This article reports the compounds identified in the leaf oils of five Clauseana species growing in Vietnam. The hydrodistilled oils were analysed for their chemical constituents by using gas chromatography-flame ionisation detector and gas chromatography coupled with mass spectrometry. The major compounds identified in Clausena dentata (Willd.) M. Roem. were α-pinene (21.7%), sabinene (18.3%) and β-myrcene (14.3%). Clausena dimidiata Tanaka comprised mainly of safrole (56.9%) and α-terpinolene (22.1%). However, 1-menthone (70.6%) and β-phellandrene (13.0%) were the most abundant compounds of Clausena indica (Dalz.) Oliver. Sesquiterpene compounds represented mainly by β-caryophyllene (16.7%), spathulenol (11.9%) and bicyclogermacrene (7.5%) were the major constituents of Clausena excavata Burm. f., while those of Clausena engleri Tanaka include bicycloelemene (12.1%), bicyclogermacrene (11.0%) and (E)-nerolidol (6.6%). This is the first report on the chemical analysis of essential oils of C. dimidiata and C. engleri.

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Herein, we report the results of our investigation on essential oils obtained by hydrodistilation of the leaves and fruits of Manglietia dandyi (Gagnep.) Dandy. The constituents of the oils were analyzed by gas chromatography-flame ionization detector (GC-FID) and gas chromatography-mass spectrometry (GC-MS). The yields of the oils were 0.25% and 0.21% (v/w, leaf and fruit respectively), calculated on a dry weight basis. The main constituents of the leaf oils were (E)-nerolidol (18.4%) and α-selinene (11.0%) while the fruit oils contained abundance of β-caryophylene (27.7%), -cadinene (13.7%), α-humulene (13.2%) and α-copaene (11.6%). The results indicated that M. dandyi leaf oil exhibited 96% and 100% mortality towards the fourthinstant larvae of Aedes albopictus at 24 h at tested concentrations of 50 µg/mL and 100 µg/mL. The oil only displayed 100% mortality at concentrations of 50 and 100 µg/mL and under 48 h. The minimum lethal concentrations, LC50, were 29.57 g/mL (24 h) and 29.02 g/mL (48 h); while the LC90 values of 46.21 g/mL and 42.29 g/mL were obtained respectively at 24 h and 48 h g/mL. The chemical constituents and larvicidal action of M. dandyi essential oils are being reported for the first time.

Chemical composition of essential oils obtained from the leaf of Syzygium bullockii and Syzygium tsoongii were reported, corresponding oil content 0,36% and 0,27%. The analysis was performed by means of gas chromatography-flame ionization detector (GC-FID) and gas chromatography coupled with mass spectrometry (GC-MS). Twenty-seven components were identified in leaf oil of Syzygium bullockii, which represented about 76,75% of the total composition of the oil and six components were not identified, which represented 15,72%. The major constituents of the essential oil were (E)-caryophyllene (49,65%), spathulenol (4,29%), caryophyllene oxide (4,14%), bicyclogermacrene (3,35%), 2-tridecanone (3,25%). Fourty-six components were identified in leaf oil of Syzygium tsoongii, which presented about 99.71% of the total composition of the oil. The major constituents of the essential oil were E-caryophyllene (23,40%), bicyclogermacrene (21,23%), (Z)-β-ocimene (10,61%), α-humulene (6,33%), (E)-β-ocimene (4,99%). For the first time, the chemical compositions of the essential oils of Syzygium bullockii and Syzygium tsoongii from Vietnam were being reported.

Chemical composition and antioxidant activity of the essential oil of Alseodaphne velutina Chev.(Lauraceae) were investigated for the first time from Viet Nam. Leaf essential oil was hydrodistilled and analysed by GC and GC-MS that totally identified 32 terpenoid compounds (accouting for 89.18% of the total oil) with β-patchoulene (25.74%) and β-caryophyllene (12.81%) as two major sesquiterpene hydrocarbons compounds. The antioxidant potential of leaf essential oil was evaluated using DPPH, ABTS and FRAP assays, and revealed a moderate-tohigh activity comparable with already known antioxidant standard Trolox.