Structure Elucidation of Prenyl- and Geranyl-Substituted Coumarins in Gerbera piloselloides by NMR Spectroscopy, Electronic Circular Dichroism Calculations, and Single Crystal X-ray Crystallography

Abstract

Crude ethyl acetate extract of Gerbera piloselloides (L.) Cass. was investigated by dual high-resolution PTP1B/α-glucosidase inhibition profiling and LC-PDA-HRMS. This indicated the presence of a series of unprecedented prenyl- and geranyl-substituted coumarin derivatives correlated with both α-glucosidase and PTP1B inhibitory activity. Repeated chromatographic separation targeting these compounds led to the isolation of 13 new compounds, of which ten could be isolated as both enantiomers after chiral separation. The structures of all isolated compounds were characterized by HRMS and extensive 1D and 2D NMR analysis. The absolute configurations of the isolated compounds were determined by comparison of experimental and calculated electronic circular dichroism spectra. Compound 6 features a rare furan-oxepane 5/7 ring system, possibly formed through addition of a geranyl unit to C-3 of 5-methylcoumarin, representing a new type of geranyl-substituted coumarin skeleton. Compounds 19 and 24 are the first examples of dimeric natural products consisting of both coumarin and chromone moieties.

Orthogonal Reversed-Phase C18 and Pentafluorophenyl HPLC Separation for Phytochemical Profiling of Serrulatanes in Eremophila denticulata

“…For ECD data acquisition, 0.1 mg of each compound was dissolved in 200 μL of MeCN and subsequently transferred to a cuvette with a 1 mm path length. The 1 R configuration of compound 3 was established by computational calculation approaches on DTU’s High-Performance Computing Cluster as described before . All density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations were performed using Gaussian16 (Gaussian, Inc., Wallingford, CT, USA) with Gaussian’s default setup for the polarizable continuum model (PCM) calculations.…”

Anticancer Meroterpenoids from Centrapalus pauciflorus leaves: Chromone- and 2,4-Chromadione-Monoterpene Derivatives

“…These compounds are synthesized by a wide range of organisms, including bacteria, fungi, algae, plants, animals, and marine organisms. − Notably, meroterpenoids derived from chromane/chromene can be condensed with hemi-, mono-, sesqui-, and diterpenoid units; their presence has been observed in various organisms, such as tunicates ( Botryllus ), brown macroalgae (Sargassum, Cystoseira) , and Rhododendron (Ericaceae), Sarcandra (Chloranthaceae), and Mimosa (Fabaceae) plant species. In addition, the genera of the Asteraceae family have been discovered to produce uncommon monoterpenoid-coupled chromones, which typically coexist with structurally related monoterpenoid coumarins. − These intriguing compounds have been identified in genera such as Nassauvia , Triptilion , and Polyachyrus from the Nassauvieae tribe, Gerbera and Mutisia from the Mutisieae tribe, and Bothriocline genus from the Vernonieae tribe and reported to accumulate as both coumarin- and chromon-based meroterpenoids. The biosynthesis of these compounds involves the acetate–malonate pathway, where 5-methylcoumarins and 5-methylchromones serve as the main building blocks for chromone-, coumarin-based meroterpenoids, which is catalyzed by polyketide synthase enzymes .…”

Myocardial protection of S-nitroso-L-cysteine in diabetic cardiomyopathy mice

“…The insulin signal is turned on insulin binding to the insulin receptor to activate the MAPK and AKT pathways. On the other hand, insulin signaling is turned off by protein tyrosine phosphatases (PTPs), mainly PTP1B, dephosphorylation of insulin receptors and their substrates to downregulate signal transduction ( 5 ). PTP1B, an extensively expressed nonreceptor classical PTP, belongs to the class 1 PTPs ( 6 ).…”