(Cholestanyloxycarbonyl)benzyl esters as peptide substituents: Conformational properties of fully protected oligo‐ L ‐lysines with C‐terminal (cholestanyloxycarbonyl)benzyl and benzyl ester moieties

This study involves L‐lysine oligo peptides, protected at the N‐terminus by the Nps and at the ε‐amino functions by Boc groups. Two series were prepared from dimer to octamer, one containing the p‐[(cholestan‐3β‐yloxy)carbonyl]benzyl, the other one the benzyl ester group at the C‐terminus. Conformational analyses were performed by IR absorption. The occurrence of the intermolecular β‐structure in the solid state and in CH2Cl2 solution was demonstrated for the highest oligomers. The relative stabilities of the self‐associated species were determined by adding a variety of polar solvents to the CH2Cl2 solutions. The cholestanyl‐containing peptides have a lower propensity to self‐aggregate than the benzyl‐ester analogues. Self‐aggregation and decreasing solubility run in parallel. It was also directly shown that soluble urea derivatives may disrupt intermolecular H‐bonds in CH2Cl2, a point of practical interest, particularly in solid‐phase peptide synthesis.