Two new clerodane-type diterpenes, tinosporins C (1) and tinosporins D (2) were isolated from the stems of Tinospora sagittata (Oliv.), together with three known ones, columbin (3), tinophylloloside (4), and tinospinoside D (5). The structures of these compounds were determined on the basis of spectroscopic data interpretation, with that of the absolute configuration of compound 1 was assigned by experimental and calculated ECD spectra. The cytotoxicity and α-glucosidase inhibitory activities of isolated compounds were evaluated in vitro.

Several diterpenes with the labdane skeleton show biological activity, including antiproliferative effects. Most of the research work on bioactive labdanes has been carried out on naturally occurring diterpenes and semisynthetic derivatives, but much less is known on the effects of diterpene dimers. The aim of the present work was to synthesize dimeric diterpenes from the labdane imbricatolic acid using esters, ethers and the triazole ring as linkers. Some 18 new derivatives were prepared and the compounds were evaluated for antiproliferative activity on human normal fibroblasts (MRC-5) and the following human tumor cell lines: AGS, SK-MES-1, J82 and HL-60. The diethers 8-10, differing in the number of CH₂ units in the linker, presented better antiproliferative activity with a maximum effect for the derivative 9. The best antiproliferative effect against HL-60 cells was found for compounds 3 and 17, with IC₅₀ values of 22.3 and 23.2 μM, lower than that found for the reference compound etoposide (2.23 μM). The compounds 9, 17 and 11 were the most active derivatives towards AGS cells with IC₅₀ values of 17.8, 23.4 and 26.1 μM. A free carboxylic acid function seems relevant for the effect as several of the compounds showed less antiproliferative effect after methylation.

Two new labdane diterpenes, sinoditerpene A (1) and B (2), were isolated from the fruits of Sinopodophyllum emodi, along with two known analogues 3 and 4. Their structures were established on the basis of extensive spectroscopic analysis. The isolation of compounds 1-4 represents the first report of diterpenes from the genus Sinopodophyllum. The cytotoxic activities of all isolated compounds were evaluated in comparison with 5-fluorouracil against the MCF-7 and HepG2 cell lines, towards which 3 showed more potent cytotoxicity.

Seven new diterpenes, named ovoideal A (1), B (2), C (3), D (4), E (5), F (6) and G (7), have been isolated along with eleven known diterpenes 8-18 from the petroleum ether soluble fraction of an ethanol extract of the aerial parts of Tirpitzia ovoidea. The structures of the new compounds were elucidated primarily by 1D and 2D NMR spectroscopy, as well as by the HR-ESI-MS spectrometry. All compounds were isolated from the Linaceae family for the first time. The in vitro cytotoxic activity of compounds 1, 3-5, 8-18 was evaluated against the Hela, HepG2 and K562 cell lines. Among them, compounds 3, 9, 11, 12, 13, 14, 15, 17, 18 showed moderate inhibitory activities.

