Coumarinolignoid and Indole Alkaloids from the Roots of the Hybrid Plant Citrus × paradisi Macfad (Rutaceae).

A phytochemical investigation of the roots of Citrus × paradisi Macfad. (Rutaceae) led to the isolation of two new compounds, namely 1-formyl-5-hydroxy-N-methylindolin-1-ium (1) and decyloxycleomiscosin D (2), along with ten known compounds: 1,1-dimethylpyrrolidin-1-ium-2-carboxylate (3), furan-2,3-diol (4), 5-methoxyseselin (5), umbelliferone (6), scopoletin (7), citracridone I (8), citracridone II (9), citracridone III (10), limonin (11) and lupeol (12). The structures were determined through the comprehensive spectroscopic analysis of 1D and 2D NMR and EI- and ESI-MS, as well as a comparison with the published data. Notably, compounds 3 and 4 from the genus Citrus are reported here for the first time. In addition, the MeOH extract of the roots and compounds 1-7 were screened against the human adenocarcinoma alveolar basal epithelial cell line A549 and the Caucasian prostate adenocarcinoma cell line PC3 using the MTT assay. While the extract showed significant activity, with IC50 values of 35.2 and 38.1 µg/mL, respectively, compounds 1-7 showed weak activity, with IC50 values of 99.2 to 250.2 µM and 99.5 to 192.7 µM, respectively.

Constituents of Croton megalocarpus with Potential Anti-HIV Activity.

Reported herein is an anti-HIV monochlorinated compound, 1ß-acetoxy-3ß-chloro-5α,6α-dihydroxycrotocascarin L (1), of the rare crotofolane diterpenoid class. Compound 1, a suspected artifact of extraction, along with the previously undescribed 11ß-acetoxycrotocascarin L (2) and a known compound, crotocascarin K (3), were isolated from the bark of Croton megalocarpus, a Kenyan oil-producing seed crop. Compounds 1 and 3 inhibited HIV-1 replication with IC50 values of 28 and 5.5 nM, respectively. Furthermore, both compounds lacked cytotoxicity toward MT-4 cells and FM-55-M1 cells at concentrations of up to 50 µM. Compounds 1 and 3 were both found to inhibit HIV-1 protease.

Chemical Constituents of the Stem Bark of the Hybrid Plant Citrus × paradisi Macfad. (Rutaceae).

The stem bark of Citrus × paradisi Macfad. (Rutaceae) gave (23S)-isolimonexic acid (1), limonin (2), citracridone II (3), citpressine II (4), citpressine I (5), grandisine (6), 2-hydroxynoracronycine (7), citracridone I (8), 5-methoxyseselin (9), umbelliferone (10), scopoletin (11), naringenin (12), apigenin (13), friedelin (14), agrostophyllinone (15) and stigmasterol-3-O-ß-D-glucopyranoside (16). The structures of the compounds were determined using NMR and MS spectroscopic data, and by comparison with published data. The relative configuration of 1 was proposed as (23S)-isolimonexic acid using NOE studies. Hydrogenation reaction of compound 3 led to the new derivative 3',4'-dihydrocitracridone II (3a). Cytotoxicity activities against the human adenocarcinoma alveolar basal epithelial cell lines A549 and the Caucasian prostate adenocarcinoma cell lines PC3, using the MTT assays showed that the methanol crude extract was significant with IC50 values of 30.1 and 31.7 µg/mL, respectively, with the positive control, doxorubicin giving an IC50 of 0.9 µM. In addition, compounds 3, 7 and 8 gave moderate cytotoxic activities with IC50 values of 33.1, 31.2 and 32.5 µM for A549 cells and 35.7, 33.8 and 34.9 µM for PC3 cells, respectively. The hydrogenated 3a was less active than 3, suggesting that the presence of the double bond in pyrans is important for structure-activity relationship.

Anti-HIV Ermiasolides from Croton megalocarpus.

