Structurally unusual C-22-nor Daphniphyllum alkaloids from the seeds of Daphniphyllum calycinum and their mitochondria-associated anti-apoptotic effects in OGD/R-injured H9c2 cells

Investigation of alkaloid constituents from the seeds of Daphniphyllum calycinum led to the isolation of 14 previously undescribed C-22-nor Daphniphyllum alkaloids, designated dcalycinumines F–S ( 1 – 4 and 6 – 15 ), together with one known analog ( 5 ). These metabolites encompass four skeletal types, including three unprecedented structural classes within the Daphniphyllum alkaloid family, namely the C-22-nor daphmanidin A-type, C-22-nor yuzurine-type, and C-22-nor daphnezomine F-type frameworks. Their structures were established by comprehensive spectroscopic analyses, X-ray crystallography, ECD calculations, and comparative 13 C NMR calculations combined with DP4 + analysis. Biological evaluation showed that several alkaloids protected H9c2 cells against OGD/R-induced injury to varying degrees. Alkaloid 14 was selected for further investigation and was found to significantly reduce OGD/R-induced apoptosis and attenuate mitochondrial membrane potential loss, suggesting a mitochondria-associated anti-apoptotic protective mechanism. These findings expand the structural diversity of C-22-nor Daphniphyllum alkaloids and provide chemical evidence supporting the value-added utilization of the oil-rich seeds of D. calycinum as a source of structurally unusual and biologically relevant non-lipid secondary metabolites.