From peptides to non-peptide peptidomimetics: design and synthesis of new piperidine inhibitors of aspartic peptidases

Isolation and Structural Characterization of Stable Carbamic-Carbonic Anhydrides: An Experimental and Computational Study

Carbamic-carbonic anhydrides are elusive species that have been only indirectly detected under controlled conditions. This functional group is transiently formed during the reaction of secondary amines with anhydrides in the...

Challenges in the design of insulin and relaxin/insulin-like peptide mimetics

Peptidomimetics are designed to overcome the poor pharmacokinetics and pharmacodynamics associated with the native peptide or protein on which they are based. The design of peptidomimetics starts from developing structure-activity relationships of the native ligand-target pair that identify the key residues that are responsible for the biological effect of the native peptide or protein. Then minimization of the structure and introduction of constraints are applied to create the core active site that can interact with the target with high affinity and selectivity. Developing peptidomimetics is not trivial and often challenging, particularly when peptides' interaction mechanism with their target is complex. This review will discuss the challenges of developing peptidomimetics of therapeutically important insulin superfamily peptides, particularly those which have two chains (A and B) and three disulfide bonds and whose receptors are known, namely insulin, H2 relaxin, H3 relaxin, INSL3 and INSL5.

Catalytic Michael/Ring-Closure Reaction of α,β-Unsaturated Pyrazoleamides with Amidomalonates: Asymmetric Synthesis of (-)-Paroxetine

A highly enantioselective tandem Michael/ring-closure reaction of α,β-unsaturated pyrazoleamides and amidomalonates has been accomplished in the presence of a chiral N,N'-dioxide-Yb(OTf)₃ complex (Tf: trifluoromethanesulfonyl) to give various substituted chiral glutarimides with high yields and diastereo- and enantioselectivities. Moreover, this methodology could be used for gram-scale manipulation and was successfully applied to the synthesis of (-)-paroxetine. Further nonlinear and HRMS studies revealed that the real catalytically active species was a monomeric L-PMe₂ -Yb³⁺ complex. A plausible transition state was proposed to explain the origin of the asymmetric induction.

Synthesis and biological activities of some new (Nα-dinicotinoyl)-bis-L-leucyl linear and macrocyclic peptides

A series of linear and macrocyclic peptides 3–12 were synthesized using 3,5-pyridinedicarboxylic acid (1) as starting material and screened for their antimicrobial, anti-inflammatory and anticancer activities. Bis-ester 3 was prepared from 1 and l-leucine methyl ester. Hydrazinolysis and hydrolysis of dipeptide methyl ester 3 with hydrazine hydrate or 1 N sodium hydroxide afforded compounds 4 and 5, respectively. Cyclization of the dipeptide 5 with l-lysine methyl ester afforded cyclic pentapeptide ester 6. Compounds 7–9 were synthesized by reacting hydrazide 4 with phthalic anhydride, 1,8-naphthalene anhydride or acetophenone derivatives. Treatment of acid hydrazide 4 with aromatic aldehydes or tetraacid dianhydrides afforded the corresponding bis-dipeptide hydrazones 10a–e and macrocyclic peptides 11 and 12, respectively. The structures of newly synthesized compounds were confirmed by IR, ¹H-NMR, MS spectral data and elemental analysis. The detailed synthesis, spectroscopic data, biological and pharmacological activities of the synthesized compounds was reported.

Stereospecific construction of substituted piperidines. Synthesis of (−)-paroxetine and (+)-laccarin

Short and efficient enantioselective syntheses of (-)-paroxetine and (+)-laccarin are described based on the highly stereospecific cleavage of C(3)-substituted 1,3-cyclic sulfamidates.

Acylguanidines as Small-Molecule β-Secretase Inhibitors

BACE1 is an aspartyl protease responsible for cleaving amyloid precursor protein to liberate Abeta, which aggregates leading to plaque deposits implicated in Alzheimer's disease. We have identified small-molecule acylguanidine inhibitors of BACE1. Crystallographic studies show that these compounds form unique hydrogen-bonding interactions with the catalytic site aspartic acids and stabilize the protein in a flap-open conformation. Structure-based optimization led to the identification of potent analogs, such as 10d (BACE1 IC(50) = 110 nM).

The discovery and preparation of disubstituted novel amino-aryl-piperidine-based renin inhibitors

Recently, trans-disubstituted oxo-aryl-piperidines have been identified as small molecule nonpeptide renin inhibitors for the modulation of hypertension. Herein, we report on the discovery and preparation of a new class of novel cis-disubstituted amino-aryl-piperidines as a mixture of enantiomers that are potent in vitro renin inhibitors and also, possess in vivo antihypertensive activity in a double transgenic mouse model.

