Sweritranslactones A–C: Unusual Skeleton Secoiridoid Dimers via [4 + 2] Cycloaddition from Swertiamarin

A Homodimer of Withaferin A Formed by Base-Promoted Elimination of Acetic Acid from 27-O-Acetylwithaferin A Followed by a Diels-Alder Reaction

Treatment of 27-O-acetylwithaferin A (2) with the non-nucleophilic base, 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), afforded 5β,6β-epoxy-4β-hydroxy-1-oxo-witha-2(3),23(24),25(27)-trienolide (3) and 4, a homodimer of withaferin A resulting from a Diels-Alder [4 + 2] type cycloaddition of the intermediate α,β-dimethylene-δ-lactone (9). Structures of 3 and 4 were elucidated using HRMS and 1D and 2D NMR spectroscopic data. The structure of 4 was also confirmed by single crystal X-ray crystallographic analysis of its bis-4-O-p-nitrobenzoate (8). Formation of withaferin A homodimer (4) as the major product suggests regio- and stereoselectivity of the Diels-Alder [4 + 2] cycloaddition reaction of 9. Acetylation of 2-4 afforded their acetyl derivatives 5-7, respectively. Compounds 2-4 and 6-8 were evaluated for their cytotoxic activities against four prostate cancer (PC) cell lines (LNCaP, 22Rv1, DU-145, and PC-3) and normal human foreskin fibroblast (HFF) cells. Significantly, 4 exhibited improved activity compared to the other compounds for most of the tested cell lines.

Swertiamarin or heat-transformed products alleviated APAP-induced hepatotoxicity via modulation of apoptotic and Nrf-2/NF-κB pathways

OBJECTIVE

Swertiamarin (STM) belongs to iridoid class of compounds, and the heat-transformed products (HTPS) are produced by STM in the process of drug processing. The purpose of this study was to explore the protective effect and mechanism of STM or HTPS on acetaminophen (APAP)-induced hepatotoxicity.

METHODS

Mice and L-O2 cells were given APAP to establish the hepatotoxicity model in vivo and in vitro. The effects of STM or HTPS on oxidative stress, inflammation, and apoptosis induced by APAP were evaluated, with N-acetylcysteine (NAC) as a positive control.

RESULTS

STM or HTPS reduced the APAP-induced apoptosis of L-O2 cells and significantly alleviated the liver injury index induced by APAP (p < 0.01, 0.005) Interestingly, HTPS had better protective effect against APAP-induced hepatotoxicity than STM (p < 0.05). In addition STM or HTPS improved the histological abnormalities; inhibited lipid peroxidation and reduced the level of inflammatory mediators. They also activated the defense system of nuclear factor erythroid 2 related factor 2 (Nrf-2) and inhibited nuclear factor-κ B (NF-κB).

(±)-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.

Sweritranslactone D, a hepatoprotective novel secoiridoid dimer with tetracyclic lactone skeleton from heat-transformed swertiamarin

Swertia mileensis, known as Qing-Ye-Dan (QYD), has been documented in Chinese Pharmacopoeia to cure hepatitis. Interestingly, its announced main active component, swertiamarin, could not be detected in the decoction, which indicated that the efficacy of QYD might be attributed to heat-transformed products of swertiamarin (HTPS). Further investigation on HTPS led to the isolation of sweritranslactone D (1), a novel secoiridoid dimer possessing a tetracyclic lactone skeleton, with better hepatoprotective activity than N-acetyl-L-cysteine in vitro.