Six new tetraprenylated alkaloids, designated as malonganenones L-Q (1-6), were isolated from the gorgonian Echinogorgia pseudossapo, collected in Daya Bay of Guangdong Province, China. The structures of 1-6 featuring a methyl group at N-3 and a tetraprenyl chain at N-7 in the hypoxanthine core were established by extensive spectroscopic analyses. Compounds 1-6 were tested for their inhibitory activity against the phosphodiesterases (PDEs)-4D, 5A, and 9A, and compounds 1 and 6 exhibited moderate inhibitory activity against PDE4D with IC50 values of 8.5 and 20.3 mu M, respectively.