engleski

Preparation and Evaluation of Stationary Phases Based on N, N-2,4- (or 4,6)-Disubstituted 4,5 (or 2,5)-dichloro-1,3-dicyanobenzenes

Regioselective functionalization of 2, 4, 5, 6- tetrachloro-1, 3-dicyanobenzene (TCDCB) by nucleophilic substitution of the chlorine at C(4) with l-Ala, l-Phe or l-Pro, followed by amide-bond formation to lipophilic amines containing strong π-donor group, and by final introduction of the spacer 3-aminopropyltriethoxysilyl (APTES), provided a number of new brush-type chiral selectors in the form of 1–2:1 mixture of 2, 4 and 4, 6-di(alkyl)amino regioisomers (8/9, 10/11, 12/13, 14/15, 20/21, 23/24). Linking these to silica gel (Nucleosil 100-5) gave new chiral stationary phases for HPLC columns (CSP I-CSP VI). Being strong π-basic selectors, most of these columns exhibited good resolution properties for π-acid test racemates (TR 1-TR 9), specifically rac 3, 5-dinitrobenzoyl-α-amino acid isopropyl- esters (DNB-AA). CSP V [1, 3-dicyano-2, 5(5, 6)- dichloro-6(2)-(γ′-silica bound propylamino)-4-N- {;[N-butyl]-N′-[(1R)-cyclohexylethyl]-N′- [naphthylmethyl]acetamido};-aminobenzene] and particularly the dipeptide-containing CSP VI [2, 5(5, 6)-dichloro-6(2)-(γ′-silica bound propylamino)-4-N-(3′, 5′-dimethylanilido)-l-alanyl- l-prolyl-aminobenzene] proved to have the highest efficiency, comparable with the best commercial brush-type columns with π-donor properties. Further evidence revealed that multiple hydrogen bonding via the amide group in the chiral environment and π–π interaction play a major role in chiral recognition, whereas steric perturbations via nonbonding VDW interactions contribute substantially only to the resolution of CSP III [2, 5(5, 6)-dichloro-6(2)-(γ′-silica bound propylamino)-4-N-(cyclohexylamido)-L-alanyl- aminobenzene]. This contribution is minor for the other CSPs

brush type CSPs ; resolution ; chiral recognition

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