Two new benzolactones from the leaves of Nicotiana tabacum and their anti-tobacco mosaic virus activities

Abstract Two new benzolactones, 5-methyl-6-prenyl-isobenzofuran-1(3H)-one (1), 5-hydroxymethyl-6-prenyl-isobenzofuran-1(3H)-one (2), together with four known phenolic compounds (3–6), were isolated from the leaves of Nicotiana tabacum. Their structures were elucidated by spectroscopic methods, including extensive 1D and 2D NMR techniques. Compounds 1–6 were evaluated for their anti-tobacco mosaic virus (anti-TMV) activities. The results showed that compounds 1–6 exhibited high anti-TMV activities with inhibition rates in the range of 16.9–26.2%, respectively.

Compounds 1-6 were tested for their anti-TMV activities. The inhibitory activity of compounds 1-6 against TMV replication were tested using the half-leaf method . Ningnanmycin (with inhibition rate of 30.4%), a commercial product for plant disease in China, was used as a positive control. The results showed that compounds 1-6 exhibited high anti-TMV activities with inhibition rates in the range of 16.9-26.2%, respectively (Table 1).

General
UV spectra were obtained using a Shimadzu UV-2401A spectrophotometer. A Tenor 27 spectrophotometer was used for scanning IR spectroscopy with KBr pellets. 1 D and 2 D NMR spectra were recorded on DRX-500 spectrometers with TMS as internal standard. Unless otherwise specified, chemical shifts (δ) were expressed in ppm with reference to the solvent signals. HReSIMS was performed on an API QSTAR time-of-flight spectrometer, or a VG Autospec-3000 spectrometer. Preparative HPLC was performed on a Shimadzu LC-8A preparative liquid chromatograph with a ZORBAX PrepHT GF (21.2 mm × 25 cm, 7 μm) column or a Venusil MP C 18 (20 mm × 25 cm, 5 μm) column. Column chromatography was performed with Si gel (200-300 mesh, Qing-dao Marine Chemical, Inc., Qingdao, China), Lichroprep RP-18 gel (40-63 μm, Merck, Darmstadt, Germany) and MCI gel (75-150 μm, Mitsubishi Chemical Corporation, Tokyo, Japan). The fractions were monitored by TLC, and spots were visualised by heating Si gel plates sprayed with 5% H 2 SO 4 in etOH.

Plant material
The leaves of N. tabacum L (tobacco leaves) were collected from Honghe County, Yunnan Province, P. R. China, in September 2013. The tobacco variety is K326, which had widely cultivated in China.

Anti-TMV assay
The Anti-TMV activities were tested using the half-leaf method , and ningnanmycin, a commercial product for plant disease in China, was used as a positive control.

Disclosure statement
No potential conflict of interest was reported by the authors.