Comparative Phytochemical Analyses of Resins of Boswellia Species (B. papyrifera (Del.) Hochst., B. neglecta S. Moore, and B. rivae Engl.) from Northwestern, Southern, and Southeastern Ethiopia
Oleogum resins of B. papyrifera, B. neglecta, and B. rivae were collected from northwestern, southern, and southeastern Ethiopia, and their respective methanol extracts and essential oils were extracted and analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The investigation on essential oils led to the identification of 6, 7, and 8 constituents for B. papyrifera, B. neglecta, and B. rivae, respectively. The essential oil of B. papyrifera is mainly characterized by the presence of octyl acetate (57.1–65.7%) and n-octanol (3.4–8.8%). B. neglecta is rich in α-pinene (32.6–50.7%) followed by terpinen-4-ol (17.5–29.9%) and α-thujene (12.7–16.5%), whereas B. rivae was predominated by α-pinene (32.5–66.2%) followed by p-cymene (5.7–21.1%) and limonene (1.1–19.6%). Methanol extracts of the three Boswellia species were found to consist of diterpines (incensole, incensyl acetate and verticilla-4(20),7,11-triene), triterpenes (β-amyrin, α-amyrin, β-amyrenone, and α-amyrenone), nortriterpenes (24-noroleana-3,12-diene and 24-norursa-3,12-diene), and α-boswellic acid. The investigation on the methanol extract showed that only B. papyrifera contains diterpenes and nortriterpenes, whereas B. rivae and B. neglecta consist of only triterpenes. The results indicate that the three Boswellia species were characterized by some terpenes and these terpenoic constituents could be recognized as chemotaxonomical markers for each species. 1. Introduction The family Burseraceae is represented by 17 genera and 500–600 species, widespread in tropical and subtropical regions. The genus Boswellia has about 25 species of small trees and shrubs occurring in dry land regions from west Africa to Arabia and from south to northeast Tanzania, in India, and one species in Madagascar. The genus is centered in northeast Africa where about 75% of the species are endemic to the area. They are trees or shrubs often with latex, resins, or oils which are strongly aromatic [1, 2]. Frankincense, gum olibanum, or olibanum are the common names given to the oleogum resin which is obtained through incisions made in the trunks of trees of the genus Boswellia (family Burseraceae). It is plant product and belongs to a group of aromatic gums and resins which contain odiferous substances [2–4]. Frankincense consists of essential oils, gum, and terpenoids [5]. It is a complex of 30–60% alcohol soluble resins (diterpenes, triterpenes), 5–10% essential oil, which is soluble in organic solvents, and the rest is made up of polysaccharides (gum), which are soluble in water [2]. Its
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