Chiral β-cyclodextrin-based polymer supports prepared via ring-opening metathesis graft-polymerization

A series of norborn-2-ene-derivatized β-cyclodextrins (β-CDs), 6-O-(norborn-2-ene-5-carboxyl)-β-CD (1), tetrakis(6-O-norborn-2-ene-5-carboxyl)-β-CD (2), 6-O-(7-oxanorborn-2-ene-5-carboxyl)-β-CD (3), 6-O-(6-norborn-2-ene-5-carbonylaminohexoyl)-β-CD (4), 6-O-(norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD (5), tris(6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD (6), tetrakis(6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD (7) and hexakis(6-O-norborn-2-ene-5-ylmethoxymethylsilyl)-β-CD (8), have been synthesized. Compounds 1–3 were prepared via reaction of β-CD with norborn-2-ene-5-carboxylic chloride and 7-oxanorborn-2-ene-5-carboxylic chloride, respectively; compounds 5–8 were synthesized from norborn-2-ene-5-yl-methyldichlorosilane and β-CD, respectively. Compound 4 was accessible by reaction of norborn-2-ene-5-carboxylaminohexoyl chloride with β-CD. Compounds 1–8 were surface grafted onto norborn-2-ene-derivatized silica-based supports using ring-opening metathesis polymerization employing the ruthenium-based initiator bis(tricyclohexylphosphino)benzylideneruthenium dichloride [Cl2Ru(CHC6H5)(PCy3)2, Cy=cyclohexyl, 9]. Generally speaking, the resulting chiral stationary phases (CSPs) I–VIII may be prepared with high reproducibility and may be used within a pH of 2–10. Thus, relative standard deviations (σn−1) of the mean resolution (Rs) are <7%. The CSPs were used for the enantioselective separation of β-blockers, N-dansyl-, N-3,5-dinitrobenzoyl- and Fmoc-protected amino acids and were characterized in terms of chemical stability, selectivity (α′) and resolution (Rs). Additionally, the role of the spacer as well as influences of capacity and the degree of substitution of the β-CD moiety on the separation characteristics were determined.