A New 30-nor Trijugin-type Limonoid , Chisotrijugin , from the Bark of Chisocheton cumingianus ( Meliaceae ) Dewa

A new 30-nor trijugin-type limonoid, chisotrijugin (1), has been isolated from the bark of Chisocheton cuminganus belong to the Meliaceae family. The chemical structure of 1 was elucidated by spectroscopic techniques such as UV, IR, MS, 1D and 2D NMR.

In our search for novel limonoid compounds from Indonesia Chisocheton plants, we started our search for novel compounds from the bark of Chisocheton cumingianus.C. cumingianus is a higher plants and widely distributed in northern part of Sulawesi island in Indonesia (Heyne, 1982).The plant is known in folklore and traditional medicine in Indonesia for the treatment of fever and skin diseases (Hidayat and Hutapea, 1991;Heyne, 1982).Although secondary metabolites from other Chisocheton species have been reported previously, the chemical constituents of C. cumingianus is yet to be reported.We report herein the isolation and structure elucidation of the new limonoid compound, 30-nor trijugin-type limonoid, chisotrijugin (1).

General
Melting points were measured on an electrothermal melting point apparatus IA9000 (Bibby Scientific Limited, Staffordshire, UK).Optical rotations were recorded on a Perkin-Elmer 341 polarimeter (Waltham, MA, USA).The IR spectra was recorded on a Perkin-Elmer 1760X FT-IR (Waltham, MA, USA) in KBr.Mass spectra was obtained with a Water Qtof HR-MS XEV otm mass spectrometer (Santa Clara, CA, USA). 1 H-and 13 C-NMR spectra were obtained with a JEOL JNM A-500 spectrometer (Tokyo, Japan) using TMS as an internal standard.Chromatographic separations were carried out on silica gel 60 and ODS (Merck, Darmstadt, Germany).TLC plates were precoated with silica gel GF 254 (Merck, Darmstadt, Germany, 0.25 mm), ODS (Fujisylisia, Tokyo, Japan), and detection was achieved by spraying with 10% H 2 SO 4 in ethanol, followed by heating.

Plant Material
The stem bark of C. cumingianus was collected in Bogor Botanical Garden, Bogor, West Java Province, Indonesia in April 2014.The plant was identified by the staff of the Bogoriense Herbarium, Bogor, Indonesia and a voucher specimen (No.Bo-1305316) was deposited at the herbarium.

Results and Discussion
Bark of C. cumingianus was grounded and successively extracted with n-hexane, ethyl acetate, and methanol.The ethyl acetate extract was chromatographed over a vacuum-liquid chromatographed (VLC) column packed with silica gel 60 by gradient elution.The fractions were repeatedly subjected to normal-phase and reverse-phase column chromatography to afford compounds 1 (Fig. 1).Chisotrijugin (1), was obtained as white needle-like crystals, m.p. (decomposed).Its molecular formula was determined as C 26 H 32 O 9 , was established from the HR-TOFMS spectra (m/z 489.2044, [M+H] + ) and NMR data (Table 1).The IR spectrum suggested the presence of a hydroxyl group (3482 cm -1 ), carbonyl ketone (1726 cm -1 ), carbonyl ester (1702 cm -1 ), olefinic (1630 cm -1 ), and ether groups (1153 cm -1 ).Twenty six carbon signals were observed in the 13 C NMR spectrum.The multiplicities of the carbons determined by DEPT spectra led to the attribution for five methyls, three methylenes, ten methines, eight quartenary carbons, including one ketone ( C 209.0), two ester carbonyls ( C 171.9 and 168.2), a β-substituted furan ( C 143.1, 141,5, 120.0, 110.3), one methine olefinic ( C 116.2), one quaternary carbon olefinic ( C 164.8), one methoxyl group ( C 52.2), three oxymethines ( C 69.1, 75.6, 81.1), and one anomeric carbons ( C 107.9).The NMR spectra of 1 showed similarities to those of trijugin C (Zhang et al., 2003).The signals of the β-substituted furan ring in the 1 H NMR spectrum occurred at  H 7.49 (H-21), 7.41 (H-23), and 6.54 (H-22) and the corresponding carbon signals at  H 141.5, 143.1, and 110.3, respectively, in the HMQC spectrum.Ring D was oxidized to a C-16 lactone, with H-17 occurring as a singlet at  C 5.18 and H-15 occurring as a pair of doublets at  H 1.92 and 2.76 (J = 15.6 Hz).The signal at  H 3.85 (3H, s) showed a HMBC correlation with an ester carbonyl at  C 169.9, indicating the presence of a methylester group at C-7. Ring A which opened was supported by the appearance of methyl doublet signal ( H 1.16, d, J=7.2 Hz, H-19) that correlated with methine at  C 36.8 (H-10), 55.9 (H-5), and an anomeric carbon at  C 107.9 (C-9).The presence of the double bond was deduced by the HMBC correlation between methine olefinic proton at  H 6.29 (H-8) to quaternary olefinic carbon at  C 164.6 (C-14), sp 3 quaternary carbon at  C 39.2 (C-13), and sp 3 methine carbon at δ C 34.1 (C-11) (Fig. 2).The presence of epoxide ring was deduced by 1 H-1 H COSY crosspeak between H-1/H-2.The relative stereochemistry at the chiral centers is suggested by comparation with previously data reported (Zhang et al., 2003).Based on the above spectral data, the structure of was determined to be as shown for 1.  (Purushothaman et al., 1987) was postulated that the trijugin may be formed by ring C contraction occurring by a Pinacol-Pinacolone rearrangement of a 9(11)-dihydroxy precursor and anticipated more detailed examination of such compounds would be necessary.In pentanortriterpenoid 1, C-30 has been removed by further oxidation of the 8(30) double bond.A continued with cleavage ether bridge at 1( 14) to form a double bond at 8( 14).The cleavage of ring A at 1(10) and formed an epoxide ring at 1(2) have not been described before.The oxidation of C-6 of tetranortriterpenoids with a lactone ring D and an opened ring B had been reported (Zhang et al., 2003).

Conclusion
The bark of C. cumingianus produce a new 30-nor trijugin-type limonoid, and was named chisotrijugin (1).This investigation indicate that Indonesian Chisocheton plants can produce an unique structure due to the environmetal condition.

Figure. 2 .
Figure. 2. Selected 1 H-1 H COSY and HMBC Correlations for 1. Usually tetranortriterpenoid with an open ring B have an 8(30) double bond.Trijugin class compounds have a rare contracted ring C and Connolly and co-workers(Purushothaman et al., 1987) was postulated that the trijugin may be formed by ring C contraction occurring by a Pinacol-Pinacolone rearrangement of a 9(11)-dihydroxy precursor and anticipated more detailed examination of such compounds would be necessary.In pentanortriterpenoid 1, C-30 has been removed by further oxidation of the 8(30) double bond.A continued with cleavage ether bridge at 1(14) to form a double bond at 8(14).The cleavage of ring A at 1(10) and formed an epoxide ring at 1(2) have not been described before.The oxidation of C-6 of tetranortriterpenoids with a lactone ring D and an opened ring B had been reported(Zhang et al., 2003).

Table 1 .
NMR data (500 MHz for 1 H and 125 MHz for 13 C, in CDCl 3 ) for 1