New Monocyclic Terpenoid Lactones from a Brown Algae Sargassum macrocarpum as Monoamine Oxidase Inhibitors.

Algae are unique natural products that can produce various types of biologically active compounds. The 70% ethanol extract of brown algae Sargassum macrocarpum collected from the East Sea of Korea inhibited human monoamine oxidases A and B enzymes ( h MAO-A and h MAO-B) at a 50 μg/mL concentration. The bioassay-guided isolation was performed through solid-phase extraction and the Sepbox system followed by serial high-performance liquid chromatography on the reverse phase condition, resulting in the identification of two new monocyclic terpenoid lactones, sargassumins A and B ( 1 and 2 ). The planar structures of the compounds were determined by a combination of spectroscopic data. The absolute configurations were determined by the interpretation of circular dichroism data. Compound 1 exhibited mild h MAO-A inhibition (42.18 ± 2.68% at 200 μM) and docked computationally into the active site of h MAO-A (-8.48 kcal/mol). Although compound 2 could not be tested due to insufficient quantity, it docked better into h MAO-A (-9.72 kcal/mol). Therefore, the above results suggest that this type of monocyclic terpenoid lactone could be one of the potential lead compounds for the treatment of psychiatric or neurological diseases.