Further New Xenicanes from a Chinese Collection of the Brown Alga Dictyota plectens.

Four new xenicanes, namely 4α-hydroxyisodictyohemiacetal (1), 4α-hydroxyisodictyoacetal (2), 13,18-diacetoxy-4-hydroxyisodictyo-19-al (3), and 4α-hydroxypachylactone (8), were isolated from a Chinese collection of the brown alga Dictyota plectens, along with four known analogues (4-7). The structures of the new diterpenes were determined by extensive spectroscopic data analysis. All compounds were evaluated for their antiviral activities against human immunodeficiency virus type 1 (HIV-1) and the highly pathogenic avian influenza A (H5N1) virus, and inhibitory effects on lipopolysaccharide (LPS)-induced nitric oxide (NO) production in mouse peritoneal macrophages (PEMΦ).