Vasorelaxant 4,5-seco-abietane diterpenoids with diverse 6/6/6, 6/6/7, and 6/6/8 architectures from Salvia prattii Hemsl

Identification of diterpenoids from Salvia castanea Diels f. tomentosa Stib and their antitumor activities

Four new diterpenoid tropolones, salvirrddones A-D (1-4), and four new icetexanes, salvirrddices A-D (9-12), along with thirteen new 11,12-seco-norabietane diterpenoids, salvirrddnor A-M (14-24, 31, 32) and sixteen known compounds (5-8, 13, 25-30, 33-37), were isolated from the roots and rhizomes of Salvia castanea Diels f. tomentosa Stib. Their structures were elucidated by comprehensive spectroscopic analyses, quantum chemical calculations, and X-ray crystallography. Structurally, compounds 1-8 represent a class of rare natural products featuring a unique cyclohepta-2,4,6-trienone moiety with diterpenoid skeletons. Bioassays showed that only diterpenoid tropolones 3, 5, 6, and 7 exhibited significant activity against several human cancer cell lines with IC50 values ranging from 3.01 to 11.63 μM. Additionally, 3 was shown to inhibit Hep3B cell proliferation, block the G0/G1 phase of the cell cycle, induce mitochondrial dysfunction and oxidative stress, promote apoptosis, as well as inhibit migration and invasion in vitro. Meanwhile, 3 demonstrated anti-proliferative, pro-apoptotic, and migration-inhibitory effects in the Hep3B xenograft zebrafish model in vivo. Network pharmacological analysis and molecular docking results suggested that 3 may treat hepatocellular carcinoma (HCC) through the PI3K-Akt signaling pathway, as well as by binding PARP1 and CDK2 targets. Overall, the present results extremely expand the repertoire of diterpenoids from natural products and may provide a novel chemical scaffold for the discovery of new antitumor drugs.

Discovery and Bioinspired Synthesis of Salpratone A

Salpratone A (1), a novel abietane diterpenoid containing a unique cis-fused A/B ring, was isolated from Salvia prattii. Bioactivity studies showed that 1 has potent activity in inhibiting platelet aggregation induced by multiple agonists as well as antithrombotic efficacy in the FeCl3-induced rat in vivo thrombosis model. Furthermore, a bioinspired synthesis of 1 from the abundant natural product ferruginol was achieved in 6 steps with a 22% overall yield. The key steps include a stereoselective allyl oxidation and a subsequent regioselective Meinwald rearrangement.

11,12-seco-Abietane-type diterpene lactones with potential antiplatelet activity from Salvia prattii

Eleven new abietane-type diterpene lactones, salpratlactones D-N (1-11), including five 11,12-seco-11-nor-abietane diterpenes (1-5), four 11,12-seco-abietane diterpenes (6-9), two 20(10 → 5)-abeo-4,5;11,12-bis-seco-abietane diterpenes (10-11), and two known analogues (12-13), were characterized from Salvia prattii. Notably, compounds 1-3 were characterized by a unique linear 6/6/6 tricyclic skeleton. The structures were established by spectroscopic data interpretation, calculated NMR-DP4+ and electronic circular dichroism analysis, as well as single-crystal X-ray diffraction. A bioactivity study showed that 1, 2, 5, 11, and 12 can potently inhibit platelet aggregation induced by arachidonic acid (AA), with IC50 values of 5.66-16.10 μg/ml, stronger than aspirin. In addition, the lactate dehydrogenase assay showed that they had no effect on platelet integrity. Structurally, the same 1,2-benzopyrone fragments of 1, 2, and 5 should be the important pharmacophore for antiplatelet activity.

