Antimicrobial and antiquorum-sensing activity of <i>Ricinus communis</i> extracts and ricinine derivatives

<p>Ricinine (<b>1</b>), a known major alkaloid in <i>Ricinus communis</i> plant, was used as a starting compound for the synthesis of six ricinine derivatives; two new and four known compounds. The new derivatives; 3-amino-5-methyl-1<i>H</i>-pyrazolo[4,3-c]pyridin-4(5<i>H</i>)-one (<b>2</b>), and 3-amino-5-methyl-1-(phenylsulfonyl)-1<i>H</i>-pyrazolo[4,3-c]pyridin-4(5<i>H</i>)-one (<b>3</b>), as well as the previously prepared derivatives (<b>4</b>–<b>7</b>) were subjected for antimicrobial and antiquorum-sensing evaluation in comparison to different <i>R. communis</i> extracts. Acetyl ricininic acid derivative (<b>5)</b> showed the highest antimicrobial activity among all tested derivatives against <i>Staphylococcus aureus</i>, <i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>, <i>Pseudomonas aeuroginosa</i> and <i>Candida albicans</i>. However, compound <b>7</b> (4-methoxy-1-methyl-2-oxo-1,2-dihydropyridine-3-carboxamide) showed the highest antiquorum-sensing activity among all tested compounds and extracts. These findings proved the usefulness of ricinine as a good scaffold for the synthesis of new antimicrobial and antiquorum-sensing derivatives in spite of its poor contribution to the antimicrobial activity of the plant extracts.</p