Improved Synthesis of Icaritin and Total Synthesis of β-Anhydroicaritin

Application of hydrophobic eutectic solvent in efficient biotransformation of total flavonoids of Herba Epimedii

Icaritin, a hydrolysate from total flavonoids of Epimedii (TFE), which has better anti-hepatoma activity than its glycosylated form. In this work, immobilized enzymes 4LP-Tpebgl3@Na-Y and DtRha@ES-107 were used to hydrolyze TFE to prepare icaritin. Five different hydrophobic deep eutectic solvents (HDES) were prepared and the most ideal HDES was successfully selected, which was composed of dodecyl alcohol and thymol with the molar ratio of 2:1. The relative enzyme activity of 4LP-Tpebgl3@Na-Y and DtRha@ES-107 was about 102.4 % and 112.5 %, respectively. In addition, the thermal and binding stability of 4LP-Tpebgl3@Na-Y and DtRha@ES-107 in HDES was not affected negatively. In the biphasic system composed of 50 % (v/v) HDES and Na2HPO4-citric acid buffer (50 mM, pH 5.5), 4LP-Tpebgl3@Na-Y (1.0 U/mL) and TFE (1 g/L) were reacted at 80 °C for 1 h, and then reacted with DtRha@ES-107 (20 U/mL) at 80 °C for 2 h. Finally, TFE was completely converted to 301.8 mg/L icaritin (0.82 mM). After 10 cycles, 4LP-Tpebgl3@Na-Y/DtRha@ES-107 still maintained 84.1 % original activity. In this study, we developed an efficient methodology for icaritin preparation through the integration of enzymatic catalysis and adsorption separation, presenting a viable approach for large-scale, cost-effective production of icaritin.

Synthesis of 3- and 5-β-anhydroicaritine norcantharidin conjugates

Using molecular hybridisation to develop conjugates of natural antitumor drugs is one of the research hotspots in recent drug development. In this study, β-anhydroicaritine with anticancer activity was conjugated to norcantharidine selectively to develop new antitumor lead candidates. In the condition of EDCI/DMAP/DCM, the C-3 and C-5 hydroxyl groups of β-anhydroicaritine was coupled with norcantharidin monoacid ester respectively, and the inhibitory activity of the synthesised conjugates against HepG2, MCF-7 and L-02 cells were tested by CCK-8 method. Most of these conjugates showed a better activity against HepG2 and MCF-7 cell lines compared to parent compound icaritin, but weaker than another parent compound norcantharidin.

Flavones and Related Compounds: Synthesis and Biological Activity

This review focuses on the synthesis and biological activity of flavones and their related flavonoidic compounds, namely flavonols and aurones. Among the biological activities of natural and synthetic flavones and aurones, their anticancer, antioxidant, and antimicrobial properties are highlighted and detailed in this review. Starting from the structures of natural flavones acting on multiple anticancer targets (myricetin, genkwanin, and other structurally related compounds), new flavone analogs were recently designed and evaluated for their anticancer activity. The most representative compounds and their anticancer activity are summarized in this review. Natural flavones recognized for their antimicrobial properties (baicalein, luteolin, quercetol, apigenin, kaempferol, tricin) have been recently derivatized or structurally modulated by chemical synthetic methods in order to obtain new effective antimicrobial flavonoidic derivatives with improved biological properties. The most promising antimicrobial agents are systematically highlighted in this review. The most applied method for the synthesis of flavones and aurones is based on the oxidative cyclization of o-hydroxychalcones. Depending on the reaction conditions and the structure of the precursor, in some cases, several cyclization products result simultaneously: flavones, flavanones, flavonols, and aurones. Based on the literature data and the results obtained by our research group, our aim is to highlight the most promising methods for the synthesis of flavones, as well as the synthetic routes for the other structurally related cyclization products, such as hydroxyflavones and aurones, while considering that, in practice, it is difficult to predict which is the main or exclusive cyclization product of o-hydroxychalcones under certain reaction conditions.

Multidisciplinary strategies to enhance therapeutic effects of flavonoids from Epimedii Folium: Integration of herbal medicine, enzyme engineering, and nanotechnology

Flavonoids such as baohuoside I and icaritin are the major active compounds in Epimedii Folium (EF) and possess excellent therapeutic effects on various diseases. Encouragingly, in 2022, icaritin soft capsules were approved to reach the market for the treatment of hepatocellular carcinoma (HCC) by National Medical Products Administration (NMPA) of China. Moreover, recent studies demonstrate that icaritin can serve as immune-modulating agent to exert anti-tumor effects. Nonetheless, both production efficiency and clinical applications of epimedium flavonoids have been restrained because of their low content, poor bioavailability, and unfavorable in vivo delivery efficiency. Recently, various strategies, including enzyme engineering and nanotechnology, have been developed to increase productivity and activity, improve delivery efficiency, and enhance therapeutic effects of epimedium flavonoids. In this review, the structure-activity relationship of epimedium flavonoids is described. Then, enzymatic engineering strategies for increasing the productivity of highly active baohuoside I and icaritin are discussed. The nanomedicines for overcoming in vivo delivery barriers and improving therapeutic effects of various diseases are summarized. Finally, the challenges and an outlook on clinical translation of epimedium flavonoids are proposed.

