Paederia scandens (Lour.) Merr. is a plant of the family Rubiaceae and genus Paederia. The aerial parts can be used as folk medicine for the treatment of pain and inflammation. The Chinese Pharmacopoeia (1977 edition) listed P. scandens as an official drug. Flavonoids [1], iridoids [2, 3], and triterpene saponins [4] were isolated in previous phytochemical studies of the plant. Recently, we have systematically investigated the chemical constituents of the aerial parts. This study was carried out with the purpose of validating the medical use of the aerial parts. In this paper, we described the isolation and structural elucidation of 15 compounds. Among them, compound 1 is a new iridoid compounds, compounds 3 and 4 were isolated from this plant for the first time, and the other compounds are known.

The aerial parts of P. scandens were collected at Medicinal Materials Corporation in Sichuan Province, China, in May 2006 and identified by Tong Wu (Shanghai Institute of the Pharmaceutical Industry). A voucher specimen was deposited in Shanghai Institute of the Pharmaceutical Industry, Shanghai, China (collection No. SIPI-060321).

The aerial parts of P. scandens (50 kg) were extracted with ethanol (70%), and the ethanol extract was partitioned with petroleum ether, CHCl3, EtOAc, and n-BuOH. Each fraction was purified by column chromatography with silica gel, Rp-18, Sephadex LH-20, and preparative HPLC to yield compounds 1–15.

The compounds were investigated by spectroscopic methods, including NMR and mass spectrometry. All compounds were identified as ethyl paederosidate (1), methyl paederosidate (2) [5], scopoletin (3) [6], liriodendrin (4) [7], paederoside (5) [5], paederosidic acid (6) [8], deacetyl-daphylloside (7) [9], dimer of methyl paederosidate and paederosidic acid (8) [2], paederoscandoside (9) [10], saprosmoside E (10) [11], cleomiscosin D (11) [12], daphylloside (12) [13], 3-hydroxy-4-methoxybenzaldehyde (13) [14], O-hydroxylbenzoic acid (14) [15], and 2,5-dihydroxybenzoic acid methyl ester (15) [16].

Compound 1 was obtained as a white amorphous powder with [α]23 D +11.52° (c 0.525, MeOH). Its molecular formula, C20H28O12S, was established by ESI-MS combined with HR-ESI-MS (m/z 515.1201 [M + Na]+, C20H28O12SNa+, calcd 515.1199). As shown in Table 1, the 1H NMR spectrum of 1 indicates the presence of two protons [δ 7.64, (d, J = 1.1, H-3) and 6.02, (d, J = 1.4, H-7)], one ethoxy [4.20 (m, J = 7.1, 11-OCH2), 1.29 (t, J = 7.1, 15-CH3)], one sulfur methyl group (2.34, s), and seven protons from the sugar moiety. The 13C NMR spectrum of 1 exhibits signals of 20 C-atoms, which are similar to 19 C-atoms in compound 2 that have 10 carbons of the main iridoid skeleton [17] and six sugar carbons, including one ester carbonyl (δ 173.17), one methyl sulfur (13.84), and one ethoxy carbon (61.57 and 14.88). The presence and position of sulfur atom were determined by HR-ESI-MS and comparison of the NMR data with paederoside [8] corresponding to methyl thiocarbonate group.

Table 1 1H (400 MHz) and 13C (100 MHz) NMR Spectroscopic Data for Compound 1 (CD3OD, δ, ppm, J/Hz)
Full size table

The HMBC data of 1 show an ester carbonyl (C-12) correlated with the sulfur methyl group and H-10, indicating the presence of the partial structure of two nonequivalent H in CH3–S–COO–CH2–. The cross peaks between 11-OCH2 and C-11 and between an anomeric carbon signal [δ 100.97, (C-1′)] of the glucopyranose and H-1 [5.06, (d, J = 9.0 Hz)] of the aglycone detected in the HMBC spectrum clearly indicate the presence of an ester functional group and the glycosidic linkage of the glucopyranosyl moiety to the C-1 position of aglycone, respectively [18, 19]. Similarities were found in the 1H and 13C NMR spectra between compound 1 and compound 2, the well-known compound methyl paederosidate [2, 3], which was also isolated in this study. Similarities were also found in the HMBC, HMQC, and NMR spectra between compounds 1 and 2, showing the optical rotation of compound 1 of [α]23 D +11.52° (c 0.525, 589 nm, MeOH) and of methyl paederosidate of [α]20 D +12.4° (c 0.90, MeOH). Therefore, compound 1 should have similar absolute configuration to the iridoid glucoside compound 2. Thus, compound 1 was identified as a novel iridoid glucoside, namely ethyl paederosidate.