Structural elucidation, total synthesis, and cytotoxic activity of effphenol A

Article abstract of DOI:10.1039/d0ob01985b

A highly substituted phenol derivative, effphenol A (1), was isolated from the deep-sea-derived fungus Trichobotrys effuse FS524. Its complete structural assignment was established through a combination of spectroscopic analysis together with single-crystal X-ray diffraction experiments and further unequivocally confirmed by a biomimetic total synthesis. Structurally, effphenol A possesses a poly-substituted 6-5/6/6 tetracyclic ring system, which represents the first case of such a skeleton found in nature. Furthermore, the cytotoxic activity of effphenol A (1) toward four human cancer cell lines was assayed. This journal is

Full text of DOI:10.1039/d0ob01985b

Organic &
Biomolecular Chemistry
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COMMUNICATION
Structural elucidation, total synthesis, and
cytotoxic activity of effphenol A†
Cite this: DOI: 10.1039/d0ob01985b
a
a
b
b,c
a
Hongxin Liu,‡ Shanchong Chen,‡ Xiao Zhang, Chunmao Dong, Yuchan Chen,
Received 29th September 2020,
Accepted 21st October 2020
a
b,c
a
Zhaoming Liu, Haibo Tan
*
and Weimin Zhang
*
DOI: 10.1039/d0ob01985b
rsc.li/obc
3
–6
A highly substituted phenol derivative, effphenol A (1), was isolated structures, and remarkable activities,
thus providing more
from the deep-sea-derived fungus Trichobotrys effuse FS524. Its prodrug molecules and model structures for new drug
7
–10
complete structural assignment was established through a combi- development.
nation of spectroscopic analysis together with single-crystal X-ray As part of our continuing research program to discover
diffraction experiments and further unequivocally confirmed by a structurally novel and biologically significant natural products
11–14
biomimetic total synthesis. Structurally, effphenol A possesses a from marine sources,
the organic extraction of Trichobotrys
poly-substituted 6-5/6/6 tetracyclic ring system, which represents effuse were originally selected for chemical investigation due to
the first case of such a skeleton found in nature. Furthermore, the its excellent anti-proliferative activity. Our previous chemical
cytotoxic activity of effphenol A (1) toward four human cancer cell investigations on this marine fungus have led to the isolation of
1
5
lines was assayed.
a number of phenol derivatives. In the current study, a highly
substituted phenol derivative, effphenol A (1), was characterized
from the deep-sea-derived fungus FS524. Notably, effphenol A
possessed an intriguing 6-5/6/6 tetracyclic ring system with a
poly-substituted skeleton, which represents the first case of
such a skeleton found in nature. Herein, we reported the iso-
lation, full structural determination, biomimetic total synthesis,
and biological activity of effphenol A.
Natural products have enjoyed tremendous growth in the
repertoire of pharmaceutical and agrochemical industries and
scientific investigations, and have been especially exemplified
in acting as pharmacologically attractive lead compounds in
biomedical research and clinical application for the assembly
1
of novel therapeutic drugs. Recent advances have demon-
strated that natural products and their related derivatives
could still behave as a powerful vehicle to fuel drug develop-
ment, especially the natural products derived from microor-
Effphenol A was isolated as a dark red crystal, and its mole-
cular formula was confirmed as C H O on the basis of
2
6
26 7
+
HRESIMS data (m/z 451.1739 [M + H] , calcd 451.1751), imply-
1
,2
ganisms, plants, vertebrates, and invertebrates.
Among
1
ing fourteen indices of hydrogen (IHDs). The H NMR spec-
them, on account of complex genomes, marine fungi are more
likely to produce natural molecules with rich varieties, novel
trum of effphenol A (Table 1) showed four aromatic proton
signals at δ 7.50 (2H, d, J = 8.8 Hz, H-13, 17) and 6.76 (2H, d,
H
J = 8.8 Hz, H-14, 16), ascribed to the presence of a para-substi-
tuted phenyl moiety. Moreover, two other aromatic protons
a
State Key Laboratory of Applied Microbiology Southern China, Guangdong
appearing at δ
methoxy protons at δ
26), and two methylene protons at δH 2.90 (2H, m) and 2.67
2H, q, J = 7.3 Hz) assigned as H -8 and H -24, together with
two methyl groups at δ 1.30 (3H, t, J = 7.5 Hz, H -9) and 1.11
3H, t, J = 7.3 Hz, H -25) were also observed. The C NMR data
H
6.31 (1H, s, H-2) and 6.20 (1H, s, H-22), two
Provincial Key Laboratory of Microbial Culture Collection and Application,
Guangdong Open Laboratory of Applied Microbiology, Guangdong Institute of
Microbiology, Guangdong Academy of Sciences, Guangzhou 510070, China.