Different approaches have been reported to enhance penetration of small drugs through physiological barriers; among them is the self-assembly drug conjugates preparation that shows to be a promising approach to improve activity and penetration, as well as to reduce side effects. In recent years, the use of drug-conjugates, usually obtained by covalent coupling of a drug with biocompatible lipid moieties to form nanoparticles, has gained considerable attention. Natural products isolated from plants have been a successful source of potential drug leads with unique structural diversity. In the present work three molecules derived from natural products were employed as lead molecules for the synthesis of self-assembled nanoparticles. The first molecule is the cytotoxic royleanone 7α-acetoxy-6β-hydroxyroyleanone (Roy, 1) that has been isolated from hairy coleus (Plectranthus hadiensis (Forssk.) Schweinf). ex Sprenger leaves in a large amount. This royleanone, its hemisynthetic derivative 7α-acetoxy-6β-hydroxy-12-benzoyloxyroyleanone (12BzRoy, 2) and 6,7-dehydroroyleanone (DHR, 3), isolated from the essential oil of thicket coleus (P. madagascariensis (Pers.) Benth.) were employed in this study. The royleanones were conjugated with squalene (sq), oleic acid (OA), and/or 1-bromododecane (BD) self-assembly inducers. Roy-OA, DHR-sq, and 12BzRoy-sq conjugates were successfully synthesized and characterized. The cytotoxic effect of DHR-sq was previously assessed on three human cell lines: NCI-H460 (IC50 74.0 ± 2.2 µM), NCI-H460/R (IC50 147.3 ± 3.7 µM), and MRC-5 (IC50 127.3 ± 7.3 µM), and in this work Roy-OA NPs was assayed against Vero-E6 cells at different concentrations (0.05, 0.1, and 0.2 mg/mL). The cytotoxicity of DHR-sq NPs was lower when compared with DHR alone in these cell lines: NCI-H460 (IC50 10.3 ± 0.5 µM), NCI-H460/R (IC50 10.6 ± 0.4 µM), and MRC-5 (IC5016.9 ± 0.5 µM). The same results were observed with Roy-OA NPs against Vero-E6 cells as was found to be less cytotoxic than Roy alone in all the concentrations tested. From the obtained DLS results, 12BzRoy-sq assemblies were not in the nano range, although Roy-OA NP assemblies show a promising size (509.33 nm), Pdl (0.249), zeta potential (-46.2 mV), and spherical morphology from SEM. In addition, these NPs had a low release of Roy at physiological pH 7.4 after 24 h. These results suggest the nano assemblies can act as prodrugs for the release of cytotoxic lead molecules.

A known norcembranoidal diterpene, 5-episinuleptolide (1), along with a new analogue, 4α-hydroxy-5-episinuleptolide (2), were isolated from a cultured-type soft coral Sinularia numerosa. The structures of 1 and 2 were elucidated on the basis of spectroscopic methods and by comparison of the data with those of the related metabolites. Cytotoxicity of metabolites 1 and 2 against a panel of tumor cells is also described. Compound 2 exhibited moderate cytotoxicity toward CCRF-CEM cells with an IC50 value 4.21 μg/mL. Preliminary SAR (structure activity relationship) information was obtained from these two compounds.

In order to reveal the constituents and their biological activities, we carried out a phytochemical study on Hedychium ellipticum Buch.-Ham. ex Sm. (Zingiberaceae). Ten labdane diterpenoids (1-10) were isolated from the rhizomes of H. ellipticum for the first time. Their structures were identified on the basis of spectroscopic analyses including two-dimensional NMR and comparison with literature data. All of these compounds were evaluated for their antimycobacterial activity against Mycobacterium tuberculosis and cytotoxicity against KB, MCF7, NCI-H187 and Vero cells. The result showed that compounds 1 and 7 exhibited moderate activity against Mycobacterium tuberculosis and compounds 4, 6 and 7 displayed remarkable cytotoxic activity. This is the first report on the presence of all compounds in H. ellipticum and the first time that their structure activity relationship has been discussed.

The combination of liquid chromatography coupled to high resolution mass spectrometry (LC-HRESMS)-based dereplication and antiproliferative activity-guided fractionation was applied on the Red Sea-derived soft coral Sarcophyton sp. This approach facilitated the isolation of five new cembrane-type diterpenoids (1-5), along with two known analogs (6 and 7), as well as the identification of 19 further, known compounds. The chemical structures of the new compounds were elucidated while using comprehensive spectroscopic analyses, including one-dimensional (1D) and two-dimensional (2D) NMR and HRMS. All of the isolated cembranoids (1-7) showed moderate in vitro antiproliferative activity against a human breast cancer cell line (MCF-7), with IC50 ranging from 22.39-27.12 µg/mL. This class of compounds could thus serve as scaffold for the future design of anticancer leads.

