Ricerc@Sapienza

A new chiral stationary phase was designed by
introducing 9-amino-9-deoxy-9-epiquinine, one of the
most versatile organocatalysts in asymmetric synthesis, as
chiral scaffold. The derivatization of its amino group with
the 3,5-dinitrobenzoyl (DNB) fragment provided hydrogen
bonding and ?–? donor/acceptor systems in addition to
the quinoline and quinuclidine moieties having two nitrogen
atoms with different basicities. The selector offers
multiple interaction sites in both typical of the Pirkle-type
phases and classical of weak-anion-exchanger phases. The
immobilization step took place through thiol-ene addition
onto 3-mercaptopropyl-silica gel and gave a grafting
density of 180 ?mol of chiral selector per gram of silica.
A silica with reduced particle size (Daisogel silica, pore
size 120 Å, particle size 2.5 ?m, and specific surface area
343 m2 g?1) has been employed to improve the efficiency
and the speed of separations. The chiral stationary phase
was packed in a small format column (50 × 4.6 mm) that
allowed, by van Deemter analysis, 180,000 plates/m and
approximately 5.1 ?m of plate height. The ability of chiral
discrimination was then studied with more than 30 test
compounds using both polar-organic and normal phase
conditions. In polar-organic mode, N-protected amino acids, ?-aryloxy carboxylic acids, as well the non-steroidal
anti-inflammatory profens were analyzed. Interesting
results were obtained in normal phase elution, where
the chiral selector behaves like a Pirkle-type stationary
phase. Aryl amides, esterified DNB-amino acids, benzodiazepines,
and binaphthol were well resolved with a very
good peak symmetry and in short analysis time (mainly in
less than 5 min).