Isoquinoline alkaloids with bioactive constituents from the roots and rhizomes of <i>Hylomecon japonica</i>

Isoquinoline alkaloids are important effective chemical components separated from the <i>Hylomecon japonica</i>, which were mostly reported as planar structures. By using chiral HPLC, we have concluded that some natural isoquinoline alkaloids exist as enantiomeric mixtures, providing a novel direction for future research on isoquinoline alkaloids. Finally, three pairs of enantiomeric isoquinoline alkaloids (<b>1-3</b>, including five undescribed compounds-<b>1a/1b</b>, <b>3a/3b</b> and <b>2b</b>), together with another eight known isoquinoline alkaloids (<b>4-9</b>) were isolated from the roots and rhizomes of <i>Hylomecon japonica</i>. Their structures were elucidated by NMR, HRESIMS, UV, IR, and their absolute configurations were further defined by quantum chemical calculations of ECD spectra. The cytotoxic activities of these isolated compounds in MCF-7 cells were evaluated by MTT methods. Among them, the alkaloids <b>1a</b>, <b>1b</b>, <b>2b</b>, <b>3b</b> and other known alkaloids <b>5a</b> and <b>5b</b> had good inhibitory effects on MCF-7 cells of breast cancer <i>in vitro</i>, with an IC₅₀ lower than 20 μM.