(±)-Gentiovarisin A and gentiovarisin B, unusual secoiridoid dimer skeletons from gentiopicroside

Gentiana scabra, a famous traditional Chinese medicine (TCM), has been documented in Chinese Pharmacopoeia for the treatment of hepatitis. Its index component gentiopicroside could not be detected in the decoction, which suggested that the quality control of the TCM with this ingredient needs attention. The transformed products were obtained from gentiopicroside, mimicking the traditional process of G. scabra. Further investigation of the heat-transformed products yielded two secoiridoid dimers, gentiovarisin A (1) and B (2), with an unprecedented 6/6/6/6/6-fused pentacyclic skeletons. Their structures were elucidated by extensive spectroscopic analyses and single-crystal X-ray diffraction analysis, and the absolute configurations of 1 were confirmed as (+)-1 and (-)-1 by ECD method. Plausible transformation pathways of the isolates were also proposed. Compounds 1 and 2 exhibited in vitro hepatoprotective activity similar to gentiopicroside, while (+)-1 displayed a more potent hepatoprotective activity than N-Acetyl-L-cysteine.