Secondary Metabolites from Durio Spp.: The Indigenous Indonesian Fruit Plant

The goal of this PhD research was directed to the isolation and structural elucidation of the secondary metabolites from four species of Durio plants, especially from those growing in the island of Borneo; This island contains most Durio species. The structures of isolated compounds were deduced using state-of-the-art approaches, including 1D and 2D nuclear magnetic resonance (NMR), mass spectrometric (MS) and circular dichroism (CD) analyses. From the bark of the woody species Durio zibethinus Murr. (Bombacaceae), that was collected in Pontianak, a chemically diverse group of oxygenated compounds was obtained. These included caffeoyl triterpenes, lignans and phenylpropanoid derivatives. During this research, one new compound 27-O-cis-caffeoylcylicodiscate was obtained which resulted from a trans to cis isomerization; this process might be caused by acid and light. Two presumed fungal metabolites were also isolated during this study, these possibly arising from fungal (unknown species) contamination of the bark. The relative stereochemistry of 4-hydroxymellein were also established by conversion to it diacetate and measurement of the coupling constant between H-3 and H-4. The absolute configuration was determined by comparison of []D values with those from the literature. Assignment of the 13C NMR spectrum for (+)-(R)-de-O-methyllasiodiplodin was completed using HSQC-TOCSY data. The methanol extract of the bark of Durio kutejensis (Hassk.) Becc. was fractionated and purified by C18-HPLC. Two new caffeoyl pentacyclic triterpenes 3-O-trans-caffeoyl-2-hydroxyolean-12-en-28-oic acid and 3-O-trans-caffeoyl-2-hydroxyurs-12-en-28-oic acid, together with five known compounds were isolated. The known compound fraxidin had previously been obtained from D. zibethinus Murr. The bark of Durio carinatus Mast., a plant species which has non edible fruit was collected in Sambas district, West Kalimantan. Three new lignans, boehmenan X, (-)-(7S,8S)-threo-carolignan X and (-)-(7R,8S)-erythro-carolignan X, and a new caffeoyl triterpene 3-O-cis-caffeoyl betulinic acid, together with three known lignans and one known caffeoyl triterpene, were obtained from the crude MeOH extract. The relative configurations and conformational models of the diastereomers threo- and erythro-carolignan X were determined by the coupling constant data for H-7′ and H-8′ and supported by 2D NMR spectroscopic analysis including NOESY and HSQC-HECADE in CDCl3. However, the magnitude of the coupling constants for both compounds in MeOH-d4 was similar. The stability of the individual conformers was solvent dependent and must be considered for their contribution to the overall conformational equilibria. This stability was determined by steric interactions, dipole repulsion effects and intramolecular hydrogen bonding. The absolute configuration of the two new diastereomers was established by application of circular dichroism (CD) and optical rotation []D measurements. Another Durio plant studied and collected in Bengkayang region, West Kalimantan, was Durio oxleyanus Griff. From the MeOH extract of its bark, two new lignans, (-)-(7S,8S)-threo-carolignan Y and (-)-(7R,8S)-erythro-carolignan Y were isolated using C18-HPLC. The relative stereochemistry of the carolignan Y diastereomers could not be deduced from the coupling constants for H-7′ and H-8′ either in CDCl3 and MeOH-d4, because of the presence of multiple conformers. The conformational model for the diastereomers of carolignan Y was similar to that of threo- and erythro-carolignan X in MeOH-d4. Using 2D NMR spectroscopic methods, including NOESY and HSQC-HECADE, the relative stereochemistry of the threo and erythro isomers of carolignan Y was confirmed. Further, the absolute configuration of threo- and erythro-carolignan Y was explored via analysis of CD spectra and by comparison of experimentally obtained []D values with literature values