Iridoid glycosides from Gmelina philippensis

Protective effects of catalpol on cardio-cerebrovascular diseases: A comprehensive review

Catalpol, an iridoid glucoside isolated from Rehmannia glutinosa, has gained attention due to its potential use in treating cardio-cerebrovascular diseases (CVDs). This extensive review delves into recent studies on catalpol's protective properties in relation to various CVDs, such as atherosclerosis, myocardial ischemia, infarction, cardiac hypertrophy, and heart failure. The review also explores the compound's anti-oxidant, anti-inflammatory, and anti-apoptotic characteristics, emphasizing the role of vital signaling pathways, including PGC-1α/TERT, PI3K/Akt, AMPK, Nrf2/HO-1, estrogen receptor (ER), Nox4/NF-κB, and GRP78/PERK. The article discusses emerging findings on catalpol's ability to alleviate diabetic cardiovascular complications, thrombosis, and other cardiovascular-related conditions. Although clinical studies specifically addressing catalpol's impact on CVDs are scarce, the compound's established safety and well-tolerated nature suggest that it could be a valuable treatment alternative for CVD patients. Further investigation into catalpol and related iridoid derivatives may unveil new opportunities for devising natural and efficacious CVD therapies.

Phytochemical investigation, molecular docking studies and DFT calculations on the antidiabetic and cytotoxic activities of Gmelina philippensis CHAM

ETHNOPHARMACOLOGICAL RELEVANCE

Gmelina philippensis CHAM is an ornamental plant that is distributed in South Asia and warm regions of the Mediterranean area. The plant is traditionally applied in folk medicine for the treatment of diabetes.

AIM OF THE STUDY

To evaluate the cytotoxic and the antidiabetic activities of the ethanolic extract of G. philippensis aerial parts. To isolate the metabolite(s) responsible for these activities and to elucidate the mechanism of action by molecular docking study.

MATERIALS AND METHODS

Compounds (1-11) were isolated using various chromatographic techniques and their structures were determined by NMR spectroscopic and mass spectrometric analysis. The cytotoxic effect was tested using viability test and MTT assay. Antidiabetic activity was evaluated by measuring the inhibitory activity of the ethanolic extracts and compounds against α-glucosidase and α-amylase activities. Modeling and docking simulations were performed using Molecular Operating Environment software and the crystal structure of protein kinases CDK2, (1PYE) and AKT1 (4GV1), in addition to α-glucosidase (3TOP) and α-amylase (2QV4).

RESULTS

Compounds 2, 3 and 8 were isolated for the first time from the plant and identified as: gmelinol (2), apigenin (3) and tyrosol (8). While β-sitosterol-3-O- β-D-glucopyranoside (4) vicenin-II (7), rhoifolin (9), isorhoifolin (11) were isolated for the first time from the genus, along with and the new iridoid 6-O-α-L-(2″-O-benzoyl-4″-O-trans-p-methoxycinnamoyl)rhamnopyranosyl-1α- β-D-glucopyranoside catalpolgenin (6). In addition, to the previously reported compounds: mixture of β -sitosterol and stigmasterol (1), and 6- O- α-L-(2″,3″,4″-tri-O -benzoyl)rhamnopyranosylcatalpol (5) and 6-O-α-L-(2″-O-trans-p-methoxycinnamoyl)rhamnopyranosylcatalpol (10). The cytotoxic activity against hepatocellular carcinoma (HepG-2) cell lines for compounds 2, 5, 7, 9 and 11 was conducted using cisplatin as a standard. Gmelinol (2) exhibited strong cytotoxic activity against HepG-2 cell lines with IC ₅₀ value of 3.6 ± 0.1 μg/ml which is more potent than the standard cisplatin IC ₅₀ = 8.7 ± 0.9 μg/ml. Molecular modeling of 2 against diverse targets of protein kinases suggested that CDK-2 and AKT-1 could be the dual probable kinase targets for its cytotoxic action. Compound 2 showed α-amylase inhibition activity with IC ₅₀ value of 60.9 (μg/ml) while, compounds 5 showed strong α-glucosidase inhibition activity with IC ₅₀ values of 41.7 (μg/ml) compared to acarbose with IC ₅₀ value of 34.7, 30.6 (μg/ml). Molecular docking of compounds 2 and 5 on α-glucosidase (3TOP) and α-amylase (2QV4) enzymes revealed high binding affinity and active site interactions comparable to native ligand acarbose.

CONCLUSION

The ethanolic extract of G. philippensis CHAM aerial parts is effective against HepG-2 cell lines, α-amylase and α-glucocidase activities. Biologically guided isolation indicated that compounds 2 and 5 are responsible for these activities. These results were supported by DMF calculations that detected the molecular areas responsible for protein interactions shown via docking studies.

Bioactivities of Natural Catalpol Derivatives

Catalpol, a famous molecule of iridoids, possesses extensive pharmacological activities. Our studies found that compounds with low-polarity substituents at the 6-O position of catalpol exhibited higher NF-κB inhibitory potency than catalpol. However, catalpol derivatives are not much focused. Here this review provides extensive coverage of naturally occurring catalpol derivatives discovered from 1888 until 2018. It covers their distribution, chemotaxonomic significance, chemical structures, and bioactivities from more than 200 peer-reviewed articles, and highlights the structure-activity relationship of catalpol derivatives.

