Plants of the genus Plectranthus (family Lamiaceae) are an interesting source of abietan diterpenoid compounds. One important species of this genus is Plectranthus amboinicus, an herbal plant that grows naturally in tropical and warm temperate regions, such as in Africa, Asia, and Australia. One of the major compounds found in Plectranthus is royleanone, which belongs to the class of abietan di…