Functionally selective signaling and broad metabolic benefits by novel insulin receptor partial agonists

Insulin analogs have been developed to treat diabetes with focus primarily on improving the time action profile without affecting ligand-receptor interaction or functional selectivity. As a result, inherent liabilities (e.g. hypoglycemia) of injectable insulin continue to limit the true therapeutic potential of related agents. Insulin dimers were synthesized to investigate whether partial agonism of the insulin receptor (IR) tyrosine kinase is achievable, and to explore the potential for tissue-selective systemic insulin pharmacology. The insulin dimers induced distinct IR conformational changes compared to native monomeric insulin and substrate phosphorylation assays demonstrated partial agonism. Structurally distinct dimers with differences in conjugation sites and linkers were prepared to deliver desirable IR partial agonist (IRPA). Systemic infusions of a B29-B29 dimer in vivo revealed sharp differences compared to native insulin. Suppression of hepatic glucose production and lipolysis were like that attained with regular insulin, albeit with a distinctly shallower dose-response. In contrast, there was highly attenuated stimulation of glucose uptake into muscle. Mechanistic studies indicated that IRPAs exploit tissue differences in receptor density and have additional distinctions pertaining to drug clearance and distribution. The hepato-adipose selective action of IRPAs is a potentially safer approach for treatment of diabetes.

NMR Assessment of Therapeutic Peptides and Proteins: Correlations That Reveal Interactions and Motions

NMR measurements of rotational and translational diffusion are used to characterize the solution behavior of a wide variety of therapeutic proteins and peptides. The timescales of motions sampled in these experiments reveal complicated intrinsic solution behavior such as flexibility, that is central to function, as well as self-interactions, stress-induced conformational changes and other critical attributes that can be discovery and development liabilities. Trends from proton transverse relaxation (R₂ ) and hydrodynamic radius (R_h ) are correlated and used to identify and differentiate intermolecular from intramolecular interactions. In this study, peptide behavior is consistent with complicated multimer self-assembly, while multi-domain protein behavior is dominated by intramolecular interactions. These observations are supplemented by simulations that include effects from slow transient interactions and rapid internal motions. R₂ -R_h correlations provide a means to profile protein motions as well as interactions. The approach is completely general and can be applied to therapeutic and target protein characterization.

Site-Selective Synthesis of Insulin Azides and Bioconjugates

A synthetic method to access novel azido-insulin analogs directly from recombinant human insulin (RHI) was developed via diazo-transfer chemistry using imidazole-1-sulfonyl azide. Systematic optimization of reaction conditions led to site-selective azidation of amino acids B1-phenylalanine and B29-lysine present in RHI. Subsequently, the azido-insulin analogs were used in azide-alkyne [3 + 2] cycloaddition reactions to synthesize a diverse array of triazole-based RHI bioconjugates that were found to be potent human insulin receptor binders. The utility of this method was further demonstrated by the concise and controlled synthesis of a heterotrisubstituted insulin conjugate.

Discovery of Novel Tricyclic Heterocycles as Potent and Selective DPP-4 Inhibitors for the Treatment of Type 2 Diabetes

In our efforts to develop second generation DPP-4 inhibitors, we endeavored to identify distinct structures with long-acting (once weekly) potential. Taking advantage of X-ray cocrystal structures of sitagliptin and other DPP-4 inhibitors, such as alogliptin and linagliptin bound to DPP-4, and aided by molecular modeling, we designed several series of heterocyclic compounds as initial targets. During their synthesis, an unexpected chemical transformation provided a novel tricyclic scaffold that was beyond our original design. Capitalizing on this serendipitous discovery, we have elaborated this scaffold into a very potent and selective DPP-4 inhibitor lead series, as highlighted by compound 17c.

2'-Modified Guanosine Analogs for the Treatment of HCV

Novel 2'-modified guanosine nucleosides were synthesized from inexpensive starting materials in 7-10 steps via hydroazidation or hydrocyanation reactions of the corresponding 2'-olefin. The antiviral effectiveness of the guanosine nucleosides was evaluated by converting them to the corresponding 5'-O-triphosphates (compounds 38-44) and testing their biochemical inhibitory activity against the wild-type NS5B polymerase.

