Synthesis of Rupestonic Acid L-Ephedrine Derivatives with Preliminary In vitro Anti-influenza Viral Activity.

Background: Influenza virus is a kind of RNA virus. Nowadays, the high incidence of influenza and the morbidity and mortality of epidemic influenza are substantial. It has been reported that one hundred million people in the world are infected with influenza viruses, and two hundred and fifty thousand to five hundred thousand people die from the flu per year. In 2021, the number of infected persons in China was reported to be 654,700, and 0.07% of the infected persons died. The flu has caused a serious threat to human survival. Although several drugs, such as Zanamivir, Oseltamivir, Peramivir, and Laninamivir, have been used in clinics for the treatment of the influenza virus, there are some shortcomings of these drugs. The strain of influenza H5N1 (avian influenza) has been found to resist the effective drug Oseltamivir. Thus, there is an urgent demand to discover new influenza virus inhibitors to overcome the emergence of influenza antigens.
Aims: This study aimed to develop new influenza virus inhibitors based on the rupestonic acid parent core.
Objective: The rupestonic acid L-ephedrine ester (A) and rupestonic acid L-ephedrine complex (B) were synthesized in this work for the development of influenza virus inhibitors.
Methods: The target compounds were synthesized using rupestonic acid and L-ephedrine as starting materials. Their structures were characterized by ¹ H NMR and ¹³ C NMR, and the purity was determined by HPLC. Then, their preliminary in vitro influenza activity was evaluated using Oseltamivir as a reference drug.
Results: The results showed that the synthesized rupestonic acid L-ephedrine derivatives A and B were more potent influenza virus inhibitors against the strains of A/PR/8/34 (H ₁ N ₁ ) and A/FM/1/47 (H ₁ N ₁ ) with the IC 50 values of 51.0, 51.0 μM and 441.0, 441.0 μM, respectively, than that of rupestonic acid. By comparing the IC 50 of compounds A and B, compound A can be regarded as a very promising lead compound for the development of influenza virus inhibitors.
Conclusion: The rupestonic acid L-ephedrine ester (A) and rupestonic acid L-ephedrine complex (B) were synthesized and characterized using ¹ H NMR and ¹³ C NMR. Moreover, their purity was determined by HPLC. Both compounds A and B exhibited more potent activities against the strains of A/PR/8/34 (H ₁ N ₁ ) and A/FM/1/47 (H ₁ N ₁ ) than rupestonic acid. Compound A can be regarded as a very promising lead compound for the development of influenza virus inhibitors. Based on these results, more rupestonic acid derivatives will be designed and synthesized in the future for the development of influenza virus inhibitors.
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