Departamento de Química Orgánica and Instituto Multidisciplinario de Biología Vegetal (IMBIV-CONICET), Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciencias Químicas II, Ciudad Universitaria, Córdoba CP 5000, Argentina.
Two new withanolides were isolated and characterized from the aerial parts of Jaborosa kurtzii, namely, jaborosalactone 43 (1), with a spiranoid delta-lactone at C-22, and jaborosalactone 44 (2), a 12-oxowithanolide, which may function as a biosynthetic precursor to 1. These new compounds were fully characterized by a combination of spectroscopic methods. Compound 1 showed selective phytotoxicity toward a dicotyledon species, Lactuca sativa (lettuce).