Direct Synthesis of 4-Arylpiperidines via Palladium/Copper(I)-Cocatalyzed Negishi Coupling of a 4-Piperidylzinc Iodide with Aromatic Halides and Triflates

A general procedure for the synthesis of 4-arylpiperidines via the coupling of 4-(N-BOC-piperidyl)zinc iodide with aryl halides and triflates is presented. The reaction requires cocatalysis with both Cl(2)Pd(dppf) and a copper(I) species. An improved, safer procedure for the activation of zinc dust is also presented.

Medicinal chemistry in academia: molecular recognition with biological receptors

Why carry out medicinal chemistry at a university, when it means competing with the billion-dollar research efforts of the pharmaceutical industry? In academic research, the race to get a drug to market is not the prime motivation. Instead, university-based medicinal chemistry is driven by the search for new knowledge and the opportunity to educate a new generation of chemists. Furthermore, academia can complement commercial efforts by addressing diseases neglected by private industry.

Novel antibiotics: macrocyclic peptides designed to trap Holliday junctions

[reaction: see text] Described are the syntheses of eight macrocyclic peptides designed to trap Holliday junctions in bacteria, thereby inhibiting bacterial growth. These macrocycles were designed from linear dimerized hexapeptides that bind to the C-2 symmetrical Holliday junction. They were synthesized from three monomers using a combinatorial-like strategy that permits elucidation of the monomer role in accumulation of Holliday junctions and antibiotic activity. These macrocycles are an important step in designing and synthesizing a new class of antibiotics.

Discovery of nonpeptide, peptidomimetic peptidase inhibitors that target alternate enzyme active site conformations

Structure-generating programs provide rational methods to rapidly design novel scaffolds targeting the biologic receptor of choice. Recent research has demonstrated proteins equilibrate between families of conformations (ensembles) for which drug design may target. New methods are currently being developed utilizing structure-generating programs to target alternate enzyme conformations in an attempt to overcome the challenge of developing therapeutically useful molecules. These new methods provide the potential to overcome bioavailability problems encountered with peptide and peptide-like molecules by identifying novel small molecule scaffolds.

Novel inhibition of porcine pepsin by a substituted piperidine. Preference for one of the enzyme conformers

Pepsin inhibition by 3-alkoxy-4-arylpiperidine (substituted piperidine; (3R,4R)-3-(4-bromobenzyloxy)-4-[4-(2-naphthalen-1-yl-2-oxo-ethoxy)phenyl]piperidine) has been studied using steady-state kinetic and pre-equilibrium binding methods. Data were compared with pepstatin A, a well known competitive inhibitor of pepsin. Steady-state analysis reveals that the substituted piperidine likewise behaves as a competitive inhibitor. Pre-equilibrium binding studies indicate that the substituted piperidine can displace a fluorescently labeled statine inhibitor from the enzyme active site. Simulation of the stopped-flow fluorescence transients provided estimates of the K(d) values of 1.4 +/- 0.2 microm and 39 +/- 2 nm for the piperidine and the fluorescently labeled statine, respectively. The effects of combinations of these two inhibitors resulted in a series of parallel lines when plotted by the method of Yonetani and Theorell (Yonetani, T., and Theorell, H. (1964) Arch. Biochem. Biophys. 106, 234-251), suggesting that the two inhibitors bind in a mutually exclusive fashion to pepsin. Fitting of the entire data set to the appropriate equation yielded an alpha factor of 8 +/- 1. The magnitude of this factor ( infinity > alpha > 1) can be explained by a conformational distinction between the enzyme species that bind each inhibitor. The effects of pH on the inhibition constants for pepstatin A and the substituted piperidine also suggest that the inhibitors bind to distinct conformational forms of the enzyme. No inhibition by the piperidine was observed at acidic pH, while pepstatin A inhibition is maximal at low pH values. Inhibition by the piperidine was maximal when a group with pK 4.8 +/- 0.2 was deprotonated and another group with pK 5.9 +/- 0.2 was protonated. Most likely these two groups are the catalytic aspartates with perturbed ionization properties as a result of a significant and unique conformational change. Taken together, these data suggest that the enzyme can readily interconvert between two conformers, one capable of binding substrate and pepstatin A and the other capable of binding the substituted piperidine.

Solid-phase synthesis of aspartic peptidase inhibitors: 3-alkoxy-4-aryl piperidines

[reaction: see text]. The 3-alkoxy-4-aryl piperidines are non-peptide peptidomimetic inhibitors of several aspartic peptidases. The solid-phase functionalization of 3,4-disubstituted piperidine scaffolds using a traceless linker strategy is described. Synthesis of diverse analogues based on this scaffold provides the potential to generate selective inhibitors of this important class of peptidase.