Abstract
We used a novel hybrid catalyst in chemo-, regio-, and diastereoselective multi-component reactions (MCR) for the synthesis of the 2-aza analogue of pyrrolizidine and spirooxindole-2-azapyrrolizidine derivatives. The nanocatalyst, W(iv)/NNBIA–SBA-15 [where NNBIA = N,N′-(ethane-1,2-diyl)bis(2-aminobenzamide)] was synthesized by covalent grafting on chloro-functionalized SBA-15. The synthesis process was followed by the anchoring of WCl6 to catch the desired catalyst. The quality of the catalyst was assessed using different analytical techniques such as X-ray diffraction spectroscopy (XRD), Fourier-transform infrared spectroscopy (FT-IR), N2 adsorption analysis, transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), ammonia Temperature Programmed Desorption (TPD), X-Ray photoelectron spectroscopy (XPS) and thermogravimetric, differential thermal analysis (TGA-DTA). The catalyst, W(iv)/NNBIA–SBA-15, with high catalytic performance is a good candidate for the diastereoselective synthesis of 2-azapyrrolizidine alkaloid scaffolds. The catalyst could be recovered for reuse without noticeable loss of activity.
Highlights
IntroductionChemical researchers are focused on the synthesis of functionalized nitrogen and oxygen-containing organic compounds that have potential medicinal and biological activities.[1,2] Diversity-oriented synthesis (DOS) is one of the strategies used to provide synthetic methods for the efficient combination of regiochemically and functionally diverse simple molecules.[3,4,5] DOS is especially useful for those structures based on natural products or drug-like molecules.[6,7] The aim of DOS is to achieve simultaneous, deliberate, and impressive syntheses of structurally diverse compounds such as drug molecules or natural products.[3,4,5,8] MCRs9 can be placed in the class of DOS chemistry due to green characteristics, straightforward reaction designs, high degrees of atom economy, lower costs and environmentally friendliness.[10]
The catalyst, W(IV)/NNBIA–SBA-15, with high catalytic performance is a good candidate for the diastereoselective synthesis of 2-azapyrrolizidine alkaloid scaffolds
A small angle X-ray diffraction method was used to monitor the effect of incorporation of the ligand, NNBIA, and the metal on the framework of SBA-15 (Fig. 1)
Summary
Chemical researchers are focused on the synthesis of functionalized nitrogen and oxygen-containing organic compounds that have potential medicinal and biological activities.[1,2] Diversity-oriented synthesis (DOS) is one of the strategies used to provide synthetic methods for the efficient combination of regiochemically and functionally diverse simple molecules.[3,4,5] DOS is especially useful for those structures based on natural products or drug-like molecules.[6,7] The aim of DOS is to achieve simultaneous, deliberate, and impressive syntheses of structurally diverse compounds such as drug molecules or natural products.[3,4,5,8] MCRs9 can be placed in the class of DOS chemistry due to green characteristics, straightforward reaction designs, high degrees of atom economy, lower costs and environmentally friendliness.[10]. One of the most important classes of biological compounds is hydantoins.[13,14,15] The presence of three disparate nucleophilic centers in hydantoin provides the ability to synthesize many biologically active molecules from several alternative cyclization pathways.[16] Pyrrolizidine alkaloids consisting of two fused vemember carbon rings with a nitrogen atom at one bridgehead belong to the aza-heterocyclic family.[17] They are commonly used in chemical biology and medicinal chemistry due to their medicinal properties.[18,19] The presence of a nitrogen-substituted carbon in the stereogenic center of pyrrolizidine alkaloids increases their biological properties Some of their derivatives such as retronecine,[20] heliotridine,[21] and platynecine[22] show anti-tumoural, anti-microbial, and anti-viral effects. The one-pot reactions of aldehyde or isatin (1 mmol), malononitrile (1 mmol), and hydantoin (1 mmol) were catalyzed by W(IV)/ NNBIA–SBA-15 in water (Scheme 1)
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