In recent years, elucidation of novel anti-HIV bioactive compounds from natural products is gaining importance rapidly, not only from the research and publications, but also from controlled clinical studies. Here we report three new anti-HIV eudesmane-type sesquiterpenes, 5ß-Hydroxy-8α-methoxy eudesm-7(11)-en-12,8-olide (1), 5ß,8α-Dihydroxy eudesm-7(11)-en-12,8-olide (2) and 5ß-Hydroxy-8H-ß-eudesm-7(11)-en-12,8-olide (3). These are trivially named ermiasolide A-C and were isolated from the bark of Croton megalocarpus. 5ß-Hydroxy-8α-methoxy eudesm-7(11)-en-12,8-olide (1), showed the highest anti-HIV activity by inhibiting 93% of the viral replication with an IC50 = 0.002 µg/mL. On the other hand, 5ß-Hydroxy-8H-ß-eudesm-7(11)-en-12,8-olide (3) and 5ß,8α-dihydroxy eudesm-7(11)-en-12,8-olide (2), inhibited viral replication by 77.5% at IC50 = 0.04 µg/mL and 69.5% at IC50 = 0.002 µg/mL, respectively. Molecular docking studies showed that the proposed mechanism of action leading to these results is through the inhibition of HIV-protease.

Antiproliferative Bufadienolides from the Bulbs of Drimia altissima.

The bulbs of the South African Drimia altissima (Asparagaceae or Hyacinthaceae sensu APGII) have yielded a range of previously undescribed bufadienolides, drimianins A-G (1-7), the known bufadienolides bovogenin A (8), 3ß-O-ß-d-glucopyranosylbovogenin A (9), scillaren F (10), and altoside (11), the known homoisoflavonoid (3S)-3-(4'-methoxybenzyl)-5,6,7-trimethoxychroman-4-one (urgineanin C), the sesquiterpenoids 1ß,6α-dihydroxy-4(15)-eudesmene and 6α-hydroxy-4(15)-eudesmen-1-one, polybotrin, adenosine, and 9R-hydroxy-(10E,12Z)-octadecadienoic acid ethyl ester. The bufadienolides isolated were tested at 10 µM in the NCI-60 cancer cell screen, and nine of these were selected for further screening at five concentrations. Drimianins C (3) and E (5) showed activity at the nanomolar level against a number of human cancer cell lines in the NCI-60 screen.

Euphorbia Diterpenes: An Update of Isolation, Structure, Pharmacological Activities and Structure-Activity Relationship.

Euphorbia species have a rich history of ethnomedicinal use and ethnopharmacological applications in drug discovery. This is due to the presence of a wide range of diterpenes exhibiting great structural diversity and pharmacological activities. As a result, Euphorbia diterpenes have remained the focus of drug discovery investigations from natural products. The current review documents over 350 diterpenes, isolated from Euphorbia species, their structures, classification, biosynthetic pathways, and their structure-activity relationships for the period covering 2013-2020. Among the isolated diterpenes, over 20 skeletal structures were identified. Lathyrane, jatrophane, ingenane, ingenol, and ingol were identified as the major diterpenes in most Euphorbia species. Most of the isolated diterpenes were evaluated for their cytotoxicity activities, multidrug resistance abilities, and inhibitory activities in vitro, and reported good activities with significant half-inhibitory concentration (IC50) values ranging from 10-50 µM. The lathyranes, isopimaranes, and jatrophanes diterpenes were further found to show potent inhibition of P-glycoprotein, which is known to confer drug resistance abilities in cells leading to decreased cytotoxic effects. Structure-activity relationship (SAR) studies revealed the significance of a free hydroxyl group at position C-3 in enhancing the anticancer and anti-inflammatory activities and the negative effect it has in position C-2. Esterification of this functionality, in selected diterpenes, was found to enhance these activities. Thus, Euphorbia diterpenes offer a valuable source of lead compounds that could be investigated further as potential candidates for drug discovery.

