Potent vasorelaxant analogs from chemical modification and biotransformation of isosteviol

Biological activity and structural modification of isosteviol over the past 15 years

Isosteviol is a tetracyclic diterpenoid obtained by hydrolysis of stevioside. Due to its unique molecular skeleton and extensive pharmacological activities, isosteviol has attracted more and more attention from researchers. This review summarized the structural modification, pharmacological activity and microbial transformation of isosteviol from 04/2008 to 10/2023. In addition, the research history, structural characterization, and pharmacokinetics of isosteviol were also briefly reviewed. This review aims to provide useful literature resources and inspirations for the exploration of diterpenoid drugs.

Synthesis and in vivo evaluation of new steviol derivatives that protect against cardiomyopathy by inhibiting ferroptosis

Cardiovascular diseases (CVDs) remain the leading cause of death globally. Inhibiting ferroptosis and thus preventing cardiac cell death is a promising and effective strategy for cardiomyopathy prevention and therapy. Steviol, an ent-kaurene diterpenoid, possesses broad-spectrum bioactivity. In the present study, with the aim to discover new agents for CVDs treatment, 30 derivatives of steviol, including 22 new ones, were synthesized, and evaluated their protective activity in vivo using the doxorubicin (DOX) induced zebrafish cardiomyopathy model. Our results firstly demonstrated that steviol has promising cardioprotective activity and further modification of steviol can greatly improve the activity. Among the new derivatives, 16d and 16e show the most potent activity. Both 16d (1 μM) and 16e (0.1 μM) effectively maintain the normal heart shape and prevent the cardiac dysfunction impaired by DOX in zebrafish. Their therapeutic efficacy is much superior to the parent natural product, steviol, and positive drug, levosimendan. Further study demonstrated that 16d and 16e inhibit DOX-induced ferroptosis and thus protect cardiomyopathy, by suppressing the glutathione depletion, iron accumulation, and lipid peroxidation, decreasing reactive oxygen species overaccumulation, and restoring the mitochondrial membrane potential. Consequently, due to their unique structure and significant cardioprotective activity with ferroptosis inhibition, new steviol derivatives 16d and 16e merit further research for the development of new cardioprotective drug candidates.

Synthesis and characterization of new pyrazole-tetrazole derivatives as new vasorelaxant agents

The synthesis of new functionalized tetrazole-pyrazole compounds is reported. They were fully characterized by spectroscopy and spectrometry methods. The vasorelaxant potency of these molecules was also investigated. All compounds showed a good vasorelaxant activity but the Compound 6 "ethyl 1-((2-(3-bromopropyl)-2H-tetrazol-5-yl)methyl)-5-methyl-1H-pyrazole-3-carboxylate" seems to have the highest effect, which reached 70% at 10^-4 M concentration. This effect was partially endothelium-dependent; also, the vasorelaxant pattern of this compound was quite similar to that of the verapamil.

Biotransformation of 1α,11α-dihydroxyisopimara-8(14),15-diene by Cunninghamella echinulata NRRL 1386 and their neuroprotective activity

The isopimarane diterpene, 1α,11α-dihydroxyisopimara-8(14),15-diene (1), is the major constituents from the rhizomes of Kaempferia marginata (Zingiberaceae), a Thai medicinal plant. The microbial transformation of parent compound 1 by the fungus Cunninghamella echinulata NRRL 1386 gave five new metabolites, 7α,11α-dihydroxy-1-oxoisopimara-8(14),15-diene (2), 3β,7α,11α-trihydroxy-1-oxoisopimara-8(14),15-diene (3), 7β,11α-dihydroxy-1-oxoisopimara-8(14),15-diene (4), 7α-hydroxy-1,11-dioxoisopimara-8(14),15-diene (5) and 1α,7β,11α-trihydroxyisopimara-8(14),15-diene (6), together with three known metabolites, 7-9. The structures of the new metabolites were elucidated by spectroscopic techniques. The known compounds were identified by comparison of the spectroscopic and physical data with those of reported values. The parent compound 1 and the metabolites have been neuroprotective activities evaluated against Aβ_25-35-induced damage in human neuroblastoma cells (SK-N-SH). Among them, compounds 1-3, 5 and 7-9 had significant neuroprotective activities at a concentration of 2.5 μM. The results demonstrated that these compounds might be worth for further development into therapeutic agents for the treatment of neurodegenerative diseases.

