation, the viabilityof
the HUVEC was assayed using a 3-(4,5-dimethylthiazol-2-y1)-
2.5-diphenyltetrazolium bromide (MTT) colorimetric pro-
liferation assay..
18. Aoki, K.; Watanabe, K.; Sato, M.; Ikekita, M.; Haka-
matsuka, T.; Oikawa, T. Eur. J. Pharm. 2003, 459, 131. Assay
Method: Formation of HUVEC tube on Matrigel (BD Bios-
ciences, Bedford, MA) was assayed in a 96-well plate. HUVEC
was plated (5000 cells/well) on 50 mL of Matrigel solidified,
and incubated for 16 h at 37 in a 5% CO2 humidified atmo-
sphere. After incubation, the cells were stained with toluidin blue
in 4% paraformaldehyde, and photographed. A blinded observer
quantified the number of tube branches. Each concentration
of the control or test compound was assayed in triplicate.
1
837cmꢀ1; H NMR (300 MHz; CDCl3) d7.39 (2H, br s, H15,
H16), 6.42 (1H, br s, H14), 5.30 (1H, d, J=1.38 Hz, H17), 4.66
(1H, t, J=5.67 Hz, H12), 4.62 (1H, d, J=1.38 Hz, H17), 3.98
(1H, dd, J=10.62 Hz, 5.22 Hz, H7), 0.94 (9H, s, t-Butyl), 0.90,
0.81, 0.67 (each 3H, s, H20, H19, H18) 0.09 (6H, d, J=4.32
Hz, Si-(CH3)2) ppm; 13C NMR (75 MHz; CDCl3) d150.2,
143.3, 138.5, 1 30.2, 108.5, 104.2, 74.9, 65.2, 53.2, 50.6, 42.0,
39.0, 38.9, 34.6, 33.4, 32.5, 26.0, 21.6, 19.3, 18.5, 14.6, ꢀ4.9
ppm; GC/MSD (m/z) retention time 22.8 (min) 432 (M+), 414,
20
399, 375, 357, 320, 300, 263, 141, 97, 75(100); 1: ½aꢂD +24.5
20
1
(c=0.28, CHCl3) (½aꢂD +25.4 (c=0.28, CHCl3) in ref 8) H
NMR (300 MHz; CDCl3) d7.37 (1H, br s, H16), 7.36 (1H, br s,
H15), 6.56 (1H, d, J=0.84 Hz, H14), 6.21 (1H, d, J=15.7 Hz,
H12), 5.99 (1H, dd, J=15.7, 9.72 Hz, H11), 5.13 (1H, s, H17),
4.74 (1H, s, H17), 4.08 (1H, dd, J=10.72 Hz, 5.28 Hz, H7),
2.35 (1H, d, J=9.63 Hz, H9), 0.92, 0.85, 0.84 (each 3H, s,
H20, H19, H18) ppm; 13C NMR (75 MHz; CDCl3) d151.8,
143.4, 139.8, 127.2, 124.4, 121.6, 108.5, 104.9, 73.4, 59.5, 52.8,
42.2, 40.4, 39.2, 33.6, 33.5, 33.2, 21.6, 19.8, 14.5 ppm.