Synthetic flavonoid derivatives targeting the glycogen phosphorylase inhibitor site: QM/MM-PBSA motivated synthesis of substituted 5,7-dihydroxyflavones, crystallography, in vitro kinetics and ex-vivo cellular experiments reveal novel potent inhibitors

Glycogen phosphorylase (GP) is an important target for the development of new anti-hyperglycaemic agents. Flavonoids are novel inhibitors of GP, but their mode of action is unspecific in terms of the GP binding sites involved. Towards design of synthetic flavonoid analogues acting specifically at the inhibitor site and to exploit the site’s hydrophobic pocket, chrysin has been employed as a lead compound for the in silico screening of 1169 new analogues with different B ring substitutions. QM/MM-PBSA binding free energy calculations guided the final selection of eight compounds, subsequently synthesised using a Baker-Venkataraman rearrangement-cyclisation approach. Kinetics experiments against rabbit muscle GPa and GPb together with human liver GPa, revealed three of these compounds (11, 20 and 43) among the most potent that bind at the site (Ki s < 4 µM for all three isoforms), and more potent than previously reported natural flavonoid inhibitors. Multiple inhibition studies revealed binding exclusively at the inhibitor site. The binding is synergistic with glucose suggesting that inhibition could be regulated by blood glucose levels and would decrease as normoglycaemia is achieved. Compound 43 was an effective inhibitor of glycogenolysis in hepatocytes (IC50 = 70 µM), further promoting these compounds for optimization of their drug-like potential. X-ray crystallography studies revealed the B-ring interactions responsible for the observed potencies

Computer-aided design and synthesis of 5,7-dihydroxyflavone derivatives as glycogen phosphorylase inhibitors

Diabetes is a chronic disease that affects approximately 415 million people worldwide and this number is expected to rise to 642 million by the year 2040. 90% of cases of diabetes are type 2. Although some treatments are already available for type 2 diabetes, there are considerable side-effects associated with these drugs that include a risk of hypoglycaemia. Hence, there is an immediate need for new and more effective drugs. Naturally occurring flavonoids are known inhibitors of glycogen phosphorylase, which is a validated target for controlling hyperglycemia in type 2 diabetes. By exploiting computational methods such as molecular docking with Glide and post-docking binding free energy calculations using advanced QM/MM-PBSA calculations, we have screened a large library of 1239 5,7-dihydroxyflavone analogues which have the potential to bind at the inhibitor site of glycogen phosphorylase. We compared these results to our benchmark ligand chrysin, which can inhibit glycogen phosphorylase with a Ki of 19.01 µm and identified thirteen ligands which are predicted to have better binding affinities exploiting a rigorous consensus scoring approach to reduce the chance of false positives. Favourable substituents on the predicted flavonoids included B ring hydroxyl and halogenated substituents in the ortho position and small hydrophobic groups on the meta/para positions directed towards the hydrophobic cavity of the binding site. Towards synthesis of these analogues, after many adjustments to the synthetic procedure it was identified that using methyl protection of the hydroxyls at the 5 and 7 position in parallel with the Baker-Venkataraman re-arrangement managed to achieve high purity initial compounds with a relatively good yield. The procedure is now ready to be employed to synthesize all other predicted 5,7-dihydroxyflavone derivatives. Kinetics experiments will validate their potency against glycogen phosphorylase and structure activity relationship analysis can help further guide lead optimization alongside pharmacokinetics and in vivo studies, until we can achieve a more potent and drug-like inhibitor of glycogen phosphorylase for the treatment of type 2 diabetes

Phytogenic polyphenols as glycogen phosphorylase inhibitors: The potential of triterpenes and flavonoids for glycaemic control in type 2 diabetes

Glycogen phosphorylase (GP) is a validated pharmaceutical target for the development of antihyperglycaemic agents. Phytogenic polyphenols, mainly flavonoids and pentacyclic triterpenes, have been found to be potent inhibitors of GP. These compounds have both pharmaceutical and nutraceutical potential for glycemic control in diabetes type 2. This review focuses mainly on the most successful (potent) of these compounds discovered to date. The protein-ligand interactions that form the structural basis of their potencies are discussed, highlighting the potential for exploitation of their scaffolds in the future design of new GP inhibitors

Demographics of responders.

Demographics of responders.</p

pone.0272446.t001 - An international consensus for mitigation of the detrimental effects of the COVID-19 pandemic on laparoscopic training

pone.0272446.t001 - An international consensus for mitigation of the detrimental effects of the COVID-19 pandemic on laparoscopic training</p

Proposed framework for recovery.

Proposed framework for recovery.</p

Impact on training.

Impact on training.</p