β-Cyclodextrin (β-CD) as a Supramolecular Catalyst for the Synthesis of Isoxazoles and Thiopyrimidines and their Antimicrobial Screening

Background: Isoxazole and pyrimidines are interesting heterocyclic molecules, which are present as structural motif in numerous natural products synthetic drugs. Isoxazole and thiopyrimidines exhibit antidiabetic, cytotoxic tuberculostatic, and anticonvulsant activities. Herein we report the synthesis of isoxazole and thiopyrimidine by the reaction of ring opening of 2-arylchromones with hydroxylamine hydrochloride and thiourea, using β-cyclodextrin as a reusable catalyst under supramolecular catalysis, for the first time in aqueous media Methods: The β-Cyclodextrin catalyzed synthesis of isoxazole and thiopyrimidine derivatives by the reaction of 2-arylchromones with hydroxylamine hydrochloride and thiourea respectively in ethanol-water under ultrasonication is reported. This reaction proceeded at 80oC giving good to excellent yield and the β-cyclodextrin can be recovered and reused. The newly synthesized isoxazoles and thiopyrimidines were evaluated for their antimicrobial activity. Results: In continuation of our work on β-CD and development of newer methodologies, we disclosed a newer methodology for the synthesis of, isoxazoles 2a-n and thiopyrimidines 3a-n involving reaction of 2-arylchromones with hydroxyl amine hydrochloride and thiourea in the presence of β-cyclodextrin as a recyclable catalyst in water at 80oC under ultrasonication in excellent yield. The general scheme for the synthesis of isoxazoles 2a-n and thiopyrimidines 3a-n from 2-arylchromones is depicted in Scheme 1. The structure of the products thus obtained was assigned by, 1H NMR, 13C NMR, elemental analysis and melting point data. Conclusion: In this paper, we describe β-cyclodextrin as suprlamolecular catalyst, for the synthesis of isoxazoles and thiopyrimidine derivatives. The key advantages of this method such as good to excellent yields of products, shorter reaction times; simple and clean workup of the desired product without column chromatography, easy recovery as well as reuse of the catalyst and the overall protocol is to be the approach towards green chemistry. And also the promising antibacterial and antifungal activities of some of the novel compounds have potential as novel drugs in pharmaceutical formulation.