Cystodamine, a new cytotoxic fused polyaromatic alkaloid from the Mediterranean ascidian Cystodytes delle chiajei

Marine pyridoacridine, pyridoacridone and pyrroloacridine alkaloids

The families of pyridoacridine, pyridoacridone, and pyrroloacridine alkaloids are fascinating classes of natural products that have attracted the attention of chemists for over 80 years. Since the first purification of a brightly colored molecule isolated from the sea anemone Calliactis parasitica in 1940, over 110 examples of these alkaloids have been reported from marine organisms. While the paucity of numbers of protons relative to carbons and nitrogens in these molecules presents challenges in structure solution, the chemist is rewarded by their bright pigmented colors and typically diverse biological activities. In the past, several authors have proposed biosynthetic relationships within the pyridoacridine family of alkaloids, formulating a family tree derived from the reaction of dopaminequinone and kynuramine to tie together over 75 alkaloids. Inclusion of two additional quinones, and one homologous diamine, building blocks, for which there is biomimetic synthesis support, is suggestive of a more expansive connected biogenesis that encompasses not only pyridoacridines, but also pyridoacridone, and pyrroloacridine alkaloids. This review covers the isolation, structure elucidation, and proposed biosynthesis and biogenesis of pyridoacridine, pyridoacridone and pyrroloacridine marine alkaloids published to the end of 2022. Biomimetic or bio-inspired syntheses of the compound classes are described and new biological activities reported since 2004 are updated.

Application of the aza-Diels–Alder reaction in the synthesis of natural products

The Diels–Alder reaction that involves a nitrogen atom in the diene or dienophile is termed the aza-Diels–Alder reaction.

Marine Pyridoacridine Alkaloids: Biosynthesis and Biological Activities

Pyridoacridines are a class of strictly marine-derived alkaloids that constitute one of the largest chemical families of marine alkaloids. During the last few years, both natural pyridoacridines and their analogues have constituted excellent targets for synthetic works. They have been the subject of intense study due to their significant biological activities; cytotoxic, antibacterial, antifungal, antiviral, insecticidal, anti-HIV, and anti-parasitic activities. In the present review, 95 pyridoacridine alkaloids isolated from marine organisms are discussed in term of their occurrence, biosynthesis, biological activities, and structural assignment.

Pyridoacridine alkaloids inducing neuronal differentiation in a neuroblastoma cell line, from marine sponge Biemna fortis

A new and three known pyridoacridine alkaloids were isolated from the Indonesian marine sponge Biemna fortis as neuronal differentiation inducers against a murine neuroblastoma cell line, Neuro 2A. The chemical structure of the new compound, labuanine A (1), was determined by spectroscopic study and chemical conversion. These pyridoacridine alkaloids induced multipolar neuritogenesis in more than 50% of cells at 0.03-3 micro M concentration. Compound 3, which showed the strongest neuritogenic activity among them, also induced increase of acetylcholinesterase, a neuronal marker in Neuro 2A and arrested cell cycle at the G2/M phase.

Marine pyridoacridine alkaloids and synthetic analogues as antitumor agents

Pyrido[4,3,2-mn]acridines are of major interest as metabolites in sponges and ascidians. During the last few years, numerous additional compounds of this family were isolated, some of them being polycyclic structures already reported with different substituents (shermilamine or kuanoniamine-derivatives), others, such as neoamphimedine, arnoamines and styelsamines having original structures. The synthesis of these compounds and analogues have been performed in order to allow their biological evaluation. In most of the cases, the cytotoxicity of analogues was improved compared to the natural product, specially in ascididemin or meridine series. The pyridoacridines have not a sole mode of action, but it seems that the reductive DNA cleavage mediated by reactive oxygen species is a potential general mode of action.

Structures and cytotoxic properties of sponge-derived bisannulated acridines

A reinvestigation of sponge natural products from additional Indo-Pacific collections of Xestospongiacf. carbonaria and X. cf. exigua has provided further insights on the structures, biological activities, and biosynthetic origin of bisannulated acridines. These alkaloids include one known pyridoacridine, neoamphimedine (2), and three new analogues, 5-methoxyneoamphimedine (4), neoamphimedine Y (5), and neoamphimedine Z (6). A completely new acridine, alpkinidine (7), was also isolated. A disk diffusion soft agar assay, using a panel of five cancer cell lines (solid tumors and leukemias) and two normal cells, was used to evaluate the differential cytotoxicity (solid tumor selectivity) of the sponge semipure extracts and selected compounds including amphimedine (1), 2, 4, and 7. While all four compounds were solid tumor selective, 1 and 2 were the most potent and 4 was the most selective. The rationale used to characterize the new structures is outlined along with the related biosynthetic pathways envisioned to generate 2 and 7.

Sebastianines A and B, novel biologically active pyridoacridine alkaloids from the Brazilian ascidian Cystodytes dellechiajei

Fractionation of the crude methanol extract of the ascidian Cystodytes dellechiajei collected in Brazil yielded two novel alkaloids, sebastianine A (1) and sebastianine B (2). The structures of both 1 and 2 were established by analysis of spectroscopic data, indicating an unprecedented ring system for both compounds, comprising a pyridoacridine system fused with a pyrrole unit in sebastianine A (1) and a pyridoacridine system fused with a pyrrolidine system condensed with alpha-hydroxyisovaleric acid in sebastianine B (2). Both alkaloids displayed a cytotoxic profile against a panel of HCT-116 colon carcinoma cells indicative of a p53 dependent mechanism.

The first synthesis of the pentacyclic pyridoacridine marine alkaloids: arnoamines A and B

The synthesis of the marine pyridoacridine alkaloids arnoamines A and B has been accomplished in six and seven steps from 4-chloro-8-methoxy-5-nitroquinoline in 13% and 4% overall yield, respectively.

Cycloshermilamine D, a new pyridoacridine from the marine tunicate cystodytes violatinctus

A new alkaloid, cycloshermilamine D, was isolated from the marine tunicate Cystodytes violatinctus, and its structure (1), which is closely related to shermilamine D, was established mainly on the basis of NMR spectroscopic data.

New lipids from the tunicate Cystodytes cf. dellechiajei, as PLA2 inhibitors

Cystodytes cf. dellechiajei collected off Djerba furnished new lipids, sphingosines 1, as inhibitors of phospholipase A2, along with inactive homologous ceramides 2. Structures were determined by spectroscopic methods and chemical transformations.