Developing new biomolecule–drug conjugates as prodrugs is a promising area for natural products and pharmaceutical chemistry. Herein, a cholesterol–doxorubicin (Chol-DOX) conjugate was synthesized using cholesteryl-4-nitrophenolate as a facile, stable, and controllable activated ester. This approach offers an alternative to the conventional HCl-emitting cholesteryl chloroformate method. Semi-empirical theoretical calculations showed that cholesteryl-4-nitrophenolate exhibits moderate reactivity, greater thermodynamic stability, a higher dipole moment, and a lower HOMO-LUMO energy gap compared to cholesteryl chloroformate, suggesting that cholesteryl-4-nitrophenolate could be used as a more controllable acylating agent. The structure of the synthesized Chol-DOX conjugate was characterized using NMR, MS, and FT-IR techniques. Biological properties of the Chol-DOX conjugate were analyzed with a comparison of theoretical and experimental data. This work provides a facile and controllable method to synthesize natural lipid–DOX prodrugs and offers an in-depth data analysis of the related biological properties.

Developing new biomolecule-drug conjugates as prodrugs is a promising area for natural products and pharmaceutical chemistry. Herein, a cholesterol-doxorubicin (Chol-DOX) conjugate was synthesized using cholesteryl-4-nitrophenolate as a facile, stable, and controllable activated ester. This approach offers an alternative to the conventional HCl-emitting cholesteryl chloroformate method, semi-empirical theoretical calculations showed that cholesteryl-4-nitrophenolate exhibits moderate reactivity, higher thermodynamic stability, and a lower HOMO-LUMO energy gap compared to cholesteryl chloroformate, suggesting cholesteryl-4-nitrophenolate could be used as a more controllable acylating agent. The structure of synthesized Chol-DOX conjugate was characterized using NMR and MS techniques. Biological properties of the Chol-DOX were analyzed with the comparison of theoretical and experimental data. This work provided a facile and controllable method to synthesize natural lipid-DOX prodrug and offered an in-depth data analysis of the related biological properties.

Ethenzamide (2-ethoxybenzamide), besides acetylsalicylic acid, is one of the mostly used salicylic acid derivatives in pharmaceuticals. It has analgesic and anti-inflammatory effects that originate from the inhibition of cyclooxygenase (COX-1) activity, thus blocking prostaglandin synthesis. In this work, efficient and eco-friendly methods were developed for the synthesis of ethenzamide via the O-alkylation reaction of salicylamide. The reactions were carried out under conventional conditions in a solvent-free system using variant solvents and different phase transfer catalysts (PTC) in the presence of microwave radiation or ultrasonic conditions. It was shown that in solvent-free conditions using TBAB as a catalyst, ethenzamide can be obtained within 15 min at 80 °C with 79% yield. Meanwhile, using microwave radiation under the same conditions, the reaction time can be shortened to 90 s with 92% yield. Notably, high yields can be achieved under PTC in water (or organic solvent-free) conditions using microwave radiation (2 min, 94%) or ultrasound (10 min, 95% efficiency). The studies prove that the PTC synthesis process of ethenzamide can be conducted under mild conditions, with a shorter reaction time and remarkably lower energy consumption in comparison to conventional processes, thus actualizing “green chemistry” for practical ethenzamide preparation.

Ethenzamide (2-ethoxybenzamide), besides acetylsalicylic acid, is one of the mostly used salicylic acid derivatives in pharmaceuticals. It has analgesic and anti-inflammatory effects that originated from the inhibition of cyclooxygenase (COX-1) activity, thus blocking prostaglandin synthesis. In this work, efficient and eco-friendly methods were developed for the synthesis of ethenzamide via the O-alkylation reaction of salicylamide. The reactions were carried out under conventional conditions in a solvent-free system using variant solvents and different phase transfer catalysts (PTC) in the presence of microwave radiation or ultrasonic conditions. It was shown that in solvent-free conditions using TBAB as a catalyst, ethenzamide can be obtained within 15 min at 80°C with 79% yield. Meanwhile, using microwave radiation under the same conditions, the reaction time can be shortened to 90 s with 92% yield. Notably, high yields can be achieved under PTC in water (or organic solvent-free) conditions using microwave radiation (2 min, 94%) or ultrasound (10 min, 95% efficiency). The studies prove that the PTC synthesis process of ethenzamide can be conducted under mild conditions, with a shorter reaction time and remarkably lower energy consumption in comparison to conventional processes, thus actualizing the ‘green chemistry’ for practical ethezamide preparation.