Cytotoxic Alkaloids from the Flowers of Senna spectabilis

Three new alkaloids, 3(R)-benzoyloxy-2(R)-methyl-6(R)-(11′- oxododecyl)-piperidine (3), 5-hydroxy-2-methyl-6-(11′-oxododecyl) -pyridine (4) and 5-hydroxy-2-methyl-6-(11′-oxododecyl)-pyridine N-oxide (5), together with a known alkaloid, (-)-cassine (1), were isolated from the flowers of Senna spectabilis. A derivative, N,O-diacetylcassine (2), was semisynthesized. Their structures and stereochemistry were established on the basis of spectroscopic analysis. Cytotoxic activity and brine shrimp lethality of these compounds were evaluated. Compounds 2, 3 and 5 exhibited cytoxicity against KB cell lines with IC₅₀ values of 5.2, 3.7 and 2.0 μg/mL, respectively.