Pipercyclobutanamide D, a new member of the cyclobutanamide-type alkaloid, from the roots of Piper nigrum

From the EtOH-soluble extract of the roots of Piper nigrum, one new dimeric alkamide, pipercyclobutanamide D (1) was isolated. Its structure was elucidated on the basis of NMR spectroscopic interpretation. The relative configuration of 1 was determined based on the NOESY analysis. Compound 1 showed α-glucosidase inhibitory activity with an IC50 value of 158.5 µM. In addition, compound 1 exhibited cytotoxicity against the MCF-7 and HepG2 cell lines with the IC50 values of 45.6 and 63.9 µM, respectively. Plausible biosynthetic pathway for the formation of 1 was proposed based on regioselective [2 + 2] cycloaddition reaction.