br Results and discussion This paper reports the synthesis

Results and discussion This paper reports the synthesis of methoxy and 4-thio derivatives of quercetin and luteolin, which includes two new derivatives (4 and 12) and explores how subtle variations in the chemical structure of flavonoids affect their biological activity, particularly in relation to their antiangiogenic activity.
Conclusion In conclusion, we have synthesised the methoxy and 4-thio derivatives of quercetin and luteolin and evaluated their resulting antiangiogenic and antiproliferative potencies, alongside quercetin and luteolin. As part of this programme we have demonstrated the impact of subtle structural modifications such as methylation and 4-thio conversion on the antiangiogenic and antiproliferative properties of quercetin and luteolin. Comparison of their antiangiogenic activities has led to identification of key structural features required for the antiangiogenic activities. It was found that the 4-CO functionality is crucial for the antiangiogenic activity and also methylation of the free hydroxyl groups provides the benefit of potential antiangiogenic activity with low cytotoxicity. Also, analysis of bilayer membrane interactions of the active compounds suggests that bilayer effects do not play a significant role in the biological mechanism of action at the concentrations tested, especially for luteolin and its derivatives. Among quercetin, luteolin and their derivatives, compound-2 and compound-10 were found to potentially inhibit the in vitro VEGF induced cell Fesoterodine Fumarate with low cytotoxicity. In addition, the molecular docking studies indicated that compound-2 and compound-10 possess high binding affinities towards VEGF and VEGFR2. Overall, compound-2 and compound-10 exhibit an appropriate balance of high antiangiogenic activity and minimal toxicity. Therefore, they have been identified as the most promising flavonoid templates from our programme of study for further development as antiangiogenic agents.
Experimental section
Acknowledgement Financial support from the Felix Trust and funding from the Royal Society (grant award reference RG110203) are gratefully acknowledged. We thank Amit Kumar Rajora and Anju Paudyal for their help with Western blotting and Olga Florek for her help with DSC experiment. We also thank the University of Reading for the provision of the Chemical Analysis Facility.
Introduction The healthy cornea is avascular and nourished by diffusion from the aqueous humor and tear film–supported circular pericorneal plexus derived from the anterior ciliary arteries that surrounds the cornea in the limbal region. The maintenance of corneal avascularity is termed “angiogenic privilege,” and in its resting state, this is an active process of homeostasis between the low level of angiogenic and high level of antiangiogenic factors. A wide range of external insults to the cornea can disturb the delicate equilibrium required for angiogenic privilege by increasing the production of angiogenic factors, which lead to corneal neovascularization with resultant loss in corneal transparency and visual acuity from scarring, stromal edema, lipid deposition, and inflammation. Currently, there is no epidemiological study that provides an accurate estimate of the incidence and prevalence of corneal neovascularization in the general population. Many of the conditions resulting in corneal neovascularization eventually require a penetrating or lamellar keratoplasty to restore vision; however, graft rejection rates are higher in vascularized corneal beds even with systemic immunosuppression , and posttransplant vision is often compromised.43, 63, 73 Many risk factors for corneal graft rejection are recognized, such as recipient age, previous rejection episodes, previous grafts, gender matching, and timing of the graft.115, 263, 278 Corneal neovascularization, however, also develops in 41% of eyes after penetrating keratoplasty, even without preexisting corneal angiogenesis. Corneal neovascularization is therefore a risk factor for graft failure after keratoplasty and also a major complication following the surgical procedure itself. Successful keratoplasty is attributed to corneal “immune privilege,” the suppressed corneal inflammation induced by the lack of afferent lymphatic and efferent blood vessels in the recipient cornea, lack of major histocompatibility antigens class II, and the anterior chamber–associated immune deviation.266, 288 Lymphatic vessels and associated blood vessels are found in neovascularized cornea. The presence of corneal neovascularization, therefore, enables access of antigenic material to regional lymph node, completes the “immune reflex arc” in cornea, and compromises its immune privilege.