Rhodium boron nitride : a recyclable catalyst for the synthesis of a-aminophosphonates and dihydropyrimidinones

Abstract

The -aminophosphonates (APs) and dihydropyrimidinones (DHPMs) exhibit a wide range of important biological activities. The great potential of these compounds in biological applications prompted an increased interest in the development of efficient synthetic methods for their preparation. A novel rhodium supported boron nitride (RhBNT) material was synthesized by simply mixing boron nitride in a solution of rhodium acetate, under inert atmosphere for 7 days followed by filtration; the yield was 95 %. It exhibited excellent catalytic properties for the synthesis of 13 novel APs and 5 DHPMs. Characterization of RhBNT was performed by several techniques: the crystalline nature of RhBNT and nano size was confirmed by SEM spectroscopy, EDX pattern for RhBNT showed signals for rhodium metal, the Brumnauer-Emmett-Teller (BET) analysis showed the specific surface area of RhBNT to be 28.12 m2/g, pore volume 0.23cm3/g and pore size of 199.8Aº thereby suggesting RhBNT as a potentially effective catalyst for organic reactions; the mesoporous nature of the material was established by a type- IV adsorption isotherm; the DSC-TGA Profile indicates that RhBNT has good thermal stability and can be used adequately for catalysis. The DSC curve showed evidence of a broad exothermic peak. The RhBNT was subsequently used in the Kabachnik-Fields and Biginelli reaction in order to assess its catalytic potential. Herein Vilsmeier-Haack reagent was used to synthesize 4-oxo-chromene-3-carbaldehyde and 4-oxo-4H-benzo[h]chromene-3-carbaldehyde from 2-hydroxyacetophenone and 1-hydroxy-2-acetonaphthone, respectively. These two carbaldehydes were subsequently used to synthesize thirteen novels APs and five DHMPs using RhBNT as the catalyst The antimicrobial activities of the synthesized compounds were assessed against Escherichia coli, Bacillus cereus, Micrococcus luteus, Staphylococcus aureus and Candida albicans using the disc diffusion method. It was found that none of the compounds inhibited growth of bacteria or fungus. The assessment of toxicity was evaluated by using the brine shrimp lethal test. It was found that six of the novel compounds exhibited more than 50% brine shrimp death and were considered toxic against Artemia sp. and hence unsuitable as a potential drug whilst four compounds were found to be less toxic, exhibiting a brine shrimp death of less than 50%. Molecular docking studies were carried out for 13 APs to estimate their binding interactions with HIV-1 reverse transcriptase. Four APs showed good potential for the inhibition of HIV-1 reverse transcriptase.