The Antiangiogenic Activity of Naturally Occurring and Synthetic Homoisoflavonoids from the Hyacinthaceae ( sensu APGII).

Excessive blood vessel formation in the eye is implicated in wet age-related macular degeneration, proliferative diabetic retinopathy, neovascular glaucoma, and retinopathy of prematurity, which are major causes of blindness. Small molecule antiangiogenic drugs are strongly needed to supplement existing biologics. Homoisoflavonoids have been previously shown to have potent antiproliferative activities in endothelial cells over other cell types. Moreover, they demonstrated a strong antiangiogenic potential in vitro and in vivo in animal models of ocular neovascularization. Here, we tested the antiangiogenic activity of a group of naturally occurring homoisoflavonoids isolated from the family Hyacinthaceae and related synthetic compounds, chosen for synthesis based on structure-activity relationship observations. Several compounds showed interesting antiproliferative and antiangiogenic activities in vitro on retinal microvascular endothelial cells, a disease-relevant cell type, with the synthetic chromane, 46, showing the best activity (GI50 of 2.3 × 10-4 µM).

Antiangiogenic Activity and Cytotoxicity of Triterpenoids and Homoisoflavonoids from Massonia pustulata and Massonia bifolia.

The Hyacinthaceae family (sensu APGII), with approximately 900 species in around 70 genera, plays a significant role in traditional medicine in Africa as well as across Europe and the Middle and Far East. The dichloromethane extract of the bulbs of Massonia pustulata (Hyacinthaceae sensu APGII) yielded two known homoisoflavonoids, (R)-5-hydroxy-3-(4-hydroxybenzyl)-7-methoxy-4-chromanone 1: and 5-hydroxy-3-(4-hydroxybenzyl)-7-methoxy-4-chromone 2: and four spirocyclic nortriterpenoids, eucosterol 3: , 28-hydroxyeucosterol 4: and two previously unreported triterpenoid derivatives, (17S,23S)-17α,23-epoxy-3ß,22ß,29-trihydroxylanost-8-en-27,23-olide 5: , and (17S, 23S)-17α,23-epoxy-28,29-dihydroxylanost-8-en-3-on-27,23-olide 6: . Compounds 1, 2, 3: , and 5: were assessed for cytotoxicity against CaCo-2 cells using a neutral red uptake assay. Compounds 1, 2: , and 5: reduced cell viability by 70% at concentrations of 30, 100, and 100 µM, respectively. Massonia bifolia yielded three known homoisoflavonoids, (R)-(4'-hydroxy)-5-hydroxy-7-methoxy-4-chromanone 1: , (R)-(4'-hydroxy)-5,7-dihydroxy-4-chromanone 7: and (R)-(3'-hydroxy-4'-methoxy)-5,7-dihydroxy-4-chromanone 9: , two previously unreported homoisoflavonoids, (E)-3-benzylidene-(3',4'-dihydroxy)-5-hydroxy-7-methoxy-4-chromanone 8: and (R)-(3',4'-dihydroxy)-5-hydroxy-7-methoxy-4-chromanone 10,: and a spirocyclic nortriterpenoid, 15-deoxoeucosterol 11: . Compounds 1, 1AC, 7, 8, 9,: and 10: were screened for antiangiogenic activity against human retinal microvascular endothelial cells. Some compounds showed dose-dependent antiproliferative activity and blocked endothelial tube formation, suggestive of antiangiogenic activity.

Pumilol, a Diterpenoid with a Rare Strobane Skeleton from Pinus pumila (Pinaceae).

Pumilol (1), a strobane diterpenoid, reported herein for the first time, was isolated from the bark of Pinus pumila (Pall.) Regel (Siberian Dwarf Pine or Japanese Stone Pine), along with 17 known compounds including serratane triterpenoids, not previously reported from this species, and four ferulate derivatives. The absolute configuration of pumilol was established using HR-ESI-MS, NMR, the DP4+ probabilities and by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Labda-8(17),13-dien-15-oic acid (4), bornyl (E)-4-hydroxycinnamate (14) and bornyl (E)-ferulate (15) showed activity against S. aureus and/or E. faecalis with MIC90 values 12.5 - 50 µm.

