The self-assembly of N-and C-protected alternating L/L and D/L amino acids containing dipeptides, Boc-L-Val-L-Ile-OMe (1), Boc-D-Val-L-Ile-OMe (2), Boc-L-Ile-L-Val-OMe (3), and Boc-L-Ile-D-Val-OMe (4) has been investigated. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) images indicated that 1 and 3 self-associated to form highly organized straight net microrods, whereas 2 and 4 self-assembled to form hexagonal hollow microtube-like architecture in the acetonitrile-water medium. To understand the physical basis of such differential behavior, we performed X-ray diffraction pattern analyses. The singlecrystal X-ray diffraction (SC-XRD) study revealed that 1 and 2 self-assembled to form slightly different helix-like architectures. The higher-order association of 2 exhibited a hollow hexagonal tube-like superstructure. The thermal stability of the nanostructures also varied based on the chiroptical composition of the dipeptides. Experimental findings were corroborated well with computational studies. The obtained results may be helpful in nano-biotechnology as well as in material science.

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A mild, practical, and straight forward method for Boc deprotection and its use in peptide synthesis both in solution and on solid support is presented. Boc protecting group is removed from the N‐terminal amino acid of the amino acid and the peptide using environment‐friendly cost‐effective Lewis acid, FeCl3. The deprotected amino group undergoes C−N bond formation with the next Boc‐protected amino acid in the presence of a suitable coupling reagent and base. A library of di‐ to tetrapeptides is synthesized with moderate to good yield from standard and nonstandard Boc‐protected amino acids in solution. Most importantly, this protocol can be used for the solid‐phase peptide synthesis (SPPS) using Boc‐protected amino acids on the acid‐sensitive Rink amide resin, which is usually used for Fmoc chemistry. This protocol thus allows practicing Boc chemistry in a greener manner, and on‐demand switching from Fmoc to Boc chemistry and vice‐versa while synthesizing one oligopeptide on the same resin. The inherent orthogonality of Fmoc and Boc chemistry allows facile synthesis of branched and cyclized peptides on the resin as well.

An efficient, convenient, and selective Lewis acid-based strategy for on-resin deprotection of the side chain tert -butyl-protected aspartic acid and glutamic acid of a peptide is achieved. The method is mild, cost-effective, and Fmoc chemistry compatible and allows on-resin incorporation of amides, esters, and thioesters in good yield. This method will find wide applicability in peptide and protein modification because it enriches the toolbox of orthogonal protection/deprotection techniques.

The self-assembly properties of all possible stereoisomers of terminally protected Boc-Val-Phe-Phe-OMe, having sequence homogeneity with Alzheimer's amyloidbeta (Aβ 18-20 ) peptide was investigated. The morphology analysis by field emission scanning microscope (FE-SEM) revealed that protected VFF and vff (small letters denote one letter code of D-amino acids) exhibited a ribbon-like fibrous network, vFF, Vff, VfF, and vFf formed rod-like structures. Although VFf exhibited a mixture of two morphologies (rod-like and spherical), vfF showed spherical structures predominantly. The single-crystal X-ray diffraction (SC-XRD) indicated that five of the stereoisomers formed a parallel beta-sheet arrangement. In higher-order packing, while Vff, VfF, and vFf exhibited supramolecular sheet-like architecture, VFf and vfF pair showed helical sheet-like arrangement. All corresponding enantiomers displayed identical morphology but opposite conformation. The chirality of amino acids in peptides played a significant role in their supramolecular arrangements. Interestingly, all self-aggregated peptides can bind with amyloid binding dye thioflavin T.