Chemical Constituents from the Stems of Manihot esculenta

Abstract Two new compounds, maniesculentins A (1) and B (6), together with four known ones were isolated from the stems of Manihot esculenta Crantz. The structures of the new compounds were elucidated by extensive spectroscopic methods including NMR spectroscopy and mass spectrometry. The two new compounds (1, 6) were assayed for antibacterial activity against four tested bacteria lines. Graphical Abstract Electronic supplementary material The online version of this article (doi:10.1007/s13659-015-0052-8) contains supplementary material, which is available to authorized users.


Results and Discussion
constructed the typical fused A/B/C-ring system of the ent-pimarane-type diterpenoid core. The relative configuration of 3-OH was a-orientation determined by the ROESY correlation ( Fig. 3) from H-3 to H-5 and the large coupling constant (dd, J = 11.4 and 4.1 Hz) of H-3 with H 2 -2 [15]. Thus, the structure of 1 was determined as 3a,12adihydroxy-pimara-8(14),15-dien.
Maniesculentin B (6) was obtained as colorless oil. Its molecular formula was deduced to be C 13 13 C NMR spectra of 6 displayed similarity to the known lariciresinol, a furan methanol lignan isolated from Araucaria angustifolia [16]. The major difference is one carbonxyl group instead of 4 0 -hydroxy-3 0 -methoxyphenmethyl group at C-4 supported by the HMBC correlation (Fig. 2) from H-4 (d H 3.46) to COOH (d C 178.6). The hydroxymethy group was ). Addition, in the HMBC spectrum (Fig. 2), the correlations from OH (d H 5.63) to C-5 0 (d C 114.4) and OMe (d C 55.9) to C-3 0 (d C 146.9) indicated that OH and OMe were connected to C-4 0 and C-3, respectively. On the basis of the above information, the planar structure of 6 was further confirmed in Fig. 1. The ROESY correlation (Fig. 3) between H-2 and H-4 manifested that H-2 and H-4 were in the same side (assigned as b-orientation). The relative configuration of H-3 was aorientation determined by coupling constants (J = 7.0 Hz), which was similar to the literature [17]. In addition, the ROESY correlations (Fig. 3) of CH 2 OH/H-4 and H-3/H-2 0 further confirmed the relative configuration of H-3. Consequently, compound 6 was determined to be tetrahydro-2a-(4 0 -hydroxy-3 0 -methoxyphenyl)-4a-carbonxyl-3b-hydroxymethyl furan (6), and named as maniesculentin B.
Maniesculentins A (1) and B (6) were assayed for antibacterial activicity against four bacteria lines (Staphylococcus aureus, Streptococcus, Escherichia.coli, Pseudomonas aeruginosa) by double-dilution [18,19]. The results of antibacterial activity showed that the two new compounds were inactive against four tested bacteria lines.

General Experimental Procedures
Optical rotations were detected with a JASCO P-1020 digital polarimeter. UV spectra were recorded on a Shimadzu UV-2401 PC spectrophotometer. IR spectra were scanned with Bruker Tensor-27 infrared spectrometer with a KBr disk. 1D and 2D NMR spectra were measured on Bruker AM-400, DRX-600 spectrometer using TMS as internal standard. MS and HREIMS spectra were carried out on Brucker HCT/E squire and Waters Autospec Premier P776 spectrum. HPLC analysis was performed on an Agilent 1100 liquid chromatograph equipped with a Waters X-Bridge C18 column (4.6 9 250 mm, 5 lm) with a flow rate of 3.0 mL/min, detected by a DAD detector. Column chromatography was carried out on silica gel (200-300 and 300-400 mesh; Qingdao Marine Chemical, Inc., Qingdao, P. R. China) and Sephadex LH-20 (40-70 lm, Amersham Pharmacia Biotech AB, Uppsala, Sweden). TLC spots were visualized under UV light and by dipping into 8 % H 2 SO4 in EtOH followed by heating.

Plant Material
The stems of M. esculenta Crantz were collected from Xishuangbanna, Yunnan Province, People's Republic of