Three Novel Biphenanthrene Derivatives and a New Phenylpropanoid Ester from Aerides multiflora and Their α-Glucosidase Inhibitory Activity

Potential role of a novel biphenanthrene derivative isolated from Aerides falcata in central nervous system diseases

Central nervous system (CNS) diseases are a significant health burden globally, with the development of novel drugs lagging behind clinical needs. Orchidaceae plants have been traditionally used to treat CNS diseases, leading to the identification of therapeutic leads against CNS diseases from the Aerides falcata orchid plant in the present study. The study isolated and characterized ten compounds, including a previously undescribed biphenanthrene derivative, Aerifalcatin (1), for the first time from the A. falcata extract. The novel compound 1 and known compounds, such as 2,7-dihydroxy-3,4,6-trimethoxyphenanthrene (5), agrostonin (7), and syringaresinol (9), showed potential activity in CNS-associated disease models. Notably, compounds 1, 5, 7, and 9 demonstrated the ability to alleviate LPS-induced NO release in BV-2 microglial cells, with IC50 values of 0.9, 2.5, 2.6, and 1.4 μM, respectively. These compounds also significantly inhibited the release of pro-inflammatory cytokines, IL-6 and TNF-α, reflecting their potential anti-neuroinflammatory effects. Additionally, compounds 1, 7, and 9 were found to reduce cell growth and migration of glioblastoma and neuroblastoma cells, indicating their potential use as anticancer agents in the CNS. In summary, the bioactive agents isolated from the A. falcata extract offer plausible therapeutic options for CNS diseases.

Known or Never before Identified Phenanthrenes: Where It Is Possible to Isolate Them and Why

The secondary metabolites of plant origin belong to different and numerous classes of organic compounds. One of these is that of dimeric phenanthrenes, symmetrical or not, characterized by a series of interesting biological activities. Of these compounds, 37 have been isolated since 1988, from only five plant families. Considering each dimer comprises two phenanthrenes and starting from the hypothesis that each dimer is obtained through a biosynthetic mechanism that involves the coupling of the corresponding radicals of the individual phenanthrene units, it is possible to identify 29 phenanthrenes, of which 6 not yet isolated. It is possible to establish that 16 known phenanthrenes can be isolated from 14 different plant species, just as 6 new phenanthrenes can be isolated from 6 different plant species. This would allow a targeted analysis of a few natural extracts from specific plant sources to identify known or new molecules, with potential and/or specific biological activities.

Phenanthrene Dimers: Promising Source of Biologically Active Molecules

To date, just over a hundred phenanthrenoid dimers have been isolated. Of these, forty-two are completely phenanthrenic in nature. They are isolated from fourteen genera of different plants belonging to only five families, of which Orchidaceae is the most abundant source. Other nine completely acetylated and five methylated dimers were also defined, which were effective in establishing the position of the free hydroxyls of the corresponding natural products, from which they were obtained by semi-synthesis. Structurally, they could be useful chemotaxonomic markers considering that some substituents are typical of a single-family, such as the vinyl group for Juncaceae. From a biogenetic point of view, it is thought that these compounds derive from the radical coupling of the corresponding phenanthrenes or by dehydrogenation of the dihydrophenanthrenoid analogs. Phenanthrenes or dihydroderivatives possess different biological activities, e.g., antiproliferative, antimicrobial, anti-inflammatory, antioxidant, spasmolytic, anxiolytic, and antialgal effects. The aim of this review is to summarize the occurrence of phenanthrene dimers in the different natural sources and give a comprehensive overview their structural characteristics and biological activities.