Solid‐State Properties and Vibrational Circular Dichroism Spectroscopy in Solution of Hybrid Foldamers Stereoisomeric Mixtures

November 2, 2018

Title

Solid‐State Properties and Vibrational Circular Dichroism Spectroscopy in Solution of Hybrid Foldamers Stereoisomeric Mixtures

Author

Nicola Castellucci, Giuseppe Falini, Lorenzo Milli, Magda Monari, Sergio Abbate, Giovanna Longhi, Ettore Castiglioni, Giuseppe Mazzeo, Claudia Tomasini 

Year

2013

Journal

ChemPlusChem

Abstract

Upon slow evaporation of a 1:1 diastereoisomeric mixture of Boc‐(L‐Phe‐L‐Oxd)2‐OBn (1; Boc=tert‐butyloxycarbonyl; L‐Oxd=trans‐(4S,5R)‐4‐carboxy 5‐methyloxazolidin‐2‐one, Bn=benzyloxycarbonyl) and Boc‐L‐Phe‐L‐Oxd‐D‐Phe‐L‐Oxd‐OBn (2) in methyl tert‐butyl ether, single crystals suitable for an X‐ray diffraction study were obtained. In contrast, the two pure oligomers lead to the formation of amorphous solids under any crystallization conditions. The preferential conformation of both oligomers was fully elucidated in the solid phase and compared with the known conformation of Boc‐(L‐Phe‐D‐Oxd)2‐OBn (3). The preferred conformation of 1 ranges from a polyproline II (PPII) helix to β strands and we can gather that longer and more structured oligomers will form PPII helices. In contrast, compound 3 forms infinite antiparallel β‐sheet structures; thus showing the strong effect of the reversal of the absolute configuration of the Oxd moieties on the secondary structure of these hybrid foldamers. The same outcome was retained in solution, as demonstrated by vibrational circular dichroism analysis. Finally, we have demonstrated that a 1:1 mixture of 1 and 2 leads to the formation of new materials with interesting properties that are missing from the two pure compounds, such as the tendency to form crystals, fibers, and globules, depending on the solvent.

Instrument

FVS-6000

Keywords

Vibrational circular dichroism, foldamer,