Application of Residual Dipolar Couplings and Selective Quantitative NOE to Establish the Structures of Tetranortriterpenoids from Xylocarpus rumphii.

Nine triterpenoid derivatives were isolated from the heartwood of Xylocarpus rumphii and were identified as xylorumphiins E (1), C (2), L (3), and M-R (4-9). Compounds 4-9 have a hemiacetal group in the triterpenoid side chain, making them impossible to purify. Purification was achieved after acetylation and subsequent separation of the epimeric mixtures of acetates; however differentiaition of the R and S epimers was not possible using standard NMR techniques. In one case, the relative configuration of a remotely located stereocenter with respect to the stereocenters in the main skeleton was unambiguously determined using residual dipolar couplings. Dipolar couplings were collected from the sample oriented in compressed poly(methyl methacrylate) gels swollen in CDCl3. In another case, the relative configuration was determined using 1D selective quantitative NOE experiments. Xylorumphiin K (10), xyloccensin E, taraxer-14-en-3ß-ol, (22S)-hydroxytirucalla-7,24-diene-3,23-dione, and 25-hydroxy-(20S,24S)-epoxydammaran-3-one were isolated from the bark of the same plant. Compounds 3-10 are new compounds. Compounds 1-6 and xyloccensin E were tested at one concentration, 1 × 10-5 M, in the NCI59 cell one-dose screen but did not show significant activity.

Phytochemical Investigations of Three Rhodocodon (Hyacinthaceae Sensu APG II) Species.

The genus Rhodocodon (Hyacinthaceae sensu APG II) is endemic to Madagascar, and its phytochemistry has not been described previously. The phytochemistry of three species in this genus has been investigated, and eight compounds, including three bufadienolides (compounds 1, 4, and 5), a norlignan (2), and four homoisoflavonoids (compounds 3 and 6-8), have been isolated and identified. Compounds 1-3 and 6-8 have not been described previously. The COX-2 inhibitory activity of compound 6 and compound 7 acetate (compound 7A) was investigated on isolated colorectal cancer cells. Compounds 6 and 7A inhibited COX-2 by 10% and 8%, respectively, at a concentration of 12.5 µM compared to 12% for 1 mM aspirin (the positive control).

New ent-Clerodane and Abietane Diterpenoids from the Roots of Kenyan Croton megalocarpoides Friis & M. G. Gilbert.

The roots of the endangered medicinal plant Croton megalocarpoides collected in Kenya were investigated and twenty-two compounds isolated. Among them were twelve new ent-clerodane (1-12) and a new abietane (13) diterpenoids, alongside the known crotocorylifuran (4 a), two known abietane and four known ent-trachylobane diterpenoids, and the triterpenoids, lupeol and acetyl aleurotolic acid. The structures of the compounds were determined using NMR, HRMS and ECD. The isolated compounds were evaluated against a series of microorganisms (fungal and bacteria) and also against Plasmodium falciparum, however no activity was observed.

Cytotoxic ent-abietane diterpenoids, banyangmbolides A-E, from the leaves of Suregada occidentalis.

The chemical investigation of a leaf extract from a herbarium specimen of Suregada occidentalis collected in Banyang Mbo Wildlife Sanctuary, Southwest Region, Cameroon, yielded five undescribed ent-abietane diterpenoids, banyangmbolides A-E, (1-5), and four known diterpenoids, gelomulides A (6), B (7), D (8) and O (9). The structures of the isolated compounds were determined using NMR, IR, ECD and HRESIMS. Compounds 5, 7 and 8, showed 48-55% inhibition at 200 µM against FM-55-M1 human melanoma cells.

Cytotoxic clerodane diterpenoids from the roots of Casearia barteri Mast.