E-mail: wmzhang@gdim.cn
H
3.56 (3H, s, H -7) and 3.53 (3H, s, H
3
3
-
(
2
2
b
Program for Natural Products Chemical Biology, Key Laboratory of Plant Resources
H
3
3
Conservation and Sustainable Utilization, Guangdong Provincial Key Laboratory of
Applied Botany, South China Botanical Garden, Chinese Academy of Sciences,
Guangzhou 510650, China. E-mail: tanhaibo@scbg.ac.cn
1
(
3
coupled with the HSQC spectrum resolved 25 carbon signals
including thirteen quaternary carbons (eight oxygenated ones),
six methines, two methylenes, and four methyls (two oxyge-
nated ones). As twelve of the fourteen IHDs were accounted for
by the three phenyl moieties, the remaining two IHDs indi-
cated that effphenol A possessed an additional double bond
with the formation of a fused ring system.
c
Xiangya School of Pharmaceutical Sciences, Central South University, Changsha
4
10013, China
†
Electronic supplementary information (ESI) available: Experimental details,
including procedures, syntheses, and the characterization of new products; 1D
and 2D NMR, UV, HRESI, as well as a CIF file. CCDC 1974672. For ESI and crys-
tallographic data in CIF or other electronic format see DOI: 10.1039/d0ob01985b
‡
These authors contributed equally.
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1
13
Table 1 H (600 MHz) and C (150 MHz) NMR data for compound 1 in
CD
3
COCD
3
1
1
No.
δ
H
(J in Hz)
δ
C
No.
δ
H
(J in Hz)
δ
C
1
2
3
4
5
6
7
8
9
153.5, C
95.8, CH
153.5, C
106.7, C
154.9, C
114.3, C
56.0, CH
17.3, CH
1a4.6, CH
—
14
15
16
17
18
19
20
21
22
23
24
25
26
6.76 (d, 8.8)
116.0, CH
157.9, C
116.0, CH
127.5, CH
102.2, C
155.3, C
110.4, C
156.6, C
92.3, CH
157.8, C
17.2, CH
14.6, CH
55.6, CH
6.31 (s)
6.76 (d, 8.8)
7.50 (d, 8.8)
Fig. 1 Structure of effphenol A (1).
3.56 (s)
2.90 (q, 7.5)
1.30 (t, 7.5)
3
2
3
6.20 (s)
10
11
12
13
150.3, C
124.5, C
127.5, CH
2.67 (q, 7.4)
1.11 (t, 7.4)
3.53 (s)
2
3
3
7.50 (d, 8.8)
a
Not detected.
Comprehensive interpretation of the 2D NMR spectra of 1
allowed the establishment of its planar structure. Readily, four
spin systems a (H -8/H -9), b (H-13/H-14), c (H-16/H-17), and d
H -24/H -25) could be confirmed by the H– H COSY corre-
2
3
1
1
Fig. 2 H– H COSY and key HMBC correlations of 1.
1
1
(
2
3
lations (Fig. 2). Moreover, the observed HMBC correlations
from H-2 to C-1, C-3, C-4, and C-6; H -7 to C-1; H -8 to C-3, C-4,
3
2
and C-5; and H -9 to C-4 and C-8 in conjunction with the
3
additional spin system a suggested the presence of the penta-
substituted benzene ring A. Similarly, the pentasubstituted
benzene ring D was also confirmed by the critical HMBC corre-
lations from H-22 to C-18, C-20, C-21, and C-23; H
2
-24 to C-19,
C-20, and C-21; and H -25 to C-20 and C-24 along with the spin
3
system d. Furthermore, the HMBC correlations from H-13 to
C-11, C-14, C-15, and C-17, and H-14 to C-12, C-15, C-16, and
C-17 along with the spin systems b and c logically confirmed
the presence of a para-substituted phenyl moiety (ring C).
