Isolation and confirmation of the proposed cleistanthol biogentic link from Croton insularis

Strophiofimbrins A and B: Two Rearranged Norditerpenoids with Novel Tricyclic Carbon Skeletons from Strophioblachia fimbricalyx

Two rearranged norditerpenoids with novel tricyclic carbon skeletons, strophiofimbrin A (1) and strophiofimbrin B (2), were isolated from Strophioblachia fimbricalyx. Their structures were established by 1D/2D NMR spectroscopy, HRESIMS, quantum chemistry calculations, and X-ray diffraction analyses. 1 and 2 represented the first examples of diterpenoids with unprecedented 5/6/7-fused ring systems. In the proposed biosynthetic pathway, they were suspected to derive from cleistanthane norditerpenoids via ring opening, expansion, cyclization, and rearrangement based on the existence of phenanthrenone and cleistanthane diterpenoids from Strophioblachia and Trigonostemon, two closely related genera of the Euphorbiaceae family. Furthermore, compounds 1 and 2 exhibited significant proliferation inhibition and obvious neuroprotective effects.

Phytochemical Analysis and Antinociceptive Properties of Hydroalcoholic Extracts of Aleurites moluccanus Bark

Aleurites moluccanus is used in folk medicine to treat many diseases including pain and inflammatory processes in general. Considering the potential of the leaf extract, evidenced in a previous study, the present study investigates the antinociceptive and anti-inflammatory properties of the hydroethanolic extract of A. moluccanus bark and isolated compounds in animal models of pain. The antinociceptive and anti-inflammatory activities of A. moluccanus bark were evaluated through hyperalgesia induced by carrageenan, PGE₂, cytokines, bradykinin, epinephrine, Freund's complete adjuvant, and lipopolysaccharide. Five compounds were isolated from the dichloromethane bark extract: acetyl aleuritolic acid, atraric acid, spruceanol, (5β,10α)-12-hydroxy-13-methoxy-8,11,13-podocarpatrien-3-one and sonderianol. To optimize the extraction conditions, ethanol 50, 70, and 90°GL were used as extracting solvent, in a 1 : 20 (w/v) drug : solvent ratio, under stirring at room temperature for 4 h. The extracts were named AMC50, AMC70, and AMC90, respectively. These extracts were administered to mice (250 mg/kg, p. o.) with reduced mechanical hyperalgesia activity in the carrageenan test. Of these, AMC90 showed the best results. Pure (5β,10α)-12-hydroxy-13-methoxy-8,11,13-podocarpatrien-3-one showed a beneficial effect for up to 48 hours after the administration of carrageenan, while acetyl aleuritolic acid was effective only in the first hour. AMC90 was able to reverse the analgesia induced only by prostaglandin E₂ and tumor necrosis factor. We also induced hyperalgesia using the lipopolysaccharide and Freund's complete adjuvant models, with positive results. These results support the antinociceptive and anti-inflammatory activity of A. moluccanus bark extract. The observed effects are partly due to the presence of acetyl aleuritolic acid, atraric acid, and (5β,10α)-12-hydroxy-13-methoxy-8,11,13-podocarpatrien-3-one.

Antiprotozoal and Antitumor Activity of Natural Polycyclic Endoperoxides: Origin, Structures and Biological Activity

Polycyclic endoperoxides are rare natural metabolites found and isolated in plants, fungi, and marine invertebrates. The purpose of this review is a comparative analysis of the pharmacological potential of these natural products. According to PASS (Prediction of Activity Spectra for Substances) estimates, they are more likely to exhibit antiprotozoal and antitumor properties. Some of them are now widely used in clinical medicine. All polycyclic endoperoxides presented in this article demonstrate antiprotozoal activity and can be divided into three groups. The third group includes endoperoxides, which show weak antiprotozoal activity with a reliability of up to 70%, and this group includes only 1.1% of metabolites. The second group includes the largest number of endoperoxides, which are 65% and show average antiprotozoal activity with a confidence level of 70 to 90%. Lastly, the third group includes endoperoxides, which are 33.9% and show strong antiprotozoal activity with a confidence level of 90 to 99.6%. Interestingly, artemisinin and its analogs show strong antiprotozoal activity with 79 to 99.6% confidence against obligate intracellular parasites which belong to the genera Plasmodium, Toxoplasma, Leishmania, and Coccidia. In addition to antiprotozoal activities, polycyclic endoperoxides show antitumor activity in the proportion: 4.6% show weak activity with a reliability of up to 70%, 65.6% show an average activity with a reliability of 70 to 90%, and 29.8% show strong activity with a reliability of 90 to 98.3%. It should also be noted that some polycyclic endoperoxides, in addition to antiprotozoal and antitumor properties, show other strong activities with a confidence level of 90 to 97%. These include antifungal activity against the genera Aspergillus, Candida, and Cryptococcus, as well as anti-inflammatory activity. This review provides insights on further utilization of polycyclic endoperoxides by medicinal chemists, pharmacologists, and the pharmaceutical industry.

