Solvent-free, green and efficient synthesis of pyrano[4, 3-b]pyrans by grinding and their biological evaluation as antitumor and antioxidant agents

Synthesis of Fe3O4@SiO2@Pr-NH2@DAP as a magnetic recyclable nano-catalyst for efficient synthesis of pyranothiazolopyrimidines and 4H-pyrans under solvent-free condition

In this research, we describe the synthesis of silica-coated nano-Fe3O4 particles, which were successfully modified by diaminopyrimidine, and their physicochemical properties were characterized using FT-IR, XRD, TEM, FE-SEM, EDX, EDX-mapping, and TGA. The catalytic activity of this novel nano-catalyst was evaluated by three-component reactions for the preparation of pyranothiazolopyrimidines and 4H-pyrans under solvent-free conditions. Recyclability of the catalyst up to six consecutive rounds, atom economy, high yield and purity of desired products, and easy work-up method are some of the exciting features of this system that make it more favorable from a green chemistry point of view.

Cysteic acid grafted to magnetic graphene oxide as a promising recoverable solid acid catalyst for the synthesis of diverse 4H-chromene

4H-chromenes play a significant role in natural and pharmacological products. Despite continuous advances in the synthesis methodology of these compounds, there is still a lack of a green and efficient method. In this study, we have designed cysteic acid chemically attached to magnetic graphene oxide (MNPs·GO-CysA) as an efficient and reusable solid acid catalyst to synthesize 4H-chromene skeletons via a one-pot three components reaction of an enolizable compound, malononitrile, an aldehyde or isatin, and a mixture of water-ethanol as a green solvent. This new heterogeneous catalyst provides desired products with a good to excellent yield, short time, and mild condition. This procedure presents an environmentally friendly approach for the synthesis of a great number of 4H-chromene derivatives.

Synthesis, biological evaluation, and computational studies of novel fused six-membered O-containing heterocycles as potential acetylcholinesterase inhibitors

An efficient, borax-catalyzed protocol for the synthesis of novel 4-aryl-substituted-4H-pyran derivatives fused to α-pyrone ring in a one-pot is described. By this achievement, some novel 4-aryl substituted 4H-pyrans fused to the α-pyrone ring as potential acetylcholinesterase inhibitors (AChEIs) with good to excellent yields are obtained from a one-pot three-component reaction between various aryl aldehydes, 4-hydroxy-6-methyl-2H-pyran-2-one and malononitrile. The method is a facile, inexpensive, practical and highly efficient one to obtain target compounds. The chemical structures of all compounds were characterized by FT-IR, FT-¹³CNMR and FT-¹HNMR, MS spectroscopy and also elemental analyses data. Furthermore, the purity of all novel compounds was checked by HPLC. In addition, both molecular modelling studies and Absorption, Distribution, Metabolism, Excretion and Toxicity (ADMETox) prediction nominated all compounds as good acetylcholinesterase inhibitors to the potential treatment of Alzheimer, Parkinson and Autism diseases that among them compound 4f showed the best activity against acetylcholinesterase enzyme.

First report of two new antioxidative meroterpeno 2H-pyranoids from short-necked yellow-foot clam Paphia malabarica (family: Veneridae) with bioactivity against pro-inflammatory cyclooxygenases and lipoxygenase

Two new meroterpeno 2H-pyranoids were isolated from the EtOAc:MeOH extract of yellow-foot clam Paphia malabarica. The structures of these newly reported compounds were elucidated based on spectroscopic interpretations. This is the first report of biogenic 2H-pyrans bearing decadienyl and allyloxy-(isopentanyl)-cyclohexene skeletons from marine biota. The extended C₁₈ sesquiterpenoid with prenylated irregular farnesene framework was characterised as 2-((E)-deca-1,8-dien-10-yl)-11,12-dihydro-13-propyl-2H-pyran (1). The compound 2, 1'-((10E)-10-(10-(pentan-4-yl)-cyclohex-4-enyl)-allyloxy)-tetrahydro-2',2'-dimethyl-2H-pyran represents the first example of naturally occurring C₂₁ prenylated bisabolene-type meroterpenoid, whereas tetrahydro-2',2'-dimethyl-2H-pyran remains attached at C-2' position of rearranged bisabolene framework formed by allyloxy linkage. The antioxidant activities (DPPH/ABTS⁺) of 1 and 2 were comparable (IC₅₀ < 1.0 mg/mL) with α-tocopherol. In addition, these compounds exhibited greater activity against cyclooxygenase-2 than COX-1, and the selectivity indices were significantly lesser (~1.1). No significant differences in anti-5-lipoxygenase activity of 1 and 2 (IC₅₀ 1.02-1.06 mg/mL) than ibuprofen (IC₅₀ 0.93 mg/mL) indicated the potential anti-inflammatory properties of title compounds.

Advances in elucidating mechanochemical complexities via implementation of a simple organic system

Mechanochemistry is becoming increasingly popular amongst both the academic and industrial communities as an alternative method for inducing physical and chemical reactions. Despite its rapidly expanding application, little is understood of its mechanisms, greatly limiting its capacity. In the present work the application of specialty devices allowed submission of the simple organic system, α-glycine + β-malonic acid, to isolated shearing and impact treatment. In doing so, unique products were observed to result from each of these major mechanical actions; shear inducing formation of the known salt, glycinium semi-malonate (GSM), and impact yielding formation of a novel phase. Correlation of these isolated treatments with a more common ball mill indicated two unique regions within the milling jar, each characterised by varying ratios of shear and impact, leading to different products being observed. It is widely accepted that, particularly when considering organic systems, mechanical treatment often acts by inducing increases in local temperature, leading to volatilisation or melting. A combination of DSC and TGA were used to investigate the role of temperature on the system in question. Invariably, heating induced formation of GSM, with evidence supporting a eutectic melt, rather than a gas-phase reaction. Shear heating alone is unable to describe formation of the novel phase obtained through impact treatment. By considering the formation and character of mechanically produced tablets, a model is described that may account for formation of this novel phase. This system and methodology for mechanochemical study offers intriguing opportunities for continued study of this widely used and exciting field.