However, there were many quaternary carbons existing far
away from the related conclusive protons, which resulted in Fig. 3 X-ray crystallographic analysis of 1.
the lack of necessary HMBC signals, thus bringing an unex-
pected challenge to distinguish the connection of ring A, ring
C, and ring D. Fortunately, a single crystal of the natural the proposed biosynthesis pathway, it mainly incorporated
product 1 suitable for X-ray diffraction analysis (Fig. 3) was with
a key spontaneous carbonyl addition/dehydration/
1
6
obtained from a methanol/water mixture solvent system, Michael addition/hemiketalization cascade process from 3
which provided conclusive evidence for furan ring B and the and 4 to furnish the rapid construction of the target scaffold
linkage of C-10/C-18 and C-11/C-12. Thus, the structure of 1 for effphenol A through the transition states TS1–TS4, thus
with a natural 6/5-6-6 tetracyclic ring system was defined as generating the pivotal intermediate 5. Therefore, the substi-
shown in Fig. 1 and given the trivial name as effphenol A.
tuted 2,3-dihydrobenzofuran 5 underwent dehydration to offer
To the best of our knowledge, effphenol A (1) is the first the targeted product effphenol A.
example of a new class of benzofuran natural products with a
The novel structure and interesting biosynthetic pathway of
poly-substituted skeleton. Regarding the fact that such a skel- effphenol A have fascinated us to explore its first biomimetic
eton exactly like effphenol A has never been reported before, a total synthesis. As shown in Scheme 2, aldehyde 3 could be
1
7
2
plausible biogenetic pathway was proposed as shown in directly derived through SeO -mediated oxidation in 80%
Scheme 1. Effphenol A might biogenetically originate from the yield from 4′-hydroxyacetophenone 7, which could be readily
bio-precursors 4-hydroxy-benzeneethanol and the phloro- prepared from the commercially available phenol 6 through
1
8
glucinol derivative 4, which have also been discovered or dis- AlCl
3
-mediated Friedel–Crafts acylation. Meanwhile, the syn-
closed as structurally constitutional units for many related thesis of phloroglucinol derivative 4 commenced with phloro-
1
5
natural products of T. effuse FS524 in our previous report. In glucin 8, which could undergo methylation to afford phenol 9
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Scheme 1 Proposed biogenetic pathway of effphenol A.
MCF-7 (breast cancer), HepG-2 (liver cancer), and A549 (lung
cancer) was also tested with cisplatin as the positive control.
Ultimately, it turned out that effphenol A (1) exhibited moder-
ate activities against four human cancer cell lines with IC50
values ranging from 30.1 to 43.3 μM, while the values of cispla-
tin were 2.5–3.2 μM.
In conclusion, effphenol A (1), a new phenol derivative with
a fascinating 6-5/6/6 tetracyclic ring system, was isolated from
the deep-sea-derived fungus T. effuse FS524. Moreover, an
efficient biomimetic total synthesis of 1 has been achieved,
which confirmed the structure proposed by a combination of
spectroscopic analysis, chemical techniques, and single-crystal
X-ray diffraction experiments. Additionally, the cytotoxic
activity of 1 toward four human cancer cell lines was assayed
with moderate anti-proliferative activity. This research not only
provided an efficient strategy and inspiration for the synthesis
of similar phenol derivatives to enrich the structural library of
these natural products but also shed light on a potential bio-
synthesis process for similar natural products.
Scheme 2 Total synthesis of effphenol A.
in a moderate yield. Further subjection of phenol 9 to Friedel–
Crafts acylation followed by reduction using conditions modi-
Conflicts of interest
1
9
fied from the literature led to the desired phloroglucinol
derivative 4 in about 55% overall yield for two steps. With the
desired aldehyde 3 and phloroglucinol derivative 4 in hand,
There are no conflicts to declare.
the
sequential
carbonyl
addition/dehydration/Michael
addition/hemiketalization tandem reaction was explored.
Gratifyingly, the key reaction did proceed, successfully deliver-
Acknowledgements
ing the desired product 1 in 68% yield, which was then proved We thank the National Natural Science Foundation of China
to be identical to effphenol A in all aspects.
(81773602, 41906106), Guangdong Provincial Special Fund for
Subsequently, cytotoxic evaluation against four human Marine
Economic Development Project ([2020]042),
cancer cell lines SF-268 (human glioblastoma carcinoma), Guangdong Special Support Program (2019TQ05Y375), Youth
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Innovation Promotion Association of CAS (2020342), and Team
Project of the Natural Science Foundation of Guangdong
Province (2016A030312014). We sincerely thank Ms. Xuan Ma
of South China Sea Institute of Oceanology for X-ray
measurement.
