Topsendines A-F, new 3-alkylpyridine alkaloids from a Hainan sponge Topsentia sp.

Six new 3-alkylpyridine alkaloids, topsendines A-F (1-6), and one new naturally occurring product, 2-methyl-12-(pyridine-3-yl)dodecanal (7), were isolated from an undescribed species of Hainan sponge Topsentia. The structures of the new compounds were determined by extensive 2D NMR experiments, HR-EI/ESI-MS spectrometry measurements, and by comparison of their NMR data with those of structurally related compounds in the literature. In bioassay, compounds 1, 3, and 5 showed inhibitory actions on delayed rectifier K+ currents (I-K) in rat acutely dissociated hippocampal neurons at the concentration of 100 mu M, with the percentage of inhibition of 85.9 +/- 3.9%, 87.1 +/- 4.4%, and 76.2 +/- 12.2%, respectively. (c) 2014 Elsevier Ltd. All rights reserved.