Crotofolane diterpenoids from the African shrub Croton dichogamus Pax

Anti-HIV crotocascarin ω from Kenyan Croton dichogamus

An anti-HIV methanol-soluble fraction of a 1:1 CH2Cl2:CH3OH extract of twigs of a Kenyan Croton dichogamus yielded seven compounds, the new crotocascarin ω (1), the known β-oplopanone (2), dihydroconiferyl acetate (3), 3'(4''-hydroxyphenyl)-propyl benzoate (4), lupeol, sitosterol and stigmasterol. Crotocascarin ω (90%) inhibited HIV-1 replication with an IC50 value of 5.3 nM, and the compound was cytotoxic towards MT-4 cells presenting an IC50 value of 84 µM. In silico modelling showed that the anti-HIV activity for compound 1 could be through the HIV-1 protease inhibition.

Crotofolanes, rearranged crotoforanes, and a novel diterpene: isocrotofolane from Croton cascarilloides, collected in Okinawa

To this day, since about 50% of all medicines are derived from natural sources, natural product chemistry, especially the search for biologically active natural components, remains extremely important (Newman and Cragg in J Nat Prod 83:770-803, 2020). In this review, we deal with our continuing research work for promising constituents from plants collected in the Ryukyu Archipelago. The isolation of islands in the archipelago by the sea or by straits gives rise to endemic plant species that are unique to the islands. The structural diversity of the constituents produced by this unique flora is of great scientific interest in various aspects, including chemical structures, biosynthesis, and biological activities. The components from this structural diversity have great potential as new pharmaceutical seeds. In our continuing studies, we have successfully investigated new but extremely unusual diterpenoids: crotofolanes and their rearranged varieties (nor-crotofolane, trinor-crotofolane, neocrotofolane) and a glycoside with a new skeletal diterpenoid (isocrotofolane glucoside) from Croton cascarilloides. This review summarizes our reports on the investigation of crotofolanes as well as those on crotofolanes by other research groups.

Molecular Docking, Validation, Dynamics Simulations, and Pharmacokinetic Prediction of Phytochemicals Isolated From Croton dichogamus Against the HIV-1 Reverse Transcriptase

The human immunodeficiency virus (HIV) infection and the associated acquired immune deficiency syndrome (AIDS) remain global challenges even after decades of successful treatment, with eastern and southern Africa still bearing the highest burden of disease. Following a thorough computational study, we report top 10 phytochemicals isolated from Croton dichogamus as potent reverse transcriptase inhibitors. The pentacyclic triterpenoid, aleuritolic acid (L12) has displayed best docking pose with binding energy of -8.48 kcal/mol and Ki of 0.61 μM making it superior in binding efficiency when compared to all docked compounds including the FDA-approved drugs. Other phytochemicals such as crotoxide A, crothalimene A, crotodichogamoin B and crotonolide E have also displayed strong binding energies. These compounds could further be investigated as potential antiretroviral medication.

[Structural Diversity of Chemical Constituents from Okinawan Plants]

In our continuing search for secondary metabolites from plants, we investigated the chemical constituents of various Okinawan plants. From the stems and leaves of Croton cascarilloides (Euphorbiaceae), a great number of rare diterpenoids: crotofolanes; crotocascarins A-Q, and new diterpenoids; rearranged nor-crotofolanes: crotocascarins α-γ; a rearranged crotofolane: neocrotocascarin; and a new skeletal diterpenoid: isocrotofolane glucoside were isolated. Their structures were mainly elucidated from NMR spectroscopic evidence. In addition, absolute configurations of crotocascarins A, B, K and O, crotocascarin α and neocrotocascarin were determined by X-ray crystallographic analyses, chiral HPLC analyses of 2-methylbutyric acid in their molecules, application of the circular dichroism rule for the α,β-unsaturated γ-lactone ring, and the modified Mosher's method. The absolute structures of crotofolanes were reported for the first time, and a biosynthetic mechanism for the formation of crotocascarin α and neocrotocascarin from crotocascarin B was proposed. Other interesting compounds, namely diosmarioside H: a dimeric ent-kaurane glycoside from the leaves of Diospyros maritima, and melionosides A-C: megastigmane glucosides with a spiro-ring structure from the leaves of Meliosma lepidota ssp. squamulata were also isolated.

Clerodane Diterpenes from Croton Species: Distribution and a Compilation of their 13C NMR Spectral Data

The present work is a review of the literature of clerodane diterpenes from Croton species. It contains a compilation of 13C NMR data of 83 of these diterpenoids and their biological activities. This review covers a period from 1969 to October 2005 and 224 references are cited.