Bioactive-guided phytochemical investigation of Euphorbia antiquorum L. growing in Vietnam led to the isolation of five ent-atisanes, one seco-ent-atisane, and one lathyrane (ingol-type). The structures were elucidated as ent-1α,3α,16β,17-tetrahydroxyatisane (1), ethyl ent-3,4-seco-4,16β,17-trihydroxyatisane-3-carboxylate (2), ent-atisane-3-oxo-16β,17-acetonide (3), ent-3α-acetoxy-16β,17-dihydroxyatisane (4), ent-16β,17-dihydroxyatisane-3-one (5), calliterpenone (6), and ingol 12-acetate (7). Their chemical structures were unambiguously determined by analysis of one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) and high resolution mass spectrometry, as well as by comparison with literature data. Among them, 1 is a new compound while 2 is an ethylated artifact of ent-3,4-seco-4,16β,17-trihydroxyatisane-3-carboxylic acid, a new compound. Isolates were evaluated for alpha-glucosidase inhibition. Compound 3 showed the most significant inhibitory activity against alpha-glucosidase with an IC50 value of 69.62 µM. Further study on mechanism underlying yeast alpha-glucosidase inhibition indicated that 3 could retard the enzyme function by noncompetitive.

An EtOAc extract of Casearia corymbosa leaves led to an allosteric potentiation of the GABA signal in a fluorometric imaging plate reader (FLIPR) assay on Chinese hamster ovary (CHO) cells stably expressing GABAA receptors with an α1β2γ2 subunit composition. The activity was tracked by HPLC-based activity profiling, and four known (2, 3, 4, and 8) and five new clerodane-type diterpenoids (1, 5-7, and 9) were isolated. Compounds 1-8 were obtained from the active time window. The absolute configuration of all compounds was established by ECD. Compounds 3, 7, and 8 exhibited EC50 values of 0.5, 4.6, and 1.4 μM, respectively. To explore possible binding sites at the receptor, the most abundant diterpenoid 8 was tested in combination with diazepam, etazolate, and allopregnanolone. An additive potentiation of the GABA signal was observed with these compounds, while the effect of 8 was not inhibited by flumazenil, a negative allosteric modulator at the benzodiazepine binding site. Finally, the activity was validated in voltage clamp studies on Xenopus laevis oocytes transiently expressing GABAA receptors of the α1β2γ2S and α1β2 subtypes. Compound 8 potentiated GABA-induced currents with both receptor subunit compositions [EC50 (α1β2γ2S) = 43.6 μM; Emax = 809% and EC50 (α1β2) = 57.6 μM; Emax = 534%]. The positive modulation of GABA-induced currents was not inhibited by flumazenil, thereby confirming an allosteric modulation independent of the benzodiazepine binding site.

The chemical investigation of the organic extract of Canistrocarpus cervicornis, collected at Drunken Man's Cay at Port Royal, Jamaica, has led to the isolation of two new dolastane diterpenes 4R-acetoxy-8S,9S-epoxy-14S-hydroxy-7-oxodolastane (1) and 4R-hydroxy-8S,9S-epoxy-14S-hydroxy-7-oxodolastane (2) and the previously isolated dolastane (4R,9S,14S)-4,9,14-trihydroxydolast-1(15),7-diene (3) as a major diterpene constituent. The structures of the new compounds were elucidated by extensive spectroscopic analyses. Compounds 1-3 were evaluated for their cytotoxicity against human tumor cell lines PC3 and HT29. The results revealed that the dolastane diterpenes (1-3) displayed moderate, concentration dependent, cytotoxicity.

Four new daphnane-type diterpenes named tianchaterpenes C-F (1-4) and six known ones were isolated from Stelleropsis tianschanica. Their structures were elucidated based on chemical and spectral analyses. The comparisons of calculated and experimental electronic circular dichroism (ECD) methods were used to determine the absolute configurations of new compounds. Additionally, compounds 1-10 were evaluated for their cytotoxic activities against HGC-27 cell lines; the results demonstrate that compound 2 had strong cytotoxic activities with IC50 values of 8.8 µM, for which activity was better than that of cisplatin (13.2 ± 0.67 µM).

