Coumaric Acid Glucosides from the Chinese Fern Polypodium hastatum

Abstract

Phytochemical investigations on Polypodium hastatum have led to the isolation of three isomers of coumaric acid glucosides. Their structures were identified as trans-melilotoside (1), trans-coumaric acid-3-O-E-Dglucopyranoside (2), and trans-coumaric acid-4-O-E-D-glucopyranoside (3) by spectroscopic analysis. Compound 2 is a new natural product.Keywords: coumaric acid glucoside, structure elucidation, Polypodium. Polypodium hastatum Thunb. (Polypodiaceae) is a fern that belongs to the genus Polypodium and grows in most areas of China. In Chinese folk medicine, it is used as a phytomedicine for the treatment of urinary diseases. Previous phytochemical investigations on the genus revealed that there were triterpenoids [1], diterpenoids [2], steroids [2], flavonoids [2], polyphenols [2], and fatty acid derivatives [3]. But to the best of our knowledge, only a coumarin was identified by Suzuki from the leaves of P. hastatum growing in Japan [4] before our investigation. In our program to discover bioactive natural products from ferns, a phytochemical investigation of this plant was carried out, and some flavonoids have been obtained [5,6]. Herein we report the isolation and structure elucidation of coumaric acid glucosides from P. hastatum.Compound 2 was obtained as white crystals. The ferric chloride reaction showed a positive result. ESI-MS gave a molecular cation peak at m/z 349 [M + Na] + . The 1 H NMR spectrum (Table 1) showed two olefinic hydrogen signals at G 7.60 (1H, d, J = 16.2 Hz) and 6.40 (1H, d, J = 16.2 Hz), which indicated the presence a trans double bond. At the same time, the signals at G 7.55 (1H, s), 7.24 (1H, d, J = 7.8 Hz), 7.14 (1H, dd, J = 7.8, 8.3 Hz), and 6.98 (1H, d, J = 8.3 Hz) implied the presence of a meta-substituted benzene ring. In the 13 C NMR spectrum (Table 1), there was a carbonyl carbon signal at G 171.8. In the range of G 110-160, there were eight unsaturated carbon signals, which is in agreement with the 1 H NMR spectrum showing the occurrence of a double bond and a substituted benzene in the structure. Compared with the 13 C NMR spectra of compounds 1 and 3, it can be concluded that there was a glucoside moiety. The E-configuration of the anomeric carbon of the glucose was deduced from the coupling constant (J = 7.4 Hz) of the anomeric hydrogen signal at G 4.9. Based on the analysis and chemical reactions, it can be concluded that compound 2 was trans-coumaric acid-3-O-E-D-glucopyranoside. HMBC and HSQC further confirmed the proposed structure and assigned the 1 H and 13 C NMR data.The trans-coumaric acid-3-O-D-D-glucopyranoside was formerly synthesized by Funayama [7] through the catalysis of glucoside synthetase, but the E anomer is reported herein for the first time, and this investigation also revealed its presence in nature for the first time. In addition, as known phytochemicals, compounds 1 and 3 were indentified through comparison of the NMR data with the literature [8,9].

Chemical Profiling, In Vivo Antioxidant Effect and Antimutagenic Evaluation of Melilotus indicus (L.) All. Extracts

“…They are identified as kaempferol (K) (1), 32 12), 36 melimessanol B (13) 39 and trans p-coumaric acid-O-glucoside (14). 40 Except for compounds (1, 7, 8, 10 and 11), all compounds were isolated for the first time from M. indicus. 10,11 Also, compounds (5 and 12) were reported for the first time for the genus Melilotus.…”