Nanofibers from oxazolidi-2-one containing hybrid foldamers: what is the right molecular size?

A series of oligomers of the type Boc-(L-Phe-D-Oxd)(n)-OBn (Boc = tert-butoxycarbonyl; Oxd = 4-methyl-5-carboxy oxazolidin-2-one; Bn = benzyl) were prepared for n = 2-5. The shortest oligomer, Boc-(L-Phe-D-Oxd)(2)-OBn, aggregates and forms a fiber-like material with an anti-parallel beta-sheet structure in which the oligopeptide units are connected to each other by only one intermolecular hydrogen bond. The longer oligomers exhibit structural heterogeneity. They start to organize into secondary structures by the formation of intramolecular hydrogen bonds at the pentamer level. Microscopy and diffraction of the oligomers indicated a crystalline character for only the shorter ones.