Microbial Transformations of Two Beyerane-Type Diterpenes by Cunninghamella echinulata

Microbial transformations of two tetracyclic beyerane-type diterpenes, ent-16β-oxobeyeran-19-oic acid (1) and its chemical reduction product, ent-16β-hydroxybeyeran-19-oic acid (2), by the filamentous fungus Cunninghamella echinulata ATCC 8688a yielded eight metabolites (3-10). Incubation of the substrate 2 with C. echinulata afforded three new hydroxylated ones (3-5) along with two known ones (6-7), while incubation of 1 gave three known ones (8-10). The new compounds were characterized by 1D and 2D NMR as well as HRESIMS analysis, and the stereostructures of 3 and 4 were confirmed by X-ray crystallography. The bioreactions were involved not only in stereoselective incorporation of hydroxyl groups at inert positions C-7, -9, -12, and -14 of the two beyerane diterpenes but also in glucosidation at C-19 of 2. This is the first report on the biotransformation of the diterpenes by using C. echinulata. All compounds were assayed for their α-glucosidase inhibitory, neurotrophic, anti-inflammatory, and phytotoxic activity, and only in neurotrophic assay compounds, 2 and 9 were found to display nerve growth factor-mediated neurite-outgrowth promoting effects in PC12 cells; the others were inactive.

A compartmental approach to isosteviol's disposition in Sprague-Dawley rats

Isosteviol has been reported to reverse hypertrophy and related inflammatory responses in in vitro models representative of cardiac muscle cells. The disposition of isosteviol is, however, characterized by secondary peaks and long plasma residence time despite reports of a relatively short half-life in liver fractions. The present study describes a compartmental approach to modelling the secondary peaks characteristic of isosteviol's concentration-time data in Sprague-Dawley rats. Oral (4 mg/kg) and intravenous (4 mg/kg) doses of isosteviol were administered to male and female Sprague-Dawley rats. Plasma samples collected between 0 and 72 h, and total bile secreted in 24 h, were analysed for isosteviol content with LC-MS/MS techniques. The disposition of isosteviol was, thereafter, described with a structural model that accounted for the sampling, liver and biliary secretion compartments, with a gap-time characterizing the accumulation and subsequent emptying of isosteviol for re-absorption. The half-life of isosteviol following oral dosing was about 103% greater in female rats than in the male, and the model-derived area under the concentration-time curve (AUC) in 72 h was about 756% greater in female animals than in males. Following the administration of intravenous doses of isosteviol, half-life and AUC in 24 h were about 332% and 595%, respectively, higher in female rats than in males. Isosteviol equivalent secreted into bile over 24 h accounted for about 94% of orally administered dose in male rats, and about 59% of oral dose in females. These findings show a differential systemic removal of isosteviol in Sprague-Dawley rats, likely explainable by gender-related differences in the glucuronidation-capacity of isosteviol.

Bioactivity Profile of the Diterpene Isosteviol and its Derivatives

Steviosides, rebaudiosides and their analogues constitute a major class of naturally occurring biologically active diterpene compounds. The wide spectrum of pharmacological activity of this group of compounds has developed an interest among medicinal chemists to synthesize, purify, and analyze more selective and potent isosteviol derivatives. It has potential biological applications and improves the field of medicinal chemistry by designing novel drugs with the ability to cope against resistance developing diseases. The outstanding advancement in the design and synthesis of isosteviol and its derivative has proved its effectiveness and importance in the field of medicinal chemical research. The present review is an effort to integrate recently developed novel drugs syntheses from isosteviol and potentially active pharmacological importance of the isosteviol derivatives covering the recent advances.

Design and Synthesis of C-19 Isosteviol Derivatives as Potent and Highly Selective Antiproliferative Agents

Six series of novel isosteviol derivatives; modified in the C-19 position; were synthesized; and their antiproliferative activity was evaluated against three human cancer cell lines (HCT-116; BEL-7402; HepG2) and the human L02 normal cell line in vitro. Most of the derivatives tested here exhibited improved antiproliferative activity with high selectivity when compared with the parent compound isosteviol and the positive control drug 5-fluorouracil. Among these derivatives; compound 5d exhibited the most potent antiproliferative activity and commendable selectivity between cancer and normal cells. In addition; compound 5d inhibited the colony formation of HCT-116 cells in a concentration-dependent manner. Further studies revealed that compound 5d arrested the HCT-116 cell cycle in the S phase; and western blot analysis demonstrated the mechanism may be correlated with a change in the expression of cyclin A; cyclin B1; and cyclin E1. Furthermore; the results of a docking study that involved placing compound 5d into the CDK2/cyclin A binding site revealed that its mode of action was possibly as a CDK2/cyclin A inhibitor.

Diterpenoids of terrestrial origin

This review covers the isolation and chemistry of diterpenoids from terrestrial as opposed to marine sources and includes labdanes, clerodanes, pimaranes, abietanes, kauranes, gibberellins, cembranes and their cyclization products. The literature from January to December 2013 is reviewed.