Strophioglanes A–E and (±)-Trigoxyphin K, <i>ent</i> -Cleistanthane Diterpenoids from <i>Strophioblachia glandulosa</i> var. <i>cordifolia</i>

Seven unusual <i>ent</i>-cleistanthane diterpenoids, strophioglanes A-E (<b>1</b>-<b>5</b>) and (±)-trigoxyphin K (<b>6a</b> and <b>6b</b>), along with 10 known analogues (<b>7</b>-<b>16</b>), were isolated from <i>Strophioblachia glandulosa</i> var. <i>cordifolia</i> using LC-MS/MS-based molecular networking. Their structures were elucidated through extensive spectroscopic techniques, ECD calculations, and X-ray crystallography. Compounds <b>1</b>-<b>5</b>, featuring a rare 6/6/6/3 fused tetracyclic skeleton, represent a class of 13,15-cyclo-<i>ent</i>-cleistanthane diterpenoids, while <b>6a</b> and <b>6b</b> are a pair of highly rearranged <i>tetranor</i>-<i>ent</i>-cleistanthane enantiomers with a rare 7/6 fused bicyclic core. Biologically, <b>1</b> and <b>6b</b> showed significant neuroprotective activity against sodium nitroprusside (SNP)-induced damage in PC-12 cells, with activity comparable to that of the clinical drug edaravone. Mechanistic investigations revealed that compound <b>1</b> exerted this activity by attenuating oxidative stress.