A study of diterpenoids as active ingredients against cancer from the active roots extract of Casearia barteri Mast. (IC50 = 1.57 µg mL-1) led to the isolation of six new clerodane diterpenoids, named as barterins A-F (1-6) alongside seven known compounds, caseamembrin A, caseamembrin E, casearlucin A, graveospene G, N-trans-feruloyltyramine, N-cis-feruloytyramine and sitosterol-3-O-ß-D-(6-O-palmitoyl)-glucopyranoside. Their structures were elucidated based on NMR spectroscopic data and mass spectrometry. The absolute configurations of 1-6 were established by the time-dependent density functional theory (TDDFT), electronic circular dichroism (ECD) calculations and experimental data analysis. The cytotoxic effects of compounds 1-6 were evaluated against a human cervix carcinoma cell line KB-3-1. Barterins A-D (1-4) showed cytotoxic effects against the KB-3-1 cell line with IC50 values ranging from 1.34-4.73 µM.

Alienusolin, a new 4α-deoxyphorbol ester derivative, and crotonimide C, a new glutarimide alkaloid from the Kenyan Croton alienus.

Two novel compounds, alienusolin, a 4α-deoxyphorbol ester (1), crotonimide C, a glutarimide alkaloid derivative (2), and ten known compounds, julocrotine (3), crotepoxide (4), monodeacetyl crotepoxide (5), dideacetylcrotepoxide, (6), ß-senepoxide (7), α-senepoxide (8), (+)-(2S,3R-diacetoxy-1-benzoyloxymethylenecyclohex-4,6-diene (9), benzyl benzoate (10), acetyl aleuritolic (11), and 24-ethylcholesta-4,22-dien-3-one (12) were isolated from the Kenyan Croton alienus. The structures of the compounds were determined using NMR, GCMS, and HRESIMS studies.

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 ß-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.

A new 30-norfriedelane triterpnoid from Caloncoba lophocarpa (Oliv.) Gilg. (Achariaceae).

The chemical investigation of the methanol extract of the roots of Caloncoba lophocarpa (Oliv.) Gilg. exhibited a new 30-norfriedelane triterpenoid, laphocarpanol (1), together with seven known compounds, caloncobalactone (2), friedelin (3), friedelanol (4), asperphernamate (5), stigmasterol (6), sitosterol (7) and sitosterol-3-O-ß-D-glucopyranoside (8). The structures of the compounds were elucidated by extensive spectroscopic and spectrometric analyses (1D and 2D NMR, ESI-MS) and by comparison with previously reported data. All the compounds were tested for their antifungal and antibacterial activities. Compound 1 displayed weak antibacterial effect with MIC value of 62.5 µg/mL against Shigella flexineri. All the isolates were found to be inactive against the tested fungal strains.

Antimicrobial prenylated acetophenones from berries of Harrisonia abyssinica.

The ripe berries of Harrisonia abyssinica yielded two new prenylated acetophenones, namely 5-(ethan-1'''-one)-4,6-dihydroxy-7-(3'',3''-dimethylallyl)-2 S-(1' S-hydroxy-1',5'-dimethylhex-4'-enyl)-2,3-dihydrobenzofuran (1) and 5-(2'''-hydroxyethan-1'''-one)-4,6-dihydroxy-7-(3'',3''-dimethylallyl)-2 S-(1' S-hydroxy-1',5'-dimethylhex-4'-enyl)-2,3-dihydrobenzofuran (2), herein named harronin I and harronin II, respectively. The compounds were isolated following activity guided fractionation and the structures were determined using 1D, 2D NMR spectroscopic, CD and MS spectrometric techniques. The methanol-dichloromethane mixture (1 : 1 v/v) crude extract exhibited strong antimicrobial activity against Candida albicans, Bacillus cereus, Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, and Lactobacillus casei. Harronin I (1) showed a MIC of 5 µg/mL against C. albicans, 6 µg/mL against B. cereus, and more than 20 µg/mL against other tested microorganisms. Harronin II (2) showed much weaker MIC values (> 100 µg/mL) against all the tested microorganisms.

