Letters in Organic Chemistry - Volume 19, Issue 10, 2022

A new cycloartane triterpenoid, 24-acetylcyclocantogenin (1), along with five cycloartane triterpenoids (2-6), eight steroids (7-14) and nine other known compounds (15-23), was obtained from the methanol extract of roots of Astragalus polycladus var. nigrescens. Their structures were elucidated based on extensive spectroscopic analysis (1D and 2D-NMR, MS and IR). They were isolated from A. polycladus var. nigrescens for the first time.

Nutrition therapy on the basis of traditional medicinal plants and herbs is common in many Asian countries, especially Iran and China. Rheum species, especially rhubarbs, belong to plant medicines recognized in 2500 BC. An online search of the literature was carried out at Pubmed/ Medline, Scopus, and Google scholar, covering all years until April 2021. The following key terms were used, usually in combinations: Rheum species, rhubarb, natural products, pharmaceutical benefits, anthraquinones and anthranone. After performing the literature search, the bibliographies of all articles were checked for cross-references that were not found in the search databases. Articles were selected if they reported any biological effects, ethnomedicinal uses, phytochemical compounds and botanical description of Rheum species. The most important components of rhubarb are anthraquinones, anthranone, stilbenes, tannins and butyrophenones. Anthraquinones consist of rhein, emodin, aloe-emodin and chrysophanl, and anthranone includes sennosides and rheinosides. The most important health benefits of rhubarb are antioxidant and anticancer activities, antimicrobial activity, wound healing action, hepatoprotective and anti-diabetic effects, and nephroprotective effect, as well as anti-inflammatory, analgesic and antibacterial activities. Integration of both traditional pharmaceutical science and modern medicines may promote sustainability, lead to organic life and promote the cultivation of medicinal plants.

A new type of NADH model compound, which has six asymmetric carbon centers, has been synthesized by an efficient and convenient method. We used NADH models combined with enzymes in the asymmetric reduction. It was the first time that dehydrogenase combined with NADH models instead of inorganic catalysts, such as MgCl2, was used in the asymmetric reduction. Furthermore, the experimental results showed that the new NADH model has the strongest fluorescence emission properties compared to previously reported models.

The first total synthesis of the natural product iopsoralenoside, isolated from the n-butyl alcohol extract of Fructus Psoraleae (FP), was achieved in 17% yield over 7 steps. The key steps of the process were glycosylation and irradiation promoted by ultraviolet light. This synthesis provided a sufficient amount of synthesized trans- and cis-isopsoralenoside for further bioassays.

A one-pot conversion of 2-hydroxy-1-naphthoic aldehyde to hydroxamic acid was described. An efficient photoorganocatalytic method of synthesis was developed. The obtained hydroxamic acid was identified by various physicochemical methods such as IR, UV- and NMR-spectroscopy. Solid colored complexes of copper (II) and iron (II), respectively, green and brown colours with the obtained hydroxamic acid were synthesized in ethanol medium for the first time. The molar ratio of ligand and metal in the complex was 2:1. Their structures were established using IR, UV- spectroscopy and thermogravimetric analysis.

In the present study, a new magnetically recyclable nanocatalyst, Fe3O4@SiO2@(CH2)3-en- SO3H/H2SO4, was prepared through the immobilization of sulfonated ethylenediamine on the silicacoated magnetite nanoparticles. The catalyst was fully characterized by several physicochemical techniques, including FT-IR, FESEM, TEM, EDS, VSM, XRD and TGA. The resultant nanocatalyst was then utilized in the green synthesis of 2,3-dihydroquinazolin-4(1H)-ones via the cyclocondensation reaction of various aldehydes and ketones with anthranilamide in refluxed EtOH. Short reaction times, high product yields, environmentally friendly reaction conditions, simple operation and reusability of the catalyst are important features of the present procedure. The catalyst can magnetically be recycled and reused several times without notable loss in the activity.

A new process that could efficiently prepare tetrasubstituted bis(3-indolyl)methanes from various indoles and acetophenones with 1,3-Dibromo-5,5-dimehtylhydantoin(DBDMH) as a catalyst was reported. The effects of catalysts, solvents, and reaction temperature were investigated. Under the optimal condition, most of the tetrasubstituted bis(3-indolyl)methanes were obtained in 90–99% yields.

