•Resveratrol oligomers was isolated from Upuna borneensis.•Absolute configurations were determined based on NMR and CD spectral properties.•Occurrence of O-glucosides bearing an epimeric aglycone of resveratrol pentamers were exhibited.A comprehensive investigation of the chemical constituents of the leaves of Upuna borneensis (Dipterocarpaceae) was performed. Three new glucosides of resveratrol oligomers having a pentameric aglycone [upunoside E (1)] and dimeric aglycones [upunosides F (3) and G (4)], as well as 14 resveratrol derivatives (2, 5–17), were isolated. The absolute configurations of the new compounds were elucidated by spectroscopic analysis, including two-dimensional NMR and CD spectra.Download high-res image (209KB)Download full-size image

•Regioisomeric synthetic cannabinoids with an N-flurobenzyl indole were synthesized.•GC–EI–MS–MS gives unambiguous information for the differentiation of regioisomers.•The fragmentation pathways were speculated by the results of the product ion spectra.Differentiating halogen positional isomers of aromatic compounds using gas chromatography and mass spectrometry is a challenging task due to insufficient chromatographic separation and close similarity in the mass spectra of the isomers. For synthetic cannabinoids (SCs), a growing number of halogen derivatives have emerged, while there is no convenient and easily accessible procedure to differentiate the regioisomers of illegal drugs. In the current study, FUB-JWH-018 and its five isomers having structural and regioisomeric features were synthesized to investigate mass spectrometric differentiation by gas chromatography–electron ionization–tandem mass spectrometry (GC–EI–MS–MS). The ions at m/z 379, 378, and 362 were selected as precursor ions for this study based on their EI mass spectra. Differences in relative intensity of product ions were observed among the isomers, enabling feasible regioisomeric differentiation by mass spectrometry. Furthermore, high reproducibility of the product ion spectra at the optimized collision energy was confirmed and FUB-JWH-018 was successfully identified from illegal drug market products, demonstrating the reliability and practicality of the method. The characteristic properties in fragmentation with the mechanistic pathways are also described. This is the first report on mass spectrometric differentiation of the isomers of SCs bearing substituted regioisomeric fluorobenzyl moiety on 1H-indole core by GC–EI–MS–MS. The procedure has great potential to help in differentiating halogen positional isomers, providing clues to discriminate newly encountered designer drugs in the fields of analytical chemistry and forensic toxicology.Download high-res image (163KB)Download full-size image

A resveratrol (Res) hexamer (vaticanol M (1)) and two O-glucosides of 1 (vatcasides E (2) and F (3)) and an epimer of 2 (vatcaside G (4)) were isolated from three Vatica species—Vatica bantamensis, Vatica chinensis, and Vatica albiramis. The structures with a 3-(3,5-dihydroxyphenyl)-4,6-dihydroxy-2-(4-hydroxyphenyl)-2,3-dihydro-1H-inden-1-yl group on the C-12 position of (−)-vaticanol B (5) were elucidated by spectroscopic analysis, including NMR experiments, conformational search by a MacroModel module, and circular dichroism data.

A new resveratrol tetramer, vaticanol K (1) was isolated from the stem of Vatica chinensis. On the basis of combined spectroscopic analyses, the compound was structurally elucidated. Compound 1 possesses an unprecedented fused 2,7-dihydrooxepine–quinone methide skeleton presumably derived from the concerted intramolecular cyclization of two resveratrol dimers followed by desaturation extending conjugation.

Dehydroxylation of naturally occurring oligomeric resveratrol derivatives resulted in the formation of compounds with dramatically reduced principal stable conformers. In addition, dehydroxylation allowed the determination of the absolute configurations of the original resveratrols via comparison of experimental and theoretical electronic circular dichroic spectra. Notably, the absolute configuration of pauciflorol B was identified using this novel procedure, which is the first application of dehydroxylated derivatives for the determination of the absolute configuration of naturally occurring polyphenols.

•Two new glucosides of resveratrol dimers were isolated from Shorea cordifolia.•Absolute configurations of isolates were determined based on CD spectral properties.•Co-occurrence of O-glucosides of resveratrol dimers with enantiomeric aglycones was exhibited.Two O-glucosides of resveratrol dimers, ampelopsin F-11b-O-β-glucopyranosides with enantiomeric aglycones [cordifoloside A (1) and cordifoloside B (2)] and an enantiomer of the aglycone [(−)-ampelopsin F] were isolated from the leaves of Shorea cordifolia (Dipterocarpaceae). These structures were identified on the basis of spectroscopic evidence and their absolute configurations were elucidated using circular dichroism data. This is the first report on oligostilbenoids that demonstrates the co-occurrence of diastereomeric O-glucosides with enantiomeric aglycones in this family.

