Resolution and Improved Synthesis of (±)-Arsenicin A: A Natural Adamantane-Type Tetraarsenical Possessing Strong Anti-Acute Promelocytic Leukemia Cell Line Activity

A Comprehensive Computational NMR Analysis of Organic Polyarsenicals including the Marine Sponge-Derived Arsenicins A-D and Their Synthetic Analogs

The adamantane structure of arsenicin A and nor-adamantane structures of arsenicins B-D have gained attention as unique natural polyarsenicals, as well as hits showing promising anticancer activity. The purpose of this study is to apply the predictive power of NMR DFT calculations in order to identify a valid tool to be used in the structural elucidation of similar molecules. 1H- and 13C-NMR chemical shifts of twelve natural and synthetic polyarsenical analogs were calculated and validated by comparison with experimental data acquired in CDCl3 solutions, in regard to mean absolute error (MAE) values under various combinations of two methods (GIAO and CSGT), four functionals and five basis sets, also considering relativistic effects. The best computational approaches are highlighted for predicting the chemical shifts of 1H and 13C nuclei and J(1H,1H) coupling constants in the series of O- and S-polyarsenicals. This comprehensive analysis contributes to making NMR spectroscopy appealing for the structural elucidation of such molecules, contrary to the first structural elucidation of natural arsenicin A, in which the experimental NMR analysis was limited by the poor presence of proton and carbon atoms in its structure and by the shortage of reference data.

Arsenic in medicine: past, present and future

Arsenicals are one of the oldest treatments for a variety of human disorders. Although infamous for its toxicity, arsenic is paradoxically a therapeutic agent that has been used since ancient times for the treatment of multiple diseases. The use of most arsenic-based drugs was abandoned with the discovery of antibiotics in the 1940s, but a few remained in use such as those for the treatment of trypanosomiasis. In the 1970s, arsenic trioxide, the active ingredient in a traditional Chinese medicine, was shown to produce dramatic remission of acute promyelocytic leukemia similar to the effect of all-trans retinoic acid. Since then, there has been a renewed interest in the clinical use of arsenicals. Here the ancient and modern medicinal uses of inorganic and organic arsenicals are reviewed. Included are antimicrobial, antiviral, antiparasitic and anticancer applications. In the face of increasing antibiotic resistance and the emergence of deadly pathogens such as the severe acute respiratory syndrome coronavirus 2, we propose revisiting arsenicals with proven efficacy to combat emerging pathogens. Current advances in science and technology can be employed to design newer arsenical drugs with high therapeutic index. These novel arsenicals can be used in combination with existing drugs or serve as valuable alternatives in the fight against cancer and emerging pathogens. The discovery of the pentavalent arsenic-containing antibiotic arsinothricin, which is effective against multidrug-resistant pathogens, illustrates the future potential of this new class of organoarsenical antibiotics.

Expanding the Chemical Space of Arsenicin A-C Related Polyarsenicals and Evaluation of Some Analogs as Inhibitors of Glioblastoma Stem Cell Growth

The marine polyarsenical metabolite arsenicin A is the landmark of a series of natural and synthetic molecules characterized by an adamantane-like tetraarsenic cage. Arsenicin A and related polyarsenicals have been evaluated for their antitumor effects in vitro and have been proven more potent than the FDA-approved arsenic trioxide. In this context, we have expanded the chemical space of polyarsenicals related to arsenicin A by synthesizing dialkyl and dimethyl thio-analogs, the latter characterized with the support of simulated NMR spectra. In addition, the new natural arsenicin D, the scarcity of which in the Echinochalina bargibanti extract had previously limited its full structural characterization, has been identified by synthesis. The dialkyl analogs, which present the adamantane-like arsenicin A cage substituted with either two methyl, ethyl, or propyl chains, were efficiently and selectively produced and evaluated for their activity on glioblastoma stem cells (GSCs), a promising therapeutic target in glioblastoma treatment. These compounds inhibited the growth of nine GSC lines more potently than arsenic trioxide, with GI₅₀ values in the submicromolar range, both under normoxic and hypoxic conditions, and presented high selectivity toward non-tumor cell lines. The diethyl and dipropyl analogs, which present favorable physical-chemical and ADME parameters, had the most promising results.

