Synthesis and biological activities evaluation of sanjuanolide and its analogues

Article abstract of DOI:10.1016/j.bmcl.2018.11.020

Sanjuanolide, psorachalcone A and its seven new analogues were synthesized via a combinatorial strategy by aldol reaction. In order to investigate the effect between electron density in π-conjugated systems and biological activities, several electron-with

Full text of DOI:10.1016/j.bmcl.2018.11.020

Accepted Manuscript
Synthesis and Biological Activities Evaluation of Sanjuanolide and its Ana-
logues
Jiadai Zhai, Lin Fu, Yuanyuan Li, Rui Zhao, Rui Wang, Hongkuan Deng,
Hongliang Liu, Ling Kong, Zhiwei Chen, Feng Sang
PII:
S0960-894X(18)30886-2
https://doi.org/10.1016/j.bmcl.2018.11.020
BMCL 26131
DOI:
Reference:
Bioorganic & Medicinal Chemistry Letters
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Revised Date:
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12 September 2018
7 November 2018
9 November 2018
Please cite this article as: Zhai, J., Fu, L., Li, Y., Zhao, R., Wang, R., Deng, H., Liu, H., Kong, L., Chen, Z., Sang,
F., Synthesis and Biological Activities Evaluation of Sanjuanolide and its Analogues, Bioorganic & Medicinal
Chemistry Letters (2018), doi: https://doi.org/10.1016/j.bmcl.2018.11.020
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Synthesis and Biological Activities Evaluation of Sanjuanolide and its
Analogues
Jiadai Zhai,a,b,d Lin Fu,a,d Yuanyuan Li,a,d Rui Zhao,c Rui Wang,c Hongkuan Deng,a Hongliang Liu,a
Ling Kong,a Zhiwei Chen,a and Feng Sang a,*
a School of Life Science, Shandong University of Technology, Zibo 255049, PR China
b School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, 300072, PR China
c College of Pharmacy, Nankai University, Tianjin 300350, PR China
*Corresponding author: Feng Sang, Phone: (86)-533-2781329，Fax: (86)-533-2781329, E-mail: fengsang@sdut.edu.cn.
dAuthor Contributions: These three authors contributed equally to this work.
Declarations of interest: none
Abbreviations: Ethyl acetate (EtOAc), Dichloromethane (DCM), Chloromethyl methyl ether (MOMCl), p-Toluenesulfonic
acid (p-TsOH), Tetrahydrofuran (THF), 4-Dimethylaminopyridine (DMAP), Tetraphenylporphyin (TPP).

ABSTRACT
Sanjuanolide, psorachalcone A and its seven new analogues were synthesized via a combinatorial strategy by aldol reaction.
In order to investigate the effect between electron density in π-conjugated systems and biological activities, several electron-
withdrawing and electron-donating groups were introduced at C-4 and the phenolic hydroxyl groups of sanjuanolide. The
two natural products and its seven new analogues were investigated for their inhibitory effects against five cancer cell lines.
Moreover, the hydroxyisoprenyl group may be important to maintain the biological activities of sanjuanolide.
Keywords: Isoprenylated chalcone; Hydroxyisoprenyl group; Natural product; Analogues; Biological activity