In this study, we isolated a new glucoside of the resveratrol trimer (hopeaside E) from the stem wood of Hopea utilis. The glucoside structure is partially composed of balanocarpol (resveratrol dimer) after oxidative condensation of the (E)-resveratrol-10-C-β-glucopyranoside. The structure elucidation was achieved by spectroscopic analysis including NMR experiments, and the absolute configuration was determined on the basis of the comparative configurational analysis with the β-d-glucopyranosyl group. Conformational analysis was also performed by considering deshielding effects due to aromatic rings using computational methods of molecular modeling. The aglycone has six asymmetric carbons with two aliphatic hydroxyl groups attached to them that has not been reported in any other resveratrol derivative studies.Graphical abstractHighlights► A new glucoside of the resveratrol trimer (hopeaside E) was isolated from Hopea utilis. ► The absolute configuration was based on the comparative configurational analysis with the β-d-glucopyranosyl group. ► Conformational analysis was performed by considering deshielding effects due to aromatic rings.

Three stereoisomeric stilbene trimers bearing an (E)-2,3,5,6-tetraphenyl-4-styryl-2,3,5,6-tetrahydrobenzo[1,2-b:5,4-b′]difuran skeleton, (+)- and (−)-(E)-cyperusphenol A (1, 2) and (E)-mesocyperusphenol A (3), were isolated from a cyperus rhizome. Moreover, the geometrical isomers (4–6) were identified as the artifacts of their (E)-forms (1–3). The isolated products are the first instance of the co-occurrence of racemates (1, 2: new compounds) and a meso isomer (3), which resembles the C2 symmetrical structure of an oligostilbenoid. These structures were characterized by NMR and CD spectroscopy. This is the first report that shows the occurrence of a racemate of a stilbenoid in the same plant material and the achievement of the optical separation of stilbene oligomers.Graphical abstractHighlight► The isolated products were the first instance of the co-occurrence of racemates and a meso isomer, which resembles the C2 symmetrical structure. ► This was the first report that shows the occurrence of a racemate of stilbenoids in the same plant material. ► This was the first achievement of the optical separation of stilbene oligomers. ► Cyperus rhizome contained oligostilbenoids bearing blocking units of resveratrol and piceatannol. ► The determination of the absolute configuration of isolates was based on optical rotations and CD spectral properties.

Our investigations of the chemical constituents in the leaves of Upuna borneensis Sym. (Dipterocarpaceae) resulted in the isolation of two novel diastereomeric acetophenone derivatives, upuborneols A (1) and B (2), along with four known derivatives (3–6). Their structures were determined by spectroscopic analysis including two-dimensional NMR and the speculation of biogenesis. Compounds 1 and 2 had a C6 unit derived from sugar unit and are the first known representatives of natural acetophenone derivatives bearing a spiroketal moiety.Graphical abstractHighlights► The isolated products were the first instance of naturally occurring spiroketal-hexosefuranosides of acetophenone. ► The leaves of Upuna borneensis contain acetophenone C-glycosides. ► Co-occurrence of biogenetically related phloroacetophenone C-glycosides was exhibited.

We isolated five bergenin phenylpropanoates, i.e., 11-O-(E)-sinapate (1), 11-O-(E)-ferulate (2), 11-O-(Z)-ferulate (3), 11-O-(E)-coumalate (4), and 11-O-(Z)-coumalate (5), and three bergenin hydroxybenzoates, i.e., 11-O-syringate (6), 11-O-vanillate (7), and 11-O-p-hydroxybenzoate (8), along with bergenin (9), from the leaves of Vatica bantamensis. Moreover, we identified the geometrical isomerization between 2 and 3. These structures were characterized by nuclear magnetic resonance (NMR). This is the first report that shows the occurrence of bergenin phenolic acid esters in dipterocarpaceaeous plants.Graphical abstractHighlights► We isolated four new and five known compounds from V. bantamensis leaves. ► Their structures were characterized by spectroscopic methods. ► This is the first report of bergenin phenylpropanoates occurrence in dipterocarpaceaeous plants. ► This was the first report on bergenin 11-O-phenolpropanoates and hydroxybenzoates co-occurrence in plants.