New 3,4-seco-diterpene and coumarin derivative from the leaves of Trigonostemon flavidus Gagnep

Two new compounds named trigoflavidus A (1) and trigoflavidus B (2), and eight known compounds, trigoflavidone (3), heterophypene (4), howpene C (5), 3,4-seco-sonderianol (6), trigonochinene C (7), fraxidin (8), isofraxidin (9), and isofraxetin (10) were isolated from the leaves of Trigonostemon flavidus Gagnep. by various chromatographic methods. Their chemical structures were elucidated via UV, IR, HR-ESI-MS and NMR spectroscopic methods and divided into two groups including six 3,4-seco-diterpenes (1, 3-7) and four coumarins (2, 8-10). Absolute configurations at stereocenters of compound 1 were confirmed by comparison of its CD spectra with those of the TD-DFT calculations. At a concentration of 30 µM, compounds 1-10 exhibited weak cytotoxic activity toward LU1, HepG2, MCF7, and SKMel2 human cell lines (cell viability all over 50%).

Aleuritin, a novel dinor-diterpenoid from the twigs of Aleurites moluccanus with an anti-lymphangiogenic effect

A phytochemical investigation of Aleurites moluccanus yielded one novel dinor-diterpenoid, aleuritin (1), along with a rare diterpenoid, aleuritone (2). Compound 1 has an unprecedented skeleton with a 6/6/5-fused tricyclic ring system. Compound 2 possesses a rare 6/6/5/3-fused tetracyclic skeleton, which is probably an artifact formed photochemically by the Norrish reaction. The structures of 1 and 2 were determined by spectroscopic methods (ECD, IR, mass, and NMR) and confirmed by single-crystal X-ray diffraction analyses. A plausible biogenetic pathway of 1 is proposed. Pharmacological study showed that these two compounds possessed mild in vitro anti-lymphangiogenic activity, which suppressed tube formation with IC50 values of 48.1 ± 1.8 and 34.2 ± 0.8 μg mL-1, respectively.

EBC-232 and 323: A Structural Conundrum Necessitating Unification of Five In Silico Prediction and Elucidation Methods

Structurally unique halimanes EBC-232 and EBC-323, isolated from the Australian rainforest plant Croton insularis, proved considerably difficult to elucidate. The two diastereomers, which consist an unusual oxo-6,7-spiro ring system fused to a dihydrofuran, were solved by unification and consultation of five in silico NMR elucidation and prediction methods [i.e., ACDLabs, olefin strain energy (OSE), DP4, DU8+ and TD DFT CD]. Structure elucidation challenges of this nature are prime test case examples for empowering future AI learning in structure elucidation.

Basimarols A, B, and C, Highly Oxygenated Pimarane Diterpenoids from Basilicum polystachyon

The highly oxygenated pimarane diterpenoids basimarols A, B, and C (3-5) were isolated from the plant species Basilicum polystachyon, which was collected within the Australian arid zone. Structure elucidation was performed using a suite of spectroscopic techniques, including X-ray crystallography. Anticancer and anti-DENV activity of 3-5 was explored, but only limited activity was observed. More extensive antiviral evaluation of stachyonic acid A (1), which was also isolated from B. polystachyon, revealed broad spectrum antiviral activity against West Nile virus (Kunjin strain, WNV_Kun) and human influenza viruses H1N1 and H3N2.