Chalcones are abundant in seeds, fruit skin or peel, bark, and flowers of most edible plants. They have been considered derivatives
of a three-carbon α,β-unsaturated carbonyl system (1,3-diphenyl-2-propen-1-one) composed of two phenolic rings. Many of the
chalcones exhibit important pharmacological properties, such as anti-inflammatory,1 anti-bacterial,2 anti-cancer,3 anti-oxidant,4
analgesic,5 and anti-pyretic effects.6,7 Sanjuanolide, a new isoprenylated chalcone which contains an unique hydroxyisoprenyl group,
was isolated from G. hypoleuca. Dalea frutescens by Shaffer et al in 2016.8 Specifically, sanjuanolide showed slightly greater cyto-
toxic activities against PC-3 and DU 145 prostate cancer cell lines.
To our knowledge, the unique hydroxyisoprenyl group was rarely in natural products of chalcones. According to Literature search
by reaxys, chalcones with hydroxyisoprenyl at A ring and three-carbon α,β-unsaturated carbonyl system have exhibited cytotoxic or
antifungal activities mostly, typically including sanjuanolide (1), psorachalcone A (2),9 xanthohumol D (3),10 xanthoangelol D (4),11
compound 5,12 paratocarpin E (7),13 bartericin A (8),14 angusticornin A (6) and angusticornin B (9)15 (Figure 1).
Figure 1. Natural Chalcones with hydroxyisoprenyl group
However, there is no work has been done on the synthesis of these natural products. In addition, further study of sanjuanolide and
its analogues by introduce electron-withdrawing and electron-donating groups at the two aromatic rings may provide new leads for
drug discovery. Herein, the first total synthesis of sanjuanolide, psorachalcone A and its seven new analogues are described, and
their inhibitory effects against PC-3, A375, PANC-1, A549 and MDA-MB-231 cell lines were investigated.
In consideration of the cytotoxic activity and typical structure, sanjuanolide was selected as the first synthetic target in our laborato-
ry. According to Jean et al, photooxygenation of ortho-prenylphenols followed by a reduction at low temperature can yield ortho-
(2-hydroxy-3-methylbut-3-enyl)phenols based on the Schenck reaction.16 In this work, we intend to obtain the unique
hydroxyisoprenyl groups from ortho-prenylphenols at the last two steps by retrosynthetic analysis of sanjuanolide (Scheme 1). Dis-
connection of isocordoin (10) through C3′–C1″ and C,C-double bond in α,β-unsaturated carbonyl system results in three commer-
cialized raw materials 3,3-dimethylallyl bromide (11), 2,4-dihydroxyacetophenone (12) and benzaldehyde (13).
Scheme 1. Retrosynthetic Analysis of Sanjuanolide (1)
As described by Jain et al,17 prenylation of 2,4-dihydroxyacetophenone with 2-methylbut-3-en-2-ol in the presence of Lewis acidic
medium, was adopted in our laboratory at the beginning. However, by the limit of low yields and high challenge in the process of
purification (Low solubility of the two monoprenylated prenylated derivatives in eluent), we used MOM (methoxymethyl) to pro-

tect the C4′-hydroxy group of 12 selectively in 92% yield (Scheme 2). Then the MOM-protected compound 14 was prenylated with
bromide 11 to afford 15 (90% yield), which was further reacted with benzaldehyde in the presence of 4 M NaOH to afford chalcone
16 by Claisen-Schmidt condensation (85% yield).18
Scheme 2. Synthesis of sanjuanolide, psorachalcone A and analogues 1b–e.
Chalcone 16 was subjected to a montmorillonite K10-promoted sigmatropic rearrangement to afford the ortho-prenylated chalcone
17 in 35% yield (along with 25% para-prenylated chalcone as a by-product).19 With the intermediate 17 in hand, photooxidation
was taken in the presence of tetraphenylporphyin (TPP) as a photosensitizer. Moreover, we chose the temperature at 10 oC (compare
to –30oC reported by Jean et al)16 to ensure 17 could be converted completely. Then PPh3 was added to the reaction mixture, and
the resulting solution was allowed to warm to room temperature naturally (55% yield). Finally, deprotection of 18 using p-TsOH at
50 oC in MeOH/THF afforded synthetic sanjuanolide (1), which was obtained as a yellow powder (88% yield).
Scheme 3. Synthesis of analogues 1f–h.
Under the same strategy, psorachalcone A (2) and 1b–e were prepared from the corresponding aldehyde 13a–e using combinatorial
approaches. Similarly, 1f was synthesized starting from intermediate 17 through 3 steps (Scheme 3). Deprotection of the intermedi-
ate 17 using p-TsOH lead to isocordoin (10), which was further reacted with iodomethane or acetic anhydride separately to afford