C-As Bond Formation Reactions for the Preparation of Organoarsenic(III) Compounds

Potential widespread applications of organoarsenic chemistry have been limited by the inherent lack of safe and effective As-C bond formation reactions. Several alternative reagents and methods have been developed in the last few decades to address the hazards and drawbacks associated with traditional arsenic synthetic strategies. Herein, this minireview summarizes the advances made in nucleophilic, electrophilic, radical and metal-mediated As(III)-C bond formations while specifically highlighting the behavior of arsenic synthons with various well-established reagents (eg. Grignard reagents, organolithium compounds, organometallic reagents, radical initiators and Lewis/Brønsted bases). Avenues for asymmetric synthesis are also discussed, as are recent advances in organoarsenic chemistry suggesting that arsines exhibit novel reactivities independent from that of other relatively more well explored Group V cogeners.

New Sulfur-Containing Polyarsenicals from the New Caledonian Sponge Echinochalina bargibanti

Arsenicin A (C₃H₆As₄O₃) was isolated from the New Caledonian poecilosclerid sponge Echinochalina bargibanti, and described as the first natural organic polyarsenic compound. Further bioguided fractionation of the extracts of this sponge led us to isolate the first sulfur-containing organic polyarsenicals ever found in Nature. These metabolites, called arsenicin B and arsenicin C, are built on a noradamantane-type framework that is characterized by an unusual As⁻As bonding. Extensive NMR measurements, in combination with mass spectra, enabled the assignment of the structure for arsenicin B (C₃H₆As₄S₂) as 2. The scarcity of arsenicin C and its intrinsic chemical instability only allowed the collection of partial spectral data, which prevented the full structural definition. After the extensive computational testing of several putative structures, structure 3 was inferred for arsenicin C (C₃H₆As₄OS) by comparing the experimental and density functional theory (DFT)-calculated ¹H and ¹³C NMR spectra. Finally, the absolute configurations of 2 and 3 were determined with a combined use of experimental and time-dependent (TD)-DFT calculated electronic circular dichroism (ECD) spectra and observed specific rotations. These findings pose great challenges for the investigation of the biosynthesis of these metabolites and the cycle of arsenic in Nature. Arsenicins B and C showed strong antimicrobial activities, especially against S. aureus, which is comparable to the reference compound gentamycin.

Synthesis and in-vitro anticancer evaluation of polyarsenicals related to the marine sponge derived Arsenicin A

In the light of the promising bioactivity of the tetraarsenic marine metabolite arsenicin A, the dimethyl analogue 2 and four isomeric methylene homologues (including the natural product itself) were obtained using a one-pot microwave-assisted synthesis, starting from arsenic (III) oxide. Due to the poor diagnostic value of the NMR technique in the structural elucidation of these molecules, they were fully characterized by mass spectrometry and infrared (IR)-spectroscopy, comparing density functional theory (DFT) simulated and experimental spectra. This synthetic procedure provided a fast and efficient access to the cytotoxicity evaluation of organoarsenical leads of the natural hit molecule. From in vitro screening, each tested compound resulted in being more active than the FDA-approved arsenic trioxide, with the most lipophilic molecule in the series showing the best growth inhibition of both leukemia and solid tumor cell lines. These results may open promising perspectives in the development of new more potent and selective arsenical drugs against solid tumors.

Nickel catalyzed enantioselective hydroarsination of nitrostyrene

A catalytic asymmetric hydroarsination reaction of an activated alkene viz. (E)-nitrostyrene was developed using chiral PCP Pt-, Pd- and Ni-pincer complexes as catalysts. The corresponding chiral tertiary arsine adduct was obtained in ees of up to 80% under mild reaction conditions using the PCP Ni-Cl pincer catalyst. The arsine adduct was furnished with catalyst loadings of 1-5 mol% and the reaction duration ranging from <5 min to 180 min. The subsequent coordination of the hydroarsination product to gold(i) chloride allowed for the confirmation of the stereochemistry of the arsine adduct via crystallographic analysis.

