Succinate- and cyclopropane-derived phosphotyrosine (pY) replacements were incorporated into a series of Grb2 SH2 binding ligands wherein the pY+1 residue was varied to determine explicitly how variations in ligand preorganization affect binding energetics and structure. The complexes of these ligands with the Grb2 SH2 domain were examined in a series of thermodynamic and structural investigations using isothermal titration calorimetry and X-ray crystallography. The binding enthalpies for all ligands were favorable, and although binding entropies for all ligands having a hydrophobic residue at the pY+1 site were favorable, binding entropies for those having a hydrophilic residue at this site were unfavorable. Preorganized ligands generally bound with more favorable Gibbs energies than their flexible controls, but this increased affinity was the consequence of relatively more favorable binding enthalpies. Unexpectedly, binding entropies of the constrained ligands were uniformly disfavored relative to their flexible controls, demonstrating that the widely held belief that ligand preorganization should result in an entropic advantage is not necessarily true. Crystallographic studies of complexes of several flexible and constrained ligands having the same amino acid at the pY+1 position revealed extensive similarities, but there were some notable differences. There are a greater number of direct polar contacts in complexes of the constrained ligands that correlate qualitatively with their more favorable binding enthalpies and Gibbs energies. There are more single water-mediated contacts between the domain and the flexible ligand of each pair; although fixing water molecules at a protein-ligand interface is commonly viewed as entropically unfavorable, entropies for forming these complexes are favored relative to those of their constrained counterparts. Crystallographic b-factors in the complexes of constrained ligands are greater than those of their flexible counterparts, an observation that seems inconsistent with our finding that entropies for forming complexes of flexible ligands are relatively more favorable. This systematic study highlights the profound challenges and complexities associated with predicting how structural changes in a ligand will affect enthalpies, entropies, and structure in protein-ligand interactions.

A prevailing hypothesis in the field of molecular recognition in chemistry and biology is that the preorganization of flexible hosts and their guests in a manner corresponding to the three-

No abstract

A prevailing hypothesis in the field of molecular recognition in chemistry and biology is that the preorganization of flexible hosts and their guests in a manner corresponding to the three-

The importance of providing safe and effective delayed-and extended-release oral formulations that can replace products requiring multiple administrations has been continually cited as an area in need of improvement for pharmaceutical companies. Such controlled release challenges become especially critical when they must be adapted for paediatrics, those suffering from dysphagia, or patients with specific dosage administration limitations. More often than not, lack of palatability and taste-masking compound this formulation challenge. Many particulate approaches show promise, but can be fraught with broad particle size distributions, initial drug burst, poor drug entrapment efficiency, low drug loading, and limited scalability. Here, we summarize the key factors that drive formulation development of format-flexible controlled-release oral powders, and the manufacturing aspects involved with some of the foremost marketed products, including next-generation singlestep layered powder manufacturing (below). Keywords: powder, particle, microsphere, taste-masking, paediatric, controlled-release The dosage form problemThe importance of providing safe, effective, and proven medicines for populations with dysphagia, such as children, geriatrics, and those suffering from debilitating illnesses, has been continually cited as an area in need of improvement for pharmaceutical companies and the providers who administer their product (Bergstrom D. et al., 2004;Bhardwaj S. and Hayward M., 1996;Cram A. et al., 2013;Dickens D.S. et al., 2008;Engelen L. et al., 2005;Imai E. et al., 1995;Ivanovska V. et al., 2014;Lopez F.L. et al., 2015;Matsui D., 2007;Milne C.P. and Bruss J.B., 2008;Rocca J.G. and Park K., 2004;Sugao H., 1997;Tyle P., 1993). The widespread lack of dispersed format oral products, however, forces clinicians and pharmacists to use alternative solutions to treat their patients that are not always backed by supporting bioavailability, stability, and safety studies. Tablets are sometimes administered extemporaneously by crushing the dosage form and mixing with food or drink. Not only are these delivery methods inconsistent, they often lead to dosing errors, decreased bioavailability or efficacy, and non-adherence because of foul-tasting active pharmaceutical ingredients (APIs) (Jayanthi B. and Manna P., 2011;Osterberg L. and Blaschke T., 2005;Sansom L., 1999;Schier J. et al., 2003).Due to taste and efficacy concerns, The Institute for Safe Medical Practices (ISMP) has issued a "Do Not Crush" list, which highlights over 400 dosage forms that cannot be compounded due to special controlled-release properties, taste-masking, or API protection (Bergstrom D. et al., 2004;Bhardwaj S. and Hayward M., 1996;Dickens D.S. et al., 2008;Engelen L. et al., 2005;Imai E. et al., 1995;Matsui D., 2007;Milne C.P. and Bruss J.B., 2008;Rocca J.G. and Park K., 2004;Sugao H., 1997;Tyle P., 1993). Lack of titratable and palatable formulations affects over half of the global population (under 18 and over 65 years of age) and can subject ...