Co-Immobilizing Two Glycosidases Based on Cross-Linked Enzyme Aggregates to Enhance Enzymatic Properties for Achieving High Titer Icaritin Biosynthesis

Icaritin is a rare and high-value isopentane flavonoid compound with remarkable activities. Increasing yields while reducing cost has been a great challenge in icaritin production. Herein, we first reported a high titer icaritin biosynthesis strategy from epimedin C through co-immobilizing α-l-rhamnosidase (Rha1) and β-glucosidase (Glu4) using cross-linked enzyme aggregates (CLEAs). The created CLEAs exhibited excellent performances in terms of catalytic activity, thermal stability, pH stability, and reusability. Notably, Rha1-CLEAs (K_i: 1 M) and Glu4-CLEAs (K_i: 0.1 M) were more tolerant to sugars (glucose or rhamnose) than free enzymes (0.1 M for Rha1 and 0.007 M for Glu4) by immobilization, achieving the highest icaritin productivity under the highest substrate concentration ever reported. Finally, about 34.24 g/L icaritin could be obtained from 100 g/L epimedin C within 8 h, indicating the great potential for industrialization. This study also provides a promising strategy for the low-cost production of other high-value aglycone compounds by solving poor stability and sugar inhibition of glycosidase.

Recent advances in the synthesis of natural products containing the phloroglucinol motif

Covering: June 2009 to 2021Natural products containing a phloroglucinol motif include simple and oligomeric phloroglucinols, polycyclic polyprenylated acylphloroglucinols, phloroglucinol-terpenes, xanthones, flavonoids, and coumarins. These compounds represent a major class of secondary metabolites which exhibit a wide range of biological activities such as antimicrobial, anti-inflammatory, antioxidant and hypoglycaemic properties. A number of these compounds have been authorized for therapeutic use or are currently being studied in clinical trials. Their structural diversity and utility in both traditional and conventional medicine have made them popular synthetic targets over the years. In this review, we compile and summarise the recent synthetic approaches to the natural products bearing a phloroglucinol motif. Focus has been given on ingenious strategies to functionalize the phloroglucinol moiety at multiple positions. The isolation and bioactivities of the compounds are also provided.

Selective alkylation of β-anhydroicaritine and their biological evaluation on anticancer

A convenient and selective alkylation of icaritin has been developed. The methodology involved initial formation of β-anhydroicaritine (3) under acidic conditions followed by selective methylation at the C-3 position and then alkylation at C-5 position. Several alkylated β-anhydroicaritine derivatives were synthesised using this methodology. These newly synthesised derivatives, especially the compounds 5b, 5c and 5j, significantly suppressed cell proliferation when tested against cancer cell lines in vitro. Compound 5j (R = Bn) exhibited a competitive inhibition against MCF7 in vivo compared to tamoxifen.

Molecular and cellular basis of the anticancer activity of the prenylated flavonoid icaritin in hepatocellular carcinoma

The prenylated flavonoid icaritin (ICT) is currently undergoing phase 3 clinical trial for the treatment of advanced hepatocellular carcinoma (HCC), based on a solid array of preclinical and clinical data. The antitumor activity originates from the capacity of the drug to modulate several signaling effectors in cancer cells, mainly the estrogen receptor splice variant ERα36, the transcription factors STAT3 and NFκB, and the chemokine receptor CXCR4. Recent studies have implicated additional components, including different microRNAs, the generation of reactive oxygen species and the targeting of sphingosine kinase-1. ICT also engages the RAGE-HMGB1 signaling route and modulates the apoptosis/autophagy crosstalk to promote its anticancer activity. In addition, ICT exerts profound changes on the tumor microenvironment to favor an immune-response. Collectively, these multiple biochemical and cellular characteristics confer to ICT a robust activity profile which can be exploited to treat HCC, as well as other cancers, including glioblastoma and onco-hematological diseases such as chronic myeloid leukemia. This review provides an update of the pharmacological properties of ICT and its metabolic characteristics. It also addresses the design of derivatives, including both natural products and synthetic molecules, such as SNG1153 also in clinical trial. The prenylated flavonoid ICT deserves attention as a multifunctional natural product potentially useful to improve the treatment of advanced hepatocellular carcinoma.