Taichunins A-D, Norditerpenes from Aspergillus taichungensis (IBT 19404)

Four new norditerpenes, taichunins A-D (1-4), were isolated from the fungus Aspergillus taichungensis (IBT 19404). Compound 1 has a new carbon framework. The absolute configurations were determined by the calculated ECD spectral method. Compound 1 was cytotoxic against HeLa cells with an IC₅₀ value of 4.5 μM, whereas 2-4 were nontoxic at 50 μM.

Chemical Constituents from Croton Species and Their Biological Activities

The genus Croton belongs to the Euphorbiaceae family, which comprises approximately 1300 species. Many Croton species have been used as folk medicines. This review focuses on the chemical constituents from Croton species and their relevant biological activities, covering the period from 2006 to 2018. A total of 399 new compounds, including 339 diterpenoids, were reported. Diterpenoids are characteristic components of the Croton species. These isolated compounds exhibited a broad spectrum of bioactivities, including cytotoxic, anti-inflammatory, antifungal, acetylcholinesterase inhibitory, and neurite outgrowth-promoting properties. The present review provides a significant clue for further research of the chemical constituents from the Croton species as potential medicines.

7-Step total synthesis of (+)-EBC-329: Photoisomerisation reveals new seco-casbane family member

The first seco-casbane, EBC-329, isolated from the Australian rainforest, was synthesised from (+)-2-carene in seven steps. This endeavour not only established the absolute stereochemical assignment as (8R,9S)-EBC-329, but also identified, via photoisomerisation, a new seco-casbane family member.

Synthesis of α-Quaternized 2,4-Cyclohexadienones from Propargyl Vinyl Ethers

A microwave-assisted and base-catalyzed domino manifold to construct 2,4-cyclohexadienone derivatives has been implemented. The domino manifold uses easily accessible tertiary propargyl vinyl ethers bearing a methine group at the homopropargylic position and imidazole as the catalyst to deliver 2,4-cyclohexadienones featuring a key formyl group and a quaternized carbon atom in good yields.

EBC-318 and 339: bicyclo[10.2.1]alkanes from Croton insularis

EBC-318 and EBC-339 were isolated from Croton insularis, an Australian rain forest plant. EBC-318 is characterised by a bridgehead double bond.

EBC-316, 325–327, and 345: New Pimarane Diterpenes from Croton insularis Found in the Australian Rainforest

Five new pimarane and related-type diterpenes (i.e. EBC-316, 325–327, and 345 (10–15)), together with two known pimaranes (EBC-221 (8) and EBC-346 (9)), were isolated from the stems of Croton insularis, found in the Australian rainforest. All pimarane diterpenes disclosed herein are suggested to be biogenetically related to the same keto-Jacobs–Reynolds intermediate 2, via ring A and C oxidation. Anticancer activities of compounds 11–13 are reported.

Stereochemistry of cleistanthane diterpenoid glucosides from Phyllanthus emblica

Theoretical calculated electronic circular dichroism and Mosher’s method were applied to elucidate the stereochemistry of cleistanthane diterpenoids.

The diterpenes ovoideal A-G from Tirpitzia ovoidea

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.

Natural products with anti-Bredt and bridgehead double bonds

Well over a hundred years ago, Professor Julius Bredt embarked on a career pursuing and critiquing bridged bicyclic systems that contained ring strain induced by the presence of a bridgehead olefin. These endeavors founded what we now know as Bredt's rule (Bredtsche Regel). Physical, theoretical, and synthetic organic chemists have intensely studied this premise, pushing the boundaries of such systems to arrive at a better understood physical phenomenon. Mother nature has also seen fit to construct molecules containing bridgehead double bonds that encompass Bredt's rule. For the first time, this topic is reviewed in a natural product context.

Unprecedented 1,14-seco-crotofolanes from Croton insularis: oxidative cleavage of crotofolin C by a putative homo-Baeyer-Villiger rearrangement

EBC-162 isolated from Croton insularis, obtained from the northern rainforest of Australia, was structurally affirmed as crotofolin C (4). Novel oxidative degradation products, EBC-233 and EBC-300, which are the first crotofolane endoperoxides, were also isolated. Both endoperoxides were found to be stable intermediates, which are proposed to undergo an unprecedented homo-Baeyer-Villiger biosynthetic rearrangement to give a new class of 1,14-seco-crotofolane diterpenes. Prolonged storage of all isolates assisted in authenticating their natural product status. Anticancer activities of reported compounds are presented.