Three types of ent-kaurane diterpenoids were isolated from the aerial parts of Isodon excisoides, including three new diterpenoids, 1α,7α,14β-trihydroxy-20-acetoxy-ent-kaur-15-one (1); 1α,7α,14β,18-tetrahydroxy-20-acetoxy-ent-kaur-15-one (2); and 1α-acetoxy-14β-hydroxy-7α,20-epoxy-ent-kaur-16-en-15-one (3); together with six known diterpenes henryin (4); kamebanin (5); reniformin C (6); kamebacetal A (7); kamebacetal B (8); and oridonin (9). The structures of the isolated compounds were elucidated by means of nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry in conjunction with published data for their analogs, as well as their fragmentation patterns. Compounds 5 and 9 were isolated from Isodon excisoides for the first time. To explore the structure-activity relationships of the isolated compounds, they were tested for their cytotoxic effects against five human cancer cell lines: HCT-116, HepG2, A2780, NCI-H1650, and BGC-823. Most of the isolated compounds showed certain cytotoxic activity against the five cancer cell lines with IC50 values ranging from 1.09-8.53 µM. Among the tested compounds, compound 4 exhibited the strongest cytotoxic activity in the tested cell lines, with IC50 values ranging from 1.31-2.07 µM. Compounds 1, 6, and 7 exhibited selective cytotoxic activity.

Two new 15-hydroxycembranoid diterpenes, 2β-hydroxy-7β,8α-epoxynephthenol (1) and 2β-hydroxy-11α,12β-epoxynephthenol (2), were isolated from extracts of the octocoral Nephthea columnaris along with a new natural cembrane, epoxynephthenol (3) and a known sterol, nephalsterol A (4). The structures of cembranes 1-3 were elucidated by spectroscopic methods and comparison of the spectroscopic data with those of related analogues. The cytotoxicity of metabolites 1-4 against a panel of tumor cells is also described.

Three new clerodane diterpenes, (4→2)-abeo-cleroda-2,13E-dien-2,14-dioic acid (1), (4→2)-abeo-2,13-diformyl-cleroda-2,13E-dien-14-oic acid (2), and 16(R&S)- methoxycleroda-4(18),13-dien-15,16-olide (3), were isolated from the unripe fruit of Polyalthia longifolia var. pendula (Annonaceae) together with five known compounds (4-8). The structures of all isolates were determined by spectroscopic analysis. The anti-inflammatory activity of the isolates was evaluated by testing their inhibitory effect on NO production in LPS-stimulated RAW 264.7 macrophages. Among the isolated compounds, 16-hydroxycleroda-3,13-dien-15,16-olide (6) and 16-oxocleroda-3,13-dien-15-oic acid (7) showed promising NO inhibitory activity at 10 µg/mL, with 81.1% and 86.3%, inhibition, respectively.

Cytotoxicity screenings have identified Plectranthus plants as potential sources of antitumor lead compounds. In this work, several extracts from Plectranthus madagascariensis were prepared using different solvents (acetone, methanol, and supercritical CO2) and extraction techniques (maceration, ultrasound-assisted, and supercritical fluid extraction), and their chemical composition was detailed using high-performance liquid chromatography with a diode array detector. The cytotoxic activity of the major compounds identified, namely, rosmarinic acid (1) and abietane diterpenes 7α,6β-dihydroxyroyleanone (2), 7α-formyloxy-6β-hydroxyroyleanone (3), 7α-acetoxy-6β-hydroxyroyleanone (4), and coleon U (5), was evaluated in a battery of human cancer cell lines, including breast (MDA-MB-231, MCF-7), colon (HCT116), and lung (NCI-H460, NCI-H460/R) cancer, and also in healthy lung (MCR-5) cells. Royleanone (3) was isolated for the first time from P. madagascariensis, and its full spectroscopic characterization (proton and carbon nuclear magnetic resonance) was accomplished. A high selectivity for lung cancer cells was observed for royleanones (2, 4) with selectivity indexes of 4.3 and 3.2, respectively. The observed results combined with literature data allowed the establishment of important structure-activity relationships for substituted royleanone abietanes, such as the requirement for an electron-donating group at positions 6 and/or 7 in the abietane skeleton, and an improved cytotoxic effect for substituents with log P values between 2 and 5.

