DAMMARANE-TYPE TRITERPENOIDS FROM THE STEMBARK OF CHISOCHETON PENTANDRUS (MELIACEAE)

Two dammarane-type triterpenoids, cabraleadiol (1) and cabraleahydroxylactone (2), have been isolated from nhexane extract of the stembark of Chisocheton pentandrus (Meliaceae). The structure of compounds 1 and 2 were determined by spectroscopic data mainly NMR and mass as well as by comparing with previously reported spectral data. Compounds 1 and 2 were reported for the first time from Chisocheton pentandrus.


INTRODUCTION
Triterpenoids are the most important group of terpenoids because they exhibit a great diversity of biological activities and they are the major constituents of tropical higher plants. Recently, research of new biologically active compounds from plants used in traditional medicine has led to the isolation of numerous triterpenoids with important biological activities (Fu et al., 2015;Nguyen et al., 2015). Higher plants are major source of triterpenoids with several biological activities and numerous reports have shown that family of Meliaceae, Rhamnaceae, Cucurbitaceae, Ganodermataceae and Apocynaceae produce a wide variety of tetracyclic triterpenoids, whereas, family of Ranunculaceae, Burseraceae, Capparidaceae, Celastraceae and Lamiaceae families are recognized to contain active pentacyclic triterpenoids (Harneti et al., 2012;Farabi et al 2017;Tian et al., 2005;Zhang et al., 2005).
In our continous search for novel constituents from Chisocheton pentandrus, we isolated new limonoids, pentandricin A from the stembark of C. pentandrus (Suprianto et al., 2018). In the further investigation for novel compounds from non polar fraction of C. pentandrus, we found two dammarane-type triterpenoids from the n-hexane extract. In this paper, we report the isolation and structural determination of two dammarane-type triterpenoids, cabraleadiol (1) and cabraleahydroxylactone (2).

Plant material
The stem bark of C. pentandrus were collected in Bogor Botanical Garden, Bogor, West Java Province, Indonesia in June 2016. The plant was identified by Mr. Ismail, the staff of the Herbarium and a voucher specimen (No. Bo-104) was deposited at the Herbarium.

RESULTS AND DISCUSSION
In comparison of 1 with literature data of a cabraleadiol (Phongmaykin et al., 2008), showed good agreement, therefore compound 1 was identified as a cabraleadiol, which shown in this plant for the first time. Compound 2 was obtained as a white amorphous powder. The IR spectra showed absorption peaks at 3550 cm -1 (OH), 2960 and 2865 cm -1 (aliphatic), 1382 and 1238 cm -1 (gem-dimethyl groups), and 1040 cm -1 (C-O). The NMR spectra of 2 was very similar with 1. The main differences was the absence of an isopropyl alcohol group at [(δ H 1.17 (3H, s) and 1.09 (3H, s), δ C 24.1 (Me-27), 27.9 (Me-26) and 70.3 (H-25)] and the presence of carbonyl lactone signal at δ C 176.9, suggested that compound 2 was a lactone derivative of 1. In the HMBC spectrum, methylene signal at δ H 2.52 was correlated to carbonyl lactone at δ C 176.9, indicated that a carbonyl lactone was located at C-24 to make a lactone ring as a side chain ring.
The relative stereochemistry of 2 was identified based on coupling constants in the 1 H-NMR and biogenetic point of view occurrence of dammarane-type triterpenoid in Chisocheton genus (Supratman et al., 2019). In comparison of 1 with literature data of a cabraleahydroxylactone (Phongmaykin et al., 2008), showed good agreement, therefore compound 1 was identified as a cabraleahydroxylactone, which shown in this plant for the first time.

CONCLUSIONS
Two dammarane-type triterpenoids have been isolated from the the stembark of Chisocheton pentandrus belong to Meliaceae family and identified by spectroscopic data as cabraleadiol (1) and cabraleahydroxylactone (2). The investigation of these dammaranetype triterpenoids were shown in this species for the first time and strenghten the occurance of this compounds in this genera.