Quantitation of catalpol in rat plasma by liquid chromatography/electrospray ionization tandem mass spectrometry and its pharmacokinetic study

A sensitive, rapid and specific liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay has been established for the quantitation of catalpol in rat plasma. Plasma samples were treated by precipitating protein with methanol and were chromatographed by a Diamonsil C(18) column (150 mm x 4.6 mm I.D., 5 microm) with the mobile phase consisting of methanol and 10 mM ammonium formate (30:70, v/v). The selected reaction monitoring (SRM) transitions were performed at m/z 380.1-->183.0 for catalpol and m/z 364.3-->167.0 for aucubin (IS) in the positive ion mode with electrospray ionization (ESI) source. Calibration curve was linear over the concentration range of 10-20,000 ng/mL. The mean recovery was 76.5+/-5.2% and the matrix effect ranged from -5.1 to 13.0%. The intra- and inter-day precisions were less than 6.3 and 14.6%, respectively, and the accuracy was within +/-5.6%. Catalpol was stable in possible conditions of storing and handling. The validated method has been successfully applied to determine the plasma concentration of catalpol for a pharmacokinetic study of catalpol after oral administration of 50 mg/kg to rats.

Chemical composition of the defensive secretion of the longhorned beetle, Chloridolum loochooanum

Adults of the longhorned beetle, Chloridolum loochooanum Gressitt (Coleoptera: Cerambycidae) emit a white frothy secretion from their metasternal glands. This defensive substance contains cyclopentanoid monoterpenoids (iridodials), whose structures were elucidated by gas chromatography-mass spectrometry (GC-MS) and nuclear magnetic resonance (NMR) analyses that compared the naturally occurring structures with synthesized versions. Optically active citronellals, [(S)-, (R)-, and (S)/(R)- mixture], were used as starting materials for synthesizing the corresponding iridodials for the determination of the absolute configuration of the natural product. The retention time of (2S)-iridodial, derived from (S)-citronellal, corresponded to that of C. loochooanum iridodial by enantioselective GC analysis. Thus, we suggest that the absolute configuration of C. loochooanum iridodial is (1R,2S,5S)-iridodial.

Iridoid glycosides from Gmelina arborea

Three iridoid glycosides 6-O-(3''-O-benzoyl)-alpha-L-rhamnopyranosylcatalpol (1a), 6-O-(3''-O-trans-cinnamoyl)-alpha-L-rhamnopyranosylcatalpol (2a) and 6-O-(3''-O-cis-cinnamoyl)-alpha-L-rhamnopyranosylcatalpol (3a) were isolated from aerial parts of Gmelina arborea and structures were elucidated by spectral analysis. Additionally a known iridoid 6-O-(3'', 4''-O-dibenzoyl)-alpha-L-rhamnopyranosylcatalpol (4) was also isolated and identified.

Naturally occurring iridoids. A review, part 1

A compilation of new naturally occurring iridoid glycosides, iridoid aglycones, iridoid derivatives and bis-iridoids reported during 1994-2005 is provided with available physical and spectral data: mp, [alpha]D, UV, IR, 1H- and 13C-NMR as well as natural source with family and references. 418 compounds with 202 references are cited.

Developments in the application of counter-current chromatography to plant analysis

Counter-current chromatography is a very versatile separation technique which does not require a solid stationary phase. It relies simply on the partition of a sample between the two phases of an immiscible solvent system. Some of the more recent applications of the method to the separation of plant-derived natural products are described here. Crude plant extracts and semi-pure fractions can be chromatographed, with sample loads ranging from milligrams to grams. Aqueous and non-aqueous solvent systems are used and the separation of compounds with a wide range of polarities is possible. The technique is complementary to other chromatographic methods and is compatible with gradient systems. The possibilities for solvent selection are almost limitless but some guidelines for the choice of successful systems are presented.

Chemotaxonomic markers in Digitalideae (Plantaginaceae)

In a chemosystematic investigation of Digitalideae (Plantaginaceae), the water-soluble part of extracts of two species of Digitalis, two species of Isoplexis, as well as Erinus alpinus and Lafuentea rotundifolia were studied with regard to their content of main carbohydrates, iridoids and caffeoyl phenylethanoid glycosides (CPGs). Digitalis and Isoplexis contained sorbitol, cornoside and a number of other phenylethanoid glycosides including the new tyrosol beta-D-mannopyranoside, sceptroside but were found to lack iridoid glucosides. Erinus contained mainly glucose, the new 8,9-double bond iridoid, erinoside, and a number of known iridoid glucosides including two esters of 6-rhamnopyranosylcatalpol, as well as the CPG poliumoside. Finally, Lafuentea was characterized by the presence of glucose, aucubin and cryptamygin B but apparently lacked CPGs. The chemosystematic significance of the isolated compounds is discussed.

Iridoid glycosides from Gmelina philippensis

Six new iridoids, 6-O-alpha-L-(2"-O-, 3"-O-, 4"-O-tribenzoyl)rhamnopyranosylcatalpol, 6-O-alpha-L-(2"-O-, 3"-O-dibenzoyl, 4"-O-cis-p-coumaroyl)rhamnopyranosylcatalpol, 6-O-alpha-L-(2"-O-, 3"-O-dibenzoyl, 4"-O-trans-p-coumaroyl)rhamnopyranosylcatalpol, 6-O-alpha-L-(2"-O-benzoyl, 3"-O-trans-p-coumaroyl)rhamnopyranosylcatalpol, 6-O-alpha-L-(2"-O-, 3"-O-dibenzoyl)rhamnopyranosylcatalpol, and gmephiloside as well as five known monoacyl and diacyl rhamnopyranosylcatalpol derivatives were isolated from the aerial parts of Gmelina philippensis. Their structures were established by spectroscopic means. Additionally, the known iridoids catalpol, geniposidic acid, gardoside, and 8-epi-loganic acid were identified and quantified by GC and GC-MS. The taxonomic significance of rhamnopyranosylcatalpol derivatives and iridoid acids as chemical characters is discussed.