Synthesis and SAR Studies of Fused Oxadiazines as γ-Secretase Modulators for Treatment of Alzheimer's Disease

Fused oxadiazines (3) were discovered as selective and orally bioavailable γ-secretase modulators (GSMs) based on the structural framework of oxadiazoline GSMs. Although structurally related, initial modifications showed that structure-activity relationships (SARs) did not translate from the oxadiazoline to the oxadiazine series. Subsequent SAR studies on modifications at the C3 and C4 positions of the fused oxadiazine core helped to identify GSMs such as compounds 8r and 8s that were highly efficacious in vitro and in vivo in a number of animal models with highly desirable physical and pharmacological properties. Further improvements of in vitro activity and selectivity were achieved by the preparation of fused morpholine oxadiazines. The shift in specificity of APP cleavage rather than a reduction in overall γ-secretase activity and the lack of changes in substrate accumulation and Notch processing as observed in the animal studies of compound 8s confirm that the oxadiazine series of compounds are potent GSMs.

Advances in gamma-secretase modulation

Inhibition of the production of insoluble amyloid-Beta (ABeta) is a widely pursued strategy for the treatment of Alzheimer's disease (AD). The final step in the generation of ABeta from the amyloid precursor protein (APP) involves cleavage by gamma-secretase, and gamma-secretase inhibitors (GSIs) have been shown to reduce the amyloid burden in animal models of AD. Unfortunately, GSIs also cause inhibition of the cleavage of other gamma-secretase substrates, including Notch, while the co-inhibition of Notch processing by GSIs in animal studies was observed to result in a gamut of side effects. A new class of compounds, known as gamma-secretase modulators (GSMs), inhibit the amyloidogenic function of gamma-secretase without interfering in the processing of Notch and other substrates. While the exact reason for the selectivity of these agents remains unclear, they are thought to intervene at an allosteric site on gamma-secretase and cause a shift of the preferred APP cleavage site so that shorter, more soluble peptides (eg, ABeta(38)) are produced instead of the highly insoluble ABeta(42). This review describes the history of the discovery of GSMs and the current medicinal chemistry efforts aimed at providing clinically useful GSM compounds.

Phosphodiesterase 5 (PDE 5) inhibitors for the treatment of male erectile disorder: Attaining selectivity versus PDE6

The role of phosphodiesterase type 5 (PDE5) in the mechanism of male erection has been well understood, and several drugs inhibiting this enzyme are being used for the treatment of erectile dysfunction (ED). Discovery of inhibitors with improved selectivity versus other PDE isozymes could lead to drugs with improved safety profile. Achievement of selectivity versus PDE6, co-inhibition of which results in disturbances of color perception, remains the most challenging aspect of current drug discovery programs. The present review describes several case studies, where significant (>100 fold) selectivity versus PDE6 has been attained via investigation of structure-activity relationships (SAR). Special attention is given to the chemical routes leading to novel chemotypes and allowing efficient exploration of their SAR's. Strategies for attaining inhibitor selectivity discussed below may be applicable for other drug discovery programs.

Design and synthesis of xanthine analogues as potent and selective PDE5 inhibitors

We have discovered potent and selective xanthine PDE5 inhibitors. Compound 25 (PDE5 IC(50)=0.6 nM, PDE6/PDE5=101) demonstrated similar functional efficacy and PK profile to Sildenafil (PDE5 IC(50)=3.5 nM, PDE6/PDE5=7).

A Modular Enantioselective Approach to Construction of the Macrolactone Core of Polycavernoside A

A program directed toward a total synthesis of polycavernoside A is described. The synthesis of five building blocks is detailed. The first of two electrophilic units, the lactone 3, was prepared in four steps from the known enantiomerically pure oxirane 15. Pyranyl aldehyde 5 was elaborated in turn from L-malic acid via 10. While the route to 30 involved 3 as a starting material, dithiane 2 was obtained in a straightforward manner from 10 as well. The merging of the chiral sectors could not be accomplished by way of the lithiated dithianyl anions, presumably as a consequence of their heightened basicity. The strategic incorporation of the trienyl sector was accomplished, although no attempt was made to control the diastereoselectivity of the process.