Sesquiterpenoid Compounds from The Stembark of Aglaia minahassae ( Meliaceae )

Two sesquiterpenoid compounds, 4(15)-eudesmen-1,6-diol (1) and spathulenol (2) have been isolated from the stembark of Aglaia minahassae belong to Meliaceae family. The chemical structures of 1 and 2 were identified on the basis of spectroscopic evidence including UV, IR, NMR 1D, NMR 2D as well as mass spectra and by comparison with those previously reported spectra data. This compounds were isolated from this plant for the first time.


INTRODUCTION
Meliaceae plant is the important plant families that have utilization and generally grow in the tropical countries. Meliaceae plant are known for the presence of the various secondary metabolite compounds that exhibit interesting biological activity such as hypoglycemia, anticancer, anti-inflammation, antifeedant, antitumor Leong et al., 2016;Su et al., 2006) and insecticidal activity (Nugroho et al., 1999).
Sesquiterpenes are less volatile than terpenes, have a greater potential for stereochemical diversity and stronger odors (Waterman, 1993). They are anti-inflammatory (Jeena et al., 2013) and have bactericidal properties (Ishnava et al., 2013). Sesquiterpenes oxidize over time into sesquiterpenols. In patchouli oil, this oxidation is thought to improve the odor. One of the most anti-inflammatory sesquiterpenes, chamazulene, only has 14 carbon atoms but is usually included with sesquiterpenes. Chamazulene and caryophyllene have strong antioxidant (Ornano et al., 2013) and antitumor activity (Feraz et al., 2013;Park, et al., 2011). Some sesquiterpenes such as α-farnesene can be effective against the bacteria that cause tooth decay (Ishnava et al 2013). Liu et al. (2014) isolated and discribed four guaian sesquiterpenes and an eudesmene sesquiterpene from the twigs of Aglaia odorata var. microphyllina. Pan et al. (2010) were isolated eudesmene-type sesquiterpene from the stem bark of Aglaia foveolata obtained in Kalimantan, Indonesia. Although sesquiterpenoids of other Aglaia species have been investigated previously, the sesquiterpenoid derivatives of A. minahassae is yet to be reported. In this communication, the isolation and structure identification of eudesmene-type and aromadendran-type sesquiterpenoids are described.

General Experiment Procedure
The IR spectra were recorded on a Perkin-Elmer spectrum-100 FT-IR (Waltwam, MA, USA) in KBr. Mass spectra were obtained with a Synapt G2 mass spectrometer instrument (Waters, Milford, MA, USA). NMR spectral data were performed on a Bruker Topspin spectrometer at 500 MHz (Bruker BioSpin GmbH, Silberstreifen 4, D-76287 Rheinstetten, Germany), with CDCl3 as a solvent, chemical shifts were given on a δ (ppm) scale and tetramethylsilane (TMS) as an internal standard. Column chromatography was conducted on silica gel 60 (Merck, Darmstadt, Germany) and octadesyl sylane (ODS, Fuji Sylisia, Japan). TLC plates were precoated with silica gel GF254 (Merck, 0.25 mm) and detection was achieved by spraying with 10% H2SO4 in EtOH, followed by heating.

Plant Material
The stembark of A. minahassae were collected in Bogor Botanical Garden, Bogor, West Java Province, Indonesia in January 2016. The plant was identified by the staff of the Bogoriense Herbarium, Research Center for Biology, Indonesian Institute of Science, Bogor, Indonesia and a voucher specimen (No. BO-1294551) has been deposited at the herbarium.

Extraction and Isolation
The dried stembark of A. minahassae (1.68 kg) was extracted with methanol (12 L) at room temperature for 3 days. The methanol extract was evaporated under vacuum to yield a dark brown residue (225.1 g). This residue was dissoved in water and partioned succesively with n-hexane (10 L), ethyl acetate (10 L) and n-butanol (10 L). Evaporated of this extracts resulted of n-hexane (9.38 g), ethyl acetate (7.05 g) and n-butanol (7.63 g), respectively.

RESULTS AND DISCUSSION
The n-hexane extract of the stembark of A. minahassae was chromatographed over a vacuum-liquid chromatographed (VLC) column packed with silica gel 60 by gradient elution. The VLC fractions were repeatedly subjected to silica gel and ODS column chromatography as well as preparative thin layer chromatography (PTLC) on silica gel GF254 to afford a compounds 1 and 2 ( Figure  1).
Compound 1 was obtained as a white amorphous solid. The molecular formula was determined to be C15H26O2 on the basis of HR-TOFMS spectrum showed [M+H] + m/z 237.1907 (calcd. m/z 237.1855) and NMR spectral data (Table 1), thus requiring three degree of unsaturations. The IR spectra of compound 2 showed absorption peaks due to of hydroxyl group (3420 cm -1 ), aliphatics (2970 and 2870 cm -1 ), isolated double bond (1580 cm -1 ) and ether group (1168 cm -1 ).  Hz, CH3-12) and 0.95 (3H, d, J=7.0 Hz, CH3-13) were assigned to an isopropyl group. Two oxygenated methine proton signals at H 3.42 (1H, dd, J= 4.8, 11.6 Hz),  H 3.71 (1H, m) were also observed in the 1 H-NMR spectrum. In addition, the presence of a sp 2 gemmethylene proton signals were observed at H 4.74 (1H, d, J=1.0 Hz), 5.02 (1H, d, J=1.0 Hz) and other aliphatic signals at upfield regions also were oberved in the 1 H-NMR spectrum. The 13 C-NMR spectrum showed fifteen carbon signals, which were classified by their chemical shifts and DEPT spectra as one tertiary methyl, two secondary methyls, two oxygenated sp 3 methines, one sp 2 methylenes, one sp 2 quaternary, four sp 3 methylenes, three sp 3 methines and one sp 3 quaternary carbons. This functionalities accounted for one out of the total three degrees of unsaturation. The remaining of two degrees of unsaturation were consistent with eudesmen-type sesquiterpenoid skeleton (Kitajima, Suzuki, Satoh, & Watanabe, 2002).
The 13 C-NMR spectrum of compound 2 in combination with DEPT experiments displayed the presence of fifteen carbon signals comprising of three tertiary methyl, one sp 2 methylene, one sp 2 quaternary carbon, one oxygenated sp 3 quaternary carbon, four sp 3 methylene, four sp 3 methines, and one sp 3 quaternary carbon. This functionalities accounted for one out of the total four degrees of unsaturation. The remaining of three degrees of unsaturation were consistent with tricyclic aromadendran-type sesquiterpenoid (Phongmaykin, Kumamoto, Ishikawa, Suttisri, Saifah, 2008).

CONCLUSIONS
Eudesmaene-type sesquiterpenoid, 4(15)eudesmen-1β,6α-diol (1) and aromadendrantype sesquiterpenoid compounds, spathulenol (2) have been isolated from the stembark of A. minahassae. Both compounds were isolated from this plant for the first time and indicated the ability of Aglaia species to produce a sesquiterpenoid compounds. The discovery of two sesquiterpene compounds from the stembark of A. minahassaealso reinforces previous phytochemical studies of the occurance of sesquiterpenoid in the Aglaia genus.