Synthesis and Biological Evaluation of Cassane Diterpene (5α)-Vuacapane-8(14), 9(11)-Diene and of Some Related Compounds

Abstract

A set of thirteen cassane-type diterpenes was synthesized and an expedient synthetic route was used to evaluate 14-desmethyl analogs of the most active tested cassane. The anti-inflammatory activities of these 13 compounds were evaluated on a lipopolysaccharide (LPS)-activated RAW 264.7 cell line by inhibition of nitric oxide (NO) production, some of them reaching 100% NO inhibition after 72 h of treatment. The greatest anti-inflammatory effect was observed for compounds 16 and 20 with an IC50 NO of 2.98 ± 0.04 μg/mL and 5.71 ± 0.14 μg/mL, respectively. Flow-cytometry analysis was used to determine the cell cycle distribution and showed that the inhibition in NO release was accompanied by a reversion of the differentiation processes. Moreover, the anti-cancer potential of these 13 compounds were evaluated in three tumor cell lines (B16-F10, HT29, and Hep G2). The strongest cytotoxic effect was achieved by salicylaldehyde 20, and pterolobirin G (6), with IC50 values around 3 μg/mL in HT29 cells, with total apoptosis rates 80% at IC80 concentrations, producing a significant cell-cycle arrest in the G0/G1 phase, and a possible activation of the extrinsic apoptotic pathway. Additionally, initial SAR data analysis showed that the methyl group at the C-14 positions of cassane diterpenoids is not always important for their cytotoxic and anti-inflammatory activities.

Semisynthesis and Evaluation of Anti-Inflammatory Activity of the Cassane-Type Diterpenoid Taepeenin F and of Some Synthetic Intermediates

“…RAW 264.7 Cell-Cycle Arrest and Distribution. Since the anti-inflammatory effect can be related to the ability to change the inflammatory processes induced by LPS in RAW 264.7 cells, including monocyte/macrophage cell differentiation and cell-cycle arrest, 22 we analyzed the cell-cycle distribution in these cells in response to LPS and compounds 16 and 21. The two compounds with the highest antiproliferative and important NO inhibitory effects were selected for this assay.…”

“…1 H NMR (500 MHz, chloroformd) δ (ppm) 0.79 (s, 3H), 1.02 (d, J = 6.9 Hz, 3H), 1.14 (d, J = 6.9 Hz, 3H), 1.25 (s, 3H), 1.26−1.31 (m, 2H), 1.54−1.66 (m, 4H), 1.79 (s, 3H), 1.81−1.90 (m, 3H), 2.08−2.15 (m, 2H), 2.38 (br d, J = 13.7 Hz, 1H), 2.97 (hept, J = 6.9 Hz, 1H), 3.64 (s, 3H), 4.38 (br s, 1H), 5.77 (br s, 1H). 13 C NMR (125 MHz, chloroform-d) δ (ppm) 13.6 (CH 3 ), 14.5 (CH 3 ), 16.9 (CH 3 ), 18.2 (CH 2 ), 21.5 (CH 3 ), 22 (16). To a solution of dienol 15 (2.58 g, 7,44 mmol) in ethyl acetate (80 mL) at room temperature, Dess-Martin periodinane (3.80 g, 8.94 mmol) was added.…”

“…1 H NMR (400 MHz, chloroform-d) δ (ppm) 1.21 (s, 3H), 1.27 (s, 3H), 1.40−1.57 (m, 2H), 1.60−1.87 (m, 5H), 2.17 (dd, J = 12.6, 2.1 Hz, 1H), 2.24 (m, 1H), 2.41 (s, 3H), 2.63 (ddd, J = 17.0, 11.2, 7.7 Hz, 1H), 2.73 (dd, J = 17.0, 7.1 Hz, 1H), 3.68 (s, 3H), 6.77 (s, 1H), 10.37 (s, 1H), 11.82 (s, 1H). 13 C NMR (100 MHz, chloroform-d) δ (ppm) 13.5 (CH 3 ), 16 (1R,4aS,10aR)-Methyl 6-hydroxy-7-(hydroxymethyl)-1,4a,8-trimethyl-1,2,3,4,4a,9,10,10a-octahydrophenanthrene-1-carboxylate (22). Sodium borohydride (60 mg, 1.58 mmol) was added to a stirred solution of 21 (265 mg, 0.80 mmol) in ethanol (6 mL), previously cooled at 0 °C, and the mixture was stirred at room temperature for 1 h. Then, it was cooled at 0 °C and quenched with saturated aqueous NH 4 Cl (2 mL).…”

Synthesis of Tricyclic Pterolobirin H Analogue: Evaluation of Anticancer and Anti-Inflammatory Activities and Molecular Docking Investigations

“…These diter-penes also exhibited anticancer activities against HT29, Hep-G2, and B16-F10 cancer cell lines, especially pterolobirin G (4), with IC 50 values of 3.87 µg /mL, 11.75 µg /mL, and 10.34 µg /mL, respectively. Pterolobirin G (4) displayed apoptotic effects in the HT29 cells, with a total rate of 80% of apoptosis at the IC 80 concentration, producing a significant cell-cycle arrest in the G0/G1 phase, and with the activation of the extrinsic apoptotic pathway [16]. On the other hand, taepeenin F (2) also inhibited NO production in RAW 264.7 macrophages with 98% at a sub-cytotoxic concentration of 150.35 µM [13].…”

“…To solve these synthetic drawbacks, function-oriented synthesis (FOS) [17] has been proposed as an approach to pursue the design of less complex targets with comparable or superior biological activity, obtaining potential analogs with simplified structures. In this context, some synthetic strategies for cassane diterpenoid analogs and their SAR investigations have been described; nevertheless, these analogs are still complex molecules [16,18,19]. Structurally, the cassane framework consists of five isoprene units constituting a tetracyclic structure composed of an aromatic ring linked to a five-membered heterocycle and a decalin.…”