Synthesis and antitubercular activity evaluation of 4-furano-coumarins and 3-furano-chromones

The synthesis of novel 4-furano-coumarins and 3-furano-chromones has been achieved using silver-mediated oxidative C–H/C–H functionalization of 4-ethynylcoumarin/3-ethynylchromone with ethyl acetoacetate in 80%–90% and 82%–90% yields, respectively. The structure of the synthesized compounds was established on the basis of their spectral data analysis and the structure of one of the 4-furano-coumarins has been further confirmed on the basis of its X-ray crystallographic study. All eight synthesized 4-furano-coumarins and 3-furano-chromones exhibited moderate antitubercular activity against sensitive reference strain H37Rv of Mycobacterium tuberculosis.     

Synthesis of functionalized furopyrazines as restricted dipeptidomimetics

Herein, an efficient synthetic approach to a furopyrazine scaffold with four points of diversity, starting from 2(1H)-pyrazinones, with dipeptomimetic properties, is presented. R-groups corresponding to amino acid side chains were introduced during the 2(1H)-pyrazinone and subsequent furopyrazine formation. The furopyrazine scaffold was further functionalized with an amino- and a carboxy-terminus resulting in a conformationally restricted dipeptidomimetic scaffold. The carboxy-terminus was introduced via a chemoselective vinylation of the 7-position followed by oxidative cleavage, while the amino-terminus was obtained via Buchwald–Hartwig amidation of the 2-position of the scaffold. The versatility of the synthetic method was demonstrated by the synthesis of a small library of diversely substituted furopyrazines having various amino acid side chains on the four points of diversity. Evaluation with an X-ray structure of the scaffold and computational analysis supports the exploitation of the furopyrazine scaffold as a restricted dipeptide mimic, which can mimic the two central residues of a β-turn.     

Influence of oxidation state of phosphorus on the thermal and flammability of polyurea and epoxy resin

The focus of this study is an investigation of the effect of oxidation state of phosphorus in phosphorus-based flame retardants on the thermal and flame retardant properties of polyurea and epoxy resin. Three different oxidation states of phosphorus (phosphite, phosphate and phosphine oxide) additives, with different thermal stabilities at a constant phosphorus content (1.5 wt.%) have been utilized. Thermal and flame retardant properties were studied by TGA and cone calorimetry, respectively. The thermal stability of both polymers decreases upon the incorporation of phosphorus flame retardants irrespective of oxidation state and a greater amount of residue was observed in the case of phosphite. Phosphate was found to be better flame retardant in polyurea, whereas phosphite is suitable for epoxy resin. Phosphite will react with epoxy resin by trans-esterification, which is demonstrated by FTIR and ³¹P NMR. Further, TG–FTIR and XPS studies also provide information on flame retardancy of both polymers with phosphorus flame retardants.