prenylated chalcones 21 and 22. And then, after the photooxidation step, analogues 1g and 1h were synthesized from 21 and 22
respectively. Additionally, photooxygenation of 10 followed by a reduction can also afford sanjuanolide in 46% yield.
The analytic data of synthetic sanjuanolide were compared with that of the natural sanjuanolide reported in the literatures,8 includ-
ing 1H and 13C NMR data (Table S1 in the Supporting Information). In addition, as described by Shaffer et al,8 the configuration of
the C-2′′ stereocenter in 1 was converted to a virtual (∼1:1) racemic mixture after several weeks of freezer storage. In this work, 1H
and 13C NMR data also showed no discernible changes in these compounds according to our observations, and the samples were
investigated as racemic mixtures by chiral HPLC.
The antiproliferative effects of sanjuanolide, psorachalcone A, isocordoin and the seven new analogues were evaluated in five can-
cer cells, using MTT assays as described in the in vitro screening protocol.20 The ability of these compounds to inhibit the growth of
cancer cells was summarized in Table 1. 1c–g exhibited obvious activity against PC-3 and A375 cell lines. Especially, 1d exhibited
3.4-fold and 3.0-fold greater potencies against the PC-3 and A375 cells compared to 1 respectively. On the contrary, isoprenylated
chalcone 10 and 4-hydroxyl-substituted sanjuanolide (2, psorachalcone A) exhibited lower potencies as compared to 1 in PC-3 and
A375 cells. In addition, 1f exhibited moderate levels of activity against PANC-1 and MDA-MB-231 cell lines.
Table 1. Effects of sanjuanolide and its analogues on proliferation of cancer cell lines.
IC50 (μM)1
Compounds
PC-3 A375 PANC-1 A549 MDA-MB-231
1
17.5
13.1
﹥252
﹥25
﹥25
﹥25
22.5
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
23.4
2
﹥25 ﹥25
﹥25 ﹥25
1b
1c
1d
1e
1f
1g
1h
10
16.7
5.1
23.5
4.3
11.4
13.5
16.6
20.4
﹥25
9.5
24.5
﹥25
12.1
9.2
13.8
18.1
17.7
23.2
﹥25
﹥25
﹥25
﹥25
﹥25
﹥25
1 Cells were exposed to compounds for 48 h. All values are the mean of three independent experiments. 2 If a specific compound is given a value >25, it
indicates that a specific IC50 cannot be calculated from the data points collected, meaning “no effect”.
In summary, total synthesis of sanjuanolide, psorachalcone A and its seven new analogues were achieved from commercially avail-
able materials in acceptable yields through 6 or 7 steps (12% overall yield for sanjuanolide in 6 steps). Furthermore, this combina-
torial approach can also be used for the preparation of chalcones with hydroxyisoprenyl group mentioned above. The compounds
were subsequently evaluated for their anti-cancer activities. This preliminary structure-activity relationship study reveals that intro-
ducing an electron-withdrawing halogen atom (Cl or F) at C4 position or replace the C2′-hydroxy group with methoxy group may
have a positive effect on their biological activities. The relationship between the hydroxyisoprenyl group and biological activities of
chalcones still needs to be further investigated.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (NO. 81602962) and the Natural Science Foundation of
Shandong Province (ZR2016HQ04) to F.S.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the online version, at xxx
References
1. Nowakowska, Z. A review of anti-infective and anti-inflammatory chalcones. Eur. J. Med. Chem. 2007, 42, 125–137.

