In the formation of amyloid fibrils from small peptides, the appearance of superhelices of (P)- or (M)-helicity has been observed for the first time; high concentrations of the peptides and extended periods of incubation at physiological pH appear to be important for this phenomenon. In view of the general importance of peptide and protein aggregation, we give a brief overview with selected examples for demonstration.

Truncation of A13-A419 fragment shows that fibrous structures are formed by all peptides bearing (13)H-LeuTyr-OH(14). Propensity to aggregation was found for (16)H-TyrLeu-OH(17) B12-B17 fragment. Tyrosine residue modification by incorporation of tert-butyl group on hydroxyl function gave analogues still predisposed to aggregation.

Dual action alkyl(aryl)amino-1,3,5-triazines functionalized with nitrogen mustards were obtained by treating 2-alkyl(aryl) amino-4-chloro-6-methoxy-1,3,5-triazines with amines or amino acid methyl esters, followed by reactions with 1,4-diazabicyclo[2.2.2]octane (DABCO) and rearrangement with an opening diazabicyclic fragment, leading to the formation of 2-chloroethylamino moiety. In vitro antitumor activity was tested in the standard human breast cancer MCF-7 and MDA-MB-231cell lines using flow cytometry, based on the detection of apoptosis through qualitative analysis of morphological changes, DNA fragmentation, DNA loss and membrane changes. For all the compounds studied, induced apoptosis was substantially stronger than necrosis at concentrations of both 5 μM and 50 μM, and in some cases there was no increase in necrotic cell death for the estrogen dependent MCF-7 cell line. The most active compounds were derivatives of triazine substituted with phenylamine (IC50 = 12.30 μM) and/or p-tolylamine fragments (IC50 = 7.40 μM).

In this study, three independent methods were used to identify short fragment of both chains of human insulin which are prone for aggregation. In addition, circular dichroism (CD) research was conducted to understand the progress of aggregation over time. The insulin fragments (deca- and pepta-peptides) were obtained by solid-phase synthesis using 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium toluene-4-sulfonate (DMT/NMM/TosO-) as a coupling reagent. Systematic studies allowed identification of the new fragments, expected to be engaged in triggering aggregation of the entire structure of human insulin under physiological conditions. It was found that the aggregation process occurs through various structural conformers and may favor the formation of a fibrous structure of aggregate.

In this study, N-methylated analogs of hot-spots of insulin were designed and synthesized, in the expectation that they would inhibit the aggregation of both insulin hot-spots and the entire hormone. Synthesis of insulin “amyloidogenic” analogs containing N-methylated amino acid residues was performed by microwave-assisted solid phase according to the Fmoc/tert-Bu strategy. As a coupling reagent 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium toluene-4-sulfonate (DMT/NMM/TosO-) was used. Three independent methods were applied in aggregation studies of the complexes of insulin with its N-methylated peptides. Additionally, circular dichroism (CD) measurements were used to confirm that aggregation processes did not occur in the presence of the N-methylated analogs of hot-spot insulin fragments, and that insulin retains its native conformation. Of the seven N-methylated analogs of the A- and B-chain hot-spots of insulin, six inhibited insulin aggregation (peptides 1 and 3–7). All tested peptides were found to have a lower ability to inhibit the aggregation of insulin hot-spots compared to the capability to inhibit native hormone aggregation.