Dimeric Amide Alkaloid Enantiomers from <i>Piper longum</i> L. with Anti-Inflammatory and Antidiabetic Effects

The fruit of <i>Piper longum</i> L. (Piperaceae), commonly used as a spice in various culinary applications, is renowned for its rich nutritional profile and potential medicinal properties. In this study, a molecular network-based dereplication strategy was employed to isolate 12 dimeric amide alkaloid enantiomers (<b>1</b>-<b>12</b>) from <i>P. longum</i> fruits, including eight pairs of cyclobutane-type dimers (<b>1</b>-<b>8</b>) and four pairs of cyclohexene-type dimers (<b>9</b>-<b>12</b>). Notably, five pairs of cyclobutane-type dimers, namely, piperlongramides E-I (<b>1</b>-<b>5</b>), and one pair of cyclohexene-type dimers, piperlongramide J (<b>9</b>), were identified as undescribed compounds. The structures of these compounds were elucidated by comprehensive spectroscopic data, electronic circular dichroism (ECD) calculations, and X-ray diffraction analysis. Additionally, these compounds, for the first time, were subjected to chiral resolution. <i>In vitro</i> bioactivity screening revealed that compounds (+)-<b>10</b>, (-)-<b>10</b>, and (+)-<b>3</b> exhibited notable anti-inflammatory effects in an LPS-induced RAW 264.7 macrophage model, with IC₅₀ values of 23.42 ± 1.04, 32.72 ± 0.54, and 33.52 ± 1.75 μM, respectively. Furthermore, compound (+)-<b>3</b> also demonstrated significant inhibitory activity againstα-glucosidase, with an IC₅₀ of 11.69 ± 0.91 μM. Compounds (+)-<b>9</b>, (+)-<b>7</b>, and (-)-<b>9</b>, exhibited promising inhibitory activity against PTP1B with IC₅₀ values of 3.30 ± 0.09, 4.30 ± 0.18, and 4.37 ± 0.37 μM, respectively, indicating their potential antidiabetic effects. This study highlights the promising application of these amide alkaloid dimers in the development of functional foods and pharmaceutical products, thereby expanding the health-promoting potential of <i>P. longum</i> fruits.