Microwave-assisted oxidation of silibinin: a simple and preparative method for the synthesis of improved radical scavengers

A new and preparative oxidation of silibinin has been developed to give access to two different silibinin derivatives known for their enhanced antioxidant properties. Conventional heating methods were compared with results obtained from microwave (MW) heating. The base-catalysed oxidation of silibinin under MW heating is a very efficient method for the preparation of 2,3-dehydrosilybin and a related silybin rearrangement product. This latter compound shows enhanced radical scavenging properties. Optimised conditions were used to prepare 2,3-dehydrosilybins A and B from optically pure silybins A and B. An efficient, preparative purification method was also developed to enable isolation of different products in high purity.     

Enhancement of bioavailability and hepatoprotection by silibinin through conversion to nanoparticles prepared by liquid antisolvent method

The current research was intended to establish the impact of Silibinin nanoparticles (SB-APSP) produced by the antisolvent precipitation with a syringe pump (APSP). The in-vivo bioavailability and hepatoprotective activity of SB-APSP were evaluated in experimental animals. To determine the pharmacokinetic parameters, silibinin and its nanoparticles were given orally to rabbits at a dose of 50 mg/Kg body weight. Blood samples were drawn at different time intervals and were analyzed using HPLC. The bioavailability of un processed silibinin was lower as compared to silibinin nanoparticles (3.45 ± 0.07 and 23.76 ± 0.07 µg/mL respectively). The AUC and C_max of SB-APSP were found to be 15.56 and 6.88 folds greater for nanoparticles when compared to silibinin. Hepatoprotective study in Male Sprague Dawley rats revealed that SB-APSP provide better recovery of the damaged liver cell induced by CCl₄. Histopathology of the liver revealed that SB-APSP provide better protection to the liver cells from the damage induced by CCl₄ and maintained the hepatic lobule histopathology more efficiently. It was concluded that the SB-APSP can more effectively protect the liver in experimental animals in a far better way compared to the un-processed Silibinin and could be used as an efficient hepatoprotective agent.     

Synthesis of New Silybin Derivatives and Evaluation of Their Antioxidant Properties

Silibinin, the major flavonolignan of silymarin, displays a broad spectrum of biological features that are generally ascribed to its antioxidant properties. Silibinin occurs in two diastereoisomeric forms, i.e., silybins A and B, in a ratio of ca. 1 : 1. With a simple and robust purification method, it is now possible to obtain silybins A and B in pure forms, in g‐scale amounts, and within a short period of time. Herein, we describe an efficient synthesis strategy to obtain a variety of new and more H₂O‐soluble derivatives from the single silybins in which the 9″‐OH group was converted to a sulfate, N₃, phosphodiester, or NH₂ group via a solution‐phase approach. Thus, eight new compounds have been synthesized, purified by HPLC analysis, and characterized by NMR and MS analyses. To conduct experiments to clarify the many biological properties of pure silibinin diastereoisomers and their derivatives, the synthetic compounds were tested by using the DPPH assay to evaluate their antioxidant activities. The results, even if only for a small number of derivatives, revealed that some of these compounds are much more active than their parent compounds. It is also interesting to consider the synergetic effects.     

Flavonolignan silibinin abrogates SDS induced fibrillation of human serum albumin

Misfolding, aggregation and fibrillation of amyloidogenic proteins have been established as hallmark events in pathophysiology of various degenerative diseases. Inhibition of protein fibrillation through use of plant derived molecular scaffolds is currently considered as one solution to it. Further, rational design of therapeutic originating with the specific plant molecular scaffolds appeared passable to aid in mitigating amyloidogenic diseases. Silibinin (SB) is a flavonolignan obtained from milk thistle plant. SB is well acclaimed as a potent hepatoprotective, cardioprotective and an attenuator of receptor signaling in case of type 2 diabetes. This work reports the inhibitory capacity of SB against protein fibrillation under experimental conditions. Human serum albumin (HSA), an ubiquitous serum protein was used and various platform studies were carried out for indepth understanding of similar effects. Biophysical studies and electron microscopy confirmed that SB inhibited HSA fibrils formations by 36% at optimal molar ratio. In silico studies further demonstrated that intermolecular hydrogen bonds and hydrophobic interactions hindered progressive aggregation and protein fibrillation.