Transient soluble oligomers of amyloid-β (Aβ) are toxic and accumulate early prior to insoluble plaque formation and cognitive impairment in Alzheimer’s disease (AD). Synthetic cyclic D,L-α-peptides (e.g., 1 ) self-assemble into cross β-sheet nanotubes, react with early Aβ species (1-3 mers), and inhibit Aβ aggregation and toxicity in stoichiometric concentrations, in vitro. Employing a semicarbazide as an aza-glycine residue with an extra hydrogen-bond donor to tune nanotube assembly and amyloid engagement, [azaGly 6 ]- 1 inhibited Aβ aggregation and toxicity at substoichiometric concentrations. High-resolution NMR studies revealed dynamic interactions between [azaGly 6 ]- 1 and Aβ42 residues F19 and F20, which are pivotal for early dimerization and aggregation. In an AD mouse model, brain positron emission tomography (PET) imaging using stable 64 Cu-labeled (aza)peptide tracers gave unprecedented early amyloid detection in 44-d presymptomatic animals. No tracer accumulation was detected in the cortex and hippocampus of 44-d-old 5xFAD mice; instead, intense PET signal was observed in the thalamus, from where Aβ oligomers may spread to other brain parts with disease progression. Compared with standard 11 C-labeled Pittsburgh compound-B ( 11 C-PIB), which binds specifically fibrillar Aβ plaques, 64 Cu-labeled (aza)peptide gave superior contrast and uptake in young mouse brain correlating with Aβ oligomer levels. Effectively crossing the blood–brain barrier (BBB), peptide 1 and [azaGly 6 ]- 1 reduced Aβ oligomer levels, prolonged lifespan of AD transgenic Caenorhabditis elegans , and abated memory and behavioral deficits in nematode and murine AD models. Cyclic (aza)peptides offer novel promise for early AD diagnosis and therapy.

Fifteen N-aminoimidazolone (Nai) dipeptides having a variety of 5-position side-chain groups were synthesized by regioselective proline-catalyzed reactions of azopeptide and aldehyde components followed by acid-mediated dehydration of an aza-aspartate semialdehyde intermediate. The introduction of 5-aryl-Nai dipeptides into cluster of differentiation 36 receptor (CD36) peptide ligands has provided insight into the conformation responsible for binding affinity and anti-inflammatory activity.

Transient soluble oligomers of amyloid-β (Aβ) are considered among the most toxic species in Alzheimer's disease (AD). Soluble Aβ oligomers accumulate early prior to insoluble plaque formation and cognitive impairment. The cyclic D,L-αpeptide CP-2 (1) self-assembles into nanotubes and demonstrates promising anti-amyloidogenic activity likely by a mechanism involving engagement of soluble oligomers. Systematic replacement of the residues in peptide 1 with aza-amino acid counterparts was performed to explore the effects of hydrogen bonding on propensity to mitigate Aβ aggregation and toxicity. Certain azapeptides exhibited improved ability to engage, alter the secondary structure, and inhibit aggregation of Aβ. Moreover, certain azapeptides disassembled preformed Aβ fibrils and protected cells from Aβ-mediated toxicity. Substitution of the L-norleucine 3 and D-serine 6 residues in peptide 1 with aza-norleucine and aza-homoserine provided, respectively, nontoxic [azaNle 3 ]-1 (4) and [azaHse 6 ]-1 (7), that significantly abated symptoms in a transgenic Caenorhabditis elegans AD model by decreasing Aβ oligomer levels.