Antiproliferative glabretal-type triterpenoids from the root bark of Dictamnus dasycarpusby Nahyun Kim, Kyu-Won Cho, Seong Su Hong, Bang Yeon Hwang, Taehoon Chun, Dongho Lee

Bioorganic & Medicinal Chemistry Letters

Text

Accepted Manuscript

Antiproliferative glabretal-type triterpenoids from the root bark of Dictamnus dasycarpus

Nahyun Kim, Kyu-Won Cho, Seong Su Hong, Bang Yeon Hwang, Taehoon

Chun, Dongho Lee

PII: S0960-894X(14)01304-3

DOI: http://dx.doi.org/10.1016/j.bmcl.2014.12.007

Reference: BMCL 22252

To appear in: Bioorganic & Medicinal Chemistry Letters

Received Date: 1 September 2014

Revised Date: 3 December 2014

Accepted Date: 4 December 2014

Please cite this article as: Kim, N., Cho, K-W., Hong, S.S., Hwang, B.Y., Chun, T., Lee, D., Antiproliferative glabretal-type triterpenoids from the root bark of Dictamnus dasycarpus, Bioorganic & Medicinal Chemistry

Letters (2014), doi: http://dx.doi.org/10.1016/j.bmcl.2014.12.007

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Antiproliferative glabretal-type triterpenoids from the root bark of Dictamnus dasycarpus

Nahyun Kima, Kyu-Won Choa,† Seong Su Honga,b, Bang Yeon Hwangc, Taehoon Chuna,*, and

Dongho Leea,* aCollege of Life Sciences and Biotechnology, Korea University, Seoul 136-713, Korea bNatural Products Research Institute, Gyeonggi Institute of Science and Technology

Promotion, Suwon 443-270, Korea cCollege of Pharmacy, Chungbuk National University, Cheongju 361-763, Korea * Corresponding authors.

Tel: +82-2-3290-3017. Fax: +82-2-953-0737. E-mail address: dongholee@korea.ac.kr. (D.

Lee)

Tel: +82-2-3290-3069. Fax; +82-2-3290-3499. E-mail address: tchun@korea.ac.kr (T. Chun) 2

ABSTRACT

Four new glabretal-type triterpenoids, dictabretols A−D (1−4), were isolated by activityguided fractionation from the root bark of Dictamnus dasycarpus T. (Rutaceae) using an in vitro antiproliferative assay on T cells using splenocytes. The structures of these compounds were determined by spectroscopic methods, including 2D NMR experiments. Compounds were evaluated for their immunosuppressive activity on T cells and demonstrated inhibition of proliferation of activated T cells, up to IC50 of 1.5 µM.

Keywords: Dictamnus dasycarpus; Rutaceae; glabretal-type triterpenoid; antiproliferative effect 3

Dictamnus dasycarpus T. (Rutaceae) is a perennial herb that is widespread across Asia and Europe; it is known as the ‘gas plant’ or ‘burning-bush’ because of the volatile oils it produces.1,2 D. dasycarpus has been used as a traditional medicine for amenorrhea, antifertilization, cough, jaundice, rheumatism, and skin disorders. Phytochemical studies of the

Dictamnus genus have shown it to contain alkaloids, limonoids, flavonoids, coumarins, sesquiterpene glycosides, and essential oils.3-10

Immunosuppressive agents have been used to treat immunologically mediated diseases and prevent activities related to the immune system, such as organ transplantation rejection.

Among these agents, cyclosporin A and FK506, initially isolated from the fungus

Cylindrocarbon lucidum and Streptomyces tsukubaensis is the most widely used and effective immunosuppressive drug in clinical use today.11-14 Given its side effects on vascular tension and plasma lipoprotein, there is a need for new immunosuppressive agents.15

In our search for immunosuppressive agents from natural origin, methanolic extract of the root bark of D. dasycarpus was found to inhibit the proliferation of T cells. The bioassayguided fractionation and purification of CHCl3-soluble fraction led to the isolation of four new glabretal-type triterpenoids, dictabretols A−D (1−4).16 The effects of the compounds on activated T cells were examined by measuring the proliferation of T cells and the secretion level of cytokines, IL-2 and IFN-γ.17 This report describes the isolation and structure elucidation of 1−4 along with their biological evaluation.

Dictabretol A (1)18 was isolated as a white amorphous powder, mp 234.4 °C. The molecular formula was determined as C35H56O7 by HRESIMS at m/z 587.3951 [M - H](calcd for C35H55O7, 587.3948), with eight degrees of unsaturation in the molecule. The IR spectrum showed the presence of hydroxy (3402 cm-1) and ester (1723 cm-1) functionalities.

The 1H NMR spectrum of 1 (in CDCl3, Table 1) displayed the signals for seven methyl 4 groups at δH 0.88 (H-19), 1.31 (H-27), 0.84 (H-28), 0.87 (H-29), 1.04 (H-30), 0.96 (H-4′), and 0.95 (H-5′). Proton signals for six oxygenated methines at δH 4.65 (H-3), 3.75 (H-7), 5.43 (H-21), 3.94 (H-23), 3.18 (H-24), and 3.65 (H-26) as well as overlapping proton signals for aliphatic methines and methylenes were exhibited. In addition, characteristic signals were observed for a cyclopropyl methylene group in a relatively high-field region at δH 0.71 (2H, doublet, J = 4.5 Hz, H-18a) and 0.46 (2H, doublet, J = 5.0 Hz, H-18b). Detailed analysis of 1H and 13C NMR spectra (Tables 1 and 2) as well as the HMBC spectrum revealed that compound 1 has a glabretal triterpene skeleton.19,20 The 1H and 13C NMR spectra of 1 displayed the signals of a trisubstituted epoxy group at C-24 [δH 3.18 (1H, doublet, J = 7.5 Hz) and δC 63.4] and C-25 (δC 60.7). In addition, the chemical shifts at δC 98.3 (C-21) and δH 5.43 (1H, overlap, H-21) suggested the presence of a hemi-acetal group. The 1H NMR signals at δH 2.21 (2H, broad doublet, J = 7.0 Hz, H-2′), 2.13 (1H, multiplet, H-3′), 0.96 (3H, doublet, J = 2.0 Hz, H-4′), and 0.95 (3H, doublet, J = 2.0 Hz, H-5′) demonstrated the presence of an isovaleric group. The position of the isovaleric acid was determined as C-3 from the longrange HMBC correlation of δH 0.84 (H-28) and δH 0.87 (H-29) with δC 77.8 (C-3), 36.2 (C-4), and 41.3 (C-5), as well as that of δH 4.65 (H-3) with δC 33.9 (C-1), 22.9 (C-2), 36.2 (C-4), 41.3 (C-5), 27.8 (C-28), 21.9 (C-29) and 172.9 (C-1′).19