Cycloaddition of Thiourea- and Guanidine-Substituted Furans to Dienophiles: A Comparison of the Environmentally-Friendly Methods

The cycloaddition strategy was employed in order to obtain a 7-oxanorbornene framework substituted with a guanidine moiety or its precursor functional groups: protected amine or thiourea. In order to optimize the conditions for the cycloaddition, several environmentally-friendly methods—microwave assisted organic synthesis, high pressure synthesis, high speed vibrational milling, and ultrasound assisted synthesis—were employed. The outcomes of the cycloaddition reactions were interpreted in terms of endo/exo selectivity, the conversion of the reactants to the product, and the isolated yields. In general, our results indicated the HP and HSVM approaches as the methods of choice to give good yields and conversions.

Transformation of hydrophobic flavonoids catechin, dihydroquercetin and quercetin into water-soluble structures

The paper describes methods for the transformation of poorly water-soluble flavonoids: dihydroquercetin, catechin and quercetin into water-soluble forms during the formation of supromolecular adducts with β-cyclodextrin and salt-type ionic complexes with the natural amino acid L-arginine, which contains a guanidine moiety properties necessary to create a cationic structure when interacting with phenolic groups. First, a methodology was developed for the synthesis of supromolecular structures, in which flavonoids were incorporated into a cyclodextrin matrix. As a result, the solubility in water at 20 °C of encapsulated flavonoids increased by more than two orders of magnitude. In the formation of complexes of cyclodextrin with flavonoids, the main role is played not by hydrogen bonds between the hydroxyl groups of flavonoids and β-cyclodextrin - in the case of dihydroquercetin and catechin, they are different and similar in the case of dihydroquercetin and quercetin, but the spatial orientation of the pyrocatechol cycle B (due to the flat conjugation of the entire molecule and due to sp2 is the structure of the second carbon atom of the pyran ring). Another implemented approach for obtaining water-soluble flavonoids at room temperature is the creation of their salts with the natural amino acid L-arginine, which is a part of proteins and is involved in several vital processes in the body. The structure of the obtained compounds was proved by the methods of NMR spectroscopy on 13C nuclei and X-ray structural analysis, the composition – by elemental analysis.

Methods to Access 2-aminobenzimidazoles of Medicinal Importance

: Benzimidazole (BI) and derivatives are interesting because several of these compounds have been found to have a diversity of biological activities with clinical applications. In view of their importance, the synthesis of BI and its derivatives is still considered as a challenge for synthetic chemists. Examples of compounds used in medicinal chemistry containing BI, as important nucleus, are Astemizole (antihistaminic), Omeprazole (antiulcerative) and Rabendazole (fungicide), some of these compounds have the 2- aminobenzimidazole (2ABI) as base nucleus. The structure of 2ABI derivatives contains a cyclic guanidine moiety, which is interesting because of its free lone pairs, labile hydrogen atoms and planar delocalized structure. The delocalized 10-π electron system and the extension of the electron conjugation with the exocyclic amino group, in 2ABI, making these heterocycles to have amphoteric character. The 2ABI has been used as building blocks for the synthesis of several BI derivatives as medicinally important molecules. On these bases, herein, we present a bibliographic review concerning the recent methodologies used in the synthesis of 2ABIs, including the substituted ones.

Stereoselective Synthesis of Protected l-allo-Enduracididine and l-Enduracididine via Asymmetric Nitroaldol Reaction

The diastereoselecetive and scalable synthesis of cyclic guanidine-containing nonproteinoginic amino acids, enduracididines, has been achieved. Both diastereomers, l-allo-enduracididine and l-enduracididine, were prepared via catalyst-controlled asymmetric nitroaldol reaction with the aldehyde precursor derived from l-aspartic acid. The cyclic guanidine of di-Cbz-protected l-allo-enduracididine was fully protected with an allyl group to suppress nucleophilic side reactions. Introduced allyl group was efficiently removed via π-allylpalladium chemistry without attaching the Cbz group on the cyclic guanidine moiety.

Decomposition products of cylindrospermopsin – a cyanotoxin produced by Raphidiopsis raciborskii (Woloszynska)

Toxins produced by cyanobacteria (cyanotoxins) and released into water have become a serious problem worldwide due to the increasing morbidity and mortality of living organisms they have caused. The ability to synthesize the cytotoxic alkaloid cylindrospermopsin (CYN) has been demonstrated in several freshwater species of cyanobacteria. CYN is highly chemically stable under environmental factors and decomposes only under alkaline conditions, where it forms derivatives. The toxicity potential of the decomposition products formed at pH 10 combined with high temperature (100°C) or UV-B irradiation (36 μmol m−2 s−1) has been research based on the crustacean Thamnocephalus platyurus (Thamnotoxkit FTM) and bacteria Vibrio fischeri (Deltatox® II) bioassays. This paper is a continuation and completion of our previous experiments and the obtained results showed that the applied conditions contributed to the decomposition of the CYN molecule to non-toxic products and its structural modifications by separating the uracil ring or/and the sulfate group from the tricyclic guanidine moiety, leading to a reduction in its toxicity. To the best of our knowledge, this is the first report describing the toxicity of CYN decomposition products formed under alkaline conditions combined with boiling temperature or UV-B irradiation.

Substituent dependence of imidazoline derivatives on the capture and release system of carbon dioxide

The imidazoline having a cyclic guanidine moiety only captured CO2 quantitatively, and then the cyclic guanidine derivative gave the guanidinium bicarbonate by CO2 fixation together with a slight amount of water.