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

The fruit of Piper longum 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 ( 1 – 12 ) from P. longum fruits, including eight pairs of cyclobutane-type dimers ( 1 – 8 ) and four pairs of cyclohexene-type dimers ( 9 – 12 ). Notably, five pairs of cyclobutane-type dimers, namely, piperlongramides E–I ( 1 – 5 ), and one pair of cyclohexene-type dimers, piperlongramide J ( 9 ), 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. In vitro bioactivity screening revealed that compounds (+)- 10, (−)- 10, and (+)- 3 exhibited notable anti-inflammatory effects in an LPS-induced RAW 264.7 macrophage model, with IC 50 values of 23.42 ± 1.04, 32.72 ± 0.54, and 33.52 ± 1.75 μM, respectively. Furthermore, compound (+)- 3 also demonstrated significant inhibitory activity againstα-glucosidase, with an IC 50 of 11.69 ± 0.91 μM. Compounds (+)- 9, (+)- 7, and (−)- 9, exhibited promising inhibitory activity against PTP1B with IC 50 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 P. longum fruits.