Evaluation of Anticancer and Anti-Inflammatory Activities of Some Synthetic Rearranged Abietanes

Synthesis of the rearranged abietane diterpenes pygmaeocins C and D, viridoquinone, saprorthoquinone, and 1-deoxyviroxocine has been successfully achieved. The anticancer and anti-inflammatory activities of selected orthoquinonic compounds 5, 7, 13, and 19, as well as pygmaeocin C (17), were evaluated for the first time. The antitumor properties were assessed using three cancer cell lines: HT29 colon cancer cells, Hep G2 hepatocellular carcinoma cells, and B16-F10 murine melanoma cells. Compounds 5 and 13 showed the highest cytotoxicity in HT29 cells (IC50 = 6.69 ± 1.2 µg/mL and IC50 = 2.7 ± 0.8 µg/mL, respectively). Cytometric studies showed that this growth inhibition involved phase S cell cycle arrest and apoptosis induction, possibly through the activation of the intrinsic apoptotic pathway. Morphological apoptotic changes, including nuclear fragmentation and chromatin condensation, were also observed. Furthermore, the anti-inflammatory activity of these compounds was evaluated on the basis of their ability to inhibit nitric oxide production on the lipopolysaccharide activated RAW 264.7 macrophage cell line. Although all compounds showed high anti-inflammatory activity, with percentages between 40 and 100%, the highest anti-inflammatory potential was obtained by pygmaeocin B (5) (IC50NO = 33.0 ± 0.8 ng/mL). Our results suggest that due to their dual roles, this type of compound could represent a new strategy, contributing to the development of novel anticancer agents.

Abietane Diterpenoids from the Hairy Roots of Salvia corrugata

Salvia corrugata Vahl. is an interesting source of abietane and abeo-abietane compounds that showed antibacterial, antitumor, and cytotoxic activities. The aim of the study was to obtain transformed roots of S. corrugata and to evaluate the production of terpenoids in comparison with in vivo root production. Hairy roots were initiated from leaf explants by infection with ATCC 15834 Agrobacterium rhizogenes onto hormone-free Murashige and Skoog (MS) solid medium. Transformation was confirmed by polymerase chain reaction analysis of rolC and virC1 genes. The biomass production was obtained in hormone-free liquid MS medium using Temporary Immersion System bioreactor RITA®. The chromatographic separation of the methanolic extract of the untransformed roots afforded horminone, ferruginol, 7-O-acetylhorminone and 7-O-methylhorminone. Agastol and ferruginol were isolated and quantified from the hairy roots. The amount of these metabolites indicated that the hairy roots of S. corrugata can be considered a source of these compounds.

Structurally Diverse Diterpenoids from the Roots of Salvia deserta Based on Nine Different Skeletal Types

Twenty-four diterpenoids (1-24), classified into nine diverse carbon skeletal types, 8-nor-7(8→14),9(8→7)-di-abeo-abietane (1, 2, and 13), 7(8→14),9(8→7)-di-abeo-abietane (3 and 4), 6-nor-6,7-seco-abietane (5 and 6), 6,7-seco-abietane (7 and 11), 9,10-seco-abietane (8), abietane (9, 10, and 14-21), 11(9→8),20(10→11)-di-abeo-abietane (12), 15(13→12)-abeo-abietane (22 and 23), and 4,5-seco-20(10→5)-abeo-abietane (24), respectively, were isolated from the roots of Salvia deserta. The structures of 10 new diterpenoids, named salviadesertins A-J (1-10), were elucidated by spectroscopic data interpretation, quantum-chemical calculations including calculated ¹³C NMR-DP4+ analysis and electronic circular dichroism as well as X-ray crystallography analysis. The absolute configurations of compounds 1-3, 7, 14, and 22 were defined by single-crystal X-ray diffraction analysis. All the isolated diterpenoids 1-24 were evaluated for their cytotoxicity against five cancer cell lines, and 6-hydroxysalvinolone (14) showed micromolar potencies against MCF-7, A-549, SMMC-7721, and HL-60 cells, whereas the other diterpenoids were inactive (half-maximal inhibitory concentration greater than 10.0 μM).