A New Pyrrolidone Alkaloid and Other Constituents from Rourea oligophlebia Stems

Abstract

Phytochemical study of Rourea oligophlebia stems led to the isolation of a new 2-pyrrolidone alkaloid (R,S)-N-(5-hydroxyl-pyrrolidin-2-one-1-yl)acetamide (1), together with 14 known compounds including friedelin (2), friedanol (3), taraxerol (4), vanillin (5), coniferyl aldehyde (6), apigenin (7), 7α-hydroxy-3β-sitosterol (8), coniferyl alcohol (9), scopoletin (10), emodin (11), protocatechuic acid (12), catechin (13), procyanidin A1 (14), and (E)-2,3,5,4’-tetrahydroxystilbene-2-β-D-glucoside (15). Several isolated compounds were evaluated for cytotoxicity and antimicrobial activity. Compound 11 exhibited good antimicrobial activity on Gram (+) strains and moderate cytotoxicity against KB, Hep-G2, and LU cancer cell lines. Compounds 6 and 8–10 showed selective activity on HepG-2 and MCF-7 over KB and LU cancer cell lines, while compound 7 exhibited similar effects on KB, HepG-2, and MCF-7 cell lines with IC₅₀ values of 36.46 ± 0.81, 32.00 ± 0.58, and 32.03 ± 0.61 µg/mL, respectively.

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

1. Introduction

The genus of Rourea is a group of climbing shrubs belonging to the family of Connaraceae which are widely distributed in the Amazon, Pacific region, Africa, and Asia [1]. Chemical investigations have revealed that Rourea species contain a substantial number of biologically active constituents, including flavonoids, phytosteroids, triterpenes, lipids, phenolic acids, and coumarins [1–6]. The Rourea plant extracts and their active components exhibited interesting biological activities such as hypoglycemic activity [1, 5, 7], antibacterial activity [1, 8], antinociceptive activity [9], antiplasmodial activity [3, 10], and antioxidant activity [1, 4, 8]. Rourea oligophlebia Merr. is a species found on mountains of central provinces of Vietnam. According to folk medicine, R. oligophlebia stems have been used for the treatment of bleeding and bone fractures [11]. A preliminary study of R. oligophlebia revealed the presence of triterpene, sterol, and phenolic constituents [12]. In this study, we described the isolation and identification of a new pyrrolidone alkaloid (R,S)-N-(5-hydroxyl-pyrrolidin-2-one-1-yl)acetamide (1) (Figure 1) and fourteen known compounds including friedelin (2), friedanol (3), taraxerol (4), vanillin (5), coniferyl aldehyde (6), apigenin (7), 7α-hydroxy-3β-sitosterol (8), coniferyl alcohol (9), scopoletin (10), emodin (11), protocatechuic acid (12), catechin (13), procyanidin A1 (14), and (E)-2,3,5,4’-tetrahydroxystilbene-2-β-D-glucoside (15) from the stems of R. oligophlebia (Figure S1). The isolated compounds were evaluated for antimicrobial activity and cytotoxicity.

[figure omitted; refer to PDF]

The known compounds were elucidated as friedelin (2), friedanol (3) [12], taraxerol (4) [18], vanillin (5), coniferyl aldehyde (6) [19], apigenin (7) [20], 7α-hydroxy-3β-sitosterol (8) [21], coniferyl alcohol (9) [22], scopoletin (10) [23], emodin (11) [24], protocatechuic acid (12), catechin (13) [25], procyanidin A1 (14) [26], and (E)-2,3,5,4’-tetrahydroxystilbene-2-β-D-glucoside (15) [27]. Compounds 2-3, 6–9, 11-12, and 15 were reported for the first time from Rourea genus.

3.2. Biological Activities

Several isolated compounds were evaluated for antimicrobial activity and cytotoxicity. Only emodin (11) showed good antimicrobial activity against Gram (+) strains S. aureus, B. subtilis, and L. fermentum with IC₅₀ values of 4.51, 15.83, and 28.94 µg/mL, respectively, but exhibited no activity against Gram (−) strains and fungus at the concentration of 128 µg/mL. Other compounds were also inactive (IC₅₀ > 128 µg/mL) in antimicrobial activity test. The cytotoxicity of isolated compounds was evaluated against KB, HepG-2, LU, and MCF-7 cancer cell lines (Table S1). Compounds 6 and 8–10 showed selective activity on HepG-2 and MCF-7 with IC₅₀ ranging from 18.73 ± 0.40 µg/mL to 43.63 ± 0.90 µg/mL over KB and LU cancer cell lines. Compound 7 exhibited similar effect on KB, HepG-2 and MCF-7 cell lines. Among the tested compounds, emodin (11) had the best cytotoxicity on LU cancer cell line with IC₅₀ values of 21.04±0.52 µg/mL, respectively.

4. Conclusions

In conclusion, fifteen compounds were isolated from the stems of Rourea oligophlebia, among which a new alkaloid (R,S)-N-(5-hydroxyl-pyrrolidin-2-one-1-yl)acetamide (1) was identified along with fourteen known compounds 2–15. Compound 11 showed good antimicrobial activity on Gram (+) strains and moderate cytotoxicity against KB, Hep-G2, and LU-1 cell lines. Compounds 6 and 8–10 showed selective activity on HepG-2 and MCF-7 over KB and LU cancer cell lines, while compound 7 was moderately active on KB, HepG-2, and MCF-7 cell lines.

Acknowledgments

This research was funded by the Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 104.01-2018.08.

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