A facile method to construct a 2,4,9-triazaadamantane skeleton and synthesize nitramine derivatives

An unusual protocol for a “one-pot” three-step reaction to build a 2,4,9-triazaadamantane skeleton from triallylcarbinol was developed.

Methylated and thiolated arsenic species for environmental and health research - A review on synthesis and characterization

Hundreds of millions of people around the world are exposed to elevated concentrations of inorganic and organic arsenic compounds, increasing the risk of a wide range of health effects. Studies of the environmental fate and human health effects of arsenic require authentic arsenic compounds. We summarize here the synthesis and characterization of more than a dozen methylated and thiolated arsenic compounds that are not commercially available. We discuss the methods of synthesis for the following 14 trivalent (III) and pentavalent (V) arsenic compounds: monomethylarsonous acid (MMA^III), dicysteinylmethyldithioarsenite (MMA^III(Cys)₂), monomethylarsonic acid (MMA^V), monomethylmonothioarsonic acid (MMMTA^V) or monothio-MMA^V, monomethyldithioarsonic acid (MMDTA^V) or dithio-MMA^V, monomethyltrithioarsonate (MMTTA^V) or trithio-MMA^V, dimethylarsinous acid (DMA^III), dimethylarsino-glutathione (DMA^III(SG)), dimethylarsinic acid (DMA^V), dimethylmonothioarsinic acid (DMMTA^V) or monothio-DMA^V, dimethyldithioarsinic acid (DMDTA^V) or dithio-DMA^V, trimethylarsine oxide (TMAO^V), arsenobetaine (AsB), and an arsenicin-A model compound. We have reviewed and compared the available methods, synthesized the arsenic compounds in our laboratories, and provided characterization information. On the basis of reaction yield, ease of synthesis and purification of product, safety considerations, and our experience, we recommend a method for the synthesis of each of these arsenic compounds.

Marine Natural Products from New Caledonia--A Review

Marine micro- and macroorganisms are well known to produce metabolites with high biotechnological potential. Nearly 40 years of systematic prospecting all around the New Caledonia archipelago and several successive research programs have uncovered new chemical leads from benthic and planktonic organisms. After species identification, biological and/or pharmaceutical analyses are performed on marine organisms to assess their bioactivities. A total of 3582 genera, 1107 families and 9372 species have been surveyed and more than 350 novel molecular structures have been identified. Along with their bioactivities that hold promise for therapeutic applications, most of these molecules are also potentially useful for cosmetics and food biotechnology. This review highlights the tremendous marine diversity in New Caledonia, and offers an outline of the vast possibilities for natural products, especially in the interest of pursuing collaborative fundamental research programs and developing local biotechnology programs.

Therapeutic and analytical applications of arsenic binding to proteins

Knowledge of arsenic binding to proteins advances the development of bioanalytical techniques and therapeutic drugs.

Synthesis and Characterization of Arsenolipids: Naturally Occurring Arsenic Compounds in Fish and Algae

Arsenic-containing lipids (arsenolipids) are natural products present in fish and algae. Because these compounds occur in foods, there is considerable interest in their human toxicology. We report the synthesis and characterization of seven arsenic-containing lipids, including six natural products. The compounds comprise dimethylarsinyl groups attached to saturated long-chain hydrocarbons (three compounds), saturated long-chain fatty acids (two compounds), and monounsaturated long chain fatty acids (two compounds). The arsenic group was introduced through sodium dimethylarsenide or bis(dimethylarsenic) oxide. The latter route provided higher and more reproducible yields, and consequently, this pathway was followed to synthesize six of the seven compounds. Mass spectral properties are described to assist in the identification of these compounds in natural samples. The pure synthesized arsenolipids will be used for in vitro experiments with human cells to test their uptake, biotransformation, and possible toxic effects.