5,5 -Oxybis(1,3,7-trihydroxy-9 H -xanthen-9-one): A New Xanthone from the Stem Bark of Garcinia porrecta (Clusiaceae)

: A new polyoxygenated dimer-type xanthone, namely 5,5 (cid:48) -oxybis(1,3,7-trihydroxy-9 H -xanthen-9-one ( 1 ), has been isolated from the stem bark of Garcinia porrecta . The structure of 1 was determined based on spectroscopic data, including 1D and 2D-NMR as well as high resolution mass spectroscopy analysis.


Introduction
The famous Garcinia genus, representing a major source of triterpenes, flavonoids, xanthones, and phloroglucinols which have pharmacological activities as antioxidants, antibacterial, antiviral, anti-HIV, and significant anticancer activity [1].
The genus Garcinia belongs to the Clusiaceae family, which consists of more than 400 species widely distributed in the Polinesia mainland, India, Indochina, Indonesia, West and Central Africa, and Brazil [2]. Indonesia is known as one of the countries rich in diversity of Garcinia, there are 64 species of Garcinia scattered across several islands in Indonesia [3]. Various parts of Garcinia plants have been used in traditional medicine for the treatment of sprue (mouth ulcer), diarrhea, dysentery and skin disease [4]. Investigations into biologically active compounds from Indonesia Garcinia plants have resulted in some bioactive compounds being isolated from G. mangostana [5][6][7], G. celebica [8,9] and G. cowa [10]. Previous investigation on the stem bark of G. porrecta had led to the isolation of dulxanthone E-G, which showed strong cytotoxic activity against murine leukemia L1210 cells [6]. In this paper, we reported the isolation and structure elucidation of new polyoxygenated dimer-type xanthone, 5,5 -Oxybis(1,3,7-trihydroxy-9H-xanthen-9-one) (1) (Figure 1).

Discussion
Compound 1 was isolated as a yellow amorphous powder. The UV spectrum showed absorption bands at λmax 322 and 262 nm attributable to a conjugated system [11,12]. Its molecular composition was established to be C26H14O11 with twenty degrees of unsaturation from HR-TOFMS m/z 503.0667 [M + H] + , calculated for C26H15O11 (m/z 503.0614) and NMR spectral data ( Table 1). The IR spectrum exhibited bands at νmax 3412 cm −1 (hydroxyl), 2962 cm −1 (C-H stretching of aliphatic) and 1755 cm −1 (carbonyl).

Discussion
Compound 1 was isolated as a yellow amorphous powder. The UV spectrum showed absorption bands at λ max 322 and 262 nm attributable to a conjugated system [11,12]. Its molecular composition was established to be C 26 H 14 O 11 with twenty degrees of unsaturation from HR-TOFMS m/z 503.0667 [M + H] + , calculated for C 26 H 15 O 11 (m/z 503.0614) and NMR spectral data ( Table 1). The IR spectrum exhibited bands at ν max 3412 cm −1 (hydroxyl), 2962 cm −1 (C-H stretching of aliphatic) and 1755 cm −1 (carbonyl).
The 13 C-NMR spectrum demonstrated the presence of a total of 26 carbon signals, which were classified by their chemical shifts, DEPT, and HSQC spectra ( Figures S3 and S4) as eight sp 2 methine carbons, two carbonyl carbon at δ C 179.53 and 179.53, 16 sp 2 quaternary carbons (including two sp 2 carbons and 14 sp 2 oxygenated carbons). These functionalities accounted for 14 out of the total 20 degrees of unsaturations. The remaining of six degrees of unsaturation were consistent with six cyclics of bixanthones [13,14].

General Experimental Procedures
UV spectra were recorded on Vilber Lourmat UV/VIS spectrophotometer. Mass spectra were measured with a Waters Xevo QTOFMS instrument (Waters, Milford, MA, USA). IR spectra were measured on a One Perkin Elmer infrared-100. NMR data were recorded on a Bruker Avance-600 spectrometer at 600 MHz for 1 H and 150 MHz for 13 C using Tetramethylsilane (TMS) as an internal standard (Billerica, MA, USA). Chromatographic separations were carried out on silica gel G60

Plant Material
The stem bark of G. porrecta was collected from Bogor Botanical Garden, Bogor, Indonesia in April 2018. The plant was identified and deposited in the Herbarium Bogoriense (No. IV.K.78a), Center of Biological Research and Development, National Institute of Science, Bogor, Indonesia.