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Abstract
A straightforward and high-yielding methodology for the synthesis of a high structural diversity of 1,2,4-oxadiazoles from different chiral N-protected α-amino acids and amidoximes under microwave (MW) irradiation is described herein. This greener approach gives the desired products using acetone/water as solvent in very short reaction times.
Highlights
IntroductionAmong the various classes of heterocyclic compounds, 1,2,4oxadiazoles are noteworthy due to their usefulness in several applications, including industrial materials, products for agriculture (such as insecticides), and pharmaceutical and medicinal products, representing the largest applicability for these compounds [1,2,3,4,5]. e 1,2,4-oxadiazole nucleus is found in various synthetic drugs displaying a broad biological spectrum of activities, including anti-inflammatory [6, 7], antifungal [8, 9], antibiotic [10, 11], antioxidant [12,13,14], anticonvulsant [15, 16], and anticancer [17, 18] properties.several approaches are described in the literature for the preparation of this class of compounds
As part of our growing interest in using α-amino acids as chiral building blocks in organic synthesis [21, 38,39,40,41,42,43,44,45] and in connection with the increasing importance of the synthesis of small libraries of compounds with programmed variations of substituents, we describe an assay, an inexpensive synthetic route for the preparation of a set of chiral Nprotected α-amino acids-derived 1,2,4-oxadiazoles under microwave irradiation, as depicted in Scheme 1
The reaction crude was dissolved in ethyl acetate and washed with water. e organic phase was dried over magnesium sulfate, and the solvent was removed under vacuum. e residue was purified by column chromatography on silica gel to afford pure products (1–5a–e)
Summary
Among the various classes of heterocyclic compounds, 1,2,4oxadiazoles are noteworthy due to their usefulness in several applications, including industrial materials, products for agriculture (such as insecticides), and pharmaceutical and medicinal products, representing the largest applicability for these compounds [1,2,3,4,5]. e 1,2,4-oxadiazole nucleus is found in various synthetic drugs displaying a broad biological spectrum of activities, including anti-inflammatory [6, 7], antifungal [8, 9], antibiotic [10, 11], antioxidant [12,13,14], anticonvulsant [15, 16], and anticancer [17, 18] properties.several approaches are described in the literature for the preparation of this class of compounds. Despite the diverse number of processes allowing the preparation of the desired 1,2,4-oxadiazoles, there are some drawbacks such as the use of high temperature, long reaction times, and the use of hazardous solvents such as DMF, diglyme, and 1,4-dioxane [19,20,21, 23, 24, 27]. The use of water as a solvent has gained increasing attention in the field of organic synthesis. The use of microwave mediating organic transformations has arisen as a very useful and effective tool for synthetic protocols due to the strict reaction control, high reaction rates, and energy savings [31, 32]. E use of water as the solvent in microwave transformations has been described. Several reports have shown that, at higher temperature and pressure, water behaves as a pseudoorganic solvent, as the dielectric constant decreases substantially and an ionic product increases the solvating
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