Naturally occurring of α,β-diepoxy-containing compounds: origin, structures, and biological activities

Diepoxy-containing compounds are widely distributed in nature. These metabolites are found in plants and marine organisms and are also produced by many microorganisms, fungi, or fungal endophytes. Many of these metabolites are antibiotics and exhibit a wide variety of biological activities. More than 80 α,β-diepoxy-containing compounds are presented in this article, which belong to different classes of chemical compounds including lipids, terpenoids, alkaloids, quinones, hydroquinones, and pyrones. The main activities that characterize α,β-diepoxy-containing compounds are antineoplastic with confidence up to 99%, antifungal with confidence up to 94%, antiinflammatory with confidence up to 92%, or antibacterial with confidence up to 78%. In addition, these metabolites can be used as a lipid metabolism regulator with a certainty of up to 81%, antiviral (Arbovirus) activity with a certainty of up to 71%, or antiallergic activity with confidence up to 69%. These data on the biological activity of diepoxy-containing compounds are of considerable interest to pharmacologists, chemists, and medical professionals who are involved in phytomedicine and related areas of science and industry.

Okinawan Subtropical Plants as a Promising Resource for Novel Chemical Treasury

The Okinawa Islands are a crescent-shaped archipelago and their natural forests hold a huge variety of unique subtropical plants with relatively high endemism. We have performed phytochemical study on Okinawan subtropical plants for many years. In this review, we describe our recent research progress on the isolation of new compounds and their various bioactivities.

Cascarinoids A-C, a Class of Diterpenoid Alkaloids with Unpredicted Conformations from Croton cascarilloides

Cascarinoids A-C (1-3), a new class of diterpenoid alkaloids with unpredicted conformations, were isolated and structurally characterized from Croton cascarilloides. It was demonstrated that the dispersion interaction might be one of the main contributors that stabilized the folded conformations for compounds 1-3. Compounds 2 and 3 showed moderate immunosuppressive activity against T and/or B lymphocyte cells.

Diterpenoids from the roots of Croton dichogamus Pax

Four previously undescribed diterpenoids including two crotofolanes, crotodichogamoin A and B, and two halimanes, crothalimene A and B, a new sesquiterpenoid, and fifteen previously reported compounds, including the crotofolane, crotohaumanoxide, the casbane, depressin, a further seven furanohalimane diterpenoids, three patchoulane and two further cadinane sesquiterpenoids and aleuritolic acid were isolated from the root of Croton dichogamus. Crotodichogamoin B is an important biosynthetic intermediate of the crotofolane class and this is the first report of patchoulene sesquiterpenoids from the genus. Compounds were tested at one concentration, 1 × 10^-5 M, in the NCI59 cell one-dose screen but did not show significant activity snd were also evaluated for their cytotoxicity against Caco-2 cell lines using the neutral red assay. 10-epi-Maninsigin D reduced Caco-2 cell viability at 10, 30 and 100 μM, with values of decreased viability of 28%, 48% and 43% respectively. None of the other tested compounds showed significant activity.

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.

Crotofolane Diterpenoids from Croton caracasanus

Four new crotofolane-type diterpenoids, crotocarasin (A-D) (1–4), together with the known crotofolin E, were isolated from a dichloromethane extract of the stems of Croton caracasanus Pittier. The structures of the new compounds were determined by spectroscopic methods, and the structure of 3 was further confirmed by single-crystal X-ray data analyses.

New antimycobacterial and antimalarial 8,9-secokaurane diterpenes from Croton kongensis

Two new 8,9-secokaurane diterpenes, ent-8,9-seco-7alpha,11beta-diacetoxykaura-8(14),16-dien-9,15-dione (1) and ent-8,9-seco-8,14-epoxy-7alpha-hydroxy-11beta-acetoxy-16-kauren-9,15-dione (2), together with two known compounds, ent-8,9-seco-7alpha-hydroxy-11beta-acetoxykaura-8(14),16-dien-9,15-dione (3) and ent-7beta-hydroxy-15-oxokaur-16-en-18-yl acetate, were isolated from Croton kongensis. This is the first report on the presence of 8,9-secokauranes in the plant genus Croton. Diterpenes 1-3 exhibited antimycobacterial activity with minimum inhibitory concentrations (MICs) of 25.0, 6.25, and 6.25 microg/mL, respectively, and possessed antimalarial activity with IC(50) ranges of 1.0-2.8 microg/mL. They also demonstrated comparable cytotoxicity toward the Vero (IC(50) ranged from 0.9 to 3.2 microg/mL), KB (IC(50) from 1.2 to 13.8 microg/mL), and BC cell lines (IC(50) from 1.1 to 2.2 microg/mL, except for compound 1, which was inactive against BC cells).

New sterols from two edible mushrooms, Pleurotus eryngii and Panellus serotinus

Two edible mushrooms, Pleurotus eryngii and Panellus serotinus, have been investigated chemically. Two new sterols, 5alpha,9alpha-epidioxy-8alpha,14alpha-epoxy-(22E)-ergosta-6,22-dien-3beta-ol (1) and 3beta,5alpha-dihydroxyergost-7-en-6-one (2), have been isolated from P. eryngii, together with six known ones (3-8). Compound 1 was also isolated from P. serotinus. The structures of the new compounds were elucidated on the basis of their spectral data.