Antivirus isoindolinone alkaloids with rare oxocyclopenta[f]isoindole frameworks isolated from the stems of flue cured tobacco

Abstract Background Since Nicotiana tabacum (tobacco) has important significance to humans for their medicinal uses, to find antivirus activities inhibitors from tobacco, increase its medicinal value, and comprehensive utilization of its by-products, our group had investigated the chemical constituents of the stems of Y-202, a cultivar of tobacco which high resistance to tobacco mosaic virus (TMV). Results Four new isoindolinone-type alkaloids, nicoisoindoles A–D ( 1 – 4 ), along with four known isoindole derivatives ( 5 – 8 ) were isolated. Compounds 1 – 4 represent a new subclass of isoindolinone alkaloids with rare cyclopenta[ f ]isoindole-1-one frameworks. Among them, nicoisoindole C ( 3 ) possesses an unusual N -2-(5-methoxy-6-methylpyridin-2-yl) ethyl moiety, while nicoisoindole D ( 4 ) has a novel a N -(3-methyl-6-oxo-1,6-dihydropyridin-2-yl)methyl substituent. Interestingly, compounds 1 , 3, and 4 showed high anti-TMV activities with inhibition rates of 43.8%, 58.8%, and 67.8% at the concentration of 20 μM, and IC 50 values of 23.6, 19.5 and 15.4 μM, respectively, even more potent than that of positive control. Conclusions The successful isolation and structure identification of new oxocyclopenta[ f ]isoindole-1-ones provide materials for the screening of antivirus activities inhibitors, and contribute to the development and utilization of the waste from tobacco cultivation. Graphical Abstract