β-Carboline Alkaloids from the Seeds of Peganum harmala and Their Anti-HSV-2 Virus Activities

Pegaharines A-G (1-6), six novel beta-carboline alkaloids representing three types of skeleton, were isolated from the seeds of Peganum harmala. Compound 1 is a peculiar beta-carboline alkaloid characterized by the unprecedented carbon skeleton of an azepine-indole system. Compounds 3-6 represent the first examples of heterodimers constructed from rare tetracyclic beta-carboline and classic tricyclic beta-carboline alkaloids. Compounds 1 and 2 were characterized by X-ray crystallography. Compound 4 exhibited strong antiviral activity against HSV-2, with an IC50 value of 2.12 +/- 0.14 mu M.