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

Abstract

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