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

Seven unusual ent-cleistanthane diterpenoids, strophioglanes A-E (1-5) and (±)-trigoxyphin K (6a and 6b), along with 10 known analogues (7-16), were isolated from Strophioblachia glandulosa var. cordifolia using LC-MS/MS-based molecular networking. Their structures were elucidated through extensive spectroscopic techniques, ECD calculations, and X-ray crystallography. Compounds 1-5, featuring a rare 6/6/6/3 fused tetracyclic skeleton, represent a class of 13,15-cyclo-ent-cleistanthane diterpenoids, while 6a and 6b are a pair of highly rearranged tetranor-ent-cleistanthane enantiomers with a rare 7/6 fused bicyclic core. Biologically, 1 and 6b 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 1 exerted this activity by attenuating oxidative stress.