2. Nielsen, S. F.; Larsen, M.; Boesen, T.; Schønning, K.; Kromann, H. Cationic chalcone antibiotics. Design, synthesis, and mechanism of action. J.
Med. Chem. 2005, 48, 2667–2677.
3. Konieczny, M. T.; Koniecany, W.; Sabisz, M.; Skladanowski, A.; Wakieć, R.; Augustynowicz-Kopeć, E.; Zwolska, Z. Synthesis of isomeric,
oxathiolone fused chalcones, and comparison of their activity toward various microorganisms and human cancer cells line. Chem. Pharm. Bull.
2007, 55, 817–820.
4. Go, M. L.; Wu, X.; Liu, X. L. Chalcones: An update on cytotoxic and chemoprotective properties. Curr. Med. Chem. 2005, 12, 483–499.
5. Viana, G. S. B.; Bandeira, M. A. M.; Matos, F. J. A. Analgesic and antiinflammatory effects of chalcones isolated from Myracrodruon
urundeuva Allemão. Phytomedicine 2003, 10, 189–195.
6. Rahim, M. A.; Nakajima, A.; Misawa, N.; Shindo, K.; Adachi, K.; Shizuri, Y.; Ohizumi, Y.; Yamakuni, T. A novel diol-derivative of chalcone
produced by bioconversion, 3-(2,3-dihydroxyphenyl)-1-phenylpropan-1-one, activates PKA/MEK/ERK signaling and antagonizes Aβ-inhibition of
the cascade in cultured rat CNS neurons. Eur. J. Pharmacol. 2008, 600, 10–17.
7. Jung, J.; Lee, Y.; Min, D.; Jung, M.; Oh, S. Practical synthesis of chalcone derivatives and their biological activities. Molecules 2017, 22, 1872.
8. Shaffer, C. V.; Cai, S. Peng, J.; Robles, A. J.; Hartley, R. M.; Powell, D. R.; Du, L.; Cichewicz, R. H.; Mooberry, S. L. Texas native plants
yield compounds with cytotoxic activities against prostate cancer cells. J. Nat. Prod. 2016, 79, 531−540.
9. ElSohly, H. N.; Joshi, A. S.; Nimrod, A. C.; Walker, L. A.; Clark, A. M. Antifungal chalcones from Maclura tinctoria. Planta Med. 2001, 67,
87−89.
10. Zhao, F.; Nozawa, H.; Daikonnya, A.; Kondo, K.; Kitanaka, S. Inhibitors of nitric oxide production from hops (Humulus lupulus L.). Biol.
Pharm. Bull. 2003, 26, 61−65.
11. Baba, K.; Nakata, K.; Taniguchi, M.; Kido, T.; Kozawa, M. Chalcones from Angelica Keiskei. Phytochemistry 1990, 29, 3907−3910.
12. Ren, Z. Y.; Qi, H. Y.; Shi, Y. P. Phytochemical investigation of Anaphalis lactea. Planta Med. 2008, 74, 859−863.
13. Hano, Y.; Itoh, N.; Hanaoka, A.; Itoh, Y.; Nomura, T. Paratocarpins A–E, five new isoprenoid-substituted chalcones form Paratocarpus
venenosa zoll. Heterocycles 1995, 41, 191–198.
14. Ngameni, B.; Ngadjui, B.; Folefoc, G. N.; Watchueng, J.; Abegaz, B. M. Diprenylated chalcones and other constituents from the twigs of
Dorstenia barteri var. subtriangularis. Phytochemistry 2004, 65, 427–432.
15. Ngadjui, B. T.; Watchueng, J.; Keumedjio, F.; Ngameni, B.; Simo, I. K.; Abegaz, B. M. Prenylated chalcones, flavone and other constituents of
the twigs of Dorstenia angusticornis and Dorstenia barteri var. subtriangularis. Phytochemistry 2005, 66, 687–692.
16. Helesbeux, J. J.; Duval, O.; Guilet, D.; Séraphin, D.; Rondeau, D.; Richomme, P. Regioselectivity in the ene reaction of singlet oxygen with
ortho-prenylphenol derivatives. Tetrahedron 2003, 59, 5091–5104.
17. Jain, A. C.; Seshadri, T. R. A study of nuclear prenylation of β-resacetophenone–II: Synthesis of bavachalcone, 4’-O-methylbavachalone and
bavachin. Tetrahedron 1970, 26, 2631–2635.
18. Sugamoto, K.; Matsusita, Y.; Matsui, K.; Kurogi, C.; Matsui, T. Synthesis and antibacterial activity of chalcones bearing prenyl or geranyl
groups from Angelica keiskei. Tetrahedron 2011, 67, 5346–5359.
19. Han, J.; Li, X.; Guan, Y.; Zhao, W.; Wulff, W. D.; Lei, X. Enantioselective biomimetic total syntheses of kuwanons I and J and brosimones A
and B. Angew. Chem. Int. Ed. 2014, 53, 1–6.
20. Liu, S.; Gao, X.; Zhang, L.; Qin, S.; Wei, M.; Liu, N.; Zhao, R.; Li, B.; Meng, Y.; Lin, G.; Lu, C.; Liu, X.; Xie, M.; Liu, T.; Zhou, H.; Qi, M.;
Yang, G.; Yang, C. A novel Anti-Cancer Stem Cells compound optimized from the natural symplostatin 4 scaffold inhibits Wnt/β-catenin signaling
pathway. Eur. J. Med. Chem. 2018, 156, 21–42.
21. Dong, X.; Fan, X.; Yu, L.; Hu, Y. Synthesis of four natural prenylflavonoids and their estrogen-like activities. Arch. Pharm. Chem. Life Sci.
2007, 340, 372–376.
22. Caamal-Fuentes, E. E.; Peraza-Sánchez, S. R.; Torres-Tapia, L. W.; Moo-Puc, R. E.; Isolation and Identification of Cytotoxic Compounds from
Aeschynomene fascicularis, a Mayan Medicinal Plant. Molecules 2015, 20, 13563–13574.
23. Nascimento, M. C. D.; Mors, W. B. Chalcones of the root bark of Derris sericea. Phytochemistry 1972, 11, 3023–3028.

1. First syntheses of two new chalcones with hydroxyisoprenyl group were achieved
2. Preliminary structure-activity relationship study of sanjuanolide was investigated
3. The "hydroxyisoprenyl" group is shown to correlate with anti-tumor activities