Structurally Diverse Triterpene-26-oic Acids as Potential Dual ACL and ACC1 Inhibitors from the Vulnerable Conifer Keteleeria fortunei

Phytochemical and biological studies on rare and endangered plants endemic to China. Part XXXVI. Tsugaforrestiacids A-O: Structurally diverse C-18 carboxylated diterpenoids from the twigs and needles of the 'vulnerable' conifer Tsuga forrestii and their inhibitory effects on ATP-citrate lyase

An extensive phytochemical investigation on the EtOAc-soluble fraction of the 90% MeOH extract from the twigs and needles of the 'vulnerable' Chinese endemic conifer Tsuga forrestii (Forrest's hemlock) led to the isolation and characterization of 50 structurally diverse diterpenoids, including 15 unreported C-18 carboxylated ones (tsugaforrestiacids A-O, 1-15, resp.). Among them, compounds 1-7 are abieten-18-oic acids, compound 8 is an abieten-18-succinate, and compounds 10-12 are podocarpen-18-oic acids, whereas compounds 13-15 are pimarane-type, isopimarane-type, and totarane-type diterpenoid acids, respectively. Their structures and absolute configurations were determined by a combination of spectroscopic methods, GIAO NMR calculations and DP4+ probability analyses, electronic circular dichroism (ECD) data, and single crystal X-ray diffraction analyses. All the isolates were evaluated for their inhibitory activities against the ATP-citrate lyase (ACL), a key enzyme in cellular metabolism. Tsugaforrestiacids E (5) and H (8) were found to have significant inhibitory effects against ACL, with IC50 values of 5.3 and 6.2 μM, respectively. The interactions of the bioactive molecules with the ACL enzyme were examined by molecular docking studies. The isolated diterpenoids also provide chemotaxonomic evidence to support the delimitation of Tsuga from its closest sister group (Nothotsuga). The above findings highlight the importance of protecting plant species with unique and diverse secondary metabolites, which may be potential sources of new therapeutic agents for the treating ACL-associated diseases.

Pentacyclic triterpenoids as potential ACL inhibitors from the rare medicinal plant Semiliquidambar cathayensis

An extensive phytochemical investigation on the rare medicinal plant Semiliquidambar cathayensis (family: Hamamelidaceae) led to the isolation of four new (1-4, named semiliquidacids A-D, respectively) and 25 related known pentacyclic triterpenoids. The new structures with absolute configurations were elucidated by spectroscopic methods, electronic circular dichroism (ECD) calculations, and single-crystal X-ray diffraction analysis. Compound 1 represents the first naturally occurring ursane-type triterpenoid featuring an uncommon C-25 formyl group. Compound 4 and oleanolic acid (13) exhibited remarkable inhibitory effects against the ATP-citrate lyase (ACL, an emerging drug target for hyperlipidemia and related metabolic disorders) with IC50 values of 6.5 and 11.9 μM, respectively. The molecular interaction and binding mode between the bioactive triterpenoids and ACL were elaborated by conducting a molecular docking study. Meanwhile, the chemotaxonomic significance of the isolated triterpenoids has been briefly discussed.

Terricoxanthones A-E, unprecedented dihydropyran-containing dimeric xanthones from the endophytic fungus Neurospora terricola HDF-Br-2 associated with the vulnerable conifer Pseudotsuga gaussenii

An investigation on the secondary metabolites from a rice culture broth of the endophytic fungus Neurospora terricola HDF-Br-2 derived from the vulnerable conifer Pseudotsuga gaussenii led to the isolation and characterization of 34 structurally diverse polyketides (1-34). Seven of them are previously undescribed, including five unprecedented dihydropyran-containing (terricoxanthones A-E, 1-5, resp.) and one rare tetrahydrofuran-containing (terricoxanthone F, 6) dimeric xanthones. The structures were elucidated by spectroscopic methods and single-crystal X-ray diffraction analyses. Terricoxanthones each were obtained as a racemic mixture. Their plausible biosynthetic relationships were briefly proposed. Compounds 6, aspergillusone A (8), and alatinone (27) displayed considerable inhibition against Candida albicans with MIC values of 8-16 μg/mL. 4-Hydroxyvertixanthone (12) and 27 exhibited significant inhibitory activities against Staphylococcus aureus, with MIC values of 4-8 μg/mL. Furthermore, compounds 8 and 27 could disrupt biofilm of S. aureus and C. albicans at 128 μg/mL. The findings not only extend the skeletons of xanthone dimers and contribute to the diversity of metabolites of endophytes associated with the endangered Chinese conifer P. gaussenii, but could further reveal the important role of protecting plant species diversity in support of chemical diversity and potential sources of new therapeutics.

Liriogerphines E-U, further unique sesquiterpene-alkaloid hybrids from the rare Chinese tulip tree

Seventeen undescribed sesquiterpene-alkaloid hybrids (liriogerphines E-U, 1-17) were isolated and identified during a further phytochemical investigation on the branches and leaves of Chinese tulip tree (Liriodendron chinense), a rare medicinal and ornamental plant endemic to China. These unique heterodimers are conjugates of germacranolide-type sesquiterpenoids with structurally diverse alkaloids [i.e., aporphine- (1-15), proaporphine- (16), and benzyltetrahydroisoquinoline-type (17)] via the formation of a C-N bond. The previously undescribed structures were elucidated by comprehensive spectroscopic data analyses and electronic circular dichroism calculations. Such a class of sesquiterpene-alkaloid hybrids presumably biosynthesized via an aza-Michael addition is quite rare from terrestrial plants. In particular, the sesquiterpene-benzyltetrahydroisoquinoline hybrid skeleton has never been reported until the present study. All the isolates were evaluated for their cytotoxic effects against a small panel of leukemia cell lines (Raji, Jeko-1, Daudi, Jurkat, MV-4-11 and HL-60), and some of them exhibited considerable activities.