Chemistry, taxonomy and ecology of the potentially chimpanzee-dispersed Vepris teva sp.nov. (Rutaceae) endangered in coastal thicket in the Congo Republic.

Continuing a survey of the chemistry of species of the largely continental African genus Vepris, we investigate a species previously referred to as Vepris sp. 1 of Congo. From the leaves of Vepris sp. 1 we report six compounds. The compounds were three furoquinoline alkaloids, kokusaginine (1), maculine (2), and flindersiamine (3), two acridone alkaloids, arborinine (4) and 1-hydroxy-3-methoxy-10-methylacridone (5), and the triterpenoid, ß-amyrin (6). Compounds 1-4 are commonly isolated from other Vepris species, compound 5 has been reported before once, from Malagasy Vepris pilosa, while this is the first report of ß-amyrin from Vepris. This combination of compounds has never before been reported from any species of Vepris. We test the hypothesis that Vepris sp. 1 is new to science and formally describe it as Vepris teva, unique in the genus in that the trifoliolate leaves are subsessile, with the median petiolule far exceeding the petiole in length. Similar fleshy-leathery four-locular syncarpous fruits are otherwise only known in the genus in Vepris glaberrima (formerly the monotypic genus Oriciopsis Engl.), a potential sister species, but requiring further investigation to confirm this phylogenetic position. We briefly characterise the unusual and poorly documented Atlantic coast equatorial ecosystem, where Vepris teva is restricted to evergreen thicket on white sand, unusual in a genus usually confined to evergreen forest. This endemic-rich ecosystem with a unique amphibian as well as plants, extends along the coastline from the mouth of the Congo River to southern Rio Muni, a distance of about 1,000 km, traversing five countries. We map and illustrate Vepris teva and assess its extinction risk as Endangered (EN B1ab(iii)+B2ab(iii)) using the IUCN, 2012 standard. Only three locations are known, and threats include port and oil refinery construction and associated activities, with only one protected location, the Jane Goodall Institute's Tchimpounga Reserve. Initial evidence indicates that the seeds of Vepris teva are dispersed by chimpanzees, previously unreported in the genus.

HIV-1 Integrase Inhibitory Effects of Major Compounds Present in CareVid™: An Anti-HIV Multi-Herbal Remedy.

In our continued study on the anti-HIV activity of compounds present in CareVidTM, we report the HIV-1 integrase ((HIV-1 IN) inhibitory effects of pellitorine (1), oleuropein (2), magnoflorine (3), crotepoxide (4), ent-kaurane-16ß,17-diol (5), crotocorylifuran (6), lupeol (7), betulin (8), and ellagic acid (9) in an in vitro enzyme assay, and in an in silico study. Ellagic acid, pellitorine, lupeol, and betulin showed an in vitro percentage inhibition against HIV-1 IN of 21.1%, 19.0%, 18.5%, and 16.8%, respectively, at a standard concentration of 25 µg/mL. However, from a pharmacokinetic perspective, ellagic acid has poor bioavailability, due to rapid elimination in metabolism in the gut microbiome. It was postulated that known gut catabolites of ellagic acid, urolithin A (10) and urolithin B (11) could be more promising candidates in exploring the anti-HIV activity of ellagic acid-rich medicinal species consumed orally. On the contrary, urolithin A and urolithin B demonstrated lower activity with comparison to ellagic acid. The binding affinity of compounds 1-9, urolithin A, and urolithin B against the catalytic domain of HIV-1 IN was also explored by in silico methods. Docking studies showed oleuropein as the best candidate, with a predicted energy of binding of ΔG -5.81 kcal/mol, while ellagic acid showed moderate predicted inhibition (ΔG -4.38 kcal/mol) caused by the interaction between the carbonyl and the key Mg2+ ion in the active site.