The essential oils and isolated constituents of Neolitsea kedahense, Neolitsea coccinea and Neolitsea zeylanica and their bioactivities

Abstract

Three Malaysian species of Neolitsea, N. kedahense Gamble, N. coccinea B. C. Stone, and N. zeylanica (Nees) Merr. have been investigated. The aims of this study were to analyse the chemical composition of the essential oils, isolate and identify the pure compounds, and screen the antibacterial, α-glucosidase inhibitory and antioxidant activities. The essential oils were extracted by hydrodistillation and analysed by capillary gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The pure compounds were isolated by sequential maceration followed by fractionation and purification using several chromatographic techniques. The structures of the pure compounds were elucidated by spectroscopic methods. δ-Cadinene (17.4%) was the main compound of the stem oil of N. kedahense, while β-caryophyllene (18.9%) and bicyclogermacrene (18.6%) were the major compounds of the leaf oil. The main compounds in the stem and leaf oils of N. coccinea were δ-cadinene (21.2%) and selin-11-en-4-α-ol (26.8%), respectively. The bark and the heartwood oils of N. zeylanica were found to be rich in α-cadinol (15.7%) and τ-cadinol (21.4%), respectively, while its leaf oil was dominated by β-caryophyllene (38.4%). Twenty nine compounds, comprising of twelve sesquiterpenoids, six triterpenes, six flavonoids and five alkaloids were isolated from three Neolitsea species. Two new sesquiterpenoids, kedahensane and coccinine, together with another three new alkaloids, kedahensines A-C, were successfully identified. Kedahensane, kedahensines A and B, taraxerone, taraxerol, pseudoneoliacine, daibucarboline A and linderaggrine A were obtained from the stem extract of N. kedahense. Purification of the stem and leaf extracts of N. coccinea afforded coccinine, kedahensine C, linderane, linderalactone, pseudoneolinderane, linderanlide C, linderanine A, epicatechin, (-)-taxifolin, astilbin, L-quercitrin and afzelin. Isolation of compounds from the bark and leaf extracts of N. zeylanica yielded zeylanidine, zeylanine, lupenone, epifriedelanol, lupeol, 29-norlupan-3,20-dione, genkwanin, zeylaninone, acutotrinol, afzelin, astilbin and L-quercitrin. The leaf oil of N. coccinea demonstrated moderate antibacterial activity against Bacillus subtilis with MIC value of 250 μg/mL. The stem oil of N. kedahense (IC50 16.76 μg/mL), linderalactone (IC50 12.72 μM) and linderanlide C (IC50 12.10 μM) showed the strongest activity against α-glucosidase enzyme. The ethyl acetate extract of the stem of N. coccinea showed the highest total phenolic content at 501.42 mg GAE/g and also displayed good DPPH radical scavenging activity (IC50 21.11 μg/mL). The presence of the new compounds in N. kedahense and N. coccinea could be used as chemotaxonomic markers for classification of the Neolitsea species.