Complex sentence: Mesembrine is a major alkaloid present in "Sceletium tortuosum" and serves as a selective serotonin reuptake inhibitor (SSRI) with less prominent inhibitory effects on phosphodiesterase 4 (PDE4).
Split into simpler sentences: Mesembrine is a major alkaloid present in "S. tortuosum". It serves as a selective serotonin reuptake inhibitor (SSRI) with less prominent inhibitory effects on phosphodiesterase 4 (PDE4).