Structural Elucidation of an Atropisomeric Entcassiflavan-(4ß→8)-Epicatechin Isolated from Dalbergia monetaria L.f. Based on NMR and ECD Calculations in Comparison to Experimental Data.

A rare dihydoxyflavan-epicatechin proanthocyanidin, entcassiflavan-(4ß→8)-epicatechin, was isolated from Dalbergia monetaria, a plant widely used by traditional people from the Amazon to treat urinary tract infections. The constitution and relative configuration of the compound were elucidated by HR-MS and detailed 1D- and 2D-NMR measurements. By comparing the experimental electronic circular dichroism (ECD) spectrum with the calculated ECD spectra of all 16 possible isomers, the absolute configuration, the interflavan linkage, and the atropisomers could be determined.

Antioxidant capacity and fragmentation features of C-glycoside isoflavones by high-resolution electrospray ionization tandem mass spectrometry using collision-induced and high-energy collisional dissociation techniques.

The rapid annotation and identification by mass spectrometry techniques of flavonoids remains a challenge, due to their structural diversity and the limited availability of reference standards. This study applies a workflow to characterize two isoflavonoids, the orobol-C-glycosides analogs, using high-energy collisional dissociation (HCD)- and collision-induced dissociation (CID)-type fragmentation patterns, and also to evaluate the antioxidant effects of these compounds by ferric reducing antioxidant power (FRAP), 2,2'-azino-bis(3-ethylbenzothiazolin acid) 6-sulfonic acid (ABTS), and 2,2-diphenyl-1-picrylhydrazyl (DPPH) methods. By the CID-type fragmentation, in positive mode and at all high-resolution mass spectrometry (HRMS) multiple stage, there were shown differences in the annotation of the compounds, mainly concerning some ratios of relative abundance. At CID-MS2 20 eV, the compounds could be efficiently characterized, because they present distinct base peaks [M + H]+ and [M + H-H2 O]+ for the orobol-8-C- and orobol-6-C-glycoside, respectively. Similarly, by the HCD-type fragmentation, in HRMS2 stage, differences between orobol analogs in both mode of ionization were observed. However, the HR HCD-MS2 at 80 eV, in positive mode, generated more ions and each isomer presented different base peaks ions, [0,2X]+ for the orobol-8-C-glycoside and [0,3X]+ for the orobol-6-C-glycoside. By the DPPH, the 8-C-derivative showed a very close value compared with the standard rutin and, in the ABTS method, a higher radical-scavenging activity. In both methods, the EC50 of orobol-8-C-glycoside was almost twice better compared with orobol-6-C-glycoside. In FRAP, both C-glycosides showed a good capacity as Fe+3 reducing agents. We could realize that combined MS techniques, highlighting the positive mode of ionization, can be used to evaluate the isoflavones analogs being useful to differentiate between the isomeric flavones; therefore, these data are important to mass spectrometry dereplication studies become more efficient. HIGHLIGHTS: The MS2, in positive mode of ionization, at low CID energies (15 and 20 eV) and at high HCD energies (50 eV), was suitable to characterize orobol 8 and 6-C-derivatives. Positive mode of ionization was effective to rapid annotation of each orobol C-glycoside. The orobol C-derivatives showed high radical scavenging effects. Orobol-8-C-glycoside showed higher antioxidant capacity.

Characterization of Antibacterial Proanthocyanidins of Dalbergia monetaria, an Amazonian Medicinal Plant, by UHPLC-HRMS/MS.

Dalbergia monetaria is an Amazonian plant whose bark is widely used to treat urinary tract infections. This paper describes a bio-guided study of ethanolic extracts from the bark and leaves of D. monetaria, in a search for metabolites active against human pathogenic bacteria. In vitro assays were performed against 10 bacterial strains, highlighting methicillin-sensitive Staphylococcus aureus and methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. Fractioning of the extracts was performed using instrumental and classical techniques, and samples were characterized by UHPLC-HRMS/MS. Ethyl acetate fractions from bark and leaves showed similar antibacterial activities. EAFB is enriched in isoflavone C-glucosides and EAFL enriched in proanthocyanidins. Subfractions from EAFL presented higher activity and showed a complex profile of proanthocyanidins constructed by (epi)-cassiaflavan and (epi)-catechin units, including dimers, trimers and tetramers. The fragmentation pattern emphasized the neutral loss of cassiaflavan units by quinone-methide fission. Fraction SL7-6, constituted by (ent)-cassiaflavan-(ent)-cassiaflavan-(epi)-catechin isomers, showed the lowest MIC against the S. aureus and P. aeruginosa with values corresponding to 64 and 32 µg/mL, respectively. Cassiaflavan-proanthocyanidins have not been found previously in another botanical genus, except in Cassia, and the traditional medicinal use of D. monetaria might be related to the antibacterial activity of proanthocyanidins characterized in the species.