Dictyotaceae algae have gained recognition as prolific producers of diterpenes, which are molecules with significant biotechnological potential. These diterpenes hold immense promise as potential active drug components, making the algae a compelling area of study. The present review aims to present the latest advancements in understanding the biopotential of Brazilian Dictyota and Canistrocarpus brown algae, shedding light on the remarkable diversity and the biological and pharmacological potential of the secondary metabolites they produce. A total of 78 articles featuring 26 distinct diterpenes are reported in this review, with their antiviral potential being the mosthighlighted biological activity. Despite considerable research on these algae and their diterpenes, significant knowledge gaps persist. Consequently, the present review is poised to serve as a pivotal resource for researchers who are actively engaged in the pursuit of active diterpenes beyond the immediate purview. Furthermore, it holds the potential to catalyze an increase in research endeavors centered around these algal species within the geographical confines of the Brazilian coastline. Also, it assumes a critical role in directing future scientific explorations toward a better comprehension of these compounds and their ecological implications.

Three new myrsinol diterpenes were isolated from the roots of Euphorbia prolifera. Their structures were elucidated as 2α-O-isobutyryl-3β,5α,7β,10,15β-penta-O-acetyl-14α-O-benzoyl-10,18-dihydromyrsinol (1), 2α-O-isobutyryl-3β-O-propion-yl-5α,7β,10,15β-tetra-O-acetyl-10,18-dihydromyrsinol (2), and 2α,14α-di-O-benzoyl-3β,5α,7β,10,15β-penta-O-acetyl-10,18-dihydromyrsinol (3) on the basis of spectroscopic data analyses (IR, ESI-MS, HR-ESI-MS, and 1D and 2D NMR). Their neuroprotective activities were evaluated and compounds 1 and 2 showed neuroprotective effects against MPP+ -induced neuronal cell death in SH-SY5Y cells.

During a 2013 cruise in the Southern Ocean we collected specimens of the octocoral Plumarella delicatissima between 800 and 950 m depth. Five new furanocembranoid diterpenes, keikipukalides A-E (1-5), the known diterpene pukalide aldehyde (6), and the known norditerpenoid ineleganolide (7) were isolated from the coral. These Plumarella terpenes lack mammalian cytotoxicity, while 2-7 display activity against Leishmania donovani between 1.9 and 12 μM. Structure elucidation was facilitated by one- and two-dimensional NMR spectroscopy and mass spectrometry, and keikipukalides A and E were confirmed by X-ray crystallography.

Gorgonian octocorals are considered a prolific source of secondary metabolites with a wide range of biological activities, including anti-inflammatory activity. In particular, the genus Briareum is known for producing a wealth of diterpenes with complex chemical structures. The chemical study of the methanolic extract of Briareum asbestinum collected in Bocas del Toro, on the Caribbean side of Panama, led to the isolation of three new eunicellin-type diterpenes: briarellin T (1), asbestinin 27 (2), asbestinin 28 (3) and the previously described asbestinin 17 (4). The structures of the new compounds were determined by extensive NMR analyses and HRMS. Anti-inflammatory activity assays showed a significant reduction of the pro-inflammatory cytokines TNF-α, IL-6, IL-1β and IL-8 as well as a downregulation of COX-2 expression in LPS-stimulated THP-1 macrophages. These findings support the potential use of these marine compounds as therapeutic agents in the treatment of inflammatory diseases.