6 H. Wen, X. Yang, Q. Liu, S. Li, Q. Li, Y. Zang, C. Chen,
J. Wang, H. Zhu and Y. Zhang, J. Nat. Prod., 2020, 83, 99–104.
7 C. Jiménez, ACS Med. Chem. Lett., 2018, 9, 959–961.
8 A. R. Carroll, B. R. Copp, R. A. Davis, R. A. Keyzers and
M. R. Prinsep, Nat. Prod. Rep., 2020, 37, 175–223.
9
J. W. Blunt, A. R. Carroll, B. R. Copp, R. A. Davis, R. A. Keyzers
and M. R. Prinsep, Nat. Prod. Rep., 2018, 35, 8–53.
1
0 W. H. Jiao, J. Li, M. M. Zhang, J. Cui, Y. H. Gui, Y. Zhang,
J. Y. Li, K. C. Liu and H. W. Lin, Org. Lett., 2019, 21, 6190–
6193.
Notes and references
1
(a) G. M. Cragg, P. G. Grothaus and D. J. Newman, Chem.
Rev., 2009, 109, 3012–3043; (b) D. J. Newman and 11 S. Chen, Z. Liu, H. Tan, Y. Chen, S. Li, H. Li, S. Zhu, H. Liu
G. M. Cragg, J. Nat. Prod., 2012, 75, 311–335;
and W. Zhang, Org. Chem. Front., 2020, 7, 557–562.
c) D. J. Newman and G. M. Cragg, J. Nat. Prod., 2020, 83, 12 Z. Liu, Q. Wang, S. Li, H. Cui, Z. Sun, D. Chen, Y. Lu,
(
7
2
70–803; (d) D. J. Newman and G. M. Cragg, J. Nat. Prod.,
016, 79, 629–661.
H. Liu and W. Zhang, J. Nat. Prod., 2019, 82, 3440–3449.
13 S. Chen, Z. Liu, H. Tan, Y. Chen, S. Zhu, H. Liu and
W. Zhang, Org. Biomol. Chem., 2020, 18, 642–645.
2
K. Zlotkowski, W. M. Hewitt, P. Yan, H. R. Bokesch,
M. L. Peach, M. C. Nicklaus, B. R. O’Keefe, J. B. McMahon, 14 S. Chen, Z. Liu, Y. Chen, H. Tan, S. Zhu, H. Liu and
K. R. Gustafson and J. S. Schneekloth Jr., Org. Lett., 2017,
9, 1726–1729.
G. M. Cragg and D. J. Newman, Biochim. Biophys. Acta,
013, 1830, 3670–3695.
(a) J. W. Blunt, B. R. Copp, R. A. Keyzers, M. H. G. Munro
and M. R. Prinsep, Nat. Prod. Rep., 2016, 33, 382–431;
W. Zhang, Tetrahedron Lett., 2020, 61, 151555.
15 S. Chen, Z. Liu, Y. Chen, H. Tan, S. Li, H. Liu, W. Zhang
and S. Zhu, Mar. Drugs, 2020, 18, 134.
16 G. X. He, J. M. Yuan, H. M. Zhu, K. Wei, L. Y. Wang,
S. L. Kong, D. L. Mo, C. X. Pan and G. F. Su, Bioorg. Med.
Chem. Lett., 2017, 27, 1660–1664.
1
3
4
2
(
b) J. W. Blunt, B. R. Copp, R. A. Keyzers, M. H. G. Munro 17 H. M. Kuo, Y. L. Chen, G. H. Lee and C. K. Lai, Tetrahedron,
and M. R. Prinsep, Nat. Prod. Rep., 2017, 34, 235–294;
2016, 72, 6843–6853.
c) Y. Buijs, P. K. Bech, D. Vazquez-Albacete, M. Bentzon- 18 A. J. Grenning, J. H. Boyce and J. A. Porco, J. Am. Chem.
(
Tilia, E. C. Sonnenschein, L. Gram and S. D. Zhang, Nat.
Prod. Rep., 2019, 36, 1333–1350.
Y. H. Gui, W. H. Jiao, M. Zhou, Y. Zhang, D. Q. Zeng,
H. R. Zhu, K. C. Liu, F. Sun, H. F. Chen and H. W. Lin, Org.
Lett., 2019, 21, 767–770.
Soc., 2014, 136, 11799–11804.
19 D. W. Chen, R. D. Chen, R. S. Wang, J. H. Li, K. B. Xie,
C. C. Bian, L. L. Sun, X. L. Zhang, J. M. Liu, L. Yang, F. Ye,
X. M. Yu and J. G. Dai, Angew. Chem., Int. Ed., 2015, 54,
12678–12682.
5
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