Synthesis and characterization of new Na+complexes ofN-benzyl cyclic peptoids and their role in the ring opening polymerization ofl-lactide

Cyclic peptoids are biocompatible/biodegradable cyclooligomers constituted byN-substituted glycines showing high binding constants with the first group alkali metals (Ka∼ 106for Na+, Li+and K+) in organic solvents. Three new metallated species bearingN-benzyl groups as side chains (a cyclic pentamer, [1·2Na]2+, and two cyclooctamer [3·Na]+and [3·2Na]2+peptoids) were synthesized together with the knownN-perbenzylated sodiated cyclohexamer [2·Na]+and [2·2Na]2+. Na+complexes were investigated by means of spectroscopic (NMR), computational (DFT) and X-ray crystallographic studies. The first application of these complexes as catalysts in the ring opening polymerization (ROP) ofl-lactide (l-LA) was examined. Our studies suggest that, for the intrinsic properties of the catalytic site (revealed by steric topographic maps) the homooligomeric pentamer complex [1·2Na]2+is the most active member of the cyclooligomeric family.