New methods for solid phase peptide synthesis of transitionstate analog inhibitors of HIV-1 protease and DPP-IV

Summary A new and stereoselective method to synthesize hydroxyethylamine and hydroxymethylamide peptide bond isosteres is developed. The key step is the addition of 2-trimethylsilylthiazole to -aminoaldehydes, followed by transformation to -hydroxy--aminoaldehydes. The stereochemistry of the addition can be manipulated by the choice of the nitrogen substitution. The isosteres are easily synthesized via Solid Phase Peptide Synthesis, which rapidly gives the desired pseudopeptides.     

Thermodynamic and kinetic characterization of hydroxyethylamine β-secretase-1 inhibitors

Alzheimer’s disease (AD) is a devastating neurodegenerative disease affecting millions of people. β-Secretase-1 (BACE-1), an enzyme involved in the processing of the amyloid precursor protein (APP) to form Aβ, is a well validated target for AD. Herein, the authors characterize 10 randomly selected hydroxyethylamine (HEA) BACE-1 inhibitors in terms of their association and dissociation rate constants and thermodynamics of binding using surface plasmon resonance (SPR). Rate constants of association (k_a) measured at 25 °C ranged from a low of 2.42 × 10⁴ M⁻¹ s⁻¹ to the highest value of 8.3 × 10⁵ M⁻¹ s⁻¹. Rate constants of dissociation (k_d) ranged from 1.09 × 10⁻⁴ s⁻¹ (corresponding to a residence time of close to three hours), to the fastest of 0.028 s⁻¹. Three compounds were selected for further thermodynamic analysis where it was shown that equilibrium binding was enthalpy driven while unfavorable entropy of binding was observed. Structural analysis revealed that upon ligand binding, the BACE-1flap folds down over the bound ligand causing an induced fit. The maximal difference between alpha carbon positions in the open and closed conformations of the flap was over 5 Å. Thus the negative entropy of binding determined using SPR analysis was consistent with an induced fit observed by structural analysis.     

Effect of prime-site sequence of retro-inverso-modified HTLV-1 protease inhibitor

The effects of additional substituents covering the prime-site of retro-inverso (RI)-modified HTLV-1 protease inhibitors containing a hydroxyethylamine isoster were clarified. Stereo-selective construction of the most potent isoster backbone was achieved by the Evans-aldol reaction. Addition of N-acetylated d-amino acid corresponding to the P₂′ site gave an RI-modified inhibitor showing superior inhibitory activity to the previous inhibitor. Inhibitory activities of the newly synthesized inhibitors suggest that partially modified RI inhibitors would interact with HTLV-1 protease in the same manner as the parent hydroxyethylamine inhibitor.     

Functionalized hydroxyethylamine based peptide nanostructures as potential inhibitors of falcipain-3, an essential proteases of Plasmodium falciparum

Self-assembled peptide based nanostructures gained enough popularity due to their easy biocompatibility and numerous potential applications. An excellent model of self-assembly of hydroxyethylamine based peptide nanostructures was synthesized and characterized by DLS and TEM. Spherical nano structures of I and III were observed with particle size ～50 and ～80 nm, respectively. Further, I and III were screened against anti-malarial target, falcipain-3 (FP3), a crucial cysteine protease involved as a major hemoglobinase of Plasmodium falciparum. Interestingly, compound III completely inhibited the activity of FP3. The effective concentration (1.5 μM) of III found to be more potent than I. This biochemical result was substantiated by molecular-docking studies indicating III to be best inhibitor of FP3. This is the first report showing that bis hydroxethylamine based peptide nanostructures could be very effective inhibitor of malarial cysteine proteases.     

Design and synthesis of hydroxyethylamine (HEA) BACE-1 inhibitors: Prime side chromane-containing inhibitors

The structure activity relationship of the prime region of conformationally restricted hydroxyethylamine (HEA) BACE inhibitors is described. Variation of the P1′ region provided selectivity over Cat-D with a series of 2,2-dioxo-isothiochromanes and optimization of the P2′ substituent of chromane–HEA(s) with polar substituents provided improvements in the compound’s in vitro permeability. Significant potency gains were observed with small aliphatic substituents such as methyl, n-propyl, and cyclopropyl when placed at the C-2 position of the chromane.     

Structure based design, synthesis and SAR of cyclic hydroxyethylamine (HEA) BACE-1 inhibitors

This Letter describes the de novo design of non-peptidic hydroxyethylamine (HEA) inhibitors of BACE-1 by elimination of P-gp contributing amide attachments. The predicted binding mode of the novel cyclic sulfone HEA core template was confirmed in a X-ray co-crystal structure. Inhibitors of sub-micromolar potency with an improved property profile over historic HEA inhibitors resulting in improved brain penetration are described.     

Design and synthesis of cell potent BACE-1 inhibitors: Structure–activity relationship of P1′ substituents

Using structure-guided design, hydroxyethylamine BACE-1 inhibitors were optimized to nanomolar Aβ cellular inhibition with selectivity against cathepsin-D. X-ray crystallography illuminated the S1′ residues critical to this effort, which culminated in compounds 56 and 57 that exhibited potency and selectivity but poor permeability and high P-gp efflux.     

Antiplasmodial activity of hydroxyethylamine analogs: Synthesis,biological activity and structure activity relationship of plasmepsin inhibitors

Malaria, particularly in endemic countries remains a threat to the human health and is the leading the cause of mortality in the tropical and sub-tropical areas. Herein, we explored new C₂ symmetric hydroxyethylamine analogs as the potential inhibitors of Plasmodium falciparum (P. falciparum; 3D7) in in-vitro cultures. All the listed compounds were also evaluated against crucial drug targets, plasmepsin II (Plm II) and IV (Plm IV), enzymes found in the digestive vacuole of the P. falciparum. Analog 10f showed inhibitory activities against both the enzymes Plm II and Plm IV (K_i, 1.93?±?0.29?µM for Plm II; K_i, 1.99?±?0.05?µM for Plm IV). Among all these analogs, compounds 10g selectively inhibited the activity of Plm IV (K_i, 0.84?±?0.08?µM). In the in vitro screening assay, the growth inhibition of P. falciparum by both the analogs (IC₅₀, 2.27?±?0.95?µM for 10f; IC₅₀, 3.11?±?0.65?µM for 10g) displayed marked killing effect. A significant growth inhibition of the P. falciparum was displayed by analog 12c with IC₅₀ value of 1.35?±?0.85?µM, however, it did not show inhibitory activity against either Plms. The hemolytic assay suggested that the active compounds selectively inhibit the growth of the parasite. Further, potent analogs (10f and 12c) were evaluated for their cytotoxicity towards mammalian HepG2 and vero cells. The selectivity index (SI) values were noticed greater than 10 for both the analogs that suggested their poor toxicity. The present study indicates these analogs as putative lead structures and could serve as crucial for the development of new drug molecules.