(±)-Meliviticines A and B: Rearranged prenylated acetophenone derivatives from Melicope viticina and their antimicrobial activity

Molecular networking-based discovery of anti-inflammatory chromene dimers from Melicope pteleifolia

With the aid of a feature-based molecular networking strategy, five undescribed C₂ and C₁ symmetric chromene dimers, namely, melptelchromenes A-E, were isolated from the leaves of Melicope pteleifolia. Four asymmetric dimers were found to be racemates and were resolved by chiral phase HPLC analyses. Their structures, including absolute configurations, were elucidated by HRMS, NMR spectroscopy, and quantum mechanical calculations of ECD spectra and NMR chemical shifts. Melptelchromenes A-D possess a unique ethylidene linkage via two 2H-chromene cores, while melptelchromene E represents the first example of a dimeric chromene featuring a 1,3-diarylbutan-1-ol moiety. Of these compounds, 6,6'-linked dimeric chromenes showed nitric oxide inhibitory activities on lipopolysaccharide-induced RAW 264 cells, and (-)- and (+)-melptelchromene E were the two most potent compounds (IC₅₀, 3.0 and 5.1 μM, respectively).

Natural Enantiomers: Occurrence, Biogenesis and Biological Properties

The knowledge that natural products (NPs) are potent and selective modulators of important biomacromolecules (e.g., DNA and proteins) has inspired some of the world’s most successful pharmaceuticals and agrochemicals. Notwithstanding these successes and despite a growing number of reports on naturally occurring pairs of enantiomers, this area of NP science still remains largely unexplored, consistent with the adage “If you don’t seek, you don’t find”. Statistically, a rapidly growing number of enantiomeric NPs have been reported in the last several years. The current review provides a comprehensive overview of recent records on natural enantiomers, with the aim of advancing awareness and providing a better understanding of the chemical diversity and biogenetic context, as well as the biological properties and therapeutic (drug discovery) potential, of enantiomeric NPs.

Neolignans and Sesquiterpenoid from Piper yunnanense

Two biphenyl-type neolignans with a rare dibenzofuran skeleton, including a new one piyunneolignan A (1) and a known one piperneolignan D (2), together with a new sesquiterpenoid piyunin A (3), were isolated from the leaves and twigs of Piper yunnanense. Their structures were established on the basis of comprehensive spectroscopic data analysis and electronic circular dichroism (ECD) calculation. Piyunneolignan A (1) featured a rare C-2-C-2'/C-3-O-C-3' linkage. Compounds 1-3 were evaluated for their antimicrobial and cytotoxic activities against a panel of bacteria, fungi, and human cancer cell lines, respectively.

New Acetophenones and Chromenes from the Leaves of Melicope barbigera A. Gray

The dichloromethane extract from leaves of Melicope barbigera (Rutaceae), endemic to the Hawaiian island of Kaua'i, yielded four new and three previously known acetophenones and 2H-chromenes, all found for the first time in M. barbigera. The structures of the new compounds obtained from the dichloromethane extract after purification by chromatographic methods were unambiguously elucidated by spectroscopic analyses including 1D/2D NMR spectroscopy and HRESIMS. The absolute configuration was determined by modified Mosher's method. Compounds 2, 4 and the mixture of 6 and 7 exhibited moderate cytotoxic activities against the human ovarian cancer cell line A2780 with IC₅₀ values of 30.0 and 75.7 µM for 2 and 4, respectively, in a nuclear shrinkage cytotoxicity assay.