Total synthesis of ascididemin via anionic cascade ring closure

Marine alkaloids as bioactive agents against protozoal neglected tropical diseases and malaria

Covering: 2000 up to 2021Natural products are an important resource in drug discovery, directly or indirectly delivering numerous small molecules for potential development as human medicines. Among the many classes of natural products, alkaloids have a rich history of therapeutic applications. The extensive chemodiversity of alkaloids found in the marine environment has attracted considerable attention for such uses, while the scarcity of these natural materials has stimulated efforts towards their total synthesis. This review focuses on the biological activity of marine alkaloids (covering 2000 to up to 2021) towards Neglected Tropical Diseases (NTDs) caused by protozoan parasites, and malaria. Chemotherapy represents the only form of treatment for Chagas disease, human African trypanosomiasis, leishmaniasis and malaria, but there is currently a restricted arsenal of drugs, which often elicit severe adverse effects, show variable efficacy or resistance, or are costly. Natural product scaffolds have re-emerged as a focus of academic drug discovery programmes, offering a different resource to discover new chemical entities with new modes of action. In this review, the potential of a range of marine alkaloids is analyzed, accompanied by coverage of synthetic efforts that enable further studies of key antiprotozoal natural product scaffolds.

Tuning the reaction pathways of phenanthroline-Schiff bases: routes to novel phenanthroline ligands

Pyrido-phenanthrolin-7-one compounds are structural analogues of the cytotoxic alkaloid, ascididemin, and would be expected to have interesting biological activities. Synthetic strategies are reported for a novel simple route to form this class of ligand. 1,10-Phenanthrolin-5,6-dione reacts with l-phenylalanine alkyl esters and their para-substituted analogues to form both a phenanthroline-oxazine and a pyrido-phenanthrolin-7-one product. The nature of the major product is dependent on the electronic properties of the para substituent. Successful metal coordination to the pyrido-phenanthrolin-7-one ligand is also presented.

Synthesis of novel 1,10-phenanthroline derivatives and it used as probes for sensitive detection of Zn2+ and Cd2+ metal ions - Spectroscopic and theoretical approach

A novel class of unexpected 1,10-phenanthrolinederivatives were synthesized from 2,3-dihydroacridin-4(1H)-ones with 3-aminonaphthalen-2-carboxylic acid in presence of phosphorus oxychloride at 130°C and simple perceptive emission intensity increasing assay was developed effectively to detect the very low concentrations of Zn²⁺ and Cd²⁺ ions. Emission intensity of compounds 3(a-c) directly related to the concentrations of Zn²⁺ and Cd²⁺ ions was due to metal chelating enhanced fluorescence (CHEF) effect and also its further validated by fluorescence lifetime measurement. Furthermore, the sensing mechanism for compounds 3(a-c) of Zn²⁺ and Cd²⁺ were sustained by theoretical calculations. Computational analysis results reveals that compounds 3(a-c) are more interested in Zn²⁺ ions than that of Cd²⁺ ions, while, compound 3c is more interested with Zn²⁺ and Cd²⁺ ions than those of the rest of the compounds. In addition, this proposed detection analysis has the direct application for monitoring Zn²⁺ and Cd²⁺ concentrations in tap and drinking water samples.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

New Perspectives in the Chemistry of Marine Pyridoacridine Alkaloids

Secondary metabolites from marine organisms are a rich source of novel leads for drug development. Among these natural products, polycyclic aromatic alkaloids of the pyridoacridine type have attracted the highest attention as lead compounds for the development of novel anti-cancer and anti-infective drugs. Numerous sophisticated total syntheses of pyridoacridine alkaloids have been worked out, and many of them have also been extended to the synthesis of libraries of analogues of the alkaloids. This review summarizes the progress in the chemistry of pyridoacridine alkaloids that was made in the last one-and-a-half decades.

Pyridinoacridine alkaloids of marine origin: NMR and MS spectral data, synthesis, biosynthesis and biological activity

This review focuses on pyridoacridine-related metabolites as one biologically interesting group of alkaloids identified from marine sources. They are produced by marine sponges, ascidians and tunicates, and they are structurally comprised of four to eight fused rings including heterocycles. Acridine, acridone, dihydroacridine, and quinolone cores are features regularly found in these alkaloid skeletons. The lack of hydrogen atoms next to quaternary carbon atoms for two or three rings makes the chemical shift assignment a difficult task. In this regard, one of the aims of this review is the compilation of previously reported, pyridoacridine (13)C NMR data. Observations have been made on the delocalization of electrons and the presence of some functional groups that lead to changes in the chemical shift of some carbon resonances. The lack of mass spectra information for these alkaloids due to the compactness of their structures is further discussed. Moreover, the biosynthetic pathways of some of these metabolites have been shown since they could inspire biomimetic synthesis. The synthesis routes used to prepare members of these marine alkaloids (as well as their analogues), which are synthesized for biological purposes are also discussed. Pyridoacridines were found to have a large spectrum of bioactivity and this review highlights and compares the pharmacophores that are responsible for the observed bioactivity.

Progress in Studies on Rutaecarpine. II.--Synthesis and Structure-Biological Activity Relationships

Rutaecarpine is a pentacyclic indolopyridoquinazolinone alkaloid found in Evodia rutaecarpa and other related herbs. It has a variety of intriguing biological properties, which continue to attract the academic and industrial interest. Studies on rutaecarpine have included isolation from new natural sources, development of new synthetic methods for its total synthesis, the discovery of new biological activities, metabolism, toxicology, and establishment of analytical methods for determining rutaecarpine content. The present review focuses on the synthesis, biological activities, and structure-activity relationships of rutaecarpine derivatives, with respect to their antiplatelet, vasodilatory, cytotoxic, and anticholinesterase activities.

Hydride-induced anionic cyclization: an efficient method for the synthesis of 6-H-phenanthridines via a transition-metal-free process

A novel procedure for hydride-induced anionic cyclization has been developed. It includes the reduction of a biaryl bromo-nitrile with a nucleophilic aromatic substitution (S(N)Ar). A range of polysubstituted 6-H-phenanthridines were so obtained in moderate to good yield with good substrate tolerance. This method involves a concise transition-metal-free process and was applied to synthesize natural alkaloids.

Iron/acetic acid mediated synthesis of 6,7-dihydrodibenzo[b,j][1,7]phenanthroline derivatives via intramolecular reductive cyclization

An efficient iron/acetic acid mediated intramolecular reductive cyclization protocol was developed for the synthesis of novel 6,7-dihydrodibenzo[b,j][1,7]phenanthroline derivatives.