Biol. Pharm. Bull. 28(12) 2258—2262 (2005)

treated with nucleoside analogs such as acyclovir (ACV). However, viruses can become resistant in immunosuppressed patients and in patients with acquired immunodeficiency syndrome. Because such ACV-resistant viruses are also resistant to other nucleoside analogs, new therapeutic agents with a different mode of anti-HSV action are required. Many natural products can inhibit viruses. Natural marine products contain an abundance of biologically active substances with novel chemical structures and favorable pharmacological activities. Marine organisms are also a promising source of antiviral compounds. Several investigators have described the inhibitory effects of algal extracts and their constituents on the replication of herpes simplex viruses. Serkedjieva recently found that a water extract of Polysiphonia denudata (Rhodomelaceae) prevents HSV-1 reproduction by inhibiting viral adsorption to susceptible cells as well as viral synthetic stages. The present paper describes the antiviral activity of MeOH extracts of seaweeds collected in Korea, their fractions and constituents. Furthermore, the therapeutic efficacy of some anti-HSV compounds isolated from Symphyocladia latiuscula (Rhodomelaceae) in vitro was evaluated in an experimental animal model in vivo.