Chemical Constituents From Trichilia connaroides and Their Anti-Tobacco Mosaic Virus Properties

Further phytochemical investigation on the twigs of Trichilia connaroides led to the isolation of nine limonoids (1, 2, and 5-11), one 3,4-seco-homo-cycloartane (3), and two steroids (4 and 12). The structures of these obtained isolates were established by means of detailed analyses of their extensive spectroscopic information and electronic circular dichroism calculations, four of them were elucidated as undescribed compounds (1-4). It is noted that an unprecedented 7-oxabicyclo[2.2.1]-heptane moiety in trichilitin M (1) was proposed by the linkage of C-11 and C-14 via an oxygen atom. All compounds were evaluated for their anti-tobacco mosaic virus (anti-TMV) activities by the conventional half-leaf method and reverse transcription polymerase chain reaction (RT-PCR) assays. Compared with the positive control ningnanmycin, compounds 1, 6, 7, and 11 showed significant anti-TMV biological activities. Furthermore, quantitative RT-PCR assays suggested that the expression level of the TMV coat protein (CP) gene in inoculated and systemic K326 leaves treated by both 1 and 6, was significantly lower than that for the control group. More importantly, compounds 1 and 6 could not only inhibit the accumulation of the TMV CP gene but also enhance the host plant's resistance to TMV infection.