## 1 Introduction  
The fortitude of traditional medicine depends on the knowledge of plant medicinal characteristics. The major drivers of the pharmacological actions of medicinal plants are plant secondary metabolites [1; 2]. Secondary metabolites are known as signal molecules for plant biosynthesis but also play defense role against herbivores, and other plants and microbes [3; 4; 5]. Terpenes are a diverse and big group of organic compounds, which are present in medicinal plants and may protect the plants that produce them by deterring herbivores and by attracting predators and parasites of herbivores [6]. The treatment of health disorders and infections with herbal medicines engages active natural products, mostly of low molecular weight, with great structural diversity such as terpenes and terpenoids [7; 8]. Terpenes and terpenoids are the main components of the essential oils of many types of plants and flowers. Their biosynthesis occurs within specific tissues or at specific stages of development in plants [9]. Many terpenoids also possess pharmaceutical properties and are currently being used in clinical practices. Nowadays, terpenoids intensively applied in traditional drugs are taxol (ditrepene) from _Taxus bucata_ L. and artemisinin (sesquietpene lactone) from _Artemisia annua_ L. as malaria and cancer medicines, respectively, and forskolin (Figure 1a) from _Coleus forskohlii_ (Willd.) Briq. (also known as _Plectrantthus forskohlii_ Willd.) (Lamiaceae) [10; 11; 12; 13]. Forskolin is known to treat conditions such as heart complications, respiratory disorders, and asthma [14; 15]. In particular, forskolin, which is exclusively found in the root of _C. forskohlii_, has been used in traditional Indian Ayurvedic, under the name \"Makandi\" or \"Mayani\", and Southeast Asian medicine since ancient times [15]. In African countries, it is commonly known as a drug in diseases of the digestive, urinary and respiratory tracts [16]. _C. forskohlii_ is commonly found in Nepal, Burma, Thailand, and India. It is also grown in many East African countries [16; 17; 18]. India is a leading exporter of _C. forskohlii_ extracts and its products to various countries, mainly USA, Poland, South Korea, Australia, Japan, Italy, Spain, South Africa, and Canada [19]. Chemically, the whole plant is rich in alkaloids, but the most desirable part of the plant is the roots, because they contain the highest concentrations  
Figure 1: The chemical structure of: (**a**) forskolin; (**b**) geranyl geranyl diphosphate; and (**c**) 13R-manoyl oxide. of forskolin. In the extracts obtained from the _C. forskolhii_, the presence of \(\alpha\)-amyrin, \(\beta\)-sitosterol, betulinic acid, \(\alpha\)-cedrol, citronellal and \(\alpha\)-cedren was also identified. Other diterpenoids such as forskoditerpenoside A and B were also detected in the ethanolic extract from _C. forskolhii_, while in the essential oil obtained from the roots of the plant were identified, among others: borneol, \(\alpha\)-humulene, 1-octadecanol, 1-decanol, decanoic acid, 4-terpineol, 1,8-cineol, \(\alpha\)- and \(\beta\)-pinene, camphene, \(\alpha\)-cedrol, \(\alpha\)-ylangene, and \(\gamma\)-terpinene [15; 16; 18]. However, the latter compounds have a weaker therapeutic effect compared to forskolin. Hence, the research results show that forskolin is mainly responsible for the pharmacological activity of herbal materials obtained from this species [20]. Forskolin, or coleonol, is a labdane diterpene synthesized in the plastid of plant cells. In the higher plant, the non-mevalonic acid pathway takes place in plastids and synthesizes hemi-, mono-, sesqui-, and diterpenes along with carotenoids and phytol tail of chlorophyll [21]. Forskolin is synthesized by diterpene synthases via the substrate protonation at the 14,15-double bond of the initial precursor geranyl geranyl diphosphate (Figure 1b) [22]. Forskolin contains some unique functional elements, notably the tetrahydropryan-derived heterocyclic ring [23].