The molecular mechanism of experimentally observed regio- and chemo-selectivity of the cycloaddition reaction of nitrosoamidine 1 and 1-methoxy butadiene 2 has been investigated using DFT calculations at M06-2X/cc-pVDZ level. Accordingly, the possible reaction pathways and factors that govern selectivity are investigated systematically. Analysis of the calculated results showed that the most favorable cyclization reaction occurs through the [2+4] endo-proximal pathway, which is kinetically and thermodynamically controlled. Moreover, analysis of the global and local reactivity indices correctly explains the source of the experimentally observed regio- and chemoselectivity. The electron localization function (ELF) analysis of some selected points along the IRC profile of the most preferred pathway suggested that the reaction takes place via a two-stage one-step mechanism. NCI topological analysis of the possible pathways of [2+4] cycloaddition reaction of 1-E and 2-Z revealed the roles of the attractive interactions between reaction sites, the weak noncovalent interactions observed in the endo approaches, and the repulsive interactions in the regio- and stereo-selectivity of the reaction.

3,4-dihydropyrimidin-2(1H)-one and octahydroquinazolinone derivatives were obtained in high-to-excellent yields and short reaction times using SCMNPs@CA-EA-SO3H as a green and heterogeneous solid acid catalyst in a one-pot multi-component condensation of ethyl acetoacetate or dimedone, urea, and aldehyde compounds under solvent-free conditions. More importantly, the green catalytic system could be easily collected from the reaction solution utilizing an external magnet and reused for five runs with a negligible decrease in yields and reaction rate.

The present work describes an efficient, green, and direct approach for the synthesis of amido alkyl naphthols via one-pot multicomponent solvent-free reaction (MCR) of substituted aromatic aldehydes, β-naphthols, and urea by the use of easily available, non-toxic, and cost-effective Lewis acid catalyst magnesium sulphate (MgSO4.7H2O). The important characteristics of this reaction include the following: eco-friendly and mild reaction conditions, excellent yields of the products, shorter reaction time, economically cheaper and environmentally friendly catalyst MgSO4.7H2O. Also, clean reaction, non-column purification, and operational simplicity are some of the additional significant features of this approach.

Recently, more and more researchers are resorting to green methods and techniques to avoid environmental pollution. Accordingly, many researchers have been working on the development of new green synthetic procedures trying to avoid the use of toxic organic solvents. A sustainable concept of green and environmentally friendly solvents in chemical synthesis nowadays encompasses a relatively new generation of solvents called deep eutectic solvents (DESs). DESs often have a dual role in the synthesis, acting as both solvents and catalysts. In this study, DESs are used in the Knoevenagel synthesis of rhodanine derivatives, with no addition of conventional catalysts. A model reaction of rhodanine and salicylaldehyde was performed in 20 different DESs at 80°C, in order to find the best solvent, which was further used for the synthesis of the series of desired compounds. A series of rhodanines was synthesized in choline chloride: acetamide (ChCl:acetamide) DES with good to excellent yields (51.4-99.7%).

We explored the most expedient pathway for phenolic compound preparation using a combination of arylboronic acids, a green oxidant (H2O2) and a catalytic amount of readily available medicinal materials (TYLENOL® and ASPIRIN®). The arylboronic acids were successfully transformed into the corresponding phenols in high yields under metal- and base-free aqueous aerobic conditions. We demonstrated that enhanced availability and sustainability are some advantages associated with the use of medicinal supports.

A new tertiary amine-thiourea organocatalyst has successfully been developed and applied into the asymmetric Michael addition of pyrazolin-5-one to nitroalkenes. The catalyst system performed well with a low catalyst loading of 5 mol% under mild reaction conditions. A series of synthetically and pharmaceutically useful chiral pyrazolone derivatives was obtained in high yields (up to 95%) with good enantioselectivities (up to 88 % ee).

A highly stereoselective methodology was developed to construct dihydrofurans. In the presence of a bifunctional squaramide catalyst, the Michael addition/cyclization between cyclohexane- 1,3-dione and α-bromonitroalkenes occurred smoothly to provide the desired dihydrofurans with high to excellent yields (90-94%) and good to high enantioselectivities (80-94% ee). This catalytic protocol was compatible with a range of structurally distinct α-bromonitroalkenes.